Observation of daunomycin and nogalamycin complexes with duplex DNA using electrospray ionisation mass spectrometry

The noncovalent binding of the antitumour drugs daunomycin and nogalamycin to duplex DNA has been studied using electrospray ionisation mass spectrometry (ESI-MS). The conditions for the preparation of drug/duplex DNA complexes and for their detection by ESI-MS have been optimised. Ions corresponding to these complexes were most abundant relative to free DNA when prepared in the pH range 8-9, and using gentle ESI interface conditions. Self-complementary oligonucleotides, 5'-d(GGCTAGCC)-3' or 5'-d(CGGCGCCG)-3', annealed in the presence of a 5-fold molar excess of either nogalamycin or daunomycin gave ESI mass spectra in which the most intense ions corresponded to three molecules of drug bound to duplex DNA, with some evidence for four drug molecules bound. For binding to 5'-d(TGAGCTAGCTCA)(2)-3', complexes containing up to four nogalamycin and six daunomycin molecules were observed. These data are consistent with the neighbour exclusion principle whereby intercalation occurs between every other base pair such that up to four bound drugs would be expected for the 8 mers and up to six for the 12 mer. Competition experiments involving a single drug in an equimolar mixture of two oligonucleotides (5'-d(TGAGCTAGCTCA)(2)-3' with either 5'-d(CGGCGCCG)(2)-3' or 5'-d(GGCTAGCC)(2)-3') showed ions arising from complexes of drug/5'-d(CGGCGCCG)(2)-3' were more intense than complexes of drug/5'-d(GGCTAGCC)(2)-3', relative to those from the 12 mer in each mixture. While this suggests ESI-MS has the potential to detect differences in sequence selectivity, more detailed experiments involving a comparison of the relative ionisation efficiency of different oligonucleotides and a wider range of intercalators are required to establish this definitively. ESI mass spectra from experiments in which both drugs were reacted with the same oligonucleotide were more complex, such that a clear preference for one drug could not be established.     

Implementation of a general multireference configuration interaction procedure with analytic gradients in a semiempirical context using the graphical unitary group approach

The graphical unitary group approach has been applied in an efficient implementation of a general multireference configuration interaction (MRCI) method for use with small active molecular orbital spaces in a semiempirical framework. Gradients can be computed analytically for molecular orbitals from a closed-shell or a half-electron open-shell Hartree-Fock calculation. CPU times for single point energy and gradient calculations are reported. The code allows MRCI geometry optimizations of large molecules, as illustrated for the singlet ground state and the four lowest triplet states of fullerene C(76).     

Ab initio studies of internal rotation barriers and vibrational frequencies of (C2H2)2, (CO2)2, and C2H2-CO2

We have performed large-scaleab initio calculations using second order Møller-Plesset perturbation theory (MP2) on the three van der Waals dimers formed from acetylene and carbon dioxide. Intermolecular geometrical parameters are reliably computed at this level of theory. Calculations of vibrational frequencies of the van der Waals modes, currently unobtainable by experimental means, give important information about the intermolecular potential and predict significant large-amplitude motion. Zero point energy contributions are shown to be vital in assessing the relative stability of conformations which are close in energy. Our studies suggest that the barrier to interconversion tunnelling in (CO₂)₂ is significantly smaller than previously inferred and is approximately the same as in (C₂H₂)₂. The reason for the rigidity of (CO₂)₂ is the difference in monomer centre-of-mass separation between ground state and transition state. We also show that, in addition to the previously observedC _2v form, the collinear form of C₂H₂-CO₂ is a local minimum on its potential energy surface.     

Estimating the matrixp-norm

Summary The Hölderp-norm of anm×n matrix has no explicit representation unlessp=1,2 or . It is shown here that thep-norm can be estimated reliably inO(mn) operations. A generalization of the power method is used, with a starting vector determined by a technique with a condition estimation flavour. The algorithm nearly always computes ap-norm estimate correct to the specified accuracy, and the estimate is always within a factorn ^1–1/p of A _p . As a by-product, a new way is obtained to estimate the 2-norm of a rectangular matrix; this method is more general and produces better estimates in practice than a similar technique of Cline, Conn and Van Loan.     

Mikrochemischer Nachweis von Europium in Gemischen seltener Erden

Zusammenfassung Zweiwertige Europiumsalze reduzieren Kakothelin zu einem violetten Farbstoff, analog wie die niederen Oxydationsstufen von Titan, Zinn, Vanadin, Niob, Molybdän, Wolfram, Uran und Rhenium. Man kann diese Reaktion zum spezifischen Nachweis von Europium in Gemischen seltener Erden benutzen. Die Erfassungsgrenze des Europiumnachweises beträgt 3/ccm, wenn man die Reduktion mit Zink und Salzsäure in Gegenwart von Kakothelin durchführt.

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Summary Bivalent europium salts, in analogy with the low oxidation steps of titanium, tin, vanadium, columbium, molybdene, tungsten, uranium, and rhenium, reduce cacotheline to a violet dyestuff. This reaction can be used for the specific detection of europium in mixtures of rare earths. The limit of identification of this test for europium is 3/ccm. if the reduction is carried out with the help of zinc and hydrochloric acid in the presence of cacotheline.

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Résumé Les sels d'europium bivalents réduisent la cacothéline à un principe colorant violet, de même que les premiers degrés d'oxydation du titane, de l'étain, du vanadium, du niobium, du molybdène, du tungstène, de l'urane et du rhénium. On peut employer cette réaction pour l'identification de l'europium dans un mélange de terres rares. On peut déceler 3 d'europium dans 1 ccm., si la réduction est produite par l'addition du zinc et de l'acide chlorhydrique, en présence de cacothéline.

     

Mild and efficient Cs2CO3-promoted synthesis of phosphonates

A mild and convenient synthesis for phosphonates using cesium carbonate (Cs₂CO₃), tetrabutylammonium iodide (TBAI) and DMF was developed at room temperature. Numerous dialkyl phosphites were screened using a diverse array of alkyl halides and these reaction conditions were found to be highly efficient producing various phosphonates exclusively in moderate to high yields.