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The PbO2 -2 wt.% sodium dodecyl sulfate composite formed from methanesulfonate electrolyte consists of 93.1% of α-phase PbO2 in contrast to the similar one synthesized from nitrate electrolyte, which contains 73.3% of β phase. The electrocatalytic activity of the obtained composites in the oxygen evolution reaction and oxidation of chloramphenicol was investigated. It was found that the Tafel slope significantly exceeds the theoretical value, which indicates a decrease in the degree of filling of the electrode surface with oxygen-containing particles. In the presence of organic compound and chloride ions in the solution, irreversible adsorption of the intermediate is observed, which leads to additional blocking of active centers on the oxide surface, which are involved in the oxidation of organic substance. It was established that the maximum rate of chloramphenicol conversion is 83.5% and 85% at 50 and 80 mA cm-2 , respectively, under kinetic control. The heterogeneous oxidation rate constant of chloramphenicol is 0.0035 min-1 . Oxidation of chloramphenicol occurs through the formation of 4-(-2-amino-1,3-dihydroxy-propanyl)-nitrobenzene with cleavage of dichloroacetic acid. Next, the amino group is oxidized to the nitro group to form 4-(2-nitro-1,3-dihydroxy-propanyl)-nitrobenzene. Subsequent electrolysis produces nitrobenzoic acid, which is oxidized to benzoic acid, later hydroquinone, then benzoquinone and a set of aliphatic compounds. PRACTITIONER POINTS: The PbO2 -2 wt.% SDS composite consists of 93.1% of α phase of PbO2 in contrast to those synthesized from nitrate electrolyte. The Tafel slope indicates a decrease of surface filling with oxygen-containing particles. Irreversible adsorption of the intermediate is observed in the presence of chloride ions.

Overcoming lignocellulosic biomass recalcitrance, especially the cleavage of cross-linkages in lignin-carbohydrate complexes (LCCs) and lignin, is essential for both the carbon cycle and industrial biorefinery. Lytic polysaccharide monooxygenases (LPMOs) are copper-containing enzymes that play a key role in fungal polysaccharide oxidative degradation. Nevertheless, comprehensive analysis showed that LPMOs from a white-rot fungus, Pleurotus ostreatus, correlated well with the Fenton reaction and were involved in the degradation of recalcitrant nonpolysaccharide fractions in this research. Thus, LPMOs participated in the extracellular Fenton reaction by enhancing iron reduction in quinone redox cycling. A Fenton reaction system consisting of LPMOs, hydroquinone, and ferric iron can efficiently produce hydroxy radicals and then cleave LCCs or lignin linkages. This finding indicates that LPMOs are underestimated auxiliary enzymes in eliminating biomass recalcitrance.

BACKGROUND Tranexamic acid (TA) can prevent melanocyte activation by various stimuli. Combining TA with either hydroquinone 4% or Q-switched Nd:YAG laser may be associated with greater improvement of melasma. OBJECTIVES We aimed to evaluate the efficacy and safety of oral TA alone and combined with either topical hydroquinone 4% or low-fluence 1064 nm Q-switched Nd:YAG laser in treatment of mixed melasma. PATIENTS & METHODS Patients were randomly divided into three groups of 20 patients each. Group A were treated with oral TA 250 mg twice daily for three months; group B were treated with TA similarly combined with topical hydroquinone 4% cream; group C were treated with TA combined with two sessions of 1064 nm low-fluence Q-switched ND:YAG laser (850-1200 mJ/cm2 , 4-5 Hz,spot size 4 mm) spaced 4 weeks apart. Patients were followed monthly for 9 months. RESULTS After cessation of therapy, the mean mMASI score was lowest in group B (2.34 ± 2.37) followed by groups A (6.38 ± 4.04) and C (7.24 ± 4.95).Mean percentage of mMASI score improvement was 35.91 ± 24.13, 77.47 ± 19.07, and 24.94 ± 27.79 in groups A, B, and C (p

BACKGROUND: A biomimetic method was developed for the synthesis of silver nanoparticles (AgNPs). Synthetic chemical compounds were used according to the metabolites present in the fungal extracts for the synthesis of AgNPs. The main objective of this study was to find a simple and effective synthesis method without the presence of a living organism. METHODOLOGY: A central composite design combined with response surface methodology was used to optimize the necessary metabolite concentrations (flavin adenine dinucleotide (FAD), hydroquinone (HQ), and l‐cysteine (l‐cys)) for the synthesis of AgNPs. The design was assessed based on the size distribution and zeta potential of the nanoparticles. In addition, the antibacterial activity of the AgNPs against Escherichia coli, Staphylococcus aureus, Serratia marcescens and Salmonella enterica was tested. RESULTS: The results demonstrated that AgNO₃ (2 mmol L⁻¹), HQ (20 mmol L⁻¹), l‐cys (20 mmol L⁻¹) and FAD (50.5 nmol L⁻¹) at pH 8.4 were the optimal reaction parameters. The characterization allowed the determination of quasi‐spherical AgNPs with an average hydrodynamic size of 101 nm, a zeta potential of −24 mV and the presence of elemental silver (Ag⁰) in their composition. Fourier transform infrared spectroscopy showed silver and l‐cys interactions, supporting the role of l‐cys as a coating agent. The antibacterial activity showed that AgNPs displayed a minimum inhibitory concentration of 20–30 μg mL⁻¹ and a minimum bactericidal concentration of 30–40 μg mL⁻¹. CONCLUSIONS: This study demonstrates the feasibility of the reduction of Ag⁺ to Ag⁰ using synthetic metabolites, which mimic the reduction and synthesis of fungal biomass. Therefore, it represents a new biocompatible, eco‐friendly and fast method to produce AgNPs. © 2021 Society of Chemical Industry (SCI).

This research investigated the effect of carnosic acid (CA), tert‐butyl hydroquinone (TBHQ), sesamol (SL) and L‐ascorbyl palmitate (AP) on the inhibition of glycidyl esters (GEs) and oxidation parameter changes in rice bran oil (RBO) during heat processing. The electron spin resonance (ESR) analysis showed that the free radical scavenging ability of them was ranked as CA > TBHQ > SL > AP. With the addition of CA, TBHQ, SL and AP (0.6 g kg⁻¹), the GEs content was reduced significantly from 987.98 ± 8.45 to 283.87 ± 4.78, 303.21 ± 4.38, 440.52 ± 3.82 and 500.55 ± 2.99 μg kg⁻¹, respectively. All four free radical scavengers had the highest inhibitory effect on C18:2‐GE, followed by C18:1‐GE and C16:0‐GE. Moreover, the free radical scavengers were also effective to inhibit oil oxidation. Overall, the natural‐free radical scavenger may be a promising candidate to mitigate GE formation and oil oxidation due to its effectiveness and safety.

Organo-radical catalysts have recently attracted great interest, and the development of this field can be expected to broaden the applications of organocatalysis. Herein, the first example of a radical-generating system is reported that does not require any photoirradiation, radical initiators, or preactivated substrates. The oxidative C-C-bond cleavage of 2-substituted cyclohexanones was achieved using an azolium salt and a hydroquinone as co-catalysts. A catalytic mechanism was proposed based on the results of diffusion-ordered spectroscopy and cyclic voltammetry measurements, as well as computational studies.

Background Robust evidence regarding the efficacy of topical tranexamic acid (TA) on melasma in Chinese population is lacking. Objective To evaluate the efficacy and safety of 1.8% liposomal TA and microneedling with 5% TA solution on melasma. Methods Sixty melasma patients were enrolled and randomized to receive 1.8% liposomal TA twice daily, microneedling with 5% TA solution weekly or 2% hydroquinone every night. Objective and subjective assessments were obtained at baseline, 4, 8 and 12 weeks. Results 27.8% of patients of liposomal TA group, 33.3% of microneedling with TA solution group and 30.0% of hydroquinone group were recognized as "more than 50% improvement". At the endpoint, the melanin index (MI) in all treatment groups were significantly decreased, while the improvement of MI in microneedling with TA solution group and hydroquinone group is higher than liposomal TA group. The erythema index (EI) was significantly diminished in liposomal TA group and microneedling with TA solution group. Dermatoscopy and reflectance confocal microscopy revealed decreased brown granules in all groups and reduced telangiectasia in liposomal TA group and microneedling with TA solution group. Conclusion 1.8% liposomal TA and microneedling with 5% TA solution are both effective and safe on melasma.

The use of molecular oxygen in palladium‐catalyzed oxidation reactions is highly widespread in organic chemistry. However, the direct reoxidation of palladium by O2 is often kinetically unfavored, thus leading the deactivation of the palladium catalyst during the catalytic cycle. In the present work, we report a highly selective palladium‐catalyzed carbocyclization of bisallenes to seven‐membered heterocycles under atmospheric pressure of O2. The use of a homogenous hybrid catalyst (Co(salophen)‐HQ, HQ=hydroquinone) significantly promotes efficient electron transfer between the palladium catalyst and O2 through a low‐energy pathway. This aerobic oxidative transformation shows broad substrate scope and functional group compatibility and allowed the preparation of O‐containing seven‐membered rings in good yields in most cases., Heterocycles: We report a PdII‐catalyzed oxidative carbocyclization of the rationally designed bisallenes using molecular oxygen. By applying a bifunctional catalyst (Co(salophen)‐HQ) as an efficient electron‐transfer mediator, bisallenes are effectively converted to the corresponding seven‐membered carbocycles in good yields (see scheme).

Polypropylene (PP) based active composite films were prepared by adding butylated hydroxy anisole (BHA), butylated hydroxytoluene (BHT), and tertiary butylated hydroquinone (TBHQ) antioxidants using the extrusion molding process. All concentrations of BHT, 2% to 3% BHA, and 3% TBHQ significantly increased the tensile strength (TS) of the composite films compared with control films. Increasing antioxidant concentration decreased TS values for BHT films, whereas an opposite trend was observed for BHA and TBHQ films. BHA at 2%, and TBHQ at all added concentrations significantly reduced elongation at break (Eb ) of the composite films compared to control films. Water vapor permeability (WVP) of 1% BHT film was not significantly different from control. However, other antioxidants especially at increased concentrations significantly increased WVP values. TBHQ films with 300% to 662% increase had the highest WVP and BHT films with 5% to 81% increase had the lowest WVP among composite films. All three antioxidants had a negative effect on the transparency of the films; however the effect of BHA at higher concentrations was greater. The antioxidants did not change the color attributes of the films. Films containing all antioxidants showed 2,2-diphenyl-1-picrylhydrazyl radical-scavenging activity, which increased with increase in their concentration, especially for those containing 3 wt.% BHT and TBHQ. Overall, incorporating BHA and BHT into a PP matrix improved mechanical, barrier, antioxidant properties, and film appearance and consequently were proposed for the development of antioxidant active PP films. TBHQ film is not recommended for food packaging because of its weak mechanical properties (lower Eb and TS values, higher WVP, and greater migration).

A visible light-induced decarboxylative alkylation of heterocyclic aromatics with aliphatic carboxylic acids was developed by using anthocyanins as a photocatalyst under mild conditions. A series of alkylated heterocyclic compounds were obtained in moderate to good yields by using the metal-free decarboxylative coupling reaction under blue light. This strategy uses cheap and readily available carboxylic acids as alkylation reagents with good functional group tolerance and environmental friendliness. It is worth noting that this is the first time that anthocyanin has been used to catalyze the Minisci-type C-H alkylation. The mechanism of decarboxylation alkylation was studied by capturing the adduct of alkyl radical and hydroquinone, thus confirming a radical mechanism. This protocol provides an alternative visible light-induced decarboxylative alkylation for the functionalization of heterocyclic aromatics.

Benzene is a human carcinogen that requires metabolic activation. We previously observed that benzene and its hydroxylated metabolites induce micronuclei in mammalian cells expressing human CYP2E1. This study was initially aimed to study another endpoint, the induction of gene mutations by those compounds in the same cell models. A V79-derived cell line expressing human CYP2E1 and sulfotransferase (SULT) 1A1 (V79-hCYP2E1-hSULT1A1) pretreated with ethanol (a CYP2E1 stabilizer) was used in the hprt gene mutagenicity assay. Phenol, hydroquinone, catechol, and 1,2,4-trihydroxybenzene all induced gene mutations, while they were inactive, or only weakly positive (hydroquinone), in parental V79-Mz cells. Unexpectedly, benzene was non-mutagenic in both cell lines, but it became positive in V79-hCYP2E1-hSULT1A1 cells using regimes of short exposure/long recovery without ethanol pretreatment, for both gene mutations and micronuclei formation. In silico molecular simulation showed binding energies and positions favorable for each compound to be oxidized by human CYP2E1, benzene demonstrating the highest affinity. By tunnel analysis, ethanol binding did not limit benzene to pass tunnel S, which was specifically active for benzene. However, its end product, acetic acid, decreased the occurrence of tunnel S from 5.4 to 2.2% and extended the length of its bottleneck from 5.5 to 9.0 Å. With residual ethanol molecules still being present in CYP2E1 for a period of time after benzene exposure, the acetic acid formed could limit the entrance of benzene, thus inhibit its metabolic activation. In summary, ethanol may interfere with the activation of benzene to mutagenic metabolites, at least in cultured cells.

Metal-organic frameworks (MOFs) have limited applications in electrochemistry owing to their poor conductivity. Now, an electroactive MOF (E-MOF) is designed as a highly crystallized electrochemiluminescence (ECL) emitter in aqueous medium. The E-MOF contains mixed ligands of hydroquinone and phenanthroline as oxidative and reductive couples, respectively. E-MOFs demonstrate excellent performance with surface state model in both co-reactant and annihilation ECL in aqueous medium. Compared with the individual components, E-MOFs significantly improve the ECL emission due to the framework structure. The self-enhanced ECL emission with high stability is realized by the accumulation of MOF cation radicals via pre-reduction electrolysis. The self-enhanced mechanism is theoretically identified by DFT. The mixed-ligand E-MOFs provide a proof of concept using molecular crystalline materials as new ECL emitters for fundamental mechanism studies.

BACKGROUND: Dihydroxybenzene (DHB) which is an important raw material and intermediate of the organic chemical industry can be prepared by hydroxylation of phenol, so it promotes the study of highly selective catalyst for hydroxylation of phenol. RESULTS: Two novel PNP ((Ph₂P)₂NPh) ligand‐substituted di‐iron complexes were synthesized under controllable reaction conditions via carbon monoxide (CO)/ligand substitution of the parent complex (μ‐budt)Fe₂(CO)₆ [budt = SCH(CH₃)CH₂CH₂)S]. The substituted complexes 1 and 2 were fully characterized by solution infrared spectroscopy, nuclear magnetoresonance spectroscopy, single crystal X‐ray diffraction, cyclic voltammetry and density functional theory calculations. Due to its favorable redox properties, Complex 1 was adopted first as an efficient catalyst for the hydroxylation of phenol to DHB (dihydroxybenzene) with hydrogen peroxide (H₂O₂) as oxidant and H₂O as solvent. Under the optimum reaction conditions, the conversion of phenol achieved 42.0%, the selectivity of DHB was ≤88.6% and the catechol:hydroquinone ratio (mol mol⁻¹) was 2.2. Furthermore, only trace amounts of benzoquinone, as a deeply oxidized product, was detected (yield c. 0.1%). CONCLUSION: Complex 1 could be a new type of catalyst for the hydroxylation of phenol to hydroquinone owing to the mild reaction conditions and excellent catalytic performance. In addition, a possible catalytic reaction mechanism was related to the special structure of Complex 1 which features an internal base of amine in PNP ligand.

Background Recent data demonstrated that an altered basal membrane, activated melanocytes and secreted factors from keratinocytes but also fibroblasts and endothelial cells are involved in the pathophysiology of melasma. Objectives To evaluate the efficacy and tolerability on melasma of a new topical skin‐lightening cosmetic product combination (CCP) targeting several factors identified to be involved in melasma pathogenesis compared to 4% hydroquinone (HQ). Methods Forty‐three women with melasma were enrolled in a 12‐week double‐blind, randomized, parallel‐group trial and treated with CCP or 4% HQ cream. Efficacy was evaluated with the modified Melasma Area Severity Index (mMASI) score and colorimetric change. Cutaneous tolerability and patient satisfaction were also investigated. Results The mMASI score decreased for both products from baseline and over the study period. At week 12, 90% of the subjects who received the combination products had an improvement in pigmentation vs. 79% with HQ. Similarly, both products significantly increased Individual Typological Angle parameters. For both measures, no statistically significant difference was observed between CCP and HQ in terms of change from baseline. CPP was very well tolerated. Conclusions Cosmetic product combination is as effective as HQ in the management of facial dyspigmentation and represents a safe alternative.

The redox reaction mechanism of a poly(phenanthrene quinone)/graphene composite (PFQ/rGO) was investigated using operando attenuated total reflection infrared (ATR‐IR) spectroscopy during cycling of Li and Mg batteries. The reference phenanthrene quinone and the Li and Mg salts of the hydroquinone monomers were synthesized and their IR spectra were measured. Additionally, IR spectra were calculated using DFT. A comparison of all three spectra allowed us to accurately assign the C=O and C−O− vibration bands and confirm the redox mechanism of the quinone/Li salt of hydroquinone, with radical anion formation as the intermediate product. PFQ/rGO also showed exceptional performance in an Mg battery: A potential of 1.8 V versus Mg/Mg2+, maximum capacity of 186 mAh g−1 (335 Wh kg−1 of cathode material), and high capacity retention with only 8 % drop/100 cycles. Operando ATR‐IR spectroscopy was performed in a Mg/organic system, revealing an analogous redox mechanism to a Li/organic cell., Charging mechanism: A new poly(phenanthrene quinone) cathode material shows exceptional electrochemical performance in Li and Mg batteries. The redox reactions during charge/discharge were investigated using operando attenuated total reflectance IR spectroscopy. In both battery systems, the hydroquinone salt was reversibly oxidized back to the quinone functional group.

Background/objectives Melasma is a common pigmentary disorder for which oral tranexamic acid has shown some efficacy in previous studies. The aim of this study was to assess the effectiveness of oral tranexamic acid in combination with hydroquinone cream in the treatment of melasma. Methods Subjects with moderate-to-severe melasma were enrolled. Group A received hydroquinone 4% cream, sunscreen and oral tranexamic acid, while Group B received hydroquinone 4% cream, sunscreen and placebo capsules for 3 months. All subjects had an additional 3-month follow-up visit on sunscreen alone. The primary outcome measure was change in modified Melasma Area and Severity Index (mMASI) score. In addition, the melanin index was measured using a mexameter. Results Fifty subjects were enrolled, and all completed the study. There was a 55% reduction in mMASI after 3 months from mean 8.96 (SD 2.45) to 4.0 (SD 1.6) in Group A compared to 10.9% from mean 8.53 (SD 2.04) to 7.6 (SD 2.0) in Group B. Three months after oral and topical therapy was discontinued, there was a 42% decrease in mMASI compared to baseline in Group A (mean 5.1 SD 1.7) vs. 4.7% in Group B (mean 8.1 SD 2.0). No serious adverse events were observed. Conclusions A combination of oral tranexamic acid and topical hydroquinone is more effective than hydroquinone alone in the treatment of melasma.

Background The increase in the pigmentation of skin grafts during the healing process is a cosmetic problem. There are a variety of medical and surgical treatment options for skin graft darkening. Aims The aim of this study was to investigate the effects of topical hydroquinone, tretinoin, and betamethasone application on hyperpigmentation of skin grafts. Methods A skin defect was created on the backs of 17 Long-Evans rats, and a 2 × 2 cm split-thickness skin graft was sutured. After 15 days, eight rats in the treatment group were treated with application of hydroquinone, tretinoin, and betamethasone cream, while nine rats in the control group were not treated. Visual evaluation was performed on days 45 and 75 using the Melasma Severity Scale (MSS), and histological evaluation was performed on day 75 using S100 and Masson Fontana (MF) staining. The Mann-Whitney U test was used for statistical analysis. Results Mean MSS values of the treatment group on days 45 were significantly lower compared to the control group (P = .036). On day 75, the mean MSS score of the treatment group was also lower; however, the difference was not statistically significant (P = .302). Histological evaluation of S100 and MF staining scores of the treatment group showed fewer melanocytes and fewer pigments in epidermis (P = .009 and P = .002, respectively). Conclusions This study showed that topical application of hydroquinone, tretinoin, and betamethasone reduced the hyperpigmentation, number of melanocytes, and melanin pigment intensity that developed on the rat skin graft models. Clinical studies are needed to assess whether a similar effect could be observed with human skin grafts.

In this work, for the first time, the electrochemical behavior of hydroquinone (H2Q) by linear voltammetry in aqueous reverse micelles (RMs) of sodium 1,4-bis(2-ethylhexyl) sulfosuccinate (AOT)/n-heptane, as well in homogenous media at different pH values, were studied. The choice of this molecular probe is because of its electrochemical response in water, strongly depend on the pH value thus, our goal is to know more about an intriguing issue in the soft matter field, what is the pH value for water encapsulated in the water pool of AOT RMs. Our work will demonstrate that the interfacial apparent pH value of AOT RMs is not strongly acidic as some of the literature works claim, but it is around a pH value of 6.7. Thus, through the electrochemistry technique, the present work reinforces the idea that the concept of is strongly dependent on the water-interface interactions and the molecular probe location. Fil: Cobo Solis, Airam Katiza. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; Argentina. Universidad Nacional de Río Cuarto. Instituto para el Desarrollo Agroindustrial y de la Salud. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto para el Desarrollo Agroindustrial y de la Salud; Argentina Fil: Luna, Maria Alejandra. Universidad Nacional de Río Cuarto. Instituto para el Desarrollo Agroindustrial y de la Salud. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto para el Desarrollo Agroindustrial y de la Salud; Argentina Fil: Falcone, Ruben Dario. Universidad Nacional de Río Cuarto. Instituto para el Desarrollo Agroindustrial y de la Salud. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto para el Desarrollo Agroindustrial y de la Salud; Argentina Fil: Correa, Nestor Mariano. Universidad Nacional de Río Cuarto. Instituto para el Desarrollo Agroindustrial y de la Salud. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto para el Desarrollo Agroindustrial y de la Salud; Argentina Fil: Molina, Patricia Gabriela. Universidad Nacional de Río Cuarto. Instituto para el Desarrollo Agroindustrial y de la Salud. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto para el Desarrollo Agroindustrial y de la Salud; Argentina

Gold nanostructures were fabricated on a transparent indium tin oxide (ITO) coated PET substrate by an electrodeposition technique from a potassium gold (III) chloride solution for two different types of applications. It was found that the optical transparency of lightweight ITO electrodes could be maintained by depositing isolated gold nanostructures while opening up the use of these electrodes for inner sphere electron reactions, such as hydroquinone oxidation, which are not possible at ITO electrodes. For practical applications the adhesion of gold to the ITO electrode was improved by modifying the ITO surface with 3-mercaptopropyl-trimethoxysilane (MPS). Compared to Au/ITO, the Au/MPS/ITO electrode showed vastly improved electrochemical activity toward various electron transfer reactions when subjected to mechanical stress. The biosensing properties of the Au/MPS/ITO electrode was also investigated by studying the detection of immobilized DNA on the Au/MPS/ITO electrode via electrochemical impedance spectroscopy (EIS).

Flavodoxins are small flavin mononucleotide (FMN)‐containing proteins that mediate a variety of electron transfer processes. The primary sequence of flavodoxin from Fusobacterium nucleatum, a pathogenic oral bacterium, is marked with a number of distinct features including a glycine to lysine (K13) substitution in the highly conserved phosphate‐binding loop (T/S‐X‐T‐G‐X‐T), variation in the aromatic residues that sandwich the FMN cofactor, and a more even distribution of acidic and basic residues. The E (ox/sq) (oxidized/semiquinone; −43 mV) and E (sq/hq) (semiquinone/hydroquinone; −256 mV) are the highest recorded reduction potentials of known long‐chain flavodoxins. These more electropositive values are a consequence of the apoprotein binding to the FMN hydroquinone anion with ~70‐fold greater affinity compared to the oxidized form of the cofactor. Inspection of the FnFld crystal structure revealed the absence of a hydrogen bond between the protein and the oxidized FMN N5 atom, which likely accounts for the more electropositive E (ox/sq). The more electropositive E (sq/hq) is likely attributed to only one negatively charged group positioned within 12 Å of the FMN N1. We show that natural substitutions of highly conserved residues partially account for these more electropositive reduction potentials.

Background The management of melasma is still challenging, and new treatment modalities with favorable side effect profile are required. Methimazole, a peroxidase inhibitor, seems to have a beneficial effect in the management of melasma but there is a paucity of studies for evaluation of its efficacy. This double-blinded trial was aimed to evaluate the efficacy and safety of methimazole vs hydroquinone 4% which is the gold standard treatment in the management of melasma. Methods Fifty patients with melasma were enrolled and randomly divided into two groups to receive 4% hydroquinone or 5% methimazole once daily for 8 weeks. Forty patients completed the study. The clinical response was assessed at 4th, 8th, and 12th weeks after treatment by MASI score, patient satisfaction, and physician scores. Results Both groups showed a reduction in the MASI score at the 8th week which was more significant in hydroquinone group but higher relapse rate was also observed in this group after discontinuing the drug. The side effects were similar between groups. Also, patient and physician satisfaction scores were also more in favor of hydroquinone 4%. Conclusion Methimazole could be an alternative treatment of melasma alone or in combination with other depigmenting drugs. Although not as effective as hydroquinone, the noncytotoxic and nonmutagenic aspects of methimazole may make it a promising alternative for the treatment of melasma.

Background/objective Melasma is a commonly acquired disorder of hyperpigmentation that often poses a therapeutic challenge for dermatologists. Recently, cysteamine cream has shown promising results compared to placebo. This study aims to determine the efficacy of cysteamine cream compared to hydroquinone cream in the treatment of melasma. Methods A randomised, double-blinded, single-centre trial was conducted in Victoria, Australia. 20 recruited participants were given either cysteamine cream or hydroquinone cream for 16 weeks. The primary outcome measure was a change in the modified Melasma Area and Severity Index (mMASI). Quality of life at baseline and week 16 as well as standard digital photography at each follow-up visit was assessed as secondary outcome measures. Results At week 16, 14 participants completed the study with 5 participants in the cysteamine group and 9 patients in the hydroquinone group. In the intention to treat analysis, there was a 1.52 ± 0.69 (21.3%) reduction in mMASI for the cysteamine group and a 2.96 ± 1.15 (32%) reduction in the hydroquinone group. The difference between groups was not statistically significant (P = 0.3). Hydroquinone cream was generally better tolerated that cysteamine cream. Conclusion Our study suggests that topical cysteamine may have comparable efficacy to topical hydroquinone. Cysteamine thus provides a possible alternative to patients and clinicians who wish to avoid or rotate off topical hydroquinone. While side effects were more common for participants using cysteamine compared with hydroquinone, these were mild and reversible. Larger studies comparing cysteamine and hydroquinone are required to support these findings.

Carpodesmia tamariscifolia is a brown alga rich in (poly)phenols with important cytotoxic and antioxidant effects. However, the relationship between its chemical composition and its effects is unknown. The aim of this study is to identify the potential compounds and mechanisms responsible for its main effects. The alga was extracted consecutively with hexane, dichloromethane and methanol and further fractionated using Sephadex LH-20 and silica gel columns when appropriate. The fractions were subjected to thin-layer chromatography and liquid chromatography-mass spectrometry analysis and evaluated for their total phenolic content (Folin-Ciocalteu assay), radical scavenging activity (DPPH assay), cytotoxic activity (MTT assay on the SH-SY5Y cell line), and ability to generate H2 O2 (Amplex Red assay). Chromatographic and phenolic analyses of the fractions indicate that abundant redox-active phenols are present in all the fractions and that a high amount of prenylated hydroquinone derivatives is present in the apolar ones. In the hexane and dichloromethane fractions, the cytotoxic and antioxidant activities are closely related to their phenolic content, whereas in the methanol fractions, the cytotoxicity is negatively related to the phenolic content and the antioxidant activity is positively related to it. In the same tests, hydroquinone behaves as both strong cytotoxic and antioxidant agent. H2 O2 assay shows that C. tamariscifolia fractions and hydroquinone can autoxidize and generate H2 O2 . Our results suggest that redox-active phenols produce the pharmacological effects described for C. tamariscifolia and that the hydroquinone moiety of prenylated hydroquinone derivatives is responsible for both cytotoxic (through a pro-oxidant mechanism secondary to its autoxidation) and antioxidant effects of the apolar fractions.

The formation of growth-mediated structures from gold nanoparticle seeds was studied in the presence of amine-modified single-strand DNA sequences and reducing agents such as hydroxylamine and hydroquinone. In the case of hydroxylamine, spherical gold nanoparticle seeds (0.45 nM) were incubated with amine-modified single-strand DNA probes PMR (amine-5'-ACATCAGT-3') and PML (amine-5'-GATAAGCT-3'), which resulted in gold nanoflowers and nanospheres, respectively. When the concentration of the nanoparticle seeds was varied (0.15-0.45 nM), only the PMR sequence showed growth-mediated development of gold nanoflowers. The size of the gold nanoparticles obtained is independent of the seed concentration for both PMR and PML sequences. In contrast, in the presence of the reducing agent hydroquinone, the growth processes are identical in for both the sequences. At a lower seed concentrations (0.15 nM), gold nanoflowers of larger size were observed for both sequences, whereas at higher seed concentrations (0.45 nM), much smaller gold nanospheres resulted. The formation and stability of nanoflowers and nanospheres for PMR and PML with hydroxylamine-based reduction were further studied in detail with diverse controlled amine-modified (5'-, 3'- and both end-modified) and non-modified DNA sequences with other mutants of these two sequences.