bluuebunny/crossref_metadata_2025 huggingface dataset:
Chemokine receptor inhibition by AMD3100 is strictly confined to CXCR4
Authors: Hatse Sigrid , Princen Katrien , Bridger Gary , De Clercq Erik , Schols Dominique
Published: October 2002

This study was undertaken to demonstrate the unique specificity of the chemokine receptor CXCR4 antagonist AMD3100. Calcium flux assays with selected chemokine/cell combinations, affording distinct chemokine receptor specificities, revealed no interaction of AMD3100 with any of the chemokine receptors CXCR1 through CXCR3, or CCR1 through CCR9. In contrast, AMD3100 potently inhibited CXCR4‐mediated calcium signaling and chemotaxis in a concentration‐dependent manner in different cell types. Also, AMD3100 inhibited stromal cell‐derived factor (SDF)‐1‐induced endocytosis of CXCR4, but did not affect phorbol ester‐induced receptor internalization. Importantly, AMD3100 by itself was unable to elicit intracellular calcium fluxes, to induce chemotaxis, or to trigger CXCR4 internalization, indicating that the compound does not act as a CXCR4 agonist. Specific small‐molecule CXCR4 antagonists such as AMD3100 may play an important role in the treatment of human immunodeficiency virus infections and many other pathological processes that are dependent on SDF‐1/CXCR4 interactions (e.g. rheumatoid arthritis, atherosclerosis, asthma and breast cancer metastasis).
X‐ray structure of Galdieria Rubisco complexed with one sulfate ion per active site
Authors: Okano Yousuke , Mizohata Eiichi , Xie Yong , Matsumura Hiroyoshi , Sugawara Hajime , Inoue Tsuyoshi , Yokota Akiho , Kai Yasushi
Published: October 2002

Ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco) catalyzes the reactions of carboxylation and oxygenation of ribulose‐1,5‐bisphosphate. These reactions require that the active site should be closed by a flexible loop (loop 6) of the large subunit. Rubisco from a red alga, Galdieria partita, has the highest specificity for carboxylation reaction among the Rubiscos hitherto reported. The crystal structure of unactivated Galdieria Rubisco has been determined at 2.6 Å resolution. The electron density map reveals that a sulfate binds only to the P1 anion‐binding site of the active site and the loop 6 is closed. Galdieria Rubisco has a unique hydrogen bond between the main chain oxygen of Val332 on the loop 6 and the ϵ‐amino group of Gln386 of the same large subunit. This interaction is likely to be crucial to understanding for stabilizing the loop 6 in the closed state and to making a higher affinity for anionic ligands.
Different protein kinase families are activated by osmotic stresses in Arabidopsis thaliana cell suspensions
Authors: Droillard Marie-Jo , Boudsocq Marie , Barbier-Brygoo Hélène , Laurière Christiane
Published: October 2002

Five Ca2+‐independent protein kinases were rapidly activated by hypoosmotic stress, moderate or high hyperosmolarity induced by several osmolytes, sucrose, mannitol or NaCl. Three of these kinases, transiently activated by hypoosmolarity, recognised by anti‐phosphorylated mitogen‐activated protein (MAP) kinase antibodies, sensitive to a MAP kinase inhibitor and inactivated by the action of a tyrosine phosphatase, corresponded to MAP kinases. Using specific antibodies, two of the MAP kinases were identified as AtMPK6 and AtMPK3. The two other protein kinases, durably activated by high hyperosmolarity, did not belong to the MAP kinase family. Activation of AtMPK6 and AtMPK3 by hypoosmolarity depended on upstream protein kinases sensitive to staurosporine and on calcium influx. In contrast, these two transduction steps were not involved in the activation of the two protein kinases activated by high hyperosmolarity.
The COOH‐terminus of parathyroid hormone‐related protein (PTHrP) interacts with β‐arrestin 1B1
Authors: Conlan Lindus A , Martin T.John , Gillespie Matthew T
Published: October 2002

Parathyroid hormone‐related protein (PTHrP) has a diverse range of proposed biological activities participating in both extracellular and intracellular signaling. In order to identify candidate protein effectors, yeast two‐hybrid screens were conducted using mature human PTHrP (residues 1–141) and the COOH‐terminus (residues 107–141). Both PTHrP baits interacted with a β‐arrestin 1B fragment, an important component of G‐protein‐coupled receptor desensitization and MAPK signaling. Co‐immunoprecipitation, in vitro binding assays and colocalization experiments confirmed this interaction in human cells and this required residues 122–141 of PTHrP. These findings suggest that β‐arrestin 1 acts as an effector for a novel function of PTHrP in cytoplasm.
Estradiol receptor potentiates, in vitro, the activity of 5‐methylcytosine DNA glycosylase
Authors: Jost Jean-Pierre , Thiry Stéphane , Siegmann Michel
Published: October 2002

At a concentration of 5×10−9 M of hemi‐methylated DNA (one order of magnitude below the K
m), MCF‐7 (a human breast carcinoma cell line) nuclear extracts potentiate the activity of 5‐methylcytosine DNA glycosylase (5‐MCDG, alias G/T mismatch DNA glycosylase). Depending on the ratio between MCF‐7 nuclear extracts and 5‐MCDG, there is an up to 10‐fold increase in 5‐MCDG activity. The potentiation of 5‐MCDG by MCF‐7 nuclear extracts requires an estradiol response element adjacent to the hemi‐methylated site. Depletion of the estradiol receptor from MCF‐7 nuclear extracts with specific antibodies abolishes the potentiation of 5‐MCDG activity. The estradiol receptor present in MCF‐7 nuclear extracts can be precipitated with antibodies directed against 5‐MCDG. Reciprocally, antibodies directed against the estradiol receptor precipitate 5‐MCDG. The results indicate the formation of a complex between the estradiol receptor and 5‐MCDG.
Activation volumes for intramolecular electron transfer in Escherichia coli cytochrome bo3
Authors: Ching Erin , Gennis Robert B , Larsen Randy W
Published: October 2002

In this report we describe the activation volumes associated with the heme–heme electron transfer (ET) and CO rebinding to the binuclear center subsequent to photolysis of the CO‐mixed‐valence derivative of Escherichia coli cytochrome bo3
(Cbo). The activation volumes associated with the heme–heme ET (k=1.2×105 s−1), and CO rebinding (k=57 s−1) are found to be +27.4 ml/mol and −2.6 ml/mol, respectively. The activation volume associated with the rebinding of CO is consistent with previous Cu X‐ray absorption studies of Cbo where a structural change was observed at the CuB site (loss of a histidine ligand) due to a change in the redox state of the binuclear center. In addition, the volume of activation for the heme–heme ET was found to be quite distinct from the activation volumes obtained for heme–heme ET in bovine heart Cytochrome c oxidase. Differences in mechanisms/pathways for heme b/heme o3
and heme a/heme a3
ET are suggested based on the associated activation volumes and previously obtained Marcus parameters.
AAA+ proteins and substrate recognition, it all depends on their partner in crime
Authors: Dougan David A , Mogk Axel , Zeth Kornelius , Turgay Kürsad , Bukau Bernd
Published: October 2002

Members of the AAA+ superfamily have been identified in all organisms studied to date. They are involved in a wide range of cellular events. In bacteria, representatives of this superfamily are involved in functions as diverse as transcription and protein degradation and play an important role in the protein quality control network. Often they employ a common mechanism to mediate an ATP‐dependent unfolding/disassembly of protein–protein or DNA–protein complexes. In an increasing number of examples it appears that the activities of these AAA+ proteins may be modulated by a group of otherwise unrelated proteins, called adaptor proteins. These usually small proteins specifically modify the substrate recognition of their AAA+ partner protein. The occurrence of such adaptor proteins are widespread; representatives have been identified not only in Escherichia coli but also in Bacillus subtilis, not to mention yeast and other eukaryotic organisms. Interestingly, from the currently known examples, it appears that the N domain of AAA+ proteins (the most divergent region of the protein within the family) provides a common platform for the recognition of these diverse adaptor proteins. Finally, the use of adaptor proteins to modulate AAA+ activity is, in some cases, an elegant way to redirect the activity of an AAA+ protein towards a particular substrate without necessarily affecting other activities of that AAA+ protein while, in other cases, the adaptor protein triggers a complete switch in AAA+ activity.
Sphingolipid trafficking and protein sorting in epithelial cells
Authors: Aït Slimane Tounsia , Hoekstra Dick
Published: October 2002

Sphingolipids represent a minor, but highly dynamic subclass of lipids in all eukaryotic cells. They are involved in functions that range from structural protection to signal transduction and protein sorting, and participate in lipid raft assembly. In polarized epithelial cells, which display an asymmetric apical and basolateral membrane surface, rafts have been proposed as a sorting principle for apical resident proteins, following their biosynthesis. However, raft‐mediated trafficking is ubiquitous in cells. Also, sphingolipids per se, which are strongly enriched in the apical domain, are subject to sorting in polarity development. Next to the trans Golgi network, a subapical compartment called SAC or common endosome appears instrumental in regulating these sorting events.
Biochemistry of arsenic detoxification
Authors: Rosen Barry P
Published: October 2002

All living organisms have systems for arsenic detoxification. The common themes are (a) uptake of As(V) in the form of arsenate by phosphate transporters, (b) uptake of As(III) in the form of arsenite by aquaglyceroporins, (c) reduction of As(V) to As(III) by arsenate reductases, and (d) extrusion or sequestration of As(III). While the overall schemes for arsenic resistance are similar in prokaryotes and eukaryotes, some of the specific proteins are the products of separate evolutionary pathways.
Control of complex formation of DNA polymerase α–primase and cell‐free DNA replication by the C‐terminal amino acids of the largest subunit p180
Authors: Smith R.W.P , Nasheuer H.-P
Published: October 2002

DNA polymerase α–primase is a heterotetrameric complex essential for simian vacuolating virus 40 (SV40) DNA replication. We show that the C‐terminal 67 amino acid residues of the human p180 subunit are essential for SV40 DNA replication as they are required for binding of the p68 subunit and play a role in the interaction with the primase subunits, p48 and p58. Furthermore, we demonstrate that exchanging these residues to those of mouse origin can only partially rescue the SV40 DNA replication activity of DNA polymerase α–primase.
Glutamate‐induced calcium increase in myotubes depends on up‐regulation of a sodium‐dependent transporter
Authors: Frank Claudio , Giammarioli Anna Maria , Falzano Loredana , Fiorentini Carla , Rufini Stefano
Published: October 2002

We report a study on the regulation by 2‐chloro adenosine (2CA) of a glutamate (Glu) transporter in myogenic C2C12 cells. Long‐term 2CA exposition significantly increased the V
max of the Glu transporter. Moreover, 2CA‐treated cells responded to Glu challenge by a rapid and transient increase in their intracellular calcium level. The above reported effects were totally abolished by treating C2C12 cells with the Na+‐dependent Glu transporter inhibitors DL‐threo‐b‐hydroxyaspartic acid and L‐trans‐pyrrolidine‐2,4‐dicarboxylic acid. We propose that the possible link between the Glu uptake increase and the Glu induction of calcium rise could be the depolarizing currents carried by Na+ coupled with transporter activity.
Cupiennin 1d*: the cytolytic activity depends on the hydrophobic N‐terminus and is modulated by the polar C‐terminus
Authors: Kuhn-Nentwig Lucia , Dathe Margitta , Walz Alfred , Schaller Johann , Nentwig Wolfgang
Published: October 2002

To investigate structural features modulating the biological activity of cupiennin 1 peptides from the spider Cupiennius salei, three truncated cupiennin 1d analogs were synthesized. The fact that their growth inhibiting effect on Gram‐negative and Gram‐positive bacteria, their lytic activity with human red blood cells and their insecticidal effect on Drosophila melanogaster correlates with structural properties shows that the hydrophobic N‐terminal chain segment includes the major determinants of structure and activity. The polar C‐terminus seems to modulate peptide accumulation at negatively charged cell surfaces via electrostatic interactions and has no important effect on the peptides’ amphipathic secondary structure.
Retinoic acid reduces the cytotoxicity of cyclopentenyl cytosine in neuroblastoma cells
Authors: Bierau Jörgen , van Gennip Albert H , Leen René , Caron Huib N , van Kuilenburg André B.P
Published: October 2002

In this paper, it is demonstrated that all‐trans, 9‐cis and 13‐cis retinoic acid (RA) decreased the sensitivity of SK‐N‐BE(2)c neuroblastoma cells towards the chemotherapeutic agent cyclopentenyl cytosine (CPEC), a potent inhibitor of cytosine‐5′‐triphosphate synthetase. Retinoic acid attenuated CPEC‐induced apoptosis as reflected by a decreased caspase‐3 induction. Retinoic acid decreased the accumulation of CPEC, whereas the salvage of cytidine was strongly increased. Metabolic labeling studies using [3H]uridine showed a strongly decreased biosynthesis of CTP via CTP synthetase. Retinoic acid likely confers resistance of neuroblastoma cells to CPEC in part by slowing down proliferation, and in part by shifting the synthesis of CTP towards the salvage of cytidine, thereby bypassing CTP synthetase.
Foot‐and‐mouth disease virus leader proteinase: a papain‐like enzyme requiring an acidic environment in the active site
Authors: Kronovetr Jakub , Skern Tim
Published: October 2002

Foot‐and‐mouth disease virus leader proteinase (Lpro), a papain‐like cysteine proteinase, has six acidic amino acids between 4 Å and 11 Å of the catalytic dyad of Cys51 and His148. In contrast, in papain and related enzymes, only one acidic residue lies within this distance. We have examined by site‐directed mutagenesis the importance of each of these residues for Lpro self‐processing and cleavage of its cellular substrate, eukaryotic initiation factor 4GI. Only substitution of the electrostatic charge of aspartate 164 affected enzyme activity. Thus, in contrast to the prototype papain, Lpro activity requires a negative charge 4.5 Å from the catalytic dyad.
p38 MAPK mediates the regulation of α1(I) procollagen mRNA levels by TNF‐α and TGF‐β in a cell line of rat hepatic stellate cells1
Authors: Varela-Rey M , Montiel-Duarte C , Osés-Prieto J.A , López-Zabalza M.J , Jaffrèzou J.P , Rojkind M , Iraburu M.J
Published: October 2002

The role of members of the mitogen‐activated protein kinase (MAPK) family on tumor necrosis factor α (TNF‐α)‐mediated down‐regulation of col1a1 gene was studied. TNF‐α increased extracellular‐regulated kinase and Jun‐N‐terminal kinase phosphorylation, but these effects were not related to its inhibitory effect on α1(I) procollagen (col1a1) mRNA levels. Phosphorylation of p38 MAPK was decreased in response to TNF‐α, and the specific p38 MAPK inhibitor SB203580 mimicked the effect of TNF‐α on col1a1 mRNA levels. Transforming growth factor β (TGF‐β) increased p38 MAPK phosphorylation and SB203580 prevented the induction of col1a1 mRNA levels by TGF‐β. These results suggest that p38 MAPK plays an important role in regulating the expression of col1a1 in hepatic stellate cells in response to cytokines.
Progress in the analysis of membrane protein structure and function
Authors: Werten P.J.L. , Rémigy H.-W. , de Groot B.L. , Fotiadis D. , Philippsen A. , Stahlberg H. , Grubmüller H. , Engel A.
Published: October 2002

Structural information on membrane proteins is sparse, yet they represent an important class of proteins that is encoded by about 30% of all genes. Progress has primarily been achieved with bacterial proteins, but efforts to solve the structure of eukaryotic membrane proteins are also increasing. Most of the structures currently available have been obtained by exploiting the power of X‐ray crystallography. Recent results, however, have demonstrated the accuracy of electron crystallography and the imaging power of the atomic force microscope. These instruments allow membrane proteins to be studied while embedded in the bi‐layer, and thus in a functional state. The low signal‐to‐noise ratio of cryo‐electron microscopy is overcome by crystallizing membrane proteins in a two‐dimensional protein–lipid membrane, allowing its atomic structure to be determined. In contrast, the high signal‐to‐noise ratio of atomic force microscopy allows individual protein surfaces to be imaged at sub‐nanometer resolution, and their conformational states to be sampled. This review summarizes the steps in membrane protein structure determination and illuminates recent progress.
Mössbauer studies of Escherichia coli biotin synthase: evidence for reversible interconversion between [2Fe‐2S]2+ and [4Fe‐4S]2+ clusters
Authors: Tse Sum Bui B , Florentin D , Marquet A , Benda R , Trautwein A.X
Published: October 2002

The nature and properties of the iron‐sulphur (Fe‐S) cluster in as‐prepared and reduced biotin synthase of Escherichia coli have been investigated by Mössbauer spectroscopy. Our data clearly demonstrate that in the as‐prepared sample, the cluster is present as [2Fe‐2S]2+ with isomer shift, δ=0.29 mm/s and quadrupole splitting, ΔE
Q=0.53 mm/s, indicating incomplete cysteinyl‐S coordination. Anaerobic reduction by dithionite in the presence of 55% (v/v) glycerol converts this form to [4Fe‐4S]2+ (δ=0.45 mm/s and ΔE
Q=1.11 mm/s) and is accompanied by some destruction to Fe2+. This cluster conversion is reversible and when exposed to air, the [4Fe‐4S]2+ cluster is quantitatively reconverted to the [2Fe‐2S]2+ cluster without any further cluster degradation.
Doses to the Embryo and Fetus from Intakes of Radionuclides by the Mother
Authors: Valentin J.
Published: October 2002

In its Publications 56, 67, 69, 71, and 72, ICRP has provided age-specific biokinetic models and, using those models, compiled dose coefficients (doses per unit intake) for intakes of radionuclides by members of the public. Committed effective doses for the inhalation or ingestion of radionuclides by workers who are occupationally exposed were given in Publication 68 based on the most recent dosimetric and biokinetic models for adults. Additionally, a compilation of dose coefficients for both workers and members of the public has been issued on a CD-ROM.

The present report complements that series by addressing doses to the embryo/fetus after intakes of radionuclides by a female member of the public or a female worker, before or during pregnancy. Ingestion and inhalation of selected radionuclides of the 31 elements for which age-dependent biokinetic models were provided in the previous reports are considered. These elements are H, C, S, Ca, Fe, Co, Ni, Zn, Se, Sr, Zr, Nb, Mo, Tc, Ru, Ag, Sb, Te, I, Cs, Ba, Ce, Pb, Po, Ra, Th, U, Np, Pu, Am, and Cm.

New biokinetic and dosimetric models for calculating doses to the developing embryo and fetus are developed and used in conjunction with the models for infants, children, and adults presented in the previous reports. The models used take account of transfer of radionuclides across the placenta, distribution and retention of radionuclides in fetal tissues, growth of the fetus, and photon irradiation from radionuclides in the placenta and maternal tissues. Human and animal data are used as available in the development of these models. Intake scenarios comprising single or continuous maternal intakes are taken into account in the compilation of effective dose coefficients following ingestion or inhalation of the radionuclides considered. A CD-ROM with more comprehensive information on doses from inhalation of different particle sizes, tissue doses, and doses at various times after birth has been developed concurrently with the report and will be available shortly.

The report does not consider doses to the offspring due to intakes of radionuclides in maternal milk and external irradiation from the mother's body after birth. The radiation sensitivity of the offspring is not discussed.
The current cost of heart failure to the National Health Service in the UK
Authors: Stewart Simon , Jenkins Andrew , Buchan Scot , McGuire Alistair , Capewell Simon , McMurray John J.J.V.
Published: October 2002

We have recently shown that heart failure admission rates continue to increase in the UK — particularly in older age groups. As hospital activity represents the major cost component of healthcare expenditure related to heart failure, this study evaluated the current cost of this syndrome to the National Health Service (NHS) in the UK. We applied contemporary estimates of healthcare activity associated with heart failure to the whole UK population on an age and sex‐specific basis to calculate its cost to the NHS for the year 1995. Direct components of healthcare included in these estimates were hospital admissions associated with a principal diagnosis of heart failure, associated outpatient consultations, general practice consultations and prescribed drug therapy. We also calculated the cost of nursing‐home care following a primary heart failure admission and the cost of hospitalisations associated with a secondary diagnosis of heart failure. Adjusting for probable increases in hospital activity and the progressive ageing of the UK population, we have also projected the cost of heart failure to the NHS for the year 2000. We estimated that there were 988000 individuals requiring treatment for heart failure in the UK during 1995. The ‘direct’ cost of healthcare for these patients was estimated to be £716 million, or 1.83% of total NHS expenditure. Hospitalisations and drug prescriptions accounted for 69 and 18% of this expenditure, respectively. The additional costs associated with long‐term nursing home care and secondary heart failure admissions accounted for a further £751 million (2.0% of total NHS expenditure). By the year 2000, we estimated that the combined total direct cost of heart failure would have risen to £905 million — equivalent to 1.91% of total NHS expenditure. Using well‐validated sets of data, these findings re‐confirm the importance of heart failure as a major public health problem in the UK. The annual direct cost of heart failure to the NHS in 2000 is likely to be of the order of 1.9% of total expenditure — the predominant cost component being hospitalisation.
The addition of pentoxifylline to conventional therapy improves outcome in patients with peripartum cardiomyopathy
Authors: Sliwa Karen , Skudicky Daniel , Candy Geoffrey , Bergemann Anette , Hopley Mark , Sareli Pinhas
Published: October 2002

We have reported previously that despite treatment with angiotensin‐converting enzyme inhibitors and β blockers, the outcome of patients with peripartum cardiomyopathy (PPC) remains unfavorable. Similar to other etiologies of left ventricular dysfunction, we found elevated levels of tumor necrosis factor‐α (TNF‐α) in this group of patients. In the present study we sought to evaluate the effects of pentoxifylline, a drug known to inhibit the production of TNF‐α, on clinical status, left ventricular function, and circulating plasma levels of TNF‐α, in patients with PPC. We followed prospectively 59 consecutive women with PPC. The first 29 patients (group 1) were treated with diuretics, digoxin, enalapril and carvedilol. The next 30 consecutive patients (group 2) received pentoxifylline 400 mg TID in addition to the previous therapy. Clinical evaluation, echocardiograms and TNF‐α determinations were performed at baseline and after 6 months of treatment. Patients in the pentoxifylline group were older and had a higher E/A ratio. Nine patients died (eight in group 1, P‐0.009 between groups). A combined end‐point of poor outcome defined as either death, failure to improve the left ventricular ejection fraction >10 absolute points or functional class III or IV at latest follow‐up, occurred in 52% of patients in group 1 and 27% of patients in group 2 (P‐0.03). Treatment with pentoxifylline (P‐0.04) was the only independent predictor of outcome. In conclusion, the results of this study suggest that the addition of pentoxifylline to conventional treatment, improves outcome in patients with peripartum cardiomyopathy.
SHARED RESPONSIBILITY IN HOME BIRTH PRACTICE: COLLABORATING WITH CLIENTS
Authors: Bailes Alice , Jackson Marsha E.
Published: October 2002

The home setting not only provides a special environment for birth and the practice of midwifery, but also has an impact on the processes used in clinical decision making. This article focuses on collaboration between the midwife and the birthing woman and also discusses the collaborative relationship between midwives and obstetric consultants. A home birth case study illustrates the interactions among the midwife, the woman, and the medical system. These critical relationships provide structure for safe, effective clinical practice in planned home birth when practice boundaries are not defined by institutional walls.
Diabetes in Pregnancy: The Midwifery Role in Management
Authors: Avery Melissa D.
Published: October 2002

Although the primary focus of midwifery is on uncomplicated pregnancy, all midwives must screen for and, in some cases, comanage the care of women with diabetes mellitus and gestational diabetes. This article will review the types of diabetes, implications for preconceptional and pregnancy care, the changing recommendations relative to diabetes in pregnancy, and the role of the midwife in providing antepartal and intrapartal care for women with diabetes in collaboration with other health care professionals and in accordance with the philosophy and standards of the American College of Nurse‐Midwives. A specific case study will highlight the role of the midwife, with an overall focus on medical consultation, collaboration, and referral, as well as client involvement in the planning of care.
Dipole and rotational strengths for overtone transitions of a C2-symmetry HCCH molecular fragment using Van Vleck perturbation theory
Authors: Abbate Sergio , Gangemi Roberto , Longhi Giovanna
Published: October 2002

Contact transformation theory up to second order is employed to treat CH-stretching overtone transitions and to calculate dipole and rotational strengths. A general Hamiltonian describing two interacting CH-stretching oscillators is considered, and the Darling–Dennison resonance is appropriately taken into account. The two CH bonds are supposed to be dissymmetrically disposed, so as to represent a chiral HCCH fragment, endowed with C2 symmetry. Analytical expressions of transition moments and dipole and rotational strengths are given in the hypothesis of general electric and magnetic dipole moments with quadratic dependence on coordinates and momenta. Dipole and rotational strengths are then calculated together with frequencies for the fundamental and first three overtone regions in the simplifying hypothesis of the valence optical approach on the coupled-oscillator framework. Simplified analytical expressions thereof in the relevant parameters are presented.
Numerical canonical transformation approach to quantum many-body problems
Authors: White Steven R.
Published: October 2002

We present a new approach for numerical solutions of ab initio quantum chemistry systems. The main idea of the approach, which we call canonical diagonalization, is to diagonalize directly the second-quantized Hamiltonian by a sequence of numerical canonical transformations.
Breakdown of the singlet and triplet nature of electronic states of the superheavy element 114 dihydride (114H2)
Authors: Balasubramanian K.
Published: October 2002

It is demonstrated that the superheavy element (114) forms a dihydride with electronic features that exhibit breakdown of the conventional singlet (X1A1) and triplet (3B1) states due to large relativistic effects including spin–orbit effects. The A11 state is shown to undergo avoided crossing with the B31(A1) state and other states in the C2v2 double group. We have carried out relativistic complete active-space multiconfiguration interaction followed by multireference configuration interaction computations including spin–orbit effects that included several million configurations including 6d electron correlations for the electronic states of the superheavy element (114)H2. The potential energy curves of both ground and excited states are computed including electron correlation and spin–orbit effects simultaneously. The curves exhibit unusual features from their traditional nonrelativistic counterparts: namely, A11, B31, and B11 states due to spin–orbit coupling. The spin–orbit effects are shown to destabilize (114)H2 by almost 2.6 eV.
Classical and quasi-classical trajectory calculations of isotope exchange and ozone formation proceeding through O+O2 collision complexes
Authors: Baker Thomas A. , Gellene Gregory I.
Published: October 2002

The isotope exchange reaction, and the three-body ozone formation rate proceeding through an ozone complex, have been studied by classical and quasi-classical trajectory techniques. The exchange rate studies indicate that the rate of this reaction is dominantly sensitive to the O+O2 entrance channel characteristics of the potential energy surface. A detailed consideration of the dynamics of the intermediate ozone complex reveals three important classes. In one class, the complex adopts an ozonelike geometry, largely undergoing asymmetric stretchinglike motion until it dissociates. In a second class, the oxygen atom and molecule never visit the ozonelike geometry but rather remain separated by relatively large distances trapped near the angular momentum barrier in the entrance channel of a pseudo-effective potential. These complexes, which cannot undergo exchange, are, nevertheless, found to contribute significantly to ozone formation at high density of the third body suggesting that the association of the high-density effective formation rate constant with twice the exchange rate may not be valid. The third class can be considered a hybrid of the first two, spending some time as an ozonelike complex and some time as a large atom-diatomic complex. This third class provides a mechanism for rearranging atom locations in the complex (e.g., end and middle position swapping) and, consequently, would not be well accounted for by statistical treatments of the ozone complex based on a single ozonelike reference geometry. In general, the survival time distributions of the complexes are found to be nonexponential. However, when the detailed survival time distributions are coupled with a Lennard-Jones collision model for the stabilization step, the experimental ozone formation rate can be adequately modeled over a broad range of temperature and density.
Predissociations in u+ and 1g states of K2
Authors: Bergeman T. , Julienne P. S. , Williams C. J. , Tiesinga E. , Manaa M. R. , Wang H. , Gould P. L. , Stwalley W. C.
Published: October 2002

Recently Wang, Gould, and Stwalley [Phys. Rev. Lett. 80, 476 (1998)] showed by exciting atomic fragments that predissociation occurs in the 1g and 0u+ states of K2. In this study, we supplement the interpretation given in the original report with a more detailed discussion. The calculations presented here use discrete variable representation, close coupling, and semiclassical methods, and incorporate an ab initio calculation of diagonal and off-diagonal spin–orbit elements. The predicted predissociation widths for the 1g state are too narrow to be observed directly, but may be correlated with the strength of the spectral lines observed by exciting atomic fragments. The missing v=90 level of the 1g state in the observed fragmentation spectrum, where the predissociation rate is calculated to be nearly maximum, is attributed to a node in the absorption line strength close to this vibrational level. Since the available information on K2 electronic states (despite recent progress) gives inadequate information on the inner walls of the A state and especially of the b state, calculations of predissociation in the 0u+ state can give only a range of possible widths. We fit widths to 0u+ spectral lines observed by monitoring trap loss. The fitted experimental widths are significantly larger than the maximum calculated predissociation widths, suggesting that there was line broadening associated with the laser power required for the observation.
Interactions of a conjugated molecular diode with small metal clusters of Cu, Ag, and Au: First-principles calculations
Authors: Majumder Chiranjib , Briere Tina , Mizuseki Hiroshi , Kawazoe Yoshiyuki
Published: October 2002

The geometries and electronic structures of a thiol-terminated molecular diode interacting with group-11 metal clusters (Cu, Ag, Au) have been investigated using density functional theory with a hybrid exchange-correlation energy functional. The charge transfer and bonding nature at the metal-molecule interface are illustrated from natural bond orbital analysis. The metal-sulfur bonds are found to be directional, and the charge transfer is localized along the bond. The extent of charge transfer to the terminal sulfur is higher for bonding with Cu and Ag (∼0.40) than with Au (∼0.17). The electronic conduction across the molecular diode has been analyzed from the change in the electronic structure and the shape of the molecular orbitals of the free molecule and metal-molecule complexes. The results suggest that while the inclusion of Au scarcely affects the unoccupied molecular orbitals, the effect is more pronounced in the cases of Cu and Ag. The threshold energy for conduction estimated for these metal-molecule complexes indicates a higher required bias voltage for Au than for Cu and Ag.
Photodissociation of carbonic dibromide at 267 nm: Observation of three-body dissociation and molecular elimination of Br2
Authors: Xu Dadong , Huang Jianhua , Francisco Joseph S. , Hansen Jaron C. , Jackson William M.
Published: October 2002

The photodissociation of Br2CO around 267 nm has been studied by time-of-flight mass spectroscopy and ion velocity imaging. The atomic (Br and Br*) and molecular products (Br2 and BrCO) are detected via multiphoton ionization with the same laser. The results show that the molecule dissociates into (1) Br(fast)+Br(slow)+CO via an asynchronously concerted three-body decay process for both ground and spin–orbit excited bromine atoms, (2) BrCO(A)+Br, and (3) Br2+CO, the molecular elimination channel. The translational energy distributions of bromine atoms from reaction (1) are bimodal. For both spin–orbit states the anisotropy parameters differ clearly for slow and fast bromine atoms, where the β values for slow bromine atoms decrease relative to those for fast atoms. The β values for the Br2 elimination channel almost reach the low limit of −1. Taking into account the translational energy and angular distributions of these reactions, an asynchronously concerted decay mechanism could be proposed for the three-body dissociation. It is concluded that the transition dipole moment is in the direction perpendicular to the C=O bond in the initial excitation, which is also consistent with all the observations for reactions (2) and (3).
Electron solvation in aqueous reverse micelles: Equilibrium properties
Authors: Laria Daniel , Kapral Raymond
Published: October 2002

Microscopic aspects of electron solvation in aqueous reverse micelles are investigated using molecular dynamics simulation techniques. Two micelle sizes, with water/surfactant ratios of 3 and 7.5, are examined. The electron is treated quantum mechanically using Feynman path integral methods while the water, surfactant head groups, and counter ions are treated classically. Through computations of the free energy as a function of the radial distance, the electron is found to be preferentially solvated in the interior of the micelle in the “bulk” water pool. For small micelles, the presence of the electron leads to a depletion of water in the central region of the micelle and thus strongly disrupts the water equilibrium structure. Contact and solvent-separated ion pairs between the electron and Na+ counter ions are found to play an important role in the equilibrium structure. For the two micelle sizes investigated, the most stable solvation structures correspond to contact ion pairs. The localization of the electronic charge distribution is found to increase with micelle size, signaling more efficient solvation in larger micelles.
Engineering the nanocrystalline structure of TiO2 films by aerodynamically filtered cluster deposition
Authors: Barborini E. , Kholmanov I. N. , Piseri P. , Ducati C. , Bottani C. E. , Milani P.
Published: October 2002

We have produced nanocrystalline titanium dioxide films with different structures (anatase or rutile) by depositing mass selected clusters from the gas phase. Nanoparticles are produced by a pulsed microplasma cluster source and are selected by aerodynamic separation effects. We have characterized nanocrystalline films by Raman spectromicroscopy and transmission electron microscopy, showing that the films assembled with very small clusters have a predominant rutile phase, whereas larger clusters form films with anatase structure. Our observations suggest that phonon confinement effects are responsible for a significant shift and broadening observed for the Raman peaks.
Electrical measurements of a dithiolated electronic molecule via conducting atomic force microscopy
Authors: Rawlett Adam M. , Hopson Theresa J. , Nagahara Larry A. , Tsui Raymond K. , Ramachandran Ganesh K. , Lindsay Stuart M.
Published: October 2002

We describe a method of measuring the electrical properties of a molecule via conducting atomic force microscopy (AFM). A dithiolated molecule is chemically inserted into defect sites in an insulating self-assembled monolayer formed on an epitaxial Au substrate and the top thiol terminus of the molecule is reacted with a Au nanoparticle. A Au-coated AFM probe is used to contact the molecule through the nanoparticle, thus electrical data can be obtained. We report preliminary transport measurements of two test molecules. Our data shows qualitative agreement with previously published results for similar molecules deposited in a nanopore containing approximately a thousand molecules. This work indicates that the measured negative differential resistance is not an intermolecular phenomenon.
Comparative study of drain-current collapse in AlGaN/GaN high-electron-mobility transistors on sapphire and semi-insulating SiC
Authors: Arulkumaran S. , Egawa T. , Ishikawa H. , Jimbo T.
Published: October 2002

The drain-current collapse at high drain voltage has been studied in AlGaN/GaN high-electron-mobility transistors (HEMTs) on both semi-insulating (SI)–SiC and sapphire substrates using small frequency (120 Hz) sinusoidal wave superimposed dc IDS–VDS characteristics. Low drain-current collapses were observed in AlGaN/GaN HEMTs on SI–SiC substrate when compared with the HEMTs on sapphire substrates. Two and three thermally activated deep traps were observed on SiC-based and sapphire-based HEMTs, respectively. The existence of an additional deep trap (ΔE=0.61 eV) could be associated with the material defects/ dislocations responsible for the severe drain current collapse in sapphire-based HEMTs. The white-light illuminated IDS–VDS characteristics support the existence of more number of deep traps in the sapphire-based HEMTs.
Size and location control of Si nanocrystals at ion beam synthesis in thin SiO2 films
Authors: Müller Torsten , Heinig Karl-Heinz , Möller Wolfhard
Published: October 2002

Binary collision simulations of high-fluence 1 keV Si+ ion implantation into 8-nm-thick SiO2 films on (001)Si were combined with kinetic Monte Carlo simulations of Si nanocrystal (NC) formation by phase separation during annealing. For nonvolatile memory applications, these simulations help to control the size and location of NCs. For low concentrations of implanted Si, NCs form via nucleation, growth, and Ostwald ripening, whereas for high concentrations Si separates by spinodal decomposition. In both regimes, NCs form above a thin NC free-oxide layer at the SiO2/Si interface. This, self-adjusted layer has just a thickness appropriate for NC charging by direct electron tunneling. Only in the nucleation regime the width of the tunneling oxide and the mean NC diameter remain constant during a long annealing period. This behavior originates from the competition of Ostwald ripening and Si loss to the Si/SiO2 interface. The process simulations predict that, for nonvolatile memories, the technological demands on NC synthesis are fulfilled best in the nucleation regime.
Microcontact printing of catalytic nanoparticles for selective electroless deposition of metals on nonplanar polymeric substrates
Authors: Ng W. K. , Wu L. , Moran P. M.
Published: October 2002

Metal patterns on polymeric substrates have been produced by microcontact printing of catalytic particles and subsequent electroless plating. These patterns include lines as narrow as 1 μm. The printing process consists of coating the surface of a stamp with polymer-stabilized catalytic nanoparticles, molding a polymer substrate against the stamp, cooling or curing the polymer, and separating the stamp from the polymer. During separation, the nanoparticles are selectively transferred to the polymer, seeding the polymer surface for selective electroless plating. Since the process does not require the substrate surface to be chemically modified prior to stamping, the polymer can be molded to the shape of the stamp, thereby allowing the formation of conformal or buried circuitry using this technique.
High temperature stability of Al2O3 dielectrics on Si: Interfacial metal diffusion and mobility degradation
Authors: Guha S. , Gusev E. P. , Okorn-Schmidt H. , Copel M. , Ragnarsson L.-Å , Bojarczuk N. A. , Ronsheim P.
Published: October 2002

We have examined the stability of Al2O3/Si heterostructures and show that significant Al diffusion occurs into the silicon for temperatures of 1000 °C and more. This may be caused by dissociation of small quantities of Al2O3 and subsequent dissolution of the Al into the silicon. Such diffusion may be reduced, though not eliminated via an interfacial silicon oxynitride diffusion barrier. Using long channel metal gate Al2O3/Si n field effect transistor data, we show that anneals at 1000 °C result in a degradation of the electron mobility by a factor of 2.
Physical aging in a hyperquenched glass
Authors: Yue Y. Z. , Jensen S. L. , deC. Christiansen J.
Published: October 2002

We report experimental data on the enthalpy relaxation of a hyperquenched silicate glass subjected to long-time aging (annealing) below the glass-transition temperature (Tg). The relaxation of a hyperquenched glass substantially differs from that of a normally cooled glass. Two mechanisms govern the relaxation of a hyperquenched glass. During relaxation of the first hyperquenched, and afterward aged glass, a relaxation endotherm occurs followed by an exotherm. This is reflected by the occurrence of crossover. By increasing the aging temperature and time, the endotherm becomes more pronounced, while the exotherm gradually disappears. The consequence of this is the shift of the crossover point to higher temperature. The relaxation of the hyperquenched glass at 0.66Tg with the aging time is highly nonexponential.
Linewidth enhancement factor in 1.3 μm GaAsSb type-II quantum-well lasers
Authors: Schlichenmaier C. , Koch S. W. , Chow W. W.
Published: October 2002

The antiguiding or linewidth enhancement factor α is computed microscopically for a series of type-II GaAsSb/GaInAs/GaAs quantum-well structures. The results predict α values below unity at peak gain suggesting highly stable laser operation with excellent linewidth properties.
Temporal and thermal studies of charge transportation in self-assembly organic photovoltaic devices
Authors: Ghebremichael F.
Published: October 2002

The charge transport of holes injected into organic nanostructure photovoltaic devices using the third harmonic of a pulsed infrared laser was studied. The devices were fabricated using the electrostatic self-assembly technique. From temporal and thermal time-of-flight studies, we determined the drift mobility to be in the range of 10−7–10−6 cm2/(V s) in 120 nm thick films. A model was adopted that accounts for the Pool–Freknel type effects to characterize the devices, including the electric-field coefficient and the activation energy. Using similar techniques, fill factor of 0.34±0.02 at 1 mW/cm2 intensity was determined for the devices.
Vapor sensing with α,ω-dihexylquarterthiophene field-effect transistors: The role of grain boundaries
Authors: Someya Takao , Katz Howard E. , Gelperin Alan , Lovinger Andrew J. , Dodabalapur Ananth
Published: October 2002

We have investigated the channel-length dependence of responses to a vapor analyte with a series of α,ω-dihexylquarterthiophene (DHα4T) field-effect transistors (FETs). Single-crystalline DHα4T devices deposited by vacuum sublimation at substrate temperatures of 70 °C are compared with polycrystalline DHα4T films deposited at room temperature. By changing the length of FET channels and/or the size of polymer grains, the number of grain boundaries per device is changed systematically. A larger response to vapor analyte is obtained by increasing the number of grain boundaries per device, showing that vapor sensing occurs mainly at grain boundaries.
Vesicle adsorption on SiO2 and TiO2: Dependence on vesicle size
Authors: Reimhult Erik , Höök Fredrik , Kasemo Bengt
Published: October 2002

Kinetics of vesicle adsorption on SiO2 and TiO2 surfaces was investigated for vesicle sizes from 25 to 200 nm. On SiO2, nonruptured vesicles are adsorbed up to a critical coverage, Θc, after which spontaneous rupture and bilayer formation occurs in qualitatively the same manner for all vesicle sizes. On TiO2, adsorption of nonruptured vesicles continues up to saturation. A comparison between the kinetics at low coverages on SiO2 and TiO2, where intact vesicles adsorb on both surfaces, reveals that the vesicles on SiO2 are more flattened than nonruptured vesicles adsorbed on TiO2, indicating a stronger vesicle-surface interaction on SiO2.
Theoretical evidence for the kick-out mechanism for B diffusion in SiC
Authors: Rurali R. , Godignon P. , Rebollo J. , Ordejón P. , Hernández E.
Published: October 2002

In this letter, we analyze by means of first-principles electronic structure calculations the diffusion of B impurities in 3C-SiC. We find, through molecular dynamics, that substitutional B at a Si lattice site is readily displaced by a nearby Si interstitial by the process known as a kick-out mechanism, in agreement with recent experimental results. This is in contrast to the situation in Si, where B has recently been shown to diffuse via an interstitialcy mechanism.
Improvement of efficiency and color purity utilizing two-step energy transfer for red organic light-emitting devices
Authors: Feng Jing , Li Feng , Gao Wenbao , Cheng Gang , Xie Wenfa , Liu Shiyong
Published: October 2002

We present organic red light-emitting devices with improved optical and electrical characteristics utilizing the two-step energy transfer. N,N′-diphenyl-N,N′-bis(1-naphthyl)-(1,1′-biphenyl)-4,4′-diamine and tris-(8-hydroxyquinoline) aluminum (Alq) are used as hole and electron-transporting layers, respectively. Quinacridone (QAD) and 4-(dicyanomethylene)-2-t- butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) are codoped into the Alq emitting layer. Compared with devices where the emitting layer is only composed of Alq and DCJTB, the emitting characteristics such as emission efficiency and purity of emission color are greatly improved, and the turn-on voltage is decreased as much as 4 V. We attribute these improvements to the assistant dopant (QAD), which leads to the more efficient energy transfer from Alq to DCJTB.