bluuebunny/crossref_metadata_2025_split huggingface dataset:
Extremely large mesoporous carbon fibers synthesized by the addition of rare earth metal complexes and their unique adsorption behaviors
Authors: Yasuda Hajime , Tamai Hisashi , Ikeuchi Makiko , Kojima Shigeyuki 
Published: December 2004

Extremely highly mesoporous activated carbon fibers (see Figure) have been synthesized for the first time from pitch fibers containing rare earth metal complexes. These fibers have potential applications in the purification of drinking water, for example, owing to their ability to absorb giant molecules such as humic acid. Investigations of the absorption behavior of the fibers are reported. fig.magnified image
Thermal and optical characterization of high purity α‐octithiophenk
Authors: Fichou Denis , te Ulade‐Fichou Marie‐Paule , Horowitz Gilles , Demanze Frédéric 
Published: December 2004

The preparation of high purity α‐octithiophene (α‐8T) by vacuum sublimation and the investigation of its optical properties in solution and as thin films and single crystals are reported. α‐8T is probably the ultimate unsubstituted oligothiophene to be processable as a pure crystalline compound. In addition, the first experimental evidence for unsubstituted α‐12T (see Figure) is presented. magnified image
Synthesis and characterization of highly efficient and thermally stable diphenylamino‐substituted thiophene stilbene chromophores for nonlinear optical applications
Authors: Jen Alex K.‐Y , Cai Yongming , Bedworth Peter V. , Marder Seth R. 
Published: December 2004

Highly nonlinear chromophores with good thermal stabilities (> 250 °C) are required if organic polymeric materials are to be developed for electro‐optical (EO) applications. The synthesis and characterization of highly efficient and thermally stable diphenylamino‐substituted thiophene stilbenes (e.g., see Figure) are reported, one of which was used to form a high‐EO‐coefficient composite with a polyquinoline. magnified image
Nitrido‐sodalite Zn6[P12N24] as a material for reversible hydrogen encapsulation
Authors: Weitkamp Jens , Ernst Stefan , Cubero Fernando , Wester Frank , Schnick Wolfgang 
Published: December 2004

Host–guest behavior in a nitrido‐sodalite is reported for the first time. The novel nitrido‐sodalite Zn6[P12N24] has the usual nitrido‐sodalite structure with PN4 corner‐sharing units, as shown i the Figure, except that the central anion and one quarter of the Zn2⊕ ions are absent, producing only partial filling of the β‐cages. Hydrogen encapsulation in the β‐cages is discussed. magnified image
Tetraethynylethene molecular scaffolding: Nonlinear optical, redox, and amphiphilic properties of donor functionalized polytriacetylene and expanded radialenes
Authors: Schreiber Martin , Tykwinski Rik R. , Diederich François , Spreiter Rolf , Gubler Ueli , Bosshard Christian , Poberaj Igor , Günter Peter , Boudon Corinne , Gisselbrecht Jean‐Paul , Gross Maurice , Jonas Ulrich , Ringsdorf Helmut 
Published: December 2004

Polymers with polytriacetylene (PTA) backbone (see the Figure), and also expanded radialenes (a new class of macrocycles with large conjugated all‐carbon cores), are of interest because of their intrinsic two‐dimensional π‐electron conjugated pathways. The synthesis, electrochemical characteristics, and linear and nonlinear optical properties of donor‐functionalized polytriacetylene and donor end‐capped expanded radialenes are reported and discussed. magnified image
Fullerenes in membranes: Structural and dynamic effects of lipophilic C60 derivatives in phospholipid bilayers
Authors: Hetzer Michael , Bayerl Sybille , Camps Xavier , Vostrowsky Otto , Hirsch Andreas , Bayerl Thomas M. 
Published: December 2004

Intercalation of lipo‐fullerenes between two monolayers of a lipid bilayer can result in the formation of rodlike structures that exhibit reversible longrange ordering (see Figure). This and other interesting properties of fullerne/membrane composite systems are reported. An arrangement of C60 in the bilayer capable of explaining of experimental observations is also suggested.magnified image
Second‐harmonic microscopy — a quantitative probe for molecular surface order
Authors: Flörsheimer Mathias , Bösch Martin , Brillert Christof , Wierschem Maria , Fuchs Harald 
Published: December 2004

Second‐harmonic microscopy—an application of which is presented in the previous article—is a fast quantitative technique for the imaging of interfaces such as that in the Figure. The theory of the technique, which is based on the generation of second‐harmonic light specifically at surfaces or interfaces due to their lack of centrosymmetry, is outlined and the interpretation of the results discussed.magnified image
Preparation and purification of metal fluorides for crystals and glasses
Authors: Kinsman B. E. , Hanney R. 
Published: December 2004

AbstractThe development of low‐loss fluoride glass fibres for transoceanic telecommunications led to an increased demand for inorganic fluorides with ultrahigh purity in respect of transition metals, rare earths and oxygen. This review paper describes the Merck Ltd strategy for achieving a wide range of metallic fluorides using methods of preparation and purification selected for a combination of technical efficacy and economic practicability. General prepative methods involving aqueous and non‐aqueous routes are described, togehther with purification methods such as ion exchange, zone refining and vacuum sublimation. The special role of ammonium fluoride complexes is discussed. The application of these general methods to the manufacture of fluoride glass components is described, with special reference to the ZBLAN formulation. Additional glass compositions and their individual requirements are also discussed. The parallel application of high‐purity metal fluorides in the growth of optical crystals is emphasised, the history of fluoride ultrapurification having begun with the early demand for high‐quality UV and IR crystals such as CaF2 and LiF.
The single‐molecule approach to the deposition of compound semiconducting materials by MOCVD and related methods
Authors: O'Brient Paul , Haggata Stephen 
Published: December 2004

AbstractThe last 10 years have seen a number of chemists begin to take a serious interest in the deposition of materials such as compound semiconductors. Chemical deposition routes have a number of potential advantages, many of which arise from the fact that growth can take place well away from equilibrium. Chemists are particularly attracted by the idea that a volatile single molecule can deliver the elements of a compound semiconductor to the reaction site. In the present article recent advances in the deposition of compound semiconductors, principally II/VI (12/16) or III/V (13/15) materials, from single‐molecule precursors will be reviewed. The chemistry of these precursors will be discussed in terms of both their synthesis and properties and the effect of the mechanism of their decomposition on the quality of deposited material.
Ion‐selective langmuir blodgett films of a chromoionophore
Authors: Lednev Igor K. , Petty Michael C. 
Published: December 2004

AbstractLangmuir–Blodgett films built up from an amphiphilic derivative of benzothiazolium styryl dye containing a 1,10‐dithia‐18‐crown‐6 ether group have been found to complex with ‘soft’ polarisable ions such as Ag+ and Hg2+ in water. The films exhibited high sensitivity (stability constant of complex formation K ≈ 105 M−1) and high selectivity (e.g. K(Ag+)/K(Pb2+)> 105) compared with aqueous solutions of similar ionophores. This was attributed to the predominant formation of complexes with ligand–cation stoichiometries of 2:1 in the films.
Kinetics of renaturation of denatured DNA. I. Spectrophotometric results
Authors: Subirana Juan A. , Doty Paul 
Published: December 2004

AbstractThe kinetics of renaturation of heat‐ or formamide‐denatured DNA have been studied by following the change of optical density at a constant temperature. Solvents of different ionic strength and various DNA samples have been used. At the lower ionic strengths studied, the reaction follows second‐order kinetics, substantiating the hypothesis that strands of native DNA separate upon denaturation and recombine during renaturation. As the ionic strength is increased at a constant temperature, the reaction deviates from simple second‐order behavior. This appears to be the result of the inhibition to rewinding caused by short helical segments in the denatured DNA which are more stable at the higher ionic strenth.
Kinetics of renaturation of denatured DNA. II. Products of the reaction
Authors: Subirana Juan A. 
Published: December 2004

AbstractThe structure of renatured T4 DNA has been studied by CsCl density‐gradient centrifugation. It has been found that the products of the reaction differ, depending on the method used for denaturation of the DNA. If denaturation is carried out without taking precautions to prevent chain degradation, for example, by heat, the DNA formed by renaturation shows approximately 70% recovery of the native structure as judged by its density. With long times of annealing, the DNA can recover the native density. This behavior is also observed with bacterial DNA samples. On the other hand, if precautions arc taken to prevent chain degradation during denaturation, two products appear as a result of renaturation. One of them is undistinguishable from native T4 DNA, whereas the second one consists of highly aggregated DNA which shows only a partial recovery of the native structure. With long times of annealing, this second species recovers the native density but retains its highly aggregated nature. At higher ionic‐strengths, renaturation follows a different pattern and a single product is formed. The relevance of all these observations to the kinetic anomalies reported in the previous communication is discussed.
Interaction during fibril formation of soluble collagen with cartilage proteinpolysaccharide
Authors: Disalvo Joseph , Schubert Maxwell 
Published: December 2004

AbstractPrecipitation of soluble forms of collagen from solutions containing the soluble protein‐polysaccharide (PP‐L) of bovine nasal cartilage, followed by centrifugation at 100,000 g, resulted in the formation of coherent elastic pellets whose wet weights increased with the concentration of PP‐L in the initial solution. Dry weights and uronic acid contents of these pellets showed that the amount of water held in the wet pellet was nearly constant for any one kind and concentration of collagen, and ranged from 20 to 100 mg./mg. PP‐L in the pellet. Soluble collagens from four different sources and PP‐L from three kinds of cartilage showed similar effects. Precipitation of soluble collagen in the presence of hyaluronate or dextran yielded pellets of much smaller size than those formed in the presence of PP‐L. The presence of chondroitin sulfate had only a slight effect on wet pellet weights. Wet weights of pellets formed in the presence of PP‐L decreased with increasing ionic strength. A model involving entanglement between insoluble collagen fibrils and the relatively stiff chondroitin sulfate chains of branched PP‐L seems qualitatively capable of accounting for these results.
Conformational change in poly‐L‐lysine on reaction with polyacids
Authors: Gratzer W. B. , McPhie P. 
Published: December 2004

AbstractWhen solutions of poly‐L‐lysine and poly(acrylic acid) in salt solutions at neutral pH are mixed, complexes are formed. Optical rotatory dispersion studies of these complexes away from the equivalence point reveals the formation of α‐helices. The α‐helix content of the polylysine never rises above about 50%. On addition of 25% by volume of dioxane, the turbidity of the complex solutions disappears, and there is some enhancement of the α‐helix content. Poly(phosphoric acid) behaves essentially in the same way as poly(acrylic acid). Poly(uridylic acid) forms complexes with polylysine but with no detectable formation of α‐helix. The same is true of ribosomal RNA and native and denatured DNA. A number of other polyacid polybase systems involving basic proteins have been examined, but again no α‐helix formation is induced. The results are related to the case of biological nucleoproitein complexes, and the conformational specificity of these systems is discussed. The effect of scattering on measured optical rotation has been investigated and is shown to be unimportant up to quite high levels.
Optical rotatory dispersion of mononucleosides and 5′‐mononucleotides
Authors: Yang Jen Tsi , Samejima Tatsuya , Sarkar P. K. 
Published: December 2004

AbstractOptical rotatory dispersions between 200 and 600 mμ are presented for mononucleosides and 5′‐mononucleotides in neutral, acid, and in some cases alkaline solutions. All display a single Cotton effect in the ultraviolet region (above 220–240 mμ); the purine ones are negative in sign and the pyrimidine ones positive, with the crossovers (zero rotations) in most cases close to the wavelengths of their respective absorption maxima. The visible rotatory dispersions obey the one‐term Drude equation, except for TMP and UMP, which show anomalous dispersions. The rotational strengths of the dichroic bands were estimated from the Cotton effect profiles; cytosine mononucleotides and mononucleotides show the strongest rotational strengths among the compounds studied.
Deuteration and solvent composition effects in the helix–coil transition of poly‐γ‐beiizyl‐L‐glutamate
Authors: Karasz F. E. , O'Reilly J. M. 
Published: December 2004

AbstractThe effects of deuteration and of changes in solvent composition on the thermo dynamics of the helix–coil transition have been studied by calorimetric and optical measurements in the poly‐γ‐benzyl‐L‐glutamate–dichloroacetic acid–1,2‐dichloro‐ethanc system. For a given solvent composition, deuteration of the polypeptide and of the acid lowers the transition temperature Tc, while an increase in the volume fraction of acid in the solvent raises Tc. A rise in Tc is accompanied by a decrease in both the van't Hoff and the calorimetric heats of transition, but at different rates. The result is a temperature dependency in the Zimm‐Bragg cooperation parameter σ. Possible causes of this result and its implications are discussed.
Molecular configuration of amylose and its complexes in aqueous solutions. Part II. Relation between the DP of helical segments of the amylose–iodine complex and the equilibrium concentration of free iodine
Authors: Szejtli J. , Richter M. , Augustat S. 
Published: December 2004

AbstractThe iodine which is added to an aqueous amylose solution is bound only partly by the amylose while forming the blue complex and partly remains free. The equilibrium normality of the free and the bound iodine at half‐saturation of amylose by iodine is designated as [If]v and [Ib]w, respectively. The stability of the poly iodine chain formed within the axis of amylose helices depends on its length, i.e., indirectly on the DP of the amylose helices: the greater this stability, the lower the [If]v value. The amylose molecule consists of helical segments. Such a molecule may behave as a random coil. The average length of the helical segments in freshly prepared amylose‐iodine complexes depends on temperature, pH, iodide concentration, the presence of other complex‐forming agents, and the DP of the amylose. This latter factor is investigated in the present paper. By the aid of an automatically recording photometrictitrating device the coherent values of [Ib] and [If] were determined. Plotting these values against DPn for mechanochemically degraded as well as for periodateo‐xidized amyloses resulted in curves consisting of two linear sections. The break of the curves occurred between DPn 110 and 130. It was concluded that below DPn = 100 the DP of helical segments (= sDPn) is identical to the DPn of the total molecule, i.e., the molecule consists of only a single, relatively stiff helix. Above this limit the molecule contains several helical segments. The DP of these helical segments can be calculated as follows: sDPn = 141.1 − 10.2 × 105[If]v. This equation is considered to be valid for 0.5–0.6 mg. amylose in 100 ml. 0.1N HCl at 20°C., λ = 650 mμ, euuvet diameter 3.4 cm., the feed rate of the iodate‐iodide titrating solution (in acid medium resulting in a 5 × 10−3N I2 solution with a molar iodide to iodine ratio of 1.5) is 0.4ml./min. Amylose molecules of, e.g., DPn = 1380 consist of an average of 11.4 segments having a DP of about 120 and consisting of an average of 15–18 helical turns.
α‐Helix formation by solvent–solvent interaction
Authors: Lotan Noah , Bixon Mordechai , Berger Arieh 
Published: December 2004

AbstractThe degree of helicity θ of a series of homologous polypeptides as a function of solvent composition was investigated. The polypeptides studied were: poly‐N5‐(3‐hydroxypropyl)‐L‐glutamine (PHPG) as well as the corresponding 2‐hydroxyethyl and 4‐hydoxybutyl derivatives (PHKG and PHBG, respectively). PHPG, which is nonhelical in formic acid, attains helicity on addition of relatively small amounts of formates, formamide, and urea to its solution in formic acid. This demonstrates that the high acidity of pure formic acid is largely responsible for its helix‐breaking power‐probably through protonation of the peptide bonds. In formic acid‐water mixtures all three polymers show a maximum in degree of helicity at a mole fraction of about 0.3 formic acid. This is interpreted as being due to interaction between the two helix‐breaking solvents, which results in the formation of an inactive molecular species. It is shown that solvent‐induced transitions with helicity maxima are predicted by the Bixon‐Lifson treatment when applied to this system.
Polarisation de fluorescence des polypeptides portant un groupe terminal fluorescent
Authors: Frey M. , Weill G. 
Published: December 2004

AbstractThe polarization of fluorescence of a chromophore chemically bound on the NH2 end of a poly(L‐benzyl glutamate) molecule has been studied as a function of temperature, viscosity, and solvent. The relaxation times depend on both the overall rotation of the helix and the local rotation of the endgroup. In m–cresol the endgroup is rigidly bound and the rotational diffusion constant of the molecule is in good agreement with the values obtained by Kerr effect and dielectric relaxation. In other helicogenic solvents (DMF, DCE, etc.) the local rotation is nearly free. In m‐cresol‐DMF mixtures a sharp decrease of the polarization around a composition of 40% DMF can be interpreted as a change in the freedom of rotation of the endgroup. No discontinuity in the optical rotation is observed in the solvent mixture. The question of how a rapidly rotating endgroup could show an extrinsic Cotton effect as observed by Bloutand Yamaoka for the system Acridine Orange–PBLG in chloroform is then raised. Polarization of fluorescence measurements on this system show a nearly complete freedom of rotation of the dye and OH D measurements show no detectable Cotton effect in the dye absorption band.
Stability of helical polyamino acids in solution at high temperatures
Authors: Franzen James S. , Harry John B. , Bobik Caroline 
Published: December 2004

AbstractOptical rotatory dispersion studies have been carried out at temperatures up to 150 °C. on poly(γ‐benzyl L‐glutamate) in α‐chloronaphthalene and N‐methylcaprolactam, and on poly‐ε‐carbobenzoxy‐L‐lysine, poly‐δ‐carbobenzoxy‐L‐ornithine, and poly(L‐glutamic acid) in N‐methylacetamide. The Moffitt‐Yang −b0 values were large in all cases, but significant decreases in −b0 were observed at the upper temperature limits of the study suggesting that a transition region was being entered. Polymer degradation generally precluded examination of the systems through the suggested transition region.
Extent and stability of the α‐helix in γ‐benzyl L‐glutamate–glycine copolymers
Authors: Block H. , Kay Josephine A. 
Published: December 2004

AbstractBlock and random copolymers of γ‐benzyl L‐glutamate and glycine were studied by optical rotatory dispersion methods in order to ascertain the extent and stability of the α‐helix formed by these polymers in appropriate solvent mixtures. Results indicate that when in solution such polymers do contain sections of α‐helix. However, it appears that glycine does not readily fit into the α‐helix which is largely due to the γ‐benzyl L‐glutamate segments. Further, there are indications that the helical sections in the random copolymers are due to the nonrandomness of the polymerization.
Effect of glycyl residues on the stability of the α‐helix
Authors: Fraser R. D. B. , Harrap B. S. , Macrae T. P. , Stewart F. H. C. , Suzuki E. 
Published: December 2004

AbstractA series of polypeptides containing ordered sequences of glyeyl and γ‐ethyl L‐glutamyl residues has been synthesized. The properties of the polymers were investigated by x‐ray diffraction, infrared spectrophotometry, and optical rotator dispersion, and the results indicate that glycine appreciably reduces the stability of the γ‐ethyl L‐glutamate helix.
Polypeptides. LIII. Water‐soluble copolypeptides of L‐glutamic acid, L‐lysine, and L‐alanine
Authors: Morita K. , Simons E. R. , Blout E. R. 
Published: December 2004

AbstractThe synthesis and some of the physical‐chemical properties of tricopolymers of L‐glutamic acid, L‐lysine, and L‐alanine are reported here. The molar ratios of the glutamyl: lysyl: alanyl residues were 1:1:X or 3:2:X, where the alanyl content X was increased in regular steps. The α‐helix content calculated from the optical rotatory dispersion of the polypeptides is compared with a predicted helix content estimated from the composition of the polymers and the known behavior of the homopolypeptides at pH 3, 8, and 12. At pH 3 copolypeptides containing 20 mole‐% or more alanine exhibit a helix content equal to the sum of their alanyl and glutamyl residue contents. At pH 8 the helix content equals the alanyl content when the latter was 40 mole‐% or higher; at lower alanyl contents the electrostatic interaction between charged glutamyl and lysyl residues makes some contribution. At pH 12 the amount of helix observed is proportional to the mole ratio of alanine residues present in the polymer. The helix content of a tricopolymer containing 1:1:3 mole ratios of glutamyl: lysyl: alanyl residues was determined in solutions of lithium bromide and in urea solutions. Both reagents led to a decrease in helix content at pH 3 and 8 to a minimum of approximately 20% helix in 8M urea or 5.5M LiBr. The helix–random chain transition curves at pH 3 and 8 are parallel when the urea concentration is varied, but differ in shape when the lithium bromide concentration is varied at pH 3 and 8. The mode of action of these two “denaturing” reagents may thus be different. Heating the same tricopolypeptide at pH 3 or 8 from 5 to 80°C. also led to a helix–random chain transition centered at approximately 45°C.
Interaction of metal ions with polynucleotides and related compounds. IX. Unwinding and rewinding of poly(A + U) and poly(I + C) by copper(II) ions
Authors: Eichhorn Gunther L. , Tarien Edward 
Published: December 2004

AbstractIt is demonstrated that, poly(A + U) and poly(I + C) are both formed under low ionic strength conditions. Continuous variation studies indicate the formation of copper(II) complexes of poly A, poly C, and poly I, but not of poly U. Copper(II) in a 1:1 ratio to polynucleotide prevents the formation of poly(A + U) and brings about the dissociation of the poly (A + U) complex produced in the absence of the metal. Poly (I + C) is similarly dissociated by copper(II) ions. The addition of sufficient electrolyte reverses the copper(II) induced dissociation of poly(I + C). The effect of copper(II) on ordered synthetic polynucleotides is thus very similar to its effect on DNA.