bluuebunny/crossref_metadata_2025_split huggingface dataset:
Properties of amphiphilic terminally substituted conjugated nonaene‐ and 2‐docosylnonaene carboxylic acids in monolayers at the air–water interface
Authors: Effenberger Franz , Meller Paul , Ringsdorf Helmut , Schlosser Hubert 
Published: December 2004

Communication: Amphiphilic, conjugated polyenes, (see figure) substituted with, for example, redox‐active groups such as ferrocene or other groups which allow for specific and selective excitation (energy intake), have been synthesized and their spectroscopic properties examined at the air‐water interface. The materials have potential applications in the storage and transfer of information on a molecular level.magnified image
Intrazeolite Topotaxy
Authors: Ozin Geoffrey A. , Özkar Saim 
Published: December 2004

The self‐assembly of semiconductor quantum dots or wires within the cavity of a zeolite or molecular‐sieve host to form qunatum supralattices has great potential in the development and study of organized systems with value in, for example, quantum electronics, nonlinear optics, optical data storage, and chemoselective sening. The organization of inorganic, organometallic, and metal‐carbonyl moieties on the internal surfaces of the hosts (e.g. see figure) is thebasis of the work and the chemsitry and its applications are reviewed. magnified image
The first example of a tridentate azamacrocyclic metallomesogen
Authors: Lattermann Günter , Schmidt Steven , Kleppinger Ralf , Wendorff Joachim Heinz 
Published: December 2004

The introduction of a metal into a mesogenic molecule can result in a complex with interesting electrical and magnetic properties. By reacting the non‐mesogenic cyclic amine shown in the figure with Ni(NO3)2 · 6H2O in absolute THF the first member of a new class of columnar liquid‐crystalline metal complexes with three nitrogen atoms as donor groups has been prepared. magnified image
Growth of GaAs and Al GaAs by chemical beam epitaxy—precursor requirements and recent developments
Authors: Jones Anthony C. 
Published: December 2004

Semiconductor layers of gallium arsenide and aluminum gallium arsenide are finding increasing application in photonic (solar cells, LEDs, etc.) and microwave (e.g. HEMTs) devices. The ultra‐high vacuum technique “chemical beam epitaxy” (see Figure) can be effectively used to produce such layers. The method and its competitors are compared. magnified image
High‐Tc superconducting thin films
Authors: Miyazawa Shintaro , Tazoh Yasuo , Asano Hidefumi , Nagai Yasuhiro , Michikami Osamu , Suzuki Minoru 
Published: December 2004

AbstractThis review describes recent advances in thin film studies of high‐Tc superconducting cuprates. Emphasis is placed on epitaxial thin film growth technologies for LnBa2Cu3Ox (Ln = Y, Eu) cuprates, and on microwave device applications. An exciting area of this research involves epitaxial multilayer structures, such as a superconductor/insulator/superconductor (SIS) combination, and so preliminary results on SIS fabrication are also described.
Conducting Polymers Intercalated in Layered Solids
Authors: Ruiz‐Hitzky Eduardo 
Published: December 2004

Inorganic–organic composite systems (e.g. see figure) with controlled electrical and optoelectronic properties are of current interest for applications including electrochromic displays, batteries, membranes, and sensors. The various methods of intercalation of the organic guests into the inorganic hosts, and the property profiles of the materials based on the intercalation of conducting polymers in layered solids are reviewed. magnified image
Molecular accessibility in interpenetrating organometallic polymer networks (IOPNs): An ESR evaluation
Authors: Corain Benedetto , Corvaja Carlo , Lora Silvano , Palma Giancarlo , Zecca Marco 
Published: December 2004

Interpenetrating organometallic polymer networks can be seen as a new type of supported metal catalysts. They are prepared by the generation of a cross‐linked organometallic copolymer (see figure) inside the macro‐ and microporous domains of organic and inorganic supports. Here, ESR analysis demonstrates that the microporous domains of such materials are accessible to molecules of substantial size. magnified image
Fullerene‐like nanocrystals of tungsten disulfide
Authors: Tenne Reshef , Margulis Lev , Hodes Gary 
Published: December 2004

Polyhedral structures akin to fullerenes, some exhibiting ‘Russian doll’‐type structures, have recently been prepared in layered chalcogenide materials such as WS2, (see figure). The materials are expected to exhibit novel electronic, optical, and mechanical properties. The method of producing the structures is presented, and the possibility of extending the approach to high‐Tc superconductors is discussed. magnified image
Inorganic—Organic Polymers
Authors: Allcock Harry R. 
Published: December 2004

Polymers with an inorganic backbone and organic or organometallic side groups are one of the most promising approaches to new materials that combine the advantages of organic polymers with those of inorganic solids. Properties conferred by particular backbone elements and side groups are discussed, and methods of synthesis briefly outlined. The figure shows the result of a novel variation of ring‐opening polymerization. magnified image
Surface investigations of silylated substrates by TOF‐SIMS
Authors: Hagenhoff Birgit , Benninghoven Alfred , Stoppek‐Langner Karl , Grobe Joseph 
Published: December 2004

Organosilicon compounds have found widespread use as protective coatings, especially agaist corrosive surface phenomena. TOF‐SIMS data are presented here that help to elucidate the products formed when organosilicon agents are coupled to oxidic surfaces. Evidence is found for silsequioxanes and their homo‐derivatives (see Figure), whose shynthesis normally requires special preparative conditions. magnified image
Stacked organometallic arrays
Authors: Rosenblum Myron 
Published: December 2004

Stacks of planar organic or organometallic units can be either a result of self‐assembly that takes place upon crystallization or a consequence of primary molecular structure. Common features in the latter case are divalent and bifacially coordinated ring bridging elements and also two‐center briding elements (Figure). The challenge of these materials is reviewed and attention is drawn to their potential as superconductors and molecular‐based ferromagnets. magnified image
Crystal structures of Copper‐Based High‐Tc Superconductors
Authors: Aranda Miguel Angel García 
Published: December 2004

Many copper‐oxide‐based superconducting compounds have been synthesized in recent years–currently more than 30 families are known, with superconducting transition temperatures up to 133 K. The structures of the various families are described, including La2CuO4, YBa2Cu3O7, single‐layer superconductors, double‐layer superconductors, and infinite layer materials (e.g., CaCuO2, as in the Figure). magnified image
Photoluminescence of chromium(III)‐doped silicoaluminophosphate with AFI structure
Authors: Demuth Dirk , Unger Kluus K. , Schüth Ferdi , Stucky Galen D. , Srdanov Vojisluv I. 
Published: December 2004

Microporous crystalline aluminophosphates, especially substituted modifications, have many potential applications in optics. As a first step, an optimized hydrothermal synthesis is described that produces large, high optical quality, single crystals of Cr‐containing silicoaluminophosphate (Cr‐SAPO‐5), see Figure, which, when calcined, exhibit photoluminescence. magnified image
Chemical imaging by scanning force microscopy
Authors: Akari Sabri , Horn Dieter , Keller Harald , Schrepp Wolfgang 
Published: December 2004

The chemical imaging of surfaces with high lateral resolution i.e. the chemical identification of the materials which make up the surface was recently reported by Lieber et al. in Science. Here, work carried out partially in parallel using chemically modified SFM tips (see Figure) confirms the power of the technique and emphasizes its use for technical surfaces which normally show little contrast in SFM. magnified image
Langmuir monolayers and Langmuir–Blodgett multilayers containing macrocyclic ionophores
Authors: Lednev Igor K. , Petty Michael C. 
Published: December 2004

Macrocyclic ionophores in thin films are of interest for sensors or novel ionophotoswitching devices. Continuing work on floating monolayers and Langmuir–Blodgett multilayers of macrocyclic ionophores—such as crown ether ionophores, cyclodextrins and valinomycin—is reviewed. The figure shows a schematic representation of the complex of valinomycin (a biopolymer based on a 36‐membered ring) with potassium. magnified image
Template synthesis of a large, self‐supporting graphite film in montmorillonite
Authors: Isayama Munetoshi , Nomiyama Kazuko , Kunitake Toyoki 
Published: December 2004

Large, self‐supporting graphite films (e.g., see Figure) have been prepared using phosphate‐treated montmorillonite, a clay, as a template. The preparation—intercalation of the montmorillonite with a copolymer from an aqueous dispersion, conversion of the copolymer component to amorphous carbon, heat treatment to give a highly oriented graphite film—and characterization of the films are described. magnified image
Chiroptical molecular switches
Authors: Feringa Ben L. , Huck Nina P. M. , Schoevaars Anne Marie 
Published: December 2004

The control of chirality by optical molecular switches offers intriguing prospects in the design of new materials. For example, photochemically induced stilbene‐type cis‐trans isomerization of 1 (see Figure) results simultaneously in reversal of the helicity. The molecular design of switching units, the possibility of highly stereoselective optical molecular switching, and an approach to a gated response are described. magnified image
Transformation of intercalated layered silicates to zeolites in the solid state
Authors: Shimizu Shinichi , Kiyozumi Yoshimichi , Maeda Kazuyuki , Mizukami Fujio , Pál‐Borbély Gabriella , Mihályi R. Magdolna , Beyer Hermann K. 
Published: December 2004

Shaping zeolites into useful forms is very important for technical applications in areas such as catalysis, separation, and sensing. Normally it is difficult to form zeolites into appropriate shapes without mixing them with binders. Here, a method is presented for transforming preformed layered silicates into silicalite zeolites (e.g. see Figure). magnified image
Nuclear magnetic resonance study of synthetic polynucleotides and transfer RNA
Authors: McTague John P. , Ross Virginia , Gibbs Julian H. 
Published: December 2004

AbstractHigh resolution proton spectra in D2O solutions have been measured as functions of temperature for the following polynucleotides: Poly A, Poly U, Poly A and Poly U, Poly I, Poly C, Poly I and Poly C, and Transfer UNA from E. coli (strain B), and from yeast. At denaturation, peaks characteristic of the mononucleotide protons appear. Areas under the peaks can be used as a direct measure of denaturation. The sharpness of the spectral lines indicates that in the denatured form internal rotation about the ribose‐phosphate and the ribose‐base links is relatively free. Linewidths also show that monomer units remain in either the ordered or freely rotating state for at least 10−4sec.
The “nondialyzable” fraction obtained from ichthyocol digested with collagenase
Authors: Franzblau Carl , Seifter Sam , Gallop Paul M. 
Published: December 2004

AbstractKinetic analysis was made of the dialysis of digests of ichthyocol gelatin prepared with collagenase. It was found that most, if not all, of the peptides in such digests are dialyzable, but at greatly different rates. First, there is a class of slowly dialyzable peptides that contain most of the tyrosine, ester groups, and carbohydrate moieties of the parent protein molecule. Second, there is a class of slowly dialyzable peptides, which are rich in the polar amino acids and appear to originate from the polar or “noncrystalline” regions of the protein molecule. Third, there is a class of rapidly dialyzable peptides that are rich in proline and hydroxyproline and appear to originate from the “crystalline” regions of the collagen molecule. After 48 hr., the most slowly dialyzable peptides remain in an aggregate fraction which, operationally, has been designated a “non‐dialyzable” fraction. It has been established that the aggregate peptides have, relative to original gelatin, increased contents of glutamic acid, aspartic acid, and lysine, and contain major portions of the carbohydrate, tyrosine, and hydroxylamine‐sensitive (“ester‐like”) bonds of gelatin. However, they have relatively decreased contents of proline, hydroxyproline, arginine, and leucine. Their Contents of glycine and alanine are relatively unchanged. Dinitrophenylation studies indicated that the average peptide length of the “nondialyzable” peptides was 11–15 residues. On the basis of these and other studies, a representation is made of the polar and nonpolar regions of the collagen molecule.
X‐ray diffraction of oriented amylose fibers. III. The structure of amylose–n‐butanol complexes
Authors: Hinkle M. E. , Zobel H. F. 
Published: December 2004

AbstractComplexes of amylose with n‐butanol were prepared both as crystalline precipitates and as oriented fibers. These complexes were subjected to x‐ray analysis, their unit cells were calculated, and the space group of P212121 was confirmed. n‐Butanol complexes exist in both hydrated and anhydrous forms. There is no evidence for methanol, ethanol, or n‐propanol structures similar to those shown by the n‐butanol complex. The Complexes are unstable in the open air and revert to V‐amylose hydrate on standing.
Stereochemical criteria for polypeptides and proteins. IV. Standard dimensions for the cis‐peptide unit and conformation of cis‐polypeptides
Authors: Ramachandran G. N. , Venkatachalam C. M. 
Published: December 2004

AbstractUsing potential energy formulas for variation of bond angles and for ω‐distortion, the conformation of minimum energy for the cisform of the petide unit has been worked out. This agrees very well with the corresponding set of atoms in the crystal structure of Leu‐Pro‐Gly and the dimensions of a standard cispeptide unit are given based on these. The conformational (ϕ,Ψ) map for a cispeptide unit has been worked out from contact criteria, both for a pair of linked units as well as for‐helices having constant (ϕ,Ψ). The small allowed region of the helical map contains the conformation experimentally observed for poly‐L‐proline I.
Nuclear magnetic resonance investigation of the helix to random coil transformation in poly‐α‐amino acids. I. Poly‐L‐alanine
Authors: Ferretti James A. , Paolillo Livio 
Published: December 2004

AbstractHigh‐resolution nuclear magnetic resonance spectra at 100 MHz and 220 MHz have been obtained on two samples of poly‐L‐alanine of differing molecular weights (2500 and 42 500) in the chloroform–trifluoroacetic acid system under various conditions of solvent composition, temperature, and polypeptide concentration. Separate helix and random coil peaks are observed for the α‐CH and peptide NH backbone proton resonances, thereby permitting the determination of helix content. This observation of separate peaks demonstrates that the lifetimes of the helix and random coil portions of poly‐L‐alanine have lower limits of about 10−1 sec. It is suggested that solvent–peptide versus peptide–peptide hydrogen bond competition, coupled with a destabilizing effect of the trifluoroacetic acid on the helix, is responsible for the helix–random coil transformation.
Spatial configuration of polynucleotide chains. II. Conformational energies and the average dimensions of polyribonucleotides
Authors: Olson Wilma K. , Flory Paul J. 
Published: December 2004

AbstractConformational energies are calculated for pairs of successive bond rotations within an internal residue of a polyribonucleotide chain. Contributions to these energies include bond torsional strain, van der Waals repulsions, London attractions, electrostatic interactions, and inductive interactions between nonbonded atoms in the nucleotide repeat unit. The average dimensions of unperturbed random‐coil polyribonucleotide chains are then evaluated on the basis of energies thus estimated, using for this purpose the previously developed virtual bond treatment. The characteristic ratio \documentclass{article}\pagestyle{empty}\begin{document}$ C_\infty = \mathop {{\rm lim}}\limits_{n \to \infty } (\langle r^2 \rangle_0/nl^2) $\end{document} of the mean‐square end‐to‐end distance calculated for polyribonucleotide chains in which all pentose rings are fixed in a C3′‐endo conformation is ≈9; for chains consisting exclusively of C2′‐endo units it is ≈25. These values are considerably greater than those obtained by giving equal weight to all conformations judged to be sterically allowed. Satisfactory agreement between the calculations here and experimental values from viscosity and light‐scattering studies is achieved by treating the chain as a random copolymer of C3′‐endo and C2′‐endo conformational isomers. The critical dependence of the characteristic ratio on the rotation about bond C3′–O3′ in the C2′‐endo chain, however, obscures the interpretation of chain dimensions. The chain is also treated in higher approximation as a sequence of independent repeat units, each of which consists of six chemical bonds. The characteristic ratio obtained in this manner is 6.5 for the C3′‐endo chain and 18.5 for the C2′‐endo chain. Finally, the effects of partially stacked conformations in polyribonucleotides are investigated using the virtual bond treatment. Chain dimensions are calculated for random coil poly rA chains in which stacking is introduced by both noncooperative and cooperative processes.
Copper(II)–DNA denaturation. I. Concentration dependence of melting temperature and terminal relaxation time
Authors: Liebe Donald C. , Stuehr John E. 
Published: December 2004

AbstractBoth kinetic and equilibrium properties of DNA denaturation in the presence of copper(II) cation were studied by using optical techniques. Equilibrium properties of the reaction, measured in terms of Tm, the melting temperature, were shown to depend not on the overall but on the equilibrium concentrations of the species involved. Although Tm did increase with DNA concentration at low copper(II) concentrations, under similar conditions an increase in Tm with increasing copper(II) concentration was not observed.The kinetic properties of the reaction, characterized by the terminal relaxation time, were also found to depend on equilibrium concentrations of reactants. Application of standard methods of relaxation kinetics led to the proposal of a mechanism for copper(II)–DNA complex formation. That mechanism involves the rapid binding of two copper(II) ions to a reaction site on the polymer, followed by a slow, rate‐limiting, first‐order decay of the complex to the denatured state.
The nature of stacking equilibria in polynucleotides
Authors: Powell Janet T. , Richards E. G. , Gratzer W. B. 
Published: December 2004

AbstractTemperature melting profiles of adenylyladenosine and cytidylylcytidine were examined by ultraviolet absorption, circular dichroism, and optical rotatory dispersion. They showed the following characteristics: profiles for different absorption wavelengths are identical as defined by least‐squares computed optical and thermodynamic parameters; melting curves obtained by the three spectroscopic methods are likewise in all cases identical by a series of criteria; in terms of the operational equilibrium constant for base‐stacking all van't Hoff plots are linear; absorption spectra and circular dichroism curves at a series of temperatures for both dinucleoside phosphates give excellent isosbestic points; a matrix‐rank analysis of the family of complete spectra at different temperatures gives a value of two for the numbers of components in both cases. Four criteria are thus fulfilled of a two‐state system for the stacking equilibrium. The results are not compatible with a multi‐state scheme in which the substates are optically distinguishable. There is no measurable effect of ionic strength up to 1.0. In a presence of high concentrations of lithium chloride the criteria for two‐state behavior are no longer fulfilled, and examination of infrared spectra gives evidence of complex formation by this salt, though not by sodium chloride. A destacking profile, similar to that observed on heating, is obtained by progressive addition of ethylene glycol to the solution. It is suggested that in dimers, though not in higher oligomers or polymers, the stacking equilibrium can be operationally regarded as a two‐state system, and that the meaningful thermodynamic parameters can be extracted by analytical treatment, of the type here developed, of the melting profiles.
Nuclear magnetic resonance and optical spectroscopic studies of copolymers of polypeptides. II. Random copoly(benzyl‐L‐glutamate: Benzyl‐L‐aspartate) and (benzyl‐D‐glutamate: benzyl‐L‐aspartate)
Authors: Paolillo L. , Temussi P. A. , Bradbury E. M. , Crane‐Robinson C. 
Published: December 2004

AbstractHigh‐resolution NMR is used to study two series of benzyl‐L‐ or D‐glutamate: benzyl‐L‐aspartate random copolymers. The helix sense of the L‐aspartate residues determined from the αCH and NH chemical shifts agrees with that obtained from ORD. The stability of the helical copolymers to TFA addition shows a minimum at the composition of helix‐sense inversion for the L‐glutamate:L‐aspartate copolymers but no minimum for the lefthanded D‐glutamate: L‐aspartate series. The helix‐coil transition of the glutamate and aspartate residues in each polymer is compared. For the D‐glutamate: L‐aspartate series no differences are found, indicating random copolymerization. In the L‐glutamate:L‐aspartate series significant differences between the transition midpoints are interpreted as resulting from irregular distribution of component residues along the chain.
Spectroscopic study of monosubstituted amides. II. Rotation isomers in amides substituted by aliphatic side‐chain models
Authors: Fillaux F. , De Lozé C. 
Published: December 2004

AbstractThe influence of the substituents upon the Amide I and νNH frequencies has been analyzed for ten amides substituted by aliphatic side chains. By considering the aliphatic chain field effect, some data are obtained as to the conformation of the NCα bond. In two amides, the presence of an equilibrium between two conformers is shown and a semiquantitative estimation of the energies involved is obtained. The consequences for polypeptides conformation, especially for poly‐L‐valine, are discussed.
Quasielastic light scattering investigation of the isothermal “helix to extended‐coil” transition of poly‐L‐lysine HBr
Authors: Jamieson A. M. , Mack L. , Walton A. G. 
Published: December 2004

AbstractThe quasielastic light scattering of poly‐L‐lysine HBr in aqueous solutions has been examined over a variety of pH values where the polymer is in different conformations. Analysis of the spectra demonstrates that as the pH is lowered, the polymer changes from an extended anisotropic from through a collapsed randomized state to a larger isotropic form. These data support the current view that the polymer undergoes a conformational change from an α‐helical form to a “kinked” extended‐coil conformation through an intermediate partially α‐helical state in which internal packing of the helical portions occurs. Finally, a value for the rate of propagation of the unwinding of the α‐helix has been obtained.
Synthesis of some amino acids, sugars, and peptides in cold plasma. Electron‐microscopic studies on some proteid forms (III)
Authors: Simionescu Cr. , Dénes F. , Macoveanu M. 
Published: December 2004

AbstractElectron‐microscopic studies of some proteid structures (synthesized in RF electrical discharge) and corresponding individual compounds resulting from acid hydrolysis were investigated. Some superior precellular structures with peptide linkages in cold plasma conditions were observed.