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F Han

Publications and source records attributed to F Han.

90 records · Page 5Linked to original sources
PubMed1995

Speciation of organotin compounds by capillary electrophoresis using indirect ultraviolet absorbance detection.

Capillary electrophoresis (CE) with indirect photometric detection was investigated for the separation of organotin species. Compounds such as dimethyltin (DMT), dibutyltin (DBT), and tributyltin (TBT) are important pollutants in the aqueous environment and techniques are needed to analyze directly aqueous environmental samples quickly and economically. By adjusting the mobile phase to pH 2.65 by HCl, tributyltin, dibutyltin and dimethyltin in aqueous solutions were separated by capillary electrophoresis using indirect ultraviolet (UV) absorbance detection. Pyridine was used as the UV absorption additive at 254 nm and separation was achieved in 6 min. Peak tailing obtained at higher pH suggests strong interaction between the dimethyltin cation and the negatively charged capillary wall. Cetyltrimethylammonium bromide (CTAB) was added to the mobile phase to improve the peak shapes when the pH of the mobile phase was greater than 3.5. Separations of organotin species in mobile phases with or without CTAB were compared. The change of electrophoretic mobility in mobile phases with different pH values indicates that DMT and DBT start to undergo hydrolysis at a pH 3.0. It was also found that the choice of the buffer anions is critical in the separation of the tin compounds as complexes appear to form with DMT and DBT in the presence of oxalate and citrate.

Electrophoresis, Capillary↗
PubMed1995

Efficient methods for the linearization and solution of phase-invariant equations.

This paper describes a linear least-squares procedure, whereby, through quadrupole relationships, the 2 pi integers that linearize sets of unique phase-invariant estimates can be determined. It is subsequently shown that the phase solutions for these linear equations can be obtained, even for basis sets of thousands of phases, without having to either build or invert the full least-squares matrix. The final r.m.s. phase errors achieved by this method can typically be less that 5 or 10 degrees.

Algorithms↗
PubMed1995

[Experimental studies on the pharmacokinetics of cefoperazone (CPZ) injection under burn eschar].

UNLABELLED: In this study, the rabbits were categorized into three groups. The scald (III degrees TBS 10%-15%) was caused by exposing these area to hot water at 90 degrees C for 40 seconds. Every rabbit was injected CPZ (25 mg/kg) three times. The changes in the concentration of CPZ were measured by employing MBPD and HPLC methods and experimental data were analyzed by using pharmacokinetic computer program. RESULTS: 1) The T1/2e of CPZ injection in subeschar region was longer and the Cmax was higher than that of intravenous route. 2) The concentration in blood was shown two times higher than after subeschar injection. 3) The levels of concentration were higher than MIC'S in an area of 6.5 cm diameter 24-36 hours after injection. CONCLUSION: CPZ injection in subeschar region was the best route of treatment and prevention of subeschar infection.

Animals↗
PubMed1993

Novel 2-substituted tetrahydro-3H-benz[e]indolamines: highly potent and selective agonists acting at the 5-HT1A receptor as possible anxiolytics and antidepressants.

The synthesis of (+)-(R)-2-cyano-N,N-dipropyl-8-amino-6,7,8,9-tetrahydro-3H- benz[e]indole [(R)-14, U92016A], a potent 5-HT1A agonist, and related analogs is described. In vitro binding studies show that the (R)-enantiomers of this series possess the highest potency for the 5-HT1A receptor. In vivo hypothermia correlates with this, with the (R)-enantiomers causing a greater temperature drop than the (S)-enantiomers. The most active compound in 5-HT1A binding and in the in vivo models was (R)-14, which was found to be highly potent as an agonist in single cell firing studies, as well as potent and of very high intrinsic activity in mouse hypothermia and the sympathetic nerve discharge (SND) models. An in vivo duration of action study, following SND, showed (R)-14 to possess a long duration of action. The synthesis via a nitrene insertion, determination of absolute configuration, and biological activities of this series is described.

Animals↗
PubMed1993

Phasing macromolecular structures via structure-invariant algebra.

Owing to the breakdown of Friedel's law when anomalous scatterers are present, unique values of the three-phase structure invariants in the whole range from 0 to 2pi are determined by measured values of diffraction intensities alone. Two methods are described for going from presumed known values of these invariants to the values of the individual phases. The first, dependent on a scheme for resolving the 2pi ambiguity in the estimate omega(HK) of the triplet phi(H) + phi(K) + phi(-H-K), solves by least squares the resulting redundant system of linear equations phi(H) + phi(K) + phi(-H-K) = omega(HK). The second attempts to minimize the weighted sum of squares of differences between the true values of the cosine and sine invariants and their estimates. The latter method is closely related to one based on the 'minimal principle' which determines the values of a large set of phases as the constrained global minimum of a function of all the phases in the set. Both methods work in the sense that they yield values of the individual phases substantially better than the values of the initial estimates of the triplets. However, the second method proves to be superior to the first but requires, in addition to estimates of the triplets, initial estimates of the values of the individual phases.

Journal Article↗
PubMed1992

Interaction of antioxidants with depth-dependent fluorescence quenchers and energy transfer probes in lipid bilayers.

Three fluorescent, lipophilic, heterocyclic antioxidants were incorporated into lipid bilayers and exposed to depth-dependent nitroxyl fatty acid quenchers. The Stern-Volmer plots curved upward at low quencher concentrations. Quantitative analysis of the results showed that this behavior is consistent with complex formation between quencher and fluorescent antioxidant, where the complex is 2-3 times more fluorescent than the parent fluorophore. At higher quencher concentrations, both free antioxidant and 'bright complex' are quenched dynamically, albeit quenching of the latter is less efficient. The complex probably results from ionic, hydrogen bond and pi-pi interactions. Formation of such a 'bright complex' is also observable in a homogeneous solution of the reactants in cyclohexane. Additional evidence for the complexation of these antioxidants with fatty acids in lipid bilayers is provided by the fact that energy transfer from the antioxidants to anthroyloxy fatty acids occurs at surface concentrations where radiative energy transfer between free molecules should be not be efficient. For directly probing the relative depths of these fluorophores in lipid bilayers we used the aqueous quenchers acrylamide and iodide. They showed that in terms of increasing depth in the bilayer, the order was U-78, 517f < U-78,518e < U-75,412e. Our results, in toto, demonstrate that the Lazaroid antioxidants are incorporated into the lipid bilayer where they occupy strictly defined positions and orientations. Complexation with fatty acyl chains should be mechanistically relevant, since it may enhance antioxidant activity by hindering free radical chain propagation.

Antioxidants↗
PubMed1991

Solution chemistry and analytical characterization of ormaplatin.

Ormaplatin is a racemic, platinum(IV), anti-cancer drug which is currently involved in phase 1 clinical trials. Characterizing the purity of ormaplatin represents an analytical challenge for several reasons. These include the lack of solution stability of ormaplatin, its process impurities and solution decomposition products, the strong concentration and pH dependence of various decomposition pathways and solution equilibria and the absence of chromatographic reproducibility. Two independent types of aqueous decomposition pathways have been observed. The first pathway involves the generation of soluble PtIV containing species which remain in equilibrium with the parent material in solution. The second pathway involves the generation of PtII containing materials which tend to be less soluble. The most interesting material in this latter class is probably the chloride bridged mixed valence material which has been characterized structurally by X-ray diffraction. Liquid chromatography and sample handling procedures have been developed which allow for the accurate determination of bulk drug purity, as well as, an understanding of numerous reversible equilibria.

Antineoplastic Agents↗
PubMed1990

Molecular structure of deoxycytidyl-3'-methylphosphonate (RP) 5'-deoxyguanidine, d[Cp(CH3)G]. A neutral dinucleotide with Watson-Crick base pairing and a right handed helical twist.

The crystal structure of d[Cp(CH3)G] has been determined as part of a project to study the mechanism of the B----Z transition in DNA. The asymmetric unit contains two dinucleotides and the equivalent of 7.5 water molecules, partially disordered over 12 definable positions. The two symmetry-independent dinucleotides form a duplex with Watson-Crick base-pairing and a right-handed helical sense. Comparison with previously determined structures of the B and A conformation showed that this duplex is closer to B than to A but significantly different from B. It corresponds to a stretched out helix with a 4 A rise per base pair and a helical twist of 32 degrees. This structure may serve as a model for the bending of DNA in certain situations. The configuration at the methyl phosphonate is RP, and a mechanism, based on this assignment, is presented for the B----Z transition in DNA.

Base Composition↗
PubMed1988

Direct methods: the identification of conditions which simplify the generation of inconsistent quadrupoles.

An algorithm is implemented to determine the form and phase shift for inconsistent type II quadrupoles for any space group having glide or screw-axis translations which are not a consequence of lattice centering. Cumulatively there are only six different Miller index restrictions and nine different phase shift forms common to all space groups of orthorhombic or lower symmetry. A similar analysis has been performed for a newly discovered type III class of quadrupoles. The configuration of the phase connections among the four triples of the type III quadrupole is different from the common configuration previously described for both normal (type I) and inconsistent (type II) quadrupoles. A knowledge of these constraint conditions for type II and III quadrupoles greatly simplifies a procedure for generating these relationships.

Crystallography↗
PubMed1988

Direct methods: the identification of space-group-specific inconsistent three-phase structure invariants.

Certain space groups often permit the generation of pairs of triple relationships involving the same three parent reflections in different symmetry forms, giving rise to two equally probable invariant estimates which, because of the space-group symmetry, must disagree by an a priori known phase shift. The 230 space groups have been examined to identify those which permit inconsistent triples, and the complete list which describes the forms of the pair of triples and their phase inconsistency is given.

Crystallography↗