Axial and Equatorial Hydrogen Bonds in the Tetrahydropyran⋅⋅⋅HCl Dimer

Two hydrogen-bond complexes formed between tetrahydropyran and hydrogen chloride have been observed by using a molecular beam Fourier transform microwave spectrometer. The rotation constants are consistent with C_s symmetry, with HCl pointing to the domain of the axial and equatorial lone pair at the oxygen atom (shown on the left and right, respectively). The axial form has been found to be the more stable one.     

The C-F⋅⋅⋅H-C “Anti-Hydrogen Bond” in the Gas Phase: Microwave Structure of the Difluoromethane Dimer

A shortening of the C−H bond lengths and a blue shift of the C−H stretching frequencies for the C-F⋅⋅⋅H-C groups indicates that anti-hydrogen bonds are present the difluoromethane dimer. The most stable conformer has three such interactions (shown schematically).     

A Photochemical Switch for Controlling Protein–Protein Interactions

Incorporation of an unnatural amino acid containing a photolabile group in the side chain allows specific interactions between two proteins to be prevented. The photocaged ras protein in which Asp 38 has been substituted by its β-nitrobenzyl ester (Nb) is unable to interact with its effector protein p120–GAP (see drawing below) although it has the same intrinsic GTPase activity. After photocleavage of the Nb group, 50% of the p120–GAP-dependent GTPase activity relative to the wild-type protein is restored.     

Unexpected Antioxidant Efficiency of Chlorogenic Acid Phenolipids in Fish Oil-in-Water Nanoemulsions: An Example of How Relatively Low Interfacial Concentrations Can Make Antioxidants to Be Inefficient

Selecting effective antioxidants is challenging since their efficiency in inhibiting lipid oxidation depends on the rate constants of the chemical reactions involved and their concentration at the reaction site, i.e., at the interfacial region. Accumulation of antioxidants at the interface of emulsions is key to modulate their efficiency in inhibiting lipid oxidation but its control was not well understood, especially in emulsions. It can be optimized by modifying the physicochemical properties of antioxidants or the environmental conditions. In this work, we analyze the effects of surfactant concentration, droplet size, and oil to water ratio on the effective interfacial concentration of a set of chlorogenic acid (CGA) esters in fish oil-in-water (O/W) emulsions and nanoemulsions and on their antioxidant efficiency. A well-established pseudophase kinetic model is used to determine in the intact emulsified systems the effective concentrations of the antioxidants (AOs). The relative oxidative stability of the emulsions is assessed by monitoring the formation of primary oxidation products with time. Results show that the concentration of all AOs at the interfacial region is much higher (20–90 fold) than the stoichiometric one but is much lower than those of other phenolipid series such as caffeic or hydroxytyrosol derivatives. The main parameter controlling the interfacial concentration of antioxidants is the surfactant volume fraction, Φ_I, followed by the O/W ratio. Changes in the droplet sizes (emulsions and nanoemulsions) have no influence on the interfacial concentrations. Despite the high radical scavenging capacity of CGA derivatives and their being concentrated at the interfacial region, the investigated AOs do not show a significant effect in inhibiting lipid oxidation in contrast with what is observed using other series of homologous antioxidants with similar reactivity. Results are tentatively interpreted in terms of the relatively low interfacial concentrations of the antioxidants, which may not be high enough to make the rate of the inhibition reaction faster than the rate of radical propagation.     

Third Order Iterative Methods Without Using Second Fréchet Derivative

A modification of classical third order methods is proposed. The main advantage of these methods is they do not need evaluate any second order Frechet derivative. A convergence theorem in Banach spaces is analyzed. Finally, some preliminary numerical results are presented.     

Growth and optical characteristics of Ce-doped and Ce : Na-codoped BaLiF3 single crystals

Ce-doped and Ce : Na-codoped BaLiF₃ single crystals were grown by the Czochralski technique under reactive atmosphere. Na⁺-ions, used as a charge-compensating impurity, compete with Ce³⁺-ions for Ba²⁺ sites in the host, reducing the Ce³⁺ incorporation and degrading the mechanical integrity of crystals. Ce-doped BaLiF₃ showed potential for UV tunable lasers.     

Polymerization of acrylamide photoinitiated by tris(2,2′‐bipyridine)ruthenium(II)–amine in aqueous solution: Effect of the amine structure

The photopolymerization of acrylamide (AA) initiated by the metallic complex tris(2,2′‐bipyridine)ruthenium(II) [Ru(bpy)₃⁺²] in the presence of aliphatic and aromatic amines as co‐initiators was investigated in aqueous solution. Aromatic amines, which are good quenchers of the emission of the metal‐to‐ligand‐charge‐transfer excited state of the complex, are more effective co‐initiators than those that do not quench the luminescence of Ru(bpy)₃⁺², such as aliphatic amines and aniline. Laser‐flash photolysis experiments show the presence of the reduced form of the complex, Ru(bpy)₃⁺¹, for all the amines investigated. For aliphatic amines, the yield of Ru(bpy)₃⁺¹ increases with temperature, and on the basis of these experiments, a metal‐centered excited state is proposed as the reactive intermediate in the reaction with these amines. The decay of the transient Ru(bpy)₃⁺¹ is faster in the presence of AA. This may be understood by an electron‐transfer process from Ru(bpy)₃⁺¹ to AA, regenerating Ru(bpy)₃⁺² and producing the radical anion of AA. It is proposed that this radical anion protonates in a fast process to give the neutral AA radical, initiating in this way the polymerization chain. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4265–4273, 2001     

Modeling and Smoothing Unequally Spaced Sequence Data

The application of the continuous state space model to unequally spaced sequence data is discussed and illustrated. The continuous model implies a discrete model for the observed data. Practical expressions for relevant discrete model quantities are given. These quantities are required for the digital processing of the data and in particular for the application of the Kalman and smoothing filter and related calculations. Applications illustrate the procedures.