bluuebunny/crossref_metadata_2025_split huggingface dataset:
Theoretical study of the magnetic exchange coupling behavior substituting Cr(III) with Mo(III) in cyano‐bridged transition metal complexes
Authors: Zhang Yi‐Quan , Luo Cheng‐Lin 
Published: January 2006

AbstractMolecular magnetism in a series of cyano‐bridged first and second transition metal complexes has been investigated using density functional theory (DFT) combined with the broken‐symmetry (BS) approach. Several exchange‐correlation (XC) functionals in the ADF package were used to investigate complexes I [−(Me3tacn)2(cyclam)NiMo2(CN)6]2+, II [−(Me3tacn)2(cyclam)Ni‐Cr2(CN)6]2+, III [(Me3tacn)6MnMo6(CN)18]2+, and IV [(Me3tacn)6MnCr6(CN)18]2+ (Me3tacn = N,N′,N‴‐trimethyl‐1,4,7‐triazacyclononane). For models A (the molded structure of complex I) and B (the modeled structure of complex II), all the XCs given qualitatively reasonable results and predict ferromagnetic coupling character between M (M = MoIII for A or CrIII for B) and NiII in coincidence with the experimental results (see Tables I and II). The calculated using Operdew, OPBE, O3LYP, and B3LYP functionals and experimental J values show that substituting CrIII with MoIII will enhance the ferromagnetic exchange coupling interactions. But VWN, PW91, PBE, VSXC, and tau‐HCTH functionals have no way to differentiate the relative strength of the intramolecular magnetic exchange coupling interactions of A and B correctly. For models C (the modeled structure of complex III) and D (the modeled structure of complex IV), all the XCs in ADF and B3LYP in Gaussian 03 with several basis sets show that substituting CrIII with MoIII will enhance the antiferromagnetic exchange coupling interactions. From the above calculations, the substitution of CrIII by MoIII will enhance the magnetic coupling interactions, whether the magnetic coupling interactions are ferro‐ or antiferromagnetic. Moreover, Kahn's model was applied to investigate the above facts. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006
Looking for high‐energy density compounds among hexaazaadamantane derivatives with CN, NC, and ONO2 groups
Authors: Xu Xiao Juan , Xiao He Ming , Ma Xiu Fang , Ju Xue Hai 
Published: January 2006

AbstractDensity functional theory (DFT) was employed to evaluate the heats of formation (HOFs) for hexaazaadamantane (HAA) derivatives with CN, NC, and ONO2 groups, respectively. This was done by designing isodesmic reactions at the B3LYP/6‐31G* level of theory, where the HAA cage skeletons were kept unbroken to produce more accurate results, and all HOFs for the required reference compounds, NH2CN, NH2NC, NH2ONO2, and (CH2NH)3, were derived from the G3 theory calculation based on the atomization energies. The calculation results show that the HOFs of HAA derivatives are mainly affected by the number and the position of substituent groups, all the obtained HOFs are positive, and the NC derivatives have the most HOFs among the three types of derivatives with the same number of substituent groups. The detonation velocity (D) and detonation pressure (P) were obtained from the empirical Kamlet–Jacobs equations. All the NC and CN derivatives of HAA have lower densities (ρ), heats of explosion (Q), D, and P. However, these properties of ONO2 derivatives are rather high and vary with the number of ONO2 groups. Considering the easiness for synthesis and relative stability, 2,4,6,8‐hexaazaadamantanenitrate is finally recommended as a potential candidate of a high‐energy density compound (HEDC). © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006
Theoretical study of electric field‐induced intramolecular electron transfer in donor–acceptor pairs via the rigid space and their suitability as molecular electronic devices
Authors: Lu Shen‐Zhuang 
Published: January 2006

AbstractThe geometries of two reaction systems have been optimized under the constraint of C2ν symmetry, using the UHF/6‐31G method. The potential energy surfaces (PES) of the two systems in different external electric field have been constructed using a linear reaction coordinate. It is concluded that the reorganization energies and electron transfer matrix elements for both systems are almost independent of the external electric field. However, the standard Gibbs energy difference changes remarkably with the change of the external electric field. Hence, the applied electric field leads to the variation of rate constant of electron transfer reaction. The threshold field, where the electron transfer becomes barrier free, is obtained to be 0.0015 a.u. for the anion system 1, and 0.00097 a.u. for the anion system 2. The threshold field for modified system 1, in which the hydrogen atoms linking to benzene rings are replaced by fluorine atom, is 0.0018 a.u. The calculations show that the best way to adjust the threshold field is to adjust the dipole moment of the reaction system by changing the length of the bridge. As the rate constant in field‐free case is taken into account, neither reaction systems could be used as molecular electronic device. But if the bridge consists of three or four HCTDs, the rate constant and threshold field will satisfy the practical demand. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006
Comprehensive mechanistic study of ion pair SN2 reactions of lithium isocyanate and methyl halides
Authors: Sun Ying‐Xin , Ren Yi , Wong Ning‐Bew , Chu San‐Yan , Xue Ying 
Published: January 2006

AbstractThe anionic SN2 reactions NCO− + CH3X and ion pair SN2 reactions LiNCO + CH3X (X = F, Cl, Br, and I) at saturated carbon with inversion and retention mechanisms were investigated at the level of MP2/6‐311+G(d,p). There are two possible reaction pathways in the anionic SN2 reactions, but eight in the ion pair SN2 reactions. Calculated results suggest that the previously reported T‐shaped isomer of lithium isocyanate does not exist. All the retention pathways are not favorable based on the analysis of transition structures. Two possible competitive reaction pathways proceed via two six‐member ring inversion transition structures. It is found that there are two steps in the most favorable pathway, in which less stable lithium cyanate should be formed through the isomerization of lithium isocyanate and nucleophilic site (N) subsequently attacks methyl halides from the backside. The thermodynamically and kinetically favorable methyl isocyanate is predicted as major product both in the gas phase anionic and the ion pair SN2 reactions. In addition, good correlations between the overall barriers relative to separated reactants, ΔH , with geometrical looseness parameter %L≠ and the heterolytic cleavage energies of the CX and LiN (or LiO) bonds are observed for the anionic and ion pair SN2 reactions. The trend of variation of the overall barriers predicts the leaving ability of X increase in the order: F < Cl < Br < I. The polarized continuum model (PCM) has been used to evaluate the solvent effects on the two inversion pathways with six‐member transition structures for the reactions of LiNCO + CH3X. The calculations in solution indicate that solvent effects will retard the rate of reactions and the predicted product, methyl isocyanate, is same as the one in the gas phase. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006
Theoretical studies on the reaction mechanism of CH2CH radical with HNCO
Authors: Li Lai‐Cai , Zheng Yan , Zha Dong , Tian An‐Min , Xu Ming‐Hou 
Published: January 2006

AbstractThe reaction mechanism of CH2CH radical with HNCO has been investigated systematically by density functional theory (DFT). The geometries and harmonic frequencies of reactants, intermediates, transition states, and products have been optimized with the B3LYP at different levels. At the same time, AIM is performed to calculate the charge density of some bonding critical points and the charges of some atoms. Nine feasible reaction pathways have been investigated. The results indicated that the main pathway is CH2CH + HNCO → IMA1 → TSA1 → CH2CH2 + NCO, which is characterized by hydrogen atom transferring. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006
Binding of 3O2 and 1O2 to dyes used in photodynamic therapy in gas phase and aqueous media
Authors: Kushwaha P. S. , Mishra P. C. 
Published: January 2006

AbstractDensity functional theory (DFT) was employed at the B3LYP/6‐31+G* level to study complexes of 1O2 and 3O2 with the dye molecules proflavine, methylene blue, and acridine orange, which are useful in photodynamic therapy. It was found that the most stable complex between 1O2 and proflavine are formed when 1O2 is located above the central ring, while the most stable complex between 1O2 and methylene blue is formed when 1O2 is located above the molecular plane, but not above any of the rings, near the sulfur atom. 1O2 can make a stable complex with acridine orange, as it is located above the outer ring of the dye. The binding energies of the complexes of 1O2 with all three dyes are enhanced considerably in going from gas phase to aqueous media. The complexes of 3O2 with the dyes will be unstable in all cases, while those of 1O2 with the same will be quite stable and will not be dissociated due to thermal fluctuations at room temperature. In the complexes of 1O2 and 3O2 with the dyes, charge transfer occurs from the dyes to the O2 moiety, the amount of charge transfer being much more to 1O2 than to 3O2 in each case. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006
F + H2 → FH + H potential energy surface: Construction of the reference configuration state function space and MR‐ACPF‐2 results
Authors: Cardoen Wim , Simons Jack , Gdanitz Robert J. 
Published: January 2006

AbstractA new electronic configuration reference space (subsequently used in multi‐reference averaged coupled pair functional (MR‐ACPF) or multi‐reference configuration interaction singles and doubles [MR‐CI(SD)] level treatments of electron correlation) is determined using the aug‐cc‐pVQZ basis set as a step toward constructing a new potential energy surface (PES) for the F + H2 → FH + H reaction. We use our new reference space to calculate several chemically important properties (e.g., barriers, exothermicity, van der Waals wells) of the F + H2 PES. We obtain nonrelativistic barrier heights of 1.32 kcal/mol−1 (bent) and 1.67 kcal/mol−1 (collinear) that are ∼0.2–0.3 kcal/mol−1 lower than those obtained from the current best PES. Our nonrelativistic value for the exothermicity is 32.45 kcal/mol−1, which is 0.7–1.1 kcal/mol−1 higher than the values obtained from some other PESs and 0.45 kcal/mol−1 higher than the experimental value. The van der Waals wells we find are slightly deeper (0.05 kcal/mol−1) than the wells on the other PES. The ≈1‐kcal/mol−1 magnitude of the differences among barrier heights, exothermicities, and well depths, obtained in our work and using the most reliable current PESs suggest that to obtain a three‐dimensional (3D) PES for the F + H2 → FH + H accurate to 0.2 kcal/mol−1, we will have to use even higher‐level methods (e.g., explicitly correlated wave functions) and include relativistic corrections. We intend to do so in the next phase of this effort that is currently under way. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006
Vibrational–rotational energies of all H2 isotopomers using Monte Carlo methods
Authors: Alexander S. A. , Coldwell R. L. 
Published: January 2006

AbstractUsing variational Monte Carlo techniques, we have computed several of the lowest rotational–vibrational energies of all the hydrogen molecule isotopomers (H2, HD, HT, D2, DT, and T2). These calculations do not require the excited states to be explicitly orthogonalized. We have examined both the usual Gaussian wave function form as well as a rapidly convergent Padé form. The high‐quality potential energy surfaces used in these calculations are taken from our earlier work and include the Born–Oppenheimer energy, the diagonal correction to the Born–Oppenheimer approximation, and the lowest‐order relativistic corrections at 24 internuclear points. Our energies are in good agreement with those determined by other methods. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006
Quantum mechanical predictions of chiroptical vibrational properties
Authors: Polavarapu Prasad L. 
Published: January 2006

AbstractThe developments in quantum mechanical calculations of vibrational circular dichroism, vibrational Raman optical activity, and vibrational contributions to optical rotation are summarized. Further developments needed in each of these areas are pointed out. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006
Simple, sensitive and rapid liquid chromatography/atmospheric pressure chemical ionization mass spectrometric method for the quantitation of Ranolazine in rat plasma
Authors: Liang Yan , Xie Lin , Liu Xiao‐Dong , Chen Wei‐Dong , Lu Tong , Xiong Ye , Wang Guang‐Ji 
Published: January 2006

AbstractA sensitive and specific method using liquid chromatography with atmospheric pressure chemical ionization mass spectrometry (LC/APCI‐MS) has been developed and validated for the identification and quantification of Ranolazine in rat plasma. A simple liquid–liquid extraction procedure was followed by injection of the extracts onto a C18 column with isocratic elution and detection using a single quadrupole mass spectrometer in selected ion monitoring (SIM) mode. The method was tested using six different batches of blank plasma. Linearity was established for the concentration range 0.02–10.0 µg/mL, with a coefficient of determination (r) of 0.9998 and good back‐calculated accuracy and precision. The intra‐ and inter‐day precision (relative standard deviation (RSD) %) was lower than 10%, and accuracy ranged from 85 to 115%. The lower limit of quantification was reproducible at 0.01 µg/mL with 20 µL plasma. The proposed method enables the unambiguous identification and quantification of Ranolazine for pre‐clinical and clinical studies. Copyright © 2006 John Wiley & Sons, Ltd.
Development of a multi‐residue method for the determination of 18 carbamates in tobacco by high‐performance liquid chromatography/positive electrospray ionisation tandem mass spectrometry
Authors: Mayer‐Helm B. , Hofbauer L. , Müller J. 
Published: January 2006

AbstractA multi‐residue method for the determination of carbamates in tobacco was developed by high‐performance liquid chromatography (HPLC) triple quadrupole mass spectrometry (MS). A rapid sample preparation consisted of an extraction step with methanol, centrifugation and 1:1 dilution with aqueous 10 mM ammonium acetate. After filtration these extracts were directly analysed by reversed‐phase HPLC coupled to positive electrospray ionisation tandem mass spectrometry operated in the multiple reaction monitoring mode. Capillary voltage and dwell times were optimised to reduce matrix effects and to increase sensitivity. The method was validated for the determination of 18 carbamates in three main types of raw tobacco and three tobacco products. The interday accuracy ranged between 80 and 110% with a relative standard deviation (RSD) of <30%. The limits of quantification (LOQs) ranged between 0.01 and 0.04 ppm for almost all carbamates, except aldicarb sulfone, carbofuran, and pebulate, with LOQs between 0.10 and 0.20 ppm. These LOQs were clearly below the guidance residue levels defined by the Agrochemical Advisory Committee of CORESTA, an association of organisations having scientific research relative to tobacco. Copyright © 2006 John Wiley & Sons, Ltd.
Hypothesized and found mechanisms for potentiation of bradykinin actions
Authors: Mueller Sylvia , Paegelow Inge , Reissmann Siegmund 
Published: January 2006

AbstractPotentiation of hormone actions can occur by different mechanisms, including inhibition of degrading enzymes, interaction with the hormone receptor leading to stabilization of bioactive conformation or leading to receptor homo‐ and hetero‐oligomerization, receptor phosphorylation and dephosphorylation or can occur by directly influencing the signal transduction and ion channels. In this review the potentiation of bradykinin actions in different systems by certain compounds will be reviewed. Despite many long years of experimental research and investigation the mechanisms of potentiating action remain not fully understood. One of the most contradictory findings are the distinct differences between the inhibition of the angiotensin I‐converting enzyme and the potentiation of the bradykinin induced smooth muscle reaction. Contradictory findings and hypothesized mechanisms in the literature are discussed in this review and in some cases compared to own results. Investigation of potentiating actions was extended from hypotension, smooth muscle reaction and cellular actions to activation of immunocompetent cells. In our opinion the potentiation of bradykinin action can occur by different mechanisms, depending on the system and the applied potentiating factor used.
Effect of elastic compression stockings on oedema prevention in healthy controls evaluated by a three‐dimensional measurement system
Authors: Hirai M. , Nukumizu Y. , Kidokoro H. , Hayakawa N. , Iwata H. , Nishikimi N. , Sho K. , Tsujisaka T. , Komatsubara R. 
Published: January 2006

Background/aims: The degree of oedema may differ at various sites on the leg. This study evaluated the degree of oedema at the calf, ankle and foot using a three‐dimensional measurement system.Methods: By three‐dimensional measurement system using the grid pattern projection method, the effects of four different types of elastic compression stockings on oedema prevention were compared in healthy subjects.Results: Without stockings, a significant increase in the circumference and volume was seen at the ankle and foot in the evening compared with morning values. The average increase in circumference was greater at the foot than that at the ankle. A significant increase in circumference and volume in the evening after a day without stockings disappeared when elastic compression stockings were worn during the day. The coefficient of variation was greater for measurements at the foot than for those at the calf and ankle.Conclusion: Oedema develops easily in order of the foot, the ankle and the calf in healthy populations. Elastic stockings, even with a pressure as low as 8 mmHg, are effective on oedema prevention. In measurement at the foot, further developments are necessary to improve this system.
Mid‐infrared spectroscopy on skin using a silver halide fibre probe in vivo
Authors: Ring A. , Schreiner V. , Wenck H. , Wittern K. P. , Küpper L. , Keyhani R. 
Published: January 2006

Background/aim: Mid‐infrared spectroscopy is a versatile method for in vivo investigation of skin after topical treatment with skin care products.Methods: FTIR‐spectrometer (Bruker Optics) with a flexible silver halide fibre probe (Infrared Fiber Sensors).Results: Absorbance spectra from 700 to 3000 cm−1 have been recorded to gain information about proteins (amide‐I and amide‐II vibrations at 1650 and 1550 cm−1), esters (1740 cm−1), carboxylic acid (1710 cm−1), polyalcohols (1050 cm−1) and hydrocarbons (CHn vibrations at 2800–3000 cm−1).Conclusions: Using the particular light guide, we were able to measure for the first time the effects of lip care products on lips directly. Furthermore, water binding and glycerol content of the skin could be determined simultaneously, as well as the replenishment of lipids by lipid‐enriched bath oil.
Oral glucose load inhibits circulating ghrelin levels to the same extent in normal and obese children
Authors: Baldelli R. , Bellone S. , Castellino N. , Petri A. , Rapa A. , Vivenza D. , Bellone J. , Broglio F. , Ghigo E. , Bona G. 
Published: January 2006

SummaryObjective  The presence of both the GH secretagogue (GHS) receptor and ghrelin in the pancreas indicates an involvement of this hormone in glucose metabolism. Ghrelin secretion is increased by fasting and energy restriction, decreased by food intake, glucose load, insulin and somatostatin in normal adults; however, food intake is not able to inhibit circulating ghrelin levels in children, suggesting that the profile of ghrelin secretion in children is different from that in adults. Moreover, how ghrelin secretion is regulated in childhood as a function of fat mass is still unclear.Design and subjects  We studied the effect of oral glucose load (75 g solution orally) on circulating total ghrelin levels in 14 obese children (group A, four boys and 10 girls, aged 9·3 ± 2·3 years) and 10 lean children (group B, five boys and five girls, aged 9·7 ± 3·8 years).Measurements  In all the sessions, blood samples were collected every 30 min from 0 up to +120 min. GH, insulin and glucose levels were assayed at each time point.Results  Glucose peaks following an oral glucose tolerance test (OGTT) in groups A and B were similar; however, both basal and OGTT‐stimulated insulin levels in group A were higher than in group B (P < 0·05). Basal total ghrelin levels in group A (281·3 ± 29·5 pg/ml) were lower (P < 0·0005) than in group B (563·4 ± 81·5 pg/ml). In both groups A and B, the OGTT inhibited total ghrelin levels (P < 0·005). In terms of absolute values, total ghrelin levels in group A were lower (P < 0·0005) than those in group B at each time point after glucose load. The percentage nadir in total ghrelin levels recorded in group A (−25% at 90 min) was similar to that recorded in group B (−31% at 120 min). Total ghrelin levels were negatively associated with BMI (r = 0·5, P < 0·005) but not with glucose or insulin levels.Conclusion  Ghrelin secretion is reduced in obese children. It is, however, equally sensitive in both obese and lean children to the inhibitory effect of oral glucose load.
Daphnia community analysis in shallow Kenyan lakes and ponds using dormant eggs in surface sediments
Authors: MERGEAY JOACHIM , DECLERCK STEVEN , VERSCHUREN DIRK , MEESTER LUC DE 
Published: January 2006

Summary1. Water fleas of the genus Daphnia are considered rare in tropical regions, and information on species distribution and community ecology is scarce and anecdotal. This study presents the results of a survey of Daphnia species distribution and community composition in 40 standing waterbodies in southern Kenya. The study sites cover a wide range of tropical standing aquatic habitats, from small ephemeral pools to large permanent lakes between approximately 700 and 2800 m a.s.l. Our analysis combines data on Daphnia distribution and abundance from zooplankton samples and dormant eggs in surface sediments.2. Nearly 70% (27 of 40) of the sampled waterbodies were inhabited by Daphnia. Although their abundance in the active community was often very low, this high incidence shows that Daphnia can be equally widespread in tropical regions as in temperate regions.3. Analysis of local species assemblages from dormant eggs in surface sediments was more productive than snapshot sampling of zooplankton communities. Surface‐sediment samples yielded eight Daphnia species in total, and allowed the detection of Daphnia in 25 waterbodies; zooplankton samples revealed the presence of only four Daphnia species in 16 waterbodies.4. Daphnia barbata, D. laevis, and D. pulex were the most frequently recorded and most abundant Daphnia species. Canonical correspondence analysis of species–environment relationships indicates that variation in the Daphnia community composition of Kenyan waters was best explained by fish presence, temperature, macrophyte cover and altitude. Daphnia barbata and D. pulex tended to co‐occur with each other and with fish. Both species tended to occur in relatively large (>10 ha) and deeper (>2 m) alkaline waters (pH 8.5). Daphnia laevis mainly occurred in cool and clear, macrophyte‐dominated lakes at high altitudes.