bluuebunny/crossref_metadata_2025_split huggingface dataset:
A solid‐state electrochromic device based on polyaniline, prussian blue and an elastomeric electrolyte
Authors: Duek Eliana A. R. , De Paoli Marco‐A. , Mastragostino Marina 
Published: December 2004

Advantages of solid‐state electrochemical devices are the ease of production, no possibility of leakage, and no electrolyte evaporation. One result of the search for such a device is the electrochromic display sketched in the Figure, which uses polyaniline and Prussian Blue as the active electrochromic materials and an elastomer containing Li‐ClO4 as the solid‐state electrolyte. magnified image
MOCVD Routes to Thin Metal Oxide Films for superconducting electronics
Authors: Schulz Douglas L. , Marks Tobin J. 
Published: December 2004

Superconducting, semiconducting and insulating oxide thin filmsare of interest for applications as active and passive components in microelectronic device technologies. Metal organic chemical vapor deposition (MOCVD) is an important method of thin film production and its use in developing device structures such as that in the figure is discussed.magnified image
Charge transfer complexes of (TTFTe)2: Preparation, structure, and electrical conductivity
Authors: Becker James Y. , Bernstein Joel , Dayan Moshe , Ellern Arkady , Shahal Leah 
Published: December 2004

Organic metals based on organo‐tellurium units are of particular interest because of the increased orbital overlap in these systems which leads to favorable conditions for conductivity. The figure shows the crystal structure of (TTFTe)2 · TCNQ, which is semiconducting, while the (TTFTe)2 · (TCNQ)2 complex has a conductivity of 8.2 S/cm at room temperature. magnified image
Conducting Stacked Metallophthalocyanines and Related Compounds
Authors: Hanack Michael , Lang Manuela 
Published: December 2004

Phthalocyanine‐related compounds have many interesting materials properties. This review concentrates on the conductive properties of phthalo‐ and naphthalocyaninatometal compounds on the (e.g., see Figure). Syntheses are presented and the relationship between the morphology of the macrocycles and the electrical properties is discussed. Particular attention is paid to the bridged transition metal complexes. magnified image
First hyperpolarizability of organotin compounds with Td symmetry
Authors: Lequan Minh , Branger Catherine , Simon Jacques , Thami Thierry , Chauchard Eve , Persoons André 
Published: December 2004

A new class of nonlinear optical materials, tetrahedral tin complexes in which the metal ion can act as a polarizable group linked to donor dimethylamino moieties, is described. An example is shown in the Figure. The quadratic hyperpolarizability coefficients determined by hyper‐Raman scattering are reported and the important characteristics of the molecules discussed. magnified image
Molecular sieve encapsulated organic dyes and metal chelates
Authors: Wöhrle Dieter , Schulz‐ekloff Günter 
Published: December 2004

Inorganic molecular sieves have a well‐defined internal structure of uniform cages, cavities, or channels–see the Figure for an example–making them suitable for many applications. Recently the inclusion of dyes and metal chelates as guests has been studied. The results are reviewed briefly, including the preparation and characterization of the host/guest system and the chemical reactivity. magnified image
Reduction in the size of features of patterned SAMs generated by microcontact printing with mechanical compression of the stamp
Authors: Xia Younan , Whitesides George M. 
Published: December 2004

Sub‐micron size features can now be produced using the microcontact printing technique. The elastomeric stamp used to produce the features in self‐assembled monolayers (see figure) is mechanically compressed both one‐ and two‐dimensionally, resulting in a reduction of the size of the features by up to a factor of almost ten (e.g. 2.5 μm) while retaining the spatial regularities in the pattern. magnified image
Rectifying properties and photoconductivity of tetraruthenated nickel porphyrin films
Authors: Araki Koiti , Angnes Lúcio , Toma Henrique E. 
Published: December 2004

Oxidation‐state selective modified electrodes based on tetraruthenated nickel porphyrin (see Figure) thin films are reported. The films are prepared by dip coating and are highly homogeneous and adherent, exhibiting a well‐controlled electrochemical and photoelectrochemical response. The films simulate a rectifying junction. magnified image
Guanidyl and phosphoraniminyl substituents: New electron donors in second‐order nonlinear optical chromophores
Authors: Boldt Peter , Eisenträger Thomas , Glania Christoph , Göldenitz Jörg , Krämer Peter , Matschiner Ralf , Rase Jens , Schwesinger Reinhard , Wichern Jürgen , Wortmann Rüdiger 
Published: December 2004

Improved donor groups for chromophores play a major role in the development of organic materials for nonlinear optics. Guanidyl and phosphoraniminyl residues are examined as donors in one‐dimensional organic nonlinear optical chromophores such as that shown in the Figure. The results of electrooptical absorption (EOAM) and electric field induced second harmonic generation (EFISH) measurements are presented and discussed. magnified image
Influence of polar substituents on the epitaxy of oligothiophenes on graphite: A systematic STM investigation
Authors: Müller Horst , Petersen Jörg , Strohmaier Rainer , Gompf Bruno , Eisenmenger Wolfgang , Vollmer Martin S. , Effenberger Franz 
Published: December 2004

The variation of substituents of oligothiophenes can be used to control the epitaxy of the materials through systematic modification of intermolecular interactions. The STM characterization of new oligothiophenes (e.g. see Figure) is reported and is shown to provide useful structural information on the supramolecular assemblies which have potential in molecular optical and electronic applications. magnified image
Electrooptical and dielectric investigations on the conformation and the electrical properties of poly‐γ‐benzyl‐L‐glutamate in mixed solvents
Authors: Watanabe Hiroshi , Yoshioka Koshiro , Wada Akiyoshi 
Published: December 2004

AbstractThe dielectric constant and the electric birefringence of poly‐γ‐benzyl‐L‐glutamate in ethylene dichloride–dichloroacetic acid mixtures have been measured as functions of the solvent composition. These properties undergo a marked decrease with the addition of a small amount of dichloroacetic acid, as well as an abrupt change accompanying the helix‐coil transition in the vicinity of 75 vol.‐% dichloroacetic acid. The former is attributed to the apparent diminution of the dipole moment of helical poly‐γ‐benzyl‐L‐glutamate molecule, which may be due to the protonation of terminal amide groups.
Far ultraviolet optical rotatory properties of poly‐L‐tryptophan. Part I
Authors: Cosani A. , Peggion E. , Verdini A. S. , Terbojevich M. 
Published: December 2004

AbstractA block copolymer [γ‐Et‐DL‐Glu]m [L‐Trp]n was prepared using N‐carboxy anhydrides (NCA) of L‐tryptohan and γ‐ethyl DL‐glutamate. The block copolymer, dissolved in trifluoroethanol (TFE)–dichloroacetic acid (DCA) mixtures, exhibited a sharp change in the specific rotation at 546 mμ when the solvent composition reached 70–75% DCA content. Optical rotatory dispersion (ORD) and circular dichroism (CD) measurement were carried out in TFE solution in the spectral range 180–350 mμ. Indole side‐chain chromophores were found to be optically active in the polymer. On the other hand, these groups exhibit very small optical activity in the model compound C6H3CH2OCO(L‐Trp)2OCH3. Indole groups therefore appear to be in a dissymmetric environment only in the polymer. From these data it was concluded that poly‐L‐Trp is in some type of helical conformation in TFE. Strong overlapping of CD bands from side‐chain chromophores and peptides chromophores in the wavelength range 185–240 mμ does not allow definite conclusions to be drawn about the type of helical conformation which exists in poly‐L‐Trp in TFE solution.
Potentiometric titrations and the helix–coil transition of poly(L‐glutamic acid) and poly‐L‐lysine in aqueous salt solutions
Authors: Ciferri A. , Puett D. , Rajagh L. , Mermans Jan 
Published: December 2004

AbstractThe objective have been to establish if those ions which are known to change the stability of the structure of proteins, have any influence on the properties of ionizable polypeptides. Potentiometric titrations and complementary optical rotation data are presented for aqueous solutions of poly‐L‐lysine (PLL) in the presence of KSCN, KCl, and KF, and for poly(L‐glutamic acid) (PLGA) in the presence of KSCN, KCl, and LiCl. The following measured quantities which are affected by salt concentration were obtained: intrinsic pK (pK0), slope of pKapp versus degree of ionization (α) curves, the degree of ionization at which the helix to coil transition occurs, and the free energy of this transition for the uncharged molecule (δG°hel). The effects of nonspecific salts (KCl and LiCl for PLL and KSCN and KCl for PLGA) are small, and about, as expected from general electrostatic considerations. In line with the observations made with isoelectric and cat ionic collagen, specific, effects were noted with KSCN–PLL and with LiCl–PLGA. In the presence of KSCN, the poly‐L‐lysine helix becomes stabilized at much lower degree of ionization than in the presence of KCl, and the slope of the pKapp versus α plots is greatly reduced. However, ΔG°hel (for the uncharged molecule) is not affected, and pK0 is only slightly higher. We interpret these data in terms of binding of SCN− primarily to the side‐chain amino groups (both to RNH3+ and to RNH2) solutions. (L‐glutamic acid) in LiCl solution has its transition at the same α value as in KCl solution. However, both the slopes of the pKapp versus α plots and the absolute values of ΔG°hel are lower than in KCl solution. We interpret these results in terms of binding of Li+ to side chains as well as to the peptide bond.
Models for hemoglobin and allosteric enzymes
Authors: Thompson Colin J. 
Published: December 2004

AbstractA model for hemoglobin is proposed and its application to allosteric enzymes is discussed with particular reference to asparate transcarbamylase. The main assumptions made are that the molecule is composed of subunits and that occupation of a sub‐unit produces a conformational change which affects the occupational probability of neighboring subunits. The results compare favorably with experiment and a number of specific predictions are made for aspartate transcarbamylase.
An estimation of the dimensions of the phycocyanin molecule
Authors: Jennings B. R. 
Published: December 2004

AbstractKnowledge of the total particle volume and the specific volumes of the constituent polar and nonpolar amino acid residues of a globular protein may be used in suitable instances to estimate the size and shape, of the macromolecule. Use has been made of the data, which is available in the literature for phycocyanin from Plectonema calothricoidcs, to predict possible models for the monomer and hexamer forms of this protein. The monomer is well represented by a prolate ellipsoid with semiaxes of 45 and 17Å and an approximate molecular weight of (46000). The hexamer is envisaged as the aggregate of six such monomers, in juxtaposition, with their major axes parallel so as to form a closed ring structure of about 268000 molecular weight. These proposed models are consistent with the previously published electron micrographs and hydrodynamic properties of this protein.
Conformations and optical rotatory properties of poly‐O‐acetylthreonine and poly‐O‐acetylallothreonine
Authors: Kubota Shigeo , Sugai Shintaro , Noguchi Junzo 
Published: December 2004

AbstractOptically active poly‐O‐acetylthreonine and poly‐O‐acetyl‐allothreonine exist in the β form in pyridine, in 2‐chloruethanol–dichloromethane mixed solvent., and in the solid state. The optical rotatory dispersion of the β form of poly‐O‐acetyl‐L‐threonine in a 2‐ehloroethanol–dichlomethane mixture showed a Cotton effect in the 230 mμ region. The ORD data in the visible spectral region fit, the Moffitt. equation. The absolute values of b0, as measured in pyridine for polypeptides with a molecular weight above 17000, varied in the range 100–200°, the sign depending on the absolute configuration of the side chain.
On the hydration of DNA. I. Preferential hydration and stability of DNA in concentrated trifluoroacetate solution
Authors: Tunis Mary‐Jane B. , Hearst John E. 
Published: December 2004

AbstractThe hydration of DNA is an important factor in the stability of its secondary structure. Methods for measuring the hydration of DNA in solution and the results of various techniques are compared and discussed critically. The buoyant density of native and denatured T‐7 bacteriophage DNA in potassium trifluoroacetate (KTFA) solution has been measured as a function of temperature between 5 and 50°C. The buoyant density of native DNA increased linearly with temperature, with a dependence of (2.3 ± 0.5) × 10−4 g/cc‐°C. DNA which has been heat denatured and quenched at 0°C in the salt solution shows a similar dependence of buoyant density on temperature at temperatures far below the Tm, and above the Tm. However, there is an inflection region in the buoyant density versus T curve over a wide range of temperatures below the Tm. Optical density versus temperature studies showed that this is due to the. inhibition by KTFA of recovery of secondary structure on quenching. If the partial specific volume is assumed to be the same for native and denatured DNA, the loss of water of hydration on denaturation is calculated to be about 20% in KTFA at a water activity of 0.7 at 25°C. By treating the denaturation of DNA as a phase transition, an equation has immmi derived relating the destabilizing effect of trifluoroacetate to the loss of hydration on denaturation. The hydration of native DNA is abnormally high in the presence of this anion, and the loss of hydration on denaturation is greater than in CsCl. In addition, trifluoroacetate appears to decrease the ΔHof denaturation.
Theory of a rapid method for determining molecular weights of giant molecules
Authors: Kotaka Tadao , Baldwin Robert L. 
Published: December 2004

AbstractA new method is proposed for finding molecular weights from the boundary condition of the ultracentrifuge. The method is more rapid than the conventional Archibald method by at least one order of magnitude and should be especially useful for giant molecules with small diffusion coefficients. It employs a preset concentration gradient. A theoretical study of the method has been made by obtaining solutions to the Lamm equation analogous to the “mirror image” solution (for early times) and the Fourier expansion solution (for late times) of Mason and Weaver. Numerical examples of theoretical results are given, and the errors are discussed. Centrifugation in a preset linear gradient can also be used to reduce the time needed to reach equilibrium.
Evaluation of lipoprotein size–density distributions from sedimentation coefficient distributions obtained at several solvent densities. I. Theory
Authors: Oncley J. L. 
Published: December 2004

AbstractA method is presented for the treatment of distribution functions obtained by ultra‐centrifugal sedimentation velocity experiments on the plasma lipoproteins, so that adequate corrections can he made for the effects of diffusion and concentration dependence of the sedimentation coefficient. The method involves the use of modified equations derived from those presented in 1952 by Gosting for the transform from g* (S) to g(S) distributions. The evaluation of the molecular parameters of lipoprotein density and size, from a set of g(Si°) distribution functions obtained in solvents of varying density, is also outlined. Preparations of the β‐lipoprotein of human plasma are found to follow a bivariate normal distribution that requires evaluation of five parameters, x̄1, σ1, x̄2, σ2and p. The first two represent the mean and standard deviation of the lipoprotein density, the third and fourth the same quantities for the size, expressed as ft “logarithmic diameter parameter”, and the final value is a measure of the correlation between these two variables.
Semiempirical energy calculations on model compounds of polypeptides. Crystal structures of DL‐acetylleucine N‐methylamide and DL‐acetyl‐amino‐n‐butyric acid N‐methylamide
Authors: Ferro Dino R. , Hermans Jan 
Published: December 2004

AbstractThe sum E of the packing and conformation energies of the crystals of DL‐acetylleucine N‐methylamide (ALNMA) and DL‐acetyl‐α‐amino‐n‐butyric acid N‐methylamide (ABAMA) is calculated as a function of the crystallographic parameters and the conformational angles. The intermolecular energy is assumed to be the pairwise sum of nonbonded and electrostatic atomic interactions, while both these terms and intrinsic terms describing barriers of internal rotation contribute to the intramolecular energy. For ALNMA E is minimized with respect to 18 parameters: the minimum found when starting from the experimental structure agrees with this within 0.07 Å and 3°, except for one angle which deviates by 6° the average deviations of the atomic coordinates are \documentclass{article}\pagestyle{empty}\begin{document}$ |\overline {\Delta x|} = 0.02,|\overline {\Delta y|} = 0.07,|\overline {\Delta z|} = 0.08 $\end{document} Å. Another minimum with about the same energy shows slightly worse agreement. A comparison between different sets of nonbonded functions is made. The prediction of conformation and intermolecular packing of ABAMA is attempted on the basis of the knowledge of the unit cell and the space group. In agreement with available experimental data it is found that only one‐di‐mensional arrays of molecules linked by pairs of hydrogen bonds are compatible with the unit cell. The more stable of two possible conformations of the main chain agrees approximately with the experimental conformation. The calculation is not conclusive with regard to the side‐chain conformation and the packing of non‐hydrogen‐bonded molecules.
Isoenzymes of tetrameric proteins
Authors: Fajszi Cs. , Keleti T. 
Published: December 2004

AbstractA theory is presented concerning the possible arrangements of protomers in tetrameric molecules. Isoenzymes may exist even in the case of homotetramers if the asymmetry of the identical protomers is detectable. The number of tetrahedral isoenzymes that can be isolated depends on the nature of the intersubunit bonds and on the level of the asymmetry of the protomers. Five isoenzymes can be distinguished only if two different types of protomers form tetrahedral tetramers and the asymmetry of protomers is not detectable with the method used. If the two types of protomers can bind each other by any pairs of binding sets and the asymmetry of both protomer types reaches the level of detection with the method used, we obtain 117 isoenzymes: 15 individual ones, and 51 stereoisomeric pairs.
Circular dichroism of polynucleotides: Dimers as a function of conformation
Authors: Johnson W. C. , Itzkowitz M. S. , Tinoco I. 
Published: December 2004

AbstractWorking within the restrictions of a model, we have calculated the circular dichroism of the dinucleoside phosphates ApA, CpC, and CpA for various conformations. Comparing the calculated curves with those measured in aqueous solution we find agreement for (1) ApA as a right‐handed helix with both bases either as in B‐form DNA, or else rotated 180° around the glycosidic bond, (2) CpC as the right‐handed conformation with both bases as in DNA, (3) ApC as either the right‐handed conformation with both bases as in DNA, or else as a left‐handed helix with both bases rotated 180°, and (4) CpA as either a left‐handed helix with both bases in a left‐handed DNA, or else in the right‐handed conformation with both bases rotated 180°. In addition, we have investigated circular dichroism as a measure of unstacking. We find that opening the bases to a 90° total angle (base planes perpendicular) reduces the intensity of the calculated bands to 20% of their original value. Further, we find that allowing the sliding of one base past the other does not lead to a temperature dependence consistent with experiment.
Dynamic mechanical and rheo‐optical studies of collagen and gelatin
Authors: Chien James C. W. , Chang E. P. 
Published: December 2004

AbstractThe frequency dependence of dynamic mechanical properties of rat tail tendon (RTT), enzyme‐solubilized collagen membranes (ESC), AKM‐23 dialysis membranes, and gelatin film have been measured at 110, 11, and 3.5 Hz from ‐ 160 to 220°C. RTT and AKM‐23 are devoid of a rubbery region; there are as many as six mechanical loss transitions. Gelatin and ESC membranes behave as rubbery materials above room temperature; only three tan δE peaks can be resolved for these materials. Strain birefringence was used to measure the crystalline and amorphous contribution of orientation induced by strain. Both the birefringence and the strain optical coefficient are sensitive to the amount of water in a sample. The effect of chemical swelling agents and of annealing on birefringence are described. Stress relaxation data on gelatin film were analyzed with the rubber elasticity theory to give the average number of chains per unit volume, the specific polarizability, the stress‐birefringence ratio and the average molecular weight between hydrogen bonds were calculated. The intrinsic amorphous birefringence for “wet” gelatin film is 1.25 × 10−2; it is estimated to be about 6 × 10−2 for “dry” gelatin film.
A comparative X‐ray study of a nucleoprotamine and DNA complexes with polylysine and polyarginine
Authors: Suwalsky M. , Traub W. 
Published: December 2004

AbstractThe high‐humidity X‐ray pattern of oriented fibers prepared from salmon spermheads strongly resembles that of DNA in the B form. However, the nucleoprotamine pattern has a more intense first layer line and increased lateral unit‐cell dimensions.Complexes of DNA with poly‐L‐lysine and poly‐L‐arginine were prepared and photographed at various relative humidities. The most crystalline patterns were obtained at 92% and also indicate DNA in the B form. However, whereas polylysine–DNA, like the spermheads, has a primitive hexagonal cell, polyarginine–DNA, like NaDNA, has three molecules in the unit cell. Polylysine–DNA, but not polyarginine–DNA, also resembles spermheads in having a strong first layer line.All three complexes show increasing intermolecular distance with increasing humidity, but with sharp maxima when photographed in water, which indicates cross‐linking between the molecules. Lowering the humidity causes the polylysine–DNA, but not polyarginine–DNA, to change conformation from the B to the C form.The structural implications of these results are discussed in the light of model‐building studies and a comparison of calculated and observed X‐ray intensities.
Thermodynamics of polyelectrolyte solutions. An empirical extension of the manning theory to finite salt concentrations
Authors: Wells J. D. 
Published: December 2004

AbstractThe range of application of the Manning theory of polyelectrolyte solutions (J. Chem. Phys., 51, 924 (1969)) is extended to finite concentrations of simple electrolyte by the empirical superposition of excess free energies arising from (i) interactions between mobile ions and polyions and (ii) mutual interactions between mobile ions. A comparison of published results with the modified theory shows excellent agreement over a wide range of concentrations. Results for a polyelectrolyte of low charge density suggest that the effective inter‐charge spacing may be less than that of the fully extended polyion.