Novel core-expanded rylenebis(dicarboximide) dyes bearing pentacene units: facile synthesis and photophysical properties

Two synthetic routes for the benzannulation in the "bay"-region of rylenebis(dicarboximide)s leading to new pi-system-expanded chromophores are described. The first route follows a two-step approach: Suzuki coupling of bromo-substituted perylenebis(dicarboximide) with 2-bromophenylboronic acid, followed by palladium-catalysed dehydrobromination. The second route is best described as a palladium-assisted cycloaddition of benzyne, formed in situ, to the bay-region of the bromo-substituted rylene core. Two new types of core-expanded rylene dyes were synthesised: yellow dibenzocoronenebis(dicarboximide)s, absorbing at 490 nm, and a green dinaphthoquaterrylenebis(dicarboximide), which absorbs at 700 nm. These new chromophores are characterised by significant hypsochromic shifts of absorption, compared to their parent rylenebis(dicarboximide)s, excellent photostabilities and high fluorescence quantum yields.     

Influence of pectins on preparation characteristics of lactoferrin bioadhesive tablets

For the treatment of chronic inflammation in the oral cavity, we attempted to develop bioadhesive tablets of bovine lactoferrin (B-LF). Pectin was used as a bioadhesive polymer, and the influence of the degree of esterification and the molecular weight of pectins on the characteristics of B-LF tablets were investigated. Concerning bioadhesive force, a tendency increasing the value according to increase of the esterification of the pectin was confirmed. Sustained release of B-LF from the tablets was observed as the esterification increased, and a possibility for prediction of the time required to release 50% of B-LF by using the equation given by the degree of esterification and the logarithm of the molecular weight was suggested. Pectin cross-linked with Ca(2+) (Ca-PC) was also used for the preparation of the B-LF tablets. Prolonged release of B-LF from the tablets was observed as the Ca(2+) in Ca-PC increased. Our findings suggest that pectin with a high degree of esterification is suitable as a bioadhesive polymer since high bioadhesive force and sustained release are shown. Furthermore, a possibility that the B-LF release could be controlled by adjusting the Ca(2+) concentration in Ca-PC was suggested.     

Dioxygen activation by diiminodipyrromethane complexes of Ni, Pd, and Pt

Diiminodipyrromethane complexes of Ni, Pd, and Pt are able to activate O2, resulting in a metal-dependent autoxidation of the ligand.     

Ab initio electron propagator calculations in molecular transport junctions: predictions of negative differential resistance

In this work we study current-voltage characteristics in transport molecular junctions with a 1,4-benzene dithiol molecule as a bridge by using different ab initio electron propagator methods such as OVGF and P3 which are both programs in a Gaussian software package. The current-voltage characteristics are calculated for different values of Fermi energy in various basis sets such as 6-311++G(p,d) and cc-pVDZ and are compared with the experimental data. A good agreement is found in almost the entire voltage range. In addition, the results of our calculations indicate that the accuracy of ab initio electron propagator methods is in the range of 0.2-0.3 eV. Since the computational methods are truly ab initio, implying no adjustable parameters, functions, or functionals, the theoretical predictions can be improved only by changing the model of a transport device. The current-voltage characteristics predict peaks, i.e., negative differential resistances, for the various values of Fermi energy. As shown, the origin of the negative differential resistances is related to the voltage dependences of overlap integrals for the active terminal orbitals, expansion coefficients of partial atomic wavefunctions in Dyson orbitals, and the voltage dependences of Dyson poles (ionization potentials). We find that two peak behavior in the current-voltage characteristics can be explained by the anharmonicity of potential energy surfaces. As a result of our studies, we predict that negative differential resistances can be experimentally found by changing a position of Fermi level, i.e., by using different metal electrodes coated by a gold atomic monolayer.     

On the combination reactions of hydrogen atoms with resonance-stabilized hydrocarbon radicals

Procedures for accurately predicting the kinetics of H atom associations with resonance stabilized hydrocarbon radicals are described and applied to a series of reactions. The approach is based on direct CASPT2/cc-pvdz evaluations of the orientation dependent interaction energies within variable reaction coordinate transition state theory. One-dimensional corrections to the interaction energies are estimated from a CASPT2/aug-cc-pvdz minimum energy path (MEP) on the specific reaction of interest and a CASPT2/aug-cc-pvtz MEP for the H + CH3 reaction. A dynamical correction factor of 0.9 is also applied. For the H + propargyl, allyl, cyclopentadienyl, and benzyl reactions, where the experimental values appear to be quite well determined, theory and experiment agree to within their error bars. Predictions are also made for the combinations with triplet propargylene, CH2CCCH, CH3CCCH2, CH2CHCCH2, CH3CHCCH, cyclic-C4H5, CH2CCCCH, and CHCCHCCH.     

Predicting new molecular species of potential interest to atmospheric chemistry: the isomers HSBr and HBrS

Coupled cluster singles and doubles with perturbative contributions of connected triples CCSD(T) theory with a series of correlation consistent basis sets was used to predict the existence and characterize for the first time the structures, harmonic frequencies, and energetic quantities of the isomeric species HSBr and HBrS, as well as the transition state connecting them. These calculations consider extrapolation to the complete basis set (CBS) limit, corrections for scalar relativistic effects using the second-order Douglas-Kroll-Hess Hamiltonian, and also correlation of the bromine d electrons in addition to the 14 valence electrons. The species HSBr was found to be more stable than HBrS by 50.93 kcal/mol, with a high barrier height of 60.00 kcal/mol for the interconversion into HBrS. The smaller barrier of 7.90 kcal/mol (ZPE included) for the reverse process, however, should favor a rapid interconversion of HBrS into HSBr if HBrS can also be initially present in a potential synthetic route. If trapped in a matrix, their harmonic frequencies will allow for an unambiguous distinction between the two species. Scalar relativistic corrections and correlation of 24 electrons, although minor for the present purpose of a first time, but accurate, characterization of these species, are needed if chemical accuracy is also pursued. A test of the DFT/B3LYP approach in describing this type of system resulted in good energetic quantities, but geometric parameters and frequencies still lack spectroscopic accuracy. Whether HSBr can act as a temporary bromine reservoir and/or a source of reactive bromine and HS radicals requires further studies that are underway in our group.     

Crystal Structures of AlCr2 and MoSi2: Same Structure Type vs. Different Bonding Pattern

In a joint effort utilizing modified sample preparation, microscopy, X-ray diffraction and micro-fabrication, it became possible to prepare single crystals of the “hidden” phase AlCr₂. High-resolution X-ray diffraction analysis is described in detail for two crystals with the similar overall composition, but different degree of disorder, which seems to be the main cause for the differing unit cell parameters. Chemical bonding analysis of AlCr₂ in comparison to prototypical MoSi₂ shows pronounced differences reflecting the interchange of main group element vs. transition metal as majority component.     

Thermogravimetric Studies of Dehydration of the Cellulose Acetate Layer in UAM-100, UAM-150, and MGA-95 Composite Films

Technical Physics - This paper presents an analytical overview of the study of the kinetic and physicochemical characteristics of composite membrane films. UAM-100, UAM-150, and MGA-95 composite...     

Low-temperature oxidation of diethyl ether: Reactions of hot radicals across coupled potential energy surfaces

Electronic structure calculations and transition state theory are used to compute rate coefficients for the low-temperature oxidation of diethyl ether. Additional rate coefficients are computed to account for rovibrationally excited species that react with O₂ prior to thermalization in a process known as non-Boltzmann reactions. A detailed, low-temperature kinetic mechanism for DEE combustion is developed. Ignition delay curves are computed using two mechanisms, one that includes only thermal reactions and a second that also includes 8 non-Boltzmann reactions. Simulations suggest that at an initial pressure of 1 atm and temperatures below 800 K, the inclusion of non-Boltzmann reactions decreases the predicted ignition delay by a factor of 2 or more. As the pressure increases, the effective contribution of these reactions diminishes. These results suggest that non-Boltzmann phenomena can have a significant effect on real-world applications.