bluuebunny/crossref_metadata_2025 huggingface dataset:
Defect chemistry of the high‐Tc superconductors
Authors: Maier Joachim , Pfundtner Gösta
Published: December 2004

In the high temperature superconductors the critical temperature is intimately connected to the electronic charge‐carrier concentration. The absolute values of this quantity and its dependencies on the controlling parameters temperature, oxygen partial pressure and doping content, is phenomenologically determined by the thermodynamics and kinetics of reactions involving point defects. Due to the low mobility of the ionic constituents the behavior at elevated temperatures is particularly important. Here, the kinetics are controlled by the mass transport parameters, essentially by the ionic conductivity.

The scientific discipline whose objective is precisely described in the above terms is called defect chemistry. It quantitatively deals with the nature of excess and lacking native ionic or electronic particles as well as with foreign species. It describes the thermodynamics and kinetics of their formation, annihilation, interaction and motion in the phase under consideration and thus determines the chemistry within this phase.
On an (Un‐)known compound in the CaSrBiCuO System
Authors: Hettich Bernhard , Bestgen Harro , Bock Joachim
Published: December 2004

Communication: The synthesis of phase‐pure HTSC materials with well‐defined superconductivity properties is facilitated by a sound knowledge of the equilibria between the various compounds present in the system. An in‐depth study of the CaSrBiCuO system has revealed new relationships between the structures of the superconducting phases and sheds light on the complex mechanism which is operational during the formation of superconducting materials.
Decamethylmanganocenium tetracyanoethenide, [Mn(C5Me5)2]⊙⊙⊕ [TCNE]⊙⊖—a molecular ferromagnet with an 8.8 K Tc
Authors: Miller Joel S. , Dixon David A. , McLean R. Scott. , Groski David M. , Flippen Richard B. , Manriquez Juan M. , Yee Gordon T. , Narayan K. S. , Epstein Arthur J.
Published: December 2004

Communication: Triplet electron‐transfer salts are predicted to exhibit bulk ferromagnetic behavior at higher temperatures than their singlet analogues. To test this expected trend, the title compound, which is isostructural with [FeCp]⊙⊕ [TCNE]⊙⊖ (Cp* = pentamethylcyloopentadienide; TCNE = tetracyanoethylene) which exhibits a Curie temperature, Tc, of 4.8 K has been synthesized. The synthesis and magnetic characterization of the new compound, which is found to have aTc of 8.8 K, are reported.
High molecular weight poly([ 1.1.1]propellane)s and a new polyamide with bicyclo[1.1.1]pentane fragments
Authors: Bothe Harald , Schlüter Arnulf‐Dieter
Published: December 2004

Communication: A polyamide, where the amide functions are connected via rigid, non‐aromatic units, which forms liquid‐crystalline phases in concentrated sulfuric acid and is thus suitable for the preparation of fibers is reported. The synthesis has been made possible by a breakthrough in the ability to produce high molecular weight poly([1.1.1]‐propellane)s (see Figure).

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Structural characterization and properties of a new tetrathiafulvalene‐based cage molecule derived from an azacrown
Authors: Jørgensen Tine , Becher Jan , Hansen Thomas Kruse , Christiansen Kim , Roepstorff Peter , Larsen Sine , Nygaard Anne
Published: December 2004

Communication: A cage molecule combining a precursor of the electroactive tetrathiafulvalene (TTF) unit with a macrocycle capable of complexing transition metals (see Figure) is reported. The preparation of this compound and the TTF‐based compound whose cavity is too small for complexing the metal are reported.

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Conformation and optical absorption properties of thiophene oligomers: 13C‐NMR, UV, and MMP2 calculations of Di‐ and tetramethyl‐quaterthiophenes
Authors: Barbarella Giovanna , Zambianchi Massimo , Bongini Alessandro
Published: December 2004

Communication: A combined calculational and experimental study of methylated oligothiophenes allows the effects of different substitution patterns on the geometry, the inter‐ring twist, and the conformational and optical properties of the oligomers, which have potential applications in molecular electronics and can be polymerized to polythiophenes, to be examined.
Aerogels
Authors: Fricke Jochen , Emmerling Andreas
Published: December 2004

Research News: Recently listed amongst the top ten scientific and technological developments, aerogels have found applications as traps for relativistic particles, in fire protection and in thermal insulation or acoustic impedance. The materials, which contain more air than gel, their synthesis, and other potential applications are described.
Organometallic molecular precursors for low‐temperature MOCVD of III–V semiconductors
Authors: Maury Francis
Published: December 2004

Metal‐organic chemical vapor deposition (MOCVD) is a suitable technique for the preparation of III–V epitaxial layers which are used in the fabrication of microelectronic and optoelectronic devices. The usual Ga and As sources for GaAs are Ga(CH3)3 and AsH3, respectively. However, the use of these precursors has some disadvantages including: The toxicity and storage of arsine, stoichiometry control, carbon incorporation and unwanted side reactions. Several groups of researchers have investigated alternative sources for both the group–III and group‐V elements. A review of these new organometallic precursors is presented in this paper. However, because group‐III and group‐V elements form Lewis‐acid/base adducts in the MOCVD reactor, we have especially investigated the use of this class of compounds as single starting molecules. Several adducts have been successfully used for the epitaxial growth of GaAs. Moreover, to avoid any stoichiometry loss due to dissociation of the adduct, the properties of organometallic molecules which feature a covalent bond between the group‐III and group‐V elements have also been investigated. These covalent compounds are probably formed in the MOCVD reactor when alkyl group‐V compounds containing acidic hydrogen R3−nMHn (M = As, P; n = 1,2) are used. Such new precursors are also briefly reviewed.
Amorphous molecular materials: Synthesis and properties of a novel starburst molecule, 4,4′,4″ ‐Tri(N‐phenothiazinyl)triphenylamine
Authors: Higuchi Akiji , Inada Hiroshi , Kobata Tomokazu , Shirota Yasuhiko
Published: December 2004

Communication: Processability, flexibility, transparency, and a lack of grain boundaries are some of the attractive properties of amorphous molecular materials. For their integration into electronics, however, it is important that the materials can form stable amorphous, glassy states with a glass‐transition temperature and, if any, a crystallization temperature as high as possible. The starburst molecule shown in the figure has a glass‐transition temperature of 141°C.

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A novel carbon material derived from pyridine–borane
Authors: Riedel Ralf , Bill Joachim , Passing Gerd
Published: December 2004

Communication: BC4N, a new carbon material containing boron and nitrogen is formed in high yield by the thermal decomposition of pyridine–borane at 1050°C in argon. X‐ray powder diffraction shows hk0 and 00l reflections indicating a turbostratic structure. X‐ray photoelectron spectroscopy and analytical investigation in the transmission electron microscope reveal the random distribution of BC, BN, and CC bonds present in the carbon residue.
An hexagonal columnar mesophase in half‐disk‐shaped thallium (i) complexes
Authors: Barberá Joaquín , Cativiela Carlos , Serrano José Luis. , Zurbano María Mar
Published: December 2004

Communication: The first example of a discotic thallium (I) metallomesogen is reported. The complex is formed by the association of two half‐disc‐shaped molecules (see figure) and the properties of the liquid crystalline material studied using DSC and X‐ray differaction. The materials, with varying numbers of alkyl groups bonded to the central aromatic cores, are also compared with the previously known copper analogues.

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Sevenfold diamond structure and conductivity of copper dicyanoquinonediimines Cu(DCNQI)2
Authors: Ermer Otto
Published: December 2004

Communication: The high substituent sensitivity of the electrical conductivity of copper DCNQI radical anion salts (see figure) is atributed to the fact that the stacks of copper atoms and bridging DCNQI ligands are covalently clamped together within the frame work of a sevenfold interpenetrating super diamond architecture. This observation should influence more quantitative approaches to explaining and modeling the conductivity behaviour of the Cu(DCNQI)2 salts.

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Highly‐ordered ultrathin lc multilayer films on solid substrates
Authors: Decher Gero , Maclennan Joseph , Reibel Jürgen , Sohling Ulrich
Published: December 2004

Research News: Freely suspended thin film of smectic liquid crystalline materials can be described as two‐dimensinal fluids with a regular layer structure in the third dimention. By reducing the internal pressure in the set up shown in the figure the films can be transferred onto solid supports allowing their study, manipulation, and potential use in applications such as integrated optics and sensors.

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The southampton/UCL interdisciplinary optoelectronics research centre
Authors: Gambling William A.
Published: December 2004

Optical methods of data transfer and processing (optoelectronics) using lasers and optical waveguides offer a great speed advantage over puprely electronic processing. The history of the development of optoelectronics thchnology, its applications both today and tomorrow, and an Interdisciplinary Research Centre in the South of England devoted to its study and application are described by the centre's Director.
Molecular materials V Part B. Molecular nonlinear optical materials–potential applications
Authors: Eaton David F. , Meredith Gerald R. , Miller Joel S.
Published: December 2004

Molecular Materials V B: Second‐ and third‐order nonlinear optical applications require materials with differing structures and properties. In this, the second part of this Research News article, applications such as frequency doubling, optical phase conjugation (four wave mixing), and optical switching are discussed and the various materials requirements examined.
An electrochromic device based on polyaniline and prussian blue
Authors: Duek Eliana A. R. , De Paoli Marco‐A. , Mastragostino Marina
Published: December 2004

Variable light‐transmission electrochromic devicesbased on the complimentary mixture of polyaniline and ferric ferrcyanide (prussian blue) are presented. Various configurations for th devices are discussed and the factors which can be manipulated in order to increase the efficiency of the devices are considered.
Large changes in optical response through chemical pre‐ordering of poly(p‐phenylenevinylene)
Authors: Halliday David A. , Burn Paul L. , Bradley Donal D. C. , Friend Richard H. , Gelsen Olaf M. , Holmes Andrew B. , Kraft Arno , Martens Josef H. F. , Pichler Karl
Published: December 2004

Conjugated polymers such as poly(p‐phenylenevinylene), (PPV, see Figure), show real promise in optoelectronic applications. A new synthetic route to improved PPV is presented, involving the thermal conversion of a precursor polymer containing rigid rod conjugated segments joined by flexible spacer groups. A high degree of interchain ordering results which influences the optical response of the material.

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Quantized Semiconductor Particles: A novel state of matter for materials science
Authors: Weller Horst
Published: December 2004

The optical, electronic, and catalytic properties of semiconductor Q‐particles differ significantly from those of either the bulk materials or of the molecules, as the nanometer‐size particles exhibit effects due to quantum confinement. The methods of preparing these materials, their characterization, their properties, and their applications are reviewed, and the requirements for future progress, even the extension of the work to nanometer‐sized metal particles, are discussed.
In situ photopolymerized, oriented liquid‐crystalline diacrylates with high thermal conductivities
Authors: Hammerschmidt Albert , Geibel Kurt , Strohmer Franz
Published: December 2004

Long‐range‐oriented liquid‐crystalline polymers (LCPs) can exhibit anisotropic mechanical, optical, electrical, and magnetic properties. The macroscopic orientation of LCPs proceeds relatively slowly and incompletely compared to low molecular weight liquid crystals. Here, the photopolymerization of thin films of nematically ordered LC monomers is shown to lead to oriented LCPs with high thermal conductivities.
Connectivity of pores and structural units in zeolites, pillared clays and nanoparticle assemblies
Authors: Hansen Staffan
Published: December 2004

Solids of the zeolite type combine pores of uniform dimensions with large void fractions and are important in applications such as catalysts and as host materials for intercalation. The regular pores influence the physical and chemical properties of the solid while the zero‐ to three‐dimensional connectivity of the pore system can determine the electronic properties of host–guest compounds. Here, a simple new method for the classification of these solids is presented, which also leads to the prediction of new classes of microporous materials.
Quasi‐perfect polar alignment of nonlinear chromophores in a crystalline H‐bonded guest–host structure: 2‐Amino‐5‐nitropyridinium‐L‐monohydrogentartrate
Authors: Zyss Joseph , Masse René , Bagieu‐Beucher Muriel , Levy Jean Pierre
Published: December 2004

The nonlinear optical properties of organo‐mineral salts based on 2‐amino‐5‐nitropyridine (2A5NP) and tartrate anions are presented. The mineral anion provides improved structural cohesion compared to van der Waals or hydrogen‐bonded organic molecular crystals while the organic species is responsible for the nonlinear optical activity. 2A5NP is known to exhibit high molecular hyperpolarizability and blue‐shifted absorption relative to p‐nitro‐ aniline‐like molecules.
Mesoporous inorganic solids
Authors: Behrens Peter
Published: December 2004

With pore sizes in the range of 20–500 Å mesoporous materials are of use for extending zeolite‐type chemistry, which is based on materials with a pore size of around 7 Å, to larger molecules. The pores can be produced by pillaring (the propping of layered materials) or by extending the template method used to produce zeolites. The new, ultra‐large‐pore materials recently presented by researchers from Mobil Oil Research are described and their production and application discussed
Compositional separation in CoCr based alloy films
Authors: Maeda Yasushi
Published: December 2004

CoCr Based alloy thin films are being studied extensively for applications as high‐density magnetic recording media. The observation of a compositional microstructure the “chrysanthemum‐like pattern” (CP) in the Figure, is the first step towards understanding the mechanisms that make such applications possible. Much work remains to be done on the origin of the compositional separation causing the CP and on methods of controlling the CP.

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Atomic layer passivation of GaAs surfaces using InP related compounds
Authors: Wada Kazumi , Wada Yoshinori
Published: December 2004

Passivation of GaAs surfaces has the important function of reducing the loss of carriers by recombination at surfaces and interfaces. This prevents degradation of the characteristics of minority‐carrier injection devices and extends the device lifetime. The new method of surface passivation reported here—the deposition of a few atomic layers of InP related compounds—can replace the far from satisfactory sulfur treatment used so far.
Poly[(silylene)diacetylene]–metal oxide composites: A new approach to SiC–metal nitride ceramics
Authors: Corriu Robert , Gerbier Philippe , Guérin Christian , Henner Bernard
Published: December 2004

Precursors to high‐performance ceramics, based on poly(silylene)diacetylene‐metal oxide composites see figure, are reported. On thermal conversion under nitrogen, carboreduction and nitridation of the encapsulated metal oxide take place, resulting in the formation of SiC‐metal nitride ceramics with well‐defined composition profiles.

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X‐ray determination of the crystal structure and orientation of vacuum evaporated sexithiophene films
Authors: Servet Bernard , Ries Simone , Trotel Marie , Alnot Patrick , Horowitz Gilles , Garnier Francis
Published: December 2004

The crystalline orientation of oligothiophenes has a profound effect on the electronic properties of the materials, which are of interest for example in the construction of all‐organic field‐effect transistors. Here, an X‐ray diffraction study of oligothiophene films is reported and the possible routes to improving the crystalline orientation discussed. It is found that α‐substitution or indeed heating of the substrate can lead to increased orientation of the oligomers.
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.

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Methylzinc or methylcadmium‐N,N,N‐trimethyl‐ propylenediaminedithiocarbamates: Precursors for zinc or cadmium sulfide. The X‐ray crystal structure of methylcadmiumtrimethylpropylene‐ diaminedithiocarbamate benzene solvate
Authors: Malik M. Azad , Motevalli Majid , Saeed Tahir , O'Brien Paul
Published: December 2004

Deposition of metal chalcogenides by metal‐organic chemical vapor deposition can be achieved using various systems, including alkyl‐metal‐dithio‐ or diselenocarbamates. Initial attempts to modify the behavior of such precursors by changing the nature of the carbamato ligand are reported. Among the results presented are the synthesis and characterization of the two title compounds and the single‐crystal X‐ray structure of one of them. For both the zinc and cadmium derivatives the films grown were of a better quality than those grown from the parent compounds or from zinc‐ or cadmium‐diethyldithiocarbamate.
Ring‐Opening Polymerization and ring‐closing depolymerization
Authors: Höcker Hartwig , Keul Helmut
Published: December 2004

Ring‐opening polymerization (ROP) of cyclic monomers is most suitable for the preparation of sequential copolymers of the type (AAB)n, the sequence being determined by the structure of the monomer. The thermodynamics and mechanisms of ROP are reviewed, including radical, cationic, anionic, and metathetical ROP, with may examples being given. As recycling becomes more important, interest in reversible polymerization, i.e., depolymerization, is increasing. The results available so far on the depolymerization of polymers obtained by ROP are discussed.
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.

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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.

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Solid‐state routes to tantalum nitrides (TaN, Ta3N5)
Authors: Parkin Ivan P. , Rowley Adrian T.
Published: December 2004

Metal nitrides are hard, durable refractory materials with a number of applications, including wear resistance, reflective coatings, and catalysts. Low‐energy approaches to the synthesis of these materials are a topic of current research. A new method for the preparation of tantalum nitride is presented which is a solid‐state reaction, a hybrid between the molecular precursor approach and a metathesis reaction.
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.

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Supramolecular orientation of conjugated porphyrin oligomers in stretched polymers
Authors: Anderson Harry L.
Published: December 2004

Conjugated porphyrin oligomers show strong optical dichroism when oriented in a stretched polymer matrix. It is shown that the zinc porphyrin polymer (∼10 repeat units) aligns, as expected, with its backbone in the stretch direction, whereas the dimer orients with its molecular plane perpendicular to the stretch. This anomalous behavior is explained as being due to the formation of supramolecular stacks that orient as single units.
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.

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Rapid chemography of porous silicon undergoing hydrolysis
Authors: Canham Leigh T. , Saunders Steven J. , Heeley Paul B. , Keir Andrew M. , Cox Timothy I.
Published: December 2004

Highly porous silicon reacts with water vapor in the air to create images on photographic plates within seconds. It is demonstrated that this process, known as chemography, can be used diagnostically to reveal inhomogeneity in porous silicon layers that is not always detectable by optical or electron microscopy. It is suggested that many dried highly porous semiconductors may constitute a significant health hazard owing to the liberation of high concentrations of toxic hydrides through hydrolysis.
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.

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Thin‐film fabrication by laser ablation of addition polymers
Authors: Blanchet Graciela B. , Fincher Curtis R.
Published: December 2004

Laser ablation can be used to deposit polymer thin films, in addition to its widespread application for the deposition of inorganic materials. The production of polytetrafluoroethylene (PTFE) and polymethylmethacrylate (PMMA) films by evaporation of the solid polymer target with a pulsed UV laser is described. The composition and morphology of the films, the lasertarget interaction, and the film characterization are discussed. Finally, possible routes are considered for how the ablation proceeds.
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.

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Molecular aggregation‐induced photocarrier generation in layered organic photoreceptors incorporating azo compounds
Authors: Niimi Tatsuya , Umeda Minoru
Published: December 2004

The high photosensitivity of azo‐compound‐based photoreceptors is considered to be due to molecular‐aggregation‐induced geminate‐pair dissociation rather than a photo‐induced electron‐transfer reaction. Both agregated and non‐aggregated carrier‐generating materials are employed on order to investigate the mechanism of this process, which has practical implications for the development of electrophotography.
Efficient two layer leds on a polymer blend basis
Authors: Pommerehne Jörn , Vestweber Horst , Guss Werner , Mahrt Rainer F. , Bässler Heinz , Porsch Michael , Daub Jörg
Published: December 2004

Polymer blends in organic LEDs offer the advantage of processibility coupled with flexibility with respect to the chromophores which can be incorporated into their structures. The polymer matrix is also though to have a positive effect on the quantum efficiency and other LED performance indicators. Two‐layer devices have also been shown recently to yield improved performances. Here, a two‐layer device based on polymer blends is reported.
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.

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Epitaxial size control by mismatch tuning in electrodeposited Cd(Se, Te) quantum dots on {111} gold
Authors: Golan Yuval , Hutchison John L. , Rubinstein Israel , Hodes Gary
Published: December 2004

Since the crystal size of semiconductor quantum dots (QDs) affects the optoelectronic properties of QDs, a method of controlling the size is important. It is demonstrated that CdSe QDs electrodeposited epitaxially on {111} Au can be tuned from <5 to ∼ 20 nm by introducing small amounts of Te into the electrodeposited CdSe, i.e., by decreasing the mismatch between the deposited layer and the substrate. A further advantage of this technique is the ability to vary the bandgap continuously and controllably.
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.

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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.

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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

The 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

A 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

The 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

A 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

Knowledge 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

Optically 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

The 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

A 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

A 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

The 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

A 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

Working 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

The 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

The 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

The 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.
Interaction of metallic cations with DNA VI. Specific binding of Mg++ and Mn++
Authors: Clement R. M. , Sturm J. , Daune M. P.
Published: December 2004

The binding of Mg2+ and Mn2+ by DNA by a divalent cation specific electrode and by ultracentrifugation. Both techniques give similar results for the stoichiometry of the reaction. An oscillating densiemete allowed us to detect small changes of volume accompanying the binding. The reaction was also followed by circular dichroism measurements. Interpretation of the results is only possible if one assumes an electrostate site‐binding of Mg2+ to phosphate group, and a chelation Mn2+ between the phosphate group and the N7 of the guanine. Physical modifications accompanying these two types of binding are discused and compared to the role of these cations in some biological systems involving DNA.
A comparison of the interactions of proflavine with DNA and with deoxyribonucleohistone using circular dichroism spectroscopy
Authors: Dalgleish D. G. , Dingsøyr E. , Peacocke A. R.
Published: December 2004

Complexes of proflavine with DNA and deoxyribonucleohistone from calf thymus show different optical activity in the visible and the ultraviolet. Although the visible CD spectra of both complexes arise from interactions of dye molecules, the variation in the optical activity with the amount of dye bound suggests that a lesser conformational mobility exists in DNH. This is confirmed by the ultraviolet CD spectra of the complexes, and it is suggested that the conformation of DNA within nucleohistone is altered by separation of the base pairs by a greater extent than occurs in DNA in free solution. Even if the protein is unequally distributed along the DNA, the conformation of all of the DNA is altered by its incorporation into the nucleoprotein complex, since no evidence could be detected to show that DNA in a “free” conformation existed.