bluuebunny/crossref_metadata_2025_split huggingface dataset:
Soluble organosilicon micronetworks with spatially confined reaction sites
Authors: Baumann Frank , Deubzer Bernhard , Geck Michael , Dauth Jochen , Sheiko Sergio , Schmidt Manfred 
Published: December 2004

Extremely small monodisperse micronetworks have potential applications as molecular containers or reaction vessels. The advantages of the sol‐gel synthesis reported here, involving endcapping with Si‐O‐SiR3 groups, are pointed out and the characterization of the resulting spherical particles (radius between 5 nm and 20 nm), see Figure, is described. The variety of functional groups and the high density of potential reaction sites are stressed.magnified image
Unprecedented thermo‐ and ion‐responsive behavior of a non‐ionic water‐soluble polysilane
Authors: Cleij Thomas J. , Jenneskens Leonardus W. , Kluijtmans Sebastiaan G. S. J. M. 
Published: December 2004

Polysilanes display remarkable optical and electronic properties that are affected by teh degree of σ‐conjugation, which depends on the conformation of the silicon backbone. The thermo‐ and ion‐responsive behavior of aqueous solutions of 1 (Figure) is described, including «inverse» abrupt termochromism and the tunability of the lower critical solution temperature (LCST) by addition of inorganic salts.magnified image
Low molecular weight and polymeric triphenylenes as hole transport materials in organic two‐layer LEDs
Authors: Bacher Andreas , Bleyl Ingo , Erdelen Christian H. , Haarer Dietrich , Paulus Wolfgang , Schmidt Hans‐Werner 
Published: December 2004

The benefits of using hexa‐alkoxytriphenylenes as hole transport materials for two‐layer light‐emitting diodes are reported. Both low molecular weight and polymeric triphenylenes are investigated. The polyacrylate shown in the figure is demonstrated to have excellent film‐forming properties and combines sufficient charge carrier mobility with good hole injection properties to make it a very suitable hole transport material.magnified image
Solution‐phase synthesis of luminescent materials libraries
Authors: Sun Xiao‐Dong , Wang Kai‐An , Yoo Young , Wallace‐Freedman William G. , Gao Chen , Xiang Xiao‐Dong , Schultz Peter G. 
Published: December 2004

The application of combinatorial methods to the synthesis and characterization of novel materials is described for the case of solution‐phase synthesis of phosphors based on rare‐earth‐activated refractory metal oxides. A scanning multiinkjet system is shown to be suitable for the fabrication of a liberry such as (LamGd1‐m)‐AlnOx:Eu, the photoluminescence image of part of which is shown in the Figure.magnified image
Electrical and optical properties of Processable Polythiophene Derivatives: Structure‐Property relationships
Authors: Leclerc Mario , Faid Karim 
Published: December 2004

Control of the electrical and optical properties of different polythiophene derivatives can be achieved, to some extent, by adjusting the nature of their substituents. The effects of flexible side chains (increase in solubility, modification of the stability of the conducting state, induction of thermo‐, iono‐, photo‐, or biochromism) such as alkyl or alkoxy moieties are reviewed and the promising self‐doped polythiophenes (see Figure) discussed.magnified image
Rewritable full‐color recording on a thin solid film of a cholesteric low‐molecular‐weight compound
Authors: Tamaoki Nobuyuki , Parfenov Alexander V. , Masaki Atsushi , Matsuda Hiro 
Published: December 2004

Rewritable full‐color recording is potentially technologically important but has not yet been realized. A cholesteric low‐molecular‐weight compound (see Figure) is presented that, in the form of a thin film, displays iridescent colors at room temperature (see the cover picture of this issue) that can be recorded and erased repeatedly to form images by thermal treatment.magnified image
Micropatterning fluid membranes
Authors: Ulman Nick , Groves Jay T. , Boxer Steven G. 
Published: December 2004

An application of photolithographic patterning is described for producing a self‐assembled membrane that is fluid over some areas and immobilized or absent in others, as directed by the patterning on the support (see Figure). This is an important step towards forming a specific interface between living cells and silicon electronics. (Figure reprinted from Science 1997 275, 651–653; ©1997 AAAS)magnified image
Does Microgravity Influence Self‐Assembly??
Authors: Dag Ömer , Ahari Homayoun , Coombs Neil , Jiang Tong , Aroca‐Ouellette Patricia P. , Petrov Srebri , Sokolov Igor , Verma Atul , Vovk Gregory , Young David , Ozin Geoffrey A. , Reber Christian , Pelletier Yanick , Bedard Robert L. 
Published: December 2004

AbstractThe templated syntheses of TMA2Sn3S7 and TBA2Sn4S9 (where TMA is tetramethylammonium and TBA is n‐tetrabutylammonium) microporous layered tin(iv) sulfides have been carried out under both microgravity (μG) and earth (1G) conditions in order to elucidate the influence of gravity on the self‐assembly and crystal‐growth processes of this class of materials. The μG experiments were conducted on board the May 1996 Endeavour STS‐77 NASA space‐shuttle flight. It was determined that the long‐range ordering of the porous layers and the population of defects but not the short‐range ordering within the layers is influenced by gravity. Bulk and surface crystallinity, smoothness of crystal faces, optical quality, crystal habits, registry of the porous layers, and accessible void volume to adsorbates were found to be improved in the space‐grown crystals. This is probably because the forces associated with the organization of the porous layers are expected to be weak and sensitive to the elimination of buoyancy‐driven convective flows and Stokes sedimentation effects in a microgravity environment. One can draw an analogy to the weak forces between protein macromolecules and the established effect of microgravity on improving the diffraction quality of crystals harvested in space.
A blue‐emitting triazole‐based conjugated polymer
Authors: Grice Alan W. , Tajbakhsh Ali , Burn Paul L. , Bradley Donal D. C. 
Published: December 2004

Improved performance of light‐emitting devices is reported for devices containing the newly synthesized, triazole‐containing polymer TRIDSB (see Figure). This fully conjugated material has a high solid‐state photoluminescence quantum efficiency, unlike other triazole polymers investigated previously, and emits blue light. TRIDSB holds promise as an electron‐transporting material.magnified image
Caspase‐1–processed interleukins in hyperoxia‐induced cell death in the developing brain
Authors: Felderhoff‐Mueser Ursula , Sifringer Marco , Polley Oliver , Dzietko Mark , Leineweber Birgit , Mahler Lieselotte , Baier Michael , Bittigau Petra , Obladen Michael , Ikonomidou Chrysanthy , Bührer Christoph 
Published: December 2004

AbstractInfants born prematurely may develop neurocognitive deficits without an obvious cause. Oxygen, which is widely used in neonatal medicine, constitutes one possible contributing neurotoxic factor, because it can trigger neuronal apoptosis in the developing brain of rodents. We hypothesized that two caspase‐1–processed cytokines, interleukin (IL)–1β and IL‐18, are involved in oxygen‐induced neuronal cell death. Six‐day‐old Wistar rats or C57/BL6 mice were exposed to 80% oxygen for various time periods (2, 6, 12, 24, and 48 hours). Neuronal cell death in the brain, as assessed by Fluoro‐Jade B and silver staining, peaked at 12 to 24 hours and was preceded by a marked increase in mRNA and protein levels of caspase 1, IL‐1β, IL‐18, and IL‐18 receptor α (IL‐18Rα). Intraperitoneal injection of recombinant human IL‐18–binding protein, a specific inhibitor of IL‐18, attenuated hyperoxic brain injury. Mice deficient in IL‐1 receptor–associated kinase 4 (IRAK‐4), which is pivotal for both IL‐1β and IL‐18 signal transduction, were protected against oxygen‐mediated neurotoxicity. These findings causally link IL‐1β and IL‐18 to hyperoxia‐induced cell death in the immature brain. These cytokines might serve as useful targets for therapeutic approaches aimed at preserving neuronal function in the immature brain, which is exquisitely sensitive to a variety of iatrogenic measures including oxygen. Ann Neurol 2005;57:50–59
Glut‐1 deficiency syndrome: Clinical, genetic, and therapeutic aspects
Authors: Wang Dong , Pascual Juan M. , Yang Hong , Engelstad Kristin , Jhung Sarah , Sun Ruo Peng , De Vivo Darryl C. 
Published: December 2004

AbstractImpaired glucose transport across the blood‐brain barrier results in Glut‐1 deficiency syndrome (Glut‐1 DS, OMIM 606777), characterized by infantile seizures, developmental delay, acquired microcephaly, spasticity, ataxia, and hypoglycorrhachia. We studied 16 new Glut‐1 deficiency syndrome patients focusing on clinical and laboratory features, molecular genetics, genotype–phenotype correlation, and treatment. These patients were classified phenotypically into three groups. The mean cerebrospinal fluid glucose concentration was 33.1 ± 4.9mg/dl equal to 37% of the simultaneous blood glucose concentration. The mean cerebrospinal fluid lactate concentration was 1.0 ± 0.3mM, which was less than the normal mean value of 1.63mM. The mean Vmax for the 3‐O‐methyl‐D‐glucose uptake into erythrocytes was 996 fmol/106 red blood cells per second, significantly less (54 ± 11%; t test, p < 0.05) than the mean control value of 1,847. The mean Km value for the patient group (1.4 ± 0.5mM) was similar to the control group (1.7 ± 0.5mM; t test, p > 0.05). We identified 16 rearrangements, including seven missense, one nonsense, one insertion, and seven deletion mutations. Fourteen were novel mutations. There were no obvious correlations between phenotype, genotype, or biochemical measures. The ketogenic diet produced good seizure control. Ann Neurol 2005;57:111–118
Nonconsensus intronic mutations cause episodic ataxia
Authors: Wan Jijun , Carr Janai R. , Baloh Robert W. , Jen Joanna C. 
Published: December 2004

AbstractWe discovered intronic mutations in two episodic ataxia type 2 (EA2) families: a four‐nucleotide GAGT deletion at IVS41+(3–6) and a single nucleotide insertion (insT) at IVS24+3. We expressed minigenes harboring the mutations in cell lines to demonstrate exon skipping from the deletion mutation and the activation of a cryptic splice donor site from the insertion mutation. The identification of these disease‐causing mutations expands the spectrum of EA2 mutations and emphasizes the importance of intronic sequences in regulating gene expression. Ann Neurol 2005;57:131–135
Conformation studies on the sodium and cesium salts of calf thymus deoxyribonucleic acid (DNA)
Authors: Cohen Gerald , Eisenberg Henryk 
Published: December 2004

AbstractSolutions of calf thymus NaDNA in 0.2M NaCl and CsDNA in 0.2M CsCl (fragmented by sonic irradiation to a molecular weight of about 5 × 105) were examined by electron microscopy, light scattering, and viscosity measurements. Electron microscopy showed that the molecular fragments are rodlike in shape and that the distribution of their lengths is sharp (Lw/Ln ∼ 1.06). The weight‐average number of nucleotides Zw per DNA molecule derived from light scattering was found to be in very good agreement with the value Lw derived from electron microscopy. The z‐average length Lz derived from light scattering at 25°C. was found to be about 89% of the corresponding value derived by electron microscopy. Similarly, the value of Lw derived from intrinsic viscosity at 25°C. on the basis of a rodlike model was found to be about 87% of the corresponding value derived by electron microscopy. It is concluded that the molecules are slightly flexible and do not, assume their full contour length in solution because of the disorienting effect of Brownian motion. The intrinsie viscosity was found to increase linearly with decreasing temperature toward a limiting value corresponding to the fully stretched length of the macromolecules at 0°K.: a reasonable value for the modulus of elasticity could be calculated. It was also found that, no differences in conformation could be delected in t he two systems CsDNA‐0.2M CsCl and NaDNA‐0.2M NaCl.
Infrared absorption spectrum of keratin. II. Deuteration studies
Authors: Bendit E. G. 
Published: December 2004

AbstractA number of new bands have been found in the spectra of deuterated α‐ and β‐keratin. In particular, the deuteration difference spectrum has been useful for the determination of frequencies of previously unsuspected bands. Thus it is found that the amide A and II frequencies of the nonhelical component in α‐keratin occur at 3310–3320 and 1520 cm.−1, respectively, and that both bands exhibit dichroism consistent with polypeptide chains which have a measure of alignment parallel to the fiber axis. The parallel dichroism of the amide II′ band of this phase at about 1435 cm.−l also indicates some alignment. A nondichroic residual band at 1513 cm.−1 in highly deuterated α‐keratin is assigned to the tyrosine residue, as a sharp band near this frequency is found in the spectrum of polytyrosine. The ν‖(o) component of the α‐helix is weak or absent in α‐keratin, and the relatively sharp band observed near this frequency is thought to be due to the tyrosine residue, while its dichroism is caused by the presence of dichroic nonhelical material. A band near 1575 cm.−1 in deuterated α‐ and β‐keratin is tentatively assigned to the deuterated guanidinium group of arginine. This band becomes progressively more prominent during deuteration, which indicates that some arginine side chains arc slow to exchange, possibly because their environment prevents interaction with D2O. The deuteration difference spectrum also shows that, contrary to earlier views, helical material in α‐keratin exchanges significantly during the early stages of deuteration, although at a slower rate than the nonhelical material, while part of the nonhelical phase does not exchange as rapidly as had been thought and makes a contribution even after many hours or days.
Solution properties of synthetic polypeptides. II. Sedimentation and viscosity of poly‐γ‐benzyl‐L‐glutamate in dimethylformamide
Authors: Fujita Hiroshi , Teramoto Akio , Yamashita Tsuneko , Okita Koichi , Ikeda Shoichi 
Published: December 2004

AbstractNine samples of poly‐γ‐benzyl‐L‐glutamate (PBLG), ranging in M̄w from 19,000 to 410,000, were examined viscomctrically and by ultracentrifugation with dimethylforma‐mide (DMF) at 25°C. as helicogenic solvent. The data for [η] and s0 (limiting sedimentation coefficient) as functions of M̄w were fitted well by the theories for a rigid prolate ellipsoid of revolution whose major axis increases linearly with M̄w, but whose minor axis is independent of M̄w. This implies that the overall shape of the PBLG molecule in DMF is represented by a straight cylinder whose cross section is independent of its length. The length per monomeric residue h evaluated from [η] is about 1.3 A., whereas that from s0 is about 1.6 A. No adequate explanation for this difference in h can be found at present. More serious is the fact that these hydrodynamically evaluated values of h are appreciably larger than, the value obtained from our light‐scattering measurements reported previously. All these values of h from our studies are not consistent with the value characteristic of the α‐helix, for which h is 1.5 A. The concentration dependence of s0 was found to agree well with the recent theoretical prediction of Peterson for cylindrical macromolecules.
Molecular configuration of amylose and its complexes in aqueous solutions. Part III. Investigation of the DP distribution of helical segments in amylose–iodine complexes
Authors: Szejtli J. , Augustat S. , Richter M. 
Published: December 2004

AbstractThe equilibrium normality [If] of free iodine in amylose‐iodine complex formation is a function of the length of the polyiodine chains. This length depends on the DP of helical segments of amylose (sDPn). Values of [If] and of the concentration of the bound iodine [Ib] were determined by the continuous photometric titration with automatic recording. Plots of [Ib] versus [If] give an integral distribution curve. Since the relation between [If] and sDPn is known, the graphic differentiation of the [Ib] versus [lf] curve furnishes the differential distribution curve, representing the mass distribution of the helical segments according to their DP. The peak of this curve is characteristic of the percentage and DP of those helical segments, which occur in the largest amount. On the basis of the differential distribution curve the polymolecularity of the investigated sample may be judged. The titration of amylose samples degraded by various methods gives different distribution curves. Titrating mixtures of samples with widely differing average DP values results in differential curves having more than one maximum.
Theory and practice of the analytical centrifugation of an active substrate–enzyme complex
Authors: Cohen R. , Giraud B. , Messiah A. 
Published: December 2004

AbstractThe active enzyme centrifugal‐ion (AEC) method presented here permits the hydrodynamic study of active enzyme–substrate(s) complexes in solutions containing micro‐gram amounts of the studied enzyme, even if the enzyme preparation is very impure. The AEC method can he used only when the specific enzymatie reaction can be measured directly in a spectrophotometer. The general equations relevant to the method and their solutions are presented in detail. Their use requires some numerical calculations. A practical summary of the AEC method is given, and the precision of the measured values of the sedimentation and diffusion coefficients is discussed.
General method for calculating helical parameters of polymer chains from bond lengths, bond angles, and internal‐rotation angles
Authors: Sugeta Hiromu , Miyazawa Tatsuo 
Published: December 2004

AbstractHelical conformations of infinite polymer chains may be described by the helical parameters, d and θ (the translation along the helix axis and the angle of rotation about the axis per repeat unit), pi (the distance of the ith atom from the axis), dij, and dij (the translation along the axis and the angle of rotation, respectively, on passing from the ith atom to the jth). A general method has been worked out for calculating all those helical parameters from the bond lengths, bond angles, and internal‐rotation angles. The positions of the main chain and side chain atoms with respect to the axis may also be calculated. All the equations are applicable to any helical polymer chain and are readily programmed for electronic computers. A method is also presented for calculating the partial derivatives of helical parameters with respect to molecular parameters.
Numerical solutions of the Lamm equation. III. Velocity centrifugation
Authors: Dishon Menachem , Weiss George H. , Yphantis David A. 
Published: December 2004

AbstractWe have generated solutions to the Lamm equation to examine the effects of concentration dependence on velocity experiments. Two forms of c dependence are considered: s/s0 = 1 – kc and s/s0 = (1 + kc)−1. Features of these solutions are discussed. The magnitude of the errors resulting from the usual procedure of measuring the rate of movement of schlieren maxima or of the position at which the concentration is one half the plateau value have been examined. These errors are usually negligible after sufficient centrifugation time. The errors in using the half‐plateau concentration are less than those using the movement of the peak. We have also examined a technique due to Fujita for determining D from boundary spreading when s/s0 = (1+kc)−1. This method is satisfactory when s/s0 is actually of this form, or under certain limitations when s/s0 = (1 + kc)−1. Creeth has shown that under certain conditions the concentration gradient, curve remains virtually unchanged in shape after separating from the meniscus. When this occurs it is possible to estimate s/D from the data. The condition for such a steady state is that kc0 be sufficiently large. Numerical confirmation of this method is presented in the final section.
Dielectric properties and oxygenation of hemoglobin
Authors: Hanss Maxime , Banerjee Ramalprasad 
Published: December 2004

AbstractDielectric properties of human and horse hemoglobin were studied at frequencies ranging from 20 kc./sec. to 7 Mc./sec. The relative errors in the measurements were usually less than 10−3 even for mildly conducting solutions (10−3M KCl). The experimental setup allowed us variation and measurement of the degree of oxygenation of the protein and to determine its dielectric parameters. Our main conclusion is that it was not possible to find any variation of the dielectric increment for hemoglobin oxygenation levels of 25, 50, 75, and 100%, approximately. This result is at variance with some previous reports. We cannot give the reason for this discrepancy but discuss some possible explanations. The specific dielectric increment, Δεs/c, of human hemoglobin was shown to be significantly smaller than that of horse hemoglobin (0.28 against 0.32). This physical property is lowered with increasing ionic strength I: Δεs/c = 0.28 and 0.20 for I = 10−4 and 10−3, respectively (human protein).
Electrostatic effects on polynucleotide transitions. II. Behavior of titrated systems
Authors: Record M. Thomas 
Published: December 2004

AbstractThe theory developed in the previous paper to discuss changes in electrostatic free energies in polynucleotide order–disorder transitions is extended to cases where one or more of the participating species is titrated to some degree α. It is shown that, for any class of transition, the melting temperature Tm at constant pH is a linear function of the logarithm of the monovalent counterion concentration M, that at high salt the logarithm of the depression of the melting temperature by pH titration is proportional to the pH change, and that the stability of the ordered form as measured by its melting temperature at neutral pH, is a monotonic function of the quantity pHm – pK, where pHm and pK are the pH of melting and the monomer base pK, both measured under similar conditions of temperature and ionic strength. For the transition from double helix to coil, the dependences of Tm and dTm/d log M on pH are determined experimentally and compared with the qualitative predictions of the theory. It is found that dTm/dlog M, a measure of – ΔF̄el (the negative of the electrostatic free energy change in the transition), decreases with increasing pH. In acid solution, where the coil is more extensively prolonated than the helix, the change in electrostatic free energy in the transition is larger than at neutral pH. Conversely, in alkali the electrostatic five energy change is smaller than at neutral pH. Hence (dTm/d log M)acid > (dTm/d log M neutral) > (dTm/d log M)alkali. At Suffeciently high pH, dTm/d log M is observed to become negative, indicating that the electrostatic free energy change is positive in the transition of this region. Date from the literature on the ionic strength dependence of the melting temperature for the acid helices of poly rA, poly rC, and poly dC are also considered from the standpoint of the theory.