Proton Resonance Signals Research Articles

A novel method to visualize liquid distribution in snow: superimposition of MRI and X-ray CT images

Abstract The relationship between the behavior of water in snow and its microstructure is crucial to improve the prediction of wet snow disasters. X-ray computed tomography (X-ray CT) is frequently used to observe snow microscopically. However, distinguishing between ice and water in the X-ray images is difficult because ice exhibits an X-ray absorption coefficient similar to that of water. In contrast, magnetic resonance imaging (MRI) acquires nuclear magnetic resonance (NMR) signals of protons in a liquid and visualizes the NMR signal intensity, enabling discrimination between water and ice signals. However, snow grains and pore spaces cannot be distinguished in MRI images because they do not generate NMR signals. To investigate the relationship between the microstructure of snow and the distribution of liquids in snow, we developed a novel method that combines X-ray CT and MRI images to compensate for the disadvantages associated with each method. Using this method, we successfully visualized where liquid (C12H24) occupied pore spaces. We also showed the possibility of using C12H24 instead of water to obtain water retention curve of snow cover, which is a fundamental aspect of hydraulic properties. Although there is room for improvement in the visualization of water in snow, such as shortening the imaging time to escape snow metamorphosis and image superimposition methods, this method is expected to effectively elucidate the behavior of water in snow and clarify the characteristics of wet snow.

Synthesis, Crystal Structure and Optical Properties of 2-(3-(Hexyloxy)-5-Methylphenoxy)-N-(4-Nitrophenyl)acetamide for Anion Detection

In this study, 2-(3-(hexyloxy)-5-methylphenoxy)-N-(4-nitrophenyl)acetamide (sensor L1) was synthesized and characterized by FT–IR, ESI–MS, 1H and 13C NMR spectroscopy, elemental analysis, and single crystal X-ray techniques. The crystal structure and space group of sensor L1 was monoclinic and P21, respectively. The crystal packing of sensor L1 was dominantly linked by two strong hydrogen bonds forming a six membered ring pattern. The binding properties of sensor L1 and various anions (F−, Cl−, Br−, CH3COO−, C6H5COO−, and H2PO4−) were investigated by UV–Vis and 1H NMR spectroscopy in DMSO. The proton resonance signals of sensor L1 and F− greatly changed positions when compared to those of anions. The solution color of sensor L1 changed from pale yellow to orange in the presence of F−. The UV–Vis results indicate that sensor L1 and F− ions underwent an internal charge transfer process. The stoichiometric complex was confirmed by Job’s method, revealing a 1:1 formation for sensor L1 and fluoride. Our results show that sensor L1 is highly selective for fluoride ions over other anions.

Spectral and microscopic analysis of fulvic acids isolated from marine fish waste and sugarcane bagasse co-compost

Abstract Fulvic acids are highly beneficial molecules promoting several soil functions such as nutrient absorption, metal transportation and improving soil structure. These activities are assisted by their molecular structure upon interaction with soil medium. The present study describes the isolation of fulvic acids (FA) from mature marine fish waste and sugarcane bagasse co-compost using alkaline extraction method and studying its molecular and structural characteristics using spectroscopic and microscopic techniques. UV–visible spectroscopic analysis of fulvic acids revealed presence of absorption peak at 264 nm due to characteristics of double bonds of aromatic or unsaturated compounds. Fluorescence spectroscopic analysis of fulvic acids showed emission (455 nm) and excitation (395 nm) spectrum respectively. The photometric ratio (E4/E6) and fluorescence index (FI) confirmed high humification degree of FA. The low color co-ordinate values (L* and b*) measured by CIELAB ensured good maturity of the FAs present in the co-compost. Especially, Proton NMR spectroscopy detected resonance signals of aliphatic protons (0.82–2.0 ppm) and aromatic proton (7.5 ppm) in the molecular structure of FA. FTIR spectrum identified functional groups such as hydroxyl; aliphatic, amide I and polysaccharide and classified the FA as type II. Stereo microscopic examination visualized presence of light brown crystalline particles. Further, SEM analysis of the FA particles revealed presence of various shapes such as spherical; cubical; flakes and micro-aggregate structures. Therefore, it is concluded that spectroscopic and microscopic tools are reliable techniques to reveal the molecular and structural characteristics of FA isolated from co-compost for usage as an organic fertilizer.

The Influence of Fatty Acids on Metoprolol - Human Serum Albumin Interaction in Low Affinity Binding Sites: A Multifactorial NMR Approach.

Metoprolol (MTP) is a cardio-selective β1-blocker used in hypertension, angina pectoris and chronic heart failure therapies. Serum albumin is the most frequently occurring protein in blood plasma. The binding of ligands to human serum albumin (HSA) has an important effect on pharmacokinetics and final clinical effects. The objectives of this study included a detailed analysis of metoprolol - serum albumin interactions in low affinity binding sites, on the surface or within the hydrophobic subdomain of a macromolecule, as well as an analysis of the competition between MTP and fatty acids in binding with protein. The analysis of the drug-albumin interaction was based on the observed chemical shifts in combination with correlation Times (T1 -1 = τ) [1/s], 2D NOESY 1H NMR spectra and association constants Ka [M-1]. For the determination of chemical shifts σ [ppm], relaxation times T1 [s] and for the NOESY experiment, the final concentrations of MTP and albumins (in the presence (HSA) and absence of fatty acids (dHSA)) were 5 x 10-3 M and 2 x 10-5 M - 4.55 x 10-4 M, respectively. In order to calculate the association constants, the final concentrations of MTP and both HSA and dHSA were 2.75 x 10-3 M - 6.25 x 10-2 M and 2.5 x 10-4 M, respectively. For the analysis, the MTP proton resonances of aliphatic H17, aromatic (H2/H6 and H3/H5) and the methoxy group H14 were chosen. Changes in the values of the 1H NMR chemical shift [ppm] are evidence of interaction between MTP, fatted (HSA) and defatted (dHSA) human serum albumin. With an increase of albumin concentration, changes in the chemical shift values were observed for the aromatic protons H2/H6 (Δσ = 0.013 ppm and 0.018 ppm) and H3/H5 (Δσ = 0.015 ppm and 0.019 ppm), the aliphatic proton H17 (Δσ = 0.018 ppm and 0.022 ppm) and the aliphatic protons of the methoxy group H14 (Δσ = 0.019 ppm and 0.022 ppm) for dHSA and HSA, respectively. Greater changes in chemical shifts in the presence of fatty acids (FA) were observed. Changes in the correlation times of MTP aromatic H2/H6 (Δτc = 0.224 1/s and 0.189 1/s) and H3/H5 (Δτc = 0.269 1/s and 0.210 1/s), aliphatic from the methoxy group H14 (Δτc = 0.472 1/s and 0.271 1/s) and aliphatic H17 protons (Δτc = 0.178 1/s and 0.137 1/s) for dHSA and HSA systems, respectively. It confirms the interaction between the drug and albumin are evidence for the dynamics of the process. In the presence of FA the relaxation time of all analyzed MTP proton resonance signals significantly increases (due to the decrease of correlation time). This phenomenon is due to the increase of electron density in the MTP protons' surroundings. Association constants for the MTP-dHSA complex in the low affinity site range between 0.29 x 102 M-1 and 0.47 x 102 M-1. The presence of FA results in a two to three-fold increase of the Ka values of protons from aromatic (H2/H6 and H3/H5), aliphatic H17 and methoxy (H14) groups. In 2D NOESY spectra proton magnetization transfer was observed between cysteine (Cys-34) and aromatic H3/H5 and H2/H6 protons. Cross-peaks were also observed between cysteine and aliphatic protons from the methoxy group. The selective changes in σ [ppm] and τc [1/s] values indicated the unequal participation of chemical groups of MTP in the interaction with HSA and dHSA. The data obtained suggest that the presence of fatty acids increases the accessibility of low affinity sites of serum albumin to MTP, which results in the higher affinity of albumin towards the drug. The results showed that the main binding site of MTP and fatty acid is probably a low affinity site in subdomain IB, where Cys-34 can be located.

The Low-Field Pulsed Mode Dynamic Nuclear Polarization in the Pentavalent Chromium Complex and Crude Oils

Measurements of the enhancement of the proton resonance signal right after applying the radiofrequency pulse with the variable duration in the magnetic field of about 100 Gauss on the homebuilt prototype of the dynamic nuclear polarization (DNP) spectrometer at near room temperature are presented. A dependence of the DNP enhancement of the solvent protons of the solution of the pentavalent chromium complex in ethylene glycol on the pumping pulse duration and incident pumping power is given. No DNP effect on the native protons of the crude oils and natural bitumen from the Russian oilfields is observed. A miserable DNP enhancement is registered on the protons of toluene by dissolving the crude oil and bitumen samples. The perspectives of using the results and technical solutions for geological exploration, studies of the asphaltene structures and their dynamics are discussed.

Synthesis and characterization of several series of 4-acyl-1-[2-aryl-1-diazenyl]piperazines

Five series of a novel class of 4-acyl-1-[2-aryl-1-diazenyl]piperazines have been synthesized and characterized: the 4-acetyl-1-[2-aryl-1-diazenyl]piperazines [series 1]; the 4-cyclohexylcarbonyl-1-[2-aryl-1-diazenyl]piperazines [series 2]; the 4-benzoyl-1-[2-aryl-1-diazenyl]piperazines [series 3]; the benzyl 4-[2-aryl-1-diazenyl]-1-piperazinecarboxylates [series 4]; and the t-butyl 4-[2-aryl-1-diazenyl]-1-piperazinecarboxylates [series 5]. The compounds were synthesized by diazotization of a primary aromatic amine and subsequent coupling to an appropriate secondary amine: 1-acetylpiperazine [series 1]; 1-(cyclohexylcarbonyl)-piperaizine [series 2]; 1-benzoylpiperazine [series 3]; benzyl 1-piperazinecarboxylate [series 4]; and t-butyl piperazine-1-carboxylate (1-BOC-piperazine) [series 5]. The compounds of series 1–5 were characterized by 1H NMR, 13C NMR, high-resolution MS and IR spectroscopy. The model compounds 1,4-di[2-aryl-1-diazenyl]piperazines, and ethyl 4-[2-aryl-1-diazenyl]-1-piperazinecarboxylates were used to facilitate the assignment of the chemical shifts specific to the piperazine ring carbons. HSQC spectra of select compounds established the correlation between proton and carbon resonance signals.

Detection of glutamate, glutamine, and glutathione by radiofrequency suppression and echo time optimization at 7 tesla

To achieve detection of glutamate (Glu), glutamine (Gln), and glutathione (GSH) by minimizing the N-acetyl-aspartate (NAA) multiplet signals at 2.49 ppm using a echo time (TE) -optimized PRESS pulse sequence and a novel J-suppression radiofrequency pulse. Using density matrix simulations, a PRESS sequence with (TE1 , TE2 ) = (69, 37) ms and an inserted 90° J-suppression pulse were found to minimize the NAA multiplet at 2.49 ppm. NAA phantom experiments confirmed the successful suppression of the NAA multiplet at 2.49 ppm. A study of eight healthy volunteers found both Glu and Gln to be significantly higher in gray matter (GM) dominant medial prefrontal cortex voxels than in white matter (WM) dominant right frontal cortex voxels. Time-course (1) H spectra acquired during intravenous [U-(13) C6 ]glucose infusion showed gradually changing Glu C4 and Gln C4 proton resonance signals in a spectral pattern predicted by numerical simulations. Reliable detection of Glu, Gln, and GSH was achieved. Glu and Gln levels were significantly higher in frontal lobe GM than in frontal lobe WM. It is feasible to use the proposed proton MR spectroscopy method to measure the kinetics of (13) C incorporation into Glu and Gln during infusion of (13) C labeled glucose.

Structural characterization of inclusion complexes between cyanidin-3-O-glucoside and β-cyclodextrin

Inclusion complex formation between the multiple equilibrium forms of cyanidin-3-O-glucoside (cy3glc) and β-cyclodextrin (β-CD) was investigated using a combined approach of NMR spectroscopy and Molecular Dynamics simulation. Diffusion ordered NMR spectroscopy (DOSY) and study of nuclear Overhauser effects (NOE) were used to determine the selective intermolecular interactions and structure of these complexes in aqueous solution.The observed chemical shift displacements of resonance signals of protons from the interior of β-CD cavity and protons belonging to the hemiketal (B) and cis-chalcone forms (Cc), the diffusion measurements using DOSY and the NOE studies have anticipated the formation of an inclusion complex between these two forms and β-CD. The analysis of the NMR spectral data has shown no evidence of internal interaction between β-CD and the flavylium cation (AH+) or trans-chalcone (Ct) forms of cy3glc.The hemiketal formed a 1:1 inclusion complex with β-cyclodextrin in which the pyranic C ring is deeply included inside the β-CD cavity while B ring lies on the plane of the wider rim of β-CD. The structure of the complexes was also clarified through a theoretical approach by Molecular Dynamics simulation.

Synthesis and binding with BSA of a new gemini surfactant

We have synthesized a new gemini surfactant, glycol bis-N-tetradecyl nicotinate dibromide (designed as P14-1-14), and probed its combination with bovine serum albumin (BSA) by fluorescence spectroscopy, dual polarization interferometry (DPI), proton nuclear magnetic resonance spectroscopy (1H NMR), Fourier transform infrared spectroscopy (FTIR) and molecular docking. The experiments revealed, in one hand, P14-1-14 quenched the intrinsic fluorescence of BSA by way of forming BSA/P14-1-14 complex with a binding constant of 2.14×104Lmol−1 at 293K, that P14-1-14 augmented the thickness, mass, the refractive index (RI) and density of BSA, and that P14-1-14 declined the contents of α-helix (from 54.01% to 29.41%) but raised the random structure (from 7.86% to 22.27%). On the other hand, BSA shifted the proton resonance signals of P14-1-14 up-field and reduced relaxation time. The molecular docking manifested P14-1-14 embedded into subdomain of BSA, which made possible the π–π stacking between the electron-deficit pyridinium rings in P14-1-14 and the electron-abundant pyrrole ring in Trp residues of BSA, and that hydrogen bonding and hydrophobic interaction also took place during the binding. Therefore, the present work offers a whole view of the interaction of BSA with a new gemini surfactant.

The bilateral action between EQ14-2-14 gemini surfactant and bovine serum albumin by DPI and 1H NMR

Gemini surfactant diglycol bis-N-tetradecyl nicotinate dibromide (designed as EQ14-2-14) has been synthesized. The interaction between EQ14-2-14 and bovine serum albumin (BSA) was studied by dual polarization interferometry (DPI), proton nuclear magnetic resonance spectroscopy (1H NMR), Fourier transform infrared spectroscopy (FTIR) and molecular docking. Owing to the binding of EQ14-2-14, the thickness and mass of BSA increased; refractive index (RI) and density firstly raised and then tended to a plateau. In addition, a decrease of α-helix was observed from 54.01% to 31.56% with an increase in random structure from 7.86% to 21.76%. Due to BSA intertwining, the proton resonance signals of EQ14-2-14 shifted up-field and relaxation time decreased with increasing concentration of BSA. The study of molecular docking indicated that EQ14-2-14 embedded into subdomain II of BSA by π–π stacking between the electron-deficit pyridinium rings in EQ14-2-14 and the electron-abundant pyrrole ring in Trp residues of BSA, by hydrogen bonding and by hydrophobic interaction. Therefore the present work offers a whole view of the interaction of BSA with a new gemini surfactant.

Steric hindrance effect on thermoresponsive behaviors of pyrrolidone-based polymers

This paper describes the steric hindrance effect on thermoresponsive behaviors of pyrrolidone-based water-soluble polymers. Two polymers, poly[N-(1-meth-2-acryloyloxyethyl)pyrrolidone] (PMEP) and poly[N-(2-acryloyloxypropyl)pyrrolidone] (PAPP) with different pyrrolidone-based side groups were synthesized via conventional free-radical polymerization. PMEP and PAPP with approximate molecular weights (MW) and polydispersities were confirmed by gel permeation chromatography. Their thermoresponsive phase transition behaviors in aqueous media were studied using dynamic light scattering (DLS) and temperature-variation 1H NMR. The cloud points of PMEP and PAPP decreased exponentially rather than linearly with the increase in concentration. PMEP exhibited a lower cloud point than PAPP at the same mass concentration. Both PMEP and PAPP showed a solvent isotopic effect, as their cloud points in deuterium oxide (D2O) were lower than those in hydrogen oxide (H2O). We also noted that the ΔCP [CPPAPP − CPPMEP] was 5.2 °C in D2O and 4.2 °C in H2O at 20.0 mg ml−1. In addition, PAPP showed more noticeable changes in proton resonance signal intensities during the temperature elevation. The differences in thermoresponsive phase transition behaviors between PMEP and PAPP resulted from the steric hindrance effect of their side groups.

Time-Domain Frequency Correction Method for Averaging Low-Field NMR Signals Acquired in Urban Laboratory Environment

Using a second-order helium-cooled superconducting quantum interference device gradiometer as the detector, ultra-low-field nuclear magnetic resonance (ULF-NMR) signals of protons are recorded in an urban environment without magnetic shielding. The homogeneity and stability of the measurement field are investigated. NMR signals of protons are studied at night and during working hours. The Larmor frequency variation caused by the fluctuation of the external magnetic field during daytime reaches around 5 Hz when performing multiple measurements for about 10 min, which seriously affects the results of averaging. In order to improve the performance of the averaged data, we suggest the use of a data processor, i.e. the so-called time-domain frequency correction (TFC). For a 50-times averaged signal spectrum, the signal-to-noise ratio is enhanced from 30 to 120 when applying TFC while preserving the NMR spectrum linewidth. The TFC is also applied successfully to the measurement data of the hetero-nuclear J-coupling in 2,2,2-trifluoroethanol.

Polymerization of acrylated epoxidized soybean oil with phenol furfural resins via repeated forward and retro diels–alder reactions

AbstractIn this work, the Diels–Alder reaction between the acrylate groups of acrylated epoxidized soybean oil and the furan rings of p‐tertiary butyl phenol furfural resin (TBPF) is described. The reaction was carried out at 110°C in presence of FeCl3 catalyst, and tough polymers were obtained in 1 h. Surprisingly, samples that were heated and cooled 5, 10, and 20 times to 140°C and room temperature had better mechanical properties than samples that were kept at 140°C for the same total duration. This unexpected behavior is attributed to a series of forward and retro Diels–Alder reactions between the functional groups. To prove this hypothesis, a model reaction between TBPF and n‐butyl acrylate was studied. At 100°C, 1H‐nuclear magnetic resonance signals of the furan ring protons disappeared, only to reappear at 140°C. Thermogravimetric analysis of the adduct showed a weight loss at 140–150°C, which was in quantitative agreement with the amount of butyl acrylate. Infrared analysis showed that furan rings were not completely consumed by extended heating at 110°C. After five heating and cooling cycles of much shorter duration at 140°C, the furan absorption in the infrared disappeared. The storage modulus of acrylated epoxidized soybean oil‐TBPF samples after 20 heating cycles was 1.15 GPa. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Synthesis and structure of heteroleptic triple-decker neodymium, europium, holmium, erbium, and ytterbium crown phthalocyaninates

Two series of heteroleptic crown-substituted tris(phthalocyaninate) complexes (Pc)Ln[(15C5)4Pc]Ln(Pc) and [(15C5)4Pc]Ln[(15C5)4Pc]Ln(Pc), where 15C5 is 15-crown-5, (Pc2−) is the phthalocyaninate dianion, Ln = Nd, Eu, Ho, Er, and Yb, were prepared by the reaction of tetra-15-crown-5-phthalocyanine H2[(15C5)4Pc] with the corresponding lanthanide acetylacetonates and lanthanum bis(phthalocyaninate) La(Pc)2, which was used as a phthalocyaninate dianion donor. The composition and structure of the synthesized complexes were confirmed by MALDI TOF mass spectrometry, UV-Vis absorption spectroscopy, and 1H NMR. Complete assignment of the proton resonance signals of the paramagnetic lanthanide complexes was based on analysis of lanthanide-induced shifts.

PROTON NMR STUDIES ON RHODAMINE B IN AN AQUEOUS CLAY SUSPENSION

The dynamics of rhodamine B (RB) in D 2 O solutions was examined in the absence and presence of a smec- tite clay mineral, synthetic sodium-saponite (SSA), by 1 H nuclear magnetic resonance (NMR) spectroscopy. Hybridization of RB with the exfoliated SSA particles significantly decreased the intensity of NMR resonance signals of RB protons with the linewidth broadening, compared to RB alone. This indicated that the dynamics of RB molecules adsorbed onto the surface of SSA clay particles was very slower than in free state. The photodegradation profiles of RB in the presence of SSA clay particles were also monitored by 1 H NMR spectroscopy. After visible light irradiation, nine new resonance signals resulting from reaction products were detected in the 1 H NMR spectrum. The analysis of two-dimensional 1 H- 1 H COSY and TOCSY spectra of the reaction mixture indicated that the ethyl group(s) of RB molecule adsorbed onto the surface of SSA particles was destroyed in the photodegradation process and that not only N-ethylamine (and/or N,N-diethylamine) as a major product but also other chemical species such as acetoaldehyde, acetic acid and formic acid were also produced. The detection of the minor products by NMR indicated the photodegradation of RB dye under the present experimental conditions involves oxidative reaction processes in which RB itself and/or the N-de-ethylation products react with the dissolved oxygen to produce the minor chemical species.

Sequestering agents for uranyl chelation: new calixarene ligands

Synthesis of sulfocatecholamide (CAMS) and hydroxypyridinone (HOPO) calixarene ligands and determination of their binding abilities for the uranyl cation were described. Chelating properties were determined by UV spectrophotometry in aqueous media under various pH conditions and further studied by 1H NMR analysis of the resonance signals of both aromatics' protons of the chelating groups. Each ligand shows a more or less pronounced affinity for uranium. HOPO calixarenes exhibit significant affinity towards uranyl ion at acidic and neutral pH while CAMS calixarene is more efficient at basic pH.

Facile Synthesis and Thermoresponsive Behaviors of a Well-Defined Pyrrolidone Based Hydrophilic Polymer

A well-defined pyrrolidone based thermoresponsive polymer, poly[N-(2-methacryloyloxyethyl) pyrrolidone] (PNMP), was synthesized via reversible addition−fragmentation chain transfer radical polymerization or RAFT polymerization of N-(2-methacryloyloxyethyl) pyrrolidone monomer in methanol under a mild visible light radiation at 30 °C. The average molecular weights and polydispersity indices of PNMP polymers were characterized by gel permeation chromatography (GPC) and static light scattering analysis. The kinetic studies indicated that this RAFT polymerization exhibited a well-controlled behavior. The living character of this RAFT polymerization was confirmed by the facile synthesis of a series of well-defined PNMP-based block copolymers via RAFT polymerization under this mild visible light radiation at 30 °C using the above-synthesized PNMP polymer as a macromolecular chain transfer agent. Temperature-variation 1H NMR unambiguously revealed that the PNMP polymer with weight-average molecular weight (Mw) of 105.4 kg mol−1 and polydispersity index (Mw/Mn) of 1.11 was molecularly dissolved in D2O at ambient temperature, e.g. 22 °C. Upon elevating the solution temperature, the dehydration process of this fully hydrated PNMP polymer was triggered at 46.1 °C, leading to a dramatic decrease of integral ratios of proton resonance signals of PNMP to that of D2O. Further elevating the solution temperature to 51.9 °C led to a sharp phase separation of PNMP polymer from aqueous solution. Laser light scattering analyses demonstrated that the cloud point of the PNMP polymer decreased with molecular weight in the Mw range of 20.6–105.4 kg mol−1. Moreover, this PNMP polymer exhibited a remarkably reversible thermoresponsive dehydration/hydration and phase transition behaviors in aqueous solution. Unlike what was observed in PNIPAM aqueous solution, no hysteresis phenomenon was observed in PNMP aqueous solution during one heating-and-cooling cycle.

Synthesis and characterization of sulphonated PEES copolymers by NMR spectroscopy

Two sulphonated PEES copolymers were synthesized by reacting 75 or 60 mol% silylated hydroquinone sulphonic acid and 25 or 40 mol% of hydroquinone with 4,4′-difluorodiphenyl sulphone. The number average molecular weights determined by GPC were 13.250 and 12.050 g/mol. In the FTIR spectra, in addition to the characteristic absorption bands due to aromatic skeleton, absorption bands associated with sulphonic acid groups were observed at ∼3500, 1172, 1080, 1026, and 706 cm −1. In 1H NMR, the aromatic proton resonance signals were observed between δ = 6.99 and 7.96 ppm. 13C{ 1H} NMR spectra of these copolymers were complex and in order to resolve this, two-dimensional (2D) NMR techniques were utilized. Heteronuclear single quantum coherence (HSQC), total correlated spectroscopy (TOCSY), and heteronuclear multiple bond correlation (HMBC) were used for assigning the structure of the copolymers.

Methacrylate/acrylate terminated derivatives of diglycidyl hexahydrophthalate: Synthesis, structural, and thermal characterization

AbstractMono‐ or di(meth)acrylate‐terminated derivatives of diglycidyl hexahydrophthalate (ER) were prepared by reacting 1 : 1 or 1 : 2M ratio of ER and methacrylic acid or acrylic acid. These vinyl ester (VE) resins were characterized by determining epoxy equivalent weight, acid number, and molecular weight by gel permeation chromatography. Structural characterization was done by FTIR and 1H NMR spectroscopy. In the 1H NMR spectra of acrylate‐terminated VE resins, three proton resonance signals were observed in the region 5.8–6.4 ppm due to vinyl group while in methacrylate‐terminated VE resins only two proton resonance signals due to vinylidene protons were observed at 5.6–6.1 ppm. The Brookfield viscosity (room temperature (25 ± 2)°C) of these resins diluted with varying amounts of MMA was determined at 20 rpm. Curing behavior was monitored by determination of gel time and differential scanning calorimetry. An exothermic transition was observed in the DSC scans in the temperature range of (81–150)°C. Isothermal curing of MMA‐diluted VE resins containing AIBN as an initiator was done at 60°C for 2 h in N2 atmosphere, and then heating for another 2 h in static air atmosphere. Thermal stability of isothermally cured resins in N2 atmosphere was evaluated by thermogravimetric analysis. All cured resins decomposed above 310°C in single step. Thermal stability of the cured resins having acrylate end caps was marginally higher than the resins having methacrylate end groups. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006

Total assignment and structure in solution of tetrandrine by NMR spectroscopy and molecular modelling

High-resolution 1- and 2D NMR spectra of tetrandrine and molecular modelling were employed to characterise its structure in solution. Complete and unambiguous assignment of all proton and carbon resonance signals is reported. Scalar couplings were determined from dihedral angles with the Karplus equation. Inter-proton distances were evaluated from NOE correlation peaks. Comparison of simulated and X-ray conformations of tetrandrine reveals only small differences.