Electroviscous Forces on a Charged Cylinder Moving Near a Charged Wall

The refined theory of the electroviscous lift forces is presented for the case when the separation distance between the particle and the wall is larger than the double-layer thickness. The theory is based on the lubrication approximation for motion of a long cylinder near a solid wall in creeping flow. The approximate analytical formula for the lift force valid for Pe相似文献   

Identification de submicroquantités d'ions Iodure

Résumé On peut déceler des submicroquantités d'ions iodure á l'aide de bathophénantroline.

---

Identification of Submicro Quantities of Iodine Ions

Summary Submicro amounts of iodide can be demonstrated using bathophen-anthroline.

---

Zusammenfassung Submikromengen Jodid lassen sich mit Hilfe von Bathophenanthrolin nachweisen.

     

CATALASE INACTIVATION FOLLOWING PHOTOSENSITIZATION WITH TETRASULFONATEDMETALLOPHTHALOCYANINES

Abstract— Catalase (CAT) in solution or incorporated in erythrocytes and K562 leukemic cells is inactivated during photosensitization with tetrasulfonated metallophthalocyantnes (MePcS₄). The effect of added scavengers and D₂0 showed that both singlet oxygen and free radical species are involved in this process. Evidence was found that direct interactions of ground or excited-stated photosensitizers with CAT are not responsible for CAT inactivation. Specific techniques to probe early damage to the CAT structure involved optical and EPR spectroscopy, HPLC and polyacrylamide gel electrophoresis analyses. Different primary events of photosensitized protein damage included oxidation of cysteine residues as well as other amino acids, as demonstrated by the formation of carbon-centered free radicals and the loss of absorbance at λ= 275 nm. In parallel, we detected degradation of the CAT heme groups, accompanied by release of Fe(II) ions in solution. These combined phenomena initiate cross-linkages between CAT subunits and subsequent degradation of the protein with formation of irreversible aggregates in solution. Phthalocyanine-mediated photoinactivation of cell-bound CAT results in loss of protection against accumulating H₂0₂, providing an additional pathway of phototoxicity.     

Semi-empirical molecular orbital studies of porphine and phthalocyanine derivatives,to simulate their intermolecular interactions

Gound-state electronic properties of porphine, phthalocyanine, and their derivatives, photosensitizers with potential use in the photodynamic therapy of tumors, were studied by semiempirical (MNDO ) molecular orbital calculations. Geometry, bond orders, electron populations, and net atomic charges were analyzed. The obtained models were applied to study the intermolecular interactions of these molecules utilizing a classical mechanics approach. The dimerization characteristics of different derivatives were obtained by a separate evaluation of the contribution of electrostatic and steric factors. © 1993 John Wiley & Sons, Inc.     

Influence of medium polarity on the photosensitizing properties of hematoporphyrin and hematoporphyrin derivative (Photofrin II)

The influence of the polarity of the medium on the efficiency of Type I and Type II photosensitization as carried out by hematoporphyrin and its derivative Photofrin II was studied by EPR techniques. Our results suggest that porphyrin aggregates do not participate as such in the photosensitized processes. Thus, the solvent-induced breakdown of the aggregated components of Photofrin II appears to determine the photosensitizing efficiency of this porphyrin.     

Comparison of the photosensitizing efficiencies of haematoporphyrin (HP) and its derivative (HPD) with that of free-base tetrasulphophthalocyanine (TSPC-H2) in homogeneous and microheterogeneous media

Using solutions of different polarity and various reducing (oxidizing) substrates, the type I (free radical) and type II (singlet oxygen) photosensitizing efficiencies of haematoporphyrin (HP), haematoporphyrin derivative (HPD, Photofrin II) and free-base tetrasulphophthalocyanine (TSPC-H2) were investigated. The quantum yields of 1O2-mediated oxidation of 2,2,6,6-tetramethyl-4-oxopiperidine (TEMP) followed the order QHP greater than QHPD greater than QTSPC-H2 in all the reaction media investigated. Monomeric TSPC-H2 effectively generates O2-. as shown by spin-trapping measurements. It is probable that both HPD and TSPC-H2 can oxidize L-tryptophan (Trp) via a mixed type I and type II mechanism, depending on the polarity of the medium. Both HP and TSPC-H2 in the monomeric form can be readily photoreduced by mild electron donors (ethylenediaminetetraacetic acid (EDTA), cysteine, sodium ascorbate, etc.). However, the reaction efficiencies differ because of the higher net negative electrical charge of TSPC-H2.     

Evaluation of Conformational dynamics properties of spin-labelled proteins at different degrees of nitroxide radicals immobilization

Spin-labelling has found wide applications in elucidation of the dynamic behaviour of biological macromolecules in aqueous media and biomembranes. Most of the proposed methods aimed at estimation of macromolecular correlation times (τ_c) assume, however, spin label molecules rigidly bound within the protein matrix. To avoid this limitation theoretical models which involve additional dynamic parameters to characterize the spin label motion should be considered. We have used ESR spectra analysis technique which permits quantitative separation of slow macromolecular rotation (described by the rotational correlation time, τ_c) and fast anisotropic relative to protein nitroxyl radical motion (described by the “order parameter”,S). This method was applied to study: i) conformational dynamics of covalently and non-covalently spin-labelled human serum albumin (HSA) in solution; ii) protein-protein (antigen-antibody) interactions in a model system containing spin-labelled bovine serum albumin (BSA) and anti-BSA immunoglobulin (IgG) in solution; and iii) dynamic properties of membrane-bound proteins: H⁺-ATPase (CF₁-CF₀ coupling factor of photophosphorylation) and Photosystem I pigment-protein reaction centre complex (PSI RC) isolated from spinach chloroplasts and reconstituted in proteoliposomes.     

Oxidation of 2'-deoxycytidine to four interconverting diastereomers of N1-carbamoyl-4,5-dihydroxy-2-oxoimidazolidine nucleosides

Modification of 2'-deoxycytidine (dCyd) by hydroxyl radicals and direct ionization leads to the formation of various oxidation products, including dCyd 5,6-glycols, 5-hydroxy-2'-deoxycytidine, and ring fragmentation products. The mechanism of oxidation is complex and poorly understood. In the present work, we have prepared four cis- and trans-diastereomers of N1-(2-deoxy-beta-D-erythro-pentofuranosyl)-1-carbamoyl-2-oxo-4,5-dihydroxyimidazolidine by bromination of dCyd followed by peroxidation of the resulting dCyd bromohydrins. The structure and stereochemistry of each product were determined by 1H NMR, 13C NMR, and 2D NOE analyses. The formation of imidazolidine products involves rearrangement of initial 5(6)-hydroxy-6(5)-hydroperoxides to C6-C2 endoperoxides, which subsequently decompose by a concerted pathway to imidazolidine products. A remarkable feature of the four diastereomers was their ability to interconvert via single and successive cycles of ring-chain tautomerism at N1-C5 and N3-C4, leading to epimerization of C5 and C4, respectively. The rate of isomerization was greater for cis-diastereomers compared to trans-diastereomers, and the rate sharply increased with pH (pH 9.0>7.0>5.5).     

In Process Citation

A spot-test, based on the formation of yellow-brown nitron tri-iodide permits detection of 0.01 ng of iodide (limit of dilution 1 in 64 x 10(7)).     

In Process Citation

Nitron dichloroiodide-Nt(ICl(2))-has been prepared and studied, and a gravimetric determination of iodine as Nt(ICl)(2) has been based on the result. For 4-40 mg of iodine the error is less than that of the determination as AgI. Bromate and chlorate do not interfere.