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At least 109 records · Page 6Linked to original sources
PubMed1994

Temperature as a variable in reversed-phase high-performance liquid chromatographic separations of peptide and protein samples. I. Optimizing the separation of a growth hormone tryptic digest.

Peptide and protein samples are often complex mixtures that contain a number of individual compounds. The initial HPLC separation of such samples typically results in the poor resolution of one or more band pairs. Various means have been suggested for varying separation selectivity so as to minimize this problem. In this study of a tryptic digest of recombinant human growth hormone, the simultaneous variation of temperature and gradient steepness was found to be a convenient and effective means of varying selectivity and optimizing the separation. The use of computer simulation greatly facilitated this investigation.

Chromatography, High Pressure Liquid↗
PubMed1989

Sequence of centromere separation: kinetochore formation and DNA replication in dicentric chromosomes showing premature centromere separation in rat cerebral cells.

A subpopulation of rat cerebral endothelial cells, designated B1, exhibits an array of multicentric chromosomes. Because of the formation of bridges at anaphase, this cell population produced new types of multicentrics at every cell division. These chromosomes showed kinetochore proteins at every centromeric site and all centromeric regions replicated their DNA at the end of the S phase, more or less simultaneously. A new subpopulation of cells, designated B2, obtained from the original sample frozen at Wayne State University displayed several dicentrics. In contrast to B1 these chromosomes exhibit premature centromere separation as reported for mouse and human cell lines. These B2 dicentrics show only one site of kinetochore protein deposition. The timing of DNA replication around the centric region of prematurely separating centromere is also changed similar to the earlier reported premature DNA synthesis for mouse dicentrics. These observations suggest a universality of relationship between premature centromere separation, a lack of kinetochore formation, and early replication of the centric/pericentric DNA associated with these centromeres. The cause of sudden change from activity to inactivity of these chromosomes, though interesting, is not clear.

Animals↗
PubMed2006

Production and separation of no-carrier-added radioactive tracers of yttrium, strontium and rubidium from heavy-ion irradiated germanium target: applicability to the standardization of a separation technique for production of positron-emitting radionuclide 86Y.

Among various positron-emitting radionuclides, certain radioisotopes of Y, Sr and Rb have important applications in diagnostic and therapeutic nuclear medicine. In the present work, an attempt has been made to produce some of those radioisotopes by irradiating a natural Ge-target material with heavy-ion oxygen ((16)O(+6)) projectiles. An effective radiochemical separation scheme was developed to isolate Y, Sr and Rb radiotracers from the irradiated Ge-matrix in no-carrier-added form with a view to applying those radiotracers for standardization of a technique for the radiochemical separation of Y from natural Sr target. The standardized separation technique could be utilized for the production of the positron-emitting (86)Y from an enriched (86)Sr target irradiated at a medical cyclotron.

Electrons↗
PubMed2005

Comparison of a static gravity screen-roll press combination separator to a PAM-assisted gravity belt thickener system for swine waste slurry solids separation.

Liquid effluent resulting from solids separation from raw swine slurry (RS) using a static gravity screen-roll press separator (SE) and a polyacrylamide (PAM) flocculant-assisted gravity belt thickener system (BE1 and 2, with BE2 designating an added belt thickening of SE) were compared. Effluent pH was 7.6-7.7. Dissolved oxygen was less than 0.01 mg/l in RS and SE and 0.50 mg/l in BE1 and 2. Solids dry weight and total phosphorus concentrations were reduced significantly (p0.05) in SE (17-27%) and in BE1 and 2 (92-96%), relative to RS. Phosphorus concentration reductions were higher than those previously found. Settleable and suspended solids, total nitrogen and chemical oxygen demand were significantly reduced in BE1 and 2 (63-99%). No significant differences (p>0.05) were found between BE1 and 2. Results indicated that the gravity belt thickener system was more efficient at solids separation than the screen-roll press system.

Acrylic Resins↗
PubMed1985

Comparison of reversed-phase and cation-exchange high-performance liquid chromatography for separating closely related peptides: separation of Asp76-human parathyroid hormone (1-84) from Asn76-human parathyroid hormone (1-84).

Cation-exchange high-performance liquid chromatography (CE-HPLC) was compared with ordinary reversed-phase high-performance liquid chromatography (RP-HPLC) for separating closely related peptides. Some synthetic samples of bradykinin and angiotensins, which were homogeneous according to RP-HPLC, were found to be inhomogeneous when analyzed by CE-HPLC. On the other hand, diastereomeric peptides could be separated much more efficiently by RP-HPLC than by CE-HPLC. These results indicated that the purity of synthetic peptides should be checked not only by RP-HPLC but also by ion-exchange HPLC. In the case of human parathyroid hormone (hPTH), baseline separation of Asp76-hPTH from Asn76-hPTH by RP-HPLC was not possible, but was by CE-HPLC. Using this method we confirmed that the Asn residue in hPTH at position 76 could not be converted into the Asp residue under the conditions used to isolate and purify it from human organs.

Angiotensin II↗
PubMed1994

Temperature as a variable in reversed-phase high-performance liquid chromatographic separations of peptide and protein samples. II. Selectivity effects observed in the separation of several peptide and protein mixtures.

Changes in band spacing as a function of temperature and/or gradient steepness were investigated for four peptide or protein samples. Reversed-phase HPLC in a gradient mode was used to separate tryptic digests of tissue plasminogen activator and calmodulin. Additionally, a synthetic peptide mixture and a storage protein sample from wheat were studied. Simultaneous changes in gradient steepness and temperature were found to provide considerable control over band spacing and sample resolution. The effects of temperature and gradient steepness on selectivity in these systems appear to be complementary. Simultaneous optimization of both temperature and gradient steepness thus represents a powerful and convenient means of controlling band spacing and separation. Because of the complexity of these sample chromatograms, computer simulation proved to be a useful tool in both interpreting these experiments and in optimizing final separations.

Calmodulin↗
PubMed1996

Separation of chiral polychlorinated biphenyls by micellar electrokinetic chromatography using beta- and gamma-cyclodextrin mixtures in the separation buffer.

Chiral polychlorinated biphenyls (PCBs) 45, 84, 88, 91, 95, 132, 136, 139, 149, 171, 183 and 196 were separated each in its two enantiomers by cyclodextrin-modified micellar electrokinetic chromatography (CD-MEKC). Mixtures of beta- and gamma-cyclodextrins were used as chiral modifiers in a 2-(N-cyclohexylamino)ethanesulphonic acid (CHES) buffer containing urea and sodium dodecyl sulphate (SDS) micelles. Separations of multicomponent mixtures of PCBs into their enantiomers were also performed. A mixture of PCBs 45, 88, 91, 95, 136, 139, 149 and 196 was separated into all sixteen enantiomers in an analysis time of approx. 35 min.

Chromatography, Affinity↗
PubMed1999

Effect of electric field on liquid chromatographic separation of peptide digests. Combining capillary separation techniques.

A system is described which allows operation of a range of capillary based liquid phase separations including capillary electrophoresis, isocratic and gradient capillary electrochromatography, isocratic and gradient capillary liquid chromatography and electrically assisted gradient capillary liquid chromatography. The system was coupled to electrospray ionization mass spectrometry in the electrically assisted capillary liquid chromatography mode to investigate the effect of applied voltage on the selectivity in peptide mapping separations. Analyses were performed on tryptic digests of recombinant human growth hormone and tissue plasminogen activator. The results show a small but useful effect on selectivity that can be used to fine tune specific separations.

Algorithms↗
PubMed2001

Separation of DNA fragments and single strand conformation polymorphism analysis in bare capillaries using poly(acrylamide-dimethylacrylamide) as a separation medium.

A short chain poly(acrylamide-dimethylacrylamide) (PADMA) was synthesized in aqueous phase using isopropanol as a chain transfer agent, and was characterized according to the chemical composition and molecular mass. This polymer can form a stable dynamic coating on the inner surface of the capillary, thereby suppressing the electroosmotic flow and DNA-capillary wall interaction. The sieving medium has low viscosity and capillary filling with this medium and medium replacement were conveniently carried out by commercial capillary electrophoresis instruments. The effects of components and concentration of copolymers on the separation of DNA fragments were investigated. Highly efficient separation of DNA fragments, successful single strand conformation polymorphism (SSCP) analysis and good reproducibility of the migration time were obtained in bare capillaries using these copolymers as sieving media. Our preliminary results demonstrate that PADMA will become an alternative matrix for DNA separation by capillary electrophoresis.

Acrylamides↗
PubMed1998

Molded rigid polymer monoliths as separation media for capillary electrochromatography. 2. Effect of chromatographic conditions on the separation.

The effect of chromatographic conditions on the performance of monolithic poly(butyl methacrylate-co-ethylene dimethacrylate-co-2-acrylamido-2-methyl-1-propanesulfonic acid) columns in capillary electrochromatography has been studied. The flow velocity was found to be proportional to the strength of the electric field and both the pH and the composition of the mobile phase. A column efficiency of 120,000 plates/m at the optimum flow velocity of 1.5 cm/min is achieved for all the monolithic capillary columns of identical composition and porosity, regardless of their length, which varied from 30 to 120 cm. The polymeric separation medium exhibits retention and selectivity properties similar to those of typical ODS packings for reversed-phase chromatography. In addition to the "classical" use of monolithic capillary columns for the electrochromatographic separation of small molecules in reversed-phase mode, larger styrene oligomers were also separated under isocratic elution conditions. In addition, the electroosmotically driven size exclusion chromatography of polystyrene standards with molecular weights up to 10(6) has been demonstrated for the first time.

Benzene Derivatives↗
PubMed2006

Statistical thermodynamics of bond torsional modes: tests of separable, almost-separable, and improved Pitzer-Gwinn approximations.

Practical approximation schemes for calculating partition functions of torsional modes are tested against accurate quantum mechanical results for H(2)O(2) and six isotopically substituted hydrogen peroxides. The schemes are classified on the basis of the type and amount of information that is required. First, approximate one-dimensional hindered-rotator partition functions are benchmarked against exact one-dimensional torsion results obtained by eigenvalue summation. The approximate one-dimensional methods tested in this stage include schemes that only require the equilibrium geometries and frequencies, schemes that also require the barrier heights of internal rotation, and schemes that require the whole one-dimensional torsional potential. Then, three classes of approximate full-dimensional vibrational-rotational partition functions are calculated and are compared with the accurate full-dimensional path integral partition functions. These three classes are (1) separable approximations combining harmonic oscillator-rigid rotator models with the one-dimensional torsion schemes, (2) almost-separable approximations in which the nonseparable zero-point energy is used to correct the separable approximations, and (3) improved nonseparable Pitzer-Gwinn-type methods in which approaches of type 1 are used as reference methods in the Pitzer-Gwinn approach. The effectiveness of these methods for the calculation of isotope effects is also studied. Based on the results of these studies, the best schemes of each type are recommended for further use on systems where a corresponding amount of information is available.

Journal Article↗
PubMed1979

The separation of peptide hormone diastereoisomers by reverse phase high pressure liquid chromatography. Factors affecting separation of oxytocin and its diastereoisomers--structural implications.

Experimental conditions and parameters involved in high performance liquid chromatography (HPLC) separations of the peptide hormone oxytocin and seven of its diastereoisomers, namely [1-hemi-D-cystine]-, [2-D-tyrosine]-, [4-D-glutamine]-, [5-D-asparagine]-, [6-hemi-D-cystine-], [7-D-proline]-, and [8-D-leucine]-oxytocin, on reverse phase columns were investigated. The effects of solvent, pH, and salt concentration were studied. Using the solvent systems 10% tetrahydrofuran-ammonium acetate buffer or 18% acetonitrile-ammonium acetate buffer and the muBondapak C18 support, oxytocin was separated from each of its diastereoisomers under all conditions studied, but the order of elution of diastereoisomers was highly dependent on solvent and to a lesser extent on pH. Separations of the hormone and its diastereoisomers on reverse phase HPLC and on classical partition chromatography on Sephadex G-25 were compared. The results are discussed in terms of the interactions of the solute with the reverse phase column and the solvent system. Implications of these findings in terms of the different solution conformations of the peptides are discussed.

Amino Acid Sequence↗
PubMed1992

Separation-individuation, family functioning, and psychological adjustment in college students: a construct validity study of the Separation-Individuation Test of Adolescence.

We evaluated the construct validity of the Separation-Individuation Test of Adolescence (SITA; Levine, Green, & Millon, 1986). Based on a review of the theoretical literature on separation-individuation issues during late adolescence, predictions were made as to how SITA scores would correlate with aspects of family functioning and psychological adjustment. The SITA and a battery of self-report family and adjustment measures were administered to 454 college students (272 females and 182 males; 74% White, 16% African American, and 10% Asian American or Hispanic). Correlational analyses offered partial support for the construct validity of the SITA. Cluster analyses revealed four distinct groups of subjects (anxious deniers, healthy separators, peaceful detachers, and succorance seekers), each with its own coherent set of scores on the SITA and instruments measuring family relations and positive and negative psychological adjustment. Criticisms concerning the labels and composition of the SITA scales are also discussed.

Adaptation, Psychological↗
PubMed1983

Divergence thresholds as functions of temporal separation, spatial separation, and retinal locus.

Human thresholds were measured for the detection of angular divergence between straight lines using pairs of line segments. The dependence of these thresholds on temporal separation between the two lines, spatial separation, and retinal locus was assessed. Results were comparable to prior divergence thresholds obtained by Harrington and Harrington in their study of "blur patterns." In blur patterns motion parameters may be processed partly or wholly as form information rather than as motion information per se. Harrington and Harrington had used moderate blurring velocities, for which information on both motion and form were present. Observers may have been responding either to motion or to form. The study reported here used briefly presented two-line "blur patterns" with only form information. Analysis suggested that the form components of fast motion-produced blur patterns could be processed by the human visual system. Neither temporal nor spatial separation was a significant determiner of thresholds in accordance with Harrington and Harrington who found no effect of blur-line density in the range studied. Retinal locus was a factor as it was with blur patterns. Some possible mechanisms for the detection of divergence indicated by these results are discussed.

Discrimination Learning↗
PubMed2000

Separation of alpha-acid glycoprotein glycoforms using affinity-based reversed micellar extraction and separation.

A new method for the preparation of the glycoforms of bovine alpha(1)-acid glycoprotein (AGP) is described relying on affinity-reversed micellar extraction and separation (ARMES). This method has proven effective in separating structurally similar glycoproteins and separating glycoproteins from nonglycosylated proteins from natural sources. In this method, individual glycoforms complex with the lectin, concanavalin A (ConA) are extracted into an organic-phase reversed micellar solution formed by Aerosol OT (AOT). The purity of three AGP glycoforms isolated was assessed by hydroxyapatite high-performance liquid chromatography (HPLC), gel-permeation chromatography and SDS-PAGE. The glycan structure of the pure glycoforms was analyzed. Oligosaccharide mapping using capillary electrophoresis (CE) and PAGE showed the glycans obtained from each glycoform to be distinctly different. ARMES can be used for the semi-preparative scale resolution of the glycoforms of bovine AGP or other therapeutic glycoproteins.

Animals↗
PubMed1990

Separation processes in biotechnology. Aqueous two-phase separations.

Aqueous two-phase systems are useful for separation of a wide range of water-compatible substances (from peptides to cells). The selectivity of the separation normally increases with the size of the partitioned molecules or particles. The partition and separation capacity can be influenced in a number of ways, including electric charge, hydrophobicity, or specific ligand binding. Because of the simpleness in operation and high capacity, aqueous two-phase systems are well suited for large-scale purification of biomaterials such as enzymes and other specific proteins.

Animals↗
PubMed2004

[Separation of parents: how is it conveyed to children? How does the content of the communication influence the separation experience of children?].

On the basis of 45 expert opinions of custody cases involving 89 children dating from 1996-1999 and of 62 questionnaires answered by the parents it was examined, how the parents told their children about the impending separation. We were interested if the way the parents told their children and the contents of the communication had an impact on coping with the separation. We found that only 48.9% of the families talked about the separation. 35.5% of the children were not informed, 12.4% of the children were not told the truth by their parents. There was no clear connection between the way the children were informed and their coping behaviour. Yet it could be shown that talking to the children had a positive effect on the relationship between the father and the child. The discussion of the results will point out the complexity and importance of this topic which has not been sufficiently considered in the literature and by parents planning a divorce. Yet looking at the rising divorce rate one can see how highly topical it is and will remain in the future.

Adaptation, Psychological↗
PubMed1997

Maternal and foetal ECG separation using blind source separation methods.

The separation of the maternal and foetal electrocardiograms (ECGs) from skin electrodes located on the mother's body may be modelled as a blind source separation (BSS) problem. This consists in the reconstruction of a set of unknown mutually independent source signals from the sole knowledge of another set of linear mixtures of the sources, where the mixture pattern is also unknown. Three BSS methods based on cumulants are considered: principal-component analysis (PCA), higher-order singular-value decomposition (HOSVD), and higher-order eigenvalue decomposition (HOEVD). All these methods are applied to the foetal-ECG extraction problem by using real ECG data. The last two methods appear to provide a more satisfactory separation than the first method, with HOEVD offering slightly better results.

Biomedical Engineering↗