A new type of solid support for HPLC separation of nucleotides, oligonucleotides, N-protected amino acids, and perfluorinated biphenyls is revealed in the form of two distinct calix[4]pyrrole-modified silica gels

Beugholt, Christian

Bögge, Hartmut

Koop, M. J.

Krickemeyer, Erich

Kögerler, Paul

Meyer, Jochen

Müller, Achim 

Peters, F

Schmidtmann, Marc

English

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First Total Synthesis of Dihydroxerulin, a Potent Inhibitor of the Biosynthesis of Cholesterol

Müller A, Meyer J, Krickemeyer E, et al. Unusual stepwise assembly and molecular growth: [H14Mo37O112](14-) and [H3Mo57V6(NO)(6)O-189(H2O)(12)(MoO)(6)](21-). CHEMISTRY-A EUROPEAN JOURNAL. 1998;4(6):1000-1006.The understanding of the formation of complex molecular systems from simple building blocks by conservative self-assembly processes is still a challenge. We report the synthesis and structural characterization of the large reduced polyoxometallate compounds (NH4)(14)[H14Mo37O112]. 35 H2O (1), (NH4)(21)[H3Mo57V6(NO)(6)O-183(H2O)(18)]. 55H(2)O (2) (by an improved synthesis) and Na-3(NH4)(18)[H3Mo63V6(NO)(6)O-195(H2O)(12)]. 41H(2)O (3). The cluster systems are formed by a stepwise growth process. This implies the appearance, during the cluster formation, of ephemeral polyoxometallate intermediates (some of which we were able to isolate). The negative charge and therefore the nucleophilicity of the intermediate cluster fragments increase when they are reduced, resulting in further attraction of electrophiles and thus in growth of molecular systems. IN the case of the cluster anion of 3 we observed, correspondingly, the loss of an [MoO](4+) oxometallate fragment by air oxidation; this implies that aits uptake and release are controlled by th degree of reduction of the cluster. correspondingly, intermediates between the anions of 2 and 3 of the {Mo57+xV6} type could be isolated. The unusual anion of 1 is formed by symmetry breaking processed

Publications at Bielefeld University

Unusual stepwise assembly and molecular growth: [H14Mo37O112](14-) and [H3Mo57V6(NO)(6)O-189(H2O)(12)(MoO)(6)](21-)

Sessler, Jonathan L.

Gale, Philip A.

Genge, John W.

Southampton (e-Prints Soton)

Calix[4]pyrroles: new solid phase HPLC supports for the separation of anions

The gas-phase reaction of pI-Me3SiC6H4(CH2)(3)C6H5 (p-TSDPP) with gaseous cations, including C2H5+, Me2Cl+ and DCO-, has been studied in the pressure range from 10(-8) to 10(3) Torr by Fourier-transform ion cyclotron resonance (FT-ICR) and by the radiolytic technique. The protonated or alkylated intermediates undergo intramolecular migration and intermolecular transfer of protons and/or Me3Si+. The results underline the role of the spectator ring in providing internal solvation to an arenium moiety, as evidenced by the noticeable stability towards Me3Si loss with respect to a single-ring model substrate, p-Me3SiC6H4Me (p-TST), upon reaction with the same gaseous ions. The extent of the alkylation route relative to the alkyldesilylation processes, measured as a function of the arenium ion lifetime, permits derivation of the rate constant for the conversion by proton transfer of the originally formed arenium ions to ipso-silylated isomers (ki). The estimated values of k(i(p-TST))= 5 x 10(9) s(-1) and k(i(p-TSDPP)) = 2 X 10(8) s(-1) at 120 degrees C suggest that intraannular H shifts are faster than ring-to-ring H transfer, in agreement with previous evidence from tert-butylated arenium ions. The reactivity of [Me3Si-arene](+) adducts, adequately described by the Wheland sigma-complex model, does not exclude the intermediacy of an ion-neutral noncovalent complex

CRESTONI, Maria Elisa

Archivio della ricerca- Università di Roma La Sapienza

The gas-phase reactivity of p-Me3Si-substituted 1,3-diphenylpropane towards charged electrophiles: intra- and interannular hydrogen migrations

Calix[4]pyrroles: new solid phase HPLC supports for the separation of anions

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Publications at Bielefeld University

Southampton (e-Prints Soton)

Archivio della ricerca- Università di Roma La Sapienza