Hybrid PVA-xanthan gum hydrogels as nucleus pulposus substitutes

Hybrid hydrogels were synthesized mixing poly(vinyl alcohol) (PVA) and xanthan gum (XG) in different molar ratios and using trisodium trimetaphosphate, as crosslinking agent, to obtain potential nucleus pulposus substitutes. Human Nucleus Pulposus (NP) is a hydrogel-like tissue with peculiar properties, which determine its role in supporting and dissipating spinal loads. Hydrogel obtained mixing PVA and XG in molar ratio 4:1 (PX25) showed mechanical, swelling, and thermal properties, i.e., heat capacity, which make it a good candidate as a potential NP substitute. Preliminary cytotoxicity tests pointed out that the developed materials did not show any signs of cytotoxicity towards NIH3T3 cells.     

Practical constraints in the kinetic plot representation of chromatographic performance data: theory and application to experimental data

It is demonstrated that the kinetic plot representation of experimental plate height data can also account for practical constraints on the column length, the peak width, the viscous heating, and the mobile-phase velocity without needing any iterative solution routine. This implies that the best possible kinetic performance to be expected from a given tested support under any possible set of practical optimization constraints can always be found using a directly responding calculation spreadsheet template. To show how the resulting constrained kinetic plots can be used as a powerful design and selection tool, the method has been applied to a series of plate height measurements performed on a number of different commercial columns for the same component (butyl-parabene) and mobile-phase composition. The method, for example, allows one to account for the fact that the advantageous solutions displayed by the silica monolith and 5 microm particle columns in the large plate number range of the free kinetic plot are no longer accessible if applying a maximal column length constraint of Lmax = 30 cm. In the plate number range that remains accessible, the investigated sub-2 mum particle columns in any case perform (at least for the presently considered parabene separation) better than the 3.5 mum particle columns or silica monolith, especially if considering the use of system pressures exceeding 400 bar. The constrained kinetic plot method can also be used to select the best-suited column length from an available product gamma to perform a separation with a preset number of plates. One of the optimization results that is obtained in this case is that sometimes a significant gain in analysis time can be obtained by selecting a longer column, yielding the desired plate number at a larger velocity than that for a shorter column.     

Surface and Interaction Characteristics of Liquid Crystal Polymers and their Miscibility with Thermoplastic Hosts

Inverse gas chromatographic measurements have shown that the surface of thermo-tropic liquid crystal polymers, (TLCP), are capable of mainly dispersion force (L/W) interactions, with only slight contributions from non-dispersion (acid-base) forces. Structural moieties capable of non-dispersive interactions are primarily oriented into the TLCP bulk, perhaps accounting for the self-assembly effects in these polymers. Moreover, nondispersive surface forces were found to be thermolabile, so that above characteristic temperatures only L/W forces remain. Blends of TLCP with polycarbonate and polyetherimide hosts prepared below the characteristic temperatures displayed morphology typical of immiscible blends. When prepared at, and quenched from, temperatures above the pertinent characteristic value, electron micrographs showed evidence of adhesion at matrix/TLCP contacts, simulating the behavior of more miscible systems.     

A high-resolution digital time-interval measurement instrument

A new method for time-interval measurements is described and the results of measurements on a prototype are given. This method uses a virtually periodic exponential signal as the reference clock and consists of measuring both the phase deviation and the number of cycles of this clock signal between the beginning and the end of the unknown time-interval. The use of two auxiliary sinusoidal signals in order to measure the phase of the corresponding periodic exponential signal is discussed, also considering the main causes of error. The functional block diagram of the prototype is described in detail and the measurement results show that a resolution improvement of two orders of magnitude with respect to the period of the clock signal can easily be obtained.     

Induction and characterization of a novel amine oxidase from the yeast Kluyveromyces marxianus

An amine oxidase from the yeast Kluyveromyces marxianus was induced, purified and completely characterized; it was shown to belong to the class of copper-containing amine oxidases (E.C. 1.4.3.6). The enzyme was induced by putrescine and, very strongly, by copper(II); structural-functional characterization of the enzyme was performed, including determination of molecular weight, glycosylation, copper and TPQ content, isoelectric point, K(M) and k(CAT) (with benzylamine as substrate), pH, temperature and ionic strength effect on catalysis, substrate and inhibitor specificity. A 700 bp clone was isolated containing the cDNA that encodes for the C-terminus of the enzyme; the amino acid sequence deduced (the first available for a benzylamine oxidase from yeast) was compared to that of other copper amine oxidases from microorganisms and higher organisms. From the results obtained, the putrescine/benzylamine oxidase from Kluyveromyces marxianus was found to have a good homology with other enzymes of this class from microorganisms, and particularly with AO I from Aspergillus niger. Nonetheless, some features resulted closer to those of animal amine oxidases and histaminases. Some potential biotechnological applications are proposed. The cDNA Accession No. is AJ320485.     

Enantioselective hydrolysis of some 2-aryloxyalkanoic acid methyl esters and isosteric analogues using a penicillin G acylase-based HPLC monolithic silica column

A technique based on liquid chromatography has been developed to facilitate studies of enantioselectivity in penicillin G acylase (PGA)-catalyzed hydrolysis of some 2-aryloxyalkanoic acid methyl esters and isosteric analogues. PGA was covalently immobilized on an aminopropyl monolithic silica support to create an immobilized HPLC-enzyme reactor. Two sets of experimental data were drawn to calculate the enantioselectivity (E) of the kinetically controlled enantiomer-differentiating reaction, the degree of substrate conversion and the enantiomeric excess of the product. The developed enzymatic reactor was coupled through a switching valve to an achiral analytical column for separation and quantitation of the hydrolysis products. The enantiomeric excess was determined off-line on a PGA-chiral stationary phase. In this way, highly precise E values were determined. A computational study related to the hydrolysis of the considered racemic esters was also carried out in order to unambiguously clarify both the substrate specificity and the enantioselectivity displayed by PGA.