Photophysical properties of acetylene-linked syn bimane oligomers: a molecular photonic wire.

Computational studies using correlated wave function methods and density functional theory were carried out on a series of acetylene-linked bimane oligomers with particular emphasis on their excitonic properties and implications for intra-chain excitation energy transfer (EET). The low energy barriers found for the rotation of bimane subunits about the longitudinal axis are such that the π-conjugation is easily disrupted. Nevertheless, a distinctive feature of the oligomer lies in the parallel alignment of the S1 transition dipole along the longitudinal axis, which sustains electronic coupling between adjacent bimane subunits over a range of torsional angles and is crucial for driving intra-chain EET. Using a model that comprises hexameric donor and acceptor fragments, we evaluated electronic couplings and spectral overlaps, and applied Fermi's golden rule (in the weak electronic coupling regime) to approximate the lower limit of intra-chain EET in an acetylene-linked bimane photonic wire.

Using non-empirically tuned range-separated functionals with simulated emission bands to model fluorescence lifetimes.

Fluorescence lifetimes were evaluated using TD-DFT under different approximations for the emitting molecule and various exchange-correlation functionals, such as B3LYP, BMK, CAM-B3LYP, LC-BLYP, M06, M06-2X, M11, PBE0, ωB97, ωB97X, LC-BLYP*, and ωB97X* where the range-separation parameters in the last two functionals were tuned in a non-empirical fashion. Changes in the optimised molecular geometries between the ground and electronically excited states were found to affect the quality of the calculated lifetimes significantly, while the inclusion of vibronic features led to further improvements over the assumption of a vertical electronic transition. The LC-BLYP* functional was found to return the most accurate fluorescence lifetimes with unsigned errors that are mostly within 1.5 ns of experimental values.

The cytotoxic effect of oxybuprocaine on human corneal epithelial cells by inducing cell cycle arrest and mitochondria-dependent apoptosis.

Oxybuprocaine (OBPC) is a widely used topical anesthetic in eye clinic, and prolonged and repeated usage of OBPC might be cytotoxic to the cornea, especially to the outmost corneal epithelium. In this study, we characterized the cytotoxic effect of OBPC on human corneal epithelial (HCEP) cells and investigated its possible cellular and molecular mechanisms using an in vitro model of non-transfected HCEP cells. Our results showed that OBPC at concentrations ranging from 0.025% to 0.4% had a dose- and time-dependent cytotoxicity to HCEP cells. Moreover, OBPC arrested the cells at S phase and induced apoptosis of these cells by inducing plasma membrane permeability, phosphatidylserine externalization, DNA fragmentation, and apoptotic body formation. Furthermore, OBPC could trigger the activation of caspase-2, -3, and -9, downregulate the expression of Bcl-xL, upregulate the expression of Bax along with the cytoplasmic amount of mitochondria-released apoptosis-inducing factor, and disrupt mitochondrial transmembrane potential. Our results suggest that OBPC has a dose- and time-dependent cytotoxicity to HCEP cells by inducing cell cycle arrest and cell apoptosis via a death receptor-mediated mitochondria-dependent proapoptotic pathway, and this novel finding provides new insights into the acute cytotoxicity and its toxic mechanisms of OBPC on HCEP cells.

Rapid intersystem crossings in anti bimanes.

We have carried out first principles electronic structure calculations on the ground and excited valence states of syn and anti bimanes. While syn bimanes fluoresce strongly after photoexcitation to the first excited singlet state (S1) and are commonly used as fluorophores in biological labeling studies, anti bimanes largely phosphoresce at low temperatures. We show that this is due to subtle differences in the energetic ordering of excited singlet and triplet states within the isomers. In particular, T2 in anti bimanes is characterized by a π→π* transition and large exchange interactions with the singlet counterpart cause it to lie below and energetically close to S1 at the Franck-Condon region. This opens up a pathway for very fast intersystem crossing (ca. 10(11) s(-1)) from the optically bright S1 state to the triplet manifold, which effectively quenches fluorescence. On the other hand, T2 is energetically inaccessible to S1 in syn bimanes and intersystem crossing via S1→ T1 cannot compete effectively with fluorescence to S0. We have also located minimum energy conical intersections between S0 and S1 in bimanes. However, these structures are significantly distorted from their equilibrium geometries as well as energetically much higher than S1 at the Franck-Condon region. They are therefore not expected to play a part in the photophysics of bimanes after excitation to S1.

Computational study of molecular properties with dual basis sets.

We have studied the performance of dual basis (DB) sets for the evaluation of molecular properties via second order Møller-Plesset perturbation theory (MP2). In addition to savings derived from using a trimmed basis set for the underlying Hartree-Fock (HF) calculation, we pursued a systematic truncation of the virtual subspace for further reductions in computational overhead during the post-HF step. Calculated total energies and molecular properties within the DB framework without virtual space truncation are generally in excellent agreement with full basis calculations. When aug-cc-pV5Z is used as the parent basis, mean absolute error for DB-HF (DB-MP2) total energies of molecules within our test set is 9.7 × 10(-5) au (8.0 × 10(-5) au) while mean absolute relative errors for static electrical response properties like dipole moments, isotropic dipole polarizabilities and polarizability anisotropies are 0.15% (0.14%), 0.56% (0.72%), and 0.76% (0.83%) respectively. When DB is coupled with virtual space truncation at the MP2 level, the corresponding errors are larger but still within 2% of full basis values.