Density-functional theory for polymer-carbon dioxide mixtures: A perturbed-chain SAFT approach

We propose a density-functional theory (DFT) describing inhomogeneous polymer-carbon dioxide mixtures based on a perturbed-chain statistical associating fluid theory equation of state (PC-SAFT EOS). The weight density functions from fundamental measure theory are used to extend the bulk excess Helmholtz free energy to the inhomogeneous case. The additional long-range dispersion contributions are included using a mean-field approach. We apply our DFT to the interfacial properties of polystyrene-CO(2) and poly(methyl methacrylate) CO(2) systems. Calculated values for both solubility and interfacial tension are in good agreement with experimental data. In comparison with our earlier DFT based on the Peng-Robinson-SAFT EOS, the current DFT produces quantitatively superior agreement with experimental data and is free of the unphysical behavior at high pressures (>35 MPa) in the earlier theory.     

On the mechanism of the photocyclization of azadienes

The photocyclization of azadienes to yield quinolines has been studied by means of CASPT2//CASSCF calculations. In order to study this extensive family of compounds, a minimal model system keeping the fundamental key features of this kind of compounds have been analyzed with the aim of explaining the general behavior of azadienes found experimentally. We show that, although several conformers of the reacting molecule are populated on the ground-state at room temperature, there is only one capable of successfully yield the products. It is shown that photocyclization takes place with fast relaxation in both S₂ and S₁ excited states, in agreement with the experimental lack of fluorescence. This fact, together with the presence of reaction paths that allow effective recovery of the starting molecule, explains not only the experimental photocyclization of azadienes under UV radiation, but also accounts for the low efficiency of the process. The mechanistic information obtained allows to provide an explanation of the found reaction outcome and to suggest some modifications to improve the synthetic utility of these reactions.     

Synthesis of bis(indolyl)methanes using silica gel as an efficient and recyclable surface

Here we describe a simple, clean, and efficient solvent-free protocol for the synthesis of bis(indolyl)methanes promoted by silica gel. The products were obtained in good to excellent yields through the reaction of indoles with cyclohexanone and a range of aldehydes. The silica gel was easily recovered and utilized for further reactions without loss of activity.     

Synthesis of novel selenium and tellurium-containing tetrazoles: a class of chalcogen compounds with antifungal activity

We describe herein the synthesis and antifungal activity of new 5-arylchalcogenoalkyl-1H-tetrazoles 4. Arylchalcogenoalkyl-1H-tetrazoles 4 have been synthesized in high yields by reaction of arylchalcogenolate anions with chloronitriles 2, and subsequent [2+3] cycloaddition of resulting arylchalcogenoalkylnitriles 3 with sodium azide by zinc catalysis in aqueous solution. The obtained compound 4a was screened for antifungal activity and presented inhibitory property against seven fungal strains. This protocol is an efficient method to produce new selenium–nitrogen compounds with antifungal activity.     

Highly stereoselective method to prepare bis-phenylchalcogen alkenes via addition of chalcogenolate to phenylseleno alkynes

The preparation of bis-phenylchalcogen alkenes starting from phenylseleno alkynes is described. The nucleophilic species of selenium, tellurium and sulfur were generated in situ from the reaction of the respective diphenyl dichalcogenide with NaBH₄ in PEG-400 as solvent. The chalcogenolate anions were efficiently and selectively added to a variety of phenylselenoalkynes at mild conditions, furnishing the respective (Z)-1,2-bis-phenylchalcogen alkenes in good yields.     

New cyclic aminals derived from rac-trans-1,2-diaminocyclohexane: synthesis and crystal structure of racemic 1,8,10,12-tetraazatetracyclo[8.3.1.1.8,1202,7] pentadecane and a route to its enantiomerically pure (R,R) and (S,S) isomers

New enantiomerically pure macrocyclic aminals (2R,7R)- and (2S,7S)-1,8,10,12-tetraazatetracyclo[8.3.1.1.^8,120^2,7]pentadecane (4a and 4b) were obtained by a three component reaction between their respective pure enantiomer of trans-1,2-diaminocyclohexane, ammonia, and formaldehyde. Additionally, the X-ray structure of the racemic compound 4 and the specific rotations of the racemic and optically pure compounds were determined. To further understand the synthetic utilities of enantiomers 4a and 4b, Mannich-type reactions with 1H-benzotriazole were performed, affording (3aR,7aR)- and (3aS,7aS)-1,1′-{[2,3,3a,4,5,6,7,7a-octahydro-1H-1,3-benzimidazole-1,3-diyl]bis(methylene)}bis-1H-benzotriazole (9 and 10) and allowing for new possibilities related to the preparation of chiral ligands for asymmetric catalysis.     

Smart portable electrophoresis instrument based on multipurpose microfluidic chips with electrochemical detection

A second generation of a battery-powered portable electrophoresis instrument for the use of ME with electrochemical detection was developed. As the first-generation, the main unit of the instrument (150 mm × 165 mm × 95 mm) consists of four-outputs high-voltage power supply (HVPS) with maximum voltage of 3 KV and acquisition system (bipotentiostat) containing 2-channels for dual electrochemical detection. A new reusable microfluidic platform was designed in order to incorporate the microchips with the portable instrument. In this case, the platform is integrated to the main unit of the instrument so that it is not necessary to have any external cable for the interconnection of both parts, making the use of the complete system easier. The new platform contains all the electrical connections for the HVPS and bipotentiostat, as well as fluidic ports for driving the solutions. The microfluidic electrophoresis instrument is controlled by means of a user-friendly interface from a computer. The possibility of wireless connection (Bluetooth?) allows the use of the instrument without any external cable improving the portability. Therefore, the second generation brings a more compact and integrated electrophoresis instrument for "in situ" applications using microfluidic chips in an easy way. The performance of the electrophoresis system was initially evaluated using single- and dual-channel SU-8/Pyrex microchips with different models of integrated electrodes including microelectrodes and interdigitated arrays. The method was tested in different analytical applications such as separation of neurotransmitters, chlorophenols, purine derivatives, vitamins, polyphenolic acids, and flavones.     

Accelerating VASP electronic structure calculations using graphic processing units

We present a way to improve the performance of the electronic structure Vienna Ab initio Simulation Package (VASP) program. We show that high-performance computers equipped with graphics processing units (GPUs) as accelerators may reduce drastically the computation time when offloading these sections to the graphic chips. The procedure consists of (i) profiling the performance of the code to isolate the time-consuming parts, (ii) rewriting these so that the algorithms become better-suited for the chosen graphic accelerator, and (iii) optimizing memory traffic between the host computer and the GPU accelerator. We chose to accelerate VASP with NVIDIA GPU using CUDA. We compare the GPU and original versions of VASP by evaluating the Davidson and RMM-DIIS algorithms on chemical systems of up to 1100 atoms. In these tests, the total time is reduced by a factor between 3 and 8 when running on n (CPU core + GPU) compared to n CPU cores only, without any accuracy loss. © 2012 Wiley Periodicals, Inc.     

Symmetry-adapted formulation of the G-particle-hole hypervirial equation method

Highly accurate 2-body reduced density matrices of atoms and molecules have been directly determined without calculation of their wave functions with the use of the G-particle-hole hypervirial (GHV) equation method (Alcoba et?al. in Int. J. Quantum Chem. 109:3178, 2009). Very recently, the computational efficiency of the GHV method has been significantly enhanced through the use of sum factorization and matrix-matrix multiplication (Alcoba et?al. in Int. J. Quantum Chem 111:937, 2011). In this paper, a detailed analysis of the matrix contractions involved in GHV calculations is carried out. The analysis leads to a convenient strategy for exploiting point group symmetry, by which the computational efficiency of the GHV method is further improved. Implementation of the symmetry-adapted formulation of the method is reported. Computer timings and hardware requirements are illustrated for several representative chemical systems. Finally, the method is applied to the well-known challenging calculation of the torsional potential in ethylene.     

Benzylidene-oxazolones as molecular photoswitches

The synthesis and photochemical study of a family of molecular switches inspired by the green fluorescent protein (GFP) chromophore is presented. These compounds can be easily synthesized, and their photophysical properties may be tuned. Due to their efficient photoisomerization and high stability, these compounds can be switched on/off by using light and heat or light with different wavelengths.