bluuebunny/crossref_metadata_2025 huggingface dataset:
Weak ternary CT salts formed by α‐keggin polyanions and tetraphenylporphyrinato ZnII in the presence of halide ions
Authors: Attanasio Donato , Bachechi Fiorella
Published: December 2004

Molecular complexes between α‐Keggin polyanions and tetraphenylporphyrinato ZnII that are uexpectedly stable have been obtained in the presence of an ancillary donor anion such as a halide. X‐ray structure determination reveals intgrated organic‐inorganic stacks with alkyl ammonium cations acting as spacers. Development of these compounds, which combine thermally and photochemically redox active units, may lead to molecular materials with interesting electro‐and photochromic properties.
Germanium nanoclusters: Chemical vapor deposition of digermane in zeolite Y and mordenite
Authors: Dag ÖMer , Kuperman Alex , Ozin Geoffrey A.
Published: December 2004

Uniform arrays of intrazeolite germanium nanoclusters have been produced by the topotactic chemical vapor deposition of digermane within the diamond network of α‐cages of acid zeolite Y and the main channel of mordenite. The conditions within the zeolite hosts enusure that the Ge2H6 CVD‐type anchored precursors self‐assemble to produce the anchored (Ge8)n⊕ nanoclusters shown in the Figure.

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Gas sensing properties of phthalocyanine langmuir—blodgett films
Authors: Mukhopadhyay Sabarna , Hogarth Cyril A.
Published: December 2004

Ideal microsensors would be cost effetive, efficient, and stable, detect low concentrations of a certain gas in a working enviornment, and be able to operate in real time, i.e., monitor continuously. Among the compounds being ivestigated for development into microsensors are the phthalocyanines (Pcs), in particular in the form of thin films. The advantages and problems of Pc thin films are discussed, and the latest results for the detection of toluene and nitrogen oxides in air, including the response and recovery times, are presented.
Raman Scattering in C60 fullerenes and fullerides
Authors: Kuzmany Hans , Matus Michael , Burger Bernhard , Winter Johannes
Published: December 2004

Buckminsterfullerene and related systems possess a strong chromophoric character resulting from the sp2 hybridization of their valence electrons. As a result, Raman scattering can be used to reveal details of the physical properties and doping dynamics, also allowing the study of the effects of chemical modifications of these systems. Due to the high symmetry of the molecules the spectra at first appear rather simple. However, crystal field effects and general symmetry breaking conditions can also be studied.
(TMTTF)2Br: The First Organic Superconductor in the (TMTTF)2X family
Authors: Balicas Luis , Behnia Kamran , Kang Woun , Auban‐Senzier Pascale , Canadell Enric , Jérome Denis , Ribault Michel , Fabre Jean‐Marc
Published: December 2004

Superconductivity in quasi‐1‐dimensional organic conductors is shown not to be confined to the selenium‐containing (TMTSF)2X series (TMTSF = tetramethyltetraselenafulvalene). The title compound is shown to exhibit superconductivity in the 1 K range provided the spin density wave ground state is suppressed by the application of pressure, leading to conclusions about the origin of pairing strength in organic conductors.
Iron(II) octaethyltetraazaporphyrin, FeOETAP, a canted ferromagnet with Tc = 5.6 K
Authors: Conklin Brenda J. , Sellers Scott P. , Fitzgerald Jeffrey P. , Yee Gordon T.
Published: December 2004

A four‐coordinate azaporphyrin, FeOETAP (see Figure), is reported that has temperature‐ and field‐dependent properties different from those of other fourcoordinate iron(II) porphyrins and related macrocycles, displaying an apparent canted ferromagnetic state. This behavior is compared to that of M2⊕(OETAP), where M = Mn, Co, Ni, Cu, and Zn.

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Broadband dielectric spectroscopy on an oxovanadium metallomesogen compound
Authors: Jubindo Miguel A. PéRez , de la Fuente M. Rosario , Marcos Mercedes
Published: December 2004

Metallo‐organic mesogens have attracted much interest recently, with particular attention being paid to copper(II) and oxovanadium complexes because of their magnetic properties. A broadband dielectric spectroscopic study of a oxovanadium complex derived from a Schiff base is described and the results are compared with those from an EPR analysis. Consequences of the results for the dynamics are discussed.
“Tailor‐Made” and charge‐transfer auxiliaries for the control of the crystal polymorphism of glycine
Authors: Weissbuch Isabelle , Leisorowitz Leslie , Lahav Meir
Published: December 2004

Crystal polymorphism is important because of the different physical and mechanical properties of the polymorphs. Based on a stereochemical approach to controlling crystal polymorphism using stereospecific nucleation inhibitors, auxiliaries have been designed for the precipitation of the yform of glycine (see Figure) from aqueous solutions. The ideas behind this work are presented, together with results.

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Inhibition of self‐aggregation of α,ω‐docosanediol into 3D Crystallites by “Tailor‐Made” amphiphilic auxiliaries
Authors: Popoiitz‐Biro Ronit , Majewski Javek , Murgulis Lev , Cohen Sidney , Leiserovvitz Leslie , Lahav Meir
Published: December 2004

The spontaneous aggregation of the bolaamphiphile α,ω‐docosanediol into embryonic three‐dimensional crystallites at the air‐water interface can be inhibited by additives. A study with the aim of determining the necessary properties of such supplements is reported, which uses additives with molecular recognition properties and methods such as X‐ray reflectivity, cryotransmission electron microscopy, and atomic force microscopy in order to detect structural changes at the nanometer level.
Porous silicon superlattices
Authors: Frohnhoff Stephan , Berger Michael G.
Published: December 2004

Porous silicon superlattices (PSSs) are a novel type of siliconbased heterostructures, in which the porosity varies periodically with depth. The two different types of PSSs and their techniques of formation are described, as are their optical properties and an example of an application: a Fabry‐Perot‐type interference filter. In combination with light emitting porous silicon, PSSs are promising candidates for optoelectronic applications based on silicon technology.
Scheibe Aggregates
Authors: Möbius Dietmar
Published: December 2004

Scheibe agregates (J‐aggregates), highly ordered systems of strongly interacting chromophores (e.g. see figure), are characterized by a strong and narrow absorption band shifted to lower energy with respect to the band of the monomer, and a narrow resonance emission band with a very small Stokes shift. The formation of such aggregates, their organization and reorganization, their structure and their optical and photophysical properties are reviewed.

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Polymeric microcapsule arrays
Authors: Martin Charles R. , Parthasarathy Ranjani V.
Published: December 2004

Enzyme immobilization in polymeric microcapsule arrays could provide an interesting method for the development of biosensors. Produced via the template synthesis method under mild conditions, the arrays exhibit high loadings of the enzyme, provide a large surface area for enzyme–substrate contact, ad are mechanically robust. A recently developed microencapsulation method is described and the potential of these materials for furter development discussed.
Polymeric Electro‐Optic Modulators: Matereials synthesis and processing
Authors: Dalton Larry R. , Harper Aaron W. , Wu Bo , Ghosn Rima , Laquindanum Joyce , Liang Ziyong , Hubbel Andrea , Xu Chengzeng
Published: December 2004

The commercialization of new NLO materials will depend not only on the mastery of the technical problems but also on the availability of investment capital. Here, the research issues most relevant to commercialization are viewed and the advantages and disadvantages of new systems, both inorganic and organic, for example the cross‐linked thin‐film structure shown in the figure, presented and discussed.

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An oligothiophene cation radical that forms π‐stacks: A model for polaron aggregation in conducting polymers
Authors: Miller Larry L. , Yu Yuan , Gunic Esmir , Duan Robert
Published: December 2004

A new class of functional units for preparing charge transfer salts, based on π‐stacks of a conducting oligomer in analogy to the well‐known stacks of TTF units, is reported and provides a connection between CT salts and conducting polymers. The synthesis of the new water‐soluble thiophene oligomer is presented and it is suggested that π‐stacks may be present in some oxidized polythiophenes and similar polymers.
Reversible photoisomerizable monolayers for the transduction of optical signals
Authors: Willner Itamar , Willner Bilha
Published: December 2004

Bioelectronic devices based on te photostimulation of the chemical and physical properties of molecules are presented. Assemblies consisting of photoswitchable biomaterials and conducive interfaces have opened new avenues in the design of architectures for molecular devices. Photosensitive self assembled monolayers on electrode surfaces provide the means for the nanoscale design of optoelectronic systems for information storage and processing, signal amplification, and biosensor devices. Recent progress in the area is reviewed.
Three–dimensional helical supramolecules—elucidation of magnetic ordering for an antiferromagnetic phase
Authors: Decurtins Silvio , Schmalle Helmut W. , Pellaux René , Huber Reto , Fischer Peter , Ouladdiaf Bachir
Published: December 2004

A novel helical three‐dimensional supramolecular system has been investigated by neutron diffraction to determine the magnetic ordering in the antiferromagnetic phase. The representative system investigated (see Figure) is a MnII‐containing chiral network based on two types of preorganized transition‐metal complexes as complementary molecular partners that form a highly organized three‐dimensional supramolecular host–guest system.

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Golden interfaces: The Surface of Self‐Assembled Monolayers
Authors: Delamarche Emmanuel. , Michel Bruno. , Biebuyck Hans A. , Gerber Christoph
Published: December 2004

Self‐assembled monolayers (SAMs) of alkanethiols and disulfides on gold form organic interfaces with properties largely controlled by the end groups of the molecules composing the film. SAMs provide a unique link between the science of organic surfaces and technologies that seek to exploit their adaptable character. Many techniques are useful for probing the structure of SAMs although only scanning tunneling microscopy (STM) at picoamperes reveals the details of the packing of their end groups at the sub‐angstrom level. This review demonstrates that STM effectively tests new types of control over the microscopic structure–property relationships characteristic of SAMs on gold that should prove useful to their application.
4,4′,4″‐Tris(stearoylamino)triphenylamine as a novel material for functional molecular gels
Authors: Yasuda Yoshiaki , Takebe Yasuo , Fukumoto Masahiro , Inada Hiroshi , Shirota Yasuhiko
Published: December 2004

Electroactive organic molecular gels based on the title compound (see Figure) are reported along with their sol‐gel behavior and ionic conductivities, and their application as electrochromic materials is discussed. Furthermore the correlation between molecular structure and gel formation is examined in order to provide guidelines on the molecular design of gel‐forming organic materials.

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Diffusions‐NMR‐Spektroskopie in der Supramolekularen und Kombinatorischen Chemie: ein alter Parameter – neue Erkenntnisse
Authors: Cohen Yoram , Avram Liat , Frish Limor
Published: December 2004

Intermolekulare Wechselwirkungen in Lösung spielen eine wichtige Rolle bei der molekularen Erkennung und sind somit von besonderer Bedeutung in der Supramolekularen und Kombinatorischen Chemie. Die Untersuchung der molekularen Diffusion liefert Aufschlüsse über solche Wechselwirkungen, wobei sich die hochaufgelöste Diffusions‐NMR‐Spektroskopie als Methode der Wahl für die gleichzeitige Bestimmung von Diffusionskoeffizienten in einem Mehrkomponentensystem erwiesen hat. Der Diffusionskoeffizient ist dabei ein Maß für die effektive Größe und Form eines Moleküls. Zu den Anwendungen dieser Technik gehören die Abschätzung von Assoziationskonstanten, die Kartierung intermolekularer Wechselwirkungen in Mehrkomponentensystemen sowie Untersuchungen zum Aggregationsverhalten, zur Ionenpaarbildung, zur Bildung von Einschlussverbindungen und zur Bestimmung der Größe und Struktur von labilen Systemen. Mithilfe der Diffusions‐NMR‐Spektroskopie kann man aber auch Gemische virtuell auftrennen und gezielt nach Liganden für Rezeptoren suchen. Diese Methode kann so bei der Identifizierung von Leitverbindungen von Nutzen sein.
Studies on dextran and dextran derivatives. I. Properties of native dextran in different solvents
Authors: Antonini E. , Bellelli L. , Bruzzesi M. R. , Caputo A. , Chiancone E. , Rossi‐Fanelli A.
Published: December 2004

Light‐scattering, sedimentation, viscosity, and reducing power measurements have been carried out on a sample of native dextran from Leuconostoc mesenteriodes B‐512. The results are discussed in relation to the structure, polydispersity, and branching of the polysaccharide. The effect of different solvents on the behavior of native dextran has been studied. The molecular weight of the dextran remains unchanged in all the solvents used, while the radius of gyration shows a significant increase in some of them (concentrated salts, urea, and glucose solutions); in water–methanol solutions the radius of gyration slightly decreases.
The method for estimation of chain macromolecule rigidity
Authors: Golub E. I.
Published: December 2004

Birefringence relaxation times on removing the electric field characterize the rigidity of a flexible linear macromolecule structure. Electrical birefringence investigation of DNA solutions supports this view. This principal regularities displayed by relaxation times of electric birefringence decay curves in solutions of chain macromolecules are considered.
Proton magnetic resonance study of the binding of purine to polyuridylic acid
Authors: Bangerter Benedict W. , Chan Sunney I.
Published: December 2004

The interaction of unsubstituted purine with polyuridylic acid in D2O solution at neutral pD has been studied by high resolution proton magnetic resonance spectroscopy. The poly U proton resonances were shifted to higher fields by the added purine, indicating that purine binds to the uracil bases of the polymer by base stacking. Severe broadening of the purine proton resonances was also observed, providing strong evidence for the intercalation of purine between adjacent uracil bases of the polymer. The line widths of the poly U proton resonances were not noticeably broadened in the presence of purine; thus, the binding of purine to poly U does not result in a more rigid or ordered structure for the polymer.
Cesium chloride density distributions in preparative equilibrium ultracentrifugation
Authors: Rüst Peter
Published: December 2004

A computer program has been developed for calculating equilibrium centrifugation density distributions by direct integration of tabulated data, which eliminates curve fitting. Error calculations showed that a high accuracy is required for the measurement of the data needed a determine a density distribution either by computation or by direct measurements. In particular, the variation in drop size during the fractionation of the contents of a centrifuge tube have been investigated by computer simulation. A direct measurement of the drop size indicated that it may increase somewhat during collection. In addition, plots are presented of the dependence upon seven parameters of the centrifugation required to approach equilibrium to a desired degree (based on the formula of Van Holde and Baldwin).
Intrinsic viscosities of cyclic and linear λ DNA
Authors: Douthart Richard J. , Bloomfield Victor A.
Published: December 2004

The ratio of the intrinsic viscosities of the linear and circular forms of λ DNA, [η]L/[η]c, has been measured as a function of ionic strength in the range [Na+] = 0.6. M–0.03MCorrections were made for the presence of uncyclizable linear contaminant in circular preparations. By combining data in the literature on the ionic strength dependence of linear DNA of various molecular weights with that obtained here, it was possible to determine the expansion parameter εL as a function of [Na+]. εL is defined by the relation 〈L2〉 = b2N1+εL, where 〈L1〉 is the mean‐square end‐to‐end distance of a chain of N segments of length b. The empirical relation εL = 0.05 − 0.11 log [Na+] for native NaDNA at 25°C is found. When εL = 0, [η]L/[η]c extrapolates to 1.6, in good agreement with the theoretical prediction of 1.55. As εL increases, [η]L/[η]c increases, in agreement with a theory of Bloomfield and Zimm.
On the hydration of DNA. II. Base composition dependence of the net hydration of DNA
Authors: Tunis Mary‐Jane B. , Hearst John E.
Published: December 2004

The dependence of the net hydration of DNA on its base composition has been measured by density gradient ultracentrifugation of three DNA's in a series of cesium and lithium salt solutions of different water activities. Extrapolation to zero water activity showed the dependence of the partial specific volume on base composition to be very small for CsDNA and aero for LiDNA. At least 99% of the dependence of buoyant density on base composition can be accounted for on the basis of a differential hydration, with a mole of adenine–thymine pairs binding about 2 moles more water than a mole of guanine–cytosine pairs in CsCl.
Chemically reacting systems of the type A + B ⇄ AB. II. Osmometry
Authors: Adams E. T. , Pekar A. H. , Soucek D. A. , Tang L. H. , Barlow Grant , Armstrong J. L.
Published: December 2004

The osmotic pressure equation for nonideal, associating systems of the type nA +mB ⇄ AnBm, has been derived, by using the assumption yAnBm/yAnyBm = 1. This treatment can also be applied to related associations such as nA + mB ⇄ AB + AB2 + A2B + …. From osmotic pressure experiments on the pure reactants it is possible to obtain the molecular weights (MA and MB) of the reactants and also the virial coefficients (BAA and BBB) of the reactants. The osmotic pressure of a nonreacting mixture of A and B can be calculated from these measurements. It can be used along with osmotic pressure measurements on equilibrium mixtures of A and B to obtain expressions containing the equilibrium constant (or constants) and the cross‐virial coefficients (BAB and BBA). Several procedures are described for the evaluation of the equilibrium constant (or constants) and the BAB or BBA terms. It appears that this procedure is a general one which is applicable to associations of the type nA + mB ⇄ AB + A2B + AB2 + …. By correcting for nonideal behavior, one should then be able to apply it to any method available for analyzing ideal associations of the types considered here. In addition it is possible, subject to certain restrictions, to analyze associations of the type 3A + B ⇄ A2 + AB.
Effects of magnesium and formaldehyde on the sedimentation behavior of rat liver ribosomes
Authors: Petermann Mary L. , Pavlovec Amalia
Published: December 2004

When rat liver ribosomes were dissociated by removing their magnesium, the two subunits had s,w of 52.6 and 28.1 S, and appeared to be quite asymmetrical. In 4M urea they became even more elongated. On restoration of magnesium, both subunits assumed more compact forms, 57.6 and 31.7 S, but only 28% of them formed larger aggregates. After brief treatment with formaldehyde, the magnesium‐free subunits still elongated in urea, but to a lesser degree than the controls. When magnesium was restored they changed to 53.4 and 31.7 S forms, but did not, aggregate. The ribosomal subunits were also separated by reducing the bound magnesium to a low level, then adding 2.2M urea. After the urea had been dialyzed out, most of the large subunits were still in a compact form and when the magnesium concentration was increased, most of the subunits did not reassociate to whole ribosomes. Formaldehyde‐treated subunits, however, did not reassociate. Even in their most compact forms, 60.0 and 35.5 S, both subunits had high frictional ratios. The 60.0 and 31.7 S forms were assumed to be the shapes that are seen in electron micrographs of negatively stained ribosomes. Both subunits seemed to be highly hydrated. Since the large subunit appeared to contain twice as much water as the small one, it might be a structure with either a deep channel or a hollow center.
Determination of the base pairing content of ribonucleic acids by infrared spectroscopy
Authors: Thomas George J.
Published: December 2004

A method is described for determining the fractions of adenine‐uracil and guanine‐cytosine base pairs of partly double‐helical ribonucleic acids in aqueous solution. The method is based upon the ability to distinguish between paired and unpaired bases by means of infrared spectroscopy of their deuterium oxide solutions in the 1500–1800 cm−1 frequency region of the infrared spectrum. An application of the method to yeast ribosomal RNA is described. At 30°C, ribosomal RNA is 64± 6% paired (35% GC, 29% AU). The method can be applied to determine the fractions of Watson‐Crick base pairs at a given temperature in any RNA containing the four common bases in known ratios.
NMR studies in solution of poly‐L‐proline
Authors: Conti Filippo , Piatelli Massimo , Viglino Paolo
Published: December 2004

The isomerization of poly‐L‐proline in different solvents has been studied by NMR spectroscopy. Different resonance signals for the CHα protons have been obtained for the two different helical conformations of thus compound, namely form I and form II.
Spatial configurations of polynucleotide chains. III. Polydeoxyribonucleotides
Authors: Olson Wilma K. , Flory Paul J.
Published: December 2004

The virtual bond scheme set forth in preceding papers for treating the average properties of polyriboadenylic acid (poly rA) is here applied to the calculation of the unperturbed mean‐square end‐to‐end distance of polydeoxyriboadenylic acid (poly dA). The modifications in structure and in charge distribution resulting from the replacement of the hydroxyl group at C2′ in the ribose residue by hydrogen in deoxyribose produce only minor modifications in the conformational energies associated with the poly dA chain as compared to those found for poly rA. The main difference is manifested in the energy associated with rotations about the C3′–O3′ bond of the deoxyribose residue in the C2′‐endo conformation; accessible rotations are confined to the range between 0° and 30° relative to the trans conformation, whereas in the ribose unit the accessible regions comprise two ranges centered at approximately 35° and 85°. The characteristic ratio 〈r2〉0/nl2 calculated on the basis of the conformational energy estimates is ≈9 for the poly dA chain with all deoxyribose residues in the C3′‐endo conformation and ≈21 with all residues in the C2′‐endo form. Satisfactory agreement is achieved between the theoretical values and experimental results on apurinic acid by treating the poly dA chain as a random copolymer of C3′‐endo and C2′‐endo conformational isomers present in a ratio of ∼1 to 9.
Copper(II)—DNA denaturation. II. The model of DNA denaturation
Authors: Liebe Donald C. , Stuehr John E.
Published: December 2004

In a continuing study of the denaturation of DNA as brought abought about by Cu(II) ions, results are presented for the dependence of Tm and τ (the terminal relaxation time) on ionic strength, pH, reactant concentrations, and temperature. Maximum stability of the double helix, as reflected by the longest relaxation times and highest Tm values, was observed between pH 5.3 and 6.2. Outside this range both Tm and τ decreased sharply. A second, faster relaxation time was deduced from the kinetic cureves. The apparent activation energies of the rapid and slow (“terminal”) relaxations were found to be 12 and 55 kcal/mole, respectively. Several lines of evidence led to the conclusions that (1) the rate‐determining step in DNA denaturation, when occurring in the transition region, is determined by chemical events and (2) the interactions which are disrupted kinetically in the rate‐determining step are those which account for the major portion of the thermal (Tm) stability of helical DNA.
Graphical approach to non‐ideal cases of self‐associating protein systems
Authors: Chun P. W. , Kim S. J. , Williams J. D. , Cope W. T. , Tang L. H. , Adams E. T.
Published: December 2004

Our previous paper described graphical procedures for evaluating the mode of association in ideal discrete and indefinite cases. This paper concerns the application of such procedures in cases where the non‐ideality term BM1 must be considered. Bovine liver L‐glutamate dehydrogenase and lysozyme are used as model systems. Several graphical procedures for dealing with cases of 1 − m, 1 − m − n, or indefinite association are developed. The procedure is based on the evaluation of the weight‐fraction monomer with‐out prior calculation of BM1, using graphical analysis to evaluate the non‐ideality term.
Far ultraviolet optical activity of saccharide derivatives. I. Xylan and cellulose acetates
Authors: Mukherjee S. , Marchessault R. H. , Sarko A.
Published: December 2004

Optial rotatory dispersion (ORD) and Circular dichroism (CD) spectra of several β‐1,4 xylan and cellulose acetates and some of their oligomers were investigated. The CD spectra proved considerably superior in terms of information content and interpretability. Comparison of the xylan and cellulose acetate series which also included partially substited cellulose acetates showed that the sign of the CD of the C(6) acetyl was negative. Likewise, the combined contribution of C(1) and C(4) to their equatorially substituted acetyls was positive (with C(1) definitely Positive) and the combined contribution of C(2)eq and C(3)eq negative. The solution conformations of both polysaccharide acetates appeared to be random. The CD of White birch xylan acetate which is substituted on the average at every tenth residue with a 4‐O‐methyl glucuronic acid substituent, was sensitive to it. The xylan oligomer series also illustrated that CD may be used to determine the degree of polymerization of these oligomers up to about 20.
Optical rotatory dispersion and circular dichroism of benzoyl polysaccharides
Authors: Keilich G. , Bittiger H.
Published: December 2004

Measurements of optical rotatory dispersion (ORD) and circular dichroism (CD) were made in the range of 400–205 nm for polysaccharide tribenzoates such as 2,3,6‐tri‐O‐benzoyl amylose (I), 2,3,4‐tri‐O‐benzoyl dextran (II), tri‐O‐benzoyl pullulan (III), 2,3,6‐tri‐O‐benzoyl cellulose (IV), 2,3,6‐tri‐O‐benzoyl mannan (V), and polyglycan dibenzoates such as 2,3,‐di‐O‐benzoyl amylose (VI), cellulose (VII), and mannan (VIII). All compounds exhibit Cotton effects in the region of their UV absorption bands (206–285 nm).

Comparison of the corresponding di‐ and tribenzoyl polysaccharides shows a qualitative agreement in number, position and sign of the CD bands but differences in ellipticity magnitude. The disubstituted derivatives exhibit smaller amplitudes than the trisubstituted ones. The contribution of the C(6) chromophore (linked by a CH2‐group to the asymmetric C(5) atom) was determined to be of the same sign as the combined contribution of the C(2) and C(3) substituents.

The CD bonds of the individual polysaccharide derivatives, which differ in number, sign, and position, were discussed in terms of the steric position of the single chromophores and the steric arrangement and interaction caused by the configuration of the polysaccharides. The optical behavior of these polysaccharide derivatives was found to be not strongly influenced by a definite chain conformation in solution.
Vibrational spectrum of cyclic tetra‐L‐alanine
Authors: Gupta V. D. , Singh R. D.
Published: December 2004

A normal coordinate analysis for cyclic tetra‐L‐alanine molecule is reported. A comparison of amide modes and other low‐frequency vibrations sensitive to conformational changes is made with those in poly‐L‐alanine. Intramolecular coupling coefficients are calculated using perturbation treatment.
Distortion of optical properties in cylinders by absorbance flattening
Authors: Day L. A. , Hoppensteadt F.
Published: December 2004

An analysis is made of the magnitude of distortions in the measured absorbance, circular dichroism, optical rotation, and other spectral properties of cylindrical structures based on Duysens' description of the absorbance flattening phenomenon. The model calculations are made for isotropic particles having the same refractive index as the solvent. Exact integral expressions for coefficients relating optical properties of chromophores in cylindrical particles with those of isolated chromophores in solution are obtained for cylinders of any radius and height which have either random or perpendicular orientation with respect to the incident radiation. The results of numerical evaluation of the integrals for specific cases are presented to demonstrate the dependence of flattening on cylinder height, radius, extinction coefficient, and orientation.
Hydration mobility in peptide structures
Authors: Chirgadze Yu. N. , Ovsepyan A. M.
Published: December 2004

The structural behavior of hydrochlorides of poly‐L‐lysine and tetraglycine depends on water vapor pressure. At low relative humidities, structural rearrangements are slow. Water molecules catalyze these structural rearrangements; thus, in tetraglycine 1 H2O molecule per 10 peptide residues. Some general aspects of the mechanism of the hydration mobility in peptide structures are discussed.
Naegeli amylodextrin and its relationship to starch granule structure. II. Role of water in crystallization of B‐starch
Authors: Kainuma Keiji , French Dexter
Published: December 2004

Although native B‐type starch loses its sharp X‐ray pattern on strong drying, the wet Nägeli amylodextrin prepared from such starch gives a sharp B‐pattern, that is only slightly reduced in sharpness by complete drying. Nägeli amylodextrin dried admixed with a noncrystalline “filler” (e.g., starch sirup) gives an X‐ray pattern essentially identical to that of the wet amylodextrin, except that the 16‐Å (No. 1) ring is greatly reduced in sharpness and intensity. Failure of the B‐structure to collapse during drying indicates that water is not intercalated between turns of a helix or otherwise required to maintain the geometry and packing arrangement of the starch molecular chains. Rather, for native starch granules or amylose fibers, water relieves intercrystallite strains and consequent crystallite distortion induced by strong drying. For Nägeli amylodextrin, the small molecules of starch sirup can penetrate the interstices between crystallites and prevent strain build‐up during drying. For native starch granules, the interstitial regions are gel‐like in character and less permeable to starch sirup molecules. A model for B‐starch is proposed, that employs intertwined (double) helices.
Renaturation of DNA in the presence of ethidium bromide
Authors: Huttpm James R. , Wetmur James G.
Published: December 2004

The rate of renaturation of T2 DNA has been studied as a fuction of ethidium bound per nucleotide of denatured DNA. The Binding constants and number of binding sites for ethidium have been determined by spectral titration for denatured DNA at 55, 65, and 75°C and for native DNA at 65°C in 0.4M Na+. The rate of renaturation of T2 DNA was found to be independentof ethidium binding up to 0.03 moles per mole of nucleotide. Above 0.03 moles, the rate drops off precipitously approaching zero at 0.08 and 0.06 moles bound ethidium per nucleotide at 65°C respectively. A study was also made of the use of bound ethidium fluorescence as a probe for monitoring DNA renaturation reactions.
The simple construction of protein alpha‐Carbon models
Authors: Rubin Byron , Richardson Jane S.
Published: December 2004

A method has been developed for the rapid construction of protein alpha‐carbon models from a continuous length of metal rod. Selected side groups can be attached, and the scale is continuously variable from 20mm/Å to 4mm/Å. At the smaller scales, models are self‐supporting.
An extended Hückel molecular orbital approach to the study of the electronic structures and barriers to Syn–Anti interconversion in Syn purine nucleosides
Authors: Jordan Frank
Published: December 2004

The total energy and the electronic properties of some syn purine nucleosides have been determined as a function of the rotation angle around the C–N glycosidic linkage. Invariably, the crystallographic coordinates provide a state lying at or very near the minimum on the potential energy curve according to the extended Hückel parametrization here employed. The ribose moiety always carries a net positive charge whereas the base is always negatively charged. Changes in dipole moment magnitudes for the overall structure as well as in net atomic charges are noted upon rotation around the glycosidic linkage indicating that potential functions for polynucleotides may be in error if such changes are ignored.
Single‐ and double‐strand breaks in 5‐bromouracil‐substituted DNA of B. subtilis and phage PBSH after irradiation with long‐wave length UV and their correlation to intramolecular energy transfer
Authors: Mönkehaus Friedrich , Köhnlein Wolfgang
Published: December 2004

5‐Bromouracil‐substituted DNA was isolated form B. Subtilis and phage PBSH. The three DNA fractions of Different densities (TT, TB, and BB) were irradiated with u.v. (313nm). The number of single‐strand and double‐strand breaks was determined. The breakage rates are given. It was found that in hybrid DNA (TB) double‐strand breaks occur depending linearly on dose. In BB–DNA the observed double‐Strand bresks can be divided into two fractions with a linear and quadratic dose dependence respectively. The results can be explained by assuming intramolecular energy transfer from the BU‐containing strand to its complementary strand.
A calorimetric study of a polymer–monomer complex formed by polyuridylic acid 3′,5′‐cyclic AMP
Authors: Franck F. , Ackermann Th.
Published: December 2004

The existence of a soluble complex formed by polyuridylic acid (poly (U)) and 3′,5′‐cyclic AMP (cAMP) is demonstrated by u.v. extinction vs. temperature curves, optical rotation, equilibrium dialysis, and reaction calorimetry. The complex hasthe stoichiometry of 2 poly (U)‐cAMP and its formation is accompanied by an enthalpy change of −13.0 kcal/mole of base triplet. The introuction of an empirical factor α in the equations given by Damle2 and Crothers2 leads to the evolution of a ΔH value of −13.4 keal/mole. The parameter α is considered as a correction factor for the concentration dependence of the binding process. There is no relation between α and the reduction of monomer activity due to self‐association of monomers. The study of the binding process at several temperatures showed that the cooperativity parameter, σ, is independent of temperature and its value of 6.5 × 10−3 is in good agreement with σ = 5 × 10−3 for the poly (U)·poly(A) system.3
Studies on cytochrome c. Part I. Synthesis of the protected hexadecapeptide (sequence 1–16) of Baker's Yeast iso‐1‐cytochrome c
Authors: Moroder Luis , Borin Gianfranco , Marchiori Fernando , Scoffone Ernesto
Published: December 2004

The general strategy for the synthesis by conventional procedure of N‐ and C‐terminal fragments and of the entire sequence of baker's yeast iso‐1‐cytochrome c is discussed. The synthesis of the N‐benzyloxycarbonylhexadecapeptide tert‐butoxycarbonylhydrazide corresponding to the sequence 1–16 of the apoprotein is described in detail.
Hydrolysis of poly‐L‐lysine by pronase
Authors: Sass R. , Thiemann W.
Published: December 2004

Pronase E is able to hydrolyze poly‐L‐lysine in 100% yield into the monomer L‐lysine. The experiments show an intermediate production of tri‐L‐lysine and di‐L‐lysine that are clipped off from the polymeric peptide. During the hydrolytic process a number of characteristic amino acids are released from the enzyme that may indicate its activation. Amino acids as well as mono‐L‐lysine are decomposed by pronase E after a period of several days.
The influence of nearest‐neighboring amino acid residues on aspects of secondary structure of proteins. Attempts to locate α‐helices and β‐sheets
Authors: Kabat Elvin A. , Wu Taite
Published: December 2004

The influence of nearest‐neighbor pairs of amino acids (n − 1) and (n + 1) on the conformation of amino acid (n) in proteins has been studied. From experimental data on eleven proteins of known three dimensional structures, our definition of an α‐helical domain in the Φ,Ψ plot has been reexamined and found to be satisfactory. On the same principle, a regular β‐sheet domain has been delineated. We then revised our 20 × 20 table of frequencies of occurrences of various conformations tabulating three values: α‐helical, β‐sheet, and neither. These frequencies were then used to locate the helixbreaking positions in cytochrome b5, papain, thermolysin, and calcium‐binding protein. In conjuction with the helical wheel method, they were useful for predicting the locations of most α‐helical segments. Similarly the β‐sheet breaking positions in papain were located and most of the β‐sheets found by X‐ray diffraction were close to or between these positions. Data on β‐sheets are extremely sparse so that extensive tests were not possible. The application of this method to abnormal hemoglobins suggested possible distortions of helices and in several instances correlated with abnormal properties of the hemoglobins and association with disease. The variable region of human immunoglobin heavy chains was found to have a very low α‐helical content though β‐sheet structures might exist.
Conformational changes of polypeptides in intense electric fields
Authors: Bean C. P. , Bennett A. J.
Published: December 2004

Employing a simple “all or none” statistical theory, a calculation is given of the phase diagram in electric field–temperature space for the helix–coil transition of a polypeptide with nonpolar residues but charged end groups. The principal results are (i) the transition field extrapolated to absolute zero is on the order of millions of volts per centimeter, (ii) the normal transition temperature of large molecules is predicted to be significantly affected by fields as low as 30,000 V/cm, and (iii) for temperatures just above the helix‐coil transition temperature, the application of a field to a large molecule causes an initial transition to the helix state and with a further isothermal increase of field the coil state returns. The theory is extended to the case of the unfolding of a globular protein in an electric field. The fields are somewhat lower than those for the helix‐coil transition and are always single‐valued at a given temperature. Lastly the effect of including the presence of charged residues is shown to decrease the estimated critical fields but keep them of the same order of magnitude as those given for the case of nonpolar residues.
Anomalies in sedimentation. II. Testing the entanglement hypothesis
Authors: Schumaker Verne N. , Zimm Bruno H.
Published: December 2004

Zones of T2 DNA were sedimented through uniform solutions of T7 DNA to determine if the smaller DNA molecules would become entangled in the larger. No entanglement could be demonstrated even at high DNA concentrations. It is suggested that molecular entanglement is not responsible for the sudden loss of DNA from solution which occurs in high centrifugal fields. This communication also includes observations on the effects of rotor speed on the sedimentation behavior of DNA in high centrifugal fields, distortion of zone shape at high concentrations, and hydrodynamic interactions between DNA and MS2 bacteriophage particles.
The solution behavior of poly‐L‐proline: II. Fluorescence behavior of labeled polyproline in water and conentrated aqueous neutral salt solytions
Authors: Lerner D. A. , Schleich Thomas
Published: December 2004

Fluorescence depolarization experiments performed on labaled poly‐L‐proline Forme II suggest the occurrence of aggrgation in water while 6M guanidinium‐HCl induces dissociation. The solvent 4M CaCl2 results in a reduction of polymer structural orgganization. These findings corroborate suggestion of polyproline aggregation and solution behavior in aqueous neutral salt solytion (see preceding article).
Theory of aggregation in solution. I. General equations and application to the stacking of bases, nucleosides, etc.
Authors: Hill Terrell L. , Chen Yi‐Der
Published: December 2004

Earlier theoretical work on aggregation in imperfect gases and in solutions of protein molecules is reformulated here in such a way as to be applicable to a number of aggregation systems in solution. The theory is most easily developed for an “osmotic” solution. It is exact, in principle, and in particular does not treat the aggregates as an ideal mixture as is usually done. If osmotic virial coefficients are diffcult to measure in a particular case, it is then necessary to relate these coefficients to properties of the more conventional “constant pressure” solution. An important special case is used as an example in the last three sections: The stacking of bases, nucleosides, etc., is represented by a statistical mecchanical model in which the aggregates resemble vertical stacks of checkers.
The self‐assembly of collagen molecules
Authors: Yuan Leon , Veis Arthur
Published: December 2004

The aggregation of native acid‐soluble collagen (N‐ASC) and of pronase‐treated acid soluble collagen (P‐ASC) was examined in solution under conditions which varied from those of minimum collagen‐collagen interaction to those leading to incipient fiber formation. Molecular weights and weight distributions were determined in the analytical ultracentrifuge using the Yphantis high speed sedimentation equilibrium and Aarchiblad approach‐to‐equilibrim techniques. The aggregation was pH and ionic strength dependent in each case. Under conditions of minimum aggregation (low pH, low ionic strength), N‐ASC showed the presence of permant aggregates. At higher pH and ionic strength, a higher fraction of aggregate was formed but these were of the same charcter and molecular weight as the permanent aggregates. The aggregates were of a single molecular size, with a weight of 1.5 × 106 daltons, compared with a monomer collagen weight of 3.1 × 105 daltons. The P‐ASC formed aggregates also but to a much lower extent and the maximum aggregate size corresponded to dimers in molecular weight. These data show the major importance of molecular end‐regions in collagen aggregation to form native type fibers and, by virtue of the discrete size of the N‐ASC aggregates, support the microfibrillar hypothesis for the assembly of collagen fibrills.
The absorption of globular proteins
Authors: Bennett Alan J.
Published: December 2004

A series of experiments is suggested to elucidate further the nature of the adsorption of globular proteins on polar solid surfaces. Two ratios of surface energies and the total protein volume are used to characterize the expected form of the adsorbed species. A simple model calculation illustrates the approach.
Observations of self‐aggregation and dissociation of E. coli ribosomes by optical mixing spectroscopy
Authors: Hocker L. , Krupp J. , Benedek G. B. , Vournakis J.
Published: December 2004

Measurements of the diffusion coefficient of E. coli ribosomes by the technique of optical mixing spectroscopy are used to show that these ribosomes, when incubated in a 4°C cold room, undergo a slow aggregation with time. Even in the presence of this aggregation, it was possible to observe the diffusive character of the single 70s ribosome. It was found that at high (≥0.100 molar) KCl concentrations the ribosomes broke into their subunits. At moderate KCl concentrations they were relatively stable and at a very low KCl concentration (0.005 M) they were observed to dimerize. The values of the diffusion coefficients of the 50s subunits, the 70s single ribosome and the ribosome dimer determined in these measurements are consistent with currently accepted values.
Electric and hydrodynamic properties of polypeptides in solution. IV. A new conformational change of poly(L‐glutamic acid) in dimethylsulfoxide–methanol mixtures
Authors: Matsumoto Mitsuhiro , Watanabe Hiroshi , Yoshioka Koshiro
Published: December 2004

The electric birefringence of poly(L‐glutamic acid) (PLGA) in dimethylsulfoxide (DMSO)–methanol mixtures has been measured by use of the rectangular pulse technique. The length distribution curve, the mean molecular length, and the mean apparent permanent dipole moment of PLGA in solution have been obtained from the decaycurve and field strength dependence of the steady‐state birefringence according to the method developed for analyzing the electric birefringence of a polydisperse system. The length distribution curve exhibits one or two peaks. The length corresponding to a high peak and the mean length of PLGA undergo an abrupt change in the vicinity of 50 to 60 vol % DMSO at 30°C. Moreover, a sharp change of the Moffitt b0 parameter with the solvent composition is observed. These results provide evidence for the existence of a solvent‐induced transition from a helical conformation (presumably α‐helix) to another helical conformation with shorter length per amino acid residue. Further, the temperature dependence of the length distribution of PLGA in 50 vol % DMSO suggests the existence of a temperature‐induced helix ⇌ helix transition.
Electroviscous effect of lysozyme in aqueous solutions
Authors: Komatsubara Michiro , Suzuki Kazuo , Nakajima Haruhiko , Wada Yasaku
Published: December 2004

Reduced viscosity of a dilute aqueous solution of hen egg white lysozyme is measured in the pH range from 1.4 to 12.7 for various NaCI concentrations. The viscosity decreases with increasing pH below the isoelectric point (pH 11) on account of diminution in the electroviscous effect, reaches a minimum at pH 11, and then increases at high pH's because of coagulation. The electroviscous effect is depressed by the increase in the small ion concentration. The dependence of reduced viscosity on small ion concentration and pH is discussed on the basis of Booth's theory and a partial agreement between theory and experiment is obtained. The discrepancy between theory and experiment is attributed to non‐spherical distribution of charges in the protein. The volume of lysozyme obtained through Einstein's equation by extrapolating the reduced viscosity to a sufficiently high ion concentration compares well with the molecular volume in the crystal.
Heats of thermally induced helix–coil transitions of DNA in aqueous solution
Authors: Shiao D. D. F. , Sturtevant J. M.
Published: December 2004

Thermal denaturation of calf thymus DNA at both alkaline and neutral pH values was studied by differential scanning calorimetry. It was shown that the dependence of the enthalpy of transition on pH and salt concentration could be accounted for on the basis of a heat capacity change of +40 cal deg−1(base pair)−1. In the pH range between 10.3 and 11.3, a release of 0.6 proton per base pair was calculated from the pH dependence of the melting temperature. The heat effect associated with the release of this proton was calculated to be 5 kcal mole−1.