Content: The application of split leather is an important issue in leather industry as most of them was not properly treated and wasted. In this study the application of choline chloride (ChCl), urea (U) and corresponding deep eutectic solvents (DES) on the modification of thermal stability and mechanical strength of mink split leather was investigated. TGA and DSC results indicated DES treatment enhanced thermal stability of split leather, and ChCl treatment reduced the stability. While, U treatment provided a kinetic inhibition during the thermal-decomposition. In terms of the mechanical strength, both ChCl and U treatment reduced burst intensity and extended height. While, after DES treatment the burst intensity and extended height increased significantly. In terms of the dosage, 7% DES provided best performance. Results mentioned above illustrated that DES formed by simply mixing ChCl and U provided strong interaction with fiber, enhanced the crosslinks. A hypothesis of [Ch(Urea)]+[Cl(Urea)]- type structure was proposed, as it enabled DES forming strong hydrogen bonds with functional groups on leather fiber, enhancing the crosslinks and therefore improving the thermal stability and mechanical strength. The DES treatment on leather fibers improved their overall performance and thereby broaden their applications. Take-Away: 1. DES obtained by mixing ChCl and urea presented very different effect in leather treatment, as the thermal stability and physical strength of leather improved significantly after the DES treatment. 2. A hypothesis of [Ch(Urea)]+[Cl(Urea)]- type structure was proposed, illustrating a formation of strong hydrogen bonds between DES and functional groups on leather fiber. This enhances the crosslinks and therefore improves the thermal and mechanical strength of leather.

A straightforward means to include explicit hydrogen bonds within the Universal Force Field (UFF) is presented. Instead of treating hydrogen bonds as non-bonded interaction subjected to electrostatic and Lennard-Jones potentials, we introduce an explicit bond with a negligible bond order, thus maintaining the structural integrity of the H-bonded complexes and avoiding the necessity to assign arbitrary charges to the system. The explicit hydrogen bond changes the coordination number of the acceptor site and the approach is thus most suitable for systems with under-coordinated atoms, such as many metalorganic frameworks; however, it also shows an excellent performance for other systems involving a hydrogen-bonded framework. In particular, it is an excellent means for creating starting structures for molecular dynamics and for investigations employing more sophisticated methods. The approach is validated for the hydrogen bonded complexes in the S22 dataset and then employed for a set of metal-organic frameworks from the Computation-Ready Experimental database and several hydrogen bonded crystals including water ice and clathrates. We show that the direct inclusion of hydrogen bonds reduces the maximum error in predicted cell parameters from 66% to only 14%, and the mean unsigned error is similarly reduced from 14% to only 4%. We posit that with the inclusion of hydrogen bonding, the solvent-mediated breathing of frameworks such as MIL-53 is nowaccessible to rapid UFF calculations, which will further the aim of rapid computational scanning of metal-organic frameworks while providing better starting points for electronic structure calculations.

Dans le contexte actuel de constante amélioration des propriétés des matériaux polymères et de l’optimisation de leur impact environnemental, la recherche se tourne de plus en plus vers les polymères biosourcés et biodégradables. Le travail de cette thèse consiste en la synthèse et le développement de nouveaux réseaux thermoréversibles à base d’acide polylactique (PLA). Cette thermo-réversibilité est assurée grâce à des interactions dynamiques comme les liaisons hydrogène et la réaction réversible de Diels-Alder. Une biomolécule, le gluthation, a été conjuguée au polymère et utilisée comme générateur de liaisons hydrogène. Ces travaux ont permis la réalisation d’une large gamme de matériaux avec des propriétés uniques comme l’autoréparation et des températures de réversibilité très variées, approchant pour certains échantillons, celle du corps humain / In the current context to constantly improve the properties of polymer materials as well as their environmental impact, the research on polymers is increasingly focused on biobased and biodegradable polymers. The aim of this work consists on the synthesis and development of new polylactic acid-based thermoreversible networks. This thermoreversible character is ensured thanks to dynamic interactions such as hydrogen bonds and the reversible Diels-Alder reaction. In a second time, a biomolecule was conjugated to the polymer and was used as a hydrogen bonds generator. This allowed the production of a wide range of materials with varied reversibility temperatures and unique properties such as self-healing ability. For some samples, the reversibility temperatures were approaching the human body temperature

Collagen is the most abundant protein in mammals and has special mechanical behavior that enables it to play an important role in the structural integrity of many tissues, e.g., skin, tendon, bone, cartilage and blood vessels. The mechanical properties of collagen are governed by hierarchical mechanisms in different length-scales from molecule to tissue level. Currently, there is no multi-scale model that can predict the mechanical properties of collagen at macroscopic length scales from the behavior of microstructural elements at smaller length scales. This dissertation aimed at developing a multi-scale model using a bottom-up approach to predict the elastic and viscoelastic behaviors of collagen at length scales spanning from nano to microscale. Creep simulations were performed using steered molecular dynamics (SMD) method on collagen molecules, cross-link, and micro-fibrils with various lengths. A micro-fibril is considered as a combination of two collagen molecules connected by a cross-link. The strain time histories for force levels in the range of 10 to 4000 pN were characterized using quasilinear viscoelastic models. These models were utilized to make a reduced model of a micro-fibril and the reduced models, in turn, were combined to make a model of a fibril up to 300 micrometers in length. The micro-fibril and fibril models were validated with available experimental measurements. Hydrogen bonds rupture and formation of collagen molecule played a central role in its viscoelastic behavior and were used to estimate the creep growth rate. The propagation of force wave in the molecule was shown to be an important factor in providing the time-dependent properties of the fibrils. This propagation was modeled with delay elements and this allowed reducing the micro-fibril model to only three degrees of freedom. In conclusion, the results confirmed that the combination of molecular dynamics simulations and viscoelastic theory could be successfully utilized to investigate the viscoelastic behavior of collagen at small scales. The model reported in this dissertation, lays the groundwork for future studies on collagen, particularly in elucidating how each particular level of hierarchy affects the overall tissue behavior. / Mechanical Engineering

L'objectif de cette étude est d'apprendre à créer de nouveaux matériaux moléculaires par design. À l'heure actuelle, il n'existe aucune méthode générale pour la prédiction des structures et des propriétés, mais des progrès importants ont été accomplis, en particulier dans la fabrication de matériaux moléculaires ordonnés tels que des cristaux. En ces matériaux, l'organisation peut être contrôlée efficacement par la stratégie de la tectonique moléculaire. Cette approche utilise des molécules appelées “tectons”, qui peuvent s’associer de manière dirigée par des interactions non covalentes prévisibles. De cette façon, la position de chaque molécule par rapport à ses voisins peut être programmée avec un degré élevé de fiabilité pour créer des cristaux et d'autres matériaux organisés avec des caractéristiques et des propriétés structurelles souhaitables. Le travail que nous allons décrire est axé sur l'utilisation de l'association des cations bis(aminidinium) avec des carboxylates, sulfonates, phosphonates et phosphates, afin de créer des réseaux moléculaires prévisibles. Ces réseaux promettent d'être particulièrement robuste, car ils sont maintenus ensemble par de multiples liaisons hydrogène assistées par des interactions électrostatiques. / The goal of this study is to learn how to create new molecular materials by design. At present, there is no general method for predicting structures and properties, but significant progress is being made, particularly in making ordered molecular materials such as crystals. In such materials, organization can be controlled effectively by the strategy of molecular tectonics. This approach uses molecules called “tectons”, which can associate in ways directed by predictable non-covalent interactions. In this way, the position of each molecule relative to its neighbors can be programmed with a high degree of reliability to create crystals and other ordered materials with desirable structural features and properties. The work that we will describe focuses on using the association of bis(aminidinium) cations with carboxylates, sulfonates, and phosphates to create predictable molecular networks. Such networks promise to be unusually robust because they are held together by multiple charge-assisted hydrogen bonds.

L'objectif de cette étude est d'apprendre à créer de nouveaux matériaux moléculaires par design. À l'heure actuelle, il n'existe aucune méthode générale pour la prédiction des structures et des propriétés, mais des progrès importants ont été accomplis, en particulier dans la fabrication de matériaux moléculaires ordonnés tels que des cristaux. En ces matériaux, l'organisation peut être contrôlée efficacement par la stratégie de la tectonique moléculaire. Cette approche utilise des molécules appelées “tectons”, qui peuvent s’associer de manière dirigée par des interactions non covalentes prévisibles. De cette façon, la position de chaque molécule par rapport à ses voisins peut être programmée avec un degré élevé de fiabilité pour créer des cristaux et d'autres matériaux organisés avec des caractéristiques et des propriétés structurelles souhaitables. Le travail que nous allons décrire est axé sur l'utilisation de l'association des cations bis(aminidinium) avec des carboxylates, sulfonates, phosphonates et phosphates, afin de créer des réseaux moléculaires prévisibles. Ces réseaux promettent d'être particulièrement robuste, car ils sont maintenus ensemble par de multiples liaisons hydrogène assistées par des interactions électrostatiques. / The goal of this study is to learn how to create new molecular materials by design. At present, there is no general method for predicting structures and properties, but significant progress is being made, particularly in making ordered molecular materials such as crystals. In such materials, organization can be controlled effectively by the strategy of molecular tectonics. This approach uses molecules called “tectons”, which can associate in ways directed by predictable non-covalent interactions. In this way, the position of each molecule relative to its neighbors can be programmed with a high degree of reliability to create crystals and other ordered materials with desirable structural features and properties. The work that we will describe focuses on using the association of bis(aminidinium) cations with carboxylates, sulfonates, and phosphates to create predictable molecular networks. Such networks promise to be unusually robust because they are held together by multiple charge-assisted hydrogen bonds.

Water is “the matrix of life” for its fascinating properties. The well-known simple water molecule consists of one oxygen atom and two hydrogen atoms, covering most of planet earth’ssurface. It is the most studied element in science; however, its properties are still not fully understood. Another essential building block of life is proteins, which manifest naturally in aqueous environments. The protein activity is controlled by the protein folding process that is dependent on the surrounding environment. It is hypothesized that the hydrogen bond network of water plays an important role in the folding process. Here, we investigate the protein lysozyme in liquid water as well as in the crystalline state ice Ih, exploring various temperatures, using FT-IR and XRD. Our main finding is that a transition occurs at approximately T=210 K, indicative of the hypothesised protein dynamic “glass” transitionobserved by previous studies in supercooled water at similar temperatures.

Diese Arbeit ermöglicht ein detailliertes Verständnis der Schwingungsdynamik und Kupplungen in einem Basenpaar-Modellsystem und in künstlichen DNA-Oligomeren bei verschiedenen Hydratationsgraden. Durch die Verwendung von nichtlinearer ultraschneller IR Pump-Probe Spektroskopie sind die Schwingungsbewegungen hydratisierter DNA und die schnellsten Veränderungen in den DNA-Wasser-Wechselwirkungen und Hydrationsgeometrien direkt zugänglich. 2-pyridone/2-hydroxypyridine ist ein Modellsystem für die gekoppelte intermolekularen Wasserstoffbrücken, deren Struktur der von DNA-Basenpaaren ähnelt. In Dichlormethan existiert das Molekül als ein zyklischer 2-Pyridon-Dimer, deren Vorkommern durch NMR-und 2D-FTIR Spektroskopie verifiziert wurde. Die beobachteten kohärente Oszillationen aufgrund niederfrequenter Wellenpaketbewegungen der Dimere können für die Dynamik und räumliche Geometrie der Basenpaare in den DNA-Molekül relevant sein. Transiente Schwingungsspektren eines poly[d(A-T)]:poly[d(A-T)] Film erlauben die Zuordnung von verschiedenen NH-Streckbanden zu einer bestimmten Schwingung der Nukleinbasen und ermöglichen deren Abgrenzung zu den Beiträgen von OH-Streckschwingungen des umgebenden Wassers. Bei einem niedrigen Hydratisierungsgrad verändern die restlichen, an die Phosphatgruppen gebundenen Wassermoleküle, ihre Ausrichtung auf ultraschnellen Zeitskalen nicht. Im Fall vollständig hydratisierter DNA ist die Dynamik der Wasserhülle dem Verhalten des reinen Wassers ähnlicher und man beobachtet spektrale Diffusion der OH-Streckschwingung im Subpikosekundenbereich sowie einen Zerfall der Schwingungsanisotropie durch Molekülrotation und/oder Energietransfer. Die Wassermoleküle der Phosphat-Hydratationshülle dienen als effiziente Wärmesenke für Überschussenergie aus der DNA, wobei die Energietransferzeiten im fs-bereich liegen. Im Gegensatz dazu erfolgt Energietransport innerhalb der DNA auf einer langsameren Zeitskala von 20 ps. / This thesis provides a detailed understanding of vibrational dynamics and couplings in a base pair model system and artificial DNA oligomers at different levels of hydration. By using nonlinear ultrafast infrared pump-probe spectroscopy, the basic vibrational motions of hydrated DNA and the fastest changes in the DNA–water interactions and hydration geometries are directly accessed. 2-pyridone/2-hydroxypyridine is used as a model molecule for coupled intermolecular hydrogen bonds with a structure resembling a DNA base pair. In dichloromethane the molecule predominantly exists as a cyclic 2-pyridone dimer as determined using a combined NMR and 2D FTIR approach. The observed coherent oscillations due to low-frequency hydrogen bond wavepacket motions of the dimers are expected to be relevant for the dynamics and spatial geometry of base pairs in DNA molecule. Transient vibrational spectra of a poly[d(A-T)]:poly[d(A-T)] film enabled the assignment of different NH stretching bands to particular nucleobase vibrations, also discerning them from the OH stretching contributions of the surrounding water. At a low hydration level, residual water molecules, bound to the phosphate groups, do not alter their orientation on ultrafast time scales. In the case of fully hydrated DNA, the dynamics of the water shell are closer to those of bulk liquid water with a sub-picosecond spectral diffusion and a loss of vibrational anisotropy as a result of molecular rotation and/or energy transfer. The water shell around the phosphates serves as a efficient heat sink accepting excess energy from DNA in a femtosecond time domain, whereas the energy transfer within DNA occurs on the time scale of 20 ps.

O objetivo do presente trabalho foi determinar as estruturas cristalinas e moleculares de cocristais de 2,4,6-trinitrofenol, ou ácido pícrico, com diversas bases orgânicas, bem como estudar as interações intermoleculares existentes nesses cocristais para tentar estabelecer um padrão de comportamento na formação de ligações de hidrogênio e de preferências estruturais, com a finalidade de contribuir para o entendimento do empacotamento cristalino. Foram sintetizados os seguintes compostos: 1:1 picrato/8-hidroxiquinolina, 1:1 picrato/isonicotinamida, 1:1 picrato/2-azaciclononanona, 1:2 picrato/2-azaciclotridecanona, 1:1 picrato/morfolina, 1:1 picrato/1,3 dimetiluréia, 1:1 picrato/4-metil-morfolina-N-óxido, 1:2 picrato/3-picolina-N-óxido, 1:2 picrato/glicina e 1:1 picrato/prolina. Esses compostos foram caracterizados por análise elementar CHN, para a confirmação da estequiometria, pelos pontos de fusão, e para o cocristal de picrato/prolina foram registrados espectros de emissão na região entre 430 e 650 nm e o espectro de excitação na região entre 360 e 500 nm, onde foi observado que o composto é transparente na região acima de 500 nm, sendo portanto favorável aos experimentos de duplicação de radiação laser Nd/YAG (λ = 1.064 nm), uma vez que não absorve na região da radiação duplicada (λ =532 nm). A coleta de dados, a obtenção das intensidades dos feixes difratados pelos monocristais, para a determinação das estruturas cristalinas foi realizada em um difratômetro Enraf-Nonius CAD4 Mach 3. As intensidades observadas medidas foram convertidas em fatores de estrutura observados através da correção pelos fatores de Lp e de absorção. As estruturas foram determinadas utilizando os chamados Métodos Diretos e refinadas por cálculos sucessivos de Fourier-Diferença e mínimos quadrados. Ao final da determinação das estruturas dos dez cocristais pôde-se analisar um total de 50 ligações de hidrogênio do tipo O-H...O, N-H...O e C-H...O. Essas ligações de hidrogênio foram analisadas geometricamente em relação às distâncias e ângulos de ligações, e também foram nomeadas e classificadas pelo método Graph-set. Através destas análises pode-se chegar a uma comparação entre as estruturas e a padrões comuns em relação às ligações intermoleculares existentes. Observa-se que as ligações de hidrogênio do tipo O-H...O mais fortes são aquelas formadas entre o grupo doador e os oxigênios fenólicos receptores do picrato. As distâncias d(H...O) das ligações de hidrogênio correspondentes a O-H...O (oxigênio fenólico) estão concentrados na região entre 1,51 e 1,82 Å, e os ângulos <OHO concentram-se na região entre 161 e 171º. As distâncias d(O...O) estão compreendidas entre 2,48 e 3,1 Å. Para as ligações O-H...O (oxigênio do grupo nitro) as distâncias d(H...O) estão entre 2,41 e 2,54 Å e ângulos <OHO na região entre 100 e 121º. Também é observado que as distâncias d(O...O) estão compreendidas entre 2,78 e 3,04 Å, mas predominantemente estão na faixa entre 2,4 e 2,55 Å. Para as interações do tipo N-H...O, observa-se que as distâncias d(H...O) estão em um intervalo entre 1,85 e 2,52 Å; e em relação aos ângulos <NHO, estão distribuídos no intervalo entre 121 e 171º. Um intervalo bastante largo é observado em relação as distâncias d(N...O), que estão compreendidas entre 2,6 e 3,2Å. Para as interações do tipo C-H...O, observa-se que as distâncias d(H...O) tem uma leve tendência crescente em função do aumento do ângulo <CHO, e encontram-se no intervalo entre 2,96 e 3,61 Å. / The objective of the present work is to determine the crystalline and molecular structures of 2,4,6 trinitrophenol (picric acid ) cocrystals, with several organic bases, as well as to study the intermoleculares interactions existent in those cocristals in order to establish a pattern of behaviour in the formation of hydrogen bonds and structural preferences, with the purpose of contributing for the understanding of crystalline packing. Was synthesized the following compounds: 1:1 picrate/8-hidroxiquinoline, 1:1 picrate/isonicotinamide, 1:1 picrate/2-azacyclononanone, 1:1 picrate/morfoline, 1:1 picrate/1,3 dimethylurea, 1:1 picrate/ 4-methyl-morfoline-N-oxide, 1:2 picrate/3-picoline-N-oxide, 1:2 picrate/glycine, 1:1 picrate/proline. Those compositions were characterized by elemental analysis (CHN) for the stoichiometry confirmation, melting points and, for the picrate/proline cocrystal, the emission and excitation spectra were recorded. It was observed that this compound is transparent above 500 nm, being therefore suitable to experiments of Nd/YAG laser radiation duplication (λ = 1.064 nm), since it does not absorb at the wavelength of the duplicated radiation (λ = 532 nm). Data collection for crystalline structure determination\'s was accomplished in an Enraf-Nonius CAD4 Mach 3 diffractometer. The observed intensities were transformed into structure factors observed through Lp and absorption corrections. The structures were determined using the direct method and refined by successive Fourier-difference calculations and least-square analysis. At the end of this determination some hydrogen bonds, O-H ...O, N-H ...O and C-H ...O could be analyzed. Those hydrogen bonds were geometrically analysed with relation to bond distances and angle, and they were also nominated and classified by the Graph-set method. Through these analyses it was possible a comparison among the structures and to common patterns in relation to intermolecular bonds. It was observed that the stronger hydrogen bonds are those formed between the donor group and the phenolic picrate oxygen. The O-H ...O (phenolic oxygen) distances d(H ...O) are concentrated in range 1.51 and 1.82 Å, and angles <OHO are concentrated between 161 and 171Å. The distances d(O...O) are between 2.48 and 3.1 Å. The distances of hydrogen bonds O-H ...O (nitro group oxygen), d(H ...0), are in the range 2.41 and 2.54 Å and angles <OHO between 100 and 121º. It is also observed that distances d(O ...O) lie between 2.78 and 3.04 Å. but predominantly they are in the interval between 2.4 and 2.55 Å. For interactions of the type N-H ...O. it is observed that distances d(H ...O) are between 1.85 and 2.52 Å, and angles <NHO, are between 121 and 171º. A quite wide area is observed with relation to the distance d(N ...O), that lie between 2.6 and 3.2 Å. For interactions of the type C-H ...O. it is observed that distances d(H ...O) increase in function of the angle <CHO; they lie between 2.96 and 3.61 Å.

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / The unit of sugar and base connected by a N-β-glycosyl linkage is named a nucleoside. In the present work the nucleoside thymidine, whose molecular formula is C10N2O5H14, was studied by Raman spectroscopy, subjecting it extreme conditions of pressure and temperature, as well as X ray diffraction measurements. An auxiliary analysis of normal crystal vibration modes was performed using first principles calculations using the B3LYP functional together with the Gaussian bases 6-31G+(d) and potential energy distribution analysis (PED). These results, together with literature data and Raman spectroscopy measurements in several thymidine scattering geometries, allowed the identification of the various normal modes of crystal vibration. X-ray diffraction experiments were performed in the temperature range between 83 and 413 K. Experiments of Raman spectroscopy under extreme temperature conditions (20 to 380 K) were performed in the spectral range of 20 to 3400 cm-1. From the analysis of the results, it is possible to draw some conclusions. (i) The thymidine crystal remained stable throughout the investigated temperature range, indicating that the temperature effect is not sufficient to modify the hydrogen bonds present between the molecules in such a way as to modify the symmetry of the crystal. (ii) The material studied showed some slight changes in the vibrational spectra in the experiment performed at low temperatures, suggesting, if not a structural phase transition, at least some conformational modification of the thymidine molecules. Raman spectra of thymidine crystal were obtained for pressures up to 5.0 GPa in a diamond anvil cell. The results show the presence of anomaly in the Raman spectrum at pressures close to 3.0 GPa. This anomaly is characterized by disappearance of lattice modes, appearance of some internal modes, splitting of high wavenumbers modes, downshift of modes associated with hydrogen bonds, changes in the intensity of internal modes and discontinuities of the slopes of the wavenumbers versus pressure for several Raman modes. This set of modifications was interpreted as consequence of a phase transition undergone by thymidine close to 3.0 GPa. Further, decompression to atmospheric pressure generates the original Raman spectrum, showing that the pressure-induced phase transition undergone by thymidine crystals is reversible. A comparison with results on other nucleosides submitted to high pressure is also furnished. / Quando a pentose (glicose) e uma base nitrogenada unem-se por meio de uma ligaÃÃo N-β glicosÃdica forma-se uma molÃcula denominada de nucleosÃdeo. No presente trabalho o nucleosÃdeo timidina, cuja fÃrmula molecular à C10N2O5H14, foi estudado atravÃs de espectroscopia Raman, submetendo-o a condiÃÃes extremas de pressÃo e de temperatura, alÃm de medidas de difraÃÃo de raios X. Uma anÃlise auxiliar a respeito dos modos normais de vibraÃÃo do cristal foi realizada atravÃs de cÃlculos de primeiros princÃpios utilizando-se o funcional B3LYP em conjunto com as bases gaussianas 6-31G+(d) e anÃlise de distribuiÃÃo de energia potencial (PED). Esses resultados, juntamente com dados da literatura e medidas de espectrocopia Raman em diversas geometrias de esplalhamento na timidina permitiram uma identificaÃÃo dos vÃrios modos normais de vibraÃÃo do cristal. Os experimentos por difraÃÃo de raios X foram realizados no intervalo de temperatura entre 83 e 413 K. Experimentos de espectroscopia Raman sob condiÃÃes extremas de temperatura (20 a 380 K) foram realizados no intervalo espectral compreendido entre 20 e 3400 cm-1. Da anÃlise dos resultados, à possÃvel tirar algumas conclusÃes. (i) O cristal de timidina manteve-se estÃvel em todo o intervalo de temperatura investigado, indicando que o efeito de temperatura nÃo à suficiente para modificar as ligaÃÃes de hidrogÃnio presentes entre as molÃculas de tal forma que haja modificaÃÃo da simetria do cristal. (ii) O material estudado apresentou algumas leves mudanÃas nos espectros vibracionais no experimento realizado a baixas temperaturas, sugerindo, se nÃo uma transiÃÃo de fase estrutural, pelo menos alguma modificaÃÃo conformacional das molÃculas da timidina. Experimentos submetendo o cristal a pressÃes de atà 5 GPa foram realizados utilizando-se uma cÃlula de pressÃo a extremos de diamantes. Os resultados mostraram anomalias nos espectros Raman por volta de 3.0 GPa. Essas anomalias foram caracterizadas pelo desaparecimento de alguns modos de rede, surgimento de alguns modos internos, deslocamento para menores nÃmeros de onda de modos associados a ligaÃÃes de hidrogÃnio e descontinuidades dos coeficientes lineares de vÃrios modos nos grÃficos de nÃmero de onda em funÃÃo da pressÃo. Essa sÃrie de modificaÃÃes foram interpretadas como consequÃncia de uma transiÃÃo de fase sofrida pela timidina por volta de 3.0 GPa. AlÃm disso, a descompressÃo da amostra atà a pressÃo atmosfÃrica mostrou que a transiÃÃo de fase à reversÃvel. TambÃm fornecemos uma comparaÃÃo com resultados de outros nucleosÃdeos submetidos a altas pressÃes.