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A selective procedure is described for the determination of amitriptyline in plasma. The method involves extraction, separation of amitriptyline from its metabolites and subsequent oxidation by ceric sulphate in 5.4 M sulphuric acid. The oxidation product, anthraquinone, is determined by means of electron-capture gas chromatography. The metabolites were separated by a column chromatographic extraction technique. The choice of oxidation reagent, optimum conditions for the oxidation, and the electron-capture properties of anthraquinone are discussed. The method can be used to determine down to 2 ng of amitriptyline in a plasma sample; the relative standard deviation at the 50-ng level was 4.0% (n = 8). The levels of amitriptyline found in a series of plasma samples are compared with those obtained by gas chromatography with use of nitrogen-specific detection; the two techniques gave coincident results. 相似文献
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The effect of AMP.PNP on the thermal stability and dynamics of myosin head were investigated by using DSC and different spin
label technique for chemically skinned muscle fibres prepared from rabbit. The thermal unfolding of the fibres in rigor, strong
as well as weak-binding state showed a complex process characterizing at least three discrete domain regions with different
stability (T
m =54, 58.4 and 62.3°C). The unfolding at 54°C refers to the catalytic domain of myosin, whereas transition at T
m =58.4°C represents the rod-like region. In the presence of AMP.PNP only the parameters of the last transition changed significantly
(T
m =70.4°C) showing an increased interaction between actin and myosin heads being attached to actin. Measurements on MSL-fibres
(labelled at Cys-707 of myosin) in the presence of AMP.PNP showed that about half of the cross-bridges dissociated from actin.
This fraction had a dynamic disorder, the other population had the same spectral feature as in rigor. In contrast, on TCSL-fibres
AMP.PNP increased the orientational disorder of myosin heads, a random population of spin labels was superimposed on the ADP-like
spectrum showing conformational and motional changes in the internal structure of myosin heads. ST EPR measurements reported
increased rotational mobility of spin labels in the presence of AMP.PNP. The DSC and EPR results suggest that in the presence
of AMP.PNP the attached heads have the same global orientation as in rigor, but the internal structure undergoes a local conformational
change.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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Nicotine was subjected to reaction at 90 degrees with trichloroethyl chloroformate in the presence of pyridine to form a carbamate in which the pyrrolidine ring was opened. Upon heat treatment, this carbamate partially formed the corresponding olefin. About 10 pg could be detected with an electron-capture detector and 60 pg with an alkali flame-ionization detector. The extraction was studied with 14C-labelled nicotine. Methylene chloride was suitable for extraction from diluted plasma, whereas toluene containing 5% of heptafluorobutanol was used in a re-extraction step and also as the chloroformate reaction medium. Due to a nicotine blank the limit for quantitative determinations was 10 ng/ml in plasma (sample volume 1 ml). N-n-Propylnornicotine was used as an internal standard. The precision at the 30 ng/ml level was +/- 8.8% (n = 7). 相似文献
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Hartvig RA van de Weert M Ostergaard J Jorgensen L Jensen H 《Langmuir : the ACS journal of surfaces and colloids》2012,28(3):1804-1815
Protein charge is an important parameter in the understanding of protein interactions and function. Proteins are subject to dynamic charge regulation, that is, the influence of the local environment (such as charged interfaces and biopolymers) on protein charge. Charge regulation is governed by differences in the dielectric and electrostatic environment between adsorbed protein and the free protein in bulk solution. In this work protein charge regulation is addressed experimentally by employing electrochemistry at interfaces between two immiscible electrolyte solutions (ITIES) as well as theoretically by developing a new protein adsorption model at ITIES. Electrochemistry at ITIES is shown to be particularly well suited to study protein charge regulation as the adsorbed protein experiences a different dielectric environment compared to the bulk phase and the external control of the water/oil potential difference allows systematic studies on how potential induced ion gradients affect protein charge. The theoretical model incorporates all the features of the experimental system and specifically takes into account protein charge regulation at ITIES as well as the impact of the formation of dielectric layers on the experimentally observed impedance. The model parameters include the protein charge-pH profile, bulk pH, and the overall potential difference. It is shown that the formation of a dielectric layer and the associated charge regulation are the main factors dictating the observed experimental behavior. Finally, the theoretical model is used to interpret literature results, and the consistency between the model and the relatively large data set suggests that the model may be used more generally for understanding and predicting protein adsorption. 相似文献
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Complexation of the bile salts (BS) taurocholate, tauro-beta-muricholate, taurodeoxycholate, taurochenodeoxycholate, glycocholate, glycodeoxycholate, and glycochenodeoxycholate common in rat, dog, and man with natural beta-CD and the chemically modified beta-CDs 2-hydroxypropyl-beta-CD and 2-O-methyl-beta-CD was studied using mobility shift ACE. The CDs were selected due to their frequent use in preformulation and drug formulation as oral excipients for the solubilization of drug substances with low aqueous solubility. ACE was demonstrated to be a feasible and efficient technique for investigation of the interactions between BS and beta-CDs. All the investigated BS possessed affinity for the three CDs with stability constants ranging from 2x10(3) to 4x10(5) M(-) (1). The requirements and assumptions related to the use of ACE for estimating high affinity stability constants were discussed. The extent and pattern of hydroxylation significantly influenced the affinity of the glyco- and tauro-conjugated BS toward the beta-CDs (chenodeoxycholates > deoxycholates > cholates) whereas the nature of the beta-CD derivatization and BS conjugation played a minor role only. The results indicate that displacement of drug substances from beta-CD inclusion complexes is likely to occur in the small intestine where BS are present potentially influencing drug bioavailability. 相似文献
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Lőrinczy D. Hartvig N. Farkas N. Belagyi J. 《Journal of Thermal Analysis and Calorimetry》2001,65(2):351-358
Differential scanning calorimetry and electron paramagnetic resonance experiments were performed on glycerinated muscle fibres
to study the effect of the binding of nucleotides (ADP and AMP⋅PNP) to myosin. The thermal unfolding of muscle fibres showed
three discrete domain regions with thermal stabilities of 52.2, 58.8 and 67.8°C. AMP⋅PNP markedly affected the transitions,
implying the strong interaction between AMP⋅PNP and catalytic domain, and partial dissociation of heads from actin. ADP produced
only small changes in transition temperatures.
Spectrum deconvolution performed on isothiocyanate-labelled fibres in AMP⋅PNP-state resulted in two populations; 50% of labels
was highly ordered with respect to fibre axis, whereas the other 50% of labels was randomly oriented. The conformation of
the myosin heads which showed high degree of order were in the strongly binding ADP-state, the heads being attached to actin
differ from those of heads in rigor. The results support the suggestion that the attached heads in strongly binding state
to actin might have different local conformations.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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René Holm Rune A. Hartvig Henrik V. Nicolajsen Peter Westh Jesper Østergaard 《Journal of inclusion phenomena and macrocyclic chemistry》2008,61(1-2):161-169
The complexation of seven bile salts, present in the small intestine of rat, dog and man, (taurocholate, tauro-β-muricholate, taurodeoxycholate, taurochenodeoxycholate, glycocholate, glycodeoxycholate and glycochenodeoxycholate) with γ-cyclodextrin and the chemically modified 2-hydroxypropyl-γ-cyclodextrin, was studied using affinity capillary electrophoresis (ACE). The cyclodextrins (CDs) were investigated due to their use in drug formulation as excipients for solubilisation of poorly soluble drugs and drug candidates. Using mobility shift ACE, the bile salt cyclodextrin interactions were characterized demonstrating 1:1 binding stoichiometry with stability constants ranging from 2 × 103 to 8 × 104 M?1. The binding constants showed a systematic dependence on the number and position of hydroxyl groups on the steroid skeleton and the stability constants were in general higher for complexation with the native cyclodextrin than with the modified cyclodextrin. Based upon the size of the complexation constants, it was suggested that the interaction between the CDs and the bile salts takes place at the C and D ring of the steroid skeleton. The complexation of bile salts with the γ-cyclodextrins may compete with drug-γ-cyclodextrin complex formation and, thus, potentially affect drug absorption and efficacy. 相似文献