Estudo conformacional de polianfóteros fracos utilizando simulações de Monte Carlo
Carregando...
Data
2012-08-01
Autores
Valle, Rafael Musa Lyrio do [UNESP]
Título da Revista
ISSN da Revista
Título de Volume
Editor
Universidade Estadual Paulista (Unesp)
Resumo
Neste trabalho utilizamos simulações de Monte Carlo para estudar as propriedades elétricas e conformacionais de polianfóteros fracos, investigando o efeito da estrutura primária, do pH da solução da valência dos contraíons. O polímero foi representado por um conjunto de esferas rígidas conectadas por um potencial harmônico (modelo bead-spring ) e os contraíons da solução, de valência 1, 2 e 3, foram tratados de maneira explícita segundo o modelo primitivo restrito. Todo o sistema foi confinado em uma célula esférica com o polímero fixado em seu centro. Dentre as análises de propriedades elétricas do polianfótero, foi observado que a fração de grupos básicos protonados se aproxima do caso ideal com o aumento da valência dos contraíons, para todas as sequências primárias estudadas. Diferentemente do que ocorre para homopolímeros carregados, nos quais os efeitos de correlação entre contraíons multivalentes provocam alta compactação da cadeia, o raio de giração de polienfóteros com contra ons trivalentes se mostrou muito próximo de cadeias (self-avoiding walk ). Em relação ao efeito da sequência primária, cadeias com baixa carga líquida apresentaram maior compactação nos casos de distribuição de monômero com menor número de blocos, assim como já previsto na literatura utilizando eletrólito implícito através da teoria de Debye-Hückel. A medida que aumentamos o valor de pH, o polinafótero ca carregado e conformações globulares não são mais observadas. Nestas condições, verificamos a formação de estruturas conhecidas como tadpoles apenas utilizando contraíons monovalente. Em nossa análise de Scaling, os valores conhecidos na literatura para o índice v da relação Rg ~ N vm foram obtidos para os casos Alternado (caso SAW) e Dibloco (caso globular) em regimes de pH nos quais a macromolécula está neutra apenas considerando diluição infinita
In this work we use the Monte Carlo simulations to study conformational and electrical properties of weak Polyampholytes and investigate the e ect of the primary structure, pH and the valency of the counterion on these conformations. The polymer was represented by a set of rigid spheres connected by a harmonic potential (bead-spring model) and the counterions of the solution of valency 1, 2 and 3 were treated explicitly according to the restricted primitive model. The system was enclosed in a spherical cell with the polymer set at its center. Among the analysis of electrical properties of the polyampholyte, it was observed that the fraction of protonated basic groups approaches the ideal case with the increase in valency of the counterion for all the primary sequence studied. Di erently from what occurs for homopolymers, in which the e ects of correlation between multivalent counterions cause high compression of the chain, the radius of gyration of polyampholytes considering trivalent counterions is very close to those obtained for Gaussian chains with excluded volume interaction (Self-Avoiding Walk ). Regarding the e ect of primary sequence, chains with low net charge showed higher compression in cases of fewer blocks monomers distribution, as already provided in previous work using implicit counterions by the Debye-H uckel theory. As the pH increased, the polyampholyte has a net charge and globular conformations are no longer observed. Accordingly, we observed the formation of structures known as tadpoles using monovalent counterions. In our analysis of Scaling, the known values for the index (in Rg N m) were obtained for Alternating case (SAW) and Diblock case (globular) in pH regimes in which the macromolecule has no net charge and only considering in nite dilution
In this work we use the Monte Carlo simulations to study conformational and electrical properties of weak Polyampholytes and investigate the e ect of the primary structure, pH and the valency of the counterion on these conformations. The polymer was represented by a set of rigid spheres connected by a harmonic potential (bead-spring model) and the counterions of the solution of valency 1, 2 and 3 were treated explicitly according to the restricted primitive model. The system was enclosed in a spherical cell with the polymer set at its center. Among the analysis of electrical properties of the polyampholyte, it was observed that the fraction of protonated basic groups approaches the ideal case with the increase in valency of the counterion for all the primary sequence studied. Di erently from what occurs for homopolymers, in which the e ects of correlation between multivalent counterions cause high compression of the chain, the radius of gyration of polyampholytes considering trivalent counterions is very close to those obtained for Gaussian chains with excluded volume interaction (Self-Avoiding Walk ). Regarding the e ect of primary sequence, chains with low net charge showed higher compression in cases of fewer blocks monomers distribution, as already provided in previous work using implicit counterions by the Debye-H uckel theory. As the pH increased, the polyampholyte has a net charge and globular conformations are no longer observed. Accordingly, we observed the formation of structures known as tadpoles using monovalent counterions. In our analysis of Scaling, the known values for the index (in Rg N m) were obtained for Alternating case (SAW) and Diblock case (globular) in pH regimes in which the macromolecule has no net charge and only considering in nite dilution
Descrição
Palavras-chave
Biologia molecular, Biofísica, Polimeros, Metodo de Monte Carlo, Polimerização, Polymers, Weak polyampholytes, Monte Carlo simulations
Como citar
VALLE, Rafael Musa Lyrio do. Estudo conformacional de polianfóteros fracos utilizando simulações de Monte Carlo. 2012. 52 f. Dissertação (mestrado) - Universidade Estadual Paulista, Instituto de Biociências, Letras e Ciências Exatas, 2012.