bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nanomachining and manipulation with the atomic force microscope
Authors: Lieber Charles M. , Kim Yun 
Published: December 2004

The ability to manipulate matter on the nanometer scale is a requirement for the full development of nanotechnology. Scanning probe microscopies show great promise in this respect and recent progress in the area is discussed. for example surface modification, pattern formation (e.g. the 150 nm high Harvard University symbol in the figure), and the manipulation of nanostructures. magnified image
Novel amorphous molecular materials: The starburst molecule 1,3,5‐tris[N‐(4‐diphenyl‐ aminophenyl)phenylamino]benzene
Authors: Ishikawa Wataru , Noguchi Kisaburo , Kuwabaru Yoshiyuki , Shirota Yasuhiko 
Published: December 2004

Photo‐ and electroactive amorphous molecular materials are attractive for use in electronics, for example in pn heterojunction‐type photovoltaic devices or in electroluminescent devices. The title compound (based on that in the Figure) exhibits a high glass transition temperature, hardly crystallizing even above this temperature making it especially suitable for electronics applications. magnified image
Semiconductor nanowhiskers
Authors: Yazawa Masamitsu , Koguchi Masanari , Muto Akiko , Hiruma Kenji 
Published: December 2004

Self‐assembled nanostructures based on indium arsenide whiskers grown using molecular beam epitaxy and metal‐organic vapor phase epitaxy (see Figure) could be of use as lead wires, connecting devices in integrated nanodevices. The procedure employed to produce these features in a controlled way is described, and the possibilities of developing nanowhisker heterojunctions discussed. magnified image
Allyl(β‐diketonato)palladium(II) complexes as precursors for palladium films
Authors: Yuan Zheng , Puddephatt Richard J. 
Published: December 2004

Chemical vapor deposition (CVD) of palladium is at present not used commercially, despite the widespread use of palladium films in electronics and data storage, because suitable precursors are not available. New palladium precursors, ally (β‐diketonato)palladium(II) complexes (see Figure) are reported, along with the conditions required for the formation of pure palladium films by CVD. magnified image
A further polymerization effect following the electrochemical synthesis of poly(2,5‐dimethoxyaniline)
Authors: Pistoia Gianfranco 
Published: December 2004

A post‐polymerization effect for poly(2,5‐dimethoxyaniline), PDMA, has been observed in which PDMA inthe form of needles grows on the porous granular surface of the polymer previously formed by electrosynthesis (see Figure). Details of voltammetry experiments are given and an explanation for the post‐polymerization effect proposed. magnified image
Arg—Gly—Asp peptides in polyurethanes: Design, synthesis, and characterization
Authors: Ho Siew Peng , Britton Dustin H. O. 
Published: December 2004

Peptide‐containing polymers have been synthesized with the aim of using polymers as synthetic scaffolds for biologically active peptide sequences. Introducing the peptide shown in the figure during polyurethane synthesis resulted in a series of peptide‐polymer hybrids containing the Arg‐Gly‐Asp sequence, which plays a central role in cel adhesion. magnified image
Oligothiophenes as models for polythiophenes. The crystal and molecular structures of 3″, 4″‐dibutylpentathiophene and 3′,3″ ″,4′, 4″ ″‐tetrabutylhexathiophene
Authors: Liao Ju‐Hsiou , Benz Michael , Legoff Eugene , Kanatzidis Mercouri G. 
Published: December 2004

Knowledge of the crystal structures of oligothiophenes is necessary if progress is to be made towards understanding the structure‐property relationships of polythiophenes, since single crystals of these conducting polymers are not available. Two oligothiophene derivatives (one of which is shown in the Figure) have been designed, synthesized, and struturally characterized. magnified image
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. magnified image
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. magnified image
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. magnified image
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. magnified image
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. magnified image
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. magnified image
Diffusion NMR Spectroscopy in Supramolecular and Combinatorial Chemistry: An Old Parameter—New Insights
Authors: Cohen Yoram , Avram Liat , Frish Limor 
Published: December 2004

AbstractIntermolecular 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractIt 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

AbstractPhase 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

AbstractPolyelectrolyte 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

AbstractThis 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

AbstractA 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

AbstractThe 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.
Flow dichroism of DNA: A new apparatus and further studies
Authors: Callis Patrik R. , Davidson Norman 
Published: December 2004

AbstractA 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

AbstractCircular 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

AbstractSeveral 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%.