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11.
Rudner MS Jeremic S Petterson KA Kent DR Brown KA Drake MD Goddard WA Roberts JD 《The journal of physical chemistry. A》2005,109(40):9076-9082
Relative strengths of amide NH...O- and carboxyl OH...O- hydrogen bonds were investigated via conformational analysis of succinamate and monohydrogen succinate anions with the aid of vicinal proton-proton NMR couplings and B3LYP DFT quantum mechanical calculations for a variety of solvents. New experimental results for succinamate are compared with those obtained from previous studies of monohydrogen succinate. While some computational results for monohydrogen succinate were published previously, the results contained herein are the product of a more powerful methodology than that used earlier. The experimental results clearly show that intramolecular hydrogen-bond formation is more favored in aprotic solvents than in protic solvents for both molecules. Furthermore, the preference of the succinate monoanion for the gauche conformation is much stronger in aprotic solvents than that of succinamate, indicating that the OH...O- hydrogen bond is substantially stronger than its NH...O- counterpart, despite the approximately 5 kcal cost for formation of the E configuration of the carboxyl group needed to make an intramolecular hydrogen bond. The actual energy differences between formation of internal hydrogen bonds for monohydrogen succinate and succinamate anion were estimated by comparison of the relative values of K1 of the respective acids in water and DMSO by a procedure first developed by Westheimer. Recent theoretical work with succinamate highlights the necessity of considering substituent orientational degrees of freedom to understand the conformational equilibria of the central CH2-CH2 torsions in disubstituted ethanes. Similar methodology is applied here to succinic acid monoanion, by mapping potential-energy surfaces with respect to the CH2-CH2 torsional, carboxyl-substituent rotational, and carboxyl-proton E/Z isomeric degrees of freedom. Boltzmann populations were compared with gauche populations estimated from the experimentally determined coupling constants. The quantum mechanical results for succinamate show a much weaker tendency toward hydrogen bonding than for the succinic acid monoanion. However, the theoretical methods employed appear to substantially overestimate contributions from intramolecularly hydrogen-bonded structures for the succinic acid monoanion when compared with experimental results. Natural bond orbital analysis, applied to the quantum mechanical wave functions of fully optimized gauche and trans structures, showed a strong correlation between the population of amide sigma*(N-H) and carboxyl sigma*(O-H) antibonding orbitals and apparent hydrogen-bonding behavior. 相似文献
12.
Igor Jerković Ani Radonić Marina Kranjac Marina Zekić Zvonimir Marijanović Senka Gudić Maja Kliškić 《Chemical Papers》2016,70(6):726-736
Headspace solid-phase micro-extraction (HS-SPME) and ultrasonic solvent extraction (USE) were used for red clover honey volatiles extraction. The extracts were analysed using gas chromatography and mass spectrometry (GC-MS). Lilac aldehyde isomers dominated in the headspace (individual range from 7.6 % to 21.4 %) followed by phenylacetaldehyde (10.1–31.2 %) and benzaldehyde (7.0–15.7 %). Higher aliphatic alcohols and hydrocarbons were the predominant constituents of the honey extracts. The honey and its extracts exhibited rather weak anti-radical activity (DPPH assay) and total antioxidant activity (FRAP assay). On the other hand, the honey’s inhibitive properties towards the corrosion of AA 2017A alloy in NaCl solution (potentiodynamic polarisation and potentiostatic pulse measurements) revealed the honey to be a very good anodic inhibitor (efficiency up to 76 %) while the honey extracts (USE) showed better inhibition efficacy. 相似文献
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Perišić-Janjić Nada U. Djaković-Sekulić Tatjana Lj. Jevrić Lidija R. Jovanović Bratislav Ž. 《平面色谱法杂志一现代薄层色谱法》2005,18(3):212-216
JPC – Journal of Planar Chromatography – Modern TLC - Quantitative structure-retention relationships (QSRR) have been used to study the chromatographic behavior of some s-triazines.... 相似文献
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JPC – Journal of Planar Chromatography – Modern TLC - Estimation of retention data by use of correlation equations and physicochemical properties is a useful tool in liquid... 相似文献
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Luka Sopta Senka Maćešić Danko Holjević Nelida Črnjarić-Žic Jerko Škifić Siniša Družeta Bojan Crnković 《Annali dell'Universita di Ferrara》2007,53(2):405-415
In this paper we present numerical simulations for the dam-break flood wave propagation from Tribalj accumulation to the town
of Crikvenica (Croatia). The mathematical models we used were the one-dimensional open channel flow and the two-dimensional
shallow water equations. They were solved with the well-balanced finite volume numerical schemes which additionally include
special numerical treatment of the wetting/drying front boundary. These schemes were tested on CADAM test problems. The aim
of this study was to assess potential damage in the village of Tribalj and the town of Crikvenica. Results of these simulations
were used as the basis for urban planning and micro-zoning of the flood-risk areas. Several different dam-break scenarios
were considered, ranging from sudden dam disappearance to partial and dynamic breach formation.
相似文献
18.
Nelida Črnjarić-Žic Senka Maćešić Bojan Crnković 《Annali dell'Universita di Ferrara》2007,53(2):199-215
Most of the standard papers about the WENO schemes consider their implementation to uniform meshes only. In that case the
WENO reconstruction is performed efficiently by using the algebraic expressions for evaluating the reconstruction values and
the smoothness indicators from cell averages. The coefficients appearing in these expressions are constant, dependent just
on the scheme order, not on the mesh size or the reconstruction function values, and can be found, for example, in Jiang and
Shu (J Comp Phys 126:202–228, 1996). In problems where the geometrical properties must be taken into account or the solution
has localized fine scale structure that must be resolved, it is computationally efficient to do local grid refinement. Therefore,
it is also desirable to have numerical schemes, which can be applied to nonuniform meshes. Finite volume WENO schemes extend
naturally to nonuniform meshes although the reconstruction becomes quite complicated, depending on the complexity of the grid
structure. In this paper we propose an efficient implementation of finite volume WENO schemes to nonuniform meshes. In order
to save the computational cost in the nonuniform case, we suggest the way for precomputing the coefficients and linear weights
for different orders of WENO schemes. Furthermore, for the smoothness indicators that are defined in an integral form we present
the corresponding algebraic expressions in which the coefficients obtained as a linear combination of divided differences
arise. In order to validate the new implementation, resulting schemes are applied in different test examples.
相似文献
19.
Mario Cetina Senka ?akovi Vladimir Rapi Amalija Golobi
《Acta Crystallographica. Section C, Structural Chemistry》2003,59(8):m328-m330
In the title compound, [Fe(C5H5)(C14H13O)], the plane of the heterocyclic ring is almost perpendicular to the plane of the substituted cyclopentadienyl ring, and the heterocyclic ring adopts a half‐chair conformation. The conformation of the nearly parallel cyclopentadienyl (Cp) rings [the dihedral angle between their planes is 2.7 (1)°] is almost halfway between eclipsed and staggered, and the rings are mutually twisted by about 19.4 (2)° (mean value). The mean lengths of the C—C bonds in the substituted and unsubstituted cyclopentadienyl ring are 1.420 (2) and 1.406 (3) Å, respectively, and the Fe—C distances range from 2.029 (2) to 2.051 (2) Å. The phenyl and unsubstituted cyclopentadienyl rings are involved in C—H⃛π interactions, with intermolecular H⃛centroid distances of 2.85 and 3.14 Å for C—H⃛π(Ph), and 2.88 Å for C—H⃛π(Cp). In two of these interactions, the C—H bond points towards one of the ring bonds rather than towards the ring centroid. In the crystal structure, the C—H⃛π interactions connect the molecules into a three‐dimensional framework. 相似文献
20.
In our study we investigated the relationship between conventional morphometric indicators of nuclear size and shape (area and circularity) and the parameters of gray level co-occurrence matrix texture analysis (entropy, homogeneity, and angular second moment) in cells committed to apoptosis. A total of 432 lymphocyte nuclei images from the spleen germinal center light zones (cells in early stages of apoptosis) were obtained from eight healthy male guinea pigs previously immunized with sheep red blood cells (antigen). For each nucleus, area, circularity, entropy, homogeneity, and angular second moment were determined. All measured parameters of gray level co-occurrence matrix (GLCM) were significantly correlated with morphometric indicators of nuclear size and shape. The strongest correlation was observed between GLCM homogeneity and nuclear area (p < 0.0001, r(s) = 0.61). Angular second moment values were also highly significantly correlated with nuclear area (r(s)= 0.39, p < 0.0001). These results indicate that the GLCM method may be a powerful tool in evaluation of ultrastructural nuclear changes during early stages of the apoptotic process. 相似文献