Bis-β-(diketonates) Zn(II) complexes substituted with thiophene: Electropolymerization,homogeneous and heterogeneous catalysis for ring opening polymerization of lactide

Two Bis-β-diketonate zinc (II) complexes were synthesized using 1-(thiophen-2-yl)butane-1,3-dione and 1-(thiophen-2-yl)-3-(thiophen-3-yl)propane-1,3-dione as ligands. By electropolymerization of their thiophenyl groups, the metallopolymers deposited on FTO electrodes were obtained. The main objective was to study the reactivity of these compounds as ROP catalysts for PLA synthesis, using directly the zinc complexes (homogeneous catalysis) and also the modified electrodes with metallopolymers (heterogeneous catalysis). The homogeneous catalysis studies allowed the optimization of the polymerization conditions, such as reaction time, catalyst concentration, and the use of benzyl alcohol as cocatalyst, as well as their influence on the conversion rate, average molecular weight and polydispersity of PLA, using rac-LA and L-LA as monomers. Also, the effect on tacticity and thermal properties were discussed. Finally, the ROP studies using immersed modified electrodes in the polymerization medium were carried out under optimized experimental conditions. These tests were positive for one of the studied compounds, reaching conversions of up to 67%. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 557–567     

Nitric Acid on Silica Gel: A Useful Nitrating Reagent for Activated Aromatic Compounds

Phenols and arylmethyl ethers are rapidly mononitrated by nitric acid adsorbed in silica gel at room temperature in high yields.     

Studies on Quinones. XIX. Improved Synthesis of 2-Nitro-1,4-benzoquinone and its Reaction with Nucleophiles

Reaction of 2-nitro-1,4-benzoquinone (4), easily obtained by oxidation of 3 with MnO₂/HNO₃, with various nucleophiles affords the corresponding adducts in high yields.     

Studies on Quinones. XX. synthesis of 2-acetonylpyranonaphthoqoinones

A short and efficient synthesis of 2-acetonylpyranonaphthoquinones (13 and 14) starting from Michael adduct 5 is described.     

Effect of Confinement on Proton‐Transfer Reactions in Water Nanopools

Proton transfer from the photoacid 8‐hydroxy‐1,3,6‐pyrenetrisulfonic acid (HPTS) to water is studied in reverse micelles with ionic (AOT=sodium dioctyl sulfosuccinate) and non‐ionic (BRIJ‐30=polyoxyethylene(4)lauryl ether) surfactants. The dynamics are studied by probing the transient electronic absorption and transient vibrational absorption, both with sub‐picosecond resolution. The reverse micelle sizes range from approximately 1.6 to 5.5 nm in diameter. For both surfactants it is found that the rate of proton transfer decreases with decreasing reverse micelle size, regardless of surfactant. In addition, for AOT reverse micelles, a fraction of the photoacid molecules exhibit non‐radiative decay, preventing proton transfer.     

Influence of Ions on Aqueous Acid–Base Reactions

We study the effects of bromide salts on the rate and mechanism of the aqueous proton/deuteron‐transfer reaction between the photoacid 8‐hydroxy‐1,3,6‐pyrenetrisulfonic acid (HPTS) and the base acetate. The proton/deuteron release is triggered by exciting HPTS with 400 nm femtosecond laser pulses. Probing the electronic and vibrational resonances of the photoacid, the conjugate photobase, the hydrated proton/deuteron and the accepting base with femtosecond visible and mid‐infrared pulses monitors the proton transfer. Two reaction channels are identified: 1) direct long‐range proton transfer over hydrogen‐bonded water bridges that connect the acid and base and 2) acid dissociation to produce fully solvated protons followed by proton scavenging from solution by acetate. We observe that the addition of salt affects the long‐range reaction pathway, and reduces both the rate at which protons are released to solution by HPTS and the rate at which solvated protons are scavenged from solution by acetate. We study the dependence of these effects on the nature and concentration of the dissolved salt.     

Salmonella surveillance in Australia--created from adversity

A national scheme of Salmonella surveillance emerged in Australia as a direct result of high-profile outbreaks in 1977. A typing laboratory in Victoria put together a working model using the computer technology available at the time. The evolving information-gathering system has stood the test of time and has provided an invaluable bank of information covering isolations from humans and other sources. The databases have been used effectively in detecting trends and outbreaks and have assisted in the solution of public health problems--even extending internationally. The way in which this has been done and the lessons learned are described.     

Enantioselective total synthesis of cytotoxic taiwaniaquinones A and F

The first synthesis of cytotoxic (-)-taiwaniaquinone A and (-)-taiwaniaquinone F has been achieved through the intramolecular aldol condensation of a ketoaldehyde and the oxidative cleavage of an isopropylidene ketal.     

Adaptive pseudospectral solution of a diffuse interface model

A diffuse interface type model, using an energy-based variational formulation with a free energy that is a function of the density and its gradients is presented. All of the boundary terms are retained and related to external surface forces, which can be of particular interest when considering the fluid–fluid–solid region. The numerical solution of these types of problems can be troublesome if a thin transition layer is desired. Here, Chebyshev pseudospectral methods with mesh adaptation for the solution of diffuse interface type problems are studied. A mesh adaptation algorithm based in the equidistribution principle following a continuation process is derived. In order to achieve high precision for problems exhibiting thin transition layers, a modified version of the arc-length monitor function is proposed which yields a sufficiently smooth coordinate transformation. At every step of the continuation process, a fixed number of iterations is implemented, so that the equidistribution equations are not solved completely at each step, which saves a considerable amount of computational effort. Numerical results for the static phase field model exhibiting thin transition layers are presented.