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Gold electrodes were modified through chemisorption of 5-(octyldithio)-2-nitrobenzoic acid (ODTNB). ODTNB includes a long chain in a short-length thio acid, providing a heterogeneous-like alkanethiol layer after adsorption on gold electrodes. Membrane-bound enzymes, in particular D-fructose dehydrogenase (FDH), D-gluconate dehydrogenase (GADH), and L-lactic dehydrogenase (cytochrome b(sub 2)) (Cyb(sub 2)), were immobilized onto ODTNB-modified gold electrodes simply by adsorption. The short-length thio acid may provide electrostatic interactions with enzyme surface charges, while the alkanethiolate enables hydrophobic interaction with the largely lipophilic, membrane-bound enzymes. The immobilization of FDH, GADH, and Cyb(sub 2) onto ODTNB-modified gold surfaces has been studied with the quartz crystal microbalance (QCM). Spectrophotometric and electrochemical assays indicate that the immobilized enzyme retains its enzymatic activity after immobilization onto the ODTNB-modified gold surface. The amount of immobilized (and active) enzyme was estimated from QCM to be of the order of 2.5 x 10(super -12) - 5.3 x 10(super -12) mol*cm(super -2). A fructose biosensor was developed, making use of a gold surface modified with ODTNB and fructose dehydrogenase, employing hydroxymethyl-ferrocene as a mediator in solution. Calibration curves exhibited a linear relation between the biosensor response and the substrate concentration up to 0.7 mM. Statistical analysis gave an excellent linear correlation (r = 0.9993) and a sensitivity of 6.1 mM(super -1) fructose. The biosensor shows a significant stable catalytic current for at least 25 days.

Dihydroxybenzaldehyde (DHB) isomers can be oxidatively electrodeposited onto glassy carbon electrodes previously activated in base solution. We have studied the mechanism of such electrodeposition as well as the electrochemical features of films derived from 2,3-DHB, 3,4-DHB, 2,5-DHB, and 2,4-DHB isomers as well as related analogs including 3,4-dihydroxybenzoic acid, 3,4-dihydroxyphenylacetic acid, and 4-nitrocatechol. The electrodeposition process and the electrochemical behavior of the modified electrodes were strongly dependent on pH as anticipated for quinone/hydroquinone functionalities. Glassy carbon electrodes modified with films derived from 2,3-DHB and 3,4-DHB exhibit catalytic activity in the electrooxidation of NADH. The catalytic currents are proportional to the concentration of NADH over the range 0.01-1.2 and 0.01-0.9 mM for films derived from 3,4-DHB and 2,3-DHB, respectively. These modified electrodes can be used in the design of biosensors based on coupled dehydrogenase enzymatic activities.

Exposure of gold surfaces to solutions of dithiobis N-succinimidyl propionate (DTSP) gives rise to the modification of the surface with N-succinimidyl-3-thiopropionate (NSTP) which can, in turn, react with amino groups allowing for the covalent immobilization of enzymes such as horseradish peroxidase (HRP). The coverage of NSTP has been estimated to be of the order of 1.3 x [10.sup.-10] from the charge consumed during its reductive desorption. The binding reaction of HRP with NSTP modified gold surfaces has been studied with the quartz crystal microbalance, and the results suggest that the immobilization process involves two steps in which the first (faster) appears to correspond to the rapid incorporation of the enzyme whereas the second is likely due to the slow incorporation of additional enzyme and/or reorganization of the immobilized layer. Spectrophotometric and electrochemical assays indicate that the immobilized HRP retains its enzymatic activity after immobilization onto the DTSP modified gold surface. The amount of immobilized (and active) HRP was estimated from QCM and spectrophotometric measurements to be of the order of 1.5 x [10.sup.-11] mol/[cm.sup.2]. A peroxide biosensor was developed making use of a gold surface modified with DTSP and HRP employing Os and Ru complexes of 1,10-phenanthroline 5,6-dione (phen-dione) of the type [[M[(phendione).sub.x][(L).sub.3-x].sup.+2] (where L = 1,10-phenanthroline or 2,2'-bipyridine, x = 1-3) as mediators with the quinone moieties being the active component. The efficiency of the mediators increased with increasing number of phendione ligands.

PURPOSE: The prevalence of people living with HIV/AIDS (PLWA) in South Africa is estimated to be approximately 14.2% of the total population. In the absence of anti-retroviral therapy, PLWA are likely to experience a steady decline in function, as their immune systems become increasingly compromised. However, there is limited information available to determine the potential role of rehabilitation interventions in the management of PLWA in a resource-poor community. SUBJECTS: Subjects were recruited from the population of beneficiaries of HIV/AIDS clinics run by Medecins Sans Frontià res, which provides anti-retroviral therapy to PLWA within a resource poor community. The subjects, who were either in WHO Stage 3 or 4 of the disease and/or had a CD4 count of less than 200, were interviewed after enrolment on the anti-retroviral programme and before treatment was initiated. They were therefore not yet receiving anti-retroviral therapy. The control group consisted of a community sample randomly selected from the same area and who were in the same age range. METHODS: As all participants were Xhosa speaking, the Xhosa version of the EQ-5D measure of HRQoL was utilized. Analysis: The Mann-Whitney U-test was used to determine whether there was a difference in the rank ordering of responses to the five different domains of the EQ-5D and the Visual Analogue Scale of Health Status scores. RESULTS: There were 123 and 108 subjects in the experimental and control groups, respectively. In the domain of mobility 30.9% of the subjects reported some or severe problems, compared to 14.8% of the control group (p < 0.001). The corresponding figures for the other domains were: self-care 14.8% and 4.6% (p = 0.016), usual activity 31.7% and 10.2% (p < 0.001), pain/discomfort 69.1% and 33.3% (p < 0.001) and anxiety/depression 33.4% and 24.2% (p = 0.123) for the experimental and control groups respectively. PLWA reported a VAS score of 60.4 (SD 22.1), which was significantly lower than that of the community sample (80.13, SD 20.4, p < 0.001). CONCLUSION: Self-reporting indicates that Health Related Quality of Life is severely comprised in PLWA in Stages 3 and 4 and limitations in the four domains of mobility, usual activities, pain/discomfort and anxiety/depression constitute major problems for PLWA. There is an obvious need to provide a continuum of care, encompassing not only medical but also physical and mental rehabilitation services as well. In an area of high HIV prevalence, the provision of appropriate, multi-disciplinary health care services to PLWA presents a major challenge to the health services. [ABSTRACT FROM AUTHOR]