bluuebunny/crossref_metadata_2025 huggingface dataset:
Attenuation of the P2Y receptor‐mediated control of neuronal Ca2+ channels in PC12 cells by antithrombotic drugs
Authors: Kubista Helmut , Lechner Stefan G , Wolf Angelika M , Boehm Stefan
Published: February 2003

In PC12 cells, adenine nucleotides inhibit voltage‐activated Ca2+ currents and adenylyl cyclase activity, and the latter effect was reported to involve P2Y12 receptors. To investigate whether these two effects are mediated by one P2Y receptor subtype, we used the antithrombotic agents 2‐methylthio‐AMP (2‐MeSAMP) and N6‐(2‐methyl‐thioethyl)‐2‐(3,3,3‐trifluoropropylthio)‐β,γ‐dichloromethylene‐ATP (AR‐C69931MX).

ADP reduced A2A receptor‐dependent cyclic AMP synthesis with half maximal effects at 0.1–0.17 μM. In the presence of 30 μM 2‐MeSAMP or 100 nM AR‐C69931MX, concentration response curves were shifted to the right by factors of 39 and 30, indicative of pA2 values of 6.1 and 8.5, respectively.

The inhibition of Ca2+ currents by ADP was attenuated by 10–1000 nM AR‐C69931MX and by 3–300 μM 2‐MeSAMP. ADP reinhibited Ca2+ currents after removal of 2‐MeSAMP within less than 15 s, but required 2 min to do so after removal of AR‐C69931MX.

ADP inhibited Ca2+ currents with half maximal effects at 5–20 μM. AR‐C69931MX (10–100 nM) displaced concentration response curves to the right, and the resulting Schild plot showed a slope of 1.09 and an estimated pKB value of 8.7. Similarly, 10–100 μM 2‐MeSAMP also caused rightward shifts resulting in a Schild plot with a slope of 0.95 and an estimated pKB of 5.4.

The inhibition of Ca2+ currents by 2‐methylthio‐ADP and ADPβS was also antagonized by AR‐C69931MX, which (at 30 nM) caused a rightward shift of the concentration response curve for ADPβS by a factor of 3.8, indicative of a pA2 value of 8.1.

These results show that antithrombotic drugs antagonize the inhibition of neuronal Ca2+ channels by adenine nucleotides, which suggests that this effect is mediated by P2Y12 receptors.

British Journal of Pharmacology (2003) 138, 343–350. doi:10.1038/sj.bjp.0705037
Tacrolimus and sirolimus decrease oxidative phosphorylation of isolated rat kidney mitochondria
Authors: Simon Nicolas , Morin Christophe , Urien Saïk , Tillement Jean‐Paul , Bruguerolle Bernard
Published: February 2003

Tacrolimus and sirolimus are potent immunosuppressors used in transplantation. Tacrolimus has been suspected to alter mitochondrial respiration of different tissues but sirolimus has not been evaluated.

We evaluated the in vitro effect of tacrolimus and sirolimus on oxidative phosphorylation of isolated rat kidney mitochondria.

Oxygen consumption was measured with a Clark‐type electrode. Tacrolimus and sirolimus increased the resting rate (state 4) and had no significant effect on ADP‐stimulated respiration (state 3). The decrease of respiratory control ratio was concentration‐dependent with a biphasic curve for tacrolimus. The EC50s were 3.4×10−11 M and 2.3×10−8 M for tacrolimus and 4.4×10−10 M for sirolimus. The maximal inhibition was 20 and 14% for tacrolimus and sirolimus, respectively.

Tacrolimus and sirolimus had an uncoupling effect on oxidative phosphorylation related to a decrease of the inner membrane fluidity. At the opposite of cyclosporin A, no effect on swelling or Ca2+ fluxes was observed.

All events occurred at therapeutic concentrations and then could appear during long‐term treatment. Cellular consequences such as chronic nephrotoxicity with tacrolimus are suggested. The risk of cyclosporin A nephrotoxicity potentiation by sirolimus is discussed.

British Journal of Pharmacology (2003) 138, 369–376. doi:10.1038/sj.bjp.0705038
Bradykinin increases intracellular calcium levels in rat testis peritubular cells via the B2 receptor subtype
Authors: Wennemuth Gunther , Blöcher Sonja , Schill Wolf‐Bernhard , Aumüller Gerhard , Monsees Thomas K
Published: February 2003

RT–PCR and Western blots were used to detect bradykinin B2 receptors in testis and isolated peritubular cells of pre‐pubertal rats. RT–PCR demonstrated expression of a single transcript, whereas Western blots showed up to three specific bands that were in accordance with the described native, glycosylated and dimeric form of B2 receptor proteins, respectively.

Fura‐2‐loaded peritubular cells responded with an instantaneous, linear and transient rise in [Ca2+]i after adding bradykinin. Stimulation of cells with bradykinin concentrations between 1 μM and 1 pM showed a dose dependent increase of [Ca2+]i. The calcium response to bradykinin was diminished after stimulation of peritubular cells in calcium‐free buffer. After blocking the SERCA‐pumps by thapsigargin and subsequent stimulation with bradykinin, no rise of [Ca2+]i was appreciated.

Multiple stimulation of a single peritubular cell by local perfusion with a brief addition of BK (10 nM) resulted in a fast and immediate response. However, the second and third stimuli had slower rise rates and diminished [Ca2+]i peaks, showing desensitization of the kinin receptor.

Addition of the bradykinin B1 receptor agonist [des‐Arg9]‐bradykinin (100 nM) to Fura‐2‐loaded peritubular cells did not change the [Ca2+]i. However, the B2 receptor antagonist HOE 140 (100 nM) strongly inhibited the bradykinin‐induced calcium response.

We conclude that the bradykinin‐induced increase in [Ca2+]i, in testicular peritubular cells is mediated by the stimulation of kinin receptors of the B2 subtype.

British Journal of Pharmacology (2003) 138, 351–358. doi:10.1038/sj.bjp.0705039
The role of the 8‐18 helix of CGRP8‐37 in mediating high affinity binding to CGRP receptors; coulombic and steric interactions
Authors: Howitt Stephen G , Kilk Kalle , Wang Yang , Smith David M , Langel Ulo , Poyner David R
Published: February 2003

The role of individual residues in the 8‐18 helix of CGRP8‐37 in promoting high‐affinity binding to CGRP1 receptors expressed on rat L6 and human SK‐N‐MC cells has been examined. The relative potencies of various derivatives were estimated from their ability to inhibit the human αCGRP‐mediated increase in cyclic AMP production and the binding of [125I]‐human αCGRP.

Arg11 and Arg18 were replaced by serines to give [Ser11,18]CGRP8‐37. These bound with pKi values <6 to SK‐N‐MC cells and had apparent pA2 values of 5.81±0.04 and 5.31±0.11 on SK‐N‐MC and L6 cells. CGRP8‐37 had a pKi of 8.22 on SK‐N‐MC cells and pKb values on the above cell lines of 8.95±0.04 and 8.76±0.04.

The arginines were replaced with glutamic acid residues. [Glu11]CGRP8‐37 had a pKb of 7.14±0.14 on SK‐N‐MC cells (pKi=7.05±0.05) and 6.99±0.08 on L6 cells. [Glu18]CGRP8‐37 had a pKb of 7.10±0.0.08 on SK‐N‐MC cells (pKi=6.91±0.23) and 7.12±0.09 on L6 cells.

Leu12, Leu15 and Leu16 were replaced by benzoyl‐phenylalanine (bpa) residues. On SK‐N‐MC cells, the apparent pA2 values of [bpa12]‐, [bpa15]‐ and [bpa16]CGRP8‐37 were respectively 7.43±0.23, 8.34±0.11 and 5.66±0.16 (pKi values of 7.14±0.17, 7.66±0.21 and <6): on L6 cells they were 7.96±0.36, 8.28±0.21 and 6.09±0.04 (all n=3).

It is concluded that the Arg11 and Arg18 are involved in specific electrostatic interactions with other residues, either on the CGRP1 receptors or elsewhere on CGRP8‐37. Leu16 is in a conformationally restricted site when CGRP8‐37 binds to CGRP1 receptors, unlike Leu12 and Leu15. 

British Journal of Pharmacology (2003) 138, 325–332. doi:10.1038/sj.bjp.0705040
Coupling of the nucleotide P2Y4 receptor to neuronal ion channels
Authors: Filippov Alexander K , Simon Joseph , Barnard Eric A , Brown David A
Published: February 2003

G protein‐linked P2Y nucleotide receptors are known commonly to stimulate the phosphoinositide signalling pathway. However, we have previously demonstrated that the cloned P2Y2, P2Y6 and P2Y1 receptors couple to neuronal N‐type Ca2+ channels and to M‐type K+ channels. Here we investigate the coupling of recombinant, neuronally expressed rat‐ and human P2Y4 receptors (rP2Y4, hP2Y4) to those channels.

Rat sympathetic neurones were nuclear‐injected with a P2Y4 cDNA plasmid. A subsequent activation of rP2Y4 or hP2Y4 by UTP (100 μM) in whole‐cell (ruptured‐patch) mode produced only about 12% inhibition of the N‐type Ca2+ current (ICa(N)). Surprisingly, in perforated patch mode, UTP produced much more inhibition of ICa(N) (maximally 51%), with an IC50 value of 273 nM. This inhibition was voltage‐dependent and was blocked by co‐expression of the βγ‐binding transducin Gα‐subunit. Pertussis toxin (PTX) pretreatment also suppressed ICa(N) inhibition.

UTP inhibited the M‐current, recorded in perforated patch mode, by (maximally) 52%, with IC50 values of 21 nM for rP2Y4 and 28 nM for hP2Y4. This inhibition was not affected by PTX pretreatment.

With rP2Y4, ATP inhibited the M‐current (IC50 524 nM, 26 times weaker than UTP), whereas ATP had no agonist activity at hP2Y4. This suggests a difference in agonist binding site between rP2Y4 and hP2Y4.

We conclude that, in contrast to other nucleotide receptors studied, the P2Y4 receptor couples much more effectively to M‐type K+ channels than to Ca2+ channels. Coupling to the Ca2+ channels involves the βγ‐subunits of Gi/o‐proteins and requires a diffusible intracellular component that is lost in ruptured‐patch recording.

British Journal of Pharmacology (2003) 138, 400–406. doi:10.1038/sj.bjp.0705043
Isolation and pharmacological characterization of a phospholipase A2 myotoxin from the venom of the Irian Jayan death adder (Acanthophis rugosus)
Authors: Wickramaratna Janith C , Fry Bryan G , Aguilar Marie‐Isabel , Kini R Manjunatha , Hodgson Wayne C
Published: February 2003

It has long been thought that death adder venoms are devoid of myotoxic activity based on studies done on Acanthophis antarcticus (Common death adder) venom. However, a recent clinical study reported rhabdomyolysis in patients following death adder envenomations, in Papua New Guinea, by a species thought to be different to A. antarcticus. Consequently, the present study examined A. rugosus (Irian Jayan death adder) venom for myotoxicity, and isolated the first myotoxin (acanmyotoxin‐1) from a death adder venom.

A. rugosus (10–50 μg ml−1) and acanmyotoxin‐1 (MW 13811; 0.1–1 μM) were screened for myotoxicity using the chick directly (0.1 Hz, 2 ms, supramaximal V) stimulated biventer cervicis nerve‐muscle (CBCNM) preparation. A significant contracture of skeletal muscle and/or inhibition of direct twitches were considered signs of myotoxicity. This was confirmed by histological examination.

High phospholipase A2 (PLA2) activity was detected in both A. rugosus venom (140.2±10.4 μmol min−1 mg−1; n=6) and acanmyotoxin‐1 (153.4±11 μmol min−1 mg−1; n=6). Both A. rugosus venom (10–50 μg ml−1) and acanmyotoxin‐1 (0.1–1 μM) caused dose‐dependent inhibition of direct twitches and increase in baseline tension (n=4–6). In addition, dose‐dependent morphological changes in skeletal muscle were observed.

Prior incubation (10 min) of CSL death adder antivenom (5 units ml−1; n=4) or inactivation of PLA2 activity with 4‐bromophenacyl bromide (1.8 mM; n=4) prevented the myotoxicity caused by acanmyotoxin‐1 (1 μM).

Acanmyotoxin‐1 (0.1 μM; n=4) displayed no significant neurotoxicity when it was examined using the indirectly (0.1 Hz, 0.2 ms, supramaximal V) stimulated CBCNM preparation.

In conclusion, clinicians may need to be mindful of possible myotoxicity following death adder envenomation in Irian Jaya.

British Journal of Pharmacology (2003) 138, 333–342. doi:10.1038/sj.bjp.0705046
Pharmacological characterization of a 1,4‐dihydropyridine analogue, 9‐(3,4‐dichlorophenyl)‐3,3,6,6‐tetramethyl‐3,4,6,7,9,10‐hexahydro‐1,8(2H,5H)‐acridinedione (A‐184209) as a novel KATP channel inhibitor
Authors: Gopalakrishnan Murali , Miller Thomas R , Buckner Steven A , Milicic Ivan , Molinari Eduardo J , Whiteaker Kristi L , Davis‐Taber Rachel , Scott Victoria E , Cassidy Christopher , Sullivan James P , Carroll William A
Published: February 2003

This study reports on the identification and characterization of a 1,4‐dihydropyridine analogue, 9‐(3,4‐dichlorophenyl)‐3,3,6,6‐tetramethyl‐3,4,6,7,9,10‐hexahydro‐1,8(2H,5H)‐acridinedione (A‐184209) as a novel inhibitor of ATP‐sensitive K+ channels.

A‐184209 inhibited membrane potential changes evoked by the prototypical cyanoguanidine ATP‐sensitive K+ channel opener (KCO) P1075 in both vascular (A10) and urinary bladder smooth muscle cells with IC50 values of 1.44 and 2.24 μM respectively.

P1075‐evoked relaxation of 25 mM K+ stimulated aortic strips was inhibited by A‐184209 in an apparently competitive fashion with a pA2 value of 6.34.

The potencies of A‐184209 to inhibit P1075‐evoked decreases in membrane potential responses in cardiac myocytes (IC50=0.53 μM) and to inhibit 2‐deoxyglucose‐evoked cation efflux pancreatic RINm5F cells (IC50=0.52 μM) were comparable to the values for inhibition of smooth muscle KATP channels.

On the other hand, a structural analogue of A‐184209 that lacked the gem‐dimethyl substituent, 9‐(3,4‐dichlorophenyl)‐3,4,6,7,9,10‐hexahydro‐1,8(2H,5H)‐acridinedione (A‐184208), was found to be a KATP channel opener, evoking membrane potential responses in A10 smooth muscle cells (EC50=385 nM) and relaxing aortic smooth muscle strips (IC50=101 nM) in a glyburide‐sensitive manner.

Radioligand binding studies demonstrated that A‐184209 displaced SUR1 binding defined by [3H]glyburide binding to RINm5F cell membranes with a Ki value of 0.11 μM whereas A‐184208 was ineffective. On the other hand, both A‐184209 (Ki=1.34 μM) and A‐184208 (Ki=1.14 μM) displaced binding of the KCO radioligand, [125I]A‐312110 in guinea‐pig bladder membranes with similar affinities.

These studies demonstrate that A‐184209 is a novel and structurally distinct compound that inhibits KATP channels in smooth muscle with potencies comparable to glyburide. The structural overlap between DHP openers and blockers, together with their differential interaction with ligand binding sites, support the notion that both openers and blockers bind to similar or very closely coupled sites on the sulfonylurea receptor and that subtle changes in the pharmacophore itself could switch functional properties from KATP channel activation to inhibition.

British Journal of Pharmacology (2003) 138, 393–399. doi:10.1038/sj.bjp.0705048
Alprostadil suppresses angiogenesis in vitro and in vivo in the murine Matrigel plug assay
Authors: Cattaneo Maria Grazia , Pola Sandra , Dehò Valeria , Sanguini Anna Maria , Vicentini Lucia Maria
Published: February 2003

Prostaglandin E1 (PGE1, alprostadil) is used as a vasodilator for the treatment of peripheral vascular diseases.

Previous reports suggested a pro‐angiogenic effect for PGE1.

We studied the in vitro and in vivo effect of PGE1, complexed with α‐cyclodextrin, on the angiogenic process. Contrary to what was expected, we found that, in human umbilical vein endothelial cells (HUVECs), PGE1 inhibited proliferation, migration and capillary‐like structure formation in Matrigel.

By RT–PCR studies, the expression of the EP2 and EP3 subtypes of the PG receptor was detected in HUVECs.

PGE1 alone stimulated adenylate cyclase activity at micromolar concentrations, while at nanomolar concentrations potentiated the forskolin‐induced cAMP accumulation.

8‐Bromoadenosine‐3′:5′‐cyclic monophosphate (Br‐cAMP) mimicked the inhibitory effect of PGE1 on endothelial cell growth, motility and tube formation.

Sulprostone, an agonist at the EP3 subtype of PG receptors, mimicked the in vitro anti‐angiogenic effects of PGE1, while butaprost, an EP2 receptor agonist, had no effect.

Finally, in the plug assay model of angiogenesis in mice, PGE1 showed a strong inhibitory effect on Matrigel neovascularization.

Thus, PGE1 possesses strong anti‐angiogenic activity in vitro and in vivo.

British Journal of Pharmacology (2003) 138, 377–385. doi:10.1038/sj.bjp.0705051
The Rho‐kinase inhibitor Y‐27632 and the soluble guanylyl cyclase activator BAY41‐2272 relax rabbit vaginal wall and clitoral corpus cavernosum
Authors: Cellek Selim
Published: February 2003

The effects of Y‐27632, a Rho‐kinase inhibitor and BAY41‐2272, a soluble guanylyl cyclase activator, on the tone and nitrergic responses of rabbit vaginal wall and clitoral corpus cavernosum were investigated. Y‐27632 and BAY41‐2272 (10 nM–10 μM) elicited concentration‐dependent relaxation of phenylephrine‐induced tone in both tissues. IC50 values of Y‐27632 for vaginal and clitoral tissues were 370±30 nM, and 467±14 nM, respectively. BAY41‐2272 had IC50 values of 478±54 nM and 304±38 nM respectively. The effect of the Y‐27632 on the tissue tone was not affected by an inhibitor of nitric oxide synthase (L‐NAME; 500 μM). However, L‐NAME reduced the potency of BAY41‐2272 in the clitoral corpus cavernosum but not in the vaginal wall. BAY41‐2272 enhanced nitrergic relaxation responses only in the clitoral corpus cavernosum. Y‐27632 had no effect on nitrergic relaxations in either tissue. These results demonstrate that Y‐27632 and BAY41‐2272 elicit relaxation of the rabbit vaginal wall and clitoral corpus cavernosum.

British Journal of Pharmacology (2003) 138, 287–290. doi:10.1038/sj.bjp.0705090
Myocardial ischaemia/reperfusion injury and preconditioning: effects of hypercholesterolaemia/hyperlipidaemia
Authors: Ferdinandy Péter
Published: February 2003

British Journal of Pharmacology (2003) 138, 283–285. doi:10.1038/sj.bjp.0705097
Attenuation of increased myocardial ischaemia‐reperfusion injury conferred by hypercholesterolaemia through pharmacological inhibition of the caspase‐1 cascade
Authors: Wang Tzung‐Dau , Chen Wen‐Jone , Mau Tzan‐Jr , Lin Jong‐Wei , Lin Wan‐Wan , Lee Yuan‐Teh
Published: February 2003

Hypercholesterolaemia has been shown to be associated with greater myocardial ischaemia‐reperfusion injury, in which apoptosis and inflammation‐mediated necrosis both play a key role.

Caspase‐1 is involved in the activation of both apoptosis and inflammation, through the intermediate of interleukin‐1β (IL‐1β). We herein examined whether pharmacological inhibition of the caspase‐1 cascade, using Ac‐Tyr‐Val‐Ala‐Asp‐CH2Cl (Ac‐YVAD.cmk), after myocardial ischaemia have greater protective effects on myocardial ischaemia‐reperfusion injury in diet‐induced hypercholesterolaemic rabbits.

Male rabbits fed with standard chow or chow supplemented with 0.5% cholesterol and 10% coconut oil for 8 weeks were subjected to 30 min of left circumflex artery occlusion followed by 4 h of reperfusion. An intravenous bolus of Ac‐YVAD.cmk (1.6 mg kg−1) or vehicle was given 20 min after coronary occlusion.

Postischaemic administration of Ac‐YVAD.cmk markedly decreased infarct size from 26±3% to 12±2% in normally fed rabbits (P=0.005) and from 41±6% to 14±2% in cholesterol‐fed rabbits (P<0.001).

In the ischaemic non‐necrotic area, treatment with Ac‐YVAD.cmk markedly reduced the percentage of terminal deoxynucleotidyl transferase‐mediated dUTP‐biotin nick end labelling (TUNEL)‐positive cardiomyocytes from 15.5±0.8% to 2.2±0.1% in normally fed rabbits (P<0.001) and from 39.0±2.3% to 2.2±0.1% in cholesterol‐fed rabbits (P<0.001).

Ac‐YVAD.cmk treatment resulted in a reduction not only of IL‐1β and caspase‐1, but also of caspase‐3 in the ischaemic myocardium in both normally fed and cholesterol‐fed rabbits.

No differences in infarct size, the percentage of TUNEL‐positive cardiomyocytes, IL‐1β levels or activity of caspase‐1 and caspase‐3 were observed between Ac‐YVAD.cmk‐treated normally fed and cholesterol‐fed rabbits.

This study demonstrates that injection of a selective caspase‐1 inhibitor after myocardial ischaemia markedly reduced the detrimental effect conferred by hypercholesterolaemia on myocardial ischaemia‐reperfusion injury by attenuating both necrotic as well as apoptotic cell death pathways through inhibition of IL‐1β production and activation of caspase‐1 and caspase‐3.

British Journal of Pharmacology (2003) 138, 291–300. doi:10.1038/sj.bjp.0705098
Quantum reactive scattering calculations of cross sections and rate constants for the N(2D)+O2(X 3Σg−)→O(3P)+NO(X 2Π) reaction
Authors: Miquel Irene , González Miguel , Sayós R. , Balint-Kurti Gabriel G. , Gray Stephen K. , Goldfield Evelyn M.
Published: February 2003

Time-dependent quantum wave packet calculations have been performed on the two lowest adiabatic potential energy surfaces (2 2A′ and 1 2A″) for the N(2D)+O2(X 3Σg−)→O(3P)+NO(X 2Π) reaction. The calculations have been carried out, on these recently published potential energy surfaces, using the real wave packet method together with a new dispersion fitted finite difference technique for evaluating the action of the radial kinetic energy operator. Reaction probabilities, corresponding to the O2 reactant in its ground vibrational-rotational state, have been calculated for both surfaces and for many different values of the total angular momentum quantum number (J), within the helicity decoupling approximation. The reaction probabilities associated with all other relevant J values have been interpolated, and to a smaller extent extrapolated, using a capture model, to yield probabilities as a function of energy. The probabilities have in turn been summed to yield energy dependent cross sections and then used to compute rate constants. These rate constants are compared with ones obtained from quasiclassical trajectory (QCT) and variational transition state theory (VTST) calculations performed on the same surfaces. There is a good agreement between the wave packet and QCT cross sections for reaction on both potential energy surfaces considered, with the exception of the near threshold region, where the reaction probability is dominated by tunnelling. Comparison of the predicted rate constants shows that for the 2 2A′ surface, above 300 K, the wave packet, QCT and VTST results are quite similar. For the 1 2A″ surface, however, significant differences occur between the wave packet and the other methods. These differences become smaller with increasing temperature. It is likely that these differences arise, at least in part, from the fact that, when calculating the rate constants, the reactants are restricted to be in their lowest vibrational-rotational state in the wave packet calculations but are selected from a thermally equilibrated population in the other methods.
Free volume coalescence and void formation in shear bands in metallic glass
Authors: Wright Wendelin J. , Hufnagel T. C. , Nix W. D.
Published: February 2003

We have investigated the possibility of void nucleation from the coalescence of excess free volume generated in shear bands during deformation of the Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 bulk metallic glass. Excess free volume in a shear band results in excess free energy relative to a relaxed glass with less free volume. To calculate the free energy of the material in a shear band with excess free volume, we model it as having the same structure as a glass solidified at an elevated glass transition temperature, which we call the fictive temperature. This excess free energy can be correlated with a free volume chemical potential that provides a driving force for void nucleation. The results of this modeling indicate that any free volume generated in the shear band during deformation is unstable, with the consequence that voids are predicted to form spontaneously from the coalescence of free volume. These voids are then expected to coarsen. Under tension, void growth and linkage would be facilitated by a tensile stress state, perhaps leading to premature fracture, whereas a compressive stress state would hinder void growth. This may explain the common observation that failure under uniaxial tension occurs as the result of the propagation of a single shear band, whereas multiple shear bands can form under uniaxial compression without causing failure.
Ultrafast crystallization of polar polymer melts
Authors: Gee Richard H. , Fried Laurence E.
Published: February 2003

Primary nucleation of poly(vinylidene fluoride) (pVDF) from bulk entangled amorphous polymer melts has been observed from molecular dynamics (MD) simulations. This is the first instance of spontaneous primary nucleation of an entangled bulk polymer in a MD simulation. The melt-to-crystal phase transition occurs via a three-stage process. The ordered phase is found to consist of mainly chain-folded lamella with predominantly adjacent re-entry. The observed crystal polymorphs correspond to either the well known β phase or form I polymorph or a crystal structure that does not coincide with any of the known experimental polymorphs for pVDF, but is found to be strikingly similar to the β structure but with antiparallel alignment of the dipole moments normal to the polymer chain axis. The time required for the onset of nucleation is found to decrease with the number of monomers in the polymer, while the opposite is found for the growth rate of the crystal. We find that the crystallization of the polymer is mediated by electrostatics; in fact the crystal structure spontaneously melts when the electrostatic interactions are removed.
Temperature dependence of Stokes shift in InxGa1−xN epitaxial layers
Authors: Sasaki Chiharu , Naito Hiroyoshi , Iwata Masaki , Kudo Hiromitsu , Yamada Yoichi , Taguchi Tsunemasa , Jyouichi Takahide , Okagawa Hiroaki , Tadatomo Kazuyuki , Tanaka Hiroyuki
Published: February 2003

Optical properties of InxGa1−xN epitaxial layers with various indium compositions (x=0.02, 0.03, 0.05, 0.06, and 0.09) have been studied by means of temperature-dependent optical absorption and photoluminescence spectroscopy. A clear peak due to the absorption of InxGa1−xN ternary alloys was observed up to 300 K, which enabled us to investigate the temperature dependence of the Stokes shift. The Stokes shift at 4 K increased with an increase in the indium composition, and was estimated to be 22 and 45 meV for the samples with x=0.02 and 0.09, respectively. With an increase in temperature up to about 50 K, the Stokes shift increased slightly. With a further increase in temperature from 50 to 100 K, the Stokes shift decreased. Above 100 K, the Stokes shift was independent of the temperature and showed an almost constant value up to 300 K. The Stokes shift at 300 K was estimated to be 19 and 34 meV for the samples with x=0.02 and 0.09, respectively. This temperature dependence of the Stokes shift was characteristically common to all of the samples used in the present work, and was observed to be more prominent for the samples with higher indium compositions.
Phase transitional studies of polycrystalline Pb0.4Sr0.6TiO3 films using Raman scattering
Authors: Naik V. M. , Haddad D. , Naik R. , Mantese J. , Schubring N. W. , Micheli A. L. , Auner G. W.
Published: February 2003

Pb 0.4 Sr 0.6 TiO 3 films with submicron size grains have been prepared on Pt substrates by the metalorganic decomposition method. X-ray diffraction analysis reveals that the films are polycrystalline with a perovskite crystal structure and negligible tetragonal splitting at room temperature. The room temperature Raman spectrum, however, shows all the characteristic phonon modes of a tetragonal ferroelectric phase. These modes lose their intensity with an increase in temperature but persist even up to 150 °C. This is in agreement with the dielectric permittivity versus temperature data which show a broad peak–room temperature, and ferroelectric hysteresis persisting up to ∼140 °C. Both Raman and dielectric data are interpreted as due to the presence of a distribution of phases in the film perhaps caused by a variation in Pb content along the film thickness and/or near grain boundary regions.
Influence of surface states on the photoluminescence from silicon nanostructures
Authors: Islam Md. N. , Kumar Satyendra
Published: February 2003

We report a phenomenological model to analyze the room temperature photoluminescence (PL) spectra observed from silicon nanostructures. We have explicitly incorporated the effects of localized surface states along with quantum confinement effects to obtain an analytical expression for the photoluminescence spectra. Normal as well as log-normal crystallite size distributions are considered for PL intensity calculations. Experimental PL data on a variety of nanocystalline silicon structures with directly measured crystallite size distribution have been analyzed. Our model is able to deduce size distribution parameters from PL data that agree well with the experiments.
Cooperative effects in one-dimensional chains of three-center hydrogen bonding interactions
Authors: Parra Rubén D. , Bulusu Satya , Zeng X. C.
Published: February 2003

Cooperative effects in a one-dimensional network of intermolecular bifurcated hydrogen bonding interactions are investigated by means of ab initio calculations. The trans–trans conformation of the diformamide molecule is used as a basic motif to model a chain of bifurcated H bonds. In this model system, the two proton–acceptor atoms belong to the same molecule. The one-dimensional network is modeled then by periodically stacking up to 12 molecules of the unit motif. Different indicators of H-bond strength such as energetic, structural, dielectric, vibrational frequencies, and isotropic chemicals shifts consistently show significant cooperative effects in the chains. The dissociation energy in the dimer is calculated to be 9.88 kcal/mol, while that of the strongest interaction in the decamer is calculated to be 26.12 kcal/mol (164% increase in cooperativity). Thus, although three-center H bonds can be viewed as a consequence of proton deficiency, in some cases they may also be viewed as the natural result of an interaction that is itself energetically favorable and capable of competing with the more conventional two-center H bonds. Natural bond orbital analysis reveals substantial charge delocalization within each molecule, and charge transfer along the chains. Interestingly, this charge delocalization makes the system a good candidate for resonance-assisted H bonding which in turn increases the covalent character of this type of bifurcated H-bonding interaction.
Influence of InN mole fraction on the recombination processes of localized excitons in strained cubic InxGa1−xN/GaN multiple quantum wells
Authors: Chichibu SF. , Onuma T. , Sota T. , DenBaars S. P. , Nakamura S. , Kitamura T. , Ishida Y. , Okumura H.
Published: February 2003

Recombination dynamics of localized excitons in the best quality strained cubic InxGa1−xN/GaN multiple quantum wells (MQWs) grown on 3C-SiC (001) were studied as functions of InN mole fraction x and temperature T. The MQWs exhibited large Stokes-type shifts although the full width at half maximum of the photoluminescence (PL) peaks being 80–120 meV is 100–300 meV smaller than those reported previously. Time-resolved PL signal showed stretched exponential decay and spectral redshift with time after excitation up to 300 K. These results are fingerprints that the spontaneous emission is due to the radiative recombination of excitons localized in disordered quantum nanostructures forming extended and localized states. Effective localization depth increased with the increase in x, which gave rise to fast exciton localization. However, nonradiative lifetime in the free states decreased more rapidly with the increase in x and T, giving the emission efficiency maximum at particular x around 0.1.
Rectification of laser-induced electronic transport through molecules
Authors: Lehmann Jörg , Kohler Sigmund , Hänggi Peter , Nitzan Abraham
Published: February 2003

We study the influence of laser radiation on the electron transport through a molecular wire weakly coupled to two leads. In the absence of a generalized parity symmetry, the molecule rectifies the laser-induced current, resulting in directed electron transport without any applied voltage. We consider two generic ways of dynamical symmetry breaking: mixing of different harmonics of the laser field and molecules consisting of asymmetric groups. For the evaluation of the nonlinear current, a numerically efficient formalism is derived which is based upon the Floquet solutions of the driven molecule. This permits a treatment in the nonadiabatic regime and beyond linear response.
Effect of structural parameter on field emission properties of semiconducting copper sulphide nanowire films
Authors: Chen Jun , Deng S. Z. , She J. C. , Xu N. S. , Zhang Weixin , Wen Xiaogang , Yang Shihe
Published: February 2003

Films of aligned crystalline copper sulphide (Cu2S) nanowire arrays were grown by using a gas-solid reaction method. By controlling the preparation condition, copper sulphide nanowire arrays with different structural parameters were fabricated. Their field emission characteristics including the total current–applied field characteristics and the distribution of field emission sites are studied and compared using the transparent anode technique. It is found that the turn-on field of the copper sulphide nanowire film relates to the structural parameters of copper sulphide nanowire arrays. Nonlinearity in Fowler–Nordheim plot was observed from film consisting of sparse nanowire arrays with varied field enhancement factor. The physical mechanism accounting for the nonlinearity is discussed.
Density functional calculations of hydrogen adsorption on palladium–silver alloy surfaces
Authors: Løvvik O. M. , Olsen R. A.
Published: February 2003

Palladium–silver alloy surfaces with and without adsorbed hydrogen have been studied through density functional theory within the generalized gradient approximations employing a slab representation of the surface. Our calculated lattice constants are in good agreement with experimental data, but we find a substantially lower surface energy for Ag(111) and Pd(111) than experiments. We have calculated adsorption energies of hydrogen on several sites on various alloy surfaces, and found that threefold hollow sites with as many palladium neighbors as possible are preferred. The difference in adsorption energy is so large that we expect trapping of hydrogen around palladium atoms in the surface, possibly resulting in a lower diffusion constant of hydrogen at low coverage on alloy surfaces than on the pure Pd and Ag surfaces. Assuming that the adsorption energy has contributions from geometric (“ensemble”) and electronic (“ligand”) effects, we found the geometric contribution to dominate. For the geometric contribution it is seen that the binding strength increases as the d-band center moves toward the Fermi level, a result also found by a number of other theoretical studies. However, for the electronic contribution we found that the variation of the adsorption energy as a function of the d-band center was opposite that reported by others: We saw that hydrogen binds less strongly to the surface as the d-band center moves toward the Fermi level. This could possibly be explained by a large variation of the interaction between the metal sp band and hydrogen.
Appropriate methods to combine forward and reverse free-energy perturbation averages
Authors: Lu Nandou , Singh Jayant K. , Kofke David A.
Published: February 2003

We consider the accuracy of several methods for combining forward and reverse free-energy perturbation averages for two systems (labeled 0 and 1). The practice of direct averaging of these measurements is argued as not reliable. Instead, methods are considered of the form β(A1−A0)=−ln[〈w(u)exp(−βu/2)〉0/〈w(u)exp(+βu/2)〉1], where A is the free energy, β=1/kT is the reciprocal temperature, u=U1−U0 is the difference in configurational energy, w(u) is a weighting function, and the angle brackets indicate an ensemble average performed on the system indicated by the subscript. Choices are considered in which w(u)=1 and 1/cosh[(u−C)/2]; the latter being Bennett’s method where C is a parameter that can be selected arbitrarily, and may be used to optimize the precision of the calculation. We examine the methods in several applications: calculation of the pressure of a square-well fluid by perturbing the volume, the chemical potential of a high-density Lennard-Jones system, and the chemical potential of a model for water. We find that the approaches based on Bennett’s method weighting are very effective at ensuring an accurate result (one in which the systematic error arising from inadequate sampling is less than the estimated confidence limits), and that even the selection w(u)=1 offers marked improvement over comparable methods. We suggest that Bennett’s method is underappreciated, and the benefits it offers for improved precision and (especially) accuracy are substantial, and therefore it should be more widely used.
Photodissociation of bromoform cation at 308, 355, and 610 nm by means of time-of-flight mass spectroscopy and ion velocity imaging
Authors: Huang Jianhua , Xu Dadong , Francisco Joseph S. , Jackson William M.
Published: February 2003

The photodissociation dynamics of bromoform cation, CHBr3+, have been studied at 308, 355, and 610 nm by means of time-of-flight mass spectrometry combined with ion velocity imaging. The bromoform cation is produced via vacuum ultraviolet photoionization at 118 nm. The only fragment ions found in the time-of-flight spectra at 355 and 610 nm are CHBr2+ ions. At 308 nm CBr+ and CHBr+ ions are also found in the time-of-flight spectrum in addition to the CHBr2+ ions. These results indicate that there is only one dissociation channel that produces CHBr2++Br at both 355 and 610 nm, while there are two more channels involved at 308 nm. One is a molecular bromine elimination channel forming CHBr++Br2, and the other is a three-body dissociation channel producing CBr++HBr+Br. Translational energy and angular distributions for each channel are deduced from the two-dimensional images of CHBr2+, CHBr+, and CBr+. A soft fragment impulsive model closely reproduces the fraction of the available energy in translation for the atomic Br channel. The absence of Br2 channel at 355 nm may indicate a highly dynamically restricted gateway for the molecular elimination, which requires a specific molecular configuration, i.e., a three-center transition state, before the molecule falls apart along the much simpler atomic elimination channel.
Phase separation in suspensions of colloids, polymers and nanoparticles: Role of solvent quality, physical mesh, and nonlocal entropic repulsion
Authors: Chen Y.-L. , Schweizer K. S. , Fuchs M.
Published: February 2003

Analytic and numerical microscopic integral equation theory for polymer–particle suspensions is employed to investigate the dependence of fluid–fluid phase separation on size asymmetry, solvent quality, and higher order polymer–polymer interactions. For athermal good solvents, our prior novel prediction of enhanced miscibility with increasing (decreasing) polymer (particle) size is found not to be fundamentally tied to physical mesh formation or strong polymer-induced colloid clustering. Rather, the key is a proper treatment of the polymer second virial coefficient, which is sensitive to how chains organize in the empty space between particles. The origin of the qualitative error made by classic mean-field theories for the shifting of phase boundaries with size asymmetry is established. The phase separation behavior predicted by integral equation theory for ideal polymers is completely different than the athermal case for all size asymmetries and particle volume fractions, thereby establishing the remarkably large consequences of polymer–polymer repulsions. For large polymers or small nanoparticles under ideal solvent conditions, the suspension miscibility worsens with increasing size asymmetry, opposite to the athermal solvent behavior. However, over a significant range of intermediate size asymmetries the spinodal curves are either nearly constant, or display a nonmonotonic shifting, as size asymmetry is varied. Higher order contributions in polymer concentration modestly stabilize the miscible phase in both athermal and ideal solvents.
Dynamics of poly(ethylene oxide) in nanoscale confinements: A computer simulations perspective
Authors: Kuppa V. , Manias E.
Published: February 2003

Molecular Dynamics simulations are used to explore the effect of severe –1 nanometer– confinement on the short-time dynamics of poly(ethylene oxide) (PEO). Bulk and intercalated systems have been atomistically modeled to comparatively illustrate their differences. In particular, we aim to trace the molecular level mechanisms responsible for the counter intuitive distribution of relaxation times recorded by solid state H2 NMR for the C–H bond reorientations in confinements. Computer simulations complement the experiments and reveal that factors such as local density inhomogeneities, proximity of Li+, and disorder in the system, combine to determine the PEO segmental dynamics. In contrast with the respective bulk PEO systems, where a clear transition from distinct solid to liquid like dynamics takes place with increasing temperatures, for the nanoscopically confined chains there persists a coexistence of fast and slow segmental relaxations over the same temperature range.
Comparison and evaluation of several models for fitting the frequency response of dispersive systems
Authors: Macdonald J. Ross
Published: February 2003

Using both simulated and experimental data, detailed comparisons are made between the different physical interpretations and responses of several important models commonly employed for fitting and analyzing conductive-system data sets, such as those for ionic glasses. Those considered are one following directly from stretched-exponential temporal response, designated the Kohlrausch K0; several ones indirectly associated with such stretched-exponential response: the original modulus formalism (OMF) model and corrected modulus formalism (CMF) ones; and the ZC model, one whose real-part conductivity expression has been termed “universal dynamic response.” In addition, several models involving dielectric dispersion, rather than resistive dispersion, are found to be less appropriate for the present data than are the CMF ones. Of the four main conductive-system models the CMF approach fits data for a wide variety of materials much better than do the others. The OMF is shown to be both experimentally and theoretically defective and leads to poor and inconsistent fitting results. The simple ZC model involves nonphysical low-frequency-limiting real-part conductivity response and is usually less appropriate even than the K0. High- and low-frequency expressions and fit results for the various dielectric elements are presented, along with discussion of characteristic, peak, and mean relaxation times for the various models, failing to confirm some proposed relations between these quantities suggested earlier.
Magnetization reversal by coherent rotation in single-domain magnets with arbitrary anisotropy
Authors: Schmidt H.
Published: February 2003

We present an exact treatment of magnetization reversal by coherent rotation in single-domain magnets with multiple crystal anisotropy axes. External switching field values can be determined for arbitrary relative orientations of crystal axes, external fields, and additional anisotropy axes (e.g., shape anisotropy) without any simplifying assumptions or approximations. The method is applied to analyze coherent rotation in particles with cubic crystal anisotropy. We find that the switching field is to first order determined by the closest crystal anisotropy axis, but influence from the next nearest axis leads to non-negligible corrections on the order of tens of percent of the switching field. We also demonstrate that during reversal the magnetization vector rotates predominantly in a single, well-defined plane with only minor deviations. The ramifications for control of the switching field values in single-domain nanomagnets are discussed.
Electrical and optical properties of n- and p-InSe doped with Sn and As
Authors: Shigetomi S. , Ikari T.
Published: February 2003

The impurity levels in Sn- and As-doped InSe have been investigated by photoluminescence (PL), photoacoustic (PA), and Hall effect measurements. The carrier transport in the Sn-doped n-type sample is governed by the donor level at 0.06 eV below the conduction band. Moreover, this donor level is related to the radiative recombination of the 1.27 eV emission band. The deep acceptor level located at 0.64 eV above the valence band dominates the carrier transport in the As-doped p-type sample. From the results of PL and PA measurements, the deep acceptor level is considered to be related to the defects or defect complexes formed by the As atoms of the interlayer.
Diffusion–transmission interface condition for electron and phonon transport
Authors: Chen Gang
Published: February 2003

This letter introduces a diffusion–transmission condition for dealing with the transport of electrons, phonons, and photons at interfaces, and boundaries. The condition can be used consistently with drift–diffusion-type transport equations and simplifies interface-dominated transport problems. This interface condition is used to establish a formulation for thermionic emission that is applicable to arbitrary barrier heights.
Dislocation-enhanced ionic conductivity of yttria-stabilized zirconia
Authors: Otsuka Kazuya , Kuwabara Akihide , Nakamura Atsutomo , Yamamoto Takahisa , Matsunaga Katsuyuki , Ikuhara Yuichi
Published: February 2003

The ionic conductivity of yttria-stabilized zirconia (YSZ) single crystals (10 mol %Y2O3–ZrO2) was enhanced by introducing high density of dislocations. YSZ single crystals were systematically deformed by compression tests at 1300 °C, and their electrical conductivity was measured by an AC impedance method. It was confirmed that a great number of dislocations were introduced in YSZ by the high-temperature deformation, and the density reached up to more than 8×1012 m−2, depending on the compression strains imposed on the samples. The electrical conductivity of the deformed samples was found to be larger than that of undeformed samples. Furthermore, samples with larger strains exhibited higher electrical conductivity, which indicates that dislocations generated by the plastic deformation play an important role to enhance the ionic conductivity of YSZ.
Fabrication of in-plane gate transistors on hydrogenated diamond surfaces
Authors: Garrido J. A. , Nebel C. E. , Todt R. , Rösel G. , Amann M.-C. , Stutzmann M. , Snidero E. , Bergonzo P.
Published: February 2003

The highly conductive surface layer induced in diamond by hydrogen termination has been used to fabricate in-plane gate transistors. The conductive channel has been separated from the Ohmic gate contacts by insulating thin lines, obtained by using a combination of electron-beam lithography with surface oxidation. Oxidized lines of about 100 nm show excellent blocking properties, with leakage current of 0.3 pA/μm at 100 V and room temperature. In-plane transistor properties are reported for operation at 77 K and room temperature with good saturation characteristic and complete pinch-off.
A new waveguide switch/modulator for integrated optics
Authors: Martin W. E.
Published: February 2003

A waveguide optical switch and/or modulator device is described that uses a single-mode waveguide version of the Mach-Zehnder interferometer. A mode selective branching waveguide is used for switching, and modulation can be accomplished without external polarizers in single-mode waveguides. The operation of a 1×2 switch fabricated by diffusion techniques in ZnSe is described.
Nonsteady-state techniques for determining the energy distribution of interface traps in MNOS (memory) devices
Authors: Uranwala J. S. , Simmons J. G. , Mar H. A.
Published: February 2003

New techniques are used to obtain the energy distribution of interface traps throughout the band gap of MNOS devices. The techniques are based on thermal and isothermal dielectric relaxation current techniques. It is demonstrated that the techniques are capable of detecting small changes in the trap distribution, such as might occur due to ageing or termperature cycling.
Low−field magnetic properties of ferromagnetic amorphous alloys
Authors: Egami T. , Flanders P. J. , Graham C. D.
Published: February 2003

The low−field magnetic properties of some amorphous magnetic alloy ribbons have been measured. The as−prepared specimens have low coercive field but rather low remanence. The application of elastic stress greatly increases the remanence, and can also decrease the coercive field. Some of the improvement due to stress can be made permanent by annealing under stress. These alloys should be useful in various magnetic devices.