2D Heteronuclear Single Quantum Coherence Research Articles

Ranking reactive glutamines in the fibrinogen αC region that are targeted by blood coagulant factor XIII

AbstractFactor XIIIa (FXIIIa) introduces covalent γ-glutamyl-ε-lysyl crosslinks into the blood clot network. These crosslinks involve both the γ and α chains of fibrin. The C-terminal portion of the fibrin α chain extends into the αC region (210-610). Crosslinks within this region help generate a stiffer clot, which is more resistant to fibrinolysis. Fibrinogen αC (233-425) contains a binding site for FXIIIa and three glutamines Q237, Q328, and Q366 that each participate in physiological crosslinking reactions. Although these glutamines were previously identified, their reactivities toward FXIIIa have not been ranked. Matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectrometry and nuclear magnetic resonance (NMR) methods were thus used to directly characterize these three glutamines and probe for sources of FXIIIa substrate specificity. Glycine ethyl ester (GEE) and ammonium chloride served as replacements for lysine. Mass spectrometry and 2D heteronuclear single quantum coherence NMR revealed that Q237 is rapidly crosslinked first by FXIIIa followed by Q366 and Q328. Both 15NH4Cl and 15N-GEE could be crosslinked to the three glutamines in αC (233-425) with a similar order of reactivity as observed with the MALDI-TOF mass spectrometry assay. NMR studies using the single αC mutants Q237N, Q328N, and Q366N demonstrated that no glutamine is dependent on another to react first in the series. Moreover, the remaining two glutamines of each mutant were both still reactive. Further characterization of Q237, Q328, and Q366 is important because they are located in a fibrinogen region susceptible to physiological truncations and mutation. The current results suggest that these glutamines play distinct roles in fibrin crosslinking and clot architecture.

New supramolecular compounds: the complexes of nickel(II), copper(II), cobalt(II), cadmium(II) and zinc(II) with anti- [N-(4-aminophenyl)aza-15-crown-5]-4-(phenoxy)phenylglyoxime ligand

A new vic-dioxime ligand (1), bearing pendant an azacrown ether moiety and its soluble mononuclear cadmium(II), zinc(II), nickel(II), copper(II) and cobalt(II) complexes were obtained with the metal: ligand ratios of 1:2 and 1:1. The structures of the ligand and its complexes were verified using Fourier transform infrared (FT-IR), ultraviolet–visible (UV–Vis), mass spectrometry (MS), 1H and 13C NMR techniques. More detailed information about the structure of the 1 was provided by the two-dimensional (2D) heteronuclear single quantum coherence and heteronuclear multiple bond correlation techniques. The complexation properties of the ligand 1 were studied in the presence of different cations such as Pb2+, Zn2+,Cu2+, Cr3+, Hg2+, Zn2+, Fe3+ and Al3+ by UV–Vis spectroscopy and 1H NMR titration methods. All experimental results indicated that the new ligand acts as a selective compound only for Hg+2 cation. The redox behaviour of the complexes, were investigated by cyclic voltammetry at the glassy carbon electrode in 0.1 M tetrabutylamoniumtetrafluoroborate in dimethyl sulfoxide.

High-sensitivity, broadband-decoupled (13) C MR spectroscopy in humans at 7T using two-dimensional heteronuclear single-quantum coherence.

Carbon-13 ((13) C) magnetic resonance spectroscopy (MRS) has an intrinsically low NMR sensitivity that often leads to large acquisition volumes or long scan times. While the use of higher magnetic fields can overcome the sensitivity limitations, high radiofrequency (RF) power deposition associated with proton-decoupling limits the achievable gain. Two-dimensional (2D) heteronuclear single quantum coherence (HSQC) MRS is a method that uses the high chemical specificity of (13) C MRS while retaining the high sensitivity of (1) H detection. Due to the 2D nature of the method, proton-decoupled (13) C MR spectra can be obtained without the use of high-powered decoupling pulses. A novel three-dimensional (3D) localized 2D HSQC method based on 3D STEAM localization is presented and implemented at 7T. The low RF power deposition of the method allows TR variation along the indirect dimension which, in combination with controlled aliasing, leads to an acceleration of 11.8 relative to a standard 2D NMR acquisition. Artifact-free, high-quality and high-sensitivity 2D HSQC spectra were obtained for all subjects in 19 min from a small (9 mL) volume placed in the leg adipose tissue. Complete proton decoupling was achieved along the indirect (13) C dimension despite the absence of broadband proton-decoupling pulses. The high chemical specificity along the indirect (13) C dimension allowed the detection of 19 unique resonances from which the lipids could be characterized in terms of saturation and omega-6/omega-3 fatty acid ratio. It has been demonstrated that high-quality 2D HSQC NMR spectra can be acquired from human adipose tissue at 7T. The HSQC method is methodologically simple and robust and is flexible regarding trade-offs between temporal and spectral resolution. 2D HSQC has a strong potential to become a default method in natural-abundance or (13) C-enriched studies of human metabolism in vivo.

1D and 2D NMR of nanocellulose in aqueous colloidal suspensions

This is the first report on surface structural elucidation of individual nanocellulose as colloidal suspensions by 1D 1H, 2D heteronuclear single quantum coherence (HSQC) as well as 13C nuclear magnetic resonance (NMR). 1H NMR of rice straw CNCs (4.7nm thick, 143nm long, 0.04 sulfate per AG or 19.0% surface hydroxyl to sulfate conversion) resembled that of homogeneous cellulose solution. Conventional 2D HSQC NMR of CNC, CNF 1.5 (2–14nm thick, several micrometers long, 0.10 COOH per AG) and CNF10 (2.0nm thick, up to 1μm long, 0.28 COOH per AG) gave H1:H2 ratios of 1.08:1, 0.97:1 and 0.94:1, respectively, all close to the theoretical 1:1 value for cellulose. The H1:H6 ratios determined from 2D HSQC NMR for CNCs, CNF1.5 and CNF10 were 1:1.47, 1:0.88 and 1:0.14, respectively, and corresponded to 26%, 56% and 93% C6 primary hydroxyl conversion to sulfate and carboxyl groups, consistent with, but more sensitive than those by conductometric titration and X-ray diffraction. Both 1H and 2D HSQC NMR data confirm that solution-state NMR detects nanocellulose surface carbons and protons primarily, validating this technique for direct surface characterization of nanocellulose in aqueous colloidal suspensions, presenting a sensitive and meaningful NMR tool for direct characterizing individual nanocellulose surfaces in never-dried state.

Combining Hydrophilic Interaction Chromatography (HILIC) and Isotope Tagging for Off-Line LC-NMR Applications in Metabolite Analysis.

The complementary use of liquid chromatography (LC) and nuclear magnetic resonance (NMR) has shown high utility in a variety of fields. While the significant benefit of spectral simplification can be achieved for the analysis of complex samples, other limitations remain. For example, 1H LC-NMR suffers from pH dependent chemical shift variations, especially during urine analysis, owing to the high physiological variation of urine pH. Additionally, large solvent signals from the mobile phase in LC can obscure lower intensity signals and severely limit the number of metabolites detected. These limitations, along with sample dilution, hinder the ability to make reliable chemical shift assignments. Recently, stable isotopic labeling has been used to detect quantitatively specific classes of metabolites of interest in biofluids. Here we present a strategy that explores the combined use of two-dimensional hydrophilic interaction chromatography (HILIC) and isotope tagged NMR for the unambiguous identification of carboxyl containing metabolites present in human urine. The ability to separate structurally related compounds chromatographically, in off-line mode, followed by detection using 1H-15N 2D HSQC (two-dimensional heteronuclear single quantum coherence) spectroscopy, resulted in the assignment of low concentration carboxyl-containing metabolites from a library of isotope labeled compounds. The quantitative nature of this strategy is also demonstrated.

MetaboQuant: A tool Combining individual Peak Calibration and Outlier Detection for Accurate Metabolite Quantification in 1D 1 H and 1 H- 13 C HSQC NMR Spectra

Solution nuclear magnetic resonance (NMR) spectroscopy is widely used to analyze complex mixtures of organic compounds such as biological fluids and tissue extracts. Targeted profiling approaches with reliable compound quantitifcation are hampered, however, by signal overlap and other interferences. Here, we present a tool named MetaboQuant for automated compound quantification from pre-processed 1D and 2D heteronuclear single quantum coherence (HSQC) NMR spectral data and concomitant validation of results. Performance of MetaboQuant was tested on a urinary spike-in data set and compared with other quantification strategies. The use of individual calibration factors in combination with the validation algorithms of MetaboQuant raises the reliability of the quantification results. MetaboQuant can be downloaded at http://genomics.uni-regensburg.de/site/institute/software/metaboquant/ as stand-alone software for Windows or run on other operating systems from within Matlab. Separate software for peak fitting and integration is necessary in order to use MetaboQuant.

Solution-State 2D NMR Spectroscopy of Plant Cell Walls Enabled by a Dimethylsulfoxide-d6/1-Ethyl-3-methylimidazolium Acetate Solvent

Lignocellulosic biomass is composed of the polysaccharides cellulose and hemicellulose and the polyphenol lignin. Many current methods for analyzing the structure of lignocelluloses involve a sequential extraction of the material and subsequent analysis of the resulting fractions, which is labor-intensive and time-consuming. The work presented here assesses the dissolution of whole lignocellulosic material, focusing on biomass derived from the perennial bioenergy grass Miscanthus. The solvent dimethylsulfoxide (DMSO)-d6 containing 1-ethyl-3-methylimidazolium acetate ([Emim]OAc) was able to dissolve lignocellulosic material completely and gave high-resolution 2D heteronuclear single quantum coherence (HSQC) NMR spectra of the entire array of wall polymers. Extrapolated time-zero HSQC was applied using DMSO-d6/[Emim]OAc-d14 and enabled quantitative analysis of structural traits of lignocellulose components.

Quantitative structural characterization of the lignins from the stem and pith of bamboo (Phyllostachys pubescens)

Abstract Milled wood lignins (MWL) were isolated from the stem (MWLS) and pith (MWLP) of bamboo (Phyllostachys pubescens). The nonacetylated and acetylated bamboo MWLs were investigated by Fourier transform infrared, quantitative 13C-nuclear magnetic resonance (NMR), 2D heteronuclear single quantum coherence (HSQC) NMR, and 31P-NMR spectroscopy. The MWL consists of p-hydroxyphenyl (1–2%), guaiacyl (21–31%), and syringyl (67–78%) units associated with p-coumarates and ferulates. A modified quantitative 13C-NMR and 2D-HSQC analysis has demonstrated that the predominant intermonomeric linkages are of the type β-O-4 (45–49 per 100 C9 units, i.e., per C900) along with small amounts of other structural units such as resinols (3.6–7.4 per C900), tetrahydrofuran (2.0–2.3 per C900), phenylcoumaran (2.8–4.5 per C900), spirodienones (1.3–2.3 per C900), and α,β-diaryl ethers (2.8–2.9 per C900). MWLP contained more p-coumarates than MWLS. The various degrees of γ-acylation (17–27%) were positively associated with S/G ratios in the lignins; however, γ-acylation was inversely correlated to the ratio between β-β and β-O-4 side chains in these lignin fractions. Moreover, a flavonoid compound (tricin) was also detected in the MWLS but not in MWLP. The two MWLs are very similar in terms of molecular weights and the contents of OHphen and OHaliph.

Refolded recombinant Siglec5 for NMR investigation of complex carbohydrate binding

Sialic-acid-binding immunoglobulin-like lectin (Siglec5) is a carbohydrate-binding surface receptor expressed on neutrophils, monocytes and B cells in human lymphoid and myeloid cell lineages. Existing structural and functional data fail to define the clear ligand specificity of Siglec5, though like other Siglec family members, it binds a variety of complex carbohydrates containing a sialic acid at the non-reducing terminus. Prokaryotic expression of this protein has proven challenging due to disulfide bonds and Asn-linked glycosylation. We developed an expression and purification protocol that uses an on-column strategy to refold Escherichia coli expressed protein that produced a high yield (2mg/L) of the single N-terminal Siglec5 carbohydrate recognition domain (CRD). A 2D heteronuclear single-quantum coherence (HSQC) nuclear magnetic resonance (NMR) spectrum showed this material was folded, and a secondary structure prediction based on the assigned chemical shifts of backbone atoms was consistent with a previously determined X-ray model. NMR chemical shift mapping of Siglec5 binding to three carbohydrate ligands revealed similarities in binding interfaces and affinities. In addition, the role of alternate protein conformations identified by NMR in ligand binding is discussed. These studies demonstrate the Siglec5 CRD alone is sufficient for binding sialylated carbohydrates and provide a foundation for further investigation of Siglec5 structure and function.

Characterization of Lignins Isolated with Alkaline Ethanol from the Hydrothermal Pretreated Tamarix ramosissima

The objective of this study was to characterize the changes in lignin structure during hydrothermal pretreatment of shrub Tamarix ramosissima. Lignins in residual wood meal were isolated with alkaline ethanol solution and recovered with acid precipitation. A comparison between the recovered lignin fractions with milled wood lignin has been made in terms of yield, purity, gel permeation chromatography, Fourier transform infrared spectroscopy, pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), 1D 13C and 2D heteronuclear single quantum coherence nuclear magnetic resonance (HSQC NMR) spectroscopic techniques. Semiquantitative HSQC NMR showed that the relative amounts of β-O-4′ (around 76 % side chains) and resinol type substructures (16 %) of lignins were significantly modified during hydrothermal pretreatment. Py-GC/MS analyses brought direct evidences of these lignin samples with high S/G ratios ranging from 1.7 to 2.6. Moreover, the results indicated that an increase in the severity of the hydrothermal pretreatment enhanced the degradation of lignin unit side chains and the condensation of lignin and decreased the molecular weight of the recovered lignin fractions. This study demonstrated that the combination of autohydrolysis and alkaline ethanol process could potentially turn the recovered lignin fractions into value added products being in accordance with the “biorefinery” concept.

THE STRUCTURAL CHARACTERIZATION OF CORN STALKS HEMICELLULOSES DURING ACTIVE OXYGEN COOKING AS A PRETREATMENT FOR BIOMASS CONVERSION

The structural characteristics of corn stalks hemicelluloses during the active oxygen cooking process as a pretreatment of biomass conversion were investigated in this work. The hemicelluloses obtained from the corn stalks, pulp, and yellow liquor were evaluated by high-performance anion-exchange chromatography (HPAEC), Fourier transform infrared spectroscopy (FT-IR), gel permeation chromatography (GPC), and 1H-13C 2D hetero-nuclear single quantum coherence (HSQC) spectroscopy. Based on the sugar and GPC analysis, FT-IR, and NMR spectroscopy, it could be concluded that the hemicelluloses were composed of backbones of (1→4)-β-D-xylopyranose substituted α-L-arabinofuranose and 4-O-methyl-α-D-glucuronic acid. During the cooking process, the hemicelluloses with more side chains were removed from raw material. The backbones were significantly damaged as well. Additionally, the ester linkages in the raw material were completely broken after the cooking.

The structural changes of the bagasse hemicelluloses during the cooking process involving active oxygen and solid alkali

This work describes the structural changes of bagasse hemicelluloses during the cooking process involving active oxygen (O2 and H2O2) and solid alkali (MgO). The hemicelluloses obtained from the bagasse raw material, pulp, and yellow liquor were analyzed by high-performance anion-exchange chromatography (HPAEC), gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FT-IR), and 1H–13C 2D hetero-nuclear single quantum coherence spectroscopy (HSQC). The results revealed that the structure of the bagasse hemicelluloses was l-arabino-(4-O-methylglucurono)-d-xylan. Some sugar units in hemicelluloses were oxidized under the cooking conditions. Additionally, the backbones and the ester linkages of hemicelluloses were heavily cleaved during the cooking process.

Stereochemical assignments of the nuclear magnetic resonance spectra of isobornyl acrylate/methacrylonitrile copolymers

AbstractIsobornyl acrylate (B)/methacrylonitrile (N) copolymers with different compositions were synthesized by the free‐radical bulk polymerization with azobisisobutyronitrile as the initiator under a nitrogen atmosphere at 70°C. The copolymer compositions were calculated from quantitative 13C(1H)NMR spectra. The reactivity ratios of the comonomers in the B/N copolymers determined from the linear Kelen–Tudos method and nonlinear error‐in‐variable method were rB = 0.66 ± 0.11 and rN = 1.54 ± 0.22 and rB = 0.74 and rN = 1.65, respectively. The complete spectral assignments of the 1H‐NMR and 13C(1H)‐NMR spectra were carried out with the help of distortionless enhancement by polarization transfer, two‐dimensional (2D) heteronuclear single quantum coherence, and 2D total correlation spectroscopy. The nitrile carbon of the N unit and the methine and OCH carbons of the B unit were assigned to triad compositional sequences, whereas the β‐methylene carbons of the B and N units were assigned to the tetrad compositional and configurational sequences. The α‐methyl carbon of the N unit was also assigned to the triad level of configurational and compositional sequences. Similarly, the nitrile and quaternary carbon resonances with the methine, methylene, and methyl protons were studied in detail with 2D heteronuclear multiple‐bond correlation spectra. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

A comparative study of bamboo (Phyllostachys incarnata Wen) milled wood lignin and the successively alkali-fractionated lignins

The chemical composition and structural characterization of the milled wood lignin (MWL) and successively alkali-fractionated lignins from bamboo (Phyllostachys incarnata Wen) were comparatively investigated using Fourier transform infrared (FT-IR), gel permeation chromatography (GPC), 2D heteronuclear single quantum coherence (HSQC), and alkaline nitrobenzene oxidation. It was found that bamboo MWL (S/G ~ 1.3) is of SGH type with a considerable amount of esterified p-coumaric acid and etherified ferulic acid. Molecular weights of 3,320 g/mol for MWL and varying weights between 970 and 3,430 g/mol for the alkali-fractionated lignins were obtained. Moreover, 2D HSQC of MWL showed a predominance of β-O-4′ linkages (65%), followed by β–β′ linkages (15%) and lower amounts of β-5′ (7%), β-1′ (4%), 5–5′ (4%) linkages, and cinnamyl acetate end groups (5%). In addition, a percentage (~45%) of the lignin side chain was found to be acylated at the γ-carbon. However, the alkali-fractionated lignins lost parts of these linkages during successive alkaline fractionation processes.

Characterization of MWLs from Tamarix ramosissima isolated before and after hydrothermal treatment by spectroscopical and wet chemical methods

AbstractTo improve enzymatic hydrolysis, hydrothermal treatment was carried out on the shrubTamarix ramosissima. Milled wood lignin (MWL) was isolated fromT. ramosissimastems before and after hydrothermal treatment, and its chemical structure was characterized by carbohydrate analysis, elemental analysis, methoxy group determination, FT-IR spectroscopy, quantitative13C NMR spectroscopy, 2D heteronuclear single quantum coherence spectroscopy, and gel permeation chromatography. The analyses confirmed thatT. ramosissimaMWL is very rich in syringyl units. It was found that the main reaction responsible for the lignin degradation is the homolytic cleavage of aryl-ether bonds resulting in a reduced amount of β-O-4′ interlinkages and, as a consequence, in elevated amounts of β-β′ and β-5′ linkages. The MWL isolated from the pretreated solid residue was more condensed and had a lower molecular weight than the MWL isolated from untreated material.

1D and 2D NMR studies of isobornyl acrylate – Methyl methacrylate copolymers

Isobornyl acrylate – methyl methacrylate (B/M) copolymers of different compositions were synthesized by atom transfer radical polymerization (ATRP) using methyl-2-bromopropionate as an initiator and PMDETA copper complex as catalyst under nitrogen atmosphere at 70 °C. 1H NMR spectrum was used to determine the compositions of copolymer. The copolymer compositions were then used to determine the reactivity ratios of monomers. Reactivity ratios of co-monomers in B/M copolymer, determined from linear Kelen–Tudos method (KT) and non linear Error-in-Variable Method (EVM), are r B = 0.41 ± 0.11, r M = 1.11 ± 0.33 and r B = 0.52, r M = 1.31 respectively. The complete resonance assignments of 1H and 13C{ 1H} NMR spectra were carried out with the help of Distortion less Enhancement by Polarization Transfer (DEPT), two-dimensional Heteronuclear Single Quantum Coherence (HSQC). 2D HSQC assignments were further confirmed by 2D Total Correlation Spectroscopy (TOCSY). The carbonyl carbon of B and M units and methyl carbon of M unit were assigned up to triad compositional and configurational sequences whereas β-methylene carbons were assigned up to tetrad compositional and configurational sequences. Similarly the methine carbon of B unit was assigned up to pentad level. 1,3 and 1,4 bond order couplings of carbonyl carbon and quaternary carbon resonances with methine, methylene and methyl protons were studied in detail using 2D Hetero Nuclear Multiple Bond Correlation (HMBC) spectra.

Impact of formic/acetic acid and ammonia pre-treatments on chemical structure and physico-chemical properties of Miscanthus x giganteus lignins

Miscanthus x giganteus was treated with formic acid/acetic acid/water (30/50/20 v/v) for 3 h at 107 °C and 80 °C, and soaking in aqueous ammonia (25% w/w) for 6 h at 60 °C. The effects of these fractionation processes on chemical structure, physico-chemical properties and antioxidant activity of extracted lignins were investigated. Lignins were characterized by their purity, carbohydrate composition, thermal stability, molecular weight and by Fourier transform infrared (FTIR), 1H and quantitative 13C nuclear magnetic resonance (NMR), adiabatic broadband {13C–1H} 2D heteronuclear (multiplicity edited) single quantum coherence (g-HSQCAD). The radical scavenging activity towards 2,2-diphenyl-1-picrylhydrazyl (DPPH) was also investigated. Formic/acetic acid pretreatment performed in milder conditions (80 °C for 3 h) gave a delignification percentage of 44.7% and soaking in aqueous ammonia 36.3%. Formic/acetic acid pretreatment performed in harsh conditions (107 °C for 3 h) was more effective for extensive delignification (86.5%) and delivered the most pure lignin (80%). The three lignin fractions contained carbohydrate in different extent: 3% for the lignin obtained after the formic/acetic acid pretreatment performed at 107 °C (FAL-107), 5.8% for the formic/acetic acid performed at 80 °C (FAL-80) and 13.7% for the ammonia lignin (AL). The acid pretreatment in harsh conditions (FAL-107) resulted in cleavage of β–O-4′ bonds and aromatic C–C. Repolymerisation was thought to originate from formation of new aromatic C–O linkages. Under milder conditions (FAL-80) less β–O-4′ linkages were broken and repolymerisation took place to a lesser extent. Ammonia lignin was not degraded to a significant extent and resulted in the highest weight average 3140 g mol −1. Despite the fact of FAL-107 repolymerisation, significant phenolic hydroxyls remained free, explaining the greater antioxidant activity.

Synthesis, electrochemical and structural characterization of novel azacrown ether containing macrocyclic redox-active vic-dioxime ligand and its mononuclear transition metal complexes: Application of DEPT, HSQC, HMBC-NMR and cyclic voltammetry

This paper presents a new azacrown containing vic-dioxime; anti-N-(4-aminophenyl)aza-15-crown-5-glyoxime (LH 2), and its mononuclear nickel(II), copper(II), cobalt(II), cadmium(II) and zinc(II) complexes. The azacrown moieties appended at the periphery of the oxime provide solubility for the vic-dioxime ligand and complexes in common organic solvents. The mononuclear M(LH) 2 (M = Ni and Cu), M(LH) 2(H 2O) 2 (M = Co) and [M(LH)(H 2O)(Cl)] (M = Cd and Zn) complexes have been obtained with the metal:ligand ratios of 1:2 and 1:1. The structure of the ligand is confirmed by elemental analysis, Fourier transform infrared (FT-IR), ultraviolet–visible (UV–Vis), mass spectrometry (MS), one-dimensional (1D) 1H, 13C NMR, distortionless enhancement by polarization transfer (DEPT) and two-dimensional (2D) heteronuclear single quantum coherence (HSQC) and heteronuclear multiple bond correlation (HMBC) techniques. The structures of the complexes are confirmed by elemental analyses, MS, UV–Vis, FT-IR and 1H, 13C NMR techniques. Redox behaviors of the ligand and its complexes have been investigated by cyclic voltammetry at the glassy carbon electrode in 0.1 M TBATFB in DMSO. The antibacterial activity was studied against Staphylococcus aureus ATCC 29213, Streptococcus mutans RSHM 676, Enterococcus faecalis ATCC 29212, Lactobacillus acidophilus RSHM 06029, Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853. The antimicrobial test results indicate that all the complexes have low levels of antibacterial activity against both Gram negative and Gram positive bacterial species.

Multiplicity editing by 2D E-HSQC NMR spectroscopy: a product operator theory study

Multiplicity editing of NMR signals into subsignals has become a useful technique to obtain simplified spectra for the separation of carbonyl groups in complex molecules. An E-HSQC experiment is an 1H-detected, signal-edited and two-dimensional (2D) heteronuclear single quantum coherence (HSQC) NMR spectroscopy experiment. The product operator theory as a quantum mechanical method not only allows the confirmation of experimental results but also offers to make experimental suggestions on NMR experiments. In this study, analytical descriptions of the 2D E-HSQC NMR experiment for two different editing pulse blocks have been presented for a weakly coupled ISn (I=1/2; S =1/2, 1; n=1, 2, 3) spin system by using the product operator theory. According to the obtained free induction decay (FID) values, theoretical predictions and experimental conditions have been suggested for spectral editing of 13C/15NH, 13C/15NH2, 13C/15NH3 and 13C/15ND, 13C/15ND2, 13C/15ND3 signals into subsignals.

Two-dimensional NMR studies of acrylate copolymers

Abstract High-resolution NMR spectroscopy is the most versatile, reliable, and generally acceptable technique for the determination of the microstructure of polymers. 2D NMR techniques, along with 1D NMR, have more potential to study absolute configurational assignments and sequence distribution of copolymers. Physical and chemical properties of polymers are influenced fundamentally by their microstructure. We discuss the detailed microstructure analysis of a large number of homopolymers, copolymers, and terpolymers. 2D NMR study of poly(methyl methacrylate) (PMMA), poly(methyl acrylate) (PMA), and poly(methacrylonitrile) (PMAN) is discussed in this article. In addition to homopolymers, 2D heteronuclear single-quantum coherence (HSQC), total correlation spectroscopy (TOCSY), and heteronuclear multiple-bond correlation (HMBC) study of different copolymers such as poly(methyl methacrylate-co-methyl acrylate), poly(styrene-co-methyl methacrylate), and poly(methyl methacrylate-co-methacrylonitrile) have also been reported here. This in turn helps in microstructural analysis of terpolymers such as poly(methacrylonitrile-co-styrene-co-methyl methacrylate), poly(acrylonitrile-co-methyl methacrylate-co-methyl acrylate), and poly(ethylene-co-vinyl acetate-co-carbon monoxide).