Polarization Transfer Spectra Research Articles

Investigation of the Complexation Activity of 2,4-Dithiouracil with Au(III) and Cu(II) and Biological Activity of the Newly Formed Complexes

The goal of this study is to synthesize, determine the structure, and examine the antimicrobial properties of novel Cu(II) and Au(III) complexes of 2,4-dithiouracil and its derivatives. These complexes were obtained by mixing aqueous solutions of the corresponding metal salts with the ligand dissolved in DMSO and aqueous NaOH, using a metal-to-ligand ratio of 1:4:2. The structures of the new compounds were analyzed by melting point determination, microwave plasma atomic emission spectrometry (MP-AES) for Cu and Au, inductively coupled plasma optical emission spectrometry (ICP-OES) for S, attenuated total reflection (ATR), solution and solid-state NMR, and Raman spectroscopy. The data for 2,4-dithiouracil obtained from the 1H NMR, 13C NMR, distortionless enhancement by polarization transfer spectrum (DEPT-135), proton–proton homonuclear correlation spectrum (1H-1H COSY), long-range 1H-13C heteronuclear multiple bond correlation experiment (HMBC), and heteronuclear single quantum coherence spectra (HSQC) aided the interpretation of the NMR data for the gold and copper complexes. Furthermore, the antimicrobial effect of the free ligands and their complexes was assessed against Gram-positive and Gram-negative bacteria, as well as yeasts.

Exploration of catalytic performance of nano-La2O3 as an efficient catalyst for dihydropyrimidinone/thione synthesis and gas sensing

In the present work, we report an proficient, elegant, and rapid one-pot synthesis of variety of 3,4-dihydropyrimidine-2(1H)-one/thione derivatives from β-dicarbonyl compounds, urea/thiourea, and various aromatic aldehydes using nano-La2O3 catalyst under ultrasonic irradiation. This novel synthetic strategy benefits with excellent yields, short reaction time, benign reaction conditions, clean transformation, and purification of products by non-chromatographic strategies. In addition, the synthesized nano-material was also explored as an effective gas sensor for NO2, LPG, methyl alcohol, and ammonia. The gas-sensing properties such as selectivity and sensitivity of selected gases along with response and recovery for nano-La2O3 sensor are reported in this paper. In this way, conferring nano-La2O3 is a multifunctional catalyst not only for organic synthesis but also for gas sensing. The synthesized La2O3 nano-material was characterized by Fourier transform IR, powder X-ray diffraction, field-emission scanning electron microscopy, high-resolution transmission electron microscopy, energy-dispersive spectroscopy, and Brunauer–Emmett–Teller isotherm. The formation of Biginelli adducts was confirmed by Fourier transform IR, 1HNMR, 13CNMR, DEPT-135 (distortionless enhancement by polarization transfer spectra), and mass spectral techniques.Graphical abstract

Reactivity ratios and sequence determination of methacrylonitrile/butyl acrylate copolymers by NMR spectroscopy

Methacrylonitrile/butyl acrylate (M/B) copolymers were prepared by bulk polymerization using benzoyl peroxide as an initiator. The Distortionless Enhancement by Polarization Transfer spectra were used to differentiate between the carbon resonance signals of methyl, methine, methylene and oxymethylene groups in the 13C{ 1H} NMR spectrum of the copolymer (M/B). Comonomer reactivity ratios were determined using Kelen–Tudos and non-linear error in variable methods. Two-dimensional Heteronuclear Single Quantum Coherence and Total Correlated Spectroscopy were used to resolve the complex 1H NMR spectrum and to determine the compositional and configurational sequences of M/B copolymers.

One- and two-dimensional NMR studies on the compositional sequence and the microstructure of trans-4-methacryloyloxyazobenzene/styrene copolymers

trans-4-Methacryloyloxyazobenzene/styrene (M/S) copolymers of different monomer concentrations were prepared by solution polymerization using benzoyl peroxide as initiator. The copolymer composition was determined from the percent nitrogen content in the copolymers. The methyl carbons of M- and quaternary carbon of S-centered resonances were used for determining the sequences in terms of the distribution of M- and S-centered triads. The sequence distribution of M- and S-centered triads determined from 13C{ 1H}-NMR spectra of the copolymer are in good agreement with triad concentration calculated from statistical model. The comonomer reactivity ratios, determined by both Kelen–Tudos and non-linear error in variables method are r M=1.02±0.12, r S=0.55±0.07; r M=1.02 and r S=0.54, respectively. 13C distortionless enhancement by polarization transfer spectrum was used to differentiate the resonance signals of M- and S-methylene and methine carbon units of S. Assignments to the methylene resonance signals have been assigned up to the tetrad levels using two dimensional (2D) heteronuclear single quantum correlation experiments. Homonuclear 2D total correlation spectroscopy NMR spectrum was used to ascertain the various compositional and configurational sequence of the copolymer.

Microstructure determination of poly ( trans-4-acryloyloxyazobenzene) by n.m.r. spectroscopy.

The microstructure of poly( trans-4-acryloyloxyazobenzene) P(AB) homopolymer, prepared by solution polymerization using AlBN as initiator is analysed by one- and two-dimensional NMR spectrotcopy. Sequence distribution was calculated from 13 C{ 1 H} n.m.r. spectrum of the homopolymer. A 13 C distortionless enhancement by polarization transfer spectrum was used to differentiate between the resonance signals of methine and methylene units in the homopolymer. The triad sequence distribution of poly( trans-4-acryloyloxyazobenzene) P(AB), determined from carbonyl resonance of the homopolymer, is in good agreement with the triad concentrations calculated from the Bernoullian statistical model. 2D heteronuclear single quantum correlation (HSQC) and correlated spectroscopy (COSY) spectroscopy was used to analyse the complex 1 H n.m.r. spectrum. Homonuclear 2D TOCSY n.m.r. spectroscopy was used to ascertain the various configurational sequence of the poly( trans-4-acryloyloxyazobenzene) P(AB) homopolymer. 2D NOESY experiment was carried out to determine one of the many probable conformations of the homopolymer in solution state.

Compositional Assignments and Sequence Distribution of Vinylidene Chloride−Methyl Acrylate Copolymers Using One- and Two-Dimensional NMR Spectroscopy

The microstructure of vinylidene chloride−methyl acrylate copolymers prepared by a photopolymerization process using uranyl ion as photosensitizer is analyzed by one- and two-dimensional NMR spectroscopy. Sequence distribution was calculated from 13C{1H} NMR spectra of the copolymers. A 13C distortionless enhancement by polarization transfer spectrum was used to differentiate between the resonance signals of methoxy and methylene units in the copolymer. Comonomer reactivity ratios were determined using Kelen−Tudos and the nonlinear error in variables methods. The sequence distribution of vinylidene chloride- and methyl acrylate-centered triads determined from 13C{1H} NMR spectra of copolymers is in good agreement with triad concentrations calculated from statistical model and Monte Carlo simulation methods. 2D heteronuclear single quantum correlation and correlated spectroscopy spectrum was used to analyze the complex 1H NMR spectrum.

Continuous-flow nuclear magnetic resonance

The effect of the volume of the detector flow cell upon peak broadening in high-performance liquid chromatography with nuclear magnetic resonance detection has been monitored using a modified fluorescence detector. The results of solvent-resonance suppression using 1331 hard pulse sequences are described. The possibility of obtaining 13C distortionless enhancement by polarization transfer spectra in the flow system is demonstrated.

Coupled polarization transfer spectra for higher-spin nuclei

We study theoretically, and confirm experimentally for specific cases, the forms of the coupled spectra arising from polarization transfer from and to systems of multiple nuclei of higher spins by use of the UPT and INEPT pulse sequences. We find that we cannot obtain a simple separable universal formula for the polarization transfer signal for the INEPT sequence, as we have done for both decoupled and coupled signals obtained by the UPT sequence. Remarkably, however, we find that, for the more common cases where the polarization is transferred from multiple spin-one and spin-half nuclei, the universal polarization transfer formula that we obtained for the decoupled UPT signals can be used to calculate directly both decoupled and coupled INEPT signals.

Carbon‐13 nuclear magnetic resonance spectra of exo‐ and endo‐2‐norbornyltrimethyl‐stannanes: Corrected assignments

AbstractThe 13C NMR spectra of pure exo‐2‐norbornyltrimethylstannane and a mixture of the exo‐ and endo‐isomers have been recorded. 1H–13C polarization transfer spectra have been obtained and require the previously reported assignments for C‐3 and C‐4 in the exo‐isomer to be reversed. The reported assignments for the endo‐isomer are correct. The new assignment for C‐4‐exo [with J(119Sn,13C) vic=12 Hz, instead of the previously assigned J(vic)=23 Hz], has a very minor effect on the nature of the Karplus curve [for 3J(119Sn,13C)] generated previously.

Proton polarization transfer enhancement for a nucleus with arbitrary spin quantum number from n scalar coupled protons for arbitrary preparation times

Polarization transfer enhancement of the NMR resonance from a nucleus with spin quantum number l (l = 1 2 , 1, 3 2 , …) from n scalar coupled protons using the pulse sequence (90 xH)-τ-(180 xH)(180 xI)-τ-(90 yH)(90 xI)-Δ-(acquire with or without H decoupling) is studied theoretically. It is shown that the enhancement of the components of the I multiplet varies with τ as Σ m I m I sin (4 πJm I τ) where J is the scalar coupling constant and m I takes the values l, l - l, …, -l. Values of τ opt which result in the maximum enhancement are calculated, as well as the size of these maximum enhancements. Values of Δ opt which yield the maximum decoupled signal are also computed, along with the maximum decoupled enhancements. The theory is confirmed experimentally for l = 3 2 and l = 3 by studying proton polarization transfer spectra of the 10B and 11B resonances in NaBH 4.