Fluorescent ratiometry of tetrahomodioxacalix[4]arene pyrenylamides upon cation complexation

[structure: see text] C-1,2-alternate tetrahomodioxacalix[4]arene pyreneamides were synthesized. Pb(2+) coordination gave a quenched monomer and excimer fluorescence emission, while upon Ca(2+) ion binding, the receptor provides an enhanced excimer and declined monomer emission with ratiometric response. The excimer emission spectra changes are rationalized by frontier molecular orbitals that the effective Py-Py interaction induces emission intensity increases upon Ca(2+) ion complexation, whereas there is no such interaction observed upon Pb(2+) binding.     

Synthesis of functionalized organotrifluoroborates via halomethyltrifluoroborates

[reaction: see text] Potassium bromo- and iodomethyltrifluoroborates have been prepared via in situ reaction of n-BuLi with dibromo- and diiodomethane, respectively, in the presence of trialkyl borates, followed by treatment with KHF(2). Moreover, a new synthetic method for the preparation of potassium organotrifluoroborates through nucleophilic substitution of the halide in these potassium halomethyltrifluoroborates is described.     

On M-hyponormal weighted shifts

Let α≡{α_n}_n=0^∞ be a weight sequence and let W_α denote the associated unilateral weighted shift on . In this paper we prove that if α is eventually increasing, then W_α is M-hyponormal and that if α has exactly two subsequential limits such that the larger one is different from the spectral radius of W_α then W_α is not M-hyponormal.     

Mechanism of action of vitamin K

We have discovered a novel, spontaneous model oxidation that leads to a powerful base capable of carrying out a carbon-carbon bond forming condensation reaction analogous to that observed in the vitamin K-mediated carboxylation of glutamate. The model sequence incorporates a novel base-strength enhancement sequence and it implicates molecular oxygen as the initiating factor in the vitamin K-dependent carboxylation. When the oxygenation is carried out under an atmosphere of (18)O2, two atoms of (18)O are incorporated into the vitamin K oxide product. Selective (18)O labelling defines the carbonyl group next to methyl as the active site of the vitamin K.     

Synthesis of 2,3-disubstituted indole on solid phase by the Fischer indole synthesis

2,3-Disubstituted indoles were synthesized by solid-phase reaction using the Fischer indole synthesis. A "traceless" silicon linker was employed with the silicon-carbon bonding being cleaved with TFA. An oxygen atom was placed into the middle of the spacer/linker so as to enhance solid-phase synthesis by better solvation.     

Statistical mechanical approach to competitive binding of metal ions to multi-center receptors

A microscopic site binding model to treat binding of several metal ions to multi-center receptors is proposed. The model introduces the appropriate parameterization in terms of microscopic complexation constants and metal-metal pair interaction energies. The model is solved with statistical mechanical techniques, including direct enumeration or transfer matrices. We obtain microscopic and macroscopic complexation constants, microstate probabilities, and binding isotherms for chain-like receptors, including the long-chain limit. Various examples to illustrate the usefulness of the model are given.     

Mathematical analysis of positive pulsed corona discharge processemployed for removal of nitrogen oxides

A mathematical model was proposed to describe the behaviour of the removal of nitrogen oxides (NO_x) in a positive pulsed corona discharge reactor. The proposed model takes into account radical production at each pulsing and subsequent radical utilization for NO_x removal. The production efficiencies of radicals such as O, OH, H, and N were derived by considering direct electron impact on dissociation of gaseous molecules, followed by excitation transfer reactions of excited oxygen atoms. The production efficiencies of those species were used for the model calculations. The proposed model could adequately predict the experimental data. Of the active species present, the ozone (O₃) produced by the reaction of O radical with oxygen was found to play the crucial role in oxidation of NO to NO₂ , both theoretically and experimentally     

Distribution of irreducible polynomials of small degrees over finite fields

D. Wan very recently proved an asymptotic version of a conjecture of Hansen and Mullen concerning the distribution of irreducible polynomials over finite fields. In this note we prove that the conjecture is true in general by using machine calculation to verify the open cases remaining after Wan's work.