bluuebunny/crossref_metadata_2025_split huggingface dataset:
Toxicity of a formulation of the insecticide indoxacarb to the tarnished plant bug, Lygus lineolaris (Hemiptera: Miridae), and the big‐eyed bug, Geocoris punctipes (Hemiptera: Lygaeidae)
Authors: Tillman P Glynn , Hammes Glenn G , Sacher Matthew , Connair Michael , Brady E Angela , Wing Keith D 
Published: August 2002

AbstractIndoxacarb is a new oxadiazine insecticide that has shown outstanding field insecticidal activity. The toxicity of a 145 g litre−1 indoxacarb SC formulation (Steward™) was studied on the tarnished plant bug Lygus lineolaris and the big‐eyed bug Geocoris punctipes. Both insect species responded very similarly to indoxacarb in topical, tarsal contact and plant feeding toxicity studies. The topical LD50 of the formulation was c 35 ng AI per insect for both species. Prolonged tarsal contact with dry indoxacarb residues did not result in mortality for either insect species. However, both species were susceptible to feeding through dried residues of indoxacarb after spraying on young cotton plants. Feeding on water‐washed plants resulted in lower mortality than that observed with unwashed plants, and toxicity declined even more dramatically after a detergent rinse, indicating that much of the indoxacarb probably resides on the cotton leaf surface or in the waxy cuticle. These results were corroborated by HPLC–mass spectrometry measurements of indoxacarb residues on the plants. Greater mortality for both species was observed in a higher relative humidity environment. Higher levels of accumulated indoxacarb and its active metabolite were detected in dead G punctipes than in L lineolaris after feeding on sprayed, unwashed plants. When female G punctipes ate indoxacarb‐treated Heliothis zea eggs, there was significant toxicity. However, only c 15% of the females consumed indoxacarb‐treated eggs, and the rest of the females showed a significant diminution of feeding in response to the insecticide. Cotton field studies have shown that indoxacarb treatments at labelled rates lead to a dramatic decline in L lineolaris, with negligible declines in beneficial populations. A major route of intoxication of L lineolaris in indoxacarb‐treated cotton fields thus appears to be via oral, and not cuticular, uptake of residues from treated cotton plants. The mechanisms for selectivity/safety for G punctipes are currently under investigation and may be a combination of differential feeding behavior and diminution of feeding by females exposed to indoxacarb‐treated eggs.© 2001 Society of Chemical Industry
Inhibition of intestinal motility by methanol extracts of Hibiscus sabdariffa L. (Malvaceae) in rats
Authors: Salah A. M. , Gathumbi J. , Vierling W. 
Published: August 2002

AbstractThe methanol extracts of Hibiscus sabdariffa (p < 0.01) showed a significant dose dependent relaxant effect (IC50 = 350 μM) on rat ileal strip comparable to the effect shown by nifedipin and papaverine as reference compounds. Similarly, the extract when administered intraperitoneally significantly (p < 0.05–0.01) reduced the intestinal transit (13%–35%) in rats (IC50 = 250 μM). The extracts (40% ± 04%) and nifedipin (51% ± 05%) also potentiated the diarrhoea inducing effect of castor oil (IC50 = 350 μM). It is postulated that these effects are possibly generated by constituents such as quercetin and eugenol via a Ca2+ channel modulated mode of action. Copyright © 2002 John Wiley & Sons, Ltd.
Thermodynamic molecular switch in sequence‐specific hydrophobic interactions
Authors: Chun Paul W. 
Published: August 2002

AbstractThis communication will demonstrate the existence of a thermodynamic molecular switch in the pairwise, sequence‐specific hydrophobic interaction of Ile–Ile, Leu–Ile, Val–Leu, or Ala–Leu over the temperature range of 273–333 K reported by Nemethy and Scheraga in 1962. Based on Chun's development of the Planck–Benzinger methodology, the change in inherent chemical bond energy at 0 K, ΔH°(T0), is 3.0 kcal mol−1 for Ile–Ile, 2.4 for Leu–Ile, 1.8 for Val–Leu, and 1.2 kcal mol−1 for Ala–Leu. The value of ΔH°(T0) decreases as the length of the hydrophobic side chain decreases. It is clear that the strength and stability of the hydrophobic interaction is determined by the packing density of the side chains, with Ala–Leu being the most stable. At 〈Tm〉, the thermal agitation energy, \documentclass{article}\pagestyle{empty}\begin{document}$\int^{T}_{0}\Delta Cp^{\circ}(T)\,dT$\end{document}, is about five times greater than ΔH°(T0) in each case. Additionally, the thermal agitation energy for the same series, evaluated at 〈Tm〉, decreases in the same order, that is, as the length of the side chain decreases. This pairwise, sequence‐specific hydrophobic interaction is highly similar in its thermodynamic behavior to that of other biological systems, except that the negative Gibbs free energy change minimum at 〈Ts〉 occurs at a considerably higher temperature, 355 K compared to about 300 K. The melting temperature, 〈Tm〉, is also high, 470 K compared to 343 K in a biological system. The implication is that the negative Gibbs free energy minimum at a well‐defined 〈Ts〉 has it origin in the hydrophobic interactions, which are highly dependent on details of molecular structure. In addition to the four specific dipeptide interactions described, we have shown in our unpublished work the existence of a thermodynamic molecular switch in the interactions of 32 dipeptides wherein a change of sign in ΔCp°(T)reaction leads to a true negative minimum in the Gibbs free energy of reaction, and hence, a maximum in the related Keq. Indeed, all interacting biological systems that we have thus far examined using the Planck–Benzinger approach point to the universality of thermodynamic molecular switches. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001
Molecular determinants of recognition and activation at GABAA/benzodiazepine receptors
Authors: Filizola Marta , Harris Danni L. 
Published: August 2002

AbstractBenzodiazepines (BDZ) are among the most widely prescribed drugs known to date. However, their broad spectrum of behavioral activity and lack of specificity circumscribe their effectiveness as drugs. With the goal of designing more selective benzodiazepine receptor ligands, Dr. Loew's research group has contributed to literature over the years with both experimental and computational studies. We report here a summary of the most recent computational work carried out in our laboratory on 21 structurally diverse benzodiazepine receptor ligands, using as a data set their in‐house experimental results of activity at the anxiolytic, sedative, and hyperphagic endpoints. The chemical and geometric determinants common to the overlapping binding regions of benzodiazepine agonists, antagonists, and inverse agonists were identified at each of these three behavioral endpoints. The three resulting 3D pharmacophores did not encompass all the molecular requirements for recognition and activation of GABAA/BDZ receptors. They provided instead a means of obtaining accurate bioactive conformations for use in statistical studies, such as quantitative structure‐activity relationship and multivariate discriminant analyses. These studies can serve as a guide to predict both ligand affinities and activities. In the present work, multivariate discriminant analysis of global physicochemical properties is performed to provide new hypotheses for activation selectivity at the sedation endpoint. Although this analysis relies on a relatively small set of compounds, its results can still aim at compound screening and future identification of novel selective benzodiazepine receptor ligands. © 2002 John Wiley & Sons, Inc. Int J Quantum Chem, 2002
Mg(H2O)62+–π(cytosine) interactions in a DNA dodecamer*
Authors: Magnuson Eric C. , Koehler Jessica , Lamm Gene , Pack George R. 
Published: August 2002

AbstractIn a recent investigation we performed extensive Monte Carlo calculations on the sequence‐specific binding of hydrated magnesium ions to DNA. One of the DNA models considered used coordinates from a high‐resolution crystal structure of the dodecamer duplex d(CGCGAATTCGCG)2 in which a hydrated magnesium ion is outer‐sphere‐coordinated to the dodecamer. In analogy with cation–π interactions in proteins, it has been suggested that the local base unstacking observed in this structure is due to similar interactions between cytosine rings and a nearby magnesium ion. As our (and most) Monte Carlo and molecular dynamics simulations of cation–DNA interactions rely only on the electrostatic and Lennard–Jones (6–12) components of standard force fields to describe such situations, we undertook a detailed ab initio study of selected cation–π interactions in this crystal structure to gauge their strength. The results of this investigation involving the 6‐31G*, 6‐31+G*, and 6‐311++G** basis sets at the restricted Hartree–Fock, Møller–Plesset second‐order perturbation and density functional levels are presented here within the context of previous cation–π studies. We find that, for this particular crystal structure, the average binding energy between the hydrated magnesium ion and one of the three nearest cytosine bases is about −1.8±1.0 kcal/mol. We therefore rule out these specific cation–π interactions between a hydrated magnesium ion and cytosine rings as the cause of the observed base unstacking. © 2002 John Wiley & Sons, Inc. Int J Quantum Chem, 2002
Electronic structure of some adenosine receptor antagonists: I. Equilibrium geometries, charge density distributions, and substituent effects
Authors: Moustafa H. , El‐Sawy K. M. , Hilal Rifaat 
Published: August 2002

AbstractAb initio molecular orbital calculations were implemented to investigate the variation of the electronic structure of a series of different xanthine derivatives. MP2(full)/6‐31G calculations have been carried out and used to investigate the geometric features of the studied compounds. Alkyl xanthines studied in the present work are highly polarized with the σ and π frameworks polarized in opposite directions. This polarization is sensitive to substitution. The trend observed for the variation of dipole moment with substitution is interesting. Thus, electron‐withdrawing substituents lower the magnitude of the dipole moment, which reaches its smallest value in the case of CF3 substituent. The NO2 group not only reduces the dipole moment but it also inverts its direction as well. The effect of the basis set on these geometric features has been investigated through implementation of polarization function in MP2(full)/6‐31G/6‐311G** calculations, where it was found that inclusion of the polarization function led to a noticeable redistribution of the charge density. Thus, charge density that was originally accumulated on the atomic centers is redistributed into the bonding regions and this is the reason for the smaller net charges and the larger bond orders predicted at the 6‐311G** level. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002
Theoretical calculation of activation energy barrier from vibrational frequencies for the reaction of O (3P) with CHFCl
Authors: Zhou Zhengyu , Cheng Xueli , Fu Aiping , Du Dongmei 
Published: August 2002

AbstractThe reaction of the oxygen atom with the chlorofluoromethyl radical has been investigated fully by the B3LYP method at the 6‐311++G** basis set level. Two new approaches of the adiabatic (actual) activation energy between all of the intermediates and transition states (TSs) are calculated using the computed frequencies. TSs are activated species: When intermediates agitated spectrographically, the TSs come into being. So the vibrational quantum number ν must be taken into account, and the agitated radicals can be considered as a whole to calculate the adiabatic activation energy, or the potential energy barrier. All IMs and TSs are assigned to their spectroscopic terms to determine the vibrational quantum numbers. This appears to be a good way to estimate activation energy barriers of all reaction channels. © 2002 Wiley Periodicals, Inc.; DOI 10.1002/qua.2002;10126
Closed‐form rectangular atomic wave functions of an N‐dimensional atom
Authors: Lo Shun S. , Morales Daniel A. 
Published: August 2002

AbstractA closed‐form expression has been derived to obtain the N‐dimensional rectangular atomic wave functions. The wave functions can be obtained straightforwardly with the knowledge of the angular momentum quantum numbers and the dimension and there is no need to employ recursive methods as in previous works. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem 88: 263–274, 2002
Radical addition to the vinyl CC bond: Quantum chemistry model of the reaction
Authors: Sokolov Alexey V. 
Published: August 2002

AbstractTransition states of radical addition of C and O centered radicals to vinyl monomers were studied by MNDO UHF. Linear relationships between activation barriers and the enthalpies of addition were found in all reaction series. To expose factors of reactivity, calculated activation barriers were subjected to energy partitioning procedure, and an attempt was made to correlate those parts with monomolecular and bimolecular indexes of reactivity (such as deformation energies of monomers, CT‐energies, etc). Shown that a satisfactory 2‐parameter linear correlation can be built. Problems of PMO theory application to considered class of reactions were discussed and alternative method of calculation of CT‐energies by using monomolecular parameters proposed. Resulting scheme of reactivity applied to existing experimental data on reactivity in radical addition reactions, optimized parameters of large group of reagents tabulated. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002
Bounds for the total π‐electron energy
Authors: Morales Daniel A. 
Published: August 2002

AbstractUpper and lower bounds for the total π‐electron energy of conjugated hydrocarbons are found in terms of the number of carbon atoms, number of carboncarbon bonds, and the determinant of the adjacency matrix of the molecular graph. From these results and the application of some theorems concerning inequalities, we have been able to express those bounds in terms of spectral moments, up to the fourth. In the particular case of benzenoids, the bounds can be expressed solely in terms of the number of vertices and edges of the graph. It is shown that the upper bounds found are better than those of McClelland and those recently reported by Koolen et al. (Chem Phys Lett 2000, 320, 213). © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002
Spectral density distribution moments of a Hamiltonian of N coupled Morse oscillators: The large‐N limit
Authors: Bancewicz Małgorzata 
Published: August 2002

AbstractThe expressions for moments of spectral density distribution of a Hamiltonian representing a system of N coupled Morse oscillators are reduced to the large‐N limit. The effect of the values of coupling constants on the spectral density distribution is analyzed. For the values of coupling constants within the pertinent range for real molecules, the relations between moments appear to be close to those for a Gaussian distribution. Outside this range, the deviations from the normal distribution are substantial. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002
Theoretical analysis of pyrrole anions addition to carbon disulfide and carbon dioxide
Authors: Kobychev Vladimir B. , Vitkovskaya Nadezhda M. , Zaytseva Irina L. , Larionova Elena Yu. , Trofimov Boris A. 
Published: August 2002

AbstractQuantum chemical analysis (MP2/6‐31+G*) of the pyrrole anions addition to carbon disulfide and the substitution effects therein shows that pyrrole‐2 (5)‐carbodithioates are thermodynamically the most stable compounds, while 1‐isomer obtained from the unsubstituted pyrrole is likely a kinetic product. Steric hindrances destabilize N‐adducts when a methyl substituent appears in a 2(5) position and the 2,5‐dimethyl‐1‐pyrrolecarbodithioate anion turns out to be even less stable than the 2,5‐dimethyl‐3‐pyrrolecarbodithioate anion. By contrast, pyrrole‐1‐carboxylates are calculated to be the most stable adducts of CO2 with pyrrole anions. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002
Polymorphism of hydrogen bonding in the short double helixes of oligonucleotides: Semiempirical quantum chemical study
Authors: Kabanov Artem V. , Komarov Vladislav M. 
Published: August 2002

AbstractThe origin of heterogeneity of nucleotide steps geometry in short double helixes is studied theoretically. By using the semiempirical MNDO/PM3 technique, the stability of “propeller‐like” and “step‐like” forms of base H‐pairing is examined in the structure of oligonucleotide duplexes of different types. The influence of end effects on the process of nucleotides packing, as well as the dependence of duplex curvature on the nature of bonded oligonucleotides, are examined. It is concluded that the structural polymorphism of base pairs most likely determines the unique packing of complementary pairs and their flexibility in DNA structure. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002
Theoretical investigations of 1,4‐butanediol and 2‐butene‐1,4‐diol cyclodehydration using postprocessing visualization of quantum chemical calculation data
Authors: Fleisher M. , Stonkus V. , Leite L. , Lukevics E. 
Published: August 2002

AbstractCyclodehydration of 1,4‐butanediol and 2‐butene‐1,4‐diol to the corresponding cyclic ethers was studied using the AM1 semiempirical method. It was established that the cyclodehydration reaction of 1,4‐butenediol and 2‐butene‐1,4‐diol is effected by converting of semicyclic conformers in the presence of acidic and basic active centers. The calculation results indicate that a concerted mechanism is probably realized in the cyclodehydration of both diols, while the sequences of the predicted steps in the cyclodehydration reaction for 1,4‐butanediol and 2‐butene‐1,4‐diol are different. The calculated reaction heats for 1,4‐butanediol and 2‐butene‐1,4‐diol transformations are −184.029 and −308.746 kcal/mol, respectively. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002
Preopening of the DNA base pairs
Authors: Kryachko Eugene S. , Volkov Sergey N. 
Published: August 2002

AbstractThe lower‐energy stable structures of the A⋅T base pair are revealed under a search of its potential energy surface in the vicinity of its Watson–Crick configuration performed at the PM3 computational level. Their properties and the mutual position of the nucleic acid bases A and T in these structures allow to partition them into three classes: partially preopened, stretched, and fully preopened. The preferable monohydration sites of the preopened, stretched, and fully preopened pairs are also determined. It is demonstrated, first, that the monohydration of the A⋅T pair at particular sites favors a base pair preopeness and, second, that a binding of the water molecule to the preopened A⋅T base pair on the major groove side enhances its stabilization. It is also shown that water molecule placing in the vicinity of the central H bond of the A⋅T pair significantly facilitates its preopening. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 82: 193–204, 2001
Theoretical studies of cyclopropylsilylenes: The structures and stability of cyclopropylsilylene C3H5SiH
Authors: Feng Shengyu , Feng Dacheng 
Published: August 2002

AbstractAb initio molecular orbital calculations at the G2(MP2) level have been carried out on cyclopropylsilylene C3H5SiH. Four equilibrium structures were located. Like H2Si, the ground state of C3H5SiH is singlet and the triplet is the low‐lying excited state. The singlet–triplet separation energy is 127.9 kJ/mol. The cis‐trans isomerization path of singlet cyclopropylsilylene was investigated by intrinsic reaction coordinate (IRC) calculations. The calculations show that no gauche conformers exist along the potential energy curve of the cis‐trans isomerization and the isomerization happens with a barrier of 30.1 kJ/mol. Changes (ΔH and ΔG) in thermodynamic functions, equilibrium constant K(T), and A factor and reaction rate constant k(T) in Eyring transition state theory of the cis‐trans isomerization were also calculated. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001
Importance of frontier orbital interactions in addition reaction of water to disilene
Authors: Takahashi Masae , Veszprémi Tamás , Kira Mitsuo 
Published: August 2002

AbstractAddition mechanisms of water to disilene were investigated in detail using the high level ab initio molecular orbital (MO) theory. We have found that the search for transition states by ab initio MO calculations combined with the frontier MO theory provides a good perspective view of the mechanisms of the reaction of disilenes and water. The initial electrophilic and nucleophilic interactions of the water with disilene give the corresponding weak complexes, CE and CN, which leads to the next nucleophilic and electrophilic attack of the water part, respectively. The latter pathway requires an antarafacial approach, while the former pathway proceeds via suprafacial addition. Whereas in the model disilene–water addition reaction, the pathway from CE is more favorable than the pathway from CN, the stereochemical ambiguity of the addition reactions found experimentally may be explained by the competition of the two pathways. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem 84: 192–197, 2001
Combined computational and experimental investigations on the diastereoselective hydrogenation of steroids by chiral oxazaborolidine
Authors: Göndös Gy. , Pálinkó I. 
Published: August 2002

AbstractIn this work the results of semiempirical quantum chemical calculations are described that support experimental findings applying the methyl derivative of oxazaborolidine‐BH3 chiral complex for the reduction of a number of pregnane derivatives (3α‐hydroxy‐5β‐pregnane‐20‐one, 3α,17α‐dihydroxy‐5β‐pregnane‐20‐one, 3α,21‐dihydroxy‐5β‐pregnane‐20‐one, and 3α,17α,21‐trihydroxy‐5β‐pregnane‐20‐one). Calculations were performed by the MNDO method. The reactants, the products, the assumed transition states, as well as the assumed intermediate structures were optimized without any constraints. Calculations were able to reproduce the observed activity sequence and explain the experimental finding that the thermodynamically less stable isomer is formed preferentially. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem 84: 253–258, 2001
Gas‐phase acidity of proline from density functional computations
Authors: Marino T. , Russo N. , Tocci E. , Toscano M. 
Published: August 2002

AbstractDensity functional computations using the B3LYP hybrid potential coupled with the extended 6‐311++G** basis set were performed to evaluate gas‐phase acidity of proline α‐amino acid. The computed value of gas‐phase acidity is 1403.8 kJ/mol in good agreement with the experimental counterpart (1395.0±13.8 kJ/mol) and is referred to the deprotonated species deriving from the first relative minimum of neutral proline characterized by the exo ring conformation with the carboxyl group in cis position. The most stable neutral proline isomer gives rise to a species for which the gas‐phase acidity value (1384.5 kJ/mol) is also close to the experimental data. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem 84: 264–268, 2001