NMR determination of pKa values of indoloquinoline alkaloids

Malaria is one of the most serious global health problems. Isolating new therapeutic agents with potential antimalarial activity from natural sources or preparing such agents either semisynthetically or synthetically is one strategy for solving the problem of resistance constantly evolving to the drugs currently in use. For alkaloids, the acid–base dissociation constant, pK_a, is an important characteristic, thought to be associated with biological activity. In this contribution, pK_a values for several indoloquinoline alkaloids were determined by using ¹H NMR spectroscopy in a mixture of solvents. The data were recalculated for water solutions using the correction factors reported previously. The structural dependence of the pK_a values for cryptolepine and its isomers neocryptolepine, isocryptolepine and isoneocryptolepine as well as some substituted neocryptolepine derivatives is discussed. Copyright © 2009 John Wiley & Sons, Ltd.     

A comparison of inductively coupled argon plasma atomic emission spectrometry and electrothermal atomization atomic absorption spectrometry in the determination of copper and zinc in serum

Summary A comparison of performance characteristics of ICAP-AES and ETA-AAS experienced in analyzing Cu and Zn in blood serum is described. Accuracy and precision were evaluated by a statistical procedure permitting graphical representation of the results. It was concluded that ETA-AAS is very suitable for monitoring and screening purposes in toxicology and clinical chemistry whereas ICAP-AES is to be preferred when more precise determinations are required.

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Vergleich von AES mit induktiv gekuppeltem Argonplasma und AAS mit elektrothermischer Atomisierung für den Fall der Kupfer- und Zinkbestimmung im Serum

Zusammenfassung Die Leistungsfähigkeit der beiden Methoden wurde verglichen, wobei Richtigkeit und Reproduzierbarkeit statistisch mit graphischer Darstellung der Ergebnisse ausgewertet wurden. Als Schlußfolgerung ergab sich, daß sich die ETA-AAS als Überwachungs- und Screeningverfahren in der Toxikologie und klinischen Chemie eignet, während für höhere Präzision die ICAP-AES vorzuziehen ist.

     

Bestimmung von Kohlenoxyd

Ohne Zusammenfassung     

Enantiospecific C?H Activation Using Ruthenium Nanocatalysts

The activation of C H bonds has revolutionized modern synthetic chemistry. However, no general strategy for enantiospecific C H activation has been developed to date. We herein report an enantiospecific C H activation reaction followed by deuterium incorporation at stereogenic centers. Mechanistic studies suggest that the selectivity for the α‐position of the directing heteroatom results from a four‐membered dimetallacycle as the key intermediate. This work paves the way to novel molecular chemistry on nanoparticles.     

Development and validation of an HPLC-method for the determination of alkaloids in the stem bark extract of Nauclea pobeguinii

A new method was developed and validated for the quantification of strictosamide in the extract of the stem bark of Nauclea pobeguinii. This plant belongs to the Rubiaceae family and is widely used in the African traditional medicine against malaria and malaria-like symptoms. Alkaloids are suspected to be responsible for the antimalarial activity. One of these alkaloids is strictosamide, already reported to be the major constituent in the root bark of this plant. Because strictosamide was not commercially available another alkaloid, ajmalicine HCl, with comparable properties was used as a secondary standard. The samples of the dried 80% ethanol extract from the stem bark of N. pobeguinii were purified on C(18) solid phase extraction cartridges and analysed using HPLC-UV. The strictosamide used for the validation of the correction factor for response was isolated and purified by means of preparative HPLC and TLC. Although the relative standard deviation (R.S.D.) of 2.6% was still acceptable, the response factor was determined for every analysis based on the ratio of the peak area of strictosamide compared to the peak area of ajmalicine HCl in a concentration of 0.01 mg/ml. The precision of the method according to the time and the concentration, had a R.S.D. value of 2.2% and 2.6%, respectively. The recovery of the method was 92.2% (R.S.D. of 9.4%) which was acceptable. The method has been proven to be suitable for the determination of alkaloids in the extract of the stem bark of N. pobeguinii, according to the ICH guidelines on the validation of analytical methods.     

NHC-Stabilized Iridium Nanoparticles as Catalysts in Hydrogen Isotope Exchange Reactions of Anilines

The preparation of N-heterocyclic carbene-stabilized iridium nanoparticles and their application in hydrogen isotope exchange reactions is reported. These air-stable and easy-to-handle iridium nanoparticles showed a unique catalytic activity, allowing selective and efficient hydrogen isotope incorporation on anilines using D₂ or T₂ as isotopic source. The usefulness of this transformation has been demonstrated by the deuterium and tritium labeling of diverse complex pharmaceuticals.     

The colorimetric determination of nickel,chromium, and manganese in steel

With the aid of the Spckkei absorptiometer the colonmetnc delerminations, of nickel (with dimethylglyoxime), chromium (with diphenylcarbazide) and manganese (after oxidation with periodate) in steel were critically sinveyed The following factors were examined. wave length of the light, concentration of the reagents, stability of the coloured solution, temperature, influence of excess non, relation of extinetion coefficient and concentration of the coloured solution, influence of Mo, V, W, Ti, Al, Co, Cu, Ni, Cr, Mn, P and Si.For each determination a recommended procedure is given, with the results of control analyses. The recommended procedures are rapid. They can be used with steels of widely differing composition. The methods are accurate within 5% of the actual Value. 1. NickleAfter neutrahsing the solution 5 ml (01 more) of concentrared ammonia (0.95) must be added. The temperature of the solution must be kept below 30° C before adding the dimethylglyoxime.The extinction coefficient is determined with light of 520 m/gm 2. ChromiumThe chromium is oxidised with hydrogen peroxide in alkaline solution. The influence of iron is ehminated by the addition of phosphoric acid. The recommended acidity is o.2 n, the quantily of diphenylcarbazide is 2 ml of a 1%'s solution in aceton. The determinations are made with a mercury lamp and filter (546 m/gm) 3. ManganeseThe solution of the sampie is boiled with ammoniumpersulphate and then oxidised with 300–500 mg of potassium periodate.The recommended acidity is 2 n, using a mixture of equal parts of sulphuric and phosphoric acids. The determinations are made with light of 520 m/gm.