Further Extensions of the Kinetic Enolate Method for Terpenoid Syntheses

New stereorandom syntheses of juvabione and dehydrojuvabione using kinetic e-nolates as synthons are described.     

The Catalytic Mechanism of Human Transketolase

We have computationally determined the catalytic mechanism of human transketolase (hTK) using a cluster model approach and density functional theory calculations. We were able to determine all the relevant structures, bringing solid evidences to the proposed experimental mechanism, and to add important detail to the structure of the transition states and the energy profile associated with catalysis. Furthermore, we have established the existence of a crucial intermediate of the catalytic cycle, in agreement with experiments. The calculated data brought new insights to hTK′s catalytic mechanism, providing free-energy values for the chemical reaction, as well as adding atomistic detail to the experimental mechanism.     

New biodegradable hydrogels based on a photo-cross-linkable polyaspartamide and poly(ethylene glycol) derivatives. Release studies of an anticancer drug

 The functionalization of α,β-poly(N-2-hydroxyethyl)-dl-aspartamide (PHEA) with glycidyl methacrylate (GMA) gives rise to a water-soluble photosensitive copolymer PHEA-GMA (PHG). Aqueous solutions of PHG alone or in combination with various concentrations of poly(ethylene glycol) dimethacrylate or poly(ethylene glycol) diacrylate (PEGDA) have been exposed to a source of UV rays at 313 nm in order to obtain polymeric networks. All samples have been prepared both as water-swellable microparticles and as gel systems. Microparticles have been characterised by Fourier transform IR spectrophotometry, dimensional analysis and swelling measurements in aqueous media mimicking biological fluids. In vitro chemical and enzymatic hydrolysis studies showed that all the prepared samples undergo a partial degradation at pH 1, 7.4 and 10 as well as after incubation with enzymes such as esterase. The effect of the cross-linking density on the rheological behavior of gel systems has also been investigated. PHG/PEGDA hydrogel is able to incorporate, during UV-irradiation, 5-fluorouracil (5-FU), chosen as a model drug, and to release it in simulated biological fluids, as confirmed by in vitro drug release studies at pH 1 and 7.4. PHG/PEGDA gel containing 5-FU is able to release this drug in a prolonged way, more slowly than a commercial ointment, as confirmed by in vitro studies at pH 5.5 and 7.4 using a Franz diffusion cell system and a synthetic membrane. Received: 3 October 2000 Accepted: 13 December 2000     

Protein immobilization at gold–thiol surfaces and potential for biosensing

Self-assembled monolayers (SAMs) provide a convenient, flexible and simple system to tailor the interfacial properties of metals, metal oxides and semiconductors. Monomolecular films prepared by self-assembly are attractive for several exciting applications because of the unique possibility of making the selection of different types of terminal functional groups and as emerging tools for nanoscale observation of biological interactions. The tenability of SAMs as platforms for preparing biosurfaces is reviewed and critically discussed. The different immobilization approaches used for anchoring proteins to SAMs are considered as well as the nature of SAMs; particular emphasis is placed on the chemical specificity of protein attachment in view of preserving protein native structure necessary for its functionality. Regarding this aspect, particular attention is devoted to the relation between the immobilization process and the electrochemical response (i.e. electron transfer) of redox proteins, a field where SAMs have attracted remarkable attention as model systems for the design of electronic devices. Strategies for creating protein patterns on SAMs are also outlined, with an outlook on promising and challenging future directions for protein biochip research and applications.     

Surface-pressure isotherms of monolayers formed by microsize and nanosize particles

The thermodynamic model of a 2D solution developed earlier for protein monolayers at liquid interfaces is generalized for monolayers composed of micro- and nanoparticles. Surface pressure isotherms of particle monolayers published in the literature for a wide range of particles sizes (between 75 microm and 7.5 nm) are described by the theoretical model with one modification. The calculations of surface pressure pi on area A provide satisfactory agreement with the experimental data. The theory also yields reasonable cross-sectional area values of the solvent molecule water in the range between 0.12 and 0.18 nm2, which is almost independent of particle size. Also, the area per particle in a closely packed monolayer obtained from the theory is quite realistic.     

High-performance liquid chromatography determination of phenyllactic acid in MRS broth

Phenyllactic acid (PLA) is an organic acid produced by some strains of lactic acid bacteria (LAB) and concentrations higher than 7.5 mg/ml inhibit growth of moulds and yeasts. Since PLA can be used to select LAB, a rapid, simple and cheap method for its determination is desirable. Typical methods for its analysis in broth are time-consuming, analytically complicated, and have poor recoveries. Herein we propose a simple and rapid method that does not require extraction, but only microfiltration of broth before injection in HPLC. The improved chromatographic conditions allow separation and quantification of PLA with a recovery of 98.7%. The method is highly reproducible with an intraday repeatability of the total peak area of 2.00%, while an interday repeatability of 2.69%.     

Determination of Se(IV) and Se(VI) in Italian mineral waters

This paper deals with determination of selenium and analysis of its speciation in some Italian mineral waters. Selenium was determined by differential pulse cathodic stripping voltammetry (DPCSV) even if square wave cathodic stripping voltammetry (SWCSV) was also taken into consideration. The selenium determined in the mineral waters here investigated is not over 600 ng L(-1); in three samples, it was found below the detection limit. Analysis of speciation revealed that Se(VI) is the highly prevailing form present: only two of the examined samples revealed a detectable amount (few ng L(-1)) of Se(IV). DPCSV made possible to detect, in two of the samples, the presence of a specie(s) able to interact with Se(IV). The apparent interaction constant for the adduct formation was evaluated and the species concentration determined. However, the nature of such compound(s) remains unknown.