Literatura científica selecionada sobre o tema "Theoritical chemistry"

The little disturbance theory in quantum mechanics was used to research the frequency and the high emissivity of far infrared emission from natural black tourmaline on basis of the electric dipole model. Comparing the theoritical and the experimental value of the frequency we found that they are in match case. So we testified that the tourmaline partical is really composed of lots of crystal electric dipole. At the same time we explained the curves of infrared absorption analysis of natural black tourmalines at room temperature are simillar despite of their diversification in chemistry component and producing area, and they have high infrared emissivity from the theory point of view. Finally we pointed out the condition under which the high infrared emissivity of tourmaline can be obtained theoritically.

A scalable CVD route to SnO₂ : Sb thin films that show resistivity as low as 4.7 × 10⁻⁴ Ω cm and a corresponding sheet resistance of 9 Ω sq⁻¹. Theoritical insight into the defect chemistry is provided by ab initio hybrid density functional theory.

Pramipexole dihydrochloride monohydrate is an antiparkinson’s agent which is known as dopamine D2 receptor agonist. It is structurally different from the ergot-derived drugs, e.g. bromocriptine or pergolide. Pramipexole is designated chemically as (S)-2-Amino-4, 5, 6, and 7-tetrahydro-6-(propylamino) benzothiazole and has the molecular formula C10H17N3S. It comes under class I of Biopharmaceutical Classification System. The purpose of this study was to develop and evaluate pramipexole dihydrochloride monohydrate extended release tablets by wet granulation method using different proportions of polymers and binder. Pre-formulation studies were done initially and the results were found to be within the limits. All the mentioned batches were prepared and granules were evaluated for pre-compression parameters such as loss on drying, bulk density, tapped density and compressibility index. Tablets were evaluated for weight variation, thickness, hardness, friability; disintegration time and assay were found to be within the limits. In vitro dissolutions were performed with 0.05M 6.8 PH phosphate buffer and effect of various polymers were explored. Final selection of formulation was based on dissolution profile, from dissolution studies formulation 9 showed 80% drug release within 20 hours, so it will be compared with innovator. Similarity and difference factors which revealed that formulation (F 9) containing HPMC K 200, Eudragit L100 and binder are most successful as it exhibited in vitro drug release that matched with innovator product. In vitro drug release profile reveals that with increased concentration of Eudragit L 100. Accelerated stability studies were performed for the optimized batch which indicated that there were no changes in drug content and in vitro dissolution.

The internal rotational barriers for formamide are calculated in gas and solution phases (acetonitrile) at the HF/6-31G* (16.64 and 16.18 kcal/mol, respectively) and MP2/6-31G* (16.86 and 16.71 kcal/ mol, respectively) level of theory. Calculated parameters are compared with experimental data and there is a good agreement between them. Orbital populations are obtained by MPA (mulliken population analysis) and NPA (natural population analysis) methods and bond energies are calculated by the NBO method (natural bond orbitals). The distribution of atomic charges are also given. These calculation indicate that the internal rotational barrier is produced because of change in the distribution of orbital populations of 2p y, 2p z, d yz, d y2 and dz2 orbitals of the nitrogen atom.

This Research aims to study Quantitative Structure-Activity Relationship (QSAR) of pyrazoline analogues, designing the new potential compounds as antiamoebic and study the interactions between the new compunds and the drugs target by molecular docking approach. This research was a theoritical research using computational chemistry method. The object of research was 21 novel of 1-N-substituted pyrazoline analogues of thiosemicarbazones with their antiamoebic biological activity. The data of research was obtained from quantum chemistry calculation and statistically analysis using Multiple Linear Regression (MLR). The resulting QSAR equation was Log IC50 = 0.869 + (0.081 x TPSA) + (0.018 x HF) + (0.527 x E-HOMO) + (3.378 x E-LUMO) + (-16.938 x Glob) + (0.234 x LogP), with statistic parameters of n = 21; R2 = 0.933; SEE = 0.14558; FHitung/FTabel = 8.607; PRESS = 0.491. This equation was used as a basic for designing and predicting the new antiamoebic compounds of pyrazoline analogues. The design of new compound of two lead compounds with the Topliss resulted 5 of 18 new compounds having theoretical better activity than the lead compound. Molecular docking study indicated that all of the best compounds have ability to bind to drug target macromolecule.

This Research aims to study Quantitative Structure-Activity Relationship (QSAR) of pyrazoline analogues, designing the new potential compounds as antiamoebic and study the interactions between the new compunds and the drugs target by molecular docking approach. This research was a theoritical research using computational chemistry method. The object of research was 21 novel of 1-N-substituted pyrazoline analogues of thiosemicarbazones with their antiamoebic biological activity. The data of research was obtained from quantum chemistry calculation and statistically analysis using Multiple Linear Regression (MLR). The resulting QSAR equation was Log IC50 = 0.869 + (0.081 x TPSA) + (0.018 x HF) + (0.527 x E-HOMO) + (3.378 x E-LUMO) + (-16.938 x Glob) + (0.234 x LogP), with statistic parameters of n = 21; R2 = 0.933; SEE = 0.14558; FHitung/FTabel = 8.607; PRESS = 0.491. This equation was used as a basic for designing and predicting the new antiamoebic compounds of pyrazoline analogues. The design of new compound of two lead compounds with the Topliss resulted 5 of 18 new compounds having theoretical better activity than the lead compound. Molecular docking study indicated that all of the best compounds have ability to bind to drug target macromolecule.

La PEP carboxylase est une enzyme impliquée dans plusieurs processus biologiques chez les plantes, tels que la maturation des graines ou les premières étapes de la capture du carbone au cours de la photosynthèse chez certaines plantes. Elle est ainsi responsable de la capture initiale du CO2 pour ¼ de la production terrestre de biomasse. Dans cette thèse nous avons étudié le mécanisme biochimique de l'enzyme PEP carboxylase. L'inconnue principale était la conformation fermée de la boucle II qui permet de protéger le site actif du solvant et d'enclencher la réaction chimique. Cette conformation n'a pas été à ce jour résolue expérimentalement, et les tentatives initiales de prédire cette conformation se sont avérées insatisfaisantes parce qu'instables. Notre but a alors été de prédire cette conformation fermée par des simulations numériques. Pour cela, nous avons développé une méthode originale pour prédire la conformation de boucles de protéines dans leur conformation fermée à partir de la détermination de la conformation ouverte. Nous avons démontré sur des exemples où les deux conformations sont connues que la méthode que nous avons développée, dénommée SETH, est capable de prédire la conformation fermée à partir de la seule conformation ouverte. De plus, nous avons développé une méthode d'analyse des trajectoires de simulations moléculaires qui permet de séparer les données en sous-groupes homogènes, facilitant ainsi leur comparaison. L'avantage de cette seconde méthode, dénommée YACARE, est qu'elle ne fait intervenir que des paramètres physiques et facilement interprétables. Nous avons alors appliqué les méthodes SETH et YACARE à la PEP carboxylase et découvert une conformation fermée candidate pour être la conformation réactive souhaitée. Celle-ci est stable numériquement au cours de simulations par échanges de de répliques de 200ns ainsi qu'au cours de simulations classique de 1 microseconde. Elle est caractérisée par la présente de ponts salins qui l'aide à se maintenir fermée. Nous avons aussi pu expliquer et prédire l'effet de mutations sur cette conformation. Ce travail ouvre désormais la possibilité d'étudier le mécanisme réactionnel de cette enzyme et de caractériser l'effet de mutations. Ceci permettra de proposer des mutants qui pourraient ouvrir la voie à des plantes qui poussent plus vite ou fournissent plus de biomasse, ce qui pourrait donc contribuer à résoudre une partie des problèmes d'alimentation à venir au niveau mondial dans les décennies futures
PEP carboxylase is an enzyme involved in several biological processes in plants, such as seed maturation and the early stages of carbon capture during photosynthesis in certain plants. It is responsible for the initial capture of CO2 for a quarter of the terrestrial biomass production. In this thesis, we studied the biochemical mechanism of the enzyme PEP carboxylase. The main unknown was the closed conformation of loop II, which protects the active site from the solvent and initiates the chemical reaction. This conformation has not been experimentally resolved to date, and initial attempts to predict this conformation have been unsatisfactory because they were unstable. Our goal was to predict this closed conformation through numerical simulations. To achieve this, we developed an original method to predict the closed conformation of protein loops based on the knowledge of the open conformation. We demonstrated with examples where both conformations are known that the method we developed, named SETH, is capable of predicting the closed conformation from the open conformation alone. Additionally, we developed a method for analyzing molecular simulation trajectories that allows clustering the data, thus facilitating their comparison. The advantage of this second method, named YACARE, is that it only involves physical parameters that are easily interpretable. We then applied the SETH and YACARE methods to PEP carboxylase and discovered a closed conformation that is a good candidate for the reactive conformation. This conformation is numerically stable during 200ns replica exchange simulations as well as 1µs classical simulations. It is characterized by the presence of salt bridges that help keep it closed. We were also able to explain and predict the effect of mutations on this conformation. This work now opens up the possibility of studying the reaction mechanism of this enzyme and characterizing the effect of mutations. This could lead to proposing mutants that might pave the way for plants that grow faster or produce more biomass, potentially helping to solve some of the global food supply issues in the coming decades

Cette thèse s'intéresse à la rationalisation du mécanisme de transfert d'excitation dans des polyphénylènes éthynylènes (PPE). Une étude statique approfondie a été réalisée en utilisant la TDDFT, permettant de confirmer la localisation des états excités de méta-PPE sur des fragments para, ainsi que la hiérarchie des interactions régissant les propriétés photochimiques des PPE. Des intersections coniques ont été identifiées, de même que les principales composantes de l'espace de branchement. Leur étude a soutenu l'hypothèse d'un transfert d'énergie par conversion interne entre états excités localisés sur des fragments para.D'autre part, nous avons proposé un modèle vibronique multiéchelles pour l'énergie des états électroniques. En particulier, nous avons exprimé les énergies des orbitales frontières de PPE en fonction des énergies des orbitales frontières du benzène et de l'acetylène via un Hamiltonien effectif de type Hückel. Un travail de mapping et d'optimisation nous a permis d'aboutir à une expression pour l'énergie de transition électronique en fonction d'un nombre réduit de coordonnées nucléaires locales
The present work is focused on the rationalization of the excitation transfer mechanism in polyphenylene ethynylenes (PPEs). A static study was performed using TDDFT, allowing to confirm both the localization of the excited states of meta-PPEs on para building blocks and the hierarchy in the interactions governing the photochemical properties of PPEs. Conical intersections were identified, along with few components of their branching spaces. Studying those supported the assumption of an energy transfer proceeding through internal conversion between excited states localized on different building blocks.In addition, we proposed a multiscale vibronic model for the energy of the eletronic states. In particular, we expressed the energies of the frontier orbitals of PPEs in terms of the energies of the frontier orbitals of benzene and acetylene, using an effective Hückel-type Hamiltonian. Perfoming different optimizations, we achieved to propose an expression for the energy of the electronic transition in terms of a reduced number of local nuclear coordinates