Carboxybetaine methacrylate polymers offer robust, long-term protection against cell adhesion

Films of poly(carboxybetaine methacrylate), poly(CBMA), grafted onto microetched gold slides are effective in preventing nonspecific adhesion of cells of different types. The degree of adhesion resistance is comparable to that achieved with the self-assembled monolayers, SAMs, of oligo(ethylene glycol) alkanethiolates. In sharp contrast to the SAMs, however, substrates protected with poly(CBMA) can be stored in dry state without losing their protective properties for periods up to 2 weeks.     

A new force field for the adsorption of H2, O2, N2, CO,H2O,and H2S gases on alkali doped carbon nanotubes

The main goal of this work is the generation of a new force field data set to the interaction of several gases such as H₂, O₂, N₂, CO, H₂O, and H₂S with alkali cation-doped carbon nanotubes (CNTs) using ab initio calculations at the MP2(full)/6-311++G(d,p) level of theory. Different alkali cations including Li⁺, Na⁺_, K⁺ and Cs⁺ were used to dope in the CNT. The calculated potential energy curve for the interaction of each gas molecule with each alkali cation-doped CNTs was fitted to an analytical potential function to obtain the parameters of the potential function. A modified Morse potential function was selected for the fitting in which the electrostatic interactions has been accounted by adding the β/r term to the Morse potential. The accuracy of the calculated force field was checked via Grand Canonical Monte Carlo (GCMC) simulation of the H₂ adsorption on Li-doped graphite and Li-doped CNT. The results of these simulations were compared with the experimental measurements and the closeness of the simulation results with the experimental data indicated the accuracy of the proposed force field. The main merit of this work is the derivation of a specific force field for interaction of each of six gases with four alkali cation-doped CNT, which can be used in molecular simulation of these 24 of systems. The simulation results showed the increase of the H₂ adsorption capacity of nanotube and graphite up to 50% and 10%, respectively, due to the insertion of Li ions.     

A bound on the scrambling index of a primitive matrix using Boolean rank

The scrambling index of an n×n primitive matrix A is the smallest positive integer k such that A^k(A^t)^k=J, where A^t denotes the transpose of A and J denotes the n×n all ones matrix. For an m×n Boolean matrix M, its Boolean rank b(M) is the smallest positive integer b such that M=AB for some m×b Boolean matrix A and b×n Boolean matrix B. In this paper, we give an upper bound on the scrambling index of an n×n primitive matrix M in terms of its Boolean rank b(M). Furthermore we characterize all primitive matrices that achieve the upper bound.     

A quest for a model of non-colloidal suspensions with Newtonian matrices

It would be convenient to have a model, albeit approximate, of particle-laden materials (suspensions) that would not need large amounts of computing and/or experimentation to implement for design purposes. There are now adequate models of the pure matrix fluid behaviour, but there are no such models for suspensions with large particles (non-colloidal suspensions). One of the obstacles has been the single-minded devotion to shearing motions of suspensions; experience with the matrix modelling has shown that it is not possible to formulate widely usable models if only shear is considered. Here some new results of axially symmetric elongational tests on suspensions are compared with shearing data. Some suggestions for modelling these and other observations based on using strain rate and strain in a modified Reiner-Rivlin constitutive equation are presented. The model generally works quite well, but it does not predict the positive storage modulus seen in small and medium amplitude oscillatory shear flows.     

Safety assessments of subcutaneous doses of aragonite calcium carbonate nanocrystals in rats

Calcium carbonate nanoparticles have shown promising potentials in the delivery of drugs and metabolites. There is however, a paucity of information on the safety of their intentional or accidental over exposures to biological systems and general health safety. To this end, this study aims at documenting information on the safety of subcutaneous doses of biogenic nanocrystals of aragonite polymorph of calcium carbonate derived from cockle shells (ANC) in Sprague-Dawley (SD) rats. ANC was synthesized using the top-down method, characterized using the transmission electron microscopy and field emission scanning electron microscope and its acute and repeated dose 28-day trial toxicities were evaluated in SD rats. The results showed that the homogenous 30 ± 5 nm-sized spherical pure aragonite nanocrystals were not associated with mortality in the rats. Severe clinical signs and gross and histopathological lesions, indicating organ toxicities, were recorded in the acute toxicity (29,500 mg/m²) group and the high dose (5900 mg/m²) group of the repeated dose 28-day trial. However, the medium- (590 mg/m² body weight) and low (59 mg/m²)-dose groups showed moderate to mild lesions. The relatively mild lesions observed in the low toxicity dosage group marked the safety margin of ANC in SD rats. It was concluded from this study that the toxicity of CaCO₃ was dependent on the particulate size (30 ± 5 nm) and concentration and the route of administration used.     

Optical modelling of P3HT:PC<Subscript>71</Subscript>BM semi-transparent organic solar cell

The optical properties of a novel semi-transparent organic solar cell were investigated both experimentally and by transfer matrix modelling to maximize photocurrent generation. The effect of multilayer anode thickness and illumination direction was studied. Bottom illumination was shown to provide enhanced exciton generation and increased photocurrent. Changing the multilayer anode thickness also influenced the device reflectance and photocurrent generation.     

Temperature dependence of AC-photoconductivity of HgI2 crystal

An ac impedance method has been used to study the electrical properties of an illuminated HgI₂ crystal as a function of temperature [10–350 K] and frequency [1–10₄ Hz]. The complex impedance plane plots enabled us to determine the bulk resistance of the crystal as a function of temperature. Activation energies of [0.08±0.005 eV] and [0.25 ±0.01eV] are then found; they are attributed to acceptor and donor trapping levels, respectively. At temperatures lower than 230 K, a weak temperature dependence of the bulk resistance is observed. This weak dependence is supposed to be due to photoconductivity.     

A novel type of geosmin biosynthesis in myxobacteria

The biosynthesis of geosmin (1) and (1(10)E,5E)-germacradien-11-ol (2), two volatile terpenoid compounds emitted by the myxobacteria Myxococcus xanthus and Stigmatella aurantiaca, was investigated in feeding experiments with different labeled precursors. In these experiments, the volatiles released by the cell cultures grown on agar plates were collected with a closed-loop stripping apparatus (CLSA) and analyzed by GC-MS. [(2)H(10)]Leucine and [4,4,4,5,5,5-(2)H(6)]dimethylacrylate were fed to wild-type strains and bkd mutant strains, which are impaired in the degradation of leucine to isovaleryl-CoA. [(2)H(10)]Leucine was incorporated into 1 and 2 only by the wild-type strains via the biosynthetic pathway that involves leucine degradation and branching into the mevalonate pathway. Dimethylacrylyl-CoA (DMA-CoA) is an intermediate in the leucine degradation and in the recently discovered pathway from HMG-CoA to isovaleryl-CoA. The corresponding free acid, [4,4,4,5,5,5-(2)H(6)]dimethylacrylic acid, was incorporated into 1 and 2 only by the mutants impaired in leucine degradation. [4,4,6,6,6-(2)H(5)]Mevalonic acid lactone (12) was synthesized and fed to M. xanthus and S. aurantiaca wild-type strains and a double mutant strain of M. xanthus. This strain does not degrade leucine and is impaired in the reduction of 3-hydroxy-3-methylglutaryl-CoA to mevalonic acid. The mass spectral analysis of labeled 1 and 2 obtained in these feeding experiments led to a biosynthetic scheme to 1 with intermediate 2. This pathway differs from that observed in the liverwort Fossombronia pusilla and thus suggests microbial geosmin biosynthesis following a route different from that in liverworts. Our results are supported by a 1,2-hydride shift of the tertiary hydrogen atom at C-4a into the ring opposite to that in F. pusilla.