Aqueous micro and nanoreactors based on alternating copolymers of phenylmaleimide and vinylpyrrolidone bearing pendant l‐proline stabilized with PEG grafted chains

Proline may work efficiently in water as catalyst of aldol reactions if it is hydrophobically activated. In this work, we have maximized this hydrophobic activation by the preparation of linear alternating copolymers of hydrophobic phenylmaleimide and a vinylpyrrolidone derivative bearing proline. These copolymers were water soluble above pH 5.0 and, unlike the free proline, exhibited efficient catalysis at pH 7.0. Moreover, they catalyzed and presented enantioselectivity in an aggregated form at pH 4.0 (close to the isoelectric point, IEP, of the polymer). This enantioselectivity has been related to the exclusion of water at this IEP. To control the size and stabilize the aggregates, PEG grafted copolymers were prepared by the incorporation of a PEG‐macromer (2–10 mol%), which rendered stable nano‐aggregates in water at the IEP. At this pH they catalyzed the aldol reaction in a higher rate than the non‐grafted polymer, but the enantioselectivity was decreased. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 55, 1228–1236     

Chiral bis(amino amides) as chiral solvating agents for enantiomeric excess determination of α-hydroxy and arylpropionic acids

A family of bis(amino amides) derived from natural amino acids has been synthesized and tested for the NMR enantiodiscrimination, as chiral solvating agents, for enantiomeric excess determination of some carboxylic acids. Those bis(amino amide) receptors contain different structural modifications and the splitting of the signals of the acids, after addition of the corresponding CSAs, depends on those structural variables. The influence of aminoacid side chain and the nature of the aliphatic spacer are important parameters to obtain good chiral discriminations. The results obtained clearly show the chiral recognition abilities of these bis(amino amide) ligands and suggest their advantageous use as chiral solvating agents for carboxylic acids. The binding between bis(amino amides) and carboxylic acids has been studied by ESI-MS, NMR, DSC, and molecular modeling. The data suggest that enantiodiscrimination involves the formation of an ionic pair after proton transfer from the carboxylic substrate to the bis(amino amides).     

Optimization of high-speed railway pantographs for improving pantograph-catenary contact

A crucial system for the operation of high-speed trains is the pantograph catenary interface as it is the sole responsible to deliver electrical power to the train. Being the catenary a stationary system with a long lifespan it is also less likely to be redesigned and upgraded than the pantographs that fit the train vehicles. This letter proposes an optimization procedure for the improvement of the contact quality between the pantograph and the catenary solely based on the redesign of the pantograph head suspension characteristics. A pantograph model is defined and validated against experimental dynamic characteristics of existing pantographs. An optimization strategy based on the use of a global optimization method, to find the vicinity of the optimal solution, followed by the use of a deterministic optimization algorithm, to fine tune the optimal solution, is applied here. The spring stiffness, damping characteristics and bow mass are the design variables used for the pantograph optimization. The objective of the optimal problem is the minimization of the standard deviation of the contact force history, which is the most important quantity to define the contact quality. The pantograph head suspension characteristics are allowed to vary within technological realistic limits. It is found that current high-speed railway pantographs have a limited potential for mechanical improvements, not exceeding 10%–15% on the decrease of the standard deviation of the contact force.     

Prodendronic polyamines from stable or labile methacrylates obtained by selective Michael addition onto asymmetric diacrylic compounds

A new synthetic strategy for the preparation of methacrylic monomers and polymers carrying acyl β‐amino groups is presented. The approach is based on the Michael addition of aliphatic amines onto asymmetric acrylic/methacrylic compounds, reacting the amine highly selectively with the acrylic unit while leaving the methacrylic moiety unreacted. The corresponding polymers are then obtained by conventional radical polymerization. The use of N,N,N′,N′‐tetraethyldiethylenetriamine (TEDETA) as the secondary amine leads to TEDETA moieties supported on polymeric chains. The new aminopolymers are sensitive to pH and to temperature exhibiting a lower critical solution temperature of between 50 and 90 °C. A further interesting feature of the new approach is that the stability toward hydrolysis of the side β‐amino acyl compounds was found to be dependent on whether an acrylamide or an acrylate is employed as the acrylic group of the asymmetric starting material. The esters exhibit an enhanced sensitivity to hydrolysis, compared to standard aliphatic esters, and decompose releasing a derivative of the amine precursor, within hours or weeks, depending on the pH and temperature conditions. The use of the amides leads to stable polymers when the same experimental conditions are applied. The novel dendronic polyamines have been proven to interact with DNA and to transfect cells with efficiency close to that obtained with polyethyleneimine vectors used as positive controls. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2297–2305     

Categorically perfect rings

An essential monoreflection is constructed on the category Sp of semiprirne commutative rings with identity, which is not a ring-of-quotients functor     

Controlling Electronic Events Through Rational Structural Design in Subphthalocyanine–Corrole Dyads: Synthesis,Characterization, and Photophysical Properties

Porphyrinoids are considered perfect candidates for their incorporation into electron donor–acceptor (D–A) arrays due to their remarkable optoelectronic properties and low reorganization energies. For the first time, a series of subphthalocyanine (SubPc) and corrole (Cor) were covalently connected through a short-range linkage. SubPc axial substitution strategies were employed, which allowed the synthesis of the target molecules in decent yields. In this context, a qualitative synthetic approach was performed to reverse the expected direction of the different electronic events. Consequently, in-depth absorption, fluorescence, and electrochemical assays enabled the study of electronic and photophysical properties. Charge separation was observed in cases of electron-donating Cors, whereas a quantitative energy transfer from the Cor to the SubPc was detected in the case of electron accepting Cors.     

Insights on the cellulose pretreatment at room temperature by choline-chloride-based deep eutectic solvents: an atomistic study

Cellulose - The pretreatment or disruption of a cellulose I $$\beta $$ crystallite by four deep eutectic solvents (DES): choline-chloride ethylene glycol, choline-chloride oxalic acid,...     

CMMSE: analysis and comparison of some numerical methods to solve a nonlinear fractional Gross–Pitaevskii system

Journal of Mathematical Chemistry - In this work, we introduce and theoretically analyze various computational techniques to approximate the solutions of solve a fractional extension of a double...