RESUMEN
Two newly synthesized symmetrical heptamethine cyanine dyes, AK7-5 and AK7-6, absorbing in the region of low autofluorescence of biological samples, have been tested for their ability to detect proteins aggregated into amyloid fibrils. In aqueous solution these probes possess three absorption bands corresponding to the monomer, dimer and H-aggregate species. The association of the dye with fibrillar lysozyme was followed by the enhancement of the monomer band and the reduction of the H-band. The absorption spectra measured at various fibril concentrations were analyzed in terms of the model allowing for the shift of equilibria between various dye species due to the binding of monomers and dimers of AK7-5 and AK7-6 to amyloid fibrils. The association constants and stoichiometries of the dye-fibril complexation have been evaluated. In contrast to fibrillar lysozyme, the native protein brought about strong J-aggregate formation accompanied by a marked drop in the absorbance of the dye monomer species. Quantum chemical calculations and simple docking studies showed that AK7-5 and AK7-6 monomers can bind to the grooves, running parallel to the fibril axis. Due to their ability to distinguish between the native and fibrillar protein states, the novel cyanines are recommended as complementary to existing amyloid markers.
Asunto(s)
Carbocianinas/síntesis química , Colorantes Fluorescentes/síntesis química , Muramidasa/química , Sitios de Unión , Carbocianinas/química , Colorantes Fluorescentes/química , Modelos Moleculares , Simulación del Acoplamiento Molecular , Agregado de Proteínas , Teoría Cuántica , Espectrometría de FluorescenciaRESUMEN
A series of symmetric pentamethine cyanine dyes derived from various N-substituted benzothiazolium/benzoselenazolium salts, and a conjugated bis-aniline derivative containing a chlorine atom at meso-position with respect to the polymethine chain, were synthesized using a novel improved synthetic approach under mild conditions at room temperature. The reaction procedure was held by grinding the starting compounds for relative short times. The novel method is reliable and highly reproducible. Some photophysical characteristics were recorded in various solvents, including absorption, and fluorescence quantum yields using Cy-5 as a reference. Additional studies on interactions with several bio-objects such as liposomes, DNA, and proteins have been investigated in the present work.
Asunto(s)
Benzotiazoles/química , Carbocianinas/química , ADN/química , Colorantes Fluorescentes/química , Colorantes Fluorescentes/síntesis química , Liposomas/química , Compuestos de Organoselenio/química , Proteínas/química , Fluorescencia , Estructura Molecular , Procesos Fotoquímicos , TemperaturaRESUMEN
The applicability of a series of novel benzanthrone dyes to monitoring the changes in physicochemical properties of lipid bilayer and to differentiating between the native and aggregated protein states has been evaluated. Based on the quantitative parameters of the dye-membrane and dye-protein binding derived from the fluorimetric titration data, the most prospective membrane probes and amyloid tracers have been selected from the group of examined compounds. Analysis of the red edge excitation shifts of the membrane- and amyloid-bound dyes provided information on the properties of benzanthrone binding sites within the lipid and protein matrixes. To understand how amyloid specificity of benzanthrones correlates with their structure, quantitative structure activity relationship (QSAR) analysis was performed involving a range of quantum chemical molecular descriptors. A statistically significant model was obtained for predicting the sensitivity of novel benzanthrone dyes to amyloid fibrils.