PROTECTION OF CHLOROPHYLL a BY CAROTENOID FROM PHOTODYNAMIC DECOMPOSITION

Abstract— The order of inhibition of the photooxidation of chlorophyll a in ethanol and ethanol-benzene is as follows: β-carotene, α-tocopherol, benzoquinone, DABCO, menadione, cholesterol and KI. The quenching of singlet oxygen by β-carotene occurs by a collisional quenching mechanism with a diffusion-controlled rate of 1.7 × 10¹⁰ M ^-1 s^-1. Photodecomposition of Chi a is faster in ethanol-D₂O than in ethanol-H₂O. Photoirradiation (660 nm) of the peridinin-Chl a -protein complex, a photosynthetic light-harvesting pigment isolated from marine dinoflagellates, did not show any photo-decomposition of its Chi a in H₂O or D₂O, even after an extended period (12 h) of irradiation. However, the carotenoid, peridinin, in the photosynthetic antenna pigment was photobleached (ca. 10%) during the irradiation. We conclude that the singlet oxygen formed as a result of the Chi photosensitization is immediately quenched by the low-lying triplet state of four peridinin molecules (per Chl a ) bound within the same protein crevice. The carotenoid thus effectively protects Chl a from photodynamic damage, providing a direct proof for the protective role of carotenoids in the photosynthetic pigment complex.     

A first principle study of hydrogen storage in titanium-doped small carbon clusters (C2nTin,n = 2–6)

Structural Chemistry - Hydrogen storage in Ti-doped small carbon clusters, C2nTin (n = 2–6), has been studied using density functional theory. Using the principle of maximum hardness (η)...     

Porous Tungsten Oxide: Recent Advances in Design,Synthesis, and Applications

Tungsten oxide (WO₃) has received ever more attention and has been highly researched over the last decade due to its being a low-cost transition metal semiconductor with tunable, yet widely stable, band gaps. This minireview briefly highlights the challenges in the design and synthesis of porous WO₃ including methods, precursors, solvent effects, crystal phases, and surface activities of the porous WO₃ base material. These topics are explored while also drawing a connection of how the morphology and crystal phase affect the band gap. The shifts in band gap not only impact the optical properties of tungsten but also allow tuning to operate on different energy levels, which makes WO₃ highly desirable in many applications such as supercapacitors, batteries, solar cells, catalysts, sensors, smart windows, and bioapplications.     

Multi-choice stochastic transportation problem involving extreme value distribution

In this paper a multi choice stochastic transportation problem is considered where the supply and demand parameters of the constraints follow extreme value distribution. Some of the cost coefficients of the objective function are multi-choice type. At first all the probabilistic constraints are transformed into deterministic constraints. Further using the binary variables, multi-choice type cost coefficients are handled. Then the transformed problem is considered as a deterministic multi-choice transportation problem. Finally, a numerical example is presented to illustrate the solution procedure.     

Studies on the Polarographic Reduction of Poly-m-xylylviologen Dibromide in Water

Polarographic studies on aqueous solutions of the redox polyelectrolyte poly-m-xylylviologen dibromide were carried out in the 1.70–7.90 pH range. The compound revealed two well-defined, diffusion-controlled cathodic waves with half-wave potentials of -0.482 and -0.906 V vs SCE. The electrode processes were found to be irreversible and independent of pH. The system did not conform to the protonation equilibrium (PXVBr₂ + H⁺?PXVBr₂H⁺) in contrast to its ortho and para isomeric compounds. A suitable mechanism for the reduction processes is suggested.     

Host–Guest Chemistry between Perylene Diimide (PDI) Derivatives and 18‐Crown‐6: Enhancement in Luminescence Quantum Yield and Electrical Conductivity

Perylene diimide (PDI) derivatives exhibit a high propensity for aggregation, which causes the aggregation‐induced quenching of emission from the system. Host–guest chemistry is one of the best‐known methods for preventing aggregation through the encapsulation of guest molecules. Herein we report the use of 18‐crown‐6 (18‐C‐6) as a host system to disaggregate suitably substituted PDI derivatives in methanol. 18‐C‐6 formed complexes with amino‐substituted PDIs in methanol, which led to disaggregation and enhanced emission from the systems. Furthermore, the embedding of the PDI ? 18‐C‐6 complexes in poly(vinyl alcohol) (PVA) films generated remarkably high emission quantum yields (60–70 %) from the PDI derivatives. More importantly, the host–guest systems were tested for their ability to conduct electricity in PVA films. The electrical conductivities of the self‐assembled systems in PVA were measured by electrochemical impedance spectroscopy (EIS) and the highest conductivity observed was 2.42×10^?5 S cm^?1.     

Phase behaviour of thermotropic banana-shaped compounds under pressure

The phase behaviour of two achiral bent core banana-shaped compounds, the hexyloxy (compound I) and decyloxy (compound II) members of the 1,3-phenylene bis[N-(2-hydroxy-4-n-alkoxybenzylidene)-4′-aminobenzoate] series was investigated under hydrostatic pressures up to 300?MPa using high pressure differential thermal analysis and light transmission methods. The reversible transition sequence crystal (Cr₁)–B₁ phase–isotropic liquid (I), observed at room pressure for compound I, remains in the pressure region up to c 70?MPa. At higher pressures a pressure-induced crystalline phase (Cr_i) appears between the Cr₁ and B₁ phases, its temperature region becoming wider with increasing pressure. The temperature vs. pressure phase diagram shows a triple point of 72.9?MPa and 160.3°C for the Cr₁, Cr_i and B₁ phases, indicating the lower limit of pressure for the Cr_i phase. In compound II the reversible transition sequence crystal (Cr₁)–B₂ phase–I is seen over the whole pressure region, and the temperature range of the B₂ phase remains unaltered. It is concluded that both the B₁ and B₂ banana phases are stable over the whole pressure region studied.