Structural characterization of manganese and iron complexes with methylated derivatives of bis(2-pyridylmethyl)-1,2-ethanediamine reveals unanticipated conformational flexibility

Iron and manganese complexes with derivatives of bis(2-pyridylmethyl)-1,2-ethanediamine (bispicen) have previously been found to be efficient catalysts for hydrocarbon oxygenation. Methylation can potentially impact the conformation of the ligand around the metal center and the electronic character of the bound metal ion; each of these, in turn, impacts reactivity. Reported are mononuclear manganese(II) and iron(II) compounds with bispicen and five increasingly methylated derivatives. The extent and sites of methylation strongly impact the optical and electrochemical properties of the manganese and iron complexes. Increased methylation is correlated with more positive M(III/II) reduction potentials. Structural analysis of the Mn(II) series reveals two ligand conformations that have never been observed for the bispicen framework, cis-β and trans, in addition to the common cis-α conformation. (1)H NMR spectra of the structurally characterized iron compounds are consistent with mixtures of these conformers, suggesting that bispicen coordination is both more flexible and more dynamic than previously thought.     

HE(I) Photoelectron spectra of 1,2-ethanediol in the liquid and gas phases

Nine bands in the He(I) gas-phase photoelectron spectrum of 1,2-ethanediol are assigned by means of ab initio calculation and by comparison with the sp     

Markov interest rate models

A general procedure for creating Markovian interest rate models is presented. The models created by this procedure automatically fit within the HJM framework and fit the initial term structure exactly. Therefore they are arbitrage free. Because the models created by this procedure have only one state variable per factor, twoand even three-factor models can be computed efficiently, without resorting to Monte Carlo techniques. This computational efficiency makes calibration of the new models to market prices straightforward. Extended Hull- White, extended CIR, Black-Karasinski, Jamshidian's Brownian path independent models, and Flesaker and Hughston's rational log normal models are one-state variable models which fit naturally within this theoretical framework. The ‘separable’ n-factor models of Cheyette and Li, Ritchken, and Sankarasubramanian - which require n(n + 3)/2 state variables - are degenerate members of the new class of models with n(n + 3)/2 factors. The procedure is used to create a new class of one-factor models, the ‘β-η models.’ These models can match the implied volatility smiles of swaptions and caplets, and thus enable one to eliminate smile error. The β-η models are also exactly solvable in that their transition densities can be written explicitly. For these models accurate - but not exact - formulas are presented for caplet and swaption prices, and it is indicated how these closed form expressions can be used to efficiently calibrate the models to market prices.     

Bioorthogonal Cycloadditions with Sub‐Millisecond Intermediates

Tetrazine‐ and sydnone‐based click reactions have emerged as important bioconjugation strategies with fast kinetics and N₂ or CO₂ as the only byproduct. Mechanistic studies of these reactions have focused on the initial rate‐determining cycloaddition steps. The subsequent N₂ or CO₂ release from the bicyclic intermediates has been approached mainly through computational studies, which have predicted lifetimes of femtoseconds. In the present study, bioorthogonal cycloadditions involving N₂ or CO₂ extrusion have been examined experimentally at the single‐molecule level by using a protein nanoreactor. At the resolution of this approach, the reactions appeared to occur in a single step, which places an upper limit on the lifetimes of the intermediates of about 80 μs, which is consistent with the computational work.     

Protein nanopores with covalently attached molecular adapters

Molecular adapters are crucial for the stochastic sensing of organic analytes with alpha-hemolysin (alphaHL) protein nanopores when direct interactions between analytes and the pore cannot readily be arranged by conventional protein engineering. In our earlier studies, cyclodextrin adapters were lodged noncovalently within the lumen of the alphaHL pore. In the present work, we have realized the controlled covalent attachment of a beta-cyclodextrin (betaCD) adapter in the two possible molecular orientations inside alphaHL pores prepared by genetic engineering. There are two advantages to such a covalent system. First, the adapter cannot dissociate, which means there are no gaps during stochastic detection, a crucial advance for single-molecule exonuclease DNA sequencing where the continuous presence of a molecular adapter will be essential for reading individual nucleotides. Second, the ability to orient the adapter allows analytes to bind through only one of the two entrances to the betaCD cavity. We demonstrate that the covalently attached adapters can be used to alter the ion selectivity of the alphaHL pore, examine binding events at elevated temperatures, and detect analytes with prolonged dwell times.