Swelling and deswelling of adsorbed microgel monolayers triggered by changes in temperature, pH, and electrolyte concentration

The formation and characterization of close-packed monolayers of negative, poly(N-isopropylacrylamide)-based microgel particles onto positively charged silicon wafers is described. The silicon wafers were rendered positive by first oxidizing their surface to silica and then adsorbing a layer of poly(ethyleneimine). The thickness of the deposited microgel monolayers (under aqueous conditions) has been determined by spectroscopic ellipsometry as a function of temperature (20-60 degrees C), pH (3-8), and added NaCl concentration (0-1 M). No actual desorption of the microgel particles was evident on changing the conditions, but a swelling/deswelling transition was observed around 32 degrees C. The thickness of the monolayer has been compared with the hydrodynamic diameter of the free microgel particles, dispersed in aqueous solution. For the poly(N-isopropylacrylamide) microgel particles, without any bulk ionisable comonomer groups present, the temperature dependence of the ellipsometric thickness of the monolayer mirrors closely that of the hydrodynamic diameter of the free particles. When ionizable (-COOH) groups are introduced into the microgel particles, however, this correspondence is largely lost because the microgel particles forming the deposited monolayer now contract strongly onto the oppositely charged substrate surface.     

Coexistence of Two Thermally Induced Intramolecular Electron Transfer Processes in a Series of Metal Complexes [M(Cat‐N‐BQ)(Cat‐N‐SQ)]/[M(Cat‐N‐BQ)2] (M=Co,Fe, and Ni) bearing Non‐Innocent Catechol‐Based Ligands: A Combined Experimental and Theoretical Study

The different thermally induced intermolecular electron transfer (IET) processes that can take place in the series of complexes [M(Cat‐N‐BQ)(Cat‐N‐SQ)]/[M(Cat‐N‐BQ)₂], for which M=Co ( 2 ), Fe ( 3 ) and Ni( 4 ), and Cat‐N‐BQ and Cat‐N‐SQ denote the mononegative (Cat‐N‐BQ^?) or dinegative (Cat‐N‐SQ^2?) radical forms of the tridentate Schiff‐base ligand 3,5‐di‐tert‐butyl‐1,2‐quinone‐1‐(2‐hydroxy‐3,5‐di‐tert‐butylphenyl)imine, have been studied by variable‐temperature UV/Vis and NMR spectroscopies. Depending on the metal ion, rather different behaviors are observed. Complex 2 has been found to be one of the few examples so far reported to exhibit the coexistence of two thermally induced electron transfer processes, ligand‐to‐metal (IET^LM) and ligand‐to‐ligand (IET^LL). IET^LL was only found to take place in complex 3 , and no IET was observed for complex 4 . Such experimental studies have been combined with ab initio wavefunction‐based CASSCF/CASPT2 calculations. Such a strategy allows one to solicit selectively the speculated orbitals and to access the ground states and excited‐spin states, as well as charge‐transfer states giving additional information on the different IET processes.     

Sliding droplets on superomniphobic zinc oxide nanostructures

This study reports on liquid-repellency of zinc oxide nanostructures (ZnO NS). The ZnO NS are synthesized by an easy and fast chemical bath deposition technique. Three different nanostructured surfaces consisting of nanorods, flowers, and particles are prepared, depending on the deposition time and the presence of ethanolamine in the reaction mixture. Chemical functionalization of the ZnO NS with 1H,1H,2H,2H-perfluorodecyltrichlorosilane (PFTS) in liquid (PFTS L) and vapor phase (PFTS V) or through octafluorobutane (C(4)F(8)) plasma deposition led to the formation of superomniphobic surfaces. A comprehensive characterization of the wetting properties (static contact angle and contact angle hysteresis) has been performed using liquids composed of deionized water and various concentrations of ethanol (surface tension between 35 and 72.6 mN/m). Depending on the nanostructures morphology, coating nature and liquid employed, high static apparent contact angles θ ≈ 150-160°, and low contact angle hysteresis Δθ ≈ 0° are obtained. The different ZnO NS are characterized using scanning electron microscopy (SEM) and contact angle measurements. The results reported in this work permit preparation of sliding omniphobic surfaces using a simple and low cost technique.     

Oligoether-strapped calix[4]pyrrole: an ion-pair receptor displaying cation-dependent chloride anion transport

A ditopic ion-pair receptor (1), which has tunable cation- and anion-binding sites, has been synthesized and characterized. Spectroscopic analyses provide support for the conclusion that receptor 1 binds fluoride and chloride anions strongly and forms stable 1:1 complexes ([1·F](-) and [1·Cl](-)) with appropriately chosen salts of these anions in acetonitrile. When the anion complexes of 1 were treated with alkali metal ions (Li(+), Na(+), K(+), Cs(+), as their perchlorate salts), ion-dependent interactions were observed that were found to depend on both the choice of added cation and the initially complexed anion. In the case of [1·F](-), no appreciable interaction with the K(+) ion was seen. On the other hand, when this complex was treated with Li(+) or Na(+) ions, decomplexation of the bound fluoride anion was observed. In contrast to what was seen with Li(+), Na(+), K(+), treating [1·F](-) with Cs(+) ions gave rise to a stable, host-separated ion-pair complex, [F·1·Cs], which contains the Cs(+) ion bound in the cup-like portion of the calix[4]pyrrole. Different complexation behavior was seen in the case of the chloride complex, [1·Cl](-). Here, no appreciable interaction was observed with Na(+) or K(+). In contrast, treating with Li(+) produces a tight ion-pair complex, [1·Li·Cl], in which the cation is bound to the crown moiety. In analogy to what was seen for [1·F](-), treatment of [1·Cl](-) with Cs(+) ions gives rise to a host-separated ion-pair complex, [Cl·1·Cs], in which the cation is bound to the cup of the calix[4]pyrrole. As inferred from liposomal model membrane transport studies, system 1 can act as an effective carrier for several chloride anion salts of Group 1 cations, operating through both symport (chloride+cation co-transport) and antiport (nitrate-for-chloride exchange) mechanisms. This transport behavior stands in contrast to what is seen for simple octamethylcalix[4]pyrrole, which acts as an effective carrier for cesium chloride but does not operates through a nitrate-for-chloride anion exchange mechanism.     

An analytical derivative procedure for the calculation of vibrational Raman optical activity spectra

We present an analytical time-dependent Hartree-Fock algorithm for the calculation of the derivatives of the electric dipole-magnetic dipole polarizability with respect to atomic Cartesian coordinates. Combined with analogous procedures to determine the derivatives of the electric dipole-electric dipole and electric dipole-electric quadrupole polarizabilities, it enables a fully analytical evaluation of the three frequency-dependent vibrational Raman optical activity (VROA) invariants within the harmonic approximation. The procedure employs traditional non-London atomic orbitals, and the gauge-origin dependence of the VROA intensities has, therefore, been assessed for the commonly used aug-cc-pVDZ and rDPS:3-21G basis sets.     

Coupled motion in proteins revealed by pressure perturbation

The cooperative nature of protein substructure and internal motion is a critical aspect of their functional competence about which little is known experimentally. NMR relaxation is used here to monitor the effects of high pressure on fast internal motion in the protein ubiquitin. In contrast to the main chain, the motions of the methyl-bearing side chains have a large and variable pressure dependence. Within the core, this pressure sensitivity correlates with the magnitude of motion at ambient pressure. Spatial clustering of the dynamic response to applied hydrostatic pressure is also seen, indicating localized cooperativity of motion on the sub-nanosecond time scale and suggesting regions of variable compressibility. These and other features indicate that the native ensemble contains a significant fraction of members with characteristics ascribed to the recently postulated "dry molten globule". The accompanying variable side-chain conformational entropy helps complete our view of the thermodynamic architecture underlying protein stability, folding, and function.     

Stereoselective synthesis of P-chirogenic dibenzophosphole-boranes via aryne intermediates

A new aryne-mediated tandem cross-coupling/P-cyclization sequence starting from tertiary phosphine-boranes and 1,2-dibromobenzenes is reported. P-chirogenic dibenzophospholes become accessible in a regio-, chemo-, and diastereoselective way.     

Air‐Stable {(C5H5)Co} Catalysts for [2+2+2] Cycloadditions

Cobalt cyclopentadienyl complexes incorporating a fumarate and a CO ligand (see picture) efficiently catalyze inter‐ and intramolecular [2+2+2] cycloadditions of alkynes, nitriles, and/or alkenes to give benzenes, pyridines, or 1,3‐cyclohexadienes. Unlike catalysts such as [CpCo(CO)₂] or [CpCo(C₂H₄)₂] (Cp=C₅H₅), they are air‐stable, easy to handle, compatible with microwave conditions, and do not necessarily require irradiation to be active.

     

Intramolecular Alkynylogous Mukaiyama Aldol Reaction Starting from Bicyclic Alkanones Tethered to Alkynyl Esters: Formal Total Synthesis of (±)‐Hamigeran B

Selecting the ring : tert‐Butyldimethylsilyltriflate (TBSOTf)/NEt₃ treatment of alkynyl esters tethered to bicycloalkanones leads to the formation of tricyclic allenoates with total diasteroselectivity at the ring junction. An intramolecular alkynylogous Mukaiyama aldol reaction promoted by a TBSOTf/NEt₃ dual activation is involved. This novel methodology was illustrated by a formal total synthesis of (±)‐hamigeran B.