New Insight on Carbon Dioxide-Mediated Hydrogen Production**

A new approach to hydrogen production from water is described. This simple method is based on carbon dioxide-mediated water decomposition under UV radiation. The water contained dissolved sodium hydroxide, and the solution was saturated with gaseous carbon dioxide. During saturation, the pH decreased from about 11.5 to 7–8. The formed bicarbonate and carbonate ions acted as scavengers for hydroxyl radicals, preventing the recombination of hydroxyl and hydrogen radicals and prioritizing hydrogen gas formation. In the presented method, not yet reported in the literature, hydrogen production is combined with carbon dioxide. For the best system with alkaline water (0.2 m NaOH) saturated with CO₂ under UV-C, the hydrogen production amounted to 0.6 μmol h⁻¹ during 24 h of radiation.     

Synthesis of unsymmetrical alkyl acetals via addition of primary alcohols to allyl ethers mediated by ruthenium complexes

Abstract  

Ru-catalyzed synthesis of mixed alkyl–alkyl acetals via addition of primary alcohols to allyl ethers has been extended to include long-chain and/or functionalized substrates. The catalytic systems for these reactions were generated from RuCl₂(PPh₃)₃ and [RuCl₂(1,5-COD)]_x and phosphines [PPh₃ or P(p-chlorophenyl)₃] or SbPh₃. Of particular importance is the almost quantitative elimination of transacetalization. The addition proceeds through allyl complexes, not via isomerization of allyl ethers––subsequent addition of ROH to vinyl ethers.     

Pentafluorophenyl Esters as Exchangeable Stoppers for the Construction of Photoactive [2]Rotaxanes

Stable pillar[5]arene-containing [2]rotaxane building blocks with pentafluorophenyl ester stoppers have been efficiently prepared on a multi-gram scale. Reaction of these building blocks with various nucleophiles gave access to a wide range of [2]rotaxanes with amide, ester or thioester stoppers in good to excellent yields. The rotaxane structure is fully preserved during these chemical transformations. Actually, the addition-elimination mechanism at work during these transformations totally prevents the unthreading of the axle moiety of the mechanically interlocked system. The stopper exchange reactions were optimized both in solution and under mechanochemical solvent-free conditions. While amide formation is more efficient in solution, the solvent-free conditions are more powerful for the transesterification reactions. Starting from a fullerene-functionalized pillar[5]arene derivative, this new strategy gave easy access to a photoactive [2]rotaxane incorporating a C₆₀ moiety and two Bodipy stoppers. Despite the absence of covalent connectivity between the Bodipy and the fullerene moieties in this photoactive molecular device, efficient through-space excited state interactions have been evidenced in this rotaxane.     

The molecular structure of the 4-nitrophenyl[bis(ethylsulfonyl)]methane and its response in the formation of the complexes with the strong organic bases

Intermolecular interactions in a synthesized C-acid, 4-nitrophenyl[bis(ethylsulfonyl)]methane have been analysed and its structure determined by X-ray diffraction. The molecular packing in the crystal is governed by CH…O. The dimensions of the hydrogen bonds and the shortest non-bonded distances are also determined. The possible implications in the formation of the hydrogen bonded complexes with the strong organic bases are also discussed.     

Numerical aspects of computing the Moore-Penrose inverse of full column rank matrices

This paper presents a comparison of certain direct algorithms for computing the Moore-Penrose inverse, for matrices of full column rank, from the point of view of numerical stability. It is proved that the algorithm using Householder QR decomposition, implemented in floating point arithmetic, is forward stable but only conditionally mixed forward-backward stable. A similar result holds also for the Classical Gram-Schmidt algorithm with reorthogonalization (CGS2). This algorithm was developed and analyzed by Abdelmalek (BIT, 11(4):354–367, 1971) and its detailed error analysis was given in Giraud et al. (Numer. Math. 101(1):87–100, 2005).     

Correction to: Foreword to the memorial issue for Professor Roberto Marassi

Journal of Solid State Electrochemistry -     

Comparative investigation of reactivity of different kinds of fly ash in alkaline media

Comparison of the influence of temperature and different alkali activators on the reactivity of two types of fly ash (conventional, fluidized) was presented. The main emphasis was put on fluidized fly ash as potential component of binding mixtures containing low amount of cement. Conventional fly ash was used as a reference. It was found that for these materials the key differences affecting products of activation are: availability of calcium and sulfate ions as well as structure of fly ash grains influencing dissolution of aluminate and silicate species. Fluidized fly ash, contrary to conventional fly ash, undergoes reaction in 0.1 M solutions of hydroxides forming mainly ettringite. In the case of 4 M hydroxides, both fly ashes undergo hydration processes. Conventional fly ash formed mainly amorphous aluminosilicate gel, while fluidized fly ash may create zeolitic products especially in the case of elevated temperature of early hydration. Sulfate and alkali ions can be incorporated into aluminosilicate structure of new formed products; however, this process depends strictly on the type of used hydroxide and its concentration. The presence of Ca(OH)₂, carbonates and alkali sulfates was also registered in the case of hydrated fluidized fly ash.

     

Lipase-catalyzed kinetic resolution approach toward enantiomerically enriched 1-(β-hydroxypropyl)indoles

In a route towards enantiomerically enriched 1-(β-hydroxypropyl)indoles, which are potentially useful building blocks for high value-added chemicals synthesis, a kinetic resolution approach by means of lipase-catalyzed enantioselective acylation as well as hydrolysis/methanolysis has been elaborated for the first time. The enzymatic resolution of chiral N-substituted indole-based sec-alcohols was successfully accomplished, yielding both enantiomeric forms of the employed derivatives with up to >99% enantiomeric purity via an enantioselective transesterification under mild reaction conditions. The most selective resolutions were obtained using fungal (CAL-B and TLL) and bacterial (PFL and BCL) lipases and vinyl acetate as the acyl?group donor. The synthetic protocol described herein is very simple, user-friendly and efficient, thus paving the way for future access towards more complex compounds of this type. The absolute configurations of novel enantiomeric derivatives, and thus stereoselectivity of the described enzymatic reactions were confirmed by application of CDA-based NMR methodology and single-crystal X-ray diffraction analysis.     

Synthesis of the four enantiomers of diethyl 1,2-di(N-Boc-amino)propylphosphonates

A simple and efficient synthetic strategy to all four enantiomerically pure diethyl 1,2-di(N-Boc-amino)propylphosphonates has been elaborated starting from the corresponding N-[(R)-(1-phenylethyl)]aziridine-(2S)- and N-[(S)-(1-phenylethyl)]aziridine-(2R)-carboxaldehydes, employing a one-pot three-components Kabachnik-Fields reaction followed by the hydrogenolytic removal of the chiral auxiliary and aziridine ring opening with simultaneous protection of the amino groups as the N-Boc derivatives.