Vicinal Hydroxyl Research Articles

Oxygen Functional Groups Regulate Cobalt‐Porphyrin Molecular Electrocatalyst for Acidic H2O2 Electrosynthesis at Industrial‐Level Current

AbstractElectrosynthesis of hydrogen peroxide (H2O2) based on proton exchange membrane (PEM) reactor represents a promising approach to industrial‐level H2O2 production, while it is hampered by the lack of high‐efficiency electrocatalysts in acidic medium. Herein, we present a strategy for the specific oxygen functional group (OFG) regulation to promote the H2O2 selectivity up to 92 % in acid on cobalt‐porphyrin molecular assembled with reduced graphene oxide. In situ X‐ray adsorption spectroscopy, in situ Raman spectroscopy and Kelvin probe force microscopy combined with theoretical calculation unravel that different OFGs exert distinctive regulation effects on the electronic structure of Co center through either remote (carboxyl and epoxy) or vicinal (hydroxyl) interaction manners, thus leading to the opposite influences on the promotion in 2e− ORR selectivity. As a consequence, the PEM electrolyzer integrated with the optimized catalyst can continuously and stably produce the high‐concentration of ca. 7 wt % pure H2O2 aqueous solution at 400 mA cm−2 over 200 h with a cell voltage as low as ca. 2.1 V, suggesting the application potential in industrial‐scale H2O2 electrosynthesis.

Oxygen Functional Groups Regulate Cobalt-Porphyrin Molecular Electrocatalyst for Acidic H2O2 Electrosynthesis at Industrial-Level Current.

Electrosynthesis of hydrogen peroxide (H2O2) based on proton exchange membrane (PEM) reactor represents a promising approach to industrial-level H2O2 production, while it is hampered by the lack of high-efficiency electrocatalysts in acidic medium. Herein, we present a strategy for the specific oxygen functional group (OFG) regulation to promote the H2O2 selectivity up to 92 % in acid on cobalt-porphyrin molecular assembled with reduced graphene oxide. In situ X-ray adsorption spectroscopy, in situ Raman spectroscopy and Kelvin probe force microscopy combined with theoretical calculation unravel that different OFGs exert distinctive regulation effects on the electronic structure of Co center through either remote (carboxyl and epoxy) or vicinal (hydroxyl) interaction manners, thus leading to the opposite influences on the promotion in 2e- ORR selectivity. As a consequence, the PEM electrolyzer integrated with the optimized catalyst can continuously and stably produce the high-concentration of ca. 7 wt % pure H2O2 aqueous solution at 400 mA cm-2 over 200 h with a cell voltage as low as ca. 2.1 V, suggesting the application potential in industrial-scale H2O2 electrosynthesis.

Heme d formation in a Shewanella benthica hemoglobin

In our continued investigations of microbial globins, we solved the structure of a truncated hemoglobin from Shewanella benthica, an obligate psychropiezophilic bacterium. The distal side of the heme active site is lined mostly with hydrophobic residues, with the exception of a tyrosine, Tyr34 (CD1) and a histidine, His24 (B13). We found that purified SbHbN, when crystallized in the ferric form with polyethylene glycol as precipitant, turned into a green color over weeks. The electron density obtained from the green crystals accommodated a trans heme d, a chlorin-type derivative featuring a γ-spirolactone and a vicinal hydroxyl group on a pyrroline ring. In solution, exposure of the protein to one equivalent of hydrogen peroxide resulted in a similar green color change, but caused by the formation of multiple products. These were oxidation species released on protein denaturation, likely including heme d, and a species with heme covalently attached to the polypeptide. The Tyr34Phe replacement prevented the formation of both heme d and the covalent linkage. The ready modification of heme b by SbHbN expands the range of chemistries supported by the globin fold and offers a route to a novel heme cofactor.

Vicinal effect on chlorination of diols

The vicinal effect on chlorination reactions of diols was investigated by computational methods. Applying density functional theory (DFT) combined with polarizable continuum model (PCM) and explicit solvent molecules, we demonstrated the effect of hydration on the leaving and vicinal hydroxyl group in SN2 reactions of selected alcohols. Our results point out to the importance of intermolecular hydrogen bonds as a stabilizing factor in reaction pre-complexes and alcohols with vicinal hydroxyl groups, highlighting the importance of solute-solvent network formation. This indicates the significance of adequately describing the solvent in the study of reaction mechanisms, in special when the interaction with solute molecules and ions are strong. Also, we found a “vinical effect” on the reactivity, in other words, alcohols with vicinal hydroxyl groups exhibit higher activation energies when compared to related monoalcohols. Moreover, 1,3-propanediol and 1,3-butanediol present the highest activation energies.

Synthesis of methyl 3,4-anhydro-6-bromo-2-o-tert-butyldimethylsilyl-6-deoxy-α-d-allopyranoside from α-d-glucose

Some of simple carbohydrates and their derivatives are used clinically for the treatment of various diseases. Epoxide derivatives, which can be obtained by the intramolecular elimination of water from two vicinal hydroxyl groups, are stable, but sufficiently reactive compounds very often used as intermediaries in various syntheses. Synthesis of epoxide derivative, methyl 3,4-anhydro-6- bromo-2-O-tert-butyldimethylsilyl-6-deoxy-?-D-allopyranoside from ?-D-glucose was achieved in high yields in the minimal number of synthetic steps. Anhydrous glucose was used as a starting material which was transformed into methyl ?-D-glucopyranoside using dry, gaseous hydrogen chloride. Thus obtained derivative was treated with benzaldehyde in the presence of zinc chloride as Lewis acid giving methyl (R)-4,6-O-benzylidene-?-D-glucopyranoside. Obtained compound was treated with NBS (N-bromosuccinimide) in dichloromethane in the presence of barium carbonate giving methyl 4-O-benzoyl-6-bromo-6-deoxy-?-D-glucopyranoside. In the next step obtained compound was treated with TBDMSCl (tert-butyldimethylsilyl chloride) in pyridine, and methyl 4-O-benzoyl-6-bromo-2-O-tert-butyldimethylsilyl-6-deoxy-?-D-glucopyranoside was further mesylated, and obtained methyl 4-O-benzoyl-6-bromo-2-O-tert-butyldimethylsilyl-6-deoxy-3- O-mesyl-?-D-glucopyranoside was treated at the end with KOH to give methyl 3,4-anhydro-6-bromo-2-O-tert-butyldimethylsilyl-6-deoxy-?-D-allopyranoside (yield 78 %).

The role of CE16 exo-deacetylases in hemicellulolytic enzyme mixtures revealed by the biochemical and structural study of the novel TtCE16B esterase

Acetyl esterases belonging to the carbohydrate esterase family 16 (CE16) is a growing group of enzymes, with exceptional diversity regarding substrate specificity and regioselectivity. However, further insight into the CE16 specificity is required for their efficient biotechnological exploitation. In this work, exo-deacetylase TtCE16B from Thermothelomyces thermophila was heterologously expressed and biochemically characterized. The esterase targets positions O-3 and O-4 of singly and doubly acetylated non-reducing-end xylopyranosyl residues, provided the presence of a free vicinal hydroxyl group at position O-4 and O-3, respectively. Crystal structure of TtCE16B, the first representative among the CE16 enzymes, in apo- and product-bound form, allowed the identification of residues forming the catalytic triad and oxyanion hole, as well as the structural elements related to the enzyme preference for oligomers. The role of TtCE16B in hemicellulose degradation was investigated on acetylated xylan from birchwood and pre-treated beechwood biomass. TtCE16B exhibited complementary activity to commercially available OCE6 acetylxylan esterase. Moreover, it showed synergistic effects with SrXyl43 β-xylosidase. Overall, supplementation of xylan-targeting enzymatic mixtures with both TtCE16B and OCE6 esterases led to a 3-fold or 4-fold increase in xylose release, when using TmXyn10 and TtXyn30A xylanases respectively.

A multifunctional true caffeoyl coenzyme A O-methyltransferase enzyme participates in the biosynthesis of polymethoxylated flavones in citrus.

Polymethoxylated flavones (PMFs) have received extensive attention due to their abundant bioactivities. Citrus peels specifically accumulate abundant PMFs, and methylation modification is a key step in PMF biosynthesis; however, the function of reported O-methyltransferase (OMT) in citrus is insufficient to elucidate the complete methylation process of PMFs. In this study, we analyzed the accumulation pattern of PMFs in the flavedo of the sweet orange (Citrus sinensis) cultivar "Bingtangcheng" at different developmental stages. We found that accumulation of PMFs was completed at the early stage of fruit development (60-d after flowering). Furthermore, we characterized a true caffeoyl-CoA O-methyltransferase (named CsCCoAOMT1) from C. sinensis. Functional analysis in vitro showed that CsCCoAOMT1 preferred flavonoids to caffeoyl-CoA and esculetin. This enzyme efficiently methylated the 6-, 7- 8-, and 3'-OH of a wide array of flavonoids with vicinal hydroxyl groups with a strong preference for quercetin (flavonol) and flavones. The transient overexpression and virus-induced gene silencing experiments verified that CsCCoAOMT1 could promote the accumulation of PMFs in citrus. These results reveal the function of true CCoAOMTs and indicate that CsCCoAOMT1 is a highly efficient multifunctional O-methyltransferase involved in the biosynthesis of PMFs in citrus.

Alginate-Gelatin Self-Healing Hydrogel Produced via Static-Dynamic Crosslinking.

Alginate-gelatin hydrogels mimicking extracellular matrix (ECM) of soft tissues have been generated by static-dynamic double crosslinking, allowing fine control over the physical and chemical properties. Dynamic crosslinking provides self-healing and injectability attributes to the hydrogel and promotes cell migration and proliferation, while the static network improves stability. The static crosslinking was performed by enzymatic coupling of the tyrosine residues of gelatin with tyramine residues inserted in the alginate backbone, catalyzed by horseradish peroxidase (HRP). The dynamic crosslinking was obtained by functionalizing alginate with 3-aminophenylboronic acid which generates a reversible bond with the vicinal hydroxyl groups of the alginate chains. Varying the ratio of alginate and gelatin, hydrogels with different properties were obtained, and the most suitable for 3D soft tissue model development with a 2.5:1 alginate:gelatin molar ratio was selected. The selected hydrogel was characterized with a swelling test, rheology test, self-healing test and by cytotoxicity, and the formulation resulted in transparent, reproducible, varying biomaterial batch, with a fast gelation time and cell biocompatibility. It is able to modulate the loss of the inner structure stability for a longer time with respect to the formulation made with only covalent enzymatic crosslinking, and shows self-healing properties.

POCl3 mediated one-pot deoxygenative aromatization and electrophilic chlorination of dihydroxy-2-methyl-4-oxo-indeno[1,2-b]pyrroles.

A class of indenopyrroles is presented by the treatment of known dihydroxy-2-methyl-4-oxoindeno[1,2-b]pyrroles with phosphorus oxychloride (POCl3). The elimination of vicinal hydroxyl groups at the 3a and 8b positions, formation of a π bond, and electrophilic chlorination of the methyl group attached to C2 resulted in the fused aromatic pyrrole structures. Benzylic substitution of various nucleophiles such as H2O, EtOH, and NaN3 with a chlorine atom gave diverse 4-oxoindeno[1,2-b]pyrrole derivatives in 58 to 93% yields. The reaction was investigated in different aprotic solvents, and the highest reaction yield was obtained in DMF. The structures of the products were confirmed by spectroscopic methods, elemental analysis, and X-ray crystallography.

Regulating the states of Ni species by controlling the silanols of MCM-41 support to promote the hydrogenation of maleic anhydride

Nickel (Ni) supported on MCM-41 zeolite as hydrogenation catalysts have been widely applied in various reactions, however, the synergism between Ni and the support remains obscure. To prepare more efficient catalysts and reveal the metal-support interaction, MCM-41 zeolite was modified with ammonium hexafluorosilicate (AHFS) before Ni loading. Results show that fluoride ions could selectively convert the vicinal silanols into isolated silanols on MCM-41 surface, which weakens the interactions between Ni precursors and the SiO2 supports. Over the modified MCM-41 zeolites, the attenuated interaction results in the agglomeration of NiO particles that is more easily to be reduced, rather than the formation of nickel phyllosilicate which is extraordinarily difficult towards reduction. The easily-reduced Ni particles provided more adsorption sites for CC bond instead of CO bond, and the adsorption strength was also regulated. Therefore, the AHFS modified catalyst demonstrated a notable enhancement in hydrogenation of maleic anhydride (MA) into succinic anhydride (SA), presenting 98.4 % MA conversion and 99.8 % SA selectivity at 90 °C under 3.0 MPa H2. Moreover, the optimum catalyst was recycled for 5 runs to analyze the deactivation mechanism, it was found out that the loss of activities stems from the leaching of large Ni particles. Overall, our work shed light on the metal-support interactions for Ni/MCM-41 catalyst, determining the vicinal hydroxyl groups were responsible for the state of Ni species, which is helpful for the rational design of other hydrogenation catalysts.

Evaluation of Crocin as green corrosion inhibitor for aluminum in NaCl solution

The role of Crocin, which is a natural organic substance from the Greek plant Crocus sativus, is investigated as a green corrosion inhibitor for the AA 1050 commercial aluminum alloy in 0.01 M sodium chloride solution. Its action was assessed by Linear and Tafel Polarization, as well as by mass loss measurements and confirmed by observation and analysis of the surface morphology of the specimens by Scanning Electron Microscopy. Corrosion inhibition efficiency of Crocin improves with concentration and at 1.25 mM was estimated in the range of 90-95%, which indicates the formation of an adsorbed layer that isolates and protects the surface. Experimental results showed that Crocin acts as a mixed-type inhibitor with predominantly anodic effectiveness, also retarding pitting corrosion process. The inhibitive action of Crocin was explained by theoretical calculations employing density functional theory, semiempirical PM6 and molecular mechanics methodologies, showing good agreement with experimental results. The reactivity of Crocin is attributed to chemisorption on the Al2O3 surface through its vicinal hydroxyls of the sugar moiety. This process is assisted by the π-conjugated system of the polyene chain together with the extended electron delocalization over the oxygen atoms of the esterified carboxyl groups, as well as by the intense electrostatic potential regions located on the sugar moiety of the Crocin molecule.

Spectral properties and modeling of knightletin, a novel aminocoumarin with intramolecular hydrogen bonding

Knightletin is a novel, high quantum-yield, substituted coumarin in the group of fluorescent 7-aminocoumarins. The molecule reveals the influence of a vicinal hydroxyl group on the aminocoumarin structure through its absorbance-fluorescence properties and interaction with several initial solvents. The substitution on the benzene ring of the coumarin affects electronic states, the molecular dipole moment and involves both intramolecular and intermolecular hydrogen bonding. This report describes the synthesis of knightletin, its absorbance-fluorescence characteristics in three solvents of varying polarity and hydrogen-bonding ability, and insights on its conformation from density functional theory modeling. The quantum yield of 0.81 in methanol is remarkable. The modeling indicates a ground state geometry with a pyramidal NH2 group interacting with the OH in an NH-donor hydrogen bond and predicts spectroscopic characteristics consistent with the experimental observations.

Identification and characterization of two Isatis indigotica O-methyltransferases methylating C-glycosylflavonoids.

Isatis indigotica accumulates several active substances, including C-glycosylflavonoids, which have important pharmacological activities and health benefits. However, enzymes catalyzing the methylation step of C-glycosylflavonoids in I. indigotica remain unknown. In this study, three O-methyltransferases (OMTs) were identified from I. indigotica that have the capacity for O-methylation of the C-glycosylflavonoid isoorientin. The Type II OMTs IiOMT1 and IiOMT2 efficiently catalyze isoorientin to form isoscoparin, and decorate one of the aromatic vicinal hydroxyl groups on flavones and methylate the C6, C8, and 3′-hydroxyl positions to form oroxylin A, wogonin, and chrysoeriol, respectively. However, the Type I OMT IiOMT3 exhibited broader substrate promiscuity and methylated the C7 and 3′-hydroxyl positions of flavonoids. Further site-directed mutagenesis studies demonstrated that five amino acids of IiOMT1/IiOMT2 (D121/D100, D173/D149, A174/A150R, N200/N176, and D248/D233) were critical residues for their catalytic activity. Additionally, only transient overexpression of Type II OMTs IiOMT1 and IiOMT2 in Nicotiana benthamiana significantly increased isoscoparin accumulation, indicating that the Type II OMTs IiOMT1 and IiOMT2 could catalyze the methylation step of C-glycosylflavonoid, isoorientin at the 3′-hydroxyl position. This study provides insights into the biosynthesis of methylated C-glycosylflavonoids, and IiOMTs could be promising catalysts in the synthesis of bioactive compounds.

The effect of the hydroxyl group position on the electrochemical reactivity and product selectivity of butanediol electro-oxidation.

This article presents a study on the effect of the hydroxyl group position on the electro-oxidation of butanediols, including 1,2-butanediol, 2,3-butanediol, 1,3-butanediol, and 1,4-butanediol. The effect of the hydroxyl group position in butanediols on their electro-oxidation reactivities is investigated by cyclic voltammetry, linear sweep voltammetry, chronopotentiometry and chronoamperometry in 1.0 M KOH. The results show that the closer the two hydroxyl groups are, the higher the reactivity, and the lower the anodic potential butanediol has. Moreover, the oxidation products from chronoamperometry are analyzed by means of HPLC and NMR. Some value-added products, such as 3-hydroxypropionic acid/3-hydroxypropionate, are produced. The DFT calculation indicates that the oxidation of vicinal diols responds to the conversion from a hydroxyl group to a carboxylate group, followed by C-C bond cleavage, where the carbon charge decreases. These results provide an insight into reactant selection for the electrochemical synthesis of value-added chemicals.

Essential features for antioxidant capacity of ascorbic acid (vitamin C).

Vitamin C or ascorbic acid is an indispensable micronutrient for human health found principally on citrus species such as lemon and orange fruits and vegetables. It was involved in the production of proteins such as collagen. Its biochemical mechanism is related to its antioxidant capacity; however, its function at the cellular level is still unclear. Several theoretical studies about antioxidant and redox mechanisms for ascorbic acid were suggested; however, no derivative was proposed. Thereby, an electronic study of antioxidant capacity for ascorbic acid derivatives was performed using theoretical chemistry at the DFT/ B3LYP/6-311 + + (2d,2p) level of theory. Simplified derivatives show that enol hydroxyls are more important than any other functional group. The vicinal enolic hydroxyl on β position is more important for antioxidant capacity of ascorbic than hydroxyl on α position. According to our molecular modifications, the keto-alkene compound showed the best values when compared to ascorbic acid in some molecular characteristics. No lactone derivatives have superior application potential as antioxidant when compared with ascorbic acid. Several structures are possible to be proposed and were related to spin density contributions and the increase of chemical stability. New promising structural derivatives related to ascorbic acid can be developed in the future.

A Concise Copper-Catalyzed Oxytrifluoromethylation of Allyl Alcohols

AbstractAn efficient oxytrifluoromethylation of 1-aryl-substituted allyl alcohols has been developed using Togni’s reagent II as a trifluoromethylation reagent and copper(I) chloride as a catalyst. This reaction proceeded through a one-pot process of trifluoromethylation followed by nucleophilic attack of the vicinal hydroxyl group. This strategy features good diastereoselectivity and broad substrate scope, which provides a facile access to various 2-aryl-3-(2,2,2-trifluoroethyl)oxiranes.

Molecular cloning and characterization of two distinct caffeoyl CoA O-methyltransferases (CCoAOMTs) from the liverwort Marchantia paleacea

Caffeoyl CoA O-methyltransferases (CCoAOMTs) catalyze the transfer of a methyl group from S-adenosylmethionine to a hydroxyl moiety of caffeoyl-CoA as part of the lignin biosynthetic pathway. CCoAOMT-like proteins also catalyze to a variety of flavonoids, coumarins, and phenylpropanoids. Several CCoAOMTs that prefer flavonoids as substrates have been characterized from liverworts. Here, we cloned two CCoAOMT genes, MpalOMT2 and MpalOMT3, from the liverwort Marchantia paleacea. MpalOMT3 has a second ATG codon downstream and the truncated version that lacks 11 amino acids was named MpalOMT3-Tr. Phylogenetic analysis placed MpalOMT3 at the root of the clade with true CCoAOMTs from vascular plants and placed MpalOMT2 between the CCoAOMT and CCoAOMT-like proteins. Recombinant OMTs methylated caffeoyl CoA, phenylpropanoids, and flavonoids containing two or three vicinal hydroxyl groups. MpalOMT3 showed higher catalytic activity for phenylpropanoids than MpalOMT2, but MpalOMT2 showed more promiscuous towards eriodictyol and myricetin. The lignin content in Arabidopsis thaliana stems increased with constitutive heterologous expression of MpalOMT3-Tr, but not MpalOMT2. Subcellular localization experiments indicated that the N-terminus of MpalOMT3 probably served as a chloroplast transit peptide and inhibited its enzymatic activity. Combining the phylogenetic analysis and functional characterization, we conclude that the liverwort M. paleacea harbors true CCoAOMT and CCoAOMT-like genes.

Effect of deposition temperature and surface reactions in atomic layer deposition of silicon oxide using Bis(diethylamino)silane and ozone

We investigated the effect of deposition temperature on the properties of the silicon oxide films produced by alternating exposures to bis(diethylamino)silane (BDEAS) and ozone (O3). The surface reactions during the deposition were studied using in situ characterization techniques and density functional theory (DFT) calculations. The atomic layer deposition (ALD) temperature window was between 250 and 350 °C with a nearly constant growth rate of ∼ 0.10 nm/cycle and the step coverage higher than 94%. The saturation doses of BDEAS and O3/O2 were 5 × 106 L and 5 × 107 L. Among the films deposited in genuine ALD mode, the film deposited at 350 °C exhibited the lowest leakage current of 2.4 × 10-8 A/cm2 at −2 MV/cm and the lowest oxide trapped charge density of 6.5 × 1011/cm2. The in situ quartz crystal microbalance analysis showed that approximately 0.5 diethylamine ligand per BDEAS molecule was expected to remain on the surface after the BDEAS feeding. The in situ Fourier-transform infrared difference spectrum confirmed the presence of the ligand on the surface. DFT simulations showed that all NEt2 ligands are released on vicinal and geminal hydroxyl groups to form –SiH2*. However, only one NEt2 ligand can be removed on isolated hydroxyls because no other hydroxyls are nearby, resulting in –SiH2(NEt2)*.

Energy dissipating poly(hydroxyurethane) elastomers – Synthesis, characterization and comparison with shear thickening fluid materials

In this article we report preparation and characterization of cross-linked non-isocyanate poly(hydroxyurethane) polymeric materials showing energy-dissipating properties. The materials were obtained by the ring-opening polyaddition reaction of hyperbranched multi(cyclic carbonate) (HBPG2) with various diamines. The hyperbranched multi(cyclic carbonate) was obtained in two step procedure including anionic polymerization of glycidol with trimethylolpropane (TMP) as a core yielding polyglycerol (HBPG1) and reaction of terminal vicinal hydroxyl groups of HBPG1 with dimethyl carbonate in the presence of potassium carbonate. HBPG1 and HBPG2 were characterized using various NMR techniques, FTIR and MALDI-ToF mass spectroscopy. Thermal and mechanical properties of elastomers, including dissipated energy capacity have been studied. Analysis of force absorbing efficiency test results showed that synthesized elastomers have the capability to dissipate about 60% of the energy. The energy dissipating properties of obtained poly(hydroxyurethane) elastomers were similar to those of shear thickening fluid materials that are currently used in human body protectors, in vibration damping devices or sound insulations. The article proves that it is possible to obtain advanced engineering materials using environmentally friendly materials.

Dextran hydrogels via disulfide-containing Schiff base formation: Synthesis, stimuli-sensitive degradation and release behaviors

Dextran hydrogels (Dex-SS) containing both disulfide and Schiff base bonds were developed via facile method based on the dextran oxidation and subsequent formation of Schiff base linkages between polyaldehyde dextran and cystamine, denoted as the disulfide-containing Schiff base reactions. Results of rheology, swelling and 13C CP/MAS NMR study indicated that cross-linking degree of Dex-SS hydrogels depended strongly on the molar ratio of -CHO/-NH2. Acidic and reductive (GSH) environment sensitive degradation behaviors of Dex-SS hydrogels were then evidenced by SEM, rheology study and Ellman’s assay. Moreover, doxorubicin (DOX) was loaded into the hydrogel matrix and pH/GSH-responsive release behaviors were demonstrated. Cytocompatibility of Dex-SS hydrogel and effective cell uptake of released DOX was finally proved by transwell assay with HepG2 cells. Take advantages of the abundance of vicinal hydroxyl on a variety of polysaccharides, the disulfide-containing Schiff base reactions is considered as versatile method to develop stimuli-sensitive hydrogels for local drug delivery.