Heteronuclear Single-quantum Correlation Nuclear Magnetic Resonance Research Articles

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.

Effect of autohydrolysis pretreatment on biomass structure and the resulting bio-oil from a pyrolysis process

Pyrolysis is a promising method for converting biomass to biofuels. However, some of pyrolysis oil's physiochemical properties still limit its commercial applications. In this study, the autohydrolysis pretreatment at 175±3°C for 40min was conducted to improve the resulting pine pyrolysis oil’s properties as a fuel. During autohydrolysis, deacetylation and decomposition of hemicellulose was observed by ion-exchange chromatography and Fourier transform infrared spectroscopy (FT-IR). In addition, the cleavage of lignin ether bonds was clearly determined by 13C cross-polarization/magic angle spinning (CP/MAS) nuclear magnetic resonance (NMR). Phosphitylation followed by 31P NMR analysis of the heavy oils gave detailed structural information of the hydroxyl groups; the results revealed that autohydrolysis pretreatment led to a reduction of carboxyl acids in the heavy oils generated at all three pyrolysis temperatures (400, 500, and 600°C). The 31P NMR analysis also revealed that autohydrolysis pretreatment led to a reduction of condensed phenolic hydroxyl groups in the heavy oils produced at 600°C. 1H-13C heteronuclear single-quantum correlation (HSQC) NMR analysis showed that at a pyrolysis temperature of 600°C, the pretreated pine produced lower methoxy group constituents. Both 31P and HSQC NMR results indicated that autohydrolysis pretreatment increased levoglucosan yields in the bio-oils.

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 ...

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 ...

Quantification of Metabolites from Two-Dimensional Nuclear Magnetic Resonance Spectroscopy: Application to Human Urine Samples

We present a general scheme for metabolite quantification from a two-dimensional (2D) (1)H-(13)C heteronuclear single quantum correlation (HSQC) nuclear magnetic resonance (NMR) experiment of body fluids observed in natural abundance. The scheme of quantification from 2D HSQC spectra consists of measurement of relaxation parameters of proton resonances, such as T(1) and T(2) of the metabolites and (1)H-(13)C heteronuclear J-coupling for accurate quantification. The measured cross-peak volume from 2D HSQC NMR spectra is multiplied by a calculated correction factor (which depends upon two-dimensional NMR experimental parameters and relaxation parameters) to measure accurate quantification of the metabolite. The correction factor is theoretically derived from the solution of the Bloch equation and product operator formalism. The accuracy of the scheme is tested on a solution containing a mixture of amino acids of known concentration. For human urine samples, the accuracy of the method for measuring the concentration of various metabolites was tested with spike-in experiments. The scheme is general in nature and can be applied to any other body fluid samples for metabonomic studies. We also test the measured cross-peak volume of various metabolites from 2D (1)H-(13)C HSQC NMR spectra of human urine samples for clustering analysis with scatter plots, making the scheme complete for metabolic profiling.

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.