Direct electron paramagnetic resonance monitoring of the peptide synthesis coupling reaction in polymeric support

This work demonstrates, for the first time, a time-resolved electron paramagnetic resonance (EPR) monitoring of a chemical reaction occurring in a polymeric structure. The progress of the coupling of a N^α-tert-butyloxycarbonyl-2,2,6,6-tetramethylpiperidine-1-oxyl-4-amino-4-carboxylic acid (Boc-TOAC) spin probe to a model peptide-resin was followed through EPR spectra. Progressive line broadening of EPR peaks was observed, indicative of an increased population of immobilized spin probe molecules attached to the solid support. The time for spectral stabilization of this process coincided with that determined in a previous coupling study, thereby validating this in situ quantitative monitoring of the reaction. In addition, the influence of polymer swelling degree and solvent viscosity, as well as of the steric hindrance within beads, on the rate of coupling reaction was also addressed. A deeper evaluation of the latter effect was possible by determining unusual polymer parameters such as the average site-site distance and site-concentration within resin beads in each solvent system.     

Atherogenic, hemostatic, and other potential risk markers in subjects with previous isolated myocardial infarction compared with long-standing uncomplicated stable angina

BACKGROUND: Several atherogenic, hemostatic, inflammatory, and genetic parameters and markers have been implicated as risk factors in coronary artery disease, although whether they are risk factors for acute as opposed to chronic coronary disease is unclear. METHODS AND RESULTS: Fifty subjects with an isolated myocardial infarction >3 months previously were compared with 50 subjects with a minimum 3-year history of stable angina, documented coronary artery disease, normal electrocardiogram and normal ventricular wall motion, and no episode suggesting infarction or unstable angina. Biologic variables analyzed included apolipoprotein B (apo B), lipoprotein (a), C-reactive protein (CRP), fibrinogen, factor VII, tissue plasminogen activator (TPA) and inhibitor (PAI-1), thrombin-antithrombin (TAT), fragment 1+2 (F1+2), von Willebrand factor (vWF), activated protein C resistance, homocyst(e)ine, anticardiolipin antibodies, blood group, and the angiotensin-converting enzyme insertion/deletion (I/D) and angiotensin II receptor gene polymorphisms. There were no significant differences between the 2 groups for any of the variables studied, although fibrinogen and F 1+2 tended to be slightly higher in the angina group (P = .09 for each). These significant correlations were present: age with fibrinogen, homocyst(e)ine, and vWF; factor VII with apo B, homocyst(e)ine, and TPA; apo B with TPA and CRP; CRP with fibrinogen, TPA, PAI-1, and factor VII; fibrinogen with vWF. CONCLUSIONS: Examination of atherogenic, hemostatic, inflammation, and genetic variables in the clinically quiescent state permitted no distinction between subjects with a previous isolated myocardial infarction in contrast to those with long-standing uncomplicated stable angina, favoring the notion that acute coronary events occur at random on a varying background of atherosclerosis. The multiple correlations found among these variables also underscore their complex interaction in the atherosclerotic process.     

Control of heat transfer and growth uniformity of solidifying copper shells through substrate temperature

To determine the optimal roll temperature in a twin-roll copper-strip caster, copper blocks preheated between 25 °C and 350 °C were immersed in a bath of molten copper for 0.5 seconds. A significant increase in the contact heat-transfer coefficient at the substrate-shell interface was obtained when the substrates were heated above 200 °C and the gain in the solidified shell thickness was 20 pct. The shell growth was also approximately 35 pct more uniform at a high substrate temperature, and micrographic examination showed the dendritic structure to be finer. The contact heat-transfer coefficient was decomposed into two constituents, one for the substrate and the other for the shell. The former was found to be the limiting factor in heat transfer.     

Association of work-related accidents with noise exposure in the workplace and noise-induced hearing loss based on the experience of some 240,000 person-years of observation

This retrospective study explores the association between occupational noise exposure at the time of hearing tests, permanent noise-induced hearing loss and work-related accident risk. Log-binomial analysis was used to first ascertain the association between study variables according to activity sector (North American Industry Classification System, NAICS) and accident context while controlling for age. Second part of the paper estimates the overall number of accidents attributable to occupational noise or the associated hearing loss (excess fraction). Study was carried on a sample of 52,982 male workers exposed to a minimum of 80dBA on a daily basis and whose hearing was examined at least once between 1983 and 1996 by public health authorities of Quebec. These participants evidenced bilateral average hearing threshold levels at 3, 4 and 6kHz ranging from normal (/=90dBA) and noise-induced hearing loss.     

TREATMENT OF THE INLET BOUNDARY CONDITIONS IN NATURAL-CONVECTION FLOWS IN OPEN-ENDED CHANNELS

The present work deals with the numerical solution of elliptic flows encountered in open-ended channels. The important question of applying boundary conditions for pressure and velocity for these flows is considered and a new method for the application of boundary conditions at the channel inlet is proposed. It is shown that the flow reversal at the channel outlet, which appears when nonsymmetric flow conditions are present, is strongly dependent on the entrance boundary conditions for pressure. Results for the straight channel in situations where flow reversal is present are reported for a wide range of Rayleigh numbers. Solutions for L-shaped channels are also reported with the aim of demonstrating the application of the model to arbitrary channels. It is shown that for certain flow situations the use of an elliptic formulation is imperative in order to predict correctly the flow behavior in open-ended channels.     

Thermal oxidation studies on reduced folate, L-5-methyltetrahydrofolic acid (L-5-MTHF) and strategies for stabilization using food matrices

The thermal stability of L-5-methyltetrafolic acid (L-5-MTHF) was investigated in model/buffer systems and food systems. L-5-MTHF degradation followed first-order reaction kinetics with relatively greater (P < 0.01) stability at pH 4 compared to pH 6.8 in the buffer systems. This was confirmed using cyclic voltammetry. The stability (for example, k-values) of L-5-MTHF in an oxygen controlled environment improved (P < 0.001) proportionally when in the presence of increasing molar ratios of sodium ascorbate (NaAsc). The addition of NaAsc to L-5-MTHF after heat treatment was also effective at returning thermally oxidized L-5-MTHF back to its original form. A scheme was developed to explain the degradation and regeneration of L-5-MTHF. The importance of antioxidant protection of L-5-MTHF from thermal oxidation was extended using 2 distinct food systems; namely skim milk and soy milk, both with known antioxidant capacities. We conclude that the antioxidant activity of food components can enhance the stability of L-5-MTHF.     

Correlation between Young’s modulus and impregnation quality of epoxy-impregnated SWCNT buckypaper

Carbon nanotube (CNT) sheets, also known as buckypaper, have high potential for structural applications due to their high volume fraction of CNT, the strongest and stiffest materials known. In this work, two different techniques, one based on positive pressure and another based on vacuum infiltration, are utilized to impregnate single-walled carbon nanotube (SWCNT) buckypaper sheets of 50–70 μm in thickness, resulting in a Young’s modulus of up to 15.4 GPa. Scanning electron microscopy demonstrates that the vacuum-based technique results in more effective impregnation of the buckypaper than the positive pressure technique. Thermogravimetry analysis of vacuum-impregnated specimens indicated a void content ranging from 5% to 32%. An advanced Mori–Tanaka-based micromechanics technique is also utilized to predict the effect of SWCNT volume fraction and void content on Young’s modulus of nanocomposites. These calculations suggest a higher void content of around 40% for the vacuum-impregnated composites.     

A new approach for the purification and characterisation of PA49.5, the main prebiotic of Lactococcus lactis subsp. cremoris

The main autolysin PA49.5, an enzyme that hydrolyzes or destroys the components of a biological endogenous cell or a tissue, was purified 3045 times from the homogenate of a whole cell extract of Lactococcus lactis subsp. cremoris ATCC 9596 (Mc5), with a recovery yield of 52%. The purification of the protein was carried out through a micro-purification technique using SDS-BigCHAP polyacrylamide gel electrophoresis and concentrated with a Microcon-10 filtration system. SDS-polyacrylamide gel electrophoresis of the purified enzyme confirmed the presence of only one band having a molecular weight of 49.5 kDa. In view of its insolubility, PA49.5 contained in the cell extract precipitate was solubilized in the presence of 0.1% (w/v) of BigCHAP, a non-ionic detergent. Higher concentrations of this detergent completely inhibited the activity of solubilized PA49.5 or prevented its solubilization. The optimal pH and temperature for PA49.5 enzymatic activity are 7.5 and 45 degrees C respectively. In addition 0.1% or less of PA49.5 significantly increased Mc5 lysis. We observed 55% more lysis with 0.25 mug of purified PA49.5 compared to the control. Gas chromatography analysis of the components of the crude cell extract, of the precipitate and of the supernatant indicates the presence of at least 6 fatty acids. The long-chained fatty acids (e.g. C18:0 and C18:3) detected represent 81.65% of the precipitate from which PA49.5 was purified. Of these two acids, the C18:0 (stearic acid) alone represents 47.40% of the precipitate. Mc5 releases proteins at the beginning (major peak) and at the end (moderate peak) of the exponential stage of growth. Analysis by denaturing polyacrylamide gel electrophoresis with Mc5 cell walls incorporated as the autolysin's substrate identified a band corresponding to PA49.5 in the second peak of protein secretion.     

hp‐Clouds in Mindlin's thick plate model

In the last few years a number of numerical procedures called as meshless methods have been proposed. Among them, we can mention the diffuse element method, smooth particle hydrodynamics, element free Galerkin method, reproducing kernel particle method, wavelet Galerkin methods, and the so‐called hp‐cloud method. The main feature of these methods is the construction of a collection of open sets covering the domain which are used as support of the classical Galerkin approximation functions. The hp‐cloud method is focused here because of its advantage of considering from the beginning the h and p enrichment of the approximation space. In this work we present, to our knowledge, the first results concerning the behaviour of this technique on the solution of Mindlin's moderately thick plate model. It is demonstrated numerically that the behaviour of the method with respect to shear locking is essentially the same as in the p‐version of the finite element method, namely, the shear locking can be controlled by using hp cloud approximations of sufficiently high polynomial degree. The computational implementation of the method and the issue of numerical integration of the stiffness matrix are also discussed. Copyright © 2000 John Wiley & Sons, Ltd.