bluuebunny/crossref_metadata_2025 huggingface dataset:
Dielectric relaxation in a new cyclic liquid‐crystalline oligosiloxane
Authors: Jakob Eckhard , Kreuzer Franz‐Heinrich , Häberle Norman , Haase Wolfgang
Published: December 2004

Polysiloxanes with mesogenic side chains are suitable model compounds dor the study of molecular dynamics. The first dielectric relaxation data are presented here for a cyclic oligosiloxane having a degree of oligomerization of 5, a cyanophenylbenzoate group as the terminal dipole, and a spacer length of 3. The phase sequence was determined by means of X‐ray diffraction, differential scanning calorimetry, and polarizing microscopy. Reasons for the strong dependence of physical properties on the degree of oligomerization are discussed.
The safety of ceramic balls on metal stems in hip arthroplasty
Authors: Heimke Günther
Published: December 2004

The safety of hip replacement systems is influenced by, for example, the materials of the ball and stem or taper, the method of joining, heir shape, and the state of their surfaces. These factors, and specifiations for manufacturers and in the operating theater, are briefly reviewed. The metal taper shown in the Figure has a typical defect —it does not meet the straightness requirement—which could lead to failure.

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A high efficiency blue‐light‐emitting diode based on novel ladder poly(p‐phenylene)s
Authors: Grüner Johannes , Hamer Peter J. , Friend Richard H. , Huber Hans‐Joachim , Scherf Ullrich , Holmes Andrew B.
Published: December 2004

Low energy losses due to non‐radiative decay are an important step towards high‐efficiency organic LEDs. The rigid, regioregular structure of the novel ladder poly(p‐phenylene)s reported here lead to a reduction in such losses and to potentially interesting internal LED efficiencies of 1%. The effect on the efficiency of varying the length of the spacers in the structure is examined.
Synthesis, X‐ray structure and application of bis[allylamine(dimethyl)gallium(III)] as a precursor for the growth of GaP layers by MOVPE
Authors: Schumann Herbert , Just Oliver , Nickel Siegbert , Weimann Roman , Gottschalch Volker , Keller Bernd P. , Schwabe Reinhard
Published: December 2004

Gallium precursors for the growth of gallium‐based materials from the vapor phase still need to be improved in terms of their safety and handling properties, especially with respect to their pyrophoricity, air and moisture sensitivity, and toxicity. A new gallium precursor is reported, the first diorganogalliumamine, which exhibits a more favorable safety profile, and its use in the preparation of N‐doped GaP is discussed.
Effects of pressure on the thermodynamic properties of C60 studied by 13C NMR
Authors: Kerkoud Rachid , Auban‐Senzier Pascale , Godard Jean , Jérome Denis , Lambert Jean‐Marc , Bernier Patrick
Published: December 2004

In fullerenes, the dynamics, molecular motion, and order‐disorder transition temperature Tc are strongly affected by the applied pressure. In this study, single‐crystal 13C NMR spectroscopy is used to study fullerenes under hydrostatic pressure as a function of temperature (200–343 K). Information is obtained on the thermodynamic properties of these materials, their phase behavior and their molecular dynamics.
Planning for the future: The role of the ESF
Authors: Rees Dai
Published: December 2004

The European Science Foundation is a federation of research councils and academies, from various European countries, that have significant responsibility for the funding of science and scholarship. The changing role of the ESF in recent years is examined, particularly in the face of tighter research budgets in all countries and the increasing part played by the European Union in encouraging collaboration of researchers throughout Europe. Future aims of the ESF are presented.
Effects of structure on the optical and redox properties of the oligothiophene— Tetrathiafulvalene hybrid system
Authors: Roncali Jean , Rasmussen Lennart , Thobie‐Gautier Christine , Frère Pierre , Brisset Hugues , Sallé Marc , Becher Jan , Simonsen Ole , Hansen Thomas K. , Benahmed‐Gasmi Amina , Orduna Jesus , Garin Javier , Jubault Michel , Gorgues Alain
Published: December 2004

The optical properties of the oligothiophene–tetrathiafulvalene system are greatly affected by structural factors. An understanding of these, as presented here, is a first step towards reducing the band gap in thiophene oligomers and thus optimizing them for device applications. The effect of spacer length and the role of planarity and rigidity, for example of the syn conformation shown in the Figure, are investigated.

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An efficient strategy towards small bandgap polymers: The rigidification of the π‐conjugated system
Authors: Roncali Jean , Thobie‐Gautier Christine
Published: December 2004

The design of narrow bandgap polymers remains a major challenge in the field of organic conductors. An alternative scheme is proposed for reducing the bandgap, namely the construction of a one‐dimensional graphitelike chain. Terthienyl frozen in a fully planar syn conformation is used as a simplified model compound for rigidified polythiophene. Its synthesis, cyclic voltammetry results, and electropolymerization are reported, which suggest that even smaller bandgaps could be produced in polythiophenes using this strategy.
The influence of alkoxy side chains on the conformational flexibility of oligo‐ and polythiophenes
Authors: Meille Stefano V. , Farina Alessandra , Bezziccheri Federica , Gallazzi Maria C.
Published: December 2004

Alkoxy‐substituted thiophenes have been shown to yield polymers with a reduced bandgap. An X‐ray investigation of two symmetrical pentoxy‐substituted 2,2′‐bithienyls is reported, and their structure and packing described. It is suggested that the extra rigidity and packing stability of the alkoxythiophene oligomers and polymers accounts for their lower solubility and higher melting points compared to their alkyl‐substituted analogues.
Molecular recognition effects in an L‐tartaric acid—Silica composite prepared using the sol‐gel method
Authors: Mizukami Fujio , Izutsu Hiroyuki , Osaka Tetsuya
Published: December 2004

Molecular recognition ability is one of the properties exhibited by a composite presented here consisting of an optically active organic compound (L‐tartaric acid) and silica. It is reported that the composite formed by the sol‐gel method can distinguish the chirality of the complex tris(2,4‐pentanedionato) cobalt(III). The reasons for the differing properties of the composites formed by impregnation and the sol‐gel method are discussed and circular dichroism spectra presented.
The formation of rings of platinum dots and the control of the size of platinum particles on silica surfaces using organic—Inorganic composites
Authors: Mizukami Fujio , Taniguchi Fumi , Kiyozumi Yoshimichi , Kobayashi Aya , Izutsu Hiroyuki , Maeda Kazuyuki
Published: December 2004

Organic‐inorganic composites can be used to tailor the properties of inorganic materials. A method of controlling the distribution and dispersion of platinum in platinum‐loaded silica using organic‐inorganic compounds prepared in two different ways is described, and an explanation for the unexpected formation of rings of platinum dots on the silica surface (see Figure) is proposed.

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Perforated monolayers
Authors: Conner Mark D. , Regen Steven L.
Published: December 2004

The synthesis of polymeric membranes that exhibit high permeation selectivity and high flux is a major challenge that has important technological implications. The concept of perforated monolayers (i.e., two‐dimensional arrays of porous surfactants) has been introduced in an attempt to rationally design such materials. The presented results indicate that these ultrathin materials have potential as novel membranes for separation.
Crosslinkable polar siloxane copolymers for ion detection devices
Authors: Gankema Harold , Lugtenberg Ronny J. W. , Engbersen Johan F. J. , Reinhoudt David N. , Möller Martin
Published: December 2004

Functionalized polysiloxanes can be used as sensing membranes in ion‐sensitive field effect transistors (ISFETs). A new 0 ue‐Si and reproducible route for obtaining well‐de‐fined polysiloxane copolymers–the anionic copolymerization of cyclotetrasiloxanes with different side groups (one of which is shown in the Figure)–is reported and the characterization and use of the copolymers in CHEM‐FETS described.

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Oxidation‐state‐dependent conformation in Cp*Mo(dmit) and antiferromagnetic ordering (TN = 8 K) of the neutral 17‐electron complex Cp*Mo(dmit)
Authors: Fourrnigué Marc , Coulon Claude
Published: December 2004

Metal dithiolene complexes are attractive for the development of novel materials with extended electronic properties. The preparation of Cp*Mo(dmit)2⊖ and its investigation by cyclic voltammetry, antiferromagnetic resonance, and electron paramagnetic resonance are described. Complexes of this class, i.e., with heteroatom substitution on the dmit dithiolene ligand, are shown to exhibit conformational flexibility directly related to the orbital occupancy.
Mono‐ and bi‐excitonic states in j‐aggregates of pseudoisocyanine studied by nonlinear polarization and nonlinear absorption spectroscopy
Authors: Stiel Holger , Voigt Bernd , Hirsch Jürgen , Teuchner Klaus , Leupold Dieter
Published: December 2004

The aggregation of pseudoisocyanine (PIC) is of interest because of the unusual properties of the aggretages which make them useful in photographic science as sensitizers as well as in photosynthesis research as model systems. Here, the room‐temperature substructure of the J‐absorption band of PIC–Cl aggregates is discussed on the basis of the results from nonlinear polarization spectroscopy in the frequency domain. The results are compared with the known substructure at 4.2 K.
Novel photocrosslinkable systems for nonlinear optics
Authors: Hanemann Thomas , Noël Caroline , Haase Wolfgang
Published: December 2004

The development of electroopic devices exploiting second harmonic generation in thin polymer films is hindered by the low stability of the dipole orientation of the chromophore in the surrounding matrix. New polymers (see figure) containing cinnamic acid derivatives as potential network‐forming units, in combination with new synthetic dyes as nonlinear optical active moieties are presented. The crosslinking leads to higher stability in the films.

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Luminescent RuII‐polypyridine complexes in poly‐2‐hydroxyethylmethacrylate matrices as oxygen sensors
Authors: Di Marco Gaetano , Lanza Maurizio , Campagna Sebastiano
Published: December 2004

Oxygen sensors based on polymer‐immobilized transitionmetal complexes are reported representing an interesting example of solid‐state luminescent sensors. The sensitivity of the luminescence lifetme of these systems is examined in relation to the mechanical properties and it is found that te plasticizing effect due to the monomer is a necessary factor to obtain systems with suitable sensor properties.
New routes to metal‐organic precursors; growth of high purity AIGaAs by CBE using a novel amine adduct of triisopropylgallium
Authors: Freer Richard W. , Whitaker Timothy J. , Martin Trevor , Calcott Phillip D. J. , Houlton Michael , Lee David , Jones Antony C. , Rushworth Simon A.
Published: December 2004

High‐purity AlGaAs has been grown using chemical beam epitaxy employing a new gallium precursor, triisopropylgallium·NEt3 in combination with AlH3(NMe2Et). The materials exhibit low oxygen concentrations and excellent optical and electrical characteristics, comparable with the best materials grown using molecular beam epitaxy or metal‐organic vapor phase epitaxy. The use of amine solvents and the complete absence of eters from the precursors has important consequences for the growth of III–V alloys by CBE, as oxygen‐containing solvents are known to lead to materials degradation.
Collective nonlinear optical properties of disordered J‐aggregates
Authors: Knoester Jasper
Published: December 2004

Collective molecular optical responses can be studied in detail in J‐aggregates. The aggregates are usually studied in a medium having intrinsic disorder (solutions, glasses, Langmuir–Blodgett films) and therefore disorder plays an important role when modeling their properties. Here, recent progress in the theoretical treatment of the optical properties of the aggregates is reviewed.
Bright blue electroluminescence from an oxadiazole‐containing copolymer
Authors: Pei Qibing , Yang Yang
Published: December 2004

Blue electroluminescence from a copolymer containing oxadiazole units is reported. The copolymer is separated in the light emitting diode device from the ITO anode by an additional layer of polyaniline in order to increase the quantum efficiency, resulting an external quantum efficiencies of 0.1%, and an intensity of the blue emitted light of 40 cm/m2.
Polyalkylthiophenes as electrochromic materials: A comparative study of poly(3‐methylthiophenes) and poly(3‐hexylthiophenes)
Authors: Arbizzani Catia , Bongini Alessandro , Mastragostino Marina , Zanelli Alberto , Barbarella Giovanna , Zambianchi Massimo
Published: December 2004

Tuning of the undoped–doped color contrast can be obtained in poly(3‐hexylthiophenes) through the electropolymerization of oligomers of different length and regiochemistry. The regiochemistry affects the optical properties of the materials and molecular design allows the production of complementary electrochromic materials for variable light transmission devices.
Unconventional mesogens of hyperbranched amides and corresponding ammonium derivatives
Authors: Stebani Uwe , Lattermann Gunter
Published: December 2004

A cyclic core is not essential for mesomorphism. But just how flexible, or “open” can be central units in a branched compound be before liquid crystallinity is no longer exhibited? Here, the influence on the substitution patterns and in particular of hydrogen bonding in the title compounds is examined and it is found that protonation of some of the less‐substituted compounds is required in order to impart the required degree of rigidity.
Polypyrrole towers grown with the scanning electrochemical microscope
Authors: Kranz Christine , Gaub Hermann E. , Schuhmann Wolfgang
Published: December 2004

Conducting‐polymer towers have been fabricated by a template‐less method from homogeneous monomer solution using the scanning electrochemical microscope (SECM). The features of the topography feedback mode of the SECM—in which the microelectrode is vibrated laterally (thin arrows in the Figure)—are described and the characterization of polypyrrole towers (illustrated on the front cover) detailed. Uses in biosensors are foreseen.

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Ultrathin graphite oxide–polyelectrolyte composites prepared by self‐assembly: Transition between conductive and non‐conductive states
Authors: Kotov Nicholas A. , Dékány Imre , Fendler Janos H.
Published: December 2004

Ultrathin films of graphite–polymer composites, which are required for sensors applications, are the target of the work reported here. The preparation and characterization of ultrathin films composed of self‐assembled graphite oxide (GO) platelets and polyelectrolytes are described, followed by the in situ reduction of GO to a conductive graphite‐like state (G) by chemical and electrochemical methods. Particular attention is paid to the non‐conductive to conductive transition that occurs on reduction and the behavior of incorporated CdS particles.
New LEDs based on soluble poly(2,6‐naphthylenevinylene)
Authors: Hanack Michael , Segura José L. , Spreitzer Hubert
Published: December 2004

A soluble polymer attractive for light emitting devices has been prepared and its performance in LED applications evaluated. The chemical synthesis of the monomers is described, followed by their polymerization to a highly soluble, readily processable, cyanosubstituted poly(2,6‐naphthylenevinylene). Electroluminescence and photoluminescence spectra are presented and an electrochemical study reported. It is shown that the presence of the naphthalene units induces a strong blue‐shift in the emission color.
Ba2ErCl7—a new near IR to near UV upconversion material
Authors: Egger Philipp , Rogin Peter , Riedener Toni , Güdel Hans Ulrich , Wickleder Mathias Siegfried , Hulliger Jürg
Published: December 2004

New near IR to near UV upconversion (UC) materials are required for the development of solid state lasers pumped by laser diodes. Two materials are reported: an air‐stable and efficient UC material emitting mostly in the yellowish‐green and a very promising UC compound, Ba2ErCl7, which is being further characterized spectroscopically. THe general requirements for UC materials are briefly discussed, and the preparation of Ba2ErCl7 detailed. The intensity of individual emission bands is compared for known and new UC materials.
Electrochemical annealing and friction anisotropy of domains in epitaxial molecular films
Authors: Last Julie A. , Ward Michael D.
Published: December 2004

The formation of high‐quality organic thin films with low defect densities and good lateral ordering is essential for many electronic and optical technologies. Here, electrochemically fabricated thin films of conducting and superconducting organic charge‐transfer salts are examined using AFM, which reveals revealing frictional anisotropy between domains in the films. The number and size of the domains can be reduced through an “electrochemical annealing” process. The role of epitaxy in domain formation and the influence of domain size on the dynamics of annealing are discussed.
Formation of non‐stoichiometric salts of tetrathiafulvalene in an acidic medium
Authors: Farnia Giuseppe , Sandonà Giancarlo , Marcuzzi Franco
Published: December 2004

A new, convenient synthetic pathway to non‐stoichiometric mixed‐valence tetrathiafulvalenium salts is presented. Study of TTF · squarilium chloride salts produced using this method provides further evidence that the generation of the radical species takes place through acid‐base reactions.
Fundamentals of the preparation of high‐TC, superconducting (Bi,Pb)2+XSr2Ca2Cu3O10+δceramics
Authors: Majewski Peter , Kaesche Stefanie , Aldinger Fritz
Published: December 2004

For the 2223 phase of the BiPbSrCaCuO superconductor, detailed knowledge of the phase relations and the homogeneity region are essential to the understanding of the fundamental issues influencing the processing of the materials. A six‐component system such as this would require a six‐dimensional phase diagram. Several ways to simplify the task to manageable dimensions, and the information one can obtain from a detailed investigation of this system are discussed.
Diffusion NMR Spectroscopy in Supramolecular and Combinatorial Chemistry: An Old Parameter—New Insights
Authors: Cohen Yoram , Avram Liat , Frish Limor
Published: December 2004

Intermolecular interactions in solution play an important role in molecular recognition, which lies at the heart of supramolecular and combinatorial chemistry. Diffusion NMR spectroscopy gives information over such interactions and has become the method of choice for simultaneously measuring diffusion coefficients of multicomponent systems. The diffusion coefficient reflects the effective size and shape of a molecular species. Applications of this technique include the estimation of association constants and mapping the intermolecular interactions in multicomponent systems as well as investigating aggregation, ion pairing, encapsulation, and the size and structure of labile systems. Diffusion NMR spectroscopy can also be used to virtually separate mixtures and screen for specific ligands of different receptors, and may assist in finding lead compounds.
Influence of thermal denaturation on the electrophoretic mobility of calf thymus DNA
Authors: Costaxtixo L. , Liquori A. M. , Vitagliaxo V.
Published: December 2004

The results of electrophoresis experiments on aqueous solutions of native and thermally denatured DNA are reported. A significant decrease of the electrophoretic mobility has been observed following thermal denaturation, which under suitable conditions gives rise to a resolution into two peaks of 1 : 1 mixtures in the electrophoretic pattern. This result is entirely consistent with the previously reported increase of the activity coefficient of sodium counterions following thermal denaturation. The hypothesis that thermal denaturation of calf thymus DNA induces a large decrease of charge density on the macroion which has been ascribed to the population of more extended conformations of the chains in the disordered region of the molecule is therefore further confirmed.
Exoenzyme kinetics with applications to the determination of nucleotide sequences
Authors: Cantor Charles R. , Tinoco Igxacio , Peller Leonard
Published: December 2004

The kinetics of the action of exoenzymes on linear polymers is developed. The results are applied to the problem of sequence determination in nucleic acids. It is found that a choice of experimental conditions different from the steady‐state situation provides a liberation of successive nucleotides in better resolved time intervals. The inference of the nucleotide sequence of a hypothetical dodecamer is explored in detail. Calculations indicate the possibility of determining the base sequences of oligomers containing up to 25 nucleotides.
Polymerization of γ‐ethyl‐L‐glutamate‐N‐carboxyanhydride initiated by di‐n‐butyl and di‐isopropyl amine
Authors: Peggion Evaristo , Cosani Alessandro , Mattucci Anna Maria , Scoffone Ernesto
Published: December 2004

The γ‐ethyl‐L‐glutamate NCA polymerization initiated by di‐n‐butyl and di‐isopropyl amine was studied. The experimental kinetic curves show an autocatalytic portion with 25–30% conversion, followed by a pseudo first‐order region which extends up to at least 85–90%. In this linear region, the reaction order appears to be 0.5 in initiator with both amines. High degrees of polymerization and high reaction rates were observed. These results are similar to those obtained in the γ‐benzyl‐L‐glutamate NCA polymerization initiated by sodium methoxide.
Conformational studies of polymers and copolymers of L‐aspartate esters. II. Infrared studies and the factors involved in the formation of the ω‐helix
Authors: Bradbury E. M. , Carpenter B. G. , Stephens R. M.
Published: December 2004

It has already been show that the helix senses of poly(β‐benzyl L‐aspartate) and poly(β‐methyl L‐aspartate) are left‐handed, while the poly esters of n‐propyl, isopropyl, n‐butyl, and phenethyl L‐asparate are all right‐handed. The effect of changes in helix sense from the left‐handed to the right‐handed α‐helical form on the infrared spectra of copolymers of benzyl L‐aspartate with ethyl, n‐butyl, isopropyl, n‐propyl, and phenethyl L‐aspartate have been studied. Those show that for the right‐handed helical form the amide band frequencies fall within the range given by Elliott,7 while for the left‐handed form the frequencies are higher. The frequency ranges for the two helix senses are given and have been used to show that poly (β‐n‐propyl L‐aspartate) in chloroform solution undergoes a transition from the right‐handed to the left‐handed helix form on heating. Polarized infrared studies of the different copolymers show that the disposition of the side chain ester groups is different for the two forms. Although methyl L‐aspartate forms a left‐handed α‐helix similar to benzyl L‐aspartate, the introduction of methyl L‐aspartate residues into poly (β‐benzyl L‐aspartate) prevents the formation of the ω‐helix. The factors involved in the formation of this helix form are discussed.
Phase equilibria of rodlike molecules in binary solvent systems
Authors: Nakajima Akio , Hayashi Toshio , Ohmori Minako
Published: December 2004

Phase relationships in solutions of rodlike, molecules were investigated with solutions of poly(γ‐benzyl L‐glutamate) having degrees of polymerization of 1500 and 3600, in N,N′‐dimethylformamide–methanol and in N,N′‐dimethylformamide–water at 30°C. With these systems, corresponding boundary curves for isotropic and anisotropic solution were obtained as a function of composition. Phase diagrams for these ternary systems were analysed on the basis of a theoretical treatment by Flory for a binary system consisting of a rodlike polymer and a solvent and found to be in good agreement with that predicted theoretically. For example, the polymer concentration above which the isotropic phase cannot exist and that of anisotropic conjugate phase agree with the values calculated. Furthermore, viscosities were measured as a function of polymer concentration by the falling‐sphere method to confirm the boundary composition between the isotropic solution and heterogeneous region. These results were also found to coincide with those on phase equilibrium.
Viscosity study of DNA. II. The effect of simple salt concentration on the viscosity of high molecular weight DNA and application of viscometry to the study of DNA isolated from T4 and T5 bacteriophage mutants
Authors: Ross Philip D. , Scruggs Robert L.
Published: December 2004

Polyelectrolyte expansion effects on high molecular weight bacteriophage DNA have been studied by examining the influence of simple salt concentration upon the intrinsic viscosity, [η]. The viscosity–molecular weight exponent a in the expression [η] = KMa diminishes from 0.8 in 0.005M simple salt to a limiting value of 0.6 for salt concentrations greater than 0.6M at 25°C. The ε parameter of the N1+ε hydrodynamic representation thus varies from approximately 0.2–0.07 over this range of salt concentration. The intrinsic, viscosity of DNA decreases slightly with increasing temperature at low and moderate salt concentrations but becomes independent of temperature at high salt concentrations. The expansion of the DNA molecular domain is linear in the reciprocal square root of the simple salt concentration. Viscosity differences among DNA's isolated from several bacteriophage T5 mutants reflect small differences in molecular weight which are in agreement, with sine determination by other techniques. The DNA's isolated from various rII mutants of T4 bacteriophage including some very large deletion mutations were found to be identically the same size in accord with current genetic ideas. Details of the representation and extrapolation of viscosity data are discussed and the sensitivity of the technique is evaluated.
Light scattering from wormlike chains with excluded volume effects
Authors: Sharp Phillip , Bloomfield Victor A.
Published: December 2004

This paper reports a calculation of the angular dependence of light scattering from wormlike chains with excluded volume effects. The Daniels distribution function, modified for excluded volume effects, is used to compute averages for scattering elements separated by contour lengths which are long with respect to the persistence length of the chain. An expansion in terms of exactly known moments of the distribution for the wormlike coil without excluded volume is used for short contour lengths. The results are applied to scattering from calf thymus (M = 18.1 × 106) and T7 (M = 25.4 × 106) DNA. It is demonstrated that the same values of excluded volume parameter (ε = 0.11) and statistical segment length (1/λ′ = 900 Å) which explain the sedimentation and viscosity behavior of DNA also account satisfactorily for the scattering behavior. Molecular weights and root‐mean‐square radii estimated by extrapolation from scattering data obtained in the angular region from 10° to 25° will be 5–10% too large for DNA of molecular weight 20 × 106–30 × 106.
Differential elution of histones from gel‐trapped nuclei
Authors: Sung M. , Smithies O.
Published: December 2004

A method has been developed for characterizing at, submicrogram levels the heterogeneity of histones from purified nuclei. The histones are eluted with a smooth concentration gradient from nuclei trapped in polyacrylamide–gel threads and are collected in a micro fraction collector suitable for volumes in the 10–100 μl range. The gradient and fraction collection systems are governed by cam driven syringes. Samples obtained are subjected to electrophoresis in a starch‐gel system and the gels are stained with a highly sensitive stain specific for guanidinium groups. Seven major and a similar number of minor components are demonstrated in the histones. The method of differential elution of trapped macromolecules is suitable for use with systems other than nuclei and histones.
Studies on the secondary structure of ribosomal ribonucleic acid components of rabbit reticulocytes
Authors: Gould Hannah J. , Simpkins Henry
Published: December 2004

The conformation in solution of fractionated 30 S and 19 S ribosomal RNA from rabbit reticulocytes has been studied by optical rotatory dispersion, analysis of thermal melting profiles and their derivatives, and spectrophotometric acid‐base titration. From a consideration of the limitations of these methods, it has been possible to set limiting values on the degree of base‐pairing and the lengths of the double helices: between 60 and 80% of the bases in 19 S and 30 S RNA are estimated to be paired. The paired segments are not shorter than 4 base pairs, and evidence from other sources is available which indicates that they are not longer than 8–16 base pairs. The spread of helix lengths is greater in the 30 S than in 19 S RNA; and other differences are noted. Several distinct populations of double helices, differing in their thermal stability, are present. Estimates are presented from spectrophotometric and titration data for the base compositions of the paired and unpaired regions.
Instability in diffusing fluid layers
Authors: Sartory W. K.
Published: December 2004

A small perturbation analysis is carried out to determine the stability of a fluid containing two layers of diffusing solutes in a common solvent and acted upon by a uniform gravitational field. It is found that instability can arise even though the unperturbed diffusion does not lead to the formation of a density inversion within the fluid.
Flow dichroism of DNA: A new apparatus and further studies
Authors: Callis Patrik R. , Davidson Norman
Published: December 2004

A new apparatus for the study of flow dichroism of macromolecules is described. The flow is down a long, narrow channel and an unpolarized light beam propagates along the flow direction. For a molecule such as DNA, in which the transition moments of the chromophores are perpendicular to the axis of orientation, an increase of absorbance is observed during flow. The apparatus is best suited for macromolecules which are readily orientable or at high shear gradients so that the extinction angle is close to 0°. The apparatus has the following advantages: dilute macromolecule solutions can be used; high shear gradients are easily obtained; only small volumes of solution are needed. The flow can be stopped rapidly so that relaxation times for disorientation can be studied. The flow dichorism of native, two‐stranded DNA has been measured for the molecular weight range of 0.6 × 106 to 125 × 106, and for the shear gradient range (in aqueous solution at 25°C) from 200 sec−1 to 21000 sec−1. At a fixed gradient the dichroism increases with molecular weight, but the curve is concave downwards. At a given molecular weight the dichroism increases with increasing shear gradient, but the curve is concave downwards. When the solvent viscosity and temperature are varied, the dichroism is a function of η〈G〉/T showing that the orientation is due to hydro‐dynamic shear stress and that the flexibility of DNA in a flow field is not due to local denaturation. The Zimm‐Rouse theory with no parameters taken from flow optical data predicts the correct order of magnitude of the dichroism but the experimentally observed shear gradient and molecular weight dependence do not fit the theory. This is an expected result, since the theory is believed to be applicable only at small distortions and extensions of the macromolecule.
Optical activity of single‐stranded polydeoxyadenylic and polyriboadenylic acids; dependence of adenine chromophore cotton effects on polymer conformation
Authors: Bush C. Allen , Scheraga Harold A.
Published: December 2004

Circular dichroism (CD) curves are reported for poly dA, (pdA)6, (pdA)2, poly A, ApAp, ApA, AMP, dApA, pdApA, A‐2′‐O‐methyl pA, and A‐2′‐O‐methyl pAp. Analysis of these curves indicated the presence of single CD bands at 228–230 mμ and at 278–280 mμ in oligomers longer than dinucleotides. In the case of dinucleotides and mononucleotides (from the literature, in addition to those studied here), the 230 mμ CD of band appears but the 280 mμ CD band does not. We assign the 230 mμ band to a very weak π–π* transition at this wavelength. From theoretical considerations, we show that the 280 mμ band is not an exciton component of the strong π–π* transition at 260 mμ in adenine. We conclude that the 280 mμ CD band must be assigned to a distinct absorption, not previously reported, which we suggest arises from an n–π* transition. The fact that the n–π* CD band at 280 mμ is not seen in mononucleotides or dinucleotides is ascribed to solvation of the adenine ring by water, which shifts the band to shorter wavelengths. Therefore, only interior residues of oligomers have the 280 mμ band, and the optical activity of a polymer cannot be computed from that of a dinucleotide, by using a nearest‐neighbor approximation. The existence of this end effect hag been tested, by taking it into account in computing the rotational strengths of the 278 mμ n–π* transition for several oligomers; it is pointed out that a more sensitive test of this end effect would require CD data for the oligo dA series of 3 to 5 residues. We speculate about the structural and optical differences between poly dA and poly A, and point out the need for a theoretical treatment of n–π* Cotton effects in polynucleotides.
Syntheses and conformational studies of poly‐β,N‐alkyl L‐asparagines
Authors: Hayakawa Tadao , Yamamoto Hiroyuki , Aoto Noriko
Published: December 2004

Several β,N‐alkyl L‐asparagines were prepared from the phthalyl and benzyloxycarbonyl derivatives. High‐molecular‐weight poly‐β,N‐benzyl L‐asparagine and poly‐β,N‐(1)‐phenethyl L‐asparagine were prepared from the corresponding N‐carboxyanhy‐drides. From the results obtained by a study of the infrared absorption spectra and the optical rotatory dispersion, poly‐β‐N‐benzyl L‐asparagine was found to be a random coil structure in dichloroacetic acid and the optical rotatory dispersion curves gradually changed into the left‐handed α‐helix structure when chloroform was added to the solution. The coil‐to‐helix transition was observed in the vicinity of 20% dichloroacetic acid in a dichloroacetic acid‐chloroform mixture. Poly‐β,N‐(d), (l), and (d + l, 1:1)

(d + l, 1:1): mixed polymer containing the same weighed poly‐β,N‐(d) and (l)‐(1)‐phenethyl L‐asparagines.

‐(1)‐phenethyl L‐asparagines showed a nearly constant specific rotation in the dichloroacetic acidchloroform solvent system. Poly‐β,N‐(dl)‐(1)‐phenethyl L‐asparagine caused a gradual folding of the helix at dichloroacetic acid content of less than 20%.
Developing a hypothesis: Native cellulose elementary fibrils are formed with metastable structure
Authors: Stöckmann Volker E.
Published: December 2004

Any spinning of high‐polymeric solutions and any extruding of high‐polymeric melts produce fibrillar textures built‐up of folded molecules with a predominantly uniform period. Because data strongly suggest extended molecules within native cellulose elementary fibrils, spinning or extruding as potential fibrillar growth mechanisms must be considered unlikely. Among the crystallization conditions known to produce extended chain structures, crystallization with simultaneous polymerization appears the most plausible mechanism for forming elementary fibrils. The mechanism yields a structure distinguished by uniformity of lateral order along the fibrillar length axis with the lateral order being paracrystalline. Because thermodynamic equilibrium requires a fibrillar structure of alternating crystalline and amorphous regions, a newly grown elementaryfibril is hypothesized to be in a thermodynamically unfacorable state. Intermolecular forces “freezing‐in” the unfavorable state provide metastability. Whenever the intermolecular cohesion is weakened, a structural transformation of the paracrystalline fibril is predicted, which consists of the creation of distinctly disordered and distinctly well‐or‐dered phases. Because disorder is created, a transforming fibril contracts longitudinally. The transformation must be expected to be gradual, which gives rise to a series of intermediate metastable structures of decreasing free energy levels. With lattice type I, a fibril, however, is believed unable to reach the stable state. The equilibrium structure characterized by coexistence of perfectly ordered crystallites with completely disordered regions is thought associated with lattice type II.
Far‐ultraviolet optical activity of saccharide derivatives. II. Dextran, amylose, and mycodextran acetes; dextran and amylose xanthates
Authors: Mukherjee S. , Sarko A. , Marchessault R. H.
Published: December 2004

The ultraviolet ORD and CD spectra of amylose, dextran, and mycodextran acetates and some of thier oligomers were recorded in trifluoroethanol solution in the 300–185nm wavelength range. Similarly, the spectra of amylose and dextran xanthates in water solution were obtained in the 400–200 nm range. In the amylose acetate series, the monomer and dimer both show a normal acetyl n → π* transition in CD, while the trimer and the polymer both exhibit an additional, shorter wavelength peak. The latter is presumed to arise from a helical conformation of the amylose chain. This interpretation is substantiated by a helix–coil type transition of the CD spectra of amylose triacetate at elevated temperatures and a reversion of the anomalous CD to the normal CD upon partial deacetylation. By contrast, neither dextran acetates nor mycodextran acetate exhibit any conformational effects. The CD of dextran acetates is quite sensitive to β‐1,6 and branch linkages. The ORD and CD of amylose xanthate are complex, suggesting the presence of organized structure in solution. The dextran xanthate shows only a simple ORD spectrum and no observable CD.
Effwct of temperature on the circular dichroism spectra of polypeptides in the extended state
Authors: Tifany M. Lois , Krimm S.
Published: December 2004

The circular dichroism (CD) spectra of poly‐L‐proline and of poly‐L‐glutamic acid and poly‐L‐lysine in their charged states have been studied as a function of temperature. The variation of CD spectra with temperature is inconsistent with the assignment of the spectrum of such charged polypetides to an unordered chain conformation, but does support our earlier assignment to a locally ordered structure—what we have called the extended helix conformation. These results also strengthen our previous assignment of the CD spectrum of an unordered chain, and indicate that three conformational states (α‐helix, extended helix, and unordered) should be incorporated in our thinking about conformational transitions in polypeptides.
Correlation between the backbone and side chain conformations in 5′‐nucleotides. The concept of a ‘rigid’ nucleotide conformation
Authors: Yathindra N. , Sundaralingam M.
Published: December 2004

Conformational energies of the 5′‐adenosine monophosphate have been computed as a function of χ and ψ, of the torsion angles about the side‐chain glycosyl C(1′)–N(9) and of the main‐chain exocyclic C(4′)–C(5′) bonds by considering nonbonded, torsion, and electrostatic interactions. The two primary modes of sugar puckering, namely, C(2′)‐endo and C(3′)‐endo have been considered. The results indicate that there is a striking correlation between the conformations about the side‐chain glyocsyl bond and the backbone C(4′)–C(5′) bond of the nucleotide unit. It is found that the anti and the Gauche–Gauche (gg), conformations about the glycosyl and the C(4′)–C(5′) bonds, respectively, are energetically the most favored conformations for 5′‐adenine nucleotide irrespective of whether the puckering of the ribose is C(2′)‐endo or C(3′)‐endo. Calculations have also shown that the other common 5′‐pyrimidine nucleotides will show similar preferences for the glycosyl and C(4′)–C(5′) bond conformations. These results are in remarkable agreement with the concept of the “rigid” nucleotide unit that has been developed from available data on mononucleotides and dinucleoside monophosphates. It is found that the conformational ‘rigidity’ in 5′‐nucleotides compared with that of nucleosides is a consequence of, predominantly, the coulombic interactions between the negatively charged phosphate group and the base. The above result permits one to consider polynucleotide conformations in terms of a “rigid” C(2′)‐endo or C(3′)‐endo nucleotide unit with the major conformational changes being brought about by rotations about the P–O bonds linking the internucleotide phosphorus atom. IT is predicted that the anti and the gg conformations about the glycosyl and the C(4′)–C(5′) bonds would be strongly preferred in the mononucleotide components of different purine and pyrimidine coenzymes and also in the nucleotide phosphates like adenodine di‐ and triphosphates.
Showing up the thermal transconformation of Na–DNA in solution by noise spectrography
Authors: Vasilescu Dane , Teboul Maurice , Kranck Hubert , Camous Bernard
Published: December 2004

Measuring the equivalent noise resistance of Na–DNA solutions in NaCl provides in formation about the free ino atmosphere. In an Arrhenius type diagram, the helix → coil transition is clearly brought Out. A Calculation of the number of free ions in the solution as function of temperature, reveals once more the process of ejection of compensating Na+ ions form the macromolecules during the thermal transconformation.
Studies on cytochrome c. Part VIII. Synthesis of the protected hexadecapeptide (sequence 93–108) of Baker's yeast iso‐1‐cytochrome c
Authors: Moroder Luis , Marchiori Fernando , Borin Gianfranco , Scoffone E.
Published: December 2004

The synthesis is described of the protected hexadecapeptide corresponding to the C‐terminal sequence 93–108 of baker's yeast iso‐I‐cytochrome c. The cysteine residue in position 107 of the natural sequence has been substituted by a threonine residue. The rationale of this substitution as well as the synthetic route to the preparation of the hexadecapeptide derivative is discussed.
Electrophoretic light scattering as a probe of reaction kinetics
Authors: Berne B. J. , Giniger Rina
Published: December 2004

A new method is proposed for determining chemical rate contants in dimerization reactions of globular proteins. Light scattering from a solution of charged macromolecules in and applied electric field gives a series of bands whose widths can be used to deduce the reaction rate contants. This method should be applicable to other types of peactions. First order reactions are also considered.
Optical absorptions of aliphatic amino acids in the far ultraviolet
Authors: Inagaki T.
Published: December 2004

The far ultraviolet absorptions of aliphatic amino acids such as glycine, alanine, aminobutyric acid, valine, and leucine were measured with their solid thin films down to 120 nm. Four absorption bands arising from the carboxyl group were observed in the 200–140 nm region. It was found that the band positions and intensities vary systematically according to the number of carbon atoms in the aliphatic side chain. This result may be interpreted as a phenomenon similar to the hyper‐and hypochromisms of aliphatic homopolypeptides in far ultraviolet region.
Sedimentation and intrinsic viscosity behavior of PM2 bacteriophage DNA in alkaline solution
Authors: Ostrander Daryl A. , Gray Horace B.
Published: December 2004

The sedimentation coefficient and intrinsic viscosity of nicked and closed circular PM2 bacteriophage DNA have been measured as a function of pH in the alkaline region. A gradual increase in the sidimentation coefficient, and a corresponding decrease in the intrinsic viscosity, are observed for the superhelical (closed) circle in the pH region from 10.5 to about 10.9. This has been tentatively interpreted in terms of the known dependence of sedimentation coefficient upon the number of superhelical turns. At slightly higher pH values, the curve passes through the minimum (sedimentation coefficient) and maximum (intrinsic viscosity) expected when the superhelical turns present at neutral pH are unwound by partial alkaline denaturation. Sedimentation studies of the relaxed (nicked) circular species have revealed the existence of DNA forms in the pH region from 11.27 to 11.37 which sediment considerably faster than the closed circle in the same pH region. These have been identified as partially denatured nicked circles, in which varying fractions of the duplex structure have undergone alkaline denaturation, but strand separation has not yet occurred. Varying fractions of a slower species, either undenatured or completely denatured nicked circles, are also observed in some of these experiments. A corresponding result is observed in the intrinsic viscosity vs. pH curve.

When nicked circular PM2 DNA is exposed to various alkaline pH's, rapidly neutralized, and sedimented at neutral pH, the expected sharp transition from native to denatured (strand‐separated) molecules is seen. However, a very narrow pH range is noted in which native and denatured forms coexist in a single experiment. The above experiments carried out upon the closed form also reveal a narrow pH range in which the bulk of the transition from native closed circles to the collapsed cyclic coil takes place, in acccord with an earlier study on a different DNA. This transition is shown never to be completely effected, however, as there is a fraction (7–8%)of the closed circles which renature to the native form, regardless of the alkaline pH employed. This same phenomenon was not observed in the case of artificially closed λb2b5c DNA circles. Possible explanations for some of the above results are discussed.
Conformation of cyclic dipeptides from empirical energy calculations
Authors: Chandrasekaran R. , Lakshminarayanan A. V. , Mohanakrishnan P. , Ramachandran G. N.
Published: December 2004

Empirical energy calculations on cyclo‐Gly‐X with X‐ Phe, Tyr, Val, and Leu as a function of the side‐chain torsion angles χ indicate that the conformation of minimum energy are characterized by χ1 = 60°, χ2 = 90° for Phe and Try, χ1 = −60° for Val and χ1 = −60°, χ2 = 180° and χ1 = 60° and χ2 = 150° for Leu. The minimum energy conformation of cyclo‐Gly‐Phe and cyclo‐Gly‐Val have the side chains of Phe and Val stacked over the poperazinedione ring as suggested by NMR and found for cyclo‐Gly‐Tyr crystal structure. In contrast, the Leu side chain is expected to exist in an extended or a quasi‐folded form.
Polymerization of DL‐phenylalanine NCA initiated by copolymer of sarcosine and DL‐phenylalanine
Authors: Imanishi Yukio , Sugihara Toshiharu , Higashimura Toshinobu
Published: December 2004

Polymerizations of DL‐phenylalanine NCA by block copolymers of sarcosine and DL‐phenylalanine, designated by (Phe)m(Sar)n and capable of reaction at the phenylalanyl terminal, were investigated in nitrobenzene solution at 25°C. With increasing n for constant m (m = 0, 1, 2, and 5), the polymerization rate greatly increased. Previously the acceleration of the initiation reaction in the polymerization of DL‐phenylalanine NCA by polysarcosine (m = 0) was reported. The present results showing the acceleration by the copolymers of sarcosine and DL‐phenylalanine indicate the presence of the polymer effect in the propagation reaction as well. However, the polymer effect was most marked with polysarcosine (m = 0), and decreased with increasing m.

The same polymerizations by sequential copolymers composed of ten sarcosine units and two DL‐phenylalanine units were also investigated. Again with these copolymer catalysts the polymerization rate was larger than that by monomeric amines. But the polymer effect decreased sharply when the phenylalanine units take positions near the terminal amine group of the copolymer catalyst.

These two deteriorating effects of the phenylalanine unit have been interpreted in terms of the decrease of the flexibility of polymer chain, caused possibly by an intramolecular hydrogen bond of the phenylalanine unit.