Application of two-dimensional NMR techniques for the elucidation of the proton spectrum of the epoxy monomer,diglycidyl ether of bisphenol A

The application of two-dimensional Fourier transform NMR spectroscopy to the study of the epoxy resin diglycidyl ether of bisphenol A is discussed. The combination of the homonuclear shift-correlated and J-resolved experiments permits the complete elucidation of the proton spectrum of the glycidyl ether moiety.     

A nuclear magnetic resonance study of three isomeric dinaphthothiophenes

The ¹H and ¹³C NMR spectra of three isomeric dinaphthothiophenes are recorded. Chemical shift assignments were made on the basis of substituent chemical shift (SCS) effect arguments, coupling considerations, proton—proton auto-correlated homonulcear (COSY) two-dimensional spectroscopy, and proton—carbon heteronuclear correlation (HETCOR) two-dimensional spectroscopy. Some previously published ¹H chemical shifts and coupling constants are compared with our data and some divergences are noted.     

Establishing vicinal proton-proton connectivities using two-dimensional proton zero quantum coherence NMR

Phenanthro[3,4:3′,4′]phenanthro[2,1-b]thiophene ( 1 ) served as the model system to evaluate two-dimensional proton zero quantum coherence nmr in order to establish the vicinal proton-proton connectivities. The utility of the two-dimensional proton zero quantum nmr experiment has been compared with the utility of the traditional autocorrelated proton-proton (COSY) experiment. In the case of a molecule such as 1 , where the proton chemical shifts are so highly congested, the zero quantum coherence experiment provides data not obtainable from the COSY experiment.     

Combined application of auto-correlated (COSY) and homonuclear J-resolved two-dimensional NMR spectra for the assignment of congested,non-first order spectra of polycyclic aromatic systems. Assignment of the 1H-NMR spectrum of benzo[2,3]phenanthro-[4,5-bcd]thiophene and an investigation of long range 1H-1H spin-coupling constants

Total assignment of the proton nmr spectrum of benzo[2,3]phenanthro[4,5-bcd]thiophene at 200 MHz is reported. Preliminary identification of the resonances comprising the individual spin Systems was accomplished by the use of auto-correlated two-dimensional proton nmr spectroscopy (COSY). Individual assignments were made on the basis of spin-coupling information which was obtained from the “titled” two-dimensional J-resolved (2DJ) proton nmr spectrum of the title compound. Because of the greater resolving power of the latter experiment relative to conventional proton nmr spectroscopy, a number of long range inter-ring spincouplings were observed. The observation of these long range couplings was crucial to the final assignment of several of the resonances in the spectrum. Resonances due to strong coupling in the 2DJ spectrum were also shown to be a useful means of correlating strongly coupled spins which provides an alternative to the COSY spectrum for this purpose.     

Stereoselective synthesis of naturally occurring alpha-methylenebis-gamma-butyrolactones: an application of novel oxiranyl "remote" anions.

Stereospecific deprotonation of the epoxy proton at the beta-position of the alpha,beta-epoxy esters 5 and 6 yielded oxiranyl "remote" anions 7 and 8, which could then be used for alkylation. The anions 7 and 8 underwent a consecutive aldol lactonization to give, respectively, epoxy lactones 11 and 13 with high stereoselectivity. Generation of the remote anions as well as their stereoselective reactions served as a new synthetic route to the naturally occurring alpha-methylenebis-gamma-butyrolactones, 1.     

近红外原位研究杂多酸引发的环氧-四氢呋喃阳离子聚合

用近红外光谱原位跟踪的方法, 研究了杂多酸催化的环氧树脂和四氢呋喃的阳离子聚合过程. 发现在低环氧树脂含量下, 环氧消耗速率在整个聚合过程中维持不变; 而在高环氧树脂含量下, 环氧消耗速率则随时间有所下降. 通过红外光谱在碳氢区域的分峰分析, 证明环氧树脂与四氢呋喃发生了共聚反应, 二维红外光谱的结果也确证了这一结果. 此外, 还探讨了环氧转化速率与环氧含量间的关系.     

A novel fluorescent epoxy resin for organophosphate pesticide detection

In this work,a novel bisbenzimidazolylpyridine-functionalized fluorescent epoxy resin was synthesized for organophosphate pesticide detection.The epoxy resin was characterized by Fourier-transform infrared spectroscopy(FT-IR),proton nuclear magnetic resonance spectroscopy(~1H NMR),gel permeation chromatography(CPC),differential scanning calorimetry(DSC) and fluorescence spectroscopy.After loading with Eu(Ⅲ) ions,the epoxy resin showed a strong fluorescence emission.The fluorescence emission was observed to be instantaneously quenched when exposed to trace amount of diethyl chlorophosphate in solution.The Stern-Volmer quenching constants K_(sv) for quenching at617 nm was determined to be 0.377 × 10~3 L/mol.This sensitive emission-quenching function and easy processing nature of the polymeric support enable the resin to be a promising chemosensor candidate for the detection of organophosphates.     

Percolation model of conductivity of calix[n]arene-p-sulfonic acids

Proton conductivity of special class of aromatic sulfonic acids is described, in particular, calixarene sulfonic acids that consist of flat anionic layers interlinked by labile two-dimensional hydrogen-bond network. High proton conductivity of their hydrates was observed earlier. The dependence of their transport characteristics (the proton conductivity, the activation energy of conductivity) was shown to have threshold character. The studied systems’ behavior is described on basis of percolation model that assumes changing of the proton transport mechanism at low water content in the structure.     

Facile large-scale fabrication of proton conducting channels

A new approach to the facile large-scale fabrication of robust silicon membranes with artificial proton conducting channels is presented. Ordered two-dimensional macroporous silicon was rendered proton conducting by growing a thick uniform polyelectrolyte brush using surface-initiated atom transfer radical polymerization throughout the porous matrix. The fabricated silicon-poly(sulfopropyl methacrylate) hybrid membranes were evaluated for their proton conductivity, ion exchange capacity, and water uptake. With proton conductivities in the range of 10(-2) S/cm, these proof-of-concept experiments highlight a promising alternative for producing tailorable proton conducting membranes. This approach constitutes a benchmark for the preparation and study of model systems and, in addition, for the large-scale fabrication of membranes suitable for a wide range of technological applications.     

Epoxy resin/poly(ϵ‐caprolactone) blends cured with 2,2‐bis[4‐(4‐aminophenoxy)phenyl]propane. II. Studies by Fourier transform infrared and carbon‐13 cross‐polarization/magic‐angle spinning nuclear magnetic resonance spectroscopy

Crystalline thermosetting blends composed of 2,2′‐bis[4‐(4‐aminophenoxy)phenyl]propane‐crosslinked epoxy resin (ER) and poly(?‐caprolactone) (PCL) were investigated by means of Fourier transform infrared (FTIR) spectroscopy and high‐resolution solid‐state NMR spectroscopy. FTIR investigations indicated that there were specific intermolecular interactions between ER and PCL and that the intermolecular hydrogen‐bonding interactions were weaker than the self‐association in pure epoxy. The intermolecular hydrogen bonding was considered to be the driving force for the miscibility of the thermosetting blends. For the examination of the miscibility of the thermosetting blends at the molecular level, high‐resolution solid‐state ¹³C cross‐polarity/magic‐angle spinning (CP‐MAS) NMR spectroscopy was employed. The line width of ¹³C CP‐MAS spectra decreased with increasing PCL contents, and the chemical shift of the carbonyl carbon resonance of PCL shifted to a low field with an increasing epoxy content in the blends. The proton spin–lattice relaxation experiments in the laboratory frame showed that all the blends possessed identical, composition‐dependent relaxation times (i.e., the proton spin–lattice relaxation times in the laboratory frame), suggesting that the thermosetting blends were homogeneous on the scale of 20–30 nm in terms of the spin‐diffusion mechanism, and this was in a good agreement with the results of differential scanning calorimetry and dynamic mechanical analysis. For the examination of the miscibility of the blends at the molecular level, the behavior of the proton lattice relaxation in the rotating frame was investigated. The homogeneity of the thermosetting blends at the molecular level was quite dependent on the blend composition. The PCL‐lean ER/PCL blends (e.g., 70/30) displayed a single homogeneous amorphous phase, and the molecular chains were intimately mixed on the segmental scale. The PCL‐rich blends displayed biexponential decay in experiments concerning the proton spin–lattice relaxation times in the rotating frame, which was ascribed to amorphous and crystalline phases. In the amorphous region, the molecular chains of epoxy and PCL were intimately mixed at the molecular level. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1099–1111, 2003     

Epoxy nanocomposites co-reinforced by two dimensionally different nanoscale particles

Comprehensive high-performance epoxy nanocomposites were prepared by simultaneous incorporating montmorillonite (MMT) and nanoSiO₂ into epoxy. Mechanical tests and thermal analyses showed that the epoxy/MMT/nanoSiO₂ nanocomposites obtained considerable improvement over basic epoxy in tensile modulus, tensile strength, flexural modulus, flexural strength, notch impact strength, glass transition temperature, and thermal decomposition temperature. X-ray diffraction measurements and transmission electronic microscopy observations revealed that the layered structure of MMT was completely exfoliated into two-dimensional nanoscale mono-platelets. These 2D mono-platelets formed intermingled structure with the zero-dimensional nanoSiO₂ spheres in the nanocomposites. This study suggests that employing the synergistic reinforcement effect of two dimensionally different nanoscale particles is one pathway to success in developing comprehensive high-performance polymer nanocomposites.     

含螺环原碳酸酯齐聚物的合成表征及与环氧树脂的固化反应

合成了一种新的带羟基的螺环原碳酸酯，根据它与ＭＤＩ或ＨＤＩ的不同配比，制备了分子量不同的预聚物，其结构得到了核磁和红外数据的证实。用示差扫描量热仪和红外跟踪环氧树脂及其与预聚物混合后的固化反应过程。     

Two-dimensional NMR spectra of poly(N-vinylcarbazole)

Two-dimensional NMR spectra of commercially available poly(N-vinylcarabazole) are presented and analyzed. Complete assignments for the aromatic region of the carbon spectrum are made using the edited spectrum and literature references for model compounds. The proton spectrum is assigned from its correlations with the carbon spectrum and with a J-correlated two-dimensional spectrum. One of the protons (number 1) is shifted to rather unusual high fields by the stacked structure of the carbazole rings, independent on the polymer tacticity. From the aliphatic carbon spectrum a meso probability of 0.45 is estimated for the commercial polymer, and another J-correlated two-dimensional spectrum helps assigning the triad and tetrad splittings in the aliphatic proton spectrum.     

Following the solvent directly during ultrafast excited state proton transfer

Excited state intramolecular proton transfer in 1-chloroacetylaminoanthraquinone is investigated from the perspective of the solvent. Using a new two-dimensional nonlinear optical spectroscopy the solvent response is probed directly as the proton transfer takes place. The measurements indicate that solvent reorganization controls the proton transfer in acetonitrile by dynamically shifting the position of equilibrium in the excited state, even on subpicosecond time scales.     

Preparation, optimization and thermal characterization of a novel conductive thermoset nanocomposite containing polythiophene nanoparticles using dynamic thermal analysis

Polythiophene nanoparticles as a conductive filler was prepared with average diameter of 20-35 nm and its molecular structure was confirmed by the FT-IR, TEM, XRD and UV-vis analysis. A new conductive epoxy nanocomposite was synthesized by curing of diglycidyl ether of bisphenol A/4,4′-(4,4′ Isopropylidenediphenoxy) bis (Phthalic Anhydride) involving various percentages of polythiophene nanoparticles. DSC and DMTA studies revealed that low percentage of the polythiophene nanoparticles, i.e. 1%, results in improved crosslink density as evidenced by increasing in the glass transition temperature. The addition of polythiophene nanoparticles into the epoxy matrix resulted in a significant increment in the electrical conductivity, mechanical properties, thermal stability and activation energy of thermal degradation. The advanced isoconversional method is utilized to describe the curing behavior and thermal degradation process of the neat epoxy and epoxy nanocomposite. We have utilized the Coats-Redfern and Criado methods to find the solid state thermal degradation reaction mechanism. For the nanocomposite, the mechanism was recognized to be two-dimensional diffusion (D₂) reaction and it changes to a nucleation and growth (A₄) for pure epoxy system.     

Total assignment of the proton and carbon NMR spectra of the alkaloid quindoline — utilization of HMQC-TOCSY to indirectly establish protonated carbon-protonated carbon connectivities

The reisolation of the indoloquinoline alkaloid quindoline (also known as norcryptolepine) from Cryptolepis sanguinolenta is reported. The structure was unequivocally confirmed by two-dimensional nmr methods; the proton and carbon spectra were assigned for the first time. Because of congestion in the proton spectrum HMQC-TOCSY was used as an alternative to the more familiar COSY experiment. In addition to establishing proton-proton connectivities, HMQC-TOCSY affords the added benefit of providing, in an indirect sense, connectivity information between protonated carbons.     

二维红外相关光谱在双氰胺固化环氧树脂体系中的应用

利用原位红外加热炉模拟双氰胺固化环氧树脂体系的固化反应过程,实时测试并记录反应过程中官能团结构的变化;将一维红外光谱和二维红外光谱相结合进行分析,给出固化过程中各官能团的变化顺序和趋势。 在双氰胺固化环氧树脂体系中,双氰胺首先分解成氰基胺,然后再和环氧树脂发生开环加成反应,生成亚胺结构,通过重排生成酰胺结构。 双氰胺分解为氰基胺的反应是可逆反应。 将原位红外、一维红外与二维红外三者结合是阐明热固性树脂固化反应机理的非常有效的手段。     

Polybenzimidazole dendrimer containing triazine rings-based high-temperature proton exchange membranes with high performances over a wide humidity range

A high-temperature proton exchange membrane with high proton conductivity over a wide humidity range still remains a challenge. PBI dendrimer containing triazine rings (TPBI) was synthesized to approach this aim considering its high content of hygroscopic terminal groups and of larger free volume. A novel proton conductor previously synthesized (zirconium 3-sulfopropyl phosphonate, ZrSP) was doped due to its good proton conductivity over a wide humidity range. TPBI was post-crosslinked with a tetrafunctional epoxy resin (N,N,N′,N′-tetraglycidyl-4,4′-diaminodiphenylmethane, TGDDM) to enhance the mechanical stability at low cross-linking degrees, which allowed high doping levels of ZrSP, and thus, high conductivity. The prepared membranes (TPBI-TGDDM/ZrSP) showed good thermal stability, high proton conductivity over wide humidity range, and good dimensional stability. At suitable degrees of branching, TPBI-TGDDM/ZrSP exhibited superior mechanical property, oxidative stability, methanol barrier property, and membrane selectivity than its linear analog (mPBI-TGDDM/ZrSP). As ZrSP instead of PA was applied as the proton conductor, TPBI-TGDDM/ZrSP showed good durability of proton conductivity, especially in comparison with TPBI-TGDDM/PA, which highly retarded decline in conductivity caused by PA leaking. The proton conductivity at 180 °C of TPBI(20)-TGDDM(10)/ZrSP(50) achieved 142, 84.2 and 23.6 mS cm^?1 at 100%, 50%, and 0 RH, respectively.     

Effect of mutual orientation of molecules on kinetics of proton transfer reactions

Conclusions We calculated the probability of proton transfer within the framework of a two-dimensional model with an arbitrary orientation of the directions of the ruptured and formed bonds. It was shown that the overlap value of the proton wave functions determines the most favorable orientation of the reactants.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2825–2827, December, 1976.     

APPLICATION OF HMBC AND HMQC-TOCSY NMR METHODS TO ASSIGN THE STRUCTURES OF BICYCLIC-PEPTIDE MIMETICS

Abstract

The structures of representative bicyclic peptides are confirmed through the NMR methods of HMBC and HMQC-TOCSY. Complete assignment of proton and carbon resonances is afforded by these two-dimensional NMR methods. HMQC-TOCSY is especially useful for assigning spectra in molecules having extensive proton spin systems and in establishing connectivities between protonated carbons. Long-range proton-carbon connectivities obtained by HMBC confirm structure in molecules containing heteroatoms or non-protonated carbons that interrupt proton spin systems.