Yes / The optimisation of a peptide-capped glycine using the novel force field FFLUX is presented. FFLUX is a force field based on the machine-learning method kriging and the topological energy partitioning method called Interacting Quantum Atoms. FFLUX has a completely different architecture to that of traditional force fields, avoiding (harmonic) potentials for bonded, valence and torsion angles. In this study, FFLUX performs an optimisation on a glycine molecule and successfully recovers the target density-functional theory energy with an error of 0.89 ± 0.03 kJ mol−1. It also recovers the structure of the global minimum with a root-mean-squared deviation of 0.05 Å (excluding hydrogen atoms). We also show that the geometry of the intra-molecular hydrogen bond in glycine is recovered accurately. / EPSRC Established Career Fellowship [grant number EP/K005472]

Modern solid state chemistry is inconceivable without theoretical treatment of solids thanks to the availability of efficient and accurate computational methods. Being developed mainly by physicist's community and deeply rooted in the formalism of reciprocal space, they often lack connections to familiar chemical concepts, indispensable for the chemical understanding of matter. Quantum chemical topology approach is a powerful theory able to efficiently recover chemical entities from the abstract description of a system given by its density matrices. It can be used to partition any many-electron system into the atoms, using the topology of electron density or for instance into atomic shells, using the topology of ELI-D field. Various characteristics of interactions between these chemical building blocks can be obtained applying bonding indicators, e.g. from the analysis of domain-averaged properties. Quantum chemical topology methods have been extended in the current work for the applications on the diversity of theoretical methods widely used for the description of solids nowadays – from the mean field Kohn-Sham density functional theory to the reduced one-electron density matrices functional theory or from the scalar-relativistic methods to the many-component formalisms employing spinor wavefunctions. It has been shown, that they provide chemically meaningful description of the bonding which is universally applicable to any class of extended systems, be it ionic insulator, covalent solid or metal. It has been shown, that the relativistic effects on the chemical bonding can be easily revealed using extensions of bonding indicators developed in the current work. Classical chemical concepts like Zintl-Klemm concept can be easily recovered with these descriptions. Intimate connection between the class of the material and the degree of chemical bonding delocalization has been also established. All these methods have been successfully applied to the various classes of solids and delivered novel insights on their crystal structure, properties, solid state transitions and reactivity.

No description available.

Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2016-02-03T20:32:41Z No. of bitstreams: 1 BrenoAlmeidaSoares_TESE.pdf: 5447488 bytes, checksum: 8e0fcaa75efcdf3b24876215c0ef7081 (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2016-02-04T00:03:56Z (GMT) No. of bitstreams: 1 BrenoAlmeidaSoares_TESE.pdf: 5447488 bytes, checksum: 8e0fcaa75efcdf3b24876215c0ef7081 (MD5) / Made available in DSpace on 2016-02-04T00:03:56Z (GMT). No. of bitstreams: 1 BrenoAlmeidaSoares_TESE.pdf: 5447488 bytes, checksum: 8e0fcaa75efcdf3b24876215c0ef7081 (MD5) Previous issue date: 2014-09-15 / Neste trabalho foram desenvolvidos estudos sint?ticos e te?ricos para clerodanos bioativos obtidos de uma das plantas medicinais mais representativas da regi?o Amaz?nica do Brasil, Croton cajucara Benth. Especificamente, utilizou-se como mol?cula alvo o biocomposto majorit?rio isolado das cascas do caule deste Croton, o diterpen?ide 19-nor-clerodano trans-desidrocrotonina (t-DCTN). Derivados semisint?ticos foram obtidos de t-DCTN utilizando-se os seguintes procedimentos sint?ticos: 1) redu??o catal?tica com H2, 2) redu??o com NaBH4 e 3) redu??o estereosseletiva com NaBH4/CeCl3). Os derivados semi-sint?ticos do tipo 19-nor-furano-clerodanos alco?licos foram denominados de t-CTN, t-CTN-??OL, t-CTN-??OL, t-DCTN-??OL e t-DCTN-??OL, tendo sido caracterizados por RMN. Os ?lcoois clerodanos derivados t-CTN-??OL e t-CTN-??OL foram obtidos a partir do derivado semi-sint?tico t-CTN, que tamb?m pode ser isolado das cascas do caule de C. cajucara. Uma metodologia te?rica (DFT/B3LYP) envolvendo a previs?o de propriedades geom?tricas e magn?ticas como ?ngulos e dist?ncias de liga??es bem como deslocamento qu?mico e constante de acoplamento, foi desenvolvida para a mol?cula alvo t-DCTN em que foram correlacionados dados te?ricos de RMN e estruturais, tendo sido obtidas correla??o satisfat?rias com dados experimentais de RMN (com coeficientes de correla??o variando entre 0,97 e 0,99) e de difra??o de Raios-X. Esta metodologia te?rica foi validada para todos os derivados semi-sint?ticos apresentados neste trabalho. Em adi??o, informa??es topol?gicas obtidas com o aux?lio da Teoria Qu?ntica de ?tomos em Mol?culas (QTAIM) evidenciaram a presen?a de intera??es estabilizantes intramoleculares do tipo H-H e (C)O--H(C) em t-DCTN e t-CTN, contribuindo para o entendimento da diferente reatividade destes clerodanos na presen?a de NaBH4. / In this work it were developed synthetic and theoretical studies for clerodane-type diterpenes obtained from Croton cajucara Benth which represents one of the most important medicinal plant of the Brazil amazon region. Specifically, the majoritary biocompound 19-nor-clerodane trans-dehydrocrotonin (t-DCTN) isolated from the bark of this Croton, was used as target molecule. Semi-synthetic derivatives were obtained from t-DCTN by using the followed synthetic procedures: 1) catalytic reduction with H2, 2) reduction using NaBH4 and 3) reduction using NaBH4/CeCl3. The semi-synthetic 19-nor-furan-clerodane alcohol-type derivatives were denominated such as t-CTN, tCTN-??OL, t-CTN-??OL, t-DCTN-??OL, t-DCTN-??OL, being all of them characterized by NMR. The furan-clerodane alcohol derivatives t-CTN-??OL and tCTN-??OL were obtained form the semi-synthetic t-CTN, which can be isolated from the bark of C. cajucara. A theoretical protocol (DFT/B3LYP) involving the prevision of geometric and magnetic properties such as bond length and angles, as well as chemical shifts and coupling constants, were developed for the target t-DCTN in which was correlated NMR theoretical data with structural data, with satisfactory correlation with NMR experimental data (coefficients ranging from 0.97 and 0.99) and X-ray diffraction data. This theoretical methodology was also validated for all semi-synthetic derivatives described in this work. In addition, topological data from the Quantum Theory of Atoms in Molecules (QTAIM) showed the presence of H-H and (C)O--H(C) intramolecular stabilized interactions types for t-DCTN e t-CTN, contributing to the understanding of the different reactivity of this clerodanes in the presence of NaBH4.

Made available in DSpace on 2015-05-14T13:21:35Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 1225184 bytes, checksum: aea7240aacf52c5036cf6d487576423c (MD5) Previous issue date: 2009-10-14 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The intramolecular hydrogen bond occurs when the same molecules has both proton donor and proton acceptor groups in satisfactory configuration space for the formation of this interaction. It is important to note the changes in the structural, electronic and vibrational properties that occur due to the formation of this interaction. In the hydrogen bonding formation is an important phenomenon called charge transfer , where part of the electronic density of the proton acceptor species, Y, is transferred o the proton donor specie, HX. With respect to the vibrational spectrum are observed changes in the way of straightening of donor and acceptor proton species. Di-carbonyl compounds (C3H2O2R2) with their substituent groups (R=CH3, CN, H, NH2, OH and SH) were studied focusing on the energetic, structural, vibrational and electron density analysis. Initially the energy and structural analysis were carried out starting from the molecules optimized geometry. We also evaluated of the strength s hydrogen bonding and the length s intramolecular bond. The QTAIM study was performed to obtain the electron density s values and the electron density s Laplacian values and verify the existence of the bond critical point in the intramolecular hydrogen bond. From the harmonic vibrational spectra was possible to identify changes in the vibrational modes, related the intramolecular interaction s formation. / A ligação de hidrogênio intramolecular ocorre quando uma mesma molécula apresenta, simultaneamente, um grupo doador e outro receptor de próton, em configuração espacial favorável à formação dessa interação. É importante salientar as mudanças nas propriedades estruturais, eletrônicas e vibracionais que ocorrem devido à formação dessa interação. Na formação da ligação de hidrogênio ocorre um fenômeno importante denominado de transferência de carga , onde parte da densidade eletrônica da espécie receptora de próton, Y, é transferida para a espécie doadora de próton, HX. Com respeito aos espectros vibracionais, são observadas modificações nos modos de estiramento das espécies doadora e receptora de próton. Compostos di-carbonílicos (C3H2O2R2) com suas substituições (R=CH3, CN, H, NH2, OH e SH) foram estudados enfocando as análises energética, estrutural, vibracional e de densidade eletrônica. Inicialmente foram realizadas as análises energéticas e estruturais a partir da geometria otimizada das moléculas. Foram avaliados a força da ligação de hidrogênio e do comprimento da ligação intramolecular. O estudo usando a QTAIM foi realizado para adquirir os valores de densidade eletrônica e do Laplaciano da densidade eletrônica e verificar a existência do ponto crítico de ligação na ligação de hidrogênio intramolecular. A partir dos espectros vibracionais harmônicos foi possível identificar as variações no infravermelho, referentes à formação da interação intramolecular.

The main focus of this work was to investigate substitution effects on the chemical bonding in compounds of AlB 2 -type and related structure types. Delocalization indices within the QTAIM approach and the topological analysis of the ELI functionals were used as tools to describe the bonding situation in digallides and diborides. Digallides of AlB 2 -type were found only within group I and II; for CaGa 2 (meta-stable phase), SrGa 2 , BaGa 2 , YGa 2 and LaGa 2 compounds. Within these compounds, QTAIM analysis showed similar trend as previously found in diborides. That is, along the period in the Periodic Table, metal-triel interactions increase at the expense of in-plane (triel-triel) ab interactions (Tr=triel). However, transition metal diborides adopt the AlB 2 -type up to group VI. To understand this difference, we simulated transition metal (TM) digallides and diborides up to group VI in the AlB 2 -type. Additionally, the puckered variants diborides ReB 2 and OsB 2 were also simulated in the AlB 2 -type. With filling of d shell, there is a delicate balance between increase of TM–Tr and decrease of in-plane (Tr–Tr) ab electron sharing. This balance is maintained as long as interlayer interactions in the c direction (Tr–Tr ) c and (TM–TM ) c are not relatively too high in comparison to in-plane electron sharing. In contrast to TM B 2 of AlB 2 -type, digallides in the same structure type build up strong interlayer interactions for early transition metal elements. Our results showed that within digallides, a relatively strong increase in interlayer electron sharing (Ga–Ga) c and (TM–TM ) c takes place. Such increase occurs already for ScGa 2 and TiGa 2 . On the other hand, diborides show a steady increase in electron sharing of TM –B and (TM–TM ) c , but not of (B–B) c . Therefore, it is reasonable to suggest that diborides will tend to adopt a 3D network composed of boron and transition metal atoms (ReB 2 and RuB 2 types). The additional high (Ga–Ga) c interlayer interactions indicate a tendency for digallides to form 3D networks composed only by gallium atoms, characteristic of CaGa 2 (CaIn 2 -type) and ScGa 2 (KHg 2 -type). The counterbalancing bonding effects of in-plane and out-of-plane interactions that give the chemical flexibility of the AlB 2 -type in diborides is thus disrupted in AlB 2 -type digallides by a further enhanced degree of interlayer interactions (Ga–Ga) c and (TM –TM ) c . This results in a smaller number of digallides than that of diborides in AlB 2 -type. The most conspicuous difference between diborides and digallides of AlB 2 -type is in the representation of the B – B and Ga – Ga bonds revealed by the ELI- D topology. Whereas AlB 2 -type diborides exhibit one ELI-D attractor at the B – B midpoint, AlB 2 -type digallides exhibit two ELI-D attractors symmetrically opposite around the Ga – Ga bond midpoint. We utilized the E 2 H 4 (E=triel, tetrel ) molecular series in the D 2h point group symmetry as model systems for solid state calculations. In particular, we addressed the appearance of ELI- D double maxima for Ga – Ga, by using orbital decomposition within the ELI framework. The ELI-D topology changes along the 13th group T r 2 H 4 series. Whereas B 2 H 4 and Al 2 H 4 exhibit one ELI-D attractor representing the Tr–Tr bond, Ga 2 H 4 and In 2 H 4 give rise to two ELI-D attractors. Partial ELI-D allows the orbital decomposition of the electron density. Partial ELI-q gives access to the decomposition of a two-particle property, which is given by the Fermi-hole curvature. We have found that the d-orbitals enable the formation of the two ELI-D attractors through pairing contributions. This has a net effect of lowering electron localizability at the Ga – Ga bond midpoint. Namely, the different ELI-D topology of Ga – Ga and B – B bonds stems from the contributions of d-orbitals to orbital pairing. We have also investigated the bonding situation in transition metal diborides of ReB 2 -type (MnB 2 , TcB 2 , ReB 2) and RuB 2 -type (OsB 2 , RuB 2). One can consider these two structure types as an extension of the trend found in TM B 2 of AlB 2 -type: an increase in TM –B interactions and an enhanced three-center bonding. The change in the structure type results in a puckered layer of boron atoms with electrons equally shared between B – B and TM –B. However, TM –B bonds exhibit a high three-center character. The ELI-D/QTAIM intersection technique also revealed a high participation of TM in the B – B bonding basin population. Moreover, ELI-D topology in the ReB 2 -type also discloses a seemingly important Re 3 three-center interaction along the flat layer of Re atoms. Such basin is absent in MnB 2 , which coincides with the fact that MnB 2 was only observed in the AlB 2 -type. In this regard, we concluded that the 3D network consists not only of covalent B – B bonds, but also of TM –B bonds.

Made available in DSpace on 2015-05-14T13:21:30Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 4538639 bytes, checksum: 981ce0eef0681003af97d1a8046c66ee (MD5) Previous issue date: 2013-08-06 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The aim of this work was to study two kinds of intermolecular hydrogen bonding, the non-usual that is represented by the interaction between acetylene and the HX species (C2H2 --- HX) and the usual that is represented by the interaction between hydrogen cyanide and HX species, with X = F, Cl, CN, and HCCH. This interaction promotes changes in the structural, electronic and vibrational properties of the species involved. In this work, we employe d not onlycomputational-quantum methods MP2/6-311 + + G (d, p) and DFT/B3LYP/6-311 + + G (d, p) in order to study the structural, electronic and vibrational properties of those two types of intermolecular hydrogen bonding, but also we employed QTAIM and NBO methods to complement our research. The results have shown no significant differences between the two correlated methods employed for both types of hydrogen bonded complexes, leading us to suggest the use of the DFT/B3LYP method for studies of similar systems to those studied here, due to the lower computational demand. The increase in bond length of the HX species are enhanced due to formation of more linear complexes than T-complexes, in both calculation levels. The intermolecular bond length values in the complex HCN --- HX are smaller than in the complexes HCCH --- HX, and the values from MP2 and DFT/B3LYP are very close in each individual type of hydrogen complex, suggesting that the linear complexes are more stabilized by the formation of hydrogen bonding than the T-complexes, which can be proved by the values of the binding energy of hydrogen in HCN --- HX. Concerning the redshift effect in the harmonic vibrational mode of species HX, due to the formation of intermolecular bond, the values obtained for linear complexes hydrogen are higher than for the corresponding T-complexes, considering both calculation levels. Values were evaluated from the increase in the intensity values of the stretch mode HX bond formation due to intermolecular and, according to the model CCFOM, the term load flow is responsible for the effect on the increase of HX intensity. We also highlight the new vibrational modes, emphasizing the stretch mode of the intermolecular bond. From studies employing QTAIM, it was possible to obtain the values of electron density and the Laplacian electron density and evaluate these parameters in critical points in HX and intermolecular hydrogen bonding, thus confirming the formation of hydrogen bonded complexes. We evaluated the energy difference between π orbitals and lone pair of nitrogen (in HCN), for the species receiving proton and sigma antibonding for the hydrogen of HX, using the method of natural bond orbital variation. / O objeto de estudo deste trabalho foi a ligação de hidrogênio intermolecular de dois tipos, a não-usual representada pela interação entre o acetileno e espécies HX (C2H2---HX) e a usual representada pela interação entre o ácido cianídrico e espécies HX, com X=F, Cl, CN e HCCH. Esta interação provoca mudanças nas propriedades estruturais, eletrônicas e vibracionais das espécies envolvidas. Neste trabalho empregamos os métodos quântico-computacionais MP2/6-311++G(d,p) e DFT/B3LYP/6-311++G(d,p) para estudar as propriedades estruturais, eletrônicas e vibracionais dos dois tipos de ligação de hidrogênio intermolecular, além de complementar nossa investigação empregando os métodos QTAIM e NBO. Os resultados não mostraram diferenças significativas entre os dois métodos correlacionados empregados para ambos os tipos de complexos de hidrogênio, nos levando a sugerir o emprego do método DFT/B3LYP para estudos de sistemas semelhantes aos aqui estudados, devido a menor demanda computacional. Os valores de incremento no comprimento de ligação das espécies HX são mais acentuados devido à formação dos complexos lineares do que dos complexos-T, em ambos os níveis de cálculo. Os valores de comprimento de ligação intermolecular nos complexos HCN---HX são menores do que nos complexos HCCH---HX, sendo os valores MP2 e DFT/B3LYP bem próximos em cada tipo individual de complexo de hidrogênio, sugerindo que os complexos lineares são mais estabilizados pela formação da ligação de hidrogênio do que os complexos-T, fato que pode ser comprovado pelos valores da energia de ligação de hidrogênio em HCN---HX. Com respeito ao efeito redshift no modo vibracional harmônico das espécies HX, devido à formação da ligação intermolecular, os valores obtidos para os complexos de hidrogênio lineares são maiores do que para os correspondentes complexos-T, considerando ambos os níveis de cálculo. Foram avaliados os valores do incremento nos valores de intensidade do modo de estiramento de HX devido à formação da ligação intermolecular e, de acordo com o modelo CCFOM, o termo de fluxo de carga é o responsável pelo efeito no aumento da intensidade de HX. Foram ainda destacados os novos modos vibracionais, dando ênfase ao modo de estiramento da ligação intermolecular. Dos estudos empregando a QTAIM foi possível obter os valores da densidade eletrônica e do Laplaciano da densidade eletrônica e avaliar os valores desses parâmetros nos pontos críticos de ligação em HX e na ligação de hidrogênio intermolecular, comprovando dessa forma a formação dos complexos de hidrogênio. Com os estudos empregando o método dos orbitais naturais de ligação foi avaliada a diferença de energia entre os orbitais π (no acetileno) e o orbital do par de elétrons livres do nitrogênio (em HCN), para as espécies receptoras de próton, e o orbital sigma antiligante do hidrogênio em HX.

Cette thèse traite de l'application des approches topologiques de la liaison chimique à des systèmes contenant des éléments lourds sujets aux effets relativistes, notamment ceux dépendant du spin. Elle présente deux volets principaux : (i) l'évaluation des effets du couplage spin-orbite (SO) sur la structure électronique à l'aide d'une analyse combinée des propriétés de la fonction ELF et de l'approche QTAIM en deux composantes et (ii) la rationalisation des distorsions structurales pour des molécules impliquant des éléments lourds et le rôle du couplage SO dans ces distorsions. Nous avons pu mettre en évidence différentes situations pour lesquelles le couplage SO peut avoir une influence très importante, modérée ou négligeable. Un résultat important de ce travail démontre la dépendance du couplage SO à son environnement chimique. Pour le second volet, nous avons élaboré une approche qui a consisté à établir une corrélation entre les interactions électrostatiques locales entre régions liantes et non liantes (bassins ELF et QTAIM) et la géométrie moléculaire du système dans l'esprit des modèles VSEPR et du Ligand Close Packing (LCP). Cette approche a notamment mis en évidence la connexion entre la structure moléculaire et les répulsions des paires non-liantes de l'atome central avec leur environnement. / This thesis deals with the aplication of topological approaches of the chemical bonding by means of analysing properties of density-based functions like Electron Localization Function (ELF) and the Quantum Theory of Atoms in Molecumes (QTAIM) to systems involving heavy elements such as 6p elements or actinides . It is divided into two main parts: (i) the evaluation of the spin-orbit coupling (SOC) effects on the electronic structure by means of combination of the QTAIM and ELF topological analyses in the field of quasirelativistic quantum calculations, and (ii) the rationalization of structural distorsions on molecules containing heavy atoms, and the role of the SOC on these distorsions. We were able to emphasize different situations for which SOC has strong, moderate or tiny influence on the chemical bonding, depending on the chemical environnement on which the heavy element is involved. In the second part of this thesis we tested our approach consisting of ELF/QTAIM interbasin repulsion energy analysis in connection with the molecular geometry of the system, in the spirit of the VSEPR and LCP models.

No description available.

The thesis entitled “Addressing subtle physicochemical features exhibited by molecular crystals via Experimental and Theoretical Charge Density Analysis” consists of five chapters. An introductory note provides a brief description of experimental and theoretical charge density methodology, followed by its utilization in obtaining certain physical and chemical properties in molecular crystals. Chapter 1 addresses not so easily accessed molecular property arising due to electron conjugation, highlighting antiaromaticity in tetracyclones. A systematic study of six tetracyclone derivatives with electron withdrawing and electron donating substituents has been carried out using experimental and theoretical charge density analysis. A three pronged approach based on quantum theory of atoms in molecules (QTAIM), nucleus independent chemical shifts (NICS), and source function (SF) has been employed to establish the degree of antiaromaticity of the central five-membered ring in all the derivatives. Electrostatic potentials mapped on the is density surface reveal the finer effects of different electron withdrawing and electron donating substituents on the carbonyl group. Chapter 2 presents a temperature induced reversible first order single crystal to single crystal phase transition (Room temperature Orthorhombic, P22121 to low temperature Monoclinic, P21) in a  hybrid peptide, Boc-γ4(R)Val-Val-OH. The thermal behavior accompanying the phase transition of the dipeptide crystal was characterized by differential scanning calorimetry, visual changes in birefringence of the sample during heating and cooling cycles on a hot-stage microscope with polarized light. Variable-temperature unit cell check measurements from 300 to 100 K showed discontinuity in the volume and cell parameters near the transition temperature, supporting the first-order behavior. The reversible nature of the phase transition is traced to be due to an interplay between enthalpy and entropy. Chapter 3 brings out an unusual stabilizing interaction involving a cooperative -hole and ¬hole character in a short NCS···NCS bond. This chapter describes structural features of four isothiocyanate derivatives, FmocXCH2NCS; X=Leu, Ile, Val and Ala. Among these it is observed that only FmocLeuCH2NCS which crystallizes in a tetragonal space group, P41, (a=b=12.4405(5) Å; c= 13.4141(8) Å) transforms isomorphously to a low temperature form, P41, (a=b=17.4665(1) Å; c= 13.1291(1) Å). The characteristics of the phase transition have been monitored by Differential Scanning Calorimetry, variable temperature IR and temperature dependent unit cell measurements. The short NCS···NCS intermolecular interaction (3.296(1) Å) is analyzed based on detailed experimental charge density analysis which reveals the nature of this stabilizing interaction. Chapter 4 explains a comparative study of syn and anti conformations of carboxylic acids in peptides from both structural aspect and charge density features. Single crystal structures of four peptides having syn conformations [BocLeuγ4(R)Valγ4(R)ValOH, BocLeuγ4(R)ValLeuγ4(R)ValOH, Boc3(S)Leu3(S)LeuOH] and one with anti conformation, BocLeuγ4(R)ValValOH have been analyzed. Experimental charge density analysis has been carried out exclusively on BocLeuγ4(R)ValValOH having anti form, because of its rare occurrence in literature. However, low temperature datasets on the four peptides with syn conformations were collected and theoretical charge density analysis has been carried out on two of these compounds. Electrostatic potentials mapped on is density surface bring out a significant difference at the oxygen atoms of the carboxyl group in the two conformations. However, lone pair orientation of different types of Oxygen atoms in the two forms (urethane, amide, acid) doesn’t exclusively indicate the differences in the corresponding charge density features. Chapter 5 addresses the issue of how sensitive are the charge density features associated with amino acid residues when the backbone conformational angles are varied. Three model systems, 1, L-alanyl–L-alanyl–L-alanine dehydrate; 2, anhydrous L-alanyl–L-alanyl–L¬alanine and 3, cyclo-(D,L-Pro)2(L-Ala)4 monohydrate have been chosen for this evaluation. Compound 1 has ant parallel alignment of tripe tide strands, and compound 2 has parallel alignment. All the alanine residues in compound 1 and 2 are in the -sheet region of the Ramachandran plot, whereas, the four Alanine residues in the cyclic hex peptide 3 span different regions of the Ramachandran plot. Theoretical multipole modelling has been carried out in order to explore the plausibility of transferring multipole parameters across different regions of Ramachandran Plot. Appendix I contains a brief description of charge shift bonding in Ph-CH2-Se-Se-CH2-Ph, as determined based on both experimental and theoretical charge density analysis. Appendix II contains a reprint of a published article on “Conformation-Changing Aggregation in Hydroxyacetone: A Combined Low-Temperature FTIR, Jet, and Crystallographic Study”.