Nitrile regio-synthesis by Ni centers on a siliceous surface: implications in prebiotic chemistry.

By means of quantum chemistry (PBE0/def2-TZVPP; DLPNO-CCSD(T)/cc-pVTZ) and small, but reliable models of Polyhedral Oligomeric Silsesquioxanes (POSS), an array of astrochemically-relevant catalysis products, related to prebiotic and origin of life chemistry, has been theoretically explored. In this work, the heterogeneous phase hydrocyanation reaction of an unsaturated CC bond (propene) catalyzed by a Ni center complexed to a silica surface is analyzed. Of the two possible regioisomers, the branched iso-propyl-cyanide is thermodynamically and kinetically preferred over the linear -propyl-cyanide ( = 200 K).

Complex Organic Matter Synthesis on Siloxyl Radicals in the Presence of CO.

Heterogeneous phase astrochemistry plays an important role in the synthesis of complex organic matter (COM) as found on comets and rocky body surfaces like asteroids, planetoids, moons and planets. The proposed catalytic model is based on two assumptions: siliceous rocks in both crystalline or amorphous states show surface-exposed defective centers such as siloxyl (Si-O•) radicals; the second phase is represented by gas phase CO molecules, an abundant C building block found in space. By means of quantum chemistry; (DFT, PW6B95/def2-TZVPP); the surface of a siliceous rock in presence of CO is modeled by a simple POSS (polyhedral silsesquioxane) where a siloxyl (Si-O•) radical is present.

On the formation of phosphorous polycyclic aromatics hydrocarbons (PAPHs) in astrophysical environments.

The formation of phosphorous-containing polycyclic aromatic hydrocarbons (PAPHs) in astrophysical contexts is proposed and analyzed by means of computational methods [B3LYP-D3BJ/ma-def2-TZVPP, MP2-F12, CCSD-F12b and CCSD(T)-F12b levels of theory]. A "bottom-up" approach based on a radical-neutral reaction scheme between acetylene (CH) and the CP radical was used investigating: (a) the synthesis of the first PAPH (CHP) "phosphinine"; (b) PAPH growth by addition of CH to the CHP radical; (c) PAPH synthesis by addition reactions of one CP radical and nCH to a neutral PAH. Results show: (I) the formation of the phosphinine radical has a strong thermodynamic tendency (-133.

Propylene Oxide Formation on a Silica Surface with Peroxo Defects: Implications in Astrochemistry.

The formation of the chiral molecule propylene oxide (CHCHCHO) recently detected in the interstellar medium (ISM) is proposed to take place on an amorphous silicate grain surface where peroxo defects are present. A computational analysis conducted at the DFT and MP2-F12 levels of theory on a neat amorphous silica model supports such a hypothesis resulting in (a) strong thermodynamic driving forces and low activation energies allowing the synthesis of CHCHCHO at low temperatures, (b) chemical defects on silica surfaces promoting heterogeneous catalysis of the increasing molecular complexity found in interstellar and circumstellar medium, and (c) chemical defects that have implications on understanding how processing phases modify the nature of the reactive groups on a silica surface affecting the surface catalytic activity.

H Formation on Cosmic Grain Siliceous Surfaces Grafted with Fe : A Silsesquioxanes-Based Computational Model.

Cosmic siliceous dust grains are involved in the synthesis of H in the inter-stellar medium. In this work, the dust grain siliceous surface is represented by a hydrogen Fe-metalla-silsesquioxane model of general formula: [Fe(H Si O )(OH) ] (n=0,1,2) where Fe behaves like a single-site heterogeneous catalyst grafted on a siliceous surface synthesizing H from H. A computational analysis is performed using two levels of theory (B3LYP-D3BJ and MP2-F12) to quantify the thermodynamic driving force of the reaction: [Fe-T7H ] +4H→[Fe-T7H (OH) ] +H .

Astrochemistry of transition metals? The selected cases of [FeN](+), [FeNH](+) and [(CO)2FeN](+): pathways toward CH3NH2 and HNCO.

Transition metals (TMs) are proposed to play a role in astrophysical environments in both gas and solid state astrochemistry by co-determining the homogeneous/heterogeneous chemistry represented by the gas-gas and gas-dust grain interactions. Their chemistry is a function of temperature, radiation field and chemical composition/coordination sphere and as a consequence, dependent on the astrophysical object in which TMs are localized. Here five main categories of TM compounds are proposed and classified as: (a) pure bulk and clusters; (b) TM naked ions; (c) TM oxides/minerals or inorganic compounds; (d) TM-L (L = ligand) with L = (σ and/or π)-donor/acceptor species like H/H2, N/N2, CO, and H2O and (e) TM-organoligands such as Cp, PAH, and R1=˙=˙=R2.

Enhanced EGFP fluorescence emission in presence of PEG aqueous solutions and PIB1000-PEG6000-PIB1000 copolymer vesicles.

An EGFP construct interacting with the PIB1000-PEG6000-PIB1000 vesicles surface reported a ~2-fold fluorescence emission enhancement. Because of the constructs nature with the amphiphilic peptide inserted into the PIB core, EGFP is expected to experience a "pure" PEG environment. To unravel this phenomenon PEG/water solutions at different molecular weights and concentrations were used.

Structural and dynamical analysis of an engineered FhuA channel protein embedded into a lipid bilayer or a detergent belt.

Engineered channel proteins are promising nano-components with applications in nanodelivery and nanoreactors technology. Because few of the engineered channel proteins have been crystallized, solution studies based on Neutron Scattering, Circular Dichroism and NMR play a major role. Consequently, the understanding of membrane proteins dynamics in water/detergent solutions or when embedded in a lipid membrane, can clarify how the environment affects protein behavior.

Polymersome surface decoration by an EGFP fusion protein employing Cecropin A as peptide "anchor".

Polymer based nanocompartments have potential applications in synthetic biology, medicine (drug release) and industrial biotechnology (chiral nanoreactors, multistep syntheses, selective product recovery). A step towards the aforementioned goals is the polymer membrane functionalization through covalent bonding of chemical anchors or insertion of proteins/peptides, to obtain specific properties like recognition, catalytic activity and facilitated diffusion, mimicking the complexity of a biological membrane. The use of genetic engineering techniques widens the possible applications of peptides and proteins specifically designed for polymer membrane interactions.

Engineering of an E. coli outer membrane protein FhuA with increased channel diameter.

Background: Channel proteins like FhuA can be an alternative to artificial chemically synthesized nanopores. To reach such goals, channel proteins must be flexible enough to be modified in their geometry, i.e.

Directed evolution of a thermophilic endoglucanase (Cel5A) into highly active Cel5A variants with an expanded temperature profile.

Cel5A is a highly active endoglucanase from Thermoanaerobacter tengcongensis MB4, displaying an optimal temperature range between 75 and 80°C. After three rounds of error-prone PCR and screening of 4700 mutants, five variants of Cel5A with improved activities were identified by Congo Red based screening method. Compared with the wild type, the best variants 3F6 and C3-13 display 135±6% and 193±8% of the wild type specific activity for the substrate carboxymethyl cellulose (CMC), besides improvements in the relative expression level in Escherichia coli system.

Effect of Na+, Mg2+, and Zn2+ chlorides on the structural and thermodynamic properties of water/n-heptane interfaces.

The effect on the structural and thermodynamic properties in water/n-heptane interfaces on addition of NaCl, MgCl(2), and ZnCl(2) has been examined through five independent 100-ns molecular dynamics simulations. Results indicate that the interfacial thickness within the framework of the capillary-wave model decreases on addition of electrolytes in the order Na(+) < Mg(2+) < Zn(2+), whereas the interfacial tension increases in the same order. Ionic density profiles and self-diffusion coefficients are strongly influenced by the strength of the first hydration shell, which varies in the order Na(+) < Mg(2+) < Zn(2+).

Engineering of the E. coli outer membrane protein FhuA to overcome the hydrophobic mismatch in thick polymeric membranes.

Background: Channel proteins like the engineered FhuA Δ1-159 often cannot insert into thick polymeric membranes due to a mismatch between the hydrophobic surface of the protein and the hydrophobic surface of the polymer membrane. To address this problem usually specific block copolymers are synthesized to facilitate protein insertion. Within this study in a reverse approach we match the protein to the polymer instead of matching the polymer to the protein.

FhuA deletion variant Δ1-159 overexpression in inclusion bodies and refolding with Polyethylene-Poly(ethylene glycol) diblock copolymer.

Membrane protein isolation is a challenging problem. In fact especially their extraction from the respective membrane is difficult and often goes along with losses in yield. Usually expensive detergents are needed to extract the target protein from the membrane.

Cloning and characterization of a thermostable and halo-tolerant endoglucanase from Thermoanaerobacter tengcongensis MB4.

A β-1,4-endoglucanase (Cel5A) was cloned from the genomic DNA of saccharolytic thermophilic eubacterium Thermoanaerobacter tengcongensis MB4 and functionally expressed in Escherichia coli. Substrate specificity analysis revealed that Cel5A cleaves specifically the β-1,4-glycosidic linkage in cellulose with high activity (294 U mg(-1); carboxymethyl cellulose sodium (CMC)). On CMC, kinetics of Cel5A was determined (K (m) 1.

Molecular understanding of sterically controlled compound release through an engineered channel protein (FhuA).

Background: Recently we reported a nanocontainer based reduction triggered release system through an engineered transmembrane channel (FhuA Delta1-160; Onaca et al., 2008). Compound fluxes within the FhuA Delta1-160 channel protein are controlled sterically through labeled lysine residues (label: 3-(2-pyridyldithio)propionic-acid-N-hydroxysuccinimide-ester).

Computational study of the binding of CuII to Alzheimer's amyloid-beta peptide: do Abeta42 and Abeta40 bind copper in identical fashion?

One of the many hypotheses on the pathogenesis of Alzheimer's disease is that the amyloid-beta peptide (Abeta) binds CuII and can catalytically generate H2O2, leading to oxidative damage in brain tissues. For a molecular level understanding of such catalysis it is critical to know the structure of the Abeta-CuII complex precisely. Unfortunately, no high-resolution structure is available to date and there is considerable debate over the copper coordination environment with no clear consensus on which residues are directly bound to CuII.