Radical-initiated Process Research Articles

Insight into Radical Initiation, Solvent Effects, and Biphenyl Production in Iron-Bisphosphine Cross-Couplings.

Iron-bisphosphines have attracted broad interest as highly effective and versatile catalytic systems for two- and three-component cross-coupling strategies. While recent mechanistic studies have defined the role of organoiron(II)-bisphosphine species as key intermediates for selective cross-coupled product formation in these systems, mechanistic features that are essential for catalytic performance remain undefined. Specifically, key questions include the following: what is the generality of iron(II) intermediates for radical initiation in cross-couplings? What factors control reactivity toward homocoupled biaryl side-products in these systems? Finally, what are the solvent effects in these reactions that enable high catalytic performance? Herein, we address these key questions by examining the mechanism of enantioselective coupling between α-chloro- and α-bromoalkanoates and aryl Grignard reagents catalyzed by chiral bisphosphine-iron complexes. By employing freeze-trapped 57Fe Mössbauer and EPR studies combined with inorganic synthesis, X-ray crystallography, reactivity studies, and quantum mechanical calculations, we define the key in situ iron speciation as well as their catalytic roles. In contrast to iron-SciOPP aryl-alkyl couplings, where monophenylated species were found to be the predominant reactive intermediate or prior proposals of reduced iron species to initiate catalysis, the enantioselective system utilizes an iron(II)-(R,R)-BenzP* bisphenylated intermediate to initiate the catalytic cycle. A profound consequence of this radical initiation process is that halogen abstraction and subsequent reductive elimination result in considerable amounts of biphenyl side products, limiting the efficiency of this method. Overall, this study offers key insights into the broader role of iron(II)-bisphosphine species for radical initiation, factors contributing to biphenyl side product generation, and protocol effects (solvent, Grignard reagent addition rate) that are critical to minimizing biphenyl generation to obtain more selective cross-coupling methods.

Oxygen-vacancy defect engineering to boost the aerobic oxidation of limonene over Co3O4 nanocubes

The heterogeneous aerobic oxidation of biomass-derived limonene under mild reaction conditions is an attractive target for the synthesis of valuable oxygenates, but qualifying catalyst represents an enormous challenge. Herein, we propose an oxygen-vacancy defect engineering strategy for steering the limonene oxidation catalysis over Co3O4 nanocubes. Comprehensive characterizations demonstrate that the incorporation of oxygen vacancy (Ov) in the Co3O4 structure triggers the redistribution of charge density and the modulation of Co chemical environment with the formation of more coordinated unsaturated Co atoms. Both the experimental findings and density functional theory (DFT) calculations explicitly evidence the boosting role of Ov in facilitating the radical initiation process, thereby substantially driving the generation of active radicals for the subsequent oxidation to proceed more feasibly. This work paves a way to structural microenvironment modulation induced by oxygen-vacancy defect engineering strategy towards high-performance limonene oxidation catalysis and beyond.

Thermally Activated Delayed Fluorescence Sensitizers As Organic and Green Alternatives in Energy-Transfer Photocatalysis

Photocatalysis has captured the imagination of synthetic chemists and is poised to become a staple of the fine chemical industry. Over the past decade, the subfield of energy-transfer (EnT) catalysis has expanded dramatically, harnessing the excited states of a photosensitizer to unlock a variety of redox-neutral, radical-based reactivities in a mild and selective fashion. However, many of the developments in this discipline rely on precious rare earth metals such as iridium. This perspective will highlight the rise of thermally activated delayed fluorescence (TADF) materials as metal-free alternatives in EnT photocatalysis for organic transformations. Emphasis will be placed on the recent progress of cycloadditions, E/Z isomerization of olefins, and other radical-initiated processes; all mediated by the mechanism of Dexter energy transfer. The tunable excited-state energetics and dynamics of TADF materials allow them to effectively compete with iridium-based sensitizers, indicating their promise as green alternatives in organocatalysis.

Unraveling the secrets of radical SAM mechanisms

Radical SAM enzymes catalyze a remarkable diversity of biological radical reactions using a common radical initiation mechanism involving a [4Fe‐4S] cluster and SAM. The initial reductive cleavage of SAM leads to the formation of a catalytically central organometallic species (Ω) in which a SAM‐derived 5′‐deoxyadenosyl radical (5′‐dAdo•) is covalently bound through the 5′‐C to an iron of the [4Fe‐4S] cluster. Homolytic Fe‐C5′ bond cleavage then forms the 5′‐dAdo• radical intermediate, which abstracts a hydrogen atom from substrate. Efforts directed towards generating, trapping, and characterizing key radical intermediates during this radical initiation process will be presented and discussed. Further, recently‐discovered photochemistry in radical SAM enzymes, which can promote radical initiation in the absence of substrate, will be presented. This photochemistry has led to fundamental new understanding of the regioselectivity of reductive S‐C bond cleavage that is central to radical SAM mechanisms.

Ammonium Persulphate Initiated Graft Copolymerization of Aniline onto Chitosan-A Comparative Kinetic Study

Ammonium persulphate (APS) has been used as efficient initiator for graft copolymerization of the aniline (ANI) onto chitosan at 25±0.1°C. Graft copolymerization of ANI onto chitosan has taken place through the cation radical initiation process. The grafting parameters have been evaluated by varying concentration of ANI, APS and chitosan. The effects of concentration of APS, ANI, chitosan and reaction time on graft copolymerization were studied by determining the grafting percentage (%G), grafting efficiency (%E) and percentage add-on. It was observed that bout rate of homopolymerization (Rh) and rate of graft coplymerization (Rg) increased with the increase in concentration of each component. On the basis of the experimental observations, initiating steps have been proposed and a suitable rate expression for graft copolymerization has been derived. Electrical conductivity of grafted polyaniline (PANI) onto chitosan (Chit-g-PANI, chitaline) was measured by the four probe method.

Recent Advances in Radical-Involved Alkynylation of Unactivated C(sp3)–H Bonds by Hydrogen Atom Abstraction

AbstractThe direct C(sp3)–H functionalization is one of the major research topics in synthetic chemistry since C(sp3)–H bonds are ubiquitous in every aspect of chemistry. Despite impressive advances in transition-metal-catalyzed C(sp3)–H activation, the radical-initiated process via hydrogen atom abstraction (HAA) of C(sp3)–H bonds represents a more appealing strategy owing to the mild reaction conditions and good regioselectivity. Given the importance of alkynes as versatile synthons in organic synthesis and key structural motifs in drug discovery, great efforts have been made toward their synthesis via the combination of HAA and alkynylation process in recent years. This review summarizes the recent progress in radical-initiated C(sp3)–H alkynylation reactions with emphasis on the alkynylating reagents and mechanistic discussion.1 Introduction2 Alkynylation of C(sp3)–H via Intermolecular Hydrogen Atom Abstraction3 Alkynylation of C(sp3)–H via Intramolecular Hydrogen Atom Abstraction4 Conclusion

Exploring Ethylene/Polar Vinyl Monomer Copolymerizations Using Ni and Pd α-Diimine Catalysts.

The most ubiquitous polymer, polyethylene (PE), is produced either through a radical-initiated process or, more commonly, through a coordination/insertion process employing early transition metal catalysts, particularly titanium- and chromium-based systems. These oxophilic early metal catalysts are not functional-group-tolerant and thus cannot be used to synthesize copolymers of ethylene and polar vinyl monomers such as alkyl acrylates and vinyl acetate. Such PE copolymers have enhanced properties relative to PE and are made through radical polymerization processes, requiring exceptionally high pressures and temperatures. Copolymerizations of polar vinyl monomers with ethylene using more functional group-tolerant late metal catalysts potentially offer an attractive alternative for generating such value-added copolymers since ligand variations may provide more control of polymer microstructures and milder reaction conditions would apply. This Account describes our efforts, particularly through detailed mechanistic studies, to probe and develop this potential using Pd(II) and Ni(II) α-diimine catalysts. To inform discussions of the copolymerizations, we briefly review key aspects of ethylene homopolymerizations using these diimine catalysts. These include ligand designs that incorporate axial blocking groups that retard chain transfer and promote production of a high polymer rather than an oligomer. These ligand designs also lead to unique branched polyethylenes via migration of the metal along the chain ("chain-walking") prior to insertion. Mechanistic investigations of copolymerizations of ethylene with polar vinyl monomers using the diimine complexes have revealed several impediments to developing practical catalysts: (1) The polar group of the comonomer can coordinate strongly to the metal center, blocking coordination of ethylene. (2) Weak binding affinity of the polar monomer relative to ethylene can result in very low levels of comonomer incorporation. (3) A metal alkyl chain bearing a heteroatom, X, on the β-carbon atom can undergo β-X elimination leading to deactivation of the catalyst. (4) Stable chelate formation following insertion of a polar comonomer can greatly retard the rate of chain growth. (5) A metal alkyl chain bearing an electron-withdrawing heteroatom at the □-carbon atom can result in a high insertion barrier. A patent disclosure by the DuPont Versipol group and our extensive mechanistic studies reveal that, remarkably, vinyl trialkoxysilanes are ideal comonomers and circumvent all of the impediments noted above. The Pd-catalyzed copolymerization of vinyl trialkoxysilanes with ethylene produces highly branched, low molecular weight copolymers with activities comparable to those of analgous ethylene homopolymerizations. A 1,2- insertion of the vinyl silane results in the formation of a five-membered Pd-O(R)Si chelate which is readily opened by ethylene and thus does not reduce the rate of chain growth. β-Silyl elimination results in chain transfer and accounts for the lower molecular weight polymer. The nickel α-diimine-catalyzed copolymerizations produce high molecular weight copolymers with structures that vary from nearly linear to moderately branched. Both four- and five-membered chelates are catalyst resting states but are rapidly opened by ethylene, and thus turnover frequencies are only slightly reduced relative to ethylene homopolymerizations. Finally, a convenient and practical nickel-based system has been developed for the efficient synthesis of this copolymer which can be cross-linked to form PEX- b, a commercial PE plastic used for hot water plumbing pipes and power cable coatings.

Low temperature cure-on-command polymerization induced via free radical initiator in an oscillating magnetic field

Three magnetic nanoparticles (Fe3O4, FeCo, Co) were prepared and modified with azo-based free radical initiators via grafting. The resulting magnetic particles underwent a free radical initiation process in an oscillating magnetic field. Three acrylated oligomers, a urethane, epoxide, and polyphosphazene, were used to investigate the curing potential of the magnetic initiators (MI). The curing temperature, Tg, and conversion of the three MI based systems were compared. All three of the MI systems underwent initiation with only a modest temperature increase. The overall conversion and Tg for the MI initiated systems were lower than expected, but with some optimization an ∼80% conversion could be obtained.

PELDOR Spectroscopy with DOPA-β2 and NH2Y-α2s: Distance Measurements between Residues Involved in the Radical Propagation Pathway of E. coli Ribonucleotide Reductase

Escherichia coli ribonucleotide reductase (RNR) catalyzes the reduction of nucleotides to 2'-deoxynucleotides. The active enzyme is a 1:1 complex of two homodimeric subunits, alpha2 and beta2. The alpha2 is the site of nucleotide reduction, and beta2 harbors a diferric tyrosyl radical (Y122*) cofactor. Turnover requires formation of a cysteinyl radical (C439*) in the active site of alpha2 at the expense of the Y122* in beta2. A docking model for the alpha2beta2 interaction and a pathway for radical transfer from beta2 to alpha2 have been proposed. This pathway contains three Ys: Y356 in beta2 and Y731/Y730 in alpha2. We have previously incorporated 3-hydroxytyrosine and 3-aminotyrosine into these residues and showed that they act as radical traps. In this study, we use these alpha2/beta2 variants and PELDOR spectroscopy to measure the distance between the Y122* in one alphabeta pair and the newly formed radical in the second alphabeta pair. The results yield distances that are similar to those predicted by the docking model for radical transfer. Further, they support a long-range radical initiation process for C439* generation and provide a structural constraint for residue Y356, which is thermally labile in all beta2 structures solved to date.

Site-Specific Replacement of Y356 with 3,4-Dihydroxyphenylalanine in the β2 Subunit of E. coli Ribonucleotide Reductase

E. coli ribonucleotide reductase (RNR), composed of the homodimeric subunits alpha2 and beta2, catalyzes the conversion of nucleotides to deoxynucleotides via complex radical chemistry. The radical initiation process involves a putative proton-coupled electron transfer (PCET) pathway over 35 A between alpha2 and beta2. Y356 in beta2 has been proposed to lie on this pathway. To test this model, intein technology has been used to make beta2 semi-synthetically in which Y356 is replaced with a DOPA-amino acid. Analysis of this mutant with alpha2 and various combinations of substrate and effector by SF UV-vis spectroscopy and EPR methods demonstrates formation of a DOPA radical concomitant with disappearance of the tyrosyl radical, which initiates the reaction. The results reveal that Y356 lies on the PCET pathway and demonstrate the first kinetically competent conformational changes prior to ET. They further show that substrate binding brings about rapid conformational changes which place the complex into its active form(s) and suggest that the RNR complex is asymmetric.

Turning on ribonucleotide reductase by light-initiated amino acid radical generation.

Ribonucleotide reductases (RNRs) catalyze the conversion of nucleotides to deoxynucleotides in all organisms, providing the monomeric precursors required for DNA replication and repair. The class I RNRs are composed of two subunits; the R1 subunit contains the active site for nucleotide reduction and allosteric effector binding sites, whereas the R2 subunit houses the essential diirontyrosyl (Y.) radical cofactor. A major unresolved issue is the mechanism by which the tyrosyl radical on R2 (Y122, Escherichia coli numbering) reversibly generates the transient thiyl radical (S.) on R1 that initiates nucleotide reduction. This intersubunit radical initiation is postulated to occur through a defined pathway involving conserved aromatic amino acids (R2: Y122, W48, Y356; R1: Y731, Y730) over a long distance of 35 A. A 20-mer peptide identical to the C-terminal tail of R2 (356-375) and containing Y356 is a competitive inhibitor with respect to R2, and it effectively blocks nucleotide reduction. We now report that a 21-mer peptide, in which a tryptophan has been incorporated at the N terminus of the 20th mer, can replace the R2 subunit and initiate nucleotide reduction by photoinitiated radical generation. The deoxynucleotide generated depends on the presence of allosteric effector and is pathway-dependent. Replacement of Y731 of R2 with phenylalanine prevents deoxynucleotide formation. These results provide direct evidence for the chemical competence of aromatic amino acid radicals and the importance of Y356 in R2 in the radical initiation process of the class I RNRs.

Generation of the R2 Subunit of Ribonucleotide Reductase by Intein Chemistry: Insertion of 3-Nitrotyrosine at Residue 356 as a Probe of the Radical Initiation Process

Escherichia coli ribonucleotide reductase (RNR) catalyzes the conversion of nucleoside diphosphates to deoxynucleoside diphosphates. The enzyme is composed of two subunits: R1 and R2. R1 contains the active site for nucleotide reduction and the allosteric effector sites that regulate the specificity and turnover rate. R2 contains the diferric-tyrosyl (Y(*)) radical cofactor that initiates nucleotide reduction by a putative long-range proton-coupled electron transfer (PCET) pathway over 35 A. This pathway is thought to involve specific amino acid radical intermediates (Y122 to W48 to Y356 within R2 to Y731 to Y730 to C439 within R1). In an effort to study radical initiation, R2 (375 residues) has been synthesized semisynthetically. R2 (residues 1-353), attached to an intein and a chitin binding domain, was constructed, and the protein was expressed (construct 1). This construct was then incubated with Fe(2+) and O(2) to generate the diferric-Y(*) cofactor, and the resulting protein was purified using a chitin affinity column. Incubation of construct 1 with 2-mercaptoethanesulfonic acid (MESNA) resulted in the MESNA thioester of R2 (1-353) (construct 2). A peptide containing residues 354-375 of R2 was generated using solid-phase peptide synthesis where 354, a serine in the wild-type (wt) R2, was replaced by a cysteine. Construct 2 and this peptide were ligated, and the resulting full-length R2 was separated from truncated R2 by anion-exchange chromatography. The purified protein had a specific activity of 350 nmol min(-1) mg(-1), identical to the same protein generated by site-directed mutagenesis when normalized for Y(*). As a first step in studying the radical initiation by PCET, R2 was synthesized with Y356 replaced by 3-nitrotyrosine (NO(2)Y). The protein is inactive (specific activity 1 x 10(-4) that of wt-R2), which permitted a determination of the pK(a) of the NO(2)Y in the R1/R2 complex in the presence of substrate and effectors. Under all conditions, the pK(a) was minimally perturbed. This has important mechanistic implications for the radical initiation process.

Graft copolymerization of ethyl acrylate onto cellulose using ceric ammonium nitrate as initiator in aqueous medium.

Ceric ammonium nitrate (CAN) in the presence of nitric acid has been used as efficient initiator for graft copolymerization of the ethyl acrylate onto cellulose at 35.0 +/- 0.1 degrees C. Graft copolymerization of ethyl acrylate onto cellulose has taken place through the radical initiation process. The graft yield and other grafting parameters have been evaluated by varying concentration of ethyl acrylate from 2.5 x 10(-1) to 15.0 x 10(-1) mol dm(-3) and ceric ammonium nitrate from 5.0 x 10(-3) to 25.0 x 10(-3) mol dm(-3) at constant concentration of the nitric acid (8.0 x 10(-2) mol dm(-3)). The rate of graft copolymerization has shown 1.5 order with respect to the concentration of the ceric ammonium nitrate. The graft copolymerization data obtained at different temperatures were used to calculate the energy of activation, which has been found to be 28.9 kJ mol(-1) within the temperature range from 20 to 50 degrees C. The effect of addition of cationic and anionic surfactants on graft copolymerization has also been studied. On the basis of the experimental observations, reaction steps have been proposed and a suitable rate expression for graft copolymerization has been derived.

Measurement of S-glutathionated hemoglobin in human erythrocytes by isoelectric focusing electrophoresis.

AbstractProtein thiol groups are susceptible to oxidation by reactive oxygen species (1). The occurrence of a specific thiol modification named protein S-glutathionation has been proposed to protect proteins from oxidative damage owing to its reversible characteristics (2–4). In addition, S-glutathionation modulates protein functions including enzyme activity (4–5), cytoskeletal protein strength (6), hemoglobin-gelling activity (7), and chaperon activity (8). Because an increase in cellular glutathione (GSSG) level is correlated with the formation of S-glutathionated protein, a mixed-disulfide exchange reaction has been proposed to be responsible for this protein modification (2–5,9–10). However, glutathione (GSH) modified proteins are also formed under a circumstance without significant change in GSSG level (11–12), and a radical-initiated process has therefore also been proposed (3). S-Gluthionated hemoglobin formation owing to oxidative stress has been noted in the red blood cells from different species (13–15). There are a total of six cysteine residues in the human hemoglobin molecule, but two of them (β93 residues) are highly reactive (16) and can form mixed disulfide with GSH (14). However, the location of reactive cysteines in hemoglobin varies in different animal species. For example, the cysteines in chicken α-hemoglobin are more active than those in β hemoglobin (15).KeywordsIodoacetic AcidMixed DisulfideErythrocyte HemolysateSample StripProtein Thiol GroupThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Release of iodine in the atmospheric oxidation of alkyl iodides and the fates of iodinated alkoxy radicals

This paper describes a study of the products of the Cl-atom-initiated oxidation of three alkyl iodides, RI=CH 3I, C 2H 5I, and 2-C 3H 7I, carried out in synthetic air at atmospheric pressure and at room temperature. Fourier-transform infrared spectroscopy was used to follow the decay of reactants and subsequent formation of products. The primary step proceeds via two channels, one of which yields HCl and an iodinated alkyl radical, and the other I atoms and an alkyl chloride. Quantitative analysis of the product yields, together with an assessment of the formation of HCl in secondary processes, allowed the fractional branching into the two channels to be calculated. The channel yielding HCl from RI constitutes a fraction 0.59, 0.93, and 0.68 for R=CH 3, C 2H 5, and 2-C 3H 7. The iodinated alkyl radical forms first a peroxy, and then an alkoxy, radical in the presence of air. The final products CH 2O, CH 3CHO, and CH 3COCH 3 were observed as expected for the decomposition of these radicals with RI=CH 3I, C 2H 5I, and 2-C 3H 7I, and the fractions of the alkoxy radicals fragmenting to the carbonyl compounds were 0.88, 0.57, and 0.86, respectively. Atomic iodine is formed concomitantly with the carbonyl species, so that these fractions also indicate the yield of I atoms in the secondary process. Alternative reaction pathways for the iodinated alkoxy radicals, in particular reaction with O 2, are evaluated and discussed. The yields of I atoms in the primary and secondary steps, taken in combination with kinetic data, make it possible to estimate the contribution of the Cl-initiated oxidation of the alkyl halides to I-atom production in the atmosphere (and, making certain assumptions, the analogous contribution from OH-initiated oxidation). Radical-initiated processes might augment the photolytic yield of I atoms from simple alkyl iodides: the maximum enhancements lie between 5% (CH 3I) and more than 30% (2-C 3H 7I).

Lipid oxidation and antioxidants

Lipid oxidation is a radical-initiated process leading to oxidative deterioration of polyunsaturated fatty acids. It is involved in the modification of low density lipoprotein and thought to play a role in the pathogenesis of atherosclerosis. Dietary antioxidants such as tocopherols, carotenoids, or flavonoids inhibit lipid oxidation and thus may contribute to the protection against cardiovascular diseases. In vitro studies provided evidence that dietary and endogenous antioxidants interact with each other. Such additive or even synergistic effects might provide additional protection against lipid oxidation.

Biomimetic oxidation studies. 10. Cyclohexane oxidation reactions with active site methane monooxygenase enzyme models and t-butyl hydroperoxide in aqueous micelles: Mechanistic insights and the role of t-butoxy radicals in the CH functionalization reaction

The oxidation of cyclohexane (CyH) in an aqueous micelle system with t-butyl hydroperoxide (TBHP) in the presence of biomimetic methane monooxygenase enzyme complexes, [Fe 2O( η 1-H 2O)( η 1-OAc)(TPA) 2] 3+, 1, [Fe 2O( η 1-H 2O)( η 1-OAc)(BPIA) 2] 3+, 2, and O 2, was studied and found to provide cyclohexanol (CyOH), cyclohexanone (CyONE), and cyclohexyl- t-butyl peroxide (CyOO t-Bu). The mechanistic aspects of this oxidation reaction in aqueous micelles were studied and included the effects of the surfactant concentration, cetyltrimethylammonium hydrosulfate; concentration of CyH and TBHP; and a trapping reagent, CCl 4. Several factors allowed us to conclude that a t-butoxy radical ( t-BuO) was generated from the favorable redox chemistry of the biomimetic complexes with TBHP, and was responsible for the free radical initiation process with CyH in the aqueous micelle system.

Free Radical-Induced Tandem Base Damage in DNA Oligomers

A new tandem base lesion has been identified in two DNA oligomers, namely d(GpT) and d(CpGpTpA), exposed to X-irradiation in deoxygenated aqueous solution. In this lesion the C6 carbon atom of thymine is hydroxylated and a covalent link is formed between the C5 carbon atom of thymine and the C8 carbon atom of the adjacent guanine base. In addition, further evidence in the form of mass spectrometric data is presented confirming the structures of previously reported tandem base lesions that are produced by ionizing radiation in the presence of oxygen. New data is presented on the prevalence of a previously reported tandem base lesion in which the methyl carbon atom of thymine is covalently linked to the C8 carbon atom of the adjacent guanine base. The free radical-initiated processes by which tandem base damages are generated are discussed. To date four different radiation-induced tandem base lesion have been identified. The evidence suggests that tandem base damage is a significant component of free radical-induced DNA damage.

38] Antioxidant effects of carotenoids in Vivo and in Vitro: An overview

This chapter discusses the antioxidant effects of carotenoids in vivo and in vitro state. It describes their role as biological antioxidants in radical-initiated processes, both in vitro and in vivo. Biological antioxidants are compounds that protect biological systems against the potentially harmful effects of processes or reactions that can cause excessive oxidations. Several mechanisms have been suggested for carotenoid protection in biological systems, which include the deactivation of electronically activated species, such as singlet oxygen and the deactivation of reactive chemical species, such as peroxyl or alkoxyl radicals that can be generated within cells and might otherwise initiate harmful oxidative reactions. Antioxidant action is well documented in a number of in vitro studies, including lipids in homogeneous solutions, liposomes, isolated membranes, and intact cells. This antioxidant activity is related to the chemical structures of the carotenoids and it has been reported to be particularly effective at low oxygen tensions. Antioxidant action of the molecules seems a likely basis for the effects of carotenoids, and this chapter evaluates the available evidence for this explanation of in vivo biological activity.

Glutathione catabolism by the ischemic rat kidney

The glutathione (GSH) content of rat kidney decreases after cessation of blood flow, falling to 40% of control levels 35 min after renal artery occlusion [R. C. Scaduto, Jr., V. H. Gattone II, L. W. Grotyohann, J. Wertz, and L. F. Martin. Am. J. Physiol. 255 (Renal Fluid Electrolyte Physiol. 24): F911-F921, 1988]. Renal GSH levels remained depressed for at least 2 h after resumption of blood flow. Because GSH functions in the removal of free radicals, and lipid peroxidation is a free radical-initiated process that occurs in the ischemic kidney, we investigated the fate of this GSH pool in the ischemic kidney. Using high-performance liquid chromatography to measure thiols, we found the loss of GSH to be associated with a stoichiometric accumulation of cysteine in the kidney. Moreover, preischemic labeling of the renal GSH pool with 35S led to accumulation of [35S]cysteine during ischemia that had the same specific activity as that of tissue GSH. Formation of cysteine during ischemia was suppressed in rats pretreated with acivicin, an inhibitor of gamma-glutamyltransferase (gamma-GT), although the degree of suppression was small in comparison to the extent of gamma-GT inhibition. During the initial 2 min of blood reflow after ischemia, tissue cysteine returned to control levels, and a transient increase in the cysteine content of renal venous blood was observed. After ischemia, renal GSH levels remained depressed, but postischemic GSH levels could be increased by administration of N-acetylcysteine during the ischemic period.(ABSTRACT TRUNCATED AT 250 WORDS)