Tyrosine nitration of human ERK1 introduces an intra-hydrogen bond by molecular dynamics simulations

Structural Chemistry - ERK1 is an important kinase in Ras–Raf–MEK signaling. We have recently demonstrated by mass spectrometry that Tyr210 of ERK1 can be nitrated, and the nitration...     

Complexes of acridine and 9-chloroacridine with I2: formation of unusual I6 chains through charge-transfer interactions involving amphoteric I2

Acridine and 9-chloroacridine form charge-transfer complexes with iodine in which the nitrogen-bound I2 molecule is amphoteric; one end serves as a Lewis acid to the heterocyclic donor, while the other end acts as a Lewis base to a second I2 molecule that bridges two acridine.I2 units. In the acridine derivative [(acridine.I2)2.I2, 1], the dimer has a "zigzag" conformation, while in the 9-chloroacridine derivative [(9-Cl-acridine.I2)2.I2, 2], the dimer is "C-shaped". The thermal decomposition of the two complexes is very different. Compound 1 loses one molecule of I2 to form an acridine.I2 intermediate, which has not been isolated. Further decomposition gives acridine as the form II polymorph, exclusively. Decomposition of 2 involves the loss of two molecules of I2 to form a relatively stable intermediate [(9-Cl-acridine)2.I2, 3]. Compound 3 consists of two 9-Cl-acridine molecules bridged through N...I charge-transfer interactions by a single I2 molecule. This compound represents the first known example, in which both ends of an I2 molecule form interactions in a complex that is not stabilized by the extended interactions of an infinite chain structure. The ability of the terminal iodine of an N-bound I2 to act either as an electron donor (complexes 1 and 2) or as an electron acceptor (complex 3) can be understood through a quantum mechanical analysis of the systems. Both electrostatic interactions and the overlap of frontier molecular orbitals contribute to the observed behavior.     

The prediction of isobaric phase equilibria for non-ideal multicomponent mixtures from heat of mixing data

A method for predicting isobaric binary and ternary vapor—liquid equilibrium data using only isothermal binary heat of mixing data and pure component vapor pressure data is presented. Three binary and two ternary hydrocarbon liquid mixtures were studied. The method consists of evaluating the parameters of the NRTL equation from isothermal heat of mixing data for the constituent binary pairs. These parameters are then used in the multicomponent NRTL equation to compute isobaric vapor—liquid equilibrium data for the ternary mixture. No ternary or higher order interaction terms are needed in the ternary calculations because of the nature of the NRTL equation. NRTL parameters derived from heat of mixing data at one temperature can be used to predict vapor—liquid equilibrium data at other temperatures up to the boiling temperature of the liquid mixture.For the systems studied this method predicted the composition of the vapor phase with a standard deviation ranging from 1–8% for the binary systems and from 4–12% for the ternary systems.     

Polymorphism,Halogen Bonding,and Chalcogen Bonding in the Diiodine Adducts of 1,3- and 1,4-Dithiane

Through variations in reaction solvent and stoichiometry, a series of S-diiodine adducts of 1,3- and 1,4-dithiane were isolated by direct reaction of the dithianes with molecular diiodine in solution. In the case of 1,3-dithiane, variations in reaction solvent yielded both the equatorial and the axial isomers of S-diiodo-1,3-dithiane, and their solution thermodynamics were further studied via DFT. Additionally, S,S’-bis(diiodo)-1,3-dithiane was also isolated. The 1:1 cocrystal, (1,4-dithiane)·(I₂) was further isolated, as well as a new polymorph of S,S’-bis(diiodo)-1,4-dithiane. Each structure showed significant S···I halogen and chalcogen bonding interactions. Further, the product of the diiodine-promoted oxidative addition of acetone to 1,4-dithiane, as well as two new cocrystals of 1,4-dithiane-1,4-dioxide involving hydronium, bromide, and tribromide ions, was isolated.     

The prediction of vapor-liquid equilibrium data from heat of mixing data for three non-ideal binary systems

The method of Hanks et al. was used with the heat of mixing data of McFall et al. for 1,3-butadiene + propylene, 1-butene + methyl tert.-butyl ether, and carbon disulfide + methanol to predict the vapor-liquid equilibrium behavior for these systems. The method involves curve-fitting an excess enthalpy model derived from an excess Gibbs energy model by means of the Gibbs-Helmholtz equation to the heat of mixing data, determining the adjustable parameters from this fit, and using the original excess Gibbs function equation to predict the vapor-liquid equilibrium behavior. The predicted vapor-liquid equilibrium values were compared with experimental values and good agreement was found.     

Sieve mechanism estimations for microfiltration membranes with elliptical pores

An established sieve mechanism model for microfiltration was modified to incorporate elliptical pore shapes that arise from uni-axial elongation of track-etch (TE) membranes. The particular membranes investigated were poly(ethylene teraphthalate) TE membranes with an average pore size of 0.6 μm and elongations up to 35.6%. The modified sieve theory predicts that a membrane that has undergone a 35.6% elongation allows for twice the throughput compared to the original membrane with circular pores, while maintaining the same removal ability for a solution containing 1 μm particles.     

Polymerization in liquid ammonia: Acrylate esters and vinyl thiolacetate

Methyl ethyl and n-propyl acrylates when polymerized by sodium in liquid ammonia, contain an average of one amino group per polymer chain, which is indicative of amide anion initiation and chain transfer to the solvent ammonia. Isopropyl acrylate and the higher homologs contain considerably less nitrogen than required by one amino group per chain indicative of another initiating and terminating mechanism. Three alternate mechanisms are discussed. Of these, alkoxide initiation seems to be the most plausible. Vinyl thiolacetate polymers prepared under the same conditions also contain less nitrogen than required by one amino group per chain. The polymer structure is predominantly poly(vinyl thiol) with intramolecular or intermolecular disulfide bridges. The acetate part of the molecule is concomitantly split off to form acetamide.