bluuebunny/crossref_metadata_2025 huggingface dataset:
DEFAULTABLE DEBT PRICING IN MULTI-FACTOR MODELS
Authors: LIM K. G. , CHANG SHIWEI , CHONG TSUI KAI
Published: November 2002

This paper employs the structural approach to study defaultable debt pricing under multi-factor models. We extend existing results under the structural approach in two directions. By incorporating multiple factors, we can capture the impact of other economic variables on the debt prices apart from the interest rate factor. In our approach, we provide credit spread pricing using both the real interest rate and inflation rate as state variables. We also extend the analyses to a more general default boundary. In our paper we assume that default happens when the firm value hits a given fraction of the corresponding risk-free debt for the first time. This is also the recovery rate of the defaulted debt. Analytical solutions for both the case of constant recovery rate and the extended case of recovery rate being a deterministic function of time in the multi-factor models are provided in our study. We also provide comparison of the performance of our model with other relevant credit spread models.
MARKET POWER AND FEEDBACK EFFECTS FROM HEDGING DERIVATIVES
Authors: DE MATOS JOÃO AMARO , DO ROSÁRIO JOÃO SOBRAL
Published: November 2002

In this paper we model how the transaction of derivatives affects the price process of the underlying asset, considering the existence of a few agents with market power and a population of liquidity traders. This setting generates an equilibrium bid-ask spread for the underlying asset. The resulting feedback effect of hedging strategies is shown to depend on what type of agent more actively hedges. We also characterize how the feedback effect is lessened as the number of market-makers increases.
MAXIMUM LIKELIHOOD EQUILIBRIA IN GAMES WITH POPULATION UNCERTAINTY
Authors: VOORNEVELD MARK
Published: December 2002

In the games with population uncertainty introduced in this paper, the number and identity of the participating players is determined by chance. Games with population uncertainty are shown to include Poisson games, random player games, and random games. The paper focuses on those strategy profiles that are most likely to yield a Nash equilibrium in the game selected by chance. Existence of maximum likelihood equilibria is established under mild topological conditions.
A RELATION BETWEEN NASH EQUILIBRIA AND CORRELATED EQUILIBRIA
Authors: HENDRICKX RUUD , PEETERS RONALD , POTTERS JOS
Published: December 2002

In this paper we investigate the set of correlated equilibria of bimatrix games. These equilibria are interesting, because they can result in outcome profiles that are not feasible as a result of Nash equilibria. After giving an example to illustrate the various concepts, we present a Projection Theorem which relates the two types of equilibria. Some lemmas are provided to clarify and extend this theorem.
TECHNOLOGICAL FAILURE, ECONOMIC SUCCESS
Authors: HALLER HANS , PAVLOPOULOS ANTHONY
Published: December 2002

A research lab has private information about failed test results. There is a finite group of potential participants in a patent race to whom this information is valuable, since it reduces research costs. The lab acts as a Stackelberg leader in a strategic game of informational rent extraction. The lab's optimum is also (constrained) socially optimal in that the lab sells all its information to all the firms. Posting a uniform per unit (per test result) price suffices to achieve that outcome.
ABSENT–MINDED DRIVERS IN THE LAB: TESTING GILBOA'S MODEL
Authors: HUCK STEFFEN , MÜLLER WIELAND
Published: December 2002

This note contributes to the discussion of decision problems with imperfect recall from an empirical point of view. We argue that, using standard methods of experimental economics, it is impossible to induce (or control for) absent–mindedness of subjects. Nevertheless, it is possible to test Gilboa's (1997) agent–based approach to games with imperfect recall. We implement his model of the absent–minded driver problem in an experiment and find, if subjects are repeatedly randomly rematched, strong support for the equilibrium prediction which coincides with Piccione and Rubinstein's (1997) ex ante solution of the driver's problem.
ON THE SURVIVAL OF COOPERATION UNDER DIFFERENT MATCHING SCHEMES
Authors: JONARD NICOLAS
Published: December 2002

In this note, the persistence of cooperation in the standard Prisoner's Dilemma is examined under five distinct matching mechanisms. The general model is a birth-and-death process, which is studied using a simple direct method and the mutation-counting technique. Mean matching is discussed first, before two variants of random matching and viscosity are analyzed. Finally payoff assortative matching is considered. In all five cases the stochastic stability of the absorbing sets of the evolutionary process is examined; assortative matching is shown to sustain significant amounts of cooperation.
COMPLEMENTARITY, SUBSTITUTABILITY AND STRATEGIC ACCUMULATION OF CAPITAL
Authors: FIGUIERES CHARLES
Published: December 2002

The preemptive role of capital is analyzed in a class of differential games of capital accumulation with reversible investment for two symmetric players. Two dynamic concepts of interaction are defined: feedback substitutability and feedback complementarity. These concepts are useful for exploring the dynamic properties of the stocks. In particular it is proved that if the equilibrium of the game is characterized by feedback substitutability, the firm with the higher initial condition overshoots his long-run level of capital.
Determinants of Notch-3 Receptor Expression and Signaling in Vascular Smooth Muscle Cells
Authors: Campos Alexandre H. , Wang Wenli , Pollman Matthew J. , Gibbons Gary H.
Published: November 2002

The Notch family of receptors and ligands plays an important role in cell fate determination, vasculogenesis, and organogenesis. Mutations of the Notch-3 receptor result in an arteriopathy that predisposes to early-onset stroke. However, the functional role of the Notch signaling pathway in adult vascular smooth muscle cells (VSMCs) is poorly characterized. This study documents that the Notch-3 receptor, the ligand Jagged-1, and the downstream transcription factor, HESR-1, are expressed in the normal adult rat carotid artery, and that this expression is modulated after vascular injury. In cultured VSMCs, both angiotensin II and platelet-derived growth factor (PDGF) markedly downregulated Notch-3 and Jagged-1 through ERK-dependent signaling mechanisms and prevented the glycosylation of Jagged-1. The downregulation of Jagged-1 and Notch-3 was associated with a decrease in CBF-1–mediated gene transcription activation and a fall in the mRNA levels of the downstream target transcription factor HESR-1. To test the hypothesis that the Notch pathway was coupled to growth regulation, we generated VSMC lines overexpressing the constitutively active form of Notch-3 (A7r5-N3IC). These cells exhibited a biphasic growth behavior in which the growth rate was retarded during the subconfluent phase and failed to decelerate at postconfluence. The lack of cell-cycle arrest in postconfluent A7r5-N3IC was associated with an attenuated upregulation of the cell-cycle inhibitor p27
kip
relative to control cells. This study documents the regulation of the Jagged-1 and Notch-3 genes in VSMCs by growth factor stimulation as well as a role for Notch-3 as a determinant of VSMC growth.
Growing by Leaps and Inches: Creative Destruction, Real Cost Reduction, and Inching Up
Authors: Darby Michael R. , Zucker Lynne G.
Published: November 2002

Most firms achieve perfective progress, incrementally improving commodities or productivity. But technological progress is concentrated in a few firms achieving metamorphic progress: forming or transforming industries with technological breakthroughs (e.g., biotechnology, lasers, semiconductors, nanotechnology). Unless congruent with incumbents' science and technology base, metamorphic progress promotes entry. Scientific breakthroughs embodied in discovering scientists, protected by natural excludability and transferred by learning‐by‐doing‐with at the bench generally drive metamorphic progress. Embodied knowledge is rivalrous and leads to entry and industry dominance by star scientist–linked firms. Incorporating this scientific entrepreneurial process is essential to improving—if not transforming—endogenous growth models.
European Business Cycles: New Indices and Their Synchronicity
Authors: Dueker Michael , Wesche Katrin
Published: November 2002

This article presents a new business cycle index that allows for cycle‐to‐cycle comparisons of the depth of recessions within a country, cross‐country comparisons of business cycle correlation, and simple aggregation to arrive at a measure of a European business cycle. The data augmentation implied by Gibbs sampling generates posterior distributions for a latent coincident business cycle index. Subsample correlations between an aggregated “Europe” index and the national business cycle indices from France, Germany, and Italy are consistent with the claim that the European economies are becoming more harmonized.
Are Consumption and Government Expenditures Substitutes or Complements? Morishima Elasticity Estimates from the Fourier Flexible Form
Authors: Fleissig Adrian R. , Rossana Robert J.
Published: November 2002

This article provides estimates of Morishima elasticities of substitution between private consumption expenditures (nondurable goods, services, and the stock of durable goods) and government expenditures (federal defense expenditures, federal nondefense expenditures, and state and local expenditures), finding consistent evidence that private consumption and government expenditures are net Morishima substitutes. Elasticities of substitution vary over our sample period, estimated elasticities are generally asymmetric, and short‐run elasticity estimates differ from unity. In the long run, substitution elasticities remain asymmetric and vary over time. Our estimates are free of arbitrary functional form assumptions that can bias statistical inferences arising from our optimization model.
Changes in Income Concentration: Taxes or Macroeconomic Conditions?
Authors: Bruce Donald , Tuttle M. H. , Garrison Charles B.
Published: November 2002

We examine the relative importance of tax rates and macroeconomic fluctuations in explaining the share of national adjusted gross income (AGI) reported by the top 0.5% of all taxpayers. Results indicate that cutting the top income or capital gains tax rate would increase the top AGI share but not by enough to increase revenues. The preponderance of evidence suggests that the top AGI share is affected more by the capital gains tax rate than by the income tax rate but that real gross domestic product fluctuations have even larger effects.
Until Death Do You Part: The Effects of Unilateral Divorce on Spousal Homicides
Authors: Dee Thomas S.
Published: November 2002

This study examines how the widespread adoption of unilateral divorce influenced the prevalence of lethal spousal violence in the United States. These evaluations are based on fixed‐effects specifications for spousal homicide counts from an annual panel of U.S. states from 1968 to 1978. The results indicate that unrestricted unilateral divorce laws had small and statistically insignificant effects on the amount of lethal spousal violence directed against wives. However, the easy access to divorce created by such laws increased spousal homicides of husbands by approximately 21%. These increases were concentrated in states where the division of marital property favored husbands.
On the Nature of Fair Behavior
Authors: Falk Armin , Fehr Ernst , Fischbacher Urs
Published: November 2002

This article shows that identical offers in an ultimatum game generate systematically different rejection rates depending on the other offers that are available to the proposer. This result casts doubt on the consequentialist practice in economics to define the utility of an action solely in terms of the consequences of the action irrespective of the set of alternatives. It means in particular that negatively reciprocal behavior cannot be fully captured by equity models that are exclusively based on preferences over the distribution of material payoffs.
Ex Ante versus Ex Post Optimal Promotion Rules: The Case of Internal Promotion
Authors: Waldman Michael
Published: November 2002

A firm deciding on its promotion practices will be concerned both with the efficient assignment of workers to tasks and with rewarding prior performance. This can result in a time‐inconsistency problem because the promotion rule that is optimal at the time of the promotion decision may differ from the rule that is optimal before performance is determined. In this article I explore the role of time inconsistency in determining promotion practices. In particular, I show that the common practice of favoring internal candidates for promotion can be understood as a response by firms to the problem of time inconsistency.
A Production Theory Approach to the Imports and Wage Inequality Nexus
Authors: Tombazos Christis G.
Published: November 2002

I employ a production theory approach to investigate the effect of fluctuations in the prices of imports of different origin on the wage differential between skilled and unskilled labor in the United States. Unlike competing methodologies, the employed framework of analysis accounts for the economy‐wide effects of imports that derive from both domestic output substitution as well as downstream production. The results of this study suggest that the overall impact of imports, including those that originate in less developed economies, on the wage differential is negligible. Economy‐wide dynamic processes of capital accumulation and technical change appear to play a far more important role in wage dispersion.
Examining Equality between Public‐ and Private‐Sector Wage Distributions
Authors: Bender Keith A.
Published: November 2002

Most comparability studies examine average pay differences, but this article explores differences in the distribution of public‐ and private‐sector wages. Applying a new type of decomposition method, the results indicate that the difference in average wages is only a small part of wage incomparability, whereas differences in the variance of the differential are a much more important factor explaining incomparability. Further results find that differences in wage structure and unobservable factors determining wages have distinct effects in different parts of the wage distribution.
Nontariff Barriers and Trade Liberalization
Authors: Anderson Simon P. , Schmitt Nicolas
Published: November 2002

This article shows that governments have no incentive to introduce nontariff barriers (NTBs) when they are free to set tariffs but they do when tariffs are determined cooperatively. Quotas are preferred to antidumping restrictions so that the model is consistent with a progression from using tariffs only to quotas and then to antidumping constraints (when quotas are eliminated). There is a corresponding narrowing of the range of industries affected by trade restrictions. Simulating the model, the degree of tariff liberalization and of replacement of tariffs by NTBs are shown to depend on industry characteristics in line with stylized facts.
Price and Enforcement Effects on Cocaine and Marijuana Demand
Authors: DeSimone Jeff , Farrelly Matthew C.
Published: November 2002

This article estimates equations for past year cocaine and marijuana use among adult and juvenile respondents of the 1990–97 National Household Surveys on Drug Abuse. Unlike most previous studies, we control for the monetary price of marijuana, probabilities of arrest for marijuana and cocaine possession, and state fixed effects. Results indicate that cocaine prices are inversely related to adult cocaine and marijuana demand but are unrelated to juvenile drug demand, marijuana price effects are always statistically insignificant, estimated price effects are inflated when state effects are omitted, and increases in each arrest probability diminish both types of drug use.
Pressure-induced phase transitions of piezoelectric single crystals from the langasite family: La3Nb0.5Ga5.5O14 and La3Ta0.5Ga5.5O14
Authors: Pavlovska A. , Werner S. , Maximov B. , Mill B.
Published: November 2002

The hydrostatic compression of piezoelectric single crystals of La3Nb0.5Ga5.5O14 (LNG) and La3Ta0.5Ga5.5O14 (LTG) was studied at pressures of up to 23 GPa in diamond-anvil high-pressure cells using single-crystal X-ray diffraction techniques. The reflection-intensity data for LNG and LTG were collected at pressures of up to 22.8 GPa and 16.7 GPa, respectively. Both compounds show anisotropic behaviour under pressure, which is caused by differences in bonding parallel to the a and c directions. The compression of strongly rigid structures leads to increasing internal strains and results, at pressures of 12.4 (3) GPa for LNG and 11.7 (3) GPa for LTG, in a transition to lower symmetry. The compressibilities along the c axis are almost the same for LNG and LTG through the whole investigated pressure range. In contrast, the pressure dependencies of the a axis of these materials are similar only for the initial phase, and the axial compressibilities for the high-pressure polymorphs of LNG and LTG are significantly different to each other. The volume compressibilities of trigonal LNG and LTG (space group P321) are about 0.007 GPa−1; respective bulk moduli are 145 (3) GPa and 144 (2) GPa. The monoclinic high-pressure phases (space group A2) of LNG and LTG show differing compressions, which can be explained by the substitution of Ta5+ for Nb5+. Thus, the bulk moduli for the high-pressure polymorphs of LNG and LTG are B
0 = 93 (2) GPa and B
0 = 128 (12) GPa, respectively. The volume compressibilities of the high-pressure phases at 0.011 GPa−1 for LNG and 0.008 GPa−1 for LTG are higher than the initial phases, this effect being more pronounced in the case of LNG.
Prediction of new displacive ferroelectrics through systematic pseudosymmetry search. Results for materials with Pba2 and Pmc21 symmetry
Authors: Kroumova E. , Aroyo M. I. , Perez-Mato J. M.
Published: November 2002

Polar structures with pseudosymmetry related to a hypothetical non-polar configuration are considered as good candidates for ferroelectrics. Recently, a procedure has been developed for a systematic pseudosymmetry search among structures with a given space-group symmetry. The aim of this paper is the extension of the pseudosymmetry procedure to the case of structures with polar symmetry and its application in the search for new ferroelectrics. The results obtained by the generalized pseudosymmetry search among the compounds with symmetries Pba2 and Pmc2_1 listed in the Inorganic Crystal Structure Database are discussed. The calculations have been performed by the program PSEUDO, which forms part of the Bilbao Crystallographic Server (http://www.cryst.ehu.es). In addition, an empirical relation between the atomic displacements necessary to reach the non-polar structure and the transition temperature is proposed and compared with the Abrahams–Kurtz–Jamieson relation.
Diastereomeric salts of lactic acid and 1-phenylethylamine, their structures and relative stabilities
Authors: Langkilde Annette , Oddershede Jette , Larsen Sine
Published: November 2002

Crystal structures have been determined for the two diastereomeric salts formed between S-lactic acid (S-LA) and 1-phenylethylamine (PEA). The relative stabilities of the salts have been investigated by differential scanning calorimetry and solubility measurements in acetonitrile. The less soluble salt obtained from water, (R-PEA)(S-LA), is the less dense. It belongs to the orthorhombic space group P2_12_12_1, Z = 4. The more soluble salt, (S-PEA)(S-LA)·H_2O, crystallized from ethanol is monoclinic, space group P2_1, Z = 2. The crystal structure showed that the water molecule is well integrated into the hydrogen-bond network in the more soluble salt, which explains the fruitless attempts made to obtain the corresponding unhydrated salt. The lactate ion adopts different conformations in the two salts. The relative energies were investigated by Hartree–Fock calculations, showing that the lactate ion is in a conformation with higher energy in the more soluble salt. The difference in solubility between the two salts can be attributed to an interplay of enthalpy and entropy effects.
Atomic thermal motions studied by variable-temperature X-ray diffraction and related to non-linear optical properties of crystalline meta-di-nitrobenzene
Authors: Wójcik Grażyna , Mossakowska Izabela , Holband Jolanta , Bartkowiak Wojciech
Published: November 2002

The meta-dinitrobenzene crystal structure has been determined at five temperatures in the 100–300 K temperature range. The thermal expansion coefficients have been calculated from the temperature variation of the lattice parameters. Rigid-body motion analysis with allowance for large-amplitude internal motions provided the T, L and S tensors' values at the temperatures studied and was used to characterize the torsional motion of two nitro groups in the molecule. Frequencies of the translational and librational modes and of the torsional modes of the nitro groups have been compared with the wave numbers at the maximum of bands in the low-frequency Raman and IR spectra. Ab initio calculations were performed in order to assess the contribution from large-amplitude internal motions to the static first-order hyperpolarizability of the m-dinitrobenzene molecule.
Crystal chemistry of orthosilicates and their analogs: the classification by topological types of suprapolyhedral structural units
Authors: Ilyushin G. D. , Blatov V. A. , Zakutkin Yu. A.
Published: November 2002

A method is developed for the analysis and classification of orthosilicates and their analogs Mx
(TO4)
y
containing M cations and tetrahedral TO4 anions. The method uses the concepts of coordination sequence and crystal structure `reduced' graphs and is optimized for orthostructures of any complexity. First, the suprapolyhedral level of crystal structure organization was studied, where T tetrahedra were considered as templates for condensing M polyhedra, constructing as a result T polyhedral microensembles. Using this methodology, the crystal structures of 54 orthosilicates and orthogermanates were analyzed within the first 12 coordination spheres of T nodes and were arranged into 21 topological types. The topological types were expanded with the analogs found within the orthostructures of phosphates, sulfates etc. T polyhedral microensembles were used for the topological classification of reconstruction mechanisms of thermal and baric phase transitions of orthosilicates.
Group-theoretical analysis of octahedral tilting in ferroelectric perovskites
Authors: Stokes Harold T. , Kisi Erich H. , Hatch Dorian M. , Howard Christopher J.
Published: November 2002

Group-theoretical methods are used to analyze perovskite structures where both ferroelectric cation displacements and simple tilting of octahedral units are present. This results in a list of 40 different structures, each with a unique space-group symmetry. The list is compared with that of Aleksandrov & Bartolomé [Phase Transit. (2001), 74, 255–335] and a number of differences are found. The group–subgroup relationships between the structures are also determined, along with an indication of those phase transitions that must be first order by Landau theory.
The formation of paracetamol (acetaminophen) adducts with hydrogen-bond acceptors
Authors: Oswald Iain D. H. , Allan David R. , McGregor Pamela A. , Motherwell W. D. Samuel , Parsons Simon , Pulham Colin R.
Published: November 2002

The crystal structures of five hemiadducts of paracetamol with 1,4-dioxane, N-methylmorpholine, morpholine, N,N-dimethylpiperazine and piperazine and a related 1:1 adduct of paracetamol with 4,4′-bipyridine are described. All structures are characterized by the formation of chains of paracetamol molecules, which are linked via either OH...O=C interactions [C(9) chains in graph-set notation] or NH...O=C interactions [C(4) chains], depending on the presence or absence of substituent groups on the guest molecule. In all cases except for the morpholine and bipyridine adducts these chains are connected by hydrogen-bond interactions with the guest molecules, which reside on crystallographic inversion centres. In the bipyridine adduct this linkage also involves a π-stacking interaction; in the morpholine adduct it is formed between the OH groups of two opposed paracetamol molecules. Most adducts (that with 4,4′-bipyridine is an exception) decompose on heating to give monoclinic paracetamol. This is the first systematic study of a series of co-crystals containing paracetamol.
The structure of orange HgI2. I. Polytypic layer structure
Authors: Hostettler Marc , Birkedal Henrik , Schwarzenbach Dieter
Published: November 2002

The metastable orange crystals of HgI_2 comprise three different crystal structures, all of which are built from corner-linked Hg_4I_{10} supertetrahedra. Two of them are end members with the maximum degree of order (MDO) of a polytypic layer structure; the third shows a three-dimensional linkage. This paper presents the determination from X-ray diffraction data of the tetragonal polytypic structures and their stacking disorder. Diffraction patterns show sharp Bragg reflections and rods of diffuse intensity with pronounced maxima. In a first step, the diffuse intensity was neglected and all maxima were treated as Bragg reflections. The crystal was supposed to be a conglomerate of the two MDO structures diffracting independently, and their parameters and volume ratio were refined against the single data set. The geometries and anisotropic displacement parameters of the layers in the two structures are shown to be nearly identical. Layer contacts in the two stacking modes are identical. The structures are fractal complications of the stable red form of HgI_2. In a second step, the stacking disorder has been quantitatively analyzed with a Markov chain model. Two probabilities describing next-nearest-layer interactions were visually adjusted to observed intensity profiles extracted from image-plate detector data. Results consistently show that the crystal comprises nearly equal volumes of MDO structures with an average domain thickness of about 5 layers or 30 Å.
The structure of orange HgI2. II. Diamond-type structure and twinning
Authors: Hostettler Marc , Schwarzenbach Dieter
Published: November 2002

The metastable orange crystals of HgI_2 comprise three different crystal structures all of which are built from corner-linked Hg_4I_{10} supertetrahedra. Two of the structures are end members with the maximum degree of order (MDO) of a polytypic layer structure. In this paper, the third structure (D) determined from X-ray diffraction, a crystal chemical discussion of the four known tetrahedral HgI_2 structures, and a twinning model are presented. All the various diffraction results published during the past 70 years are now explained. The Hg_4I_{10} supertetrahedra of the tetragonal structure D are corner-linked into two interpenetrating diamond-type networks. The stable red form and the three orange structures show the same cubic densest packing of I atoms and differ only in the distribution of Hg atoms in the tetrahedral voids. Transformations between the structures may involve only movements of Hg atoms, as implied by larger thermal displacement parameters of Hg than of I. A multiply twinned conglomerate of MDO1, MDO2 and D, each structure occurring in three orientations, results in metrically cubic crystals whose Bragg reflections are very close to reciprocal lattice points.
The incommensurate modulation of the structure of Sr2Nb2O7
Authors: Daniels Peter , Tamazyan Rafael , Kuntscher Christine A. , Dressel Martin , Lichtenberg Frank , van Smaalen Sander
Published: November 2002

The incommensurately modulated structure of Sr_{2}Nb_{2}O_{7} at room temperature is reported, as determined by single-crystal X-ray diffraction. The crystal structure of Sr_{2}Nb_{2}O_{7} comprises slabs with a perovskite-type structure that are separated by planes of additional O atoms. The driving force for the modulation is shown to be internal strain around the Sr atoms that lie at the interface between the slabs. At room temperature, Sr_{2}Nb_{2}O_{7} crystallizes in the superspace group Cmc2_{1}(\alpha00)0s0, with lattice parameters a = 3.9544\,(7), b = 26.767\,(6) and c = 5.6961\,(8) Å. The modulation wave vector is determined as {\bf q} = 0.488\,(3)\,{\bf a}^{*}. X-ray diffraction data were collected at a synchrotron using a CCD area detector. A total of 3626 unique main reflections and 1262 unique first-order satellites with I \,\gt \,3 \sigma (I\,) were obtained. Refinements using a single harmonic modulation wave converged at R = 0.057 (R = 0.051 for the main reflections and R = 0.121 for the satellite reflections). The modulated structure is interpreted in terms of rotations of NbO_{6} octahedra and displacements of the Sr atoms.
CH3CN: X-ray structural investigation of a unique single crystal. β → α phase transition and crystal structure
Authors: Enjalbert Renée , Galy Jean
Published: November 2002

The phase transition from the low- (β) to the high-temperature (α) form of acetonitrile, CH3CN, has been directly observed and studied on a unique single crystal. Both the β and α structures have been determined at temperatures close to the transition temperature (206 K and 201 K), taking advantage of the hysteresis. A single crystal of the β form was obtained for the first time.
Commensurate and incommensurate structures of the hexabromotellurate(IV) bis{dibromodiselenate(I)} ion – [(C2H5)
n
(C6H5)4−n
P]2[TeBr6(Se2Br2)2], n = 0,1
Authors: Janickis Vitalijus , Nečas Marek , Novosad Josef , Dušek Michal , Petříček Václav
Published: November 2002

Structure analysis of [(C2H5)
n
(C6H5)4−n
P]2[TeBr6(Se2Br2)2] is presented for n = 1 and 0 [hereafter (I) and (II)]. Crystal (I) has been synthesized from elemental selenium, tellurium tetrabromide, ethyltriphenylphosphonium bromide and bromine. It has a standard monoclinic structure, space group P2_1/c, and has been solved and refined to R = 0.0357 for 4803 observed X-ray reflections by traditional techniques. Crystal (II), which has been prepared from elemental selenium, tellurium tetrabromide, tetraphenylphosphonium bromide and bromine, is an incommensurately one-dimensionally modulated structure with planar monoclinic superspace group. (II) has been refined to R = 0.0501 for 4247 observed reflections. The modulation of the atoms that belong to the anion switches between two different basic positions, which are described by the crenel function algorithm. The modulation of the phenyl groups is much weaker and it could be refined within the rigid-body approximation. The TeBr6 octahedron is nearly regular in both structures. The two Br atoms of the octahedron have a bond to one of the Se atoms in an Se2Br2 molecule. For (I) both bonded Br atoms are trans positioned, while for (II) they can be either trans or cis positioned. The alternations of those arrangements are caused by modulation. The point group of the anion is -1 for crystal (I) and 2/m for the average structure of crystal (II).
Atomic displacement parameters for spessartine Mn3Al2Si3O12 and their lattice-dynamical interpretation
Authors: Gramaccioli Carlo Maria , Pilati Tullio , Demartin Francesco
Published: November 2002

A rigid-ion lattice-dynamical treatment accounts reasonably well for most of the atomic displacement parameters (ADPs) reported in the literature for a synthetic sample of spessartine Mn3Al2Si3O12; the model accounts less well for the ADPs of the Mn atom. These results are similar to those obtained for the corresponding garnets pyrope Mg3Al2Si3O12 and almandine Fe3Al2Si3O12. The results are confirmed by a very good agreement of the lattice-dynamical estimates with the experimental values of the heat capacity that are currently available, as well as those of the Raman and infrared vibrational spectra. The anomalous behaviour of the Mn atom is reflected in the entropy values. As is the case for pyrope and almandine, here the agreement with the experimental results can be markedly improved if the existence of a low-temperature order–disorder transition concerning the Mn atom is considered. The lattice-dynamical estimates for all the atoms presented here do not agree with the corresponding ADPs obtained in a crystal structure refinement of a supposedly `pure' natural sample from Elba. In turn, these experimental ADPs do not agree with those observed for the synthetic sample, thereby showing a physical difference; such a possibility is in agreement with recent observations by other authors, who found an unexpected fluorine content in several natural specimens of spessartine. Therefore, theoretical estimates of ADPs are reliable enough to point out unexpected situations if disagreement with the observed values occurs.
Structural investigations of phosphorus–nitrogen compounds. 5. Relationships between molecular parameters of 2,2-diphenyl-4,6-cis-oxytetra(ethyleneoxy)-4,6-R
2-cyclotriphosphazatrienes (R = Cl, OCH2CF3, OPh, OMe, NHPh, NHBu
t
) and substituent basicity constants
Authors: Beşli Serap , Coles Simon J. , Davies David B. , Hursthouse Michael B. , Kılıç Adem , Mayer Thomas A. , Shaw Robert A.
Published: November 2002

A systematic study of the products of nucleophilic substitution reactions of cis-ansa N3P3Ph2[O(CH2CH2O)4]Cl2 (3) is reported. These reactions give a number of new structures with the general formula N3P3Ph2[O(CH2CH2O)4]R
2 [where R = OCH2CF3 (4), OPh (5), OMe (6), NHPh (7·H2O), NHBu
t
(8)]. A comparison has been made between the sum of the substituent basicity constants, \textstyle\sumα
R
, that are obtained in nitrobenzene solution and eight molecular parameters of the N3P3 ring [the P—N bond lengths a, b, c; the internal bond angles α, β, γ, δ; and the difference between the bond lengths a and b, Δ(P—N)]. It is found that the systematic changes in the molecular parameters of (3)–(8) are in line with changes in α
R
values. This result implies the similarity in relative electron-releasing capacity of substituents R in the solid state and in solution.
Electron density study of 2H-chromene-2-thione
Authors: Munshi Parthapratim , Guru Row T. N.
Published: November 2002

The charge-density distribution in 2H-chromene-2-thione (2-thiocoumarin), C9H6OS, has been determined from X-ray diffraction data measured at 90 K using a CCD detector, to a resolution of sinθ/λ < 1.08 Å−1. A multipolar-atom density model was fitted against 6908 reflections with I > 2σ(I) [R(F) = 0.021, wR(F) = 0.022, goodness of fit = 1.81] in order to generate the difference Fourier maps. The topological properties of the molecular electron density in terms of the bond critical points and the evaluation of the dipole moment show that the molecular dipole moment in the crystal is higher than the corresponding value derived from theoretical calculations.
Pressure-induced polymorphism in phenol
Authors: Allan David R. , Clark Stewart J. , Dawson Alice , McGregor Pamela A. , Parsons Simon
Published: November 2002

The high-pressure crystal structure of phenol (C6H5OH), including the positions of the H atoms, has been determined using a combination of single-crystal X-ray diffraction techniques and ab initio density-functional calculations. It is found that at a pressure of 0.16 GPa, which is just sufficient to cause crystallization of a sample held at a temperature just above its ambient-pressure melting point (313 K), a previously unobserved monoclinic structure with P21 symmetry is formed. The structure is characterized by the formation of hydrogen-bonded molecular chains, and the molecules within each chain adopt a coplanar arrangement so that they are ordered in an alternating 1-1-1 sequence. Although the crystal structure of the ambient-pressure P1121 phase is also characterized by the formation of molecular chains, the molecules adopt an approximate threefold arrangement. A series of ab initio calculations indicates that the rearrangement of the molecules from helical to coplanar results in an energy difference of only 0.162 eV molecule−1 (15.6 kJ mole−1) at 0.16 GPa. The calculations also indicate that there is a slight increase in the dipole moment of the molecules, but, as the high-pressure phase has longer hydrogen-bond distances, it is found that, on average, the hydrogen bonds in the ambient-pressure phase are stronger.
A reexamination of the low-temperature crystal structure of the p-tert-butylcalix[4]arene–toluene inclusion compound. Differences in spatial averaging with Cu and Mo Kα radiation
Authors: Enright Gary D. , Brouwer Eric B. , Udachin Konstantin A. , Ratcliffe Christopher I. , Ripmeester John A.
Published: November 2002

The low-temperature crystal structure of the p-tert-butylcalix[4]arene–toluene inclusion compound, C44H56O4·C7H8, exhibits significant guest-induced distortion of the host calixarene molecule. This distortion persists long enough to establish a correlation in the orientation of guests in adjacent host molecules. Remarkably, the space group and unit cell that best describe the structure appear to depend on the wavelength of the incident radiation. This behaviour appears to arise from spatial averaging over the different scattering volumes required to establish the diffraction peaks.
X-ray studies on crystalline complexes involving amino acids and peptides. XL. Conformational variability, recurring and new features of aggregation, and effect of chirality in the malonic acid complexes of DL- and L-arginine
Authors: Saraswathi N. T. , Vijayan M.
Published: November 2002

The crystal structures of the complexes of malonic acid with DL- and L-arginine, which contain positively charged argininium ions and negatively charged semimalonate ions, further demonstrate the conformational flexibility of amino acids. A larger proportion of folded conformations than would be expected on the basis of steric consideration appears to occur in arginine, presumably because of the requirements of hydrogen bonding. The aggregation pattern in the DL-arginine complex bears varying degrees of resemblance to patterns observed in other similar structures. An antiparallel hydrogen-bonded dimeric arrangement of arginine, and to a lesser extent lysine, is a recurring motif. Similarities also exist among the structures in the interactions with this motif and its assembly into larger features of aggregation. However, the aggregation pattern observed in the L-arginine complex differs from any observed so far, which demonstrates that all the general patterns of amino-acid aggregation have not yet been elucidated. The two complexes represent cases where the reversal of the chirality of half the amino-acid molecules leads to a fundamentally different aggregation pattern.
Crystal structure of the inclusion complex of β-cyclodextrin with mefenamic acid from high-resolution synchrotron powder-diffraction data in combination with molecular-mechanics calculations
Authors: Pop Mihaela M. , Goubitz Kees , Borodi Gheorghe , Bogdan Mircea , De Ridder Dirk J. A. , Peschar Rene , Schenk Henk
Published: November 2002

The crystal structure of the inclusion complex of β-cyclo-dextrin with mefenamic acid has been determined from a combination of high-resolution synchrotron powder-diffraction data and molecular-mechanics calculations. A grid search indicates two possible solutions, which are corroborated by molecular-mechanics calculations, while Rietveld-refinement results suggest the crystal structure that is more likely to be formed in the solid state. Mefenamic acid is partially included in β-cyclodextrin with either the xylyl or the benzoic-acid moiety being inside its cavity. In both solutions mefenamic acid and β-cyclodextrin form a monomeric complex in a herringbone packing scheme.
Modified photoreactivity due to mixed crystal formation. II. Enhanced reactivity upon conformational mimicry and cavity enlargement
Authors: Vithana Champika , Uekusa Hidehiro , Sekine Akiko , Ohashi Yuji
Published: November 2002

The 2-cyanopropyl (β-cyanopropyl) group in the cobaloxime complex of (2-cyanopropyl)(3-methylpyridine)bis(dimethylglyoximato)cobalt(III) takes a trans conformation around the Co—C—C—CN bond in the crystal and undergoes isomerization to the 1-cyanopropyl (α-cyanopropyl) group with a low reaction rate when the powdered crystals are irradiated with a xenon lamp. When the complex was mixed with (2-cyanoethyl)(3-methylpyridine)bis(dimethylglyoximato)cobalt(III) or (2-cyanoethyl)(3-ethylpyridine)bis(dimethylglyoximato)cobalt(III), a mixed crystal, Mix-I or Mix-II, was obtained. The cell parameters of Mix-I and Mix-II were considerably different. When the crystals of Mix-I and Mix-II were irradiated with the xenon lamp, the 2-cyanopropyl group and the 2-cyanoethyl group isomerized to the 1-cyanopropyl and 1-cyanoethyl groups, respectively, in the crystalline state as well as in the solid state. The isomerization rates of the 2-cyanopropyl and 2-cyanoethyl groups of the mixed crystals became significantly higher than the corresponding rates in the component crystals. For the 2-cyanopropyl group, the conformational change from trans to cis in the mixed crystals caused reaction rates to be enhanced, and the expanded volume of the reaction cavity in the mixed crystals increased the reactivity for the 2-cyanoethyl group, when compared with the reactivity of each component crystal. A quantitative discussion of the increased rate constants is presented, which is based on the crystal structures. The shapes of the reaction cavities for the reactive groups undergoing isomerization control the conformation and configuration of the produced1-cyanoethyl and 1-cyanopropyl groups.
Crystal packing in vicinal diols C
n
H
m
(OH)2
Authors: Brock Carolyn Pratt
Published: November 2002

The O—H...O bonds in vic-diols C
n
H
m
(OH)2 have been studied using data retrieved from the Cambridge Structural Database. About half of these diols form complete, or almost complete, sets of intermolecular O—H...O bonds (i.e. two satisfied donors per molecule). For this half of the structures the frequencies of high-symmetry space groups and of structures with Z′ > 1 (more than one molecule in the asymmetric unit) are substantially elevated. The most common motif among fully bonded structures is an R_{\rm{2}}^{\rm{2}} {\rm{(10)}} dimer, which can be linked in a variety of ways to form one-, two- or even three-dimensional patterns. Most of the other half of the vic-diols form simple O—H...O chains in which each OH group participates in only one intermolecular hydrogen bond. The space-group frequencies for this second group of structures are unexceptional. The most important factor determining the extent of O—H...O bond formation is the degree of substitution of the vic-diol. The spatial segregation of OH groups that is necessary for the formation of O—H...O bonds is found to make the dense filling of space more difficult because the intermolecular spacings that are appropriate for the O—H...O bonds may be inappropriate for the rest of the molecule.
Effects of low dose dexamethasone treatment on basal cardiovascular and endocrine function in fetal sheep during late gestation
Authors: Fletcher Andrew J. W. , McGarrigle Hugh H. G. , Edwards C. Mark B. , Fowden Abigail L. , Giussani Dino A.
Published: November 2002

This study investigated the effects on ovine fetal basal cardiovascular and endocrine functions of fetal intravenous dexamethasone treatment, resulting in circulating concentrations that were one‐fifth of the values measured clinically in human infants following maternal antenatal glucocorticoid therapy. Between 117‐120 days gestation (dGA; term: ca 145 dGA), 26 Welsh Mountain sheep fetuses were surgically prepared under general anaesthesia with vascular catheters and a Transonic flow probe positioned around a femoral artery. At 125 ± 1 dGA, fetuses were infused with dexamethasone (2.06 ± 0.13 μg kg−1 h−1i.v.; n= 13) or saline (n= 13) for 48 h. Daily fetal arterial blood samples were taken and cardiovascular data were recorded continuously (data acquisition system). Pressor, vasoconstrictor and chronotropic responses to exogenously administered doses of phenylephrine, angiotensin II and arginine vasopressin (AVP) were determined at 124 ± 1 (pre‐infusion), 126 ± 1 (during infusion) and 128 ± 1 (post‐infusion) dGA. Fetal cardiac baroreflex curves were constructed using peak pressor and heart rate responses to phenylephrine. Dexamethasone treatment elevated fetal mean arterial blood pressure by 8.1 ± 1.0 mmHg (P < 0.05), increased femoral vascular resistance by 0.65 ± 0.12 mmHg (ml min−1)−1 (P < 0.05), depressed plasma noradrenaline concentrations and produced a shift in set‐point, but not sensitivity, of the cardiac baroreflex (P < 0.05). Elevations in fetal arterial blood pressure, but not femoral vascular resistance and the shift in baroreflex set‐point, persisted at 48 h following dexamethasone treatment. By 48 h following dexamethasone infusion, basal plasma noradrenaline concentration was restored, whilst plasma adrenaline and neuropeptide Y (NPY) concentrations were enhanced, compared with controls (P < 0.05). Fetal dexamethasone treatment did not alter the fetal pressor or femoral vasoconstrictor responses to adrenergic, vasopressinergic or angiotensinergic agonists. These data show that fetal treatment with low concentrations of dexamethasone modifies fetal basal cardiovascular and endocrine functions. Depending on the variable measured, these changes may reverse, persist or become enhanced by 48 h following the cessation of treatment.
Cytoskeletal disrupting agents prevent calmodulin kinase, iq domain and voltage‐dependent facilitation of l‐type ca2+ Channels
Authors: Dzhura Igor , Wu Yuejin , Colbran Roger J. , Corbin Jackie D. , Balser Jeffrey R. , Anderson Mark E.
Published: November 2002

A calmodulin (CaM) binding ‘IQ’ domain on the L‐type Ca2+ channel (LTCC) C terminus and calmodulin kinase II (CaMK) both signal increases in LTCC opening probability (Po) by shifting LTCCs into a gating mode (mode 2) with long openings through a process called facilitation. However, the mechanism whereby CaMK and the IQ domain are targeted to LTCCs is unknown. Endogenous CaMK is targeted to LTCCs in excised cell membrane patches because LTCC Po increased significantly in CaM‐enriched (20 μm) bath solution and this effect was prevented by a specific CaMK inhibitory peptide, but not by an inactive control peptide. Pre‐exposure of myocytes to the cytoskeletal disrupting agents nocodazole (microtubule specific) or cytochalasin D (microfilament specific) prevented the effects of CaM‐dependent increases in Po of LTCCs in excised membrane patches. Neither cytochalasin D nor nocodazole altered the distribution of LTCC gating modes under basal conditions in on‐cell mode or excised cell membrane patches, but each of these agents occluded the response of LTCCs to exogenous, constitutively active CaMK and to an IQ‐mimetic peptide (IQmp). Cytochalasin D and nocodazole pretreatment also prevented LTCC facilitation that followed a cell membrane depolarizing prepulse. In contrast, cytochalasin D and nocodazole did not affect the increase in LTCC Po or prevent the shift to mode 2 gating in response to protein kinase A, indicating that cytoskeletal disruption specifically prevents prepulse, CaMK and IQ‐dependent LTCC facilitation.