Micellization of Sliding Polymer Surfactants

Following up a recent paper on grafted sliding polymer layers (Macromolecules 2005, 38, 1434-1441), we investigated the influence of the sliding degree of freedom on the self-assembly of sliding polymeric surfactants that can be obtained by complexation of polymers with cyclodextrins. In contrast to the micelles of quenched block copolymer surfactants, the free energy of micelles of sliding surfactants can have two minima: the first corresponding to small micelles with symmetric arm lengths, and the second corresponding to large micelles with asymmetric arm lengths. The relative sizes and concentrations of small and large micelles in the solution depend on the molecular parameters of the system. The appearance of small micelles drastically reduces the kinetic barrier signifying the fast formation of equilibrium micelles.Comment: Submitted to Macromolecule

Domains in Melts of Comb-Coil Diblock Copolymers: Superstrong Segregation Regime

Conditions for the crossover from the strong to the superstrong segregation regime are analyzed for the case of comb-coil diblock copolymers. It is shown that the critical interaction energy between the components required to induce the crossover to the superstrong segregation regime is inversely proportional to mb = 1 + n/m, where n is the degree of polymerization of the side chain and m is the distance between successive grafting points. As a result, the superstrong segregation regime, being rather rare in the case of ordinary block copolymers, has a much better chance to be realized in the case of diblock copolymers with combs grafted to one of the blocks.

Заболеваемость детей сальмонеллезом и уровень резистентности клинических штаммов сальмонелл к антибактериальным препаратам в Санкт-Петербурге

The aim of the study was to study the dynamics of the incidence of salmonellosis children in St. Petersburg and phenotypic resistance of clinical isolates of S. Enteritidis and S. Typhimurium to antibiotics in recent years. Materials and methods. The incidence of salmonellosis children studied according to the report for the first nine months of Rospotrebnadzor in 2013–2014. Incidence of salmonellosis in the structure of bacterial intestinal infections caused by pathogens in children hospitalized in the Department of intestinal infections in 2013–2014, studied according to annual reports. Antibiotic sensitivity was studied 86 Salmonella isolates (S. Enteritidis strain 64 and strain 22 S. Typhimurium), isolated from patients in children 2010–2014. Used the method of serial microdilution broth. Salmonella isolates were divided into sensitive, resistant, intermediate sensitivity to antibiotics. The Results. Analysis of the incidence of salmonellosis children of St. Petersburg has revealed its decline in 2014 (109.2) compared to 2013 (123,9) but relatively long-term average level was an increase in incidence (107,6). In the structure of salmonellosis in children prevailed salmonellosis Group D. In hospitalized children in the structure of bacterial intestinal infections detected Excess of share of salmonellosis in 2014 (36,9±3,4%) compared to 2013 (24,5±2,4%; p <0,01). A reduction in the frequency sensitivity of S. Enteritidis to ampicillin, cefepime, ceftazidime and chloramphenicol. Compared to S. Enteritidis S. Typhimurium isolates were more resistant to ceftazidime and ampicillin, but more sensitive to ciprofloxacin. Conclusion. Morbidity of salmonellosis in recent years characterized by a relatively long-term average increase of the level. In the structure of salmonellosis in children prevailed salmonellosis Group D. There was a reduction of sensitivity S. Enteritidis isolates to cephalosporins new generations, and S. Typhimurium isolates to cephalosporins new generations, ampicillin, chloramphenicol.Цель исследования: изучение динамики заболеваемости сальмонеллезом детей в Санкт-Петербурге и фенотипической антибиотикорезистентности изолятов S. Enteritidis и S. Typhimurium в последние годы. Материалы и методы: заболеваемость сальмонеллезом детей изучали по данным отчета Роспотребнадзора за девять месяцев 2013–2014 гг. Частоту сальмонеллеза в структуре бактериальных кишечных инфекций, вызванных патогенными возбудителями, у детей, госпитализированных в отделение кишечных инфекций НИИДИ в 2013–2014 гг., изучали по данным годовых отчетов. Исследовали антибиотикочувствительность 86 изолятов сальмонелл (64 штамма S. Enteritidis и 22 штамма S. Typhimurium), выделенных от больных детей в 2010– 2014 гг. Использовали метод серийных микроразведений в бульоне, изоляты сальмонелл разделяли на чувствительные, резистентные, с промежуточной чувствительностью к антибиотикам. Результаты: анализ заболеваемости сальмонеллезом детей Санкт-Петербурга выявил ее снижение в 2014 г. (109,2 на 100 тыс. нас.) по сравнению с 2013 г. (123,9 на 100 тыс. нас.), относительно многолетнего уровня отмечалось повышение заболеваемости (107,6 на 100 тыс. нас.). В структуре сальмонеллезов преобладали сальмонеллезы группы D. У госпитализированных детей в структуре бактериальных кишечных инфекций выявлено превышение доли сальмонеллеза в 2014 г. (36,9±3,4%) по сравнению с 2013 г. (24,5±2,4%; p<0,01). Установлено снижение частоты чувствительности изолятов S. Enteritidis к ампициллину, цефепиму, цефтазидиму и хлорамфениколу. По сравнению с S. Enteritidis изоляты S. Typhimurium были более резистентны к цефтазидиму и ампициллину, но более чувствительны к ципрофлоксацину. Заключение: заболеваемость детей сальмонеллезом в последние годы характеризовались нарастанием относительно среднего многолетнего уровня. В структуре сальмонеллезов преобладали сальмонеллезы группы D. Выявлено снижение чувствительности изолятов S. Enteritidis к цефалоспоринам новых генераций, а изолятов S. Typhimurium – к цефалоспоринам новых генераций, ампициллину, хлорамфениколу. 

Child morbidity of salmonellosis and the level of resistance of clinical isolates of salmonella to antibacterial preparations in saint Petersburg

The aim of the study was to study the dynamics of the incidence of salmonellosis children in St. Petersburg and phenotypic resistance of clinical isolates of S. Enteritidis and S. Typhimurium to antibiotics in recent years. Materials and methods. The incidence of salmonellosis children studied according to the report for the first nine months of Rospotrebnadzor in 2013–2014. Incidence of salmonellosis in the structure of bacterial intestinal infections caused by pathogens in children hospitalized in the Department of intestinal infections in 2013–2014, studied according to annual reports. Antibiotic sensitivity was studied 86 Salmonella isolates (S. Enteritidis strain 64 and strain 22 S. Typhimurium), isolated from patients in children 2010–2014. Used the method of serial microdilution broth. Salmonella isolates were divided into sensitive, resistant, intermediate sensitivity to antibiotics. The Results. Analysis of the incidence of salmonellosis children of St. Petersburg has revealed its decline in 2014 (109.2) compared to 2013 (123,9) but relatively long-term average level was an increase in incidence (107,6). In the structure of salmonellosis in children prevailed salmonellosis Group D. In hospitalized children in the structure of bacterial intestinal infections detected Excess of share of salmonellosis in 2014 (36,9±3,4%) compared to 2013 (24,5±2,4%; p <0,01). A reduction in the frequency sensitivity of S. Enteritidis to ampicillin, cefepime, ceftazidime and chloramphenicol. Compared to S. Enteritidis S. Typhimurium isolates were more resistant to ceftazidime and ampicillin, but more sensitive to ciprofloxacin. Conclusion. Morbidity of salmonellosis in recent years characterized by a relatively long-term average increase of the level. In the structure of salmonellosis in children prevailed salmonellosis Group D. There was a reduction of sensitivity S. Enteritidis isolates to cephalosporins new generations, and S. Typhimurium isolates to cephalosporins new generations, ampicillin, chloramphenicol

Mixed Systems of Hydrophobically Modified Polyelectrolytes: Controlling Rheology by Charge and Hydrophobe Stoichiometry and Interaction Strength

Rheology and phase separation were investigated for aqueous mixtures of two oppositely charged hydrophobically modified polyelectrolytes. The typical phase separation, normally seen for oppositely charged polymer mixtures, is dramatically reduced by the presence of hydrophobic modification, and phase separation is only detected close to the point of charge neutralization. While the two polyelectrolytes separately can give high viscosities and a gel-like behavior, a pronounced maximum in viscosity and storage modulus with the mixing ratio of the polyelectrolytes is observed; the maximum is located between the points of charge and hydrophobe stoichiometry and reflects a combination of hydrophobic and electrostatic association. Lowering the charge density of the anionic polymer leads to a strengthened association at first, but at lower charge densities there is a weakened association due to the onset of phase separation. The strength of the electrostatic interaction was modified by adding salt. Increased ionic strength can lead to phase separation and to increased or decreased viscosity depending on the polyelectrolyte mixing ratio