bluuebunny/crossref_metadata_2025_split huggingface dataset:
Temperature effects on supercritical carbon dioxide extractions of hydrocarbons from geological samples
Authors: Jafféa Rudolf , Gong Yumin , Furton Kenneth G. 
Published: May 2005

AbstractThe extraction of aliphatic and aromatic hydrocarbons from New Albany Shale by supercritical carbon dioxide at different extraction temperatures is described. The main goal of this work was to determine the effect of the temperature on the extraction process (i.e. relative extraction rate and efficiency). The data suggest that temperature changes of 20 and 40 degrees for the relatively moderate extraction temperatures tested (55, 75, and 95°C), can have significant effects on both relative extraction rates and yields. While lower molecular weight aromatics presented exponential extraction profiles, similar to those of the aliphatic hydrocarbons, higher molecular weight aromatics, such as the phenanthrenes, showed a linear extraction profile. This behavior cannot be explained by solubility differences in the supercritical fluid alone, and are, therefore, most likely based on differences in the speciation of the hydrocarbons within the sample matrix. Extractions at elevated temperatures (300°C) resulted in significant increments in the relative recoveries of all compounds, but particularly for the aromatic hydrocarbons. This may be caused by structural rearrangement of the sample matrix with subsequent release of trapped hydrocarbons and possibly by C‐S and S‐S bond breakage.
Comparison of mathemical methods for the calculation of retention indices at high temperature in gas chromatography
Authors: Didaoui L. , Touabet A. , Meklati B. Y. 
Published: May 2005

AbstractThe retention indices of three homologous series (2‐alkanones, 1‐alkanols, cycloalksanones) have been determined at high temperature by the application of two new adaptation methods: A multiparametric least‐squares regressions iterative method based on the dertermination of the adjusted retention times and a cubic interpolation directly using the uncorrected retention times without dead time correction. The two methods were applied to two types of columns. The first group includes eight packed columns (seven OV polymethylphenylsiloxane and Apolane‐87 stationary phases), while the second includes five glass capillary columns (four methyl‐silicons with different film thicknesses and Apolane‐87 stationary phases). The retention indices obtained with a multiparametric and a cubic interpolation methods were compared with each other and with those calculated by Grobler's, Guardino's, Kaiser's and Kovàts' methods. The influence of coating, film thickness, and temperature on them was investigated.
Comparision of varuious bulk fluids and modifiers as near‐crtical mobile phases on a polymeric column using linear solvatio energy realationships
Authors: Blackwell John A. , Stringham Rodger W. 
Published: May 2005

AbstractLinear solvation energy realationships (LSERS) were used to qunatitatively compare the relative contributions of dipolarity/polarizability, hydrogen bonding, and other types of intermolecular interactions to retention and selectivity using various bulk moblie phase component. Using experimental condition which differ only by the compostion of the bulk moble phase component, the factors which cause selctivity to differ between HPLC, subcritical fluid chromatography and supercritical fluid charomatography were decovoluted. Heptance‐based HPLC mobile phases showed superior selectivities towards analytes which differ in hydrogen bond donating ability, gas‐to‐hexadecane partion coefficint and dipolarity/ploarizability. subcritical fluid chromatography with HFC‐134a (1, 1, 1, 2‐tetrafluoroethane) as the bulk fluid produced superior seclectivities for which differ in hydrogen bond accepting ability and execess molar refraction properties. Many of these factors showed temperature dependences which act to attenuate or accenture the particular intermolcular interaction.
Capillary electrophoresis with post‐column addition of terbium and sensitized lanthanide‐ion luminescence detection for the determination of diflunisal and salicylic acid
Authors: Milofsky Robert , Bauer Eve 
Published: May 2005

AbstractA detection scheme based on the Post‐column addition of terbium followed by sensitized luminescence detection has been developed. Two model Compounds‐ saliculic acid and diflunisa‐ were separated by capillary electophoresis in an alkaline phosphate buffer. A Solution containing terbium and CTAB was added post‐column via a “home‐built” reactor resulting in the rapid fromation of the strongly luminescent terbium‐salicylic acid and terbium‐diflunisal complexes in a reaction capillary. Following complexationn in the reaction capillarty, the 325 nm line from a HeCd laser was used to excite the analytes which efficiently transfer their energy to terebium. Resuulant luminescence of terebium was liner of 2 orders of magnitude. This novel and practical system enables the detection of micromolar concentrations of diflunisal and salicylic acid‐ a 10 fold improvement over UV absorbance detection in the same system. Post‐column addition of terbium also eliminates the problems associated with strong adsorption of the lanthanide ion to the silica walls of the separation capillary and the formation of metal‐ligand complexes with different coordination numbers.
Analysis of tinuvin 1577 polymer additive in edible oils using on‐line coupled HPLC‐GC
Authors: Baner Albert L. , Guggenberger Andreas 
Published: May 2005

AbstractAn application of automated on‐line HPLC‐HRGC is described for direct analysis of edible oils for migrated polymer additives. The sample preparation, separating the additive from the oil triglycerides, is carried out using normal phase HPLC. The fraction of the eluent containing the additive is automatically transferred to a HRGC where a second and final separation of the additive from minor oil components takes place. The method compares well with off‐line separation methods. Migration data for Tinuvin 1577 from PET and PC polymers as well as an unspecified experimental polymer is given. The advantages and disadvantages of using different edible oils as food simulants are discussed.
A reversed phase high‐performance liquid chromatography method for determination of cephalexin in human plasma
Authors: Pecavar Anika , Šmidovnik Andrej , Milivojevic Dušan , Prošek Mirko 
Published: May 2005

AbstractA reversed‐phase HPLC method for the analysis of cephalexin (7‐[(aminophenylacetyl)amino]‐3‐methyl‐8‐oxo‐5‐thia‐1‐azabicyclo[4.2.0]oct‐2‐ene‐2‐carboxylic acid) by isocratic separation is described. A comparison is made between the ultrafiltration land the extraction procedure developed in our laboratory. The extraction procedure, based on the deproteinization of plasma with perchloric acid followed by the extraction with dichloroethane and separation of cephalexin on a reversed phase column, gave better recovery. Quantitative validation of our method has been performed by an external standard technique. The relative standard deviations were between 1.1 and 1.9% in the within‐day assay and between 1.2 and 2.2% in the inter‐day assay. The limit of detection was 0.14ug/ml and the limit of quantification was 0.28ug/ml. This method is rapid, sensitive, simple, and reproducible. The LC MS/MS technique was successfully used for identification and quantification of cephalexin in human plasma samples.
A design approach to the structural analysis of interleukin‐2
Authors: Ciardelli T. L. , Landgraf B. , Gadski R. , Strnad J. , Cohen F. E. , Smith K. A. 
Published: May 2005

AbstractA semi‐synthetic protein design approach has been employed for the structural investigation of a putative helical region at the C‐terminus of Interleukin‐2. With crystallographic or NMR derived conformational data as yet unavailable, we have relied only on primary sequence information and computer‐assisted modelling to direct the analysis. By employing both chemical peptide synthesis and recombinant DNA methods, the C‐terminus of IL‐2 was modified according to a strategy designed to stabilize helical secondary structure. A semi‐synthetic protein incorporating 12 simultaneous amino acid replacements was constructed, which possessed potentiated biological activity and displayed a far UV circular dichroism spectrum comparable to a hybrid protein with the authentic sequence. By comparison, another hybrid protein containing a C‐terminal region designed to contain helix breaking residues was totally devoid of bioactivity. These findings provide evidence that the modelling method correctly identified a helix necessary for the formation of a bioactive tertiary fold. Moreover, by employing semi‐synthesis it was possible to circumvent the difficulties associated with the preparation, purification and analysis of multiple recombinant proteins, and also to avoid the unreliability of total chemical synthesis for proteins greater than 100 residues.
Theoretical analysis of compartmented coupling in linear enzyme systems
Authors: Brooks S. P. J. , Storey K. B. , Suelter C. H. 
Published: May 2005

AbstractExact equations which describe the kinetic patterns of enzyme/enzyme complexes, when compartmented coupling occurs between them, are presented. Compartmented coupling refers to the creation of a local environment in which the concentration of an intermediate, shared by two enzymes, is higher than its solution concentration. This result in a higher coupling enzyme activity, a condition reflected in a shorter transition time for the system. In this paper, equations are presented which allow experimenters to quantitate the effect of compartmented coupling in terms of changes in the apparent Km and Vmax values. The equations presented in this paper are more exact than those previously derived since they do not incorporate first order assumptions before derivation.
Zymogen activation: Effect of peptides sequentially related to the bovine β‐trypsin N‐terminus on kazal inhibitor and benzamidine binding to bovine trypsinogen
Authors: Ascenzi Paolo , Coletta Massimo , Amicoi Gino , Bolognesi Martino , Guarneri Mario , Menegatti Enea 
Published: May 2005

AbstractThe activating effect of peptides sequentially related to the Ile 16‐Vall7‐Gly 18 N‐terminus of bovine β‐trypsin (nemely Ile‐Val‐Gly, Ile‐Val, Ile‐Leu Ile‐Ala, Val‐Val, Leu‐Val, and Val‐Leu) on the thermodynamic parameters for the binding of the porcine pancreatic secretory trypsin inhibitor (Kazal inhibtor) and benzamidine to bovine trypsinogen was investigated at pH 5.5 (Bis tris‐HCI buffer, I=0.1 M) and T=21 ± 0.5°C. Thermodynamic parameters for Kazal inhibitor and benzamidine association to the binary peptide/zymogen adducts are more favorable than those observed for ligand binding to the proenzyme alone, although never as much as those reported for the formation of bovine β‐trypsin/Kazal inhibitor and bovine β‐trypsin/benzamidine adducts. Analogously, the affinity of activating peptides for the binary proenzume/Kazal inhibitor and binary proenzyme/benzamidine complexes is higher than that observed for peptide binding to free bovine trysinogen. Differences in affinity for ligand binding to free bovine trypsinogen. Differences in affinity for ligand binding to free bovine trypsinogen, to its binary adducts and to bovine β‐trypsin suggest the presence of different activation levels of the proenzyme, none of which structurally coincide with that achieved in bovine β‐trypsin. The existence of different discrete states suggests that the zymogen‐to‐active enzyme transition should not be considered as a two‐state process but as a multistep event.
Hidden self‐association of proteins
Authors: Muramatsu Nobuhiro , Minton Allen P. 
Published: May 2005

AbstractSedimentation equilibrium measurements were carried out on solution bovine serum albumin, aldolase, and ovalbumin in phosphte‐buffered saline, pH7.2, at 10°C. The data obtain for each protein were analyzed to yield the dependence of apparent weight‐average molecular weight upon protein concentration, over a concentration range of ca 1–200 g/L. Using the approximate theory of Chatelier and Minton ((1987) Biopolyymers 26, 507–524), models are formulated for the dependence of apparent weight‐average molecular weight upon cocentration in non‐ideal solutions containing proteins which may self‐associate accroding to a monomer/n‐mer or a monomwer/dimer/tetramer scheme. The concentration dependence data for serum albumin may be accounted for, assuming either no self‐asociation or weak monomer/dimer/association. The data for aldolase may be accounted for assuming either weak monomer/dimer or weak monomer/timer association. The data for ovalbumin may be accounted for assuming eiether weak monomer/trimer or weak monomer/dimer/tetramer association. The association do not approach saturation at the hightest concentrations studied, and the standard‐state free energy change accompanying self‐association amount to less than 4 kcal/mol off intermolecular contacts, suggesting that non‐specific clustering of protein molecules at high concentration rather than the formation of specific complexes is being observed.
Differences between sites of binding to DNA and strand cleavage for complexes of bleomycin with iron of cobalt
Authors: McLean Michael J. , Dar Ahsana , Waring Michael J. 
Published: May 2005

AbstractThe sequence specificity of bleomycin A5 and of its light‐activated cobalt complex were compared by examining the relative cleavage of each strand of two DNA fragments by either species. Significant differences between the two metallobleomycins were observed. The iron–bleomycin (Fe–BLM) complex cleaved the DNA molecules preferentially at dinucleotides GpT and GpC, whereas the light‐activated cobalt‐bleomycin complex (Co–BLM) showed a preference for cutting at the dinucleotide Gp A in addition to cleavage at every GpT dinucleotide. Further, new sites of preferential cleavage were noted for Co–BLM in regions of the DNA where enhanced reaction with DNAaseI can be observed in the presence of the antibiotic. No differences in the cutting behaviour of the Fe–BLM were evident upon irradiation of the reaction mixture. A reduction in the relative efficiency of cutting at GpC sequences by Co–BLM is responsible for the previously observed diminution of double‐strand breaks under condition of photoactivated cleavage. The results are discussed in terms of the likely production of highly reactive, diffusible cutting elements in the light activated reaction, which cause cleavage of the DNA in regions where the antibiotic is not bound.
pH regulation of calcium recognition by an amino acid containing acyclic ionophore
Authors: Spisni A. , Franzoni L. , Corradini R. , Marchelli R. , Dossena A. 
Published: May 2005

AbstractCalcium ion recognition by a dicarboxylic ionophore containing two (S)‐phenylalanine residues joined via an amide bond by a flexible tri‐oxa‐undecanoyl bridge (Phe‐3‐O) has been investigated in a wide pH range (from pH 2 to 12). Experiments were performed in methanol and chloroform by 1H and 13C NMR, relaxation times and 2D NMR (COSY, NOESY and J‐resolved experiments). Recognition is shown to be regulated by pH, as it occurs in at least three different coordination modes according to the experimental conditions. Even at low pH (pH 2) the ion is already complexed in the compartment created by the ethereal oxygens and the amide carbonyls. At higher pH, it becomes fully encapsulated in a pseudo‐cyclic structure and at very basic pH it is localized between the amide carbonyls and the carboxylates. For these peculiar properties Phe‐3‐O appears to be a very promising ionophore in a transmembrane pH gradient system.
Recognition in cell adhesion. A comparative study of the conformations of RGD‐containing peptides by Monte Carlo and NMR methods
Authors: Cachau Raul E. , Serpersu Engin H. , Mildvan Albert S. , August J. Thomas , Amzel L. Mario 
Published: May 2005

AbstractMany of the proteins that mediate cell adhesion processes–fibronectin, fibrinogen, vitronectin, von Willebrand factor, osteopontin, laminin and various collagens – contain the amino acid sequence Arg‐Gly‐Asp. Short peptides that include this sequence have been shown to inhibit the interactions of cell adhesion proteins with their receptors and to have dramatic effects on developmental processes involving cellular recognition. In order to determine which conformations are accessible to Arg‐Gly‐Asp containing peptides, we analyzed tri‐, tetra‐ and pentapeptide using molecular mechanics and Monte Carlo methods, and studied the solution conformations of the pentapeptide Gly‐Arg‐Gly‐Asp‐Ser using nuclear magnectic resonance techniques. The Monte Carlo method was used to: (a) identify the low energy conformations of the peptides and (b) evaluate their thermodynamic properties. In the case of the pentapeptide Gly‐Arg‐Gly‐Asp‐Gly, the four stable conformations include three with reverse turns and one open structure. The conformations found in this analysis are compatible with the nuclear magnetic resonance (nuclear Overhauser effect) data.
Interaction of the peptide CF3‐Leu‐Ala‐NH‐C6 H4‐CF3 (TFLA) with porcine pancreatic elastase. X‐ray studies at 1.8 Å
Authors: de la Sierra Ines Li , Papamichael Emmanuel , Sakarellos Constantinos , Dimicoli Jean‐Luc , Prangé Thierry 
Published: May 2005

AbstractThe peptide trifluoroacetyl‐Leu‐Ala‐(p‐trifluoromethylanilide), is a reversible inhibitor of pancreatic porcine elastase and is characterized by a Km of 2.5 × 10−8 M. Co‐crystals of the 1:1 complex were obtained in an acetate buffer + dimethylformamide solution at pH 5.7. Diffraction data were recorded on films at the LURE synchrotron facility. The inhibitor was localized on difference Fourier maps, and the refinement of the structure was performed by simulated annealing (XPLOR). The current agreement factor is R = 19% (for 13224 observed structure factors and 1.8 Å effective resolution). The RMS deviations from ideality of bond distances and angles are 0.02 Å and 2°, respectively. The inhibitor molecule was found in the active site, bent around the side chain of Phe‐215 in a geometry that resembles the previously reported structure of the CF3‐Lys‐Ala complex at 2.5 Å, in a parallel β‐sheet association with the loop 214–216. The analysis of the close contacts (less than 3.5 Å) indicates that the trifluoromethylamide bond interacts with the active site and not the Leu‐Ala or Ala‐anilide bonds. The two fluorinated groups of the inhibitor exhibit different specificities: the trifluoroacetyl group (N terminus) is tightly stacked between the two chain loops 191–195 and 213–215, while the trifluoromethylanilide (C terminus) shows less specificity and only a single contact.
Ligand‐binding properties of estrogen receptor proteins after interaction with surface‐immobilized Zn(II) ions: Evidence for localized surface interactions and minimal conformational changes
Authors: Hutchens T. William , Li Chee Ming 
Published: May 2005

AbstractThe site‐ or domain‐specific immobilization of steroid receptor proteins with preserved structure and function would facilitate the identification and purification of receptor‐associated regulatory components and nucleic acids. We have demonstrated previously that restricted surface regions of the estrogen receptor protein contain high affinity binding sites for immobilized Zn(II) ions. Possible conformational changes in receptor at the stationary phase immobilized metal ion interface were evaluated by monitoring alterations in the equilibrium dissociation constant (Kd) for [3H]estradiol. Soluble estrogen receptor proteins (unliganded) present in immature calf uterine cytosol were immobilized via surface‐exposed Zn(II)‐binding sites to beads of agarose derivatized with iminodiacetate (IDA)‐Zn(II) ions. The IDA‐Zn(II) bound receptor was incubated with increasing concentrations of [3H]estradiol (0.01–20 nM) in the presence and absence of unlabeled competitor (diethylstilbestrol) to determine the level of specific hormone binding. Steroid‐binding experiments were performed in parallel with identical aliquots of soluble receptor. Analyses of the equilibrium binding data revealed the presence of a single class of high‐affinity (Kd = 2.44 ± 1.5 nM, n = 10) steroid‐binding sites which were only marginally affected by receptor immobilization via surface‐exposed Zn(II) bindings sites (Kd = 2.58 ± 0.56 nM, n = 4). These data are consistent with the location of surface accessible Zn(II) binding site(s) on the receptor at or near the DNA binding domain which, upon occupancy, do not influence the steroid binding domain. The high affinity of receptor for immobilized metal ions and lack of evident conformational changes in the immobilized receptor suggest that stationary phases of immobilized metal ions loaded with receptor proteins may be useful as affinity tools for the analysis and purification of receptor‐associated macromolecules.
Specific isolation by anhydrotrypsin‐agarose chromatography of a recombinant protein tagged with an affinity tail arginine at the C‐terminus
Authors: Hirabayashi Jun , Kasai Ken‐ichi 
Published: May 2005

AbstractA characteristic property of anhydrotrypsin, i.e., its ability to strongly bind C‐terminal arginine, proved to be useful as a tool for specific enrichment of a recombinant protein. An arginine tail was introduced at the C‐terminus, for example, of a human β‐galactoside‐binding lectin by site‐directed mutagenesis. The resulting mutant recombinant lectin, which retained sugar‐binding activity as high as the wild‐type lectin, became recognizable by anhydrotrypsin. It was adsorbed on an anhydrotrypsin‐agarose column and eluted with benzoylglycylarginine. The added arginine tail could be specifically removed by carboxypeptidase B. When E. coli lyzate containing the mutant lectin was applied to the column more than 10‐fold enrichment of the mutant lectin was attained. This procedure should be generally applicable and may be advantageous because the addition of a single arginine residue may have minimal effect on the structure and function of the target protein.
Detection of antigen—antibody interactions by surface plasmon resonance. Application to Epitope Mapping
Authors: Fägerstam Lars G. , Frostell Åsa , Karlsson Robert , Kullman Mari , Larsson Anita , Malmqvist Magnus , Butt Helena 
Published: May 2005

AbstractSurface plasmon resonance (SPR) detection requires no labelling of antigen or antibodies and allows quantification of two or more interacting molecular species. The automated SPR instrument used here consists of an optical detection unit, an integrated liquid handling unit, and an autosapler. A first molecule is immobilized to the dextran modified surface of the sensor chip. By sequential introduction, the stepwise formation of multimolecular complexes can then be monitored. A two‐site binding assay which allows characterization of MoAb epitope specificities is described. A polyclonal rabbit anti‐mouse IgG1 (RAMG1) immobilized to the dextran surface is used to capture the first MoAb from unprocessed hybridoma culture supernatants. After introducing the antigen, and ability of a second MoAb to bind to the antigen is tested. The analysis cycle which is fully automated can be performed more than 100 times using the same RAMG1 surface. Since the detection principle allows monitoring of each reactant in the consecutive formation of a multimolecular complex, multi‐site binding experiments can be performed. Five MoAbs recognizing different epitopes on an antigen were shown to bind sequentially, forming a hexamolecular complex. MoAbs were further characterized by inhibition analysis using synthetic peptides derived from the primary structure of their antigen. As a model system MoAbs against recombinant HIV‐1 core protein p24 were used in all experiments.