Phenolic OH Research Articles

MD-DFT Computational Studies on the Mechanistic and Conformational Parameters for the Chemoselective Tyrosine Residue Reactions of G-Protein-Coupled Receptor Peptides with [Cp*Rh(H2O)3](OTf)2in Water To Form Their [(η6-Cp*Rh-Tyr#)-GPCR peptide]2+Complexes: Noncovalent H-Bonding Interactions, Molecular Orbital Analysis, Thermodynamics, and Lowest Energy Conformations

Bioconjugation of important G-protein-coupled receptor (GPCR) peptides with organometallic aqua complexes has proven to be an exciting new approach for discovering potential drugs acting on their respective GPCR receptors. Thus, in this study, we report on the mechanistic and conformational aspects for the chemoselective reactions of tyrosine-containing GPCR peptides with [Cp*Rh(H2O)3](OTf)2, in water, at room temperature (J. Am. Chem. Soc. 2012, 134, 10324). We have focused on three critically important GPCR peptides; namely, [Tyr1]-Leu-enkephalin (1), [Tyr4]- neurotensin(8–13) (2), and [Tyr3]-octreotide (3), each having a different position for the tyrosine residue, together with competing functionalities. The e-donating effect of the tyrosine phenol OH group was assumed to have provided high chemoselectivity. Therefore, we have concentrated on the important mechanistic and conformational pathways to the chemoselective tyrosine products, the [(η6-Cp*Rh-Tyr1,4,3)-GPCR peptide](OTf)2 complexes, utilizing molecular dynamics (MD) and density functional theory (DFT) methods, and have provided a mechanistic rationale for these chemoselective reactions, including noncovalent interactions, molecular orbital analysis, and thermodynamics. Furthermore, the influence of the [Cp*Rh]2+ group on the lowest energy conformations for the structures of [(η6-Cp*Rh-Tyr1)-Leu-enkephalin](OTf)2, 4, [(η6-Cp*Rh-Tyr4)-neurotensin(8–13)](OTf)2, 5, and [(η6-Cp*Rh-Tyr3)-octreotide](OTf)2, 6, were also assessed, including the essential intramolecular, noncovalent interactions that determined the lowest energy conformations of [(η6-Cp*Rh-Tyr1,4,3) GPCR peptide]2+ complexes, 4–6, in comparison to their ligands, GPCR peptides, 1–3. This represented, to our knowledge, the first MD/DFT study on mechanisms of an organometallic aqua complex reacting in an aqueous media with GPCR peptides, while also determining the critical secondary forces; for example, intramolecular, noncovalent H-bonding interactions that further defined the most stable conformations of the GPCR peptides and those of their [(η6-Cp*Rh-Tyr1,4,3) GPCR peptide]2+ complexes.

Acacia Wood Fractionation Using Deep Eutectic Solvents: Extraction, Recovery, and Characterization of the Different Fractions.

The selective extraction and recovery of different lignocellulosic molecules of interest from forestry residues is increasing every day not only to satisfy the needs of driving a society toward more sustainable approaches and materials (rethinking waste as a valuable resource) but also because lignocellulosic molecules have several applications. For this purpose, the development of new sustainable and ecologically benign extraction approaches has grown significantly. Deep eutectic solvents (DESs) appear as a promising alternative for the processing and manipulation of biomass. In the present study, a DES formed using choline chloride and levulinic acid (ChCl:LA) was studied to fractionate lignocellulosic residues of acacia wood (Acacia dealbata Link), an invasive species in Portugal. Different parameters, such as temperature and extraction time, were optimized to enhance the yield and purity of recovered cellulose and lignin fractions. DESs containing LA were found to be promising solvent systems, as the hydrogen bond donor was considered relevant in relation to lignin extraction and cellulose concentration. On the other hand, the increase in temperature and extraction time increases the amount of extracted material from biomass but affects the purity of lignin. The most promising DES system, ChCl:LA in a ratio of 1:3, was found to not significantly depolymerize the extracted lignin, which presented a similar molecular weight to a kraft lignin. Additionally, the 31P NMR results revealed that the extracted lignin has a high content of phenolic OH groups, which favor its reactivity. A mixture of ChCl:LA may be considered a fully renewable solvent, and the formed DES presents good potential to fractionate wood residues.

A TCF-Based Carbon Monoxide NIR-Probe without the Interference of BSA and Its Application in Living Cells.

As toxic gaseous pollution, carbon monoxide (CO) plays an essential role in many pathological and physiological processes, well-known as the third gasotransmitter. Owning to the reducibility of CO, the Pd0-mediated Tsuji-Trost reaction has drawn much attention in CO detection in vitro and in vivo, using allyl ester and allyl ether caged fluorophores as probes and PdCl2 as co-probes. Because of its higher decaging reactivity than allyl ether in the Pd0-mediated Tsuji-Trost reaction, the allyl ester group is more popular in CO probe design. However, during the application of allyl ester caged probes, it was found that bovine serum albumin (BSA) in the fetal bovine serum (FBS), an irreplaceable nutrient in cell culture media, could hydrolyze the allyl ester bond, and thus give erroneous imaging results. In this work, dicyanomethylenedihydrofuran (TCF) and dicyanoisophorone (DCI) were selected as electron acceptors for constructing near-infrared-emission fluorophores with electron donor phenolic OH. An allyl ester and allyl ether group were installed onto TCF-OH and DCI-OH, constructing four potential CO fluorescent probes, TCF-ester, TCF-ether, DCI-ester, and DCI-ether. Our data revealed that ester bonds of TCF-ester and DCI-ester could completely hydrolyze in 20 min, but ether bonds in TCF-ether and DCI-ether tolerate the hydrolysis of BSA and no released fluorescence was observed even up to 2 h. Moreover, passing through the screen, it was concluded that TCF-ether is superior to DCI-ether due to its higher reactivity in a Pd0-mediated Tsuji-Trost reaction. Also, the large stokes shift of TCF-OH, absorption and emission at 408 nm and 618 nm respectively, make TCF-ether desirable for fluorescent imaging because of differentiating signals from the excitation light source. Lastly, TCF-ether has been successfully applied to the detection of CO in H9C2 cells.

One-step lignocellulose fractionation using acid/pentanol pretreatment for enhanced fermentable sugar and reactive lignin production with efficient pentanol retrievability

To valorize whole lignocellulosic biomass, this study proposed a biphasic solvent system using dilute acid (DA)/pentanol pretreatment. Effects of the key factors, i.e., temperature and pentanol concentration, on aspen were evaluated. Under identified optimal pretreatment conditions (160 °C, 60% pentanol), 85% and 91% of lignin and hemicellulose were solubilized in separate organic and liquid phases, respectively, while 91.1% of cellulose was retained in solid fraction. Enzymatic digestibility efficiency of pretreated cellulose was ∼ 6.4-times higher than that of untreated biomass. Notably, excellent pentanol recovery rates were obtained after four-times recycling (84%) with great cellulose digestibility (81%) and delignification (71%) performance. The recovered lignin contained low levels of contaminated sugars (<1%), while it could stabilize and protect high amounts of β-O-4 bonds. Besides, high phenolic OH content was found in lignin, which could be utilized for lignin-based biomaterials. Therefore, DA/pentanol pretreatment is an innovative promising technology for lignocellulosic valorization towards biorefinery.

Synthesis, Catalysis and Antimicrobial activity of 5d- metal chelate complex of Schiff base ligands

The metal chelates of Iridium, platinum and gold with schiff base were synthesized using metal perchlorates of the respective metal ions, and schiff base formation was done by reaction of anthranilic acid and ortho hydroxybenzaldehyde in ethanolic environment. Various analytical techniques, like, UV–Visible, FT-IR, elemental analysis, molar conductance and magnetic susceptibility have been used for crystal structural analysis. A general formula of the type [M (HL) OH] of the metal complexes have been proposed by elemental and spectral analysis. The ligand to metal ratio was found to be 1:1 in all the metal chelate complexes. As per the Infrared spectral data study the interaction of oxygen (phenolic OH and acidic COOH) and an azomethine nitrogen of ligand have been found to coordinate tridentately with central metal ion. For the synthesis of metal chelate complexes the utilized activation energy was evaluated by the broido method. The synthesized metal chelate complexes and the parent ligands were analyzed also for the antibacterial activity determination against gram positive (B. subtilis, Bacillus anthracis) and gram negative (Yersinia pestis, Escherichia coli) bacterial species.

Enhancing α-etherification of lignin in Eucalyptus diol pretreatment to improve lignin monomer production

In this work, α-etherification of lignin in diol pretreatment was selectively enhanced at mild temperature for lignin isolation and subsequent valorisation. More than 90 % of lignin was removed from Eucalyptus at 120 °C in diol (ethylene glycol and 1,4-butanediol) pretreatment, resulting in >90 % cellulose conversion in 24 h at 7.5 FPU/g glucan cellulase loading. Subsequent catalytic transfer hydrogenolysis of the isolated lignins with Ru/C in ethanol gave 15 % monomer yield on native lignin basis, 5 times of that from the technical ethanol process (170 °C). HSQC NMR analysis revealed that diol pretreated lignin (120 °C) contained ∼23 % α-etherified β–O–4 interunit bonds, indicating that lignin degradation (i.e. cleavage of β–O–4 bonds) was suppressed via etherification by grafting a hydroxyl group at the α position of lignin. This finding was consistent with the isolated lignin (120 °C) had less number of phenolic OH and higher molecular weight via31P NMR and GPC analysis. 31P NMR analysis also revealed that diol isolated lignin contained more number of aliphatic OH than ethanol-isolated lignin, which increased lignin solubility and maintained the high yield (>80 %) of isolated lignin from Eucalyptus at 120 °C as expected. In summary, diol pretreatment of woody biomass can effectively isolate more lignin for hydrogenolysis to valued-added monomers without compromising the isolated yield of lignin and hydrolysis yield of remained cellulose.

Effect of structural changes of lignin during the microwave-assisted alkaline/ethanol pretreatment on cotton stalk for an effective enzymatic hydrolysis

Effective delignification of lignocellulosic biomass is an important factor to improve the efficiency of enzymatic hydrolysis and ensure the economic feasibility of bio-refining. Cotton stalk (CS) was treated by a microwave-assisted alkaline/ethanol pretreatment (MAAP) (at 160 °C for 15 min) process to separate high-purity lignin and digestible cellulose-rich residue. Results showed that the MAAP process resulted in homogeneous lignin fractions with narrow polydispersity index (PI), and the isolated lignin fragments exhibited relatively smaller molecular weights and numerous phenolic OH groups than those in MWL. The crystallization index of cellulose-rich substrates was increased after the MAAP integrated process. Meanwhile, the glucose yield of the integrated residue reached the maximum (82.41%) after enzymatic hydrolysis. The utilization of MAAP process was a beneficial and promising scheme for the generation of lignin fractions with satisfactory purity and chemical reactivity, which will facilitate the value-added application of CS in the future biorefinery.

Phenolic acids and their carboxylate anions: Thermodynamics of primary antioxidant action

Phenolic acids represent naturally occurring antioxidants and play important role in free radicals scavenging. In this work, we have studied thermodynamics of the first step of primary antioxidant action for phenolic OH groups of benzoic and cinnamic acid derivatives, and their carboxylate anions. M06–2X/6–311++G(d,p) reaction enthalpies related to Hydrogen Atom Transfer (HAT), Single Electron Transfer – Proton Transfer (SET-PT), and Sequential Proton-Loss Electron-Transfer (SPLET) mechanisms were computed for model non-polar environment (benzene) and aqueous solution. The effect of acid structure on found reaction enthalpies was investigated, as well. For HAT, representing relevant reaction path in both environments, the lowest O–H bond dissociation enthalpies, BDE, were found for sinapic acid (347 kJ mol−1 in benzene and 337 kJ mol−1 in water). With two exceptions, carboxylate anions show lower BDEs than parent acids. In aqueous solution, enthalpies of the first step of SPLET from phenolic OH groups are low (135–199 kJ mol−1). It indicates thermodynamic feasibility of the mechanism for acids, as well as their carboxylate anions. Although enthalpies of electron transfer from dianions formed after successive deprotonations of carboxyl and phenolic groups in water are usually higher than BDEs, differences are within 25 kJ mol−1. Demethylation of OCH3 groups may affect radical scavenging activity of studied substances due to O–CH3 BDE considerably lower (230–269 kJ mol−1) in comparison to O–H ones.

A prodrug of 3-(ferrocenylaminocarbonyloxymethyl)phenol activated by reactive oxygen species in cancer cells

Hybrid drugs containing ferrocene and phenol residues, whose π systems are not conjugated with each other, exhibit potent anticancer activity as previously reported. Few important open questions are remaining before practical application of these drugs becomes possible. First, their mode of action is not fully clarified. Second, it is not known whether these drugs exhibit cancer cell specificity. Third, due to the presence of the phenol moiety, these drugs can potentially be oxidatively deactivated and eliminated via phase II metabolism when applied in vivo. In this paper we report on synthesis of three prodrugs of aminoferrocene-phenol hybrids, where the phenolic OH group is masked as a boronic acid pinacol ester. We confirmed that the best prodrug in this small series p5 is activated in human ovarian cancer A2780 and Burkitt's lypmphoma BL-2 cells, but remains inactive in representative normal SBLF9 cells. Since p5 does not contain free phenolic OH groups, it will not be metabolized as phenols in vivo. We confirmed that the mechanism of anticancer activity of aminoferrocene-phenol prodrug p5 relies on generation of reactive oxygen species in cells.

Molecular and crystal structures of N-picryl-m-phenolidine and investigation of single crystal polarized Raman spectra

The molecular and crystal structures of N-picryl-m-phenolidine (or, 3-(2,4,6-trinitrophenylamino)phenol; TAP) were investigated by quantum chemical electronic structure calculations (including state-of-the-art fully-periodic DFT calculations for the crystal) and single crystal X-ray diffraction. The molecule of the compound has four low-energy conformers, which have calculated relative energies within 0.7 kJ mol–1. In all conformers, an N–H…O intramolecular hydrogen bond exists, which is established between the bridging amine moiety and one of the nitro groups of the picryl fragment, and an average angle between the two rings of ca. 55°. The crystals of the compound are monoclinic, P21/n space group, with a = 11.8098(3), b = 6.5706(2) and c = 16.5172(4) Å, β = 91.5640(10)°, Z = 4 and Z’ = 1, and is constituted by molecules assuming a geometry similar to that of the second most stable conformer of the isolated molecule. In the crystal, besides the N–H…O intramolecular hydrogen bond already present for the isolated molecule, a strong intermolecular H-bond exists where the OH group works as proton donor. The geometric constrains resulting from the establishment of this strong intermolecular H-bond is suggested to be the main factor precluding the existence of easily obtainable additional crystalline phases, contrarily to what has been found for similar molecules. Single crystal polarized Raman spectra of TAP and of the three polymorphs exhibiting different colors of its analogue N-picryl-m-toluidine (2,4,6-trinitro-N-(m-tolyl)aniline; TMA), where the phenol OH group is replaced by a methyl group, were also studied at light of fully periodic first principle calculations. Both TAP and TMA belong to the family of the prominent N-picryl-p-toluidine compound, which is well-known for showing color polymorphism, the obtained results thus being also a contribution for the available knowledge about this rare and interesting phenomenon.

Characterization of different types of lignin and their potential use in green adhesives

Lignin is the second most abundant component of lignocellulosic biomass after cellulose. This aromatic polymer has an immense potential for applications in composite materials, organic synthesis and pharmaceutical industries. In this study, different types of lignin (Kraft and three organosolv lignins from different processes) were characterized and incorporated into a pressure sensitive adhesive (PSA) aqueous formulation based on polycarboxylate polyether (PCE), which was selected for its low ecotoxicity. All lignin samples were evaluated and compared using various characterization methods, such as GPC, 13C NMR and 31P NMR spectroscopy. Thermal properties were investigated using TGA and DSC techniques. Based on these analyses, organosolv lignin samples presented lower molecular weight (Mw), lower polydispersity and higher amounts of phenolic OH groups. Optimizing molecular weight and hydroxyl contents were found to be the main factors affecting PSA properties. One of our formulations (5-OL-B2), which incorporated the organosolv lignin of lowest molecular weight (Mw ≈ 1270 g/mol) and highest OH content (~7.08 mmolOH/glignin), leads to an adhesive performance similar to that the commercial PSA, such as low peel-off losses and lower distance traveled by the ball (higher tackiness).

Screening of 1,3,4-Thiadiazole Derivatives by in silico Molecular Docking to Target Estrogen Receptor for Breast Cancer

Estrogen receptor plays a key role in physiological functions and is activated by estrogens. Breast cancer is the leading cancer among women all over the world. The molecular docking research began with the use of Schrödinger software to find the lead molecule from the 1,3,4-thiadiazole derivatives. Also, ADME drug-likeness properties were predicted to find a suitable lead candidate. Out of fifty 1,3,4-thiadiazole derivatives, TOH62 and TF62 showed the highest binding energies, and gscores are -9.36 and -8.85 kcal/mol, respectively. These results proved that the phenolic OH has a certain role in the binding with the targeted protein and is responsible for the activity. In the near future, we are willing to do the in-vitro and in-vivo anti-breast cancer evaluation of these compounds.

Cationization of Eucalyptus Kraft LignoBoost Lignin: Preparation, Properties, and Potential Applications.

Current changes toward a more biobased economy have recently created tremendous renewed interest in using lignin as a valuable source for chemicals and materials. Here, we present a facile cationization approach aiming to impart kraft lignin water-solubility, with similar good features as lignosulfonates. Eucalyptus globulus kraft lignin obtained from a paper mill black liquor by applying the LignoBoost process was used as the substrate. Its reaction with 3-chloro-2-hydroxypropyl-trimethylammonium chloride (CHPTAC) in an aqueous alkaline medium was studied to assess the impact of different reaction conditions (temperature, time, educt concentration, molar CHPTAC-to-lignin ratio) on the degree of cationization. It has been shown that at pH 13, 10 wt % lignin content, 70 °C, and 3 h reaction time, a CHPTAC-to-lignin minimum molar ratio of 1.3 is required to obtain fully water-soluble products. Elemental analysis (4.2% N), size-exclusion chromatography (Mw 2180 Da), and quantitative 13C NMR spectroscopy of the product obtained at this limit reactant concentration suggest introduction of 1.2 quaternary ammonium groups per C9 unit and substitution of 75% of the initially available phenolic OH groups. The possible contribution of benzylic hydroxyls to the introduction of quaternary ammonium moieties through a quinone methide mechanism has been proposed. Since both molecular characteristics and degree of substitution, and hence solubility or count of surface charge, of colloidal particles can be adjusted within a wide range, cationic kraft lignins are promising materials for a wide range of applications, as exemplarily demonstrated for flocculation of anionic dyes.

Correlation between physicochemical characteristics of lignin deposited on autohydrolyzed wood chips and their cellulase enzymatic hydrolysis

Enzymatic hydrolysis is a method to generate biofuel from biomass, and autohydrolysis is a popular method to pretreat biomass prior to enzymatic hydrolysis. The primary aim of the present study was to determine the role of lignin produced in the autohydrolysis process on the enzymatic hydrolysis of biomass. The HSQC and 31P NMR analyses confirmed that β-O-4 of lignin was reduced, while β-5, β-β, and S/G-ratio of lignin were increased with intensifying the hydrolysis intensity.The increase in the hydrolysis intensity significantly enhanced the condensed and non-condensed phenolic OH group of lignin. Interestingly, the cellulase enzyme adsorbed more on lignin that had more phenolic content, and its association with lignin reduced its activity for hydrolyzing cellulose microcrystals. Strong negative correlations were observed between the enzymatic hydrolysis yield and the condensed S-OH (r2 = 0.978) and G-OH (r2 = 0.961) of lignin generated in the autohydrolysis process.

A New Pt(II) Complex with Anionic s-Triazine Based NNO-Donor Ligand: Synthesis, X-ray Structure, Hirshfeld Analysis and DFT Studies.

The reaction of PtCl2 with s-triazine-type ligand (HTriaz) (1:1) in acetone under heating afforded a new [Pt(Triaz)Cl] complex. Single-crystal X-ray diffraction analysis showed that the ligand (HTriaz) is an NNO tridentate chelate via two N-atoms from the s-triazine and hydrazone moieties and one oxygen from the deprotonated phenolic OH. The coordination environment of the Pt(II) is completed by one Cl−1 ion trans to the Pt-N(hydrazone). Hirshfeld surface analysis showed that the most dominant interactions are the H···H, H···C and O···H intermolecular contacts. These interactions contributed by 60.9, 11.2 and 8.3% from the whole fingerprint area, respectively. Other minor contributions from the Cl···H, C···N, N···H and C···C contacts were also detected. Among these interactions, the most significant contacts are the O···H, H···C and H···H interactions. The amounts of the electron transfer from the ligand groups to Pt(II) metal center were predicted using NBO calculations. Additionally, the electronic spectra were assigned based on the TD-DFT calculations.

Enhancing Lignin Dispersion and Bioconversion by Eliminating Thermal Sterilization

Thermal sterilization is widely applied in fermentation to ensure a pure culture. In this study, a facile and energy-efficient strategy by eliminating thermal sterilization (ETS) was unveiled for upgrading lignin bioconversion. Through alkaline solubilization and neutralization, lignin dispersion in aqueous fermentation media was significantly enhanced by ETS. Small-angle X-ray scattering and dynamic light scattering analyses indicated that the lignin colloid size was dramatically reduced. Compared to 20.5 wt % lignin precipitation during the conventional thermal sterilization, precipitated lignin was not observed within the ETS medium. 31P NMR characterization demonstrated an 11.7% increase of phenolic OH in ETS lignin. Ionization of phenolic OH presented more negatively charged groups, strengthening electrostatic repulsion, resulting in smaller colloidal particles. Interestingly, the pure culture of Rhodococcus opacus PD630 was achieved within the ETS medium due to the lack of lignin degradation ability with most natural microbes. R. opacus PD630 cell amount, lignin degradation, and lipid production by ETS increased by 330, 16.6, and 20.7%, respectively. Overall, an energy-efficient ETS strategy that promoted lignin dispersion and bioconversion significantly is reported in this study.

Elucidation of the effect of fast pyrolysis and hydrothermal liquefaction on the physico-chemical properties of bio-oil from southern yellow pine biomass as a chemical feedstock

Bio-oils obtained from southern yellow pine biomass from two thermochemical conversion processes, fast pyrolysis (FP) and hydrothermal liquefaction (HTL), were investigated. The effects of FP and HTL on the physical and chemical properties of the bio-oils were characterized. The HTL and FP bio-oil yields were 67 and 36 wt%, respectively. The results indicated that the physical properties of the HTL bio-oil and FP bio-oil were similar; however, there were variations in the composition of the bio-oils from the same biomass. The pH values of the FP and HTL bio-oils were 2.3 and 2.8, respectively. From the GC-MS (gas chromatography–mass spectrometry) analysis, esterified chemical compounds were prevalent in the HTL bio-oil, while phenols and phenolic derivatives were found in both bio-oils. The 31P-NMR (phosphorous nuclear magnetic resonance) analysis of the bio-oils further revealed that both FP and HTL bio-oils are rich in phenolic OH and aliphatic OH functionalities, which could serve as a potential bio-polyol.

Scalable single-step synthesis of lignin-based liquid polyols with ethylene carbonate for polyurethane foams

A new method for the synthesis of lignin-based liquid polyols was developed. Organosolv lignin was reacted with ethylene carbonate in polyethylene glycol as solvent, leading to a full conversion of the phenolic OH into primary aliphatic OH groups. These aromatic polyols are obtained in a single step, without any purification. Upon modification of the polyethylene glycol molar mass, a wide range of hydroxyl values (IOH) can be covered. The polyols with up to 30%wt lignin have a viscosity suitable for the direct elaboration of polyurethane (PUR) foams. The method presents significant advantages over oxypropylation, the most common method for producing lignin-based polyols since it is performed at ambient pressure, without any toxic chemicals, does not require purification or post treatment, and allows to produce polyols with tunable properties. Four different aromatic polyols were then synthesized to produce rigid PUR foams, with substitution of up to 100% of a standard polyether polyol. The developed polyols showed very high reactivity, allowing to reduce the catalyst content in the PUR formulation by 75%. Rigid PUR foams prepared with 25% substitution of the standard polyol showed properties in the range of commercial PUR foams, with more than 90% closed cells and thermal conductivity of about 25 mW m−1/K, perfectly adequate for thermal insulation applications.

Revealing the mechanism of lignin re-polymerization inhibitor in acidic pretreatment and its impact on enzymatic hydrolysis

Phenolic additives, including 2-naphthol, 2-naphthol-7-sulfonate, and resorcinol were evaluated for their impact on the lignin re-polymerization and subsequent hydrolysis of bamboo residues. Low surface lignin concentration (65.68%) of the substrate and high Tg value (185 °C) of lignin was observed for 2-naphthol-7-sulfonate assisted pretreatment, leading to the most significant increase (14%) in enzymatic hydrolysis efficiency of pretreated bamboo residues. Meanwhile, physicochemical properties of lignin revealed that the introduced sulfonic acid groups increased the surface charge, decreased the molecular weight, promoted the cleavage of β-O-4 linkages, and prevented the re-condensation of lignin. Even though resorcinol-assisted pretreatment, by contrast, was found to be an inhibitor for enzymatic hydrolysis. NMR analysis of modified lignin showed that resorcinol led to a higher amount of non-condensed phenolic OH groups and promoted the cleavage of β-O-4 linkages, acting as an inhibitor in lignin re-polymerization during the dilute acidic pretreatment. In short, the above findings present a detailed view of suppressing lignin re-polymerization for boosting the utilization of bioresources with acidic pretreatment.

Effect of Magnesium Ion on the Radical-Scavenging Rate of Pterostilbene in an Aprotic Medium: Mechanistic Insight into the Antioxidative Reaction of Pterostilbene.

Pterostilbene (PTS), a methylated analog of resveratrol (RSV), has recently attracted much attention due to its enhanced bioavailability compared to RSV. However, little is known about the radical-scavenging mechanism of PTS. In this study, we investigated the effect of Mg(ClO4)2 on the scavenging reaction of galvinoxyl radical (GO•) by PTS in acetonitrile (MeCN). GO• was used as a model for reactive oxygen radicals. The second-order rate constant (kH) for the GO•-scavenging reaction by PTS was more than threefold larger than that by RSV, although thermodynamic parameters, such as the relative O–H bond dissociation energies of the phenolic OH groups, ionization potentials, and HOMO energies calculated by the density functional theory are about the same between PTS and RSV. The oxidation peak potential of PTS determined by the cyclic voltammetry in MeCN (0.10 M Bu4NClO4) was also virtually the same as that of RSV. On the other hand, no effect of Mg (ClO4)2 on the kH values was observed for PTS, in contrast to the case for RSV. A kinetic isotope effect of 3.4 was observed when PTS was replaced by a deuterated PTS. These results suggest that a one-step hydrogen-atom transfer from PTS to GO• may be the rate-determining step in MeCN.