Single-quantum Correlation Nuclear Magnetic Resonance Research Articles

Enhanced production of sugars and UV-shielded lignin/PAN fiber mats from chemi-mechanical pulps

This study investigated poplar pretreatments by chemi-mechanical pulping (CMP) under different beating degrees and alkali concentrations. The enzyme-mediated hydrolysis of pretreated poplar was enhanced by deacetylation and delignification. Meanwhile, the remaining lignin residues were used to produce lignin/polyacrylonitrile (PAN) fiber mats by electrospinning. These mats exhibited excellent mechanical and UV-blocking performance when the lignin was obtained from pulps under milder alkali concentrations (5 g/L). 31P nuclear magnetic resonance (31P NMR) and two-dimensional heteronuclear single-quantum correlation nuclear magnetic resonance (2D HSQC NMR) data revealed that increasing the beating degree at low alkali concentration during the CMP process led to the cleavage of β-O-4′ interunit linkages and re-condensation in lignin, releasing several phenolic groups. Lignin with more linear β-O-4′ interunit linkages and lesser phenolic groups, obtained from treatment of CMP with lower alkali concentration (5 g/L) and beating degree (20°SR), resulted in the corresponding lignin/PAN fiber mats exhibiting better mechanical performance. Further, lignin, along with the increased phenolic-OH and COOH, and p-hydroxybenzoate (PB) units with a more extended conjugate structure, derived from CMP under lower alkali concentration (5 g/L) and higher beating degree (45°SR), led to a stronger ultraviolet (UV) absorption in the corresponding lignin/PAN mats. To summarize, this study reports a mild and low-pollution biomass pretreatment method (CMP) that can efficiently regulate the lignin structure and exhibit efficient anti-ultraviolet properties. The corresponding UV-blocking fiber mats can be potentially used as materials for wearable fabrics.

Fast pyrolysis of guaiacyl-syringyl (GS) type milled wood lignin: Product characteristics and CH4 formation mechanism study

It is anticipated that the insight into the demethylation and mechanism of CH4 formation from natural lignin using in-situ diffuse reflectance infrared Fourier transform spectroscopy (in-situ FTIR) combined with two-dimensional perturbation correlation infrared spectroscopy (2D-PCIS) and density functional theory (DFT) calculation analysis would contribute to a deeper insight of bond cleavage mechanism of lignin pyrolysis. Herein, GS-type lignin (poplar MWL) was characterized by Fourier transform infrared spectroscopy (FTIR) and heteronuclear Single-Quantum Correlation Nuclear Magnetic Resonance (HSQC), and its pyrolysis at different temperatures was performed in a lab-scale fixed-bed reactor. The biochar, gaseous and liquid products were qualitative, and quantitative analysis of gases and bio-oil is demonstrated using gas chromatography (GC) and gas chromatography–mass spectrometry (GC–MS). The key of CH4 formation is the homolytic cleavage of the methoxyl functional group generating methyl radical and further verified via in-situ FTIR combined with 2D-PCIS and DFT calculation. The study established a new methodology based on multiple factor analysis to evaluate the CH4 formation mechanism in GS-type milled wood lignin at the molecular level, which is of positive significance for increasing lignin valorization and improving the environment.

Synthesis and Characterization of Lignin-grafted-poly(ε-caprolactone) from Different Biomass Sources

Modification of lignin with poly(ε-caprolactone) is a promising approach to valorize industrial low-value lignins and to advance the bioeconomy. We have synthesized lignin grafted poly(ε-caprolactone) (lignin-g-PCL) copolymers via ring-opening polymerization of ε-caprolactone with different types of lignins of varying botanical sources (G-type pine lignin, S/G-type poplar lignin, and C-type Vanilla seeds lignin) and lignin extraction methods (Kraft and ethanol organosolv pulping). The lignin-g-PCL copolymer showed remarkably improved compatibility and dispersion in acetone, chloroform, and toluene in comparison to non-modified lignins. The structure and thermal properties of the lignin-g-PCL were investigated using Fourier-transform infrared spectroscopy (FTIR), 31P nuclear magnetic resonance (NMR), 2D heteronuclear single quantum correlation (HSQC) NMR, gel permeation chromatography (GPC), and differential scanning calorimetry (DSC). We have found that all the technical lignins were reactive to the copolymerization reaction regardless of their plant source and isolation methods. The molecular weights of the synthesized lignin-g-PCL copolymers were positively correlated with the content of aliphatic lignin hydroxyls, suggesting that the copolymerization reaction tends to occur preferentially at the aliphatic hydroxyls rather than the phenolic hydroxyls of lignin. Thermal analyses of the lignin-g-PCL copolymers were studied, and in general, a reduction of melting temperature and crystallinity percentage in comparison to the neat PCL was observed. However, the thermal behavior of lignin-g-PCL copolymers varied depending on the lignin feedstocks employed in the copolymerization reaction.

Effect of ionic liquid pretreatment on the physicochemical properties of hemicellulose from bamboo

Ionic liquid (IL) pretreatment of lignocellulosic biomass has been the focus of attention due to its numerous advantages compared with conventional methods. The change in the physicochemical properties of the three main components of this biomass during IL pretreatment is the key factor for their further utilization and conversion. In this study, hemicellulose extracted from bamboo was dissolved in three ILs with different imidazolium cations and the same anion of acetate, including 1-ethyl-3-methylimidazolium acetate (EmimAc), 1-butyl-3-methylimidazolium acetate (BmimAc), and 1-allyl-3-methylimidazolium acetate (AmimAc). The solubility of hemicellulose in the ILs was measured as a function of temperature from 120 °C to 150 °C. Hemicelluloses regenerated from the saturated IL solutions were characterized by using Fourier transform infrared spectroscopy, gel permeation chromatography, gas chromatography–mass spectrometry, 13C–1H heteronuclear single-quantum correlation nuclear magnetic resonance, and thermogravimetry. The solubility of hemicellulose in the three ILs was greatly affected by temperature, and the solubility increased with increasing temperature. The highest solubilities per 100 g of IL were 15.56, 15.09, and 6.73 g in BmimAc, EmimAc, and AmimAc, respectively. Hemicelluloses regenerated from saturated IL solutions showed similar physicochemical features with that of the original hemicellulose before being pretreated with ILs. These features included molecular weight, relative neutral sugar composition, structural feature, and thermal stability. Hence, hemicellulose was litter degraded during IL solving. In addition, the recovered EmimAc was analyzed after dissolving hemicellulose to a saturated state at 150 °C by using 13C and 1H NMR. The recovered IL contained minimal amounts of ethanol and other impurities.

Evaluating the Effects of Fibrinogen αC Mutations on the Ability of Factor XIII to Crosslink the Reactive αC Glutamines (Q237, Q328, Q366).

Fibrinogen (Fbg) levels and extent of fibrin polymerization have been associated with various pathological conditions such as cardiovascular disease, arteriosclerosis, and coagulation disorders. Activated factor XIII (FXIIIa) introduces γ-glutamyl-ε-lysinyl isopeptide bonds between reactive glutamines and lysines in the fibrin network to form a blood clot resistant to fibrinolysis. FXIIIa crosslinks the γ-chains and at multiple sites in the αC region of Fbg. Fbg αC contains a FXIII binding site involving αC (389-402) that is located near three glutamines whose reactivities rank Q237 >> Q366 ≈ Q328. Mass spectrometry and two-dimensional heteronuclear single-quantum correlation nuclear magnetic resonance assays were used to probe the anchoring role that αC E396 may play in controlling FXIII function and characterize the effects of Q237 on the reactivities of Q328 and Q366. Studies with αC (233-425) revealed that the E396A mutation does not prevent the transglutaminase function of FXIII A2 or A2B2. Other residues must play a compensatory role in targeting FXIII to αC. Unlike full Fbg, Fbg αC (233-425) did not promote thrombin cleavage of FXIII, an event contributing to activation. With the αC (233-425) E396A mutant, Q237 exhibited slower reactivities compared with αC wild-type (WT) consistent with difficulties in directing this N-terminal segment toward an anchored FXIII interacting at a weaker binding region. Q328 and Q366 became less reactive when Q237 was replaced with inactive N237. Q237 crosslinking is proposed to promote targeting of Q328 and Q366 to the FXIII active site. FXIII thus uses Fbg αC anchoring sites and distinct Q environments to regulate substrate specificity.

Isolation and characterization of lignin from beech wood and chestnut sawdust for the preparation of lignin nanoparticles (LNPs) from wood industry side-streams

Abstract Lignin was isolated through mild acidolysis from local wood sources such as beech wood and chestnut wood sawdust, a high-volume side product of wood industries. The lignin fractions were characterized by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), Fourier-transform infrared (FTIR), ultraviolet-visible (UV-Vis) and two-dimensional heteronuclear single-quantum correlation nuclear magnetic resonance (2D HSQC NMR) spectroscopies and size exclusion chromatography (SEC). The Klason lignin (KL) content and polysaccharide composition were determined using traditional methods. Lignin nanoparticles (LNPs) were prepared via a non-solvent method involving dialysis and characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and FTIR and UV-VIS spectroscopies. Semi-porous as well as hollow nanoparticles endowed with a spherical shape were observed. The large majority of the LNPs exhibited an average particle diameter of 90–120 nm. Dynamic light scattering (DLS) analysis showed that both distribution and frequency of dimensional classes of LNPs are clearly affected by the lignin solvent system, i.e. solvent selection governs the size distribution of LNPs.

Comparative Study of the Structure of Hydroproducts Derived from Loblolly Pine and Straw Grass

The structural characteristics of products derived from the hydrothermal carbonization (HTC) of loblolly pine (LP) and straw grass (SG) were investigated via solid-state cross-polarization/magic angle spinning nuclear magnetic resonance (CP/MAS 13C NMR), heteronuclear single-quantum correlation nuclear magnetic resonance (HSQC-NMR), and solution 13C NMR and 31P NMR techniques. Results revealed that after HTC, hydrochars from both LP and SG mainly consisted of a combination of lignin, furfural, and condensed polyaromatic structures with a high level of fixed carbon content and higher heating value (HHV). Hydrochar from LP exhibited a higher aryl to furan ratio, and those from SG contained more aliphatic functional groups. Solution 13C NMR and HSQC revealed that both liquid chemicals were condensed polyphenolic structures with aliphatic groups that exist mainly in the form of side chains. Although the LP products exhibited a higher proportion of aromatic structures, the types of polyphenol and aliphatic C–H...

Characterization of Pyrolytic Sugars in Bio-Oil Produced from Biomass Fast Pyrolysis

This study characterizes the pyrolytic sugars in three bio-oils (with a total sugar content range of 55.6–69.2 mg g–1 bio-oil) produced from biomass fast pyrolysis by high performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) and two-dimensional 1H–13C heteronuclear single-quantum correlation–nuclear magnetic resonance (HSQC-NMR). Depending on bio-oil sample, glucose (mainly derived from cellulose) contributes ∼67–79 wt % of total pyrolytic sugars in the bio-oil, and the rest of the sugars are derived from hemicellulose. The majority (>96%) of pyrolytic sugars are present in the water-soluble fraction of bio-oil, mainly in the form of cellulose-derived anhydrosugars such as levoglucosan and cellobiosan. A small portion of hemicellulose-derived sugar structures are also found in the water-soluble fraction of bio-oil. Unlike six-carbon sugars (glucose, galactose, and mannose) which are mainly present as anhydrosugars (i.e., ∼ 79–86% on a carbon basis for glucose), a large ...

Specific Binding of a β-Cyclodextrin Dimer to the Amyloid β Peptide Modulates the Peptide Aggregation Process

Alzheimer's disease involves progressive neuronal loss. Linked to the disease is the amyloid β (Aβ) peptide, a 38-43-amino acid peptide found in extracellular amyloid plaques in the brain. Cyclodextrins are nontoxic, cone-shaped oligosaccharides with a hydrophilic exterior and a hydrophobic cavity making them suitable hosts for aromatic guest molecules in water. β-Cyclodextrin consists of seven α-d-glucopyranoside units and has been shown to reduce the level of fibrillation and neurotoxicity of Aβ. We have studied the interaction between Aβ and a β-cyclodextrin dimer, consisting of two β-cyclodextrin monomers connected by a flexible linker. The β-cyclodextrin monomer has been found to interact with Aβ(1-40) at sites Y10, F19, and/or F20 with a dissociation constant (K(D)) of 3.9 ± 2.0 mM. Here (1)H-(15)N and (1)H-(13)C heteronuclear single-quantum correlation nuclear magnetic resonance (NMR) spectra show that in addition, the β-cyclodextrin monomer and dimer bind to the histidines. NMR translational diffusion experiments reveal the increased affinity of the β-cyclodextrin dimer (apparent K(D) of 1.1 ± 0.5 mM) for Aβ(1-40) compared to that of the β-cyclodextrin monomer. Kinetic aggregation experiments based on thioflavin T fluorescence indicate that the dimer at 0.05-5 mM decreases the lag time of Aβ aggregation, while a concentration of 10 mM increases the lag time. The β-cyclodextrin monomer at a high concentration decreases the lag time of the aggregation. We conclude that cyclodextrin monomers and dimers have specific, modulating effects on the Aβ(1-40) aggregation process. Transmission electron microscopy shows that the regular fibrillar aggregates formed by Aβ(1-40) alone are replaced by a major fraction of amorphous aggregates in the presence of the β-cyclodextrin dimer.

Elucidation of Acid-induced Unfolding and Aggregation of Human Immunoglobulin IgG1 and IgG2 Fc

Understanding the underlying mechanisms of Fc aggregation is an important prerequisite for developing stable and efficacious antibody-based therapeutics. In our study, high resolution two-dimensional nuclear magnetic resonance (NMR) was employed to probe structural changes in the IgG1 Fc. A series of (1)H-(15)N heteronuclear single-quantum correlation NMR spectra were collected between pH 2.5 and 4.7 to assess whether unfolding of C(H)2 domains precedes that of C(H)3 domains. The same pH range was subsequently screened in Fc aggregation experiments that utilized molecules of IgG1 and IgG2 subclasses with varying levels of C(H)2 glycosylation. In addition, differential scanning calorimetry data were collected over a pH range of 3-7 to assess changes in C(H)2 and C(H)3 thermostability. As a result, compelling evidence was gathered that emphasizes the importance of C(H)2 stability in determining the rate and extent of Fc aggregation. In particular, we found that Fc domains of the IgG1 subclass have a lower propensity to aggregate compared with those of the IgG2 subclass. Our data for glycosylated, partially deglycosylated, and fully deglycosylated molecules further revealed the criticality of C(H)2 glycans in modulating Fc aggregation. These findings provide important insights into the stability of Fc-based therapeutics and promote better understanding of their acid-induced aggregation process.

Heteronuclear Single-Quantum Correlation–Nuclear Magnetic Resonance (HSQC–NMR) Fingerprint Analysis of Pyrolysis Oils

The pyrolysis of softwood kraft lignin, cellulose, and Loblolly pine wood was examined at 400, 500, and 600 °C. The analysis of the yields of pyrolysis products indicated that lignin yielded the largest amount of a heavy oil and char and only trace levels of a light oil. In contrast, cellulose produced minor amounts of a heavy oil and char and more light oil. All of the pyrolysis oils were analyzed by heteronuclear single-quantum correlation–nuclear magnetic resonance (HSQC–NMR) to analyze the structural components of the bio-oils, and three chemical-shift databases of compounds reported to be presented in pyrolysis oils produced from lignin, cellulose, and pine wood were employed for data analysis. On the basis of databases, analysis of the HSQC–NMR spectral data provides chemical-shift assignment of 27 different types of C–H bonds presented in the pyrolysis oils. The HSQC–NMR analysis of these pyrolysis oils indicated that there are two different types of methoxyl groups presented in the pyrolysis oils ...

Kinetics of Core‐Shell Nanoparticle Formation by Two‐Dimensional Nuclear Magnetic Resonance

We have studied the kinetics of polymeric nanoparticle formation for poly(styrene-block-4-vinylpyridine) [P(S-b-4-VPy)], chains in a non-selective solvent using 1,4-dibromobutane (DBB) as a cross-linker by means of different nuclear magnetic resonance (NMR) spectroscopy techniques. The kinetic process was followed using (1) H, (13) C, and 2-D Heteronuclear Single Quantum Correlation (HSQC) NMR experiments. The kinetic data obtained from 2-D HSQC and (1) H NMR experiments were in good agreement between them, proving the reliability of the 2-D HSQC NMR technique for the in situ study of the kinetics of core-shell nanoparticle formation. A value of 1.5 × 10(-5) s(-1) was determined for the apparent kinetic constant of the P(S-b-4-VPy)-DBB core-shell nanoparticle formation process.

A Small Subset of Signal Peptidase Residues are Perturbed by Signal Peptide Binding

Perturbations of the chemical shifts of a small subset of residues in the catalytically active domain of Escherichia coli signal peptidase I (SPase I) upon binding signal peptide suggest the contact surface on the enzyme for the substrate. SPase I, an integral membrane protein, is vital to preprotein transport in prokaryotic and eukaryotic secretory systems; it binds and proteolyses the N-terminal signal peptide of the preprotein, permitting folding and localization of the mature protein. Employing isotopically labeled C-terminal E. coli SPase I Delta2-75 and an unlabeled soluble synthetic alkaline phosphatase signal peptide, SPase I Delta2-75 was titrated with the signal peptide and 2D (1)H-(15)N heteronuclear single-quantum correlation nuclear magnetic resonance spectra revealed chemical shifts of specific enzyme residues sensitive to substrate binding. These residues were identified by 3D HNCACB, 3D CBCA(CO)NH, and 3D HN(CO) experiments. Residues Ile80, Glu82, Gln85, Ile86, Ser88, Gly89, Ser90, Met91, Leu95, Ile101, Gly109, Val132, Lys134, Asp142, Ile144, Lys145, and Thr234, alter conformation and are likely all in, or adjacent to, the substrate binding site. The remainder of the enzyme structure is unperturbed. Ramifications for conformational changes for substrate docking and catalysis are discussed.