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51.
We report a common HPLC method for the single or simultaneous determination of four calcium channel blockers (CCB), namely diltiazem (DTZ), verapamil (VER), nifedipine (NIF) and nitrendipine (NIT) and their active metabolites demetildiltiazem and deacetildiltiazem (MA and M1), norverapamil (NOR), and dehydronifedipine (DHN). DHN was first synthesised in our laboratory and different pH values of the mobil phase were subsequently prepared and tested for chromatographic separation. The detection system and the environmental light conditions were optimised. The best separations of all analytes were obtained using a C18 column and a mobile phase of methanol, 0.04 M ammonium acetate, acetonitrile and triethylamine (2:2:1:0.04 v/v). Quantitation was performed using imipramine (IMI) as the internal standard. For DTZ and its metabolites (M1 and MA), the wavelength chosen was 237 nm; for VER and its metabolite NOR, it was 210 nm; and, finally for NIF and its metabolite DHN and NIT it was 216 nm. When a simultaneous analysis was carried out the wavelength was of 230 nm. The optimum pH were 7.90 and 7.10 when the separation of NIT and DTZ or VER and NIF were carried out, respectively, and 7.90 when a simultaneous separation was carried out. The detection limit of the assay was less than 8 ng ml−1 for all compounds, with coefficients of variation less than 7% (for inter- and intra-day) over the concentration range of 1–1000 ng ml−1. The retention times were less than 11 min. When NIF or NIT were studied, it was necessary to use a sodium vapour lamp in order to avoid the photodegradation which takes place under daylight conditions. 相似文献
52.
Marengo E Liparota MC Robotti E Bobba M Gennaro MC 《Analytical and bioanalytical chemistry》2005,381(4):884-895
A new method has been developed for monitoring the degradation of paintings. Two inorganic pigments (ultramarine blue and red ochre) were blended with linseed oil and spread on canvas. Each canvas was subjected to simulated accelerated ageing in the presence of typical degradation agents (UV radiation and acidic solution). Periodically the painted surfaces were analysed by FT-Raman, to investigate the status of the surface. The data obtained were analysed by principal component analysis (PCA). Finally the Shewhart and cumulative sum control charts based on the relevant principal components (PC) and the so called scores monitoring and residuals tracking (SMART) charts were built. The method based on the use of PC to describe the process was found to enable identification of the presence of relevant modification occurring on the surface of the samples studied.Electronic supplementary material Supplementary material is available for this article at 相似文献
53.
A new algorithm model-oriented for variable selection is presented in this study. It is based on the combination of genetic algorithms (GA) for hyperspace exploration, and counterpropagation artificial neural network (CP ANN) for deriving the fitness score. The proposed method performed very well on both well defined synthetic data sets and real academic data sets. 相似文献
54.
Angelini N Micali N Mineo P Scamporrino E Villari V Vitalini D 《The journal of physical chemistry. B》2005,109(39):18645-18651
Changes in the UV-vis spectra and induced circular dichroism (ICD) signals observed, in correspondence with the porphyrin Soret region, for aqueous solutions of achiral 5,10,15,20-tetrakis{p-[omega-methoxy poly(oxy-ethylene)]phenyl}porphyrin cobalt (II) (Co-P) and aromatic alpha-L-amino acids (Trp and Phe) give direct evidence for the coordination between the Co-P and amino acids. Considering that Co-P, besides the Co atom (one-fixation-point system), does not contain in the molecule active ligand groups and that no ICD signals have been observed in the case of Co-P/Ala, it has been concluded that hydrophobic interactions or stacking interactions between the aromatic rings of the porphyrin and those of Trp or Phe, acting as further amino acid (AA) fixation points, can strongly reduce the mobility of the chiral guest, thus permitting the generation of ICD signals. The effects of changes of both pH (in the range 2-9) and amino acid structure on the ICD phenomenon have also been investigated. In particular, the following have been observed: (i) strong ICD signals for all of the Co-P/N-acetyl amino acid aqueous solutions at pH 7, (ii) an unexpected ICD band with a bisignate form for the Co-P/Ala solution at pH 9 after long aging, and (iii) an opposite ICD signal when alpha-D-Phe and alpha-D-Trp enantiomers have been used. The data reported in this paper show how the binding mechanism between receptor and AAs changes by modulating properly the pH or the molecular structures and indicate that in these aqueous solutions the coordination Co-N is not the fundamental mechanism giving rise to the formation of the complexes and that the binding can be driven by hydrophobic interactions. These occurrences, through the analysis of the spectroscopic response (and, in particular, the form of the ICD band), can allow the recognition of AAs. 相似文献
55.
Interaction of antimicrobial arginine-based cationic surfactants with liposomes and lipid monolayers 总被引:1,自引:0,他引:1
Castillo JA Pinazo A Carilla J Infante MR Alsina MA Haro I Clapés P 《Langmuir : the ACS journal of surfaces and colloids》2004,20(8):3379-3387
The present work examines the relationship between the antimicrobial activity of novel arginine-based cationic surfactants and the physicochemical process involved in the perturbation of the cell membrane. To this end, the interaction of these surfactants with two biomembrane models, namely, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) multilamellar lipid vesicles (MLVs) and monolayers of DPPC, 1,2-dipalmitoyl-sn-glycero-3-[phospho-rac-(1-glycerol)] sodium salt (DPPG), and Escherichia coli total lipid extract, was investigated. For the sake of comparison, this study included two commercial antimicrobial agents, hexadecyltrimethylammonium bromide and chlorhexidine dihydrochloride. Changes in the thermotropic phase transition parameters of DPPC MLVs in the presence of the compounds were studied by differential scanning calorimetry analysis. The results show that variations in both the transition temperature (Tm) and the transition width at half-height of the heat absorption peak (deltaT1/2) were consistent with the antimicrobial activity of the compounds. Penetration kinetics and compression isotherm studies performed with DPPC, DPPG, and E. coli total lipid extract monolayers indicated that both steric hindrance effects and electrostatic forces explained the antimicrobial agent-lipid interaction. Overall, in DPPC monolayers single-chain surfactants had the highest penetration capacity, whereas gemini surfactants were the most active in DPPG systems. The compression isotherms showed an expansion of the monolayers compared with that of pure lipids, indicating an insertion of the compounds into the lipid molecules. Owing to their cationic character, they are incorporated better into the negatively charged DPPG than into zwitterionic DPPC lipid monolayers. 相似文献
56.
Spectrofluorimetric methods to determine cisatracurium and mivacurium are proposed and applied to the determination of both substances in human serum and to the determination of mivacurium in pharmaceuticals. The fluorimetric methods allow the determination of 5-500 ng ml(-1) of mivacurium in aqueous solutions and 5-500 ng ml(-1) of cisatracurium in water-acetonitrile solutions, both containing acetic acid-sodium acetate buffer (pH 5.5) with lambda(exc)=230 nm and lambda(em)=324 nm. 相似文献
57.
Ana I. Olives Emiliano E. Romero-Ale M. Antonia Martín Benito del Castillo Pilar López-Alvarado J. Carlos Menéndez 《Journal of inclusion phenomena and macrocyclic chemistry》2007,57(1-4):553-559
Carbazole-9-carbonyl chloride (C9CC) and 9-carbazolylacetic acid (9CAA) were selected as model fluorescent reagents. The effect
of different chemically modified cyclodextrins (CDs) added to the aqueous solutions of these reagents was studied in water
and in buffered aqueous solutions at pH 4.5 and 8.8. The CDs employed were 2-hydroxypropyl-β-cyclodextrin (HP-βCD), 2,3-di-O-methyl-β-cyclodextrin (DM-βCD) and 2,3,6-tri-O-methyl-β-cyclodextrin (TM-βCD). The inclusion of these reagents inside the cavities of the CDs was verified and this process
can affect the derivatization reaction because CDs can modify the reactivity of the guest molecules. The basic conditions
necessary for the derivatization reaction between C9CC and amines lead to the formation of carbazole anion through hydrolysis
followed by decarboxylation. In the presence of CDs, the hydrolysis-decarboxylation of carbazole-9-carbonyl chloride is faster
than in buffered aqueous homogeneous solutions. The behaviour observed for these reagents in aqueous solutions of CDs was
compared to the one observed in basic ethanolic solutions. These changes are particularly noticeable in the case of 2,3-di-O-methyl-β-CD and 2-hydroxypropyl-β-CD. The characteristics of the fluorescent reagents are compared to carbazole and 9-methylcarbazole
as model compounds.
This paper was presented at XIIIth International Cyclodextrin Symposium. Torino, Italy, May 14–17, 2006. 相似文献
58.
The fat of mixture of goat and cow milk, extracted by di-ethylic ether, was gas chromatographically analysed in order to propose an analytical procedure suitable to reveal small additions of cow milk to goat milk. The obtained results show evident differences in the percentages of some fatty acids. An attempt to apply the peak area ratios, corresponding to the methyl esters of fatty acids, suggested by the literature for cow milk did not yield good results. Other ratios suitable to reveal even the presence of low percentages (up to 5 %) of cow milk in goat milk were found and proposed in this paper. Such ratios are sensitive and can be defined markers towards cow or goat milk and also towards extraneous fat like lard or colza seeds oil. 相似文献
59.
Zhi-Yong Yang Emilio Jimenez-Vicente Hayden Kallas Dmitriy A. Lukoyanov Hao Yang Julia S. Martin del Campo Dennis R. Dean Brian M. Hoffman Lance C. Seefeldt 《Chemical science》2021,12(20):6913
The electronic structure of the active-site metal cofactor (FeV-cofactor) of resting-state V-dependent nitrogenase has been an open question, with earlier studies indicating that it exhibits a broad S = 3/2 EPR signal (Kramers state) having g values of ∼4.3 and 3.8, along with suggestions that it contains metal-ions with valencies [1V3+, 3Fe3+, 4Fe2+]. In the present work, genetic, biochemical, and spectroscopic approaches were combined to reveal that the EPR signals previously assigned to FeV-cofactor do not correlate with active VFe-protein, and thus cannot arise from the resting-state of catalytically relevant FeV-cofactor. It, instead, appears resting-state FeV-cofactor is either diamagnetic, S = 0, or non-Kramers, integer-spin (S = 1, 2 etc.). When VFe-protein is freeze-trapped during high-flux turnover with its natural electron-donating partner Fe protein, conditions which populate reduced states of the FeV-cofactor, a new rhombic S = 1/2 EPR signal from such a reduced state is observed, with g = [2.18, 2.12, 2.09] and showing well-defined 51V (I = 7/2) hyperfine splitting, aiso = 110 MHz. These findings indicate a different assignment for the electronic structure of the resting state of FeV-cofactor: S = 0 (or integer-spin non-Kramers state) with metal-ion valencies, [1V3+, 4Fe3+, 3Fe2+]. Our findings suggest that the V3+ does not change valency throughout the catalytic cycle.Active site FeV-cofactor of the V-nitrogenase and the EPR spectrum of the reduced cofactor showing 51V-hyperfine coupling. 相似文献
60.
G. Giraudi Claudio Baggiani Antonella Cosmaro Emilio Santià Adriano Vanni 《Fresenius' Journal of Analytical Chemistry》1998,360(2):235-240
A very selective polyclonal antiserum against 1,1,1-trichloro-2,2-bis-(4-chlorophenyl)-ethane (p,p′-DDT) was obtained by a careful choice of the haptenic structure (2,2-bis(4-chlorophenyl)-ethanol hemisuccinate). This hapten
was conjugated to BSA to prepare the immunogen. The effects of different types of solid phases on the equilibrium reaction
between the hapten on solid phase and the polyclonal antiserum were evaluated to obtain a fine tuning of the antiserum performances
in terms of specificity for p,p′-DDT and sensitivity to low levels of this pesticide. The calibration curves obtained show that it is possible to set up
a sensitive assay for p,p′-DDT, employing a p,p′-dichlorodiphenylacetic acid-based solid phase, with a detection limit of 0.12 ng/mL and a working range of about 0.21–40
ng/mL. Selectivity towards several p,p′-DDT-related substances was good (o,p-DDT 17%, p,p′-DDD 1.2% o,p-DDD 6.3%, p,p′-DDE 6.7%).
Received: 4 November 1996 / Revised: 9 June 1997 / Accepted: 16 June 1997 相似文献