Electron hopping in pi-stacked covalent and self-assembled perylene diimides observed by ENDOR spectroscopy

We have carried out room-temperature, solution-phase electron paramagnetic resonance and electron-nuclear double resonance studies on a series of radical anions based upon perylene-3,4:9,10-bis(dicarboximide) (PDI). The following systems were studied: two PDI monomers, a covalent, cofacial dimer, and two covalent trefoil-PDI3 molecules, one of which self-assembles into pi-stacked dimers. Full sharing of the unpaired electron in the covalent and self-assembled dimers is revealed by a halving of the hyperfine coupling constants in these species, relative to those of the monomers. These results and the electronic absorption spectra show that electron hopping on a >107 Hz time scale occurs between a reduced and neutral chromophoric pair.     

Molecules-in-molecules fragment-based method for the evaluation of Raman spectra of large molecules

We present the first implementation of the evaluation Raman spectra of large molecules using the molecules-in-molecules (MIM) fragment-based method (MIM-Raman). Molecular fragments and associated overlapping subsystems are constructed by cutting the C–C bonds in the large molecule based on the connectivity information and a number-based fragmentation scheme. After saturating the dangling bonds with hydrogen link-atoms, independent energy and Raman frequency calculations are performed on each subsystem. Subsequently, link-atom-related forces, Hessian and polarisability derivative matrix elements are projected back onto the corresponding host and supporting atoms through the Jacobian projection method. In the two-layer model (MIM2), the long-range interactions, absent in the single layer model (MIM1), are taken into account through a second layer at a lower level of theory. The MIM-Raman method is benchmarked on a set of large linear and cage molecules. The MIM extrapolated energy and Raman spectra are compared with the full calculations at B3LYP/6-311G(d,p) or B3LYP/6-311+G(d,p) levels of theory. The benchmark analysis of 21 molecules at MIM2 show an accuracy improvement of 85% in energies, 74% in Raman frequencies and 66% in intensities over MIM1. The implementation and benchmark analysis validates the MIM-Raman model for exploring Raman spectra of large molecules in the future.     

Novel properties of PES fabrics modified by corona discharge and colloidal TiO2 nanoparticles

The objective of this study was to highlight the potential application of the corona discharge at atmospheric pressure for the surface activation of polyester (PES) fabrics in order to improve the binding efficiency of colloidal TiO₂ nanoparticles. The obtained nanocomposite textile materials provide desirable level of UV protection, self‐cleaning properties, and photodegradation activity. The measured UV protection factor (UPF) of fabrics corresponds to UPF rating of 50+, designating the maximum UV protection. Additionally, the total photodegradation of methylene blue in aqueous solution was achieved after 24 hr of UV illumination and this capability was preserved and even improved after four repeated cycles. The results showed that the corona treated PES fabrics loaded with TiO₂ nanoparticles had considerably enhanced the overall efficiency compared to PES fabrics loaded only with TiO₂ nanoparticles. Copyright © 2009 John Wiley & Sons, Ltd.     

Imaging mass spectrometry using peptide isoelectric focusing

Imaging Mass Spectrometry (IMS) has emerged as a powerful technique in the field of proteomics. The use of Immobilized pH Gradient-IsoElectric Focusing (IPG-IEF) is also a new trend, as the first dimension of separation, in shotgun proteomics. We report a combination of these two outstanding technologies. This approach is based on the separation of shotgun-produced peptides by IPG-IEF. The peptides are then transferred by capillarity to a capture membrane, which is then scanned by the mass spectrometer to generate MS images. This high-throughput methodology allows a preview of the sample to be obtained in a single day. We report the application of this new pipeline for differential comparison of the membrane proteome of two different strains of Staphylococcus aureus bacteria in a proof-of-principle experiment.     

Dynamic programming—neural network real-time traffic adaptive signal control algorithm

In this paper, an “intelligent” isolated intersection control system was developed. The developed “intelligent” system makes “real time” decisions as to whether to extend (and how much) current green time. The model developed is based on the combination of the dynamic programming and neural networks. Many tests show that the outcome (the extension of the green time) of the proposed neural network is nearly equal to the best solution. Practically negligible CPU times were achieved, and were thus absolutely acceptable for the “real time” application of the developed algorithm.     

An analytical expression for the electric field in MSM structures

In this work the conformal mapping is used to determine an analytical expression for the electric field in MSM structures. The expression simplifies the analysis of optically generated carriers transport, i.e. the determination of the response of the MSN photodetectors. It can also be useful in the analysis of MSM electrooptical modulators operation.     

The stereochemistry of fragmentation products formed in the lead tetraacetate and related oxidations of alcohols. Part. I. β-fragmentation of cis-and trans-4-t-Butylcyclohexanemethanol

The stereochemistry of β-fragmentation products formed in the oxidation of cis-and trans-4-t-butylcyclohexaanemethanol with lead tetraacetate and with lead tetraacetate-metal chloride combinations, under various reaction conditions, has been investigated, and the results compared with those obtained, under similar conditions, in the oxidative decarboxylation of cis-and trans-4-t-butylcyclohexanecarboxylic acid with the same reagents. It was found that all four substrates afford, under comparable conditions, identical cis-trans proportions of the respective fragmentation products, and that, therefore, so far as steric course is concerned, both the initial homolytic and subsequent heterolytic processes involved in the lead tetraacetate fragmentation reaction are independent of the nature and configuration of the starting material.     

Self-assembly of supramolecular light-harvesting arrays from covalent multi-chromophore perylene-3,4:9,10-bis(dicarboximide) building blocks

We report on two multi-chromophore building blocks that self-assemble in solution and on surfaces into supramolecular light-harvesting arrays. Each building block is based on perylene-3,4:9,10-bis(dicarboximide) (PDI) chromophores. In one building block, N-phenyl PDI chromophores are attached at their para positions to both nitrogens and the 3 and 6 carbons of pyromellitimide to form a cross-shaped molecule (PI-PDI(4)). In the second building block, N-phenyl PDI chromophores are attached at their para positions to both nitrogens and the 1 and 7 carbons of a fifth PDI to produce a saddle-shaped molecule (PDI(5)). These molecules self-assemble into partially ordered dimeric structures (PI-PDI(4))(2) and (PDI(5))(2) in toluene and 2-methyltetrahydrofuran solutions with the PDI molecules approximately parallel to one another primarily due to pi-pi interactions between adjacent PDI chromophores. On hydrophobic surfaces, PDI(5) grows into rod-shaped nanostructures of average length 130 nm as revealed by atomic force microscopy. Photoexcitation of these supramolecular dimers in solution gives direct evidence of strong pi-pi interactions between the excited PDI chromophore and other PDI molecules nearby based on the observed formation of an excimer-like state in <130 fs with a lifetime of about 20 ns. Multiple photoexcitations of the supramolecular dimers lead to fast singlet-singlet annihilation of the excimer-like state, which occurs with exciton hopping times of about 5 ps, which are comparable to those observed in photosynthetic light-harvesting proteins from green plants.     

An ab initio investigation on (CO2)n and CO2(Ar)m clusters: geometries and IR spectra

An ab initio investigation on CO(2) homoclusters is done at MPWB1K6-31++G(2d) level of theory. Electrostatic guidelines are found to be useful for generating initial structures of (CO(2))(n) clusters. The ab initio minimum energy geometries of (CO(2))(n) with n=2-8 are T shaped, cyclic, trigonal pyramidal, tetragonal pyramidal, tetragonal bipyramidal, pentagonal bipyramidal, and pentagonal bipyramid with one CO(2) molecule attached to it. A test calculation on (CO(2))(20) cluster is also reported. The geometric parameters of the energetically most favored (CO(2))(n) clusters match quite well their experimental counterparts (wherever available) as well as those derived from molecular dynamics studies. The effect of clustering is quantified through the asymmetric C-O stretching frequency shift relative to the single CO(2) molecule. (CO(2))(n) clusters show an increasing blueshift from 1.8 to 9.6 cm(-1) on increasing number of CO(2) molecules from n=2 to 8. The energetics and geometries of CO(2)(Ar)(m) clusters have also been explored at the same level of theory. The geometries for m=1-6 show a predominant T type of the argon-CO(2) molecule interaction. Higher clusters with m=7-12 show that the argon atoms cluster around the oxygen atom after the saturation of the central carbon atom. The CO(2)(Ar)(m) clusters exhibit an increasing redshift in the C-O asymmetric stretch relative to CO(2) molecule of 0.7-5.6 cm(-1) with increasing number of argon atoms through m=1-8.