Controlled membrane translocation provides a mechanism for signal transduction and amplification.

Transmission and amplification of chemical signals across lipid bilayer membranes is of profound significance in many biological processes, from the development of multicellular organisms to information processing in the nervous system. In biology, membrane-spanning proteins are responsible for the transmission of chemical signals across membranes, and signal transduction is often associated with an amplified signalling cascade. The ability to reproduce such processes in artificial systems has potential applications in sensing, controlled drug delivery and communication between compartments in tissue-like constructs of synthetic vesicles. Here we describe a mechanism for transmitting a chemical signal across a membrane based on the controlled translocation of a synthetic molecular transducer from one side of a lipid bilayer membrane to the other. The controlled molecular motion has been coupled to the activation of a catalyst on the inside of a vesicle, which leads to a signal-amplification process analogous to the biological counterpart.We thank the University of Cambridge Oppenheimer Fund for an Early Career Research Fellowship (M.J.L); the Wiener-Anspach Foundation (FWA) for postdoctoral fellowship (FK) ; and Franziska Kundel and David Klenerman for TIRFM imaging experiments

Brønsted versus Lewis Acid Type Anion Recognition by Arylboronic Acids

Interactions between arylboronic acids and a series of anions as tetrabutylammonium salts in DMSO and MeCN were studied by ¹H and ¹¹B NMR as well as spectrophotometrically. Boronic acids act as Brønsted acid type receptors through hydrogen bonding with B­(OH)₂ hydroxyl groups toward Cl^–, Br^–, HSO₄^–, and AcO^–, but they act as Lewis acid type receptors toward F^– and H₂PO₄^–, which form tetrahedral adducts with the B­(III) center of boronic acids, although there is also evidence for some contribution of hydrogen bonding with these anions. The Hammett plot for the binding constants of AcO^– with 3- and 4-substituted phenylboronic acids in DMSO is nonlinear, with a small negative slope for electron-donating and weakly electron-accepting substituents and a large positive slope for strongly electron-accepting substituents. 3-Nitrophenylboronic acid recognizes zwitterions of amino acids in DMSO, and its UV absorption maximum undergoes a significant red shift in the presence of acetate anions, providing a means for sensing anions optically. Arylboronic acids as Brønsted acid type receptors show relatively low sensitivity to solvent polarity and are equally or even more efficient than widely employed proton donors such as ureas or dicarboxamides

The Structure and Catalytic Activity of Pt Complexes Heterogenized on a Silica Surface

The catalytic activity of complex compounds containing different metal contents immobilized on a silica surface towards the oxidation of carbon monoxide and hydrogen has been investigated. In addition, the influence of the concentration of hydrogen and oxygen and the treatment of such catalysts by the individual components in the reaction mixture on their catalytic activity in the hydrogen oxidation reaction has also been studied. The structural peculiarities of platinum complexes heterogenized on a silica surface have been established by diffuse reflectance electronic spectroscopy

Immobilized Pt Complex Compounds as Catalysts for the Oxidation Reactions of Small Molecules

A heterogeneous catalyst for the oxidation of small molecules has been prepared by the immobilization of Pt II and Pt IV complex compounds on the surface of amorphous macroporous silica. The structure of the surface platinum complex compounds has been established by means of vibrational and electronic spectroscopy while the catalytic activity of the catalyst was investigated for the hydrogen (or carbon monoxide) oxidation reaction by molecular oxygen under mild conditions

The Hydrophobisation of Activated Carbon Surfaces by Organic Functional Groups

A technique of hydrophobic surface design with a high degree of structural homogeneity has been developed for catalytic materials. Mesoporous activated carbons and silica gel were modified by (A) treatment with vinyltrimethoxysilane (vtms) or (B) chlorination with carbon tetrachloride followed by reaction with a Grignard reagent. Evidence for silica gel modification was obtained from FT-IR and 13 C NMR spectroscopy and from elemental analysis. Carbons chemically modified with alkanes and olefins were studied using thermogravimetry (TG) and the results compared with those for the modified silica gel. TG and differential scanning calorimetry (DSC) revealed that the polymerisation of vinyl groups occurred on the carbon surface. The participation of the carrier surface in the initiation of radical processes has been discussed

Substituent Effects and pH Profiles for Stability Constants of Arylboronic Acid Diol Esters

Stability constants of boronic acid diol esters in aqueous solution have been determined potentiometrically for a series of <i>meta</i>-, <i>para</i>-substituted phenylboronic acids and diols of variable acidity. The constants β_11‑1 for reactions between neutral forms of reactants producing the anionic ester plus proton follow the Hammett equation with ρ depending on p<i>K</i>_a of diol and varying from 2.0 for glucose to 1.29 for 4-nitrocatechol. Observed stability constants (<i>K</i>_obs) measured by UV–vis and fluorometric titrations at variable pH for esters of 4,5-dihydroxy-1,3-benzenedisulfonate (Tiron) generally agree with those expected on the basis of β_11‑1 values, but the direct fitting of <i>K</i>_obs vs pH profiles gives shifted p<i>K</i>_a values both for boronic acids and diol as a result of significant interdependence of fitting parameters. The subsituent effects on absorption and fluorescence spectra of Tiron arylboronate esters are characterized. The <i>K</i>_obs for Tiron determined by ¹¹B NMR titrations are approximately 1 order of magnitude smaller than those determined by UV–vis titrations under identical conditions. A general equation, which makes possible an estimate of β_11‑1 for any pair of boronic acid and diol from their p<i>K</i>_a values, is proposed on the basis of established Brönsted-type correlation of Hammett parameters for β_11‑1 with acidity of diols. The equation allows one to calculate stability constants expected only on basis of acid–base properties of the components, thus permitting more strict evaluation of contributions of additional factors such as steric or charge effects to the ester stability