bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ring‐opening polymerization of metallocenophanes
Authors: Manners Ian 
Published: December 2004

AbstractThe development of processable high molecular weight polymers with skeletal transition metal atoms represents a synthetic challenge that, if overcome, can be expected to yield a variety of materials with novel electrical, optical, magnetic, or preceramic properties. Recent work has shown that the ringopening polymerization (ROP) of strained, ring‐tilted [11]‐ or [2] metallocenophanes provides a route to a variety of welldefined, ferrocene‐backbone polymers with molecular weights of over 1000000 in several cases.
Efficient luminescence from zeolites
Authors: Kynast Ulrich , Weiler Volker 
Published: December 2004

Zeolites as potential luminescent materials is a subject that has received little attention previously. The optical properties–UV emission and reflectance/absorbance spectra–of zeolites X and Y prepared with various degrees of Ce doping are described and an interpretation of the results is proposed based on the occupation of the various zeolitic coordination sites (see Figure). magnified image
Morphology‐dependent spectroelectrochemical behavior of pbs nanoparticulate films grown under surfactant monolayers
Authors: Tian Yongchi , Wu Changiun , Kotov Nicholas , Fendler Junos H. 
Published: December 2004

Template‐dependent epitaxial growth of lead sulfide nanoparticulate films leads to three different morphologies, one of which is shown in the Figure. It is demonstrated that these structural differences are reflected in the spectroelectric, electric, and electrochemical properties, which is a step towards developing new colloid‐chemical techniques for fabricating nanoparticulate‐film‐based semiconductor devices. magnified image
Self‐assembling phospholipid tubules
Authors: Schnur Joel M. , Shashidhar Ranganathan 
Published: December 2004

Lipid‐based tubules serve as models for the development of advanced materials based upon molecular self‐assembly. The processes by which tubules are formed and how they are coated with metals (nickel in the Figure) or used as templates in order to increase the strength of the final material are described. Their electrical and magnetic properties are discussed. magnified image
Molecular arrangement and thermal reorganization of merocyanine J‐aggregate monolayers on solid substrates
Authors: Wolthuus Lydia , Gnade Michael , Möbius Dietmar 
Published: December 2004

Amphiphilic merocyanine dyes form J‐aggregates at the air–water interface. For any application the thermal behavior of the monolayers in an important issue and hermally induced phase transitions in monolayers have been intensively studied. Langmuir–Blodgett monolayers of two merocyanine dyes mixed with matrix molecules (see figure) have been examined and the optimization of the thermal stability of such systems discussed. magnified image
Microstructure of block copolymer reinforced interfaces observed with frictional force microscopy
Authors: Jandt Klaus D. , Dai Chi‐An , Krämer Edward J. 
Published: December 2004

The microstructure of block copolymer‐reinforced interfaces of homopolymers has been studied by frictional force microscopy (FFM). The FFM micrograph in the Figure shows details, e.g., lamellar branching, of a poly(styrene)/poly(2‐vinylpyridine) (PS/PVP) homopolymer interface reinforced with a PVP–PS–PVP triblock copolymer. An explanation for the need to “develop” the FFM image is proposed and the advantages of FFM over TEM are discussed. magnified image
Technology‐transfer analysis of the materials research program “Matfo”
Authors: Preusser Steffen , Bremer Franz‐Josef 
Published: December 2004

AbstractThe commercial success of the German Federal Ministry's materials research program “Mafto” (1985–1994) was recently evaluated to determine the effectiveness of the direct‐funding model in supporting innovative industrial research. Based on the results of a questionnaire, where a 97% return rate was achieved, it was found that the results obtained in 27% of the projects have already been commercialized to some degree, for 26% of the projects a commercialization of the results is planned but has not yet taken place, and for 54% of the projects no commercialization is planned. This study included only projects where at least four years had elapsed since project completion. The reasons why scientifically and technically successfully projects were not commercialized were also surveyed.
Switchable smectic C* main chain liquid crystalline polymers
Authors: Sierra Teresa , Omenat Ana , Barberá Joaquìn , Serrano José Luis 
Published: December 2004

Main chain liquid crystalline polymers (MCLCPs) are the basis of a number of high‐performance polymeric materials, examples being Kevlar and Vectra. For optical and electro‐optical applications, side‐chain LCPs have attracted much interest since their behavior is similar to low molecular weight LCs. Here, a ferroelectric MCLCP (see Figure) is reported. magnified image
Electrophoresis of DNA. II. Specific interactions of univalent and divalent cations with DNA
Authors: Ross Philip D. , Scruggs Robert L. 
Published: December 2004

AbstractThe effect of small quantities of metal ions on the electrophoretic mobility of calf thymus DNA in solutions maintained at 0.2 ionic strength with weakly interacting (CH3)4N+ ions yields information about interactions occurring in a region very close to the polymer chain. By means of this technique, it is demonstrated that the binding order to DNA is Li+ > Na+ > K+ for the alkali metal ions and Mn++ > Mg ++ > Ca++ for the divalent ions studied. The quantitative details are compared to earlier work on the long‐chain polyphosphates. Close agreement between the two systems is obtained indicating that an intrinsic property of individual phosphate groups is being observed and that minor discrepancies probably arise from secondary factors. Three types of stability constants representing the binding of alkali metal ions to DNA are calculated and although differing in absolute magnitude, they all satisfactorily represent the result that the order of interaction is Li+ > Na+ > K+ with respective relative strengths of 1.5 : 1 : 0.8.
Properties and modifications of a cryomacroglobulin possessing cold agglutinin activity
Authors: Deutsch H. F. 
Published: December 2004

AbstractThe physical properties of a pathological γM‐globulin with cold agglutinin activity and cryoglobulin solubility could be modified by changes in temperature and pH and upon dilution. The type of changes noted appear to simulate those expected in a readily dissociable antigen‐antibody complex. Naturally occurring and chemically produced subunits of the γM‐globulin and Fc‐fragments of myeloma proteins diminished the cryoproperty of the γM‐globulin and effected changes in its physical properties but did not alter its cold agglutinin activity. Cryoglobulin properties could be conferred upon some purified γM‐globulins by reacting them with Fc‐fragments. Mercaptan dissociation of the Cryomacroglobulin produces subunits with loss of the noted activities. Reaggregation of these subunits restores some of the native properties, but variable results which are dependent on the type of mercaptan employed are obtained. Attempts to explain the cold agglutinin activity of γM‐globulin hybrids containing variable amounts of mercaptan‐produced active and inert subunits suggest that activity requires two of the five subunits to be derived from the γM‐cold agglutinin and to be adjacent to each other.
Determination of diffusion coefficients by spreading from thin layers
Authors: Polson A. , Parkyn D. G. 
Published: December 2004

AbstractTwo new methods for the measurement of diffusion coefficients were introduced. In the first method the spreading is measured from a. thin layer in a cylindrical tube containing a suitable gel. To avoid convection in the gel the tube is rotated horizontally round its long axis. In the second method the diffusion spreading is measured from an initial thin layer under a column of solvent in a Tiselius electrophoresis cell or a micro cuvet of a spectrophotometer. The great advantage is the economy on the material investigated.
Intrachain potential energy of the α‐helix and of a coiled coil strand
Authors: Tarry D. A. D. , Suzuki E. 
Published: December 2004

AbstractA comparison has been made of the intrachain potential energy of an infinite straight α‐helix of poly‐L‐alanine with that of the distorted form adopted in a coiled coil conformation. The energy terms included were the van der Waal's, electrostatic, hydrogen‐bond, and the rotational potential terms. The results indicate that the potential energies of the structures investigated are almost the same, and so a transformation from one state to another may occur without significant changes in potential energy. Particular care has been taken to ensure that the electrostatic and van der Waal's interaction terms are fully convergent. The values obtained for the α‐helix were compared with those already published, and some significant differences were found.
Structure of β‐chitin or parallel chain systems of poly‐β‐(1→4)‐N‐acetyl‐D‐glucosamine
Authors: Blackwell J. 
Published: December 2004

AbstractThe structure of β‐chitin has been reexamined in an X‐ray diffraction study of the highly crystalline material available from pogonophore tubes. Oriented specimens were prepared by suspending the dispersed deproteinized tube in a fibrin clot which was then stretched into an oriented fiber. The X‐ray diffraction patterns of pogonophore β‐chitin were explained by proposing that this material consists of a mixture of two structural phases which have been named β‐chitins A and B. This view was confirmed by the preparation of specimens which gave only the diffraction pattern of the A phase by treating the tubes with diaphanol. Both A and B phases gave rise to a series of hydrate structures. The lowest hydrate of β‐chitin A has been studied in detail and shown to consist of an anhydrous system of parallel chitin chains. For this form, the unit cell was monoclinic with dimensions a = 4.85 Å, b = 10.38 Å (fiber axis), c = 9.26 Å, and β = 97.5°, and space group P21. Reasonable agreement was obtained between the observed X‐ray intensities and those calculated for such a structure. Examination of the β‐chitin of Loligo pen and diatom spines showed that these materials also consist of these A and B phases.
Relation of amino acid composition and the moffitt parameters to the secondary structure of proteins
Authors: Goldsack D. E. 
Published: December 2004

AbstractA statistical analysis of the relation between the amino acid composition of proteins and the amount of helical secondary structure as characterized by the Moffitt b0 parameter has shown a high degree of correlation of the b0 parameter with those amino acids whose homopolymers can form helical structures. Using the data for 107 proteins, a linear relation was found between b0 and the sum of the residue percentages of alanine, arginine, aspartic acid, cysteine, glutamic acid, leucine, andlysine. A statistical analysis of the Moffitt a0 parameter, on the other hand, showed no statistically significant grouping of amino acids in relation to the amount of secondary β structure in a protein. A plot of b0 versus a0–a, where a represents the a0 parameter for a fully denatured protein, for 55 proteins showed distinct nonlinearity. This nonlinearity was postulated to be due to presence of β structure, and a nomagram was constructed which allowed a semiquantitative estimate of the amount of helical and β‐type secondary structures from the b0 versus a0–a plot.
Helix–coil transition in poly(γ‐benzyl‐L‐glutamate) and poly‐ε‐carbobenzoxy‐L‐lysine
Authors: Cortijo M. , Roig A. , Blanco F. Garcia 
Published: December 2004

AbstractIn this paper two points are considered: the methods of evaluating the helical content θ and the calculation of the parameters of the transition from experimental data and its interpretation. The parameter ΔH obtained is in good agreement with the calorimetric one and v is found to be independent of temperature and solvent and in agreement with the ordinarily accepted value for poly(γ‐benzyl‐L‐glutamate). The different methods of estimating θ are discussed for both polypeptides.
Early time expansions for sedimentation of weakly nonideal solutions
Authors: Nossal Ralph J. , Weiss George H. 
Published: December 2004

AbstractAn expansion valid for short times is presented for the rectangular approximation to the Lamm equation when the sedimentation coefficient can be expressed as s = S0(1−kc). The expansion allows the study of meniscus perturbations on the Faxén approximation, as well as a determination of when reflections from the base become significant.
Local effects of partial adenine‐N1‐oxidation on poly A · poly U and poly A · 2 poly U helix conformations
Authors: Fink T. R. , Crothers D. M. 
Published: December 2004

AbstractWe prepared helices with noncomplementary bases by N1‐oxidation of poly A, followed by reaction with poly U. Mixing curves indicate that doubly and triply helical structures form, with only the unmodified adenines involved in base pair formation. Circular dichroism spectra were examined particularly at the absorbance maximum of the adenine N1‐oxide (A*). In the single strand poly (A,A*), there is a relatively strong pair of positive and negative CD bands from the A*. These are greatly reduced in the double helix, and abolished in the triple helix. We conclude that A* stacks in a conventional manner with A in the single strand, but is rotated out of the double and triple helix. In the double helix the A* probably maintains a preferred orientation with respect to the helix, but rotates randomly in the triple helix.
The dichroism of DNA in electric fields
Authors: Ding Da‐Wen , Rill Randolph , Van Holde K. E. 
Published: December 2004

AbstractWe have studied the dichroism of various samples of calf thymus DNA (of molecular weight from 3 × 105 to 7 × 106) in pulsed electric fields. The results may be summarized as follows:

We find that calf thymus DNA behaves in electrical orientation as if it possessed a large permanent dipole moment. This apparent moment is sensitive to such effects as Mg++ binding which lower the net charge on DNA.
The limiting dichroism at infinite field corresponds to an angle of at least 80% between the transition moments at 265 nm and the helix axis, and could be consistant with a number of known forms of DNA. This result is independent of DNA molecular weight. There is evidence that the conformation may be different in 80% ethanol.
The dichroism relaxation curves contain a component with a relaxation time of about 8 μsec, which is nearly independent of molecular weight, and a longest component which behaves either according to the Broersma theory for low‐molecular‐weight samples, or the Zimm‐Rouse theory at high molecular weights.
Conformational analysis of substituted pyrrolidones
Authors: Schellman John A. , Lifson Shneior 
Published: December 2004

AbstractConsistent force‐field calculations were performed on a series of methyl substituted pyrrolidones. Methyl substitution enhances the non‐planarity of the pyrrolidone ring in a way wich varies with the position of the substituent. The effect of ring distortion is to produce skeletal contributions to the rotatory strength of the nπ* transition of the amide group. Depending on position of substitution, these reinforce or oppose the substituent contribution to optical activity. There is favorable agreement between the conformational calculations and the quadrant rule for the optical activity of the nπ* transition of the peptide chromophore.
Melting studies on spin‐labeled polyadenylic–polyuridylic complexes
Authors: Pan Yu‐Ching E. , Bobst Albert M. 
Published: December 2004

AbstractTemperature‐dependent conformational transitions of spin‐labeled poly rA, spin‐labeled poly rU and the two‐stranded helical complexes consisting either of spin‐labeled rA·poly rU or spin‐labeled poly rU·poly rA have been measured by electron spin resonance spectrocopy. The polynucleotides were spin labeled with 4‐(2‐iodoacetamido)2,2,6,6‐tetramethylpiperidinooxyl and the spin label to nucleotide base ratio was approximately 1:600. The relationship between the log of tumbling time τ and the reciprocal absolute temperature for the spin‐labeled single and double‐stranded polynucleotides is presented. An agreement between TmOD (optical density melting) and Tmsp (spin melting) is found for the complexes, which strongly supports the conclusion that the same temperature‐dependent structural changes are monitored with both techniques.
Theoretical optical properties of poly‐L‐proline
Authors: Tterlikkis L. , Loxsom F. M. , Rhodes William 
Published: December 2004

AbstractA non‐perturbational technique is used to calculate the circular dichroism and absorption spectra of polypeptide chains having conformations similar to that of poly‐L‐proline II. The method employs a Bogoliubov exciton formalism, from which the various optical terms associated with parallel and perpendicular components of the exciton band are obtained. A simple model for the peptide unit, consisting of three Gaussian absorption bands, leads to reasonable results for the polymer spectra, provided the lowest energy peptide π → π* transition is taken at 207 mμ and the value of the Ramachandran angle Ψ is taken to be 390°. The calculations suggest that the polymer circular dichroism spectrum is the resultant of strong interference among the two Gaussian exciton terms and the non‐Gaussian helix term. Consequently, the CD spectrum is very sensitive to the value of Ψ. It is found that the small positive CD band in the vicinity of 230 mμ arises partly from the effect of the static (crystal) field interactions on the n → π* CD band.
A temperature‐jump kinetic study of the binding of proflavine to poly I·poly C
Authors: Steenbergen Charles , Mohr Scott C. 
Published: December 2004

AbstractThe kinetics of interaction between proflavine and poly I.poly C at 25°C, neutral pH, and moderate ionic strength have been studied by relaxation methods. The qualitative features of this system resemble those previously reported by Crothers and co‐workers for proflavine–DNA and proflavine–poly A·poly U interactions–two relaxations are observed coresponding to a fast bimolecular step followed by a slower isomerization. These results can best be accommodated by a two‐step mechanism leading from the free dye through an “outside‐bound” complex to the intercalated complex. Quantitative comparison of the various rate constants for proflavine binding to different double‐helical polynucleotides shows that the rates are slower for both ribohomopolymer pairs than for DNA. The rates for poly I·poly C are approximately three times faster than these for poly A·poly U.
Unit fibril models derived from the molecular topography of collagen
Authors: Segrest Jere P. , Cunningham Leon W. 
Published: December 2004

AbstractThe geometrical properties of collagen molecules place certain restrictions on possible three‐dimensional packing models. With certain reasonable assumptions involving the macromolecular structure of collagen, a model for the surface topography of the monomeric unit is developed and two possible models for molecular packing, one hexagonal and the other non‐hexagonal, are inferred. The non‐hexagonal packing model is identical to the pentagonal unit fibril first postulated by J. W. Smith on different grounds, while the hexagonal model is one of three previously suggested by us on more general assumptions. The two models are compared to available data on collagen packing, and the bulk of the evidence would seem to favor the pentagonal model.
Circular dichroism of the alkyl amino acids in the vacuum ultraviolet
Authors: Snyder Patricia Ann , Vipond Prudence M. , Johnson W. Curtis 
Published: December 2004

AbstractThe circular dichroism and absorption for five alkyl amino acids as zwitterions has now been measured to 160 nm. Two bands are found, the nπ* at long wavelengths and ππ* at short wavelengths. In an effort to extract conformal information from the circular dichroism measurmenths, the circular dichroism spectra for these molecules is calculated using an independent systems apporach. It is found that the signs calculated using these methods are quite reliable, but that reliable magnitudes must await more accurate data to use in the calculations. Comparing the signs for both the measured and calculated circular dichriosm it if possible to determine the region inhabited by the carboxylate anion chromophore of these amino acid zwitterions. The greatest failure of the calculations is that thay are unable to explain the sigmoidal shape of the nπ* transition in proline. The problems facing workers trying to make calculations to relate circular dichroism measurements to conformation are discussed.
Kerr constants of amides and peptides
Authors: Ingwall R. T. , Czurylo E. A. , Flory P. J. 
Published: December 2004

AbstractMolar Kerr contants mK have been determined for N‐methylacetamide, N‐ethyl‐acatamide, N‐methylpropionamide, N‐acetylglycine‐N′‐methylamide, N‐acetyl‐L‐ala‐nine‐N′‐methylamide, and N‐acetyl‐L‐leucine‐N′‐methylamide from electric birefringence measurements on dilute solutions in dioxane. The resultes are compared with configurational averatges 〈mK〉 calculated on the basis of conformational energies. Values ofmK calculated for various fixed confromations on the peptides vary over a wide range depending on the choice of conformation; hece, the configurational averages 〈mK〉 are sensitive to smalll changes in the conformational enerey. Kerr constants are calculated for random coiled oligoglycine and oligoalanine peptides as functions of chain length. The Kerr constant is an especially acute index of the average conformation.
The circular dichroism of poly d(AAT): d(ATT) and poly r(AAU):r(AUU). A test of the first‐neighbor hypothesis
Authors: Gray Donald M. , Ratliff Robert L. , Williams D. Lloyd 
Published: December 2004

AbstractWe present absorption and circular dichroism (CD) spectra for the synthetic polymers poly d(AAT):d(AAT) and poly r(AAU):r(AAU), in both native and heat‐denatured forms. As a means of evaluating the first‐neighbor hypothesis, the CD spectra are compared with approximations derived from spectra of other synthetic polymers containing the same first‐neighbor sequences. This is the first instance where such a comparison has been possible using spectra of double‐stranded RNA sequences, and the agreement between the measured and approximated spectra for poly r(AAU):r(AUU) is surprisingly good. We have also subjected the CD spectrum of poly d(AAT):d(AAT) to a previously published analytical procedure for obtaining estimates of first‐neighbor frequencies. In this first independent test of the procedure, we find that the analysis does infer the existence of a majority (86%) of AA, TT, AT, and TA first neighbors but does not precisely indicate their relative proportions.
Surface electric potential on rod‐like polyelectrolyte
Authors: Sugai Shintaro , Nitta Katsutoshi 
Published: December 2004

AbstractThe electric potential on the surface of the rod‐like polyelectrolyte with uniform charge distribution or periodically changing charge distribution on the surface is solved numerically by use of a power series method and an electronic computer. The deviation from the Linderstrøm‐Lang's linear relation in the modified pH titration diagram, and the dependence of the surface electric potential on the radius of rod are discussed. Also, the radius of counterion and ionic strength, and the effect of non‐uniformity of charge distribution are considered. Molecular radii were determined by comparing the calculated results with the pH titration data. The molecular radii of stereoregular poly‐(methacrylic acid) and α‐helical poly(glutamic acid) were found to be 5.5 Å and 15.0 Å, respectively, assuming uniform charge distribution. If nonuniform charge distribution was assumed, the molecular radii were calculated to be 5.0 Å and 14.0 Å, respectively. These values are discussed in relation to their molecular structures.