The phototoxicity of photodynamic therapy may be suppressed or enhanced by modulation of the cutaneous vasculature

In photodynamic therapy, the threshold for light induced toxicity depends on the drug concentration and the light dose. This study was aimed to show for vascular photosensitizers that the toxicity threshold on normal tissue may be predictably modified by modulation of the cutaneous vasculature. Albino rabbits were injected with 1.0 mg/kg of a vascular photosensitizer, benzoporphyrin derivative monoacid ring-A. The threshold light dose for toxicity to normal skin was determined at an absorption maximum of the drug (694 nm), 1 h after drug injection. The cutaneous vasculature was dilated by prior skin exposure to ultraviolet radiation or was constricted by iontophoretic application of epinephrine. Threshold toxicity was determined clinically and by assessing the effective concentration of hemoglobin in the skin by diffuse reflectance spectroscopy (DRS). Tissue samples that received threshold doses were investigated with light and electron microscopy. The toxicity threshold increased by 3.2+/-0.9 (mean+/-S.D.) following vasoconstriction and decreased by 3.6+/-0.8 following vasodilation, compared to control sites. Light and electron microscopy showed similar findings at threshold for both vasodilated and vasoconstricted sites. Therefore vascular modulation may be used to predictably enhance or suppress the level of phototoxicity of normal skin.     

Comparison of embedded cluster models to study zeolite catalysis: Proton transfer reactions in acidic chabazite

A number of cluster models used to study the interaction of NH₃ and NH⁻₄ with the Bronsted sites of the acidic zeolite, chabazite, are assessed by comparison with the results from full periodic Hartree-Fock calculations. Corrections to bare cluster models to take account of the electrostatic environment due to the periodic zeolite are found to agree well with periodic calculations, and appear to be more successful than a more sophisticated embedding procedure. © 1997 by John Wiley & Sons, Inc.     

Cephalexin: a channel hydrate

The antibiotic cephalexin [systematic name: d ‐7‐(2‐amino‐2‐phenyl­acet­amido)‐3‐methyl‐8‐oxo‐5‐thia‐1‐aza­bi­cyclo­[4.2.0]oct‐2‐ene‐2‐carboxyl­ic acid] forms a range of isomorphic solvates, with the maximum hydration state of two water mol­ecules formed only at high relative humidities. The water content of the structure reported here (C₁₆H₁₇N₃O₄S·1.9H₂O) falls just short of this configuration, having three independent cephalexin mol­ecules, one of which is disordered, and 5.72 observed water mol­ecules in the asymmetric unit. The facile nature of the cephalexin solvation/desolvation process is found to be facilitated by a complex channel structure, which allows free movement of solvent in the crystallographic a and b directions.     

Biomedical Engineering and Cognitive Science as the Basis for Secondary Science Curriculum Development: A Three Year Study

This study reports on a multiyear effort to create and evaluate cognitive‐based curricular materials for secondary school science classrooms. A team of secondary teachers, educational researchers, and academic biomedical engineers developed a series of curriculum units that are based in biomedical engineering for secondary level students in physics and advanced biology classes. These units made use of an instructional design based upon recent cognitive science research called the Legacy Cycle. Over a 3‐year period, comparison of student knowledge on written questions related to central concepts in physics and/or biology generally favored students who had worked with the experimental materials over students in control classrooms. In addition, experimental students were better able to solve applications type problems, as well as unit‐specific near transfer problems.     

Rheology of a dilute suspension: analytical expression for the viscosity in the limit of low zeta-potentials

A modified theoretical model on the primary electroviscous effect, based upon the inclusion of the condition of that the ions within the Stern layer are allowed to move tangential to the surface of the particle, is proposed. Booth's analysis (Booth 1950a), valid for spherical particles at low zeta-potentials, is the start point, and the effect of a dynamic Stern layer is included. The analytic results are compared with full numerical computations and a good agreement is found for zeta-potentials less than 25 mV. Received: 15 June 2000 Accepted: 11 September 2000     

Chemoenzymatic synthesis of optically active Mugetanol isomers: use of lipases and oxidoreductases in fragrance chemistry

Straightforward synthetic strategies for the preparation of optically active Mugetanol isomers have been developed through different independent chemoenzymatic routes implying the use of either alcohol dehydrogenases in aqueous media or lipases in organic solvents coupled with a catalytic hydrogenation process. Among the alcohol dehydrogenases tested, ADH RS1 showed the best activities in the bioreduction of 4-isopropylacetophenone. The lipase from Pseudomonas cepacia (PSL-C I) reached high activity values in the lipase-catalyzed transesterification of 4-isopropylphenyl)ethanol, while Candida antarctica lipase B showed the best stereopreference in the acetylation of 4-isopropylcyclohexylethanol.     

Representations and the Jacobian Conjecture

In this paper we apply the representation theory of the Lie algebra sl₂(C) to the problem of describing Hessian nilpotent polynomials, which are important in the theory of the Jacobian Conjecture. In the two variable case we describe them as the maximal and minimal weight vectors of the irreducible representations of sl₂(C). For the first time this gives a characterization of the Hessian nilpotent polynomials in terms of linear differential operators.     

Determination of plasma cytidine deaminase activity by HPLC

Cytidine deaminase is an enzyme of nucleic acid metabolism, the measurement of which has been proposed as a useful test for the early detection of pre-eclamptic toxaemia in pregnancy. The enzyme converts the nucleoside cytidine to uridine, with the release of ammonia, and it is the measurement of this latter compound that forms the basis of the conventional methods for the assay of cytidine deaminase. The low activity of the enzyme requires long incubation times, which in turn increase the possibility of contamination by exogenous ammonia. We have developed a new method for determining cytidine deaminase activity, utilising high performance liquid chromatography to measure the production of uridine. This method uses much shorter incubation times and is unaffected by ammonia contamination. This paper describes the development of the method and its comparison with the established assay. The relative merits of each are discussed. Finally, the adaptation of incubation and chromatographic conditions, in order to measure other enzymes of nucleic acid metabolism which are of clinical interest, is briefly mentioned.