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At least 55 records · Page 3Linked to original sources
PubMed2005

Analytical and semipreparative high performance liquid chromatography enantioseparation of new substituted 1-thiocarbamoyl-3,5-diaryl-4,5-dihydro-(1H)-pyrazoles on polysaccharide-based chiral stationary phases in normal-phase, polar organic and reversed-phase conditions.

The direct HPLC enantioseparation of five pairs of new chiral pyrazole derivatives on coated cellulose- and amylose-based chiral stationary phases (Chiralpak AD, Chiralcel OJ and Chiralcel OJ-RH) and new immobilised amylose-based Chiralpak IA CSP was performed. Very high enantioselectivity factor (alpha) values were achieved in polar organic and reversed-phase conditions by using OJ-RH as CSP. Chiralpak IA exhibited an excellent chiral resolving ability in normal-phase mode and it allowed the enantioseparation of analytes investigated with resolution factors (Rs) >20. Due to its bonded nature, it was successfully employed at analytical and semipreparative scale in combination with normal-phase eluents containing "non-standards" solvents such as acetone.

Amylose↗
PubMed2006

Observation of zwitterion formation in the gas-phase H/D-exchange with CH(3)OD: solution-phase structures in the gas phase.

Infrared spectroscopy of gas-phase singly deuterated [Trp + K](+) (formed by H/D exchange with CH(3)OD) shows that some (approximately 20%) kinetically stable zwitterionic (ZW) conformer is formed, based on the diagnostic antisymmetric CO stretch of the deprotonated carboxylate moiety, upsilon(as)(CO(2)(-)), at 1680 cm(-1). A majority of the deuterated [Trp + K](+) is found to be in the charge solvation (CS) conformation, with deuterium exchange occurring on both the acid and amino groups, which is consistent with H/D scrambling. Interestingly, H/D exchange with the more basic ND(3) reagent did not result in the stabilization of a kinetically stable zwitterion, although it is not clear yet what causes this observation. The result for CH(3)OD shows that H/D exchange can in fact alter the structure of the analyte and, hence, care needs to be taken when interpreting gas-phase H/D exchange studies. Moreover, this result shows the possibility of forming solution-phase structures that are thermodynamically disfavored in the gas phase, thus opening a new area of study.

Deuterium↗
PubMed1985

Mobile phase effects in reversed-phase chromatography. VII. Dependence of retention on mobile phase composition and column temperature.

The relationship between logarithmic retention factor, kappa, in reversed-phase chromatography and operating conditions including mobile phase composition and column temperature is still controversial. Earlier, the following analytical relationship was proposed for use with alkyl benzenes: kappa = A1 phi (1 - Tc/T) + A2/T + A3 where phi is volume fraction organic co-solvent of the hydro-organic mobile phase, T is absolute temperature and A1-A3 are parameters appropriate to the eluite and stationary phase. Insofar as its use had not been tested with polar eluites that are retained by only one mechanism, its description of the retention of 54 polar and apolar eluites was examined and compared to equations with other, usually more complex, relationships between retention and operating conditions. The following four-parameter equation described best most data: kappa = A1 phi (1 - Tc/T) + A2/T + A3 + A4 phi. But neither this nor any other four-parameter equation under examination here emerged solely as the best expression for the dependence of retention on the eluent composition and temperature. The average relative errors were 7.8% and 6% with use of the three- and the four-parameter equations which were found to be best for a given eluite, respectively. In view of the small decrease in error but significant increase in complexity and in data points with the use of the four-parameter equation, the three-parameter equation is recommended for general use.

Chemical Phenomena↗
PubMed2005

Hydrophobically assisted switching phase synthesis: the flexible combination of solid-phase and solution-phase reactions employed for oligosaccharide preparation.

Hydrophobically assisted switching phase (HASP) synthesis is a concept that allows the choice between the advantages of solid-supported chemistry and those of solution-phase synthesis. Starting from the examination of adsorption and desorption properties of hydrophobic molecules to and from reversed-phase silica, we designed a dilipid as a quantitative and fully reversible HASP anchor, permitting final product release. The utility of this new tool in synthetic organic chemistry was demonstrated on oligosaccharide preparation. The synthesis of a pentarhamnoside was accomplished by repetitive glycosylation reactions. Glycosylations were conducted preferably in solution, whereas all protecting group manipulations were performed on solid support. Without the need for chromatographic purification of intermediates, the HASP system furnished the final product after 12 linear steps with average yields of 94% per step at a scale of 0.1 mmol, thus overcoming several of the limitations encountered in the solid-phase synthesis of complex carbohydrates.

Epichlorohydrin↗
PubMed2005

Phase retrieval with a three-frame phase-shifting algorithm with an unknown phase shift.

A three-frame phase-shifting algorithm with a constant but unknown phase shift is proposed. The algorithm is based on background-intensity removal prior to phase retrieval to eliminate an undetermined factor in a fringe pattern. The proposed method is validated on three-dimensional profilometry by fringe projection and on deformation measurement by means of digital speckle shearing interferometry. For a fringe pattern with slow-varying background intensity, the background removal is achieved in the frequency domain. For a speckle pattern, a background removal technique is integrated with the three-frame algorithm. In this process, manual intervention is minimal, and high computational speed is achieved. In addition, high-frequency phase signals would not be removed in the noise-reduction process as is the case in the bandpass-filtering technique. Accuracy of the method is discussed.

Journal Article↗
PubMed2005

Tandem mass spectrometry with online high-flow reversed-phase extraction and normal-phase chromatography on silica columns with aqueous-organic mobile phase for quantitation of polar compounds in biological fluids.

In this work, high-flow online reversed-phase extraction was coupled with normal phase on silica columns with aqueous-organic mobile phase liquid chromatography/tandem mass spectrometry (LC/MS/MS) to quantify drug candidates in biological fluids. The orthogonal separation effect obtained from this configuration considerably reduced matrix effects and increased sensitivity for highly polar compounds as detected by selected reaction monitoring. This approach also significantly improved the robustness and limit of detection of the assays. An evaluation of this system was performed using a mixture of albuterol and bamethan in rat plasma. Assay validation demonstrated acceptable accuracy (< 8% difference) and precision (< 6% CV) for these model compounds. The system has been used for the quantitation of polar ionic compounds in biological fluids in support of drug discovery programs. This assay was used to analyze samples for a BMS proprietary compound (A) in a rat pharmacokinetic study and is shown as an example to demonstrate the precision, accuracy, and sufficient sensitivity of this system.

Albuterol↗
PubMed2005

Phase II study of all-trans retinoic acid in the accelerated phase or early blastic phase of chronic myeloid leukemia: a study of the Eastern Cooperative Oncology Group (E1993).

The aims of this study were to evaluate the safety and efficacy of all-trans retinoic acid (ATRA) in the treatment of the accelerated and blastic phase of chronic myeloid leukemia (CML) and to evaluate in vitro correlates of biological activity. ATRA was administered in an intermittent schedule to patients with CML in the accelerated or blastic phases for a 6 week induction period, which was continued if there was evidence of clinical response or stable disease. If the patient was progressing at 6 weeks, interferon-alpha could be added to the ATRA. Laboratory correlative studies were performed prior to treatment and at intervals during treatment to evaluate effects on maturation and differentiation, and on CML progenitor cell growth by assessment of colony-forming cells (CFC). Eighteen patients were enrolled. There was 1 complete response, 1 partial response and 2 with hematological improvement. A fifth patient was stable on ATRA and interferon for several months. Laboratory data for the responders demonstrated high sensitivity of primary CFC to ATRA prior to treatment and low serial CFC counts on ATRA therapy. ATRA demonstrated clinical and hematological activity in 5 of 18 patients with the accelerated phase of CML, and there was evidence of a biological effect in laboratory studies of 3 of the 5 patients' progenitor cells. Combination therapy with other differentiating agents may be useful in this disease.

Adult↗
PubMed2004

A toxic reagent-free method for normal-phase matrix solid-phase dispersion extraction and reversed-phase liquid chromatographic determination of aldrin, dieldrin, and DDTs in animal fats.

A method for the determination of aldrin, dieldrin, DDT, DDE, and DDD contamination in animal fats (beef tallow, lard, and chicken fat) without using toxic reagents is developed, that uses high-performance liquid chromatography after the sample has been prepared by matrix solid-phase dispersion (MSPD) with acidic alumina oxide. A reversed-phase C(1)-silica column with a mobile phase of 50% (v/v) ethanol solution (in water) and a photo-diode array detector were used for the determination. Average recoveries of the target compounds (0.2-5.0 microg g(-1)) ranged from 84-98%, with coefficients of variation of <5%. The limits of quantitation were </=0.16 microg g(-1 )for AD, </=0.10 microg g(-1) for DD, </=0.06 microg g(-1) for DDT, </=0.07 microg g(-1) for DDE, and </=0.05 microg g(-1 )for DDD. No toxic reagents were used at all.

Aldrin↗
PubMed2002

Prediction of the retention in reversed-phase liquid chromatography using solute-mobile phase-stationary phase polarity parameters.

A previously reported algorithm, based on the equation: log k = (log k)o + p(PN(m) - PN(s)), that relates the retention in reversed-phase liquid chromatography with solute (p), mobile phase (PN(m)) and stationary phase (PN(s)) relative polarity parameters, is improved. The retention data reported by several authors for different sets of compounds, eluted with acetonitrile-water and methanol-water mixtures, are used to test the algorithm and elaborate a database of p values. The methodology is successfully applied to predict the retention using PN(m), values calculated as PN(m) = 1.00 - (2.13phi)/(1+1.4phi) for acetonitrile-water and PN(m) = 1.00 - (1.33phi)/(l1 + 0.47phi) for methanol-water, phi being the organic solvent volumetric fraction. The polarity parameters are demonstrated to be useful to transfer retention data between solvent systems and between columns. Accordingly, the retention in a solvent system is predicted by characterising the working column with a small training set of compounds having diverse polarities, and using the p values known for another solvent system or column. The p polarity parameter is found to be a good descriptor of the retention, allowing the prediction of the expected elution order and peak overlaps.

Algorithms↗
PubMed2002

Two dimensional reversed-phase-reversed-phase separations isomeric separations incorporating C18 and carbon clad zirconia stationary phases.

Informational theory and a geometric approach to factor analysis were employed to evaluate the degree of orthogonality of a two-dimensional reversed-phase-reversed-phase chromatographic system. The system incorporated a C18 column as one dimension and a carbon clad zirconia column as the second dimension. In order to study the resolving power of this system, the separation of a sample matrix containing an artificial mix of 32 isomers (structural and diastereoisomers) was evaluated. Using this system, between 25 and 28 of the 32 isomers could be separated, depending on the mobile phase combinations--with resolution that could not possibly be achieved in a single one dimensional separation. The results from this study indicate that in order to fully evaluate the resolving power of a 2D system multiple methods of analysis are most appropriate. This becomes increasingly important when the sample contains components that are very closely related and the retention of solutes is clustered in one quadrant of the 2D space. Ultimately, the usefulness of the 2D separation is determined by the goals of analyst.

Carbon↗
PubMed1997

High-performance liquid chromatography determination of praziquantel enantiomers in human serum using a reversed-phase cellulose-based chiral stationary phase and disc solid-phase extraction.

A sensitive HPLC method for the quantification of praziquantel enantiomers in human serum is described. The method involves the use of a novel disc solid-phase extraction for sample clean-up prior to HPLC analysis and is also free of interference from trans-4-hydroxypraziquantel, the major metabolite of praziquantel. Chromatographic resolution of the enantiomers was performed on a reversed-phase cellulose-based chiral column (Chiralcel OJ-R) under isocratic conditions using a mobile phase consisting of 0.1 M sodium perchlorate-acetonitrile (66:34, v/v) at a flow-rate of 0.5 ml/min. Recoveries for R-(-)- and S-(+)-praziquantel enantiomers were in the range of 84-89% at 50-500 ng/ml levels. Intra-day and inter-day precisions calculated as R.S.D. were in the ranges of 3-8% and 1-8% for both enantiomers, respectively. Intra-day and inter-day accuracies calculated as percent error were in the 0.2-5% and 0.3-8% ranges for both enantiomers, respectively. Linear calibration curves were in the concentration range 10-600 ng/ml for each enantiomer in serum. The limit of quantification of each enantiomer was 10 ng/ml. The detection limit for each enantiomer in serum using a UV detector set at 210 nm was 5 ng/ml (S/N=2).

Antiplatyhelmintic Agents↗
PubMed1997

High-performance liquid chromatographic analysis of ondansetron enantiomers in human serum using a reversed-phase cellulose-based chiral stationary phase and solid-phase extraction.

A stereospecific HPLC method was developed for the assay of R-(-)- and S-(+)-ondansetron enantiomers in human serum. The method involves the use of solid-phase extraction for sample clean-up and is also free of interference from 6-hydroxyondansetron, 7-hydroxyondansetron and 8-hydroxyondansetron, the three major metabolites of ondansetron. Chromatographic resolution of the enantiomers was performed on a reversed-phase cellulose-based chiral column (Chiralcel OD-R) under isocratic conditions using a mobile phase consisting of 0.7 M sodium perchlorate-acetonitrile (65:35, v/v) at a flow-rate of 0.5 ml/min. Recoveries at 200 ng/ml levels were more than 90% for both ondansetron enantiomers. Intra-day and inter-day precisions calculated as R.S.D.s were in the 0.3-5% and 2-8% ranges for both enantiomers, respectively. Intra-day and inter-day accuracies calculated as percent error were in the 0.3-11.5% and 0-3% ranges for both enantiomers, respectively. Linear calibration curves were obtained for each enantiomer in serum in the concentration range 15-750 ng/ml. The limit of quantitation of each enantiomer was 15 ng/ml. The detection limit for each enantiomer in serum using UV detection at 210 nm was 7 ng/ml (S/N=2).

Antiemetics↗
PubMed1997

Resolution and quantitation of pentazocine enantiomers in human serum by reversed-phase high-performance liquid chromatography using sulfated beta-cyclodextrin as chiral mobile phase additive and solid-phase extraction.

A sensitive and stereospecific HPLC method was developed for the analysis of (-)- and (+)-pentazocine in human serum. The assay involves the use of a phenyl solid-phase extraction column for serum sample clean-up prior to HPLC analysis. Chromatographic resolution of the pentazocine enantiomers was performed on a octadecylsilane column with sulfated-beta-cyclodextrin (S-beta-CD) as the chiral mobile phase additive. The composition of the mobile phase was aqueous 10 mM potassium dihydrogenphosphate buffer pH 5.8 (adjusted with phosphoric acid)-absolute ethanol (80:20, v/v) containing 10 mM S-beta-CD at a flow-rate of 0.7 ml/min. Recoveries of (-)- and (+)-pentazocine were in the range of 91-93%. Linear calibration curves were obtained in the 20-400 ng/ml range for each enantiomer in serum. The detection limit based on S/N=3 was 15 ng/ml for each pentazocine enantiomer in serum with UV detection at 220 nm. The limit of quantitation for each enantiomer was 20 ng/ml. Precision calculated as R.S.D. and accuracy calculated as error were in the range 0.9-7.0% and 1.2-6.2%, respectively, for the (-)-enantiomer and 0.8- 7.6% and 1.2-4.6%, respectively, for the (+)-enantiomer (n=3).

Analgesics, Opioid↗
PubMed1993

Response latency, latency-based receiver-operating characteristics, and uncertainty about interaural phase in the detection of in-phase and out-of-phase tones presented in noise.

Subjects were given the task of detecting tonal signals presented in a continuous background of white noise which was always in phase at the ears (No). The signals were either in phase (So), or phase-reversed (S pi) at the ears. The analysis of response latencies (for similar levels of performance) indicated that there were consistent differences in the processing of the two types of signals. Latencies were longer, and somewhat more variable, for S pi than for So signals. It was also found that the theory of signal detectability can contribute to an understanding of what and how decisions are made. Latencies were treated as confidence ratings in order to determine latency-based receiver operating characteristics (LROCs) for the detection task. It was observed that the LROCs for the interaural condition No-So tend to leave the origin at a steeper angle than do those for the interaural condition No-S pi, presumably reflecting the different sensory and decision processes employed in the two conditions. When the two interaural conditions were intermixed within blocks of trials, performance was slightly impaired in comparison to the situation in which the interaural condition remained constant throughout blocks of trials.

Acoustic Stimulation↗
PubMed2003

Enhancement of phase separation by the addition of de-emulsifiers to three-phase (diesel oil/biocatalyst/aqueous phase) emulsion in diesel biodesulfurization.

Ethanol, added as a de-emulsifier to separate oil and biocatalyst (or bacterial cells) from a three-phase (oil/biocatalyst/aqueous phase) emulsion, formed in diesel biodesulfurization employing Gordonia nitida, improved oil recovery by centrifugation from about 50% in its absence to almost 100% at 3% (v/v). The biocatalyst recovered with ethanol addition showed similar specific growth rates (0.03 h(-1)) and dibenzothiophene desulfurization rates (6-7.2 mol l(-1) h(-1)) to those (0.03 h(-1) and 7.1 mol l(-1), respectively) of the biocatalyst recovered with no ethanol addition. The desulfurization activity significantly increased as the number of the repeated recovery and reuse of the biocatalyst.

Actinomycetales↗
PubMed2004

Gel-phase 19F NMR spectral quality for resins commonly used in solid-phase organic synthesis; a study of peptide solid-phase glycosylations.

The spectroscopic properties for seven different commercial resins used in solid-phase synthesis were investigated with (19)F NMR spectroscopy. A fluorine-labeled dipeptide was synthesized on each resin, and the resolution of the (19)F resonances in CDCl(3), DMSO-d(6), benzene-d(6) and CD(3)OD were measured with a conventional NMR spectrometer, i.e. without using magic angle spinning. In general, resins containing poly(ethylene glycol) chains (ArgoGel, TentaGel and PEGA) were found to be favorable for the (19)F NMR spectral quality. Three serine containing tri-, penta-, and heptapeptides were then prepared on an ArgoGel resin functionalized with a fluorine-labeled linker. The resin bound peptides were glycosylated utilizing a thiogalactoside glycosyl donor carrying fluorine-labeled protective groups. Monitoring of the glycosylations with gel-phase (19)F NMR spectroscopy allowed each glycopeptide to be formed in similar 80% yield, using a minimal amount of glycosyl donor (3 x 2 equivalents). In addition, it was found that the glycosylation yields were independent of peptide length.

Combinatorial Chemistry Techniques↗
PubMed1996

Direct-space methods in phase extension and phase refinement. VI. PERP (phase extension and refinement program).

Several techniques for extending and refining phases for macromolecular structures have been incorporated into a program package PERP. In addition to previously employed techniques such as solvent flattening and histogram matching, PERP includes a new way of applying the Sayre equation [Refaat, Tate & Woolfson (1995). Acta Cryst. D51, 1036-1040], low-density elimination [Shiono & Woolfson (1992). Acta Cryst. A48, 451-456] and two double-histogram methods [Refaat, Tate & Woolfson (1996). Acta Cryst. D52, 252-256]. PERP is an easy-to-use package controlled by keywords and provided with default parameters that usually give near-optimum results. Examples are given of refinement, and also extension and refinement, for six known protein structures with a variety of characteristics. In each case PERP gives a very satisfactory outcome as measured by improvements in the mean-phase-error and conventional map-correlation coefficient. The main conclusion is that the several methods used in sequence give more effective extension and refinement than using any single method alone.

Journal Article↗
PubMed1992

[The indirect measurement of arterial pressure as a function of cuff width in patients in the immediate preoperative phase, the phase of entry into the operating room and in the postanesthesia phase].

The goal of this study was to compare blood pressure measures using two sizes of cuffs: one standard width (12 cm) and other with correct width that is 0.38 of arm circumference as recommended by American Heart Association. The comparisons were done among surgical patients in mediate perioperative phase, reception area of operation room and postoperative phase during the staying of the patient in the recovery room. The results demonstrated that the arterial blood pressure was hypoestimated by the use of the standard width cuff, reaching values up 30 mmHg in the systolic arterial pressure and 30 mmHg in the diastolic ones.

Adolescent↗