Chiral aldehyde catalysis enables direct asymmetric α-substitution reaction of N-unprotected amino acids with halohydrocarbons.

The direct catalytic α-hydrocarbylation of readily available amino acids with halohydrocarbons is one of the most straightforward methods leading to α,α-disubstituted non-proteinogenic α-amino acid compounds. However, all the reported methodologies depend on N-protected amino acids as starting materials. Herein, we report on three highly efficient aldehyde-catalyzed direct α-hydrocarbylations of N-unprotected amino acid esters with aryl-, allyl-, and benzyl halides. By promoting a simple chiral BINOL-aldehyde catalyst or combining catalysts of a chiral aldehyde and Lewis acid ZnCl2, the asymmetric α-arylation, α-allylation, and α-benzylation of amino acid esters with the corresponding halohydrocarbons proceed smoothly, producing α,α-disubstituted α-amino acids in moderate-to-high yields and good-to-excellent enantioselectivities. The asymmetric α-arylation reaction can be applied in the formal synthesis of the clinical candidate compound (+)-AG-041R. Based on the results given by control experiments, three reaction models are proposed to illustrate the stereoselective-control outcomes.

Theoretical design study on photophysical property on oligomers based on spirobifluorene and carbazole-triphenylamine for PLED applications.

The photophysical properties of five blue light-emitting polymers based on spirobifluorene applied in polymer light-emitting diodes (PLED) materials have been studied by quantum chemistry. In order to understand the intrinsic reasons for the different performances displayed by the polymers, we carried out density functional theory (DFT) and Marcus theory investigations on their oligomers in terms of structure and properties stability, absorption and emission properties, and carrier injection and transport properties. Especially, some important parameters which had not been reported to our knowledge were given in this contribution, such as the ionization potentials (IPs), electron affinities (EAs), reorganization energies (λ), ke/kh (the ratio between the electron transfer rate (ke) and hole transfer rate (kh)), and the radiative lifetimes (τ). The main results indicate that the co-oligomers of PCC-1, PCC-2, and PCC-3 with push-pull interactions produced by the existing D-A segments have better carrier injection and transport properties than the oligomers of PSF and PCF. Especially PCC-2 co-oligomer, its large radiation lifetime (7.46 ns) and well balanced and adequate carrier transport guarantee its champion performance for PLED. The calculated results coincide with the experimental ones. Besides, PNF structurally similar to PCC-2 has similar photoelectric properties to PCC-2 in theory, and the fluorescence emission of PNF co-oligomer is superior to PCC-2 co-oligomer. Therefore, we predict that PNF is a promising candidate for PLED.

A terbium(III)-organic framework for highly selective sensing of cytidine triphosphate.

Highly selective sensing of cytidine triphosphate (CTP) against other triphosphate nucleosides including ATP, GTP and UTP is successfully achieved with a luminescent terbium(III)-organic framework (TbOF) of [Tb(2)(2,3-pzdc)(2)(ox)(H(2)O)(2)](n) (2,3-pzdc(2-) = 2,3-pyrazinedicarboxylate, ox(2-) = oxalate).

Selectively light scattering spectrometric detection of copper (II) based on a new synthesized oxamide ligand.

Light scattering (LS) signals have been applied for analytical detections, but the selectivity is poor. In order to improve the selectivity, pre-separation or new machines are generally considered. Differing from these methods, we synthesized a highly selective oxamide ligand, N',N'-bis (2-aminophenyl) oxamide (NAPO). It was found that the LS signals of NAPO, measured with a common spectrofluorometer, could be selectively enhanced by copper ion in neutral medium. Thus, a new highly selective detection method for copper ion could be developed over the range of 0.9-31.0 microM with the limit of determination of 97.6 nM (3sigma). Foreign ions including Cd(II), Al(III) could be allowed even if present at the level of 7-fold more than that of Cu(2+), avoiding pre-separation procedures from complicated samples such as real wastewater samples. Mechanism studies showed that the reaction between NAPO and copper ion could form some kinds of clusters and induce the enhanced LS signals.

Theoretical investigation of spectral properties and tautomerization mechanism of 2-aminopurine.

In this work the spectral properties and tautomerization mechanism of 2-aminopurine are investigated using quantum chemical calculations. TD-DFT results lead to a conclusion that two tautomers of 2-aminopurine discussed in this work are fluorescent and present the pi-->pi* transition feature of vertical excitation and emission. It is predicted that the tautomerization of 2-aminopurine hardly occurs in a direct isomerization mechanism because of the high barrier. However, the explicit involvement of water molecules into the system reduces the barrier height considerably and hence makes the ground state reaction feasible. An explanation for the almost equal populations of the two tautomers in polar solvent is given through reaction mechanism analysis.

Continuous medium theory for nonequilibrium solvation: IV. Solvent reorganization energy of electron transfer based on conductor-like screening model.

In this work the authors present some evidences of defects in the popular continuous medium theories for nonequilibrium solvation. Particular attention has been paid to the incorrect reversible work approach. After convincing reasoning, the nonequilibrium free energy has been formulated to an expression different from the traditional ones. In a series of recent works by the authors, new formulations and some analytical application models for ultrafast processes were developed. Here, the authors extend the new theory to the cases of discrete bound charge distributions and present the correct form of the nonequilibrium solvation energy in such cases. A numerical solution method is applied to the evaluation of solvent reorganization energy of electron transfer. The test calculation for biphenyl-cyclohexane-naphthalene anion system achieves excellent agreement with the experimental fitting. The central importance presented in this work is the very simple and a consistent form of nonequilibrium free energy for both continuous and discrete charge distributions, based on which the new models can be established.

Time-dependent density functional theory study on intramolecular charge transfer and solvent effect of dimethylaminobenzophenone.

The lower singlet excited states for dimethylaminobenzophenone have been investigated as a function of the twisting motion with inclusion of solvent effects. Theoretical calculations have been performed using time-dependent density functional theory. The B3LYP and MPW1PW91 functionals with a 6-311+G(2d,p) basis set have been used to compute transition energies. The solvent effects have been described within the polarizable continuum model. Ground-state geometries are optimized using density functional theory with both B3LYP and MPW1PW91 functionals combined with 6-31G(d) basis sets. Vertical absorption energy calculations characterize the lower singlet excited states both in vacuum and in different kinds of solvents. A large redshift of the absorption maximum in the polar solvent suggests an intramolecular charge transfer character of the excited state. We have constructed the potential energy curves of two possible twisting motions of the excited states both in vacuum and in the polar solvent of acetonitrile: the twisting of only the dimethylamino group and the twisting of the dimethylaminophenyl group with respect to the benzoyl group. Both twisting processes predict the formation of the twisted intramolecular charge transfer state associated with the crossing of a low barrier. The presence of the polar solvent significantly changes the shape of the energy curves. Calculated emission energies for both the isolated and the solvated systems show a large Stokes shift between the absorption and fluorescence maxima. Two possible twisting motions produce similar fluorescence spectroscopic consequences. Our results including solvent effects explain the weak "dual-fluorescence" feature of dimethylaminobenzophenone, and imply that the two possible twisting motions may occur in the excited-state relaxation dynamics, but the twisting of the dimethylamino group seems to take place easier.

Quantum chemical study on excited states and electronic coupling matrix element in a catechol-bridge-dicyanoethylene system.

The excited states of a donor-bridge-acceptor (DBA) model system have been investigated using time-dependent density-functional theory (TD-DFT) in vacuo and in solution. It is found that the MPW1PW91 functional always gives higher excitation energies than those with a B3LYP functional. Results from both TD-B3LYP and TD-MPW1PW91 are found consistent with the experimental observations. The two most intense absorptions of the DBA system, one resulting from the local excitation of catechol moiety and the other from that of dicyanoethylene, possess the pipi* transition feature. It seems that the solvent polarity does not remarkably influence the positions of absorption peaks. The spectroscopic properties of isolated donor, acceptor, and bridge and the donor-bridge compound have been investigated at the TD-B3LYP/6-31+G* and TD-MPW1PW91/6-31+G* levels. Results indicate that the donor and the acceptor are weakly coupled with the bridge. Therefore, it is more likely that the electron transfer takes place through a superexchange mechanism. In addition, we calculate the electronic coupling matrix elements according to the generalized Mulliken-Hush theory, and the detailed analyses also predict that the strong absorptions are due to the local excitation of the DBA system.