A high-performance liquid chromatography/tandem mass spectrometry method for the determination of artemisinin in rat plasma

Artemisinin is a widely used antimalarial drug. To evaluate the pharmacokinetics of artemisinin in rats, a sensitive and specific liquid chromatography/tandem mass spectrometric (LC/MS/MS) method was developed and validated for the determination of artemisinin in rat plasma. For detection, a Sciex API 4000 LC/MS/MS instrument with an electrospray ionization (ESI) TurboIonSpray inlet in the positive ion multiple reaction monitoring (MRM) mode was used to monitor precursor ([M+NH4]+) --> product ions of m/z 300.4 --> 209.4 for artemisinin and m/z 316.4 --> 163.4 for artemether, the internal standard (IS). The plasma samples were pretreated by a simple liquid-liquid extraction with ether. The standard curve was linear (r > 0.99) over the artemisinin concentration range of 1.0-200.0 ng/mL in plasma. The method had a lower limit of quantification of 1.0 ng/mL for artemisinin in 100 microL of plasma, which offered a satisfactory sensitivity for the determination of artemisinin. The intra- and inter-day precisions were measured to be within +/-5.3% and accuracy between -2.6% and 1.2% for all quality control samples, lower limit of quantification and upper limit of quantification samples. The extraction recoveries of artemisinin and the IS were 95.4 +/- 4.5% and 92.8 +/- 3.9%, respectively. This present method was successfully applied to the characterization of the pharmacokinetic profile of artemisinin in rats after oral administration.     

Artemisinin evaluation in Romanian Artemisia annua wild plants using a new HPLC/MS method

Artemisinin, a sesquiterpene lactone from Artemisia annua L., has received considerable attention in the last few decades as a potent antimalarial drug. Artemisinin has rather low toxicity; it is effective against drug-resistant Plasmodium species and against cerebral malaria. This study reports the development of a rapid and sensitive assay for the quantification of artemisinin in A. annua by reversed phase HPLC/MS. In the selected optimal experimental conditions, artemisinin exhibited a well-defined chromatographic peak with a retention time of 2 ± 0.2 min. The chromatographic signal shows a linear dependence with artemisinin concentration, enabling the use of this signal for artemisinin quantification according to the following regression equation: y = 2665.40x - 14697.61. The correlation coefficient (R(2)) was 0.9989. For every concentration within the range of the standard curve (0.1-2 μg mL(-1)), accuracy was between 95 and 104%. Artemisinin content in Romanian A. annua wild plants varies between 0.17 and 0.21% (dry weight basis).     

Dissolution of Nickel Ferrite in Aqueous Solutions Containing Oxalic Acid and Ferrous Salts

The dissolution of nickel ferrite in oxalic acid and in ferrous oxalate-oxalic acid aqueous solution was studied. Nickel ferrite was synthesized by thermal decomposition of a mixed tartrate; the particles were shown to be coated with a thin ferric oxide layer. Dissolution takes place in two stages, the first one corresponding to the dissolution of the ferric oxide outer layer and the second one being the dissolution of Ni(1.06)Fe(1.96)O(4). The kinetics of dissolution during this first stage is typical of ferric oxides: in oxalic acid, both a ligand-assisted and a redox mechanism operates, whereas in the presence of ferrous ions, redox catalysis leads to a faster dissolution. The rate dependence on both oxalic acid and on ferrous ion is described by the Langmuir-Hinshelwood equation; the best fitting corresponds to K(1)(ads)=25.6 mol(-1) dm(-3) and k(1)(max)=9.17x10(-7) mol m(-2) s(-1) and K(2)(ads)=37.1x10(3) mol(-1) dm(-3) and k(2)(max)=62.3x10(-7) mol m(-2) s(-1), respectively. In the second stage, Langmuir-Hinshelwood kinetics also describes the dissolution of iron and nickel from nickel ferrite, with K(1)(ads)=20.8 mol(-1) dm(3) and K(2)(ads)=1.16x10(5) mol(-1) dm(3). For iron, k(1)(max)=1.02x10(-7) mol of Fe m(-2) s(-1) and k(2)(max)=2.38x10(-7) mol of Fe m(-2) s(-1); for nickel, the rate constants k(1)(max) and k(2)(max) are 2.4 and 1.79 times smaller, respectively. The factor 1.79 agrees nicely with the stoichiometric ratio, whereas the factor 2.4 implies the accumulation of some nickel in the residual particles. The rate of nickel dissolution in oxalic acid is higher than that in bunsenite by a factor of 8, whereas hematite is more reactive by a factor of 9 (in the absence of Fe(II)) and 27 (in the presence of Fe (II)). It may be concluded that oxalic acid operates to dissolve iron, and the ensuing disruption of the solid framework accelerates the release of nickel. Copyright 2000 Academic Press.     

Fast nitroxyl trapping by ferric porphyrins

Iron(II) porphyrin nitrosyl complexes are obtained in high yields from the reaction of iron(III) porphyrins with the nitroxyl donors sodium trioxodinitrate and toluensulfohydroxamic acid. The reaction was found to proceed both in organic solvents and in aqueous media from iron(III) (meso-tetraphenyl) porphyrinate ([FeIII(TPP)]+) and iron(III) meso-tetrakis (4-sulfonatophenyl) porphyrinate ([FeIII(TPPS)]3-) or iron(III) protoporphyrin IX, respectively. The kinetic rate constant for the reaction of ([FeIII(TPPS)]3-) with sodium trioxodinitrate (kon) was estimated to be 1.00 +/- 0.04 x 107 M-1 s-1. As well as resulting in a versatile method for obtaining ferrous nitrosyl porphyrins, the reaction points at ferric porphyrins as efficient nitroxyl traps and provides a tool to model nitroxyl reactivity toward hemeproteins.     

Mechanisms of NO release by N1-nitrosomelatonin: nucleophilic attack versus reducing pathways

A new type of physiologically relevant nitrosamines have been recently recognized, the N(1)-nitrosoindoles. The possible pathways by which N(1)-nitrosomelatonin (NOMel) can react in physiological environments have been studied. Our results show that NOMel slowly decomposes spontaneously in aqueous solution, generating melatonin as the main organic product (k = (3.7 +/- 1.1) x 10(-5) s(-1), Tris-HCl (0.2 M) buffer, pH 7.4 at 37 degrees C, anaerobic). This rate is accelerated by acidification (k(pH 5.8) = (4.5 +/- 0.7) x 10(-4) s(-1), k(pH 8.8) = (3.9 +/- 0.6) x 10(-6) s(-1), Tris-HCl (0.2 M) buffer at 37 degrees C), by the presence of O(2) (k(o) = (9.8 +/- 0.1) x 10(-5) s(-1), pH 7.4, 37 degrees C, [NOMel] = 0.1 mM, P(O(2)) = 1 atm), and by the presence of the spin trap TEMPO (2,2,6,6-tetramethylpiperidine 1-oxyl; k(o) = (2.0 +/- 0.1) x 10(-4) s(-1), pH 7.4, 37 degrees C, [NOMel] = 0.1 mM, [TEMPO] = 9 mM). We also found that NOMel can transnitrosate to l-cysteinate, producing S-nitrosocysteine and melatonin (k = 0.127 +/- 0.002 M(-1) s(-1), Tris-HCl (0.2 M) buffer, pH 7.4 at 37 degrees C). The reaction of NOMel with ascorbic acid as a reducing agent has also been studied. This rapid reaction produces nitric oxide and melatonin. The saturation of the observed rate constant (k = (1.08 +/- 0.04) x 10(-3) s(-1), Tris-HCl (0.2 M) buffer, pH 7.4 at 37 degrees C) at high ascorbic acid concentration (100-fold with respect to NOMel) and the pH independence of this reaction in the pH range 7-9 indicate that the reactive species are ascorbate and melatonyl radical originated from the reversible homolysis of NOMel. Taking into account kinetic and DFT calculation data, a comprehensive mechanism for the denitrosation of NOMel is proposed. On the basis of our kinetics results, we conclude that under physiological conditions NOMel mainly reacts with endogenous reducing agents (such as ascorbic acid), producing nitric oxide and melatonin.     

Mercurous nitrate as a reductimetric reagent : The determination of copper

It has been found that in the presence of excess thiocyanate ions, cupric copper will oxidise ferrous ions. Use has been made of this reaction to determine copper by titration of the ferric iron produced, with mercurous nitrate. Although this reaction is the reverse of that usually observed, where the cuprous ion reduces the ferric iron, it has been found that the large excess of thiocyanate is responsible for this effect.     

Design, synthesis, and study of a mycobactin-artemisinin conjugate that has selective and potent activity against tuberculosis and malaria

Although the antimalarial agent artemisinin itself is not active against tuberculosis, conjugation to a mycobacterial-specific siderophore (microbial iron chelator) analogue induces significant and selective antituberculosis activity, including activity against multi- and extensively drug-resistant strains of Mycobacterium tuberculosis. The conjugate also retains potent antimalarial activity. Physicochemical and whole-cell studies indicated that ferric-to-ferrous reduction of the iron complex of the conjugate initiates the expected bactericidal Fenton-type radical chemistry on the artemisinin component. Thus, this "Trojan horse" approach demonstrates that new pathogen-selective therapeutic agents in which the iron component of the delivery vehicle also participates in triggering the antibiotic activity can be generated. The result is that one appropriate conjugate has potent and selective activity against two of the most deadly diseases in the world.     

Synthesis of New 1,2,4-Trioxanes and their Antimalarial Activity

The three dihydronaphtho[1,2,4]trioxines 9 – 11 have been synthesized and two of them converted to the five carbamate and ester derivatives 12 – 16 (Schemes 1 and 2). The resulting new trioxanes together with two already known and ascaridole ( 7 ) were tested for antimalarial activity against the sensitive N strain of Plasmodium berghei in mice. On comparison with artemisinin ( 1 ) and dihydroartemisinin ( 2 ), modest activity was found. The four most active compounds were some 12–18 times less potent than 1 .     

不同电极上血红素对青蒿素的电催化还原

 在含20%乙醇的Britton-Robinson缓冲液介质(pH=7.2)中,采用循环伏安法在玻碳电极和银电极上比较了血红素对青蒿素还原的催化作用. 由于血红素和青蒿素加合物的形成及血红素中Fe2+的催化作用,青蒿素在玻碳电极和银电极上的还原过电位分别降低了0.32和0.09 V,还原活化能分别降低了62.1和17.6 kJ/mol. 还比较了血红素和配合物EDTA-Fe3+对青蒿素的催化还原效果,结果表明,EDTA-Fe2+的催化作用远低于血红素. 进一步证实了血红素在青蒿素的药理研究中起着关键作用.     

Kinetics and mechanism of acid-catalyzed oxidation of bromide ions by the aqueous chromyl(IV) ion

The reaction between the aqueous chromyl ion, CraqO2+, and Br- is acid-catalyzed and generates Br2. Kinetic studies that utilized a superoxochromium ion, CraqOO2+, as a kinetic probe yielded a mixed third-order rate law, -d[CraqO2+]/dt=k[CraqO2+][Br-][H+], where k=608+/-11 M-2 s-1. Experimental data strongly favor a one-electron mechanism, but the reaction is much faster than predicted on the basis of the reduction potential for the Br*/Br- couple. The reduction of CraqO2+ by transition-metal complexes, on the other hand, exhibits "normal" behavior, that is, k=(1.37x10(3)+1.94x10(3) [H+]) M-1 s-1 for Os(1,10-tris-phenanthroline)(3)2+ and <10 M-1 s-1 for Ru(2,2'-bipyridine)3(2+) at 0.1 M H+. The reduction of CraqOO2+ by Br2*- takes place with a rate constant k=(1.23+/-0.20)x10(9) M-1 s-1, as determined by laser-flash photolysis.     

Hydrogen bonding and catalysis of solvolysis of 4-methoxybenzyl fluoride

Values of k(o) = 8.0 x 10(-3) s(-1) and k(H) = 2.5 x 10(-2) M(-1) s(-1), respectively, were determined for the spontaneous and the acid-catalyzed cleavage of 4-methoxybenzyl fluoride (1-F) to form the 4-methoxybenzyl carbocation (1+). Values of k(F) = 1.8 x 10(7) M(-1) s(-1) and k(HF) = 7.2 x 10(4) M(-1) s(-1) were determined for addition of F- and HF to 1+ for reaction in the microscopic reverse direction. Evidence is presented that the reversible addition of HF to 1+ to give 1-F + H+ proceeds by a concerted reaction mechanism. The relatively small 250-fold difference between the reactivities of fluoride ion and neutral HF toward 1+ is attributed to the tendency of the strong aqueous solvation of F- to decrease its nucleophilic reactivity and to the advantage for the concerted compared with the usual stepwise pathway for addition of HF. There is no significant stabilization of the transition state for cleavage of 1-F from general acid catalysis by 0.80 M cyanoacetate buffer at pH 1.7. The estimated 3 kcal/mol larger Marcus intrinsic barrier for heterolytic cleavage of 1-F than for cleavage of 1-Cl is attributed to a lag in the development at the transition state of the ca. 30 kcal/mol greater stabilizing solvation of the product ion F- compared with Cl-. The decrease in the electronegativity of X along the series X = F, OH, Cl is accompanied by a ca. 10(10)-fold increase in the carbon basicity compared with the proton basicity of X-.     

Kinetic isotope effect and extended pH-dependent studies of the oxidation of hydroxylamine by hexachloroiridate(IV): ET and PCET

The oxidation of hydroxylamine by [IrCl6]2- has been studied spectrophotometrically in deoxygenated aqueous solutions in the range of pH 4-9 at 25 degrees C. The reaction is catalyzed by Cu2+, Fe2+, and impurities of aquochloroiridium complexes. Oxalate is a very effective inhibitor of catalysis by copper and iron ions. With excess hydroxylamine, the reaction follows pseudo-first-order kinetics, and the stoichiometric ratio (DeltanIr(IV)/Deltanhydroxylamine) is 1.05 at pH 5.9. Over the pH range 4.2-8.8, the empirical rate law is -d[IrCl(6)2-]/dt=k[IrCl6(2-)][NH2OH]tot, with k=k1Ka1/([H+]+Ka1)+k'Ka1/([H+]([H+]+Ka1)), where Ka1 is the dissociation constant of NH3OH+. Least-squares fitting yields k1=(17.05+/-0.47) M-1 s(-1) and k'=(2.59+/-0.09)x10(-6) s(-1) at ionic strength of 0.1 M (adjusted by NaClO4) and 25 degrees C. The kinetic isotope effects (KIE) (kH/kD) for k1 and k' are 4.4 and 9.8, correspondingly. A mechanism is inferred in which k1 corresponds to concerted proton-coupled electron transfer (PCET) and k' corresponds to electron transfer from NH2O-. In this mechanism, the large KIE for k' is due almost entirely to the equilibrium isotope effect for the pKa of NH2OH.     

Kinetics and Mechanism of the Formation and Acid Dissociation of Cobalt(II), Nickel(II), and Copper(II) Complexes with the Highly Enolized beta-Diketone 3-(N-Acetylamido)pentane-2,4-dione (=Hamac) in Aqueous Solution

The beta-diketone Hamac = 3-(N-acetylamido)pentane-2,4-dione was characterized by potentiometric, spectrophotometric, and kinetic methods. In water, Hamac is very soluble (2.45 M) and strongly enolized, with [enol]/[ketone] = 2.4 +/- 0.1. The pK(a) of Hamac is 7.01 +/- 0.07, and the rate constants for enolization, k(e), and ketonization, k(k), at 298 K are 0.0172 +/- 0.0004 s(-1) and 0.0074 +/- 0.0015 s(-1), respectively. An X-ray structure analysis of the copper(II) complex Cu(amac)(2).toluene (=C(21)H(28)CuN(2)O(6); monoclinic, C2/c; a = 20.434(6), b = 11.674(4), c = 19.278(6) ?; beta = 100.75(1) degrees; Z = 8; R(w) = 0.0596) was carried out. The bidentate anions amac(-) coordinate the copper via the two diketo oxygen atoms to form a slightly distorted planar CuO(4) coordination core. Rapid-scan stopped-flow spectrophotometry was used to study the kinetics of the reaction of divalent metal ions M(2+) (M = Ni,Co,Cu) with Hamac in buffered aqueous solution at variable pH and I = 0.5 M (NaClO(4)) under pseudo-first-order conditions ([M(2+)](0) > [Hamac](0)) to form the mono complex M(amac)(+). For all three metals the reaction is biphasic. The absorbance/time data can be fitted to the sum of two exponentials, which leads to first-order rate constants k(f) (fast initial step) and k(s) (slower second step). The temperature dependence of k(f) and k(s) was measured. It follows from the kinetic data that (i) the keto tautomer of Hamac, HK, does not react with the metal ions M(2+), (ii) the rate constant k(f) increases linearly with [M(2+)](0) according to k(f) = k(0) + k(2)[M(2+)](0), and (iii) the rate constant k(s) does not depend on [M(2+)](0) and describes the enolization of the unreactive keto tautomer HK. The pH dependence of the second-order rate constant k(2) reveals that both the enol tautomer of Hamac, HE, and the enolate, E(-), react with M(2+) in a second-order reaction to form the species M(amac)(+). At 298 K rate constants k(HE) are 18 +/- 6 (Ni), 180 +/- 350 (Co), and (9 +/- 5) x 10(4) (Cu) M(-1) s(-1) and rate constants k(E) are 924 +/- 6 (Ni), (7.4 +/- 0.6) x 10(4) (Co), and (8.4 +/- 0.2) x 10(8) (Cu) M(-1) s(-1). The acid dissociation of the species M(amac)(+) is triphasic. Very rapid protonation (first step) leads to M(Hamac)(2+), which is followed by dissociation of M(Hamac)(2+) and M(amac)(+), respectively (second step). The liberated enol Hamac ketonizes (third step). The mechanistic implications of the metal dependence of rate constants k(HE), k(E), k(-HE), and k(-E) are discussed.     

Flash photolytic generation and study of p-quinone methide in aqueous solution. An estimate of rate and equilibrium constants for heterolysis of the carbon-bromine bond in p-hydroxybenzyl bromide

Flash photolysis of p-hydroxybenzyl acetate in aqueous perchloric acid solution and formic acid, acetic acid, biphosphate ion, and tris(hydroxymethyl)methylammonium ion buffers produced p-quinone methide as a short-lived species that underwent hydration to p-hydroxybenzyl alcohol in hydronium ion catalyzed (k(H(+)) = 5.28 x 10(4) M(-1) s(-1)) and uncatalyzed (k(uc) = 3.33 s(-1)) processes. The inverse nature of the solvent isotope effect on the hydronium ion-catalyzed reaction, k(H(+))/k(D(+)) = 0.41, indicates that this process occurs by rapid and reversible protonation of the quinone methide on its carbonyl carbon atom, followed by rate-determining capture of the p-hydroxybenzyl carbocation so produced by water, while the magnitude of the rate constant on the uncatalyzed process indicates that this reaction occurs by simple nucleophilic addition of water to the methylene group of the quinone methide. p-Quinone methide also underwent hydronium ion-catalyzed and uncatalyzed nucleophilic addition reactions with chloride ion, bromide ion, thiocyanate ion, and thiourea. The solvent isotope effects on the hydronium ion-catalyzed processes again indicate that these reactions occurred by preequilibrium mechanisms involving a p-hydroxybenzyl carbocation intermediate, and assignment of a diffusion-controlled value to the rate constant for reaction of this cation with thiocyanate ion led to K(SH) = 110 M as the acidity constant of oxygen-protonated p-quinone methide. In a certain perchloric acid concentration range, the bromide ion reaction became biphasic, and least-squares analysis of the kinetic data using a double-exponential function provided k(Br(-)) = 3.8 x 10(8) M(-1) s(-1) as the rate constant for nucleophilic capture of the p-hydroxybenzyl carbocation by bromide ion, k(ionz) = 8.5 x 10(2) s(-1) for ionization of the carbon-bromine bond of p-hydroxybenzyl bromide, and K = 4.5 x 10(5) M(-1) as the equilibrium constant for the carbocation-bromide ion combination reaction, all in aqueous solution at 25 degrees C. Comparisons are made of the reactivity of p-quinone methide with p-quinone alpha,alpha-bis(trifluoromethyl)methide as well as p-quinone methide with o-quinone methide.     

Dynamic in situ spectroscopic ellipsometry of the reaction of aqueous iron(II) with 2,2'-bipyridine in a thin Nafion film

Dynamic in situ spectroscopic ellipsometry studies of the chemical reaction between ferrous ion and 2,2'-bipyridine (bpy) in a thin Nafion film are presented. A simple prototype system composed of a thin Nafion film on a glass substrate was used throughout the work. The reaction was detected by optically monitoring the formation of the strongly absorbing complex ion, Fe(bpy)3(2+) (epsilon 520 = 7.70 x 10(3) M(-1) cm(-1) in 0.1 M NaCl). The changes in film optical constants, n and k, and the thickness upon exposure of it to various solutions were monitored in a flow cell with the film on the backside of the substrate relative to the interrogation by light. A "step-by-step" approach was used to isolate the component parts of the system in which the film was consecutively exposed to solutions in the following order: supporting electrolyte, bpy, and, last, ferrous iron solution. The optical properties of the materials were quantitatively described before and during mass transport within the film by modeling using the appropriate multilayer optical models, i.e., the Cauchy equation for nonabsorbing media and the Urbach and Tauc-Lorentz (oscillator) functions for a film that absorbed. The experiments done allowed study of the diffusion in the film and the chemical reactions that are important in the sensing scheme for ferrous iron. Ligand (bpy) diffusion followed a two-stage diffusion mechanism described by a Berens-Hopfenberg model for incremental sorption (D25 = 7.04 x 10(-13) cm2 s(-1)). The stabilities of the appropriate systems, i.e., Nafion film with bpy, iron, and iron complex, were studied by exposing equilibrated films to circulating supporting electrolyte solutions. The measurements gave important insights into a set of film chemical reactions and, in turn, selective film dynamics. This work exemplifies the usefulness of spectroscopic ellipsometry in monitoring the kinetics of a chemical reaction in situ, as well as the changes in the film physical properties under dynamic conditions.     

Electrocatalytic determination of ascorbic acid on a glassy carbon electrode chemically modified with cobalt pentacyanonitrosylferrate.

An electrochemically prepared thin film of cobalt pentacyanonitrosylferrate (GC/CoPCNF) was used as a surface modifier for glassy carbon electrodes. The oxidation of ascorbic acid on a glassy carbon electrode modified with GC/CoPCNF as a working electrode was studied using cyclic voltammetry, rotating disk electrode (RDE) voltammetry and chronoamperometry in a 0.25 M KNO3 + 0.25 M phosphate buffer (pH 7) solution. The glassy carbon modified with CoPCNF showed good electrocatalytic activity toward ascorbic acid oxidation. The kinetics of the catalytic reaction was investigated, and the average value of the rate constant (k) for the catalytic reaction and the diffusion coefficient (D) were evaluated by different approaches for ascorbic acid, and were found to be 3.3 +/- 0.3 x 10(2) M(-1) s(-1) and 3.2 +/- 0.3 x 10(-6) cm2 s(-1), respectively.     

青蒿素及其衍生物电化学性质的研究I. 青蒿素在汞电极上的电化学还原

青蒿素及其衍生物代表着一类新型抗疟药。青蒿素分子中过氧基与抗疟活性密切相关。本文采用多种电化学方法研究了青蒿素分子中过氧基在Hg电极上的还原, 还原电位在0.0V(vs.Ag/AgCl)附近, 电极过程为不可逆还原, 反应电子数n=2, 半波电位E1/2=0.012V, 电子转移系数α=0.66, 表观标准电极反应速率常数ks'=6.34×10^-^6cm/s, 扩散系数D=4.3×10^-^6cm^2/s。反应产物在电极表面具有吸附性, 文中提出了可能的电化学反应机理。     

Advances in the Chemical Synthesis of Artemisinin

Artemisinin, existing in the Chinese medicinal plant Artemisia annua L., is a kind of sesquiterpenoid lactone endoperoxide. It has received extensive attention from all over the world owing to its unusual trioxane structure and potent antimalarial properties. Here we demonstrate the complete chemical synthetic pathway of artemisinin, investigated the past three decades, including the total and partial syntheses.     

Characterization of noncovalent complexes of antimalarial agents of the artemisinin-type and Fe(III)-heme by electrospray mass spectrometry and collisional activation tandem mass spectrometry

In this study, we demonstrate, using electrospray ionization mass spectrometry (ESI-MS) and collision-induced dissociation tandem mass spectrometry (ESI-MS/CID/MS), that stable noncovalent complexes can be formed between Fe(III)-heme and antimalarial agents, i.e., quinine, artemisinin, and the artemisinin derivatives, dihydroartemisinin, alpha- and beta-artemether, and beta-arteether. Differences in the binding behavior of the examined drugs with Fe(III)-heme and the stability of the drug-heme complexes are demonstrated. The results show that all tested antimalarial agents form a drug-heme complex with a 1:1 stoichiometry but that quinine also results in a second complex with the heme dimer. ESI-MS performed on mixtures of pairs of various antimalarial agents with heme indicate that quinine binds preferentially to Fe(III)-heme, while ESI-MS/CID/MS shows that the quinine-heme complex is nearly two times more stable than the complexes formed between heme and artemisinin or its derivatives. Moreover, it is found that dihydroartemisinin, the active metabolite of the artemisinin-type drugs in vivo, results in a Na(+)-containing heme-drug complex, which is as stable as the heme-quinine complex. The efficiency of drug-heme binding of artemisinin derivatives is generally lower and the decomposition under CID higher compared with quinine, but these parameters are within the same order of magnitude. These results suggest that the efficiency of antimalarial agents of the artemisinin-type to form noncovalent complexes with Fe(III)-heme is comparable with that of the traditional antimalarial agent, quinine. Our study illustrates that electrospray ionization mass spectrometry and collision-induced dissociation tandem mass spectrometry are suitable tools to probe noncovalent interactions between heme and antimalarial agents. The results obtained provide insights into the underlying molecular modes of action of the traditional antimalarial agent quinine and of the antimalarials of the artemisinin-type which are currently used to treat severe or multidrug-resistant malaria.     

Heteropolyacids dispersed within a polymer matrix as a new catalytic systems with controlled oxidative-reductive and acid-base active centers

Polymer support such as polypyrrole was selected as a matrix for heteropolyacid H₅PMo₁₀V₂O₄₀ in an attempt to prepare heterogeneous catalysts containing two different active centers: protons and transition metal ions. Exchanging protons from heteropolyanions dispersed in polymer matrix into ferric or ferrous ions cause the modifications of their catalytic properties. It is manifested by decrease of activity of acid-base centers and increase of activity of oxidative-reductive centers. Oxidation state of iron in all samples before and after catalytic reaction is the same (Fe(III)), but their structure is not similar. For catalysts doped with ferric ions the structural order is much more pronounced than for these doped with ferrous ions.