L’accès à de nouveaux composés hétérocycliques originaux biologiquement actifs nécessite la mise au point de nouvelles méthodes de synthèse rapides et efficaces. Dans ce contexte, nous nous sommes intéressés à la réactivité des indazoles. Dans la première partie, nous avons étudié la sélectivité des couplages de type Suzuki, pour fonctionnaliser la position 3 d’indazoles possédant la fonction NH libre. Par la suite, un nouveau procédé d’(hétéro)arylation direct pallado-catalysé régiosélectif a été mis à profit pour synthétiser des indazoles fonctionnalisés tant sur la position 3 que sur le sommet 7. Nous avons ensuite montré la possibilité d’accéder à des entités disubstituées indazoliques en une seule étape, via une procédure "one-pot". Afin d’accroître la diversité autour du noyau indazole, nous avons mis au point une réaction d’alcénylation oxydative pallado-catalysée, des (2H)- et (1H)-indazoles sur les sommets C-3 et C-7. Pour exemplifier cette méthodologie, nous avons développé une synthèse en trois étapes du Gamendazole, composé actuellement en phase clinique pour la contraception masculine et ce, en utilisant l’alcénylation directe en C3 d’(1H)-indazoles convenablement fonctionnalisés. Le dernier volet de ce mémoire a été consacré à la préparation de composés à structure indazolique contenant une fonction sulfonamide afin de générer des librairies de dérivés substitués par un tel motif, dans le but de les tester biologiquement dans le domaine des anticancéreux. / Access to new biologically active compounds requires the development of new rapid and efficient methods for the synthesis of original heterocyclic scaffolds. In this context, we decided to focus particularly on the reactivity of indazoles. First, we studied the selectivity of Suzuki cross-coupling reaction to functionalize position 3 of the indazole with the free NH function. Indeed, we have described the first example of the direct and regioselective palladium-catalyzed (hetero)arylation of indazoles, the reaction may be induced to occur at either in position 3 and 7. We then showed the possibility of "one-pot" synthesis of disubstituted indazolic entities. Moreover, in order to increase diversity around the indazole scaffold, we developed a direct and regioselective alkenylation of (2H)- and (1H)-indazoles by oxidative palladium catalyzed at the C-3 and C-7, then we envisaged a three staps synthesis of Gamendazole, molecule currently in clinical phase for male contraception, by using the direct alkenylation at C3 of the suitably functionalized (1H)-indazoles. The last part of this report was dedicated to the preparation of indazoles containing a sulphonamide function, with the aim of biological testing them as potentially anti-cancer candidates.

Chapter 1: Metal carbenoids in organic synthesis The chapter describes the phenomena of metal carbenoid insertion reactions in two parts: Part A, and Part B. The study of N-tosylhydrazones as diazo precursor was commenced by Jose Barluenga in 2007,1 which demonstrated an in-situ generation of diazo species and trapping of that with low valent palladium catalyst (Scheme 1). Later, this palladium-carbenoid assumption was supported by few reports. Some of these discoveries were by D. F. Taber in 1986 followed by van Vranken in 1999 & 2001.2 These studies of palladium carbenes were supplemented by several groups in subsequent years. The consequent developments with N-tosylhydrazones as diazo source were very fruitful and produced exceptional chemical transformations in recent years. Though the precursor is also vastly customary for other metals such as Cu, Ni, Rh and Co, the primary focus has been given to Pd catalysis due to its wide utility and applicability. 1) Barluenga, J.; Moriel, P.; Valdes, C.; Aznar, F. Angew. Chem., Int. Ed. 2007, 46, 5587. 2) (a) Taber, D. F.; Amedio, J. C., Jr.; Sherrill, R. G. J. Org. Chem. 1986, 51, 3382. (b) Hoye, T. R.; Dinsmore, C. J.; Johnson, D. S.; Korkowski, P. F. J. Org. Chem. 1990, 55, 4518. (c) Greenman, K. L.; Carter, D. S.; Van Vranken, D. L Tetrahedron 2001, 57, 5219. 3) Palladium catalysed coupling of tosylhydrazones with aryl and heteroaryl halides in the absence of external ligands: synthesis of substituted olefins, Ojha, D. P.; Prabhu, K. R. J. Org. Chem., 2013, 78, 12136. Modes of reactivity of a metal-carbene Scheme 1 Cascade carbene migratory insertion process Part A: Ligand-free coupling of tosylhydrazones with aryl & heteroaryl halides In this part, Palladium catalysed cross-coupling reaction of hydrazones with aryl halides in absence of an external ligand is reported. The versatility of this coupling reaction has been demonstrated by showcasing the selectivity of coupling reaction in presence of hydroxyl and amine functional groups. This method allows synthesizing a variety of heterocyclic compounds, which are otherwise difficult to access from traditional methods. Application of the present methodology is validated in tandem reaction of ketones to the corresponding substituted olefins in a single pot experiment. Few examples are illustrated below in Scheme 2.3 Scheme 2: Scope of aryl halide coupling with tosylhydrazones Part B: Pd-catalysed Synthesis of Highly Branched Dienes The regioselective formation of highly branched dienes is a challenging task. Design and exploration of alternative working models to achieve such a regioselectivity to accomplish highly branched dienes is considered to be a historical advancement of Heck reaction to construct branched dienes. On the basis of the utility of carbene transfer reactions, in the reaction of hydrazones with Pd(II) under oxidative conditions, we envisioned obtaining a Pd-bis-carbene complex with α-hydrogens, which can lead to branched dienes. Herein, we report a novel Pd catalyzed selective coupling reaction of hydrazones in presence of tert-BuOLi and benzoquinone oxidant to form corresponding branched dienes (Scheme 3).4 The utility of the Pd catalyst for cross-coupling reactions for synthesizing branched conjugated dienes are rare. The reaction is very versatile and compatible with a variety of functional groups and is useful in synthesizing heterocyclic molecules. We anticipate that this Pd-catalyzed cross-coupling reaction will open new avenues for synthesizing useful compounds. 4) Pd-catalyzed cross-coupling reactions of hydrazones: regioselective synthesis of highly branched dienes, Ojha, D. P.; Prabhu, K. R. J. Org. Chem., 2012, 77, 11027. 5) Furrow, M. E.; Myers, A. G. J. Am. Chem. Soc. 2004, 126, 5436. 6) Taber, D. F.; Guo, P.; Guo, N. J. Am. Chem. Soc. 2010, 132, 11179. Scheme 3: diene synthesis via bis-carbene insertion process Chapter 2: Tosylhydrazones: Role in modern day organic synthesis In recent days, hydrazone based reactions are focused on the donor-acceptor ability of the hydrazones or the in-situ generated diazo species (Scheme 4). This commenced with the Myers’s report in 2004,5 which simplifies the Barton vinyl halide preparation with a remarkable revision on synthesis of alkyl-silyl-hydrazones and its applications. Improved methods of using tosylhydrazones were demonstrated by Aggarwal in successive years. Cycloadditions were implemented by Douglass F. Taber. 6 This study was enriched in a quite fascinating way by several groups such as Jose Barluenga, with many reductive coupling reactions and 1, 3-dipolar reactions. Thomson, in a very interesting report shows the traceless petasis reaction with hydrazones and also worked in many other prospects such as three component reactions and the acid catalysed [3+3] sigmatropic reactions of hydrazones. 7 Wang has also impressed with very attractive transformations in the past decade. 8 7) Thomson, R. J. et al. Nat. Chem. 2009, 1, 494. 8) Xiao, Q.; Zhang, Y.; Wang, J. Acc. Chem. Res. 2012, 46, 236. 9) Regioselective Synthesis of vinyl halides, vinyl sulfones, and alkynes: A tandem intermolecular nucleophilic and electrophilic vinylation of tosylhydrazones, Ojha, D. P.; Prabhu, K. R. Org. Lett. 2015, 17, 18. Scheme 4: Trapping diazo species in intermolecular fashion Part A: Synthesis of vinyl halides Trapping diazo species in an intermolecular fashion by attack of two independent ions (a cation followed by an anion) in tandem at the carbene center is unprecedented. As part of our efforts on the utility of tosylhydrazones, herein we report a novel approach of using ambiphilic diazo species to perform a tandem attack of a nucleophile followed by an electrophile in an intermolecular fashion for synthesizing various types of vinyl halides. A few representative examples are shown in Scheme 5.9 Scheme5: Synthesis if vinyl halides Part B: Synthesis of vinyl sulfones Vinyl sulfones are potential synthetic targets due to their presence in biologically and pharmaceutically important molecules ranging from small natural metabolites to proteins, and have found widespread applications in biological research as covalent protease inhibitors. Vinyl sulfones represent one of the important sulfur containing functional groups in organic chemistry, which are generally synthesized through elimination reactions, oxidation of vinyl sulfides or witting reactions using multistep sequence. Following this technique, we were able to synthesize a variety of vinyl sulfones with rich mechanistic features in a single step. A few such examples are documented in Scheme 6.9 Scheme 6: synthesis of vinyl sulfones Part C: Synthesis of alkynes The functional group conversion to achieve alkyne frameworks are generally a difficult transformation. There are very few limited and tedious processes are available in literature, mainly containing multi-step procedures. Additionally these reactions are require harsh conditions. Considering all these factors, there is a need for developing methods to synthesize alkynes from common functional groups under mild reactions conditions. In a similar way, to introduce different halogens at the same carbon, we expected the eliminations of the leaving groups in tandem formed alkynes. After extensive screening studies, it was pleasing to find that the reaction of tosylhydrazones with NCS−BTEAC, NBS−TBAB, or NIS−TBAI combination in presence of K2CO3 in dioxane as solvent at 110 °C can furnish corresponding acetylene derivatives in good yields. Few examples are shown in Scheme 7.9 Scheme 7: Trapping diazo species in intermolecular fashion Chapter 3: Pd catalysed hydroboration This chapter shows a hydroboration study of terminal alkynes in a highly regioselective manner (Scheme 8). Organoboron derivatives have become essential intermediates in organic and medicinal chemistry. Pioneering contributions are made by Brown and Akira Suzuki, who both instigated the development of new synthetic tools for the introduction of boron atoms onto organic molecules. 10 10) (a) Barbeyron, R.; Benedetti, E.; Cossy, J.; Vasseur, J.-J.; Arseniyadis, S.; Smietana, M. Tetrahedron 2014, 70, 8431. (b) Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457. 11) Pd-Catalysed regioselective borylation of alkynes: A ligand controlled synthesis of α- and β vinyl boronates (manuscript submitted). Scheme 8: possibility of site selectivity in hydroboration Part A: Pd-catalysed regioselective borylation of alkynes: A ligand controlled synthesis of α and β – vinyl boronates The metal catalyzed borylations of alkynes proceeds in a two-step process. Initially M-Bpin species undergo an addition onto the alkynes to generate organometallic species followed by quenching of the organometallic species with electrophiles. The addition M-Bpin species is regioselective governed by the steric and electronics factors of both metal complex as well as alkyne substituents. In this direction, a palladium catalysed α-selective borylation was achieved for terminal alkynes. A broad range of substrates were successfully borylated under optimized reaction conditions with very high selectivity. Interestingly, the selectivity was reversed to terminal site by using a NHC ligand. A few examples are shown in Scheme 9.11 Scheme 9: α & β-vinyl boronates Chapter 4: Pd/borane unit: Behavior towards isomerization vs reduction of alkenes This study presents a unique behaviour of palladium-boronate unit responsible for olefin chain walking and olefin reduction reactions (Scheme 10). The catalytic system stands efficient against both functionalized and unfunctionalized olefin isomerization as well as reductions. This study has been presented in two parts. Scheme 10: isomerization vs reduction Part A: Pd/ boronates or borane unit as efficient catalytic systems for olefin chain walk This study presents the behaviour of palladium-boronate unit responsible for olefin chain walking. The catalytic system is efficient for both functionalized and unfunctionalized olefin isomerizations (Scheme 11). Cycloisomerization of transient conjugated alkenes to synthesize heterocycles are prominent applications of this technique. The system describes a concept of olefin activation by coordination with Pd-borane complex, this complex assists in a facile [1,3]-hydride shift. This technique allows us to facilitate an isomerization in functionalized as well as unfunctionalized olefinic systems. Considering the substrates scope, the catalytic cycle tolerates various sensitive functional groups and shows good selectivity. In the following Scheme 11 few examples are depicted.12 12) Palladium/boron catalytic unit for olefin chain-walk (manuscript under preparation). Scheme 11: chain-walking of olefins. Part B: Palladium catalysed boronate promoted alkene reduction in water In this work, water has been employed as a source of hydrogen. The reduction of alkenes was achieved using Pd catalyst in presence of bis(pinacolato)diboron and H2O. In this aspect, the utility of water as hydrogen equivalent is the pertinent as well as beneficial with many advantages. Few representative examples are shown in Scheme 12.13 13) Pd-Catalysed homogeneous hydrogenation of olefins by using water as hydrogen source (manuscript under preparation). Scheme 12: synthesis of alkenes reduced products.

Les propriétés optiques et vibrationnelles de nanoparticules métalliques individuelles ont été étudiées par spectroscopie par modulation spatiale (SMS), avec une attention particulière aux effets de forme, composition, environnement local, ainsi que de couplage inter-particule. La réponse optique de nanoparticules (métalliques au cœur-couronne métal-diélectrique) allongées et des particules bimétalliques (hétérodimères or-argent) a été mesuré et en suite interprétée grâce à une corrélation avec la caractérisation morphologique de la même particule obtenue par microscopie à transmission électronique et avec des simulations par éléments finis prenants en compte la réelle géométrie du nano-objet et le substrat. Une technique pompe sonde résolue en temps a été en suite utilisée pour étudier le profil Fano dans l'absorption d'une particule d'or au sein d'un hétérodimères or-argent. Sur une échelle de temps des quelques dizaines de picosecondes, les vibrations acoustiques multimodales de nanobipyramides d'or individuelles ont été optiquement détectées et caractérisées par rapport à un modèle élastique classique / Optical and vibrational properties of individual metal-based nanoparticles have been investigated by spatial modulation spectroscopy (SMS), focusing on their dependence on nano-object shape, composition, environment and inter-particle coupling. Quantitative investigations of the optical response, and in particular, the surface plasmon resonance (extinction cross-section amplitude, spectral position and linewidth) of elongated metal or metal-dielectric (gold nanorods, nanobipyramids with or without silica coating) and bimetallic (gold-silver heterodimers) nanoparticles deposited on a substrate have first been performed. The same nanoparticles were characterized by electron microscopy permitting quantitative interpretation of their optical response using finite element numerical simulations, taking into account the influence of the substrate. Combining SMS microscopy with a high sensitivity femtosecond two-color pump-probe setup, the ultrafast dynamics of single nano-objects has been investigated. The Fano absorption profile of a gold nanoparticle within a single gold-silver heterodimer, a parameter not accessible by linear spectroscopy, was directly measured. On a picosecond time-scale, multimodal acoustic vibrations of single gold nanobipyramids were optically lunched and detected, and their features compared to a model based on continuum elasticity

The thesis entitled “Copper-Catalyzed Novel Oxidative Transformations: Construction of Carbon-Hetero Bonds” is divided into two main sections. Section A deals with the utility of azide as a nitrogen source for C-N bond formation, which is further divided into 4 chapters, and section B presents decarboxylative radical coupling reaction for C-heteroatom bond formation which is further divided in to two chapters. Section A Chapter 1 describes an approach for the direct synthesis of nitrile from the corresponding alcohols using azide as a nitrogen source. Nitrile functionality is a versatile and ubiquitous which occurs in a variety of natural products. Nitrile functionality can be easily transformed into a variety of functional groups and products such as aldehydes, ketones, acids, amines, amides and nitrogen-containing heterocycles, such as tetrazoles and oxazoles. In this chapter a successful attempt for developing a novel methodology to oxidize benzylic and cinnamyl alcohols to their corresponding nitriles in excellent yields has been described. This strategy uses DDQ as an oxidant and TMSN3 as a source of nitrogen in the presence of a catalytic amount of Cu(ClO4)2·6H2O. A few representative examples are highlighted in Scheme 1.1 Scheme 1. Oxidative conversion of alcohols to nitriles Second chapter represents a protocol for the synthesis of 1,5-disubstituted tetrazoles from the corresponding secondary alcohols. Among heterocyles, tetrazole and its derivatives are important class of nitrogen containing molecules. Due to their well-known biological activities as well as vast applications in pharmaceuticals and material science, they are potential targets for synthetic organic chemists. Therefore, a simple and user-friendly method for the synthesis of tetrazole is desirable. In this chapter, a mild and convenient method to synthesize 1,5-disubstituted tetrazoles using easily accessible secondary alcohols by employing TMSN3 as a nitrogen source is developed. This reaction is performed in the presence of a catalytic amount of Cu(ClO4)2·6H2O using DDQ as an oxidant under ambient conditions (Scheme 2).2 Scheme 2. Oxidative conversion of secondary alcohols to tetrazoles Third chapter presents a method for synthesizing amides from their corresponding secondary alcohols. Amide functionality is a crucial backbone in peptide chemistry, it also serve as an important precursor or intermediate for variety of organic transformations. In this contention, a mild and convenient method to synthesize amides using easily accessible secondary alcohols by employing TMSN3 as a nitrogen source is developed. This reaction is performed in the presence of a catalytic amount of Cu(ClO4)2·6H2O using DDQ as an oxidant under ambient conditions (Scheme 3).3 Scheme 3. Oxidative conversion of secondary alcohols to amides Additionally, the application of this methodology has also been revealed for the synthesis azides directly from their alcohols. Some of the representative examples are shown in the Scheme 4.3 Scheme 4. Direct conversion of alcohols to their azides. Fourth chapter describes highly chemoselective Schmidt reaction. The classical Schmidt reaction involves the formation of new carbon-nitrogen bonds in a reaction of a carbon-centred electrophile with hydrazoic acid followed by loss of nitrogen, which usually occurs via a rearrangement. It is well known that under the Schmidt reaction conditions, ketones and carboxylic acids are converted into their corresponding amides and amines respectively, whereas aldehydes furnish a mixture of formanilides and nitriles. In this chapter, Schmidt reaction of aldehydes to obtain their nitriles without formation of the corresponding formanilide is presented (Scheme 5).4 It was also observed that aromatic ketones and acids functionalities were intact under the reaction condition, unlike the conventional Schmidt reaction. Scheme 5. Highly chemoselective Schmidt reaction Section B It is divided into two chapters, describes a copper catalyzed decarboxylative radical coupling for the synthesis of vinyl sulfones and nitroolefins (Scheme 6). Scheme 6. General strategy for the second part First chapter narrates a strategy for synthesizing nitroolefins from the α,β-unsaturated carboxylic acids. Nitroolefins represent a unique class of nitro compounds, which have multifaceted utility in organic synthesis. They possess antibacterial, rodent-repelling, and antitumor activities. They serve as important intermediates in organic synthesis. Nitroolefins also react with a variety of nucleophiles, and their electron-deficient character renders them as a powerful dienophiles in Diels-Alder reactions. In our attempt to use the decarboxylative strategy, this chapter describes a method for the nitrodecarboxylation of substituted cinnamic acid derivatives to their corresponding nitroolefins. This nitrodecarboxylation reaction is performed using catalytic amount of CuCl in the presence of air using TBN as a nitrating source (Scheme 7).5 Besides, the reaction provides a useful method for the synthesis of β,β-disubstituted nitroolefin derivatives which are generally difficult to access from other conventional methods. Scheme 7. Decarboxylative nitration Second chapter presents a new protocol for the synthesis of vinyl sulfones from the α,β-unsaturated carboxylic acid. Vinyl sulfones are versatile building blocks, which find their utility as Michael acceptors and used in cycloaddition reactions. This functional group has also been shown to potently inhibit a variety of enzymatic processes, and thus provides unique properties for drug design and medicinal chemistry. Vinyl sulfones are prominent in medicinal chemistry owing to their wide presence in pharmaceutically active molecules, such as enzyme inhibitors and biological activity. In this chapter, we report a method for the construction of C-S bonds via ligand promoted decarboxylative radical sulfonylation of ,-unsaturated carboxylic acids to synthesize vinyl sulfones using Cu catalysis (Scheme 8).6 This is the first report for this particular conversion. Scheme 8. Decarboxylative sulfonation

Les transferts d'électron sont au cœur de nombreux processus d'intérêts chimiques, biologiques ou photochimiques comme, par exemple, dans la technologie du photovoltaïque ou la photosynthèse où ils ne sont que rarement isolés. Par ailleurs, des résultats expérimentaux tendent à montrer que les phénomènes quantiques, notamment les superpositions d'états ou cohérences, peuvent se maintenir sur l'échelle de temps du transfert d'électron même en présence d'un environnement. Dans ce travail, le transfert d'électron est étudié dans trois types de systèmes moléculaires. Le premier est un transfert intermoléculaire dans une hétérojonction oligothiophène-fullerène modélisant une interface de séparation de charge pour de futures cellules photovoltaïques organiques. Le second est un transfert intramoléculaire dans des composés organiques à valence mixte où l'on étudie l'effet d'un pont avec une chaîne croissante de n-paraphénylènes dans des polymères aromatiques avec des sites donneur-accepteur (1,4-diméthoxy-3-méthylphénylènes). Le troisième est le transfert intermoléculaire dans une chaîne de tryptophanes dans une chromoprotéine cryptochrome. Dans tous ces cas, une attention particulière est portée à une modélisation réaliste. Dans ce contexte, il est crucial de faire une partition judicieuse entre l'ensemble des degrés de liberté et de décrire proprement l'interaction entre ceux impliqués dans le transfert et ceux qualifiés d'environnement. A cette fin, un hamiltonien décrivant un système électronique donneur-accepteur couplé à un bain d'oscillateurs harmoniques a été paramétré en utilisant notamment la méthode de la DFT contrainte (cDFT). Le bain d'oscillateurs a été décrit par une analyse en modes normaux ou via la fluctuation de l'écart énergétique obtenue par des calculs de type QM/MM. Les systèmes étudiés présentent tous des environnements fortement couplés et structurés nécessitant d'explorer des stratégies peu conventionnelles. Dans un modèle d'environnement formé d'un nombre fini d'oscillateurs traités explicitement, le traitement dynamique nécessite d'utiliser des méthodes multidimensionnelles telles que la méthode multi-couches multiconfigurationnelle de produits de Hartree dépendant du temps (ML-MCTDH). Dans l'approche de dynamique dissipative où le bain intervient seulement par ses propriétés statistiques il est alors nécessaire de se tourner vers une méthode non perturbative telle que les matrices hiérarchiques. A côté de ces approches exactes, une autre stratégie consiste à effectuer une transformation de coordonnées afin de définir une coordonnée collective incluse avec le système électronique qui est elle-même couplée à un bain secondaire. La propagation dynamique peut alors être effectuée par une équation-maîtresse approchée s'appuyant sur la théorie de perturbation. Comme principaux résultats, nous analysons en détail le domaine de validité des différentes méthodes utilisées puis expliquons le comportement dynamique des différents cas amenant à une délocalisation facile ou à un piégeage de la charge. Par là même, nous montrons que la méthodologie proposée, appliquée à des systèmes-modèles dans ce travail, est bien adaptée pour l'analyse de l'influence mutuelle entre le transfert de charge et les déformations nucléaires, une situation prototypique pour de nombreux processus importants dans les systèmes chimiques et biologiques. / Electron transfer reactions are at stake in several chemical, biological or photochemical processes of great interest as, for instance, photovoltaic technology or photosynthesis where they are rarely isolated. Furthermore, experimental results show that quantum phenomena, notably superpositions of states or coherences, can persist on the time scale of the electron transfer even in the presence of an environment. In this work, electron transfer is studied in three types of molecular systems. The first one is an intermolecular transfer in an oligothiophene-fullerene heterojonction modelling a charge separation interface for future organic photovoltaic devices. The second one is an intramolecular transfer in mixed-valence organic compounds where the bridge effect of an increasing n-paraphenylens chain is studied on aromatic polymers with donor-acceptor sites (1-4,dimethoxy-3-methylphenylens). The third one is an intermolecular transfer in a tryptophan chain of a cryptochrome chromoprotein. In all these cases, a special attention is given to realistic modelling. In this context, it is crucial to define carefully the partition between the degrees of freedom, in particular amongst those implied in the transfer and those qualified to be part of an environment. To this end, a Hamiltonian describing a donor-acceptor electronic system coupled to a bath of harmonic oscillators is parameterized using the constrained DFT method (cDFT). The oscillators' bath is described by a normal mode analysis or via the electronic gap fluctuation obtained by QM/MM calculations. The systems under study turn out to be strongly coupled, and structured which requires to explore non-conventional strategies. In a model environment constituted of a finite number of oscillators treated explicitly, the dynamics is performed by multidimensional quantum propagation methods such as the multi-layer multiconfigurational time-dependent Hartree method (ML-MCTDH). In the dissipative approach, where the bath acts only by its statistical properties, it is mandatory to turn to non-perturbative methods such as the hierarchical equations of motion approach. Apart from these exact approaches, an alternative strategy consists in carrying out a change of coordinates in order to define a collective bath mode included in the electronic system, which itself is coupled to a secondary bath. The dynamical propagation can then be done by an approximated quantum master equation using perturbation theory. As main results, we show in detail the domain of validity of the different methods presented and explain the dynamical behaviour of the different cases leading to an easy delocalization or a trapping of the charge. Hence, we show that the methodology applied in model systems are well suited for the analysis of the mutual interplay between the charge transfer and nuclear deformations, a prototypical situation in many important chemical and biological processes.

This thesis titled, “Nature of Local Interactions at cisPro-Aro Peptide Sequences in Proteins: Evidences for van der Waals type Interactions. Design and Synthesis of Novel Covalent Surrogates for the Peptide Hydrogen Bond”, describes two important studies. The first is to gain a thorough understanding of the nature of interactions that govern cisPro stability at Pro-Aro sequences, which described in the first four chapters. The final chapter describes the synthesis of novel 4-carbon covalent surrogates for the peptide H-bonding interaction. Chapter 1: Local Interactions Governing cisPro Stability: Refining the Model Peptides Chapter 1 Section A: Understanding the role of inter-side chain CH•••Aro interaction in cis-trans isomerization at Pro-Aro and Aro-Pro Sequences. This chapter is divided into two sections. In the first section an exhaustive overview of earlier investigations into the nature of local interactions at Xaa-cisPro-Aro and Aro-cisPro-Xaa peptide sequences, by various groups, are discussed. Most studies have found evidence for the close assemblage between side chains of residues flanking cisPro motifs, when at least one of them is an aromatic group. An electronic C-H•••π nature has been proposed for these assemblies and they are proposed to influence the cisPro stability. We highlight those features in these studies that indicate that these interactions are not always electronically tunable, are insensitive to presence of strong chaotropes in the solvent and occur at protein sequences lacking Pro or cisPro; all of which contradict the electronic C-H•••π model for these inter-side chain assemblages and their perceived influence on cisPro stability. Chapter 1 Section B: Investigation of the Nature of H Xaa•••Aro interaction at Xaa-Pro-Pro-Phe-sequences In Section B, we design and synthesize Pro-Aro containing short peptide models to investigate the nature of local C-H•••Aro interactions in them. We synthesize a series of homologous Pro-Pro-Aro containing peptides (modeled based on earlier studies) and investigate the relative populations of its four Xaa-Pro rotamers using extensive 1D and 2D NMR techniques including TOCSY, HSQC and ROESY. We find several drawbacks that make this a relatively deficient model. Firstly, their relative populations of the rotamers (the most important data for current investigation) cannot be determined with high fidelity as they are dependent on the solvent polarity, solute concentration and chemical shift degeneracy of crucial NMR signals for the rotamers. Importantly, the populations of a few rotamers are influenced by strong 13-membered ring backbone H-bonds. Notably, some of the cisPro rotamers do not even contain the inter-side chain assembly, whose nature is under investigation. Design of novel models – unconstrained by H-bonds We design the Acyl-Pro-Pro-Aro-OMe peptides that lack the possibility of forming the 13-membered ring H-bonded structures. Thorough 1D and 2D NMR analyses of these models reveal that strong Type VI β-turn type 10-membered ring H-bonds are formed in the rotamers of these models – hence precluding their applications for current study. Interestingly, the relative rotamer populations are strongly influenced by solvent polarity and are entirely different from those of the corresponding C-terminal amide models. We further discover that the Pro-Pro-Aro motif is not essential to express the inter-side chain interactions – Ala-Pro-Aro are sufficient. Formation of the 10-membered H-bonding interactions, however, are not precluded. Chapter 2: Design and Synthesis of Acyl-Pro-Phe-OMe: Novel models to investigate the role of HαXaa•••Aro interactions on Xaa-cisPro-Aro stability. Chapter 2 Section A: Design, Synthesis and Conformational Analysis of Ibu-Pro-Phe-OMe Chapter 2 is divided into two sections. In Section A, we replace the amino acid at the N-terminal of the putative Pro residue with simple isosteric isobutyryl group, the resulting minimalist dipeptide model shows the exclusive influence of desired inter-side chain interactions in the cisPro rotamer. Solvent polarity and temperature coefficient studies reveal that absence of any intramolecular H-bonding or Oπ* interactions in it. 1D and 2D NMR analyses clearly indicate the close proximity between the side chains of Ibu and Phe exclusively in the cisPro rotamer. The Kc/t value decreases upon mutation of Phe to Ala. All these features favor the Ibu-Pro-Phe-OMe as an ideal minimalistic model for investigating the nature of Ibu•••Ph assemblages in the cisPro rotamer. Chapter 2 Section B: Investigation of CH•••Aro /Alp•••Alp interactions in Ibu-cisPro-Xaa-OMe In Section B, the 1D and 2D NMR analyses of the complete set of the aliphatic and aromatic analogues Ibu-Pro-Xaa-OMe were investigated. DMSO-d6 was found to be the best solvent for mimicking both the folded and the unfolded local environments of these short peptide sequences. The HαIbu•••Aro assemblage is observed in Aro analogues, but cannot be electronically tuned. The aliphatic analogues also surprisingly contain the HαIbu•••Alp interactions! The Kc/t values (cisPro %) increase in the aliphatic analogues too, where the aliphatic side chain is long. Increase in cisPro stability is not due to ring current effects or intramolecular H-bonds or Oπ* interactions. It seems to be due to van der Waals type interactions between the involved side chains, either of which need not be aromatic in nature. Chapter 3: Nature of Inter-Side Chain Interactions at Acyl-cisPro-Aro Sequences: Evidence for van der Waals Interactions Chapter 3 Section A: Investigation of nature of inter-side chain interactions in R-CO-cisPro-Phe-OMe Chapter 3 has two sections. Section A describes the systematic design and synthesis of Acyl-Pro-Phe-OMe homologues where first the steric bulk and hence the surface area of the aliphatic side chain of the acyl group is varied. Interaction of the phenyl ring of Phe seems to occur with the Cα-Cβ σ-bond of the acyl group. Branching at either Cα or Cβ seems to destabilize the cisPro rotamer. Aliphatic•••Aromatic interactions overwhelm the cisPro rotamer population to be greater than that of transPro. In the analogues where the acidity of the acyl Cα-H bond is increased, the Kc/t does not increase correspondingly. The Δδ(trans-cis) ppm shifts of HαAcyl protons are dependent exclusively on its acidity rather than on the Kc/t values. In carbamyl-Pro, which entirely lack the HαAcyl proton, the Kc/t values are significantly high and improve as the aliphatic surface on the alkoxy group increases. Introduction of benzyloxy carbamyl group at Pro renders almost the same Kc/t values as that of ethyloxy carbamate. All these data contradict the C-H•••π interaction model and strongly support a van der Waals type interaction between the Acyl (preceding cisPro) group’s Xα-Yβ σ-bond and the Aro or Alp side chains (succeeding cisPro). Chapter 3 Section B: Evidence for the Van der Waals nature of Inter Side Chain (Acyl•••S.C.Aro/Alp) interactions- Determination of Interactions energies In Section B, a thorough investigation of both aliphatic•••aliphatic and aliphatic•••aromatic interactions on the background of homologous Acyl-Pro-Aro/Alp-OMe peptide models is undertaken. These models uniquely allow the delineation of contribution of the van der Waals interactions and the ring current effects to the cis/trans isomerization in these peptides. We see that the energy of the van der Waals component of these aliphatic•••aliphatic and aliphatic…aromatic interactions increase linearly with increase in Kc/t, in both DMSO-d6 and D2O. On other hand, energy from the ring current effects largely remains invariant. The Acyl•••Aro/Alp interactions are not hydrophobic and are facilitated by conformational effects. Chapter 4: Crystallographic evidence for van der Waals interaction-mediated stabilization of cisPro conformers Chapter 4 Section A: Systematic crystallization and crystal structure analyses of homologous Xaa-cisPro-Alp and Xaa-cisPro-Aro rotamers: Evidence for van der Waals interactions Chapter 4 has two sections, both of which present crystallographic evidence for the van der Waals nature of the Xaa•••Aro interactions at Xaa-cisPro-Aro sequences. Section A describes the unique crystal structures of five of the Acyl-Pro-Alp-OMe analogues that have been synthesized in the current study. All of them remarkably crystallize with two features: 1) the Acyl-Pro peptide bond adopts the cisPro rotamer in all; and 2) the aliphatic side chains of the acyl group and the Alp side chain are involved in van der Waals type interactions. The cisPro rotamers of even the bulkiest motifs, namely Ibu-Pro-Val-OMe, Piv-Pro-Ile-OMe and Piv-Pro-Leu-OMe crystallize, stabilized by van der Waals packing between aliphatic groups of the acyl and the Leu/Ile/Val side chains. Where the side chains are not long enough to make sub-van der Waals contacts with each other, their acyl C′-Cα σ-bond rotations are restricted due to Oσ* interactions involving the charge on the acyl carbonyl O. Where this occurs, the short space between the acyl and Alp side chains are filled in by aliphatic groups from neighbouring molecules at sub van der Waals distances. The Pro, Alp and χ1(Alp) dihedral angles are restricted to narrow range of values, irrespective of the length of Alp side chain, indicating that this backbone conformation is a conformational minimum when i+3i backbone H-bond is removed, with Pro at the i+1st position. This is further substantiated in Piv-Pro-Gly-OMe, which crystallizes in trans-Pro form, but still adopts similar backbone dihedral angles in spite of lacking any Alp side chain for interactions with the acyl group. Three of the Acyl-Pro-Aro-OMe models also crystallize in cisPro rotamer forms – both exhibit van der Waals type contacts between the Acyl group and backbone of Phe, rather than the aromatic ring of Phe. The phenyl ring of Phe may or may not form intramolecular Ph•••Pro inter-side chain contacts – which is not a pre-requisite for cisPro stabilization. No C-H••• interactions are observed anywhere in these peptides – van der Waals type contacts alone predominate in all cases. There are no abnormal distortions in bond angles or lengths even in the most sterically hindered cases, signifying that the conformations of these cisPro rotamers involving aliphatic•••aliphatic type contacts are natural minima. Chapter 4 Section B: Mining the PDB for Statistical Evidence of van der Waals interactions Section B of chapter 4 describes the data mining and statistical analyses of Xaa-cisPro-Phe, Xaa-cisPro-Val and Xaa-cisProLeu sequences in the PDB. The PEARL program was used to mine the PDB data. The overall frequency of 5.3% for appearance of cisPro among all Xaa-Pro peptide bonds, improves when Xaa is Phe or Tyr. However, several anomalies highlight the need for refining the analyses set to only those sequences where the side chains of Xaa and Aro/Alp face each other. In this refined set, clearly, inter side chain Xaa•••Alp/Aro contacts take precedence over even Aro•••Pro interactions at Aro-cisPro sequences (where Xaa is Aro). The Phe and the Leu side chains induce similar conformational effects on the preceding Xaa-Pro backbone. So does Val. Strong aliphatic•••aliphatic inter side chain contacts at van der Waals distances are observed to flank cisPro in several proteins. Substitution at the Cα of Xaa governs the proximity of the approaching side chain of Alp / Aro residue. The Cα-H of Xaa steers away from the Aro side chain at Xaa-Pro-Phe sequences, as the Aro group gets closer to it – implying the absence of ordered C-H••• contacts between them. There is consistent parallel alignment between Cα-Cβ -bond of Xaa and the C -C bond of the approaching side chain of Alp or Aro group – clearly highlighting the presence of van der Waals type interactions between them. All these evidences clearly point towards the van der Waals nature of local interactions at cisPro-Aro/Alp peptide sequences. Chapter 5: A novel 4-carbon covalent surrogate model for peptide H-Bond Chapter 5 describes the design and synthesis of novel 4-carbon covalent surrogates for the peptide H-bond (HBS). These surrogates would allow the unique constraining of two peptide strands in their extended conformations. The covalent HBS contain four orthogonal functional groups for independent extension at all of the four ends – similar to an endogenous inter-strand peptide H-bond. The synthesis of the surrogate is achieved by directly using natural chiral amino acid derivatives, beginning from amino alcohols obtained from reduction of desired amino acids. Suitably N-protected alcohols undergo oxidation to aldehyde followed by Grignard addition of allyl magnesium bromide, TBDMS protection of the homoallylic alcohol and reductive ozonolysis of the olefin to get a primary alcohol which is subject to Fukuyama-Mitsunobu reaction with desire protected peptide. The residue preferences that produce strongest inter-strand H-bonds were explored. The designed 4-carbon covalent HBS was incorporated using this methodology in a Gramicidin-S analogue, its first structural mimic containing only a single turn motif. This HBS model will have wide applications for constraining peptides in a number of secondary structures.

V této diplomové práci je nejprve ve zkratce uvedena teorie fyziky solárních článků, kde jsou zmíněny klíčové procesy ovlivňující účinnost konverze slunečního záření na elektrickou energii. Dále je předložena rešerše o fotovoltaických nanostrukturách (nanodráty, nanokrystaly), jejichž implementací je možné účinnost solárních článků zvýšit. V přehledu experimentálních technik ke zkoumání fotovoltaických nanostruktur je důraz kladen zejména na korelativní měření pomocí SEM a AFM, vodivostního AFM, měření EBIC a mikroskopické měření elektroluminiscence. V experimentální části jsou předloženy výsledky měření struktur mikrokrystalického křemíku, vzorku hetero-přechodového Si solárního článku s kontakty na zadní straně (IBC-SHJ z projektu NextBase) a V-pitů vzorku InGaN/GaN kvantových jam. Měření elektroluminiscence bylo provedeno na vzorcích III-V polovodičů (InGaP, GaAs). Byly vypočítány jinak těžko dostupné charakteristiky III-V tandemových solárních článků pomocí elektroluminiscence a srovnání vlastností IBC-SHJ zjištěných pomocí mikroskopického měření elektroluminiscence a EBIC. Provedením experimentů bylo zjištěno, jakým způsobem se dělí proud vybuzený svazkem elektronů mezi hrot AFM a vzorek mikrokrystalického křemíku.

The aim of this master’s thesis is familiar with the problems of optical fibers and possi- bilities creating functional optical structures in optical fibers. first section focuses on the optical fibers and their properties. Another chapter deals with the functional structures of optical fiber and their production. Next section is devoted to the analysis of combinations of these functional structures and their potential applications in sensors. Subsequently, a combined structure is proposed, which is later produced, measured and evaluated for possible use in the sensors

Les glucides constituent la classe de molécules organiques la plus abondante et ceux-ci jouent des rôles cruciaux dans divers processus biologiques. De part leur importance médicinale, la préparation des désoxy-sucres, des C-glycosides et des C-disaccharides est devenue un sujet de pointe en synthèse organique. De façon générale, cette thèse décrit une nouvelle synthèse de novo des 4-désoxy hexopyrannoses en plus de la préparation de C-glycosides biologiquement actifs. De plus, une attention particulière a été portée à la préparation de novo de 4-désoxy-C-disaccharides. Dans un premier temps, le catalyseur de Cr(III) de Jacobsen et un complexe binaphtol/titane ont été utilisés pour réaliser des hétéro-Diels-Alder énantiosélectives. Les dihydropyrannes ainsi générés ont été transformés en 4-désoxy hexopyrannoses présents dans la nature. De cette façon, un dérivé de l’acide ézoaminuroïque, un précurseur de la désosamine et de la néosidomycine, a été préparé suivant cette approche de novo. De plus, à titre comparatif, la néosidomycine a également été fabriquée selon une approche chiron, à partir du méthyl alpha-D-mannopyrannoside. Finalement, une évaluation biologique préliminaire de la néosidomycine a été effectuée sur une la concanavaline-A (Chapitre 2). Dans un deuxième temps, une allylation stéréosélective sur un aldéhyde lié via des liens C-C à une unité mannoside a permis de générer un alcool homoallylique. Cette dernière fonctionnalité a été transformée en 4-désoxy hexopyrannose de configuration D ou L. De cette façon, la préparation de pseudo 4-désoxy-C-disaccharides, de 4-désoxy-C-disaccharides et de pseudo 4-désoxy aza-C-disaccharides a facilement été réalisée. Les rapports diastéréoisomériques de la réaction d’allylation ont été déterminés en plus de la configuration absolue des nouveaux centres stéréogéniques formés. La transformation des alcools homoallyliques en pyrannes poly hydroxylés ou en lactames poly hydroxylés a été réalisée, en plus de la déprotection de certains membres de cette famille pour une évaluation biologique préliminaire sur la concanavaline-A (Chapitre 3). Finalement, la synthèse de C-glycosides biologiquement actifs a été réalisée selon deux volets: i) préparation de 3-C-mannopyrannosyl coumarines et ii) synthèse de C-galactosides, inhibiteurs de la lectine PA-IL. Pour ce faire, le couplage de Heck a été utilisé à partir d’un ester alpha,bêta-insaturé, attaché à une unité glycosidique via des liens C-C, pour générer un dérivé glycosyl cinnamate de méthyle. Cependant, lorsque le 2-iodophénol est utilisé comme partenaire de Heck, la coumarine correspondante a été isolée. Les dérivés C-galactopyrannosyl cinnamates de méthyle représentent de bons inhibiteurs monovalents de la PA-IL avec un Kd aussi bas que 37 micro M (Chapitre 4). / Carbohydrates represent a large family of organic molecules that play key roles in various biological processes. Due to their medicinal importance, preparation of deoxy-sugars, C-glycosides and C-disaccharides have become an important topic in organic synthesis. Mostly, this thesis presents a new de novo synthesis of 4-deoxy hexopyranoses, along with the preparation of biologically relevant C-glycosides. Moreover, a special attention has been focussed on the de novo synthesis of 4-deoxy-C-disaccharides. Firstly, Jacobsen Cr(III) catalyst and a binaphthol/titanium complex have been used to catalyze enantioselective hetero-Diels-Alder reactions. The dihydropyran thus formed has been transformed into naturally occurring 4-deoxy hexopyranoses. Therefore, the ezoaminuroic acid core, a desosamine precursor and neosidomycin have been prepared following a de novo approach. Moreover, as a comparative study, neosidomycin has also been synthesized using a chiron approach from methyl alpha-D-mannopyranoside. Finally, a preliminary biological evaluation of neosidomycin has been applied on concanavalin-A (Chapter 2). Secondly, homoallylic alcohols have been generated from a stereoselective allylation on aldehyde linked via C-C bonds to a mannoside residue. Then, the homoallylic alcohols have been transformed into 4-deoxy hexopyranoses in various configurations (D or L). Thereby, the syntheses of pseudo 4-deoxy-C-disaccharides, 4-deoxy-C-disaccharides and pseudo 4-deoxy aza-C-disaccharides have been easily performed. Determinations of the diastereoisomeric ratio of the allylation reactions along with the absolute configuration of the newly formed chiral center have been easily achieved. Various members of this new family have been deprotected for a preliminary biological evaluation on concanavalin-A (Chapter 3). Finally, the syntheses of relevant C-glycosides have been realized regarding two aspects: i) 3-C-mannopyranosyl coumarin synthesis and ii) synthesis of C-galactosides as PA-IL inhibitors. Methyl glycosyl cinnamates have been isolated using a Heck coupling on alpha,beta-insaturated ester linked to glycosidic moieties via C-C bonds. However, when 2-iodophenol is used as a Heck partner, the corresponding coumarins have been isolated. C-Galactosyl methyl cinnamate derivatives represent good monovalent inhibitors with Kd as low as 37 micro M against PA-IL (Chapter 4).

The aetiological diagnosis of recessive non-syndromic hearing loss poses a challenge owing to marked heterogeneity and the lack of identifying clinical features. The finding that up to 50% of recessive non-syndromal genetic hearing loss among Caucasians was due to mutations in GJB2, the gene encoding Connexin 26 (Cx26) was a breakthrough, whose value as a diagnostic tool has been limited by the significant variation in the prevalence of deafness genes and loci among population groups. The significant association of the GJB6-D13S1830 deletion among individuals with one mutant GJB2 allele highlighted the need to explore population specific genetic mutations for NSHL. Although data from Sub-Saharan Africa is limited, reported studies found a high prevalence of R143W GJB2 mutation among Ghanaian, the 35delG mutation in 5 out of 139 Sudanese and a low prevalence of GJB2 variations among 385 Kenyan deaf children. The mutation spectrum of Waardenburg Syndrome (WS) in Africans has not been documented. During a visit to a School for the Deaf in the Limpopo Province of South Africa in 1997, it was noted that a high number of students came from Nzhelele sub-district. All had childhood onset hearing loss with no associated anomalies or disorders. The question arose as to whether there was a high-risk area for deafness in the Limpopo Province and what the aetiology of this hearing loss was.The main aim of this study was to investigate the role of GJB2, the GJB6-D13S1830 deletion, and the four common mitochondrial mutations, A1555G, A3243G, A7511C and A7445G, in the African hearing-impaired population of Limpopo province in South Africa, and to identify the mutation spectrum of the deafness genes found. The type and degree of hearing loss in this hearing impaired population would also be assessed. Secondly, this study sought to identify the mutations in a sibling pair with 2 clinical WS and to use the findings in a future study to establish the mutation spectrum of WS in the African population of the Limpopo province and of South Africa in general. The study was designed as a two phase study, in which phase 1 was used for hypothesis formulation and phase 2 was for hypothesis testing. While phase 1 was a descriptive retrospective case study, phase 2 was a combination of sample survey and prospective descriptive case study. In phase 1, demographic data of 361 students in two schools of the deaf in the Limpopo province was analyzed for evidence of areas of high risk populations for deafness in the province. In phase 2, a group of 182 individuals with genetic non-syndromic hearing loss (NSHL) and two siblings with clinical WS from two schools for the Deaf in the Limpopo Province of South Africa were investigated. A thorough clinical examination, audiological evaluation and urinalysis were done. Mutational screening was carried out in all 184 subjects using genomic DNA using single-strand conformation polymorphism (SSCP), multiplex polymerase chain reaction (PCR), and direct sequencing for GJB2, and Restriction Fragment-Length Polymorphism (PCR–RFLP) analysis for GJB6, and SSCP, hetero-duplex analysis, and direct sequencing of the first 8 exons of PAX3 and all of MITF for Waarenburg syndrome. Data analysis was by geographical mapping, frequency tables, tests of association with calculation of odds ratios, and binary logistic regression analysis using STATA and GIS mapping systems. The results indicate that there seem to be areas of genuine populations at risk for hearing loss in the Limpopo province of South Africa, namely Mutale and parts of Makhado and Thulamela municipalities. In Thulamela (NP343) wards 11-15, 26-30 and 31-35, and in Mutale (NP 344) wards 6-10, together accounted for 67 (18%) of participants in phase 1, and 33 (18%) of the participants in phase 2 of the study. Mutale municipality in the Vhembe 3 district gave with a projected prevalence of at least 13.14 deaf children per 100,000 African population attending the local school for the deaf. The observed hearing loss is a genetic, non-syndromic form, which is mainly severe and severe to profound, although without any clear defining configuration or shape. It is a stable, non-progressive and prelingual form of hearing loss, implying that this may be a recessive form of deafness. No identifiable environmental confounding factors or associations were identified. The deafness is not linked the common known auditory gene mutations in GJB2, the GJB6-D13S1830 deletion, or the common mitochondrial mutations A1555G, A3243G, A7511C and A7445G. Severe and profound levels of hearing loss were found in 22.8% and 75% of the cohort respectively, with the majority exhibiting flat (70.1%) or sloping (23.4%) audiograms that were commonly symmetrical (81.5%). However, as indicated, there was no clear pattern in the audiological findings overall. None of the 184 hearing impaired individuals exhibited any of the reported disease causing mutations of GJB2, including 35delG. There was, however, a high prevalence of two variants, the C>T variant at position g.3318-15 and the C>T variant at position g.3318-34, occurring in 21.4% and 46.2% of the deaf cohort respectively. The same variants were found to occur in 35% and 42.6% of a normal hearing control group (n = 63) respectively, indicating that these variations are polymorphisms. In three subjects (1.63% of the cohort), a T>A homozygous variation at position g.3318-6 was detected. Its significance in the causation of NSSNHL is yet to be determined. The GJB6-D13S1830 deletion was not detected in any of the participants. None of the four mitochondrial mutations screened for were found. 4 These results indicate that GJB2 is not a significant deafness gene in the African population of the Limpopo Province of South Africa and that significant genes for non-syndromic recessive hearing loss in this population are yet to be found. The geographical clustering of deafness found in this study, combined with the lack of identifiable common associated clinical features among the subjects of this study (excluding the WS sibling pair), suggests that these subjects have a genetic recessive non-syndromal type of hearing loss. In the context of historical and cultural evidence of consanguinity in this population, a founder effect cannot be ruled out. A rare mutation, R223X, previously identified only once out of 470 WS patients, was identified in the PAX3 gene among the WS sibling pair. A novel silent change GGG>GGT at amino acid 293, was also identified. These identical findings document, for the first time, a molecular defect in WS in an African sibling pair, and confirm WS Type I in this family, which could be found in other WS type I South Africans in the Limpopo Province of South Africa. The current study demonstrated that parents of genetically hearing impaired children in these areas are able to detect hearing loss at an early age, with over 60% suspecting their children’s hearing loss below 6 months of age. A child-centered management model encompassing all the areas relevant to childhood deafness/hearing impairment, which takes into consideration the prevailing logistical and financial constraints of the available healthcare system, is proposed. The implementation of this model requires a paradigm shift from the current fragmented model of service delivery to a cohesive patient-centered approach, based on concrete data from appropriate community based research, in which all the relevant parties communicate and share resources. 5 It would achieve the goals of early detection and intervention, as well as inclusive education for all. The relevant health and education policies are already in place and the posts funded. Equitable implementation of these policies would require appropriate community based research, as well as improved communication and consultation between the various stakeholders to ensure an efficient and affordable quality healthcare service for all hearing impaired South Africans.