bluuebunny/crossref_metadata_2025 huggingface dataset:
Ferromagnetically coupled decamethylmetallocenium salts of 2, 5‐dimethyl‐N,N′‐dicyanoquinonediimine, [M(C5Me5)2]⊕[Me2DCNQI]⊙⊖, (M = Fe, Mn)
Authors: Miller Joel S. , Vazquez Carlos , McLean R. Scott , Reiff William M. , Aumüller Alexander , Hünig Siegfried
Published: December 2004

Cooperative magnetic interactions in organic materials (such as ferri‐ or ferromagnetic behavior) have been observed in only a few cases. The title compound, shown in the Figure, has been synthesized and represents a further step in the study of structure–function relationships in these materials, from which it is hoped the structures of higher performance materials can be predicted.

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Optical, electrochemical and photoelectrochemical properties of polyazulenes with substituents at C‐2. Photoelectrochemical switching by light‐pulse treatment
Authors: Mirlach Albert , Feuerer Michaela , Daub Jörg
Published: December 2004

Conducting, ferromagnetic, and electrochromic behavior is exhibited by polyazulene materials. Here, the synthesis and properties of a range of polyazulenes substituted at C‐2 in the five membered ring are presented (the C‐1 and C‐3 positions are involved in the polymerization). The non‐alternant azulenes are known to have a low ionization energy, a high electron affinity, and a narrow bandgap. The effect of the substituents on these properties is examined.
Scanning Acoustic Microscopy—recent applications in materials science
Authors: da Fonseca Raul J. M. , Ferdj‐Allah Lahouari , Despaux Gilles , Boudour Amar , Robert Laurent , Attal Jacques
Published: December 2004

A convergent beam of ultrasonic waves at very high frequencies can be used in an acoustic microscope to achieve resolutions of the order of 1 μm at depths of up to 1 mm. One application of the acoustic microscope are welding tests (e.g. the Figure which shows an Si/Mo structure welded at 475°C).

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Synthesis of some higher thienylpyrrole oligomers
Authors: Niziurski‐Mann Renée E. , Cava Michael P.
Published: December 2004

Mixed thiophene–pyrole oligomers containing four to seven heterocyclic rings (see Figure) are reported which are of interest in teh modeling of the structure and the study of teh properties of polymeric organic metals.

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Thiophene oligomers as polythiophene models 3. conductive and capacitive behavior of end‐capped oligothienyls as thin films. A contribution to the conduction mechanism and to the faradaic–capacitive debate of conducting polymers
Authors: Zotti Gianni , Schiavon Gilberto , Berlin Anna , Pagani Giorgio
Published: December 2004

The real nature of the mechanism of bipolaron conduction in conducting polymers and the discussion as to whether the charging–discharging currents in these materials are of a capacitive or a redox nature are central questions in conducting polymer research. Here, a number of methyl endcapped thiophene oligomers are studied using cyclic voltammetry in order to provide some of the answers.
A new method for the production of Mg–Ni hydrogen storage materials
Authors: Li Jinping , Ji Xinfang , Wu Feng , Wang Guoqing
Published: December 2004

Hydrogen storage materials based on magnesium alloys are interesting because they exhibit light weight, a large hydrogen capacity, and have a low cost. The Figure shows Mg2Ni which has been produced using powder metallurgical methods. It is found to have an attractive property profile compared to material prepared using induction melting.

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Microemulsions and organogels: Properties and novel applications
Authors: Rees Gareth D. , Robinson Brian H.
Published: December 2004

The phase behavior of surfactant – oil – water mixtures gives rise to a wide variety of possible equilibrium systems, including microemulsions. The Figure shows one model for a gelatin‐containing microemulsion‐based organogel deduced from data from small‐angle neutron scattering. The conditions required and the stability of microemulsions are briefly reviewed before their applications, and the supramolecular architectures they provide, are considered in more detail.

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Nanometer‐sized colloidal germanium particles: Wet‐chemical synthesis, laser‐induced crystallization and particle growth
Authors: Kornowski Andreas , Giersig Michael , Vogel Ralf , Chemseddine Abdelkarim , Weller Horst
Published: December 2004

Nanometer‐sized semiconductor particles are currently being intensively investigated in many fields of physics and chemistry—especially since the discovery of visible luminescence in porous silicon. This is one of the first papers to concentrate on the synthesis of IV – IV nanoparticles. A purely wet‐chemical room‐temperature synthesis is described that leads to stable nanometer colloidal germanium particles after laser illumination. The size of the crystallites can be controlled by adjusting the illumination conditions. The preparation technique detailed here is not restricted to germanium but can also be applied to other IV–IV semiconductor particles.
Calcite crystallization on gelatin films containing polyelectrolytes
Authors: Falini Giuseppe , Gazzano Massimo , Ripamonti Alberto
Published: December 2004

The promotion of oriented calcie crystallization by various polyelectrolytes, in particular their relative efficiency, has been investigated. Gelatin containing polyelectrolytes was found to overcome the compatibility problem between an inert matrix and the water‐soluble polyelectrolytes as sociated with biomineralization (the Figure shows calctie crystals grown on such a substrate).

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Monocrystalline Si3N4 filaments
Authors: Hüttinger Klaus J. , Pieschnick Torsten W.
Published: December 2004

In the search for structural materials suitable for high temperatures. monocrystalline silicon nitride filaments have been synthesized by catalyzed chemical vapor deposition. Such a filament with a catalyst particle at the tip is shown in the Figure. The effect of various flow rates of N2/NH3 and H2, the X‐ray emission spectra, and the mechanical properties of the filaments are presented.

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Self‐supporting films of clay minerals and metal oxides: Molecular ceramics
Authors: Isayama Munetoshi , Kunitake Toyoki
Published: December 2004

Self‐supporting, flexible films of montmorillonite that retain the fundamental characteristics of the mineral have been produced (The Figure shows a cross‐sectional view). This demonstrates that one practical disadvantage of clay minerals‐that they are usually only available as powders‐can be overcome. Further examples of the extension of microscopic layer structures to the macroscopic scale to produce “molecularly defined ceramics” are presented.

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Conjugated polymers exhibiting liquid crystallinity
Authors: Yu Luping , Bao Zhenan
Published: December 2004

Various solubel and fusible liquid crystalline conjugated polymers can be synthesized due to recent progress in the use of the Stille coupling reaction and the Heck reaction. Evidence of nematic liquid‐crystalline phases in these polymers–arising from the rigid‐rod nature of the conjugated polymer backbone—is provided, and it is demonstrated that properties such as Tm, Tc, the solubility and the fusibility can becontrolled by changing the side groups.
Aerosol‐assisted chemical vapor deposition (AACVD) of silver, palladium and metal alloy (Ag1−xPdx, Ag1−xCux and Pd1−xCux) Films
Authors: Xu Chongying , Hampden‐Smith Mark J. , Kodas Toivo T.
Published: December 2004

Thermally labile, low‐volatility molecules are usually unsuitable as precursors for the chemical vapor deposition of high‐quality metal films. Here, a new method, aerosol‐assisted CVD (see Fig.), is reported, and used to produce crystalline silver, palladium, and binary metal alloy thin films from just such precursors.

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A “proton‐pump” electrode based on poly(3‐carboxymethylpyrrole)
Authors: Youssoufi Hafsa Korri , Garnier Francis , Yassar Abderrahim , Baïteche Selima , Srivastava Pratima
Published: December 2004

Electroactive pH‐controlled membranes are a potential application of materials presented here. The functionalization of conjugated pyrroles with pendant carboxylic groups has been used to produce polymer electrodes exhibiting the electrochemically‐controlled release of protons. The synthesis and the electrochemical characterization at varying pH are reported.
Fabrication of PbS nanoparticles embedded in a polymer Film by a gas‐aerosol reactive electrostatic deposition technique
Authors: Salata Oleg V. , Dobson Peter J. , Hull Peter J. , Hutchison John L.
Published: December 2004

Semiconductor nanoparticles embedded in an inert matrix can be seen as a type of quantum‐dot composite, materials which have great potential in optoelectronic applications such as lasers. Room‐temperature electrostatic spraying is used to produce composites based on PbS nanoparticles in a polyvinyl alcohol matrix (e.g. see Fig.) and their potential for application is discussed.

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Static SIMS investigation of immobilized molecules on polymer surfaces
Authors: Leute Angelika , Rading Derk , Benninghoven Alfred , Schroeder Kathrin , Klee Doris
Published: December 2004

The covalent immobilization of molecules on polymer surfaces is interesting for example in the development of vascular prostheses, where the immobilization of biological molecules is used to improve the biocompatibility of synthetic materials. Here, TOF‐SIMS is used to investigate the immobilization of amino acids on such surfaces, and the results compared with those from XPS and other methods.
Polytriacetylenes: Conjugated polymers with a novel all‐carbon backbone
Authors: Schreiber Martin , Anthony John , Diederich François , Spahr Michael E. , Nesper Reinhard , Hubrich Michael , Bommeli Frank , Degiorgi Leonardo , Wachter Peter , Kaatz Phil , Bosshard Christian , Günter Peter , Colussi Martin , Suter Ulrich W. , Boudon Corinne , Gisselbrecht Jean‐Paul , Gross Maurice
Published: December 2004

New, synthetically accessible, soluble, stable all‐carbon‐backbone polymers are reported. The polytriacetylenes (see Fig.) represent an intermediate step between polydiacetlylenes and carbyne and as such are of interest as alternatives for known conjugated polymers. The synthesis, film casting, and interesting properties are discussed.

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Time‐frequency domain optical storage in rare‐earth‐doped materials
Authors: Kachru Ravinder , Bai Yu Sheng , Shen Xiao‐An
Published: December 2004

The storage of information in the time domain through the use of spectral hole burning rare‐earth‐doped crystals is described. The technique, which is also known as stimulated echo, makes serial read/write data rates of 100 MHz possible. Applications include high‐speed memory, signal processing, high‐speed optical switching, optical interconnects, image processing, and logic operations.
Molecular conductors from neutral heterocyclic π‐radicals
Authors: Cordes A. Wallace , Haddon Robert C. , Oakley Richard T.
Published: December 2004

Stable radical species (e.g. see Fig.) can form an alternative source of organic conducting materials. Suppressing the Peierls distortion and stabilizing the metallic state can be achieved by applying pressure or by developing materials with enhanced two and three‐dimensional interactions. Recent progress in the synthesis, and stabilization, for example through doping, is discussed.

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Langmuir monolayer assemblies on chemical oscillators
Authors: Yoneyama Mitsuru , Fujii Akiteru , Maeda Shuichi
Published: December 2004

Oscillatory chemical reactions are exemplified by the Belousov‐ Zhabotinskii (BZ) reaction. A new type of structurally ordered chemical oscillator is reported: the BZ reactor‐Langmuir monolayer coupled system (see Figure), where the monolayer contains Ru(bpy)32⊕ (bpy is bipyridyl), which luminesces. The preparation and spatio‐temporal properties of this system are described.

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Observation of phase‐separated polymeric LB films using scanning probe microscopy
Authors: Yuba Tomoyuki , Yokoyama Shiyoshi , Kakimoto Masa‐Aki , Imai Yoshio
Published: December 2004

Formation of polyimide films by the Langmuir‐Blodgett (LB) method is described. The preparation and possible applications of the films are detailed. In a mixed LB film of two different polyimides, friction force microscopy reveals hexagonal islands (see Figure), which is the first observation of two‐dimensional phase separation in a polymer mixture.

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Photo‐ and electroluminescence efficiency in soluble poly(dialky1‐p‐phenylenevinylene)
Authors: Staring Emiel G. J. , Demandt Robert C. J. E. , Braun David , Rikken Geert L. J. , Kessener Yves A. R. R. , Venhuizen Ton H. J. , Wynberg Hans , Hoeve Wolter Ten , Spoelstra Karin J.
Published: December 2004

Efficient green electroluminescence from PPV derivatives that are readily processible in the conjugated state is reported. Derivatives of poly(p‐phenylenevinylene), PPV, offer possible ways of controlling the emission color, facilitating processing, and enhancing the emission efficiency. The synthesis of soluble poly(dialky1‐p‐phenylenevinylene) is described and the dependence of the efficiency of photoluminescence and electroluminescence on the degree of conjugation 1s discussed.
Laser spectroscopy and organic dyes
Authors: Friedrich Josef , Schneider Siegfried
Published: December 2004

Laser Spectroscopy and Organic Dyes is the topic of this specal issue. The Review, many of the Communications, and several of the Research News articles this month are devoted to various aspects of the applications of this technology in areas ranging from the application of this technology in areas ranging from the application shown on the cover and discribed above, nonlinear optics and optical data storage, and the study of disorder phenomena in glasy materials, to artificial light‐collecting antennae mimicking, for example, photosynthetic systems. The significance and potential of organic dyes and the exploitation of their interesting optical properties are introduced.
The primary steps in photography: Excited J‐aggregates on AgBr Microcrystals
Authors: Trösken B. , Willig F. , Schwarzburg K. , Ehret A. , Spitler M.
Published: December 2004

The primary process in the photographic emulsion is interfacial electron transfer. The electron is transferred from the excited state of a dye species to empty electron acceptor states in silver bromide. There have been no detailed measurements of the rate constants of this commercially important process. The fluorescence decay curves of thiocarbocyanine dye (see figure) yield these rate constants.

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Shaping of phase and amplitude of ultrashort laser pulses with organic spectral hole burning materials
Authors: Schwoerer Heinrich , Erni Daniel , Rebane Alexander , Wild Urs P.
Published: December 2004

Thin films of spectral hole burning materials (dyes such as chlorin or phthalocyanines in a matrix) are shown to serve well as highly spectrally selective, linear filters for ultrashort laser pulses. The materials exhibit a large ratio of width of the inhomogeneously broadened absorption band to the width of the zero phonon lines of the photochromic materials and have been used to shape both the phase and amplitude of the output of a Ti:sapphire laser. The preparation of the materials and a variety of their applications are presented.
Exciton band structures in 2D aggregates of cyanine dyes
Authors: Kirstein Stefan , Möhwald Helmuth
Published: December 2004

Herring‐bone structures (see figure, where the rectangles are the dye molecules and the arrows indicate the oscillation of the transition dipoles) can be classified on the basis of the angle of mutual orientation of the two molecules per unit cell. Those with small angles showing nearly resonant fluorescence emission from the most redshifted transition (J‐aggregates).

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Surface emitting SHG light by counter propagation of guided waves in a plane parallel poled DANS side chain polymer
Authors: Mittler‐Neher Silvia , Otomo Akira , Stageman George I. , Bosshard Christian , Horsthuis Winfried H. G. , Möhlmann Gustaaf R.
Published: December 2004

Large nonlinear optical coefficients and easy processing and fabrication techniques make organic materials, especially polymers, very attractive condidates for counter propagating mixing applications. Here a spincoated waveguide based on a 4‐dimethylamino‐4'‐nitrostilbene side chain polymer is shown to generate surface emitted second harmonic light. The preparation of the waveguide, its experimental operation, and the theoretical background are discussed.
Doping of polyaniline via pseudoprotonation by an ionic salt
Authors: Chen Show‐An , Lin Liang‐Chang
Published: December 2004

Polyaniline can be converted into a conducting form by either protonation of the imine site or oxidative doping at the amine site. Here, a new class of dopant is reported, ionic salts. An ionic‐salt‐doped polyaniline is obtained by mixing the emeraldine base of polyaniline and solutions of, for example, LiClO4, LiBF4, or Zn(ClO4)2 in 1‐methyl‐2‐pyrrolidone, and then casting the solution to form films. Materials synthesis, film production, and the demonstration that the material is intrinsically, rather then ionically, conducting are discussed.
Real space evidence for reversible metal–metal bond rearrangement induced by AFM tip force
Authors: Bengel Hardy , Cantow Hans‐Joachim , Magonov Sergei N. , Whongbo Myung‐Hwan
Published: December 2004

The reversible rearrangement of weak metal‒metal bonds in layered transition metal chalcogenides is shown to be induced by the force exerted by the tip of an atomic force microscope. The figure shows how the ribbon chains which make up the layers of NbTe2 are reversibly switched by 60° by increasing ad decreasing the force at the tip.

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Aligned carbon nanotubes in a thin polymer film
Authors: Ajayan Pulickel M.
Published: December 2004

Carbon nanotubes (see figure) constitute one of the smallest one‐dimensional and nearly perfect structures available and these materials should exhibit a wide range of interesting properties. Most of these properties, however, will only be of use if te structures can be manipulated into a controlled configuration here the alignment of nanotubes in thin polymer films is discussed.

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Nanometric surface design of size‐quantized semiconductor microcrystals
Authors: Yoneyama Hiroshi , Torimoto Tsukasa
Published: December 2004

Semiconductor microcrystals (Q‐particles) with diameters less that 100 Å, modified with viologen have recently been produced. One potential application for such particles would be for light energy conversion devices such as photocatalysts and photosenstizers in wet solar cells. The viologen moieties have the ability to function as electron mediators between the semiconductor particles and acceptors in solution. The preparation and potential applications of these ineresting materials are discussed.
Present limits of data storage using dye molecules in solid matrices
Authors: Ao Rong , Kümmerl Lothar , Haarer Dietrich
Published: December 2004

Optical data storage offers the potential advantages of high storage densities, fewer mechanical problems, low reading and writing energies, ruggedness, and higher data rates. Currently, the only true photonic optical storage medium is the spectral hole burning scheme. The features of the technique are presented, the materials (e.g. see figure) and necessary laser technology presented, and a view is given of the prospects and requirements for future commercial development.

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Materials technology in automotive recycling
Authors: Frisch Arnulf , Razim Claus
Published: December 2004

The growing number of dissed cars and the resulting amount of waste contribute to the increasing pressure on disposal sites. The materials selection for, and the design of, new motor veicles are influenced by teh need to reuse the constituent materials. The current situation often involves shredding old vehicles and sorting the resulting mixture of materials before disposing of a large proportion of the remainder on a dump. The possibilities for the future, including a new concept developed by Mercedes Bez involving the reuse of the energy potential of the materials, is dscussed.
Microcavity effect in a single‐layer polymer light‐emitting diode
Authors: Wittmann Hermann F. , Grüner Johannes , Friend Richard H. , Spencer George W. C. , Moratti Steve C. , Holmes Andrew B.
Published: December 2004

The luminescence of conjugated polymers is of great interest both as a tool for the investigation of electronic processes in these materials and ecause of its significance for applications in light‐emitting devices. The first demonstration of an electroluminescence‐pumped microcavity using a conjugated polymer is reported, representing the first step towards the development of an electrically or optically pumped organic laser.
Unsaturated ladder polymers: Structural variations and improved molecular weights
Authors: Schlicke Benediki , Schirmer Heike , Schlüter Arnutlf‐Dieter
Published: December 2004

All‐carbon ladder polymers with extended π systems are of interest for electroluminescence and photovoltaics applications. The synthesis of two new ladder polymers (e.g. see Figure) exhibiting relatively high molecular weights and pronounced film‐forming abilities, is reported. It is also shown that the degree of saturation in these polymers can be chemically closly controlled.

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Triplet radical pairs of 3‐carboxyproxyl encapsulated in a dendritic box
Authors: Meijer E. W. , Jansen Johan F. G. A. , Janssen René A. J. , de Brabandero‐van den Berg Ellen M. M. , Meijer E. W.
Published: December 2004

The encapsulation of small molecules inside a dendrimeric “box” has recently been reported. Here, the encapsulation and mobility of triplet radical moieties is described. For “boxes” (e.g. see Figure) containing two or more radicals the intermolecular ferromagnetic alignment of the encapsulated radicals to triplet state radical pairs is observed.

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A new class of electron transport compounds: 1,3‐bis‐dicyanomethylene indanes
Authors: Rommens Johan , van der Auweraer Mark , De Sclryver Frans C. , Borsenberger Paul M.
Published: December 2004

Electron transport layers, comprised of polymers doped with electron acceptor compounds have proved difficult to develop as teh inclusion of the acceptors generally results in poor solubility in coating solvents, limited miscibility and even toxic properties. The title compounds (see Figure) are soluble, miscible with a wide range of polymers, and show essentially to absorption in the visible region of the spectrum.

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Photo‐induced cross‐linking of poly(ethynyl)carbosilane fibers in the solid state: New insights on the application of atomic force microscopy
Authors: Johnson Stephen E. , Mostafavi Homan , Rahman Jay , Thorne Kevin J.
Published: December 2004

The cross‐linking of carbosilane polymers is part of the process used to produce silicon carbide fibers. AFM observations of the photo‐induced reactions occurring on the surface of the materials during the cross‐linking process reveal substantial material transport during the phase transformations. It is also reported that the cross‐linking occurs through the ethynyl and hydrosilyl moieties of the title materials. The AFM also allows the study of the details of the reactions as the information obtained is not averaged out as in other surface analytical techniques.
Molecular organization of bacterio‐ rhodopsin films in optoelectronic devices
Authors: Koyama Koichi , Yamaguchi Naoto , Miyasaka Tsutomu
Published: December 2004

Bacteriorhodopsin (bR) is a protein with a molecular weight of 26 000 found in the plasma membrane of Halobacterium sarinarium. The versatile optical functions of bR, especially when it is organized in oriented membranes, make it a material of potential interest for the development of intelligent optoelectronic devices. Recent progress in the orientation of the bR moieties and in the application of the oriented structures in devices is reviewed.
Dielectric relaxation processes in a brick‐like metallomesogen ferroelectric liquid crystal
Authors: Merino Santos , de Daran François , De La Fuente M. Rosario , Jubindo Miguel Angel Pérez , Iglesias Raquel , Marcos Mercedes
Published: December 2004

A non‐typical ferroelectric liquid crystal (LC), i.e., one that is brick shaped—rather than cylindrical—with an oxovanadium metallic center incorporated in its mesogenic core, is shown to exhibit an unusual dielectric response, owing to its highly biaxial molecular nature, with frequencies lower than those found in other ferroelectric LCs. This is the first time that both the Goldstone mode (related to azimuthal fluctuations) and the soft mode (related to fluctuations in the tilt angle) have been characterized for a ferroelectric metallomesogen.
Turning down the heat on semiconductor growth: Solution‐chemical syntheses and the solution‐liquid‐solid mechanism
Authors: Buhro William E. , Hickman Kathleen M. , Trentler Timothy J.
Published: December 2004

Semiconductor crystal growth at low temperatures and under mild reaction conditions would usher in a technological revolution. Following a brief discussion of the processes that occur during crystal growth, several growth techniques are described, including electrodeposition and surfactant‐interface growth. Particular attention is paid to solution–liquid–solid growth, a technique discovered by the authors that resembles a living polymerization and a phase transfer reaction, by which crystalline III—V materials are produced at the lowest known growth temperatures.
Hybrid molecular materials formed by alternating layers of bimetallic oxalate complexes and tetrathiafulvalene molecules: Synthesis, structure, and magnetic properties of TTF4(Mn(H2O)2)[Cr(ox)3]2)·14 H2O
Authors: Coronado Eugenio , Galán‐Mascarós José Ramón , Giménez‐Saiz Carlos , Gó;mez‐García Carlos J. , Ruiz‐Pérez Catalina , Triki Smaïl
Published: December 2004

Hybrid bimetallic–TTF materials in which the organic layer adopts an unprecedented dimerized structure and the inorganic layer is formed by the first ferromagnetic CrIII–MnII–CrIII complex are reported. These materials provide valuable information on the magnetic interactions between these metal ions which should help in the understanding of the behavior of extended magnetic lattices based on oxalate complexes. A method is also provided to prepare materials combining the ferromagnetic properties of the bimetallic oxalate network with the conducting properties of the TTF‐type donors.
Second‐order nonlinear optical properties of a chromophore‐functionalized polypeptide
Authors: Verbiest Thierry , Samyn Celest , Boutton Carlo , Houbrechts Stephan , Kauranen Martti , Persoons André
Published: December 2004

The attachment of a nonlinear optical chromophore to a polypeptide backbone yields a structure in which the chromophores are oriented non‐centrosymmetrically, likely due to the supramolecular helix structure of the polypeptide. This structure exhibits enhanced nonlinear optical properties and can be easily poled in an electrostatic field. The result demonstrates the great potential of supramolecular engineering for optimizing NLO properties.
Shadowed sputtering of gold on V ‐shaped microtrenches etched in silicon and applications in microfabrication
Authors: Xia Younan , Whitesides George M.
Published: December 2004

Silicon micromachining has a wide range of applications in, for example, microelectronics. Here, a combination of several techniques is used in modifying the surface properties of V‐shaped microtrenches (see Figure) and for fabricating complex surface relief structures.

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Partial specific volumes of synthetic polypeptides in dilute solution
Authors: De Loźe C. , Saludjian P. , Kovacs A. J. , Schermutzki B.
Published: December 2004

We report a simple method for measuring partial specific volumes, of polymers in dilute solutions with an accuracy of 3 parts per thousand. This method has been applied to 7 polypeptides in 4 organic solvents. The residue volumes deduced from these data are compared to those calculated by a differential method. The discrepancy is generally of the order of 1.5%.
On the theory of order‐disorder transition and copolymer structure of DNA
Authors: Lifson Shneior , Allegra Giuseppe
Published: December 2004

The statistical mechanical theory of the helix‐coil transition of DNA has been recently discussed by one of the authors, who considered an assembly of DNA molecules with a Markoff distribution of nucleotide sequences. The present communication improves upon the above mentioned theory by introducing approximate normalization factors for the unnormalized statistical weights of finding a given molecule of the assembly in a given microscopic state.
Synthesis of tritiated poly‐L‐lysine (γ, δ‐T2)
Authors: Fridkin M. , Sokolovsky M. , Katchalski E.
Published: December 2004

Tritiated poly‐L‐lysine (γ, δ‐T2) (IX) was prepared according to the following procedure: Tritiated DL‐lysine (γ, δ‐T2) (III) was derived from acetamino‐(‐4‐amino‐Δ2‐butenyl)‐diethylmalonate (I) by tritiation followed by acid hydrolysis. The racemic tritiated lysine was converted to its ε, N‐trifluoroacetyl derivative IV, and the latter resolved via its chloroacetyl derivative by means of hog kidney acylase. The optically active tritiated ε, N‐trifluoroacetyl‐L‐lysine (VI) was converted into the corresponding N‐carboxyanhydride VII with phosgene, and polymerization carried out in dioxane using triethylamine as initiator. The required tritiated poly‐L‐lysine (IX, n = 250) was obtained from the blocked polymer VIII after removal of the protecting groups with piperidine. The tritiated polypeptide possessed an activity of 250 mC. per mmole lysine residue. The procedure described enables, however, the preparation of poly‐L‐lysine with up to 25 times higher specific activity.
Polarographic reducibility of denatured DNA
Authors: Paleček E. , Vetterl V.
Published: December 2004

The de polarographic behavior of native and denatured DNA at pH 7.0 was studied. Whereas native DNA was polarographically inactive under the given conditions, denatured DNA yielded a reduction polarographic step at the potential of about −1.4 V. Native DNA produced a single desorption wave on ac polarograms, while denatured DNA yielded, in addition to this wave, another more negative wave approximately corresponding, as to its potential, to the dc polarographic step of denatured DNA. The behavior of apurinic acid was similar to that of denatured DNA. The course of DNA denaturation at elevated temperature was studied by means of the two above techniques and changes at temperatures below the melting temperature observed. This finding is in agreement with earlier results obtained by oscillopolarographic and the pulse‐polarographic method.
Solution properties and structure of brain proteolipids
Authors: Zand Robert
Published: December 2004

Bovine white matter proteolipids have been studied by several physical methods and have been found to exist as micelles in 2 : 1 (v/v) chloroform–methanol solution. The data would indicate the existence of a critical micelle concentration at 0.017–0.022 g/100 ml. The curve appears linear in the range 0.017–0.2 g/100 ml, but from the data at higher concentrations it would appear that a change in slope is occurring in the region 0.2–0.3 g/100 ml. Light‐scattering measurements on 2 : 1 (v/v) chloroform–methanol solutions containing more than 0.2 g/100 ml of proteolipid yielded a weight‐average aggregate weight of 2.9 × 106and a radius of gyration of 64.5 Å. The intrinsic viscosity of the solutions was 0.32 dl/g and the Huggins constant was 1.085. Light‐scattering measurements in 88.5% formic acid–0.5M sodium formate yielded a weight‐average aggregate weight of 7.1 × 106 and a radius of gyration of 241 Å. The intrinsic viscosity observed for this solvent system is 0.14 dl/g and the Huggins constant is 1.005. Osmotic pressure measurements in 2 : 1 (v/v) chloroform–methanol containing less than 0.2 g/ 100 ml of proteolipid yielded a number‐average aggregate weight of 7.2 × 104 Ultracentrifugal analysis in 1.5:1 (v/v) methylene chloride–methanol showed two broad peaks with, s values of s1.5% = 20.05 S, s2% = 19.79 S for the minor peak and s1.5%,2% = 1.86 S for the major peak. Optical rotatory dispersion studies revealed large changes in b0 with change in solvent and proteolipid concentration. The present data suggest that the mode of attachment of protein to lipid is primarily of a noncovalent type. The results of this investigation also suggest that the proteolipid micelle above 0.2 g/100 ml is cylindrical (prolate ellipsoid) in 2:1 (v/v) chloroform‐methanol and approaches a more spherical shape in 88.5% formic acid. A structure for the proteolipid micellar complex above concentrations of 0.2 g/100 ml is proposed.
Dynamic‐elastic investigation of the chemical denaturation of collagen fibers
Authors: Reich S. , Katchalsky A. , Oplatka A.
Published: December 2004

The dynamic elastic behavior of collagen fibers treated by LiBr solutions was studied by the method of free longitudinal vibrations. The frequency response functions and the stress–strain relationship were evaluated for fibers denatured to different extents by various concentrations of the salt solution. The James and Guth model for rubber elasticity was applied to the experimental data. The elastometric parameter β, which is a measure of the degree of folding of the macromolecular chains, was found to decrease on increasing the salt concentration. It might thus serve as a characteristic of the degree of denaturation of fibrillar proteins.
On the triplet states of polynucleotide–acridine complexes. I. Triplet energy delocalization in the 9‐aminoacridine–DNA complex
Authors: Galley W. C.
Published: December 2004

Phosphorescence and fluorescence from the dye in complexes of DNA with 9‐amino‐acridine and acridine orange in a glycerol‐H2O glass have been measured at 77°K. The dependence of the p/fratio for 9‐aminoacridine on the exciting wavelength demonstrates triplet–triplet energy transfer from DNA to dye. The result provides evidence for π electron overlap between the dye and the bases of native DNA. The observation that the magnitude of the enhancement in ultraviolet‐excited dye phosphorescence increases with the base to dye ratio indicates triplet delocalization in the polymer. Preliminary flash experiments provide evidence that this delocalization is not limited by slow diffusion of the triplet exciton. The inability to detect transfer on denaturation of the DNA illustrates the sensitivity of triplet–triplet energy transfer to the conformation of the macromolecular complex.
Convection induced by hydrostatic pressure in sedimentation velocity experiments
Authors: Kegeles Gerson
Published: December 2004

A consideration of the meaning of the second moment method for the determination of sedimentation coefficients reveals potential convective instability in the sedimentation of all reversibly aggregating systems for which dissociation is favored by pressure.
Studies on the myosin molecule from smooth muscle
Authors: Kotera Akira , Yokoyama Masao , Yamaguchi Masahiro , Miyazawa Yuji
Published: December 2004

The myosin molecule was extracted from the smooth muscle parts of horse esophagus and purified by ammonium sulfate fractionation. The schlieren pattern of the sedimentation velocity run showed a very sharp single peak of.5.9. S (s20,w). Molecular weight of the protein was measured by means of the Archibald and sedimentation equilibrium methods, both in 0.5M KCI buffered by 1/150 M phosphate at pH 7.5 and at 5°C. The values obtained were 6.25 × 105 and 5.81 × 105respectively, for the two methods. The second virial coefficients were 1.1 × 104 and 1.2 × 10−4 ml/g. Denatured smooth muscle myosin was prepared in a solution of 5M guanidine HC1 containing 0.4 M KC1 and 0.2 M β‐mercaptoet hanol buffered at pH 8.0. The weight‐average molecular weight of the denatured smooth muscle myosin was 2.24 × 105 and the second virial coefficient was 7.6 × 10−4 ml/g. The values described above are in good agreement with those reported for rabbit skeletal myosin with ammonium sulfate fractionation. The molecular dimension of the molecule is estimated as the value for an axial ratio of 100, assuming a rigid rod molecular model for this molecule, both the thermodynamical and hydrodynamical treatment being in a good agreement with this estimation.
Optical rotatory dispersion of mucopolysaccharides and mucopolysaccharide–dye complexes. II. Ultraviolet cotton effects in the amide transition bands
Authors: Stone A. L.
Published: December 2004

Ultraviolet optical rotatory dispersion curves of mucopolysaccharides exhibit particular Cotton effects in the spectral region of the n–π and π–π amide transitions. Two general patterns emerge: (1) enhancement of negative rotation and of the first negative Cotton effect (troughs 217–220 mμ) and (2) relative dominance of the positive Cotton effect in the π–π transition region (peak ∼198 mμ). Groups (1) and (2) can be correlated with a structural difference in the linkages of the amino sugars: (1) occurs with polymers containing 3‐1‐linked glycosamino sugars and (2) with glycosamino moieties linked 4–1 by either α‐ or β‐glycosidie bonds. Measurements of the circular dichroic absorption bands support the qualitative conclusions from optical rotation. All mucopolysaccharides exhibit a first, negative band centered at 208–211 mμ, while only those in group (2) show, in addition, a positive band centered at 189–192 mμ. A suggested unifying model considers that difference in kind and/or degree of preferred geometry of the amide groups obtains from two forms of secondary order: (1) having a linear hydrogen bond from the N (acceptor) to the (C2)O—H of the preceding uronic acid and (2) having a linear hydrogen bond from the N (acceptor) to the (C2 or 3) O—H of the following sugar. The hydrogen bonds would have similar strength but opposite directions in two systems towards the nonreducing end (1) or towards the reducing end (2)], closing eight‐membered rings magnified image
Quantum mechanical approach to the conformational analysis of macromolecules in ground and excited states
Authors: Hoffmann Roald , Imamura Akira
Published: December 2004

Molecular orbital calculations of the extended Hückel type have been used to study the conformations of glycyl and alanyl residues in ground and excited states. The ground‐state surfaces show features similar to those obtained with the standard calculational methods in which the total energy is partitioned into components such as torsions, nonbonded and electrostatic interactions. The molecular orbital calculations provide the first independent theoretical check on such calculations. The excited‐state surfaces, Uniquely available from the molecular orbital calculations, exhibit a better definition and sharpening of potential minima in the sterically allowed regions.
Formation of a streaming convective disturbance which may occur at one gravity during preparation of samples for zone centrifugation
Authors: Nason Paul , Schumaker Verne , Halsall Brian , Schwedes Jean
Published: December 2004

Zone centrifugation experiments are occasionally ruined by convective processes which occur at one gravity subsequent to layering a solution of macromolecules on a supporting density gradient. The factors which contribute to this convection have been little understood. In most of the experiments described in this communication, Blue Dextran 2000 is used as the macromolecular component. The convective disturbance may be clearly seen and accurately measured. The effects of macromolecular concentration, composition and density of the supporting gradient, diffusion coefficient of the solute, and several other variables are studied, and an empirical equation constructed to describe the phenomenon. This convective disturbance appears to be minimized or prevented by layering and fractionating in the presence of a centrifugal field.
Dependence of polynucleotide helix–coil transition theory on the ring closure exponent
Authors: Klotz L. C.
Published: December 2004

Formulas are derived which relate the maximum slope of the helix‐coil transition in synthetic polynucleotides to the stacking free energy and to the exponent k in the expression for the probability of ring closure for polymer chains. The exact value of k has not yet been determined. By use of the derived formulas, it is then shown that estimates of the stacking free energy are sensitive enough to the value chosen for k, so that exact values of these energies must await a precise determination of k.
Hydrogen‐tritium exchange of the random chain polypeptide
Authors: Englander S. W. , Poulsen A.
Published: December 2004

The Hydrogen–tritium exchange character of poly‐D,L‐alanine was studied in detail as a model for the hydrogen exchange behavior of the unhindered, polymeric peptide group. The random chain nature of poly‐D,L‐alanine was evident in the uniformity of exchange rate of all its hydrogens and in the similarity between this rate and that of random chain poly‐D,L‐lysine and other known, unhindered secondary amide groups. An equilibrium isotope effect favoring the binding of tritium over protium to the extent of 21% was measured. Specific acid and base catalysis of the exchange and the absence of detectable general catalysis were demonstrated. Apparent energy of activation is 17 kcal/mole for deprotonation, largely due to dependence of Kw on temperature, and 15 kcal/mole for protonation, which correlates with the extreme apparent pK. The hydrogen –tritium exchange half‐time rate; of poly‐D,L‐alamine at any pH and temperature (T: °C) is given by the equation:
Synthesis of poly‐L‐asparagine and poly‐L‐glutamine
Authors: Ariely S. , Fridkin M. , Patchornik A.
Published: December 2004

Poly‐β‐N‐diphenylmethyl‐L‐asparagine and poly‐γ‐N‐diphenylmethyl‐L‐glutamine were prepared from the corresponding N‐carboxyanhydrides. Poly‐L‐aspuragine and poly‐L‐glutamine were obtained by removal of the diphenylmethyl protecting groups with liquid anhydrous hydrofluoric acid.
Spatial configurations of polynucleotide chains. I. Steric interactions in polyribonucleotides: A virtual bond model
Authors: Olson Wilma K. , Flory Paul J.
Published: December 2004

A simplified scheme for treating the spatial configurations of polynucleotide chains is developed using the rotational isomeric state approximation and statistical methods applicable to linear systems of interacting subunits. As a consequence of geometric constraints imposed by the skeletal structure and of the severity of certain steric interactions, it is possible to represent the repeat unit comprising six skeletal bonds by two virtual bonds of fixed length. The configuration of the polynucleotide chain as a whole may be conveniently described by an alternating succession of these two virtual bonds. Moreover, analysis of steric interactions suggests that bond rotations governing the mutual orientation of a given pair of successive virtual bonds should be sensibly independent of the rotations affecting the mutual orientation of other pairs. The statistical mechanical treatment of configuration‐dependent properties is much simplified in consequence of this mutual independence. Mean‐square dimensions calculated by giving equal weights to all sterically allowed conformations are much smaller than values determined by Felsenfeld and co‐workers. The calculated dimensions are markedly increased, however, by placing certain arbitrary restrictions on the rotations about selected pairs of skeletal bonds. It is thus demonstrated that steric interactions alone are insufficient to account for the spatial characteristics of polynucleotide chains. The dimensions are also found to be sensitive to the conformation of the ribose ring of each nucleotide unit, but, insofar as the influences of steric interactions are concerned, the dimensions do not depend on the heterocyclic base attached to the ribose ring.
“Active monomer” polymerization of δ‐benzyl L‐α‐aminoadipate
Authors: Choi Nam S. , Goodman Murray
Published: December 2004

The N‐carboxyanhydride of δ‐benzyl L‐α‐aminoadipate polymerizes when initiated by strong base through an “active monomer” mechanism. This is shown by the isolation of 6‐oxo‐L‐pipecolic acid from the product mixture, since this byproduct could only arise from an “active monomer” pathway. This study also specifies conditions for preparing high molecular weight poly(δ‐benzyl L‐α‐aminoadipate) in high yield.
X‐Ray and stereochemical studies on xylan diacetate
Authors: Gabbay S. M. , Sundararajan P. R. , Marchessault R. H.
Published: December 2004

By means of x‐ray fiber diffraction, it has been found that xylan diacetate crystallizes with two chains or four residues in a monoclinic cell (space group P21): a = 7.64, b = 12.44, c (fiber axis) = 10.31 Å, and γ = 85°. Pairs of residues are related by a twofold screw axis in the c direction. Based on the observed fiber repeat and chain symmetry, the probable conformation of a pair of xylose diacetate residues joined via a β‐1,4′ linkage has been obtained by energy minimization methods. The conformations corresponding to a threefold screw axis and a twofold screw axis along the chain have been compared and the reason why xylan diacetate assumes a twofold screw axis seems to be due to intermolecular packing effects rather than intramolecular non‐bonded interactions.
Sodium counter ion activity of poly‐S‐carboxyethyl‐L‐cysteine
Authors: Maeda Hiroshi
Published: December 2004

Counterion activity of poly‐S‐carboxyethyl‐L‐cysteine in salt‐free solutions neutralized to various degrees with sodium hydroxide was determined either directly from the e.m.f measurements of concentration cells formed across a Na–glass electrode, or from the potentiometric titrations at different sodium chloride concentrations assuming the additivity rule.

From e.m.f. measurements, the activity coefficient of counterions was confirmed to display the β‐structure random coil transition of the polymer.

For random coil state, both methods gave identical results. Observed values of the activity coefficient was generally smaller than those for other randomly coiled polypeptides. The activity coefficient was found to decrease with the increase of the polymer concentration.

The activity coefficient of counterions for β‐structure was extremely small as compared with that for random coil at the same degree of neutralization. The activity coefficient obtained from titrations was almost independent of degree of neutralization and increased with the increase of the polymer concentration.
Determination of pK's of trinucleotides
Authors: Javaherian K.
Published: December 2004

pK's of trinucleotides are calculated according to the theory of Kirkwood and Westheimer for ellipsoids. In order to compare the calculated values with some experimental results, a number of trimers were prepared and their pK's were measured. The question of syn and anti conformations for monomers are discussed in light of the above considerations.
Viscosity of heparin as a function of dielectric constant and of desulfation
Authors: Yuan L. , Stivala S. S.
Published: December 2004

The effect of dielectric constant (D) of the solvent on the viscosity of heparin was examined using the relation \documentclass{article}\pagestyle{empty}\begin{document}$ \eta _{{\rm sp}} /c = [\eta ]_\infty (1 + k/\sqrt c) $\end{document}, where [η]∞ is the shielded intrinsic viscosity obtained by extrapolating \documentclass{article}\pagestyle{empty}\begin{document}$ \eta _{{\rm sp}} /c\,{\rm vs}{\rm . }\,1/\sqrt c ) $\end{document} to infinite concentration, and k is an interaction parameter independent of the dielectric constant of the solvent. This equation was previously reported by the authors9 for describing the reduced viscosities of strong polyelectrolytes in salt‐free polar solvents. It was found that the [η]∞ of heparin increases linearly with increasing dielectric constant of the solvent whereas the k values were, within experimental error, independent of D in the range 54.7 < D < 93.2 examined. Graded hydrolysis of heparin from its acid form (heparinic acid) at 57°C resulted in samples of varying degree of desulfation with corresponding decrease in biological activity. It was found that both [η]∞ and k decrease with increasing desulfation.