The effects of the charge density and structure of the polymer on the dye-binding characteristics of some cationic polyelectrolytes

The interaction of various structurally different water-soluble cationic polyelectrolytes with methyl orange, an anionic dye, has been studied. The changes in the UV-Vis spectra of methyl orange in the presence of methyl and benzyl quaternized polyvinylpyridines and trialkylammonium and triphenylphosphonium salts of polyvinylbenzyl chloride have been used to investigate the effect of the structure on the dye-binding characteristics of the polycations. The results are interpreted in the light of a simple theory of cooperative binding to a linear lattice. The extent of binding of the dye aggregates on the polymers has been calculated. The binding ability of the above-mentioned polyelectrolytes has been found to depend on the nature of the substituent on the polycation. The contribution of the coulombic forces on binding of the dye by these polymers has been emphasized. © 1995 John Wiley & Sons, Inc.     

A P−H Functionalized Al/P Frustrated Lewis Pair: Substrate Activation and Selective Hydrogen Transfer

Hydroalumination of an alkynylphosphine gave an unprecedented P?H functionalized frustrated Lewis pair (FLP). The reactive P?H group does not influence the typical FLP properties, but the activation of substrates follows a new reaction pattern involving hydrogen transfer to yield unusual compounds with phosphaurea, iminophosphine, or phosphanyltriazene structural motifs.     

Reversible Dihydrogen Activation and Hydride Transfer by a Uranium Nitride Complex

Cleavage of dihydrogen is an important step in the industrial and enzymatic transformation of N₂ into ammonia. The reversible cleavage of dihydrogen was achieved under mild conditions (room temperature and 1 atmosphere of H₂) by the molecular uranium nitride complex, [Cs{U(OSi(O^tBu)₃)₃}₂(μ‐N)] 1, leading to a rare hydride–imide bridged diuranium(IV) complex, [Cs{U(OSi(O^tBu)₃)₃}₂(μ‐H)(μ‐NH)], 2 that slowly releases H₂ under vacuum. This complex is highly reactive and quickly transfers hydride to acetonitrile and carbon dioxide at room temperature, affording the ketimide‐ and formate‐bridged U^IV species [Cs{U(OSi(O^tBu)₃)₃}₂(μ‐NH)(μ‐CH₃CHN)], 3 and [Cs{U(OSi(O^tBu)₃)₃}₂(μ‐HCOO)(μ‐NHCOO)], 4 .     

Applicability of Positive Cooperativity Model of Enzyme Catalysis on Surfactant-Mediated Reaction of Pararosaniline Hydrochloride Carbocation with Hydroxide Ion

The reaction of hydroxide ion with stabilized pararosaniline hydrochloride carbocation was investigated in the presence of cationic micelles of cetyltrimethylammonium bromide (CTAB) and anionic micelles of sodium dodecyl sulfate (SDS). Pseudo-first-order kinetics were followed by the reaction system and rate constant depends on surfactant concentration. The reaction was strongly inhibited in the presence of SDS micelles whereas catalyzed in the presence of CTAB micelles. Micellar data were analyzed by applying positive cooperativity model of enzyme catalysis. The value of index of cooperativity (n) was greater than 1 for all reaction systems. Inhibitory and catalytic effect in the presence of micelles had been explained on the basis of hydrophobic and electrostatic interactions of various species present in the reaction systems. Presence of counterions in the reaction system inhibited the reaction rate.     

Association of symmetrical alkane diols with pyridine: DFT/GIAO calculation of 1H NMR chemical shifts

Proton nuclear magnetic resonance (NMR) shifts of the free diol and of its 1 : 1 and 1 : 2 hydrogen‐bonded complexes with pyridine have been computed for five symmetrical alkane diols on the basis of density functional theory, by applying the gauge‐including atomic orbital method to geometry‐optimized conformers. For certain conformers, intramolecular OH ···OH interactions, evidenced by high NMR OH proton shifts, are further enhanced on going from the free diol to the corresponding 1 : 1 diol/pyridine complex. This is confirmed by atoms‐in‐molecules and non‐covalent interaction plots. The computed OH and CH proton shifts for the diol and the two complexes correlate well with values obtained by analysing data from the NMR titration of the diols in benzene against pyridine. Shift values for the diols in neat pyridine are calculated by weighting the shifts of the various protons in the three forms (free diol, 1 : 1 and 1 : 2 diol/pyridine complexes) according to the experimentally determined association constants. The results are in good agreement with those observed, and after empirical scaling, the root mean square difference is 0.18 ppm. Copyright © 2016 John Wiley & Sons, Ltd.     

Distinct Bimetallic Cooperativity Among Water Reduction Catalysts Containing [CoIIICoIII], [NiIINiII], and [ZnIIZnII] Cores

Three binuclear species [LCo^III₂(μ-Pz)₂](ClO₄)₃ ( 1 ), [LNi^II₂(CH₃OH)₂Cl₂]ClO₄ ( 2 ), and [LZn^II₂Cl₂]PF₆ ( 3 ) supported by the deprotonated form of the ligand 2,6-bis[bis(2-pyridylmethyl) amino-methyl]-4-methylphenol were synthesized, structurally characterized as solids and in solution, and had their electrochemical and spectroscopic behavior established. Species 1 – 3 had their water reduction ability studied aiming to interrogate the possible cooperative catalytic activity between two neighboring metal centers. Species 1 and 2 reduced H₂O to H₂ effectively at an applied potential of −1.6 V_Ag/AgCl, yielding turnover numbers of 2,820 and 2,290, respectively, after 30 minutes. Species 3 lacked activity and was used as a negative control to eliminate the possibility of ligand-based catalysis. Pre- and post-catalytic data gave evidence of the molecular nature of the process within the timeframe of the experiments. Species 1 showed structural, rather than electronic cooperativity, while species 2 displayed no obvious cooperativity. DFT methods complemented the experimental results determining plausible mechanisms.     

Bulky PNP Ligands Blocking Metal-Ligand Cooperation Allow for Isolation of Ru(0), and Lead to Catalytically Active Ru Complexes in Acceptorless Alcohol Dehydrogenation

We synthesized two 4Me−PNP ligands which block metal-ligand cooperation (MLC) with the Ru center and compared their Ru complex chemistry to their two traditional analogues used in acceptorless alcohol dehydrogenation catalysis. The corresponding 4Me−PNP complexes, which do not undergo dearomatization upon addition of base, allowed us to obtain rare, albeit unstable, 16 electron mono-CO Ru(0) complexes. Reactivity with CO and H₂ allows for stabilization and extensive characterization of bis-CO Ru(0) 18 electron and Ru(II) cis and trans dihydride species that were also shown to be capable of C(sp²) −H activation. Reactivity and catalysis are contrasted to non-methylated Ru(II) species, showing that an MLC pathway is not necessary, with dramatic differences in outcomes during catalysis between ⁱPr and ^tBu PNP complexes within each of the 4Me and non-methylated backbone PNP series being observed. Unusual intermediates are characterized in one of the new and one of the traditional complexes, and a common catalysis deactivation pathway was identified.     

Quantifying cooperativity in water clusters: an attempt towards obtaining a generalised equation

The current study describes the development of a general equation of cooperativity energy (CE) for an n-mer system based on the difference between interaction energy of the system and the sum of interaction energy of its dimeric subunits. The counterpoise corrected generalised CE equation of n-mer system has also been developed. In order to validate these two generalised equations, we have considered four different kinds of water clusters, viz. W1D, W2D, W2D-H and W3D, ((H₂O)_n: n = 3–10), with the increasing cluster size as well as changing arrangements. The CE obtained from the two generalised equations follow the trend W3D > W2D-H > W2D > W1D. The deviation at n = 6 for W3D clusters in the plot of CE with cluster size has also been observed for O–H stretching frequencies, electron density and the Laplacian of the electron density plots. The contrastingly higher CE for cyclic pentamer compared to hexamer is in accordance with earlier observations as well as computed average hydrogen bond lengths. We have observed that the average charge value is more on oxygen atoms of pentamer than hexamer resulting in the shortening of hydrogen bond in pentamer and hence the CE values are more for pentamer than hexamer. We have shown that CE has the capability to quantify the cooperativity effect in water clusters.