Magnetic field effects on spin-rephasing in a photochemically produced radical pair investigated by a double-pulse technique using a nitrogen laser

The effect of an external magnetic field on the yield of the benzophenone ketyl radical has been investigated by a new, double-pulse technique. The technique and its variants can be used not only for studying geminate recombination of photochemically produced radical pairs but also for continuous photoelectric recording of fluorescence spectra of the free radicals which can be generated by nitrogen laser irradiation.     

Nanosecond laser photolysis studies of chlorosomes and artificial aggregates containing bacteriochlorophyll e: evidence for the proximity of carotenoids and bacteriochlorophyll a in chlorosomes from Chlorobium phaeobacteroides strain CL1401

Time-resolved, laser-induced changes in absorbance, delta A(lambda; t), have been recorded with a view to probing pigment-pigment interactions in chlorosomes (control as well as carotenoid-depleted) and artificial aggregates of bacteriochlorophyll e (BChle). Control chlorosomes were isolated from Chlorobium phaeobacteroides strain CL1401, whose chromophores comprise BChle, bacteriochlorophyll a (BChla) and several carotenoid (Car) pigments; Car-depleted chlorosomes, from cells grown in cultures containing 2-hydroxybiphenyl. Artificial aggregates were prepared by dispersing BChle in aqueous phase in the presence of monogalactosyl diglyceride. In chlorosomes delta A(lambda; t) shows, besides a signal attributable to triplet Car (with a half-life of about 4 microseconds), signals in the Qy regions of both BChl. The BChla signal decays at the same rate as the Car signal, which is explained by postulating that some Car are in intimate contact with some baseplate BChla pigments, and that when a ground-state Car changes into a triplet Car, the absorption spectrum of its BChla neighbors undergoes a concomitant change (termed transient environment-induced perturbation). The signal in the Qy-region of BChle behaves differently: its amplitude falls, under reducing conditions, by more than a factor of two during the first 0.5 microsecond (a period during which the Car signal suffers negligible diminution), and is much smaller under nonreducing conditions. The BChle signal is also attributed to transient environment-induced perturbation, but in this case the perturber is a BChle photoproduct (probably a triplet or a radical ion). The absence of long-lived BChle triplets in all three systems, and of long-lived BChla triplets in chlorosomes, indicates that BChle in densely packed assemblies is less vulnerable to photodamage than monomeric BChle and that, in chlorosome, BChla rather than BChle needs, and receives, photoprotection from an adjacent Car.     

Performance improvement of a PGNAA setup due to change in moderator design: A Monte Carlo study

Effect of neutron source-moderator geometry has been studied on the performance of a thermal neutron capture-based prompt gamma neutron activation analysis (PGNAA) setup. In the study prompt gamma-ray and thermal neutron yield was calculated for various positions of the neutron source inside 3–10 cm long high density polyethylene moderators. The study has been carried out for a Portland cement sample using Monte Carlo calculations. The maximum yields of the thermal neutrons and prompt gamma-rays have been observed for a neutron source at a distance of 1 cm from the sample. The maximum yield of the 1.94 and 6.42 MeV prompt gamma-ray from a Portland cement sample has been observed for moderators having length equal to or greater than 7 cm. The yield of both gamma rays is 2.57 times higher than the previously reported value for a PGNAA setup with the source placed outside a 5 cm thick moderator. The higher yield of gamma rays will result in higher sensitivity of the PGNAA setup.     

Electronic energy transfer involving carotenoid pigments in chlorosomes of two green bacteria: Chlorobium tepidum and Cholroflexus aurantiacus

Electronic energy transfer processes in chlorosomes isolated from the green sulphur bacterium Chlorobium tepidum and from the green filamentous bacterium Chloroflexus aurantiacus have been investigated. Steady-state fluorescence excitation spectra and time-resolved triplet-minus-singlet (TmS) spectra, recorded at ambient temperature and under non-reducing or reducing conditions, are reported. The carotenoid (Car) pigments in both species transfer their singlet excitation to bacteriochlorophyll c (BChlc) with an efficiency which is high (between 0.5 and 0.8) but smaller than unity; BChlc and bacteriochlorophyll a (BChla) transfer their triplet excitation to the Car's with nearly 100% efficiency. The lifetime of the Car triplet states is approximately 3 micros, appreciably shorter than that of the Car triplets in the light-harvesting complex II (LHCII) in green plants and in other antenna systems. In both types of chlorosomes the yield of BChlc triplets (as judged from the yield of the Car triplets) remains insensitive to the redox conditions. In notable contrast the yield of BChlc singlet emission falls, upon a change from reducing to non-reducing conditions, by factors of 4 and 35 in Cfx. aurantiacus and Cb. tepidum, respectively. It is possible to account for these observations if one postulates that the bulk of the BChlc triplets originate either from a large BChlc pool which is essentially non-fluorescent and non-responsive to changes in the redox conditions, or as a result of a process which quenches BChlc singlet excitation and becomes more efficient under non-reducing conditions. In chlorosomes from Cfx. aurantiacus whose Car content is lowered, by hexane extraction, to 10% of the original value, nearly one-third of the photogenerated BChlc triplets still end up on the residual Car pigments, which is taken as evidence of BChlc-to-BChlc migration of triplet excitation; the BChlc triplets which escape rapid static quenching contribute a depletion signal at the long-wavelength edge of the Qy absorption band, indicating the existence of at least two pools of BChlc.     

Nonelectrolyte-Induced CP Variation of TX-114+TBAB System

The effects of nonelectrolytes (ureas, amino acids, sugars) on the cloud point (CP) of nonionic surfactant Triton X-114 (TX-114) and tetra-n-butylammonium bromide (TBAB) system were studied. Ureas as well as thioureas increased the CP. Behaviors of amino acids depended upon their nature. Nonpolar and uncharged polar amino acids were less effective in changing the CP. However, tryptophan and phenylalanine increased the CP sharply. Acidic amino acid (aspartic acid) and sugars decreased the CP. The results were explained in terms of their effect on water structure. Amino acids got solubilized either in the micellar interior or in the bulk phase.     

Surface wave modes in PEMC backed chiral slab

The characteristics of surface wave modes in a PEMC backed chiral slab are studied theoretically. First, the analytical solution of electromagnetic fields and dispersion relations are carried out. Then, the fractional field solutions are found using the fractional curl operator. The numerical results are given by assuming that wave numbers k and k_± are either real or imaginary. These results are also evaluated at real and imaginary values of fractional parameter describing the order of curl operator. The discussion contains fractional dispersion curves at various cut-off frequencies and the fractional surface waves in chiral-PEMC and achiral-PMC slabs respectively. For numerical analysis it is assumed that the fractional order of the curl operator is related to chiral admittance, thickness of the slab, and PEMC admittance. For the values of the fractional order equal to 0, 1, and 2 geometry corresponds to PMC backed ordinary dielectric slab, PEMC backed chiral slab, and PEC backed chiral slab respectively. Consequently TE, HE (even), and HE (odd) modes are produced in the respective geometries.     

Synthesis,in vitro lipoxygenase inhibition,docking study and thermal stability analyses of novel indole derivatives

A series of indole derivatives has been synthesized and biologically evaluated to identify potent new lipoxygenase (LOX) inhibitors. All selected indole derivatives were screened for their LOX inhibition studies. Most of compounds showed good in vitro LOX inhibition properties exhibiting IC₅₀ values in the range of 53.61 ± 0.14 to 198.61 ± 0.11 μM (mean ± SEM), as compared to the standard inhibitor baicalein with IC₅₀ value 22.4 ± 1.3 μM. Structure activity relationship has been discussed and docking stimulation of most active compound 4f has also performed. Thermal stability and melting point of indole derivatives have been performed by thermal gravimetric analysis and differential scanning calorimetry analysis under nitrogen atmosphere at heating rate of 20 °C min^?1. Compound 4f bearing bis-phenyl moiety has been found to be the most potent (IC₅₀ 53.61 ± 0.14 μM) and thermally most stable among the tested compounds. Imine (C=N) was found to be the key moiety for increasing the thermal stabilities of indole derivatives. FT-IR, NMR and elemental analysis techniques were performed for structural characterization.     

Study of the cloud point variation of amitriptyline hydrochloride solutions in presence of amines and amino acids

In this paper clouding phenomenon in aqueous solutions of an amphiphilic drug amitriptyline hydrochloride is reported. The effect of adding ethylamine, butylamine, hexylamine, heptylamine, octylamine, ethylenediamine, diethylenetriamine, tetraethylenepentramine, aniline, and benzylamine on the cloud point of solutions containing a fixed drug concentration (50 mM) was seen. All the amines decrease the cloud point by intercalating between the head groups with protonated amine groups at the micellar surface. The amino acids used (lysine, arginine, histidine) also behave similarly. The results are discussed in the light of a particular additive’s ability to remove water from the head group region of the drug micelles.     

Synthesis and biological screening of 4‐(3,3‐dimethylspiro{bicyclo[2.2.1]heptan‐2,5′‐isoxazoline‐2}‐ 3′‐yl)‐2‐aryl‐2,3‐dihydro‐1H‐1,5‐benzodiazepines

A series of novel 4‐(3,3‐dimethylspiro{bicyclo[2.2.1]heptan‐2,5′‐isoxazoline‐2}‐3′‐yl)‐2‐phenyl‐2,3‐dihydro‐1H‐1,5‐benzodiazepines were synthesized. These molecules were screened in vitro for their antifungal and antibacterial activity, and none of the tested compounds showed promising antimicrobial or antifungal activity. J. Heterocyclic Chem., 2011.     

Band gap narrowing and fluorescence properties of nickel doped SnO2 nanoparticles

Nickel-doped tin oxide nanoparticles (sub-5 nm size) with intense fluorescence emission behavior have been synthesized by sol-gel route. The structural and compositional analysis has been carried out by using XRD, TEM, FESEM and EDAX. The optical absorbance spectra indicate a band gap narrowing effect and it was found to increase with the increase in nickel concentration. The band gap narrowing at low dopant concentration (<5%) can be assigned to SnO₂−SnO_2−x alloying effect and for higher doping it may be due to the formation of defect sub-bands below the conduction band.