bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hyphenation of gas chromatography and resonance‐enhanced laser mass spectrometry (REMPI‐TOFMS): A multidimensional analytical technique
Authors: Zimmermann Ralf , Boesl Ulrich , Heger Hang‐Jörg , Rohwer Egmond R. , Orthner Erla K. , Schlag Edward W. , Kettrup Antonius 
Published: May 2005

AbstractAnalysis of environmental samples usually requires time consuming sample preparation and clean‐up procedures prior to instrumental detection. Faster analysis requires an enhanced instrumental selectivity in order to reduce the necessary clean‐up effort. In this context we present a novel concept for coupling gas chromartography/mass spectrometry (GC‐MS) with high resolution UV spectoscopy to increase selectivity. We use UV‐laser induced, resonance‐enhanced multi‐photon ionization (REMPI)as a compound specifie ion source for time‐of‐flight mass spectrometry (TOFMS). The REMPI ionization involves the UV absorption spectroscopy into the ionization process as an aditional analytical dimension. The heart of the GC‐REMPI‐TOFMS coupling is a specially designed valve, which repetitively (20 Hz) expands the chromatographic eluent as short supersonic jet gas pulses (≈ 150 μs duration) into the vacuum of the mass specrtrometer. The sample molecules are cooled down to temperatures of 10‐40 K within the jet expansion. Under these conditions, UV absorption spectriscopy (i.e. REMPi spectroscopy) becomes highly compound selective, even able to distinguish isomeric compounds. The ions formed by REMPI ionization are mass analyzed in the TOFMS. Thus the GC‐REMPI‐TOFMS coupling presented here is actually a three‐dimensional analytical instrument, providing gas chromatographic (retention time) as well as mass spectrometric (molecular mass) and UV ‐spectroscopic (excitation laser wavelength) selectivity. In combination with gas phase sampling and concentration techniques for semi‐volatile organic air pollutants based,e.g., on silicone rubber traps the GC‐LAMS technique can be a powerful tool for fast environmental target analysis,e.g. for industrial emission control purposes.
The variation of carrier gas viscosities with temperature
Authors: Hinshaw John V. , Ettre Leslie S. 
Published: May 2005

AbstractAfter describing simplified equations exspressing the temparature dependency of the viscosity of carrier gases (helium, nitrogen and hydrogen ) relative to a base value, absolute relationships based on the kinetic theory of gases are discussed. Comparative data obtained using various calculation methods are given and are compared to measured values. Based on the kinetic relationshipsm, of viscosity. Finally, the influence of pressure on the viscosity is also briefly discussed. As a supplement, Viscosity data are tabulated for the three gases in the range of 0°C to 400°C in increments of 2 K, calculated using the kinetic relationships.
On‐line determination of organophosphorus pesticides in water by solid‐phase microextraction and gas chromatography with thermionic‐selective detection
Authors: Lopez‐Avila Viorica , Young Richard , Beckert Werner F. 
Published: May 2005

AbstractThis paper describes the extraction of 49 organophosphorus pesti‐cides (OPPs) from water samples using solid‐phase microextraction (SPME). Three fibers, including a 15‐μm XAD‐coated fiber, a 85‐μm polyacrylate‐coated fiber, and a 30‐μm polydimethylsilox‐ane‐coated fiber (PDMS), were evaluated here. The effects of stirring and the addition of NaCl to the sample were examined for the polyacrylate‐coated fiber. The precision of the technique was examined for all three fibers and the extraction kinetics were investigated using the XAD‐ and polyacrylate‐coated fibers. With some exceptions, the XAD‐ and polyacrylate‐coated fibers performed better than the PDMS‐coated fiber. The superiority of the XAD‐nd polyacrylate‐coated fiber. The superiority of the XAD‐ and polyacrylate‐coated fibers over the PDMS‐coated fibers can be attribuibuted to the aromatic functionalities of the XAD and the polar functionalities in the polyacrylate. The relatively high percent RSDs indicate that the SPME technique needs to be further refined before it can be used for anything other than screening. A more effective form of agitation than mechanical stirring may be neccessary to reduce variability and achieve a faster equilibrium between the sample and the SPME fiber.
Determination of acyclovir in plasma by high performance liquid chromatography with UV detection. Method development and method validation
Authors: Šmidovnik A. , Wondra Alenka Golc , Prošek Mirko 
Published: May 2005

AbstractA HJPLC method for the determination of acyclovir in plasma is described. The method is simple and sensitive enough for bioequiva‐lence studies, where a large number of plasma samples with low acyclovir concertration are involved. The procedure is based on the deproteinization of plasma with perchloric acid and separation of acyclovir on a Hypersil ODS Column at pH 5.6 with UV detection. The calibration standards are linear up to at least 4000 ng/mL and the limit of quantification is 10 ng/mL.
Separation of basic proteins and peptides by capillary electrophoresis using a cationic surfactant
Authors: Ding Weiliang , Frit James S. 
Published: May 2005

AbstractIncorporation of a low concentration of cetyltrimethylammonium bromide (CTAB) in the running electrolyte is shown to dynamically coat the silica capillary and to reverse the direction of electroosmotic flow. The CTAB coating prevented interaction of proteins with the capillary surface and enabled sharp peaks to be obtained in the electropherograms. A systematic study of experimental parameters demonstrated the importance of selecting a suitable buffer electrolyte and an appropriate pH. Excellent separations were obtained for five proteins, three enkephalins, and six dipeptides with an efficiency of approximately 500,000 theoretical plates per meter. The method developed is very simple to perform and was found to give excellent reproducibility.
Solid phase extraction of organophosphorus, triazine, and triazole‐derived pesticides from water samples. A critical study
Authors: Báez Maria E. , Rodriguez Manuel , Lastra Olga , Contreras Paola 
Published: May 2005

AbstractA critical study using C18 SPE columns for the determination of organophosphorus, triazine, and triazole‐derived pesticides, nap‐ropamide, and amitraz is presented. The type of sorbent, sorbent mass, flow rate in the extraction process, sample concentration of the different compounds, sample volume, pH, and ionic strength were evaluated. Special emphasis was placed on the evaporation step of eluates prior to GC determinations and on prefiltration of sample waters. Pesticide recovery is linear over a wide range of concentrations for most of compounds under study. Under general extraction conditions losses can be expected for amitraz, pro‐metryn, prometon, dimethoate, penconazole, and propiconazole. At 100 ng L−1, enhanced responses are produced for mevinphos, simazine, malathion, triadimefon, methidathion, and phosmet, which can be attributed to matrix effects. At basic pH, recovery of prometon, prometryn, and penconazole are improved. Low flow rates and high ionic strength enhance the recovery of prometon and prometryn. For phosmet, the influence of sample volume was established. Likewise, the influence of sorbent quantity was established for phosmet and dimethoate. Losses during the evaporation step were observed for mevinphos, dimethoate (> 50%), penconazole, propiconazole, and prometon (30%). Prefiltration of sample waters did not cause significant variations in the whole process of extraction. Impurities arising from the sorbent materials were not detected.
Tris (2,2′‐bipyridyl)ruthenium (III) as a chemiluminescent reagent for detection in capillary electrophresis
Authors: Dickson James A. , Ferris Matt M. , Milofsky Robert E. 
Published: May 2005

AbstractA post‐ column chemiluminescent technique for thedetection of compounds that are poor chromoshores using electorogenerated chemiluminescence following separation by capillartgy electrophoresis is described. The luminrescent signal is generated followintg the reaction of anlyres (e.g. amines) with Ru(bpy)33+, which isx electrochemically generated post‐columan from Ru(bpy)32+. Tripropylamine and proline are used as two model compounds to demostrate the feasibility of the method. Detection limits for the prototype system were in the micromolar rage, suggesting that this technnique offers an alternative to indirect detection of compounds that are poor chromophores with an added selectivity advangage. The system includes the use of a conductive joint to isolate the separation field from the potential necessary to drive the elctrogenerated chemiluminescent reactiion. Addition of the chemiluminescent reagent Ru(bpy)32+ post‐column did not decrease the efficiency of the separation. The design and favrication of the novel cell is discussed.
Molecular recognition: Model studies with convergent functional groups
Authors: Rebek Julius 
Published: May 2005

AbstractModel studies of molecular recognition are reviewed with emphasis on contributions from macrocyclic chemistry. Recent developments concerning new molecular shapes are discussed. The advantages of a molecular cleft are presented. In these structures functional groups converge to create a microenvironment complementary to substrates. Specifically, di‐, tri‐ and tetracarboxylic acids of varying sizes are shown to recognize smaller molecules of complementary shape. The new receptors function by a combination of hydrogen bonding and aryl stacking interactions. Substrates include amines, acids, amino acids, metal ions and nucleotide components. The relationship between functional group orientation and catalysis is explored and two systems capable of concerted acid/base catalysis are introduced.
Monosized, magnetic polymer particles: Their use in separation of cells and subcellular components, and in the study of lymphocyte functionin vitro
Authors: Lea T. , Vartdal F. , Nustad K. , Funderud S. , Berge A. , Ellingsen T. , Schmid R. , Stenstad P. , Ugelstad J. 
Published: May 2005

AbstractBy employing the principles of “activated swelling”, monosized, superparamagnetic polymer particles have been prepared ranging in size from 1–100 μm. Both during and after the swelling process, the particles can be modified to meet a series of specific demands making them potentially very interesting for many separation and assay purposes.Using monoclonal antibodies to direct the magnetic beads to their targets, immunomagnetic separation has turned out to be one of the most specific, reliable and, above all, the fastest technique available today to isolate particulate material for further studies. So far, most efforts have been concentrated on methodology for fractionation of cells in suspension, such as removal of tumour cells from bone marrow or isolation of lymphoid cells from peripheral blood. These studies have both established the parameters necessary for optimal performance and at the same time laid the groundwork for future developments making immunomagnetic separation an exciting new tool in many research areas.High speed and specificity are the most conspicuous features of immunomagnetic cell separation. These properties have been exploited in the successful development of a new technique for tissue typing of cells directly from peripheral blood specimens. Both higher sensitivity and specificity have been obtained. The same principles can be used for fast and safe quantification of cell populations and subpopulations in blood and cell suspensions.The functions of, and interactions between, peripheral blood cell populations or subpopulations in the immune response have also been studied with high precision. The significance of direct cell contact on the one hand, and soluble factors on the other, can now be established in detail. Immunomagnetic beads have also been used to study the interaction between various T lymphocyte membrane molecules in the early phases of the activation process.Finally, the usefulness of specially developed particles for the fractionation of subcellular components is described.
Substance P synthesis by enzymatic fragment condensation using product–directed antibodies as molecular traps
Authors: Nyberg Fred 
Published: May 2005

AbstractThis paper describes the enzyme catalyzed synthesis of the undecapeptide substance P from its non‐associated fragments (1–7) and (8–11) or (1–8) and (9–11). The fragment condensation was mediated by the use of product specific antibodies as molecular traps. As catalyst a previously purified endopeptidase was used which specifically hydrolyzes substance P at the Phe7–Phe8 and Phe8–Gly9 bonds. The synthesis was performed in analytical scale and product formation was guided by reversed phase HPLC combined with radioimmunoassay. It appeared that the substance P fragments (1–8) and (9–11) were condensed to a larger extent than (1–7) and (8–11). This observation may well result from the higher affinity of the antibodies observed for substance P (8–11) as compared to that found for the other fragments. Increased concentration of the antibodies also seemed to result in enhanced resynthesis of substance P.
Estrogen receptor interaction with immobilized metals: Differential molecular recognition of Zn2+, Cu2+ and Ni2+ and separation of receptor isoforms
Authors: Hutchens T. William , Li Chee Ming 
Published: May 2005

AbstractWe have utilized iminodiacetate (IDA) gels with immobilized Zn2+, Cu2+ and Ni2+ ions to evaluate the metal binding properties of uterine estrogen receptor proteins. Soluble (cytosol) receptors labeled with [3H]estradiol were analyzed by immobilized metal affinity chromatography (IMAC) before as well as after (1) 3 M urea‐induced transformation to the DNA‐binding form, and (2) limited trypsin digestion to separate the steroid‐ and DNA‐binding domains. Imidazole (2–200 mM) affinity elution and pH‐dependent (pH 7–3.6) elution techniques were both evaluated and found to resolve several receptor isoforms differentially in both the presence and absence of 3 M urea. Individual receptor forms exhibited various affinities for immobilized Zn2+, Cu2+ and Ni2+ ions, but all intact receptor forms were strongly adsorbed to each of the immobilized metals (Ni2+ > Cu2+ » Zn2+) at neutral pH. Generally, similar results were obtained with IDA–Cu2+ and IDA–Ni2+ in the absence of urea. Receptors were tightly bound and not eluted before 100 mM imidazole or pH 3.6. Different results were obtained using IDA–Zn2+; at least four receptor isoforms were resolved on IDA–Zn2+. Receptor–metal interaction heterogeneity and affinity for IDA–Zn2+ and IDA–Cu2+, but not IDA–Ni2+, were substantially decreased in the presence of 3 M urea. The receptor isoforms identified and separated by IDA–Zn2+ chromatography were not separable using high‐performance size‐exclusion chromatography, density gradient centrifugation, chromatofocusing or DNA‐affinity chromatography. The affinity of trypsin‐generated (mero) receptor forms for each of the immobilized metals was decreased relative to that of intact receptor. High‐affinity metal‐binding sites were mapped to the DNA‐binding domain, but at least one of the metal‐binding sites is located on the steroidbinding domain. Recovery of all receptor forms from the immobilized metal ion columns was routinely above 90%. These results demonstrate the differential utility of various immobilized metals to characterize and separate individual receptor isoforms and domain structures. Receptor‐metal interactions warrant further investigation to establish their effects on receptor structure/function relationships. In addition to the biological implications, recognition of estrogen receptor proteins as metal‐binding proteins suggests new and potentially powerful receptor immobilization and purification regimes previously unexplored by those in this field.
Conformational and receptor binding properties of human EGF and TGF‐α second loop fragments
Authors: Han Kyou‐Hoon , Ferretti James A. , Niu Chien‐Hua , Lokeshwar Vinatu , Clarke Robert , Katz Deborah 
Published: May 2005

AbstractThe solution conformation of the second loop fragment of human EGF, [Ala20]EGF(14–31), was determined using two‐dimensional NMR homonuclear Hartmann–Hahn and rotating frame nuclear Overhauser enhancement spectroscopy. The results are compared with the conformation of the second loop fragment of human TGF‐α, [Ala21] TGF‐α(16–32), and with that of the second loop of intact EGF. Comparison of the two experimentally determined structures of the second loop fragments shows significant differences in the turn regions of each peptide. For the EGF fragment, hydrophobic side chain groups protrude away from the ring, whereas for the TGF‐α fragment hydrophilic groups are directed away from the ring. Although these turn regions represent the putative receptor binding sites, neither second loop fragment binds to the EGF receptor. The biological activity is discussed in terms of the conformational differences found for the two second loop fragments.
Chemical probes reveal no evidence of Hoogsteen base pairing in complexes formed between echinomycin and DNA in solution
Authors: McLean Michael J. , Waring Michael J. 
Published: May 2005

AbstractFive different DNA fragments have been treated with a range of conformationally sensitive reagents in an effort to probe structural chages in DNA associated with binding of the bis‐intercalating antibiotic echinomycin. For each probe, the intensity and pattern of its reactivity with DNA have been analyzed in order to elucidate the effect of antibiotic binding on the accessibility of a specific site of sites to chemical attack. It was found that in one of the DNA fragments, pTyr2DNA, several purine residues exhibit enhanced reactivity to diethyl pyrocarbonate (DEPC) in the absence of bound antibiotic, and that this strongly sequence specific reaction is enhanced in the presence of quite low echinomycin concentrations. The echinomycin‐dependent reactivities towards DEPC of three homologous DNA fragments, chosen for their subtly different antibiotic binding characteristics, were also investigated. It was found that small changes in base sequence generate striking changes in susceptibility to modification by DEPC. The abolition of one antibiotic binding site leads to the creation of an new, intense DEPC‐reactive site. In the presence of moderate concentrations of echinomycin, specific thymidine residues exhibit enhanced reactivity towards osmium tetroxide. No differences in the reactivities of the DNA fragments towards bromoacetaldehyde, S1 nuclease, dimethyl sulphate of potassium tetrachloropalladinate were observed in the presence of the antibiotic. DEPC reactions were performed on tubercidin (7‐deaza‐adenosine) to determine the DEPC reactive positions in situations where N‐7 is inaccessible. Tubercidin was found to be generally resistant to attack by DEPC followed by treatment with base. We conclude that the bulk of structural changes induced by the binding of echinomycin to DNA do not involve Hoogsteen base pairing, but rather are due to sequence‐specific unwinding of the helix in a manner which is strongly dependent on the nature of surrounding nucleotide sequences.
Molecular recognition between oligopeptides and nucleic acids. Sequence specific binding of (4S)‐(+)‐ and (4R)‐(−)‐dihydrokikumycin B to DNA deduced form 1H NMR, footprinting studies and thermodynamic data
Authors: Lee Moses , Shea Regan G. , Hartley John A. , Lown J. Willliam , Kissinger Koren , Dabrowiak James C. , Vesnaver Gorazd , Breslauer Kenneth J. , Pon Richard T. 
Published: May 2005

AbstractThe sequence specific binding of the antibiotic (4S)‐(+)‐dihydrokikumycin B and its (4R)‐(−)enantiomer, [(S)‐I and (R)‐I, respectively] to DNA were characterized by DNase I and MPE footprinting, calorimetry, UV, spectroscopy, circular dichroism, and 1H NMR studies. Footprinting analyses showed that both enantiomers [(S)‐I and (R)‐I] bind to AT‐rich regions of DNA. 1H NMR studies (ligand induced chemical shift changes and NOE differences) of the dihydrokikumycins with d‐[CGCAATTGCG]2 show unambiguously that the N to C termini of the ligands are bound to 5′‐A5T6T7‐3′ reading from left to right. From quantitative 1D‐NOE studies, the AH2(5)‐ligand H7 distance of complex A [(S)‐I plus decamer (which is bound more strongely)] and complex B[(R)‐I and decamer] are estimated to be 3.8 ± 0.3 Å and 4.9 ± 0.4 Å, respectively. This difference in binding properties is reflected in the thermodynamic profiles of the two enantiomeric ligands determined by a combination of spectroscopic and calorimetric techniques. The binding freee energies (ΔG°) of (S)‐I and (R)‐I to poly d(AT)·poly d(AT) at 25°C are −31.8 and −29.3 kJ mol−1, respectively while the corresponding binding enthalpies (ΔH°) are −11.3 and −0.8 kJ mol−1. These data permit the construction of models for the binding of the enantiomeric dihydrokikumycins to DNA and account for the more efficient binding of the natural (S) isomer to DNA.
Evidence for the presence of disulfide bridges in opioid receptors essential for ligand binding. Possible role in receptor activation
Authors: Gioannini T. L. , Liu Y. F. , Park Y‐H. , Hiller J. M. , Simon E. J. 
Published: May 2005

AbstractThe mobility of purified μ opioid binding protein in SDS‐polyacrylamide gek electrophoresis is sensitive to the presence of reducing agents. In the presence of increasing concentrations of DTT the apparent molecular weight increases in a stepwise fashion from 53 kDa to 65 kDa. This reduction in mobility is attributed to the successive breakage of disulfide bridges, resulting in an increasingly asymmetric molecule. Treatment of cell membranes from various brain areas with reducing agents, such as DTT, produced a concentration‐dependent inhibition of opioid binding. Sensitivity to DTT inhibition varied between receptor types, μ > δ ≫ κ. For μ receptors, agonist binding was considerably more sensitive to DTT than antagonist binding. Inhibition by DTT is readily reversible and is unaffected by Na+ and/or Mg2+ ions. Reversibility may be partially prevented by the inclusion of a low concentration of a reducing reagent such as glutathione which does not inhibit binding but blocks reformation of disulfide bonds. Scatchard analysis of saturation data shows that DTT causes a pronounced decrease in binding affinity with little effect on receptor number. It is suggested that disulfide bonds are essential for ligand binding and that cleavage of one or more of these bonds may play a role in opioid receptor activation by agonists.
Regional ligand domain is involved in scavenger receptor‐mediated recognition of maleyl‐albumin by rat sinusoidal liver cells
Authors: Horiuchi Seikoh , Takata Kyoko , Araki Norie , Morino Yoshimasa 
Published: May 2005

AbstractScavenger receptor‐mediated endocytosis of maleyl‐albumin was studied with rat sinusoidal liver cells. Upon maleylation of > 28 mol lysine residues per protein, bovine serum albumin became an active ligand. Further modification of up to 37 mol lysine residues per protein resulted in a sharp increase in the ligand acitivity, reaching a maximum level thereafter. Removal of maleyl moieties from maleyl‐albumin (demaleylation) from 53 mol to 14 mol lysine residues per protein did not affect the ligand acitivity. However, further demaleylation to less than 5 mol lysine residues per protein led to complete loss of the ligand activity. Thus, the covalently incorporated maleyl moieties are needed for the ligand activity. The ligand activity was also generated when two peptides (Frag N and Frag C) from cyanogen bromide‐cleaved albumin were maleylated, indicating that the formation of an active ligand would not require a whole albumin molecule. Maleyl Frag C was further separated into three peptides; maleyl Frag C‐1 (261 amino acid residues), maleyl Frag C‐2 (102 residues) and maleyl Frag C‐3 (36 residues). The cellular binding and endocytic degradation of maleyl‐albumin or acetylated low density lipoprotein were effectively competed for by maleyl Frag C‐1 and maleyl Frag C‐2 but not by maleyl Frag C‐3. Thus, regional domains might be involved in the ligand recognition by the scavenger receptor.