Navegando por Palavras-chave "Theoretical calculations"

Agora exibindo 1 - 10 de 10
  • Nenhuma Miniatura disponível
    Item
    Somente Metadadados
    Addition of kinetic boron enolates generated from beta-alkoxy methyl ketones to aldehydes. Density functional theory calculations on the transition structures
    (Elsevier B.V., 2009-10-17) Dias, Luiz C.; Pinheiro, Savio M.; Oliveira, Vanda M. de; Ferreira, Marco A. B.; Tormena, Claudio F.; Aguilar, Andrea M. [UNIFESP]; Zukerman-Schpector, Julio; Tiekink, Edward R. T.; Universidade Estadual de Campinas (UNICAMP); Universidade Federal de São Paulo (UNIFESP); Universidade Federal de São Carlos (UFSCar)
    Herein we report that good to excellent levels of 1,5-anti stereoinduction are obtained in boron enolate aldol reactions of 1,2-syn beta-alkoxy methyl ketones with achiral aldehydes, when the beta-alkoxy protecting group is part of a benzylidene acetal. We have also investigated the effects of the ligands on boron, the alpha-, beta-, and gamma-substituents and the beta-alkoxy protecting group on the boron enolates, using density functional theory (B3LYP) and Moller-Plesset perturbation theory (MP2) calculations. (C) 2009 Elsevier B.V. All rights reserved,
  • Imagem de Miniatura
    Item
    Acesso aberto (Open Access)
    Análise conformacional e das interações eletrônicas de algumas 2-acetamido-3-metil-3-nitrososulfanil-N-arilbutanamidas: S-nitrosotióis com potencial atividade biológica
    (Universidade Federal de São Paulo (UNIFESP), 2012-02-29) Santana, Rafael Germano [UNIFESP]; Reis, Adriana Karla Cardoso Amorim [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)
    We carried out a conformational study on the S-nitrosothiols (R-SNO), 2-acetamido-3-methyl-3-(nitrososulfanyl)-N-arylbutanamides and their thiol precursors 2-acetamido-3-mercapto-3-methyl-N-arylbutanamides. The lowest energy conformation for both compounds is stabilized by intramolecular hydrogen bonds. Trans conformation was determined as the predominant conformation after geometrical analysis of R-SNO. Orbital interactions for 2-acetamido-3-mercapto-3-methyl-N-arylbutanamides were calculated using Natural Bond Orbital (NBO) methodology. Calculations indicated that orbital interactions for these compounds are stabilized by the following interactions: no (N2) →  (C3-O4) and no(N10) → (C11-O12). NBO results showed that the hyperconjugative interaction is very effective, weakening the σ bond and resulting in increasing length of the S-N bond in R-SNO. The strong delocalization induces partial character to the S-N bond. The bond S-N indicates a strong delocalization of the electron pair of O(NO) due to interaction. This interaction is responsible for the elongation of the S-N bond which increases the ability of the compound to release nitric oxide (NO). Based on the enhanced capacity to release NO by these compounds, our findings suggest that both compounds may display biological activity.
  • Nenhuma Miniatura disponível
    Item
    Somente Metadadados
    Conformational analysis and electronic interactions of some 2-ethylsulfinyl-(4 '-substituted)-phenylacetates
    (Elsevier Science Bv, 2016) Rodrigues, Daniel N. S.; Olivato, Paulo R.; Rodrigues, Alessandro [UNIFESP]; Dal Colle, Maurizio
    The analysis of the infrared carbonyl bands of some 2-ethylsulfinyl-(4'-substituted)-phenylacetates bearing the substituents NO2(1), Cl(2), Br(3), H(4), Me(5) and OMe(6), along with B3LYP/6-31G(d,p), SM5.42R solvation model calculations and natural bond orbital (NBO) analysis was carried out. Theoretical data indicated the existence in the gas phase of three stable gauche conformers, whose relative abundances in condensed phase change at different extent in the series 1-6, depending on the solvent permittivity. The comparison between the IR spectra in solvents of increasing permittivity (from CCl4 to CH3CN) and the calculated SM5.42R data in solution allows a precise assignment of the experimental band components to the distinct conformers. The sum of the main relevant NBO orbital interactions energies does not match the calculated B3LYP relative energies of the three stable conformers of 1-6 in the gas phase. On the contrary, the short contact analysis indicates that the electrostatic interactions largely control their relative stability and play a basic role to determine the calculated v(CO) frequencies order. Moreover, as these contacts dictate the specific geometry assumed by each conformer, the electrostatic interactions determine their different solvation properties too, thus accounting for the experimental stability observed in solution. (C) 2015 Elsevier B.V. All rights reserved.
  • Nenhuma Miniatura disponível
    Item
    Somente Metadadados
    Conformational analysis of some N,N-diethyl-2-[(4 '-substituted) phenylthio] acetamides
    (Elsevier B.V., 2013-11-01) Vinhato, Elisangela [UNIFESP]; Olivato, Paulo R.; Zukerman-Schpector, Julio; Dal Colle, Maurizio; Universidade Federal de São Paulo (UNIFESP); Universidade de São Paulo (USP); Universidade Federal de São Carlos (UFSCar); Univ Ferrara
    The conformational analysis of some N,N-diethyl-2[(4'-substituted)phenylthio]acetamides bearing the substituents OMe 1, Me 2, H 3, Cl 4, Br 5 and NO2 6, was performed by v(co) IR analysis, along with B3LYP/6-311++G(d,p) and Polarisable Continuum Model (PCM) calculations, as well as NBO analysis for 1, 3, and 6 and X-ray diffraction for 4. the results of the calculations indicated the existence of two stable conformation pairs, i.e. gauche (anti; syn) (most stable) and cis (anti; syn) in the gas phase. the gauche conformers were less polar with respect to the cis ones for 1 and 3, but more polar for 6. the most intense IR carbonyl doublet component observed at the lower frequency can be ascribed to the gauche conformers g(anti; syn) for 3-6 in n-C6H14, which is in agreement with the gauche and cis relative stabilities and frequencies resulting from the PCM calculations. Similarly, the single IR band for 1 and 2 in n-hexane may be attributed to the gauche conformers. the PCM calculations compared well with the IR data for the compounds in solution, showing that there is a progressive increase of the cis/gauche population ratio as the solvent polarity increases. the NBO analysis indicated that the gauche(anti; syn) conformation in the gas phase was stabilized by the relevant Lp(s4) pi(*)(c2)=cn sigma(*)(C3-s4), sigma(c3-S4) 21, iCa2.31 > 03_S4, and LPol a* a 1-H28 orbital interactions, which were absent in the cis(anti; syn) conformer. On the contrary, the cis conformer for derivatives 1, 3, and 6 were stabilized by the aa. Cr c2 N5 orbital interaction (through bond coupling), along with the additional LP01 crs4-cio interaction for 6. Moreover, the electrostatic repulsion between the C8 S' and C8*=08- dipoles (Repulsive Field Effect) contributed to both the larger destabilization and increase of the vco frequency of the cis conformer with respect to the gauche conformer. X-ray single crystal analysis indicates that compound 4 assumes the c2(anti) conformation in the solid state, which is the conformation obtained by compound 6 in the gas phase. To obtain the largest energy gain, the molecules were arranged in the crystal in a six-molecules synthon mediated by C-H center dot center dot center dot O and Cl center dot center dot center dot Cl interactions, where the chlorine atoms were related by a crystallographic inversion center. (C) 2013 Elsevier B.V. All rights reserved.
  • Nenhuma Miniatura disponível
    Item
    Somente Metadadados
    Conformational and electronic interaction studies of some p-substituted alpha-methylsulfonyl-alpha-diethoxyphosphorylacetophenones
    (Elsevier B.V., 2008-12-15) Reis, Adriana Karla C. A. [UNIFESP]; Olivato, Paulo R.; Tormena, Claudio F.; Rittner, Roberto; Dal Colle, Maurizio; Universidade de São Paulo (USP); Universidade Federal de São Paulo (UNIFESP); Universidade Estadual de Campinas (UNICAMP); Univ Ferrara
    The analysis of the IR carbonyl band of the alpha-methylsulfonyl-alpha-diethoxyphosphoryl p-substituted acetophenones p-Y-Ph-C(O)CH(SO(2)Me)[P(O)(OEt)(2)] (Y = OMe 1, H 2, F 3, Cl 4, Br 5 and NO(2) 6) supported by HF/6-31G(d,p) ab initio calculations of the alpha-methylsulfonyl-alpha-diethoxyphosphoryl acetophenone 2, indicated the existence of a single stable cl conformer in gas phase and in solvents of increasing polarity, along with the presence of second less stable conformation in gas phase. the cl conformer present the (SO(2)Me) group and the [P(O)(OEt(2))] groups in a syn-clinal (gauche) geometry and is stabilised through of the 0('60)... P(%), 01NO(owl Crco), ONO)... C(,C*.), 060)... S(`S`02.,) and 0('S-02) q o) electronic interactions 08along with H(8S*o2M,). 0(660). HU(5C_H2)lP0Erl- 0(8so2m), H(6 +Ph)- - - (co) and H(8o+'-Ph). 0( 'Po) intramolecular hydrogen bonds. the almost co nstant negative carbonyl frequency shifts (Av) for the title compounds 1-6 with respect to the parent acetophenones 7-14 corroborates the prevalence of the electronic interactions over the -l(y inductive effect of the ot-substituents for the title compounds and gives strong support for the existence of the crossed 0'('C-O)... S'(1S+02m,) and 0(S-02) C('C+O) (charge transfer and electrostatic); 08-) (co P('i o) and 01'M-OFt)l C(' o), (electrostatic) interactions. 0 2008 Elsevier B.V. All rights reserved.
  • Nenhuma Miniatura disponível
    Item
    Somente Metadadados
    Conformational preferences for some 2-substituted N-methoxy-N-methylacetamides through spectroscopic and theoretical studies
    (Elsevier B.V., 2010-08-10) Olivato, Paulo R.; Gomes, Roberto da Silva; Rodrigues, Alessandro; Reis, Adriana K. C. A. [UNIFESP]; Domingues, Nelson L. C.; Rittner, Roberto; Dal Colle, Maurizio; Universidade de São Paulo (USP); Universidade Federal de São Paulo (UNIFESP); Fundacao Univ Fed Grande Dourados; Universidade Estadual de Campinas (UNICAMP); Univ Ferrara
    The analysis of the IR carbonyl band of the 2-substituted N-methoxy-N-methylacetamides Y-CH(2)C(O)-N(OMe)Me (Y = F1, OMe 2, OPh 3, Cl 4), supported by B3LYP/6-311++G(3df, 3pd) calculations along with the NBO analysis for 1-4, indicated the existence of cis-gauche conformers i.e. (c) and (g) for 1 and 3, (c(1), c(2)) and (g(1), g(2)) for 2, and (c) and (g(1), g(2)) for 4. in the gas phase, the g conformer population prevails over the c one, for 1 and 3, the (c(1) + c(2)) population prevails over the (g(1) + g(2)) one for 2, and the (g(1) + g(2)) conformer population is more abundant than (c) one for 4. in n-hexane solution, the cis conformer is more abundant for 1-3. the occurrence of Fermi resonance in the nu(CO) region, in n-hexane, precludes the estimative of relative populations of the (c, g(1), g(2)) conformers for 4. the SCI-PCM calculations agree with the solvent effect on the nu(CO) band component relative intensities for 1-3. NBO analysis showed that the n(N) -> pi.(CO), orbital interaction is the main factor which stabilizes the gauche (g, g(1), g(2)) conformers for 1-4 into a larger extent relative to the cis (c, c(1), c(2)) ones. the n(y) -> pi(.)(Co,) sigma(C-Y) -> pi.(CO,) pi(CO) -> sigma(C-Y) and 7co orbital interactions still contribute, but into a minor extent for the stabilization of the gauche conformers relative to the cis ones. the existence of some pyramidalization at the nitrogen atom of the Weinreb amides 1-4 is responsible for the occurrence of Y(delta)-(4)center dot center dot center dot O(delta)-(9) and Y(delta)-(4)center dot center dot center dot N(delta)-(7) short contacts in the gauche (g, g(1), g(2)) conformers, which originates strong repulsive Coulombic interactions, acting in opposition to the large orbital stabilization of the gauche conformer with respect to the cis one. Therefore, a delicate balance of the Coulombic and orbital interactions seems to be responsible for the observed stabilization of the gauche (g, g(1), g(2)) and cis (c, c(1), c(2)) conformers, both in the gas phase and in the solution for 1-4. However, the cis conformer predominance, in non polar solvents, for the 2-substituted N-methoxy-N-methyl acetamides 1-3, bearing in a first raw (fluorine and oxygen) atoms, is in the opposite direction to the gauche conformer preference for the corresponding 2-substituted N,N-dialkyl-acetamides. (C) 2010 Elsevier B.V. All rights reserved.
  • Nenhuma Miniatura disponível
    Item
    Somente Metadadados
    Simplified estimates of ion-activity products of calcium oxalate and calcium phosphate in mouse urine
    (Springer, 2012-08-01) Tiselius, Hans-Goran; Nogueira Ferraz, Renato Ribeiro [UNIFESP]; Heilberg, Ita Pfeferman [UNIFESP]; Karolinska Inst; Universidade Federal de São Paulo (UNIFESP)
    This study aimed at formulating simplified estimates of ion-activity products of calcium oxalate (AP(CaOx)) and calcium phosphate (AP(CaP)) in mouse urineto find the most important determinants in order to limit the analytical work-up. Literature data on mouse urine composition was used to determine the relative effect of each urine variable on the two ion-activity products. AP(CaOx) and AP(CaP) were calculated by iterative approximation with the EQUIL2 computerized program. the most important determinants for AP(CaOx) were calcium, oxalate and citrate and for AP(CaP) calcium, phosphate, citrate, magnesium and pH. Urine concentrations of the variables were used. A simplified estimate of AP(CaOx) (AP(CaOx)-index(MOUSE)) that numerically approximately corresponded to 10(8) x AP(CaOx) was given the following expression:AP(CaOx)-index(MOUSE) = 0.70 x Calcium(1.05) x Oxalate(0.95)(0.90-0.0225 x Citrate) + (6.6 x 10(-8) x Citrate(3.98))For a series of urine samples with various composition the coefficient of correlation between AP(CaOx)-index(MOUSE) and 10(8) x AP(CaOx) was 0.99 (p = 0.00000). A similar estimate of AP(CaP) (AP(CaP)-index(MOUSE)) was formulated so that it approximately would correspond numerically to 10(14) x AP(CaP) taking the following form:Ap(CaP)-index(MOUSE) = 0.05 x Calcium(1.17) x Phosphate(0.85) x Magnesium(0.18) x (pH - 4.5)(6.8) / Citrate(0.76)For a series of variations in urine composition the coefficient of correlation was 0.95 (p = 0.00000). the two approximate estimates shown in this article are simplified expressions of AP(CaOx) and AP(CaP). the intention of these theoretical calculations was not to get methods for accurate information on the saturation levels in urine, but to have mathematical tools useful for rough conclusions on the outcome of different experimental situations in mice. It needs to be emphasized that the accuracy will be negatively influenced if urine variables not included in the formulas differ very much from basic concentrations.
  • Nenhuma Miniatura disponível
    Item
    Somente Metadadados
    Spectroscopic and theoretical studies of some 2-substituted N-methoxy-N-methyl-amides
    (Elsevier B.V., 2013-01-16) Olivato, Paulo R.; Gomes, Roberto da Silva; Rodrigues, Alessandro [UNIFESP]; Domingues, Nelson L. C.; Rittner, Roberto; Dal Colle, Maurizio; Universidade de São Paulo (USP); Universidade Federal de São Paulo (UNIFESP); Fundacao Univ Fed Grande Dourados; Universidade Estadual de Campinas (UNICAMP); Univ Ferrara
    B3LYP/6-311++G(3df,3pd) calculations along with the NBO analysis of some 2-substituted N-methoxy-N-methyl-amides Y-C(R)(2)C(O)N(OMe)Me [Y = Br 1, SEt 2, SePh 4 (for R = H) and SEt 3 (for R = Me)] indicated the existence of three conformers for 1, 2, 4, namely one cis (c) and two gauche (g(1), g(2)), and two gauche (g(1), g(2)) forms for 3. the g(1) conformer is the most stable and the least polar for all derivatives, while the c one is the most polar for 1, 2 and 4. As far as the stability is concerned, the g(2) conformer is more abundant with respect to the c one for compounds 1 and 2, and slightly less stable than c for 4. for the derivative 3, the g(1) conformer is more stable and slightly less polar than the g(2) one. Moreover, the computed (nu(co)) frequencies and the relative populations of the two forms correlate quite well with the IR (nu(co)) doublet frequency components and their relative intensities in solution.The occurrence of Fermi resonance in the fundamental nu(co) region, in solution, precludes the estimative of the relative populations of the c, g(1), g(2) conformers for 1, 2 and 4. NBO analysis showed that the n(N) -> pi(center dot)(co) orbital interaction is the main factor which stabilizes the gauche (g(1), g(2)) conformers into a larger extent relative to the cis (c) one for 1, 2, 4. for these compounds along with the 3 derivative, the same interaction stabilizes more the g(1) conformer than the g(2) one. the sum of the orbital interactions from NBO analysis and the trend of the electrostatic interactions justifies quite well the populations of the (c) and gauche (g(1), g(2)) conformers for 1, 2 and 4, along with the (g(1), g(2)) conformers populations for 3 found in the gas phase. (C) 2012 Elsevier B.V. All rights reserved.
  • Nenhuma Miniatura disponível
    Item
    Somente Metadadados
    Spectroscopic and theoretical studies of some N,N-diethyl-2-[(4 '-substituted)phenylsulfonyl]acetamides
    (Elsevier B.V., 2011-09-14) Vinhato, Elisangela; Olivato, Paulo R.; Rodrigues, Alessandro [UNIFESP]; Zukerman-Schpector, Julio; Dal Colle, Maurizio; Universidade de São Paulo (USP); Universidade Federal de São Paulo (UNIFESP); Universidade Federal de São Carlos (UFSCar); Univ Ferrara
    The analysis of the IR carbonyl band of the N,N-diethyl-2-[(4'-substituted)phenylsulfonyl]acetamides Et(2)NC(O)CH(2)S(O)(2)-C(6)H(4)-Y (Y = OMe 1, Me 2,1-13, Cl 4, Br 5, NO(2) 6) supported by B3LYP/6-31G(d,p) calculations for 3, indicated the existence of three pairs (anti and syn) of cis (c) and gauche (g(1) and g(2)) conformers in the gas phase, being the gauche conformers significantly more stable than the cis ones. the anti geometry is more stable than the syn one, for each pair of cis and gauche conformers. the summing up of the orbital (NBO analysis) and electrostatic interactions justifies quite well the populations and the v(CO) frequencies of the anti and syn pairs of c, g(1) and g(2) conformers. the IR higher carbonyl frequency component whose population is ca. 10%, in CCl(4), may be ascribed to the least stable and most polar cis conformer pair (in the gas phase) and the lower frequency component whose population is ca. 90%, to the summing up of the populations of the two most stable and least polar gauche conformer pairs (g(1) and g(2)) (in the gas phase). the reversal of the cis(c)/gauche (g(1) + g(2)) population ratio observed in chloroform ca. 60% (cis)/40% (gauche) and the occurrence of the most polar cis(c) conformer only, in acetonitrile, strongly suggests the coalescence of the two gauche components in a unique carbonyl band in solution. A further support to this rationalization is given by the single point PCM solvation model performed by HF/6-31G(d,p) method, which showed a progressive increase of the c/(g(1) + g(2)) ratio going from gas to CCl(4), to CHCl(3) and to CH(3)CN. X-ray single crystal analysis of 4 indicates that this compound assumes, in the solid state, the syn-clinal (gauche) conformation with respect to the [O=C-CH(2)-S] moiety, and the most stable anti geometry relative to the [C(O)N(CH(2)CH(3))(2)] fragment. in order to obtain larger energy gain from the crystal packing the molecules of 4 are linked in centrosymmetric dimers through two C-H center dot center dot center dot O interactions (C-H([O-Ph])center dot center dot center dot O([SO2])) forming a step ladder. (C) 2011 Elsevier B.V. All rights reserved.
  • Nenhuma Miniatura disponível
    Item
    Somente Metadadados
    Spectroscopic and theoretical studies of some N-methoxy-N-methyl-2-[(4 '-substituted) phenylsulfonyl]propanamides
    (Elsevier B.V., 2009-10-29) Olivato, Paulo R.; Domingues, Nelson L. C.; Reis, Adriana K. C. A. [UNIFESP]; Vinhato, Elisangela; Mondino, Mirta G.; Zukerman-Schpector, Julio; Rittner, Roberto; Dal Colle, Maurizio; Universidade de São Paulo (USP); Fundacao Univ Fed Grande Dourados; Universidade Federal de São Paulo (UNIFESP); Universidade Federal de São Carlos (UFSCar); Universidade Estadual de Campinas (UNICAMP); Univ Ferrara; Fac Osvaldo Cruz
    The analysis of the IR carbonyl band of the N-methoxy-N-methyl-2-[(4'-substituted)phenyisulfonyI]propanamides Y-PhSO(2)CH(Me)C(O)N(OMe)Me (Y = OMe 1, Me 2, H 3, Cl 4, NO(2) 5), supported by HF/6-31G(d,p) calculations of 3,, indicated the existence of two gauche conformers (g(1) and g(2)), the g, conformer being the most stable and the least polar one (in gas phase and in solution). Both conformers are present in solution of the non polar solvent (CCl(4)) for 1-5 and in solution of the more polar solvents (CHCl(3)) for 1. 4, 5 and (CH(2)Cl(2)) for 5, while only the g(1) conformer is present in solution of the most polar solvent (CH(3)CN) for 1-5. the g, and g2 conformers correspond to the enantiomeric pairs of diastereomers (diast(1) and diast(2)) whose relative configurations are [C(3)(R)N(R)]/[C(3)(s)N(s)] and [C(3)(R)N(s)]/[C(3)(s)N(R)], respectively. the computed carbonyl frequencies for g(1) (diast(1)) and g(2) (diast(2)) stereoisomers of3 match well the experimental values. the NBO analysis, for 3 shows the important role of the orbital interactions in conformer stabilization and the overall balance of these interactions corroborates that the g, conformer is more stable than the 92 one. the observed abnormal solvent effect on the relative intensities of the carbonyl doublet components is attributed to the molecular crowding in the g2 conformer which hinders its solvation in comparison to the g, conformer (diast(1)). X-ray single crystal analysis performed for 3 shows the existence of two 92, and g(1b) conformers of diastereomers (diast2, and diast(1b)) whose absolute configurations are [C(3)(R)N(s)] and [C(3)(R)N(R)], respectively. the larger population and. thus, the larger stabilization of the g(2), conformer over the gib form in the crystals may be associated with a larger energy gain deriving from dipole moment coupling in the former conformer along with a series of C-H center dot center dot center dot O electrostatic and hydrogen bond interactions, (C) 2009 Elsevier B.V. All rights reserved.