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PubMed1992

Degradation of phenol and phenolic compounds by Pseudomonas putida EKII.

The phenol-degrading strain Pseudomonas putida EKII was isolated from a soil enrichment culture and utilized phenol up to 10.6 mM (1.0 g.l-1) as the sole source of carbon and energy. Furthermore, cresols, chlorophenols, 3,4-dimethylphenol, and 4-chloro-m-cresol were metabolized as sole substrates by phenol-grown resting cells of strain EKII. Under conditions of cell growth, degradation of these xenobiotics was achieved only in co-metabolism with phenol. Phenol hydroxylase activity was detectable in whole cells but not in cell-free extracts. The specificity of the hydroxylating enzyme was found during transformation of cresols and chlorophenols: ortho- and meta-substituted phenols were degraded via 3-substituted catechols, while degradation of para-substituted phenols proceeded via 4-substituted catechols. In cell-free extracts of phenol-grown cells a high level of catechol 2,3-dioxygenase as well as smaller amounts of 2-hydroxymuconic semialdehyde hydrolyase and catechol 1,2-dioxygenase were detected. The ring-cleaving enzymes were characterized after partial purification by DEAE-cellulose chromatography.

Biodegradation, Environmental↗

PubMed2003

Enhancing volatile phenol concentrations in wine by expressing various phenolic acid decarboxylase genes in Saccharomyces cerevisiae.

Phenolic acids, which are generally esterified with tartaric acid, are natural constituents of grape must and wine and can be released as free acids (principally p-coumaric, caffeic, and ferulic acids) by certain cinnamoyl esterase activities during the wine-making process. Some of the microorganisms present in grape can metabolize the free phenolic acids into 4-vinyl and 4-ethyl derivatives. These volatile phenols contribute to the aroma of wine. The Saccharomyces cerevisiae phenyl acrylic acid decarboxylase gene (PAD1) is steadily transcribed, but its encoded product, Pad1p, shows low activity. In contrast, the phenolic acid decarboxylase (PADC) from Bacillus subtilis and the p-coumaric acid decarboxylase (PDC) from Lactobacillus plantarum display substrate-inducible decarboxylating activity in the presence of phenolic acids. In an attempt to develop wine yeasts with optimized decarboxylation activity on phenolic acids, the padc, pdc, and PAD1 genes were cloned under the control of S. cerevisiae's constitutive phosphoglyceratekinase I gene promoter (PGK1(P)()) and terminator (PGK1(T)()) sequences. These gene constructs were integrated into the URA3 locus of a laboratory strain of S. cerevisiae, Sigma1278b. The overexpression of the two bacterial genes, padc and pdc, in S. cerevisiae showed high enzyme activity. However, this was not the case for PAD1. The padc and pdc genes were also integrated into an industrial wine yeast strain, S. cerevisiae VIN13. As an additional control, both alleles of PAD1 were disrupted in the VIN13 strain. In microvinification trials, all of the laboratory and industrial yeast transformants carrying the padc and pdc gene constructs showed an increase in volatile phenol formation as compared to the untransformed host strains (Sigma1278b and VIN13). This study offers prospects for the development of wine yeast starter strains with optimized decarboxylation activity on phenolic acids and the improvement of wine aroma in the future.

Bacillus subtilis↗

PubMed2000

An examination of the phenol-croton oil peel: part IV. Face peel results with different concentrations of phenol and croton oil.

In Part IV of this examination of the phenol-croton oil peel, the author presents peeling solutions using phenol in concentrations between 16% and 50% as the carrier for croton oil. Previously, in Part I, the author showed that phenol alone in concentrations of less than 50% has no significant peeling effect on the skin in the absence of taping. All of these formulas are dependent on the addition of croton oil for their peeling action. A topographic map of the face is presented that divides the face into the zones that the author believes are best treated with different strengths of croton oil. Five patients peeled between late 1992 and late 1995 were chosen as examples to illustrate the effect of different strengths of croton oil between 0.25% and 2.78%. The author has documented their immediate postoperative course photographically to show the effect of the different concentrations. It is clinically apparent that peels using croton oil between 0.25% and 0.5% generally heal within 7 days; peels between 0.6% and 1.0% usually heal within 9 or 10 days, and peels using concentrations higher than 1% heal later and have some risk of pigmentation loss. Peels using croton oil concentrations at 2% and above almost always have pigmentation loss and have healing delays in areas other than the thick skin of the lower nose and perioral area. The practical clinical formulas distributed at the time of the presentation of this article at the 1996 Annual Meeting of the American Society for Aesthetic Plastic Surgery in Orlando, Florida, entitled "Heresy Phenol Formulas--1996," are provided here. These have been used in both the United States and Europe over the past few years. A metric standard for drop size is suggested at 0.04 ml. This relates to the drop size used clinically over the years to measure croton oil. The adoption of this unit will make formulas around the world easier to calculate and compare. The author has produced a metric formula using the suggested standard size drop for croton oil. This uses 35% phenol as the carrier and provides the same range of treatment dilutions as the 1996 "Heresy Phenol Formulas." The need for research into "carriers" and solvents for croton oil is pointed out. Despite what is not known about how it works, the combination of croton seed extract and phenol has been a success story in providing facial rejuvenation from the 1920s to the present. The croton oil-phenol peel in its many formulas still sets the standard for facial rejuvenation.

Chemexfoliation↗

PubMed1999

Phenol degradation by an enterobacterium: a Klebsiella strain carries a TOL-like plasmid and a gene encoding a novel phenol hydroxylase.

Although phenol catabolism is described for many different microorganisms, there is no example for such a pathway in an enterobacterial strain. Here we characterize a Klebsiella oxytoca strain that grows on phenol as the only source of carbon and energy. As the key enzyme of phenol degradation, phenol hydroxylase was purified to apparent homogeneity. Compared with other phenol hydroxylases, the Klebsiella enzyme differs with respect to several properties: (i) SDS-PAGE and gel-filtration analysis of the purified protein revealed that the enzyme is a monomer with a molecular mass of 156 kDa; (ii) steady-state kinetic measurements resulted in a K(m) value of 0.22 mM for phenol; and (iii) the enzyme is both dependent on NADPH/FAD and sensitive to EDTA. Further degradation of catechol, the reaction product of phenol hydroxylase, may occur via the effective meta-fission pathway often located on TOL or TOL-like plasmids. Such a plasmid was prepared from the Klebsiella strain and further characterized. The given data demonstrate that the isolated strain exhibits all characteristics of an efficient phenol-degrading microorganism.

Biodegradation, Environmental↗

PubMed1989

Iron absorption and phenolic compounds: importance of different phenolic structures.

The phenolic compounds (phenolic monomers, polyphenols, tannins) are considered to interfere with iron absorption by complex formation with iron in the gastro-intestinal lumen, making the iron less available for absorption. Very little is known about the extent to which different types of phenolic compounds of different size and chemical structure inhibit iron absorption. The relationship between iron absorption and the amount and type of phenolic compounds was studied by the extrinsic tag method. The aims of the studies were as follows: (i) To study the effect of small phenolic compounds with different hydroxylation patterns (gallic acid, catechin, chlorogenic acid) on iron absorption, (ii) To study the effect of different amounts of a hydrolysable tannin containing ten gallic acid residues (tannic acid) on iron absorption. (iii) To study the degree of inhibition of iron absorption by some foods and beverages (oregano, spinach, coffee and tea) in relation to their respective content of iron-binding phenolic groups, measured by a newly developed method. The inhibition of iron absorption by tannic acid was strongly dose-related. The smallest amount (5 mg) inhibited absorption by 20 per cent, 25 mg by 67 per cent and 100 mg by 88 per cent. Gallic acid inhibited iron absorption to the same extent as tannic acid, per mol galloyl groups, whereas no inhibition was observed when catechin was added to the test meal. Chlorogenic acid inhibited iron absorption to a lesser extent. Oregano and tea inhibited iron absorption in proportion to their respective content of galloyl groups, whereas the inhibitory effect of spinach was less marked. The inhibiting effect of coffee was explained mainly by its content of galloyl groups, but also by some other factor, probably chlorogenic acid. It is concluded that the content of iron-binding galloyl groups might be a major determinant of the inhibitory effect of phenolic compounds on iron absorption from the diet, whereas the phenolic catechol groups seem to be of minor importance. The results further suggest that the group of condensed tannins do not interfere with iron absorption.

Absorption↗

PubMed1964

MICROBIAL METABOLISM OF AROMATIC COMPOUNDS. I. DECOMPOSITION OF PHENOLIC COMPOUNDS AND AROMATIC HYDROCARBONS BY PHENOL-ADAPTED BACTERIA.

Tabak, Henry H. (Robert A. Taft Sanitary Engineering Center, Cincinnati, Ohio), Cecil W. Chambers, and Paul W. Kabler. Microbial metabolism of aromatic carbon compounds. I. Decomposition of phenolic compounds and aromatic hydrocarbons by phenol-adapted bacteria. J. Bacteriol. 87:910-919. 1964.-Bacteria from soil and related environments were selected or adapted to metabolize phenol, hydroxy phenols, nitrophenols, chlorophenols, methylphenols, alkylphenols, and arylphenols when cultured in mineral salts media with the specific substrate as the sole source of carbon. A phenol-adapted culture (substrate-induced enzyme synthesis proven) was challenged in respirometric tests with 104 related compounds; probable significant oxidative activity occurred with 65. Dihydric phenols were generally oxidized; trihydric phenols were not. Cresols and dimethylphenols were oxidized; adding a chloro group increased resistance. Benzoic and hydroxybenzoic acids were oxidized; sulfonated, methoxylated, nitro, and chlorobenzoic acids were not; m-toluic acid was utilized but not the o- and p-isomers. Benzaldehyde and p-hydroxybenzaldehyde were oxidized. In general, nitro- and chloro-substituted compounds and the benzenes were difficult to oxidize.

Bacteria↗

PubMed1998

Turnover capacity of coprinus cinereus peroxidase for phenol and monosubstituted phenols

Coprinus cinereus peroxidase (CIP) and other peroxidases are susceptible to mechanism-based inactivation during the oxidation of phenolic substrates. The turnover capacity (defined as the molar or mass concentration of substrate oxidized per unit concentration of enzyme inactivated) of CIP was quantified for phenol and 11 monosubstituted phenols under conditions in which enzyme inactivation by mechanisms involving hydrogen peroxide alone were minimized. Turnover capacities varied by nearly 2 orders of magnitude (absolute values on the order of 10(5)-10(6) on a molar basis), depending on the substituent. On a mass basis, the enzyme consumption corresponding to the lowest turnover capacities is considerable and may influence the economic feasibility of proposed industrial applications of peroxidases. Within a range of substituent electronegativity values, molar turnover capacities correlated well (r2 = 0.89) with substituent effects quantified by radical sigma values and semiquantitatively with homolytic O-H bond dissociation energies of the phenolic substrates, suggesting that phenoxyl radical intermediates are probably involved in the suicide inactivation of CIP. The correlation range in each case did not include phenols with highly electron-withdrawing (nitro and cyano) substituents because they are not oxidized by CIP, nor phenols with highly electron-donating (hydroxy and amino) substituents because they led to virtually complete inactivation of the enzyme with minimal substrate removal. In the latter case we conclude that inactivation of CIP during the oxidation of hydroxy- and amino-substituted phenols occurs by a different mechanism than that of the other phenolic substrates.

Journal Article↗

PubMed1987

Effect of phenolic acids and phenolics from plant cell walls on rumenlike fermentation in consecutive batch culture.

Information on the interaction between mixed populations in the rumen and plant phenolics is required to fully elucidate the limitations of phenolic compounds on forage digestibility. The objective of this study was to examine the degradation of Italian ryegrass (Lolium multiflorum L.) hay incubated with mixed ruminal populations in consecutive batch culture (CBC) with or without phenolic acids or phenolic compounds extracted from plant cell walls. Each CBC consisted of a series of 10 cultures (3 replicates per culture) inoculated (10%, vol/vol) in sequence at 48-h intervals with microbial suspension from the previous set of cultures. All cultures were grown on a semidefined medium containing Italian ryegrass hay, and each CBC was initiated with an inoculum from the rumen. Rumenlike fermentation characteristics were maintained in control CBCs by repeated inoculum transfer. Treatment CBCs were transferred as described above, but cultures 5, 6, and 7 were incubated in the presence of trans-p-coumaric, cis-p-coumaric, or trans-ferulic acid or phenolics extracted from the cell walls of maize stem or barley straw. Mean apparent dry matter disappearance in control CBC cultures was 495 mg per g of hay, whereas the presence of phenolics reduced the initial dry matter disappearance by 6.3 to 25.6%. trans-p-Coumaric acid and, to a lesser extent, the phenolics from cell walls of maize stem were the most inhibitory compounds for dry matter disappearance and for the production of volatile fatty acids; trans-p-coumaric acid altered the molar ratio of acetate/propionate/butyrate. The CBC further showed variations in the ability of the rumen microbial population to adapt to phenolic compounds.

Animals↗

PubMed1988

Thiol- and pH-modulated slow conformational changes and cooperativity of phenol-binding sites in phenol hydroxylase.

Spectrophotometric titration of phenol hydroxylase (EC 1.14.13.7) with phenol indicated interacting sites for phenol binding. In the absence of added thiol, the cooperativity was positive up to a pH around 8.0 but negative at higher pH values. With added thiol-ethylenediaminetetraacetate, the cooperativity was negative at all investigated pH values. Conversely, a corresponding titration of an enzyme preparation that had been selectively modified in its two most reactive SH groups indicated positive cooperativity at all studied pH values. This selective modification affects the activity of the enzyme to a very minor degree, in contrast to more extensive SH blocking, which displaces flavin adenine dinucleotide with a corresponding loss of activity [Neujahr, H. Y., & Gaal, A. (1975) Eur. J. Biochem. 58, 351-357]. The reactivity of SH groups in the enzyme was significantly decreased after turnover. Thiol treatment restored it to that of the native enzyme. Adding phenol prior to reduced nicotinamide adenine dinucleotide phosphate (NADPH) in the assay of phenol hydroxylase gave immediate linearity and higher initial rates than when NADPH was added first. In the absence of added thiol, there was then a shift of the pH optimum. The results indicate slow conformational changes limiting the rate of the overall reaction. The two most reactive SH groups of phenol hydroxylase, though not participating in any obvious redox reactions, are important for these slow conformational changes and for the cooperativity of phenol-binding sites, wherein the anionic S- forms may be involved (pKa for cysteine is 8.35).

Binding Sites↗

PubMed1993

Conservation of regulatory and structural genes for a multi-component phenol hydroxylase within phenol-catabolizing bacteria that utilize a meta-cleavage pathway.

Pseudomonas sp. strain CF600 can degrade phenol and some of its methylated derivatives via a plasmid (pVI150)-encoded pathway. The metabolic route involves hydroxylation by a multi-component phenol hydroxylase and a subsequent meta-cleavage pathway. All 15 structural genes involved are clustered in an operon that is regulated by a divergently transcribed transcriptional activator. The multi-component nature of the phenol hydroxylase is unusual since reactions of this type are usually accomplished by single component flavoproteins. We have isolated and analysed a number of marine bacterial isolates capable of degrading phenol and a range of other aromatic compounds as sole carbon and energy sources. Southern hybridization and enzyme assays were used to compare the catabolic pathways of these strains and of the archetypal phenol-degrader Pseudomonas U, with respect to known catabolic genes encoded by Pseudomonas CF600. All the strains tested that degraded phenol via a meta-cleavage pathway were found to have DNA highly homologous to each of the components of the multicomponent phenol hydroxylase. Moreover, DNA of the same strains also strongly hybridized to probes specific for pVI150-encoded meta-pathway genes and the specific regulator of its catabolic operon. These results demonstrate conservation of structural and regulatory genes involved in aromatic catabolism within strains isolated from diverse geographical locations (UK, Norway and USA) and a range of habitats that include activated sludge, sea water and fresh-water mud.

Base Sequence↗

PubMed1992

Carboxylation of phenylphosphate by phenol carboxylase, an enzyme system of anaerobic phenol metabolism.

Several lines of evidence indicate that the first step in the anaerobic metabolism of phenol is phenol carboxylation to 4-hydroxybenzoate; this reaction is considered a biological Kolbe-Schmitt carboxylation. A phenol carboxylase system was characterized by using a denitrifying Pseudomonas strain, K 172, which catalyzes an isotope exchange between 14CO2 and the carboxyl group of 4-hydroxybenzoate. The enzymatic isotope exchange activity (100 nmol min-1 mg-1 of protein) requires Mn2+ and K+. We show that this system also catalyzes the carboxylation of phenylphosphate (the phosphoric acid monophenyl ester) to 4-hydroxybenzoate and phosphate. The specific activity of phenylphosphate carboxylation at the optimal pH of 6.5 is 12 nmol of CO2 fixed min-1 mg-1 of protein. Phenylphosphate cannot be replaced by Mg(2+)-ATP and phenol. The carboxylase activity requires Mn2+ but, in contrast to the isotope exchange activity, does not require K+. The apparent Km values are 1.5 mM dissolved CO2 and 0.2 mM phenylphosphate. Several convenient assays for phenylophosphate carboxylation are described. The isotope exchange reaction and the net carboxylation reaction are catalyzed by the same oxygen-sensitive enzyme, which has a half-life in an air-saturated solution of less than 1 min. Both activities cochromatographed with a protein with a Mr of 280,000, and both activities were induced only after anaerobic growth on phenol. The carboxylation of phenylphosphate suggests that phenylphosphate itself is the physiological CO2 acceptor molecular of this novel CO2 fixation reaction. Alternatively, phenylphosphate could simulate the unknown natural precursor. It is suggested that the formation of an enzyme-bound phenolate anion from the activated phenolic compound is the rate-determining step in the carboxylation reaction.

Adenosine Triphosphate↗

PubMed1993

[The effects of two and five percent aqueous phenol on the cat tibial nerve in situ--the local anesthetic-like effect of aqueous phenol].

Phenol is well known as a neurolytic agent because of its denaturing property on protein, but many pain clinicians recognized that it has transient nerve blocking effect like local anesthetics in some cases. This investigation was planned to understand the local anesthetic like effect of phenol with the cat tibial nerve model, while its blood flow was kept intact. The tibial nerve was stimulated electrically every one second, and the compound action potentials of its A-fibers were recorded with an oscilloscope for two hours. Physiological saline solution (PSS), 2% lidocaine and 2% and 5% aqueous phenol were injected into the nerve fibers through a glass capillary tube. In the case of PSS, no remarkable change was recognized during the experiment. The action potentials were depressed to 26.5% of control value 10 minutes after injection in 2% lidocaine group and returned to control levels at the end of observation. In almost all cases of 5% aqueous phenol group the action potentials vanished soon after injection. Some interesting phenomena, the biphasic depression of the action potentials, were observed in 2% aqueous phenol group. The first depression was recognized soon after injection of 2% aqueous phenol, which was faster than that with the 2% lidocaine. After the transient recovery of the action potential, the second depression appeared after thirty minutes. This delayed depression was considered to be due to circulatory damage of the nerve fibers by phenol.

Anesthetics, Local↗

PubMed2003

Soluble and wall-bound phenolics and phenolic polymers in Musa acuminata roots exposed to elicitors from Fusarium oxysporum f.sp. cubense.

The accumulation of soluble and wall-bound phenolics and phenolic polymers in Musa acuminata roots exposed to cell wall-derived elicitor from the pathogen, Fusarium oxysporum, f.sp. cubense, race four, was investigated. The root tissue from the banana cultivar "Goldfinger" was found to respond strongly and rapidly towards the elicitor through the increased synthesis of phenolic compounds. Following elicitation, the conjugated and non-conjugated phenolic metabolites in the induced root tissue were extracted and quantified. Induced phenolic synthesis was rapid and reached near maximum values after 16 h. High-performance liquid chromatography revealed both compositional and quantitative differences between induced phenolics (p-coumaric, ferulic, and sinapic acids) and those constitutively present (p-coumaric- and ferulic acid). In addition, vanillic acid was found in the ester-bound fraction and protocatechuic acid in the cell-wall bound fraction of elicited tissue. The deposition and accumulation kinetics of polymerized phenolic monomers as lignin and lignin-like polymers was quantified over a time period of 0-36 h and found to reach maximum values after 24 h. Ionization difference UV spectra of lignin indicated compositional differences in the newly synthesized lignin fraction and correlated with increased concentrations of ferulic acid and sinapic acids esters. The results show that the increased flux through the phenylpropanoid pathway resulted in the synthesis of cinnamic acid and benzoic acid derivatives that were esterified and incorporated into the cell wall fraction as part of the anti-microbial defenses activated in the root tissue.

Biopolymers↗

PubMed1982

Mutagenicity testing in the Salmonella typhimurium assay of phenolic compounds and phenolic fractions obtained from smokehouse smoke condensates.

Smokehouse smoke, which is used for flavouring meat products, was investigated for its mutagenic activity in the Salmonella typhimurium assay. We were chiefly concerned with the fractions free of polycyclic aromatic hydrocarbons but containing phenol compounds, which are responsible for the preservative and aromatizing properties of the smoke. The most abundantly occurring phenol compounds (phenol, cresols, 2,4-dimethylphenol, brenzcatechine, syringol, eugenol, vanilline and guaiacol) gave negative results when they were tested for mutagenicity at five concentrations up to 5000 micrograms/plate, with and without S-9 mix, using five strains of S. typhimurium. Even when phenol was further investigated in a variety of test conditions, no induction of his+ revertants was observed. When smokehouse smoke was condensed and fractionated the majority of the various phenolic fractions also gave negative results when tested at five concentrations using five strains of S. typhimurium. However there was a slight increase in the number of revertants in a few cases. The presence in the phenolic fractions of very small amounts of mutagenic impurities, the nature of which needs further investigation, cannot be excluded. These results support the further development of non-hazardous smoke-aroma preparations, based on the phenolic components of smokehouse smoke.

Animals↗

PubMed2002

Phenolic removal in olive oil mill wastewater by strains of Pleurotus spp. in respect to their phenol oxidase (laccase) activity.

The ability of several Pleurotus spp. strains to remove phenolic compounds from an olive oil mill wastewater (OMW) was studied. All strains tested in this work were able to grow in OMW without any addition of nutrients and any pre-treatment, except sterilization. High laccase activity was measured in the growth medium, while 69-76% of the initial phenolic compounds were removed. The black color of OMW became yellow-brown and brighter as the strains grew. The lowest phenolic concentrations were reached after 12/15 days. A decrease of the phytotoxicity, as described by the parameter Germination Index, was noticed in the OMW treated with some Pleurotus spp strains, although this decrease was not proportional to the phenolic removal. A new parameter, namely Phenol-toxicity Index, was considered in the present paper. Using this parameter it was found that the remaining phenolics and/or some of the oxidation products of the laccase reaction in the treated OMW were more toxic than the original phenolic compounds.

Biodegradation, Environmental↗

PubMed2005

Moving a phenol hydroxyl group from the surface to the interior of a protein: effects on the phenol potential and pK(A).

De novo protein design and electrochemistry were used to measure changes in the potential and pK(A) of a phenol when its OH group is moved from a solvent-exposed to a sequestered protein position. A "phenol rotation strategy" was adopted in which phenols, containing a SH in position 4, 3, or 2 relative to the OH group, were bound to a buried protein site. The alpha(3)C protein used here is a tryptophan to cysteine variant of the structurally defined alpha(3)W protein (Dai et al. (2002) J. Am. Chem. Soc. 124, 10952-10953). The protein characteristics of alpha(3)C and the three mercaptophenol-alpha(3)C (MP-alpha(3)C) proteins are shown to be close to those of alpha(3)W. Moreover, the phenol OH group is fully solvent exposed in 4MP-alpha(3)C and more sequestered in 3MP-alpha(3)C and 2MP-alpha(3)C. Here we compare the redox properties of the three mercaptophenols when bound to alpha(3)C and to cysteine free in water. The pK(A) and E(peak) values are essential identical when 4MP is ligated to alpha(3)C relative to when it is free in solution. In contrast, these values are increased in 3MP-alpha(3)C and 2MP-alpha(3)C relative to the solvated compounds. The E(peak) vs pH plots all display a approximately 59 mV/pH unit dependence. We conclude that interactions with the OH group dominate the phenol redox characteristics. In 3MP-alpha(3)C and 2MP-alpha(3)C, hydrogen bonds between the protein and the bound phenols appear to either stabilize the reduced phenol or destabilize the radical, relative to the aqueous buffer, raising the potential by 0.11 and 0.12 V, respectively.

Amino Acid Sequence↗

PubMed2005

Contribution of the intramolecular hydrogen bond to the shift of the pKa value and the oxidation potential of phenols and phenolate anions.

Intramolecularly OHO[double bond, length as m-dash]C hydrogen bonded phenols, 2-HO-C6H2-3,5-(t-Bu)2-CONH-t-Bu (1-OH), 2-HO-C6H2-5-t-Bu-1,3-(CONH-t-Bu)2 (2-OH) and 2-HO-C6H2-3,5-(t-Bu)2-NHCO-t-Bu (4-OH), were synthesized and their phenolate anions were prepared as tetraethylammonium salts (-1O-(NEt4+), 2-O-(NEt4+) and 4-O-(NEt4+)) with intramolecular NHO(oxyanion) hydrogen bonds. 4-HO-C(6)H(2)-3,5-t-Bu(2)-CONH-t-Bu (3-OH) and its phenolate anion, 3-O-(NEt4+), were synthesized as non-hydrogen bonded references. The presence of intramolecular hydrogen bonds was established through the crystallographic analysis and/or (1)H NMR spectroscopic results. Intramolecular NHO(phenol) hydrogen bonds shift the pK(a) of the phenol to a more acidic value. The results of cyclic voltammetry show that the intramolecular OH...O=C hydrogen bond negatively shifts the oxidation potential of the phenol. In contrast, the intramolecular NHO(oxyanion) hydrogen bond positively shifts the oxidation potential of the phenolate anion, preventing oxidation. These contributions of the hydrogen bond to the pKa value and the oxidation potentials probably play an important role in the formation of a tyrosyl radical in photosystem II.

Anions↗

PubMed1988

Effect of phenol and halogenated phenols on energy transfer reactions of rat liver mitochondria.

The in vitro effects of phenol and p-halogenated phenols on mitochondrial energy transfer reactions were examined using isolated rat liver mitochondria. The relationship between physiochemical properties of phenolic compounds and their effects on mitochondria were studied. Phenol and p-halogenated phenols induced the release of K+ ions from mitochondria, suggesting a change in permeability to K+ ions. A decrease in the respiratory control index, an increase in K+ release and stimulation of latent ATPase activity were observed with these compounds in the descending order of p-iodophenol, p-bromophenol, p-chlorophenol, p-fluorophenol and phenol. The concentrations of the phenolic compounds resulting in fifty percent inhibition of the respiratory control index and those resulting in fifty percent release of K+ ions significantly correlated with Hammett's substituent constant (sigma) and the hydrophobic binding constant (pi) of the compounds.

Adenosine Triphosphatases↗