Organosilyl/‐germyl Polyoxotungstate Hybrids for Covalent Grafting onto Silicon Surfaces: Towards Molecular Memories

Organosilyl/‐germyl polyoxotungstate hybrids [PW₉O₃₄(tBuSiO)₃Ge(CH₂)₂CO₂H]^3? ( 1 a ), [PW₉O₃₄(tBuSiO)₃Ge(CH₂)₂CONHCH₂C?CH]^3? ( 2 a ), [PW₁₁O₃₉Ge(CH₂)₂CO₂H]^4? ( 3 a ), and [PW₁₁O₃₉Ge(CH₂)₂CONHCH₂C≡CH]^4? ( 4 a ) have been prepared as tetrabutylammonium salts and characterized in solution by multinuclear NMR spectroscopy. The crystal structure of (NBu₄)₃ 1 a? H₂O has been determined and the electrochemical behavior of 1 a and 2 a has been investigated by cyclic voltammetry. Covalent grafting of 2 a onto an n‐type silicon wafer has been achieved and the electrochemical behavior of the grafted clusters has been investigated. This represents the first example of covalent grafting of Keggin‐type clusters onto a Si surface and a step towards the realization of POM‐based multilevel memory devices.     

A Simple Colorimetric Enzymatic-Assay for Okadaic Acid Detection Based on the Immobilization of Protein Phosphatase 2A in Sol-Gel

Okadaic acid (OA), a lipophilic toxin, is produced by Dinophysis and Prorocentrum, and causes diarrheic shellfish poisoning to humans. The mechanism of OA action is based on the reversible inhibition of protein phosphatase type 2A (PP2A) by the toxin. Therefore, this inhibition could be used to develop assay for OA detection. In this work, a colorimetric test based on the PP2A inhibition was developed for OA detection. PP2A from GTP and Millipore was immobilized on silica sol-gel, and the detection was performed. A limit of detection of 0.29 and 1.14 μg/L was respectively observed for enzyme from GTP and Millipore. The immobilization technique provided a tool to preserve the enzymatic activity, which is very unstable in solution. The PP2A immobilized sol-gel exhibited a storage stability of near 5 months, when microtiter plate with enzyme-immobilized polymer was kept at −18C°. The combination of the simplicity of the colorimetric method, along with long storage stability achieved by sol-gel immobilization, demonstrated the potentiality of this technique to be used for commercial purpose.     

Perfluoroalkyl chains direct novel self-assembly of insulin

The self-assembly of biopharmaceutical peptides into multimeric, nanoscale objects, as well as their disassembly to monomers, is central for their mode of action. Here, we describe a bioorthogonal strategy, using a non-native recognition principle, for control of protein self-assembly based on intermolecular fluorous interactions and demonstrate it for the small protein insulin. Perfluorinated alkyl chains of varying length were attached to desB30 human insulin by acylation of the ε-amine of the side-chain of LysB29. The insulin analogues were formulated with Zn(II) and phenol to form hexamers. The self-segregation of fluorous groups directed the insulin hexamers to self-assemble. The structures of the systems were investigated by circular dichroism (CD) spectroscopy and synchrotron small-angle X-ray scattering. Also, the binding affinity to the insulin receptor was measured. Interestingly, varying the length of the perfluoroalkyl chain provided three different scenarios for self-assembly; the short chains hardly affected the native hexameric structure, the medium-length chains induced fractal-like structures with the insulin hexamer as the fundamental building block, while the longest chains lead to the formation of structures with local cylindrical geometry. This hierarchical self-assembly system, which combines Zn(II) mediated hexamer formation with fluorous interactions, is a promising tool to control the formation of high molecular weight complexes of insulin and potentially other proteins.     

Conjugation of Methacrylamide Groups to a Model Protein via a Reducible Linker for Immobilization and Subsequent Triggered Release from Hydrogels

An efficient strategy is reported to introduce methacrylamide groups on the lysine residues of a model protein (lysozyme) for immobilization and triggered release from a hydrogel network. A novel spacer unit was designed, containing a disulfide bond, such that the release of the protein can be triggered by reduction. The modified proteins were characterized by MALDI‐TOF MS, titration of free NH₂ residues and spectral analysis. The modification reaction is well controlled, and the number of introduced functions can be tailored by changing the reaction conditions. Gel electrophoresis experiments showed that the methacrylamide modified protein can be immobilized in a polyacrylamide hydrogel and subsequently released by reduction of the spacer by which the protein was grafted to the polymeric network.

     

Twists and turns in the hierarchical self-assembly pathways of a non-amphiphilic chiral supramolecular material

The formation of helical self-assembled fibres by a C(3) symmetric molecule incorporating three tetrathiafulvalene units is shown to be influenced dramatically by the processing conditions, leading to a variety of different chiral forms, including unprecedented croissants.     

Conformational analysis. 24. Structure and composition of gaseous oxalyl fluoride, C(2)F(2)O(2): electron-diffraction investigation augmented by data from microwave spectroscopy and molecular orbital calculations

The molecular structure and composition of gaseous oxalyl fluoride (OXF) has been investigated by electron diffraction (GED) at nozzle-tip temperatures of -10, 149, and 219 degrees C. The GED data were augmented by molecular orbital calculations, and the analysis was aided by use of rotational constants from microwave (MW) spectroscopy. As in the other oxalyl halides, there are two stable species, of which the more stable is periplanar anti (i.e., trans). However, unlike these other halides in which the second form is gauche, the second form of oxalyl fluoride was known from MW work to be periplanar syn (i.e., cis). Our results are consistent with a mixture of trans and cis forms, and yield values for the structural parameters, the composition of the system at the three temperatures cited, and the thermodynamic quantities deltaG(o), deltaH(o), and deltaS(o) for the reaction trans --> cis. Some trans/cis distances (r(g)/Angstrom) and angles (<(alpha)/deg) at -10 degrees C are r(C=O) = 1.178(2)/1.176(2), r(C-F) = 1.323(2)/1.328(2); r(C-C) = 1.533(3)/1.535(3), <(C-C=O) = 126.4(2)/124.2(2), <(C-C-F) = 109.8(2)/112.2(2), and <(O-C-F) = 123.8(2)/123.6(2). The mixture compositions (percent trans) at -10 degrees C/149 degrees C/219 degrees C are 75(3)/58(7)/52(8), from which deltaH(o) and deltaSO) are found to be 1.14 kcal/mol and 2.12 cal/(mol x deg). The system properties are discussed.