Lyapunov Pairs in Semilinear Differential Problems with State-Dependent Impulses

Set-Valued and Variational Analysis - The paper deals with semilinear differential inclusions with state-dependent impulses in Banach spaces. Defining a suitable Banach space in which all the...     

The existence of viable trajectories in state-dependent impulsive systems

Suitable topological tools for studying the existence of viable and periodic viable trajectories in state-dependent impulsive differential equations and inclusions are provided. Some results based on the Wa?ewski retract method are applied. The techniques presented in the paper are illustrated with several examples.     

Toward a Bioartificial Pancreas: Diffusion of Insulin and IgG Across Immunoprotective Membranes with Controlled Hydrophilic Channel Diameters

Research continued toward a bioartificial pancreas (BAP). Our BAPs consist of a perforated nitinol scaffold coated with reinforced amphiphilic conetwork membranes and contain live pancreatic islets. The membranes are assemblages of cocontinuous hydrophobic domains and hydrophilic channels whose diameters were varied by the MW of hydrophilic segments between crosslinks (M_c,HI = 32, 44, and 74 kg · mol^?1). We studied the diffusion rate of insulin, BSA, and IgG across the membrane of the BAP in the absence of islets. Membranes of M_c,HI = 74 kg · mol^?1 showed rapid insulin and BSA transport and negligible IgG diffusion. BAPs containing ≈300 mouse islets showed appropriate response upon glucose challenge in vitro. The BAP implanted into diabetic mice reduced hyperglycemia and maintained islet viability for at least 4 d.

     

Effect of the molecular weight and architecture on the size and glass transition of arborescent polyisobutylenes

This article discusses the characterization of arborescent (hyperbranched) polyisobutylenes (arb‐PIBs) by size exclusion chromatography and differential scanning calorimetry, in comparison with linear PIB standards. The radius of gyration (〈r〉^1/2 = R_z), measured from the angle dependence of light scattering of high‐molecular‐weight arb‐PIBs, was significantly larger than the hydrodynamic radius (R_h) from size exclusion chromatography/viscometry, and the R_h values were significantly smaller than R_h of linear PIBs. The glass‐transition temperature of arb‐PIBs having a branch molecular weight higher than the critical entanglement molecular weight was dependent on both the total number‐average molecular weight and BR up to BR ～ 15. A modified Fox–Flory equation is proposed to describe the effect of architecture on the thermal transition. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1770–1776, 2006     

Synthesis of cyclic phosphonate analogues of (lyso)phosphatidic acid using a ring-closing metathesis reaction

We describe a versatile and efficient method for the preparation of acyloxy-substituted six-membered cyclic phosphonates using the ring-closing metathesis. After closure, the key cyclic phosphonate intermediate was dihydroxylated and converted to a new class of conformationally constrained PA and LPA analogues. The oleoyloxy-substituted cyclic phosphonate 4 had unique receptor-selective properties as a ligand, showing partial activation of the LPA2 GPCR and weak antagonism of the LPA1 GPCR.     

pH-dependent transitions in xanthorhodopsin

Xanthorhodopsin (XR), the light-driven proton pump of the halophilic eubacterium Salinibacter ruber, exhibits substantial homology to bacteriorhodopsin (BR) of archaea and proteorhodopsin (PR) of marine bacteria, but unlike them contains a light-harvesting carotenoid antenna, salinixanthin, as well as retinal. We report here the pH-dependent properties of XR. The pKa of the retinal Schiff base is as high as in BR, i.e. > or =12.4. Deprotonation of the Schiff base and the ensuing alkaline denaturation cause large changes in the absorption bands of the carotenoid antenna, which lose intensity and become broader, making the spectrum similar to that of salinixanthin not bound to XR. A small redshift of the retinal chromophore band and increase of its extinction, as well as the pH-dependent amplitude of the M intermediate indicate that in detergent-solubilized XR the pKa of the Schiff base counterion and proton acceptor is about 6 (compared to 2.6 in BR, and 7.5 in PR). The protonation of the counterion is accompanied by a small blueshift of the carotenoid absorption bands. The pigment is stable in the dark upon acidification to pH 2. At pH < 2 a transition to a blueshifted species absorbing around 440 nm occurs, accompanied by loss of resolution of the carotenoid absorption bands. At pH < 3 illumination of XR with continuous light causes accumulation of long-lived photoproduct(s) with an absorption maximum around 400 nm. The photocycle of XR was examined between pH 4 and 10 in solubilized samples. The pH dependence of recovery of the initial state slows at both acid and alkaline pH, with pKas of 6.0 and 9.3. The decrease in the rates with pKa 6.0 is apparently caused by protonation of the counterion and proton acceptor, and that at high pH reflects the pKa of the internal proton donor, Glu94, at the times in the photocycle when this group equilibrates with the bulk.     

Synthesis of photoactivatable analogues of lysophosphatidic acid and covalent labeling of plasma proteins

[reaction: see text] Lysophosphatidic acids bearing a benzophenone group in either the sn-1 or sn-2 chain of an oleoyl-type ester or oleyl-type ether chain and (32)P in the phosphate group were synthesized. The benzophenone moiety was introduced by selective hydroboration of the double bond of enyne 11 at low temperature, followed by a Suzuki reaction with 4-bromobenzophenone. The key intermediates for the preparation of ester-linked lysophosphatidic acid (LPA) 1 and 3 were obtained in one pot by a modified DIBAL-H reduction of orthoformate intermediate 22. These probes were shown to covalently modify a single protein target in rat plasma containing albumin and several protein targets in rat plasma containing a low level of albumin.