Phenolic OH Group Research Articles

INFLUENCE OF CHEMICAL MODIFICATION ON THE COMPOSITION AND PROPERTIES OF ORGANOMINERAL COMPOSITE MATERIALS

The structure characteristic and polyfunctionality of humic substances makes it possible to obtain new products by chemical modification. The aim of this work is to study the regularities of sodium humate modification processes with phosphogypsum and phosphogypsum with polyacrylamide (PAA) mixture, to establish the composition and properties of obtained organomineral composite materials. Methods. Chemical analysis, infrared spectroscopy, differential thermal analysis and scanning electron microscopy. Results and discussion. The possibility of obtaining new types of products by modifying sodium humate with phosphogypsum and its mixture with PAA is shown. The dependence of the composition and properties of obtained organomineral composite materials on the modifier nature has been revealed. The chemical modification has been shown to increase the content of COOH groups to 0.24 mg-eq/g, phenolic OH groups to 1.83 mg-eq/g, total pores to 0.44 cm3/g, static exchange capacity to 27.25 mg-eq/g, P2O5 to 1.34%, nitrogen up to 1.71% and the humic acid yield - up to 42.83%. The reaction between sodium humate and phosphogypsum proceeds leads to an increase in the content of total, digestible and water-soluble forms of P2O5. Conclusion. It has been established that the use of phosphogypsum for humic substances modification contributes to the phosphorus production waste processing. Organo-mineral materials obtained by modifying sodium humate acquire growth-stimulating, fertilizing, reclamation, water-retaining, and sorption properties. The complexity and multi-component composition of synthesized compositions is determined by DTA, IR, SEM methods. It has been shown that when sodium humate is modified with phosphogypsum, ion exchange reactions and complex formation occur.

Fiber Melt Spinning and Thermo-Stabilization of Para-Rubber Wood Lignin: An Approach for Fully Biomass Precursor Preparation.

Para-rubber wood (PRW) lignin, extracted from agricultural waste, was successfully melt-spun to fibers and thermo-stabilized without employing auxiliary additives. 31P NMR analysis revealed that PRW-lignin contained mainly a syringyl unit of phenolic C5-substituted OH group, which enabled melt flow during fiber spinning, as well as a guaiacyl unit which offered the ability to cross-link during thermo-stabilization. Thermo-stabilized fibers with no fusion were achieved at 250 °C with the heating rate of 0.1 °C/min. Structural changes in the fibers during stabilization were systematically investigated using FTIR and XPS analyses. From the results, changes in the intensities of characteristic bands relating to C-H stretching, aromatic C-H stretching, and C=O stretching indicated structural changes of lignin toward aromaticity via oxidation reactions. XPS analysis of the fibers carbonized at 900, 1000, and 1200 °C revealed an increase in carbon content from 72 to 87 wt %. and a decrease in oxygen content from 28 to 13 wt %. with the increasing carbonization temperature. The weight loss of carbonized fibers was in the range of 73.6 to 88.7%. The high weight loss of fibers carbonized at 1200 °C was explained partly due to the thermal decomposition of disordered carbon. The tensile strength and modulus of carbonized fibers were 163.0 and 275.1 MPa, respectively. This study demonstrates an approach to prepare a fully biomass precursor fiber and contributes to the exploration of the potential use of lignin from biomass waste.

Controlling the reactivity of hydrophilic bark extractives as biopolyols in urethane-formation reactions using various catalysts

The composition, functionality, and reactivity of black alder (Alnus glutinosa) bark extractives as a biopolyol with polymeric diphenyl methane diisocyanate (PMDI) have been studied using a variety of methods, including HPLC, GPC, GC, wet chemistry, and isothermal calorimetry. The Black alder (BA) bark extractives were identified as a prospective polyol consisting mainly of the oregonin-xyloside form of diarylheptanoid, which contains OH groups that are almost equally represented by phenolic and aliphatic origins. To identify catalysts that effectively increase the reactivity of low-active phenolic OH groups in urethane formation reactions, the kinetics of extractives and model compounds' interaction with PMDI catalyzed with tin organic, dibutyl tin dilaurate (DBTDL) and tertiary amine, 1,4-diazabicyclo[2.2.2]octane (DABCO) catalyst in dimethylsulfoxide (DMSO) solution were studied. The results showed that DABCO resulted in a fourfold higher reactivity of phenolic groups with PMDI compared to DBTDL catalyzed reactions. Furthermore, the reactivity of phenolic groups with PMDI catalyzed by DABCO was almost twofold greater than that of aliphatic OH catalyzed by DBTDL. The second-order constants of 31.9 × 10−4 mol·L−1·s−1 and 53.7 × 10−4 mol·L−1·s−1 were determined for the interaction of extractives with PMDI in the presence of DBTDL and DABCO, respectively. The disappearance of the radical scavenging effect of phenolic compounds in extractives derived PU elastomers obtained with DABCO catalyst indicates complete reactions of phenolic groups with isocyanate, while these groups remain partly free in the case of DBTDL catalysis. It is assumed that a combination of DBTDL and DABCO catalysts will be necessary to achieve high crosslinking while leaving a small portion of free phenolic groups in the bio-based PU network, thus obtaining material with high mechanical properties and thermal oxidative stability.

Impact of Bark-Sourced Building Blocks as Substitutes for Fossil-Derived Polyols on the Structural, Thermal, and Mechanical Properties of Polyurethane Networks.

The hydrophilic extractives isolated from black alder (Alnus glutinosa) bark through hot water extraction were characterized as novel renewable macromonomers capable of forming polyurethane (PU) networks based on a commercial polyisocyanate, with partial or complete replacement of petroleum-derived polyol polyether. The bark-sourced bio-polyol mainly consists of the xyloside form of the diarylheptanoid oregonin, along with oligomeric flavonoids and carbohydrates, resulting in a total OH group content of 15.1 mmol·g-1 and a molecular weight (Mn) of approximately 750 g∙mol-1. The 31P NMR data confirmed a similar proportion of aliphatic OH and phenolic groups. Three-component PU compositions were prepared using polyethylene glycol (Mn = 400 g∙mol-1), bio-polyol (up to 50%), and polymeric diphenylmethane diisocyanate, which were pre-polymerized in tetrahydrofuran (THF) solution with tin organic and tertiary amine catalysts. The resulting mixture was cast and subjected to thermal post-curing. Calculation and experimental data confirmed the crosslinking activity of the bark-sourced bio-polyol in PU, leading to an increase in glass transition temperature (Tg), a decrease in sol fraction yield upon leaching of cured PU networks in THF, a significant increase in Young's modulus and tensile strength. The macromonomers derived from bark promoted char formation under high temperature and oxidative stress conditions, limiting heat release during macromolecular network degradation compared to bio-polyol-free PU. It was observed that amine catalysts, which are active in urethane formation with phenolic groups, promoted the formation of PU with higher Tg and modulus at tensile but with less limitation of heat liberation during PU macromolecular structure degradation. The high functionality of the bark-derived bio-polyol, along with the equal proportion of phenolic and aliphatic OH groups, allows for further optimization of PU characteristics using three variables: increasing the substitution extent of commercial polyethers, decreasing the NCO/OH ratio, and selecting the type of catalyst used.

Drastic differences between the release kinetics of two highly related porphyrins in liposomal membranes: mTHPP and pTHPP

HypothesisThe release of hydrophobic compounds from liposomal membranes occurs by partitioning and is thus determined by the physicochemical properties (e.g. logP and water solubility) of the drug. We postulate that even minor structural differences, e.g. the position of the phenolic OH-group of the hydrophobic porphyrins mTHPP and pTHPP (meta vs. para substitution), distinctly affect their partitioning and release behavior from liposomes. ExperimentsThe release and redistribution of mTHPP and pTHPP from lecithin or POPC/POPG liposomes to different acceptor particles (DSPE-mPEG micelles and liposomes) was studied by asymmetrical flow field-flow fractionation to separate donor and acceptor particles. Reversed phase HPLC was applied to detect differences in partitioning. Molecular dynamics (MD) simulations were carried out to obtain molecular insight in the different behavior of the two compounds inside a lipid bilayer. FindingsDespite the minor differences in chemical structure, mTHPP is more hydrophobic and redistributes much slower to both acceptor phases than pTHPP. MD simulations indicate that compared to pTHPP, mTHPP makes stronger hydrogen bonds with the lipid head groups, is oriented more parallel to the lipid tails and is embedded slightly deeper in the membrane.

Selective recognition of Fe2+ in aqueous solution by chalcones

Recognition of metal ions in aqueous media has direct impact for designing new supramolecular hosts for targeting biochemical pathways. In the present work we have studied the binding behavior of three simple chalcones with variation in number of phenolic OH groups. These chalcones showed very good binding capabilities towards metal ions in CH3OH-H2O (1:1, v/v) solvent system. The receptors R1 has interacted with all metal ions, which are used in the present study through 2:1 mode of complexation whereas R2 have showed equilibrium between the complexes of 2:1 and 1:1 with few exceptions. The highest association constants (K21) of R1 and R2 for Fe2+ is observed as 1.1 × 109 (4) M−1 and 2.3 × 108 (7) M−1 respectively by fluorescence titration method. But R3, which is lack of any phenolic OH group, binds all the metal ions through the formation of 1:1 mode of complex formation by exploiting the only one donor site as carbonyl ‘O’ atom resulting lower association constant for all the metal ions. So intermolecular hydrogen bonding as well as π- π stacking interaction forced the receptors R1 and R2 to arrange in a pseudo cleft orientation for the recognition of metal ions in 2:1 mode of complex formation. The binding behaviour of the receptors with few alkali metal ions (Na+, K+ and Cs+) and alkaline-earth metal ions (Mg2+, Ca2+ and Ba2+) are also studied and observed weak binding nature in compared with the transition metal ions.

Reactivity of tert‐butylperoxyl radical with some phenylthiazolidine derivatives and probucol

AbstractThe hybrid molecule phenylthiazolidine derivatives and probucol were kinetically examined as antioxidants (AOs) in scavenging tert‐butylperoxyl radical (t‐BuOO•) with comparable to the reference AO, butylated hydroxytoluene (BHT). The anti‐t‐BuOO• reactivity of phenylthiazolidine derivatives and probucol was established using the direct kinetic electron paramagnetic resonance (EPR) technique with pulse reactant injection. Absolute values of the bimolecular reaction rate constants and antiradical capacities of the studied compounds were measured from −63 to 0°C. The main antiperoxylradical sites of the compounds under study were revealed.High removal ability of t‐BuOO• by (2‐(4‐hydroxyphenyl)thiazolidine), 4‐[thiazolidin‐2‐yl]benzene‐1,2‐diol, 2‐(4‐hydroxyphenyl)thiazolidine‐4‐carboxylic acid and probucol was connected with the reaction of hydrogen atom abstraction from phenolic OH group.Weaker antiperoxylradical reactivity of 2‐phenylthiazolidine was connected with the slower reaction of hydrogen atom abstraction from benzylic C–H bond in reference to nitrogen and sulfur atoms compared with the phenolic OH group. It is found that sulfide groups had much weaker participation in antiperoxylradical reactivity of the studied compounds. It is concluded that removal of alkylperoxyl radicals by oxidizable phenylthiazolidine derivatives and probucol may partially account for biological activity of their compounds.

The Effect of Sample Preparation Techniques on Lignin Fourier Transform Infrared Spectroscopy.

The characterization and quantification of functional groups in technical lignins are among the chief obstacles of the utilization of this highly abundant biopolymer. Although several techniques were developed for this purpose, there is still a need for quick, cost-efficient, and reliable quantification methods for lignin. In this paper, three sampling techniques for fourier transform infrared (FTIR) spectroscopy were assessed both qualitatively and quantitatively, delineating how these affected the resultant spectra. The attenuated total reflectance (ATR) of neat powders and DMSO-d6 solutions, as well as transmission FTIR using the KBr pelleting method (0.5 wt%), were investigated and compared for eight lignin samples. The ATR of neat lignins provided a quick and easy method, but the signal-to-noise ratios in the afforded spectra were limited. The ATR of the DMSO-d6 solutions was highly concentration dependent, but at a 30 wt%, acceptable signal-to-noise ratios were obtained, allowing for the lignins to be studied in the dissolved state. The KBr pelleting method gave a significant improvement in the smoothness and resolution of the resultant spectra compared to the ATR techniques. Subsequently, the content of phenolic OH groups was calculated from each FTIR mode, and the best correlation was seen between the transmission mode using KBr pellets and the ATR of the neat samples (R2 = 0.9995). Using the titration measurements, the total OH and the phenolic OH group content of the lignin samples were determined as well. These results were then compared to the FTIR results, which revealed an under-estimation of the phenolic OH groups from the non-aqueous potentiometric titration, which was likely due to the differences in the pKa between the lignin and the calibration standard 4-hydroxybenzoic acid. Further, a clear correlation was found between the lower Mn and the increased phenolic OH group content via SEC analyses. The work outlined in this paper give complementary views on the characterization and quantification of technical lignin samples via FTIR.

Effect of antioxidants on kidney damage repair in - diabetes-induced animal: a literature study

Diabetes mellitus is a disease characterized by hyperglycemia. Chronic hyperglycemia indiabetes mellitus can cause various complications, one of which is diabetic nephropathy,which affects the kidney. Chronic hyperglycemia causes an increase in free radicals and adecrease in antioxidant activity resulting in oxidative stress conditions. This study aims to determine kidney damage caused by oxidative stress and the role of antioxidants in reducingthis damage through literature studies. The literature used comes from Google search results such as PubMed, Google Scholar, ResearchGate, and ScienceDirect. From the search results, ten journals meeting the inclusion and exclusion criteria were selected for review and comparison so that a conclusion could be drawn. The results of this literature study have demonstrated that biochemical parameters, such as increased levels of creatinine, urea, malondialdehyde (MDA), and decreased antioxidant enzymes, as well as kidney histological parameters, such as changes in the shape of tubules, glomeruli, and increased kidney expression, are indicators of kidney damage caused by oxidative stress. The mechanism of antioxidants in reducing kidney damage is through DNA cutting, binding to phenolic OH groups, down-regulation of the oxidase expression of nitrogen oxides 4 nicotinamide adenine dinucleotide phosphate (Nox4 NADPH), antioxidant enzyme systems, activation of the activated protein kinase pathway - silent mating type information regulation 2 homolog 1- peroxisome proliferator-activated receptor-γ coactivator 1α (AMPK-SirT1- PGC-1 α), protein glycation reactions, and inhibition of protein 53 (P53) so that erythroid nuclear factor 2-related factor 2 (Nrf2) can activate antioxidant gene transcription.

Synthesis, Modification and Characterization of New Phenolic Resins linked to Tetrabromophthalimide

The present work aimed to synthesize new phenol resins via incorporation of structural modification through introducing new phenolic compounds containing cyclic imide moiety in reaction with formaldehyde. The synthesis of these new resins involved three steps. First, one of the three N-(hydroxyphenyl)tetrabromophtalamic acids 1-3 were processed via a reaction between tetrabromophthalic anhydride and aminophenols. Amic acids 1-3 were dehydrated in the second step by smelting, producing the identical N-(hydroxyphenyl)tetrabromophthalimides 4-6. The new imides represent the new phenolic component that was presented in condensation reaction with formaldehyde in the third step, creating the target phenolic resins 7-9. The work also involved curing the new resins through esterification of phenolic OH groups by treatment with benzoyl chloride. The chemical structures of prepared compounds were confirmed according to FT-IR, 1H NMR, and 13C NMR spectral data. As a conclusion, the present work supply of new phenolic resins and the presence of the cyclic imide (tetrabromophthalimide) moiety in their structures exhibit high softening points and resistance to solubility, which fit with some applications, while subsequent curing through esterification exhibits better solubility and lower softening points, which fit with other applications.

SPECTROPHOTOMETRIC DETERMINATION OF THE TANNIDITY OF LIGNOSULFONATES IN THE PRODUCTION OF REAGENT SYSTEMS FOR OILFIELD CHEMISTRY

The article is devoted to the issue of quantitative determination of the main qualitative indicator of lignosulfonates - a product of processing of vegetable wood raw materials. For a number of reasons of various nature, the quality of lignosulfonates has declined sharply over the past decades. The consequence was the need for additional operations to modify the lignosulfonate matrix in the technological cycles of obtaining reagent systems for oilfield chemistry, in the case of supplies of lignosulfonate with a low tannidity index. The tannidity index characterizes the inhibitory or tanning ability of reagent systems based on lignosulfonate and is quantitatively determined by the content of OH-phenolic functional groups in the composition of the lignosulfonate macromolecule (20-30 monomer units). The paper presents a comparative study of the results of determining the tannidity index of lignosulfonates of various methods of obtaining by adsorption on collagen and spectrophotometric method with ammonium molybdate. The results of the determinations were processed by the method of mathematical statistics and it was found that the variances of the results of experimental studies are homogeneous and belong to one general population according to the Fisher criterion. Based on the results of the work carried out, it can be considered mathematically justified to replace the long-term collagen method with a spectrophotometric express method for determining tannidity with ammonium molybdate at a wavelength of 400 nm and calculating the quantitative content of OH-phenolic groups. The determination of the values of the confidence intervals of the analytical methods under study shows a relatively high accuracy of the spectrophotometric method compared to the collagen method, which is characterized by overestimated results. Recommendations were issued on the inclusion of a spectrophotometric method for determining the tannidity of the process of obtaining reagent systems as an input control operation of raw materials. For citation: Teptereva G.A., Rolnik L.Z., Pugachev N.V., Zhuravleva A.A., Lukmanova I.F. Spectrophotometric determination of the tannidity of lignosulfonates in the production of reagent systems for oilfield chemistry. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2023. V. 66. N 6. P. 23-30. DOI: 10.6060/ivkkt.20236606.6797.

Manganese oxides mediated dissolve organic matter compositional changes in lake sediment and cadmium binding characteristics

In sediment environments, manganese (Mn) minerals have high dissolved organic matter (DOM) affinities, and could regulate the changes of DOM constituents and reactivity by fractionation. However, the effects of DOM fractionation by Mn minerals on the contaminant behaviors remain unclear. Herein, the transformations of mineral phases, DOM properties, and Cd(II) binding characteristics to sediment DOM before and after adsorption by four Mn oxides (δ-MnO2, β-MnO2, γ-MnOOH, and Mn3O4) were investigated using multi-spectroscopic tools. Results showed a subtle structural variation of Mn oxides in response to DOM reduction, and no phase transformations were observed. Two-dimensional correlation spectroscopy based on synchronous fluorescence spectra and Fourier transform infrared spectroscopy indicated that tryptophan-like substances and the amide (II) N–H groups could preferentially interact with Cd(II) for the original DOM. Nevertheless, preferential bonding of Cd(II) to tyrosine-like substances and phenolic OH groups was exhibited after fractionations by Mn oxides. Furthermore, the binding stability and capacity of each DOM fraction to Cd(II) were decreased after fractionation based on the modified Stern-Volmer equation. These differences may be attributed to DOM molecules with high aromaticity, hydrophobicity, molecular weight, and amounts of O/N-containing group were preferentially removed by Mn oxides. Overall, the environmental hazard of Cd will be more severe after DOM fractionation on Mn minerals. This study facilitates a better understanding of the Cd geochemical cycle in lake sediments under the DOM–mineral interactions, and recommends being careful with outbreaks of aquatic Cd pollution when sediments are rich in dissolved protein-like components and Mn minerals.

Diazo-coupled porous organic polymers as efficient catalysts for metal-free Henry and Knoevenagel reactions

Owing to linkage and building block diversity, Porous Organic Polymers (POPs) are versatile materials with high potential in organic catalysis. Herein, nitrogen-rich POPs bearing –OH phenolic groups were synthesized via the diazo-coupling reactions between phloroglucinol and benzidine (PgBd-POP), and between 1,3,5-tris(4-aminophenyl)triazine and 4,4'-[1,1′-biphenyl]-4,4′-diylbis(diazene-2,1-diyl))diphenol (TAPT-Bd(PhOH)2-POP), under mild reaction conditions. The mesoporous polymers exhibited a BET surface area of 276 ± 4 m2 g−1 and 1.94 ± 0.06 m2 g−1, and chemical stability up to 315 °C and 330 °C, respectively. Both POPs were used as catalysts in metal-free Henry and Knoevenagel condensation reactions between aromatic aldehydes and nitromethane and ethyl cyanoacetate, respectively, under mild conditions. PgBd-POP showed a remarkable efficiency of up to 99% conversion and >99% selectivity, for the Henry nitroaldol reaction between 4-nitrobenzaldehyde and nitromethane, after only 1 h at room temperature, whereas TAPT-Bd(PhOH)2-POP generally exhibited the highest catalytic activity towards the Knoevenagel reaction, with up to 99% conversion for the condensation of 4-nitrobenzaldehyde with ethyl cyanoacetate, after 1 h at room temperature. These results confirm the potential of this class of porous materials as green catalysts for organic reactions.

Modified 1,4-butanediol organosolv pretreatment on hardwood and softwood for efficient coproduction of fermentable sugars and lignin antioxidants

In this work, 1,4-butanediol (BDO) organosolv pretreatment was modified with different additives for efficient coproduction of fermentable sugars and lignin antioxidants from hardwood poplar and softwood masson pine. It was found additives more greatly improved pretreatment efficacy of softwood than hardwood. 3-hydroxy-2-naphthoic acid (HNA) addition introduced hydrophilic acid groups to lignin structure, while 2-naphthol-7-sulphonate (NS) addition promoted lignin removal, both improving cellulose accessibility for enzymatic hydrolysis. Consequently, BDO pretreatment with 90 mM acid and 2-naphthol-7-sulphonate addition achieved near complete cellulose hydrolysis (97.98%) and maximized sugar yield of 88.23% from masson pine at 2% cellulose and 20 FPU/g enzyme loading. More importantly, the recovered lignin possessed great antioxidant activity (RSI = 2.48), due to increased phenolic OH groups, reduced aliphatic OH groups and molecular weight. Results indicated the modified BDO pretreatment could significantly improve enzymatic saccharification of highly-recalcitrant softwood, while enabling coproduction of high-performance lignin antioxidants for full biomass utilization.

ESIPT-Capable 4-(2-Hydroxyphenyl)-2-(Pyridin-2-yl)-1H-Imidazoles with Single and Double Proton Transfer: Synthesis, Selective Reduction of the Imidazolic OH Group and Luminescence.

1H-Imidazole derivatives establish one of the iconic classes of ESIPT-capable compounds (ESIPT = excited state intramolecular proton transfer). This work presents the synthesis of 1-hydroxy-4-(2-hydroxyphenyl)-5-methyl-2-(pyridin-2-yl)-1H-imidazole (LOH,OH) as the first example of ESIPT-capable imidazole derivatives wherein the imidazole moiety simultaneously acts as a proton acceptor and a proton donor. The reaction of LOH,OH with chloroacetone leads to the selective reduction of the imidazolic OH group (whereas the phenolic OH group remains unaffected) and to the isolation of 4-(2-hydroxyphenyl)-5-methyl-2-(pyridin-2-yl)-1H-imidazole (LH,OH), a monohydroxy congener of LOH,OH. Both LOH,OH and LH,OH demonstrate luminescence in the solid state. The number of OH···N proton transfer sites in these compounds (one for LH,OH and two for LOH,OH) strongly affects the luminescence mechanism and color of the emission: LH,OH emits in the light green region, whereas LOH,OH luminesces in the orange region. According to joint experimental and theoretical studies, the main emission pathway of both compounds is associated with T1 → S0 phosphorescence and not related to ESIPT. At the same time, LOH,OH also exhibits S1 → S0 fluorescence associated with ESIPT with one proton transferred from the hydroxyimidazole moiety to the pyridine moiety, which is not possible for LH,OH due to the absence of the hydroxy group in the imidazole moiety.

Quantitative Methylation of Lignin Monomers Using Tetrabutylammonium Hydroxide and MeI and Applications in Organic Synthesis.

Efficient O-alkylation of phenols and carboxylic acids has essential applications in organic synthesis. A mild alkylation method for phenolic and carboxylic OH groups is developed using alkyl halides as alkylation reagents and tetrabutylammonium hydroxide as a base, and lignin monomers can be fully methylated in quantitative yields. Additionally, phenolic and carboxylic OH groups can be alkylated by different alkyl halides in one pot in different solvent systems.

Revealing structural features of lignin macromolecules from microwave-assisted carboxylic acid-based deep eutectic solvent pretreatment

Lignin is the most abundant aromatic source in nature, whose efficient utilization has been recognized as a key challenge in biorefinery. Deep eutectic solvents (DES) exhibit excellent solubility for lignin, and are promising solvent for facilitating the lignin-first biorefinery and valorization of lignin. Herein, microwave-assisted carboxylic acid-based DES pretreatment was applied on corncob; the effects of the pretreatment on physical and chemical structures of lignin was investigated. The results showed that microwave-assisted DES pretreatment enhanced the deconstruction efficiency of corncob in terms of the high removal ratio and recovery yield of DES-lignin; Moreover, the resultant DES-lignin exhibited lower molecular weights and particle size than that from conventional DES pretreatment, and presented abundant phenolic OH groups. This study provide a highly efficient pretreatment approach for the agricultural residues and the sufficient understanding on structural and chemical characteristics of resultant DES-lignin will promote its subsequent conversion and application.

Fabrication of tannin-based hydroxyl-rich, uniform and size-controllable nanospheres as carriers for silver nanoparticles

High loading of Ag nanoparticles (Ag NPs) with small sizes on catalyst carriers/support is crucial to achieve efficient catalysis, such as catalytic degradation of organic dyes in wastewater; however, it is still challenging to develop Ag NPs catalyst carriers/support with excellent Ag NPs loading. In this work, we developed bio-based (tannin and lignin-derived catechol) nanospheres (TCR) that are hydroxyl-rich, highly uniform, size-controllable, and the resultant TCR nanospheres were subsequently used as catalyst carriers/support for Ag NPs (TCR@Ag), achieving a high loading of Ag NPs yet with the ultrafine nanoparticles. The size of as-prepared TCR nanospheres can be adjusted from 737 nm to 403 nm by regulating the amount of tannin added, and the polydispersity index (PDI) of TCR nanospheres is as low as 0.042, indicating remarkable nanosphere uniformity. As catalyst carriers of Ag NPs, the use of tannin makes TCR nanospheres rich in phenolic-OH groups, which is responsible for the well-dispersed and high-density loading of Ag NPs, and the highest loading is 48.4 wt%; meanwhile, the size of Ag NPs is only 16.8 nm. The as-prepared TCR@Ag catalysts show superior catalytic performance for the typical organic dye-containing wastewater samples, and the reaction rate constants are 2.44 min−1 and 4.87 min−1 for methylene blue (MB) and methyl orange (MO), respectively, outperforming those of the most reported Ag-based catalysts. In addition, TCR@Ag catalysts also possess good environmental adaptability, dispersion stability, reusability, antioxidation activity, and negligible biological toxicity, so the novel TCR@Ag catalysts have great potential as effective catalysts for environmental remedy purpose.

Theoretical Study of the Reaction Mechanism of Phenol–Epoxy Ring-Opening Reaction Using a Latent Hardening Accelerator and a Reactivity Evaluation by Substituents

The mechanism of the phenol-epoxide ring-opening reaction using tetraphenylphosphonium-tetraphenylborate (TPP-K) was investigated using the density functional theory (DFT) method. The reaction was initiated by breaking the P-B bond of TPP-K. The generated tetraphenylborate (TetraPB-) reacted with phenol to form a phenoxide ion, which combined with tetraphenylphosphonium (TPP+) to produce the active species, i.e., tetraphenylphosphonium phenolate (TPP-OPh). The phenoxide ion in TPP-OPh nucleophilically attacked the epoxide. Simultaneously, the H atom in the phenolic OH group moved to the O atom of the ring-opened epoxide. The formed phenoxide ion bound to TPP+ again, and TPP-OPh was regenerated. The rate-determining steps in the reaction were the cleavage of the P-B bond and the triphenylborane-forming reaction. The free energies of activation were calculated to be 36.3 and 36.1 kcal/mol, respectively. It is also suggested that these values in the rate-determining steps could be manipulated by substituents introduced on the Ph group of TetraPB-. Based on these results, it is possible to construct new design guidelines for latent hardening accelerators such as TPP-K.

Effect of chemical modifications of tannins on their antimicrobial and antibiofilm effect against Gram-negative and Gram-positive bacteria.

Tannins have demonstrated antibacterial and antibiofilm activity, but there are still unknown aspects on how the chemical properties of tannins affect their biological properties. We are interested in understanding how to modulate the antibiofilm activity of tannins and in delineating the relationship between chemical determinants and antibiofilm activity. The effect of five different naturally acquired tannins and their chemical derivatives on biofilm formation and planktonic growth of Salmonella Typhimurium, Pseudomonas aeruginosa, Escherichia coli and Staphylococcus aureus was determined in the Calgary biofilm device. Most of the unmodified tannins exhibited specific antibiofilm activity against the assayed bacteria. The chemical modifications were found to alter the antibiofilm activity level and spectrum of the tannins. A positive charge introduced by derivatization with higher amounts of ammonium groups shifted the anti-biofilm spectrum toward Gram-negative bacteria, and derivatization with lower amounts of ammonium groups and acidifying derivatization shifted the spectrum toward Gram-positive bacteria. Furthermore, the quantity of phenolic OH-groups per molecule was found to have a weak impact on the anti-biofilm activity of the tannins. We were able to modulate the antibiofilm activity of several tannins by specific chemical modifications, providing a first approach for fine tuning of their activity and antibacterial spectrum.