Random and cooperative sequential adsorption on infinite ladders and strips

We analyze various processes where particles are added irreversibly and sequentially at the sites of infinite ladders or broader strips (i.e., on terraces) of adsorption sites. For sufficiently narrow strips or ladders, exact solution in closed form is possible for a variety of processes. Often this is most naturally achieved by mapping the process onto an equivalent one-dimensional process typically involvingcompetitive adsorption. We demonstrate this procedure for sequential adsorption with nearest-neighbor exclusion on a 2× square ladder. For other select processes on strips slightly too broad for exact solution, almost exact analysis is possible exploiting an empty-site shielding property. In this way, we determine a jamming coverage of 0.91556671 for random sequential adsorption of dimers on a 2× square ladder. For broader strips, we note that the complexity of these problems quickly approaches that for × lattices.     

Structure and cooperativity of the hydrogen bonds in sodium dihydrogen triacetate

Geometry and energetics of low energy conformers of sodium dihydrogen triacetate (SDHTA) and its anion are studied using density functional theory (DFT) at the Becke, Lee‐Yang‐Parr hybrid functional (BLYP) and Becke, three‐parameter, Lee‐Yang‐Parr hybrid functional (B3LYP) levels. For both cases, two structures of comparable energy are found, which have different symmetry with respect to the two hydrogen bonds (HBs). DFT‐based Born–Oppenheimer molecular dynamics simulations are performed for SDHTA, which show that both structures are visited at room temperature conditions. The trajectory analysis further reveals that the two HBs behave anticooperative, that is, on average elongation of one HB is accompanied by a compression of the other one. This is in accord with nuclear magnetic resonance (NMR) experimental studies for a similar counter ion–dihydrogen triacetate complex. © 2012 Wiley Periodicals, Inc.     

Organo-Polyoxometalate-Based Hydrogen-Bond Catalysis

Several urea-inserted organo-polyoxometalates (POMs) derived from polyoxotungstovanadate [P₂V₃W₁₅O₆₁]⁹⁻ were prepared. The insertion of the carbonyl into the polyoxometallic framework activates the urea toward Hydrogen-bond catalysis. This was shown on the Friedel-Crafts arylation of trans-β-nitrostyrene. Modelling shows that the most stable form of the organo-POMs features a cis-trans arrangement of the two N−H bonds, but that the likely catalytically active trans-trans form is accessible at room temperature. Finally, it is possible that the oxo substituents next to the vanadium atoms may help the approach of the nucleophile via H-bonding.     

Co (II)‐C12 alkyl carbon chain multi‐functional ionic liquid immobilized on nano‐SiO2 nano‐SiO2@CoCl3‐C12IL as an efficient cooperative catalyst for C–H activation by direct acylation of aryl halides with aldehydes

Nano‐silica supported ionic liquids composed of alkyl carbon chain and transition metal chlorides anions have been prepared and successfully applied as a heterogeneous catalyst in the direct aldehyde C‐H activation. Catalytic results indicated that nano‐SiO₂ supported ionic liquid consisting C12 alkyl carbon chain and CoCl₃ anion nano‐SiO₂@CoCl₃‐C12IL showed excellent catalytic properties with good to excellent yields towards the desired aryl ketones. The excellent recyclability of the supported catalyst, mild reaction conditions, low catalyst loading, and operational simplicity are the important features of this methodology.     

Enhancement of Acid‐Catalyzed Esterification by the Addition of Base

General acid‐catalyzed reaction can be enhanced by the addition of base. Self‐catalyzed esterification of benzoic acid and octan‐1‐ol was enhanced by the addition of certain base such as imidazole. The rate of the esterification was accelerated as the concentration of imidazole increased. Trans‐esterification of 4‐nitrophenyl acetate was promoted in chloroform by the mixture of benzoic acid and imidazole, but not by benzoic acid or imidazole alone.     

Double‐crosslinked reversible redox‐responsive hydrogels based on disulfide–thiol interchange

We present novel redox‐responsive hydrogels based on poly(N‐isopropylacrylamide) or poly(acrylamide), consisting of a reversible disulfide crosslinking agent N,N′‐bis(acryloyl)cystamine and a permanent crosslinking agent N,N′‐methylenebisacrylamide for microfluidic applications. The mechanism of swelling/deswelling behavior starts with the cleavage and reformation of disulfide bonds, leading to a change of crosslinking density and crosslinking points. Raman and ultraviolet‐visible spectroscopy confirm that conversion efficiency of thiol–disulfide interchange up to 99%. Rheological analysis reveals that the E modulus of hydrogel is dependent on the crosslinking density and can be repeatedly manipulated between high‐ and low‐stiffness states over at least 5 cycles without significant decrease. Kinetic studies showed that the mechanical strength of the gels changes as the redox reaction proceeds. This process is much faster than the autonomous diffusion in the hydrogel. Moreover, cooperative diffusion coefficient (D_coop) indicates that the swelling process of the hydrogel is affected by the reduction reaction. Finally, this reversibly switchable redox behavior of bulky hydrogel could be proven in microstructured hydrogel dots through short‐term photopatterning process. These hydrogel dots on glass substrates also showed the desired short response time on cyclic swelling and shrinking processes known from downsized hydrogel shapes. Such stimuli‐responsive hydrogels with redox‐sensitive crosslinkers open a new pathway in exchanging analytes for sensing and separating in microfluidics applications. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 2590–2601