High-resolution F and H NMR of a vinylidenefluoride telomer

The reaction products of vinylidenefluoride (VDF) with methanol as a telogen have been analysed in the solution state by ¹H and ¹⁹F nuclear magnetic resonance (NMR) spectroscopy. High-resolution ¹⁹F and ¹H NMR spectra were achieved using high-power ¹H and ¹⁹F decoupling, respectively, giving superior resolution and revealing previously unresolved signals of the vinylidenefluoride telomer (VDFT). ¹H and ¹⁹F homo- and hetero-nuclear scalar coupling constants are presented and the spectra of functional groups and reverse units (including the identification of short-chain structures) are discussed. Furthermore, the application of ¹⁹F or ¹H decoupling for the correct assessment of reverse-unit content and degree of polymerisation is demonstrated. This work highlights the need for high-resolution NMR spectroscopy to determine both the chemical structure and the composition of these important fluoropolymers.     

Towards Profiling of the G-Quadruplex Targeting Drugs in the Living Human Cells Using NMR Spectroscopy

Recently, the ¹H-detected in-cell NMR spectroscopy has emerged as a unique tool allowing the characterization of interactions between nucleic acid-based targets and drug-like molecules in living human cells. Here, we assess the application potential of ¹H and ¹⁹F-detected in-cell NMR spectroscopy to profile drugs/ligands targeting DNA G-quadruplexes, arguably the most studied class of anti-cancer drugs targeting nucleic acids. We show that the extension of the original in-cell NMR approach is not straightforward. The severe signal broadening and overlap of ¹H in-cell NMR spectra of polymorphic G-quadruplexes and their complexes complicate their quantitative interpretation. Nevertheless, the ¹H in-cell NMR can be used to identify drugs that, despite strong interaction in vitro, lose their ability to bind G-quadruplexes in the native environment. The in-cell NMR approach is adjusted to a recently developed 3,5-bis(trifluoromethyl)phenyl probe to monitor the intracellular interaction with ligands using ¹⁹F-detected in-cell NMR. The probe allows dissecting polymorphic mixture in terms of number and relative populations of individual G-quadruplex species, including ligand-bound and unbound forms in vitro and in cellulo. Despite the probe’s discussed limitations, the ¹⁹F-detected in-cell NMR appears to be a promising strategy to profile G-quadruplex–ligand interactions in the complex environment of living cells.     

Investigation of microstructure of the N‐vinyl‐2‐pyrrolidone/methyl methacrylate copolymers by NMR spectroscopy

The copolymers containing N‐vinyl‐2‐pyrrolidone (V) and methyl methacrylate (M) units of different compositions were synthesized by free radical bulk polymerization. The copolymer composition of these copolymers was determined by CHN analysis. The distortionless enhancement by polarization transfer (DEPT) technique was used to resolve the methine, methylene, and methyl resonance signals in the V/M copolymer. Comonomer reactivity ratios were determined by the Kelen–Tudos (KT) and nonlinear least‐square error‐in‐variable (EVM) methods. ¹H–¹³C Heteronuclear shift quantum correlation spectroscopy (HSQC) and ¹H–¹H homonuclear total correlation spectroscopy (TOCSY) spectra were used for the resolution of the proton nuclear magnetic resonance (¹H NMR) spectrum of the V/M copolymers. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1328–1336, 2002     

Direct Detection of Glutathione Biosynthesis,Conjugation, Depletion and Recovery in Intact Hepatoma Cells

Nuclear magnetic resonance (NMR) spectroscopy was used to monitor glutathione metabolism in alginate-encapsulated JM-1 hepatoma cells perfused with growth media containing [3,3′-¹³C₂]-cystine. After 20 h of perfusion with labeled medium, the ¹³C NMR spectrum is dominated by the signal from the ¹³C-labeled glutathione. Once ¹³C-labeled, the high intensity of the glutathione resonance allows the acquisition of subsequent spectra in 1.2 min intervals. At this temporal resolution, the detailed kinetics of glutathione metabolism can be monitored as the thiol alkylating agent monobromobimane (mBBr) is added to the perfusate. The addition of a bolus dose of mBBr results in rapid diminution of the resonance for ¹³C-labeled glutathione due to a loss of this metabolite through alkylation by mBBr. As the glutathione resonance decreases, a new resonance due to the production of intracellular glutathione-bimane conjugate is detectable. After clearance of the mBBr dose from the cells, intracellular glutathione repletion is then observed by a restoration of the ¹³C-glutathione signal along with wash-out of the conjugate. These data demonstrate that standard NMR techniques can directly monitor intracellular processes such as glutathione depletion with a time resolution of approximately < 2 min.     

Characterization of epoxidized natural rubber by 2D NMR spectroscopy

Assignment of signals in aliphatic region of ¹H NMR spectrum for epoxidized natural rubber was carried out through NMR spectroscopy. The epoxidized natural rubber was prepared by epoxidation of purified natural rubber with peracetic acid in latex stage followed by degradation with propanal and ammonium persulfate. The resulting liquid epoxidized natural rubber was characterized through 1D- and 2D-NMR spectroscopy. The unknown signals in the aliphatic region of the ¹H NMR spectrum were assigned through ¹³C NMR and two-dimensional heteronuclear shift correlation (HETCOR) measurement. The assignments were proved by two-dimensional inverse detected heteronuclear long-range shift correlation (HMBC) and two-dimensional homonuclear shift correlation (COSY) measurements, and they were supported with epoxidized squalene as a model compound through NMR spectroscopy.     

Microstructure determination of isobornyl methacrylate-styrene copolymer by NMR spectroscopy

An investigation of the microstructure of isobornyl methacrylate - styrene (I/S) copolymers prepared by the atom transfer radical polymerization (ATRP) using methyl-2-bromopropionate as an initiator and PMDETA copper complex as catalyst under nitrogen atmosphere at 70 °C has been done by two-dimensional NMR techniques. 2D- HSQC and TOCSY have been utilized to resolve the complex ¹H NMR spectrum and to establish the compositional and configurational sequences of isobornyl methacrylate-styrene (I/S) copolymers. 2D HSQC and TOCSY spectra showed compositional and configurational sensitivity of α-methyl carbon of I unit and methine proton of S unit and are assigned up to the triad level. The methylene carbon (C₁₀) also shows triad level of compositional sensitivity in 2D HSQC spectra. Heteronuclear multiple-bond correlation (HMBC) spectroscopy has been used to study carbonyl/quaternary carbon-proton coupling. The carbonyl and quaternary carbons showed compositional and configurational sensitivity upto the triad level. The values of reactivity ratios were determined by Kelen-Tudos (KT) and nonlinear error in variable method (RREVM) using copolymer composition data that were determined by ¹H NMR spectrum. Reactivity ratios of co-monomers in I/S copolymer, determined from a linear Kelen-Tudos method (KT) and non-linear Error-in-Variable Method (EVM), are r_I?=?0.39?±?0.09, r_S?=?0.44?±?0.08 and r_I?=?0.42, r_S?=?0.47, respectively.     

Synthesis, X-ray structure and Hg, Se CP MAS NMR studies on the first tris(imidazolidine-2-selone) mercury complex: {Chloro-tris[N-methyl-2(3H)-imidazolidine-2- selone]mercury(II)}chloride

A novel cationic Hg(II) complex has been synthesized with N-methyl-imidazolidine-2-selone ligand. The tris(N-Methyl-imidazolidine-2-selone) mercury(II) complex, [(MeImSe)₃HgCl]⁺Cl⁻ (1), has been characterized by single crystal X-ray analysis and CP MAS ¹⁹⁹Hg and ⁷⁷Se NMR.     

Absolute configurational assignments for the1H-NMR spectrum of poly(vinyl alcohol) by use of two-dimensional NMR methods

Summary FOCSY two-dimensional J-resolved NMR spectroscopy is used to resolve¹H NMR resonances corresponding to triad and tetrad configurations of poly(vinyl alcohol). Two-dimensional auto correlation with ₁-scaling NMR spectroscopy is used to observe connectivities between triad and tetrad¹H NMR resonances. Comparison of these connectivities to the necessary compositional relationships at triad-tetrad level leads to absolute configurational assignments for the¹H NMR spectrum of poly(vinyl alcohol).     

Fluorinated siloxane amine oligomers

Fluorine‐containing siloxane oligomers were made from bis(aminopropyl)tetramethyldisiloxane and trimethyltris(trifluoropropyl)cyclotrisiloxane. These materials were characterized by IR spectroscopy, size exclusion chromatography, nonaqueous colorimetric end group titration, and ¹H‐NMR. The end groups of one oligomer were chemically modified for an increased NMR signal for molecular weight determination. The cyclic trimeric siloxane starting material was additionally studied via ¹³C‐, ²⁹Si‐, and ¹⁹F‐NMR. Two forms of it were used: a white solid obtained at room temperature, and a colorless liquid isolated at low temperature. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1315–1320, 2000     

Reactions of benzene based half sandwich ruthenium(II) complex with 2,6-bis((phenylseleno)methyl)pyridine: Preferential substitution of ring resulting in a catalyst of high activity for oxidation of alcohols

[2,6-Bis((phenylseleno)methyl)pyridine] (L) a (Se, N, Se) pincer ligand synthesized by reacting PhSe^? (in situ generated) with 2,6-bis(chloromethyl)pyridine reacts with [{(η⁶-C₆H₆)RuCl(μ-Cl)}₂] (2:1 molar ratio) by preferential substitution of ring resulting in the first Ru-(Se, N, Se) pincer ligand complex, mer-[Ru(CH₃CN)₂Cl(L)][PF₆](1).H₂O. Similar reaction in 4:1 molar ratio results in mer-[Ru(L)₂][ClO₄]₂(2). The ¹H, ¹³C{¹H} and ⁷⁷Se{¹H} NMR spectra of L, 1 and 2 were found characteristic. The single crystal structures of 1 and 2 were studied by X-ray crystallography. The geometry of Ru in both the complexes is distorted octahedral. The Ru–Se distances are in the ranges 2.4412(16)–2.4522(16) and 2.4583(14)–2.4707(15) ? respectively for 1 and 2. The structural solutions from the crystal data in case of 2, due to inferior quality of its crystals, are suitable for supporting bonding mode of L with Ru(II) only. The 1 shows high catalytic activity for oxidation of primary and secondary alcohols (TON up to 9.7 × 10⁴).     

Solid-state nuclear magnetic resonance (NMR): Application to precursors of ceramics—Polycarbosilane

The chemical structures of oxidation- and electron irradiation-cured polycarbosilane fibers has been studied by IR and chemical analysis, but its structure has not been identified in detail. In this work, the chemical structure and curing mechanism was examined by solid-state high-resolution NMR spectroscopy. From the analysis of NMR spectra, it is explained that (i) in oxidation curing of PCS fibers, oxygen attacks first the SiC₃H bond and forms the SiC₃O bond and, next, the SiC₄ backbone bond and forms the SiC₂O₂ units; (ii) in electron irradiation curing, the signal intensity of SiC₃H units decreases with the increase in dose, the increase in the signal being due to the formation of SiC₄ units; (iii) solid-state²⁹Si high-resolution (CP/MAS) NMR spectroscopy is a powerful tool for investigating the chemical structure and curing mechanism of PCS fibers complementing infrared and solid-state¹³C high-resolution NMR spectroscopy; and (iv)¹H CRAMPS NMR spectroscopy is very useful for investigating the chemical structure and curing mechanism of PCS fibers.     

Luminescent monomeric and polymeric cuprous halide complexes with 1,2-bis(3,5-dimethylpyrazol-1-ylmethyl)-benzene as ligand

Reaction of cuprous bromide with equimolar amounts of 1,2-bis(3,5-dimethylpyrazol-1-ylmethyl)-benzene (dpb) affords a mononuclear three-coordinated complex [CuBr(dpb)] (F2) with dpb acting as a chelating ligand. In contrast, using cuprous iodide instead under the same conditions gives the polymeric compound [Cu₂I₂(dpb)]_n (F1) which contains double-bridging iodine atoms. The complexes were characterized by element analysis and ¹H NMR spectroscopy, and the crystal structures were determined by single-crystal X-ray diffraction methods. The Cu(I) complexes are luminescent in the solid state at ambient temperature. Intense orange emission for complex F1 is observed, with maxima at 593 nm, probably ascribed to a combination of a halide-to-metal charge transfer and copper-centered d → s, p transitions. F2 exhibits a blue photoluminescence, with emission maximum at 515 nm, assigned to metal-to-ligand charge-transfer excited states, probably mixed with some halide-to-ligand characters.     

Transesterifications of poly(bisphenol A carbonate) with aromatic and aliphatic segments in ethylene terephthalate–caprolactone copolyester

In this article, transesterification of poly(bisphenol A carbonate) (PC) with a ethylene terephthalate–caprolactone copolyester at a weight ratio 50/50 (TCL50) was investigated by infrared spectroscopy (IR), proton nuclear magnetic resonance spectroscopy (¹H‐NMR), and a model compound. The IR and ¹H‐NMR results showed that transesterification occurred between PC and ethylene terephthalate (ET) segments in TCL50 and resulted in the formation of bisphenol A–terephthalate ester units as in the annealed blend of PC with the PET homopolyester. By comparison with a model compound, the new signal at 2.55 ppm in the ¹H‐NMR spectrum confirmed the appearance of bisphenol A–caprolactone ester units resulting from the exchange reaction of PC with caprolactone (CL) segments. The ¹H‐NMR analysis of the transesterification rates revealed that the reactions of PC with aromatic and aliphatic segments in TCL50 proceeded in a random or free manner. In addition, we separately examined the interchange reaction between a PC and poly(ε‐caprolactone) (PCL) homopolyester in an annealed blend. It was found that in the presence of a Ti compound catalyst the predominant reaction was a transesterification rather than a thermooxidative branching reaction. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1558–1565, 2001     

A Solid-State NMR Study of Selenium Substitution into Nanocrystalline Hydroxyapatite

The substitution of selenium oxyanions in the hydroxyapatite structure was examined using multinuclear solid-state resonance spectroscopy (ssNMR). The study was supported by powder X-ray diffractometry (PXRD) and wavelength dispersion X-ray fluorescence (WD-XRF). Samples of pure hydroxyapatite (HA₃₀₀) and selenate (HA₃₀₀-1.2SeO₄) or selenite (HA₃₀₀-1.2SeO₃) substituted hydroxyapatites were synthesized using the standard wet method and heated at 300 °C to remove loosely bonded water. PXRD data showed that all samples are single-phase, nanocrystalline hydroxyapatite. The incorporation of selenite and selenate ions affected the lattice constants. In selenium-containing samples the concentration of Se was very similar and amounted to 9.55% and 9.64%, for HA₃₀₀-1.2SeO₄ and HA₃₀₀-1.2SeO₃, respectively. PXRD and ssNMR data showed that the selenite doping significantly decreases the crystallite size and crystallinity degree. ³¹P and ¹H NMR experiments demonstrated the developed surface hydrated layer in all samples, especially in HA₃₀₀-1.2SeO₃. ¹H NMR studies showed the dehydroxylation of HA during the selenium oxyanions substitution and the existence of hydrogen bonding in structural hydroxyl group channels. ¹H→⁷⁷Se cross polarization NMR experiments indicated that selenites and selenates are located in the crystal lattice and on the crystal surface.     

Synthesis of novel copoly(ether ether ketones): Property evaluation and microstructure analysis by NMR

A series of copolymers were prepared by the reaction of various bisphenols with a 50:50 molar ratio of two bisfluoro compounds, 4,4′‐bis(1‐fluoro‐2‐trifluoromethyl benzyl) benzene and 4,4′‐difluorobenzophenone. The synthesized polymers were well characterized for their thermal, mechanical, and electrical performances. The copolymers showed a better set of properties than their analogous homopolymers derived from 4,4′‐bis(1‐fluoro‐2‐trifluoromethyl benzyl) benzene and bisphenols. The microstructures of the copolymers were analyzed by ¹H‐, ¹³C‐, ¹⁹F‐, distortionless enhancement by polarization transfer 90, two‐dimensional ¹H–¹H homonuclear correlation spectroscopy, and ¹³C–¹H correlation spectroscopy NMR techniques. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1292–1305, 2005     

The synthesis,spectroscopy, electrochemistry and photophysical properties of novel,sandwich europium(III) complexes with a porphyrin ligand bearing four pyrenyl groups in meso-positions

Novel, metal free porphyrins containing four pyrenyl groups in the meso-positions were used to provide novel, sandwich-type mixed tetrapyrrole europium double- and triple-deck complexes. The sandwich-type complexes together with the metal free porphyrin were characterized using electronic absorption, IR and ¹H NMR spectroscopy in addition to elemental analysis. The electrochemical behaviour of the sandwich complexes was investigated by cyclic voltammetry and differential pulse voltammetry in CH₂Cl₂, their photophysical properties were studied in comparison to those of the metal free porphyrin ligand. Fluorescence quenching observed was tentatively attributed to efficient and rapid energy transfer from the pyrenyl groups to porphyrin followed by electron transfer from porphyrin to phthalocyanine.     

Microstructure analysis of poly(styrene‐co‐vinylidene chloride) copolymers by NMR spectroscopy

Poly(styrene‐co‐vinylidene chloride) (S/V) copolymers were prepared by free‐radical photopolymerization using uranyl nitrate as an initiator. The microstructure of the copolymer S/V was investigated by ¹H‐ and ¹³C{¹H}‐NMR, ¹H–¹³C‐heteronuclear shift quantum correlation (HSQC) NMR, and homonuclear total correlated spectroscopy (TOCSY). The ¹H‐NMR spectra of the copolymers is complex due to overlapping resonance signals of the various triad configurations. Assignments were made up to the triad and tetrad levels for the methylene and methine regions using two‐dimensional HSQC experiments. A ¹³C‐distortionless enhancement by polarization transfer (DEPT) spectrum was used to differentiate between the carbon resonance signals of methine and the methylene units. The geminal couplings in the methylene protons and vicinal coupling between the methine and methylene protons were detected from the TOCSY spectra. Monte Carlo simulations were used to investigate the effect of the degree of polymerization on the triad fractions. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 544–554, 2001     

Metal Complexes of a Novel Terpolymer Ligand: Synthesis, Spectral, Morphology, Thermal Degradation Kinetics and Antimicrobial Screening

2-amino-6-nitro-benzothiazole and thiosemicarbazide with formaldehyde (BTF) terpolymer ligand and its metal complexes have been synthesized. The plausible structure of the synthesized BTF terpolymer ligand was elucidated on the basis of elemental analysis and spectral studies such as FTIR, UV-Vis, ¹H and ¹³C NMR spectroscopy. Gel permeation chromatography (GPC) was used to determine the molecular weight of the terpolymer. The terpolymer metal complexes were analyzed by elemental analysis, molar conductivity measurements, and magnetic susceptibilities. The structure and geometry of the metal complexes were confirmed by various spectral techniques viz. electronic, ESR, FTIR and NMR spectroscopy. The morphology of the BTF terpolymer ligand and its metal complexes was examined using scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. The thermal decomposition behaviour of the terpolymer ligand and its complexes was determined using thermogravimetric analysis (TGA). Freeman–Carroll (FC), Sharp–Wentworth (SW) and Phadnis–Deshpande (PD) methods were used to calculate the thermal activation energy (E_a), order of reaction (n), entropy change (ΔS), free energy change (ΔF), apparent entropy (S*) and frequency factor (Z) from the TGA data. Phadnis–Deshpande method was also used to propose the thermal degradation model for the decomposition pattern of the terpolymer ligand. The terpolymer ligand and its metal complexes were screened for its antimicrobial activity against chosen microbes.     

Investigation of microstructure of the acrylonitrile‐styrene‐glycidyl methacrylate terpolymers by 1D and 2D NMR spectroscopy

Acrylonitrile‐styrene‐glycidyl methacrylate (N/S/G) terpolymers were prepared by bulk polymerization by using benzoyl peroxide as initiator and analyzed by NMR spectroscopy. The compositions of terpolymers were determined by quantitative ¹³C{¹H}‐NMR spectra and compared with those calculated by Goldfinger's equation by using comonomer reactivity ratios: r_NS = 0.04, r_SN = 0.40; r_NG = 0.22, r_GN = 1.37; r_SG = 0.44, r_GS = 0.53. The ¹³C{¹H}‐ and ¹H‐NMR spectra were overlapping and complex. The spectral assignments were done with the help of distortionless enhancement by polarization transfer and two‐dimensional ¹³C‐¹H heteronuclear single quantum correlation experiments. 2D total correlated spectroscopy was used to ascertain the various coupling between the protons. The methyl, methine, methylene, and oxymethylene carbon resonances showed compositional sensitivity. 2D nuclear Overhauser enhancement spectroscopy (NOESY) experiment was used to ascertain the spatial proton–proton couplings. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1779–1790, 2003