Complexes of vanadium(III) with aromatic amino acids and l-proline in aqueous solution

The equilibria of the complexation processes of V³⁺ ion with l-phenylalanine, l-tyrosine, l-tryptophan and l-proline in aqueous solution were studied by potentiometric and spectroscopic (UV, Vis, CD) methods. The results indicate that all ligands (except l-tyrosine) form only 1:1 species with vanadium(III) ion in the pH range about 2–5. More complex equilibria were observed in the vanadium(III)–l-tyrosine system. Only in this system relatively stable ML₂ species predominantly exists in the pH range 3–5. The results of spectroscopic measurements indicate that in ML and ML₂ species chelated bounds through O and N atoms appear in all investigated systems. Above pH 5 strong hydrolysis processes of vanadium(III) occurred.     

Benzophenone‐(phenylthio)acetic acid phosphonium salts as initiators of free‐radical photopolymerization of vinyl monomers: Mechanistic studies

The mechanism of the benzophenone‐sensitized photooxidation of phosphonium salts of (phenylthio)acetic acid was studied as a means for understanding how these salts function as coinitiators in the free‐radical photopolymerization of vinyl monomers. Both steady‐state and nanosecond flash photolytic methods were used to determine, in a quantitative manner, the mechanism of primary and secondary photoreactions for three quaternary phosphonium salts containing butyl and/or phenyl groups, i.e., P⁺(C₄H₉)₄, P⁺(C₄H₉)(C₆H₅)₃, and P⁺(C₆H₅)₄. It was found that the initial polymerization rates were the same for all three phoshonium salts of (phenylthio)acetic acid and were equal to those found previously for tetralkyl ammonium salts. The polymerization rates were more than twice the rates found for direct initiation by benzophenone and by the benzophenone‐(phenylthio)acetic acid initiating system. These results correlate well with the large quantum yields of ^?CH₂SC₆H₅ radicals (the main initiating radicals) found in the complementary photochemical investigation. It was found that a detailed knowledge of the photochemical reactions in the photoinitiating systems was critical to understand the kinetics of polymerization. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 8013–8022, 2008     

MODEL CONSIDERATIONS OF THE LIGHT CONDITIONS IN NONCYLINDRICAL PLANT CELLS

Abstract— A geometric model of a noncylindrical plant cell has been constructed using optical and geometrical parameters obtained for the cells of Funaria hygrometrica and Lemna trisulca leaves. The distribution of the incident light intensity and the absorption profile in the monomolecular photoreceptor layer on the walls of the model cell irradiated with the parallel beam have been calculated. Calculations were performed for two surrounding media with refractive indices of 1.33 (water) and 1.00 (air). Various chloroplast arrangements were considered. The course and kinetics of the phototactic movements of Funaria and Lemna chloroplasts have been discussed on the basis of the results obtained. The best agreement between the theoretical and experimental data is obtained by assuming that the transition moments at 450 nm of the dichroic photoreceptor molecules are oriented parallel to the surface of the cell wall.     

Vibrational spectroscopy of 4-hydroxybenzhydrazide and its O,N-deuterated isotopologue accompanied by X-ray structure refinement

The vibrations of crystalline 4-hydroxybenzhydrazide were investigated by IR and Raman spectroscopy. Spectral changes resulting from O,N-deuteration together with DFT calculations were employed for band assignment presented in terms of potential energy distribution. The characteristic absorptions of the hydrazide group were located at 1623 (CO stretching), 1588 (NH₂ bending) and 1532 cm⁻¹ (NH bending). The greatest contributions of the NN and CN stretching vibrations were found in the 1208 and 1109 cm⁻¹ modes, respectively. The predominant contribution of the CO stretching vibration was observed for the 1282 cm⁻¹ absorption. The computations at the B3LYP level with 6-311++G(d,p) basis set were based on structural parameters taken from refined single crystal X-ray investigations. The details of hydrogen bonding and crystal packing are also presented.     

Size Ramsey numbers for some regular graphs

P. Erdös, R.J. Faudree, C.C. Rousseau and R.H. Schelp [P. Erdös, R.J. Faudree, C.C. Rousseau, R.H. Schelp, The size Ramsey number, Period. Math. Hungar. 9 (1978) 145-161] studied the asymptotic behaviour of for certain graphs G,H. In this paper there will be given a lower bound for the diagonal size Ramsey number of K_n,n,n. The result is a generalization of a theorem for K_n,n given by P. Erdös and C.C. Rousseau [P. Erdös, C.C. Rousseau, The size Ramsey numbers of a complete bipartite graph, Discrete Math. 113 (1993) 259-262].Moreover, an open question for bounds for size Ramsey number of each n-regular graph of order n+t for t>n−1 is posed.     

Measurement of the index of refraction of single microparticles

The refractive index of single microparticles is derived from precise measurement and rigorous modeling of the stiffness of a laser trap. We demonstrate the method for particles of four different materials with diameters from 1.6 to 5.2 microm and achieve an accuracy of better than 1%. The method greatly contributes as a new characterization technique because it works best under conditions (small particle size, polydispersion) where other methods, such as absorption spectroscopy, start to fail. Particles need not be transferred to a particular fluid, which prevents particle degradation or alteration common in index matching techniques. Our results also show that advanced modeling of laser traps accurately reproduces experimental reality.     

Thiolactame als Reagenzien in der quantitativen Analyse

Zusammenfassung Die hohe Empfindlichkeit und große Selektivität der zwischen Thiocaprylolactam und Halogenwisniutaten stattfindenden Reaktion ermöglicht die kolorimetrische Wismutbestimmung. Die gefärbten Jod-, Bromund Chlorwismutat-Tkp-Komplexe werden mit Chloroform extrahiert und im VSU-1 -Photometer gemessen. Nach dieser Methode können l bis 30g Bi³⁺/ml bestimmt werden.

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Summary The high sensitivity and great selectivity of the reaction between thiocaprylolactam and halogen bismuthates makes feasible a colorimetric determination of bismuth. The colored iodo-, bromo- and chloro-bismuthate Tkp complexes are extracted into chloroform and measured in a VSU-l-photometer. Bismuth can be determined by this method in the concentration range of 1–30 Bi³⁺/ml.

     

Hemolysis of Erythrocytes and Erythrocyte Membrane Fluidity Changes by New Lysosomotropic Compounds

This work contains the results of studies on the influence of newly synthesized lysosomotropic substances (lysosomotropes) on human erythrocytes. Six homologous series of the compounds differing in the alkyl chain length and counterions were studied. They were found to hemolyse erythrocytes and to change their osmotic resistance. The observed hemolytic effects were dependent both on the compounds structure (polar head dimension and alkyl chain length of compound) and its form (the kind of the counterion). In parallel, the influence of lysosomotropes on fluidity of the erythrocyte membrane was studied. Three different fluorescent probes were used; 1,6-diphenyl-1,3,5-hexatriene (DPH), 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene, p-toluenesulfonate (TMA-DPH) and 6-dodecanoyl-2-dimethylaminonaphthalene (laurdan). Their anisotropy (DPH and TMA-DPH) or general polarization (laurdan) values after incorporation into ghost erythrocyte membranes were measured. The results obtained show that fluidity changes accompanied the effects observed in hemolytic experiments both quantitatively and qualitatively.