Nuclear Magnetic Resonance Spectroscopy Methods Research Articles

Isolation and structural determination of ursane-type triterpene from <i>Neolamarckia cadamba</i> dried leaves

This article documents the first time isolation of Carissic acid from <i>Neolamarckia cadamba</i> (Roxb.) Bosser (Family: Rubiaceae) leaves. This bioactive triterpenic acid was isolated with a yield of 3.26% by ultrasonic waves. One-dimensional Nuclear Magnetic Resonance (NMR) spectroscopic techniques such as proton NMR (<sup>1</sup>H NMR), carbon-13 NMR (<sup>13</sup>C NMR), distortionless enhancement by polarisation transfer (DEPT), and two-dimensional NMR spectroscopic methods such as heteronuclear single quantum coherence (HSQC) were used to identify the structure. About 63.0 mg of pure carissic acid was isolated from 1.931 grams of acetone extract using sonomaceration as an extraction technique.

PECULIARITIES OF THE SPECTRAL CHARACTERISTICS OF BRASSINOSTEROIDS OF THE 24-EPIBRASSINOLIDE AND 6-DEOXO-24-EPITHEASTERONE SERIES IN NMR SPECTRA IN DEUTEROPYRIDINE AND DEUTEROCHLOROFORM

Assignment of signals of the nuclei of hydrogen and carbon atoms in a group of steroids belonging to the group of 6-deoxo-24-epiteasterone and 24-epibrassinolide has been fulfilled using the two-dimensional Nuclear magnetic resonance spectroscopy methods. The effect of solvents on the chemical shift has been
 studied.

A Nuclear Magnetic Resonance Spectroscopy Method in Characterization of Blood Metabolomics for Alzheimer's Disease.

There is currently a crucial need for improved diagnostic techniques and targeted treatment methods for Alzheimer’s disease (AD), a disease which impacts millions of elderly individuals each year. Metabolomic analysis has been proposed as a potential methodology to better investigate and understand the progression of this disease. In this report, we present our AD metabolomics results measured with high resolution magic angle spinning (HRMAS) nuclear magnetic resonance (NMR) on human blood plasma samples obtained from AD and non-AD subjects. Our study centers on developments of AD and non-AD metabolomics differentiating models with procedures of quality assurance (QA) and quality control (QC) through pooled samples. Our findings suggest that analysis of blood plasma samples using HRMAS NMR has the potential to differentiate between diseased and healthy subjects, which has important clinical implications for future improvements in AD diagnosis methodologies.

Nanofiber Material with Hydrophobic-Hydrophilic Properties Based on Poly(3-Hydroxybutyrate) and Poly(2-Hydroxyethyl Methacrylate)

A new material with hydrophobic-hydrophilic properties is obtained based on ultrathin poly(3-hydroxybutyrate) (PHB) fibers modified with poly(2-hydroxyethyl methacrylate). The supramolecular structure of the samples is investigated by structurally dynamic methods: scanning electron microscopy, differential scanning calorimetry, and electron paramagnetic resonance. The equilibrium-kinetic characteristics of water sorption by the material are determined. Evidence is obtained by the method of 1H NMR (proton nuclear magnetic resonance spectroscopy) for the chemical modification of the PHB surface due to the participation of its terminal groups in the transesterification reaction of 2-hydroxyethyl methacrylate.

Structural Identification of Individual Helical Amyloid Filaments by Integration of Cryo-Electron Microscopy-Derived Maps in Comparative Morphometric Atomic Force Microscopy Image Analysis

The presence of amyloid fibrils is a hallmark of more than 50 human disorders, including neurodegenerative diseases and systemic amyloidoses. A key unresolved challenge in understanding the involvement of amyloid in disease is to explain the relationship between individual structural polymorphs of amyloid fibrils, in potentially mixed populations, and the specific pathologies with which they are associated. Although cryo-electron microscopy (cryo-EM) and solid-state nuclear magnetic resonance (ssNMR) spectroscopy methods have been successfully employed in recent years to determine the structures of amyloid fibrils with high resolution detail, they rely on ensemble averaging of fibril structures in the entire sample or significant subpopulations. Here, we report a method for structural identification of individual fibril structures imaged by atomic force microscopy (AFM) by integration of high-resolution maps of amyloid fibrils determined by cryo-EM in comparative AFM image analysis. This approach was demonstrated using the hitherto structurally unresolved amyloid fibrils formed in vitro from a fragment of tau (297–391), termed ‘dGAE’. Our approach established unequivocally that dGAE amyloid fibrils bear no structural relationship to heparin-induced tau fibrils formed in vitro. Furthermore, our comparative analysis resulted in the prediction that dGAE fibrils are structurally closely related to the paired helical filaments (PHFs) isolated from Alzheimer’s disease (AD) brain tissue characterised by cryo-EM. These results show the utility of individual particle structural analysis using AFM, provide a workflow of how cryo-EM data can be incorporated into AFM image analysis and facilitate an integrated structural analysis of amyloid polymorphism.

An Investigation on the Synthesis, Structure and Specific Properties of Zn(II) and Cu(II) Complexes with Tryptophan

In this work, [Zn(Tryp)2(H2O)2] and [Cu(Tryp)2H2O] complexes were synthesized by using Zn2+ and Cu2+ (from Zn(CH3COO)2, Cu(CH3COO)2.H2O, respectively) as central metal ions with tryptophan (HTryp) as ligand. The compositions and structures of the synthesized [Zn(Tryp)2(H2O)2] and [Cu(Tryp)2H2O] complexes have been investigated by energy-dispersive X-ray spectroscopy (EDS), infrared (IR), nuclear magnetic resonance (NMR) spectroscopy, mass spectrometry (MS), thermal analysis (TG, TGA/DTG), and electrical conductivity methods. The obtained results demonstrated that in the synthesized complexes, tryptophan is a bidentate ligand. The bonding between the tryptophan with central metal is with (O, Namino) donor sets. The coordination number of Zn2+ and Cu2+ in the complexes is 6 and 5, respectively. The stability of synthesized complexes was also confirmed via testing in simulated gastric fluid environments.

Major Antioxidant Compound of Polyporus Parvovarius Culture Filtrate

During the screening of natural antioxidants from the culture broths of fungi of mushroom origin, the culture broth of Polyporus parvovarius was found to exhibit potent antioxidant activity. An antioxidative substance, compound 1, was isolated by solvent partitioning and column chromatography, and its chemical structure determined by nuclear magnetic resonance spectroscopic methods to be 3,4-dihydroxybenzaldehyde. Compound 1 exhibited potent free radical scavenging activity with a half-maximal inhibitory concentration of 101.4 µg/mL against the 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) radical. These results indicate that the culture filtrate of P. parvovarius has antioxidant properties, with the major antioxidant compound confirmed as a protocatechuic aldehyde; these findings provide novel insights regarding mushroom-induced antioxidant resources.

Influence of the length of the spacer group on the performance of the sulfate-based Gemini surfactants

PurposeA series of sulfate-based Gemini anionic surfactants were synthesized via etherification, ring opening and sulfation reactions using epichlorohydrin, fatty alcohol, ethylene glycol and chlorosulfonic acid as the main raw materials. Orthogonal experiments for 1,8-bisalkoxymethylene-3,6-dioxin-1,8-octane disulfate were performed on the sulfation reaction to determine the optimal reaction conditions.Design/methodology/approachA series of sulfate-based Gemini anionic surfactants were synthesized via etherification, ring opening and sulfation reactions using epichlorohydrin, fatty alcohol, ethylene glycol and chlorosulfonic acid as the main raw materials. Orthogonal experiments for 1,8-bisalkoxymethylene-3,6-dioxin-1,8-octane disulfate were performed on the sulfation reaction to determine the optimal reaction conditions. The structures of the intermediate and final products were characterized by FT-IR (Fourier transform infrared spectroscopy analysis), 1H-NMR (proton nuclear magnetic resonance spectroscopy) methods. The thermal performance of surfactants was analyzed using thermogravimetric analysis (TGA). The thermogravimetric results showed that the sulfate-based Gemini surfactants had good heat resistance (the thermal decomposition temperature of which was in the range of 140∼170?). The Krafft point, surface tension, foaming, Hydrophile–Lipophile Balance Number (HLB), emulsifying, wetting, and lime-soap dispersing performance were measured by visual observation, hanging drop method, aqueous surfactant solution method and Borghetti–Bergman method, respectively. The results have shown that all the sulfate-based Gemini surfactants had good water solubility and lime-soap dispersing ability. When spacer group was -(CH2)2-, with the increase of the carbon chain length from C12 to C14, the micellar concentration critical micelle concentration and surface tension (CMC) gradually increased from 8.25 × 10–4 mol/L to 8.75 × 10–4 mol/L and 27.5 mN/m to 30.9 mN/m, respectively. Also, the sulfate-based Gemini surfactants with the different length of the spacer group had a different effect on their performance on foaming properties and foam properties, HLB and emulsifying ability and wetting ability. FindingsIn view of the important role of the spacer group and the general use of anionic surfactants in oil fields, this article considers the preparation of a series of sulfate-based Gemini surfactants by changing the spacer group and the chain length of the hydrophobic group and evaluating their surface activity, and finally its Kraffi, on the foam properties, HLB value, emulsifying performance, lime soap dispersing ability etc.Originality/valueSulfate-based Gemini surfactants have broad application prospects in the fields of oil and gas exploitation, environmental protection, chemistry and daily chemical industry and so on.

Meet the IUPAB councilor - Angela M. Gronenborn.

As an incoming IUPAB Councilor, I have been asked to write a short commentary describing myself and my career in science. Throughout my scientific life, my interests have evolved from initially trying to understand the physical and chemical properties of small molecules toward unraveling biological systems. To that end, I now apply biophysical, biochemical and chemistry tools. Along my journey, I developed and applied nuclear magnetic resonance (NMR) spectroscopy methods to figure out how proteins work at the atomic level and this voyage took me from Germany, where I earned degrees in Physics and Chemistry, to the UK and back to Germany, finally dropping anchor in the USA, where I have led research programs at both the National Institutes of Health and the University of Pittsburgh. I am now the UPMC Rosalind Franklin Professor and Chair of the Department of Structural Biology, University of Pittsburgh School of Medicine, a Professor of Bioengineering, Swanson School of Engineering, and a Professor of Chemistry, Dietrich School of Arts and Sciences, University of Pittsburgh.

Design and synthesis of a novel chemosensor for simultaneous detection of CN−, HCO3− and AcO− anions and Fe2+ cation in an organic-aqueous environment: An experimental and Density Functional Theory studies

• A novel Schiff base ligand, namely 2-((E)-(2-(1H-indol-3-yl)ethylimino)methyl)-4-((E)-(2-nitrophenyl)diazenyl)phenol (L) was synthesized. • The receptor (L) (5 × 10 −5 M) in DMF solution exhibited very good sensing behavior towards CNˉ, HCO 3 −, AcO− and Fe2+ ions. • The stabilization energy of the optimized complexes was more negative than the energy of free receptor (L) proving the greater stability of the formed complexes. • The reversibility of the synthesized receptor (L) was successfully approved. • The receptor (L) can be candidate as an operational colorimetric chemosensor with low-cost detection, high selectivity and nice reversibility in DMF solutions. A new azo–azomethine chemosensor, 2-((E)-(2-(1H-indol-3-yl)ethylimino)methyl)-4-((E)-(2-nitrophenyl)diazenyl)phenol, L, was synthesized and characterized by Infrared spectroscopy (IR), Ultraviolet–visible spectroscopy (UV-Visible) and Nuclear magnetic resonance spectroscopy (NMR) methods. The sensory properties of this Schiff base compound (L) were investigated in Dimethyl sulfoxide (DMSO)/H 2 O (9.5:0.5 v/v) solution. It was selectively sensitive to CN ˉ and HCO 3 ˉ and AcO ˉ anions, and in the presence of them, the color of solution L through deprotonating mechanism changed from yellow to orange. This chemosensor also sensitive to Fe 2+ . Then, by using Job's method and Benesi–Hildebrand equation, the binding stoichiometry of L with anions and binding constant (k a ) were determined (CN − : 1:1, 3.47×10 +5 ; HCO 3 − : 1:1, 2.44×10 +5 ; AcO − : 1:1, 1.76×10 +5 ), respectively. Also, the Limit of Detection (LOD) was calculated. Finally, the observed experimental results were confirmed by Density Functional Theory (DFT) calculations. A new Schiff base chemosensor, 2-((E)-(2-(1H-indol-3-yl)ethylimino)methyl)-4-((E)-(2-nitrophenyl)diazenyl)phenol, L, was synthesized. The L sensor successfully detected both cations (Fe 2+ ) and anions (AcO ˉ , CN ˉ , HCO 3 ˉ ) by the naked-eye and UV–Vis spectroscopy in an organic-aqueous environment. Through DFT calculations, the experimental results were confirmed. So, we believe that L can be an efficient sensor for detecting said ions in aqueous media.

Extending the Scope of 1H NMR-Based Blood Metabolomics for the Analysis of Labile Antioxidants: Reduced and Oxidized Glutathione.

Glutathione is a ubiquitous cellular antioxidant, which is critically required to protect cells from oxidative damage and free radical injury. It is practically impossible to analyze glutathione in its native form after isolation from biological mixtures since the active form (reduced glutathione, GSH) spontaneously gets converted to the oxidized form (oxidized glutathione, GSSG). To address this challenge, numerous highly sensitive detection methods, including mass spectrometry, have been used in conjunction with derivatization to block the oxidation of GSH. Efforts so far to quantitate GSH and GSSG using the nuclear magnetic resonance (NMR) spectroscopy method have remained unsuccessful. With a focus on addressing this challenge, in this study, we describe an extension to our recent whole blood analysis method [ Anal. Chem. 2017, 89, 4620-4627] that includes the important antioxidants GSH and GSSG. Fresh and frozen human whole blood specimens as well as standard GSH and GSSG were comprehensively investigated using NMR without and with derivatization using N-ethylmaleimide (NEM). NMR experiments detect two diastereomers, distinctly, for the derivatized GSH and enable the analysis of both GSH and GSSG in human whole blood with an accuracy of >99%. Interestingly, the excess (unreacted) NEM used for blocking the GSH can be removed from the samples during a drying step after extraction, with no need for additional processing. This is an important characteristic that offers an added advantage for simultaneous analysis of the antioxidants (GSH and GSSG), redox coenzymes (oxidized nicotinamide adenine dinucleotide (NAD+), reduced nicotinamide adenine dinucleotide (NADH), oxidized nicotinamide adenine dinucleotide phosphate (NADP+), reduced nicotinamide adenine dinucleotide phosphate (NADPH)), energy coenzymes (adenosine 5'-triphosphate (ATP), adenosine 5'-diphosphate (ADP), adenosine 5'-monophosphate (AMP)), and a large number of other blood metabolites using the same one-dimensional (1D) NMR spectrum. The presented method broadens the scope of global metabolite profiling and adds a new dimension to NMR-based blood metabolomics. Further, the method demonstrated here for human blood can be extended to virtually any biological specimen.

Antifouling Performance of Cellulose Acetate Films Based on a New Benzoxazine Derivative

AbstractFouling is an industrial problem that affects the maritime sector, and it has caused damages to equipment and vessels used in this industry. This research focuses on the synthesis of a novel arylidene‐based benzoxazine compound (HBC) and its use as a modifier for cellulose acetate (CA) matrix to form film samples and the investigation of their antifouling efficacy. The HBC compound was synthesized from a bis(arylidene)cyclopentanone diol compound and characterized appropriately using Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopic methods, respectively. Different weight ratios: 0, 10, 20, 30, and 40 %w/w of HBC to CA were mixed to give the films; CA‐0, CA‐10, CA‐20, CA‐30, and CA‐40, respectively. The fabricated films were characterized by FTIR analysis, and their morphology was examined by scanning electron microscopy (SEM). The thermal stability of the films was also studied using thermal gravimetric analysis (TGA), while the antifouling performance of the films was tested against strains of natural, biofilm‐forming bacteria isolated from artificial nets submerged in the Red Sea. Biofilm inhibitory test and bactericidal assay were conducted on the fabricated film materials using well established standard methods. The results of this investigation indicate that the HBC modified CA films contain relevant bioactive molecules that can inhibit primary colonizers in biofouling formation and will make a good antifouling coating film candidate. The CA‐40 revealed an inhibitory activity of 37 % and a bacterial killing efficacy of 87 %.

Gas Chromatography–Mass Spectrometric Analysis of Derivatives of Dibenzalacetone Aldol Products

The aldol condensation reaction is one of the many synthesis reactions carried out in second semester organic chemistry laboratories. This reaction was integrated into a novel experiment requiring students to synthesize dibenzalacetone derivatives using the crossed-aldol condensation by reacting different types of benzaldehyde derivatives with acetone, followed by analyzing those products using spectrometric and spectroscopic methods, especially gas chromatography–mass spectrometry (GC–MS). The main objective of this 2 week lab experiment compared to other procedures in the literature was the analysis of the final aldol product using GC–MS methods rather than solely nuclear magnetic resonance (NMR) spectroscopic methods. During the first week’s 3 h laboratory period, students completed the reaction with a known benzaldehyde derivative and acetone to synthesize their aldol product. In the second week, students calculated the percent yield of their product, determined the product’s melting point range, and analyzed the product by thin-layer chromatography, NMR, and GC–MS methods. Students also strengthened their skills of spectral interpretation using NMR spectroscopy, especially distortionless enhancement by polarization transfer NMR, an NMR technique rarely covered in undergraduate organic laboratory sections. Students spent more classroom time during week two, analyzing GC–MS data. Students were shown how to use molecular model kits to understand the fragmentation of compounds in the mass spectrum. As a result, the students who performed this experiment increased their general knowledge of GC–MS spectrometric techniques, including identification of compounds based on their fragmentation pattern.

Estimation of Enantiomeric Excess Based on Rapid Host–Guest Exchange

Chiral molecules possess enantiomers that have non-superimposable chemical structures but exhibit identical nuclear magnetic resonance (NMR) spectra. This feature prevents the use of NMR spectroscopic methods for the determination of enantiomeric excesses (ee) of chiral molecules, using simple mixtures of their enantiomers. Recently, however, it was reported that the addition of a symmetrical prochiral molecule (a reporter or host) into a solution of chiral analyte can lead to estimation of ee through interactions involving rapid exchange of the chiral analyte (guest) in the formed host–guest complex. This is due to the ee-dependent splitting of NMR resonances of the prochiral host molecule based on averaging the chemical shift non-equivalency caused by the presence of a chiral guest. The mechanism is not dependent on diastereomer formation, and 1:1 host–guest complexes can also show ee-dependent NMR peak splitting. Prochiral molecules capable of ee sensing using the NMR technique are now referred to as so-called prochiral solvating agents (pro-CSAs). pro-CSAs represent a family of reagents distinct from the commonly used NMR chiral derivatizing reagents (where chiral auxiliaries are used to derivatize enantiomers to diastereomers) or chiral solvating agents (where chiral auxiliaries interact in an asymmetric manner with analyte enantiomers). pro-CSA methods are unique since neither pro-CSA nor NMR contains chiral factors, making the technique neutral with respect to chirality. Here, we review our recent work on this matter involving several different nominally achiral receptor molecules whose unique guest binding properties and solution characteristics (especially with regard to NMR spectroscopy) allow for the estimation of ee in the corresponding chiral guests.

Identification and quantification of 10 indole/indazole carboxamide synthetic cannabinoids in 36 herbal blends by gas chromatography-mass spectrometry and nuclear magnetic resonance spectroscopy.

Herbal blends containing synthetic cannabinoids have become popular alternatives to marijuana. The number of synthetic cannabinoids and speed of their emergence enable this group of compounds particularly challenging in terms of detection, monitoring, and responding. In this work, both gas chromatography-mass spectrometry (GC-MS) and nuclear magnetic resonance spectroscopy (NMR) methods were developed for the identification and quantification of synthetic cannabinoids in herbal blends. Ten types of indole/indazole carboxamide synthetic cannabinoids, which showed different types of substitutions connected to nitrogen of the indole/indazole carboxamide, were detected in 36 herbal blends. The GC-MS fragmentation routes of indole/indazole carboxamide synthetic cannabinoids were discussed in detail for structure identification purpose. The concentration range of synthetic cannabinoid in 36 herbal blends was 1.9-50.6mg/g using GC-MS method, while 1.5-49.0mg/g by NMR method. Nicotine in herbal blends was quantified by NMR method without using reference material, and showed a variation of 5.3-44.7mg/g. For quantitative analysis, NMR method showed great advantage in the absence of reference material, while GC-MS method showed great merit for multiple-compound analysis when reference material was available. Therefore, for the quantitative analysis of new emerged synthetic cannabinoid in herbal blends, different methods could be chosen by considering whether reference material is available, as well as the number and types of synthetic cannabinoids detected in a single sample.

Complexation in situ of 1-methylpiperidine, 1,2-dimethylpyrrolidin, and 1,2-dimethylpiperidine with rhodium(II) tetracarboxylates: Nuclear magnetic resonance spectroscopy, chiral recognition, and density functional theory studies.

Complexation in situ of 1-methylpiperidine, racemic 1,2-dimethylpyrrolidin, and racemic 1,2-dimethylpiperidine with rhodium(II) tetracarboxylates in chloroform was studied by 1 H and 13 C nuclear magnetic resonance (NMR) spectroscopy and density functional theory (DFT) methods. As substrates, three dirhodium(II) compounds were applied, tetraacetate, tetrakistrifluoroacetate, and a derivative of optically pure Mosher's acid. Due to conformational flexibility, free and complexed ligands can adopt potentially various conformations. The NMR titration experiments revealed the subsequent formation of 1:1 and 1:2 complexes, depending on the molar ratio of substrate to ligand. Conformations of free and complexed ligands were examined by the comparison of experimental and DFT gauge-independent atomic orbital (GIAO) calculated chemical shifts and by the analysis of the internal energy of the compounds. For some ligand and substrate combinations, a mixture of complexes differing in ligand conformations was formed. Complexes of Mosher's acid derivative of rhodium(II) with racemic 1,2-dimethylpyrrolidin and 1,2-dimethylpiperidine exhibited NMR chiral recognition phenomenon, manifested by splitting of signals in 13 C NMR and 1 H,13 C HSQC spectra.

Forest land-use increases soil organic carbon quality but not its structural or thermal stability in a hedgerow system

How land-use and soil depth affect soil organic carbon (SOC) quality and stability, properties that are key to the long-term storage of C, is poorly understood in agroforestry systems. We examined the effects of land-use (forest vs. annual cropland) and soil depth (0–10 vs. 10–30 cm) on the quality (availability of C for decomposition), structural stability (composition of C functional groups), and thermal stability (energy yield and temperature characteristics during thermal oxidation) of SOC in a hedgerow system in central Alberta, using solid-state 13C nuclear magnetic resonance (NMR) spectroscopy and thermal analysis methods. The SOC quality (proportion of O-alkyl C) was higher, while the proportion of H- and C-substituted aromatic C and structural stability (hydrophobicity index (HB/HI), aromaticity index (ARM), and alkyl index (A/OA)) were all lower in the forest than in the cropland. The SOC also had lower thermal stability (higher energy density and lower temperature at which 50% of the mass was lost (TG-T50)) in the forest than in the cropland. Between the two soil depths, SOC quality (proportion of N-alkyl C, O-alkyl C and di-O-alkyl C) was higher, but the proportion of H- and C-substituted aromatic C and structural and thermal stabilities were lower, within the surficial 0–10 cm layer than in the 10–30 cm soil. We conclude that while the forest land-use within the hedgerow system had a higher SOC quality, it had lower SOC structural and thermal stabilities, suggesting that SOC under the forest land-use may be more susceptible to decline under climate change or other forms of anthropogenic disturbance.

A Review article on Analytical Method Development for the combination of Azelnidipine and Telmisartan

The literature survey explains that there is not any stability indicating method reportedly for combination of Azelnidipine and Telmisartan till date. Validation and development of stability indicating analytical methods is possible as per ICH Guidelines. There are several of Spectroscopic methods such as Ultraviolet Spectroscopy, Mass spectroscopy, infrared spectroscopy, Nuclear magnetic resonance spectroscopy and Chromatographic methods such as High performance liquid chromatography, Thin layer Chromatography, High Performance thin layer chromatography, Gas chromatography and Ultra performance liquid chromatography etc. used for stability indicating method development and validation.

Castor 오일과 HER 기반 폴리우레탄: 합성, 분석, 구조-열 안정성 상관관계

Polyurethanes (PUs) were prepared from solvent and catalyst free reaction mixture containing polyethylene glycol (PEG), 4,4’-methylene diphenyl diisocyanate (MDI) and 1,3-bis(2-hydroxyethoxy) benzene (HER) and/or castor oil (CAO). PUs were characterized using the Fourier-transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance (¹H NMR) spectroscopic methods. Thermal studies on PUs using differential scanning calorimetric (DSC) and thermogravimetric analysis coupled with FTIR (TG/FTIR) proved that CAO-extended PUs were thermally more stable than HER extended PUs. The partial and complete replacement of HER content in PUs using CAO enhanced the thermal stability by shifting degradation temperature to higher temperature (5-15 ℃) and enhancing the char residue. The parameters derived from DSC traces, thermogram and differential thermogram confirmed that PUs synthesized using PEG 1500 are thermally more stable than the PUs prepared using PEG 4000. The probable degradation mechanism to study the role of β-hydrogen on the thermal stability was proposed and discussed based on the results of TG/FTIR.

Correlation between nuclear magnetic resonance spectroscopy and traditional biochemical determination methods analyzer for determining blood lipid

Correlation between nuclear magnetic resonance spectroscopy and traditional biochemical determination methods analyzer for determining blood lipid