High-resolution 13C NMR Spectra Research Articles

High resolution NMR spectra of fluorotrimethylsilane

High resolution 19F, 1H, 13C, and 29Si NMR spectra of (CH3)3SiF are reported, including chemical shifts, and coupling constants for all isotopologues.

Exploring the tuning patterns of cyclopentyl amine hydrate for potential application to CH4 storage

With the increasing demand on world energy consumption, natural gas has received attention as the near-term primary energy source that produces fewer CO2 emissions than other fossil fuels. Accordingly, developing eco-friendly gas storage and transport technology has remained a significant challenge. Gas hydrate is a crystalline inclusion compound formed by water molecules and has emerged as alternative option for natural gas storage. Despite the benefits of hydrates, relatively high pressure and low temperature formation conditions need to be mitigated for practical application. Here, we introduce cyclopentyl amine (CPA) as a new thermodynamic promoter for potential application for CH4 storage. We measured the synchrotron high-resolution powder diffraction and 13C NMR spectra, and the results revealed that the CPA could form sII hydrate without help gas. We also measured the pressure – temperature phase equilibria of CPA + CH4 hydrate, and the results revealed that CPA works as a thermodynamic promoter for CH4. Further, the tuning phenomena were observed below the stoichiometric concentration of the CPA. Specifically, the tuning factor was obtained as ~ 0.34, which exhibited a critical guest concentration was 0.9 mol%. We believe that these findings provide better understanding of the tuning phenomena for potential application to CH4 storage media.

The heterospin cobalt complexes: peculiarities of high-resolution NMR spectra

The high-resolution 1H and 13C NMR spectra (CHCl3 solution) of sterically non-rigid heterospin complexes CoL2, CoL2-dipy, and CoL2-phen (where L is 4-(3′,3′,3′-trifluoro-2′-oxopropylidene)-2,2,5,5-tetramethyl-3-imidazolidine-1-oxyl) have been studied. The specific of the NMR phenomenon in paramagnetic systems is briefly analyzed. It is shown that the NMR spectra modified by hyperfine coupling can be successfully employed for investigation of the complexation processes. In accordance with the common protocols, the 1H and 13C NMR signals are assigned using the information on 13С – 1Н spin-spin coupling. In addition, the preliminarily recorded 1H and 13C NMR spectra of radical L are also used in the work.The temperature dependences of 1H and 13C paramagnetic shifts in the complexes under study have been obtained. A fundamental feature of these dependences is that they obey to the Curie law in a fairly wide temperature range (up to 100 °C). This observation can be used to control intramolecular processes of sterically nonrigid heterosystems in solutions.

Free radical polymerization of acrylates bearing acetylene for preparation of clickable polymers

It is still a challenge to directly, without any control means, synthesize polymers bearing acetylene groups by normal free radical polymerization (FRP) of acetylenyl vinyl monomers, such as propargyl (meth)acrylates, because the reactive acetylene groups result in chain branching and gelation. Some propargyl acrylates with alkyl substitutes, however, can afford linear and soluble polymers. To clarify the substitute effects the FRP behaviours of a series of acrylates bearing acetylene groups with or without substitutes are studied. Homopolymerizations of acetylenyl acrylates without or with mono-substitute on propargyl led to branched polymers at early reaction stage, and became gelled after 0.5 h with monomer conversion over 12% and gel content over 50%. The acetylenyl acrylates with di-substitutes on propargyl can afford linear and soluble homo- and copolymers with‾Mn up to over 10,000 and with 45–75% monomer conversion, except for monomer 2-(2-methylbut-3-yn-2-yloxy)ethyl acrylate (DMPOEA) which has di-substitutes and a spacer connecting to the propargyl. Reactivities of vinyl and acetylene groups were found within 20 times difference by laser flash photolysis (LFP) experiments. The substitute effects of acetylenyl acrylates on FRP are explained by the intramolecular cycloaddition between CC and CC to form lactone from the s-cis conformers of the di-alkyl substituted acetylenyl acrylates. Propagating radicals can transform to stable allyl radicals by α-H atom transfer and thus the chain propagations stop. Both real-time FT-IR monitoring of photo-polymerization and high resolution 13C NMR spectra of the polymer confirmed the existence of lactone units on polymer chains. The hypothesis is also accordance with facts obsorved in the FRP. Finally postpolymerization modification through acetylene groups on polymer chains by photo thiol-yne click reaction is exemplified.

Crystal structures of {1,1,1-tris-[(salicylaldimino)-meth-yl]ethane}-gallium as both a pyridine solvate and an aceto-nitrile 0.75-solvate and {1,1,1-tris[(salicylaldimino)-meth-yl]ethane}-indium di-chloro-methane solvate.

The sexa-dentate ligand 1,1,1-tris-[(salicyl-idene-amino)-meth-yl]ethane has been reported numerous times in its triply deprotonated form coordinated to transition metals and lanthanides, yet it has been rarely employed with main-group elements, including in substituted forms. Its structures with gallium and indium are reported as solvates, namely, ({[(2,2-bis-{[(2-oxido-benzyl-idene)amino-κ2 N,O]meth-yl}prop-yl)imino]-meth-yl}phenololato-κ2 N,O)gallium(III) pyridine monosolvate, [Ga(C26H24N3O3)]·C5H5N, the aceto-nitrile 0.75-solvate, [Ga(C26H24N3O3)]·0.75C2H3N, and ({[(2,2-bis-{[(2-oxido-benzyl-idene)amino-κ2 N,O]meth-yl}prop-yl)imino]-meth-yl}phenololato-κ2 N,O)indium(III) di-chloro-methane monosolvate, [In(C26H24N3O3)]·CH2Cl2. All three metal complexes are pseudo-octa-hedral and each structure contains multiple weak C-H⋯O and/or C-H⋯N inter-molecular hydrogen-bonding inter-actions. The syntheses and additional characterization in the forms of melting points, high-resolution mass spectra, infra-red (IR) spectra, and 1H and 13C NMR spectra are also reported.

Synthesis and Biological Evaluation of Novel Anthranilic Diamides Containing N-H/CH3-1H-Pyrazole

In order to systematically study the structure-activity relationship of anthranilic diamides and develop insecticides with simple structure and high efficiency, a series of novel anthranilic diamides containing N-H/CH3-1H-pyrazole was designed and synthesized. Their chemical structures were characterized by 1H NMR spectra, high resolution mass spectrometry(HRMS) or 13C NMR spectra. The preliminary bioassay results indicated that all title compounds displayed moderate insecticidal activity against oriental armyworm(Mythimna separata) at 200 mg/L and fungicidal activities against six kinds of fungi at 50 mg/L, especially compound 5i showed 50% insecticidal activity at 25 mg/L. In addition, some compounds exhibited certain antitumor activities. It was demonstrated that the introduction of CH3 group into pyrazole ring was superior to H for the insecticidal activity.

(R,S)-5-(4-Chlorophenyl)-3-{(E)-2-[(R,S)-2,6,6-trimethylcyclohex-2-en-1-yl]vinyl}-4,5-dihydro-1H-pyrazole-1-carboximidamide Hydrochloride

Pyrazoline and amidine motifs are important in medicinal chemistry due to their broad spectrum of bioactivities. This work’s goal was to synthesize a new hybrid amidino pyrazoline from terpenyl chalcone. The chosen method consists of making the terpenyl chalcone react with aminoguanidine hydrochloride in the presence of potassium hydroxide using ethanol as solvent. The reaction was carried out under ultrasonic irradiation. The resulting terpenyl amidino pyrazoline was isolated after separation in a silica-gel chromatographic column in 86% of yield. The product structure was confirmed by the analysis of the high resolution mass, 1H and 13C-NMR spectra. The data was consistent with the expected structure. In summary, the method was efficient for the synthesis of a new hybrid terpenyl amidino pyrazolines under sonochemical conditions.

Quick analysis of composition of semi-aromatic copolyamide via 13C NMR study

Standard high resolution 13C NMR spectra of PA10T, PA6T, PA106, and PA66 were obtained by a nonacidic solvent mixture of HFIP and CDCl3. Several chemical shifts were found extremely sensitive to the polyamide type. According to the standard spectra, semi-aromatic copolyamides comprising PA10T, PA6T, PA106, and PA66 units could be distinguished. The ratio of each polyamide component in the copolyamide was determined through the integration of the methylene carbon peak associated with the amine group. 13C NMR analysis results were consistent with the theoretical values and copolyamide hydrolysis test results, making 13C NMR analysis quite reliable on the quick composition analysis of semi-aromatic copolyamides. Based on this technique, several commercial semi-aromatic copolyamides were further examined and their compositions were easily determined.

Remarkably enhanced H2 evolution activity of oxidized graphitic carbon nitride by an extremely facile K2CO3-activation approach

The photocatalytic activity enhancement of graphitic carbon nitride (g-C3N4) in water splitting were commonly achieved by introducing various functional groups onto/into its planar structure. Herein, oxidized g-C3N4 (CNO) was prepared via an extremely facile K2CO3 activation approach. The high-resolution XPS spectra and solid-state 13C NMR spectra confirmed the successful introduction of O-containing groups and O atoms were inherited the original molecular framework of g-C3N4, but exhibited effectively enlarged bonded with C atoms rather than N atoms in the tri-s-triazine structure of g-C3N4. CNO inherited the original molecular framework of g-C3N4, but exhibited effectively enlarged surface area and enhanced visible light absorption, and more attrractively, the band structure of g-C3N4 could be well-tuned with the introduction of oxygen species. Importantly, the surface O-containing moieties could strongly interact with cocatalyst Pt and thus remarkably promote interfacial electron transfer and consequent photo-generated charge carrier separation. Consequently, the as-obtained CNO exhibited the remarkably enhanced photocatalytic performance with a H2 evolution rate of 199.7 μmol h−1, which is 9 times that of g-C3N4 (22.2 μmol h−1).

NMR investigation of magnesium chelation and cation-induced signal shift effect of testosterone

We have previously reported that testosterone (Tes) is able to interact with magnesium chloride dissolved in methanol. In this study, we have applied 1H and 13C NMR spectroscopies to a series of Tes solutions containing Mg2+ at various concentrations. High-resolution 13C NMR spectra of Tes/Mg2+ revealed well-resolved 13C signals, and the intensities of those arising from C3, C5, C16, and C17 decreased linearly with increasing Mg2+ concentration. The magnitude of the chelation affinity could be deduced from the slopes of the 13C intensity variations; typically, the greater the slope the higher the chelation affinity. The results revealed Tes/Mg2+ chelation to be mediated by the oxygen atom attached to C3 in ring A, and the hydroxyl group attached to C17 in ring D. With regard to the chelation specificity, we showed that Tes chelates Mg2+, but not Ca2+ or Zn2+. We also explored the cation-induced signal shift effects of Tes in the presence of Mg2+, Ca2+, or Zn2+. We demonstrate that high-resolution 13C NMR spectroscopy provides a better probe than 1H NMR for the detection of cation chelation and cation-induced signal shift effects for steroid compounds such as Tes.

Efficient Protocol for the Synthesis of Novel Spiro[acenaphthylene-1,2′-pyrrolidin]-2-one Compounds

An efficient catalyst-free synthesis of 3′-benzoyl-4′,5′-diphenyl-2H-spiro[acenaphthylene-1,2′-pyrrolidin]-2-one derivatives via one-pot 1,3-dipolar cycloaddition of acenaphthenequinone, arylmethyl amines, and chalcones with high regioselectivity is described. The structure of the cycloadducts were characterized by infrared, high-resolution mass spectrometry (electrospray ionization), 1H NMR, and 13C NMR spectra, and the structure of 4a was confirmed using x-ray single-crystal structure analysis.

Al2(OH)2(TCPB)] – An Al-MOF based on a tetratopic linker molecule

High-throughput methods were employed in the discovery and synthesis optimization of the new microcrystalline metal-organic framework (MOF) [Al2(OH)2(TCPB)] · 2 DMF (denoted CAU-9as), which contains the tetratopic linker ion 1,2,4,5-tetrakis-(4-carboxylatophenyl)-benzene (TCPB4−). The compound is obtained under solvothermal reaction conditions and activation at 150 °C leads to the removal of the guest molecules (CAU-9act). Detailed characterization was carried out by FT-IR and NMR spectroscopy, thermogravimetric analysis, gas sorption measurements and X-ray powder diffraction. CAU-9act crystallizes in an orthorhombic unit cell (space group Cmmm) with the cell parameters: a = 31.562(4), b = 6.642(7), c = 10.6612(7) Å. Modeling by force field calculations in combination with Rietveld refinement was used to determine the structure of CAU-9. The content of the asymmetric unit was corroborated based on NMR crystallographic strategies evaluating high-resolution 1H, 13C and 27Al MAS NMR spectra. The structure of CAU-9 is isoreticular to the one of MIL-118B [Al2(OH)2(BTEC)] (BTEC = 1,2,4,5-benzenetetracarboxylate) and Al-PMOF [Al2(OH)2(TCPP)] (TCPP = meso-tetra(4-carboxylato-phenyl)porphyrin). According to the temperature dependent PXRD measurements and the thermogravimetric analysis, it is stable up to 480 °C in air. The nitrogen sorption measurement at 77 K has given a Brunauer–Emmett–Teller (BET) surface area of 1118 m2 g−1 and a micropore volume of 0.45 cm3 g−1. In contrast to MIL-118 no rearrangement of the carboxylate groups from a mono-to bidentate coordination mode was observed upon activation.

Cation ion specifically induces a conformational change in trans-dehydroandrosterone – A solid-state NMR study

In this work, we demonstrated that calcium (Ca+2) is able to induce a conformational change in trans-dehydroandrosterone (DHEA). To this respect, solid-state NMR spectroscopy was applied to a series of DHEA molecules that were incubated with Ca+2 under different concentrations. The high-resolution 13C NMR spectra of the DHEA/Ca+2 mixtures exhibited two distinct sets of signals; one was attributed to DHEA in the free form, and the second set was due to the DHEA/Ca+2 complex. Based on chemical shift isotropy and anisotropy analyses, we postulated that Ca+2 might have associated with the oxygen attached to C17 via a lone-pair of electrons, which induced a conformational change in DHEA. Apart from Ca+2, we also incubated DHEA with magnesium (Mg+2) to determine whether Mg+2 was able to interact with DHEA in a similar manner to Ca+2. We found that Mg+2 was able to induce a conformational change in DHEA deviated from that of Ca+2. These solid-state NMR observations indicate that DHEA is able to interact with cations, such as Mg+2 and Ca+2, with specificity.

Combined experimental and computational NMR study of crystalline and amorphous zeolitic imidazolate frameworks.

Zeolitic imidazolate frameworks (ZIFs) have attracted great interest in recent years due to their high chemical and thermal stability with promising applications in gas storage and separations. We investigate the structures of three different crystalline ZIFs - ZIF-4, ZIF-8, ZIF-zni - and their amorphous counterparts using high field (13)C and (15)N CP MAS NMR. The high field (20 T) allows for the observation of all crystallographically independent carbon and nitrogen atoms in the crystalline ZIFs. Combining our experimental results with density functional theory calculations enabled the assignment of all chemical shifts. The crystalline spectra reveal the potential of high field NMR to distinguish between two ZIF polymorphs, ZIF-4 and ZIF-zni, with identical [Zn(C3H3N2)2] chemical compositions. (13)C and (15)N CP MAS NMR data obtained for the amorphous ZIFs clearly showed signal broadening upon amorphization, confirming the retention of chemical composition and the structural similarity of amorphous ZIF-4 and ZIF-zni. In the case of amorphous ZIF-8, we present evidence for the partial de-coordination of the 2-methyl imidazole linker.

Multi-Spectroscopic Analysis of Seed Quality and 13C-Stable-Iotopologue Monitoring in Initial Growth Metabolism of Jatropha curcas L.

In the present study, we applied nuclear magnetic resonance (NMR), as well as near-infrared (NIR) spectroscopy, to Jatropha curcas to fulfill two objectives: (1) to qualitatively examine the seeds stored at different conditions, and (2) to monitor the metabolism of J. curcas during its initial growth stage under stable-isotope-labeling condition (until 15 days after seeding). NIR spectra could non-invasively distinguish differences in storage conditions. NMR metabolic analysis of water-soluble metabolites identified sucrose and raffinose family oligosaccharides as positive markers and gluconic acid as a negative marker of seed germination. Isotopic labeling patteren of metabolites in germinated seedlings cultured in agar-plate containg 13C-glucose and 15N-nitrate was analyzed by zero-quantum-filtered-total correlation spectroscopy (ZQF-TOCSY) and 13C-detected 1H-13C heteronuclear correlation spectroscopy (HETCOR). 13C-detected HETOCR with 13C-optimized cryogenic probe provided high-resolution 13C-NMR spectra of each metabolite in molecular crowd. The 13C-13C/12C bondmer estimated from 1H-13C HETCOR spectra indicated that glutamine and arginine were the major organic compounds for nitrogen and carbon transfer from roots to leaves.

Analysis of Molecular Motion of Proton-conductive Imidazolium Hydrogen Succinate Crystal Using Solid-state NMR

Abstract The dynamics of imidazolium ion and its influence on proton conductivity were investigated for imidazolium hydrogen succinate crystal using solid-state 2H and 13C NMR. A 180° flip and libration (rotational vibration) of the imidazolium ion were observed from 2H NMR broad line spectra, quadrupole Carr–Purcell–Meiboom–Gill (QCPMG) spectra and high-resolution 13C NMR spectra. From a comparison of the rates of these motions and proton transfer, the libration of imidazolium ion is important for the proton conductive process.

Hydrogen Bonding in Pyridine N-Oxide/Acid Systems: Proton Transfer and Fine Details Revealed by FTIR, NMR, and X-ray Diffraction

The H-bonded complexes of pyridine N-oxide (PyO) with H(2)O, acetic, cyanoacetic, propiolic, tribromoacetic, trichloroacetic, trifluoroacetic, hydrochloric, and methanesulfonic acids have been studied by FTIR and NMR spectroscopy, X-ray diffraction, and quantum chemical DFT calculations. Correlations between vibrational frequencies of the NO stretching and PyO ring modes and geometric parameters of the H-bond have been established. FTIR experiments show and DFT calculations confirm that definite discontinuity is present in the vicinity of the midpoint in the proton transfer pathway. The established correlations significantly aid in the understanding of fine effects such as the isotope (deuteration) effect, crystal-to-solution transition, or criticality of aqueous solutions induced by ionic pairs. Geometric isotope effect in the ionic H-bond aggregate of PyO·H(D)Cl was found to be extraordinary large. Measured FTIR, CP/MAS, and high-resolution (13)C NMR spectra indicate that H-bond in the PyO·HCl complex in polar solvent can potentially be more ionic than in the crystal. Vibrational modes of ionic pairs originating via proton transfer in H-bond complexes can provide new information concerning the interionic interaction and its role in the phase separation and mezo-structuring processes. The results are compared to the relevant data for PyO·HCl complex in argon matrix.

Novel biotransformation of betulin to produce betulone by Rhodotorula mucilaginosa

In this study, betulin was biotransformed to betulone by a strain of yeast. A primary screening was carried out using 47 microbial strains isolated from soil, that was able to grow in the presence of betulin as sole carbon source. The strain of yeast was identified as Rhodotorula mucilaginosa by Bruker MALDI Biotyper and 26S rDNA analysis. Under the optimum conditions, this yeast converted 52.65% of the added 4mg/ml betulin to two products. One was betulone detected by high performance liquid chromatography (HPLC), isolated by preparative HPLC and characterized by high resolution mass spectrum (HRMS), 13C NMR and 1H NMR spectra. The other was a semi-volatile aromatic compound identified as 11,14-Octadecadienoic acid methyl ester by GC–MS. In the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging system, the activity of betulone was about 2 times higher than that of betulin.

An experimental study of 19F-19F and 13C-19F spin-spin coupling in molecules of difluoro(fluorosulfonyl)- and difluoro(fluorosulfonyloxy)acetyl fluorides

High-resolution 19F and 13C NMR spectra of difluoro(fluorosulfonyl)- and difluoro(fluorosulfonyloxy) acetyl fluorides were studied, and specific features of complex spin-spin coupling of fluorine and carbon nuclei were characterized. The mechanisms of 19F and 13C coupling were interpreted.

Two new phenethanol glycosides from Ligustrum robustum

Two new phenethanol glycosides, named ligurobustoside P (1), ligurobustoside Q (2) have been isolated from the leaves of Ligustrum robustum, together with the known compound angoroside A (3) which was firstly isolated from this species. The structures of the two new phenethanol glycosides (1–2) were elucidated by a combination of high-resolution electron ionization mass spectrometry (HR-ESI-MS), 1H NMR, 13C NMR, HMQC, and HMBC spectra for the first time.