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PubMed2006

Diminishing catalyst concentration in atom transfer radical polymerization with reducing agents.

The concept of initiators for continuous activator regeneration (ICAR) in atom transfer radical polymerization (ATRP) is introduced, whereby a constant source of organic free radicals works to regenerate the Cu(I) activator, which is otherwise consumed in termination reactions when used at very low concentrations. With this technique, controlled synthesis of polystyrene and poly(methyl methacrylate) (Mw/Mn < 1.2) can be implemented with catalyst concentrations between 10 and 50 ppm, where its removal or recycling would be unwarranted for many applications. Additionally, various organic reducing agents (derivatives of hydrazine and phenol) are used to continuously regenerate the Cu(I) activator in activators regenerated by electron transfer (ARGET) ATRP. Controlled polymer synthesis of acrylates (Mw/Mn < 1.2) is realized with catalyst concentrations as low as 50 ppm. The rational selection of suitable Cu complexing ligands {tris[2-(dimethylamino)ethyl]amine (Me6TREN) and tris[(2-pyridyl)methyl]amine (TPMA)} is discussed in regards to specific side reactions in each technique (i.e., complex dissociation, acid evolution, and reducing agent complexation). Additionally, mechanistic studies and kinetic modeling are used to optimize each system. The performance of the selected catalysts/reducing agents in homo and block (co)polymerizations is evaluated.

Catalysis↗
PubMed2000

A simplified method for the cultivation of extreme anaerobic Archaea based on the use of sodium sulfite as reducing agent.

The extreme sensitivity of many Archaea to oxygen is a major obstacle for their cultivation in the laboratory and the development of archaeal genetic exchange systems. The technique of Balch and Wolfe (1976) is suitable for the cultivation of anaerobic Archaea but involves time-consuming procedures such as the use of air locks and glove boxes. We describe here a procedure for the cultivation of anaerobic Archaea that is more convenient and faster and allows the preparation of liquid media without the use of an anaerobic chamber. When the reducing agent sodium sulfide (Na2S) was replaced by sodium sulfite (Na2SO3), anaerobic media could be prepared without protection from oxygen outside an anaerobic chamber. Exchange of the headspace of serum bottles by appropriate gases was sufficient to maintain anaerobic conditions in the culture media. Organisms that were unable to utilize sulfite as a source for cellular sulfur were supplemented with hydrogen sulfide. H2S was simply added to the headspace of serum bottles by a syringe. The use of H2S as a source for sulfur minimized the precipitation of cations by sulfide. Representatives of 12 genera of anaerobic Archaea studied here were able to grow in media prepared by this procedure. For the extremely oxygen-sensitive organism Methanococcus thermolithotrophicus, we show that plates could be prepared outside an anaerobic chamber when sulfite was used as reducing agent. The application of this method may faciliate the cultivation and handling of extreme anaerobic Archaea considerably.

Anaerobiosis↗
PubMed1981

Influence of reducing agents on adrenochrome-induced changes in the heart.

To elucidate the role of oxidation products of catecholamines play in myocardial necrosis, we examined the effects that adrenochrome in the presence of some reducing agents and that autoxidized solution of adrenochrome have on the ultrastructure and force of contraction in the isolated rat heart. Addition of ascorbic acid (1 mM) or cysteine (0.5 mM) into a perfusion medium containing 25 mg/L of adrenochrome produced ultrastructural damage greater than that seen with adrenochrome alone, whereas addition of dithiothreitol (0.5 mM) did not. The rate of failure of the heart due to adrenochrome was accelerated by use of ascorbic acid and dithiothreitol. Reduction of adrenochrome into other oxidation products of catecholamines by these reducing agents was indicated by the results of spectral analysis studies. Myocardial damage or contractile failure did not occur if the adrenochrome solution was allowed to autoxidize for 24 hours before perfusion. These data indicate that oxidation products of epinephrine other than adrenochrome are involved in the genesis of catecholamine-induced cardiotoxicity. This effect may occur through the formation of cardiotoxic free radicals, as well as through interaction of these oxidation products with sulfhydryl groups.

Adrenochrome↗
PubMed2006

One-step synthesis of gold and silver hydrosols using poly(N-vinyl-2-pyrrolidone) as a reducing agent.

Synthesis of gold and silver hydrosols was carried out in a one-step process by reduction of aqueous solutions of metal salts using poly(N-vinyl-2-pyrrolidone) (PVP). Both kinds of metal nanoparticles were obtained without the addition of any other reducing agent, at low temperatures and using water as the synthesis solvent. Shape, size, and optical properties of the particles could be tuned by changing the employed PVP/metal salt ratio. It is proposed that PVP acts as the reducing agent suffering a partial degradation during the nanoparticles synthesis. Two possible mechanisms are proposed to explain the reduction step: direct hydrogen abstraction induced by the metal ion and/or reducing action of macroradicals formed during degradation of the polymer. Initial formation of the macroradicals might be associated with the metal-accelerated decomposition of low amounts of peroxides present in the commercial polymer.

Journal Article↗
PubMed1988

Prostaglandins as reducing agents: a model of adenylate cyclase activation?

It has been suggested that adenylate cyclase activation involves reduction of a disulfide linkage. Prostaglandin E1 (PGE1), prostaglandin E2 (PGE2), prostaglandin I2 (PGI2) and prostaglandin F2 alpha (PGF2 alpha) were tested for their ability to act as reducing agents with either cytochrome c, or the disulfide 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB), the latter with a catalytic amount of ferric chloride. PGE1, PGE2, and PGI2 significantly reduced cytochrome c while PGF2 alpha did not. PGE1, PGE2 and PGI2 reduced DTNB while PGF2 alpha did not. The results are consistent with the postulate that prostaglandins which are effective in activating adenylate cyclase can act as reducing agents and might be involved in reductive activation of adenylate cyclase.

Adenylyl Cyclases↗
PubMed1988

Reducing agents and Entamoeba histolytica.

Entamoeba histolytica remains an important but enigmatic parasite. It displays both non-pathogenic and invasive pathogenic types, which can be distinguished clinically and by isoenzyme markers. Yet as debated in Parasitology Today last year(1), the relationship between these two forms remains unclear. Bacterial associates and reducing agents are known to play on important role in the culture of E. histolytica, and possibly in its differentiation and invasive mechanisms. This article briefly reviews available information on the role o f reducing agents, and explores the possibility that bacteria may play a role in reduction o f toxic oxygen product - thereby promoting the virulence of E. histolytica. The review is not definitive, but should help to stimulate further research in this neglected area.

Journal Article↗
PubMed1981

99mTc-labelled compounds prepared with sodium dithionite as reducing agent.

The paper deals with the applications of Na2S2O4 as reducing agent in the preparation of 99mTc-labelled compounds. The reduction of pertechnetate can advantageously be carried out in neutral solutions of pH 7. Using this procedure, DTPA, HEDSPA, MDP, gluconate, citrate and trypsin were successfully labelled. In HEDSPA and MDP labelling, a high as cumulation of 99mTc in rat bones (50%) was obtained. In gluconate labelling, under various reaction temperatures, two types of complexes were prepared. Complex I shows a 99mTc biodistribution which is comparable with the kidney diagnosticum 99mTc-Sn-gluconate (24% of 99mTc in kidneys). Complex II, on the other hand, exhibited a reduced affinity of 99mTc to kidneys (2.2%) which, however, increases in bone to 15.4%. The experimental results indicated that Tc(V) is bound in Complex I. In technetium complexing no "mixed complex" is formed technetium being complexed directly by chelate-forming groups on the labelled compound.

Animals↗
PubMed2004

Synthesis of aqueous Au core-Ag shell nanoparticles using tyrosine as a pH-dependent reducing agent and assembling phase-transferred silver nanoparticles at the air-water interface.

We demonstrate that the amino acid tyrosine is an excellent reducing agent under alkaline conditions and may be used to reduce Ag+ ions to synthesize stable silver nanoparticles in water. The tyrosine-reduced silver nanoparticles may be separated out as a powder that is readily redispersible in water. The silver ion reduction at high pH occurs due to ionization of the phenolic group in tyrosine that is then capable of reducing Ag+ ions and is in turn converted to a semi-quinone structure. These silver nanoparticles can easily be transferred to chloroform containing the cationic surfactant octadecylamine by an electrostatic complexation process. The now hydrophobic silver nanoparticles may be spread on the surface of water and assembled into highly ordered, linear superstructures that could be transferred as multilayers onto suitable supports by the versatile Langmuir-Blodgett technique. Further, tyrosine molecules bound to the surface of Au nanoparticles through amine groups in the amino acid may be used to selectively reduce silver ions at high pH on the surface of the Au nanoparticles, thus leading to a simple strategy for realizing phase-pure Au core-Ag shell nanostructures.

Air↗
PubMed1991

Effects of alloxan and reducing agents on macrophages in culture.

The diabetogenic effect of the quinonoid compound alloxan is not understood in detail although it supposedly involves reactions mediated by alloxan and oxygen radicals. These reactive species may form extra- or intracellularly and cause cell damage through a variety of complex interactions with several macromolecules. The purpose of this study was to elucidate early (less than or equal to 60 min) effects of alloxan and reducing agents (cysteine and ascorbic acid) on cultured macrophages, as assayed by the trypan blue dye exclusion test and the sensitive fluorescein diacetate and propidium iodide (FDA/PI) double staining technique. During the reactions between alloxan and reducing agents, oxygen was consumed as a sign of superoxide anion radical formation. When alloxan alone was added to two different culture media without serum, oxygen was still consumed, indicating formation of oxygen radicals due to the occurrence of reducing substances in cell culture media. This finding demonstrated the necessity of performing further studies in solutions without reducing capacity, e.g. in phosphate-buffered saline. The experiments showed that exposure of normal and malignant macrophages to alloxan and reducing substances resulted in rapidly occurring plasma membrane damage and ensuing cell death. Separate addition of catalase, desferrioxamine or superoxide dismutase resulted in evident, slight and no protection, respectively. The combinations of (i) catalase and desferrioxamine, and (ii) catalase, desferrioxamine and superoxide dismutase, however, inhibited cell damage in a pronounced and complete way, respectively. The results are interpreted as indicating cell damage due to the extracellular formation of hydrogen peroxide and hydroxyl radicals. The latter in close proximity to the cells and acting on the plasma membrane, while the former, after diffusing into the cell, may have several intracellular targets. The FDA/PI technique proved its value as a quantifiable method for the evaluation not only of cell death but also of cell damage with computer-based fluorometry.

Alloxan↗
PubMed1989

[Visible-light cured resin. Selection of reducing agent amine, its appropriate amount and effect on physical properties].

Studies were done to improve the physical properties, especially degree of conversion of visible-light cured resin (VLCR), and accordingly to lower its water sorption and solubility in water. Trial products of VLCR were prepared using various kinds of amine, reducing agent, and the photoinitiator to be mixed with cyclophosphazene monomer, 4 PN-(TF)1-(EMA)7. As amines ethyl-p-dimethylaminobenzoate (DMAB), methacryloxyethyl-p- dimethylaminobenzoate (DMAB-EMA) and methacryloxyglycidyl-p-dimethylaminobenzoate (DMAB-GMA) were used. Of their set products immersed in water and MeOH, their water sorption, solubility in water, MeOH sorption and solubility in MeOH were examined. The resin with DMAB-EMA used was preferable, showing comparatively small solubility. Next, VLCR, with various amounts of DMAB-EMA mixed, 0.5-5.0 in mol ratio to photosensitizer (CQ + DB), and of their set products water sorption, solubility in water, MeOH sorption, solubility in MeOH, THF sorption and their mechanical properties after immersion in water were examined. Immersion of the resin products in water and MeOH for 30 days, lowered the solubility in water and MeOH to a minimum at the mixing ratio of 3.0 in mol ratio. Solubility in MeOH (HPLC) became minimum at 2.0 in mol ratio, and at less than 2.0, the photosensitizer and monomer were dissolved, while at more than 2.0, the photosensitizer and DMAB-EMA were dissolved. THF sorption decreased in accordance with the increase in the mixed amount of DMAB-EMA, became almost constant at more than 3.0 in mol ratio. The compressive strength of set product after immersion in water for 7 days increased in accordance with the increase of the mixed amount of DMAB-EMA, while the transverse strength also increased up to 2.0 in mol ratio. The optimum reducing agent to be mixed with VLCR was DMAB-EMA, and the mixing ratio should be 2.0-3.0 in mol ratio to photosensitizer.

Acrylic Resins↗
PubMed2000

Cardiac ischemia oxidizes regulatory thiols on ryanodine receptors: captopril acts as a reducing agent to improve Ca2+ uptake by ischemic sarcoplasmic reticulum.

We tested the hypothesis that ischemia alters sarcoplasmic reticulum (SR) Ca2+ transport by oxidizing regulatory thiols on ryanodine receptors (RyRs), and that membrane-permeable sulfhydryl-containing angiotensin-converting enzyme (ACE) inhibitors protect against ischemia-induced oxidation and explain in part, the therapeutic actions of captopril. Ca2+ uptake and adenosine triphosphatase (ATPase) activity was measured from SR vesicles isolated from control or ischemic dog and human ventricles and compared with or without sulfhydryl reductants. The rate and amount of Ca2+ uptake was lower for canine ischemic SR compared with control (6.5 +/- 0.2 --> 18.5 +/- 1.1 nmol Ca2+/mg/min and 123.1 +/- 4.7 --> 235.0 +/- 17.3 nmol Ca2+/mg; n = 8 each). Captopril, dithiothreitol (DTT), glutathione (GSH), and L-cysteine increased the rate and amount of Ca2+ uptake by canine and human ischemic SR vesicles by approximately 50%. Reducing agents had no effect on Ca2+- ATPase activity in either canine control or ischemic (approximately 40% less than control) SR. Captopril was as potent as DTT at reversing the oxidation of skeletal and cardiac RyRs induced by reactive disulfides (RDSs) or nitric oxide (NO). In neonatal rat myocytes, RDSs or NO triggered SR Ca2+ release and increased cytosolic Ca2+, an effect reversed by captopril and DTT but not GSH or cysteine. Pretreatment of myocytes with captopril (exposure and then wash) inhibited Ca2+ elevation elicited by RDSs or NO, indicating that captopril is an effective, membrane-permeable intracellular reducing agent. Thus, net SR Ca2+ accumulation is reduced by ischemia in part due to the oxidation of thiols that gate RyRs, an effect reversed by captopril.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1987

Improving the in vitro protein digestibility of sorghum with reducing agents.

We have shown in previous reports that cooked sorghum protein is less digestible than other cooked cereal proteins. The pepsin-indigestible proteins in sorghum were found to be mainly prolamin proteins. Cooking sorghum in the presence of 2-mercaptoethanol increased protein digestibility (in vitro with pepsin or trypsin/chymotrypsin) to a level comparable with other cereals. At a concentration of 100 mM, other reducing agents (dithiothreitol, sodium bisulfite, and L-cysteine) were equally effective in improving sorghum digestibility. When maize was cooked in the presence of 2-mercaptoethanol, protein digestibility increased 5% compared to 25% for sorghum. Cooking barley, rice, and wheat with 2-mercaptoethanol had no significant effect on protein digestibility. The addition of reducing agents appears to prevent the formation of protein polymers linked by disulfide bonds.

Journal Article↗
PubMed1992

Lipogenesis from n-butyrate in colonocytes. Action of reducing agent and 5-aminosalicylic acid with relevance to ulcerative colitis.

Cell membranes of colonic epithelial cells (CEC) in ulcerative colitis show structural abnormalities which are specific to the disease and which suggest impaired lipogenesis in CECs. Lipogenesis from [1-14C]-n-butyrate, the chief oxidative fuel of colonic epithelial cells, was measured in isolated CECs under control conditions, with or without glucose and in the presence of mercaptoacetate, a major reducing agent in the colonic lumen. Glucose significantly (p < 0.01) stimulated lipogenesis from [1-14C]-butyrate which was reversed by 5 mM mercaptoacetate. Mercaptoacetate significantly diminished CEC thiolase activity (EC 2.3.1.9). 5-Aminosalicylic acid reversed the adverse effects of mercaptoacetate in the saponifiable fraction of extracted lipids. Changes in lipogenesis due to colonic luminal reducing agents would affect the barrier function of CECs a feature relevant to the disease process of ulcerative colitis.

Aminosalicylic Acids↗
PubMed1990

Secretion of immunoglobulin M assembly intermediates in the presence of reducing agents.

There are several demonstrations that misfolded or unassembled proteins are not transported along the secretory pathway, but are retained intracellularly, generally in the endoplasmic reticulum. For instance, B lymphocytes synthesize but do not secrete IgM, and only the polymeric form of IgM is secreted by plasma cells. The C-terminal cysteine of the mu heavy chain of secreted IgM (residue 575) is involved in the intracellular retention of unpolymerized IgM subunits. Here we report that the addition of reducing agents to the culture medium, at concentrations which do not affect cell viability, terminal glycosylation, or retention of proteins in the endoplasmic reticulum through the KDEL mechanism, induces secretion of IgM assembly intermediates by both B and plasma cells. Free joining (J) chains, which are not normally secreted by plasma cells unless as part of IgM or IgA, are also secreted in the presence of reducing agents. We propose a role for free thiol groups in preventing the unhindered transport of proteins through the secretory pathway. Under the scheme, assembly intermediates interact through their thiol groups between themselves and/or with unknown proteins of the endoplasmic reticulum. Such interactions may be prevented by altering the intracellular redox potential or by site-directed mutagenesis of the relevant cysteine residue(s).

Animals↗
PubMed2002

Inhibition of Mrp2- and Ycf1p-mediated transport by reducing agents: evidence for GSH transport on rat Mrp2.

Mammalian Mrp2 and its yeast orthologue, Ycf1p, mediate the ATP-dependent cellular export of a variety of organic anions. Ycf1p also appears to transport the endogenous tripeptide glutathione (GSH), whereas no ATP-dependent GSH transport has been detected in Mrp2-containing mammalian plasma membrane vesicles. Because GSH uptake measurements in isolated membrane vesicles are normally carried out in the presence of 5-10 mM dithiothreitol (DTT) to maintain the tripeptide in the reduced form, the present study examined the effects of DTT and other sulfhydryl-reducing agents on Ycf1p- and Mrp2-mediated transport activity. Uptake of S-dinitrophenyl glutathione (DNP-SG), a prototypic substrate of both proteins, was measured in Ycf1p-containing Saccharomyces cerevisiae vacuolar membrane vesicles and in Mrp2-containing rat liver canalicular plasma membrane vesicles. Uptake was inhibited in both vesicle systems in a concentration-dependent manner by DTT, dithioerythritol, and beta-mercaptoethanol, with concentrations of 10 mM inhibiting by approximately 40%. DTT's inhibition of DNP-SG transport was noncompetitive. In contrast, ATP-dependent transport of [(3)H]taurocholate, a substrate for yeast Bat1p and mammalian Bsep bile acid transporters, was not significantly affected by DTT. DTT also inhibited the ATP-dependent uptake of GSH by Ycf1p. As the DTT concentration in incubation solutions containing rat liver canalicular plasma membrane vesicles was gradually decreased, ATP-dependent GSH transport was now detected. These results demonstrate that Ycf1p and Mrp2 are inhibited by concentrations of reducing agents that are normally employed in studies of GSH transport. When this inhibition was partially relieved, ATP-dependent GSH transport was detected in rat liver canalicular plasma membranes, indicating that both Mrp2 and Ycf1p are able to transport GSH by an ATP-dependent mechanism.

ATP-Binding Cassette Transporters↗
PubMed1997

The impact of thiazide diuretics on the initiation of lipid-reducing agents in older people: a population-based analysis.

OBJECTIVE: The objective of this study was to examine how often treatment for hyperlipidemia followed the use of thiazides, compared with the use of other antihypertensive drugs, in older patients. DESIGN: Retrospective follow-up of all health claims filed over a 12-month period. SETTING: New Jersey Medicaid and Medicare programs. PARTICIPANTS: A total of 9274 enrollees, aged 65 to 99, who were newly initiated on antihypertensive medications from 1981-1989. MEASUREMENTS: We measured rates of lipid-reducing agent (LRA) initiation among patients in the 2 years following antihypertensive initiation (thiazide, non-thiazide drug, or combinations of the two) compared with rates among patients not currently taking antihypertensive agents. We used Cox regression analyses to estimate relative risks (RR), accounting for switching in antihypertensive therapy and for time when drug therapy was not currently available according to pharmacy refill records. RESULTS: There were 226 patients (2.4%) in the cohort who were started on LRA during the follow-up period. After adjusting for potential confounders, we found no significant relationship between LRA initiation and overall thiazide use (RR 1.47, 95% CI 0.89-2.40), or other antihypertensive use, relative to no current exposure. However, use of high-dose thiazides (> or = 50 mg) was associated significantly with LRA initiation (RR 1.97, 95% CI 1.12-3.45). Factors associated with decreased incidence of LRA use included age > or = 85 (RR 0.59, 95% CI 0.36-0.96), black race (RR 0.58, 95% CI 0.37-0.91), and nursing home residency (RR 0.20, 95% CI 0.11-0.35). CONCLUSION: Use of low-cost and effective thiazide diuretics in older hypertensives was not associated with more common initiation of lipid-reducing agents, except with high-dose use of thiazides currently seen as inappropriate in most cases. Age and race were important determinants of LRA use.

Aged↗
PubMed1982

Influence of disulfide-reducing agents on fractionation of the chromatin complex by endogenous nucleases and deoxyribonuclease I in aging mice.

Age-related alterations in chromatin were evaluated by a fractionation procedure involving limited digestion of liver cell nuclei from young adult and old mice with endogenous nucleases and deoxyribonuclease I. The results suggest that in the chromatin the bulk of the nuclear deoxyribonucleic acid (DNA) may be folded or compacted into domains or loops and associated at a few points with a nuclear protein skeleton structure represented by the final pellet fraction which is resistant to deoxyribonuclease I. Disulfide bonds appear to play a role in the linkage of regions of DNA with this nuclear protein skeleton structure. The amount of DNA that could be released from the pellet fraction by disulfide-reducing agents was significantly greater with old than with young adult mice. In addition, the amount of chromatin material released into the first soluble fraction decreased and that in the second soluble fraction increased with age. Treatment of the nuclei with disulfide-reducing agents did not correct this particular age-related change. Previous results had shown a similar alteration with age of chromatin subjected to digestion by micrococcal nuclease. The combined results suggest the existence of a supranucleosomal alteration in chromatin structure during aging.

Aging↗
PubMed1991

Improvements in detection of antibody to hepatitis B core antigen by treating specimens with reducing agent in an automated microparticle enzyme immunoassay.

A fully automated microparticle enzyme immunoassay (EIA), IMx Core, was developed for the detection of antibody against hepatitis B core antigen (anti-HBc). IMx Core sensitivity was less than 0.5 Paul Ehrlich Institut units per ml and was greater than that of the commercial radioimmunoassay (RIA) or EIA, Corab and Corzyme, respectively. Specimens from blood donors and diagnostic and hospital patients, which included individuals with a variety of infectious and immune diseases, were tested in parallel by the IMx Core and EIA. Overall agreement of 99.1% (4,797 of 4,841) was obtained. Prevalence of anti-HBc tested by IMx Core ranged from 1.2% in volunteer blood donors to 9.1% in hospital laboratories. Discordant specimens reactive by IMx Core but negative by Corzyme or Corab resulted from the increased sensitivity of the IMx Core assay, since other hepatitis B markers were usually present. However, most discordant specimens were positive by the EIA or RIA but negative by IMx Core. No other hepatitis B markers could be detected in these discordants, and after addition of reducing agent, these specimens also became negative by EIA or RIA. In clinical trials, 30% (14 of 47) of volunteer blood donors and 8% (9 of 119) of hospital patients testing repeatedly reactive by the EIA had reduction-sensitive (unspecific) anti-HBc reactivity. The reducing agent, dithiothreitol, was added to each specimen automatically in the IMx assay to eliminate these unspecific reactions without significantly affecting anti-HBc reactivity resulting from hepatitis B virus infection as judged by the correlation with other hepatitis B markers.

Evaluation Studies as Topic↗