bluuebunny/crossref_metadata_2025 huggingface dataset:
Unproductive cleavage and the inactivation of protease‐activated receptor‐1 by trypsin in vascular endothelial cells
Authors: Nakayama Tetsuzo , Hirano Katsuya , Shintani Yoshinobu , Nishimura Junji , Nakatsuka Akio , Kuga Hirotaka , Takahashi Shosuke , Kanaide Hideo
Published: January 2003

Using fura‐2 fluorometry of [Ca2+]i in response to thrombin, trypsin and protease‐activated receptor activating peptides (PAR‐APs), we determined whether trypsin cleaves protease‐activated receptor 1 (PAR1) and activates it in the endothelial cells of the porcine aortic valves and human umbilical vein.

Once stimulated with thrombin, the subsequent application of trypsin induced a [Ca2+]i elevation similar to that obtained without the preceding stimulation with thrombin in the valvular endothelial cells. However, the preceding stimulation with trypsin abolished the subsequent response to thrombin, but not to bradykinin or substance P.

The response to PAR1‐AP (SFLLRNP) was significantly (P<0.05) reduced by the preceding stimulation with thrombin and PAR1‐AP in the valvular endothelial cells, while, importantly, it remained unaffected by the preceding stimulation with either trypsin or PAR2‐AP (SLIGRL). The response to PAR2‐AP was reduced by the preceding stimulation with trypsin and PAP2‐AP. PAR1‐AP attenuated the subsequent responses not only to thrombin and PAR1‐AP but also to trypsin and PAR2‐AP, while PAR2‐AP specifically attenuated the subsequent responses to trypsin and PAR2‐AP.

In human umbilical vein endothelial cells, a higher affinity PAR1‐AP (haPAR1‐AP) (Ala‐pF‐Arg‐Cha‐HArg‐Tyr‐NH2) specifically attenuated the responses to thrombin but not trypsin. On the other hand, the response to haPAR1‐AP was significantly (P<0.05) attenuated by the preceding stimulation with thrombin but not trypsin.

In conclusion, trypsin cleaved PAR1 but did not activate it in the endothelial cells. Moreover, the trypsin‐cleaved PAR1 was no longer responsive to thrombin.

British Journal of Pharmacology (2003) 138, 121–130. doi:10.1038/sj.bjp.0705008
Butyrylcholinesterase and acetylcholinesterase activity and quantal transmitter release at normal and acetylcholinesterase knockout mouse neuromuscular junctions
Authors: Minic Jasmina , Chatonnet Arnaud , Krejci Eric , Molgó Jordi
Published: January 2003

The present study was performed to evaluate the presence and the physiological consequences of butyrylcholinesterase (BChE) inhibition on isolated phrenic‐hemidiaphragm preparations from normal mice expressing acetylcholinesterase (AChE) and BChE, and from AChE‐knockout mice (AChE−/−) expressing only BChE.

Histochemical and enzymatic assays revealed abundance of AChE and BChE in normal mature neuromuscular junctions (NMJs).

In normal NMJs, in which release was reduced by low Ca2+/high Mg2+ medium BChE inhibition with tetraisopropylpyrophosphoramide (iso‐OMPA) or bambuterol decreased (∼50%) evoked quantal release, while inhibition of AChE with fasciculin‐1, galanthamine (10, 20 μM) or neostigmine (0.1–1 μM) increased (50–80%) evoked quantal release. Inhibition of both AChE and BChE with galanthamine (80 μM), neostigmine (3–10 μM), O‐ethylS‐2‐(diisopropylamino)ethyl‐methylphosphono‐thioate (MTP) or phospholine decreased evoked transmitter release (20–50%).

In AChE−/− NMJs, iso‐OMPA pre‐treatment decreased evoked release.

Muscarinic toxin‐3 decreased evoked release in both AChE−/− and normal NMJs treated with low concentrations of neostigmine, galanthamine or fasciculin‐1, but had no effect in normal NMJs pretreated with iso‐OMPA, bambuterol, MTP and phospholine.

In normal and AChE−/− NMJs pretreatment with iso‐OMPA failed to affect the time course of miniature endplate potentials and full‐sized endplate potentials.

Overall, our results suggest that inhibition or absence of AChE increases evoked quantal release by involving muscarinic receptors (mAChRs), while BChE inhibition decreases release through direct or indirect mechanisms not involving mAChRs. BChE apparently is not implicated in limiting the duration of acetylcholine action on postsynaptic receptors, but is involved in a presynaptic modulatory step of the release process.

British Journal of Pharmacology (2003) 138, 177–187. doi:10.1038/sj.bjp.0705010
Pertussis toxin sensitive and insensitive effects of adenosine and carbachol in murine atria overexpressing A1‐adenosine receptors
Authors: Neumann Joachim , Boknik Peter , Matherne G Paul , Lankford Amy , Schmitz Wilhelm
Published: January 2003

It was investigated how A1‐adenosine receptor overexpression alters the effects of carbachol on force of contraction and beating rate in isolated murine atria. Moreover, the influence of pertussis toxin on the inotropic and chronotropic effects of adenosine and carbachol in A1‐adenosine receptor overexpressing atria was studied.

Adenosine and carbachol alone exerted negative inotropic and chronotropic effects in electrically driven left atrium or spontaneously beating right atrium of wild‐type mice.

These effects were abolished or reversed by pre‐treatment of animals with pertussis toxin which can interfere with signal transduction through G‐proteins.

Adenosine and carbachol exerted positive inotropic but negative chronotropic effects in atrium overexpressing A1‐adenosine receptors from transgenic mice.

The positive inotropic effects of adenosine and carbachol were qualitatively unaltered whereas the negative chronotropic effects were abolished or reversed in atrium overexpressing A1‐adenosine receptors after pre‐treatment by pertussis toxin.

Qualitatively similar effects for adenosine and carbachol were noted in the presence of isoprenaline, β‐adrenoceptor agonist.

It is concluded that overexpression of A1‐adenosine receptors also affects the signal transduction of other heptahelical, G‐protein coupled receptors like the M‐cholinoceptor in the heart. The chronotropic but not the inotropic effects of adenosine and carbachol in transgenic atrium were mediated via pertussis toxin sensitive G‐proteins.

British Journal of Pharmacology (2003) 138, 209–217. doi:10.1038/sj.bjp.0705012
Restoration of chronic‐ Δ9‐THC‐induced decline in sexuality in male rats by a novel benzoflavone moiety from Passiflora incarnata Linn
Authors: Dhawan Kamaldeep , Sharma Anupam
Published: January 2003

The present study comprised treatment of healthy male rats with Δ9‐tetrahydrocannabinol (THC, 10 mg kg−1, p.o.), and combinations of THC with benzoflavone moiety (BZF, 10 and 20 mg kg−1, p.o.) isolated from Passiflora incarnata Linneaus, over a period of 30 days.

Upon 30‐days chronic administrations, the THC‐treated male rats had a significant loss of libido (mounting behaviour with non‐oestrous female rats), decrease in sperm count, and number of impregnated pro‐estrous female rats.

Co‐administration of BZF (10 and 20 mg kg−1 p.o.) afforded significant protection against the chronic‐THC‐induced decrease in libido, mating performance and fertility during 30‐day experimental regimen. The 20 mg kg−1 dose of BZF exhibited better results.

Upon discontinuation of THC, treatment with BZF (10 and 20 mg kg−1 p.o.) also facilitated the early restoration chronic‐THC‐induced decline in libido, sperm count and sexual fertility within 7 days.

British Journal of Pharmacology (2003) 138, 117–120. doi:10.1038/sj.bjp.0705015
ADP stimulation of inositol phosphates in hepatocytes: role of conversion to ATP and stimulation of P2Y2 receptors
Authors: Dixon C Jane , Hall John F , Boarder Michael R
Published: January 2003

Accumulation of inositol (poly)phosphates (InsPx) has been studied in rat hepatocytes labelled with [3H]inositol. Stimulation with ADP resulted in a significant increase in total [3H]InsPx, whereas 2‐MeSADP had only a small effect and ADPβS was ineffective. UTP and ITP also stimulated substantial increases in [3H]InsPx.

The dose–response curve to ADP was largely unaltered by the presence of the P2Y1 antagonist, adenosine‐3′‐phosphate‐5′‐phosphate (A3P5P). Similarly, inclusion of MRS 2179, a more selective P2Y1 antagonist, had no effect on the dose–response curve to ADP.

The inclusion of hexokinase in the assay reduced, but did not abolish, the response to ADP.

HPLC analysis revealed that ADP in the medium was rapidly converted to AMP and ATP. The inclusion of hexokinase removed ATP, but exacerbated the decline in ADP concentration, leading to increased levels of AMP. 2‐MeSADP was stable in the medium and ATP was largely unaffected.

The addition of the adenylate kinase inhibitor, diadenosine pentaphosphate (Ap5A) significantly reduced the ADP response. HPLC analysis conducted in parallel demonstrated that this treatment inhibited conversion of ADP to ATP and AMP.

Inclusion of the P1 antagonist CGS 15943 had no effect on the dose–response curve to ADP.

These observations indicate that hepatocytes respond to ADP with an increase in inositol (poly)phosphates following conversion to ATP. P2Y1 activation in hepatocytes does not appear to be coupled to inositol 1,4,5‐trisphosphate (Ins(1,4,5)P3) production.

British Journal of Pharmacology (2003) 138, 272–278. doi:10.1038/sj.bjp.0705016
Interaction between cysteines introduced into each transmembrane domain of the rat P2X2 receptor
Authors: Spelta Valeria , Jiang Lin‐Hua , Bailey R Jayne , Surprenant Annmarie , North R Alan
Published: January 2003

ATP‐gated ion channels (P2X receptors) contain two hydrophobic segments that are presumed to span the plasma membrane (TM1 and TM2). Pairs of cysteines were introduced by mutagenesis into the rat P2X2 receptor, one in TM1 one in TM2, at positions where single substitutions have previously been shown to confer sensitivity to methanethiosulfonates. The receptors were expressed in HEK293 cells; interactions between the cysteines were sought by measuring the effects on ionic currents of dithiothreitol and methanethiosulfonates.

Nine pairs gave normally functioning channels: F44C/I328C, F44C/N333C, F44C/L338C, Q37C/I328C, Q37C/N333C, Q37C/T336C, Q37C/L338C, G30C/I328C, G30C/N333C. None formed functionally detectable disulfide bonds.

Currents at the F44C/L338C receptor had time course and ATP‐sensitivity similar to those for the F44C mutation alone. Methyl‐methanethiosulfonate bound to L338C but did not inhibit ionic current. Methyl‐methanethiosulfonate inhibited currents at F44C, but not at F44C/L338C.

Ethylammonium‐methylthiosulfonate inhibited currents at both F44C and L338C, but not at F44C/L338C. It reversed the rapid current deactivation at F44C/L338C.

The results suggest that a methanethiosulfonate binding to L338C prevents binding to F44C; this might indicate proximity of these two residues.

British Journal of Pharmacology (2003) 138, 131–136. doi:10.1038/sj.bjp.0705018
Adrenergic mechanisms in canine nasal venous systems
Authors: Wang Min , Lung Mary A
Published: January 2003

We investigated the adrenergic mechanisms of the two venous systems that drain the nasal mucosa, thereby their exact role in eliciting nasal decongestion. The action of endogenously released noradrenaline and exogenous adrenergic agonists on different segments of the nasal venous systems, i.e. collecting (LCV, SCV) and outflow (SPV) veins of posterior venous system, collecting (ACV) and outflow (DNV) veins of anterior venous system and venous sinusoids of the septal mucosa (SM), were studied. In vitro isometric tension of the vascular segments was measured.

Transmural nerve stimulation (TNS) produced constriction in ACV, DNV and SM, primary constriction followed by secondary dilatation in LCV and SCV and dilatation in SPV. Tetrodotoxin (10−6 M) abolished all responses. Phentolamine (10−6 M), prazosin (10−6 M) and rauwolscine (10−7 M) inhibited the constriction in all venous vessels. Propranolol (10−6 M), atenolol (10−6 M) and ICI 118,551 (10−6 M) inhibited the relaxation in SPV but not in LCV and SCV. Phenylephrine and clonidine constricted whereas dobutamine and terbutaline relaxed all venous vessels dose‐dependently.

These results indicate α1‐, α2‐, β1‐ and β2‐adrenoceptors are present in both venous systems. TNS causes constriction of anterior venous system, venous sinusoids and posterior collecting veins primarily via postjunctional α2‐adrenoceptors but relaxation of posterior outflow vein equally via postjunctional β1‐ and β2‐adrenoceptors. The combined action of the two adrenergic mechanisms can reduce nasal airway resistance in vivo by decreasing vascular capacitance and enhancing venous drainage via the posterior venous system.

British Journal of Pharmacology (2003) 138, 145–155. doi:10.1038/sj.bjp.0705020
Shaker‐type Kv1 channel blockers increase the peristaltic activity of guinea‐pig ileum by stimulating acetylcholine and tachykinins release by the enteric nervous system
Authors: Vianna‐Jorge Rosane , Oliveira Cyntia F , Garcia Maria L , Kaczorowski Gregory J , Suarez‐Kurtz Guilherme
Published: January 2003

A constant intraluminal pressure system was used to evaluate the effects of Kv1 channel blockers on the peristaltic activity of guinea‐pig ileum.

The nortriterpene correolide, a non‐selective inhibitor of all Kv1 sub‐types, causes progressive and sustained reduction of the pressure threshold for eliciting peristaltic contractions.

Margatoxin (MgTX), alpha‐dendrotoxin (α‐DTX) and dendrotoxin‐K (DTX‐K), highly selective peptidyl inhibitors of certain Kv1 sub‐types, cause immediate reduction of the pressure threshold. This effect subsides with time, irrespective of the peptides' concentration in the bath. In preparations pretreated with saturating concentrations of MgTX, correolide further stimulates the peristaltic activity.

Iberiotoxin (IbTX), a selective inhibitor of the high‐conductance Ca2+‐activated K+ (BK) channels, and charybdotoxin (ChTX), which inhibits Kv1.2 and Kv1.3 as well as BK channels, fail to stimulate the peristaltic activity.

Blockade of muscarinic receptors by atropine reduces, and occasionally suppresses the peristaltic activity of guinea‐pig ileum. In atropine‐treated preparations, correolide and MgTX retain their abilities to reduce the pressure threshold and are able to restore the peristaltic reflex in the preparations where this reflex was suppressed by atropine.

The stimulatory effect of correolide and MgTX in atropine‐treated preparations is abolished by subsequent addition of selective antagonists of both NK1 and NK2 receptors.

In conclusion, blockade of Kv1, particularly Kv1.1 channels, increases the peristaltic activity of guinea‐pig ileum by enhancing the release of neurotransmitters at the enteric nervous system. In contrast, stimulation of the myogenic motility by blockade of BK channels does not affect the threshold for the peristaltic reflex.

British Journal of Pharmacology (2003) 138, 57–62. doi:10.1038/sj.bjp.0705023
Inhibition of hEAG1 and hERG1 potassium channels by clofilium and its tertiary analogue LY97241
Authors: Gessner Guido , Heinemann Stefan H
Published: January 2003

We investigated the inhibition of hEAG1 potassium channels, expressed in mammalian cells and Xenopus oocytes, by several blockers that have previously been reported to be blockers of hERG1 channels.

In the whole‐cell mode of mammalian cells, LY97241 was shown to be a potent inhibitor of both hEAG1 and hERG1 channels (IC50 of 4.9 and 2.2 nM, respectively). Clofilium, E4031, and haloperidol apparently inhibited hEAG1 channels with lower potency than hERG1 channels, but they cannot be considered hERG1‐specific.

The block of hEAG1 channels by LY97241 and clofilium was time‐, use‐, and voltage‐dependent, best explained by an open‐channel block mechanism.

Both drugs apparently bind from the intracellular side of the membrane at (a) specific site(s) within the central cavity of the channel pore. They can be trapped by closure of the activation gate.

In inside‐out patches from Xenopus oocytes, hEAG1 block by clofilium was stronger than by LY97241 (IC50 of 0.8 and 1.9 nM, respectively). In addition, hEAG1 block by clofilium was much faster than by LY97241 although there was no difference in the voltage dependence of the on‐rate of block.

Physico‐chemical differences of clofilium and the weak base LY97241 determine the access of the drugs to the binding site and thereby the influence of the recording mode on the apparent block potencies. This phenomenon must be considered when assessing the inhibitory action of drugs on ion channels.

British Journal of Pharmacology (2003) 138, 161–171. doi:10.1038/sj.bjp.0705025
P2Ys go neuronal: modulation of Ca2+ and K+ channels by recombinant receptors
Authors: Boehm Stefan
Published: January 2003

British Journal of Pharmacology (2003) 138, 1–3. doi:10.1038/sj.bjp.0705044
The anti‐relapse compound acamprosate inhibits the development of a conditioned place preference to ethanol and cocaine but not morphine
Authors: Mcgeehan Andrew J , Olive M Foster
Published: January 2003

The effects of the anti‐relapse compound acamprosate (calcium acetylhomotaurinate) on the conditioned rewarding effects of ethanol, cocaine and morphine were studied using the conditioned place preference (CPP) paradigm. During 3 days of drug conditioning, mice were pretreated with saline or acamprosate (30, 100 or 300 mg kg−1 i.p.) 10 min prior to the administration of ethanol (2 g kg−1 i.p.), cocaine (15 mg kg−1 i.p.) or morphine (10 mg kg−1 i.p.), and subsequently confined to one of two distinct conditioning chambers. On the following day, mice were tested for the expression of CPP. Acamprosate dose‐dependently reduced the development of CPP to ethanol and cocaine but not morphine. When tested as the conditioning drug, acamprosate alone produced neither a conditioned place preference nor aversion. These data suggest that acamprosate can suppress the conditioned rewarding effects of ethanol and certain classes of abused substances.

British Journal of Pharmacology (2003) 138, 9–12. doi:10.1038/sj.bjp.0705059
Calcium‐impermeable monovalent cation channels: a TRP connection?
Authors: Nilius Bernd
Published: January 2003

British Journal of Pharmacology (2003) 138, 5–7. doi:10.1038/sj.bjp.0705073
The velocity-scalar cross spectrum of stretched spiral vortices
Authors: O’Gorman P. A. , Pullin D. I.
Published: January 2003

The stretched-spiral vortex model is used to calculate the velocity-scalar cross spectrum for homogeneous, isotropic turbulence in the presence of a mean scalar gradient. The only nonzero component of the cospectrum is that contributed by the velocity component in the direction of the imposed scalar gradient while the quadrature spectrum is identically zero, in agreement with experiment. For the velocity field provided by the stretched-spiral vortex, the velocity-scalar spectrum can be divided into two additive components contributed by the velocity components along the vortex axis, and in the plane normal to this axis, respectively. For the axial velocity field, a new exact solution of the scalar convection-diffusion equation is found exhibiting scalar variation in the direction of the vortex tube axis. An asymptotic expression was found for the cospectrum contributed by this solution and the axial velocity, with the leading order term showing a k−5/3 range. This term is produced by the winding of the initial axial velocity field by the axisymmetric vortex core. The next order term gives a k−7/3 range, and arises from the lowest order effect of the nonaxisymmetric vorticity on the evolution of the axial velocity. Its coefficient can be of either sign or zero depending on the initial conditions. The contribution to the cospectrum from the velocity in the plane of the vortex is also calculated, but no universal high wave number asymptotic form is found. The integrals are evaluated numerically and it is found that the resulting cospectrum does not remain of one sign. Its form depends on the choice of the vortex core velocity profile and time cutoff in the spectral integrals. The one-dimensional cospectrum contributed by the axial velocity is compared with the experimental data of Mydlarski and Warhaft [J. Fluid Mech. 358, 135–175 (1998)].
The permanent electric dipole moments of the B̃ 2Σ+ and X̃ 2Σ+ states of lanthanum imide, LaNH
Authors: Steimle Timothy C. , Bousquet Robert R. , Merer Anthony J. , Rixon Scott J.
Published: January 2003

The optical Stark effect has been measured for the B̃ 2Σ+−X̃ 2Σ+, 301, and 201(P′=3/2) bands of lanthanum imide, LaNH, prepared in a supersonic molecular beam. The permanent electric dipole moment, μ, for the X̃ 2Σ+ state was determined to be 2.53±0.06 D from measurements of the second-order Stark shifts in the B̃ 2Σ+−X̃ 2Σ+, 301 band. (ν3 is the La–N stretching vibration, of symmetry σ+.) The dipole moment in the B̃ 2Σ+ state is too small to be determined from the Stark shifts in this band, but could be determined from the first-order Stark splittings in the P′=3/2 component of the B̃ 2Σ+, 21 bending fundamental (of upper state π symmetry); it was found to be 0.3±0.2 D. A comparison is made with LaO and other isovalent molecules involving Group IIIA atoms.
Ab initio transition state theory calculation of the rate constant for the hydrogen abstraction reaction H2O2+H→H2+HO2
Authors: Tarchouna Y. , Bahri M. , Jaı̈dane N. , Ben Lakhdar Z. , Flament J. P.
Published: January 2003

Large basis set and two levels of ab initio calculation (ROHF and MCSCF) are used to determine the electronic structure of reactants, products, and saddle point involved in the hydrogen abstraction reaction H2O2+H→H2+HO2. The calculated ROHF and MCSCF imaginary frequency ω≠ corresponds to the motion of an hydrogen atom between H2O2 and H and has respectively, a magnitude of 6826.5 and 2909.9 cm−1. Calculated (MP2//ROHF and MP2//MCSCF) values of 8.92 and 7.92 Kcal/mol are, respectively, found for the barrier height of the title reaction. The ab initio results are used with the transition state theory (TST) to evaluate the rate constant kTST(T) over the range of temperature 200⩽T⩽2000 K. Tunneling corrections to kTST(T) are considered through the evaluation of the transmission coefficient by Wigner (W) and zero curvature tunneling (ZCT) methods. Our results show that the calculated rate constants based on the ROHF electronic structure results do not agree with the experimental values. The best agreement with the preferred experimental values measured by Baulch et al. for 300⩽T⩽800 K and with the values measured by Stang and Hampson for 850⩽T⩽2000 K is found for the calculation based on the MCSCF electronic structure results and using the ZCT method to account for tunneling correction to kTST.
Core shell excitation of 2-propenal (acrolein) at the O 1s and C 1s edges: An experimental and ab initio study
Authors: Duflot D. , Flament J.-P. , Walker I. C. , Heinesch J. , Hubin-Franskin M.-J.
Published: January 2003

The carbon and oxygen K-shell spectra of gaseous 2-propenal (acrolein) have been measured using the inner-shell electron energy loss spectroscopy method. Large scale ab initio configuration interaction calculations have been carried out to enable firm assignments of the observed bands. The overall shapes of the spectra are similar to previous low resolution monolayer and multilayer phases NEXAFS spectra recorded by photoabsorption of synchrotron radiation, but the spectral bands are much better resolved than the earlier ones. The spectra are dominated by excitation of π* type states and by interaction between the C=C and C=O π* orbitals.
Study of the benzene⋅N2 intermolecular potential-energy surface
Authors: Lee Soohyun , Romascan Joann , Felker Peter M. , Pedersen Thomas Bondo , Fernández Berta , Koch Henrik
Published: January 2003

The intermolecular potential-energy surface pertaining to the interaction between benzene and N2 is investigated theoretically and experimentally. Accurate intermolecular interaction energies are evaluated for the benzene–N2 van der Waals complex using the coupled cluster singles and doubles including connected triples [CCSD(T)] method and the aug-cc-pVDZ basis set extended with a set of 3s3p2d1f1g midbond functions. After fitting the energies to an analytic function, the intermolecular Schrödinger equation is solved to yield energies, rotational constants, and Raman-scattering coefficients for the lowest intermolecular levels of several benzene–N2 isotopomers. Experimentally, intermolecular Raman spectra of jet-cooled h6- and d6-benzene–N2 measured at 0.03 cm−1 resolution by mass-selective, ionization-detected stimulated Raman spectroscopies are reported. Seven intermolecular bands are assigned for each isotopomer, including transitions involving intermolecular bending and stretching vibrations and internal rotation about the benzene C6 axis. These Raman data, together with measured rotational constants and binding energies obtained by other groups on benzene–N2, agree well with the theoretical results. Such agreement points to the promise of the quantum chemical methodology employed herein in future investigations of larger van der Waals complexes.
Structure of an inhomogeneous fluid mixture: A new weighted density-functional theory within a perturbative approach
Authors: Choudhury Niharendu , Ghosh Swapan K.
Published: January 2003

A simple density-functional approach is developed for an inhomogeneous fluid mixture where the functional Taylor expansion of the perturbative approach has been used along with a nonperturbative weighted density prescription. The functional Taylor expansion of the one-particle direct correlation function (DCF) of the inhomogeneous fluid mixture is truncated at second order in density inhomogeneity and the effect of various higher-order terms is taken into account by evaluating the third-order DCF at an weighted density obtained by using a suitable weight function which obeys certain conditions in the homogeneous limit. The proposed approach uses the two-particle DCFs of the corresponding uniform fluid mixture and their various density derivatives as inputs. The calculated numerical results for the density and concentration profiles of hard sphere mixtures near hard walls for different set of bulk parameters are shown to be in very good agreement with the available simulation data.
Influence of hydrodynamic interaction on the diffusion-controlled reaction kinetics of molecules with highly anisotropic reactivity
Authors: Shushin A. I.
Published: January 2003

In this work we analyze the effect of hydrodynamic interaction (HI) on diffusion-controlled reaction rate of molecules with highly anisotropic reactivity, modeled by small reactive hemispheres around the reactive centers (RCs) on the surfaces of molecules. The effect of the HI (that manifests itself in the coordinate dependence of relative diffusion coefficients) is shown to be mainly determined by the HI at short distances between molecules (where the traditional long distance analysis of the HI is irrelevant) and very sensitive to the local shape of molecules near the RCs. The effect is analyzed within three models of the shape: spherical, non-spherical spheroidal, and non-spherical of truncated-sphere type, with the use of the method of local analysis based on the approximation of the general curvilinear coordinates of pairs of reacting molecules by the Cartesian ones in the region close to the reactive orientations. Simple analytical expressions for the reaction rate are derived, which show that the HI effect can manifest itself in fairly strong (about 3–5 times and larger) reduction of the rate.
Interaction of a spherical particle with linear chains
Authors: Kłos J. , Pakula T.
Published: January 2003

Linear flexible polymers both at low and high concentrations surrounding a single hard sphere are simulated using the cooperative motion algorithm on the face-centered cubic lattice. The excluded-volume condition between different monomers is taken into account and the size ratio q=R/Rg of the sphere radius and the mean radius of gyration of the chains is considered as a parameter. Structure of the system in the vicinity of the sphere is analyzed in comparison with the structure of the bulk solution for a wide range of q. The limiting case of the infinite sphere radius R→∞, i.e., the effect of the neutral wall on the chains, is also presented. The simulations indicate (1) a depletion layer in the neighborhood of the sphere, (2) an enhancement of the chain ends concentration at the particle surface, (3) an enhancement of the chain center-of-mass concentration at some distance from the surface for large q, (4) a penetration of the centers of mass into the sphere for small q, (5) an orientation ordering of the chains in the region of interest.
A general method for implementing vibrationally adiabatic mixed quantum-classical simulations
Authors: Thompson Ward H.
Published: January 2003

An approach for carrying out vibrationally adiabatic mixed quantum-classical molecular dynamics simulations is presented. An appropriate integration scheme is described for the vibrationally adiabatic equations of motion of a diatomic solute in a monatomic solvent and an approach for calculating the adiabatic energy levels is presented. Specifically, an iterative Lanczos algorithm with full reorthogonalization is used to solve for the lowest few vibrational eigenvalues and eigenfunctions. The eigenfunctions at one time step in a mixed quantum-classical trajectory are used to initiate the Lanczos calculation at the next time step. The basis set size is reduced by using a potential-optimized discrete variable representation. As a demonstration the problem of a homonuclear diatomic molecule in a rare gas fluid (N2 in Ar) has been treated. The approach is shown to be efficient and accurate. An important advantage of this approach is that it can be straightforwardly applied to polyatomic solutes that have multiple vibrational degrees-of-freedom that must be quantized.
A Lorentzian function based spectral filter for calculating the energy of excited bound states in quantum mechanics
Authors: Vijay Amrendra
Published: January 2003

In this paper, we study a Lorentzian function based spectral filter suitable for computing highly excited bound states of a quantum system. Using this filter, we have derived an expression for spectral intensities and also implemented a filter diagonalization scheme. We have used a Chebyshev polynomial based series expansion of the filter operator, and this allows us to accomplish a partial resummation of the double series analytically when computing the necessary matrix elements; this saves considerable computational effort. The exponential damping term in the Lorentzian provides a convenient control over the resolution of the computed spectrum in the spectral intensity plot. As a numerical test, we have computed eigenvalues and spectral intensities of a model Hamiltonian in an arbitrary energy window. For situations where eigenvalues are distributed nonuniformly we suggest a computational protocol, which judiciously combines the spectral intensity information with the filter diagonalization method. This protocol is efficient only with the Lorentzian filter studied here.
Inhomogeneous suspensions of rigid rods in flow
Authors: Dhont Jan K. G. , Briels W. J.
Published: January 2003

An expression for the divergence of the stress tensor is derived for inhomogeneous suspensions of very long and thin, rigid rods. The stress tensor is expressed in terms of the suspension flow velocity and the probability density function for the position and orientation of a rod. The expression for the stress tensor includes stresses arising from possibly very large spatial gradients in the shear rate, concentration, and orientational order parameter. The resulting Navier–Stokes equation couples to the equation of motion for the probability density function of the position and orientation of a rod. The equation of motion for this probability density function is derived from the N-particle Smoluchowski equation, including contributions from inhomogeneities. It is argued that for very long and thin rods, hydrodynamic interactions are of minor importance, and are therefore neglected, both in the expression for the stress tensor and in the equation of motion for the above-mentioned probability density function. The thus obtained complete set of equations of motion can be applied to describe phenomena where possibly very large spatial gradients occur, such as phase coexistence under shear flow conditions, including shear-banding, and phase separation kinetics.
Quasirelativistic theory for the magnetic shielding constant. I. Formulation of Douglas–Kroll–Hess transformation for the magnetic field and its application to atomic systems
Authors: Fukuda Ryoichi , Hada Masahiko , Nakatsuji Hiroshi
Published: January 2003

A two-component quasirelativistic theory based on the Douglas–Kroll–Hess (DKH) transformation has been developed to study magnetic properties of molecules. The proposed Hamiltonian includes the relativistic magnetic vector potential in the framework of the DKH theory, and is applicable to the calculations of magnetic properties without further expansion in powers of c−1. By combining with the finite-perturbation theory and the generalized-UHF method, new pictures of the magnetic shielding constant are derived. We apply the theory to calculations of the magnetic shielding constants of He isoelectronic systems, Ne isoelectronic systems, and noble gas atoms. The results of the present theory compare well with those of the four-component Dirac–Hartree–Fock calculations; the differences were within 3%. We note that the quasirelativistic theory that handles the magnetic vector potential at a nonrelativistic level greatly underestimates the relativistic effect. The so-called “picture change” effect is quite important for the magnetic shielding constant of heavy elements. The change in the orbital picture plays a significant role in the valence-orbital magnetic response as well as the core-orbital one. The effect of the finite nucleus is also studied using Gaussian nucleus model. The present theory reproduces the correct behavior of the finite-nucleus effect that has been reported with the Dirac theory. In contrast, the nonrelativistic theory and the quasirelativistic theory with the nonrelativistic vector potential underestimate the finite-nucleus effect.
Quasirelativistic theory for magnetic shielding constants. II. Gauge-including atomic orbitals and applications to molecules
Authors: Fukuda Ryoichi , Hada Masahiko , Nakatsuji Hiroshi
Published: January 2003

Quasirelativistic theory of magnetic shielding constants based on the Douglas–Kroll–Hess transformation of the magnetic potential presented in a previous paper is extended to molecular systems that contain heavy elements. The gauge-including atomic orbital method is adapted to the quasirelativistic Hamiltonian to allow origin-independent calculations. The present theory is applied to the proton and halogen magnetic shielding constants of hydrogen halides and the Hg199 magnetic shielding constants and chemical shifts of mercury dihalides and methyl mercury halides. While the relativistic correction to the magnetic interaction term has little effect on the proton magnetic shielding constants, this correction is a dominant origin of the heavy atom shifts of the magnetic shielding constants of heavy halogens and mercury. The basis set-dependence of mercury shielding constants is quite large in the relativistic calculation; it is important to use the basis functions that are optimized by the relativistic method to properly describe the relativistic effect. The relativistic correction to the magnetic interaction term is quite important for mercury dihalides in which the relativistic effects from mercury and halogen are strongly coupled. Without this correction, we obtain quite incorrect results. The origin of the Hg199 chemical shifts in mercury dihalides is the spin–orbit interaction from heavy halogens. In methyl mercury halides, the paramagnetic shielding term as well as the spin–orbit interaction from heavy halogens dominates the Hg199 chemical shifts.
Angular momentum in solid-harmonic-Gaussian integral evaluation
Authors: Dunlap Brett I.
Published: January 2003

Solid-harmonic derivatives of generalized Gaussian functions—exponential functions of a scalar argument that has no third derivatives with respect to any nuclear coordinate—are evaluated for three, four, and five centers without coupling any of the original angular momenta. Generalized Gaunt coefficients arise in this approach. They represent scalar coupling of all angular momenta lost from cross differentiation. All formulas are independent of all original angular momenta, which aids the evaluation of all integrals involving n centers at one time. Recurrence relations are given for the 3-j generalized Gaunt coefficient. The methods of Racah are used to obtain the coefficients that transform the generalized Gaunt coefficients into a representation in which the angular momentum lost due to cross differentiation are arbitrarily coupled, and thus show directly that the generalized Gaunt coefficients always represent scalar coupling. More intermediate information can be reused if the coupled generalized Gaunt coefficients are used to evaluate all the integrals involving a given set of centers.
Coherent structures in an energy-enstrophy theory for axisymmetric flows
Authors: Lim Chjan C.
Published: January 2003

The equilibrium statistical mechanics of a version of an energy-enstrophy theory for the axisymmetric Euler equations is solved exactly in the sense that a configurational integral is calculated in closed form. Under the assumption that the energy and the enstrophy (mean squared azimuthal vorticity) are conserved, a long range version of Kac’s spherical model with logarithmic interaction is derived and solved exactly in the zero total circulation case in the standard thermodynamic limit. The spherical model formulation is based on the fundamental observation that the conservation of enstrophy expressed microcanonically is mathematically equivalent to Kac’s spherical constraint. Two-point vorticity correlations are calculated exactly in two qualitatively different phases separated by β̃*=0. Physical interpretations of the results in this paper are obtained and applied to the relaxed end-states of turbulent high Reynolds number round jets. The negative temperature phase is a very high energy (flow rate) and relatively low enstrophy turbulent flow state which has the form of an axially uniform axial round jet plus a long wavelength axial perturbation. The positive temperature phase corresponds to a low energy and high enstrophy (shear) flow state which consists of a disordered vorticity distribution.
Electronic structure of isolated PtX62− (X=F,Cl,Br) dianions
Authors: Sommerfeld Thomas , Feuerbacher Sven , Pernpointner Markus , Cederbaum Lorenz S.
Published: January 2003

The dianions PtCl62− and PtBr62− belong to the small class of doubly charged species whose gas phase photoelectron spectra have been measured and show clearly discernible structures. Here we study the electronic structure of the PtX62− (X=F,Cl,Br) dianions and the associated electron detachment energies theoretically. Relativistic effects including spin–orbit splittings are investigated at the self consistent field level by comparing nonrelativistic all-electron computations with results obtained using the Douglas–Kroll and the Dirac–Fock Hamiltonians as well as relativistic effective core potentials. Electron correlation effects, which are known to substantially influence detachment energies of mono- and dianionic species, are addressed at the configuration interaction and two propagator based levels of theory employing the relativistic effective core potentials. Moreover, we study the repulsive Coulomb barriers of the PtX62− systems within the dianion frozen orbital static approximation. Our findings strongly disagree with the standard textbook molecular orbital diagram of coordination compounds as well as with the tentative assignment of the spectroscopists. In particular, the five highest orbitals of PtCl62− and PtBr62− exhibit almost exclusively ligand character. The theoretical results are explained in terms of the charge distribution within the gas phase dianions, and the impact on assigning the photoelectron spectrum is discussed.
A path integral approach to molecular thermochemistry
Authors: Glaesemann Kurt R. , Fried Laurence E.
Published: January 2003

The calculation of thermochemical data requires accurate molecular energies. When such high accuracy is needed, often a method such as G1, G2, or G3 is used to calculate the energy. These methods rely upon the standard harmonic normal mode analysis to calculate the vibrational and rotational contributions to the energy. We present a method for going beyond the harmonic analysis, which uses path integral Monte Carlo to calculate the vibrational and rotational contributions. Anharmonic effects are found to be as large as 2.5 kcal/mol for the molecules studied. Analytical methods for determining an optimal path discretization are presented. A novel potential energy caching scheme, which greatly improves computational efficiency, is also presented.
Fluid phase transitions at chemically heterogeneous, nonplanar solid substrates: Surface versus confinement effects
Authors: Sacquin Sophie , Schoen Martin , Fuchs Alain H.
Published: January 2003

The phase behavior of a “simple” Lennard-Jones (12,6) fluid confined between planar substrates has been investigated by means of Monte Carlo simulations in the grand canonical ensemble (GCEMC). The interaction of fluid molecules with the upper wall is purely repulsive and attractive with the lower one. A spherical cap of radius ξ is embedded in the surface of the upper wall. The cap also attracts fluid molecules. For ξ=0, that is, in the case of two planar homogeneous substrates, one observes classical prewetting, namely a first-order phase transition from thin to thick films adsorbed on the lower substrate. When ξ≠0, that is, when the upper substrate is decorated with a three-dimensional pattern of finite size, system properties are no longer translationally invariant in any spatial dimension. Thus, the grand potential Ω is not a homogeneous function of degree one in any of its extensive variables which precludes a “mechanical” expression for Ω in terms of stresses and conjugate strains. Therefore, in order to determine the phase behavior through plots of Ω versus chemical potential μ we employ a thermodynamic integration scheme under isothermal conditions (T=const). We observe a partially condensed phase, where the molecules are preferentially adsorbed in the gap between the spherical cap and the lower substrate, associated with either a thin or a thick film adsorbed on the lower substrate.
Molecular dynamics study of cristobalite silica using a charge transfer three-body potential: Phase transformation and structural disorder
Authors: Huang Liping , Kieffer John
Published: January 2003

Structural and dynamic properties of cristobalite silica have been studied using molecular dynamics simulations based on a charge transfer three-body potential model. In this potential model, the directional covalent bonding of SiO2 is characterized by a charge transfer function of the interatomic distance between Si and O atoms, and in the form of Si–O–Si and O–Si–O three-body interactions. The dynamic properties such as infrared spectra and density of states at room and elevated temperatures are in excellent agreement with experiments, and are also consistent with the recently proposed rigid unit modes model. The α- and β-cristobalite crystallographic structures are well reproduced in this model, and the transition between these modifications occurs reversibly and reproducibly in simulations, both as a result of changes in pressure and temperature. The thermally induced transition results in a significantly more disordered β-cristobalite than the pressure-induced β-cristobalite at room temperature. While simulated α-cristobalite exhibits a positive thermal expansion coefficient, it is almost zero for β-cristobalite up to 2000 K and slightly negative at higher temperatures, confirming results from recent x-ray diffraction experiments and other simulations with potential models based on ab initio calculations.
Channel flow induced by wall injection of fluid and particles
Authors: Féraille Thierry , Casalis Grégoire
Published: January 2003

The Taylor flow is the laminar single-phase flow induced by gas injection through porous walls, and is assumed to represent the flow inside solid propellant motors. Such a flow is intrinsically unstable, and the generated instabilities are probably responsible for the thrust oscillations observed in the aforesaid motors. However particles are embedded in the propellants usually used, and are released in the fluid by the lateral walls during the combustion, so that there are two heterogeneous phases in the flow. The purpose of this paper is to study the influence of these particles on stability by comparison with stability results from the single-phase studies, in a plane two-dimensional configuration. The particles are supposed to be chemically inert and of a uniform size. In order to carry out a linear stability study for this flow modified by the presence of particles, the mean particle velocity field is first determined, assuming that only the gas exerts forces on the particles. This field is sought in a self-similar form, which imposes a limit on the size of the particles. However, the particle mass concentration cannot be obtained in a self-similar form, but can only be described by a partial differential equation. The mean flow characteristics being determined, the spectrum of the discretized linear stability operator shows first that particle addition does not trigger any new “dangerous” modes compared with the single-phase flow case. It also shows that the most amplified mode in the case of the single-phase flow remains the most amplified mode in the case of the two-phase flow. Moreover, the addition of particles acts continuously upon stability results, behaving linearly with respect to the particle mass concentration when the latter is small. The linear correction to the monophasic mode, as well as the evolution of the modes with weak values of the particle mass concentration at the wall, are shown to be proportional to the ejection velocity of the particles. Then, the evolution of the eigenmodes from a given injection speed of the particles to another one is deduced by affinity, all other parameters being fixed. With a fixed Stokes number, stability results for a finite Reynolds number and results for the inviscid flow bring together when augmenting the particle mass concentration at the wall. Therefore, by knowing single-phase flow results and the evolution of stability characteristics of the two-phase flow in the inviscid case, it is easy to determine whether particle-laden Taylor flow is more or less stable than the monophasic Taylor flow for large particle mass concentration.
Studying the affinity and kinetics of molecular association with molecular-dynamics simulation
Authors: Zhang Yingkai , McCammon J. Andrew
Published: January 2003

Given a long molecular dynamics trajectory which consists of hundreds of association and dissociation events, the theoretical formulas to calculate the affinity and dissociation rate constant are presented. The derivation is based on the survival function of the associated complex, and it emphasizes the nearest-neighbor distribution function. The applicability of this brute-force approach is demonstrated by the simulation of methane association in water.
Comment on “Classical polarizable force fields parametrized from ab initio calculations” [J. Chem. Phys. 117, 1416 (2002)]
Authors: Chelli Riccardo , Procacci Piero
Published: January 2003

Recently [J. Chem. Phys. 117, 1416 (2002)], Tabacchi et al. proposed a treatment, based on the chemical potential equalization, to account for polarization in classical molecular mechanics. In view of a possible generalization of that approach, intended to build a transferable polarizable force field, we discuss several shortcomings that may arise when the Tabacchi’s model is applied to complex molecular systems.