Spelling suggestions: "subject:"semiempirical"" "subject:"asemiempirical""
21 |
Implementação de uma correção de dispersão empírica aos métodos semiempíricos RM1 (Recife Model 1) e PM6 (Parametric method 6) / Implementation of an empirical dispersion correction to semiempirical methods RM1 (Recife Model 1) and PM6 (Parametric method 6)Silva, Danylo Alves da 28 August 2017 (has links)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / In the present study, the implementation and parameterization of the dispersion
correction functions, denominated DM1 and DM2, was carried out to the quantum
semiempirical methods RM1 and PM6, in the program Mopac2007. The aim of
this study is to improve the description of weak interactions by the methods above
mentioned with the addition of na energy correction. The DM1 methodology
contains 7 parameters while the DM2 model presents 13 parameters for the
correction function. Unlike previous work, the correction was used to adjust not
only the energy, but also the geometric parameters. The parameterization was
performed using a training set composed by 10 structures from S22 database
and 24 structures from S66 database. The results show that RM1-DM1 and RM1-
DM2 improved the total response function when compared to RM1, the RM1-
DM1 is better at describing the geometries of the complexes on the other hand,
the RM1-DM2 is more efficient in reproducing the dispersion energy. The PM6-
DM1 and PM6-DM2 methods, for the test set, had a smaller response function
than PM7 and PM6 and their extensions with correction of dispersion forces. The
best response function for PM6-DM1 and PM6-DM2 is related to the description
of the geometries of the complexes, with the dispersion energy being slightly
higher than that obtained by the PM6-DH2 method. The semiempirical methods
discussed here, together with the theory of density functional, with the most
popular B3LYP functional, were used to calculate the geometry of
cyclodextrin/guest complexes. The results obtained, with semiempirical methods,
showed that AM1, PM3, PM6-DM1 and PM6-DM2 presented the lowest values
of RMSD and variability for a set of 43 cyclodextrins. The DFT methodology was
used to calculate the geometry of a set of 9 cyclodextrins/guest complexes, the
result was compared to semiempirical methods. The best DFT result was
obtained with the 6-31G base, it is similar to obtained by the RM1 method. For
this set, the methods AM1, PM6-DM1 and PM6-DM2 presented the best results
in the description of the geometries. / No presente estudo foi realizada a implementação e parametrização das funções
de correção de dispersão, denominadas DM1 e DM2, aos métodos
semiempíricos quânticos RM1 e PM6, no programa Mopac2007. O estudo tem o
como finalidade melhorar a descrição de interações fracas pelos métodos
supracitados com a adição de uma correção de energia. A metodologia DM1
contém 7 parâmetros enquanto, o modelo DM2 apresenta 13 parâmetros para a
função de correção. Diferente de trabalhos anteriores a correção foi usada para
ajustar, não somente, a energia, mas também parâmetros geométricos. A
parametrização foi executada usando um conjunto treinamento que usa 10
estruturas do banco de dados S22 e 24 estruturas do banco de dados S66. Os
parâmetros obtidos através do conjunto treinamento foram aplicados ao conjunto
teste, o qual é formado pelas 54 estruturas que não fizeram parte do conjunto
treinamento. Os resultados mostram que RM1-DM1 e RM1-DM2 melhoraram a
função resposta total quando comparado ao RM1, sendo o RM1-DM1 melhor em
descrever as geometrias dos complexos e RM1-DM2 mais eficiente em
reproduzir a energia de dispersão. Os métodos PM6-DM1 e PM6-DM2 para o
conjunto teste apresentaram uma função resposta menor do que o PM7 e PM6
e suas extensões com correção das forças de dispersão. A melhor função
resposta para PM6-DM1 e PM6-DM2 está relacionada a descrição das
geometrias dos complexos, sendo a energia de dispersão um pouco maior do
que a obtida pelo método PM6-DH2. Os métodos semiempíricos, aqui
abordados, junto com a teoria do funcional da densidade, com o funcional mais
popular B3LYP, foram usados para calcular a geometria de complexos
ciclodextrina/convidado. Os resultados obtidos com os métodos semiempíricos
mostraram que os métodos AM1, PM3, PM6-DM1 e PM6-DM2 apresentam os
menores valores de RMSD e variabilidade para um conjunto de 43 ciclodextrinas.
A metodologia DFT foi usada para calcular a geometria para um conjunto de 9
complexos ciclodextrinas/convidado, o resultado foi comparado aos métodos
semiempíricos. O melhor resultado DFT foi obtido com a base 6-31G, esse é
semelhante ao obtido pelo método RM1. Para esse conjunto os métodos AM1,
PM6-DM1 e PM6-DM2 apresentaram os melhores resultados na descrição das
geometrias. / São Cristóvão, SE
|
22 |
Análise de solubilização micelar através do uso de parâmetros derivados de química quântica / Analysis of micellar solubilization through use of parameters derived from quantum chemistryGilson Alberto Rosa Lima 26 January 2000 (has links)
Uma das propriedades fundamentais de soluções de micelas aquosas é sua capacidade de solubililizar uma ampla faixa de solutos orgânicos com diferentes graus de polaridade e hidrofobicidade. Recentemente Quina et. aI., estudaram as interações químicas específicas que governam a solubilidade para um ampla faixa de solutos orgânicos em micelas usando relações lineares de energia livre de solvatação (LSERs), baseado nos parâmetros empíricos do soluto desenvolvido por Abraham. O presente trabalho trata a solubilização de solutos orgânicos em micelas baseado em parâmetros obtidos unicamente da estrutura molecular do soluto através de cálculos de química quântica. Nossos resultados mostram que valores experimentais de Ks para solubilização de solutos orgânicos em detergentes aniônicos (micelas de SDS, dodecil sulfato de sódio e agregados de SDS com PEG-polietilenoglicol) podem ser reproduzidos usando parâmetros teóricos. A relação linear teórica de energia livre de solvatação resultante é quimicamente condizente com LSERs baseados em parâmetros empíricos do soluto. No caso de detergentes catiônicos e não iônicos, a metodologia apresenta limitações, por que o método de cálculo de cargas formais usando a definição de análise populacional de Mulliken não descreve de maneira apropriada o caráter ácido e básico das pontes de hidrogênio entre os solutos e a água. Alternativas para resolver o problema da limitação imposta pelos parâmetros teóricos, mantendo a aproximação linear de energia livre, são discutidas. / One of the most fundamental properties of aqueous micelar solutions is their ability to solubilize a wide variety of organic solutes with quite distinct polarities and degree of hydrophobicity. Recently Quina et al., studied the specific chemical interactions governing the solubilities of a wide range of solutes in micelles using linear solvation energy relationships (LSERs) based on empirical solute parameters developed by Abraham. This work reports an investigation of the solubilization of organic solutes in micelles based on the use of theoretical solute parameters derived from quantum chemical calculations Our results show that the experimental Ks values for solubilization of organic solutes in anionic detergents (micelles of SDS-sodium dodecyl sulfate and aggregate formed between SDS and PEG-poly(ethylene glycol)) can be reproduced using theoretical parameters. The resultant theoretical linear solvation energy relationships are chemically consistent with LSERs based on empirical solute parameters. In the case of cationic and nonionic detergents, the theoretical parameters used to describe hydrogen bonding fail because methods of calculating formal charges using the concept of Mulliken populational analysis cannot describe hydrogen bonding donor and acceptor character in an appropriate way. Possible strategies to solve the theoretical descriptor problem in the context of the linear free energy approximation are discussed.
|
23 |
Estudo químico-quântico de propriedades estruturais e eletrônicas de oligofluorenos com potenciais aplicações tecnológicas / Quantum chemical study on structural and electronic properties of oligofluorenes with potential technological applicationsMelissa Fabíola Siqueira Pinto 05 November 2007 (has links)
Nesta tese foi analisada a evolução das propriedades eletrônicas e estruturais de oligômeros do fluoreno e de dois derivados, relacionada com a inserção gradativa de unidades monoméricas, utilizando-se os métodos de química quântica semi-empríricos, ab initio Hartree-Fock e Teoria do Funcional da Densidade (DFT). Para tal finalidade, foram realizadas análises metodológicas assaz detalhadas com os monômeros e dímeros (fluoreno, FF e TFFF), cujos resultados mostraram que os métodos semi-empíricos AM1 e PM3 são inadequados para descrever as distribuições das cargas derivadas do potencial eletrostático e, por conseguinte, as propriedades que dependem das mesmas. Além disso, as análises conformacionais realizadas para as três espécies de dímeros mostraram que ambas as estruturas estáveis do TFFF apresentaram o mesmo momento de dipolo total, provavelmente devido à influência dos átomos de flúor sobre o sistema. Ademais, com as investigações concernentes ao crescimento gradual das cadeias oligoméricas foi constatado que os espectros de UV e as energias dos orbitais fronteira calculados para os oligômeros seguiram a mesma tendência exibida por seus polímeros correspondentes, segundo os resultados de voltametria cíclica e de UV divulgados na literatura. Enquanto que os ângulos diedros adotados pelos oligômeros indicaram que suas conformações não são planares. Quanto à energia total, verificou-se que o decaimento linear relativo aos oligômeros do TFFF sucedeu aproximadamente três vezes mais rápido que o observado para os do fluoreno. Portanto, as aplicações dos fundamentos da Química Quântica e a correlação entre esses resultados teóricos e medidas experimentais reportadas na literatura, evidenciaram que com estas informações é factível estimar algumas propriedades de polímeros orgânicos ?-conjugados a partir de seus oligômeros, utilizando-se métodos de química quântica apropriados. / In this thesis, the evolution of electronic and structural properties of fluorene oligomers and two derivatives were accomplished relating to the gradual insertion of monomeric units using the quantum chemical methods semiempirical, ab initio Hartree-Fock and Density Functional Theory (DFT). For this purpose, detailed methodological analyses were performed with their monomers and dimers (fluorene, FF and TFFF). These results showed that the semiempirical methods AM1 and PM3 are inadequate to describe the atomic charges derived from electrostatic potential distributions and, hence, for the properties depending of them. In addition, the conformational analysis achieved for these three dimers showed that both stable structures found for the TFFF dimer possess the same total dipole moment, this is probably due to the influence of the fluorine atoms on the system. Moreover, with investigations regarding to the gradual increase in the oligomeric chain, it was verified that the UV spectra and the frontier orbital energies calculated for the oligomers provided the same tendency bespoken by their relative polymers from cyclic voltametry and UV measurements shown in the literature. Besides, the dihedral angles found in the oligomers indicated that their conformations are not planar. Furthermore, the total energy linear decay of the TFFF oligomers behaves approximately three times faster than that exhibited by the fluorene oligomers. In this way, the applications of the Quantum Chemistry principles and the correlation between these theoretical results and experimental data reported in the literature evidenced that using these information is feasible to estimate some properties of polymers from their oligomers by means of appropriate methods of quantum chemistry.
|
24 |
Estudo das propriedades de agregados supramoleculares contendo metais de transição / Properties of Supramolecular Aggregates Containing Transition Metals -- A StudyNaidel Antônio Moreira dos Santos Caturello 17 November 2015 (has links)
O estudo das reações de agregação em sistemas automontados é de grande interesse científico pela grande variedade de aplicações que tais colunas podem desempenhar. O presente trabalho teve como objetivo investigar as propriedades gerais de colunas supramoleculares formadas por complexos de coordenação que contêm platina, paládio e zinco. Esta investigação foi feita através do método semiempírico PM7. Os agregados supramoleculares investigados tiveram suas geometrias otimizadas e foram submetidos a cálculos termoquímicos. Pôde-se investigar as influências do metal e dos ligantes nos mecanismos gerais e propriedades das colunas, uma vez que utilizaram-se dois ligantes distintos. Estudou-se compostos de coordenação cujos ligantes foram o 2,6-bis(1H-1,2,4-triazol-5-il)piridina e oligofenilenoetinilenos (OPE) piridínicos. Realizou-se cálculos utilizando o modelo de solvatação contínua COSMO com água e metilciclohexano (MCH), o que permitiu avaliar os efeitos dos solventes nas energias de dimerização dos sistemas estudados. Os resultados obtidos para os derivados de OPE indicaram que as colunas supramoleculares desta classe que contêm Zn(II) apresentam anticooperatividade, exibindo energias de Gibbs de formação para o vácuo a 298 K positivas do dímero ao decâmero. Os resultados de solvatação contínua indicaram que a formação de um dímero deste composto é termodinamicamente favorável de 278 K para água e 267 K para o MCH, enquanto que para o vácuo a temperatura na qual a energia de Gibbs de dimerização é negativa ocorre em 246 K. Tal resultado aponta que o principal efeito de formação de colunas baseadas neste composto em altas temperaturas é primariamente um efeito solvofóbico que depende da polaridade do solvente. Observou-se a cooperatividade em vácuo e em ambos os solventes das colunas de derivados de OPE que contêm Pd(II) e Pt(II). Além destes fatos, as distâncias entre os centros metálicos diminuíram conforme monômeros eram adicionados à coluna, o que indica a existência de interações metalofílicas no sistema. Este resultado é corroborado experimentalmente por um artigo de Albuquerque el al. no caso do sistema de derivado de OPE que contém Pd(II). Para os sistemas cujos ligantes eram a 2,6-bis(1H-1,2,4-triazol-5-il)piridina, houve cooperatividade para ambas as colunas baseadas em Pd(II) e Pt(II), e houve para o sistema cujos centros metálicos são o Pt(II) uma transição não observada para todos os outros sistemas estudados; houve comportamento distinto das mudanças de distâncias entre monômeros no sistema triazol pridínico baseado em Pd(II) em relação àquele baseado em Pd(II) derivado de OPE. Este resultado indica a soma de dois efeitos no sistema OPE baseado em Pd(II): o de interações metalofílicas e de empilhamentos π-π. Como um todo, os resultados indicam que as principais interações envolvidas nas formações das colunas supramoleculares são interações de empilhamento π-π e metalofílicas para quatros compostos em graus diversos, exceto para o derivado de OPE baseado em Zn(II), que tem como principal força-motriz de agregação interações solvofóbicas. Perspectivas para este projeto: continuação da modelagem dos sistemas estudados por dinâmica molecular, com a simulação das interações de várias colunas formadas pelos monômeros estudados através do CP2K e publicação de um artigo com os resultados obtidos. / The study of aggregation reactions in self-assembled systems is of great scientific interest due to the wide range of applications which such resulting columns can play. Herein, we had the objective of investigating the general properties of supramolecular columns formed coordination complexes which contain platinum, palladium and zinc. This investigation was carried through the semiempirical method PM7. The investigated supramolecular aggregates were optimized, and their optimized geometries were subjected to thermochemical calculations. In this sense we could probe the influences of metals and ligands onto the general mechanisms and columnar properties, once were herein used two different ligands. The two ligands were 2,6-bis(1H-1,2,4-triazol-5-il)pyridine and oligophenyleneethynediyl (OPE) pyridine derivatives. COSMO solvation model -based calculations in water and methylcyclohexane (MCH) were performed in order to evaluate solvents effects on dimerization Gibbs energies of the studied systems. The results obtained for the OPE derivative based on Zn(II) pointed an anticooperative process in vacuum at 298K, exhibiting positive Gibbs energies of formation from the dimer to the decamer. The results from continuum solvation calculations indicate the formation of a dimer based on this Zn(II) molecule to be thermodynamically favorable at 278 K for water and at 267 K for MCH, while in vaccum this point lies at 246 K. This results indicates the formation of supramolecular columns based on this compound are formed in higher temperatures primarily due to solvophobic effects, and the intensity of this effect depends on the solvent polarity. The columns of OPE derviatives which contained Pd(II) and Pt(II) both showed cooperativity in the aggregation process. Besides these thermodynamic results, both of those columns showed monotonic distance shortening due to columns increasing process. This is an indicative of metallophilic interactions taking place in these aggregates. This result for Pd(II) is experimentally supported by a paper od Albuquerque et al. for the columns containing 2,6-bis(1H-1,2,4-triazol-5-il)pyridine cooperativity was observed for both the columns--those which contain Pd(II) and Pt(II)--, and for the Pt(II)-based columns of this class it was observed a transition not of most eneregetically favoured mechanisms not observed for all the other systems studied. A difference on the behavior of average monomer distances took place in the triazol pyridine Pd(II) compound when compared to its metal-related OPE derivative. This result indicates the summation of effects in the OPE-based Pd(II) system: the one of metallophilic interactions and π-π stacking interactions. As a whole, the results indicate π-π stacking and metallophilic interactions to be responsible for aggregation processes in diverse intensities for four of the compounds, except for that in the Zn(II)-based OPE derivative, which has the main aggregation effect as solvophobic interactions. The main perspectives for this project are the continuation of the modelling of the herein studied systems by molecular dynamics, simulating the interactions of many columns by the CP2K program, and the publication of a paper which contains the results obtained and presented in this dissertation.
|
25 |
Combining Semiempirical QM Methods with Atom Dipole Interaction Model for Accurate and Efficient Polarizability CalculationsRyan Scott Young (14221652) 03 February 2023 (has links)
<p>Utilizing a genetic algorithm training of the atom dipole interaction model was performed to arrive at C,H, N, & O atomic polarizabilities that constitute a correction to semiempirical molecular polarizability calculations increasing the accuracy of these calculations to near parity with DFT at a fraction of the computational load.</p>
|
26 |
Análise químico-computacional de sistemas catalíticos a base de paládio contendo ligantes do tipo Brookhart-Guan modificados. / Chemical computational analysis of palladium based catalytic systems containing Brookhart-Guan type liganos.Ferreira, Daví Alexsandro Cardoso 07 March 2008 (has links)
We were accomplished modeling employing chemical-computational tools in order to
foreknow the influence of a chiral environment on the active center of catalytic diimina
Brookhart-Guan modified systems proposed by our Group. These complexes are used to
produce branched or linear chains of polyethylene, having ethene as the single monomer.
In this study, a computational design of a cyclophane diiminie chiral ligand,
Brookhart-Guan modified type, and its respective palladium complex have been attained.
Also, a computational studied related to the microstructure of the polyethylene obtained have
been achieve. For that, growing chains have been simulated bearing branches that must be
correctly oriented due to the esteric and chiral (using the FTFT like ligand) environments
present at the active center also, modeling for possibilities of transition state in the insertion
step for desired complex. This work can lead to a suitable design of a catalyst, besides to
forecast the structural characteristics of the polymers obtained from this type of catalytic
system. At the same way, those simulations allow to understand the effect observed in those
type of Pd-diimine catalytic complexes for ethane polymerization. / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Neste trabalho foram realizadas modelagens empregando ferramentas químicocomputacionais,
com o objetivo de prever a influência que um ambiente quiral em torno do
centro de atividade de sistemas catalíticos Pd-diimínicos do tipo Brookhart-Guan
modificados, proposto pelo nosso Grupo. Estes complexos catalíticos podem ser utilizados
para a obtenção de cadeias lineares ou ramificadas de polietileno, tendo-se como único
monômero o eteno.
Neste estudo foi realizado o design computacional de um pré-ligante do tipo ciclofano
diimínico quiral, do tipo Brookhart-Guan modificado, e de seu respectivo complexo de
paládio. Além disso, foi realizado o estudo computacional relativo à microestrutura do
polímero a ser obtido empregando eteno como único monômero. Para tanto, foram modeladas
cadeias em crescimento apresentando ramificações que devem ser orientadas em função do
ambiente estéreo e assimétrico (usando o ligante FTFT) em torno do centro catalítico, além de
modelagens para os possíveis estados de transição na etapa de inserção para o complexo
desejado. Este trabalho de poderá proporcionar o adequado design do catalisador, além de
prever as características estruturais do polímero obtido com este sistema catalítico. Da mesma
forma, as simulações permitem compreender os efeitos observados para catalisadores a base
de Pd-diimina na polimerização do eteno.
|
27 |
Dynamiques moléculaires utilisant un champ de force quantique semiempirique : développement et applications à des systèmes d'intérêt biologique / Molecular dynamics using a semiempirical quantum force field : development and applications to systems of biological interestMarion, Antoine 08 December 2014 (has links)
Ce travail est destiné au développement de méthodes approchées de chimie quantique capables de traiter des systèmes biologiques de grande taille. En particulier, nous réalisons des simulations de dynamique moléculaire dans l'approximation de Born-Oppenheimer, permettant une description quantique de l'Hamiltonien électronique du système dans son entier : SEBOMD (SemiEmpirical Born-Oppenheimer Molecular Dynamics). Notre approche se base sur un Hamiltonien électronique semiempirique (SE). L'une des principales difficultés rencontrées lors d'une simulation SEBOMD de la phase condensée est représentée par le choix de la méthode SE. La plupart des méthodes courantes ne permettant pas une bonne description de certaines interactions fondamentales, nous avons développé une nouvelle approche. Cette méthode, dénommée PM3-PIF3, a été appliquée à l'étude par dynamique moléculaire de molécules organiques dans l'eau. Les résultats obtenus montrent que notre méthode est appropriée pour le traitement de molécules comportant des groupements hydrophobes et/ou hydrophiles en milieu aqueux. L'analyse des propriétés électroniques et vibrationnelles de ces molécules en présence du solvant valide également nos résultats vis-À-Vis d'autres études expérimentales et théoriques présentes dans la littérature. Finalement, nous nous sommes intéressés au processus d'autoprotolyse de l'eau en milieux confinés. Après avoir discuté du choix de l'Hamiltonien SE à utiliser pour cette étude, nous avons caractérisé le transfert de proton dans un agrégat d'eau. Nous avons établi une corrélation entre l'énergie libre associée à la première étape de ce transfert et certaines propriétés physiques collectives / The present work is devoted to the development of approximate quantum chemistry methods that are suitable to treat biological systems of large size. In particular, we run molecular dynamics under the Born-Oppenheimer approximation, allowing a quantum mechanical description of the electronic Hamiltonian of the full system: SEBOMD (SemiEmpirical Born-Oppenheimer Molecular Dynamics). Our method is based on a semiempirical (SE) electronic Hamiltonian. One of the key issues arising in a condensed phase SEBOMD simulation is represented by the choice of the SE method. Since most of the currently available approaches fail in describing some relevant intermolecular interactions, we developed a new correction of SE Hamiltonians. This method, which we named PM3-PIF3, was applied to study the molecular dynamics of organic molecules in water. The results that we obtained showed that our technique is suitable to treat molecules having hydrophobic and/or hydrophilic groups in an aqueous medium. The analysis of the electronic and vibrational properties of these molecules in the presence of the solvent validates our results with respect to experimental and theoretical studies in the literature. Finally, we investigated the water self-Dissociation process in confined environments. After discussing the choice of the SE Hamiltonian to be used for this purpose, we characterized the proton transfer in a water cluster. We established a correlation between the free energy of the first step of this process and some collective physical properties
|
28 |
Darstellung und Charakterisierung neuartiger C-Arylcalix(4)resorcinareneHünig, Hagen 03 March 2001 (has links) (PDF)
In der vorliegenden Arbeit wird die Darstellung und Charakterisierung von aromatisch substituierten Calix(4)resorcinarenen behandelt. Im zweiten Kapitel werden die Grundlagen und Besonderheiten bei Calix(4)resorcinarenen angesprochen. Ein Überblick über die wichtigsten Verbindungen dieser Gruppe von Makrocyclen wird gegeben. Im Kapitel 3 werden wesentliche Methoden zur vollständigen O-Alkylierung bei Calix(4)resorcinaren genannt. Außerdem werden Methoden zur partiellen O-Alkylierung von C-Arylcalix(4)resorcinarenen vorgestellt. Das Kapitel 4 stellt die Methoden zur Strukturaufklärung mittels 2D-NMR-Spektroskopie bei diesen Verbindungen vor. Möglichkeiten zur Unterscheidung des rccc-Isomer vom rctt-Isomer werden beschrieben. Das Kapitel 5 zeigt wesentliche Ergebnisse der semiempirischen Rechnungen zu C-Arylcalix(4)resorcinarenen und ihrer Acetate. Am Beispiel einer Verbindung werden Energiewerte aller Isomere und Konformere verglichen. Eine Deutung der ROESY-Spektren von Standpunkt der Quantenchemie aus wird gegeben. Im Ergebnis aller gewonnener Daten werden Aussagen zum wahrscheinlich ablaufenden Mechanismus gemacht. Der Vorgeschlagene Mechanismus geht von dimeren Verbindungen aus und berücksichtigt die Stereochemie der erhaltenen Produkte. / In this work the preparation and characterisation of aromatic substituted Calix(4)resorcinarens are shown. In the second chapter the basis's and the peculiarity's of the Calix(4)resorcinarens are given. A summary of the most important compounds of this class is shown. In chapter 3 preparation methods for the complete O-alcylation of Calix(4)resorcinarens are given. Methods for the particular O-alcylation of C-Arylcalix(4)resorcinarens are introduced. Chapter 4 presents the methods for the characterisation of this class of compounds with 2D-NMR-spectroscopy. Methods for the distinction of the rccc-isomer from the rctt-isomer are described. The chapter 5 shows important results of the semiempirical calculations with C-Arylcalix(4)resorcinarens and their acetates. The energy values of all isomers and conformers of one compound are compared. A interpretation of the ROESY-spectras with quantum chemical methods is given. As a result of this work a new mechanism is proposed.
|
29 |
Darstellung und Charakterisierung neuartiger C-Arylcalix(4)resorcinareneHünig, Hagen 08 March 2001 (has links)
In der vorliegenden Arbeit wird die Darstellung und Charakterisierung von aromatisch substituierten Calix(4)resorcinarenen behandelt. Im zweiten Kapitel werden die Grundlagen und Besonderheiten bei Calix(4)resorcinarenen angesprochen. Ein Überblick über die wichtigsten Verbindungen dieser Gruppe von Makrocyclen wird gegeben. Im Kapitel 3 werden wesentliche Methoden zur vollständigen O-Alkylierung bei Calix(4)resorcinaren genannt. Außerdem werden Methoden zur partiellen O-Alkylierung von C-Arylcalix(4)resorcinarenen vorgestellt. Das Kapitel 4 stellt die Methoden zur Strukturaufklärung mittels 2D-NMR-Spektroskopie bei diesen Verbindungen vor. Möglichkeiten zur Unterscheidung des rccc-Isomer vom rctt-Isomer werden beschrieben. Das Kapitel 5 zeigt wesentliche Ergebnisse der semiempirischen Rechnungen zu C-Arylcalix(4)resorcinarenen und ihrer Acetate. Am Beispiel einer Verbindung werden Energiewerte aller Isomere und Konformere verglichen. Eine Deutung der ROESY-Spektren von Standpunkt der Quantenchemie aus wird gegeben. Im Ergebnis aller gewonnener Daten werden Aussagen zum wahrscheinlich ablaufenden Mechanismus gemacht. Der Vorgeschlagene Mechanismus geht von dimeren Verbindungen aus und berücksichtigt die Stereochemie der erhaltenen Produkte. / In this work the preparation and characterisation of aromatic substituted Calix(4)resorcinarens are shown. In the second chapter the basis's and the peculiarity's of the Calix(4)resorcinarens are given. A summary of the most important compounds of this class is shown. In chapter 3 preparation methods for the complete O-alcylation of Calix(4)resorcinarens are given. Methods for the particular O-alcylation of C-Arylcalix(4)resorcinarens are introduced. Chapter 4 presents the methods for the characterisation of this class of compounds with 2D-NMR-spectroscopy. Methods for the distinction of the rccc-isomer from the rctt-isomer are described. The chapter 5 shows important results of the semiempirical calculations with C-Arylcalix(4)resorcinarens and their acetates. The energy values of all isomers and conformers of one compound are compared. A interpretation of the ROESY-spectras with quantum chemical methods is given. As a result of this work a new mechanism is proposed.
|
30 |
QM/MM Applications and Corrections for Chemical ReactionsBryant J Kim (15322279) 18 May 2023 (has links)
<p>In this thesis, we present novel computational methods and frameworks to address the challenges associated with the determination of free energy profiles for condensed-phase chemical reactions using combined quantum mechanical and molecular mechanical (QM/MM) approaches. We focus on overcoming issues related to force matching, molecular polarizability, and convergence of free energy profiles. First, we introduce a method called Reaction Path-Force Matching in Collective Variables (RP-FM-CV) that efficiently carries out ab initio QM/MM free energy simulations through mean force fitting. This method provides accurate and robust simulations of solution-phase chemical reactions by significantly reducing deviations on the collective variables forces, thereby bringing simulated free energy profiles closer to experimental and benchmark AI/MM results. Second, we explore the role of pairwise repulsive correcting potentials in generating converged free energy profiles for chemical reactions using QM/MM simulations. We develop a free energy correcting model that sheds light on the behavior of repulsive pairwise potentials with large force deviations in collective variables. Our findings contribute to a deeper understanding of force matching models, paving the way for more accurate predictions of free energy profiles in chemical reactions. Next, we address the underpolarization problem in semiempirical (SE) molecular orbital methods by introducing a hybrid framework called doubly polarized QM/MM (dp-QM/MM). This framework improves the response property of SE/MM methods through high-level molecular polarizability fitting using machine learning (ML)-derived corrective polarizabilities, referred to as chaperone polarizabilities. We demonstrate the effectiveness of the dp-QM/MM method in simulating the Menshutkin reaction in water, showing that ML chaperones significantly reduce the error in solute molecular polarizability, bringing simulated free energy profiles closer to experimental results. In summary, this thesis presents a series of novel methods and frameworks that improve the accuracy and reliability of free energy profile estimations in condensed-phase chemical reactions using QM/MM simulations. By addressing the challenges of force matching, molecular polarizability, and convergence, these advancements have the potential to impact various fields, including computational chemistry, materials science, and drug design.</p>
|
Page generated in 0.0649 seconds