Bis(germyl)ketones: Toward a New Class of Type I Photoinitiating Systems Sensitive Above 500 nm?

The ability of a bis(germyl)ketone Ph₃GeCOGePh₃ to act as a photoinitiator of free radical polymerization under visible light is investigated. The results suggest that this compound could be the starting point of a new high performance class of photoinitiators. The excited state processes, as well as the generation and the reactivity of the germyl radicals, are studied by laser flash photolysis, ESR spin trapping experiments, and molecular orbital calculations; they are compared to the results obtained on a mono‐ (germyl)ketone CH₃COGePh₃. Time dependent density functional theory calculations allow discussion of the strongly red‐shifted ground state absorption of Ph₃GeCOGePh₃.

     

Patroids

A matroid M over a set E of elements is semiseparated by a partition {S¹, S²} of E iff rank E = rank S¹ + rank S² + 1. Such a semiseparation defines in each Sⁱ a pair of matroids or patroid Pⁱ = (Mⁱ, mⁱ); the two patroids P¹, P² weld to form M. The operations of removing and contracting a non-degenerate element of a matroid produce a patroid. The properties of patroids, their bases, and circuits are discussed.     

Effect of Different Electron Elastic-Scattering Cross Sections on Inelastic Mean Free Paths Obtained from Elastic-Backscattering Experiments

Inelastic mean free paths (IMFPs) of electrons with energies between 100eV and 5,000eV have been frequently obtained from measurements of elastic-backscattering probabilities for different specimen materials. A calculation of these probabilities is also required to determine IMFPs. We report calculations of elastic-backscattering probabilities for gold at energies of 100eV and 500eV with differential elastic-scattering cross sections obtained from the Thomas-Fermi-Dirac potential and the more reliable Dirac-Hartree-Fock potential. For two representative experimental configurations, the average deviation between IMFPs obtained with cross sections from the two potentials was 11.4%.     

Scanning electrochemical microscopy #54. Application to the study of heterogeneous catalytic reactions-hydrogen peroxide decomposition

A scanning electrochemical microscopy (SECM) approach for the analysis of heterogeneous catalytic reactions at solid-liquid interfaces is described and applied. In this scheme, reactant, generated at a tip, undergoes a reaction (e.g., disproportionation) at the substrate. The theoretical background for this study, performed by digital simulations using a finite difference method, considers a chemical reaction at the substrate with general stoichiometry. In this case, the fraction of regenerated mediator (nu(S)) may differ with respect to a substrate reaction that is the reverse of the tip reaction, resulting in an asymmetric mediator loop. Simulated tip current transients and approach curves at different values of the kinetic rate constant for reactions where nu(S) < 1 were used to analyze this new SECM situation. This approach was used to study the catalytic decomposition of hydrogen peroxide (HO2- --> 1/2O2 + OH-), where nu(S) = 0.5, on supported catalysts. A gold-mercury amalgam tip was used to quantitatively reduce dissolved O2 (mediator) to HO2-, which was decomposed back to oxygen at the catalyst substrate. Rate constants for the decomposition reaction on immobilized catalase and Pt particles were measured at different pH values by the correlation of experimental approach curves with the theoretical dependencies.     

Stereocartography: a computational mapping technique that can locate regions of maximum stereoinduction around chiral catalysts

A hypothesis concerning asymmetric induction by chiral catalysts is posited, tested, and found to be valid. The hypothesis states that chiral catalysts that are efficient at inducing asymmetry will have their region of maximum stereoinduction spatially congruent with the site of chemistry but inefficient catalysts will not. A simple mapping strategy (stereocartography) is used to assess where the region of maximum stereoinduction is located around a given catalyst. The protocol compares interaction energies between mirror image probes at each point in space around the catalyst being considered. The probes are models of the actual transition states of the reaction being catalyzed by a particular catalyst. The hypothesis was tested on three Diels-Alder reactions. Seventeen of the eighteen catalysts conform to the hypothesis. The idea of using this as a catalyst design tool is presented.     

A DNA‐Encoded Chemical Library Incorporating Elements of Natural Macrocycles

Here we show a seven‐step chemical synthesis of a DNA‐encoded macrocycle library (DEML) on DNA. Inspired by polyketide and mixed peptide‐polyketide natural products, the library was designed to incorporate rich backbone diversity. Achieving this diversity, however, comes at the cost of the custom synthesis of bifunctional building block libraries. This study outlines the importance of careful retrosynthetic design in DNA‐encoded libraries, while revealing areas where new DNA synthetic methods are needed.     

Vitamin D Fortification of Consumption Cow’s Milk: Health,Nutritional and Technological Aspects. A Multidisciplinary Lecture of the Recent Scientific Evidence

Vitamin D is essential in assuring bone health at all stages of life, but its non-skeletal effects are also essential: This vitamin impacts the physiology of the immune system, skeletal muscles and adipose tissue, glucose metabolism, skin, cardiovascular and reproductive systems, neuro-cognitive functions and cell division. The incidence of vitamin D deficiency is widespread worldwide, at any age, in young and healthy subjects, as well as in pregnant women and the elderly population, due to several factors, including inadequate sunlight exposure, skin pigmentation and coverage, adiposity, lifestyle and low dietary intakes. To overcome this problem, the fortification of foods that are consumed on a daily basis, such as milk, is strongly advisable. This opinion paper aims to discuss, in a multidisciplinary way, the current evidence supporting the importance of vitamin D in health and disease and the role of milk as an optimal carrier of this vitamin, to promote adequate intakes, highlighting its unique physico-chemical characteristics linked to both fat globule membrane and casein micelle structure. Moreover, it addresses the impact of industrial processing and storage of consumption milk on the stability of these structures, thus in determining vitamin D bioavailability and the achievement of adequate intakes.     

Use of specific functionalised tips with STM: a new identification method of ester groups and their molecular structure in self-assembled overlayers

The influence of chemical modification of scanning tunnelling microscopy tips on image contrast is studied. This technique is applied to the identification of an ester functional group, hardly visible otherwise. Self-assembled overlayers of wax esters [CH3-(CH2)14-CO-O-(CH2)15-CH3], adsorbed at the interface between highly oriented pyrolitic graphite and a solution of phenyloctane, are imaged. The gold tips used are chemically modified by 4-mercaptobenzoic acid and 4-mercaptotoluene. The stability of the ordered overlayers formed facilitates the reproducible set of images with submolecular resolution. This allows the identification of the layer regular structure and of other features within molecules, which can be unambiguously related to the fingerprints of the COO bond. Moreover, we are interested in finding evidence of molecular motions observed at domain boundaries.     

Novel reaction products from the hypervalent iodine oxidation of hydroxylated stilbenes and isoflavones

Novel reaction pathways for the hypervalent iodine-mediated oxidation of bioactive phenols containing extended conjugated pi-systems are described. Oxidation of 4-hydroxystilbenes in methanol using a hypervalent iodine-based oxidant led to the formal 1,2-addition of methoxy groups across the central stilbene double bond. Treatment of the structurally related 4-hydroxyisoflavone with di(trifluoroacetoxy)iodobenzene leads to the surprising formation of 2,4'-dihydroxybenzil. Potential mechanisms for these new reaction pathways are discussed, and the X-ray crystal structure of 2,4'-dihydroxybenzil is presented. In contrast, oxidation of the corresponding 3-hydroxystilbenes and 3-hydroxyisoflavone led to conventional dienone oxidation products. The antitumour implications of these oxidation processes are briefly highlighted; the novel 4-substituted phenolic oxidation products were found to be inactive in terms of in vitro antitumour cellular activity, whereas the 3-substituted phenol products gave novel agents with potent and enhanced antitumour activity in the HCT 116 cancer cell line.