28 documentos corresponden a la consulta.
Palabras contadas: resonance: 86, nuclear: 192, magnetic: 559
Alkorta, I. - Elguero, J. - Provasi, P.F. - Pagola, G.I. - Ferraro, M.B.
J Chem Phys 2011;135(10)
2011
Temas: Chiral discrimination - Hartree-fock - Homogeneous electric field - Isotropic medium - Lithium cations - Nuclear magnetic shieldings - Nuclear shielding - Chirality - Density functional theory - Enantiomers
Descripción: The set of 1:1 and 2:1 complexes of XOOX′ (X, X′ H, CH 3) with lithium cation has been studied to determine if they are suitable candidates for chiral discrimination in an isotropic medium via nuclear magnetic resonance spectroscopy. Conventional nuclear magnetic resonance is unable to distinguish between enantiomers in the absence of a chiral solvent. The criterion for experimental detection is valuated by the isotropic part of nuclear shielding polarisability tensors, related to a pseudoscalar of opposite sign for two enantiomers. The study includes calculations at coupled Hartree-Fock and density functional theory schemes for 17O nucleus in each compound. Additional calculations for 1H are also included for some compounds. A huge static homogeneous electric field, perpendicular to the magnetic field of the spectromer, as big as ≈1.7 108 V m -1 should be applied to observe a shift of ≈1 ppm for 17O magnetic shielding in the proposed set of complexes. © 2011 American Institute of Physics.
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Nicotra, V.E. - Gil, R.R. - Oberti, J.C. - Burton, G.
Molecules 2000;5(3):514-515
2000
Temas: withanolide - angiosperm - carbon nuclear magnetic resonance - circular dichroism - conference paper - infrared spectroscopy - jaborosa caulescens - mass spectrometry - molecular model - phytochemistry
Descripción: The phytochemical study of two species of Jaborosa caulescens (var. caulescens and var. bipinnatifida) yielded the four new withanolides 1-4. The structures of the new compounds were determined using a combination of spectroscopic techniques (including 1D and 2D NMR) and Molecular Modeling.
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Maier, M.S. - Araya, E. - Seldes, A.M.
Molecules 2000;5(3):348-349
2000
Temas: hydroxysteroid - animal tissue - carbon nuclear magnetic resonance - conference paper - drug isolation - echinoderm - extraction - fast atom bombardment mass spectrometry - Gorgonocephalus chilensis - nonhuman
Descripción: Five disulfated steroids and a mixture of monosulfated steroids were isolated from the ethanolic extract of the antarctic ophiuroid Gorgonocephalus chilensis. The structures were determined by 1H-NMR, 13C-NMR and FABMS.
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Gros, E.G. - Deulofeu, V. - Galmarini, O.L. - Frydman, B.
Experientia 1968;24(4):323-324
1968
Temas: antibiotic agent - glycoside - hexose - hydrazone derivative - article - chemistry - nuclear magnetic resonance spectroscopy - stereoisomerism - Antibiotics - Chemistry, Pharmaceutical
Descripción: Fil:Gros, E.G. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.
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Tettamanzi, M.C. - Veleiro, A.S. - De La Fuente, J.R. - Burton, G.
Molecules 2000;5(3):449-450
2000
Temas: carbon - plant extract - proton - salpichrolide - unclassified drug - withanolide - carbon nuclear magnetic resonance - chemical structure - conference paper - controlled study
Descripción: From the aerial parts of Salpichroa origanifolia a new withanolide in which the C-13 angular methyl has migrated to C-17, was isolated and characterized by spectroscopic methods.
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Martinez Esperón, M.F. - Fascio, M.L. - D'Accorso, N.B.
Molecules 2000;5(3):418-419
2000
Temas: 3 (1',2' o isopropylidene alpha dextro xylofuranos 4' yl) 5 phenyl 2 isoxazole - carbohydrate derivative - heterocyclic compound - isoxazole derivative - unclassified drug - carbon nuclear magnetic resonance - conference paper - cycloaddition - drug activity - drug synthesis
Descripción: The synthesis of some isoxazolic compounds from carbohydrate derivatives is described. These products are obtained by 1,3-dipolar cycloaddition reaction and their functionalization leads to derivatives with potential biological activities.
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Cirigliano, A.M. - Veleiro, A.S. - Oberti, J.C. - Burton, G.
Molecules 2000;5(3):441-442
2000
Temas: jaborosa odonelliana extract - plant extract - unclassified drug - withanolide - animal cell - antineoplastic activity - carbon nuclear magnetic resonance - conference paper - controlled study - jaborosa odonelliana
Descripción: From whole Jaborosa odonelliana plants four new withanolides containing a spiranic lactone in the side chain, were isolated and their structures elucidated by spectroscopic methods.
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Zaccari, D.G. - De Azúa, M.C.R. - Melo, J.I. - Giribet, C.G.
J Chem Phys 2006;124(5)
2006
Temas: Elimination of the small component (ESC) - Linear response (LR) - Molecular magnetic properties - Relativistic effect - Magnetic properties - Magnetic shielding - Mathematical operators - Nuclear magnetic resonance - Tensors - Molecular dynamics
Descripción: In the present work a set of formal relations connecting different approaches to calculate relativistic effects on magnetic molecular properties are proven. The linear response (LR) within the elimination of the small component (ESC), Breit Pauli, and minimal-coupling approaches are compared. To this end, the leading order ESC reduction of operators within the minimal-coupling four-component approach is carried out. The equivalence of all three approaches within the ESC approximation is proven. It is numerically verified for the NMR nuclear-magnetic shielding tensor taking HX and C H3 X (X=Br,I) as model compounds. Formal relations proving the gauge origin invariance of the full relativistic effect on the NMR nuclear-magnetic shielding tensor within the LR-ESC approach are presented. © 2006 American Institute of Physics.
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Bellozas Reinhard, M.E. - Licastrode, S.A.
Molecules 2000;5(3):602-604
2000
Temas: acetylcholinesterase - insecticide - organophosphorus compound - sulfoximine - unclassified drug - computer simulation - conference paper - infrared radiation - insecticidal activity - measurement
Descripción: New organophosphorus insecticides of dialkylsulphoximines derived with activity upon acetylcholinesterase were synthesized. The obtained compounds were characterized by NMR and IR, and anticholinesterase activity and toxicity was measured. A simulation through computer was done in order to establish the relationship between structure and activity.
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Pagola, G.I. - Caputo, M.C. - Ferraro, M.B. - Lazzeretti, P.
J Chem Phys 2004;120(20):9556-9560
2004
Temas: Computational methods - Diamagnetism - Magnetic anisotropy - Magnetic field effects - Magnetic shielding - Magnetic susceptibility - Molecular dynamics - Natural frequencies - Nuclear magnetic resonance - Perturbation techniques
Descripción: A computational scheme was developed for a fourth-rank hyprmagnetizability tensor denoted by Xαβγδ. It was shown that this instrinsic property of diamagnetic atoms and molecules was useful to rationalize their nonlinear response to intense magnetic field. The terms connected with the fourth power of the perturbing field which represent the fourth-rank hypermagnetizability of the H2, HF, H2O, NH3, and CH4 molecules were evaluated at the coupled Hartree-Fock level of accuracy. The Gaugeless basis sets of increasing size and flexibility that adopted two different coordinate systems to estimate the degree of convergence of theoretical tensor components was employed.
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Brousse, B.N. - Moglioni, A.G. - Alho, M.M. - Álvarez-Larena, Á. - Moltrasio, G.Y. - D'Accorso, N.B.
Arkivoc 2002;2002(10):14-23
2002
Temas: Asymmetric spiro-heterocyclic compounds - Terpenones - Thiadiazolines - Thiosemicarbazones - 1,3,3 trimethyl 2 norcamphanone - camphor - heterocyclic compound - menthone - n [aza(1,7,7 trimethylbicyclo[2.2.1]hept 2 ylidene)methyl]acetamide - terpene derivative
Descripción: Preparation of chiral heterocyclic compounds of the thiadiazoline types, starting from natural terpenones such as fenchone, camphor and menthone, is described. Stereochemical assignment of the compounds synthesized was performed by NMR spectroscopy and X-ray analysis.
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Turjanski, A.G. - Estrin, D.A. - Rosenstein, R.E. - Mccormick, J.E. - Martin, S.R. - Pastore, A. - Biekofsky, R.R. - Martorana, V.
Protein Sci. 2004;13(11):2925-2938
2004
Temas: Calmodulin - Fluorescence - Melatonin - Molecular dynamics - NMR - Weak interactions - calcium - calmodulin - melatonin - amino terminal sequence
Descripción: Pineal hormone melatonin (N-acetyl-5-methoxytryptamine) is thought to modulate the calcium/calmodulin signaling pathway either by changing intracellular Ca2+ concentration via activation of its G-protein-coupled membrane receptors, or through a direct interaction with calmodulin (CaM). The present work studies the direct interaction of melatonin with intact calcium-saturated CaM both experimentally, by fluorescence and nuclear magnetic resonance spectroscopies, and theoretically, by molecular dynamics simulations. The analysis of the experimental data shows that the interaction is calcium-dependent. The affinity, as obtained from monitoring 15N and 1H chemical shift changes for a melatonin titration, is weak (in the millimolar range) and comparable for the N- and C-terminal domains. Partial replacement of diamagnetic Ca2+ by paramagnetic Tb3+ allowed the measurement of interdomain NMR pseudocontact shifts and residual dipolar couplings, indicating that each domain movement in the complex is not correlated with the other one. Molecular dynamics simulations allow us to follow the dynamics of melatonin in the binding pocket of CaM. Overall, this study provides an example of how a combination of experimental and theoretical approaches can shed light on a weakly interacting system of biological and pharmacological significance.
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Arcisauskaite, V. - Melo, J.I. - Hemmingsen, L. - Sauer, S.P.A.
J Chem Phys 2011;135(4)
2011
Temas: Atomic numbers - Basis sets - Coulomb potential - Exchange-correlations - Experimental data - Functionals - Gaussians - Linear response - NMR shielding - Nuclear magnetic resonance shielding
Descripción: We investigate the importance of relativistic effects on NMR shielding constants and chemical shifts of linear HgL2 (L = Cl, Br, I, CH 3) compounds using three different relativistic methods: the fully relativistic four-component approach and the two-component approximations, linear response elimination of small component (LR-ESC) and zeroth-order regular approximation (ZORA). LR-ESC reproduces successfully the four-component results for the C shielding constant in Hg(CH3)2 within 6 ppm, but fails to reproduce the Hg shielding constants and chemical shifts. The latter is mainly due to an underestimation of the change in spin-orbit contribution. Even though ZORA underestimates the absolute Hg NMR shielding constants by ∼2100 ppm, the differences between Hg chemical shift values obtained using ZORA and the four-component approach without spin-density contribution to the exchange-correlation (XC) kernel are less than 60 ppm for all compounds using three different functionals, BP86, B3LYP, and PBE0. However, larger deviations (up to 366 ppm) occur for Hg chemical shifts in HgBr 2 and HgI2 when ZORA results are compared with four-component calculations with non-collinear spin-density contribution to the XC kernel. For the ZORA calculations it is necessary to use large basis sets (QZ4P) and the TZ2P basis set may give errors of ∼500 ppm for the Hg chemical shifts, despite deceivingly good agreement with experimental data. A Gaussian nucleus model for the Coulomb potential reduces the Hg shielding constants by ∼100-500 ppm and the Hg chemical shifts by 1-143 ppm compared to the point nucleus model depending on the atomic number Z of the coordinating atom and the level of theory. The effect on the shielding constants of the lighter nuclei (C, Cl, Br, I) is, however, negligible. © 2011 American Institute of Physics.
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Encinar, J.A. - Mallo, G.V. - Mizyrycki, C. - Giono, L. - González-Ros, J.M. - Rico, M. - Cánepa, E. - Moreno, S. - Neira, J.L. - Iovanna, J.L.
J. Biol. Chem. 2001;276(4):2742-2751
2001
Temas: Biochemistry - DNA - Electrophoresis - Fourier transform infrared spectroscopy - Nuclear magnetic resonance spectroscopy - Gel shift analysis - Proteins - cyclic AMP dependent protein kinase - DNA - high mobility group B1 protein
Descripción: We have studied the biochemical features, the conformational preferences in solution, and the DNA binding properties of human p8 (hp8), a nucleoprotein whose expression is affected during acute pancreatitis. Biochemical studies show that hp8 has properties of the high mobility group proteins, HMG-I/Y. Structural studies have been carried out by using circular dichroism (near- and far-ultraviolet), Fourier transform infrared, and NMR spectroscopies. All the biophysical probes indicate that hp8 is monomeric (up to 1 mM concentration) and partially unfolded in solution. The protein seems to bind DNA weakly, as shown by electrophoretic gel shift studies. On the other hand, hp8 is a substrate for protein kinase A (PKA). The phosphorylated hp8 (PKAhp8) has a higher content of secondary structure than the nonphosphorylated protein, as concluded by Fourier transform infrared studies. PKAhp8 binds DNA strongly, as shown by the changes in circular dichroism spectra, and gel shift analysis. Thus, although there is not a high sequence homology with HMG-I/Y proteins, hp8 can be considered as a HMG-I/Y-like protein.
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Merino, E.R. - Cerezo, A.S. - Matulewicz, M.C.
Molecules 2000;5(3):551-552
2000
Temas: polysaccharide - potassium chloride - callophyllis variegata - carbon nuclear magnetic resonance - conference paper - Fourier analysis - fractionation - methylation - molecular dynamics - plant
Descripción: The crude polysaccharide from cystocarpic Callophyllis variegata was fractionated with potassium chloride yielding three minor fractions which precipitated between 0.05-0.10 M KCl, 1.20-1.25 M KCl and 1.80-2.00 M KCl, and a main product soluble in 2.00 M KCl. These fractions were analysed and structural analysis of the major one was carried out by methylation, FT-IR and 13C NMR.
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Battista, M.E. - Vitale, A.A. - Pomilio, A.B.
Molecules 2000;5(3):489-490
2000
Temas: cyclopeptide - fungal protein - toxic substance - ab initio calculation - Amanita phalloides - carbon nuclear magnetic resonance - conference paper - empiricism - hydrogen bond - molecular interaction
Descripción: The electronic structures and conformational studies of the cyclopeptides, O-methyl-α-amanitin, phalloidin and antamanide, were obtained from molecular parameters on the basis of semiempiric and ab initio methods.
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Reinicke, K.E. - Bey, E.A. - Bentle, M.S. - Pink, J.J. - Ingalls, S.T. - Hoppel, C.L. - Misico, R.I. - Arzac, G.M. - Burton, G. - Bornmann, W.G. - Sutton, D. - Gao, J. - Boothman, D.A.
Clin. Cancer Res. 2005;11(8):3055-3064
2005
Temas: 2,2 dimethyl 6 (4 bromophenylimino) 3,4,5,6 tetrahydro 2h naphth[1,2 b]oxin 5 one - 2,2 dimethyl 6 (4 methoxyphenylimino) 3,4,5,6 tetrahydro 2h naphth[1,2 b]oxin 5 one - 2,2 dimethyl 6 (4 methylphenylimino) 3,4,5,6 tetrahydro 2h naphth[1,2 b]oxin 5 one - 2,2 dimethyl 6 (4 nitrophenylimino) 3,4,5,6 tetrahydro 2h naphth[1,2 b]oxin 5 one - 2,2 dimethyl 6 phenylimino 3,4,5,6 tetrahydro 2h naphth[1,2 b]oxin 5 one - 4 bromophenylimine lapachone - 4 methoxyphenylimine lapachone - 4 methylphenylimine lapachone - 4 nitrophenylimine lapachone - acetylcysteine
Descripción: β-Lapachone, an o-naphthoquinone, induces a novel caspase- and p53-independent apoptotic pathway dependent on NAD (P) H:quinone oxidoreductase 1 (NQO1). NQO1 reduces β-lapachone to an unstable hydroquinone that rapidly undergoes a two-step oxidation back to the parent compound, perpetuating a futile redox cycle. A deficiency or inhibition of NQO1 rendered cells resistant to beta;-lapachone. Thus, β-lapachone has great potential for the treatment of specific cancers with elevated NQO1 levels (e.g., breast, non - small cell lung, pancreatic, colon, and prostate cancers). We report the development of mono(arylimino) derivatives of β-lapachone as potential prodrugs. These derivatives are relatively nontoxic and not substrates for NQO1 when initially diluted in water. In solution, however, they undergo hydrolytic conversion to β-lapachone at rates dependent on the electron-withdrawing strength of their substituent groups and pH of the diluent. NQO1 enzyme assays, UV-visible spectrophotometry, high-performance liquid chromatography-electrospray ionization-mass spectrometry, and nuclear magnetic resonance analyses confirmed and monitored conversion of each derivative to β-lapachone. Once converted, β-lapachone derivatives caused NQO1-dependent, μ-calpain-mediated cell death in human cancer cells identical to that caused by β-lapachone. Interestingly, coadministration of N-acetyt-L-cysteine prevented derivative-induced cytotoxicity but did not affect β-lapachone lethality. Nuclear magnetic resonance analyses indicated that prevention of β-lapachone derivative cytotoxicity was the result of direct modification of these derivatives by N-acetyl-L-cysteine, preventing their conversion to β-lapachone. The use of β-lapachone mono(arylimino) prodrug derivatives, or more specifically a derivative converted in a tumor-specific manner (i.e., in the acidic local environment of the tumor tissue), should reduce normal tissue toxicity while eliciting tumor-selective cell killing by NQO1 bioactivation. © 2005 American Association for Cancer Research.
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Martins Alho, M.A. - Moglioni, A.G. - Brousse, B. - Moltrasio, G.Y. - D'Accorso, N.B.
Arkivoc 2000;2000(4 SPECISS):627-640
2000
Temas: 3,4 dihydronaphthalen 1(2h) one thiosemicarbazone - 3,4' dimethoxybenzophenone thiocarbamazone - 4 methoxybenzophenone thiocarbamazone - 4,4' dimethoxybenzophenone thiocarbamazone - 5 acetamido 3 n acetyl 2 (3',4' dimethoxyphenyl) 2 phenyl 1,3,4 thiadiazoline - 5 acetamido 3 n acetyl 2 (4' methoxyphenyl) 2 phenyl 1,3,4 thiadiazoline - 5 acetamido 3 n acetyl 2,2 bis(4' methoxyphenyl) 1,3,4 thiadiazoline - 5 acetamido 3 n acetyl 2,2 diphenyl 1,3 thiadiazoline - 5 methoxyindan 1 one thiosemicarbazone - 6 methoxyindan 1 one thiosemicarbazone
Descripción: Fil:Martins Alho, M.A. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.
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Caputo, M.C. - Ferraro, M.B. - Lazzeretti, P.
J Chem Phys 2000;112(14):6141-6151
2000
Descripción: A procedure, based on a continuous transformation of the origin of the (quantum mechanical) current density that sets the diamagnetic contribution to zero (CTOCD-DZ) all over the molecular domain, is applied to determine shielding polarizabilities to first order in a perturbing electric field. In any calculations relying on the algebraic approximation, irrespective of size and quality of the (gaugeless) basis set employed, all the components of the CTOCD-DZ magnetic shielding polarizability are origin independent, and the constraints for charge and current conservation are exactly satisfied. The effects of a static uniform electric field on the nuclear magnetic resonance (NMR) shielding of H2O2, F2, H2C2, H2CO, NH3, HCN, and HNC molecules have been investigated within the CTOCD-DZ method, and compared with the conventional results evaluated via the same basis sets, and with theoretical results taken from the literature. © 2000 American Institute of Physics.
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