C?H Bond dissociation of acetylene: Local density functional calculations

The C? H bond dissociation energy of acetylene was computed by both ab initio approaches and density functional theory in a local density approximation (DFT–LDA ). Structures and energies for acetylene and its dissociation products (the ethynyl and hydrogen radicals) are presented and compared. Using directly computed HCCH and HCC· energies and the exact H· value, the DFT–LDA calculations are found to yield C? H dissociation energies ranging from 129 to 131 kcal/mol, in good agreement with recent experimental and the highest level theoretical results. The DFT–LDA results show little dependence upon the computational procedure used to obtain geometries.     

Structure and dynamics of self-assembled poly(ethylene glycol) based coiled-coil nano-objects.

Herein we describe the structure and dynamics of self-assembled nano-objects generated from poly(ethylene glycol) based (PEG-ylated) coiled-coil hybrid block copolymers. Electron paramagnetic resonance (EPR) experiments on spin-labeled samples provided a strong indication for a parallel alignment of the peptide helices in at least the dimeric coiled-coil nano-object and indicated that the PEG chains are folded rather closely around the peptide core of the nano-objects. The EPR results were supported by AFM studies, which revealed the presence of discrete nanosized objects in thin, spin cast films of the block copolymers on mica substrates. Since their size and structure may be engineered via directed mutations in the amino acid sequence, these nano-objects may be interesting building blocks for the development of supramolecular materials with various potential applications.     

Preparation of Silica-Bonded S-Sulfonic Acid: A Recyclable Catalyst for the Synthesis of Bis-Indolylmethanes

Silica bonded S-sulfonic acid (SBSSA) was prepared by the reaction of 3-mercaptopropylsilica (MPS) and chlorosulfonic acid in chloroform. Silica-bonded S-sulfonic acid, as a reusable solid acid catalyst, was used for the condensation reactions of indole with carbonyl compounds at ambient temperature. Tetra-(indolyl)methanes were also obtained by the condensation reaction of indole with dialdehyde compounds. Silica bonded S-sulfonic acid was recovered and reused.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.     

Incorporation of β-Alanine in Cu(II) ATCUN Peptide Complexes Increases ROS Levels,DNA Cleavage and Antiproliferative Activity**

Redox-active Cu(II) complexes are able to form reactive oxygen species (ROS) in the presence of oxygen and reducing agents. Recently, Faller et al. reported that ROS generation by Cu(II) ATCUN complexes is not as high as assumed for decades. High complex stability results in silencing of the Cu(II)/Cu(I) redox cycle and therefore leads to low ROS generation. In this work, we demonstrate that an exchange of the α-amino acid Gly with the β-amino acid β-Ala at position 2 (Gly2→β-Ala2) of the ATCUN motif reinstates ROS production (^•OH and H₂O₂). Potentiometry, cyclic voltammetry, EPR spectroscopy and DFT simulations were utilized to explain the increased ROS generation of these β-Ala2-containing ATCUN complexes. We also observed enhanced oxidative cleavage activity towards plasmid DNA for β-Ala2 compared to the Gly2 complexes. Modifications with positively charged Lys residues increased the DNA affinity through electrostatic interactions as determined by UV/VIS, fluorescence, and CD spectroscopy, and consequently led to a further increase in nuclease activity. A similar trend was observed regarding the cytotoxic activity of the complexes against several human cancer cell lines where β-Ala2 peptide complexes had lower IC₅₀ values compared to Gly2. The higher cytotoxicity could be attributed to an increased cellular uptake as determined by ICP-MS measurements.     

Investigation of a novel serpentine micromixer based on Dean flow and separation vortices

Meccanica - Passive micromixers, due to their relatively high mixing efficiency and simple fabrication, have wide applications in biological, medical, and chemical processes. Serpentine and...     

The glassy state of the amorphous V2O5–NiO–TeO2 samples

The glass transition temperature dependence to heating rate and therefore the activation energy (ΔH^?) of the glass transition of (60-x)V₂O₅–xNiO–40TeO₂ oxide glasses with 0≤x≤20 (in mol%) were investigated at heating rates φ (=3 6, 9, 10 and 12 K/min) using differential scanning calorimetry (DSC). The heating rate dependence of T_g was used to investigate the applicability of different theoretical models describing the glass transition. Using the application of Moynihan and Kissinger et al. models to the present data, different values of (ΔH^?) at each different heating-rate regions were obtained. The fragility parameter (m=ΔH^?/R T_g) was ∼24.98 for x=10 mol%, suggesting that this glass may be considered as a rather strong glass (fragility index m∼>20 is an indication of fragile glass). Also the compositional dependence of T_g and ΔH^? was investigated.     

Impregnated copper ferrite on mesoporous graphitic carbon nitride: An efficient and reusable catalyst for promoting ligand‐free click synthesis of diverse 1,2,3‐triazoles and tetrazoles

Magnetic CuFe₂O₄/g‐C₃N₄ hybrids were synthesized through a facile method and their catalytic performances were evaluated in click chemistry for the first time. The structural and morphological characterization of prepared materials was carried out by different techniques such as X‐ray diffraction, high‐resolution transmission electron microscopy, field emission scanning electron microscopy, Fourier infrared spectroscopy, vibrating sample magnetometry, thermogravimetric analysis, and N₂ adsorption–desorption analysis (Brunauer–Emmett–Teller surface area). The utilization of magnetic CuFe₂O₄/g‐C₃N₄ enabled superior performance in the one‐pot azide–alkyne cycloaddition reaction in water using alkyl halides and epoxides as azide precursors without the need of any additional agents. The present system is broad in scope and especially practical for the synthesis of macrocyclic triazoles and also tetrazoles. In addition, the catalytic system highly fulfills the demands of “green click chemistry” with its convenient conditions, especially easy access to a variety of significant products in low catalyst loading and simple work‐up and isolation procedure.     

Tuning Human Serum Albumin (HSA) Hydrogels through Albumin Glycation

The changes of technological properties of albumin-based hydrogels induced by increasing degrees of post-translational modification of the protein are reported. Maillard-type modification of amino acids arginine and lysine of albumin is achieved through glyoxal as an α-dicarbonyl compound. The degrees of modification are fine-tuned using different molar ratios of glyoxal. Hydrogels are thermally induced by heating highly concentrated precursor solutions above the protein's denaturation temperature. While the post-translational modifications are determined and quantified with mass spectrometry, continuous-wave (CW) electron paramagnetic resonance (EPR) spectroscopy shed light on the protein fatty acid binding capacity and changes thereof in solution and in the gel state. The viscoelastic behavior is characterized as a measure of the physical strength of the hydrogels. On the nanoscopic level, the modified albumins in low concentration solution reveal lower binding capacities with increasing degrees of modification. On the contrary, in the gel state, the binding capacity remains constant at all degrees of modifications. This indicates that the loss of fatty acid binding capacity for individual albumin molecules is partially compensated by new binding sites in the gel state, potentially formed by modified amino acids. Such, albumin glycation offers a fine-tuning method of technological and nanoscopic properties of these gels.     

Protein recognition by a self-assembled deep cavitand monolayer on a gold substrate

This paper details the first use of a self-folding deep cavitand on a gold surface. A sulfide-footed deep, self-folding cavitand has been synthesized, and its attachment to a cleaned gold surface studied by electrochemical and SPR methods. Complete monolayer formation is possible if the cavitand folding is templated by noncovalent binding of choline or by addition of space-filling thiols to cover any gaps in the cavitand adsorption layer. The cavitand is capable of binding trimethylammonium-tagged guests from an aqueous medium and can be deposited in 2 × 2 microarrays on the surface for characterization by SPR imaging techniques. When biotin-labeled guests are used, the cavitand:guest construct can recognize and immobilize streptavidin proteins from aqueous solution, acting as an effective supramolecular biosensor for monitoring protein recognition.     

Reactivity of N-nitrosoamides in confined spaces

The thermal rearrangement of several N-nitrosoamides was studied by ¹H NMR in the context of reversible encapsulation. The N-nitrosoamide guests were isolated from the bulk solvent in a hydrogen-bonded dimeric host capsule which prevented their rearrangement. The guests appear to be preserved in their ground state conformations by the pressure exerted by the host. The conformations of the free and bound N-nitrosoamides are of comparable relative energies as determined by DFT calculations.