Will water act as a photocatalyst for cluster phase chemical reactions? Vibrational overtone-induced dehydration reaction of methanediol

The possibility of water catalysis in the vibrational overtone-induced dehydration reaction of methanediol is investigated using ab initio dynamical simulations of small methanediol-water clusters. Quantum chemistry calculations employing clusters with one or two water molecules reveal that the barrier to dehydration is lowered by over 20 kcal/mol because of hydrogen-bonding at the transition state. Nevertheless, the simulations of the reaction dynamics following OH-stretch excitation show little catalytic effect of water and, in some cases, even show an anticatalytic effect. The quantum yield for the dehydration reaction exhibits a delayed threshold effect where reaction does not occur until the photon energy is far above the barrier energy. Unlike thermally induced reactions, it is argued that competition between reaction and the irreversible dissipation of photon energy may be expected to raise the dynamical threshold for the reaction above the transition state energy. It is concluded that quantum chemistry calculations showing barrier lowering are not sufficient to infer water catalysis in photochemical reactions, which instead require dynamical modeling.     

On an inverse problem in mixture failure rates modelling

Mixtures of decreasing failure rate (DFR) distributions are always DFR. It turns out that very often mixtures of increasing failure rate distributions can decrease or show even more complicated patterns of dependence on time. For studying this and other relevant effects two simple models of mixing with additive and multiplicative failure rates are considered. It is shown that for these models an inverse problem can be solved, which means that given an arbitrary shape of the mixture failure rate and a mixing distribution, the failure rate for a governing distribution can be uniquely obtained. Some examples are considered where this operation can be performed explicitly. Possible generalizations are discussed. Copyright © 2001 John Wiley & Sons, Ltd.     

Ink‐Jet Printing of Luminescent Ruthenium‐ and Iridium‐Containing Polymers for Applications in Light‐Emitting Devices

Summary: Defined films of luminescent ruthenium(II ) polypyridyl‐poly(methyl methacrylate) (PMMA) and iridium(III ) polypyridyl‐polystyrene (PS) copolymers could be prepared by ink‐jet printing. The copolymers were deposited on photoresist‐patterned glass substrates. Films as thin as 120 nm could be printed with a roughness of 1 to 2%. In addition, the film thickness could be varied in a controlled way through the number of droplets deposited per unit area. The topography of the ink‐jet printed films was analyzed utilizing an optical profilometer. The absorbance and emission spectra were measured using fast parallel UV‐vis and fluorescence plate reader.

Photo of the solutions of luminescent ruthenium (left) and iridium (right) containing polymers in a glass microtiter plate (top). The subsequently prepared films using ink‐jet dispensing techniques are shown below.     

Selective epoxidation of monoterpenes with H2O2 and polymer-supported methylrheniumtrioxide systems

A convenient and efficient synthesis of monoterpene epoxides by application of heterogeneous poly(4-vinylpyridine)/methyl rhenium trioxide (PVP/MTO) and polystyrene/methyl rhenium trioxide (PS/MTO) systems is described. Even highly sensitive terpenic epoxides were obtained in excellent yield. Environment friendly, easily available, and low cost H₂O₂ was used as oxidant. Catalysts were stable systems for at least five recycling experiments.     

Periodic solutions for functional-differential equations of mixed type

In this paper we study the existence of ω-periodic solutions for some functional-differential equations of mixed type. Among the main results are the averaging principle and existence theorems for some equations with homogeneous nonlinearities. We use here the coincidence degree theory of Mawhin.     

Mixed iridium(III) and ruthenium(II) polypyridyl complexes containing poly(ε‐caprolactone)‐bipyridine macroligands

A hydroxy‐functionalized bipyridine ligand was polymerized with ε‐caprolactone utilizing the controlled ring‐opening polymerization of ε‐caprolactone in the presence of stannous octoate. The resulting poly(ε‐caprolactone)‐containing bipyridine was characterized by ¹H NMR and IR spectroscopy, and gel permeation chromatography, as well as matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry, revealing the successful incorporation of the bipyridine ligand into the polymer chain. Coordination to iridium(III) and ruthenium(II) precursor complexes yielded two macroligand complexes, which were characterized by NMR, gel permeation chromatography, matrix‐assisted laser desorption/ionization time‐of‐flight MS, cyclic voltammetry, and differential scanning calorimetry. In addition, both photophysical and electrochemical properties of the metal‐containing polymers proved the formation of a trisruthenium(II) and a trisiridium(III) polypyridyl species, respectively. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4153–4160, 2004     

Experimental absolute intensities of the 4ν9 and 5ν9 O–H stretching overtones of H2SO4

This work uses cavity ring-down spectroscopy to measure two high vibrational overtones (4ν₉ and 5ν₉) of the O–H stretch in sulfuric acid. The frequencies, bandwidths, and intensities are obtained for these previously unobserved transitions. The atmospheric J-values for the overtone-induced photodissociation are calculated using the experimental cross-sections. Accurate J-values are essential for understanding the formation of the springtime polar sulfate layer by overtone-induced dehydration of H₂SO₄. The results are compared to previous experimental and theoretical studies of sulfuric acid.     

Recent Reviews. 41

Reviews are listed in order of appearance in the sources indicated. In multidisciplinary review journals, only those reviews which fall within the scope of this Journal are included. Sources are listed alphabetically in three categories: regularly issued review journals and series volumes, contributed volumes, and other monographs. Titles are numbered serially, and these numbers are used for reference in the index. Major English-language sources of critical reviews are covered. Encyclopedic treatises, annual surveys such as Specialist Periodical Reports, and compilations of symposia proceedings are omitted. This installment of Recent Reviews covers principally the early part of the 1996 literature. Previous installment: J. Org. Chem. 1996, 61(7), 2572-80. These Recent Review articles are now also available in a database form on the ACS Organic Division WWW site http://www.organic.emory.edu/acsorg/index.html.