INCREASED ENERGY TRANSFER FROM PHYCOBILISOMES TO PHOTOSYSTEM II IN HIGH LIGHT ADAPTED Anabaena cylindrica

Excitation energy transfer from phycobilisomes to photosystem II in high-light adapted cells of Anabaena cylindrica was studied by fluorescence spectroscopy and compared to that of low-light adapted cells. Measurements were made on membrane fragments containing phycobilisomes, photosystem I and II, isolated in 0.75 M K-phosphate. Relative efficiency of 430 to 590 nm light in the excitation of F₆₈₀ chlorophyll fluorescence was compared in low and high light adapted cells, respectively. The values indicate that light energy absorbed by phycobilisomes is transferred to photosystem II antenna chlorophylls with higher efficiency in high-light adapted cells than in low-light adapted cells. Partial dissociation and uncoupling of energy transfer caused by low ion concentration were different in the membrane fragments isolated from the two kinds of cells and indicated a higher aggregation state of pigment-protein complexes of phycobilisomes in high-light adapted A. cylindrica cells.     

Solid state spin densities in triplet-exciton TCNQ salts

The combination of molecular spin densities and of structural data is shown to provide a sensitive test for the fine structure splittings and principal axes of triplet spin excitons in organic ion-radical crystals, in support of weakly-perturbed molecular sites in these solids. The exchange pathway in Rb(TCNQ) and the occurrence of dimer radicals, with fractional charges, in several tetrameric (TCNQ)₄^2? stacks illustrate the comparisons afforded by computations of fine structure parameters for triplets states in the solid.     

Comparative Evaluation of CE and HPLC for Determination of Cotinine in Human Urine

Two rapid and popular methods—capillary electrophoresis (CE) and high-performance liquid chromatography (HPLC) have been compared for analysis of cotinine in human urine. Cotinine was analyzed in less than 7 min, with detection limits of 5 and 3.2 ng mL⁻¹ for CE and HPLC, respectively. The performance of the methods was evaluated in terms of sensitivity, specificity, precision, accuracy, and limits of detection and quantification. Calibration plots were linear in the range 50–4,000 ng mL⁻¹, at least, and mean recoveries were satisfactory for both techniques. The methods were successfully used for quantification of cotinine in urine.     

Semi-preparative liquid-chromatographic separation of all four stereoisomers of α-bisabolol on tribenzoylcellulose

Summary A semi-preparative low-pressure liquid-chromatographic procedure using tribenzoylcellulose has been developed for the separation and isolation of the four -bisabolol stereoisomers. Stereochemical assignments were made by HPLC-polarimeter coupling and by using the authentical isomers. This method can be applied to the quality control of chamomile preparations, as it allows the detection of adulterations resulting from admixtures of synthetic -bisabolol. In addition, the isolation of all four -bisabolol stereoisomers from commercially available synthetic -bisabolol has been made possible.     

Polarization and polarizability in extended one-dimensional organic materials

The modern theory of polarization in extended insulators is applied to one-dimensional models for conjugated polymers and charge transfer salts. Closed expressions for the dependence of the polarization on the site and bond energy alternations are presented for uncorrelated models, and results from exact real-space diagonalization are obtained for correlated models. Changes in polarization induced by lattice phonons or molecular vibrations are directly related to the intensity of infrared bands in the far and mid-IR, respectively. We model intensities by introducing linear electron-vibration coupling and show that coupling to delocalized electrons generates a combination band consisting of a lattice phonon and a molecular vibration. The displaced dipole operator is defined on a real-space basis allowing for the finite field calculation of linear polarizability in finite size systems with periodic boundary conditions. Size-consistency arguments are used to demonstrate that the resulting polarizability becomes exact in the thermodynamic limit, and numerical calculations demonstrate that this approach leads to reliable results that converge rapidly to the thermodynamic limit.     

DSC investigation of the thermal behaviour of (NH4)2SO4, NH4HSO4 and NH4NH2SO3

Gaseous products evolved from (NH₄)₂SO₄, NH₄HSO₄ and NH₄NH₂SO₃ during successive heating and cooling cycles were flushed with inert gas into analyzer Dräger tubes hooked tightly to the terminal port of the DSC cell base. This simple procedure allowed the starting temperature of the decomposition to be determined and the amount of the individual gases in the mixture to be identified and even estimated. NH₄NH₂SO₃ at 523 K in humid air produced HNH₂SO₃ initially and, on further cycling, (NH₄)₂SO₄ and NH₄HSO₄ also appeared. The ΔH_f values for NH₄HSO₄ were (kJ mole^?1): in an airtight sample holder 12.67, in a dry argon atmosphere 11.93, and in a static air atmosphere 10.92. Endothermic peaks for (NH₄)₂SO₄ and 498 and 411 K represented the incongruent melting point and the polymorphic transition of (NH₄)₂SO₄·NH₄HSO₄. After the first heating in air to 530 K, (NH₄)₂SO₄ and NH₄HSO₄ exhibited closely similar cyclic DSC curves. The endothermic peaks at about 393–420 K may be assigned to different combinations of (NH₄)₂SO₄ and NH₄HSO₄.     

Poly-N-vinylamides,complexation and conformational changes in aqueous solution

Interaction between small molecules (iodine and 1-anilinonaphthalene-8-sulphonate) and poly-N-methylacetamide (PVMA), poly-N-vinylcaprolactam (PVCL), poly-N-vinylpyrrolidone (PVP) and copolymers of N-vinyleaprolactam with N-vinylpyrrolidone (CP VCL-VP) and with N-vinyl-N-methylacetamide (VMA) were studied. All the polymers formed complexes with the small molecules. The stability constant for the complexes with the probe increases in the series PVMA < PVP < copolymer < PVCL indicating the essential role of hydrophobic interactions in the complex formation. With increasing temperature of aqueous solution from 18 to 33°, the constant decreased for PVP, PVMA and copolymers with low VCL content and increased for PVCL. A folding of PVC coils was observed over the temperature range, demonstrating a relationship between the conformational changes of macromolecules and the polymer complex formation. Addition of PVCL, PVMA and PVP to aqueous I₃^? solution brings about a shift of λ_max from 350 nm for free triiodide ions to 372, 367 and 364 nm respectively. It is explained by different dipole moments of the side substituents. The stability constant for the polymers and I₃^? was estimated as approx. 10⁵ M. The ability of the polymers to form complexes depends on chainlength. The greatest loss of the ability was observed for PVCL with $\text{M}{}_{\mathrm{n}}$ changing from 6 × 10³ to 2 × 10³. Interaction of the polymers with I₃^? is accompanied by a conformational shrinking of coils. In the case of the probe, forces of electrostatic repulsion between negative charges of sulphonate groups result in an unfolding of polimer coils.     

Synthesis of New Cobalt(III) Meso-Porphyrin Complex,Photochemical, X-ray Diffraction,and Electrical Properties for Photovoltaic Cells

The present work describes the preparation and characterization of a new cobalt(III) porphyrin coordination compound named (chlorido)(nicotinoylchloride)[meso-tetra(para-chlorophenyl)porphyrinato]cobalt(III) dichloromethane monosolvate with the formula [Co^III(TClPP)Cl(NTC)]·CH₂Cl₂ (4). The single-crystal X-ray molecular structure of 4 shows very important ruffling and waving distortions of the porphyrin macrocycle. The Soret and Q absorption bands of 4 are very red-shifted as a consequence of the very distorted porphyrin core. This coordination compound was also studied by fluorescence and cyclic voltammetry. The efficiency of our four porphyrinic compounds—the H₂TClPP (1) free-base porphyrin, the [Co^II(TClPP)] (2) and [Co^III(TClPP)Cl] (3) starting materials, and the new Co(III) metalloporphyrin [Co^III(TClPP)Cl(NTC)]·CH₂Cl₂ (4)—as catalysts in the photochemical degradation was tested on malachite green (MG) dye. The current voltage of complexes 3 and 4 was also studied. Electrical parameters, including the saturation current density (J_s) and barrier height (ϕ_b), were measured.