Search results for "NMR spectra"
showing 10 items of 113 documents
Protonation of a Spherical Macrotricyclic Tetramine: Water Inclusion, Allosteric Effect, and Cooperativity
2017
The spherical macrotricyclic cryptand tetramine "C24" (1) displays remarkable protonation behaviour. It undergoes protonation in four successive steps for which pKa values of 11.17±0.05, 10.28±0.04, 6.00±0.06 and 3.08±0.08 have been determined at 298 K. The unusually close values for the first two protonations provide evidence for the encapsulation of a water molecule serving as effector for the second protonation, which is consistent with earlier observations that the exchange of protons bound in the diprotonated species with solvent protons is unusually slow and that 17 O NMR spectra show the presence of an oxygen centre in the same species quite distinct from that of solvent water. Encap…
Highly Stable Neutral and Positively Charged Dicarbollide Sandwich Complexes
2005
Novel sandwich metallacarboranes commo-[3,3'-Ni(8-SMe2-1,2-C2B9H10)2] (1), commo-[3,3'-Co(8-SMe2-1,2-C2B9H10)2]+ (2+), commo-[3,3'-Ru(8-SMe2-1,2-C2B9H10)2] (4) and commo-[3,3'-Fe(8-SMe2-1,2-C2B9H10)2] (5) have been prepared by reaction of [10-SMe2-7,8-nido-C2B9H10]- with NiCl2 x 6 H2O, CoCl2, [RuCl2(dmso)4] and [FeCl2(dppe)], respectively. Reduction of 2+ with metallic Zn leads to the neutral and isolable complex commo-[3,3'-Co(8-SMe2-1,2-C2B9H10)2] (3). Theoretical calculations using the ZINDO/1 semiempirical method show three energy minima for complexes 1-3 and 5 that agree with the presence of three different rotamers in solution at low temperature, while four relative energy minima have…
“Twin” phosphorous atoms of tetraethyl 2-methyl-piperyd-1-ylmethylenebisphosphonates
2007
Recently, bisaminophosphonates found applications as therapeutic agents for curing bone disorders. When trying to relate the structures of substituted piperid-1-ylmethylenebisphosphonic with their biological properties, non-typical findings that in 31P NMR spectra of 2-methyl-piperid-1-ylmethylenebisphosphonic and 2-ethyl-piperid-1-ylmethylenebisphosphonic acids, two separate singlets from each of the phosphonic groups were observed, while their analogues bearing substituent in position 3 exhibit only one signal. Their presence was explained by freezing of the molecular motions by strong hydrogen bonding between NH and P = O atoms. In this work, synthesis as well as spectroscopic and theore…
Metabolite identification in human liver needle biopsies by high-resolution magic angle spinning1H NMR spectroscopy
2006
High-resolution magic angle spinning (HR-MAS) 1 H NMR spectroscopy of intact human liver needle biopsies has not been previously reported. HR-MAS NMR spectra collected on 17 specimens with tissue amounts between � 0.5 and 12 mg showed very good spectral resolution and signal-to-noise ratios. One-dimensional 1 H spectra revealed many intense signals corresponding to cellular metabolites. In addition, some high molecular weight metabolites, such as glycogen and mobile fatty acids, could be observed in some spectra. Resonance assignments for 22 metabolites were obtained by combining the analysis of three different types of 1D 1 H spectral editing, such as T2 filtering or the nuclear Overhauser…
Enantiodifferentiation of acyclic phosphonium salts in chiral liquid crystalline solutions
2006
Abstract The enantiodifferentiation of acyclic phosphonium salts bearing a stereogenic centre, whether on the phosphorus atom or on one of its substituents, was investigated by 2 H–{ 1 H}, 13 C–{ 1 H} and 31 P–{ 1 H} NMR in chiral liquid crystals composed of a polypeptide dissolved in an organic solvent. For the first time, the enantiomers of P-chirogenic phosphorus compounds were discriminated in these anisotropic media, affording good to excellent separation of the signals, allowing the determination of their proportion. While 31 P–{ 1 H} NMR spectra showed no chiral separation, 2 H–{ 1 H} NMR was efficient in the enantiodifferentiation of an isotopically labelled compound. Better still, …
A study of dimethyltin(IV)-L-cysteinate in aqueous solution
1988
The in vivo activity of some R2Sn-L-cysteinate complexes (R = Me, Et, n-Bu) against murine P-388 leukaemia has been tested. Only the Et2Sn(IV) complex showed a marginal positive effect. Trigonal bipyramidal tin environments with two carbon (R) atoms and the sulfur atom in the equatorial plane and oxygen (carboxylate) and nitrogen (NH2) in apical positions have been proposed for the solid compexes (R = Me, Et, n-Bu, Ph) on the basis of experimental Mossbauer parameters and infrared (IR) data. Aqueous solutions of the Me2SnL-cysteinate have been studied by IR, 1H NMR and 119Sn Mossbauer spectroscopy (in frozen solution) at different pH values to identify the Me2Sn(IV) species present. At pH >…
Sensitivity of noble gas NMR parameters to the heterocyclic ring proximity. Density functional theory studies of Ne–furan and Ar–furan complexes
2014
Theoretical modeling of noble gas interaction with furan as a simple heterocyclic ring was performed. The structures of neon–furan and argon–furan complexes were calculated at the MP2, M06-2X, CAM-B3LYP, APFD, and VSXC levels of theory using 6-311++G** basis set. The predicted 21Ne and 39Ar NMR chemical shifts for the Ne–furan and Ar–furan complexes calculated with pcS-3 and aug-pcS-3 basis sets were sensitive to the presence of the aromatic furan ring. Our results indicate a higher sensitivity of the neon and argon NMR probes than the previously reported 3He NMR spectroscopic parameters in studies of small heterocyclic rings containing the oxygen atom.
Crystal and molecular structure studies of (Z)-N-methyl-C-4-substituted phenyl nitrones by XRD, DFT, FTIR and NMR methods
2017
Abstract (Z)-N-methyl-C-4-substituted phenyl nitrones –O+N(Me)=C(H)R (Z-2a R = 4-ClC6H4, Z-2b R = 4-NO2C6H4, Z-2c R = 4-CH3OC6H4) were synthesized and characterized by elemental analyses, FTIR, 1H, 13C and DEPT-135 NMR spectroscopy and also by single crystal X-ray diffraction (in the case of Z-2a and Z-2b). The geometries of the nitrone molecules Z-2a, Z-2b and Z-2c and their E-isomers; (E)-N-methyl-C-4-chlorophenyl nitrone E-2a, (E)-N-methyl-C-4-nitrophenyl nitrone E-2b and (E)-N-methyl-C-4-methoxyphenyl nitrone E-2c were optimized using density functional theory (DFT) at the B3LYP/6-311++G(d,p) level of theory. The theoretical vibrational frequencies obtained by DFT calculations are in go…
Novel bile acid conjugates with aryl/alkenyl linker: Synthesis and characterization
2008
Abstract Eight potential precursors for the design of bile acid derived receptors viz. 2,6-bis[dimethyl(3α-hydroxy-5β-cholan-24-amidoethyl)ammonio-methyl]naphthalene dibromide (1), 3,3′-bis[dimethyl(3α-hydroxy-5β-cholan-24-amidoethyl)ammoniomethyl]biphenyl dibromide (2), 3,3′-bis[dimethyl(3α,7α,12α-trihydroxy-5β-cholan-24-amidoethyl)ammoniomethyl]biphenyl dibromide (3), 4,4′-bis[dimethyl(3α-hydroxy-5β-cholan-24-amidoethyl)ammoniomethyl]stilbene dibromide (4), 4,4′-bis[dimethyl(3α,7α,12α-trihydroxy-5β-cholan-24-amidoethyl)ammoniomethyl]stilbene dibromide (5), allyl-dimethyl(3α,7α,12α-trihydroxy-5β-cholan-24-amidoethyl)ammonium bromide (6), 1,4′-bis[dimethyl(3α-hydroxy-5β-cholan-24-amidoethyl…
An ab initio study of the relation between NMR chemical shifts and solid-state structures: hexabenzocoronene derivatives
2000
The assignment of solid-state NMR spectra is studied by the use of model systems computed with ab initio methods. The investigated system is a hexabenzocoronene derivative, for which a T-like arrangement of dimer units is found in the solid-state structure. Here, a tetramer model is required to explain the intermolecular interactions influencing the spectrum, whereas a dimer model is found to be inadequate. For the tetramer model, agreement of the computed NMR spectrum with the experimental solid-state magic angle spinning MAS-NMR data is observed. This study implies that the combination of experimental NMR data with quantum chemical calculations can be employed as a useful tool in determin…