bluuebunny/crossref_metadata_2025 huggingface dataset:
Ferroelectric domains in epitaxial PbZr0.65Ti0.35O3/La0.5Sr0.5CoO3 heterostructures
Authors: Plekh M. , Tyunina M.
Published: August 2010

In epitaxial heterostructures of PbZr0.65Ti0.35O3/La0.5Sr0.5CoO3/MgO(001) with large lattice mismatch, ferroelectric domains were studied using piezoresponse force microscopy and microstructure analysis. In the c-oriented tetragonal PbZr0.65Ti0.35O3 films, random arrays of 0.1–1 μm sized ferroelectric domains with facet-type 180° boundaries were found. The lateral inhomogeneity of the switching fields and of the field-induced strains was detected. The results are discussed in terms of island growth and dislocation generation in epitaxial heterostructures having large lattice mismatch.
Ferroelectric transistors with improved characteristics at high temperature
Authors: Salvatore Giovanni A. , Lattanzio Livio , Bouvet Didier , Stolichnov Igor , Setter Nava , Ionescu Adrian M.
Published: August 2010

We report on the temperature dependence of ferroelectric metal-oxide-semiconductor (MOS) transistors and explain the observed improved characteristics based on the dielectric response of ferroelectric materials close to the Curie temperature. The hysteretic current-voltage static characteristics of a fully depleted silicon-on-insulator transistor, with 40 nm vinylidene fluoride trifluorethylene, and 10 nm SiO2 gate stack, are measured from 300 to 400 K. In contrast with conventional MOS field effect transistors (MOSFETs), the subthreshold swing and the transconductance show, respectively, a minimum and a maximum near the Curie temperature (355 K) of the ferroelectric material. A phenomenological model is proposed based on the Landau–Ginzburg theory. This work demonstrates that a MOSFET with a ferroelectric layer integrated in the gate stack could have nondegraded or even improved subthreshold swing and transconductance at high temperature even though the hysteresis window is reduced. As a consequence, we suggest that for ferroelectric transistors with appropriately designed Curie temperatures, the performance degradation of logic or analog circuits, nowadays operating near 100 °C, could be avoided.
Experiments and global model of inductively coupled rf Ar/N2 discharges
Authors: Kimura Takashi , Kasugai Hiroki
Published: August 2010

Experiments with a Langmuir probe and optical emission spectroscopy are carried out in inductively coupled rf (13.56 MHz) Ar/N2 discharges at three total pressures of 30, 60, and 110 mTorr, varying the Ar fractions from 50% to 95%. The electron energy probability functions (EEPFs) measured at all Ar fractions can be approximated using different exponentials in the bulk and high-energy regions, resulting in two temperature approximation of the measured EEPFs. The electron density slightly increases with increasing the Ar fraction at the Ar fractions below 70%, beyond which it relatively abruptly increases. On the other hand, the electron temperatures gradually decrease with the increase in the Ar fraction. The vibrational temperature does not strongly depend on the Ar fraction, whereas the rotational temperature gradually increases with the increase in the Ar fraction. The density of nitrogen atoms remains constant at the Ar fractions below 80%, beyond which it monotonically decreases with increasing the Ar fraction. A global model for electropositive plasma is used in order to investigate the plasma chemistry in Ar/N2 discharges assuming the Maxwellian electron energy distribution. The model results are compared with the experimental results, obtaining reasonably good agreement.
Dynamically skewed lines: Rotations in superfluid helium
Authors: van Staveren Marie N. , Apkarian V. A.
Published: August 2010

Dynamically skewed spectral lines arise for chirped damped oscillators. We extend this to the chirped damped rotor and apply it to treat the rovibrational line shapes of small molecules isolated in superfluid helium. The simple analysis generates valuable physical insights on the prevailing dynamics of a rotor coupled to its environment.
Impact of heavy hole-light hole coupling on optical selection rules in GaAs quantum dots
Authors: Belhadj T. , Amand T. , Kunold A. , Simon C.-M. , Kuroda T. , Abbarchi M. , Mano T. , Sakoda K. , Kunz S. , Marie X. , Urbaszek B.
Published: August 2010

We report strong heavy hole-light hole mixing in GaAs quantum dots grown by droplet epitaxy. Using the neutral and charged exciton emission as a monitor we observe the direct consequence of quantum dot symmetry reduction in this strain free system. By fitting the polar diagram of the emission with simple analytical expressions obtained from k⋅p theory we are able to extract the mixing that arises from the heavy-light hole coupling due to the geometrical asymmetry of the quantum dot.
A density functional theory study of the zero-field splitting in high-spin nitrenes
Authors: Misochko Eugenii Ya. , Korchagin Denis V. , Bozhenko Konstantin V. , Chapyshev Sergei V. , Aldoshin Sergei M.
Published: August 2010

This work presents a detailed evaluation of the performance of density functional theory (DFT) for the prediction of zero-field splittings (ZFSs) in high-spin nitrenes. A number of well experimentally characterized triplet mononitrenes, quartet nitrenoradicals, quintet dinitrenes, and septet trinitrenes have been considered. Several DFT-based approaches for the prediction of ZFSs have been compared. It is shown that the unrestricted Kohn–Sham and the Pederson–Khanna approaches are the most successful for the estimation of the direct spin-spin (SS) interaction and the spin-orbit coupling (SOC) parts, respectively, to the final ZFS parameters. The most accurate theoretical predictions (within 10%) are achieved by using the PBE density functional in combination with the DZ, EPR-II, and TZV basis sets. For high-spin nitrenes constituted from light atoms, the contribution of the SOC part to ZFS parameters is quite small (7%–12%). By contrast, for chlorine-substituted septet trinitrenes, the contribution of the SOC part is small only to D value but, in the case of E value, it is as large as the SS part and has opposite sign. Due to this partial cancellation of two different contributions, SS and SOC, the resulting values of E in heavy molecules are almost two times smaller than those predicted by analysis of the widely used semiempirical one-center spin-spin interaction model. The decomposition of DSS into n-center (n=1–4) interactions shows that the major contribution to DSS results from the one-center spin-spin interactions. This fact indicates that the semiempirical SS interaction model accurately predicts the ZFS parameters for all types of high-spin nitrenes with total spin S=2 and 3, if their molecules are constructed from the first-row atoms.
Magnetic domain compensation effect on the magnetodynamic response of ferromagnetic elements
Authors: Patschureck C. , Kaltofen R. , Mönch I. , Schäfer R. , Schultz L. , McCord J.
Published: August 2010

The capacity to tune the ferromagnetic resonance frequency in a soft ferromagnetic film relies on the ability to tailor the uniaxial anisotropy of the film material. We achieved a systematic change in anisotropy field with all other material properties remaining constant by preparing Ni18Fe19/Co60Fe20B20 multilayers. We show that in patterned films deviations from the regular Landau domain pattern occur, which compensate magnetic anisotropy effects and thereby lead to a precessional frequency independent of anisotropy. These results demonstrate that even small changes in the magnetic domain structure counteracts anisotropy adjustments in optimizing the magnetodynamic response in mesoscopic thin film elements.
On the energy of elliptical vortices
Authors: Vanneste J. , Young W. R.
Published: August 2010

Consider a two-dimensional axisymmetric vortex with circulation Γ. Suppose that this vortex is isovortically deformed into an elliptical vortex. We show that the reduction in energy is ΔE=−Γ2 ln[(q+q−1)/2]/(4π), where q2 is the ratio of the major to the minor axis of any particular elliptical vorticity contour. It is notable that ΔE is independent of the details of vorticity profile of the axisymmetric vortex and, in particular, independent of its average radius. The implications of this result for the two-dimensional inverse cascade are briefly discussed.
Mode hybridization in photonic crystal molecules
Authors: Vignolini Silvia , Riboli Francesco , Intonti Francesca , Wiersma Diederik Sybolt , Balet Laurent , Li Lianhe H. , Francardi Marco , Gerardino Annamaria , Fiore Andrea , Gurioli Massimo
Published: August 2010

A complete control of the coupling between the modes of two photonic crystal microcavities is obtained by using a combination of several local tuning techniques. By a local and controlled modification of one cavity we are able to bring into resonance modes with a different polarization and spatial distribution, producing heteroatomic photonic molecules. Clear anticrossing is observed, denoting the mode hybridization which is in a very good agreement with finite difference time domain calculations.
Effect of n+GaN cap polarization field on Cs-free GaN photocathode characteristics
Authors: Tripathi N. , Bell L. D. , Nikzad S. , Shahedipour-Sandvik F.
Published: August 2010

We report on a Cs-free GaN photocathode structure in which band engineering at the photocathode surface caused by Si delta doping eliminates the need for use of cesium for photocathode activation. The structure is capped with a highly doped n+GaN layer. We have identified that n+GaN cap thickness plays an important role in limiting the effect of polarization induced charges at the GaN surface on the photocathode emission threshold. Physics based device simulations is used for further analysis of the experimental results. Our findings clearly illustrate the impact of polarization induced surface charges on the device properties including its emission threshold.
Minority carrier lifetime in type-2 InAs–GaSb strained-layer superlattices and bulk HgCdTe materials
Authors: Donetsky Dmitry , Belenky Gregory , Svensson Stefan , Suchalkin Sergei
Published: August 2010

Minority carrier lifetime, τ, in type-2 strained-layer superlattices (SLSs) and in long-wave Hg0.78Cd0.22Te (MCT) was measured by optical modulation response technique. It was shown that at 77 K radiative recombination can contribute to the measured τ values. The Shockley–Read–Hall (SRH) lifetimes were attained as 100 ns, 31 ns, and more than 1 μs for midwave infrared superlattices, long-wave infrared (LWIR) superlattices, and MCT correspondingly. The nature of the difference between the SRH lifetimes in LWIR superlattice and MCT is discussed.
Enhancement of thermoelectric efficiency in (Ca,Dy)MnO3–(Ca,Yb)MnO3 solid solutions
Authors: Wang Yang , Sui Yu , Wang Xianjie , Su Wenhui
Published: August 2010

Transport and thermoelectric (TE) properties have been investigated for the (Ca,Dy)MnO3–(Ca,Yb)MnO3 solid solutions. Resistivity is found to be closely correlated with the structural distortions in this system. The enhanced TE efficiency in the solid solutions can be well attributed to the distortion of electronic density of states along with a strong point defect scattering. Such band structure engineering and phonon engineering have resulted in an effective improvement of the TE performance in these solid solutions and could be applied to more systems.
Laser-induced melting of a single crystal gold sample by time-resolved ultrafast relativistic electron diffraction
Authors: Musumeci P. , Moody J. T. , Scoby C. M. , Gutierrez M. S. , Westfall M.
Published: August 2010

We report the experimental demonstration of time-resolved relativistic electron diffraction. Single shot diffraction patterns from a single crystal gold sample were recorded using ultrashort 3.5 MeV electron bunches from a radio frequency photoinjector. By scanning the pump pulse time-delay, we studied the Bragg peaks amplitude change due to the laser-induced melting of the sample. The observed time scale matches the one predicted using a simple two temperature model of the heating of the thin foil. Time-resolved relativistic electron diffraction using megaelectronvolt electron beams with 107 particles in 100 fs bunch length opens exciting possibilities in ultrafast structural dynamics.
Improved luminescence properties of Eu-doped GaN light-emitting diodes grown by atmospheric-pressure organometallic vapor phase epitaxy
Authors: Nishikawa A. , Furukawa N. , Kawasaki T. , Terai Y. , Fujiwara Y.
Published: August 2010

We investigated the luminescence properties of Eu-doped GaN (GaN:Eu) grown by atmospheric-pressure organometallic vapor phase epitaxy. The GaN:Eu exhibited radiant red emission due to the intra-4f shell transition of Eu3+ ions at room temperature. The intensity of the dominant peak was about 4 times higher than that in the sample grown at 10 kPa, even though the Eu concentration was only half that of the 10 kPa sample. This was mainly caused by the enhancement of the energy transfer from the GaN host to Eu ions. The enhanced energy transfer resulted in improved luminescence properties of a GaN:Eu light-emitting diode.
Controlling the thermal contact resistance of a carbon nanotube heat spreader
Authors: Baloch Kamal H. , Voskanian Norvik , Cumings John
Published: August 2010

The ability to tune the thermal resistance of carbon nanotube mechanical supports from insulating to conducting could permit the next generation of thermal management devices. Here, we demonstrate fabrication techniques for carbon nanotube supports that realize either weak or strong thermal coupling, selectively. Direct imaging by in situ electron thermal microscopy shows that the thermal contact resistance of a nanotube weakly coupled to its support is greater than 250 K m/W and that this value can be reduced to 4.2−2.1+5.6 K m/W by imbedding the nanotube in metal contacts.
Simultaneous in situ measurements of x-ray reflectivity and optical spectroscopy during organic semiconductor thin film growth
Authors: Hosokai T. , Gerlach A. , Hinderhofer A. , Frank C. , Ligorio G. , Heinemeyer U. , Vorobiev A. , Schreiber F.
Published: August 2010

Simultaneous in situ real-time measurements of x-ray reflectivity and differential reflectance spectroscopy were conducted during deposition of perfluorinated copper-phthalocyanine thin films on SiO2/Si. We found a continuous spectral change coinciding with structural changes from submonolayer coverage, to standing βbilayer-phase and to β-phase for thicker films. This combined measurement enables us to study the relationship between structural and optical properties of organic semiconductor thin films.
Astrocyte-to-neuron signaling in response to photostimulation with a femtosecond laser
Authors: Zhao Yuan , Liu Xiuli , Zhou Wei , Zeng Shaoqun
Published: August 2010

Conventional stimulation techniques used in studies of astrocyte-to-neuron signaling are invasive or dependent on additional electrical devices or chemicals. Here, we applied photostimulation with a femtosecond laser to selectively stimulate astrocytes in the hippocampal neural network, and the neuronal responses were examined. The results showed that, after photostimulation, cell-specific astrocyte-to-neuron signaling was triggered; sometimes the neuronal responses were even synchronous. Since photostimulation with a femtosecond laser is noninvasive, agent-free, and highly precise, this method has been proved to be efficient in activating astrocytes for investigations of astrocytic functions in neural networks.
Ferroelectric properties of Ge2Sb2Te5 phase-change films
Authors: Gervacio Arciniega J. J. , Prokhorov E. , Espinoza Beltran F. J. , Gonzalez-Hernandez J.
Published: August 2010

The aim of this work is to investigate the NaCl-type to a hexagonal phase transition in Ge2Sb2Te5 films using impedance and piezoresponse force microscopy (PFM) measurements. The temperature dependence of the capacitance shows an abrupt change with a maximum at the temperature of 259 °C, which corresponds to the end from a NaCl-type to a hexagonal transition. In addition, the reciprocal capacitance for temperatures above 259 °C shows the Curie–Weiss dependence, which is typical for ferroelectric materials. Application of the external electrical field increases the degree of polarization in the NaCl-type Ge2Sb2Te5 films which allowed observing the ferroelectric domains in PFM measurements.
Bistable switching of twist direction in a twisted-nematic liquid crystal cell
Authors: Song Dong Han , Lee Joong Ha , Lee Seung Ju , Kim Sang-il , Lim Soonkwon , Shin Sung Tae , Kim Jae Chang , Yoon Tae-Hoon
Published: August 2010

We propose a bistable liquid crystal mode based on switching of the twist direction in a conventional π/2-twisted nematic cell. Switching between the −π/2 and +π/2 twist states can be performed by applying vertical and/or in-plane electric fields. The proposed bistable mode has an infinite memory time because the two stable twist states have the same elastic free energy.
Volatile and semi-volatile organic compounds in smoke exposure of firefighters during prescribed burning in the Mediterranean region
Authors: Barboni Toussaint , Cannac Magali , Pasqualini Vanina , Simeoni Albert , Leoni Eric , Chiaramonti Nathalie
Published: August 2010

Prescribed fires can be used as a forest management tool to reduce the severity of wildfires. Thus, over prolonged and repeated periods, firefighters are exposed to toxic air contaminants. This work consisted in collecting and analysing smoke released by typical Mediterranean vegetation during prescribed burning. Sampling was performed at five active zones on the island of Corsica. Seventy‐nine compounds were identified: volatile organic compounds and semi‐volatile organic compounds, including polycyclic aromatic hydrocarbons. Depending on exposure levels, the toxins present in smoke may cause short‐term or long‐term damage to firefighters’ health. The dangerous compounds emitted, benzene, toluene, ethylbenzene and xylenes, were quantified. Their concentrations varied as a function of the study site. These variations were due to the intrinsic and extrinsic characteristics of the fire site (e.g. plant species, fire intensity and wind). Our results show that benzene concentration is high during prescribed burning, close to the exposure limit value or short‐term exposure limit. Benzene can be considered as a toxicity tracer for prescribed burning because its concentration was above the exposure limit value at all the study sites. The authors suggest that respirators should be used to protect staff during prescribed burning operations.
Structure of the Sec13–Sec16 edge element, a template for assembly of the COPII vesicle coat
Authors: Whittle James R.R. , Schwartz Thomas U.
Published: August 2010

Ancestral coatomer element 1 (ACE1) proteins assemble latticework coats for COPII vesicles and the nuclear pore complex. The ACE1 protein Sec31 and Sec13 make a 2:2 tetramer that forms the edge element of the COPII outer coat. In this study, we report that the COPII accessory protein Sec16 also contains an ACE1. The 165-kD crystal structure of the central domain of Sec16 in complex with Sec13 was solved at 2.7-Å resolution. Sec16 and Sec13 also make a 2:2 tetramer, another edge element for the COPII system. Domain swapping at the ACE1–ACE1 interface is observed both in the prior structure of Sec13–Sec31 and in Sec13–Sec16. A Sec31 mutant in which domain swapping is prevented adopts an unprecedented laminated structure, solved at 2.8-Å resolution. Our in vivo data suggest that the ACE1 element of Sec31 can functionally replace the ACE1 element of Sec16. Our data support Sec16 as a scaffold for the COPII system and a template for the Sec13–Sec31 coat.
On some new and disputed synonymy in British Collembola
Authors: Goto H. E. , Lawrence P. N.
Published: August 2010

Synopsis

The validity of 5 species of British Collembola is discussed. Two species of Hypogastrura, one species of Parafolsomia and one species of Bourletiella are regarded as synonyms. A species of Xenyllodes is transferred to the genus Schaefferia.
N‐ACYLSUCCINIMIDES AS ACYLATING AGENTS FOR PROTEINS: THE SELECTIVE ACYLATION OF LYSINE RESIDUES
Authors: Boyd Helen , Leach S. J. , Milligan B.
Published: August 2010

The suitability of N‐acylsuccinimides as reagents for the selective acylation of reactive side chains in proteins has been examined. A detailed study of the reaction of N‐acetylsuccinimide with ribonuclease and bovine serum albumin showed that acetylation occurred in the pH range 3 to 8. Lysine side chains were acetylated selectively, with little or no modification of tyrosine side chains. There was no evidence for acetylation of serine, threonine or histidine side chains. The analogous N‐propionyl, N‐n‐butyryl, N‐i‐butyryl and N‐n‐valerylsuccinimides also selectively acylate lysine side chains in proteins. This series of reagents, capable of changing the charge of lysine side chains and adding acyl groups of increasing hydrocarbon chain length, should prove a useful tool in studies of protein structure.
MICROCALORIMETRIC STUDY OF BINDING BY LYSOZYME OF N‐ACETYL GLUCOSAMINE OLIGOMERS
Authors: Stasiw R. O. , Zaun J. W. , Patel A. B. , Brown H. D.
Published: August 2010

Binding heats of monomer, dimer, trimer, tetramer, pentamer and hexamer of N‐acetyl glucosamine to hen's egg white lysozyme (E.C. 2.3.1.17) were measured using a Tian‐Calvet conduction‐type microcalorimeter. Monomer and oligomers of N‐acetylglucosamine were prepared by molecular sieve chromatography from the acid hydrolysate of crab shell chitin. Lysozyme activity was evaluated by a chemical method based upon reducing group activity. When plotted as log Q/(Qm‐Q)/vs. log I, the binding phenomena fall into two distinct classes with regard to energetic character, while measurements for the hexamer are a departure from both classes. Data has been interpreted in terms of the six hypothesized lysozyme‐binding‐sites. We have concluded that the mode of binding of the monomer and dimer is different from that of the trimer, tetramer, pentamer and hexamer. The monomer and dimer comprise one group (utilizing sites C and CB, respectively) while the trimer, tetramer and pentamer comprise the second group deriving additional stability principally from site A, with the hexamer falling between them.
DUCK INSULIN: ISOLATION, CRYSTALLIZATION AND AMINO ACID SEQUENCE
Authors: Markussen Jan , Sundby Finn
Published: August 2010

Duck insulin was isolated and crystallized, and its amino acid sequence was elucidated. A comparison with chicken insulin, the only avian insulin so far sequenced, shows three differences. In the A‐chain, duck insulin has glutamic acid at position 8 and proline at position 10, where chicken insulin exhibits histidine and threonine, respectively. In the B‐chain, the only difference in sequences is located at position 30, where duck insulin has a threonine residue while chicken insulin has an alanine residue.
AN AB INITIO QUANTUM‐MECHANICAL INVESTIGATION ON THE ROTATIONAL ISOMERISM IN AMIDES AND ESTERS
Authors: Perricaudet M. , Pullman A.
Published: August 2010

The ab initio self‐consistent field molecular orbital method is utilized for the computation of the principal characteristics of the rotational Isomerism in formamide, formic acid and their C‐ and N‐methylated derivatives which may be considered as reasonable models for amide and ester bonds in polypeptide and depsipeptide environments. The calculated barrier to rotation is of the order of 20.3 kcal/mol in formamide and 12.3 kcal/mol in formic acid. The energy difference between the trans and cis form is about 1.8 kcal/mol in favor of the trans form in formamide and about 4.8 kcal/mol in favor of the trans form (see text for notation) in formic acid. In formamide, N‐methylation increases slightly the barrier, while C‐methylation decreases it. In formic acid, O‐methylation decreases the barrier while C‐methylation increases it and also increases the cis‐trans energy difference. The loss of stability of the peptide link upon rotation from the preferred trans‐planar conformation is about 1 kcal/mol for a torsion of 10° and 2 kcal/mol for a torsion of 20°. The theoretical results are in very satisfactory agreement with the most recent experimental data in this field.
DETERMINATION OF THE MOLECULAR WEIGHT AND PARTIAL SPECIFIC VOLUME OF HUMAN TRANSFERRIN BY MEANS OF A NEW TWO‐STAGE DENSITY GRADIENT EQUILIBRIUM METHOD
Authors: Lundh Søren
Published: August 2010

Using sodium diatrizoate as the gradient forming substance, the partial specific volume and molecular weight of human transferrin are determined by use of a new two‐stage density gradient equilibrium method. In the first stage of the method, equilibrium is reached with so low an angular velocity (24,630 rev./min) and column length (3.5 mm) that the resulting protein distribution corresponds to only a section of an isopycnic band. In the second stage of the method the initial protein concentration is determined by layering the salt solution on top of the protein solution in the centrifuge cell. The difference in refractive index between the two phases is studied as a function of time and appears to fall in a sequence of steps in one of the experiments. The difference between the first and second plateau of the graph is assumed to stem from a loss of water after the fluid injection and is used to correct the liquid density. The second plateau is used as a measure of the initial protein concentration in the first stage of the method.
THE AMINO ACID SEQUENCE OF MYOGLOBIN FROM THE MOLLUSC Aplysia limacina
Authors: Tentori L. , Vivaldi G. , Carta S. , Marinucci M. , Massa A. , Antonini E. , Brunori M.
Published: August 2010

The amino acid sequence of the globin prepared from the myoglobin contained in the radular muscle of the gasteropod mollusc Aplysia limacina was determined.

According to the results thus obtained, the polypeptide chain of Aplysia limacina myoglobin is composed of 145 amino acid residues, in good agreement with the overall number of amino acid residues contained in the polypeptide chain of the vertebrate myoglobins studied to date. A particularly interesting feature of the myoglobin studied appears to be the presence in its polypeptide chain of only one histidine which occupies the 95th position.
THERMAL TRANSITIONS OF ACYLATED RIBONUCLEASE
Authors: Leach S. J. , Boyd Helen
Published: August 2010

The amino groups of ribonuclease have been specifically acylated using five N‐acyl‐succinimides in which the RCO‐moieties varied in hydrocarbon chain length. The effects of these groups on the optical rotatory dispersion, circular dichroism, enzymic activity and stability to thermal denaturation have been determined. Thermal transitions, measured by changes in specific rotation at 365 nm, obeyed the criteria for a two‐state process both before and after the acylation treatments. The transitions were fully reversible under the conditions of measurement and the observed standard enthalpies were constant over at least 80% of the transitions. The effect of acetylation was to decrease the transition temperature by 7°. Longer hydrocarbon chains decreased this further but only by a fraction of a degree per extra ‐CH2‐ group.

The calculation of thermodynamic quantities is limited by the precision with which enthalpies can be measured but indicates that the standard free energy for the transition process decreases by about 270 cal per acetyl group and a further 20 cal per additional ‐CH2‐ group. The major source of destabilisation on acetylation appears to be the introduction of eleven hydrophobic CH3 groups per protein molecule rather than the increase in net negative charge. The thermodynamic data permit inferences to be drawn about changes in the nature of the side chain environment on thermal denaturation.
QUANTUM‐MECHANICAL STUDIES OF ENVIRONMENTAL EFFECTS ON BIOMOLECULES I. HYDRATION OF FORMAMIDE
Authors: Alagona G. , Pullman A. , Scrocco E. , Tomasi J.
Published: August 2010

As a first step in a general quantum‐mechanical investigation of environmental effects on the structure and properties of biomolecules, the non‐empirical ab initio self‐consistent field molecular orbital method has been employed for the determination of the principal hydration sites of formamide and of the essential characteristics of the monohydrates. In view of the extension of the study to more complex systems, the validity of a simplified treatment taking into account only the electrostatic parts of the interaction energy between formamide and water has also been investigated.
SEQUENCE DEPENDENT DEAMIDATION RATES FOR MODEL PEPTIDES OF HEN EGG‐WHITE LYSOZYME
Authors: Robinson Arthur B. , Tedro Siv
Published: August 2010

The rates of deamidation in pH 7.5, 0.15 M, 37°C potassium phosphate buffer of eleven pentapeptide models of the sequences found near asparaginyl and glutaminyl residues in egg white lysozyme were measured. These rates and rate estimates from previous measurements were used to calculate a sequence‐determined half‐life for non‐deamidated egg white lysozyme. Deamidation of the peptides during synthesis and purification was also measured. The implications of these measurements for biological deamidation and deamidation during peptide synthesis are discussed.
Mn++ BINDING BY PLASMA PROTEINS
Authors: Nandedkar Arvind K.N. , Nurse Clotelle E. , Friedberg Felix
Published: August 2010

54Mn2+ added to human or rabbit plasma in vitro combines selectively with the albumin fraction. At pH 7.0, the Scatchard plot yields a curve that may be resolved for two classes of sites: one, where n1 = 1 and K1 = 2.4 × 104, the other where n2 = 0.5 and K2 = 0.5 × 103.Zn2+, Ni2+ and Co2+ can compete effectively for these sites.
SOLID PHASE SYNTHESIS OF BOVINE PITUITARY GROWTH HORMONE‐(123–131) NONAPEPTIDE
Authors: Wang S. S. , Yang C. C. , Kulesha I. D. , Sonenberg M. , Merrifield R. B.
Published: August 2010

A nonapeptide, Arg‐Glu‐Leu‐Glu‐Asp‐Gly‐Thr‐Pro‐Arg, corresponding to the 123–131 sequence of bovine pituitary growth hormone, was prepared by a modified solid phase synthesis. To avoid an acid‐ or base‐catalysed rearrangement at the Asp‐Gly bond, which gives rise to an aspartimide‐containing peptide, a new combination of protecting groups was introduced. The 2‐(4‐biphenylyl)‐2‐propyloxycarbonyl group was used for Nα‐protection, a t‐butyl ester for the β‐carboxyl of aspartic acid, and a p‐alkoxybenzyl alcohol ester for the anchoring bond to the resin support. The nonapeptide showed growth hormone activity in the hypophysectomized rat tibia epiphyseal width test, but was inactive in the hypophysectomized rat body weight gain test.
PREPARATION AND CHARACTERIZATION OF MONOIODOINSULIN
Authors: Linde Susanne , Hansen Bruno
Published: August 2010

Monoiodoinsulin has been prepared from heterogeneous iodoinsulin containing on an average 1 I/mole using ion exchange chromatography. The isolated monoiodoinsulin showed in contrast to the iodinated insulin essentially a single band examined by disc‐electrophoresis. The iodine content as judged by the specific radioactivity was 1.0 atom of iodine per molecule of insulin. The distribution of the iodine was 1% in the B‐chain and 99%, in the A‐chain, 30% in Tyr A14 and 70% in Tyr A19 respectively. The biological activity of the isolated monoiodoinsulin was 67% in comparison to crystalline insulin tested on isolated rat fat cells. The immunological reactivity using the double‐antibody method with pre‐precipitation was unchanged in comparison to crystalline insulin
A PANCREATIC RIBONUCLEASE ACTIVE AT pH 4.5
Authors: Batholeyns Jacques , Moore Stanford , Stein William H.
Published: August 2010

When a homogenate of beef pancreas prepared at neutral pH is assayed for RNase activities at pH 4.5 and at pH 7.5, the specific activity at the acid pH is more than half that at neutral pH. Yet the procedures normally employed for the isolation of the well‐characterized RNase A from the pancreas yield an enzyme that is almost devoid of activity at pH 4.5. Experiments designed to isolate from the pancreas the protein responsible for the RNase activity at acid pH have utilized chromatography and gel filtration under conditions that avoid both the strong acidification and the heat which are common features of the methods for the preparation of RNase A. The purified protein active at pH 4.5 (yield, 10 mg per 100 g of tissue) is also active at pH 7.5. The protein is labile to both strong acid and high temperature and it is this sensitivity that has contributed to its being overlooked during the decades when RNase A has been so thoroughly studied.

Acid or heat treatment converts the enzyme active at pH 4.5 to a protein which is currently indistinguishable from RNase A, with as yet no detectable change in amino acid composition. Further research is required to define the small but significant chemical or physical changes which accompany this transformation.
A GENERAL METHOD OF PURIFICATION OF ADENOSINE DEAMINASE BY AFFINITY CHROMATOGRAPHY
Authors: Rossi C. A. , Lucacchini A. , Montali U. , Ronca G.
Published: August 2010

Affinity chromatography has been used to purify adenosine deaminase from various sources: calf spleen, calf intestinal mucosa, chicken duodena and human erythrocytes. For this purpose a specific inhibitor, 9‐(p‐aminobenzyl) adenine, was synthesized and covalently joined to agarose. Adenosine deaminase is selectively retained by such an inhibitor‐resin when highly impure solutions are chromatographed through it. After elution from the resin with guanylurea, a competitive inhibitor, the enzyme is homogeneous and can be recovered in yields of 80% or more and the same number of multiple forms of the enzyme is present in the purified preparation and in the crude extract.
TRINITROPHENYLATION OF THE BILIRUBIN BINDING SITE OF HUMAN SERUM ALBUMIN
Authors: Jacobsen Christian
Published: August 2010

Human serum albumin has been modified with 2,4,6‐trinitrobenzenesulphonic acid and picryl chloride in low ratios of reagent/albumin. The derivatives have been investigated by spectrophotometry and by thin layer chromatography of the hydrolysates in order to assess the specificity of the reagents. The same reaction conditions were used to modify albumin previously complexed with bilirubin in the ratio of 1:1. The affinity of bilirubin to the modified albumins was estimated by an improved peroxidase method. It is concluded that TNBS and picryl chloride react almost quantity for quantity with ‐amino groups of lysine on the albumin molecule. The results also suggest that at least one TNBS reactive amino group and at least one picryl chloride reactive amino group are located in or near the high‐affinity bilirubin binding site.
DENATURATION OF THERMOPHILIC AND MESOPHILIC 6‐PHOSPHOGLUCONATE DEHYDROGENASE BY 8M UREA
Authors: Veronese F. M. , Boccu‘ E. , Fontana A.
Published: August 2010

The denaturation reaction of 6‐phosphogluconate dehydrogenase (6‐phospho‐D‐gluconate: NADP oxidoreductase (decarboxylating EC 1.1.1.44) from B. Stearothermophilus and E. coli in 8 M urea has been compared. The rates of denaturation were evaluated from the fluorescence quenching that occurs at 334 nm. The thermophilic enzyme has been found about ten times more resistant to the action of the denaturating agent, and showed a biphasic denaturation process, whereas the E. coli enzyme followed a single first‐order kinetics.
BINDING OF PYRIDOXAL 5‘‐PHOSPHATE TO BOVINE SERUM ALBUMIN AND ALBUMIN FRAGMENTS OBTAINED AFTER PROTEOLYTIC HYDROLYSIS. LOCALIZATION AND NATURE OF THE PRIMARY PLP BINDING SITE
Authors: Hilak Michel C. , Harmsen Ben J. M. , Joordens Jos J. M. , van Os. Gerard A. J.
Published: August 2010

The binding of pyridoxal 5′‐phosphate (PLP) to bovine serum albumin (BSA), and to large BSA fragments obtained after proteolytic hydrolysis, was investigated in order to study the structure of these fragments in relation to the albumin structure itself, and to get information about the PLP binding sites on albumin.

From absorbance and circular dichroism spectra, combined with peptide mapping of the tryptic digests of the reduced PLP‐protein complexes, it could be concluded that the primary binding site is localized within the NH2‐terminal part of the albumin molecule. The COOH‐terminal part contains one or more secondary sites. It appeared that in albumin and in the largest NH2‐terminal fragment, the environment of the primary binding site is rather apolar in character. However, in the smallest NH2‐terminal fragment this site is more exposed to the solvent. This suggests that the part of the peptide chain which is not common in both fragments has a stabilizing effect on the structure around the primary binding site.
STUDIES ON PROTEIN FOLDING, UNFOLDING AND FLUCTUATIONS BY COMPUTER SIMULATION
Authors: Taketomi Hiroshi , Ueda Yuzo , Gō Nobuhiro
Published: August 2010

A lattice model of proteins is introduced. “A protein molecule” is a chain of non‐intersecting units of a given length on the two‐dimensional square lattice. The copolymeric character of protein molecules is incorporated into the model in the form of specificities of inter‐unit interactions. This model proved most effective for studying the statistical mechanical characteristics of protein folding, unfolding and fluctuations. The specificities of inter‐unit interactions are shown to be the primary factors responsible for the all‐or‐none type transition from native to denatured states of globular proteins. The model has been studied by the Monte Carlo method of Metropolis et al., which is now shown applied to approximately simulating a kinetic process. In the strong limit of the specificity of the inter‐unit interaction the native conformation was reached in this method by starting from an extended conformation. The possible generalization and application of this method for finding the native conformation of proteins from their amino acid sequence are discussed.
HEAT DENATURATION OF HUMAN SERUM ALBUMIN. MIGRATION OF BOUND FATTY ACIDS
Authors: Brandt Johnny , Andersson Lars‐Olov
Published: August 2010

Prolonged heat treatment of solutions of human serum albumin at 60°C resulted in formation of one aggregate fraction and one fraction that was stable against further heat treatment. Fatty acid analyses on these fractions indicate that the heat stable fraction is formed by migration of fatty acids from the aggregating molecules to the remaining monomer thereby stabilizing the latter against heat denaturation. Disulphide and SH groups are involved in the aggregation process.
SYNTHESIS OF PEPTIDES BY FRAGMENT CONDENSATION ON A SOLID SUPPORT
Authors: Larsson Lars‐Eric , Melin Per , Ragnarsson Ulf
Published: August 2010

A convenient scheme for the synthesis of 4,8‐disubstituted vasopressins has been designed and its usefulness evaluated in the preparation of one of the parent hormones, 8‐arginine‐vasopressin. The main feature of the scheme involves preparation of two protected tripeptide fragments, Z‐Cys(Bzl)‐Tyr(Bzl)‐Phe and Boc‐Asn(Mbh)‐Cys(Bzl)‐Pro which are incorporated in a synthesis on a solid support. Both tripeptides were prepared conventionally with the carboxyl groups protected as benzyl esters. The benzylester groups were removed by transesterification with 2‐dimethylaminoethanol and subsequent hydrolysis. To avoid racemization in the coupling step with the fragment containing a C‐terminal phenylalanine, N‐hydroxysuccinimide was added. After removal of the peptide from the resin, deprotection, oxidation and desalting, final purification was effected by ion‐exchange chromatography. Apart from the main product, which exhibited full pressor activity, only small amounts of impurities could be isolated.
CIRCULAR DICHROISM OF HUMAN PITUITARY LUTEINIZING HORMONE AND ITS GLYCOPEPTIDES
Authors: Puett David , Nureddin Aida , Holladay Leslie A.
Published: August 2010

The circular dichroic (CD) spectrum of the glycoprotein hormone, human pituitary luteinizing hormone (hLH), has been determined between 195–320 nm and resolved into gaussian constituents. Below 230 nm the CD spectrum is characterized by a negative extremum at 207 nm with a shoulder at 217 nm. Resolution into gaussian constituents of the 200–230 nm CD spectrum resulted in two resolved negative bands, one at 206 nm and the other at 215 nm. The latter band is assigned to β‐structure which is estimated to be about 25%. The 206 nm resolved band is assigned to the N‐acetylated carbohydrate groups (e.g. N‐acetyl glucosamine, galactosamine, and neuraminic acid). This is based partly on the evidence that the CD spectrum of the hLH glycopeptide fraction (prepared by a pronase digestion of s‐carboxymethylated hLH) exhibited a negative extremum at 207.5 nm, which is close to the resolved 206 nm band in hLH. Above 230 nm the CD spectrum is characterized by a negative extremum at about 275 nm. Most of the ellipticity in this region is attributed to the disulfides in hLH. Both strong acid (0.1 N HCl) and concentrated guanidine hydrochloride (4 M) affect the ellipticity in the vicinity of 275 nm, but only the latter (as well as concentrated urea) has a major effect on the CD spectrum below 230 nm indicating extensive conformational changes. There is, however, some loss of β‐structure in 0.1 N HCl. Thus, it appears that the conformation of the hLH subunits in these subunit‐dissociating agents is rather different. There was no dramatic change in the magnitude of the 207 nm extremum of native hLH between 10–50°C.
PHYSICO‐CHEMICAL STUDIES ON THE 11S GLOBULIN IN SOYBEAN SEEDS: SIZE AND SHAPE DETERMINATION OF THE MOLECULE
Authors: Koshiyama Ikunori , Fukushima Danji
Published: August 2010

The molecular shape of the 11S globulin, the major storage protein of soybean seeds, was estimated to be an oblate ellipsoid with a revolution axial ratio of 8.11–8.38 with or without scarce hydration according to the procedure of Simha & Perrin by measuring the partial specific volume, diffusion coefficient, molecular weight and volume fraction intrinsic viscosity. The length of the major axis of the molecule is 178–180 Å and that of the minor axis 22 Å. Subsequently, the shape factor β, and the hydrodynamically effective volume, Ve, of the protein were calculated by the procedure of Scheraga & Mandelkern. Consequently, the 11S globulin molecule was also an oblate ellipsoid from β. Ve was found to be equal to MV̄/N, the anhydrous volume of protein. It was therefore concluded that the protein existed in a rigid and nearly anhydrous state in solution.
A SQUARE PYRAMIDAL MODEL FOR RIBONUCLEASE ACTION
Authors: Holmes Robert R.
Published: August 2010

A mechanism incorporating a square pyramidal model (SP) is presented for the action of bovine pancreatic ribonuclease. Its formulation is based on structural principles governing pentacoordinate behavior. The model is compared with a previous trigonal bipyramidal (TP) representation with regard to the geometry of the active site and enzyme constraints. Of two variants of the SP model, an adjacent (cisdisplacement) and in‐line (transdisplacement) process, the in‐line mechanism, as with the TP model, fits existing model studies. Consideration of the energetics of the SP vs. the TP model leads to an estimated energy difference of about 1–2 kcal/mol. This suggests that the preferred model may be intermediate in geometry between the two idealized representations for the enzymatic hydrolysis. Comparisons are made showing that pseudorotation is an unlikely process in either model.
RETRO ANALOGS RELATED TO OXYTOCIN
Authors: Nakagawa Satoe Hase , Yang Frances , Kato Tetsuo , Flouret George , Hechter Oscar
Published: August 2010

[D‐alle3]‐retro‐D‐deaminotocinamide (I), retro‐L‐deaminotocinamide (III) and their respective N‐formyl derivatives (II and IV) were synthesized by the stepwise active ester method: deaminotocinamide was prepared by the solid‐phase method. The retroanalogs of deaminotocinamide, tested at concentrations up to 10‐5M, were found to be without activity as agonists or antagonists in the oxytocic assay. At 10‐4M, [D‐alle3]‐retro‐D‐deaminotocinamide is a weak competitive inhibitor of oxytocin. [D‐alle3, Gly7]‐retro‐D‐deaminooxytocin (V) was synthesized either by the active ester method or by a fragment condensation method employing the retro‐D‐ring, [D‐alle3]‐retro‐D‐deaminotocinamide, and “D‐tail”, Boc‐Gly‐D‐Leu‐Gly, as the fragments. The N‐formyl derivative (VI) of V was prepared by selective N‐formylation with p‐nitrophenyl formate. Additionally, [D‐alle3, Gly7, Malonamide9]‐retro‐D‐deaminooxytocin (VII) and the model compound [Gly7]‐retro‐L‐deaminooxytocin (VIII) were synthesized by the fragment condensation method. In the oxytocic assay, the retro‐analogs were found to be neither agonists nor antagonists at concentrations up to 10‐5M, except for [D‐alle3, Gly7]‐retro‐D‐deaminooxytocin which showed weak oxytocic activity in the range of 10‐5to 10‐4M and may be a partial agonist. It is concluded that the addition of the tripeptide “tail” to the retro‐D‐ring did not significantly alter the biological activity of the latter, which remains about 105times lower than that of the active hormone analog [Gly7]‐oxytocin and about 107times lower than the hormone itself. The marginal activity of all these retro‐D‐analogs appears to be directly related to the peptide bond reversal and suggests that the peptide backbone may play an essential role in peptide hormone action.
THEORY OF LARGE‐AMPLITUDE CONFORMATIONAL FLUCTUATIONS IN NATIVE GLOBULAR PROTEINS. Independent Fluctuating Site Model
Authors: Ueda Yuzo , Gö Nobuhiro
Published: August 2010

A theory is developed about large‐amplitude conformational fluctuations in globular proteins in their native or predenaturational state. A model is introduced, an independent fluctuating site model, in which we assume that there is more than one independent fluctuating site, each one localized in some part of a protein molecule. Without assuming any further details for each fluctuating site, the entropy S versus enthalpy H curve of this model is shown to be convex. From this fact the predenaturational excess heat capacity can be derived, as observed in recent experimental studies of a few systems of a protein in solution.
KINETIC AND CONFORMATIONAL STUDIES ON SOME PARTIALLY SYNTHETIC RIBONUCLEASE S‘ ANALOGUES MODIFIED IN POSITION 8*
Authors: Borin Gianfranco , Filippi Bruno , Moroder Luis , Santoni Cesare , Marchiori Fernando
Published: August 2010

Syntheses are described of two S‐peptide analogues where the arginyl residue in position 10 has been replaced by ornithine and the phenylalanine in position 8 has been substituted by the unnatural amino acids cyclohexylalanine or p‐fluorophenylalanine.

In order to regenerate the arginyl residue, which is present in position 10 in the natural sequence, the S‐peptide analogues belonging to the [Orn10]‐series are transformed into the corresponding guanidinated derivatives by treatment with O‐methylisourea. 1∈, 7∈, 10δ triguan‐[Cha8, Orn10]‐, 1∈, 7∈, 10δ‐triguan‐[pF‐Phe8, Orn10]‐ and 1∈, 7∈, 10δ‐triguan‐[Tyr8, Orn10]‐S‐peptides were prepared.

The ability to bind to and activate the S‐protein of the synthetic S‐peptide analogues, before and after guanidination, was tested by exploring their capacity to generate ribonuclease activity using RNA and C > p as substrates.

The affinity of the different peptides for the S‐protein in the absence of substrate was evaluated by difference spectroscopy.
SYNTHESIS, BIOLOGICAL ACTIVITY, AND TRITIATION OF L‐3, 4‐DEHYDROPROLINE‐CONTAINING PEPTIDES
Authors: Felix Arthur M. , Wang Ching‐Tso , Liebman Arnold A. , Delaney Charles M. , Mowles Thomas , Burghardt Barbara A. , Charnecki Annette M. , Meienhofer Johannes
Published: August 2010

A series of analogs of thyroliberin (TRH) ([L‐3Pro3]‐TRH, [D‐3Pro3]‐TRH, [L‐3‐MeHis2, L‐3Pro3]‐TRH) in which proline was replaced by L‐ or D‐3, 4‐dehydroproline was synthesized. The analogs exhibited approximately the same biological activity as the corresponding proline‐containing peptides. These analogs and others in which 3, 4‐dehydroproline is present at the NH2‐terminal, COOH‐terminal or internal positions in the peptide were successfully reduced with deuterium or tritium to provide the 3, 42‐H2‐proline or 3, 43‐H2‐proline analogs, respectively, with near theoretical values of substitution. A novel procedure for the chemical resolution of DL‐3, 4‐dehydroproline is also described.