Use Of Proton NMR Research Articles

Dissociative electron attachment to gold(I)-based compounds: 4,5-dichloro-1,3-diethyl-imidazolylidene trifluoromethyl gold(I).

With the use of proton-NMR and powder XRD (XRPD) studies, the suitability of specific Au-focused electron beam induced deposition (FEBID) precursors has been investigated with low electron energy, structure, excited states and resonances, structural crystal modifications, flexibility, and vaporization level. 4,5-Dichloro-1,3-diethyl-imidazolylidene trifluoromethyl gold(I) is a compound that is a uniquely designed precursor to meet the needs of focused electron beam-induced deposition at the nanostructure level, which proves its capability in creating high purity structures, and its growing importance in other AuImx and AuClnB (where x and n are the number of radicals, B = CH, CH3, or Br) compounds in the radiation cancer therapy increases the efforts to design more suitable bonds in processes of SEM (scanning electron microscopy) deposition and in gas-phase studies. The investigation performed of its powder shape using the XRPD XPERT3 panalytical diffractometer based on CoKα lines shows changes to its structure with change in temperature, level of vacuum, and light; the sensitivity of this compound makes it highly interesting in particular to the radiation research. Used in FEBID, though its smaller number of C, H, and O atoms has lower levels of C contamination in the structures and on the surface, it replaces these bonds with C-Cl and C-N bonds that have lower bond-breaking energy. However, it still needs an extra purification step in the deposition process, either H2O, O2, or H jets.

Visualization of enantiomers using natural abundant 13C-filtered single and double quantum selective refocusing experiments: Application to small chiral molecules

The routine use of proton NMR for the visualization of enantiomers, aligned in the chiral liquid crystal solvent poly-γ-benzyl-l-glutamate (PBLG), is restricted due to severe loss of resolution arising from large number of pair wise interaction of nuclear spins. In the present study, we have designed two experimental techniques for their visualization utilizing the natural abundance 13C edited selective refocusing of single quantum (CH-SERF) and double quantum (CH-DQSERF) coherences. The methods achieve chiral discrimination and aid in the simultaneous determination of homonuclear couplings between active and passive spins and heteronuclear couplings between the excited protons and the participating 13C spin. The CH-SERF also overcomes the problem of overlap of central transitions of the methyl selective refocusing (SERF) experiment resulting in better chiral discrimination. Theoretical description of the evolution of magnetization in both the sequences has been discussed using polarization operator formalism.

Separation and Complete Analyses of the Overlapped and Unresolved 1H NMR Spectra of Enantiomers by Spin Selected Correlation Experiments

NMR spectroscopic discrimination of optical enantiomers is most often carried out using (2)H and (13)C spectra of chiral molecules aligned in a chiral liquid crystalline solvent. The use of proton NMR for such a purpose is severely hindered due to the spectral complexity and the significant loss of resolution arising from numerous short- and long-distance couplings and the indistinguishable overlap of spectra from both R and S enantiomers. The determination of all the spectral parameters by the analyses of such intricate NMR spectra poses challenges, such as, unraveling of the resonances for each enantiomer, spectral resolution, and simplification of the multiplet pattern. The present study exploits the spin state selection achieved by the two-dimensional (1)H NMR correlation of selectively excited isolated coupled spins (Soft-COSY) of the molecules to overcome these problems. The experiment provides the relative signs and magnitudes of all of the proton-proton couplings, which are otherwise not possible to determine from the broad and featureless one-dimensional (1)H spectra. The utilization of the method for quantification of enantiomeric excess has been demonstrated. The studies on different chiral molecules, each having a chiral center, whose spectral complexity increases with the increasing number of interacting spins, and the advantages and limitations of the method over SERF and DQ-SERF experiments have been reported in this work.

Determination of Solvent Effects on Keto—Enol Equilibria of 1,3-Dicarbonyl Compounds Using NMR

The use of proton NMR to determine the equilibrium position of tautomeric 1,3-dicarbonyl compounds in various solvents has been a classic physical chemistry experiment. We are presenting an expansion of the excellent description of this experiment by Garland, Shoemaker, and Nibler. Often the assumption is made that the keto tautomer is always the more polar tautomer and hence the concentration of the keto tautomer is greater in polar solvents. However, the keto tautomers of acyclic 1,3-dicarbonyl molecules such as acetyl acetone are often not the more polar of the two tautomers, so this cannot be the only important factor that determines this equilibrium. Rather there are several factors that contribute to the tautomeric equilibrium of which solute dipole moment is just one. The study of the cyclic 1,3-diketone dimedone is especially helpful in this regard. The student is asked to analyze his/her results based on these factors. Molecular modeling is used as an aid in this analysis.

Thiodiglycol, the hydrolysis product of sulfur mustard: Analysis of in vitro biotransformation by mammalian alcohol dehydrogenases using nuclear magnetic resonance

Thiodiglycol (2,2'-bis-hydroxyethylsulfide, TDG), the hydrolysis product of the chemical warfare agent sulfur mustard, has been implicated in the toxicity of sulfur mustard through the inhibition of protein phosphatases in mouse liver cytosol. The absence of any inhibitory activity when TDG was present in assays of pure enzymes, however, led us to investigate the possibility for metabolic activation of TDG to inhibitory compound(s) by cytosolic enzymes. We have successfully shown that mammalian alcohol dehydrogenases (ADH) rapidly oxidize TDG in vitro, but the classic spectrophotometric techniques for following this reaction provided no information on the identity of TDG intermediates and products. The use of proton NMR to monitor the oxidative reaction with structural confirmation by independent synthesis allowed us to establish the ultimate product, 2-hydroxyethylthioacetic acid, and to identify an intermediate equilibrium mixture consisting of 2-hydroxyethylthioacetaldehyde, 2-hydroxyethylthioacetaldehyde hydrate and the cyclic 1,4-oxathian-2-ol. The intermediate nature of this mixture was determined spectrophotometrically when it was shown to drive the production of NADH when added to ADH and NAD.

Quantitative Elemental Analysis of Sodium(23Na) by NMR Spectroscopy

Na-NMR, Shift reagent, Quantitative analysis, Complex of dysprosiumOne of the most useful components in NMR spectroscopyis the application of the peak area for the quantitativeanalysis. Although the use of proton NMR has been appliedfor the determination of trace components such as theresidual hydrogen in D

Standardization of Methodology for Chemical Functions in Starch Derivatives. Part 2

AbstractThe work of Work Group 3, of the International Standards Organization Technical Committee 93 (ISO/TC 93/WG3), concerning the determination of functional groups in starch derivatives, has been progressed. The Netherlands Normalisatie Instituut (NNI) is the secretariat and Part I of this paper outlined the total work programme and reported the finalised work on acetyl and carboxyl functions.Following modifications, the available methodology for the adipyl function was improved, and has been validated. The methodology for the determination of the carboxymethyl function by titration of the carboxyl group, has also been refined and validated by collaborative testing. Draft International Standards have been made of these two methods so that they can be voted on by members of ISO and the European Committee for Standardization (CEN) in a parallel process.Work on the hydroxypropyl function has not yet come to a successful conclusion. A colorimetric method showed poor reproducibility, due probably to its empirical nature; little support was found for gas chromatographic methods. However, the use of proton NMR might yield a satisfactory means. While all members of the Work Group are not equipped with the required instrument, a preliminary study will be done with the help of other laboratories.

Inter‐ and intra‐molecular ionic interactions of polyampholyte: Carboxymethyl‐2‐diethylaminoethylcellulose

AbstractCarboxymethyl‐2‐diethylaminoethylcellulose (CM‐DEAE cellulose) was prepared by etherification of carboxymethylcellulose with diethylaminoethyl chloride in a NaOH solution. The behaviour of CM‐DEAE cellulose in aqueous solution was studied by viscosity and GPC measurements. The degree of substitution (DS) and existing states of DEAE substituents were examined by the use of proton NMR, and those of the CM substituents were observed with FT‐IR. The results reveal that the reduced viscosity and apparent molecular size of CM‐DEAE cellulose vary with the concentration of sodium chloride and changes in pH and DS. These phenomena can be explained in terms of inter‐ and intra‐molecular ionic interactions.

Determination of the conformation of d(GGAAATTTCC)2 in solution by use of proton NMR and restrained molecular dynamics

The conformation of the putative bent DNA d(GGAAATTTCC)2 in solution was studied by use of 1H NMR and restrained molecular dynamics. Most of the resonances were assigned sequentially. A total of 182 interproton distance restraints were determined from two-dimensional nuclear Overhauser effect spectra with short mixing times. Torsion angle restraints for each sugar moiety were determined by qualitative analysis of a two-dimensional correlated spectrum. Restrained molecular dynamics was carried out with the interproton distances and torsion angles incorporated into the total energy function of the system in the form of effective potential terms. As initial conformations for restrained molecular dynamics, classical A-DNA and B-DNA were adopted. The root mean square deviation (rmsd) between these two conformations is 5.5 A. The conformations obtained by use of restrained molecular dynamics are very similar to each other, the rmsd being 0.8 A. On the other hand, the conformations obtained by use of molecular dynamics without experimental restraints or restrained energy minimization depended heavily on the initial conformations, and convergence to a similar conformation was not attained. The conformation obtained by use of restrained molecular dynamics exhibits a few remarkable features. The second G residue takes on the BII conformation [Fratini, A. V., Kopka, M. L., Drew, H. R., & Dickerson, R. E. (1982) J. Biol. Chem. 257, 14686-14707] rather than the standard BI conformation. There is discontinuity of the sugar puckering between the eighth T and ninth C. The minor groove of the oligo(dA) tract is rather compressed. As a result, d(GGAAATTTCC)2 is bent.

Use of proton NMR to study low symmetry bonding effects in transition metal complexes

Abstract The 300 MHZ proton NMR chemical shifts of the mixed complex (salicylaldehyde)(acetyl-acetone)ethylenediimino nickel(II) and the two corresponding non-mixed complexes were studied. The differences in chemical shifts were very small, ∼ 0.05 ppm, but by looking at both the mixed and non-mixed species in the same solution relative values could be determined. The differences in chemical shifts were attributed to both a geometry effect and a basicity effect.