Substrate selected polymorphism of epitaxially aligned tetraphenyl-porphyrin thin films

Porphyrin molecules, of interest as versatile materials for organic electronics, are highly prone to formation of significantly different polymorphic phases. To elucidate the determinants for the specific polymorphic phase formed in thin films as well as for the arrangement of the molecules on a given substrate two different anisotropic substrate surfaces have been selected: KCl(100) and the oxygen reconstructed Cu(110) surface. We observe that the crystal structure of the thin films depends on the substrate, whereas the relative molecular orientations in both cases are similar. X-Ray and transmission electron diffraction of 30 nm thick tetraphenyl-porphyrin (H(2)TPP) and platinum tetraphenyl-porphyrin (PtTPP) thin films deposited on KCl(100) surfaces reveals that both kinds of molecules crystallize in a tetragonal polymorph with the (001) lattice planes, i.e. with their macrocycles, parallel to the substrate. Films deposited on the oxygen reconstructed Cu(110)-(2 × 1)O surface exhibit in contrast the triclinic polymorph even though molecules again align nearly parallel to the substrate surface as observed by LEED and X-ray diffraction. On both substrates we identify two driving forces for the epitaxial alignment of porphyrins: (i) molecules aligning with their macrocycles (nearly) parallel to the substrate surface and (ii) the porphyrin molecules forming a commensurate unit cell with the respective substrate. The polymorphic phase meeting both requirements is the most favorable to be formed on a given substrate and due to this structural flexibility in both cases well-ordered, epitaxially aligned porphyrin thin films are achieved.     

Thermodynamic transferability of coarse-grained potentials for polymer-additive systems

In this work we study the transferability of systematically coarse-grained (CG) potentials for polymer-additive systems. The CG nonbonded potentials between the polymer (atactic polystyrene) and three different additives (ethylbenzene, methane and neopentane) are derived using the Conditional Reversible Work (CRW) method, recently proposed by us [Brini et al., Phys. Chem. Chem. Phys., 2011, 13, 10468-10474]. A CRW-based effective pair potential corresponds to the interaction free energy between the two atom groups of an atomistic parent model that represent the coarse-grained interaction sites. Since the CRW coarse-graining procedure does not involve any form of parameterisation, thermodynamic and structural properties of the condensed phase are predictions of the model. We show in this work that CRW-based CG models of polymer-additive systems are capable of predicting the correct structural correlations in the mixture. Furthermore, the excess chemical potentials of the additives obtained with the CRW-based CG models and the united-atom parent models are in satisfactory agreement and the CRW-based CG models show a good temperature transferability. The temperature transferability of the model is discussed by analysing the entropic and enthalpic contributions to the excess chemical potentials. We find that CRW-based CG models provide good predictions of the excess entropies, while discrepancies are observed in the excess enthalpies. Overall, we show that the CRW CG potentials are suitable to model structural and thermodynamic properties of polymer-penetrant systems.     

Array-based capture, distribution, counting and multiplexed assaying of beads on a centrifugal microfluidic platform

We present a novel centrifugal microfluidic platform for the highly efficient manipulation and analysis of particles for applications in bead-based assays. The platform uses an array of geometrical V-cup barriers to trap particles using stopped-flow sedimentation under highly reproducible hydrodynamic conditions. The impact parameters governing the occupancy distribution and capture efficiency of the arrayed traps are investigated. The unique, nearly 100% capture efficiency paired with the capability to establish sharply peaked, single occupancy distributions enables a novel, digital readout mode for color-multiplexed, particle-based assays with low-complexity instrumentation. The presented technology marks an essential step towards a versatile platform for the integration of bead- and cell-based biological assays.     

The Layered Coordination Polymer Bi(SCN)3·1/2H2O

Yellow crystals of Bi(SCN)₃·1/2H₂O are obtained by reacting (BiO)₂CO₃ and HSCN in aqueous solution. X‐ray diffraction on a single‐crystal revealed a triclinic lattice (space group P ) with a = 843.6(2) pm, b = 920.4 (2) pm, c = 1210.7(2) pm, α = 109.16(3) °, β = 109.06(3) °, γ = 90.22(3) °, V = 832.8(3)·10⁶ pm³, and Z = 4. All thiocyanate anions bind with both ends to different cations. The coordination network expands in plane layers parallel (1 0). The water molecule coordinates one of the two independent Bi³⁺ cations. Dehydration sets in at 100 °C, followed by stepwise thermal decomposition to Bi₂S₃.     

Symmetric powers of modular representations,hilbert series and degree bounds

Let G = Z _p be a cyclic group of prime order p with a representation G → GL(V) over a field K of characteristic p. In 1976, Almkvist and Fossum gave formulas for the decomposition of the symmetric powers of V in the case that V is indecomposable. From these they derived formulas for the Hilbert series of the invariant ring K[V]^G. Following Almkvist and Fossum in broad outline, we start by giving a shorter, self-contained proof of their results. We extend their work to modules which are not necessarily indecomposable. We also obtain formulas which give generating functions encoding the decompositions of all symmetric powers of V into indecomposables. Our results generalize to groups of the type Z _p ×H with |H| coprime to p. Moreover, we prove that for any finite group G whose order is divisible by p but not by p ² the invariant ring A,K[V]G is generated by homogeneous invariants of degrees at most dim (V).(|G| – 1).     

Facile routes to alkyl-BIAN ligands

The Alkyl-BIAN ligands tert-Butyl-BIAN and 1-Adamantyl-BIAN have been synthesized and their structures have been determined by single-crystal X-ray diffraction along with that of the ZnCl2 complex of tert-Butyl-BIAN.     

A single-bonded cationic terminal borylene complex

The cationic terminal borylene complex [(eta5-C5H5)(CO)2FeB(eta5-C5Me5)][AlCl4] has been isolated from the reaction of [(eta5-C5H5)(CO)2FeB(Cl)(eta1-C5Me5)] with AlCl3 and on the basis of X-ray crystallographic data, spectroscopic data and a DFT calculation it is concluded that the B-->Fe bond order is one.     

Optical force field mapping in microdevices

We present a method for characterizing microscopic optical force fields. Two dimensional vector force maps are generated by measuring the optical force applied to a probe particle for a grid of particle positions. The method is used to map out the force field created by the beam from a lensed fiber inside a liquid filled microdevice. We find transverse gradient forces and axial scattering forces on the order of 2 pN per 10 mW laser power which are constant over a considerable axial range (>35 microm). These findings suggest future useful applications of lensed fibers for particle guiding/sorting. The propulsion of a small particle at a constant velocity of 200 microm s(-1) is shown.     

A QXP-based multistep docking procedure for accurate prediction of protein-ligand complexes

The two great challenges of the docking process are the prediction of ligand poses in a protein binding site and the scoring of the docked poses. Ligands that are composed of extended chains in their molecular structure display the most difficulties, predominantly because of the torsional flexibility. On the basis of the molecular docking program QXP-Flo+0802, we have developed a procedure particularly for ligands with a high degree of rotational freedom that allows the accurate prediction of the orientation and conformation of ligands in protein binding sites. Starting from an initial full Monte Carlo docking experiment, this was achieved by performing a series of successive multistep docking runs using a local Monte Carlo search with a restricted rotational angle, by which the conformational search space is limited. The method was established by using a highly flexible acetylcholinesterase inhibitor and has been applied to a number of challenging protein-ligand complexes known from the literature.