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1.
The geometries of the enol forms of malondialdehyde and its lithium analog have been investigated using the INDO MO method in its original parametrization. The former molecule is predicted to have a planar, symmetric structure nearly identical with that of acetylacetone. Optimization of the geometry of lithium malondialdehyde yielded questionable results. The covalent bonding in both molecules is discussed with the aid of localized molecular orbitais and calculated interference energies. 相似文献
2.
V. S. Bogdanov L. I. Ukhova N. F. Uskova A. N. Sergeeva A. P. Marochkin A. M. Moiseenkov A. A. Akhrem 《Chemistry of Heterocyclic Compounds》1973,9(8):999-1002
The configurations of a number of 1,2-, 1,2,7-, and 1,2,9-substituted decahydroquinolin-4-ones and decahydroquinolin-4-ols have been established by the PMR method. The values of the vicinal spin-spin coupling constants in the heterocyclic ring A of the compounds studied are characteristic and permit the conformation of a methyl group in position 2 to be determined. The nature of the PMR spectra in the series studied depends on the nature of the solvent, and in a number of cases this can be used for analytical purposes.For a preliminary communication, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1078–1081, August, 1973. 相似文献
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A. Yu. Denisov V. I. Mamatyuk O. P. Shkurko 《Chemistry of Heterocyclic Compounds》1988,24(9):1027-1034
The 13C-{1H} NMR spectra of monomethyl substituted diazines, protonated at the picoline and 2-methylopyrimidine nitrogen atoms, have been analyzed, along with that of pyridine N-oxide and its 2-methyl derivatives protonated at the oxygen atom. Direct and vicinal 13C-13C spin-spin coupling constants (SSCC) have been measured. It was found that the 13C-13C SSCC in diazines follow additivity rules which are based on consideration of the number and mutual orientation or distribution of nitrogen atoms in the ring. It has also been demonstrated that increased direct 1JCC values involving methyl group carbon atoms in -positions to nitrogen atoms in the aromatic ring are due to effects associated with unshared electron pairs.Translated from Khimiya Geterotsiklieheskikh Soedinenii, No. 9, pp. 1243–1250, September, 1988. 相似文献
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An investigation of the metal coordination of l-norepinephrine and ATP by nuclear magnetic resonance
《Journal of Inorganic and Nuclear Chemistry》1978,40(9):1719-1726
The interactions of l-norepinephrine (NE) and adenosine-5-triphosphate (ATP) with Cu(III) and Zn(II) were investigated by Proton Nuclear Magnetic Resonance (NMR) spectroscopy. The results indicated significant coordination of Cu(II) by NE even at the p[D] of mixing (i.e. p[D] = 4). Both the pyrocatechol and the ethanolamine groups of the NE molecule were involved in the chelation. The Cu(II)-ATP interaction resulted in the coordination of the metal by the adenine nitrogens and the phosphate group. In the combined presence of ATP and NE, it was found that Cu(II) was predominantly bound by ATP at low p[D]'s, i.e. p[D] = 3–5, followed by additional chelation with NE at p[D] = 7. These observations were in agreement with our earlier conclusions based on potentiometric equilibrium data[3]. In the case of the Zn(II)-ATP system, the coordination was mainly with the phosphate group. At the p[D] of mixing (p[D] = 6) the interaction of NE was not clearly indicated. In the mixed ligand system, i.e. ATP+NE, Zn(II) was mainly chelated with ATP at low p[D] (p[D] = 5). In the combined presence of Cu(II) and Zn(II), a predominant chelation of the mixed ligands with Cu(II) was strongly indicated. 相似文献
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A proton magnetic resonance and relaxation investigation has been carried out on solid poly-L-alanine, poly-L-leucine, poly-L-valine and polyglycine, between 110 and 350 K. For the first three the relaxation is attributed to methyl group reorientation characterized by activation energies of 7 to 9 kJ mole?1. Significant non-exponential recovery of magnetization was encountered and ascribed to correlated motion of three-spin systems. Relaxation in polyglycine was two orders of magnitude longer. 相似文献
6.
L. Paolillo S. Andini L. Ferrara S. Wurzburger 《International journal of quantum chemistry》1984,26(5):873-888
In this paper a detailed study of the structural properties of the three main fractions YI, YII, and Z of clupeine (protamines) has been performed with the aid of nuclear magnetic resonance methods. The investigation includes chemical shift data of protons and C-13 nuclei and measurement of the T1 relaxation times of the C-13 nuclei. These data demonstrate that the flexibility of the three fractions is different and that in the presence of inorganic phosphate fraction YI exhibits structural changes more relevant than the other two fractions. The measurement of the relaxation times, under the assumption of a rigid ellipsoid model, gives an estimate of the rough molecular size of the clupeine fractions. Different side chain mobilities that complement the previous observations based on chemical shift data are determined. A further extension of this work concerns the interaction of the clupeines with natural mononucleotides. An appreciable interaction takes place between fraction YI and purinic nucleotides while a simple electrostatic interaction seems to exist with the other two fractions. A possible explanation of this different behavior seems to involve the formation of large aggregates solely in the case of fraction YI. 相似文献
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A nuclear magnetic resonance method is described which yields precise estimates of competitive equilibrium constants for systems in which two or more complexing agents compete for common species. Chemical-shift data under rapid exchange conditions are required, but neither analytical not equilibrium concentrations are needed. The method is demonstrated by estimating equilibria of proton exchange between aniline and pyridinium ion, proton exchange between triethylamine and diisopropylammonium ion, and cyclohexaamylose exchange between m- and p-hydroxybenzoic acids. The precisions of the equilibrium constants are similar to or better than those obtained from classical methods and are relatively free from interferences. 相似文献
9.
A Gd(III) complex bearing pendant acetoxymethyl esters is activated on exposure to porcine liver esterase; the 84% increase in relaxivity is a result of suppression of HCO(3)(-)/CO(3)(2-) binding by the resulting negative charge. 相似文献
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Ernest Giralt Roser Viladrich Enrique Pedroso 《Magnetic resonance in chemistry : MRC》1983,21(3):208-213
The acid dissociation constant of the imidazolium ring of the decapeptide luliberin has been determined by 1H NMR-followed titration in D2O. The normal procedure for the analysis of the titration curve, i.e. direct use of the Henderson-Haselbalch equation, is still applicable in this case, but for more complex peptides a modified calculation procedure is proposed. Results obtained when both methods were applied to luliberin are compared. The influence of D2O when used as the solvent in this type of determination has been studied using Nα-acetyl-L -histidine methyl ester as a model compound. The difference between the acid dissociation constant of this molecule determined in H2O and in D2O implies that a correction of ?.25 unit is needed for those pKa values calculated by plotting the chemical shifts in D2O vs the apparent pH meter readings. The pKa found for Nα-acetyl-L-histidine methyl ester, 6.30 ± 0.04, can be taken as a standard value for histidine-containing peptides. 相似文献
12.
Didier Gagnaire Daniel Mancier Marc Vincendon 《Journal of polymer science. Part A, Polymer chemistry》1980,18(1):13-25
Four solvents of cellulose have been studied by using 13C-NMR spectroscopy. All these solvents, N-methyl morpholine-N-oxide, methylamine, hydrazine, and paraformaldehyde (PF), contained dimethyl sulfoxide (DMSO) as a cosolvent. Oligomers of cellulose of DP = 10 soluble in hot DMSO have been used as model compounds. 13C chemical shifts and line shapes show that three of the mentioned solvents are “true solvents” of cellulose. On the other hand, dissolution of cellulose in DMSO-PF system occurs by the formation of a statistical derivative of cellulose. Enriched 13C bacterial cellulose on C-1 and C-6 positions have been used to identify the 13C positions mainly in DMSO-N-methyl morpholine-N-oxide system. This solvent has been found to be degradative for the macromolecule when the solution is kept at 100°C over a long period. Viscosity measurements show a reduction of the molecular weight in these conditions. Polarimetry indicates that no glucose is present in solution and hence there is a statistical break of the chain. Enriched cellulose solution in DMSO–N-methyl morpholine-N-oxide has been also used for relaxation time (T1) determination both of the solvent and of the enriched carbons of the polymer. Nuclear Overhauser enhancement (NOE) was found to be 1.8 for C-1 and 2.1 for C-6 showing that relaxation phenomenon is not purely dipolar. T1 values of 97 and 65 msec are found for C-1 and C-6 of cellulose, in good agreement with the values known for polysaccharides. Determination of T1 for the different carbon atoms of the solvent DMSO-N-methyl morpholine-N-oxide with and without cellulose shows a large reduction of T1 for N-methyl morpholine-N-oxide molecule. This denotes a slower molecular motion of this molecule and a preferential interaction with the cellulose macromolecule. 相似文献
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Masoud Mehrpour Anahita Kyani Mohsen Tafazzoli Fariba Fathi Mohammad‐Taghi Joghataie 《Magnetic resonance in chemistry : MRC》2013,51(2):102-109
Multiple sclerosis (MS) is a nervous system disease that affects the fatty myelin sheaths around the axons of the brain and spinal cord, leading to demyelination and a broad range of signs and symptoms. MS can be difficult to diagnose because its signs and symptoms may be similar to other medical problems. To find out which metabolites in serum are effective for the diagnosis of MS, we utilized metabolic profiling using proton nuclear magnetic resonance spectroscopy (1H‐NMR). Random forest (RF) was used to classify the MS patients and healthy subjects. Atomic absorption spectroscopy was used to measure the serum levels of selenium. The results showed that the levels of selenium were lower in the MS group, when compared with the control group. RF was used to identify the metabolites that caused selenium changes in people with MS by building a correlation model between these metabolites and serum levels of selenium. For the external test set, the obtained classification model showed a 93% correct classification of MS and healthy subjects. The regression model of levels of selenium and metabolites showed the correlation (R2) value of 0.88 for the external test set. The results indicate the suitability of NMR as a screen for identifying MS patients and healthy subjects. A novel model with good prediction outcomes was constructed between serum levels of selenium and NMR data. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
16.
We perform a systematic examination on the dependence of the calculated nuclear magnetic shielding constants on the chosen geometry for a selective set of density functional methods of B3LYP, PBE0, and OPBE. We find that the OPBE exchange-correlation functional performs remarkably well when either the optimized geometries or the experimental geometries are used. The popular B3LYP and PBE0 functionals have a clear tendency of deshielding, giving shieldings that are usually too low and shifts that are usually too high, at the experimental geometries. Combined with the Hartree-Fock geometries, however, much improved magnetic constants are obtained for B3LYP and PBE0, due to the compensation effect from the systematic underestimation of bond lengths by the Hartree-Fock method. 相似文献
17.
Nuclear magnetic resonance (NMR), as a powerful technology, is widely used to characterize the physicochemical properties of surfactants in solution. As a sensitive technique to molecular environment, NMR is beyond the reach of other spectral methods in surfactant systems. Recent years, intensive investigations of surfactants by NMR were reported but not well summarized; therefore, we highlight these significant progresses, which may shed light on the challenges to understand their behavior and mechanisms in surfactant systems. The theory of various NMR methods was introduced, including chemical shifts, diffusion, relaxation, 2D nuclear Overhauser effect spectroscopy and rotating frame nuclear Overhauser effect spectroscopy. The behavior, interaction, and mechanisms among surfactants and other molecules from NMR technologies were discussed. Challenges to understand the behavior and mechanisms in surfactant systems and instrumentation limits are addressed as perspectives. 相似文献
18.
The theory of the J-OC-PSP (decomposition of J into orbital contributions using orbital currents and partial spin polarization) method is derived to distinguish between the role of active, passive, and frozen orbitals on the nuclear magnetic resonance (NMR) spin-spin coupling mechanism. Application of J-OC-PSP to the NMR spin-spin coupling constants of ethylene, which are calculated using coupled perturbed density functional theory in connection with the B3LYP hybrid functional and a [7s,6p,2d/4s,2p] basis set, reveal that the well-known pi mechanism for Fermi contact (FC) spin coupling is based on passive pi orbital contributions. The pi orbitals contribute to the spin polarization of the sigma orbitals at the coupling nuclei by mediating spin information between sigma orbitals (spin-transport mechanism) or by increasing the spin information of a sigma orbital by an echo effect. The calculated FC(pi) value of the SSCC (1)J(CC) of ethylene is 4.5 Hz and by this clearly smaller than previously assumed. 相似文献
19.
Leah B. Casabianca 《Magnetic resonance in chemistry : MRC》2020,58(7):611-624
The nuclear magnetic resonance (NMR) chemical shift is extremely sensitive to molecular geometry, hydrogen bonding, solvent, temperature, pH, and concentration. Calculated magnetic shielding constants, converted to chemical shifts, can be valuable aids in NMR peak assignment and can also give detailed information about molecular geometry and intermolecular effects. Calculating chemical shifts in solution is complicated by the need to include solvent effects and conformational averaging. Here, we review the current state of NMR chemical shift calculations in solution, beginning with an introduction to the theory of calculating magnetic shielding in general, then covering methods for inclusion of solvent effects and conformational averaging, and finally discussing examples of applications using calculated chemical shifts to gain detailed structural information. 相似文献
20.
Lara Sulcek Ramona Langner Ulrike Werner-Zwanziger Josef W. Zwanziger Charlotte Martineau-Corcos Michael Fechtelkord 《Magnetic resonance in chemistry : MRC》2020,58(11):1099-1108
In the present work, our aim is to decipher the cationic ordering in the octahedral and tetrahedral sheets of two Al-rich synthetic materials, namely, phlogopites of nominal composition K(Mg3-xAlx)[Al1+xSi3-xO10](OH)yF2-y and lepidolites in the system trilithionite–polylithionite with composition K (LixAl3-x)[Al4-2xSi2xO10](OH)yF2-y, by directly probing the aluminium distribution through 27Al and 17O magic-angle spinning, multiple-quantum magic-angle spinning, and 27Al-27Al double-quantum single-quantum nuclear magnetic resonance (NMR) experiments. Notably, 27Al-27Al double-quantum single-quantum magic-angle spinning NMR spectra, recorded at 9.34 and/or 20.00 T, show the spatial proximity or avoidance of the Al species inside or between the sheets. In both studied minerals, the ensemble of NMR data suggests a preference for [4]Al in the tetrahedral sheet to occupy position close to the [6]Al of the octahedral sheets. 相似文献