Free Phenolic Hydroxyl Research Articles

Rhodium-Catalyzed Asymmetric Transfer Hydrogenation of Aryl Ketones Involving Free Phenolic Hydroxyl Group(s).

A straightforward asymmetric transfer hydrogenation for accessing enantiomerically enriched secondary benzyl alcohols involving free phenolic hydroxyl group(s) under mild conditions was developed. Various of optical pure aryl alcohols with a remarkable functional group compatibility were achieved with 78 %-97 % yields, 84 %->99 % ee's and up to 10 000 TON. This rhodium-catalyzed reaction could be performed in a gram-scale without loss of the efficiency. Furthermore, the synthetic utility has also been demonstrated in the asymmetric synthesis of (S)-adrenaline and (S)-phenylephrine.

Catechol- and Phenolic Hydroxyl-Functionalized Partially Bio-Based (Co)poly(ether sulfone)s with Multifarious Applicability

A largely bio-based new bisphenol, namely, 4,4′-((3,4-dimethoxyphenyl)methylene)-bis(2-methoxyphenol) (DMBM) was synthesized by the reaction of veratraldehyde with guaiacol. DMBM and varying compositions of DMBM and bisphenol A were polycondensed with bis(4-fluorophenyl) sulfone to afford reasonably high molecular weight film-forming (co)poly(ether sulfone)s possessing built-in methoxyl groups. T10 and Tg values of (co)poly(ether sulfone)s were in the range 382–478 °C and 171–187 °C, respectively indicating their good thermal stability and the values decreased with increase in mol % incorporation of DMBM. The methoxyl groups present in (co)poly (ether sulfone)s were quantitatively de-blocked resulting in the formation of corresponding polymers possessing pendant catechol moieties and free phenolic hydroxyl groups. By virtue of the presence of these functional moieties, (co)poly(ether sulfone)s are amenable for post-polymerization modifications, and exhibited properties such as antimicrobial (23 mm against Staphylococcus aureus and 18 mm against Escherichia coli)), antioxidant (72 % scavenger of free radicals), adhesive (2.24 MPa lap shear strength) and usefulness as redox-active agent in zinc-ion batteries. These data underscore the promise of DMBM as a versatile monomer of wider utility for the synthesis of functional (co)poly(ether sulfone)s capable of expanding their applicability beyond the conventional ones.

Molecular Docking Studies of Ortho-Substituted Phenols to Tyrosinase Helps Discern If a Molecule Can Be an Enzyme Substrate.

Phenolic compounds with a position ortho to the free phenolic hydroxyl group occupied can be tyrosinase substrates. However, ortho-substituted compounds are usually described as inhibitors. The mechanism of action of tyrosinase on monophenols is complex, and if they are ortho-substituted, it is more complicated. It can be shown that many of these molecules can become substrates of the enzyme in the presence of catalytic o-diphenol, MBTH, or in the presence of hydrogen peroxide. Docking studies can help discern whether a molecule can behave as a substrate or inhibitor of the enzyme. Specifically, phenols such as thymol, carvacrol, guaiacol, eugenol, isoeugenol, and ferulic acid are substrates of tyrosinase, and docking simulations to the active center of the enzyme predict this since the distance of the peroxide oxygen from the oxy-tyrosinase form to the ortho position of the phenolic hydroxyl is adequate for the electrophilic attack reaction that gives rise to hydroxylation occurring.

Preparation of high antioxidant nanolignin and its application in cosmetics

Lignin, as a natural polyphenol, displays anti-oxidant activity by trapping and binding free radicals through its free phenolic hydroxyl groups. However, the most accessible form, industrial lignins, generally has low phenolic hydroxyl content, which severely limits their application value and scenarios. Herein, we showed that potassium-glycerate deep eutectic solvent (PG-DES) treatment can be combined with laccase oxidation to afford prepared high antioxidant lignin nanoparticles (HA-LNPs) with notably improved anti-oxidant activities benefiting from both the enhanced phenolic hydroxyl content 170.8 % and reduced average particle size (59.0 nm). At concentrations as low as 60 μg/mL, HA-LNPs showed favorable effects in promoting collagen formation. When HA-LNPs were used as an active ingredient in the anti-aging mask formulation, the reactive oxygen species (ROS) scavenging activity of mask samples containing 0.4 % HA-LNPs reached 37.2 %. The data suggest great promise of HA-LNPs as a natural antioxidant for formulating in anti-aging skin care products.

Facile synthesis of multifunctional magnetic porous organic polymers with high catalytic performance and dye adsorption capacity

Multifunctional magnetic porous organic polymers (MOPs) rich in sulfide and free phenolic hydroxyl groups were synthesized. The MOPs exhibit a large surface area and can interact strongly with metal ions and cationic dyes, including methylene blue.

Mechanism insights into enol ether intermediate formation during β-O-4-type lignin pyrolysis

Enol ether (EE) is considered to be one of the important intermediates in lignin pyrolysis, but its formation process is still unclear. In this study, the generation of EE structure from the pyrolysis of β-O-4 linkages under vairous structural environments was studied systematically with simplified lignin models, covering phenyl dimers, phenolic dimers, and phenolic polymers, and its formation mechanism and inducing factors were summarily proposed. Results showed that EE intermediates were difficult to generate in β-O-4-type phenyl structures, but the activation of α/β-substituted side chains promoted the EE formation, confirming that elimination reactions in pyrolysis was the main driving force for EE generation. Free phenolic hydroxyl groups and corresponding phenoxy radicals were very effective EE formation activators, as they can both induce the production of quinone intermediates, which were easily converted to EE structure. These conclusions provided a new connotation for the pyrolysis of lignin β-aryl ether linkages.

Collagen/poly(acrylic acid)/MXene hydrogels with tissue‐adhesive, biosensing, and photothermal antibacterial properties

AbstractThe application of collagen‐based hydrogel is severely restricted due to its poor mechanical strength and functional singleness. In this paper, two‐dimensional MXene nanosheets were introduced into collagen/acrylic acid (AA) system, which was polymerized in situ to produce versatile hydrogel (GCol‐MX‐PAA). The tensile stress and compressive stress values of the resultant hydrogel at the MXene concentration of 5 mg/mL reached 211.5 kPa and 7.8 MPa, respectively, which were approximately 4.0 and 1.4 times higher than those of GCol‐PAA. The bonding strength of the hydrogel reached 30.7 kPa in the porcine skin‐adhesive model owing to the large number of free phenolic hydroxyl groups on GCol. Furthermore, GCol‐MX‐PAA could be applied to monitor large and subtle activities of human body due to the excellent electrical conductivity of MXene. Thanks to the outstanding photothermal conversion performance of MXene, the hydrogel could kill E. coli and S. aureus effectively under NIR irradiation. In addition, in vitro cytotoxicity test performed on L929 fibroblasts demonstrated the desirable biocompatibility of GCol‐MX‐PAA. The design strategy in this work gives guidance for the development of multifunctional collagen‐based hydrogel in a wide range of applications.Highlights Versatile hydrogel constructed from GA‐modified collagen, PAA, and MXene. The composite hydrogel displays improved mechanical properties. This hydrogel possesses superior tissue adhesion and strain sensitivity. This hydrogel shows desired photothermal antibacterial property and biocompatibility.

PEPPSI-Type Pd(II)—NHC Complexes on the Base of p-tert-Butylthiacalix[4]arene: Synthesis and Catalytic Activities

The creation of effective catalytic systems for cross-coupling reactions, reduction, etc., capable of working in water-organic or pure aqueous media is in great demand. The article presents the synthesis of NHC-palladium complexes of the PEPPSI type based on monoimidazolium derivatives of thiacalix[4]arene. The structure of the imidazolium precursors, obtained in 81–88% yields and the complexes themselves, obtained in 40–50% yields, is established using modern methods, including X-ray structural analysis and high-resolution mass spectrometry. It is shown that the obtained complex with bulk substituents near the palladium atom is not inferior to the well-known PEPPSI-type Organ’s catalyst in the catalysis of Suzuki-Miyaura coupling and is four times superior to the latter in the p-nitrophenol reduction reaction. Given the presence of free phenolic hydroxyl groups in the macrocycle, the obtained complexes are of interest for further post-modification or for immobilization on a carrier.

Demethyleneberberine alleviated the inflammatory response by targeting MD-2 to inhibit the TLR4 signaling.

The colitis induced by trinitrobenzenesulfonic acid (TNBS) is a chronic and systemic inflammatory disease that leads to intestinal barrier dysfunction and autoimmunedisorders. However, the existing treatments of colitis are associated with poor outcomes, and the current strategies remain deep and long-time remission and the prevention of complications. Recently, demethyleneberberine (DMB) has been reported to be a potential candidate for the treatment of inflammatory response that relied on multiple pharmacological activities, including anti-oxidation and antiinflammation. However, the target and potential mechanism of DMB in inflammatory response have not been fully elucidated. This study employed a TNBS-induced colitis model and acute sepsis mice to screen and identify the potential targets and molecular mechanisms of DMB in vitro and in vivo. The purity and structure of DMB were quantitatively analyzed by high-performance liquid chromatography (HPLC), mass spectrometry (MS), Hydrogen nuclear magnetic resonance spectroscopy (1H-NMR), and infrared spectroscopy (IR), respectively. The rats were induced by a rubber hose inserted approximately 8 cm through their anus to be injected with TNBS. Acute sepsis was induced by injection with LPS via the tail vein for 60 h. These animals with inflammation were orally administrated with DMB, berberine (BBR), or curcumin (Curc), respectively. The eukaryotic and prokaryotic expression system of myeloid differentiation protein-2 (MD-2) and its mutants were used to evaluate the target of DMB in inflammatory response. DMB had two free phenolic hydroxyl groups, and the purity exceeded 99% in HPLC. DMB alleviated colitis and suppressed the activation of TLR4 signaling in TNBS-induced colitis rats and LPS-induced RAW264.7 cells. DMB significantly blocked TLR4 signaling in both an MyD88-dependent and an MyD88-independent manner by embedding into the hydrophobic pocket of the MD-2 protein with non-covalent bonding to phenylalanine at position 76 in a pi-pi T-shaped interaction. DMB rescued mice from sepsis shock induced by LPS through targeting the TLR4-MD-2 complex. Taken together, DMB is a promising inhibitor of the MD-2 protein to suppress the hyperactivated TLR4 signaling in inflammatory response.

Stabilized Lignin Nanoparticles for Versatile Hybrid and Functional Nanomaterials.

Spherical lignin nanoparticles are emerging biobased nanomaterials, but instability and dissolution in organic solvents and aqueous alkali restrict their applicability. Here, we report the synthesis of hydroxymethylated lignin nanoparticles and their hydrothermal curing to stabilize the particles by internal cross-linking reactions. These colloidally stable particles contain a high biobased content of 97% with a tunable particle size distribution and structural stability in aqueous media (pH 3 to 12) and organic solvents such as acetone, ethanol, dimethylformamide, and tetrahydrofuran. We demonstrate that the free phenolic hydroxyl groups that are preserved in the cured particles function as efficient reducing sites for silver ions, giving rise to hybrid lignin-silver nanoparticles that can be used for quick and facile sensing of hydrogen peroxide. The stabilized lignin particles can also be directly modified using base-catalyzed reactions such as the ring-opening of cationic epoxides that render the particles with pH-dependent agglomeration and redispersion properties. Combining scalable synthesis, solvent stability, and reusability, this new class of lignin nanoparticles shows potential for its use in circular biobased nanomaterials.

Multifunctional lignin-poly (lactic acid) biocomposites for packaging applications.

Lignin is the most abundant aromatic biopolymer with many promising features but also shortcomings as a filler in polymer blends. The main objective of this work was to improve the processability and compatibility of lignin with poly (lactic acid) (PLA) through etherification of lignin. Commercial kraft lignin (KL) and oxypropylated kraft lignin (OPKL) were blended with PLA at different weight percentages (1, 5, 10, 20, and 40%) followed by injection molding. Low lignin contents between 1 and 10% generally had a favorable impact on mechanical strength and moduli as well as functional properties of the PLA-based composites. Unmodified lignin with free phenolic hydroxyl groups rendered the composites with antioxidant activity, as measured by radical scavenging and lipid peroxidation tests. Incorporating 5–10% of KL or OPKL improved the thermal stability of the composites within the 300–350°C region. DSC analysis showed that the glass transition temperature values were systematically decreased upon addition of KL and OPKL into PLA polymer. However, low lignin contents of 1 and 5% decreased the cold crystallization temperature of PLA. The composites of KL and OPKL with PLA exhibited good stabilities in the migration test, with values of 17 mg kg−1 and 23 mg kg−1 even at higher lignin content 40%, i.e., well below the limit defined in a European standard (60 mg kg−1). These results suggest oxypropylated lignin as a functional filler in PLA for safe and functional food packaging and antioxidant applications.

Synthesis and characterization of novel potentially biodegradable aromatic polyesters consisting of divanillic acids with free phenolic hydroxyl groups

Potentially biodegradable bio-based polyesters (P6DVAs) were synthesized from 1,6-hexanediol and divanillic acid (DVA) with free hydroxyl groups. Four DVA-based monomers with different silyl protecting groups were synthesized. Each silyl protected monomer was polymerized with 1,6-hexanediol by bulk transesterification using tetraisopropyl orthotitanate as a catalyst at 140–180 °C (first step), and 200–220 °C under vacuum (second step). Triisopropylsilyl (TIPS) -protected DVA polymerization proceeded without the elimination of TIPS groups, and a TIPS-protected DVA polyester was obtained. After deprotection of the TIPS groups, a P6DVA (weight-average molecular weight; Mw = 3.9 × 104, polydispersity; 1.4) was obtained. The P6DVA was an amorphous polymer with a glass transition point of 108 °C. Environmental degradability was assessed by a biochemical oxygen demand (BOD) test using a mixture of fresh water and soil collected from a pond. The BOD degradability of the P6DVA was 8% over 40 days, indicating its potential as a degradable polymer.

Catalyst‐free reprocessable crosslinked biobased polybenzoxazine‐polyurethane based on dynamic carbamate chemistry

AbstractThe introduction of dynamic covalent chemistry into the field of polymer chemistry has resulted in a new class of network polymer materials named covalent adaptable networks (CANs). These new materials have effectively bridged two antagonistic materials, that is, conventional thermoplastic and thermoset polymers together, thanks to these dynamic exchangeable covalent bonds, making them recyclable. In this work, we report a catalyst‐free reprocessable polybenzoxazine‐polyurethane thermosetting system with activation of carbamate dynamic bond exchange. The curing characteristics and properties of this biobased polybenzoxazine‐polyurethane network have been determined by Fourier transform infra‐red (FTIR), differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMA). Moreover, the tests of the recyclability of the material were successfully achieved under mild reprocess conditions (130°C, 10 min) thanks to the formation of abundant free phenolic hydroxyl groups. This work provides a promising potential for industrial applications as a new recyclable and reprocessable thermosetting polybenzoxazine material.

Improving antioxidant ability of functional emulsifiers by conjugating polyphenols to sodium caseinate

Sodium caseinate (NaCas), a commonly used food emulsifier, is prone to oxidation, resulting in decreased emulsion quality and stability. This study aims to understand the effect of polyphenol structures on protein's antioxidant activity and develop protein-polyphenol complexes (PPCs) with better physical and oxidation stabilities. NaCas' antioxidant abilities with or without polyphenols were examined by DPPH, FRAP, and β-carotene blenching test. The binding mechanism between protein and polyphenols was also investigated using multispectral technology and molecular docking. The results show that the addition of kaempferol, phloretin, catechin, resveratrol, and hydroxytyrosol improved NaCas' free radicals scavenging ability, reducing power and lipid protection effect. In contrast, adding apigenin, coumarin, p-hydroxybenzoic acid, and p-coumaric acid caused unsatisfactory results. The number and location of free phenolic hydroxyl groups, the binding affinity between protein and polyphenol, and protein conformation are the criteria dictating the antioxidant properties of PPCs. Finally, four novel antioxidant emulsifiers were obtained, including NaCas-catechin, NaCas-resveratrol, NaCas-phloretin, and NaCas-hydroxytyrosol complexes. Our results explored the potential application of nano-delivering functional oil using PPCs as antioxidant emulsifiers.

Synthesis of water-soluble ester-linked ursolic acid–gallic acid hybrids with various hydrolytic stabilities

To obtain derivatives of ursolic acid with improved water solubility and antioxidant activity, new ester-linked hybrids of ursolic acid and gallic acid were synthesized. In the reaction of methyl gallate with ursoloyl chloride acetate, both mono- and diacylation products were obtained. To prepare mono-alkylated and mono-acylated derivatives of gallic acid, 4,5-O-methoxymethylene-protected methyl gallate was used. It was found that ursolic-gallic acid hybrids containing phenolic ester linkage readily underwent hydrolysis at C-28 of triterpenoid. The dioxolane protection allowed selective hydrolysis of the methyl ester at the aromatic moiety of the hybrid compound leaving intact the labile C-28 ester at the triterpenoid moiety. The hybrids possessing an ester–ether linker (terpenoid-COO–CH2CH2–O-aryl) are stable to the hydrolysis. The majority of the obtained ursolic–gallic acid hybrids containing free phenolic hydroxyl groups possess excellent antioxidant activity. Notable water solubilities (∼0.5 mg/mL) of novel hybrids containing both carboxyl group and hydroxyls at aromatic moiety were found.

Discovery of Anti-TNBC Agents Targeting PTP1B: Total Synthesis, Structure-Activity Relationship, In Vitro and In Vivo Investigations of Jamunones.

Twenty-three natural jamunone analogues along with a series of jamunone-based derivatives were synthesized and evaluated for their inhibitory effects against breast cancer (BC) MDA-MB-231 and MCF-7 cells. The preliminary structure-activity relationship revealed that the length of aliphatic side chain and free phenolic hydroxyl group at the scaffold played a vital role in anti-BC activities and the methyl group on chromanone affected the selectivity of molecules against MDA-MB-231 and MCF-7 cells. Among them, jamunone M (JM) was screened as the most effective anti-triple-negative breast cancer (anti-TNBC) candidate with a high selectivity against BC cells over normal human cells. Mechanistic investigations indicated that JM could induce mitochondria-mediated apoptosis and cause G0/G1 phase arrest in BC cells. Furthermore, JM significantly restrained tumor growth in MDA-MB-231 xenograft mice without apparent toxicity. Interestingly, JM could downregulate phosphatidylinositide 3-kinase (PI3K)/Akt pathway by suppressing protein-tyrosine phosphatase 1B (PTP1B) expression. These findings revealed the potential of JM as an appealing therapeutic drug candidate for TNBC.

Porous Organic Polymer Synthesized by Green Diazo-Coupling Reaction for Adsorptive Removal of Methylene Blue.

A porous organic polymer (marked as DT-POP), which contains abundant free phenolic hydroxyl groups, is synthesized by the well-known green azo-coupling reaction in water, characterized, and utilized as an effective adsorbent for the elimination of methylene blue (MB) from water solutions. The presence of permanent mesopores, abundant active functional groups, and π-electron enrichment ascribed to phenyl rings make DT-POP an efficient adsorbent for MB due to strong hydrogen bonding, π–π, and electrostatic interactions with the cationic dye MB. DT-POP with high stability and high adsorption capacity can be reused many times and thus shows high applicability in pollutant disposal.

Analysis of the functional group composition of the spruce and birch phloem lignin

In this article, the functional group composition of the spruce (Pícea ábies) and birch (Bétula péndula) phloem lignin is described. The features of the chemical structure were studied by analyzing dioxane lignin using the elemental analysis, UV–Vis, FT-IR, and 1D NMR spectroscopy. For comparison, samples of xylem dioxane lignin isolated from the corresponding wood species were also analyzed. FT-IR spectroscopy data suggest that the lignins of birch phloem and xylem are similar in chemical structure. However, there are differences in absorption bands in the spectra of spruce dioxane lignin, which indicate the opposite. Quantitative analysis of the functional group composition was performed using 13C and 31P NMR data. It was found that free phenolic hydroxyl groups of catechol and p-hydroxyphenyl types are dominated in the composition of spruce phloem lignin. Birch phloem lignin has a qualitative and quantitative composition of functional groups characteristic of hardwood lignins. However, the content of G-units is greater than S-units, in contrast to the birch xylem lignin, where S-units predominate. The revealed differences are relevant from the point of view of plant physiology. The practical significance of the study is connected with understanding the reactivity of lignins when considering the chemical processing of tree bark.

Tracing Sweetgum Lignin's Molecular Properties through Biorefinery Processing.

Changes to the molecular properties of lignin over the course of biorefinery processing were investigated by using sweetgum as a feedstock. Hydrothermal pretreatment has been used because it is an economically attractive, green process. Three representative biorefinery lignin preparations were obtained, with about 70 % yield based on raw lignin. The three fractions included soluble lignin adsorbed on resin (XADL), solvent-extracted lignin (HTCELp), and an additional ball-milled residual lignin (HTRELp). By comparing the raw and biorefinery lignin preparations, it can be concluded that lignin undergoes both degradation and condensation throughout the various stages of the hydrothermal-based biorefinery process. The two fractions made soluble by biorefinery processing, XADL and HTCELp, were found to be low-molecular-weight degradation products enriched with free phenolic hydroxyl groups. In addition, about 15 % of noncondensed phenolic units were involved in condensation reactions. Quantitative NMR spectroscopy analysis revealed that at least about 28 % of β-O-4' substructures were cleaved. Hibbert's ketones were identified in XADL and HTRELp, which provided evidence of lignin undergoing acidolysis. The contents of β-5' and β-β' did not change significantly upon biorefinery processing. Finally, episyringaresinol was detected in XADL and HTCELp. It is hoped that these findings will help to further demonstrate the specific effects of biorefinery processing on lignin in hardwood and facilitate its utilization to improve biorefinery economics.

Characterization of Ionic Liquid Lignins Isolated from Spruce Wood with 1-Butyl-3-methylimidazolium Acetate and Methyl Sulfate and Their Binary Mixtures with DMSO.

Ionic liquids (ILs) based on 1-butyl-3-methylimidazolium (bmim) cation have proved to be promising solvents for the fractionation of plant biomass with the production of cellulose and lignin. This study deals with the characterization of lignins isolated from coniferous (spruce) wood using [bmim]OAc and [bmim]MeSO4 ionic liquids and their binary mixtures with DMSO (80:20). Molecular weight distributions, functional composition, and structural features of IL lignins were studied by size-exclusion chromatography, NMR spectroscopy (1D and 2D) and atmospheric pressure photoionization high-resolution mass spectrometry. It was shown that the interaction of ILs with lignin leads to significant chemical changes in the biopolymer; a decrease in the degree of polymerization and in the content of free phenolic hydroxyl groups due to alkylation, the disappearance (in the case of [bmim]OAc) of carbonyl groups and a significant destruction of β-O-4 bonds. The chemical reactions between lignin and 1-butyl-3-methylidazolium cation with covalent binding of ionic liquids or products of their decomposition is evidenced by the presence of a large number of nitrogen-containing oligomers in IL lignins.