Weak intermolecular interactions have very strong impact on the structures and properties of life giving molecules like H2O, DNA, RNA etc. These interactions are responsible for many biological phenomena. The directional preference of some of these interactions is used for designing different synthetic approaches in the supramolecular chemistry. The work reported in this Thesis comprises of investigations of weak intermolecular interactions in gas phase using home-built Pulsed Nozzle Fourier Transform Microwave (PN-FTMW) spectrometer as an experimental tool and ab-initio and Atoms in Molecules (AIM) theory as theoretical tools. The spectrometer which is coupled with a pulsed nozzle is used to record pure rotational spectra of the molecular clusters in a jet cooled molecular beam. In the molecular beam molecules/complexes are free from interactions with other molecules/complexes and thus, spectroscopy in the molecular beams provides information about the 'isolated' molecule/complex under investigation. The rotational spectra of the molecules/complexes in the molecular beam provide their geometry in the ground vibrational states. These experimental geometries can be used to test the performance and accuracy of theoretical models like ab-initio theory, when applied to the weakly bound complexes. Further the AIM theory can be used to gain insights into the nature and strength of the intermolecular interactions present in the system under investigation. Chapter I of this Thesis gives a brief introduction of intermolecular interactions. Other than hydrogen bonding, which is considered as the most important intermolecular interaction, many other intermolecular interactions involving different atoms have been observed in past few decades. The chapter summarizes all these interactions. The chapter also gives a brief introduction to the experimental and theoretical methods used to probe these interactions. In Chapter II, the experimental and theoretical methods used in this work are summarized. Details of our home-built PN-FTMW spectrometer are given in this chapter. The chapter also discusses briefly the theoretical methods like ab-initio, AIM and Natural bond orbital (NBO) analysis. We have made few changes in the mode of control of one of our delay generators which have also been described. Chapter III and Chapter V of this Thesis are dedicated to the propargyl alcohol complexes. Propargyl alcohol (PA) is a molecule of astrophysical interest. It is also important in combustion chemistry since propargyl radical is considered as the precursor in soot formation. Moreover, PA is a multifunctional molecule, having a hydroxyl (-OH) and an acetylenic (-C≡C-H) group. Both of the groups can individually act as hydrogen bond acceptor as well as donor and thus PA provides an exciting possibility of studying many different types of weak interactions. Due to internal motion of -OH group, PA monomer can exist in gauche as well as trans form. However, rotational spectra of PA-monomer show the presence of only gauche conformer. In Chapter III, rotational spectra of Ar•••PA complex are discussed. The pure rotational spectra of the parent Ar•••PA complex and its two deuterated isotopologues, Ar•••PA-D (OD species) and Ar•••PA-D (CD species), could be observed and fitted within experimental uncertainty. The structural fitting confirmed a structure in which PA is present as gauche conformer and argon interacts with both the O-H group and the acetylenic group leading to Ar•••H-O and Ar•••π interactions respectively. Presence of these interactions was further confirmed by AIM theoretical analysis. In all the three isotopologues c-type rotational transitions showed significant splitting. Splitting patterns in the three isotopologues suggest that it originates mainly due to the large amplitude motion of the hydroxyl group and the motion is weakly coupled with the carbon chain bending motion. No evidence for the complex with trans conformer of PA was found. Although, we could not observe Ar•••trans-PA complex experimentally, we decided to perform ab-initio and AIM theoretical calculations on this complex as well. AIM calculations suggested the presence of Ar•••H-O and a unique Ar•••C interaction in this complex which was later found to be present in the Ar•••methanol complex as well. This prompted us to explore different possible interactions in methanol, other than the well known O-H•••O hydrogen bonding interactions, and eventually led us to an interesting interaction which we termed as carbon bond. Chapter IV discusses carbon bonding interaction in different complexes. Electrostatic potential (ESP) calculations show that tetrahedral face of methane is electron-rich and thus can act as hydrogen/halogen bond acceptor. This has already been observed in many complexes, e.g. CH4•••H2O/HF/HCl/ClF etc., both experimentally and theoretically. However, substitution of one of the hydrogens of methane with -OH leads to complete reversal of the properties of the CH3 tetrahedral face and this face in methanol is electron-deficient. We found that CH3 face in methanol interacts with electron rich sites of HnY molecules and leads to the formation of complexes stabilized by Y•••C-X interactions. This interaction was also found to be present in the complexes of many different CH3X (X=OH/F/Cl/Br/NO2/NF2 etc.) molecules. AIM, NBO and C-X frequency shift analyses suggest that this interaction could be termed as "carbon bond". The carbon bonding interactions could be important in understanding hydrophobic interactions and thus could play an important role in biological phenomena like protein folding. The carbon bonding interaction could also play a significant role in the stabilization of the transition state in SN2 reactions. In Chapter V of this Thesis rotational spectra of propargyl alcohol dimer are discussed. Rotational spectra of the parent dimer and its three deuterated (O-D) isotopologues (two mono-substituted and one bi-substituted) could be recorded and fitted within experimental uncertainty. The fitted rotational constants are close to one of the ab-initio predicted structure. In the dimer also propargyl alcohol exists in the gauche form. Atoms in molecules analysis suggests that the experimentally observed dimer is bound by O-H•••O, O-H•••π and C-H•••π interactions. Chapter VI of the thesis explores the 'electrophore concept'. To observe the rotational spectra of any species and determine its rotational constant by microwave spectroscopy, the species should have a permanent dipole moment. Can we obtain rotational constants of a species having no dipole moment via microwave spectroscopy? Electrophore concept can be used for this purpose. An electrophore is an atom or molecule which could combine with another molecule having no dipole moment thereby forming a complex with a dipole moment, e.g. Argon atom is an electrophore in Ar•••C6H6 complex. The microwave spectra of Ar•••13CC5H6 and Ar•••C6H5D complexes were recorded and fitted. The A rotational constant of these complexes was found to be equal to the C rotational constant of 13CC5H6 and C6H5D molecules respectively and thus we could determine the C rotational constant of microwave 'inactive' 13CC5H6. This concept could be used to obtain the rotational spectra of parallel displaced benzene-dimer if it exists. We recently showed that the square pyramidal Fe(CO)5 can act as hydrogen bond acceptor. Appendix I summarizes the extension of this work and discusses interactions of trigonal bipyramidal Fe(CO)5 with HF, HCl, HBr and ClF. Our initial attempts on generating a chirped pulse to be used in a new broadband spectrometer are summarized in Appendix II. Preliminary investigations on the propargyl•••water complex are summarized in Appendix III.

The importance of weak interactions between molecules to life and all parts of science and engineering is unquestionable and there have been an enormous interest in such interactions. Among all the weak interactions, hydrogen bonding is the most popular and it has enjoyed the most attention of the scientific community. Halogen bonding is gaining more popularity in the recent time, as its importance to biological molecules and crystal engineering has been recognized. In this work, a Pulsed Nozzle Fourier Transform Microwave spectrometer has been used to study the rotational spectra of molecules and hydrogen bonded complexes. Structural information is obtained from the rotational spectra. Ab initio electronic structure, Natural Bond Orbital (NBO) and Atoms in Molecules (AIM) theoretical methods have been used to characterize the weak intermolecular interactions, including hydrogen bonding, halogen bonding and lithium bonding. In Chapter I, introduction to weak interaction is discussed. A brief introduction of different experimental and theoretical methods is presented. Chapter II discusses in detail about the different methods used to investigate weak interaction, both experimentally and theoretically, in this work. In our lab, we use Pulsed Nozzle Fourier Transform Microwave spectrometer to determine the complexes spectra and structures. We generate MW radiation with the help of electronic devices and use Balle-Flygare cavity where molecular interaction takes place. We inject the sample inside the cavity in form of supersonic molecular beam through a pulsed nozzle, parallel to MW radiation. The detailed instrumental discussion about MW spectrometer has been done in this Chapter. We extensively use theoretical methods to probe weak bonding and characterize them. Ab initio and DFT calculations are used to optimize the structure of the complexes and predict their rotational spectra. Atoms in Molecules theory and Natural Bond Orbital theory are then used with the ab initio wave functions to understand the weak interactions in depth. Discussion about these methods and software used for the analysis will also be discussed. In Chapter III, rotational spectrum of Hexafluoroisopropanol (HFIP) monomer is presented. HFIP is an interesting molecule as it offers many possibilities as hydrogen bond donor and acceptor. It has the OH group which can both accept/donate a hydrogen bond and in addition it has a very acidic CH group. It is the only solvent that can dissolve polyethylene terephthalate, a normally difficult-to-dissolve polymer, and clearly it has unique interactions with this difficult to solve polymer. We have recorded and fitted rotational spectra of five different isotopologues of HFIP which helped us in determining its accurate structure. Though, it can exist in synclinical and antiperiplanar conformers, only the later has been detected in our molecular beam spectrometer. This happens to be the global minimum structure of HFIP. Combination of experimental observations and ab initio calculations provided many evidences which confirmed the presence of antiperiplanar conformer, experimentally. Since, the rotational constants for both conformers were very close, it was always challenging to pick up one conformer as experimentally observed structure. A prototype molecule, hexafluoroisobutene (HFIB) shows doubling of rotational transitions due to tunnelling/counter rotation of the two CF3 groups through a small barrier. Interestingly, such motion has no barrier in HFIP and hence no splitting in transitions was observed. Potential energy surface calculated for counter-rotation of the two CF3 groups is consistent with this observation. This barrier is different from eclipsed-staggered exchange barrier, observed by 60 counter rotation of both terminal CF3 groups, for which the barrier height is very large and tunnelling cannot occur. The origin/lack of the small barrier in HFIB/HFIP has been explored using Natural Bond Orbital (NBO) method which helped in understanding intramolecular bonding in these molecules. Along with HFIB, other prototype molecules were also considered for the analysis e.g. hexafluoroacetone, hexafluoroacetone imine, hexafluoroisobutane, hexafluoroisopropylamine. In the last section of this Chapter, we have discussed the generalized behaviour of molecules which have CF3-C-CF3 groups. In Chapter IV, rotational spectrum of HFIP•••H2O complex is presented. Aqueous solution of HFIP stabilizes α-helical structure of protein, a unique property of this solvent. The main objective of this Chapter is understanding the interaction between HFIP and H2O. Microwave spectrum of HFIP•••H2O was predicted and recorded. Three isotopologues were investigated. Though, this complex could in principle have several structural conformers, detailed ab initio calculations predicted two conformers and only one was observed. Though, the rotational constants for both structures were somewhat similar, lack of a dipole transitions, larger intensity of b-dipole transitions over c-dipole transitions and isotopic substitution analysis positively confirm the structure in which HFIP acts as the hydrogen bond donor. The linear O-H•••O hydrogen bond in HFIP-H2O complex is significantly stronger than that in water dimer with the H•••O distance of 1.8 Å. The other structure for this complex, not found in experiment is cyclic with both C-H•••O and O-H•••O hydrogen bonds, both of which are bent with H•••O distances in the range 2.2-2.3 Å. Both AIM and NBO calculations have been used to characterize the hydrogen bond in this complex. In Chapter V, a comprehensive study on hydrogen bonding, chlorine bonding and lithium bonding have been done. A typical hydrogen bonded complex can be represented as A•••H-D, where A is the acceptor unit and H-D is the hydrogen bond donor unit. Many examples are known in literature, both experimentally and theoretically, in which the A-H-D bond angles are not linear. Deviation from linearity also results in the increase in A•••H bond lengths, as noted above for the two structures of HFIP•••H2O complex. Though this has been known for long, the distance between A and D being less than the sum of their van der Waals ‘radii’ is still used as a criterion for hydrogen bonding by many. Our group has recently shown the inappropriateness of van der Waals ‘radii’ and defined hydrogen bond ‘radii’ for various donors, DH and A. A strong correlation of DH hydrogen bond ‘radii’ with the dipole moment was noted. In this Chapter, we explored in detail the angular dependence of hydrogen bond ‘radii’. Electron density topology around DH (D = F, Cl and OH) has been analyzed in detail and shown to be elliptical. For these molecules, the two constants for H atom treated as an ellipse have been determined. It is hoped that these two constants will be used widely in analyzing and interpreting H•••A distances, as a function of D-H•••A angles, rather than one ‘radius’ for H and acceptor atoms. In Chapter VI, Detailed analysis and comparisons among hydrogen bond, chlorine bond and lithium bond, have been done. Hydrogen can be placed in group 1 as well as group 17 of the periodic table. Naturally, lithium bonding and halogen bonding have been proposed and investigated. There have been numerous investigations on the nature of hydrogen bonding and the physical forces contributing to it. In this Chapter, a total of one hundred complexes having H/Cl/Li bonding have been investigated using ab initio, AIM and NBO theoretical methods. Various criteria proposed in the literature have been examined. A new criterion has been proposed for the characterization of closed shell (ionic/electrostatic) and open shell (covalent) interactions. It has been well known that the D-H bond weakens on the D-H•••A hydrogen bond formation and H•••A bond acquires a fractional covalency. This Chapter shows that for D-Li•••A complexes, the ionicity in D-Li is reduced as the Li•••A bond is formed This comprehensive investigation of H/Cl/Li bonding has led us to propose a conservation of bond order, considering both ionic and covalent contributions to both D-X and X•••A bonds, where DX is the X-bond donor and A is the acceptor with X = H/Cl/Li. Hydrogen bond is well understood and its definition has been recently revised [Arunan et al. Pure Appl. Chem., Vol. 83, pp. 1619–1636, 2011]. It states “The X–H•••Y hydrogen bond angle tends toward 180° and should preferably be above 110°”. Using AIM theory and other methods, this fact is examined and presented in Appendix A. In second part of appendix A, a discussion about calling H3¯ complex as trihydrogen bond and its comparison with FHF¯ complex, is presented. In Appendix B, there is tentative prediction and discussion about the HFIP dimer. Condense phase studies show that HFIP have strong aggregation power to form dimer, trimer etc. During, HFIP monomer study, we have unassigned lines which are suspected to be from HFIP dimer. These are tabulated in the Appendix B as well.

No description available.

Les alpha oléfines linéaires courtes sont des molécules de base en pétrochimie donc le marché est en constante augmentation notamment pour les oléfines légères (butène-1, hexène-1, octène-1). Ces oléfines, utilisées massivement dans l’industrie des plastiques, sont produites par la réaction catalytique d’oligomerisation de l’éthylène. IFPEN a contribué à développer plusieurs procédés homogènes d’oligomérisation de l’éthylène (AlphaButol, AlphaHexol, AlphaSelect) à base des complexes de titane, chrome ou zirconium. A travers une collaboration avec l’Université d’Amsterdam de nouvelles stratégies de développement de ligands ont été entreprises afin de rendre les catalyseurs à base de nickel sélectifs pour cette transformation. Ainsi, une approche supramoléculaire basée sur des interactions par liaison hydrogène, jusqu’alors décrite pour les métaux nobles, a été développée et appliquée aux complexes de nickel. Des complexes organométalliques originaux ont pu être générés et les interactions supramoléculaires ont été caractérisées par diffraction aux rayons X notamment. Ces complexes se présentent sous forme zwitterionique et sont formés par la combinaison de deux ligands simples donneurs et/ou accepteurs d’hydrogène. Ces complexes se sont avérés très actifs vis-à-vis de l’éthylène et ne nécessite pas l’ajout d’activateur du fait de la présence d’une liaison nickel-carbone réactive. Ils ont permis d’accéder à des sélectivités très importantes en butène-1. Appuyé par des expériences in situ et l’évaluation en catalyse de plusieurs complexes aux propriétés électroniques et stériques variées, cette approche a permis d’identifier l’espèce active et de mesurer l’impact de plusieurs descripteurs permettant de moduler la sélectivité et l’activité de la réaction catalytique en profondeur. / The demand for short linear alpha olefins is constantly increasing and motivates the development of robust and selective catalysts. In this thesis, several libraries of phosphorus ligands with the capacity to form dissymmetric or supramolecular assemblies were synthesized. The variability observed within the aminophosphine libraries, clearly reflected by the various tautomeric equilibrium of the ligand, was also observed in the nickel complexes as a single ligand could generate several complexes with different structures. Sulphonyliminobisphosphine were then introduced as a new class of ligands. These precursors rearrange in the presence of nickel to generate diphosphinamine nickel complexes. Activated by MAO, these complexes are active in the reaction of ethylene oligomerisation and produce short chain olefins. A new approach that forms stable supramolecular nickel complexes was developed by combining two phosphorus ligands with Ni(0). These complexes stabilised by hydrogen bonding are directly active in the reaction of ethylene oligomerisation with some catalysts leading to high selectivity to 1-butene (up to 84%). To understand the origin of that selectivity, the scope of complexes was extended to ligands with different steric and electronic properties. Their evaluation in the reaction of ethylene oligomerisation evidenced a relation between the catalyst structure and the selectivity of the reaction. Mechanistic studies, under an ethylene atmosphere, reveals that cationic complexes rearrange to neutral complexes, which are likely, the active species.

Department of Chemistry / PhD (Chemistry) / This thesis is concerned with the computational study of naphthylisoquinoline alkaloids having antimalarial properties. The study was considered interesting because of the importance of gathering information on antimalarial molecules and because these molecules had not yet been studied computationally. The alkaloids considered in this study had been isolated from tropical lianas belonging to the Dioncophyllaceae and Ancistrodaceae families. They comprise alkaloids with both monomeric and dimeric structures. The monomeric structures consist of one unit and the dimeric ones of two units, with each unit containing a naphthalene moiety and an isoquinoline moiety. 33 monomeric molecules were studied, which represent a large portion of all the monomeric naphthylisoquinoline alkaloids isolated so far. Two dimeric molecules with antimalarial activity were investigated, namely, jozimine A2 and mbandakamine A. A third dimeric molecule, with a structure close to that of jozimine A2 but different activity (michellamine A, anti-HIV) was also calculated for comparison purposes. This work utilised electronic structures methods and involved the conformational study of all the molecules selected to identify the stabilising factors in vacuo and in solution. Two levels of theory (HF/ 6-31G (d,p) and DFT/B3LYP/ 6-31+G(d,p)) were utilised to compare their performance for compounds of this type, also in view of a future study extending to other compounds of the same class. The molecules were firstly studied in vacuo and secondly in three different solvents – chloroform, acetonitrile and water – characterized by different polarities and different H-bonding abilities. Quantum chemical calculations in solution were carried out using the Polarisable Continuum Model (PCM). The main stabilizing factors are the presence and types of intramolecular hydrogen bonds (IHBs), which are the dominant factors, and also the mutual orientation of the moieties. The possible IHBs comprise OH⋯O (or OH⋯N and NH⋯O for mbandakamine A) and other H-bond types interactions such as OH⋯ and CH⋯O (or CH⋯O and CH⋯N for mbandakamine A). The moieties prefer to be perpendicular one to another, which is a common tendency of aromatic vii systems. In monomeric structures, there may be only one OH⋯O and possibly also one of each of the other two types of IHBs interactions. In dimeric structures, there may be up to four (five in mbandakamine A) OH⋯O IHBs simultaneously and also other H-bond type interactions. The results provide a comprehensive picture of the molecular properties of these compounds, such as conformational preferences, dipole moments, HOMO-LUMO energy gaps, harmonic vibrational frequencies, solvent effect and influence of the solvent on molecular properties which respond to polarisation by the solvent. Altogether, these results may contribute to a better understanding of their biological activity and to the design of molecular structures with enhanced biological activity. This is the reason of focusing the efforts on the investigation of chemical and physical properties of these alkaloids molecules. / NRF

No description available.

The title compound, C20H18O3, crystallizes in the space group P21/c with one mol­ecule in the asymmetric unit of the cell. The fluorene skeleton is nearly planar and the crystal structure is composed of mol­ecular layers extending parallel to the (302) plane. Within a layer, one formyl oxygen atom participates in the formation of a Carene—H...O bond, which is responsible for the formation of an inversion symmetric supra­molecular motif of graph set R22(10). A second oxygen atom is involved in an intra­molecular Carene—H...O hydrogen bond and is further connected with a formyl hydrogen atom of an adjacent mol­ecule. A Hirshfeld surface analysis indicated that the most important contributions to the overall surface are from H...H (46.9%), O...H (27.9%) and C...H (17.8%) inter­actions.

La compréhension et le contrôle des interactions intermoléculaires est d'une importance fondamentale dans les domaines de la reconnaissance moléculaire et de l'ingénierie cristalline, ainsi que dans les systèmes biologiques. Parmi les contacts faibles les plus fréquents qui lient les molécules dans les solides organiques nous trouvons la liaison halogène, la liaison chalcogène, et la liaison hydrogène faible. Dans cette thèse, des études expérimentales et théoriques de densité de charge rhô(r) basées sur la méthodologie QTAIM ont été effectuées pour l'analyse des liaisons halogènes et chalcogènes, et pour leur comparaison avec les liaisons hydrogène faibles. Pour ce faire, nous avons réalisé l'affinement multipolaire de la densité électronique obtenue à partir de la diffraction des rayons-X sur monocristal, ainsi qu'à partir des calculs périodiques DFT. A l'issue de nos résultats, nous avons définie la nature de ces interactions faibles (électrophile-nucléophile) et caractérisé leur intensité et directionnalité. Basé sur la topologie de L(r) = ¬rhô delta inversé2 rhô(r), le descripteur électrostatique (delta(L/rhô)) nous a permis d'évaluer quantitativement l'interaction électrostatique entre les régions de concentration (CC) et de dilution (CD) de charge de la couche de valence des atomes. L'énergie d'interaction (Eint) a été décrite à partir de descripteurs topologiques de rhô(r). Nous nous sommes intéressés également à la formation de fragments structuraux récurrents, appelés synthons. Il a été prouvé que le synthon peut être créé non seulement par des groupements d'atomes similaires, mais aussi par des ensembles de sites CC et CD qui sont impliqués de façon similaire dans la formation de contact / Understanding and control of intermolecular interactions play a crucial role in molecular recognition, crystal engineering, and biological systems. Three very frequent weak contacts linking the molecules in organic solids are halogen, chalcogen, and weak hydrogen bondings. In this thesis, we perform experimental and theoretical charge density rho(r) studies based on the QTAIM methodology for analyzing halogen and chalcogen bonding, and for comparing them with weak hydrogen bonding, as derived from the high-resolution single crystal X-ray diffraction multipole-refined electron density and from density functional theory (DFT) calculations. Defining the nature of these weak interactions as electrophilic-nucleophilic, we particularly focus on their strength and directionality. Based on the topology of L(r) = ¬rho inverted delta2 rho(r), a proposed electrostatic descriptor (delta(L/rho)) permitted us to evaluate quantitatively the electrostatic intensity between charge concentration (CC) and charge depletion (CD) regions belonging to the valence shell of the interacting atoms. The interaction energy (Eint) was described from the topological properties of rho(r). The attention has been also paid to the formation of recurrent structural fragments, called synthons. By the developed approach, it is proved that the synthon arrangement can be created not only by groups of atoms, but also by sets of CC and CD sites similarly involved in the contact formation

Die Energierelaxationsdynamik und strukturelle Dynamik der DNA spielen eine entscheidende Rolle für das Verständnis der photochemischen Eigenschaften und biologischen Funktion von DNA. Die schnellsten Prozesse geschehen dabei auf Zeitskalen im Femto- bis Pikosekundenbereich und können durch zeitaufgelöste (ultraschnelle) Messungen an molekularen Schwingungsanregungen in Echtzeit beobachtet werden. In dieser Arbeit werden NH-Streck Schwingungsmoden der Nukleobasen sowie OH-Streckmoden der Hydrathülle mittels linearer infrarot (IR) Spektroskopie sowie ultraschneller Pump-Probe und zweidimensionaler IR Spektroskopie untersucht. Messungen an monomerartigen Nukleobasen, wasserstoffverbrückten Nukleobasenpaaren und kurzen DNA Fragmenten in Doppelhelixstruktur ermöglichen es, die Effekte der verschiedenen Wasserstoffbrücken und Schwingungskopplungen separat voneinander zu untersuchen. Im Zusammenspiel mit exzitonischen und quantenchemischen Rechnungen werden so weitreichende Einsichten in die spektroskopischen Eigenschaften und die Relaxationsdynamik von Schwingungsanregungen in DNA gewonnen. Es wird u.a. gezeigt, dass Wasserstoffbrücken zwischen Nukleobasen eine Lebensdauer größer 1 ps besitzen und eine beschleunigte Energierelaxation durch Fermiresonanzen mit niederfrequenten Schwingungsmoden des Fingerprintbereichs bewirken. Die DNA-Hydrathülle zeigt eine ultraschnelle strukturelle Dynamik unabhängig von der Basenpaarzusammensetzung und fungiert als effiziente Wärmesenke für hochfrequente Schwingungsanregungen. / Energy relaxation and structural dynamics in DNA play a crucial role for the understanding of the photochemical properties and biological function of DNA. The fastest of such processes occur on the femto- to picosecond time scale and can be followed in real time through time-resolved (ultrafast) measurements on molecular vibrations. In this work, NH stretching excitations of nucleobases and OH stretching modes of the hydration shell are analyzed through linear infrared (IR) spectroscopy as well as ultrafast pump-probe and two-dimensional IR spectroscopy. Measurements on monomeric nucleobases, hydrogen-bonded nucleobase pairs, and short DNA fragments in double helix structure allow one to examine the effects of the different hydrogen bonds and vibrational couplings separately from each other. The combination with excitonic and quantum chemical calculations provides profound new insights into the spectroscopic properties and relaxation dynamics of vibrational excitations in DNA. This work shows that hydrogen bonds between nucleobases have a lifetime greater than 1 ps and lead to an accelerated dissipation of energy due to Fermi resonances with vibrational modes in the fingerprint range. The hydration shell of DNA exhibits ultrafast structural dynamics independent of the base pair composition and serves as an efficient heat sink for high-energy vibrational excitations.

Les nucléolipides sont des molécules amphiphiles dont la structure bio-inspirée dérive de celle des acides nucléiques. Leur auto-assemblage en milieu aqueux aboutit à la formation d’objets supramoléculaires de morphologies et structures très diverses. La morphologie a été caractérisée par des techniques complémentaires de microscopie optique et de diffusion de la lumière, tandis que leur structure a été déterminée par la diffusion des rayons X. Il a ainsi été mis en évidence l’existence et le rôle fondamental des interactions faibles entre têtes polaires, au sein des auto-assemblages. La nature de ces interactions faibles a été déterminée par des techniques de spectroscopies IR et UV. Un premier objectif a été de mettre en évidence l’importance de ces interactions, ainsi que leur corrélation avec d’autres facteurs qui régissent le mécanisme d’auto-assemblage, tels que la nature chimique des amphiphiles, ou la morphologie et la structure des objets supramoléculaires en présence.Par ailleurs, la tête polaire nucléotide permet également d’imaginer la formation d’interactions faibles entre les auto-assemblages et un monobrin d’acide nucléique, à l’image des interactions spécifiques entre bases azotées présentes dans l’ADN. Lors de ce travail, nous nous sommes intéressés à une méthode de vectorisation d’acides nucléiques par des objets eux aussi chargés négativement. Contrairement aux approches classiques, l’interaction électrostatique est ici défavorable et l’association repose alors uniquement sur des interactions faibles spécifiques, estimées en spectroscopie. De façon surprenante, la formation des complexes a pu être mise en évidence par des expériences de diffraction des rayons X et un modèle approprié a permis de proposer des mécanismes de formation des complexes. Les propriétés thermodynamiques des différents complexes formés ont été évaluées par la technique de Calorimétrie à Titration Isotherme (ITC). Un point remarquable a été la mise en évidence systématique de trois types de comportements sur l’ensemble des complexes étudiés en fonction de la nature et de la spécificité des interactions mises en jeu. Ceci nous a ainsi permis de proposer différents mécanismes de formation pour chaque type de complexe observé. / Nucleolipids are amphiphilic molecules which bio-inspired structure derives from nucleic acid structure. Their self-assembling behaviour in aqueous medium leads to the formation of supramolecular objects of very different morphologies and structures. The morphology has been characterized with optical microscopy and light scattering complementary techniques, whereas their structure has been determined with X-ray scattering. Thus the existence and the fondamental role of weak interactions between polar heads inside the self-assemblies have been highlighted. The nature of these weak interactions has been determined with IR and UV spectroscopies techniques. A first objectif has been to highlight the importance of these interactions, as well as the their correlation with other factors which drive the mechanism of self-assembly, such as the chemical nature of amphiphiles or the morphology and structure of the supramolecular objects.Moreover the nucleotide polar hear also allows to imagine the formation of weak interactions between the self-assemblies and a single-stranded nucleic acid, such as those highlighted in DNA. In this work, we found interest in a nucleic acid vectorisation method with negatively charged objects as well. On the contrary of classic approaches, electrostatic interaction was here defavorable and assembling relies only on specific weak interactions, estimated with spectroscopy methods. Surprisingly, complexes formation could be highlighted with X-ray scattering experiments, and an appropriate model has allowed the proposal of mechanisms for the formation of complexes. Thermodynamic properties of the different complexes formed have been evaluated with Isothermal Titration Calorimetry (ITC) technique. A remarkable point was the systematic highlighting of three types of behaviour on the whole set of complexes studied, depending of the nature and the specificity of the weak interactions implied. This led us to different proposals for the mechanism of formation of each type of complex studied.