bluuebunny/crossref_metadata_2025 huggingface dataset:
The synthesis and magnetic behavior of the first mesogenic μ‐oxo‐bridged iron(III) complex
Authors: Galyametdinov Yury , Ivanova Galina , Griesar Klaus , Prosvirin Andrew , Ovchinnikov Igor , Haase Wolfgang
Published: December 2004

Metallomesogens are under investigation as potential molecular ferromagnets, ferroelectrics, and second order nonlinear optical materials. Metallomesogens containing FeIII ions are rare but here, the first liquid crystal containing two FeIII ions and teh first complex of FeIII exhibiting a nematic mesophase is reported. The synthesis and magnetic behavior of the μ‐oxo‐bridged complex of FeIII and Schiff's base are discussed.
Direct synthesis of semiconductor quantum‐wire and quantum‐dot structures
Authors: Nötzel Richard , Ploog Klaus H.
Published: December 2004

The quantum confinement of electrons and holes in low‐dimensional semiconductor structures strongly influences the properties of “quantum wires and dots” and therefore has an important impact on the performance of high‐speed electron and optoelectronic devices. The fabrication of such structures using, for example, molecular beam epitaxy and metal–organic vapor phase epitaxy, their characterization, and their use in heterojunctions, quantum wells, and high electron mobility transistors are reviewed.
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.

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A new way of making diamond? A new way of publishing?
Authors: Bachmann Peter K.
Published: December 2004

Scientists from Penn State's Materials Research Laboratory recently disclosed to the press what they claim is a radically innovative approach to the synthesis of diamond. Peter Bachmann of Philips examines the science involved and comments on the way it was made public.
High‐Tc superconducting thin films
Authors: Miyazawa Shintaro , Tazoh Yasuo , Asano Hidefumi , Nagai Yasuhiro , Michikami Osamu , Suzuki Minoru
Published: December 2004

This 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.
Heteroepitaxy of InP on Si substrates
Authors: Mori Hidefumi , Sugo Mitsuru , Itoh Yoshio
Published: December 2004

Applications in optoelectronic integration have generated interest in the heteroepitaxy of III–V compounds on Si. However, the high dislocation density and high tensile stress in heteroepitaxial layers are serious problems in producing optical devices such as laser diodes. This article reports the growth of a high‐quality InP layer on Si using a combination of organometallic vapor phase epitaxy and vapor mixing epitaxy. A laser diode has been produced whose stability with time is much better than that of a GaAs/Si laser diode.
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.

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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.

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DNA technology in chip construction
Authors: Di Mauro Ernesto , Hollenberg Cornelis P.
Published: December 2004

The use of photolithography of produce 3 nm features sounds like a pipe dream. But is it? The circuit size achievable with X‐ray lithography cannot be pushed below 0.25 μm due to limiting lens technology. Now it has been shown that the genetic material DNA can be used to form micro‐photomasks with features 100 times smaller than those on current silicon chips. The construction of nucleic and networks, their conversion into electron‐conducting networks, and their use in photolithography are described.
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.

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Prediction of the stoichiometry of cation radical salts of organic metals by thin layer cyclic voltammetry
Authors: Carlier Roger , Frère Pierre , Sallé Marc , Roncali Jean , Jubault Michel , Tallec André , Gorgues Alain
Published: December 2004

The detection of mixed valences in organic metals using thin layer cyclic voltammetry is reported. Although mixed valence is recognized as a prerequisite for superconductivity in cation radical salts this is the first report of a method which enables the reliable prediction of the conditions necessary for the production of a suitable cation radical stoichiometry. The method and its application to TTF derivatives are described.
Polymeric materials with arylenevinylene segments—synthesis and architecture
Authors: Greiner Andreas
Published: December 2004

Poly‐p‐phenylenevinylene is of interest due to its electrical and optical properties. It is electrically conductive upon doping, it is photoconductive, NLO active, and exhibits electrically induced luminescence. Recent progress made in the synthesis of pure and well‐defined materials of this type are reviewed and the various strategies for the design of materials yielding the required properties discussed.
A novel supramolecular device with a tunable absorption spectrum
Authors: Voyer Normand , Maltais François
Published: December 2004

Supramolecular systems whose spectroscopic properties are influenced by the recognition of specific guest species are of interest in the development of molecular probes and optical sensors. Here, peptidic frameworks and metalloporphyrins are combined to develop a new way of signalling recognition phenomena and molecular‐based devices with tunable spectroscopic properties.
New chromophores containing sulfonamide, sulfonate, or sulfoximide groups for second harmonic generation
Authors: Beecher Jody E. , Durst Tony , Fréchet Jean M. J. , Godt Adelheid , Pangborn Amy , Robello Douglas R. , Willand Craig S. , Williams David J.
Published: December 2004

Efficient blue light generation by SHG for use in optical storage etc. requires materials that display not only a large nonlinear response and but also optical transparency at the wavelengths of both the laser and the blue light. New chromophores containing sulfonamide, sulfonate, or sulfoximide groups are described that come nearer to this ideal. The optical transparency of electron‐donor and electron‐acceptor substituted conjugated π systems studied previously, which was found to be poor owing to a low‐lying charge‐transfer absorption, is shown to improve when the acceptor group is sulfonamide or sulfonate ester.
Copernicus
Authors: Hussla Ingo , Us Natasha
Published: December 2004

COPERNICUS is a European Community program supporting cooperation in science and technology with Central and Eastern European countries and the Newly Independent States of the former Soviet Union. The conditions of the call for proposals that has just been issued by the Commission of the European Communities are explained, and the opportunities offered by “joint research projects” and “concerted actions/networks” outlined. The COPERNICUS research sectors and priority themes that are especially relevant to advanced materials are introduced in more detail.
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.

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Tuning of photo‐ and electroluminescence in alkylated polythiophenes with well‐defined regioregularity
Authors: Gill Richard E. , Malliaras George G. , Wildeman Jurjen , Hadziioannou Georges
Published: December 2004

Color tuning of luminescence via molecular engineering of the active polymer is important for the commercial application of π‐conjugated polymers in photonic devices. The synthesis of a series of regiospecific alkylated polythiophenes is described, in which the effective conjugation length could be varied by altering the length of the coplanar blocks between head‐to‐head dyads. It is demonstrated that the color‐tuned materials obtained by this novel approach are potentially suitable for applicationin displays and other devices.
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.

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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.

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Materials research support in the UK—The role of the EPSRC
Authors: Ward Stuart D.
Published: December 2004

The Engineering and Physical Sciences Research Council has recently taken responsibility in Britain for coordinating the Government funding of materials science (among other fields). The new organization is presented, and its role and objectives, the current program, the mode of proposal assessment, the support of Interdisciplinary Research Centres (IRCs) and national laboratories, and the priorities for future programs are discussed.
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).

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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.

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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.

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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.

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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.

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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.

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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).

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Phosphorescent oxygen sensors utilizing sulfur–nitrogen–phosphorus polymer matrices
Authors: Pang Zhen , Gu Xijia , Yekta Ahmad , Masoumi Zahra , Coll John B. , Winnik Mitchell A. , Manners Ian
Published: December 2004

Luminescent sensors based on composites comprising transition metal complexes immobilized in polymer matrices have attracted attention as oxygen sensors for both biomedical and barometric applications. Typically, phosphorescent dyes are dispersed in a polymer matrix of high gas permeability are used. Here, S–N–P polymers are used as a novel matrix material allowing the sensitivity of the sensors to be controlled over a wide range.
Nuclear magnetic resonance study of synthetic polynucleotides and transfer RNA
Authors: McTague John P. , Ross Virginia , Gibbs Julian H.
Published: December 2004

High 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

Kinetic 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

Complexes 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

Using 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

High‐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

Conformational 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

Both 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

Temperature 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

High‐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

The 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

The 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

Electron‐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.
Circular dichroism and molecular conformation of copper(II)–gramicidin S complexes
Authors: Santis P. De , D'Ilario L. , Lamanna G. , Morosletti S. , Savino M.
Published: December 2004

Optical properties in different solvents of gramicidin‐bis (salicylaldimine) Cu(II) and (5‐I‐salicyladimine) Cu(II) chelates are intercepted in terms of their molecular structure. A molecular model for the inversion of Contton effects in two different classes of solvents is proposed. This explanation is supported by the study of optical properties of model compounds.
Theory of melting of the triple helix poly (A + 2U) for a 1 : 2 mixture of Poly A to Poly U
Authors: Goldstein Byron
Published: December 2004

The Zimm‐Bragg theory is extended to treat the melting of the triple helix poly (A + 2U) for a solution with a 1 : 2 mole ratio of poly A to poly U. Only the case for long chains is considered. For a given set of parameters the theory predicts the fraction of segments in the triple helix, double helix, and random coil states as a function of temperature.

Four nucleation parameters are introduced to describe the two order–disorder transitions (poly (A + 2U) ⇄ poly A + 2 poly U and poly (A + U) ⇄ poly A + poly U) and the single order–order transition (poly (A + 2U) ⇄ poly (A + U) + poly U). A relation between the nucleation parameters is obtained which reduces the number of independent parameters to three. A method for determining these parameters from experiment is presented. From the previously published data of Blake, Massoulié and Fresco8 for [Na+] = 0.04, we find σT = 6.0 × 10−4, σD = 1.0 × 10−3, and σσ* = 1.5 × 10−3. σT and σD are the nucleation parameters for nucleating a triple helix and double helix, respectively, from a random coil region. σσ* is the nucleation parameter for nucleating a triple helix from a double helix and a single strand.

Melting curves are generated from the theory and compared with the experimental melting curves.
Etude par Spectroscopie Infrarouge de la Transformation Hélice—Chaine Statistique des Polypeptides. I. Etude Comparée de l'Interaction de la Poly‐L‐alanine et d'un Amide Modèle avec l'Acide Trifluoroacétique
Authors: Combelas P. , Garrigou‐Lagrange C. , Lascombe J.
Published: December 2004

Infrared spectra of poly‐L‐alanine in trifluoroacetic acid‐chloroform mixtures have been investigated and compared with those of a model amide (N‐methylacetamide). The purpose of this work is to determine the nature of peptide‐acid specific interactions responsible for the helix‐random coil transition of polymer chains. Analysis is made in using amide (A, I, II, III) and acid (νCO, νOH) vibrations which are specially sensitive to molecular interactions.

We examined a model compound to determine the spectral characteristics of the different complexes or species formed between amide and acid. At a low acid concentration, hydrogen‐bonded complexes: (NH) CO…︁HOOCCF3 (1) are evidenced but no association between amide NH and acid CO groups (complexes A) is observed. For higher acid concentrations complexes (I) are progressively changed into ions pairs and free ions, which result from amide protonation by acid, according to the exothermic equilibrium (I)⇌(NH)COH+, −OOCCF3(II). Amidium and carboxylate bands are localized between 1680–1705 cm−1 and 1620–1625 cm−1, respectively. If the cation band is always clearly seen, the anion band is only observed for the most acidic solutions.

For the polymer, a gradual complexation of type (I) is observed for all acid concentrations. From our results, the assumption of an (A) type interaction seems very unlikely but cannot be excluded. Moreover, proton transfer—similar to that observed with a model amide—is never evidenced since, in particular, the amidium band characteristic of protonation is never seen. In contrast to previous investigations, we conclude that the helix‐random coil transition of polypeptides is not due to the protonation of the peptide functions. This transition does suggest a strong interaction by hydrogen bonds between polymer and acid molecules.
Ultraviolet circular dichroism of polyproline and oriented collagen
Authors: Mandel Richard , Holzwarth George
Published: December 2004

The ultraviolet absorption, linear dichroism, circular dichroism, and oriented circular dichroism of collagen are reported and the spectra are resolved into a self‐consistent set of bands in accord with exciton theory. The parallel band at 200 nm has 40% of the π → π* intensity; the perpendicular band is placed at 189 nm yielding a splitting of 2700 cm−1. The circular dichroism is resolved into two Gaussians at λ∥ and λτ (rotational strengths +14 × 10−40 and −32 × 10−40 esu2. cm2) plus a large non‐Gaussian (“helix”) band with ampplitude −25,000° at 201 nm. These data appear to be in reasonably good accord with recent calculations.

Measurements of the absorption, linear dichroism and circular dichroism of polyproline I and II are also reported and are resolved into their component bands. Polyproline I is in good accord with exciton theory, whereas polyproline II remains unsatisfactory.
Studies on cytochrome c. Part VI. Synthesis of the protected pentadecapeptide (sequence 67–81) of Baker's yeast iso‐I‐cytochrome c
Authors: Moroder Luis , Marchiori Fernando , Borin Gianfranco , Scoffone Ernesto
Published: December 2004

The syntheses are reported of two N‐benzloxycarbonylpeptide tert‐butoxycarbonylhydrazides corresponding to the amino acid sequences 67–74 and 75–81 of the baker's yeast iso‐1‐cytochrome c and their subsequent assembly to the N‐benzyloxycarbonylpentadecapeptide tert‐butoxycarbonylhydrazide corresponding to the sequence 67–81 of the protein.
X‐Ray studies on the conformation of poly‐Nγ‐carbobenzoxy‐L‐α,γ‐diaminobutyric acid and poly‐Nδ‐carbobenzoxy‐L‐ornithine
Authors: Del Pra A. , Spadon P. , Valle G.
Published: December 2004

X‐ray diagrams from oriented films and fibers of poly‐Nγ‐carbobenzoxy‐L‐α,γ‐diaminobutyric acid (PCLB) and of poly‐Nδ‐carbobenzoxy‐L‐ornithine (PCLO) have been examined. The conformation in the solid state for both polymers is that of an α‐helix, 18/5 for PCLB and 11/3 for PCLO, respectively.

Furthermore, while the PCLB molecules are packed in a trigonal lattice whose dimensions, on hexagonal axes, are a = 27.5 and c = 27.0 Å, the PCLO unit cell is monoclinic with a = 23.3, b = 22.7, c = 16.2 Å, and γ = 119.2°.
Depolarized light scattering by amides and peptides
Authors: Ingwall R. T. , Flory P. J.
Published: December 2004

The Rayleigh ratios RH have been measured for the depolarized scattering dilute solutions of N‐ethylacetamide (EA), N‐methylpropionamide (MP), and N‐acetyl‐pyrrolidine (AP) in P‐dioxane, and dilute aqueous solutions of N‐methylacetamide (MA), N,N‐dimethylacetamide (DMA), EA, and MP. Squares of the optical anisot‐ropies γ of the amides are obtained through extrapolation of these mesurements to infinite dilution. Values of γ2 found for EA and MP in dioxane are in good agreement with calculations based principally on the previously evaluated polarizability tensor of the amide group in conjunction with CC and CH bond polarizabilities. The calculations also involve averaging over all conformations, each being weighted according to the estimated conformational energy. The mean‐squared optical anisotropies (γ2) of the oligoglycines and oligoalanines are calculated by similarly averaging over all skeletal conformations. The anistropic polarizability tensor \documentclass{article}\pagestyle{empty}\begin{document}$ \hat \alpha $\end{document} for the prolyl structural unit
magnified image
is derived for γ2 for AP. The much larger optical anisotropies exhibited by the amides when dissolved in water as compared with those observed in dixane are discussed.
The effect of temperature on acid condensation of DNA
Authors: Dore E. , Frontali C. , Gratton E.
Published: December 2004

The temperature dependence of the condensation phenomenon observed for DNA at low pH is studied in 1M NaCl. The similarity of the effects of an increase in temperature and of a decrease in pH gives some insight into the physical nature of the interactions hindering the unwinding of the DNA molecule in the condensed state.
Intensities and other spectral parameters of infrared amide bands of polypeptides in the β‐ and random forms
Authors: Chirgadze Yu. N. , Shestopalov B. V. , Venyaminov S. Yu.
Published: December 2004

The intensities and other spectral parameters of the main components of infrared amide bands for the random and anti‐parallel pleated sheet forms have been determined for poly‐S‐carbobenzoxymethylcysteine, poly‐S‐carboxymethylcysteine, polylysine and silk fibroin of Bombyx mori in heavy water solutions and in organic solvents. Assuming that the optical spectra of these two types of structure are additive, the method was proposed for determining relative contents and molar absorption coefficients of amide I band. Integral intensity and maximum frequency values of the main components of the amide I band for all the samples in the β‐form turned out to be specific. In contrast to this the integral intensity of the band of amide I in the random coil form varied within certain limits, while the main maximum frequency for all samples remained the same.
Vibrational spectra and dispersion curves of poly‐L‐proline II chain
Authors: Gupta V. D. , Singh R. D. , Dwivedi A. M.
Published: December 2004

Using Wilson's GF‐matrix method as modified by Higgs for infinite helical polymers, dispersion curves and the frequency distribution function have been calculated for poly‐L‐proline II chain. Infrared spectrum is obtained and a Urey‐Bradley force field, which provides best fit with the observed frequencies, is evaluated. The result are discussed from the viewpoint of the conformational characteristics of forms I and II.
Interactions between purine derivatives: Electronic spectral studies. I. Electronic transitions in caffeine monomer and exciton coupling in caffeine dimer
Authors: Kikkert J. N. , Kelly G. R. , Kurucsev T.
Published: December 2004

The concentration dependence of the ultraviolet absorption spectrum of aqueous solutions of caffeine has been studied. Individual species spectra have been derived for the monomer, dimer, and tetramer of caffeine. The emission spectrum of caffeine in aqueous solution and the dichroic spectra in oriented poly(vinyl alcohol) and polyethylene films have been measured. The long‐wavelength tail of the absorption spectrum of caffeine in non‐polar environment has been found to incorporate at least one carbonyl(π*, n) transition. Dichroic spectral data and molecular orbital calculations have been used to assign transition moment directions to the (π*,π) transitions. The lowest energy (π*,π) transition, responsible for the near‐ultraviolet absorption peak in aqueous solution of caffeine, has been used for the study of degenerate exciton interactions in the dimeric species of caffeine. Assuming that the caffeine molecules in the dimer are stacked in parallel planes, theoretical calculations of the ground‐state interactions and of the degenerate exciton interactions have been combined with experimental data and a unique model for the dimer of caffeine has been derived. The transfer rate of energy between the molecules in the dimer is of the order of 1013S−1.
Molecular field theory of hysteresis in helix–coil transitions of polynucleotides
Authors: Weisbuch G. , Neumann E.
Published: December 2004

A molecular field theory, taking into account long‐range electrostatic forces is used to study helix–coil transitions of polynucleotides. The theory predicts the existence of hysteresis when the electrostatic interaction parameter is large compared to the thermal energy. The theory is applied to the acid–base titration of poly(A)·2 poly(U).
The vibrational spectra and conformations of some peptide compounds: An application of the additive interatomic interaction model
Authors: Dakhis M. I. , Dashevsky V. G. , Kitaigorodsky A. I.
Published: December 2004

The vibrational spectra of N‐methylformamide, N‐methylacetamide, and acetylglycine N‐methylamide were calculated by use of the additive model of interatomic interactions. The rotation angles ϕ,ψ for acetylglycine N‐methylamide in the crystalline form were determined by the calculation of the spectra of the compound in various conformations. In the A form these angles are equal to 120° and 180°, respectively, and in the B form to 90° and 0°, respectively. The sensitivity of the proposed method to conformational changes, the choice of parameters, and the scope of the method's application are discussed.
Interactions between mucopolysaccharides and cationic polypeptides in aqueous solution: Chondroitin 4‐sulfate and dermatan sulfate
Authors: Gelman R. A. , Blackwell J.
Published: December 2004

Circular dichroism spectroscopy has been used to study the interactions of both dermatan sulfate and chondroitin 4‐sulfate with the cationic polypeptides; poly(L‐arginine), poly(L‐lysine), and poly(L‐ornithine). The results indicate that the mucopolysaccharides have a conformation directing effect on both poly(L‐arginine) and poly‐(L‐lysine) such that these polypeptides adopt the α‐helical conformation. The extent of interaction in each polypeptide‐polysaccharide system can be judged by the degree of induced helicity and the “melting temperature” at which the interaction is disrupted On comparison of these results with those previously obtained for chondroitin 6‐sulfate‐polypeptide mixtures, the extent of interaction can be seen to depend on the length of the amino acid side chain and the positions of the anionic groups on the mucopolysaccharide chain. Such considerations place the three mucopolysaccharides in order of increasing interaction: chondroitin 4‐sulfate < chondroitin 6‐sulfate < dermatan sulfate. These results are correlated with observations that dermatan sulfate is bound more tightly to collagen in connective tissues than are the other two polysaccharides.
Studies on the bacteriophage MS2. XXII. Conformation of MS2 RNA in acid medium
Authors: Slegers H. , Fiers W.
Published: December 2004

MS2 RNA, which sediments at 27S in a neutral buffer, can be converted to a compact 57S conformation at pH 3.8. Requirements for this conversion, besides protonation, are small concentrations of Mg++ ions and a low ionic strength. On the other hand, after heating in the presence of EDTA and at low ionic strength, the RNA can be unfolded to an 11.7S form at pH 6.8 and to 10.5S at pH 3.8. The compact 57S form has lost at least 50% of its secondary structure, as determined by its hypochromicity. It corresponds to a monomer species, as will be shown in a following paper (XXIV). Comparative studies with the homopolymers poly A and poly C and with the heteropolymers poly A,U, poly A,C, and poly A,G indicate that the interactions involved in the acid RNA conformation are not simply explainable by the known interactions of the A–A+, C–C+, and/or A–C+ type.
Circular dichroism and proton magnetic resonance studies of random chain poly‐L‐lysine
Authors: Epand Richard M. , Wheeler Graham E. , Moscarello Mario A.
Published: December 2004

The 218‐nm peak, characteristic of the circular dichroism of randomly coiled poly‐α‐amino acids can be demonstrated in solutions of penta‐L‐lysine, α‐glycyl‐L‐lysine, as well as poly‐L‐lysine. The thermal stability of the particular state that gives rise to this 218‐nm band in the CD is similar for all three peptides. These results eliminate the possibility that poly‐L‐lysine forms a structure with long‐range order in acidic aqueous solution since the stability of such a structure would be expected to be greater for a higher molecular weight polymer than for a pentamer. The intrinsic viscosity of poly‐L‐lysine of molecular weight 180,000 varies only slightly between 25 and 60°C. The proton magnetic resonance spectra of poly‐L‐lysine and penta‐L‐lysine are indistinguishable on the basis of the chemical shift of all resonances, their line widths, and the exchange rates of the NH protons. This demonstrates that poly‐L‐lysine does not possess a cooperatively formed ordered structure in acidic solutions.

A weak band at 238 nm is observed in the circular dichroism of poly‐L‐lysine and other peptides. It is suggested that the effects of change in temperature, salt concentration, or polymer on both the magnitude and position of the 238‐nm band may be explained if it is assumed that it is a shoulder of a lower wavelength peak.
Migration intramoléculaire de l'energie d'excitation dans la poly‐DL‐phenylalanine etude par extinction de fluorescence
Authors: Leroy E. , Lapp C. F. , Laustriat G.
Published: December 2004

Electronic energy transfer at the singlet level in poly‐DL‐phenylalanine was studied by comparing the experimental and theoretical values of the rate constants of fluorescence quenching by CCl4 and of energy transfer on a fluorescent acceptor (biacetyl). The fitting of the experimental and calculated values leads to a diffusion coefficient of the excitation energy of 3.8 to 4.8 × 10−5 cm2/s, consistent with 40 residues implied in the migration process.