Formation Of Certain Products Research Articles

ELECTROCHEMICAL PHOSPHORYLATION OF TERMINAL ACETYLENES

Electrocatalytic phosphorylation of terminal acetylenes with diarylphosphine oxides in the presence of a bpyCo(BF4)2 catalyst was first implemented under electro-reducing conditions with yields up to 75%. The nature of the solvent and the background electrolyte, the presence of oxygen and water determine the formation of certain products of phosphorylation of acetylenes. The variation of the above factors was carried out in order to select optimal conditions for electrosynthesis to achieve stereo and chemoselectivity. Voltammetric studies were used to establish the redox properties of participants to optimize processes involving a cobalt catalyst.

Dynamic Covalent Chemistry as a Facile Route to Unusual Main-Group Thiolate Assemblies and Disulfide Hoops and Cages.

Dynamic Covalent Chemistry (DCC) - combining the robustness of covalent bonds with the self-correcting nature of supramolecular chemistry - facilitates the modular synthesis of complex molecular assemblies in high yields. Although numerous reactions form covalent bonds, only a small set of chemical transformations affect covalent bond formation reversibly under suitable conditions for DCC. Further progress in this area still requires the identification of dynamic motifs and greater insights into their reversibility. We have fruitfully employed DCC of both thiolate coordination to main-group elements and disulfide formation for the facile self-assembly of: (1) metal/metalloid-thiolate assemblies, and (2) purely organic cyclic and caged disulfides, thioethers, and even hydrocarbons, many of which have remained elusive by traditional stepwise synthesis yet form readily through our methods. In this Minireview, we highlight the approaches to prepare these unusual compounds and the factors inducing structural transformations or favoring the formation of certain products over others, given a set of external stimuli or reaction conditions.

10.5937/timsact8-5341 = Responsible marketing for sustainable tourism

The biggest challenge associated with the concept of sustainable tourism is its operationalisation and perception as a process to be applied through development plans, projects and ongoing activities of tour operators. The traditional approach to marketing, focused on a limited idea of maximising profit businesses, was not able to respond to a number of social and environmental requirements imposed by the concept of sustainable development. This paper discusses the ways in which marketing could play a more important role in the sustainable development of tourism. This refers to the determination of consumer needs and preferences, the formation of certain products and pricing, product information and advertising to consumers of their benefits in a sustainable manner, as well as adequate distribution channels used by businesses to deliver products to consumers. Environmental and social marketing are now being confirmed as important elements of a much broader marketing perspective. In order to develop tourism with sustainable outcomes, responsible marketing can be crucial. The concept of marketing mix for sustainable tourism was used as a starting point to explore the specific role of responsible marketing in tourism.

Quaternizing Diboranes(4): Highly Divergent Outcomes and an Inorganic Wagner–Meerwein Rearrangement

Apart from a few compounds under heavy use in organic chemistry, diboranes are relatively exotic and poorly understood. Recently, interest in these molecules has intensified with the advent of so-called "sp(2)-sp(3)" diboranes which exhibit useful reactivity toward organic substrates. In our hands, addition of Lewis bases to dihalodiorganyl diboranes(4) has previously shown some very surprising reactivity, including a substituent exchange between the boron atoms, and diboranes in which halide atoms bridge the B-B bond. Herein we have expanded the range of diborane(4) and Lewis base reaction partners, in the process uncovering three new reactivity patterns as well as some cases where mixtures are obtained. Trends are established for the preferential formation of certain products which rationalize the results based on electronic and steric effects. The substituent exchange, clearly based on an inorganic version of the well-known Wagner-Meerwein rearrangement, was also found to be an equilibrium reaction with the halide-bridged Lewis adducts on the other side.

Water formation through O2 + D pathway on cold silicate and amorphous water ice surfaces of interstellar interest

The formation of the first monolayer of water molecules on bare dust grains is of primary importance to understand the growth of the icy mantles that cover dust in the interstellar medium. In this work, we explore experimentally the formation of water molecules from O(2) + D reaction on bare silicate surfaces that simulates the grains present in the diffuse interstellar clouds at visual extinctions (A(V) < 3 mag). For comparison, we also study the formation of water molecules on surfaces covered with amorphous water ice representing the dense clouds (A(V) ≥ 3 mag). Our studies focus on the formation of water molecules in the sub-monolayer and monolayer regimes using reflection absorption infrared spectroscopy and temperature-programmed desorption techniques. We provide the fractions of the products, such as D(2)O and D(2)O(2) molecules formed on three astrophysically relevant surfaces held at 10 K (amorphous olivine-type silicate, porous amorphous water ice, and nonporous amorphous water ice). Our results showed that the formation of D(2)O molecules occurs with an efficiency of about 55%-60% on nonporous amorphous water ice and about 18% on bare silicate grains surfaces. We explain the low efficiency of D(2)O water formation on the silicate surfaces by the desorption upon formation of certain products once the reaction occurs between O(2) and D atoms on the surface. A kinetic model taking into account the chemical desorption of newly formed water supports our conclusions.

Morphological evidence for lipid peroxidation and protein glycoxidation in spinal cords from sporadic amyotrophic lateral sclerosis patients

For determining whether both the spinal cord motor neurons and glial cells are exposed to increased oxidative stress in amyotrophic lateral sclerosis (ALS), we performed an immunohistochemical investigation of end products of lipid peroxidation and protein glycoxidation in spinal cords from seven sporadic ALS patients and seven age-matched control individuals. In the ALS spinal cords, immunoreactivities for adducts of 4-hydroxy-2-nonenal-histidine and crotonaldehyde–lysine as markers of lipid peroxidation, N ϵ -(carboxymethyl)lysine as a marker of lipid peroxidation or protein glycoxidation, and pentosidine as a marker of protein glycoxidation were localized in the gray matter neuropil and almost all of the motor neurons, reactive astrocytes and microglia/macrophages, whereas none of the immunoreactivities for N ϵ -(carboxyethyl)lysine or argpyrimidine as markers of protein glycoxidation or enzymatic glycolysis, or pyrraline or imidazolone as markers of nonoxidative protein glycation were detectable. The control spinal cords displayed no significant immunoreactivities for any of these examined products. Our results indicate that in sporadic ALS, both lipid peroxidation and protein glycoxidation are enhanced in the spinal cord motor neurons and glial cells, and suggest that the formation of certain products in these abnormal reactions is implicated in motor neuron degeneration.

Identification of the products resulting from the direct effects of γ-radiation on thymidine

The products formed upon γ-irradiation of thymidine in frozen aqueous solution have been identified. These products may all be explained in terms of the fates of now well documented primary charged radical species, and our results complement well those of previous e.s.r. studies on those primary and secondary radicals. In order to probe the mechanisms of formation of the major products, we have carried out experiments using heavy isotopes, including deuterium oxide and 18O2. The radical cation undergoes both hydration, yielding the four isomers of 6-hydroxy-5,6-dihydrothymidine, and deprotonation at the methyl group to yield 5-hydroxymethyl-2′-deoxyuridine. As expected, the radical anion reacts primarily by protonation at C-6 to yield the (5R)- and (5S)- diastereoisomers of 5,6-dihydrothymidine and 5-hydroxy-5,6-dihydrothymidine. Excitation processes were shown to occur by the observation of the thymidine cyclobutane dimers. The release of significant amounts of thymine and 2-deoxy-D-ribono-1,4-lactone indicates the formation of radicals centred within the sugar moiety. The proposed role of the initial charged radicals in the formation of certain products has been supported by quantitative experiments carried out using compounds expected to be electron scavengers and electron donors with respect to thymidine. Finally, subsequent to our earlier paper on the e.s.r. identification of the radicals formed upon irradiation of thymidine bromohydrin in frozen aqueous solution, we have isolated the products formed on annealing and identified them as thymidine and 5-hydroxymethyl-2′-deoxyuridine. We discuss their mechanisms of formation.

Addendum: Radiolysis of Aqueous Glycine

At the National Institutes of Health we have been looking into some of the details of the radiolysis of aqueous glycine. We have concentrated on two aspects of the problem: first, the identification of additional products in an effort to obtain a more complete material balance; and second, the specific mechanism for the formation of certain products. Products containing basic functional groups are retained on Dowex 50-H and separated by gradient elution with HC1. Ammonia, methylamine, aspartic acid, DL-diaminosuccinic acid, and meso-a,l-diaminosuccinic acid have been previously reported. In addition, we have now identified DL-erythro-f3-hydroxyaspartic acid and DL-threo-#-hydroxyaspartic acid. On Dowex 50 these are eluted as one peak ahead of the aspartic acid, but when rechromatographed on Dowex 2-formate they are easily resolved into two peaks of approximately the same size. In neutral 1 M glycine (pH 6.3) the combined yield of these products is 0.17 molecule per 100 ev absorbed. In the pH range from 2 to 5 the yield is less, approximately 0.1 molecule per 100 ev. We can propose no mechanism for the formation of these acids, but do believe that we have ruled out one of the more obvious schemes-that is, formation as a secondary product by the addition of an electron to the carbonyl group of glyoxalic acid followed by neutralization and dimerization with the NH2CHCOOH radical. The yields in both acid and neutral solutions are independent of dose and unaffected by the addition of substantially large amounts of glyoxalic acid prior to irradiation. Organic acids not retained on Dowex 50 can be retained and separated with gradient elution on Dowex 2-formate. Acetic, formic, glyoxalic, and succinic acids have been previously reported. We have, in addition, identified glycolic acid. In 1 M neutral glycine this acid is produced with a G value of 0.08 in the absence of air and of 0.17 in the presence of air. Again, we have no mechanism for the formation of this acid, but believe that an obvious scheme-that is, the addition of an OH radical to -CH2COOH-is ruled out, since glycolic acid exhibits the same dependence on the glycine concentration as the other products studied. Another organic acid has been separated but not identified. It is produced in

Isotopic carbon as a tracer in combustion research

Several researches are described in which the solution of combustion problems has been facilitated by the use of carbon-13 and carbon-14 tracer methods. One of the widest applications is in the elucidation of the mechanism of formation of combustion products and some work is described in which the position of the isotopic carbon has been determined in the principal products formed from [2-C14] and [4-C14]-2-methyl-but-2-enes. Another use is in the determination of the most probable points of oxidative attack of fuel molecules and in this connection 2-methylpentane has been labeled specifically in all its skeletal positions and the isotopic enrichment of the final combustion products has been measured. The technique of isotopic labeling has also been applied to discover which component of a mixed fuel is responsible for the formation of a given product; thus measurement of the activity of the carbon deposits formed from samples of gasoline containing each constituent labeled in turn with carbon-14 gives quantitative information about their deposit-forming tendency. The role of additives in fuel+oxygen systems may be elucidated by labeling either the additive or the fuel. If the additive is an intermediate combustion product, the origin of certain of the other intermediate and final products may be found; some work is described in which the mechanism of formation of certain products has been investigated by addition of [1,3-C14]-acetone to isobutane+oxygen mixtures. Another example of the power of tracer techniques is their use in the determination of the actual rates of formation and consumption of intermediates (as opposed to their net rate of accumulation) even when these two processes occur concurrently and work is discussed from which it has been possible to calculate the rates of certain elementary reactions occurring during the combustion of paraffins and olefins. Determination of the rates of competing processes has also been effected by the use of fuels and additives labeled with isotopic carbon; measurement of the total isotopic concentrations in the products enables their relative rates of formation from a given labeled intermediate to be determined irrespective of their concurrent production by other routes. Finally consideration is given to possible further applications of isotopic carbon in combustion research.

Ion-Molecule Reactions

This paper is concerned with the implications of the recently noted very large specific rates of reactions between gaseous ions and molecules for the formulation of the mechanisms of reactions induced by such ionizing radiation as beta or gamma rays. It is concluded that such ion-molecule reactions play an important role in not only the formation of free radicals but also in the formation of certain products.