bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ferromagnetic order in the sulfur‐containing nitronyl nitroxide radical, 2‐(4‐thiomethyl)phenyl‐4,4,5,5‐tetramethylimidazoline‐l‐oxyl‐3‐oxide, NIT(SMe)Ph
Authors: Caneschi Andrea , Ferraro Fabrizio , Gatteschi Dante , le Lirzin Antoine , Novak Miguel A. , Rentschler Eva , Sessoli Roberta 
Published: December 2004

Low‐temperature magnetic measurements on powdered samples of the title nitronyl nitroxide radical (see figure) are reported. Evidence for ferromagnetic order with a Tc of ca. 0.2 K is found. It is proposed that the diffuse electronic cloud of the sulfur atom in the radical substituent generates sufficiently strong ferromagnetic interactions even at large distances. magnified image
Lateral deposition of polypyrrole lines over insulating gaps. Towards the development of polymer‐based electronic devices
Authors: Kranz Christine , Ludwig Markus , Gaub Herrmann E. , Schuhnrann Wolf Gang 
Published: December 2004

Molecular wires connecting gold electrodes separated by a 100 μm insulating gap (see Figure) have been produced using a novel method for the microstructured deposition of polypyrrole lines on conducting substrates. The scanning electrochemical microscope used to deposit the lines is described and a microelectrochemical transitor produced using the technique presented. magnified image
Graphene in 3‐dimensions: Towards graphite origami
Authors: Ebbesen Thomas W. , Hiura Hidefumi 
Published: December 2004

The systematic construction of graphite structures (for example see Figure and Cover picture) is within reach. These structures are formed accidentally on the surface of HOPG graphite due to the friction exerted by the tip of an atomic force microscope but could also be designed “to order”. The origin of the structures and various approaches for their design are discussed. magnified image
Electrophoresis of DNA. I. On a relationship between electrophoresis and donnan equilibrium experiments on DNA
Authors: Ross Philip D. 
Published: December 2004

AbstractA calculation based upon Gorin's equation for the electrophoresis of a rigid cylinder is used to compare the available results of electrophoresis and membrane equilibrium experiments on DNA. The distribution of chloride ions across a membrane impermeable to DXA is considered. For a reasonable choice of parameters, agreement within about 2% is obtained between the values calculated from electrophoresis and the results of membrane equilibrium studies over a twenty‐fold range of NaCl concentration.
Effect of glucosylation on sedimentation velocity of DNA from T2 and T6 coliphages
Authors: Davison Peter F. , Freifelder David 
Published: December 2004

AbstractIn order to study the effect of glucose substitution on the sedimentation velocities of the T‐even phage DNA's, T2 and T2*, and T6 and T6* bacteriophages were grown with H3and P32 labeling. Zone sedimentation of the DNA's isolated from these phagea showed that the glucosylated DNA's from both T2 and T6 sediment faster than the nonglucosylated molecules. Nonglucosylated DNA from TG and T2 phages sedimented with the same velocity, suggesting that the molecules of these phages are of the same length.
Electrical and hydrodynamical properties of polypeptides in solution. I. Poly(L‐glutamic acid) in methanol‐water mixtures
Authors: Matsumoto Mitsuhiro , Watanabe Hiroshi , Yoshioka Koshiro 
Published: December 2004

AbstractThe electric birefringence of poly(L‐glutamic acid) (PLGA) in methanol–water mixtures has been measured by the use of the rectangular pulse technique at 25°C. The permanent dipole moment, the anisotropy of electrical polarizability, and the optical anisotropy factor of PLGA in solution were obtained from the dependence of the steady‐state birefringence on the electric field strength. Further, the mean length of PLGA in solution was calculated by a parameter method developed for analyzing the decay curve of electric birefringence. The permanent dipole moment per unit length obtained from these studies was 2.96, 2.48, 2.30, 2.66 D/Å in pure methanol, 10, 30, and 50 vol‐% water, respectively. The increase of water content caused the decrease of the mean length and broadened the length distribution of PLGA. These results are discussed in relation to the viscosity and the electrical conductivity of PLGA solutions.
Deoxyribonueleate solutions: Sedimentation in a density gradient, partial specific volumes, density and refractive index increments, and preferential interactions
Authors: Cohen Gerald , Eisenberg Henryk 
Published: December 2004

AbstractDensity increments (∂ρ/∂c2)°μ in solutions of NaDNA in NaCl and CsDNA in CsCl were determined over a wide range of salt concentrations; calf thymus DNA, fragmented by sonic irradiation to a molecular weight of 4–6 × 105 was used. The partial specific volume v̄2° of NaDNA at 25°C was found to ho 0.500 ml/g in water, and that of CsDNA 0.440 ml/g. Both values increase with increasing NaCl and CsCl concentration. Refractive index increments under various experimental conditions were also determined. The relevance of the density increments (at constant, chemical potential of diffusible solutes) to equilibrium sedimentation in a density gradient and the evaluation of molecular weights is discussed. Distribution coefficients of diffusible components, sometimes referred to as preferential solvation or net hydration, were derived from the density increments and partial volumes and compared with direct experimental results, whenever available, from membrane distribution and isopiestic distillation. The thermo‐dynamic significance of the distribution coefficients as well as possible interpretations in terms of specific molecular mechanisms are considered.
Mechanochemical melting of collagen fibers. I. Mechanical contractions
Authors: Yonath J. , Oplatka A. 
Published: December 2004

AbstractThe correlation between mechanical and chemical Processes in the contractile system collagen fibers–aqueous KCNS sulutions was investigated. Melting and contraction of the fibers were induced by applying a force sufficiently high as to prevent melting in a KCNS solution and then decreasing it either suddenly, or continuously at a constant rate. The kinetics of both processes are characterized by an initial rapid elastic response of the crystalline collagen, followed by a stationary region. The force–velocity relationship in this region was found to be the same under different types of mechanical deformations. It is probable that under the prevailing conditions, the behavior in the stationary state is determined by the melting process and is not markedly influenced by diffusional changes. Part of the experimental data could be explained by assuming a linear, rigid model or, better, by taking into account the highly elastic properties of the amorphous collagen. The kinetic, unit seems to be composed of several hundred amino acid residues.
Mechanochemical melting of collagen fibers. II. Diffusion‐controlled contractions
Authors: Oplatka A. , Yonath J. 
Published: December 2004

AbstractCollagen fibers were contracted “chemically,” i.e., by transferring them from water into KCNS solutions either isometrically or isotonically. Both changes in force and fiber length and in salt and water contents were measured as functions of time. The mechanical changes were found to follow the diffusional processes. The diffusion of water exhibited a plasmolytie effect. The role of water in the melting process is discussed.
Specific heat studies of various wool–water systems
Authors: Haly A. R. , Snaith J. W. 
Published: December 2004

AbstractMeasurements of specific heat of wool‐water systems were made at approximately 5°C intervals over the temperature range −70 to 100°C. Ten different, samples were used, each with a different amount of absorbed water in the range from dry ness to saturation at 0°C. The graph of specific heat against temperature for dry wool is precisely linear over the complete temperature range, suggesting that thermal motion is entirely vibrational. When absorbed water is present the data can be conveniently discussed in terms of behavior below and above an amount of absorbed water of 22.7 g in 100 g of wool (22.7% of absorbed water). Below 22.7% there is only one temperature range in which the results indicate an appreciable transition in heat absorbing properties. The temperature of transition depends on water content but is higher than 0°C. Above 22.7% a second transition appears in the range −30 to 0°C and grows rapidly larger with increase of water content. The first transition is tentatively ascribed to a slightly cooperative breakdown of polar bonds in wool, and the second to a process analogous to melting in the absorbed water. The results are discussed in these terms as well as with reference to specific heat theories, the heat absorption of the wool component and the water component, and enthalpy differences between the various samples.
Preparative fractionation of lignin by gel‐permeation chromatography
Authors: Kirk T. K. , Brown W. , Cowling E. B. 
Published: December 2004

AbstractThe combination of an agarose gel (Bio‐Gel A) and a dioxane–water (1:1) solvent system allowed the fractionation, on a preparative scale, of a very polydisperse, non‐derivatized lignin preparation (enzymatically liberated lignin prepared from sweetgum sapwood with Lenzites trabea). Three fractions differing markedly in molecular weight were obtained. A gel of crosslinked alkylated dextran (Sephadex LH‐20) with the same solvent system allowed division of the lowest molecular weight fraction into two fractions. These materials were characterized by measurements of intrinsic viscosity and number‐average molecular weights in dimethylformamide and dioxane–water. It was established that the two highest molecular weight fractions were associated in an average trimeric form in dioxane‐water (1:1) as compared to the form (considered to be molecular) that occurred in dimethylformamide. Molecular size distributions and eluant volumes of the fractions were determined with a Sephadex G‐100–formamide system, the latter being one of the most powerful nonaqueous solvents for lignin. Adsorption effects were known to be absent in this case, and the lignin molecules were considered to be unassociated in formamide. The four fractions were distinguishable with the formamide–G‐100 system, thus indicating that the original fractionation was based on molecular size. The enzymatically liberated lignin contained molecules that comprised a continuum of molecular weights from approximately monomeric to molecules that were at the limit of the solvating power of dioxane–water (1:1) and dimethylformamide. Limited physicochemical data were consistent with a compact, approximately spherically symmetric shape of the lignin in solution.
Experimental thermodynamics of the helix–random coil transition. II. Calorimetric measurement of transition enthalpies of poly A in acid aqueous solution
Authors: Klump H. , Ackermann Th. , Neumann E. 
Published: December 2004

AbstractThe enthalpy change accompanying the double helix–coil transition of polyriboadenylic acid (poly A) in aqueous solution has been measured optically and calorimetrically in the pH range 5.7–4.5. The course of this cooperative transition was followed optically by measuring changes in ultraviolet absorption as a function of temperature at different pH values, and calorimetrically by determining the heat capacity of the solution through the transition region. From the latter measurements, the enthalpy of transition was calculated. It is shown, that ΔH is dependent on pH as it is expected from the influence of protonation of the double helix of poly A.
Potentiometric titration of polyelectrolytes having stiff backbones
Authors: Muroga Yoshio , Suzuki Kazutoshi , Kawaguchi Yoshikazu , Nagasawa Mitsuru 
Published: December 2004

AbstractThe potentiometric titration curves of carboxymethylcellulose, which has a relatively stiff backbone, and also of poly(D‐glutamic acid) in the helical region are compared with the theoretical curves calculated assuming that the polyions are rods and have smeared charges on their surfaces. For carboxymethylcellulose good agreement is observed when its charge density is high, whereas as the charge density decreases the calculated curves deviate from the observed ones. The main reason for the disagreement at low charge densities may be attributed to the flexibility of the polymer backbone. For helical poly(D‐glutamic acid) satisfactory agreement between calculated and observed curves is found if a radius thicker than the realistic radius is employed. The reason for the excessively large radius may be attributed to the inapplicability of the smeared charge model.
The nucleic acid distribution function: Evaluation of the loop closure probability
Authors: De Lisi Charles 
Published: December 2004

AbstractWe present a detailed theoretical study of nucleic acid distance distribution functions for chain lengths up to thirty‐five nucleotides. The distribution functions were found by the Monte Carlo techniques described previously and, where they are symmetric, by reconstruction from their even moments. A comparison of the two approaches allows an assessment of the utility of expansion procedures for stiff chains (C∞ ≈ 17), as a function of length and extension. It was found that for chains with fewer than fourteen nucleotides over seventy even moments were required to obtain a reliable function for extensions R ≥ (〈R2〉)1/2. On the other hand at thirty‐five nucleotides the first ten even moments were sufficient to reconstruct the distribution for all but extreme extensions.The other feature of the calculation is the prediction of a loop weighting function. It was found that for a thirty‐five nucleotide chain, the form of the distribution function is very nearly gaussian for R < (〈R2〉)1/2. Consequently a loop weighting function based on detailed crystallographic data is now known for all values of N. The first derivative of the function is within 8% of the Jacobson‐Stockmayer value at 170 nucleotides, but differs severely from the latter for chains with less than twenty nucleotides.
Effects of deuterium on the thermal stability of the poly A–poly U helix.
Authors: Klump H. 
Published: December 2004

AbstractThe effect of deuterium on the thermal stability of the polynecleotide double helix formed by the homopolymers polyadenylie acid (poly A)and polyuridylic acid (poly U)has been invertigated by measuring the best capacity as a function of temperature in an automatic scanning adiabatic calorimeter. Hydrogen‐bounded and deuterium‐bonded helical conformations of the polynecleotides used have been melted in H2O and D2O2 respectively, as solvent. Within the limits of experimental error, there is no dfference in the measured enthallpy change accompanying the helix‐random coil transition. The enthalpy change ΔH is 6.6 Kcal/MBP ub any case. The half‐conversion temperatures Tm differ by two degrees. Tm for poly (AU) in H2O is 45.8°C, Tm for poly (AU) in D2is 47.7.°C.
Volume effects in aqueous solutions of macromolecules containing non‐polar groups
Authors: Bøje Lars , Hvidt Aase 
Published: December 2004

AbstractSpecific volumes at 25° of aqueous solutions of poly(N‐methyl acrylamide) and poly‐(ethylene oxide) have been measured, and the data obtained is compared with corresponding data on low‐molecular‐weight compounds. The results support the notion, that the volume changes following the interaction between aliphatic groups and water are positive. They are discussed with particular reference to pressure effects on protein conformations.
Electrical properties of hydrated collagen. I. Dielectric properties
Authors: Tomaselli V. P. , Shamos M. H. 
Published: December 2004

AbstractThe effect of water on the low‐frequency (102‐105 Hz) complex permittivitv of native, sold‐state collagen has been investigated experimentally. Measurements at ambient temperature show that dry collagen exhibits essentially no frequency or temperature dependence. As water is absorbed, both dielectric constant and loss factor increase simultaneously and rise sharply upward at a hydration level which may be associated with the completion of the primary absorption layer as determined from independent water absorption studies. The behaviour is qualitatively identical to that observed for other proteins and related materials.Temperature‐dependent measurements made under vacuum conditions in the range −196°C to +100°C are characteristic of the dielectric properties of the water in the sample. Dehydration produced by successive temperature recycling to the maximum temperature effectively eliminates any temperature or frequency dependence. A maximum in the temperature‐dependent curves is found at about +40°C and is explained as the superposition of two processes: (1) the transition of water molecules from bound to free states, and (2) the difffusion of water molecules out of the system.The dielectric constant of dry collagen, after desorption at ambient temperature, is about 4.5. Desorption at elevated temperatures reduced the room temperature value to about 2.3 and the liquid nitrogen temperature value to a number indistinguishable from the optical value of n2 = 2.16.
A dihedral angle‐vicinal proton coupling constant correlation for the α–β bond of amino acid residues
Authors: Kopple Kenneth D. , Wiley Gary R. , Tauke Ralph 
Published: December 2004

AbstractA coupling constant‐dihedral angle correlation for the HCαCβH system of amino acid residues in peptides has been derived from a set of model compounds covering the full range of dihedral angles. The expression obtained, J = 11.0 cos2 θ −1.4 cos θ + 1.6 sin2θ, is close to those already used in pmr studies of peptide conformation, and provides a firmer foundation for them. A factor limiting the precision of this and other “Karplus relations” is illustrated.
Anomalies in sedimentation. I. Stability theory of sedimenting entanglements in the “tight‐bending” limit
Authors: Goldstein Byron , Zimm Bruno H. 
Published: December 2004

AbstractA simple model is introduced to investigate the stability of a sedimenting entanglement. The sedimenting entanglement is represented by a sedimenting sieve. Solvent can pass through it, but single‐chain molecules that flow into it become entangled and their flow decreases or, if permanent entanglements form, ceases entirely. With this model we are able to find the conditions under which the mass of a sedimenting entanglement remains constant, grows or decays to a stable value, grows beyond limit, or decays to the mass of a single chain. The theory is applied to the sedimentation of small concentrations of large chain molecules in solutions of small chain molecules in solutions of small chain molecules for the case in which the entanglements are long‐lived. Equations are derived which, (1) give the stable entanglement mass as a function of rotor speed and concentration and, (2) for a given concentration predict the rotor speed at which the entanglement mass grows without limit. Numerical results for small concentrations of T2 DNA sedimenting in solutions of T7 DNA are presented.
Anomalies in sedimentation. III. A model for the inherent instability of solutions of very large particles in high centrifugal fields
Authors: Schumaker Verne N. , Zimm Bruno H. 
Published: December 2004

AbstractSedimentation, diffusion, and hydrodynamic interaction are included in a simplified model for the behavior of a solution macromolecules in a centrifugal field. The model is simulated by a program on a digital computer. As the diffusion coefficient is allowed to decrease, the simulation shows that the molecules tend to cluster in high centrifugal fields. The clusters move through the solution in the direction of sedimentation in a wave‐like fashion, acquiring new molecules at the front and shedding old ones to the rear. It is suggested that this tendency to cluster could account for the loss of DNA and other very large molecules from solution which is observed to occur at high centrifugal fields.
Flow properties of high‐molecular‐weight DNA solutions: Viscosity, recoil, and longest retardation time
Authors: Massa D. J. 
Published: December 2004

AbstractViscosity η, recoil Γ, and longest retardation time τ1R were measured for buffered aqueous solution of T2 DNA (M = 1.3 × 108) and cell lysattes of Bacillus subtiles W23 (DNA M = 2 × 109) as a function of concetration, shear stress σ, and time of shear t, using a cartesian‐diver‐suspended couette flow system. For the T2 solution, η decreased with increasing σ, Γ(t) going through a maximum with t. For the B. subtiles lysates, the preponderant rheological component of which is chromatin DNA, above a critical σ, the η, Γ(t), and τ1R increased t over 15 to 45 minutes duration to values up to several times larger, indicating the formation of intermolecular aggregates. The onset of such effects and their significance in th e measurement of molecular properties by hydrodynamic means is disscussed.
The optical rotatory properties of poly‐γ‐D‐glutamic acid
Authors: Marlborough D. I. 
Published: December 2004

AbstractMeasurement of the optical rotatory dispersion spectra of poly‐γ‐D‐glutamic acid (obtained from Bacillus anthracis) dawn to 200 nm wavelength reveal difference between the unionized and ionized froms. The profile of the unionized polyacid shows similarities to those obtained for α‐helical polypeptides, although with displaced frequencies of the respective maxima and minima. It is suggested that the relative position and magnitudes of the Cotton effect are consistent with a helical structure such as proposed by Rydon (J. Chem. Soc., 1964, 1328). The optical rotatory dispersion spectrum of the ionized from resembles those obtained from the β‐chain from of α‐L polypeptides. From model‐building studies an extended chain similer to the β‐from would seen the most reasonable structure for the ionized poly‐γ‐acid to adopt, since the charged groups in such a conformation would be at their maximal distances from each other. Such an ordered structure for a polymer is consistent with the hypotheses put forward in the recent literature that charged polypeptides adopt ordered rather than random‐coiled conformations.
Induced circular dichroism of DNA–dye complexes
Authors: Lee Cheng H. , Chang Chiang‐Tung , Wetmur James G. 
Published: December 2004

AbstractThe binding of methylene blue, proflavine, and ethidium bromide with DNA has been studied by spectrophotometric titration. Methylene blue and proflavine or methylene blue and ethidium bromide were simultaneously titrated by DNA. The results indicate that all of these dyes compete for the same bindine sites. The binding properties are discussed in terms of symmetry.The optical properties of the dye–DNA complexes have been studied as a function of DNA/dye ratio. The induced circular dichriosm due to dye–dye interaction was measured at low dye/DNA ratios for cases involving both the same dye and different dyes. A positive Cotton effect for DNA–proflavine complex may be induced at 465 mμ by eithr proflavine or ethidium bromide, whereas a netgative Cotton effect at 465 mμ may be induced by methylene blue. The limiting circular dichroism, with no dye–dye interaction, and the induced circular dichroism spectra are discussed in terms of symmetry rules.