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Journal of Physical Organic Chemistry 2009 May; 22(6)
Reactivity of C4indolyl substituted 1,4dihydropyridines toward superoxide anion (O2•) in dimethylsulfoxide
Reactivity of two new C4-indolyl substituted 1,4-dihydropyridines (1,4-DHPs) toward superoxide anion (O2•) in dimethylsulfoxide (DMSO) is reported. Reactivity was followed by electrochemical and spectroscopic techniques. Gas chromatography-mass ... expand abstractspectrometry (GC–MS) was used to identify the final products of the reaction. C4 indolyl-substituted-1,4-DHPs reacted toward O2• at significant rates, according to the calculated kinetic rate constants. Results are compared with 4-phenyl-DHP and the commercial 1,4-DHPs, nimodipine, nisoldipine, and amlodipine. Indolyl-substituted 1,4-DHPs were more reactive than the commercial derivatives. The direct participation of proton of the 1-position of the secondary amine in the quenching of O2• was demonstrated. Copyright © 2008 John Wiley & Sons, Ltd. collapse abstract
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Electroanalysis 2008 Jun; 20(13)
Voltammetric Reduction of a 4Nitroimidazole Derivative on a Multiwalled Carbon Nanotubes Modified Glassy Carbon Electrode
We report the electrochemical behavior of a 4-nitroimidazole derivative, 1-methyl-4-nitro-2-hydroxymethylimidazole (4-NImMeOH), on glassy carbon electrode (GCE) modified with multiwalled carbon nanotubes (MWCNT). As dispersing agents, dimethylformami... expand abstractde (DMF) and water were used. The electrochemical response of the resulting electrodes was evaluated using linear sweep, cyclic and square-wave voltammetry (LSV, CV and SWV). Several parameters such as medium pH, nature and concentration of the CNTs dispersion and accumulation time were tested. The optimal conditions determined for obtain better response were: pH 2, dispersion concentration=4 mg/mL of CNT in water, accumulation time=7 min. The MWCNT-modified GCE exhibited attractive electrochemical properties producing enhanced currents with a significant reduction in the overpotential and good signal-to-noise characteristics, in comparison with the bare GCE. The modified electrode is highly repeatable for consecutive measurements, reaching a variation coefficient of 2.9% for ten consecutive runs. collapse abstract
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Talanta 2008 May; 75(3)
Voltammetric reduction of finasteride at mercury electrode and its determination in tablets.
Finasteride in hydroalcoholic solutions (ethanol/Britton-Robinson buffer, 30/70) exhibits cathodic response in a wide range of pH (-0.5 to 12) using differential pulse (DPP) and test polarography (TP). The reduction peak of finasteride at acidic pH, ... expand abstractis a catalytic proton peak resulting from a mechanism involving a first protonation of finasteride followed by the reduction of the protons combined with finasteride in order to regenerate finasteride and liberate hydrogen. Based on the catalytic hydrogen wave, a novel method for the determination of finasteride can be proposed. For analytical purposes we selected DPP technique in an ethanol/0.0625 mol L(-1) H(2)SO(4) (30/70) solution medium. In this condition the I(p) varied linearly with finasteride concentration between 5 x 10(-5) and 5 x 10(-4) mol L(-1). Within-day and inter-day reproducibility's were adequate with R.S.D. values lower than 2%. The selectivity of the method was checked with both accelerated degradation trials and typical excipients formulations. The developed method was applied to the assay and the uniformity content of finasteride tablets and compared with the standard HPLC method. The DPP-developed method was adequate for the finasteride determination in pharmaceutical forms as that exhibited an adequate accuracy, reproducibility and selectivity. Furthermore, treatment of the sample was not required as in HPLC; the method is not time-consuming and less expensive than the HPLC ones. collapse abstract
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ChemInform 2007 Nov; 38(45)
Synthesis of Some C3,4,5Substituted 2,6Dimethyl1,4dihydropyridines (4DHPs)
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
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Electroanalysis 2007 Jun; 19(14)
Micellar Effects on the Reduction of 4Nitroimidazole Derivative: Detection and Quantification of the Nitroradical Anion
The reductive electrochemistry of 1-methyl-4-nitro-2-hydroxymethylimidazole, a 4-nitroimidazole derivative, was examined in the presence of surfactants anionic as sodium dodecyl sulfate (SDS), nonionic, Triton-X, Cationic, Hyamine and Cetyl Trimethyl... expand abstract Ammonium Bromide (CTAB). The reductive mechanism of the nitroimidazole derivative was found to be dependent of both, nature and concentration of the surfactants. collapse abstract
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Talanta 2007 Oct; 73(5)
Voltammetric behaviour of bromhexine and its determination in pharmaceuticals.
A complete electrochemical study and a novel electroanalytical procedure for bromhexine quantitation are described. Bromhexine in methanol/0.1molL(-1) Britton-Robinson buffer solution (2.5/97.5) shows an anodic response on glassy carbon electrode bet... expand abstractween pH 2 and 7.5. By DPV and CV, both peak potential and current peak values were pH-dependent in all the pH range studied. A break at pH 5.5 in E(P) versus pH plot revealing a protonation-deprotonation (pK(a)) equilibrium of bromhexine was observed. Spectrophotometrically, an apparent pK(a) value of 4.3 was also determined. An electrodic mechanism involving the oxidation of bromhexine via two-electrons and two-protons was proposed. Controlled potential electrolysis followed by HPLC-UV and GC-MS permitted the identification of three oxidation products: N-methylcyclohexanamine, 2-amino-3,5-dibromobenzaldehyde and 2,4,8,10-tetrabromo dibenzo[b,f][1,5] diazocine. DPV at pH 2 was selected as optimal pH for analytical purposes. Repeatability, reproducibility and selectivity parameters were adequate to quantify bromhexine in pharmaceutical forms. The recovery was 94.50+/-2.03% and the detection and quantitation limits were 1.4x10(-5) and 1.6x10(-5)molL(-1), respectively. Furthermore, the DPV method was applied successfully to individual tablet assay in order to verify the uniformity content of bromhexine. No special treatment of sample were required due to excipients do not interfered with the analytical signal. Finally the method was not time-consuming and less expensive than the HPLC one. collapse abstract
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Bioorganic & medicinal chemistry 2007 Jun; 15(12)
Oxidation of C4-hydroxyphenyl 1,4-dihydropyridines in dimethylsulfoxide and its reactivity towards alkylperoxyl radicals in aqueous medium.
This work reports the electrochemical oxidation of three newly synthesized C4-hydroxyphenyl-substituted 1,4-dihydropyridine derivatives in dimethylsulfoxide. The reactivity of the compounds with ABAP-derived alkylperoxyl radicals in aqueous buffer pH... expand abstract 7.4, was also studied. The oxidation mechanism involves the formation of the unstable dihydropyridyl radical, which was confirmed by controlled-potential electrolysis (CPE) and ESR experiments. The final product of the CPE, that is, pyridine derivative, was identified by GC-MS technique for the three derivatives. A direct reactivity of the synthesized compounds toward ABAP-derived alkylperoxyl radicals was found. The pyridine derivative was identified by GC-MS as the final product of the reaction. Results reveal that this type of 1,4-DHPs significantly reacts with the radicals, even compared with commercial 1,4-DHP drugs with a well-known antioxidant ability. collapse abstract
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Journal of pharmaceutical and biomedical analysis 2007 May; 44(1)
Analyses by GC-MS and GC-MS-MS of the Hantzsch synthesis products using hydroxy- and methoxy-aromatic aldehydes.
EI mass spectra of products of the dihydropyridine Hantzsch synthesis using hydroxy and methoxy aldehydes as starting materials are reported. The reaction products (C-4 hydroxy- and methoxyphenyl-1,4-dihydropyridines and chromeno[3,4,c]-pyridines) we... expand abstractre derivatized with N-methyl-N-(trimethylsilyl)-trifluoracetamide to be analyzed by gas chromatographic techniques. Fragmentation pathways for 1,4-dihydropyridines and chromeno-pyridines are proposed. The study provides (mainly through MS-MS technique) useful data for the confirmation of the structure of the compounds and also is a valuable tool for further analytical purposes to follow both photostability and reactivity studies with free radicals for these types of compounds. collapse abstract
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Journal of AOAC International 88(6)
Stability study of simvastatin under hydrolytic conditions assessed by liquid chromatography.
In this work, a liquid chromatography stability-indicating method was developed and applied to study the hydrolytic behavior of simvastatin in different pH values and temperatures. The selected chromatographic conditions were a C18 column; acetonitri... expand abstractle-28 mM phosphate buffer solution, pH 4 (65 + 35) as the mobile phase; 251 degrees C column temperature; and flow rate 1 mL/min. The developed method exhibited an adequate repeatability and reproducibility (coefficient of variation 0.54 and 0.74%, respectively) and a recovery higher than 98%. Furthermore, the detection and quantification limits were 9.1 x 10(-7) and 2.8 x 10(-6) M, respectively. The degradation of simvastatin fitted to pseudo-first order kinetics. The degradation was pH dependent, being much higher at alkaline pH than at acid pH. Activation energy, kinetic rate constants (k) at different temperatures, the half life (t1/2) and the time for 10% degradation to occur (t90) values are also reported. collapse abstract
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Electroanalysis 2006 Feb; 18(5)
Electrochemical Approach to the Radical Anion Formation from 2′Hydroxy Chalcone Derivatives
Three 2′-hydroxy chalcone derivatives were electrochemically reduced to the radical anion by a reversible one-electron transfer followed by a chemical dimerization reaction. Under suitable conditions of the medium, the one-electron reduction pr... expand abstractoduces very well resolved cyclic voltammograms due to the formation of the radical anion. By using appropriately the wide versatility of the cyclic voltammetric technique, was possible to study the generation of the radical anion and its stability. collapse abstract
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Bioelectrochemistry (Amsterdam, Netherlands) 2006 Aug; 69(1)
Nitro radical anion formation from nitrofuryl substituted 1,4-dihydropyridine derivatives in mixed and non-aqueous media.
Three new nitrofuryl substituted 1,4-dihydropyridine derivatives were electrochemically tested in the scope of newly found compounds useful as chemotherapeutic alternative to the Chagas' disease. All the compounds were capable to produce nitro radica... expand abstractl anions sufficiently stabilized in the time window of the cyclic voltammetric experiment. In order to quantify the stability of the nitro radical anion we have calculated the decay constant, k2. Furthermore, from the voltammetric results, some parameters of biological significance as E7(1) (indicative of in vivo nitro radical anion formation) and KO2 (thermodynamic indicator of oxygen redox cycling) have been calculated. From the comparison of E7(1), KO2 and k2 values between the studied nitrofuryl 1,4-DHP derivatives and well-known current drugs an auspicious activity for one of the studied compounds i.e. FDHP2, can be expected. collapse abstract
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Acta crystallographica. Section C, Crystal structure communications 2005 Dec; 62(Pt 1)
Hydrogen-bonded supramolecular structures of three related 4-(5-nitro-2-furyl)-1,4-dihydropyridines.
In ethyl 5-cyano-2,6-dimethyl-4-(5-nitro-2-furyl)-1,4-dihydropyridine-3-carboxylate, C15H15N3O5, the molecules are linked into chains by a single N-H...O hydrogen bond. The molecules in diethyl 2,6-dimethyl-4-(5-nitro-2-furyl)-1,4-dihydropyridine-3,5... expand abstract-dicarboxylate, C17H20N2O7, are linked by a combination of one N-H...O hydrogen bond and two C-H...O hydrogen bonds into sheets built from equal numbers of R(2)(2)(17) and R(4)(4)(18) rings. In 2,6-dimethyl-4-(5-nitro-2-furyl)-1,4-dihydropyridine-3,5-dicarbonitrile, C13H10N4O3, the molecules are linked by a combination of a three-centre N-H...(O)2 hydrogen bond and two independent two-centre C-H...O hydrogen bonds into complex sheets containing four types of ring. collapse abstract
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Journal of AOAC International 88(4)
Voltammetric behavior of zaleplon and its differential pulse polarographic determination in capsules.
In this work both the electrochemical behavior and the analysis of the hypnotic pyrazolopyrimidine derivative zaleplon were studied. Zaleplon in ethanol-0.1M Britton Robinson buffer solution (30-70) showed 2 irreversible, well-defined cathodic respon... expand abstractses in the pH range of 2-12 using differential pulse polarography (DPP), tast polarography, and cyclic voltammetry. From chronocoulometric studies, it was possible to conclude that one electron was transferred in each reduction peak or wave. For analytical purposes, the DPP technique working at pH 4.5 for peak I was selected, which exhibited adequate repeatability, reproducibility, and selectivity. The recovery was 99.97 +/- 1.52%, and the detection and quantitation limits were 5.13 x 10(-7)M and 1.11 x 10(-6)M, respectively. The DPP method was applied successfully to the individual assay of capsules in order to verify the content uniformity of zaleplon. Treatment of the sample is not required because the excipients do not interfere, the method is not time consuming, and it is less expensive than column liquid chromatography. collapse abstract
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Pharmaceutical research 2005 Sep; 22(10)
Reaction of 5-aminosalicylic acid with peroxyl radicals: protection and recovery by ascorbic acid and amino acids.
PURPOSE: The aims of the study are to analyze the interaction between 5-aminosalicylic acid (5-ASA) and peroxyl radicals and to evaluate the effect of some endogenous compounds such as ascorbic acid and amino acids on the oxidation of 5-ASA induced b... expand abstracty 2,2'-azo-bis(2-amidinopropane) dihydrochloride. METHODS: The consumption and/or the recovery of 5-ASA (7.6 microM) exposed to a peroxyl radical source [2,2'-azo-bis(2-amidinopropane)] was followed by techniques such as spectrofluorescence, high-performance liquid chromatography, and differential pulse voltammetry. RESULTS: 5-Aminosalicylic acid was found to readily react with peroxyl radicals at micromolar concentrations and to protect c-Phycocyanin in a very similar fashion to that shown by Trolox. Exposure of 5-ASA to peroxyl radicals led to its oxidation into the corresponding quinone-imine. Disappearance of 5-ASA was prevented by tryptophan, cysteine, glutathione, and ascorbic acid. Furthermore, some of these compounds induced the partial (cysteine and glutathione) or total (ascorbic acid) recovery of 5-ASA when added after its almost total consumption. CONCLUSIONS: 5-Aminosalicylic acid is a very efficient peroxyl radical scavenger. The 5-ASA oxidation by peroxyl radicals was prevented by ascorbic acid, cysteine, and glutathione. In addition, 5-ASA can be regenerated by these endogenous compounds, which would be a valuable mechanism to preserve 5-ASA in tissues undergoing oxidative stress conditions. collapse abstract
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Electroanalysis 2005 Aug; 17(18)
Nitroradical Anion Formation from some IodoSubstituted Nitroimidazoles
The electrochemical behavior of iodo nitroimidazole derivatives such as 1-methyl-4-iodo-5-nitroimidazole (M-I-NIm) and 1-methyl-2,4-diiodo-5-nitroimidazole (M-I2-NIm) and the parent compound 1-methyl-5-nitroimidazole (M-NIm), was studied in protic, m... expand abstractixed and non-aqueous media. The electrochemical study was carried out using Differential Pulse Polarography (DPP), Cyclic Voltammetry (CV), Differential Pulse Voltammetry (DPV) and coulometry and as working electrodes mercury and glassy carbon were used. As can be expected, in all media, the effect of introduce iodo as substituent in the nitroimidazole ring produced a decrease of the energy requirements of the nitro group reduction. Certainly, this fact can be explained by the electron withdrawing character of the iodo substituent that acts diminishing the electronic density on the nitro group thus facilitating their reduction. In all the studied media the reduction of M-NIm produced a detectable signal for a nitro radical anion derivative. In the case of M-I-NIm the nitro radical anion was only detectable in both mixed and non-aqueous media. On the other hand the nitro radical anion for the M-I2-NIm was detected only in non-aqueous medium. When glassy carbon electrode was used as the working electrode in a mixed medium a detectable nitro radical anion derivative appeared for all compounds, thus permitting an adequate comparison between them. The obtained values of k2 for M-NIm, M-I-NIm and M-I2-NIm in non-aqueous medium were 5.81×102, 132×102 and 1100×102 M−1 s−1, respectively. From the obtained k2 and t1/2 values in this medium, it is concluded that there is a direct dependence between the presence of iodo substitution in the nitroimidazole ring with the stability of the nitro radical anion. collapse abstract
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Microchimica Acta 2005 Mar; 100(s 5-6)
Differential pulse voltammetric determination of famotidine
A differential pulse voltammetric method for the determination of famotidine in pharmaceutical preparations is described. The method is based on electrochemical oxidation of famotidine at a glassy carbon or platinum electrode. The proposed method sho... expand abstractws good reproducibility, and sample preparation is simple.Key words differential pulse voltammetry - famotidine - pharmaceuticals collapse abstract
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Electroanalysis 2005 Jan; 17(2)
Electrochemical Study of 4Substituted Analogues of Megazol
The electrochemical behavior of three different megazol analogues substituted at position 4 and their comparison with the parent compound megazol in protic and aprotic media by cyclic voltammetry, Tast and differential pulse polarography was studied.... expand abstract All the compounds were electrochemically reducible in both media with the reduction of the nitroimidazole group the main voltammetric signal. The one-electron reduction couple due to the nitro radical anion formation was visualized only in aprotic media for all these compounds. By applying cyclic voltammetric methodology we have calculated the dimerization reaction decay constants (k2) of the corresponding nitro radical anions in aprotic media. The nitro radical anion obtained from the synthesized nitroimidazole compound having a bromine substituent in 4-position (GC-141) was significantly more stable than the corresponding radical formed from the compound lacking of the substituent in 4-position, megazol. collapse abstract
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Pharmaceutical research 2004 Sep; 21(10)
Reactivity of 1,4-dihydropyridines toward SIN-1-derived peroxynitrite.
PURPOSE: To study the reactivity of C4-substituted 1,4-dihydropyridines (1,4-DHP), with either secondary or tertiary nitrogen in the dihydropyridine ring, toward SIN-1-derived peroxynitrite in aqueous media at pH 7.4. METHODS: Reactivity was followed... expand abstract by changes in the absorptivity of the UV-Vis bands corresponding to 1,4-DHP. Gas Chromatography/ Mass Spectrometer (GC-MS) and Electron Paramagnetic Resonance (EPR) spin trap techniques were used to characterize the final product and the intermediates of the reaction, respectively. RESULTS: 1,4-DHPs significantly reacted toward peroxynitrite at varied rates, according to the calculated kinetic rate constants. By EPR spectroscopy, a carbon-centered radical from the 1,4-DHP was intercepted with N-tert-butylamine-alpha-phenylnitrone (PBN), as the intermediate for the reaction with peroxynitrite. Likewise, the oxidized derivative (i.e., the pyridine) was identified as the final product of the reaction by GC-MS. By using the technique of deuterium kinetic isotope effect, the participation of the hydrogen of the 1-position on the 1,4-DHP ring was shown not to be the rate-limiting step of the reaction. CONCLUSIONS: The direct participation of the 1,4-DHP derivatives in the quenching of SIN-1-derived peroxynitrite has been demonstrated. Kinetic rate constant of tested 1,4-DHP toward peroxynitrite showed a direct relationship with the oxidation peak potential values; that is, compounds reacting faster were more easily oxidized. collapse abstract
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Free radical research 2004 Jun; 38(7)
1,4-dihydropyridines: reactivity of nitrosoaryl and nitroaryl derivatives with alkylperoxyl radicals and ABTS radical cation.
In the present paper, a direct quenching of radical species by a number of synthesized nitrosoaryl 1,4-dihydropyridines and their parent nitroaryl 1,4-dihydropyridines was determined in aqueous media at pH 7.4. These two series of compounds were comp... expand abstractared with the C-4 unsubstituted 1,4-dihydropyridines derivatives and the corresponding C-4 aryl substituted 1,4-dihydropyridines derivatives. Kinetic rate constants were assessed by UV-Vis spectroscopy. Nitrosoaryl derivatives were more reactive than the parent nitroaryl 1,4-dihydropyridines. Our results strongly support the assumption that the reactivity between the synthesized 1,4-dihydropyridines derivatives with alkylperoxyl radicals involves electron transfer reactions, which is documented by the presence of pyridine as final product of reaction and the complete oxidation of the nitroso group to give rise the nitro group in the case of the nitrosoaryl 1,4-dihydropyridines derivatives. collapse abstract
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ChemInform 2004 May; 35(20)
Synthesis of New 4Nitrosophenyl1,4dihydropyridines of Pharmacological Interest.
For Abstract see ChemInform Abstract in Full Text.
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Bioorganic & medicinal chemistry 2004 Apr; 12(9)
Structural effects on the reactivity 1,4-dihydropyridines with alkylperoxyl radicals and ABTS radical cation.
A series of eight commercial C-4 substituted 1,4-dihydropyridines and other synthesized related compounds were tested for direct potential scavenger effect towards alkylperoxyl radicals and ABTS radical cation in aqueous Britton-Robinson buffer pH7.4... expand abstract. A direct quenching radical species was established. The tested 1,4-dihydropyridines were 8.3-fold more reactive towards alkylperoxyl radicals than ABTS cation radical, expressed by their corresponding kinetic rate constants. Furthermore, NPD a photolyte of nifedipine and the C-4 unsubstituted 1,4-DHP were the most reactive derivatives towards alkylperoxyl radicals. The pyridine derivative was confirmed by GC/MS technique as the final product of reaction. In consequence, the reduction of alkylperoxyl and ABTS radicals by 1,4-dihydropyridines involved an electron transfer process. Also, the participation of the hydrogen of the 1-position appears as relevant on the reactivity. Results of reactivity were compared with Trolox. collapse abstract
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Electroanalysis 2004 Mar; 16(7)
Spectroelectrochemical Study on the Electrooxidation in Aqueous Medium of some 1,4Dihydropyridines: Effects of Substitution in 1Position and 4Position
Spectroelectrochemical and HPLC characterization of the electrochemical oxidation in aqueous medium of a series of six N-1 and C-4 substituted 1,4-dihydropyridines is presented. Based on the analysis of spectra obtained by in situ spectroscopic measu... expand abstractrements it was possible to detect the generation of final oxidation products, which resulted in differences depending of the nature of the substitution on the nitrogen in the dihydropyridine ring. Controlled potential electrolysis (CPE) in aqueous medium was followed by the HPLC technique using EC and PDA detectors. This latter resulted adequately to follow the parent 1,4-DHP derivatives and their respective oxidation products. Electrochemical oxidation of parent N-H substituted 1,4-dihydropyridines generated the corresponding neutral pyridine derivative as final oxidation product. However, the N-ethyl substituted 1,4-dihydropyridine derivatives gave rise to the pyridinium salt derivatives. collapse abstract
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Journal of pharmaceutical and biomedical analysis 2004 Mar; 35(1)
Spectrophotometric and electrochemical study of the inclusion complex between beta-cyclodextrin and furnidipine.
Inclusion complexation between furnidipine (2,6-dimethyl-4-(2-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylic acid 3-tetrahydrofurfuryl 5-methyl diester), a calcium-channel antagonist, and beta-cyclodextrin (beta-CyD) was studied in aqueous solutio... expand abstractn by using both spectrophotometric and electrochemical measurements. The phase solubility profile was classified as A(L)-type, indicating the formation of 1:1 stoichiometric inclusion complex of furnidipine with beta-CyD. Based on the spectrophotometric absorbance's variations, a formation constant value, K(f), of 156 M(-1) was determined. Electrochemical measurements using chronocoulometric experiments were used for the determination of the diffusion coefficients. In absence of beta-CyD, a diffusion coefficient value of 4.32 x 10(-6) cm2 s(-1) was obtained for furnidipine. The addition of beta-CyD produced a decrease of 30% for the diffusion coefficient. Formation of inclusion complexes of furnidipine with beta-CyD was proved to increase more than three times the solubility of furnidipine. collapse abstract
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Electroanalysis 2003 Oct; 15(22)
Differential Pulse Polarographic and UVVis Spectrophotometric Study of Inclusion Complexes Formed by 1,4Dihydropyridine Calcium Antagonists, Nifedipine and Nicardipine with βCyclodextrin
The formation of inclusion complexes of well-known 1,4-dihydropyridine calcium antagonists, such as nifedipine (NF) and nicardipine (NC), with β-cyclodextrin (βCD) was investigated by differential pulse polarography (DPP) and UV-vis spectro... expand abstractphotometry. The equimolar variation method indicated the formation of the NF-βCD (1 : 1, M : M) and a NC-βCD (1 : 1, M : M) inclusion complexes. Titrations using the DPP peak currents for NF and NC permitted one to determine formation constant values of (135±20) M−1 and (357±41) M−1 for NF-βCD and NC-βCD, respectively. For comparative purposes we have also applied phase solubility studies with spectrophotometric detection obtaining formation constant values of (129±5) M−1 and (385±19) M−1 for NF-βCD and NC-βCD, respectively. According to the DPP studies, we can postulate that the inclusion moiety were the nitroaromatic group, in the case of NF-βCD, and the phenyl group on 3-position of the 1,4-DHP, in the case of NC-βCD. The solubility of NF in water was increased about three times due to the formation of an inclusion complex with βCD. For NC the solubility was increased almost seven times. collapse abstract
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Journal of AOAC International 85(6)
Differential pulse voltammetric assay of lercanidipine in tablets.
Lercanidipine in ethanol-0.04M Britton-Robinson buffer (20 + 80) gives an irreversible anodic response on a glassy carbon electrode in a broad pH range (2-12) that depends on pH. This signal can be attributed to oxidation of the 1,4-dihydropyridine r... expand abstracting to give the corresponding pyridine derivative. For analytical purposes, differential pulse voltammetry at pH 4 was selected. Under these conditions, good values of both within- and interday reproducibility were obtained, with coefficient of variation (CV) values of 1.56 and 1.70%, respectively, for 10 successive runs. For quantitation, the calibration curve method was used for lercanidipine concentrations ranging from 1 x 10(-5) to 1 x 10(-4) M. The detection and quantitation limits were 1.39 x 10(-5) and 1.49 x 10(-5), respectively. A liquid chromatographic method with electrochemical detection was used for comparison. The voltammetric method showed good selectivity with respect to both excipients and degradation products. The recovery study exhibited a CV of 0.94% and an average recovery of 98.3%, and it was not necessary to treat the sample before the analysis. The method was successfully applied to the individual tablet assay of lercanidipine in commercial tablets. collapse abstract
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