Contributions to cytochrome c inner- and outer-sphere reorganization energy

Cytochromes c are small water-soluble proteins that catalyze electron transfer in metabolism and energy conversion processes. Hydrogenobacter thermophilus cytochrome c₅₅₂ presents a curious case in displaying fluxionality of its heme axial methionine ligand; this behavior is altered by single point mutation of the Q64 residue to N64 or V64, which fixes the ligand in a single configuration. The reorganization energy (λ) of these cytochrome c₅₅₂ variants is experimentally determined using a combination of rotating disc electrochemistry, chronoamperometry and cyclic voltammetry. The differences between the λ determined from these complementary techniques helps to deconvolute the contribution of the active site and its immediate environment to the overall λ (λ_Total). The experimentally determined λ values in conjunction with DFT calculations indicate that the differences in λ among the protein variants are mainly due to the differences in contributions from the protein environment and not just inner-sphere λ. DFT calculations indicate that the position of residue 64, responsible for the orientation of the axial methionine, determines the geometric relaxation of the redox active molecular orbital (RAMO). The orientation of the RAMO with respect to the heme is key to determining electron transfer coupling (H_AB) which results in higher ET rates in the wild-type protein relative to the Q64V mutant despite a 150 mV higher λ_Total in the former.

Efficient delocalization of the redox-active molecular orbital (RAMO) in HtWT results in an increase in H_AB value which in turn accelerates the electron transfer (ET) rate in spite of the higher reorganization energy (λ) than the HtQ64V mutant.     

Simultaneous determination of chlorophyll a and chlorophyll b by derivative spectrophotometry

Chlorophyll a (Chl a) and chlorophyll b (Chl b) plant pigments, which are important in the food industry and are beneficial as environmental pollution indicators, have been extracted with a novel solvent mixture (1:1 v/v acetone–propanol) not containing chloroform and simultaneously determined by first-derivative spectrophotometry. The results were statistically compared to those obtained by the ordinary absorption spectrophotometric reference utilizing the principle of additivity of absorbances. The testing of the developed method in synthetic mixtures of Chl a and Chl b and in real plant material samples (grass, spinach, chard, purslane, black cabbage, crisp lettuce, rocket, dill and seaweed) proved successful in that the developed extractive derivative spectrophotometric method was both rapid and precise, and was not dependent on the Chl a/b ratio in contrast to the reference method which was adversely affected by the latter parameter.     

Facile Synthesis of Some 3-(Benzimidazol-2-yl)- and 3,6-Di(Benzimidazol-2-yl)-9-ethyl-9H-carbazoles

A simple and efficient synthesis of novel 3-(benzimidazol-2-yl)- and 3,6-di(benzimidazol-2-yl)-9-ethyl-9H-carbazoles is described. The synthetic approach for the preparation of 2-substituted benzimidazoles 4–8 and bis-benzimidazoles 9–12 was achieved by the condensation of carbazole-3-carbaldehyde 2 and carbazole-3,6-dicarbaldehyde 3 with o-phenyldiamines in dimethylformamide or dimethylsulfoxide in moderate to excellent yield. The identities of synthesized compounds were confirmed using ¹H NMR, ¹³C NMR, infrared (IR), and high-resolution mass spectrometry (HRMS).     

A study of the optical properties of polypropylene based polymer composite films

The optical clarity of the polymeric material can be influenced by changing the preparations parameters and thus the polymer structure. In this study, the transmittance, absorptance and reflectance of the polypropylene (PP) based polymer composites, synthesized by pressing method, changing the thickness between 8 — 29 μm, are investigated. Infrared and ultraviolet spectra of PP/diamond and PP/fiber composite in the wavelength range 200–25000 nm are examined. Optical absorption spectra recorded in the UV-Visible range are presented; the determined values of energy gaps are listed. The results indicate that both mechanism, direct and indirect transitions may exist. The analysis of absorption peaks corresponding to oxygen groups, for PP/diamond (0.3–0.5 %) and PP/fiber (20–30 %) composites, show low optical densities which complies with our other studies.