Benzyl Ether Linkages Research Articles

The pretreatment and enzymatic hydrolysis behaviors of lignocellulosic biomass (oak and larch) based on structural changes in its lignin-carbohydrate complex

This study investigated the structural changes in oak and larch lignin-carbohydrate complexes (LCCs) during hydrothermal treatment and enzymatic hydrolysis. Hydrothermal treatment caused hemicellulose degradation (degradation rate at 170 ℃: larch 19.40%; oak, 22.26%). The LCC1 (glucan-lignin) fraction was the highest in the raw material of both biomasses. The LCC3 (xylan-lignin) and LCC2 (glucomannan-lignin) fractions were high in oak and larch, respectively; these fractions decreased as the hydrothermal treatment temperature increased (owing to hemicellulose degradation). Both biomasses had phenyl glycoside, benzyl ether (BE), and γ-ester (Est) linkages. The BE and Est linkages decreased as the hydrothermal treatment temperature increased; the Est linkages decrease was more significantly in oak than in larch. The efficiency of enzymatic hydrolysis was higher in oak than that in larch and increased as the hydrothermal treatment temperature increased. Furthermore, enzyme adsorption on the LCC1 sensor was higher in oak than in larch. The chemical compositions and LCC linkages of the biomass were changed by the hydrothermal treatment, which affected the efficiency of enzymatic hydrolysis. Moreover, the efficiency of enzymatic hydrolysis was higher for oak than for larch because of the difference hemicellulose and cellulose contents and LCC linkages.

Nature-Derived Epoxy Resin Monomers with Reduced Sensitizing Capacity─Isosorbide-Based Bis-Epoxides.

Epoxy resin systems (ERSs) are a class of thermosetting resins that become thermostable and insoluble polymers upon curing. They are widely used as components of protective surfaces, adhesives, and paints and in the manufacturing of composites in the plastics industry. The diglycidyl ether of bisphenol A (DGEBA) is used in 75-90% of ERSs and is thus by far the most used epoxy resin monomer (ERM). Unfortunately, DGEBA is a strong skin sensitizer and it is one of the most common causes of occupational contact dermatitis. Furthermore, DGEBA is synthesized from bisphenol A (BPA), which is a petroleum-derived chemical with endocrine-disruptive properties. In this work, we have used isosorbide, a renewable and nontoxic sugar-based material, as an alternative to BPA in the design of ERMs. Three different bis-epoxide isosorbide derivatives were synthesized: the diglycidyl ether of isosorbide (1) and two novel isosorbide-based bis-epoxides containing either a benzoic ester (2) or a benzyl ether linkage (3). Assessment of the in vivo sensitizing potency of the isosorbide bis-epoxides in the murine local lymph node assay (LLNA) showed that all three compounds were significantly less sensitizing than DGEBA, especially 2 which was nonsensitizing up to 25% w/v. The peptide reactivity showed the same order of reactivity as the LLNA, i.e., 2 being the least reactive, followed by 3 and then 1, which displayed similar peptide reactivity as DGEBA. Skin permeation of 2 and 3 was compared to DGEBA using ex vivo pig skin and static Franz cells. The preliminary investigations of the technical properties of the polymers formed from 1-3 were promising. Although further investigations of the technical properties are needed, all isosorbide bis-epoxides have the potential to be less sensitizing renewable replacements of DGEBA, especially 2 that had the lowest sensitizing potency in vivo as well as the lowest peptide reactivity.

Elucidation of lignin and polysaccharide linkages in wheat straw by 2H/13C isotopic tracer

To elucidate chemical linkages between lignin and polysaccharides, the aqueous mixed solutions of coniferin-[α-13C], syringin-[α-13C], D-glucose-[6-2H], and phenylalanine ammonia-lyase inhibitor were injected into a living wheat stalk. Internode tissues with high abundance of 2H-13C were collected. The milled wood lignin, lignin-carbohydrate complex (LCC), and residual LCC (R-LCC) with enrichment of 2H-13C were isolated. The 13C and 2H abundances showed that the lignin and polysaccharides of internode tissues were labeled by 13C and 2H, respectively. Analysis with carbon-13 nuclear magnetic resonance (13C-NMR) showed that ketal and benzyl ether bonds were formed between α-C of lignin and carbohydrates. The R-LCC and LCC were further treated with enzymes to obtain enzymatic degraded R-LCC (ED-R-LCC) and enzymatic degraded LCC (ED-LCC). 13C-NMR spectra of ED-LCC showed that the α-C of lignin side chain was combined with 6-C of carbohydrates by ether, ester, and ketal linkages. 1H-NMR differential spectra of ED-LCCs revealed an LC linkage of benzyl ether bond. Glucan-lignin (En-R-GL) and xylan-lignin (En-R-XL) complexes were separated from ED-R-LCC by ionic liquid. A part of lignin α-C was linked to cellulose 6-C by benzyl ether and α-ketal linkages. 13C-NMR spectra of En-R-XL showed there were α-benzyl ether and α-ketal bonds between lignin and xylan.

Strategy to improve the performance of solution-processed phosphorescent organic light-emitting diodes using heteroleptic green Ir(III) complexes bearing multi-functional units

For solution-processed phosphorescence organic light-emitting diodes (PHOLEDs), two multi-functional units functionalized green triplet emitters Ir(ET)-Pic and Ir(HT)-Pic were designed and synthesized. They were synthesized by employing a 2-ethylhexyl substituted amide-bridged phenylpyridine moiety applied as main ligand and picolinate (Pic) as an ancillary ligand. In addition, the 1,3-bis(N-carbazolyl)benzene (mCP) and 1,3,4-oxadiazole (OXD) groups were introduced into 3-position of main ligand via non-conjugated benzyl ether linkage. Ir(ET)-Pic and Ir(HT)-Pic exhibited an intensive green photoluminescence (PL) emission at 502 nm, narrowed full-width at half maximum (FWHM), high PL quantum yields (PLQYs) and good solubility in organic solvents. Hence, the hole injection layer optimized device using Ir(ET)-Pic and Ir(HT)-Pic as dopants showed excellent performances with a maximum external quantum efficiency (EQEmax) of 21.5 and 19.6%, and the maximum current efficiency (CEmax) of 79.4 and 69.2 cd A−1 with Commission International L'Eclairage (CIE x,y) color coordinates of (0.36, 0.60) and (0.31,0.62), respectively. In addition, we found that the presence of bulky mCP unit in the Ir(III) complex affect the hole transport characteristics in the emissive layer. The result findings, the construction of multi-functional Ir(III) complexes are an attractive design strategy for fabrication of highly efficient green solution-processed PHOLEDs.

Elucidation of the Structure of Lignin-Carbohydrate Complexes in Ginkgo CW-DHP by 13C-2H Dual Isotope Tracer.

To elucidate the chemical linkages between lignin and carbohydrates in ginkgo cell walls, 13C-2H-enriched cell wall-dehydrogenation polymers (CW-DHP) were selectively prepared with cambial tissue from Ginkgo biloba L. by feeding D-glucose-[6-2H2], coniferin-[α-13C], and phenylalanine ammonia-lyase (PAL) inhibitor. The abundant detection of 13C and 2H confirmed that D-glucose-[6-2H2] and coniferin-[α-13C] were involved in the normal metabolism of ginkgo cambial cells that had been effectively labelled with dual isotopes. In the ginkgo CW-DHP, ketal and ether linkages were formed between the C-α of lignin side chains and carbohydrates, as revealed by solid state CP/MAS 13C-NMR differential spectroscopy. Furthermore, the DMSO/TBAH ionic liquids system was used to fractionate the ball-milled CW-DHP into three lignin-carbohydrate complex (LCC) fractions: glucan–lignin complex (GL), glucomannan–lignin complex (GML), and xylan–lignin complex (XL). The XRD determination indicated that the cellulose type I of the GL was converted into cellulose type II during the separation process. The molecular weight was in the order of Ac-GL > Ac-GML > XL. The 13C-NMR and 1H-NMR differential spectroscopy of 13C-2H-enriched GL fraction indicated that lignin was linked with cellulose C-6 by benzyl ether linkages. It was also found that there were benzyl ether linkages between the lignin side chain C-α and glucomannan C-6 in the 13C-2H-enriched GML fraction. The formation of ketal linkages between the C-α of lignin and xylan was confirmed in the 13C-2H-enriched XL fraction.

Structural characterization of the lignin-carbohydrate complex in biomass pretreated with Fenton oxidation and hydrothermal treatment and consequences on enzymatic hydrolysis efficiency

In this study, lignin-carbohydrate complexes (LCCs) were isolated from biomass (raw and pretreated) to investigate the structural changes in biomass pretreated by Fenton oxidation and hydrothermal treatment, and their effect on enzymatic hydrolysis. The composition and structure of the LCCs fractions were investigated via carbohydrate analysis, XRD, FT-IR, and 2D HSQC NMR. The biomass degradation rate of yellow poplar and larch during Fenton oxidation and hydrothermal treatment was approximately 30%. Most of the hemicellulose was degraded during pretreatment, while xylan remained in the yellow poplar, and galactan, mannan, and xylan remained in the larch. The fractional yield of glucan-rich LCC (LCC1) in the yellow poplar (raw and pretreated biomass) was high, while that of glucomannan-rich LCC (LCC3) in larch was higher than the yield yellow poplar. Phenyl glycoside, γ-ester, and benzyl ether linkages were observed in the LCCs of yellow poplar, while phenyl glycoside and γ-ester were detected in those of larch. Following pretreatment, the frequencies of β–β′, β-5, and γ-ester in the LCCs of larch were found to be higher than in those of yellow poplar. The efficiencies of enzymatic hydrolysis for the pretreated yellow poplar and larch were 93.53% and 26.23%, respectively. These finding indicated that the β–β′, β-5, and γ-ester linkages included in the pretreated biomass affected the efficiency of enzymatic hydrolysis.

Isolation and Identification of a Novel Anti-protein Aggregation Activity of Lignin-Carbohydrate Complex From Chionanthus retusus Leaves.

Lignin-carbohydrate complex (LCC) is the biological macromolecule that has been demonstrated to exert multiple biological functions, including antioxidant, anti-inflammation and anti-tumorigenesis, which support its broad application in the bioengineering field. However, it remains elusive the involvements of LCC in human neurological disorders, especially those with the overproduction of reactive oxygen species (ROS), such as spinocerebellar ataxias (SCAs). In this study, we found a previously undetermined anti-protein aggregation activity of LCC. Initially, two individual LCC preparations and carbohydrate-free lignin were isolated from the water-extracted waste residues of Chionanthus retusus (C. retusus) tender leaves. The chemical compositional analysis revealed that lignin (61.5%) is the predominant constituent in the lignin-rich LCC (LCC-L-CR), whereas the carbohydrate-rich LCC (LCC-C-CR) is mainly composed of carbohydrate (60.9%) with the xylan as the major constituent (42.1%). The NMR structural characterization showed that LCC-L-CR preparation is enriched in benzyl ether linkage, while phenyl glycoside is the predominant type of linkage in LCC-C-CR. Both LCC and lignin preparations showed antioxidant activities as exemplified by their abilities to scavenge free radicals in cultured mammalian cells and ROS in zebrafish. We further demonstrated a pronounced capability of LCC-L-CR in inhibiting the aggregation of expanded Ataxin-3, disease protein of SCA type 3, in human neuronal cells. Taken together, our study highlights the antioxidant and novel anti-protein aggregation activities of the C. retusus tender leaves-derived LCC.

Structural elucidation of lignin-carbohydrate complexes (LCCs) from Chinese quince (Chaenomeles sinensis) fruit

The lignin-carbohydrate complexes (LCCs) of the mesocarp (MS) and near the endocarp (NE) of Chinese quince (Chaenomeles sinensis) fruits were analyzed using three different methods of fractioning: milled wood lignin (MWL), LCC extracted from crude MWL with acetic acid (LCC-AcOH), and Bjorkman LCC. The MWL and LCC fractions were characterized by carbohydrate composition analysis, SEC, FT-IR, Py-GC/MS, thermal analysis and 2D HSQC NMR. Notably, large amounts of arabinose and galactose remained in the Björkman LCC fractions suggesting a chemical bond between the lignin and pectin. MWL and LCC-AcOH fractions showed better thermal stability than the Björkman LCC fractions. The structure of MS lignin was similar to that of NE lignin; however, fractions from the different fractionation methods revealed differences. The MWL fractions were rich in benzyl ether and γ-ester linkages, while the Björkman LCC fractions contained phenyl glycoside and γ-ester linkages, and the LCC-AcOH fractions contained phenyl glycoside and benzyl ether linkages. These findings are helpful in understanding the nature of lignin and LCC in Chinese quince fruits and provide a theoretical support for their potential application.

Synthesis of Well-Defined Three- and Four-Armed Cage-Shaped Polymers via “Topological Conversion” from Trefoil- and Quatrefoil-Shaped Polymers

This paper describes a novel synthetic approach for three- and four-armed cage-shaped polymers based on the topological conversion of the corresponding trefoil- and quatrefoil-shaped precursors. The trefoil- and quatrefoil-shaped polymers were synthesized by the following three reaction steps: (1) the t-Bu-P4-catalyzed ring-opening polymerization of butylene oxide using multiple hydroxy- and azido-functionalized initiators to produce the three- or four-armed star-shaped polymers possessing three or four azido groups at the focal point, respectively, (2) the ω-end modification to install a propargyl group at each chain end, and (3) the intramolecular multiple click cyclization of the clickable star-shaped precursors. The topological conversion from the trefoil- and quatrefoil-shaped polymers to the cage-shaped polymers was achieved by the catalytic hydrogenolysis of the benzyl ether linkages that had been installed at the focal point. The amphiphilic cage-shaped block copolymers together with the corresponding trefoil- and quatrefoil-shaped counterparts were synthesized in a similar way using 2-(2-(2-methoxyethoxy)ethoxy)ethyl glycidyl ether as a hydrophilic monomer and decyl glycidyl ether as a hydrophobic monomer. Interestingly, significant changes in the critical micelle concentration and micellar morphology were observed for the amphiphilic block copolymers upon the topological conversion from the trefoil- and quatrefoil-shaped to cage-shaped architectures.

Effect of Lignin Carbohydrate Complexes of Hardwood Hybrids on the Kraft Pulping Process

Lignin-carbohydrates complexes influence many chemical properties in the wood, such as difficult-to-remove lignin from Kraft pulps at the end of pulping due to the occurrence of lignin carbohydrates bonds. Therefore, this study aimed to study the influence of lignin-carbohydrate complexes on eucalyptus Kraft pulping. Spectroscopic techniques (13C NMR and HSQC-2D) were applied for the determination and quantification of lignin-carbohydrate complex (LCC) structures, and then evaluated the effect of LCC on Kraft pulping of eucalyptus hybrids. The analytical tools allowed the identification and quantification of the benzyl ether, γ-ester, and phenyl glucoside linkages of the lignin-carbohydrate complexes in eucalyptus hybrid wood. The glycosidic phenyl and γ-ester linkages are, respectively, more and less significant from the quantitative point of view. Analysis of 13C NMR of the samples showed that the eucalyptus hybrid GxGL contained high β-O-4 linkages content and also higher pulping yield than the other samples, suggesting that the linkages between lignin are more important than LCC linkages in pulping.

Efficient Synthesis of Chiral Binaphthol Aldehyde with Phenyl Ether Linkage for Enantioselective Extraction of Amino Acids

A binaphthol aldehyde with phenyl ether linkage, compound 2, has been synthesized starting from binaphthol‐3‐carboxylic acid. The axially chiral binaphthol ring was racemized during the synthesis due to high temperatures required in O‐phenylation reaction. The enantiomerically pure form of 2 was obtained from the resolution of the diastereomeric imine of 2. Optically pure compound (S)‐2 was applied to the enantioselective liquid–liquid extraction of amino acid between CH2Cl2 and aqueous layers. The stereoselectivities, that is, d/l ratio of the amino acid extracted, ranged from 3.57 to 11.1. One carbon was absent in compound (S)‐2 compared to the compound (S)‐1 with benzyl ether linkage, which differentiated the conformations of their imines formed with amino acids.

Study on the residual lignin in Eucalyptus globulus sulphite pulp

Abstract The residual lignin (LR sample) was isolated from unbleached acid sulphite pulp from Eucalyptus globulus with kappa number 18.2 by acidolysis and structurally characterized by wet chemistry and NMR techniques. The main structural features of LR were compared with lignin isolated from sulphite spent liquor (LSSL sample) and dioxane lignin (DL sample) from eucalypt wood. LR contains less sulphonic groups (4.4%) compared to LSSL (11.3%), and its molecular weight (2200 Da) is very close to that of DL (2600 Da). A part of sulphonic groups is located at the benzylic carbon in β-O-4′ and β-5′ structures. LR revealed ca. 20% lower abundance of β-O-4′ structures than DL, but ca. 40% higher abundance of these structures than LSSL. The degree of condensation of LR was higher than that of DL but lower than that of LSSL. The condensed structures in LR mainly originate from C6-linked syringyl units. The structural peculiarities of LR consisted of the relatively high proportion of syringyl units compared to DL and the strong structural association with hemicelluloses via benzyl ether linkages. The differences in the structure of residual lignins from eucalypt sulphite and kraft pulps have been discussed.

Analysis of lignin–carbohydrate and lignin–lignin linkages after hydrolase treatment of xylan–lignin, glucomannan–lignin and glucan–lignin complexes from spruce wood

Xylan-lignin (XL), glucomannan-lignin (GML) and glucan-lignin (GL) complexes were isolated from spruce wood, hydrolyzed with xylanase or endoglucanase/β-glucosidase, and analyzed by analytical pyrolysis and 2D-NMR. The enzymatic hydrolysis removed most of the polysaccharide moieties in the complexes, and the lignin content and relative abundance of lignin-carbohydrate linkages increased. Analytical pyrolysis confirmed the action of the enzymatic hydrolysis, with strong decreases of levoglucosane and other carbohydrate-derived products. Unexpectedly it also revealed that the hydrolase treatment alters the pattern of lignin breakdown products, resulting in higher amounts of coniferyl alcohol. From the anomeric carbohydrate signals in the 2D-NMR spectra, phenyl glycoside linkages (undetectable in the original complexes) could be identified in the hydrolyzed GML complex. Lower amounts of glucuronosyl and benzyl ether linkages were also observed after the hydrolysis. From the 2D-NMR spectra of the hydrolyzed complexes, it was concluded that the lignin in GML is less condensed than in XL due to its higher content in β-O-4' ether substructures (62 % of side chains in GML vs 53 % in XL) accompanied by more coniferyl alcohol end units (16 vs 13 %). In contrast, the XL lignin has more pinoresinols (11 vs 6 %) and dibenzodioxocins (9 vs 2 %) than the GML (and both have ~13 % phenylcoumarans and 1 % spirodienones). Direct 2D-NMR analysis of the hydrolyzed GL complex was not possible due to its low solubility. However, after sample acetylation, an even less condensed lignin than in the GML complex was found (with up to 72 % β-O-4' substructures and only 1 % pinoresinols). The study provides evidence for the existence of structurally different lignins associated to hemicelluloses (xylan and glucomannan) and cellulose in spruce wood and, at the same time, offers information on some of the chemical linkages between the above polymers.

The influence of lignin–carbohydrate complexes on the cellulase-mediated saccharification I: Transgenic black cottonwood (western balsam poplar, California poplar) P. trichocarpa including the xylan down-regulated and the lignin down-regulated lines

The influence of the putative lignin–carbohydrate complexes (LCCs) on enzymatic saccharification was elucidated for the first time by examining two groups of transgenic black cottonwood (P. trichocarpa) comprised of the lignin down-regulated and the xylan down-regulated lines. Any adventitious contaminants that could affect the characterization of LCCs and the enzymatic saccharification were removed by performing a thorough extraction on the samples. The crude milled wood lignin was subsequently isolated from which the phenyl glycoside, benzyl ether and γ-ester linkages representative of the LCCs were identified and quantified with the combination of 13C and 1H–13C Heteronuclear Single Quantum Coherence (HSQC) NMR. The result indicated that the samples showed different levels of the three LCC linkages, depending on the xylan and/or lignin content. The correlation between the LCCs and enzymatic saccharification nearly conclusively demonstrated that the LCCs accounting for the recalcitrance of lignocellulosic biodegradation.

Synthesis and characterisation of a monotropic dendritic liquid crystalline aziridine monomer

We synthesised a novel mesogenic dendritic aziridine, 2-(aziridin-1-yl)ethyl 3,4,5-tris[4-(n-dodecan-1-yloxy)benzyloxy)]benzoate (compound 2), by the esterification method with N,N′-dicyclohexylcarbodiimide. A crystalline compound was obtained with a melting point of 65°C and a monotropic columnar liquid crystalline (LC) phase on cooling. Preliminary polymerisation tests were performed in the presence of several initiators and conditions, and showed that in some cases cleavage of the benzyl ether linkage happened, while in some others polymerisation did not occur at all. Finally, we could polymerise compound 2 to some extent in deuterated tetrachloroethane in the presence of 1 mol% BF3 · EtNH2 at 125°C, as shown by 1H NMR spectrum and polarised optical microscopic (POM) observation. Therefore, compound 2 could become a mesogenic precursor for the preparation of columnar polyamines.

ChemInform Abstract: Synthesis and anti‐HCV Activity of 2,6‐Bisarylmethyloxy‐5‐hydroxy‐7‐phenylchromones.

AbstractTitle compounds (X) are synthesized starting from ketone (I).

The influence of lignin–carbohydrate complexes on the cellulase-mediated saccharification II: Transgenic hybrid poplars (Populus nigra L. and Populus maximowiczii A.)

Twelve transgenic hybrid poplars (Populus nigra L. and Populus maximowiczii A.) were used to demonstrate the influence of the lignin–carbohydrate complexes (LCCs) on enzymatic saccharification. The samples have different levels of the syringaldehyde (S) to vanillin (V) ratio from 0.1 to 2.6 and the lignin content from 10.5% to 24.3%, compared to the control (the S/V ratio 1.7 and the lignin content 22.0%). Any adventitious contaminants that could affect the final enzymatic saccharification were removed by performing thorough extraction on the samples. The crude milled wood lignins were subsequently isolated from which the phenyl glycoside, benzyl ether and γ-ester linkages representative of the LCC were identified and quantified by 13C and 1H–13C HSQC NMR. It was found that the samples showed different levels of the three LCC linkages, depending on the lignin content and/or the S/V ratio. The correlation between the LCCs and enzymatic saccharification nearly conclusively demonstrated that the LCCs accounted for the recalcitrance of lignocellulosic biodegradation.

Synthesis and Anti-HCV Activity of 2,6-Bisarylmethyloxy-5-hydroxy-7-phenylchromones

Hepatitis C virus (HCV) was identified to be the causative agent of non-A-non-B viral hepatitis in the late 1989. Approximately 80% of the acute infections become chronic, leading to liver cirrhosis and hepatic cellular carcinoma, but a protective vaccine does not exist yet and the current therapeutic options are very limited. Previously, we reported potent anti-HCV activity of the 5hydroxychromone derivatives, 6-arylmethyl-5-hydroxy-7phenylchromone (1, Fig. 1) and 2-arylmethyloxy-6-(3chlorobenzyloxy)-5-hydroxychromome (2, Fig. 1), of which aromatic substituents (R, Fig. 1) were found to play the critical role for antiviral activity. In both cases, electron withdrawing substituents on the aromatic C-3 or C-3' position provided the resulting 5-hydroxychromone derivative with significantly enhanced antiviral activity against HCV. In addition, compound 2 having 3'-substituted arylmethoxy group showed higher anti-HCV activity than the corresponding analogue of 1. This result suggests that the HCV RdRp might have a binding site specific for the 5-hydroxychromone scaffold around which two hydrophobic pockets are located. In this study, as a part of our ongoing efforts to discover a potent anti-HCV compound, we designed a novel 5-hydroxychromone derivative with a combination of structures 1 and 2. Herein, we report synthesis of 2,6-bis(arylmethyloxy)-5-hydroxy-7-phenylchromone derivatives (3) with various metaor paraelectron withdrawing aromatic substituents (R = F, Cl, Br, I, CN, NO2, CF3) and evaluation of their anti-HCV activities. The synthetic route to the title compounds, 2,6-bis(arylmethyloxy)-5-hydroxy-7-phenylchromes (3a-3k) is outlined in Scheme 1. Following our previous protocols, 1-[5-hydroxy-2,3-dimethoxy-(1,1'-biphenyl)-4-yl]ethanone (4) was prepared from commercially available 5-bromovanilline. Treatment of 4 with a mixture of LiHMDS, CS2, and MeI in THF provided the corresponding ketene dithioacetal, which was then cyclized under basic conditions to give 5 in 41% yield. Oxidation of 5 was accomplished by mCPBA to 6 (83% yield), of which methanesulfonyl group was displaced with benzyloxy moiety upon treatment with benzyl alcohol and NaH in THF to furnish 7 in 49% yield. Lewis acid-catalyzed cleavage of methyl and benzyl ether linkages of 7 provided the free chromone 8 in 90% yield. Due to the intramolecular hydrogen bonding between 4-keto and 5-OH

Readily accessible fluorescent probes for sensitive biological imaging of hydrogen peroxide.

Hydrogen peroxide is a major component of oxygen metabolism in biological systems that, when present in high concentrations, can lead to oxidative stress in cells. Noninvasive molecular imaging of H(2)O(2) using fluorogenic systems represents an effective way to detect and measure the accumulation of this metabolite. Herein, we detail the development of robust H(2)O(2)-sensitive fluorescent probes using a boronic ester trigger appended to the fluorophore through a benzyl ether linkage. A major advantage of the probes presented here is their synthetic accessibility, with only one step needed to generate the probes on the gram scale. The sensitivity of the probes was evaluated in simulated physiological conditions, showing micromolar sensitivity to H(2)O(2). The probes were tested in biological model systems, demonstrating effective imaging of unstimulated, endogenous H(2)O(2) levels in RAW 264.7 cells and murine brain tissue.

Unveiling the Structural Heterogeneity of Bamboo Lignin by In Situ HSQC NMR Technique

One of the primary challenges for efficient utilization of lignocellulosic biomass is to clarify the complicated structure of lignin. In this study, in situ heteronuclear single quantum coherence nuclear magnetic resonance (NMR) characterization of the structural heterogeneity of lignin polymers during successively treated bamboo was emphatically performed without componential separation. Specially, the NMR spectra were successfully obtained by dissolving the acetylated and non-acetylated bamboo samples in appropriate deuterated solvent (CDCl3 and DMSO-d 6). The heterogeneous lignin polymers in bamboo samples were demonstrated to be HGS-type and partially acylated at the γ-carbon of the side chain by p-coumarate and acetate groups. The major lignin linkages (β–O–4, β–β, and β–5, etc.) and various lignin–carbohydrate complex linkages (benzyl ether and phenyl glycoside linkages) can be assigned, and the frequencies of the major lignin linkages were quantitatively obtained. In particular, the residual enzyme lignin (REL) contained a higher amount of syringyl units and less condensed units as compared to other samples. Inspiringly, the method gives us a vision to track the structural changes of plant cell wall (e.g., lignin polymers) during the different pretreatments.