Triisopropyltriazacyclononane copper(II): an efficient phosphodiester hydrolysis catalyst and DNA cleavage agent

A 6000-fold rate enhancement has been observed for the hydrolysis of bis(p-nitrophenyl)phosphate (BNPP) in the presence of 0.2 mM Cu(i-Pr(3)[9]aneN(3))(2+) at pH 9.2 and 50 degrees C. In a direct comparison, the rate of hydrolysis of BNPP is accelerated at least 60-fold over the previously reported catalyst Cu([9]aneN(3))(2+). As observed for Cu([9]aneN(3))(2+), hydrolysis is selective for diesters over monoesters. Hydrolysis of BNPP by Cu(i-Pr(3)[9]aneN(3))(2+) is catalytic, exhibiting both rate enhancement and turnover. The reaction is inhibited by both p-nitrophenyl phosphate and inorganic phosphate. The reaction is first-order in substrate and half-order in metal complex, with a k(1.5) of 0.060 +/- 0.004 M(-1/2) s(-1) at 50 degrees C. The temperature dependence of the rate constant results in a calculated activation enthalpy (Delta H(++) of 51 +/- 2 kJ mol(-1) and activation entropy (Delta S(++)) of -110 +/- 6 J mol(-1) K(-1). The kinetic pK(a) of 7.8 +/- 0.2 is close to the thermodynamic pK(a) of 7.9 +/- 0.2, consistent with deprotonation of a coordinated water molecule in the active form of the catalyst. The active catalyst [Cu(i-Pr(3)[9]aneN(3))(OH)(OH(2))](+) is in equilibrium with an inactive dimer, and the formation constant for this dimer is between 216 and 1394 M(-1) at pH 9.2 and 50 degrees C. Temperature dependence of the dimer formation constant K(f) indicates an endothermic enthalpy of formation for the dimer of 27 +/- 3 kJ mol(-1). The time course of anaerobic DNA cleavage by Cu(i-Pr(3)[9]aneN(3))(2+) is presented over a wide range of concentrations at pH 7.8 at 50 degrees C. The concentration dependence of DNA cleavage by Cu([9]aneN(3))(2+) and Cu(i-Pr(3)[9]aneN(3))(2+) reveals a maximum cleavage efficiency at sub-micromolar concentrations of cleavage agent. DNA cleavage by Cu(i-Pr(3)[9]aneN(3))(2+) is twice as efficient at pH 7.8 as at pH 7.2.     

Synthesis, characterization, and preliminary intramolecular energy transfer studies of rigid, emissive, rhenium-linked porphyrin dimers

The reaction of pyridyl functionalized porphyrins with Re(CO)(5)Cl in THF results in the formation of porphyrin dimers which, despite incorporation of rhenium into the assemblies, remain fluorescent. The rigid compounds provide an efficient geometry and/or orbital pathway for singlet energy transfer, rendering these compounds suitable, in principle, for the study of both through-bond and through-space energy transfer. Derivatives containing both metallated and freebase porphyrins connected via the metal corners display efficient porphyrin-porphyrin energy transfer. The photophysical properties of the assemblies have been studied by both steady-state and time-resolved fluorescence techniques, yielding approximate rates and efficiencies for porphyrin-porphyrin energy transfer.     

The proton affinity of proline analogs using the kinetic method with full entropy analysis

The proton affinity of proline analogs, L-azetidine-2-carboxylic acid (Aze), L-proline (Pro), and L-pipecolic acid (Pip), have been measured using the Armentrout modification of the extended kinetic method in a quadrupole ion trap instrument. Experimental values of 223.0 +/- 1.5, 224.9 +/- 1.6, and 225.6 +/- 1.6 kcal/mol have been determined for the 298K proton affinities of Aze, Pro, and Pip respectively. High level theoretical calculations using both MP2 and B3LYP methods at a variety of basis sets were carried out in order to give theoretical predictions for the 298 K proton affinity and gas phase basicity of all three analogs. Recommended values for the gas phase basicity and proton affinity for proline based on our work and other recent determinations are 216 +/- 2 and 224 +/- 2 kcal/mol.     

Photofragment coincidence imaging of small I-(H2O)n clusters excited to the charge-transfer-to-solvent state

The photodissociation dynamics of small I-(H2O)n(n=2-5) clusters excited to their charge-transfer-to-solvent (CTTS) states have been studied using photofragment coincidence imaging. Upon excitation to the CTTS state, two photodissociation channels were observed. The major channel (approximately 90%) is a two-body process forming neutral I+(H2O)n photofragments, and the minor channel is a three-body process forming I+(H2O)n-1+H2O fragments. Both processes display translational energy [P(ET)] distributions peaking at ET=0 with little available energy partitioned into translation. Clusters excited to the detachment continuum rather than to the CTTS state display the same two channels with similar P(ET) distributions. The observation of similar P(ET) distributions from the two sets of experiments suggests that in the CTTS experiments, I atom loss occurs after autodetachment of the excited [I(H2O)n-]* cluster or, less probably, that the presence of the excess electron has little effect on the departing I atom.     

Atom transfer cyclization catalyzed by InCl3 via halogen activation

[reaction: see text] Indium trichloride was found to be an efficient catalyst for the cyclization of allylic halides and alkynes with atom transfer in methylene chloride. Mechanistic evidence supports a cationic reaction pathway with Lewis acid activation of the allylic halogen. Concomitant nucleophilic attack by the alkyne and trapping with halide led to atom transfer cyclization products. Depending on alkyne substitution, a bromine atom was transferred from the substrate or a chlorine atom was transferred from the solvent.     

Formation of silver nanoparticles at the air-water interface mediated by a monolayer of functionalized hyperbranched molecules

Nanofibrillar micellar structures formed by the amphiphilic hyperbranched molecules within a Langmuir monolayer were utilized as matter for silver nanoparticle formation from the ion-containing water subphase. We observed that silver nanoparticles were formed within the multifunctional amphiphilic hyperbranched molecules. The diameter of nanoparticles varied from 2-4 nm and was controlled by the core dimensions and the interfibrillar free surface area. Furthermore, upon addition of potassium nitrate to the subphase, the Langmuir monolayer templated the nanoparticles' formation along the nanofibrillar structures. The suggested mechanism of nanoparticle formation involves the oxidation of primary amino groups by silver catalysis facilitated by "caging" of silver ions within surface areas dominated by multibranched cores. This system provides an example of a one-step process in which hyperbranched molecules with outer alkyl tails and compressed amine-hydroxyl cores mediated the formation of stable nanoparticles placed along/among/beneath the nanofibrillar micelles.     

Supported ionic liquid catalysis investigated for hydrogenation reactions

The concept of supported ionic liquid catalysis (silc) has successfully been applied to hydrogenation reactions, which significantly reduced the required amounts of ionic liquid phase and enabled the usage of fixed-bed technology; the resulting catalysts exhibited high activity and outstanding stability.