RESUMEN
The guanidinium functional group is commonly used in nature to recognize and bind anions through ion pairing and hydrogen bonding. Specific hydrogen-bonding patterns can be found in crystal structures of simple guanidinium salts. Analysis of these simple salts reveals a variety of features which are found in natural systems. These features have been applied to a series of artificial phosphodiesterases for RNA. These receptors incorporate guanidinium groups positioned to mimic the hydrogen-bonding patterns found in simple guanidinium salts and natural enzymes. This paper outlines general guanidinium hydrogen-bonding patterns. Next, the complexation of phosphodiesters with a series of artificial receptors are analyzed in terms of counterions, solvent mixtures, and cavity flexibility. In addition, strategies to enhance catalysis through a pKa analysis of phosphoranes are addressed. Next, we describe how our findings were incorporated into second generation receptors/catalysts. Finally, our future work is discussed.
Asunto(s)
Guanidinas/metabolismo , ARN/metabolismo , Catálisis , ADN/metabolismo , Productos del Gen tat/metabolismo , Guanidina , Enlace de Hidrógeno , Hidrólisis , Cinética , Nucleasa Microcócica/metabolismo , Conformación de Ácido Nucleico , ARN Viral/metabolismo , Activación TranscripcionalAsunto(s)
Fumar , Administración Cutánea , Femenino , Cardiopatías/etiología , Humanos , Masculino , Nicotina/administración & dosificación , Nicotina/envenenamiento , Relaciones Médico-Paciente , Fumar/efectos adversos , Fumar/psicología , Cese del Hábito de Fumar/métodos , Prevención del Hábito de Fumar , Factores Socioeconómicos , Contaminación por Humo de TabacoRESUMEN
Poliovirus, coliphages, Giardia lamblia cysts, Clostridium perfringens spores, and Legionella pneumophila were concentrated simultaneously in a single pass by sequential filtration of large volumes of drinking water through 3- and 1-micron wound electronegative fiberglass cartridge filters (25.4 cm). Filtration was performed under acidic conditions (pH 3.5) in the presence of 0.001 M aluminum chloride to enhance adsorption. Elution of all the microorganisms entrapped or adsorbed to the filters was obtained by a slow backwash elution with a 1.5% beef extract solution, pH 9.75, containing 0.5% Tween 80. Tween 80 was shown to enhance recovery of the bacteriophages, bacteria, and parasites. Giardia cysts were efficiently eluted (71%) and could be reconcentrated by low-speed centrifugation and purified by sucrose density gradient flotation at a final recovery of 52%. Legionella pneumophila cells were eluted at 64% and were further concentrated by low-speed centrifugation at an overall recovery of 55%. C. perfringens spores and coliphages were eluted at efficiencies of 82 and 86%, respectively, and reconcentrated with minimal loss by a detergent - protein flotation method. Poliovirus was eluted at 93% and reconcentrated at 78% efficiency by organic flocculation.