Model system for cell adhesion mediated by weak carbohydrate-carbohydrate interactions

The multivalent carbohydrate-carbohydrate interaction between membrane-anchored epitopes derived from the marine sponge Microciona prolifera has been explored by colloidal probe microscopy. An in situ coupling of sulfated and non-sulfated disaccharides to membrane-coated surfaces was employed to mimic native cell-cell contacts.The dynamic strength of the homomeric self-association was measured as a function of calcium ions and loading rate. A deterministic model was used to estimate the basic energy landscape and number of participating bonds in the contact zone.     

Facile synthesis, antioxidant and antimicrobial activity of amino methylene bisphosphonates

A green and efficient preparation method for the amino bisphosphonates is accomplished by simple mixing and stirring of diethylphosphite, triethylorthoformate and various amines in the presence of amberlyst-15 as catalyst at room temperature under solvent free conditions. The title compounds are characterized by IR, (1)H-, (13)C-, (31)P-NMR and mass spectra, also studied their antimicrobial and antioxidant activity.     

Electromagnetically induced transparency with quantum interferometry

We have shown that electromagnetically induced transparency can be achieved by control-probe interferometry using two delayed phase-locked ultrashort pulses. Two vibrational wavepackets on the excited state, excited by two delayed phase-locked ultrashort pulses, interfere constructively or destructively leading to enhancement or suppression of absorption to a selective set of vibrational levels. Depending on the phase difference and the delay between the pulses with same carrier frequency, one can design different transparency windows between absorption peaks at consecutive even(odd) vibrational levels by eliminating absorption at odd(even) vibrational levels. We have shown that by switching the phase difference of two delayed femtosecond pulses, one can switch to complete elimination of absorption from enhanced absorption to a particular set of vibrational levels in the excited state. Thus, switching of transparency through window between odd vibrational levels to that between even vibrational levels is possible. By properly choosing the temporal width and the carrier frequency of the pulses, lossless transmission of complete or bands of frequencies of the pulses can be achieved through these transparency windows. Hence, designing of single- or multi-mode transparency windows in NaH molecule is feasible by control-probe quantum interferometry.     

Ab initio calculations of the lowest electronic states in the CuNO system

The lowest singlet and triplet electronic levels of the A' and A" symmetry species of the neutral copper-nitrosyl (CuNO) system are calculated by ab initio methods at the multi-reference configuration interaction (MRCI) level of theory with single and double excitations, and at the coupled cluster level of theory with both perturbational (CCSD(T)) and full inclusion of triple excitations (CCSDT). Experimental data are difficult to obtain, hence the importance of carrying out calculations as accurate as possible to address the structure and dynamics of this system. This paper aims at validating a theoretical protocol to develop global potential energy surfaces for transition metal nitrosyl complexes. For the MRCI calculations, the comparison of level energies at linear structures and their values from C(2v) and C(s) symmetry restricted calculations has allowed to obtain clear settings regarding atomic basis sizes, active orbital spaces and roots obtained at the multi-configurational self-consistent field (MCSCF) level of theory. It is shown that a complete active space involving 18 valence electrons, 11 molecular orbitals and the prior determination of 12 roots in the MCSCF calculation is needed for overall qualitatively correct results from the MRCI calculations. Atomic basis sets of the valence triple-zeta type are sufficient. The present calculations yield a bound singlet A' ground state for CuNO. The CCSD(T) calculations give a quantitatively more reliable account of electronic correlation close to equilibrium, while the MRCI energies allow to ensure the qualitative assessment needed for global potential energy surfaces. Relativistic coupled cluster calculations using the Douglas-Kroll-Hess Hamiltonian yield a dissociation energy of CuNO into Cu and NO to be (59 ± 5) kJ mol(-1) ((4940 ± 400) hc?cm(-1)). Favorable comparison is made with some of previous theoretical results and a few known experimental data.     

Fluorescent acridine-based receptors for H2PO4(-)

Two new pseudopeptidic molecules (one macrocyclic and one open chain) containing an acridine unit have been prepared. The fluorescence response of these receptors to a series of acids was measured in CHCl(3). Receptors are selective to H(2)PO(4)(-) versus HSO(4)(-), and an even higher selectivity is found over other anions such as Cl(-), Br(-), CH(3)COO(-), and CF(3)COO(-). We show that the macrocyclic receptor is more selective for H(2)PO(4)(-) than the related open chain receptor. The supramolecular interactions of triprotonated receptors with different anions have been modeled in silico and have been studied by different experimental techniques. Optimized geometries obtained by computational calculations agree well with experimental data, in particular fluorescence experiments, suggesting that the selective supramolecular interaction takes places through coordination of the anions to the triprotonated form of the receptor.     

Aminomethylene peptide nucleic acid (am-PNA): synthesis, regio-/stereospecific DNA binding, and differential cell uptake of (α/γ,R/S)am-PNA analogues

Inherently chiral, cationic am-PNAs having pendant aminomethylene groups at α(R/S) or γ(S) sites on PNA backbone have been synthesized. The modified PNAs are shown to stabilize duplexes with complementary cDNA in a regio- and stereo-preferred manner with γ(S)-am PNA superior to α(R/S)-am PNAs and α(R)-am PNA better than the α(S) isomer. The enhanced stabilization of am-PNA:DNA duplexes is accompanied by a greater discrimination of mismatched bases. This seems to be a combined result of both electrostatic interactions and conformational preorganization of backbone favoring the cDNA binding. The am-PNAs are demonstrated to effectively traverse the cell membrane, localize in the nucleus of HeLa cells, and exhibit low toxicity to cells.     

Regio-selective synthesis of 1,2-aminoalcohols from epoxides and chlorohydrins

A simple and efficient procedure for the regio-selective synthesis of 1,2-aminoalcohols from terminal epoxides and chlorohydrins by using NaHMDS as the source of amine is reported. The wider scope and utility of this method is demonstrated.     

An efficient sequential one-pot base mediated C-O and Pd-mediated C-C bond formation: synthesis of functionalized cinnamates and isochromenes

An efficient sequential one-pot intermolecular oxy-Michael addition and intermolecular Heck coupling for the synthesis of functionalized cinnamates is presented. Bulky tert-butyl acrylate was identified as a more suitable Michael acceptor for initial oxy-Michael addition, as it precludes the formation of undesired cross condensed ester. Most importantly, the present method was further divergently extended to the successful synthesis of isochromenes via a sequential one-pot O-allylation and subsequent intramolecular Heck cyclization.