Type V deep eutectic solvents: Design and applications

Type V deep eutectic solvents are a novel class of sustainable solvents. They are prepared by physically mixing solid, non-ionic components and are characterized by strong negative deviations from thermodynamic ideality. This work provides guidelines for the rational design of these solvents and reviews some of their recent applications. Emphasis is given on the choice of hydrogen bond donors and acceptors to achieve the necessary liquid phase non-ideality, namely on the use of pairs of molecules with high polarity asymmetry, and stresses the importance of assessing their solid–liquid phase diagrams. Polymorphism and cocrystal formation are also briefly addressed, together with predictive methodologies that have been developed to estimate their properties.     

Block preconditioners for linear systems arising from multiscale collocation with compactly supported RBFs

Symmetric collocation methods with RBFs allow approximation of the solution of a partial differential equation, even if the right‐hand side is only known at scattered data points, without needing to generate a grid. However, the benefit of a guaranteed symmetric positive definite block system comes at a high computational cost. This cost can be alleviated somewhat by considering compactly supported RBFs and a multiscale technique. But the condition number and sparsity will still deteriorate with the number of data points. Therefore, we study certain block diagonal and triangular preconditioners. We investigate ideal preconditioners and determine the spectra of the preconditioned matrices before proposing more practical preconditioners based on a restricted additive Schwarz method with coarse grid correction. Numerical results verify the effectiveness of the preconditioners. Copyright © 2015 John Wiley & Sons, Ltd.     

Feedback control in a collective flashing ratchet

An ensemble of Brownian particles in a feedback controlled flashing ratchet is studied. The ratchet potential is switched on and off depending on the position of the particles, with the aim of maximizing the current. We study in detail a protocol which maximizes the instant velocity of the center of mass of the ensemble at any time. This protocol is optimal for one particle and performs better than any periodic flashing for ensembles of moderate size, but is defeated by a random or periodic switching for large ensembles.     

Collective decision making and paradoxical games

We study an ensemble of individuals playing the two games of the so-called Parrondo paradox. In our study, players are allowed to choose the game to be played by the whole ensemble in each turn. The choice cannot conform to the preferences of all the players and, consequently, they face a simple frustration phenomenon that requires some strategy to make a collective decision. We consider several such strategies and analyze how fluctuations can be used to improve the performance of the system.     

Characterization of distributivity in a solid

We give a characterization of the validity of the distributive law in a solid. There exists equivalence between the characterization and the modified axiom of distributivity valid in a solid.     

Simultaneous quantification of tramadol and O‐desmethyltramadol in hair samples by gas chromatography–electron impact/mass spectrometry

Over recent years, hair has become the ideal matrix for retrospective investigation of chronic abuse, including for tramadol. However, in order to exclude the possibility of external contamination, it is also important to quantify simultaneously its main metabolite, O‐desmethyltramadol (M1), which presence in hair reflects systemic exposure. In the present study a methodology aimed at the simultaneous quantification of tramadol and M1 in human hair was developed and validated for the first time. After decontamination of hair samples (60 mg), tramadol and M1 were extracted with methanol in an ultrasonic bath (~5 h). Purification was performed by solid‐phase extraction using mixed‐mode extraction cartridges. Subsequently to derivatization, analysis was performed by gas chromatography–electron impact/mass spectrometry (GC‐EI/MS). The method proved to be selective. The regression analysis for both analytes was shown to be linear in the range of 0.1–20.0 ng/mg with correlation coefficients of 0.9995 and 0.9997 for tramadol and M1, respectively. The coefficients of variation oscillated between 3.85 and 13.24%. The limits of detection were 0.03 and 0.02 ng/mg, and the lower limits of quantification were 0.08 and 0.06 ng/mg for tramadol and M1, respectively. The proof of applicability was performed in hair samples from six patients undergoing tramadol therapy. All samples were positive for tramadol and M1. Copyright © 2013 John Wiley & Sons, Ltd.     

Membrane‐permeable Triphosphate Prodrugs of Nucleoside Analogues

The metabolic conversion of nucleoside analogues into their triphosphates often proceeds insufficiently. Rate‐limitations can be at the mono‐, but also at the di‐ and triphosphorylation steps. We developed a nucleoside triphosphate (NTP) delivery system (TriPPPro‐approach). In this approach, NTPs are masked by two bioreversible units at the γ‐phosphate. Using a procedure involving H‐phosphonate chemistry, a series of derivatives bearing approved, as well as potentially antivirally active, nucleoside analogues was synthesized. The enzyme‐triggered delivery of NTPs was demonstrated by pig liver esterase, in human T‐lymphocyte cell extracts and by a polymerase chain reaction using a prodrug of thymidine triphosphate. The TriPPPro‐compounds of some HIV‐inactive nucleoside analogues showed marked anti‐HIV activity. For cellular uptake studies, a fluorescent TriPPPro‐compound was prepared that delivered the triphosphorylated metabolite to intact CEM cells.