Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “GALLIC ACID”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 685 records · Page 38Linked to original sources
PubMed1990

Trypanosoma cruzi: a possible control of transfusion-induced Chagas' disease by phenolic antioxidants.

The following phenolic antioxidant food additives were evaluated against Trypanosoma cruzi epimastigotes: BHT, BHA, gallic acid and its methyl, propyl, octyl, and lauryl esters, 2,4-di-tert-butyl-6-(4-methoxybenzyl)-phenol, 4,4'-isopropilidenediphenol, and protocatechuic acid and its ethyl ester. The inhibition of the respiration; the changes in motility, shape, and lysis of the parasites; and the human blood hemolysis caused by these chemicals were studied. Human blood samples experimentally contaminated with 2000 or 150,000 trypomastigotes per milliliter were freed of parasites after treatment for 24 hr at 4 degrees C with 5 or 10 mM BHT (2,6-di-tert-butyl-4-hydroxytoluene), respectively. Consequently, BHT and other phenolic compounds deserve further study to determine their role in preventing the transmission of Chagas' disease by blood transfusion.

Animals↗
PubMed2004

[Isolation and structure identification of grape seed polyphenols and its effects on oxidative damage to cellular DNA].

AIM: To isolate polyphenols from grape seeds and to evaluate their antioxidant effects. METHODS: Pure compounds were isolated by using Diaion HP20, Toyopearl HW40 chromatography repeatedly, as well as semi-preparative RP-HPLC, from ethyl acetate extract of grape seeds. IR, MS, NMR, CD, X-Ray crystal diffraction spectral analysis were used to identify the structures. The antioxidant effects of different type of structures were screened by reducing power and DPPH (alpha,alpha-diphenyl-beta-picrylhydrazyl) free radical scavenging tests. Then, SCGE (single cell gel-electrophoresis) technique was used to investigate the effects of these potent antioxidant phytochemicals on cellular DNA oxidative damage with mice spleen cells, damage was induced by H2O2. RESULTS: Eleven compounds were obtained including 3 novel structures, viniferones A, B and C. Proanthocyanidin B4, catecin, epicatechin and gallic acid showed strong antioxidant power, and at lower concentration (10 micromol x L(-1), 25 micromol x L(-1)), they can prevent cellular DNA damage, while 150 micromol x L(-1) catechin induced damage by itself. CONCLUSION: Viniferones A, B and C were reported for the first time. That polyphenols investigated were shown to be good cellular DNA oxidative damage-preventing phytochemicals at lower concentration, could be used to explain the nutrient effect of grape seed polyphenols at certain degree. At the same time, higher concentration of polyphenols can induce oxidative damage, suggesting that dose is one factor to determine the nutrient effects.

Animals↗
PubMed2006

Effects of the aerial parts of Orostachys japonicus and its bioactive component on hepatic alcohol-metabolizing enzyme system.

In the course of screening medicinal plants that modulate hepatic alcohol-metabolizing enzymes and lipid peroxidation, effects of the methanol extract (ME) of Orostachys japonicus and its major bioactive compound, gallic acid (GA), were investigated in rats treated with 10% ethanol solution for 6 weeks. The ME and GA greatly enhanced the activities of hepatic alcohol dehydrogenase (ADH), the microsomal ethanol-oxidizing system (MEOS), and aldehyde dehydrogenase (ALDH) in a dose-dependent manner, but had no effect on catalase. The hepatic lipid peroxide level increased by ethanol administration was moderately reduced by treatment with ME or GA. The results suggest that the detoxification of hepatic alcohol by O. japonicus ME under our experimental conditions was due to the enhanced activities of the alcohol-oxidizing enzymes, ADH, MEOS, and ALDH. In addition, GA may be partly responsible for the effects.

Alcohol Dehydrogenase↗
PubMed2006

Automatic method for the determination of Folin-Ciocalteu reducing capacity in food products.

In the present work, an automatic flow procedure based on multi-syringe flow injection analysis was developed for the assessment of Folin-Ciocalteu reagent (FCR) reducing capacity in several types of food products using gallic acid as the standard. Different strategies for mixing of sample and reagent were tested (continuous flow of FCR, merging zones, and intercalated zones approaches); lower reagent consumption and higher determination throughput were attained for the merging zones approach (100 microL of sample+100 microL of FCR). The application of the proposed method to compounds with known antioxidant activity (both phenolic and nonphenolic) and to samples (wines, beers, teas, soft drinks, and fruit juices) provided results similar to those obtained by the conventional batch method. The detection limit was 0.6 mg L-1, and the determination frequency was about 12 h-1. Good repeatability was attained (RSD<1.3%, n=10).

Antioxidants↗
PubMed2003

Cocoa has more phenolic phytochemicals and a higher antioxidant capacity than teas and red wine.

Black tea, green tea, red wine, and cocoa are high in phenolic phytochemicals, among which theaflavin, epigallocatechin gallate, resveratrol, and procyanidin, respectively, have been extensively investigated due to their possible role as chemopreventive agents based on their antioxidant capacities. The present study compared the phenolic and flavonoid contents and total antioxidant capacities of cocoa, black tea, green tea, and red wine. Cocoa contained much higher levels of total phenolics (611 mg of gallic acid equivalents, GAE) and flavonoids (564 mg of epicatechin equivalents, ECE) per serving than black tea (124 mg of GAE and 34 mg of ECE, respectively), green tea (165 mg of GAE and 47 mg of ECE), and red wine (340 mg of GAE and 163 mg of ECE). Total antioxidant activities were measured using the 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assays and are expressed as vitamin C equivalent antioxidant capacities (VCEACs). Cocoa exhibited the highest antioxidant activity among the samples in ABTS and DPPH assays, with VCEACs of 1128 and 836 mg/serving, respectively. The relative total antioxidant capacities of the samples in both assays were as follows in decreasing order: cocoa > red wine > green tea > black tea. The total antioxidant capacities from ABTS and DPPH assays were highly correlated with phenolic content (r2 = 0.981 and 0.967, respectively) and flavonoid content (r2 = 0.949 and 0.915). These results suggest that cocoa is more beneficial to health than teas and red wine in terms of its higher antioxidant capacity.

Antioxidants↗
PubMed2001

Lauryl gallate inhibits the activity of protein tyrosine kinase c-Src purified from human platelets.

The inhibitory effect of gallic acid (3,4,5-trihydroxybenzoic acid), and its ester derivatives methyl, propyl, octyl and lauryl has been tested on the tyrosine kinase activity of affinity purified c-Src from human platelets, using the artificial substrate Poly (Glu,Na,Tyr) 4:1. When tested as inhibitor of the autophosphorylation of the enzyme and the phosphorylation of the protein tyrosine phosphatase SHP-1 by c-Src, lauryl gallate was found to be a more potent inhibitor than other widely used protein tyrosine kinase (PTK) inhibitors such as genistein and herbimycin A. However, lauryl gallate did not inhibit the activity of the serine threonine kinases protein kinase A (PKA) and casein kinase II (CKII) from rat brain.

Animals↗
PubMed2001

Chemiluminescence of hemoglobin and identification of related compounds with the hemoglobin chemiluminescence in plasma.

A low level of chemiluminescence by hemoglobin (Hb) was detected in the reaction with H2O2 and hydrogen donors such as gallic acid and catechins. The photon intensity was affected by the ferric state of Hb (methemoglobin > oxyhemoglobin), and was roughly correlated with the radical-scavenging potential of catechins. We hypothesized the reversible activation reaction of Hb as the chemiluminescence mechanism of the H2O2/gallic acid/Hb system. It is indicated that the oxidized-Hb (Hb-OOH) formation was a chemiluminescence-rate-determining step and one-electron reduction by a hydrogen donor of the compound-I-type intermediate ([.XFeIV] = O) proved a chemiluminescence-specificity-determining step. Spectral analysis showed that the photon emission from the H2O2/gallic acid/Hb system was produced without singlet oxygen generation. The concentration dependence of photon intensity suggests a high consumption ratio of H2O2 leading to protection from H2O2 toxicity. Albumin was defined as a hydrogen donor by the isolation of chemiluminescent substance in plasma using this chemiluminescence system.

Catechin↗
PubMed2002

Hamamelitannin from Hamamelis virginiana inhibits the tumour necrosis factor-alpha (TNF)-induced endothelial cell death in vitro.

The tumour necrosis factor-alpha (TNF) inhibitory activity of hamamelitannin from Hamamelis virginiana was investigated by assessing the TNF-mediated EAhy926 endothelial cell death and adhesiveness to monocytes. Treatment of the cells by TNF (25 ng/ml) and actinomycin D (0.1ng/ml) resulted in significant DNA fragmentation (34+/-0.6, n=4) and cytotoxicity (97+/-4.5%, n=6) following treatment for 8 and 24h, respectively. One to 100 microM concentrations of hamamelitannin inhibited the TNF-mediated endothelial cell death and DNA fragmentation in a dose-dependent manner. One hundred % protection against TNF-induced DNA fragmentation and cytotoxicity was obtained for hamamelitannin concentrations higher than 10 microM. The protective effect of hamamelitannin was comparable with that of a related compound epigallocatechin gallate while gallic acid was a weak protective agent (<40% protection). EAhy926 endothelial cells upregulated (by 4- to 7-fold) the surface expression of intercellular adhesion molecule-1 (ICAM-1) and adhesiveness to monocytic U937 cells after treatment with TNF (0.5ng/ml) for 6 or 24h. Concentrations (1-100 microM) of hamamelitannin that inhibited the TNF-mediated cell death and DNA fragmentation, however, failed to inhibit the TNF-induced ICAM-1 expression and EAhy926 cell adhesiveness to U937 cells. Thus, hamamelitannin inhibits the TNF-mediated endothelial cell death without altering the TNF-induced upregulation of endothelial adhesiveness. The observed anti-TNF activity of hamamelitannin may explain the antihamorrhaegic use of H. virginiana in traditional medicine and its claimed use as a protective agent for UV radiation.

Apoptosis↗
PubMedDate not supplied

[Effect of media composition on properties of polydisulfide bioantioxidants].

Characteristics of polydisulfides of gallic acid (PDSG), 2-amino-4-nitrophenol (PDSANP), and biuret (PDSB) depending on the composition of the aqueous medium were studied. In contrast to PDSANP and PDSB, there was oxidation of PDSG with accumulation of products of polydisulfide transformation in the medium. The rate of PDSG autoxidation depended on pH, concentration of polydisulfide and buffers, and increased at high pH. The rate of oxidation significantly increased if addition of dimethylformamide and/or ethanol in the medium or solubilization of polydisulfide with cetyltrimethylammonium bromide, surface-active compound (SAC), prevented the association of PDSG. Decreasing pH of the solution and adding ovalbumin and/or Triton X-100 to the medium can decrease the rate of autoxidation of PDSG in aqueous medium. Exogenous H2O2 inhibited the oxidation of PDSG. The secondary structure of catalase was changed by PDSG. Electrical conductivity of PDSG and PDSANP solutions was studied. Possible mechanisms of PDSG autoxidation and polydisulfides-protein interaction due to forces of cooperative electrostatic interaction, thiol-disulfide exchanges and nucleophilic replacements were discussed.

Antioxidants↗
PubMed2000

Antioxidative effects of green tea polyphenols on free radical initiated and photosensitized peroxidation of human low density lipoprotein.

Antioxidative effects of the main polyphenolic components extracted from green tea leaves, i.e. (-)-epicatechin (EC), (-)-epigallocatechin (EGC), (-)-epicatechin gallate (ECG), (-)-epigallocatechin gallate (EGCG) and gallic acid (GA), against free radical initiated peroxidation of human low density lipoprotein (LDL) were studied. The peroxidation was initiated either thermally by a water-soluble initiator 2,2'-azobis(2-amidinopropane hydrochloride) (AAPH), or photochemically by a triplet sensitizer benzophenone (BP). The reaction kinetics was monitored by the uptake of oxygen and the depletion of alpha-tocopherol (TOH) presented in the native LDL. Kinetic analysis of the antioxidation process demonstrates that these green tea polyphenols are effective antioxidants against both AAPH-initiated and BP-photosensitized LDL peroxidation. The antioxidative action of the green tea polyphenols includes trapping the initiating and/or propagating peroxyl radicals with the activity sequence EC>EGCG>ECG>EGC>GA for the AAPH initiated peroxidation, and reducing the alpha-tocopheroxyl radical to regenerate alpha-tocopherol with the activity sequence of ECG>EC>EGCG>EGC>GA and ECG>EGCG>GA>EC>EGC for the AAPH-initiated and BP-photosensitized peroxidations respectively.

Antioxidants↗
PubMed1998

Growth-inhibitory effects of Galla Rhois-derived tannins on intestinal bacteria.

The growth-inhibitory activity of Galla Rhois-derived materials towards 17 intestinal bacteria was evaluated using an impregnated paper disc method. The biologically active components of Galla Rhois were characterized as the tannins methyl gallate (MG) and gallic acid (GA) by spectral analysis. The growth responses varied with bacterial strain tested. In the test using 10 mg disc-1, MG and GA produced a clear inhibitory effect on harmful bacteria such as Clostridium perfringens, Cl. paraputrificum, Eubacterium limosum, Bacteroides fragilis, Staphylococcus aureus and Escherichia coli. Methyl gallate showed no growth-inhibitory activity towards Bifidobacterium adolescentis or B. longum whereas the growth of B. bifidum, B. breve, B. infantis, B. animalis, B. thermophilum, Lactobacillus acidophilus, Lact. plantarum and Streptococcus faecalis was slightly affected. However, GA did not adversely affect the growth of the bifidobacteria and lactobacilli. At 5 mg disc-1, MG significantly inhibited the growth of Cl. perfringens and Cl. paraputrificum but did not affect the growth of the bifidobacteria and lactobacilli. At 1 mg disc-1, MG greatly inhibited the growth of Cl. perfringens alone. These results may be an indication of at least one of the pharmacological actions of Galla Rhois.

Anti-Bacterial Agents↗
PubMed2000

[Human thyroid peroxidase: inhibition of iodide ion and 3,3',5,5'-tetramethylbenzidine hydrolysis by phenol antioxidants].

A comparative kinetic study on the poly(gallic acid disulfide) (poly(DSGA)) inhibition of the iodide ion oxidation and on the 2-hydroxy-3,5-di-tert-butyl-N-phenylaniline (butaminophene) inhibition of 3,3',5,5'-tetramethylbenzidine (TMB) oxidation involving human thyroid peroxidase (hTPO) and horseradish peroxidase (HRP) was performed. The inhibition processes were characterized with the inhibition constants Ki and stoichiometric inhibition coefficients f, indicating the number of radical particles perishing on one inhibitor molecule. In the case of poly(DSGA), the Ki values for the I- oxidation were 0.60 and 0.04 microM, and the coefficients f were 13.6 and 16.5 for hTPO and HRP, respectively, which evidences the regeneration and high effectiveness of the polymeric inhibitor. In the case of butaminophene, the Ki values for TMB oxidation were 38 and 46 microM for hTPO and HRP, respectively. The coefficients f were 1.33 and 1.47, respectively, to reveal that butaminophene does not regenerate. The inhibition mechanisms for I- and TMB oxidation involving the two peroxidases are discussed.

Anions↗
PubMed2003

Polyphenolics in grape seeds-biochemistry and functionality.

Grape seeds are waste products of the winery and grape juice industry. These seeds contain lipid, protein, carbohydrates, and 5-8% polyphenols depending on the variety. Polyphenols in grape seeds are mainly flavonoids, including gallic acid, the monomeric flavan-3-ols catechin, epicatechin, gallocatechin, epigallocatechin, and epicatechin 3-O-gallate, and procyanidin dimers, trimers, and more highly polymerized procyanidins. Grape seed extract is known as a powerful antioxidant that protects the body from premature aging, disease, and decay. Grape seeds contains mainly phenols such as proanthocyanidins (oligomeric proanthocyanidins). Scientific studies have shown that the antioxidant power of proanthocyanidins is 20 times greater than vitamin E and 50 times greater than vitamin C. Extensive research suggests that grape seed extract is beneficial in many areas of health because of its antioxidant effect to bond with collagen, promoting youthful skin, cell health, elasticity, and flexibility. Other studies have shown that proanthocyanidins help to protect the body from sun damage, to improve vision, to improve flexibility in joints, arteries, and body tissues such as the heart, and to improve blood circulation by strengthening capillaries, arteries, and veins. The most abundant phenolic compounds isolated from grape seed are catechins, epicatechin, procyanidin, and some dimers and trimers.

Antioxidants↗
PubMedDate not supplied

Changes in intracellular concentrations of polyamines during apoptosis of HL-60 cells.

Possible changes in the intracellular concentrations of polyamines were investigated during the apoptosis of human promyelocytic leukemic HL-60 cells. Treatment of HL-60 cells with gallic acid and epigallocatechin gallate (EGCG) resulted in the rapid decline of the intracellular concentration of putrescine, whereas that of spermidine and spermine was not significantly changed during the first 3 hours after treatments. Irradiation with UVB also selectively reduced the intracellular concentration of putrescine. On the other hand, cytotoxic concentrations of anticancer agents, such as etoposide and doxorubicin, only marginally reduced the intracellular concentration of putrescine during the first 3 hours. A significant decline of putrescine was observed at later stages when DNA fragmentation became more prominent. Three normal human cells (gingival fibroblast, pulp cell, periodontal ligament fibroblast) and human tumor cell lines (squamous cell carcinoma, submandibular carcinoma, malignant malanoma, hepatoma), which showed higher resistance to apoptosis inducers, had significantly higher putrescine concentrations than HL-60 cells. These data suggest that the intracellular concentration of putrescine may be a useful marker for the apoptosis induction or the sensitivity of the cells to apoptosis inducers.

Antineoplastic Agents↗
PubMed2004

Peroxidase-catalyzed co-oxidation of 3,3',5,5'-tetramethylbenzidine in the presence of substituted phenols and their polydisulfides.

The steady-state kinetics of the horseradish peroxidase (HRP)-catalyzed oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) has been studied in the presence of 2-amino-4-nitrophenol (ANP), gallic acid (GA) or 4,4'-dihydroxydiphenylsulfone (DDS) and their polydisulfides poly(ADSNP), poly(DSGA), poly(DSDDS) at 20 degrees C in 10 mM phosphate buffer, pH 6.4, supplemented with 5-10% dimethylformamide. The second-order rate constants for the reactions of ANP, GA, poly(DSGA) and poly(DSDDS) with HRP-Compound I (k2) and Compound II (k3) have been determined at 25 degrees C in 10 mM phosphate buffer, pH 6.0 by stopped-flow spectrophotometry. ANP, GA and their polydisulfides strongly inhibited HRP-catalyzed TMB oxidation. Inhibition constants (Ki) and stoichiometric coefficients of inhibition (f) have been determined for these reactions. The most effective inhibitor was poly(DSGA) (Ki=1.3 microM, f=35.6). The oxidation of substrate pairs by HRP, i.e., TMB-DDS and TMB-poly(DSDDS) at pH 7.2 resulted in a approximately 8- and approximately 12-fold stimulation of TMB oxidation rates, respectively. The mechanisms of the HRP-catalyzed co-oxidation of TMB-phenol pairs are discussed.

Antioxidants↗
PubMed2005

[Effect of tea polyphenols on oxidative metabolism of polymorphonuclear neutrophils in healthy and obese people].

UNLABELLED: Obese people are at high risk for developing diabetes, dyslipidemia, hypertension, and cardiovascular diseases, which lead to an increased risk of mortality. Evidence for the potential role of oxidative stress in various diseases and pathophysiological processes suggests that the dietary intake and the therapeutic use of antioxidants may have positive health effects. The aim of the study was: 1) to investigate the ability of the major tea polyphenols: (-)-epigallocatechin gallate (EGCG), theaflavins (TF) and gallic acid (GA) to protect in vitro human neutrophils from oxidative damage induced by phorbol myristate acetate (PMA), 2) estimation the level of reactive oxygen species (ROS) production in obese patient depending on the red tea Pu-Erh drinking, 3) estimation inflammatory marker: CRP. MATERIAL AND METHODS: We tested 14 obese patients (aged 45+/-12 years, women, BMI=34+/-5.1 kg/m2). The inclusion criteria were based on physical examination, BMI, WHR, and the body composition examination based on bioimpedance method. PMA were isolated and oxidant production, in response to 1 microg/ml PMA, was characterized by the production of hydrogen peroxide, nitric oxide and chemiluminescence intensity. CRP level was assayed by the immunoturbidimetric test in serum. Control group consisted of healthy blood donors. RESULTS: Women consuming red tea revealed alteration in reactive oxygen species generation; the relative decrease of RFT was greater after 5 months than that after 1 month of treatment. A decrease in ROS generation after red tea consumption was accompanied by the decrease of ROS in response to tested compounds in normal cells. EGCG and TF showed similar potency in antioxidative activities. Tea polyphenols were not found to modulate CRP level in obese women. CONCLUSIONS: Tea may thus represent an important source of dietary antioxidants; there is need for more detailed studies to improve our understanding of the role of tea in reducing risk of major disease states.

Adult↗
PubMed2004

Cellular toxicity of catechin analogues containing gallate in opossum kidney proximal tubular (OK) cells.

A variety of catechins exist in green tea and Chinese rhubarb. It is also known that the green tea tannin mixture and its individual tannin components such as (-)-epicatechin 3-O-gallate (ECG) and (-)-epigallocatechin 3-O-gallate (EGCG) suppress renal failure in animals and inhibit the growth of mesangial cells. In addition, gallic acid (GA), a structural constituent of these catechins, induces apoptosis in tumor cell lines. However, the effects of catechins on renal tubular cells have not been investigated. In this experiment, the growth of opossum kidney proximal tubular (OK) cells was inhibited by GA (36.9 +/- 9.5%, p < 0.01) and EGCG (48.6 +/- 16.7%, p < 0.01) at 50 microM, and was almost completely inhibited by these compounds at concentrations over 100 microM. Furthermore, ECG inhibited the growth of OK cells at concentrations over 200 microM (52.6 +/- 16.5%, p < 0.01). The numbers of in situ end-labeled (ISEL) cells in cultures treated with GA at 25 and 50 microM, ECG at 100 and 200 microM, or EGCG at 25 microM were significantly less than those in the cultures treated with high-concentration EGCG (50 microM). In addition, exposure to 50 microM EGCG or 400 microM GA for 24 hr led to a significant increase in fragmented DNA, but ECG did not significantly induce DNA fragmentation compared to the control. These results suggest that EGCG induces mostly apoptosis in OK cells, but the cellular toxicity of GA involves both apoptosis and other mechanisms. Finally, ECG inhibits the growth largely via some mechanism other than apoptosis. This chemical-specific difference of cytotoxic pattern may be dependent on the combination of GA and basal catechin structures, or NADH oxidase (NOX) activity on the OK cell surface.

Animals↗
PubMed2005

Oxidation of tea extracts and tea catechins by molecular oxygen.

Tea polyphenols (PP) are known as potent antioxidants. At the same time, PP have been repeatedly reported to oxidize by molecular oxygen with the formation of active forms of oxygen. In this work, the Clark electrode technique was applied to study the kinetics of the autoxidation of tea extracts and individual tea PP as well as model PP, catechol, gallic acid, and pyrogallol. Aqueous extracts of both green and black teas were found to undergo extensive autoxidation under physiological conditions. The addition of superoxide dismutase (SOD) and milk resulted in a significant decrease in the rate of oxidation. Studied individually, PP were found to autoxidize at a rate, which increased with pH, proportional to PP concentration and nearly proportional to oxygen concentration. The collected data were used for the extrapolation/interpolation of the starting rates of oxidation to the standard conditions (at pH 7.40, 100 microM PP, 200 microM O2). PP oxidizability is basically determined by that of the key PP fragment (pyrogallol > gallate > catechol). Meta-OH groups do not contribute to the oxidation even at pH 13.0. Similar to tea brew, the oxidation of individual PP was inhibited by milk and SOD addition, with catechol being the only exception (the oxidation of catechol was accelerated when SOD was added). Comparison of the autoxidation of PP (o-hydroquinones) with that of p-hydroquinones (Roginsky, V.; Barsukova, T. K. J. Chem. Soc., Perkin Trans. 2 2000, 1575-1582) displays the dramatic difference both in the oxidizability and in the kinetic regularities. The difference in the kinetics has been suggested to be due to the difference in the initiation of the chain process. Whereas for p-hydroquinones the oxidation is initiated by the reaction between hydroquinone and a corresponding quinone, the oxidation of o-hydroquinones is likely started by direct interaction between substrate and molecular oxygen. As the second process is much slower, this may explain the relatively low oxidizability of PP as compared to p-hydroquinones.

Catechols↗