PubMed Health⌕ Search

Biomedical subjects

Xiangli Liu

Publications and source records attributed to Xiangli Liu.

7 recordsLinked to original sources
PubMed2005

Determination of lipophilicity by reversed-phase high-performance liquid chromatography. Influence of 1-octanol in the mobile phase.

Lipophilicity was evaluated using a novel RP-HPLC stationary phase (Discovery-RP-Amide-C16) with and without 1-octanol added to the mobile phase. A set of 46 drugs and flavonoids characterized by a broad structural diversity and a wide log Poct range (-0.69 to 5.70) was selected for this study. This set consists of neutral solutes and solutes with acidic or ampholytic functionalities which were maintained neutral at pH 2.5 or 4. In our conditions, the addition of 1-octanol in the mobile phase proved a key factor to derive a lipophilicity index log k(w) highly correlated with log Poct for all investigated solutes. 1-Octanol improved the correlation between log Poct and log k(w) mainly by influencing the retention behavior of the solutes with log Poct values below +3. This study brings additional evidence that under proper experimental conditions of stationary and mobile phases, RP-HPLC is a very useful method to obtain log Poct values.

1-Octanol↗
PubMed2005

A study of interlaboratory influence on column evaluation.

A liquid chromatography method for the characterization of base deactivated columns was investigated in a collaborative study involving six laboratories. This work was carried out on two chromatographic supports (Xterra RP 18 and Symmetry Shield). Different cooling systems, namely water bath and air oven, were tested and it was shown that column thermoregulation did not significantly influence chromatographic data. In order to control the mobile phase composition, the latter was prepared by weight rather than volume. Thanks to the injection of a set of selected neutral compounds, extra-column effects were evaluated in each of the participating laboratories. The results showed that chromatographic supports tested in different laboratories and following the same test protocol could be effectively compared.

Chromatography, High Pressure Liquid↗
PubMed2005

Novel RPLC stationary phases for lipophilicity measurement: solvatochromic analysis of retention mechanisms for neutral and basic compounds.

An RPLC was developed to rapidly determine lipophilicity of neutral and basic compounds using three base deactivated RPLC stationary phases particularly designed for the analysis of basic compounds, namely, Supelcosil ABZ(+)Plus, Discovery RP Amide C16, and Zorbax Extend C18. The work consisted of three sets of experiments. In the first log kw values of neutral compounds were extrapolated using hydroorganic mobile phases at different compositions. Good correlation between log kw and log Poct indicated that the method was appropriate for these supports, without adding a silanol masking agent. In the second set of experiments, isocratic log k values of neutral and basic compounds were measured with three different mobile phases. The best estimation of lipophilicity was obtained for neutral and basic compounds when the secondary interactions were strongly reduced (i. e., when basic compounds were under their neutral form). In the third set of experiments, isocratic retention factors of basic compounds (in their neutral form) were measured with a high-pH mobile phase, on a chemically stable support (Zorbax Extend C18). Under these chromatographic conditions, correlation between the isocratic retention factors and log Poct (log D10.5) for basic compounds was similar to that for neutral compounds.

Chromatography, Liquid↗
PubMed2005

Application of a stepwise flow ratiometry without phase separation to the determination of the chloroform/water distribution coefficients of volatile diazines.

The chloroform/water distribution coefficients (K(D)) of sixteen diazine compounds were determined by a stepwise flow ratiometry. An aqueous solution of analyte was delivered and merged with chloroform. The flow rate ratio of both the phases was varied stepwise under a constant total (chloroform+aqueous) flow rate. The analyte was extracted to chloroform while both the phases, which were segmented by each other, were passing through an extraction coil. The segmented stream was then led to a UV/Vis detector directly without phase-separation. The absorbance of the chloroform and aqueous phases (A(o) and A(a), respectively) was each measured at the maximum absorption wavelength of the analyte. The plots of A(-1) against R(f), (AR(f))(-1) against R(f)(-1), and AR(f) against A gave straight lines, where A was A(o), A(a) or the sum of them (A(S)). The K(D) of the analyte was calculated from the slopes and intercepts of the plots. The log K(D) values obtained for the analytes (-0.5-1.4) were agreed well with the values measured by a shake-flask method. The present method is simple, rapid (5 min/determination) and applicable to the volatile compounds with reasonable precision (standard deviation of log K(D)<0.07).

Chemical Phenomena↗
PubMed2003

Partition coefficients of ionizable compounds in o-nitrophenyl octyl ether/water measured by the potentiometric method.

The objective of this study was to investigate the reliability of potentiometric measurements of partition coefficients (log P) in the o-NPOE/water system, o-nitrophenyl octyl ether being an organic solvent widely used for the voltammetric determination of the partition coefficient of ions. Three sets of ionizable model compounds were explored in this study. The results showed that the potentiometric technique gave precise and reliable log P(npoe) values in the explored range of 0.1-4.3.

Journal Article↗
PubMedDate not supplied

Synthesis of chlorambucil-tempol adduct and its delivery using fluoroalkyl double-ended poly (ethylene glycol) micelles.

In our pursuit to find potent anticancer drugs, we have covalently bonded free radical tempol to chlorambucil giving a chlorambucil-tempol (CT) adduct in which both of the anticancer active sites in tempol and chlorambucil were left intact. Analysis using NMR, Maldi-TOF, and EPR verified the designed chemical structure. Because the CT adduct is more hydrophobic than chlorambucil, its delivery also was investigated using fluoroalkyl double-ended poly (ethylene glycol) (Rf-PEG) micelles. Results from EPR spectra and(19) F and(1) H NMR spin lattice relaxation times show that the Rf-PEG micelles are able to encapsulate CT into the Rf cores of the micelles.

Antineoplastic Agents, Alkylating↗