Resonances of triatomic van der Waals molecules by the complex discrete variable representation

Summary The results of Light and co-workers [J. Chem. Phys. 85:4594 (1986); 86:3065 (1987); 92:2129 (1990)] for the Hamiltonian matrix of a triatomic van der Waals molecule in the discrete variable representation, DVR, is extended to complex-scaled Hamiltonians. As an illustrative numerical example theJ=1 resonances positions and widths of a van der Waals model system were obtained by the calculation of the complex-scaled Hamiltonian matrix in the DVR formalism.Supported in part by the Albert Einstein Research Fund, and the Fund for the Promotion of Research at the Technion     

Structural characterization of a degradation product of tin ethyl etiopurpurin (SnET2): Comparison of the long‐range heteronuclear correlations detected using conventional GHMBC and IMPEACH‐MBC in conjunction with submicro NMR probe technology

During the terminal heat sterilization of the lipid emulsion final dose formulation of the photodynamic therapeutic (PDT) agent tin ethyl etiopurpurin (SnET2), a new degradant was observed at very low levels. The degradant, which was prone to photo‐instability, was isolated by preparative chromatography and subsequently characterized by mass spectrometry and NMR methods. Reproducible parent ion clusters were only observable via negative ion APCI methods. Because of the limited isolate sample, NMR characterization was done using 1.7 mm SMIDG (SubMicro Inverse‐Detection Gradient) NMR probe technology in conjunction with the accordion‐optimized IMPEACH‐MBC long‐range heteronuclear shift correlation experiment. The “static” 8 Hz optimization of the GHMBC experiment failed to allow the observation of a number of long‐range correlations that were of critical importance to the determination of the structure of the impurity. In contrast, all of the correlations required to assemble the structure were obtained from an IMPEACH‐MBC experiment optimized for long‐range heteronuclear couplings in the range from 2–10 Hz.     

Synthesis of AX7593, a quinazoline-derived photoaffinity probe for EGFR

[structure: see text] The synthesis of a photoaffinity probe for EGFR is described. O-Alkylation of 4-(meta-azidoanilino)-6-methoxy-7-hydroxy-quinazoline with a protected tetraethyleneglycol linker followed by the attachment of tetramethylrhodamine yielded the fluorescent probe AX7593. Photoaffinity labeling of EGFR by AX7593 (K(b) = 280 nM) was shown to have an efficiency of 34% and to be competitive with the EGFR inhibitors PP2 and AG1478.     

Recursive polynomial curve schemes and computer-aided geometric design

A class of polynomial curve schemes is introduced that may have widespread application to CAGD (computer-aided geometric design), and which contains many well-known curve schemes, including Bézier curves, Lagrange polynomials, B-spline curve (segments), and Catmull-Rom spline (segments). The curves in this class can be characterized by a simple recursion formula. They are also shown to have many properties desirable for CAGD; in particular they are affine invariant, have the convex hull property, and possess a recursive evaluation algorithm. Further, these curves have shape parameters which may be used as a design tool for introducing such geometric effects as tautness, bias, or interpolation. The link between probability theory and this class of curves is also discussed.Communicated by Klaus Höllig.     

Rational design of transglutaminase substrate peptides for rapid enzymatic formation of hydrogels

Short peptide substrates with high specificity toward transglutaminase (TGase) enzyme were designed, characterized, and coupled to a biocompatible polymer, allowing for rapid enzymatic cross-linking of peptide-polymer conjugates into hydrogels. Eight acyl acceptor Lys-peptide substrates and three acyl donor Gln-peptide substrates were rationally designed and synthesized. The kinetic constants of these peptides toward tissue transglutaminase were measured by enzyme assay using RP-HPLC analysis with the aid of LC-ESI/MS. Several acyl donor and acyl acceptor peptides with high specificities toward TGase were identified, including a few containing the unusual amino acid l-3,4-dihydroxylphenylalanine (DOPA), which is found in the adhesive proteins secreted by marine and freshwater mussels. Acyl donor and acyl acceptor peptides with high substrate specificities were separately coupled to branched poly(ethylene glycol) (PEG) polymer molecules. Equimolar solutions of these polymer-peptide conjugates rapidly formed hydrogels in less than 2 min in the presence of transglutaminase under physiological conditions. The use of biocompatible building blocks, their rapid solidification from a liquid precursor under physiologic conditions, and the ability to incorporate adhesive amino acid residues using biologically benign enzymatic cross-linking are advantageous properties for the use of such materials for tissue repair, drug delivery, and tissue engineering applications.     

Temperature dependence of inhomogeneous broadening: on the meaning of isosbestic points

An isosbestic point in the temperature dependence of an absorption spectrum is commonly viewed as a sign of interconverting chemical or structural species. Here I explore an alternative microscopic origin of temperature-independent absorbance in inhomogeneously broadened spectra: While the equilibrium probability of observing a particular frequency generally changes with the magnitude of thermal fluctuations, the weight of at least one frequency is insensitive to small changes in temperature. The range of temperature accessible to aqueous solutions at ambient pressure is sufficiently small that such insensitivity would appear in experiments as an isosbestic point. This mechanism depends only on the continuity of equilibrium distributions, not on the presence of multiple components. Even the simplest model of a single solute species in a fluctuating environment exhibits isosbestic points, van't Hoff behavior, and, with appropriate dependence of transition frequency on configuration, multiple absorption peaks.     

Platelet adhesion to photodynamic therapy-treated extracellular matrix proteins

Photodynamic therapy (PDT) produces reactive species that alter vascular wall biology and vessel wall proteins. In this study, we examined platelet adhesion to PDT-treated (photosensitizer = Photofrin; fluence 100 J/cm2; lambda = 630 nm) extracellular matrix (ECM), fibrinogen, von Willebrand factor (vWF) and collagen Types I and III, under flow conditions in a recirculating perfusion chamber. Platelet adhesion was quantified by image analysis. The effect of PDT on vWF was assessed by measuring the binding of domain-specific antibodies to treated vWF. PDT significantly decreased platelet adhesion to the ECM, fibrinogen and vWF. However, PDT of collagen resulted in significantly increased platelet adhesion, with large aggregate formation. PDT affected mostly the A1 (glycoprotein [GP]-Ib-binding site), A2 and A3 (collagen-binding site) domains of vWF but not the D'-D3 (factor VIII-binding site) and B-C1 (GP-IIb/IIIa-binding site) domains. In conclusion, PDT can alter the ECM, resulting in decreased platelet adhesion. However, vessels with high collagen content, such as veins and small arteries, may become increasingly prone to thrombosis. The results of this study may thus play a role in understanding the thrombogenic properties and mechanisms of vascular PDT.     

Interactions of Methyl Orange with Cyclodextrin/Sodium-Montmorillonite Systems Probed by UV-Visible Spectroscopy

Clay mineral colloids play important roles in the adsorption of polar organic contaminants in the environment. Similarly, cyclodextrins (CD) can entrap poorly water-soluble organic compounds. A combination of CDs and clay minerals affords great opportunities to investigate simultaneously complexation and adsorption processes involving organic contaminants. In this work, we investigated in situ the extent of adsorption and/or complexation of a molecular probe, methyl orange (MO), in CD/sodium montmorillonite systems using UV-visible spectroscopy. The anion form of MO interacts with the clay surface via cationic bridges, whereas the cation form is weakly adsorbed by a cation-exchange mechanism. Further, in acidic media, there is a local competition between MO and the montmorillonite surface for H(+) ions. This inhibits protonation of MO in the immediate vicinity of the clay. The presence of CDs, however, perturbs the favored process of proton scavenging by the clay. In particular, in betaCD-clay systems, betaCD-complexed MO can compete successfully with the clay for H(+) ions. The shielding effect of betaCD appears to play a key role in preventing the deprotonation of complexed MO. Copyright 2001 Academic Press.     

Excited-State Energy Level Does Not Determine the Differential Effect of Violaxanthin and Zeaxanthin on Chlorophyll Fluorescence Quenching in the Isolated Light-Harvesting Complex of Photosystem II

Abstract— The mechanism of action of xanthophyll cycle carotenoids in controlling the quenching of chlorophyll fluorescence in the major light-harvesting complex of photosystem II (LHCIIb) has been investigated. Auroxanthin, a diepoxy carotenoid with 7 conjugated carbon double bonds, violaxanthin (9 conjugated double bonds) and zeaxanthin (11 conjugated double bonds) have been compared with regard to their effects in vitro on fluorescence quenching and LHCIIb oligomerization. It was found that auroxanthin stimulated fluorescence quenching, similar to the effect of zeaxanthin and in contrast to the inhibition caused by violaxanthin. Auroxanthin caused an increase in the oligomerization of LHCIIb and an increase in relative emission of long-wavelength fluorescence at 77 K. It is concluded that auroxanthin can mimic the effect of zeaxanthin on LHCII, strongly suggesting that the xanthophyll cycle carotenoids control quenching in vitro by an indirect structural effect and not by direct quenching of chlorophyll excited states.