bluuebunny/crossref_metadata_2025_split huggingface dataset:
Formation of Two-Dimensional Crystals of Membrane-Anchored and Water-Soluble Proteins
Authors: Engelhardt Harald , Scheybani T. , Von Gustedt W. , Baumeister W. 
Published: March 2011

ABSTRACTThe formation of two-dimensional (2-D) crystals of biological macromolecules is of interest for nanotechnological applications. Protein 2-D crystals may be used as molecular sieves and/or support devices as components of biosensors etc. [1]. Functionally specialized 2-D crystals, containing transport or catalytic proteins, provide a certain function in a highly efficient and vectorial manner. Future developments may allow the design of more complex structures such as multilayers made from different proteins or arrays of functionally linked oligo- or multimeric complexes consisting of multiple protein species [2]. Regular 2-D arrays, either truely crystalline or densely packed molecules, are one of the basic structures taht might be used to construct more sophisticated protein-based devices. 2-D crystals have some interesting features:
Biomolecular Self-Assembly of Quantum-Dot Composites
Authors: Lawton Carl W. , Fiddy Michael A. , Flynn Geoff , Aboughanem Fadi 
Published: March 2011

ABSTRACTA biomimetic approach utilizing biomolecular self-assembly was used to tailor quantum-dot composites for use as nonlinear optical media. Yeast tRNA was utilized as an ion-exchange/nucleation site within a polymeric matrix (polyacrylamide). Cadmium ion-exchange and subsequent sulfide precipitation resulted in quantum-dot formation. Illumination of samples with an Argon laser (514 nm) utilizing the Z-scan measurement method resulted in χ3 values of +3.7 ×10−6 esu.
Disulfide Bonds in Recombinant Repeat Units From an Aquatic Insect's Silk Protein
Authors: Case Steven T. , Smith Stanley V. , Bratton Melyssa R. 
Published: March 2011

ABSTRACTrCAS is a recombinant Constant And Subrepeat (rCAS) protein modelled after tandem core repeats found in a 1000-kDa silk protein synthesized by larvae of the midge,Chironomus tentans. rCAS is encoded by a synthetic gene (synCAS) which is expressed in bacteria. Purified rCAS has four cysteine residues that participate in formation of two intramolecular disulfide bonds. Here we report the results of amino acid sequencing and electrospray ionization mass spectroscopic analyses of tryptic fragments of native and reduced rCAS which suggest that these disulfide bonds are heterogeneous. To assist in studying the formation of disulfide bonds in reduced and refolded rCAS, a series of synCAS mutants were constructed with cysteine to alanine substitutions. In comparison to wild-type rCAS and a Cys79→Ala mutant, the refolding of Cys9→Ala appears to be partially inhibited.
Smart Muscle Under Electrochemical Control of Molecular Movement in Polypyrrole Films
Authors: Otero T. F. , Rodriguez J. , Santamaria C. 
Published: March 2011

ABSTRACTA bilayer device: consisting of a conducting, flexible polypyrrole layer and an adherent, elastic non conducting film was constructed. One end of the bilayer was fixed with a clamp, allowing the electrical contact with polypyrrole. Polypyrrole volume increases and decreases reversibly during electrochemical oxidation and reduction processes in aqueous solutions. Reversible stress gradient across the flexible film promotes reversible angular movements of the free end of the bilayer, around the fixed end. The effect of the anodic and cathodic potential gradients, as well as the effect of the concentration of movable ions on a 180° angular movement, in the electrolytic solution, were studied. Weights of 1000 times the bilayer weight adhered at the bottom of the bilayer were reversibly trailed across 180° by electrochemically controlled oxidation and reduction processes, in a few seconds. As an electric current promotes chemical reactions giving a change of volume and promoting a mechanical energy, the device was named artificial muscle. Similarities and differences between muscles and artificial muscles are discused.
Biological Self-Assembly: A Paradigm for Materials Science
Authors: McGrath Kevin P. , Kaplan David L. 
Published: March 2011

ABSTRACTComplex organized systems evolved from the prebiotic soup approximately three billion years ago, relying on simple molecules which spontaneously and synergistically combine to accomplish certain tasks. As life evolved, the sophistication of these interactions also increased. Organisms evolved by linking the needed functional groups together in proteins to improve the efficiency of the process, and now rely almost exclusively on protein interactions to accomplish needed tasks. It is for this reason that considerable effort has been expended on understanding how such complexes are formed and how the individual components contribute to overall function. The code for these interactions lies buried in the amino acid sequences of the constituent proteins. Biologists are beginning to unravel the secrets of this code, and see how small changes to individual residues can affect the overall stability and function of the complex.
Preparation of 6-O-Acyl Amylose Derivatives
Authors: Cimecioglu A. L. , Ball D. H. , Kaplan D. L. , Huang S. H. 
Published: March 2011

ABSTRACTTwo new direct approaches for selective 6-O-acylation of amylose under homogeneous conditions were investigated. In the first method, amylose was initially brominated at C-6 using Nbromosuccinimide and triphenylphosphine in N,N-dimethyfformamide containing lithium bromide. The procedure was found to be highly selective and proceeded with no detectable reaction at the secondary positions. Several 6-bromo-6-deoxyamylose derivatives were prepared with different degrees of substitution by changing the molar equivalence of the reactants. In the second stage these were converted into 6-laurate esters by treatment with cesium laurate in dimethylsulfoxide, which proceeded rapidly under mild conditions. In the second method, the feasibility of 6-O-benzoylation in one step using the Mitsunobu reaction was evaluated. Amylose was treated with diethylazodicarboxylate in the presence of triphenylphosphine and benzoic acid in dimethysulfoxide under ambient conditions. While exclusively 6-O-benzoylation resulted up to degree of substitutions of ca. 0.5, at higher values a small amount of esterification at secondary hydroxyl groups also occurred. Products were characterized by 13C NMR, FTIR and elemental analyses.
Computer Simulations of Nonlinear Optical Chromophore Containing Polypeptides
Authors: Pachter Ruth , Fairchild Steven B. , Lupo James A. , Sennett Brian S. , Crane Robert L. , Adams W. Wade 
Published: March 2011

ABSTRACTIn our continuing efforts towards the design of nonlinear (NLO) optical chromophore containing polypeptides we present an integrated computational approach, in which the design of biomolecular materials with defined secondary and tertiary structures is investigated by means of novel predictive tools, while the effects of the nonlinear optical chromophores are studied with molecular dynamics simulations. A neural network that was trained to predict the spatial proximity of Cα atoms that are less than a given threshold apart, is applied. The double-iterated Kalman filter (DIKF) technique is then employed with a constraints set that includes these pairwise atomic distances, and the distances and angles that define the structure as it is known from the protein's sequence. The results for test cases, particularly Crambin and genetically engineered Eglin-C, demonstrate that this integrated approach is useful for structure prediction at an intermediate resolution. Defined structural motifs of NLO chromophore containing polypeptides are investigated by using molecular dynamics techniques, particularly for the design of coil coiled amphiphatic biopolymers.
Preliminary Characterization of Organic Nucleator and Framework Macromolecules in Mollusc Shells
Authors: Humbert Richard , Sarikayat M. , Aksay I. A. , Crabb J. W. , Furlong C. E. 
Published: March 2011

ABSTRACTThe nacreous (mother-of-pearl) sections of molluscan shells are natural laminates of aragonitic calcium carbonate platelets and an organic matrix. The multi-edged platelets are sub-micrometer thick and surrounded on all sides by 10–20 nm-thick organic matrix that contains several proteins and polysaccharides. Our goal is to identify the components and structure of the organic matrix and determine their function in shell formation and organization. We have extracted organic material from red abalone-Haliotis rufescens, and chambered nautilus-Nautilus pompilius. From the soluble portion, we have partially purified two proteins and determined their amino acid compositions.
Tumor Cell - Substrate Stabilization Mediated by Integrins
Authors: Patton John T. , McIntire Larry V. , Menter David G. , Nicolson Garth L. 
Published: March 2011

AbstractMetastasis formation is dependent on the arrest and stabilization of adhesive interactions to prevent detachment from secondary sites. Primary receptor-ligand interactions are not sufficient to maintain prolonged adhesive contacts without secondary events that lead to stabilization. Tumor cell arrest and stabilization were studied under physiologically relevant shear conditions. We used a parallel-plate flow chamber with surfaces coated with human plasma fibronectin or vitronectin. Our previous work suggested that stabilization of cells to immobilized proteins is in part attributed to transglutaminase covalently cross-linking cytoskeletal-integrin-fibronectin multiprotein complexes via lysine-glutamine linkages. To study the role of integrins in mediating arrest and initiating stabilization we used a human melanoma line (70w) and polyclonal antibodies that inhibit the function of the fibronectin (α5β1) and vitronectin (αvβ3/β5) integrin receptors. To confirm the role of integrins in initiating stabilization we used CHO (Chinese hamster ovary) cells selected for low levels of α5β1integrin expression and integrin transfected CHO cells selected for α5βloverexpression. The level of fibronectin receptor surface expression was inversely related to the adhesion stabilization lag time. These studies confirmed that integrins are essential for mediating arrest and initiating stabilization. They also confirm that secondary events are necessary for complete stabilization to occur. Finally, it is important to note that the arrest and stabilization methods we have developed are capable of detecting biologic effects at far greater sensitivity than static adhesion assays. Some examples of pharmacologic agents or biomaterials effects that can be detected using stabilization assays include: 1) very low drug doses, 2) very low levels of peptide, carbohydrate, and antibody inhibitors, 3) slight modification of endogenous protein expression by antisense oligonucleotides or transfected genetic expression constructs.
Characterization of Biodegradable Polyester Films and their Interaction with Hepatocytes
Authors: Park Ann , Cima Linda Griffith , Kaufmann P.-Matthias 
Published: March 2011

AbstractPolymers derived from lactic and glycolic acid have achieved success in many medical applications and have been investigated as possible materials for degradable scaffolds required in tissue transplantation. Previous investigators have found significant differences in the behavior of cells cultured on chemically similar polyesters of this family but the mechanisms for these differences have remained unclear.In this study, we fabricated polylactic acid, polylactic-co-glycolic acid, and blend films by melt-processing. The bulk and surface properties of these films were characterized by GPC, DSC, WAXS, SEM, and contact angle. All films were smooth and amorphous and differed only in chemical composition. The films were assessed for their ability to sustain or promote hepatocyte attachment, growth, and function. Cells adhered to and exhibited similar morphology on all substrates. Cells decreased in number to 50–60% of the initial cell number but exhibited high retention of differentiated function on all of the polymer substrates over five days. Cell response was not statistically different on the different substrates indicating that chemical composition, in our range of polymer formulations, does not affect cell behavior.
Theoretical Prediction of Gas-Phase Nucleation Kinetics of SiO
Authors: Zachariah Michael R. , Tsang Wing 
Published: March 2011

AbstractThis paper describes the application of ab-initio molecular orbital (MO) theories in conjunction with reaction rate theory to obtain thermochemistry and energetics of nucleation processes. The specific example used for the illustration of this approach is the nucleation of SiO. MO computations on the equilibrium structures have shown the polymers up to the tetramer to be planar rings and exothermic to addition of the monomer. Transition state analysis has shown that subsequent addition of the monomer (SiO) most likely proceeds without an energy barrier. Reaction rate theory analysis of the polymerization shows the rate coefficients to be very pressure dependent, with the dimer formation process rate limiting. Oxidation of clusters however showed a substantial barrier which should result in oxygen deficient clusters.
New Organometallic Selenium Reagents for Low Temperature Omcvd of Znse
Authors: Danek M. , Huh J-S. , Jensen K. F. , Gordon C. , Kosar W. P. 
Published: March 2011

AbstractZnSe epitaxial films have been grown on (100) GaAs by reduced pressure organometallic chemical vapor deposition (OMCVD) from tertiary-butyl(allyl)selenium (tBASe) and dimethylzinc triethylamine adduct (DMZnNEt3) at temperatures of 325-450ΰC. Good surface morphology, film crystallinity and interface quality have been found with scanning electron microscopy (SEM), double crystal X-ray diffraction (DCD) and Rutherford back scattering spectroscopy (RBS). Secondary ion mass spectrometry (SIMS) shows negligible carbon concentration (below 5x1017atoms/cm3). Low temperature photoluminescence (PL) exhibits a strong near band-edge emission with a dominant donor-bound peak. Gas-phase pyrolysis of tBASe has been probed at reduced pressure in a molecular beam mass spectrometric system in hydrogen and deuterium carrier gases. The precursor decomposes above 200ΰC by β-hydrogen elimination and by homolysis of the Se-C bonds. High isobutene vs. isobutane ratios (50-100) indicate a predominance of β-hydrogen elimination over homolysis at temperatures below 400ΰC. Diallylselenium is present in the gasphase in low concentrations at temperatures of 200-350ΰC. Diallylselenium, methylallylselenium and dimethyl-selenium have been observed as minor by-products during pyrolysis of co-dosed tBASe and DMZnNEt3. The effect of the retro-ene decomposition pathway of allylselenium reagents on carbon incorporation into ZnSe films is further probed by growth experiments with in situ generated 2-methylpropaneselenal.
Picosecond Optical Second Harmonic Studies of Adsorbate Reduction Kinetics on Cadmium Sulfide
Authors: Scott T. W. , Martorell J. , Chang Y. J. 
Published: March 2011

AbstractTime resolved surface second harmonic generation has been used to probe the photoreduction kinetics of malachite green adsorbed onto single crystal cadmium sulfide. A detailed analysis is presented of how the adsorbates and the noncentrosymmetric substrate contribute separately to the total second harmonic signal. Conditions under which the adsorbates can be cleanly detected are described. To complement kinetic measurements of adsorbate reduction, the time evolution of conduction band carriers was determined using sum frequency up conversion of the recombination luminescence. In addition, the formation and decay of surface trapped carriers was monitored using near infrared transient absorption. Comparing the time scale for photoreduction with the relaxation kinetics of mobile and trapped charge carriers indicates that short lived mobile carriers rather than longer lived surface trapped carriers dominate interfacial charge transfer in this system.
Adsorption and Reaction of TiCl4 on W(100)
Authors: Chen Wei , Roberts Jeffrey T. 
Published: March 2011

AbstractThe adsorption and reaction of titanium tetrachloride (TiC14) on W(100) was investigated using temperature programmed desorption mass spectrometry (TPRS), x-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and low energy electron diffraction (LEED). TiC14 adsorbs molecularly on W(100) at 100 K. Desorption from the molecularly bound state occurs near 220 K. Competing with desorption is dissociation to adsorbed TiCl3, which reacts to form gaseous TiCl4 near 450 K. TiC13 also decomposes into atomically adsorbed Ti and Cl on the surface upon heating to 700 K.
Ecr Plasma Enhanced MOCVD of Titanium Nitride
Authors: Gross M.E. , Weber A. , Nikulski R. , Klages C.-P. , Charatan R.M. , Brown W.L. , Dons E. , Eagleshamn D.J. 
Published: March 2011

AbstractThe ability to deposit high purity TiN by a CVD process that can provide improved conformality over current sputter deposition processes is critical for multilevel Si ULSI device applications. Low temperature deposition of high quality TiN films has been achieved by an ECR plasma enhanced CVD process using the metal-organic precursor, tetrakis(dimethylamido) titanium, Ti(N(CH3)2)4 (TDMAT). TDMAT is introduced into the downstream region of either a N2 or NH3 ECR plasma to deposit highly conducting films at deposition temperatures of as low as 100°C. The electrical resistivity of the TiN films decreases from 100-150μΩ-cm at a deposition temperature of 100°C to 45μΩ-cm at 600°C. The choice of plasma gas, N2 or NH3, affects the composition as well as the crystallographic texture of the films, which exhibit preferred (200) and (111) orientations, respectively. Pretreatment of the Si substrate with N2 or NH3 plasmas also affects the film morphologies, as demonstrated by switching the plasma gas between pretreatment and deposition.
Investigations of Tin and Ti Film Deposition by Plasma Activated Cvd Using Cyclopentadienyl Cycloheptatrienyl Titanium, a Low Oxidation State Precursor
Authors: Charatan Robert M. , Gross Mihal E. , Eaglesham David J. 
Published: March 2011

AbstractSequential Ti and TiN thin film deposition by CVD is highly desirable for advanced Si integrated circuit applications. To date, most CVD TiN work has been performed using Ti(IV) compounds. We have investigated plasma assisted CVD using a lower oxidation state precursor, cyclopentadienyl cycloheptatrienyl titanium, (C5H5)Ti(C7H7) (CPCHT), which might provide a more facile pathway to both Ti and TiN film formation. CPCHT was introduced with H2 carrier gas into the downstream region of an NH3, N2 or H2 plasma. Low resistivity (100-250 μΩ-cm), nitrogen rich TiN films with little C or O incorporation were deposited at 300 to 600°C, inclusive with either activated N2 or NH3. Although the film texture was influenced by the chosen plasma gas, the average grain size of the N2 and NH3 plasma deposits was similar. Annealing studies showed that the CVD TiN was an effective diffusion barrier between aluminum and silicon to at least 575°C. TEM micrographs revealed that, in contrast to many CVD metal films, the growth of this TiN was not columnar. Film conformality was investigated by scanning electron microscopy (SEM). Experiments performed with activated H2 resulted in deposits of Ti contaminated with C. No depositions were observed in the absence of plasma excitation.
Characterization of Silicon-Nitride Film Growth by Remote Plasmaenhanced Chemical-Vapor Deposition (Rpecvd)
Authors: Lu Zhong , Ma Yi , Habermehl Scott , Lucovsky Gerry 
Published: March 2011

AbstractWe have characterized RPECVD formation of Si-nitride films by relating the chemical bonding in the deposited films to the growth conditions. Gas flow rates for different N- and Si-atom source gases have been correlated with (i) the film stoichiometry, i.e., the Si/N ratio, and the (ii) the growth rate. N2 and NH3 were used as N-atom source gases, and were either delivered (i) up-stream through the plasmageneration tube, or (ii) down-stream. Different flow-rate ratios of NH3/SiH4 were found for deposition of stoichiometric Si-nitride films using up-stream or down-stream introduction of NH3. This is explained in terms of competition between excitation and recombination processes for the N-atom precursor species. Stoichiometric nitride films could not be obtained using the N2 source gas for (i) either up-stream or down-stream delivery, and (ii) for plasma powers up to 50 W. This is attributed to the higher relative binding energy of N-atoms in N2 compared to NH3, and to significant N-atom recombination at high N2 flow rates through the plasma generation region.
Flow Tube Kinetics of Gas-Phase Cvd Reactions
Authors: Weiller Bruce H. 
Published: March 2011

AbstractThis paper explores the use of a flow-tube reactor coupled to an FTIR spectrometer to study gas-phase chemical reactions in CVD systems. We show that our apparatus can generate reliable kinetics data by reproducing the literature rate constant for the reaction between O3 and isobutene. We present data from this apparatus on two technologically important systems: TiN from Ti(NMe2)4 (TDMAT) and NH3 and SiO2 from tetraethoxysilane (TEOS) and O3. The results presented include kinetics data for the reaction of Ti(NMe2)4 with NH3 and ND3 at room temperature and the IR spectra of the products from the reaction of TEOS with O3 at 175°C.
Krf Excimer Laser Induced Photochemical Modification of Polyphenylenesulfide Surface Into Hydrophilic Property
Authors: Kashiura H. , Okoshi M. , Murahara M. 
Published: March 2011

AbstractCarboxyl groups were photochemically substituted for hydrogen atoms at a polyphenylenesulfide surface by using an KrF excimer laser light and vaporized formic acid. In the process, the polyphenylenesulfide film was placed in the formic acid vapor, and the surface was irradiated with the KrF excimer laser light. Irradiating with the laser, the surface was dehydrogenated by the hydrogen atoms which were photodissociated from the formic acid; the dangling bonds on the surface combined with the COOH radicals which were also photodissociated. The hydrophilic property of the photomodified surface was evaluated by the measurement of the contact angle with water. The dehydrogenation reaction and the substitution reaction of the COOH radicals were inspected by XPS analysis. Surface morphology of the sample was observed by SEM photograph.
Scanning Tunneling Microscopy Observation of the Reaction of AlCl3 on Si(111)-7×7 Surface
Authors: Uesugi Katsuhiro , Takiguchi Takaharu , Izawa Michiyoshi , Yoshimura Masamichi , Yao Takafumi 
Published: March 2011

AbstractThe initial stage of the reaction of aluminum trichloride (AlCl3) with the Si(111)-(7×7) surface and the annealing effects of the adsorbed surface are investigated with a scanning tunneling microscope (STM). Reacted and unreacted sites manifest in the contrast of adatom sites on the AlCl3-exposed surface. An AlCl3 molecule dissociatively adsorbs onto the Si( 111)-(7×7) surface at room temperature, which yields C1 atoms. Preferential adsorption site is found to be the center adatom site rather than the corner adatom site, and Cl atom adsorbs onto the top site of the center Si adatom. The migration of adsorbed molecules (AlClx) in the (7×7) unit cell is observed at room temperature. The SiCl,, species desorb from the surface by thermal annealing at 600 'C, leaving vacancies behind. After annealing at 1200 0C, Al deposition occurs in a limited area and the surface shows the V/7×V7 reconstruction, which is a characteristic Al-induced surface structure.