When,in the context of drug design,can a fluorine atom successfully substitute a hydroxyl group?

In this article, we deal with the question of whether a fluorine atom can substitute a hydroxyl group in such a way that will lead to a compound showing a desired biologic activity, that is, a potential new drug. It is obvious that a fluorine atom differs from a hydroxyl group, as it cannot donate hydrogen bonds. However, it can accept them. Moreover, both fluorine and oxygen are of similar size and are the most electronegative elements. Therefore, a fluorine atom is thought to be a good substitute for a hydroxyl group. However, it was shown that for conformationally labile aliphatic compounds a replacement of a hydroxyl by a fluorine increases conformational diversity, so the fluorine‐containing aliphatic molecules are present in equilibrium at room temperature as a mixture of several different conformers. In contrast, for cyclic compounds the substitution of an OH group by an F atom does not much change shape and electrostatic potential around corresponding conformers. Moreover, these compounds are present in equilibrium at room temperature in aqueous solution as a mixture of the same most favored structures. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

Arithmetic of divisibility in finite models

We prove that the finite‐model version of arithmetic with the divisibility relation is undecidable (more precisely, it has Π⁰₁‐complete set of theorems). Additionally we prove FM‐representability theorem for this class of finite models. This means that a relation R on natural numbers can be described correctly on each input on almost all finite divisibility models if and only if R is of degree ≤ 0 ′. We obtain these results by interpreting addition and multiplication on initial segments of finite models with divisibility only. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis of Monofunctionalized Silsesquioxanes (RSiMe2O)(iBu)7Si8O12 via Alkene Hydrosilylation

The research presented in this work comprehensively describes hydrosilylation of a wide spectrum of alkenes which contain one or more reactive groups with (HSiMe₂O)(iBu)₇Si₈O₁₂, in the presence of different types of catalysts. Special attention is paid to the influence of alkene, catalyst, and reaction conditions on process effectiveness and selectivity by the precise monitoring of the experiments with in situ FTIR and NMR spectroscopies. More than twenty silsesquioxanes bearing reactive groups (OH, Br, NR₂, CO, COOR, NCO, epoxy, SiR₃) commonly used in organic and polymer chemistry, were obtained, isolated and characterized by ¹H, ¹³C, ²⁹Si NMR and MALDI TOF. Importantly, in the presented syntheses, commercially available reagents and catalysts were used, meaning that the presented methods could be easily repeated, rapidly scaled up, and widely applied.     

A Spin‐Active,Electrochromic, Solvent‐Free Molecular Liquid Based on Double‐Decker Lutetium Phthalocyanine Bearing Long Branched Alkyl Chains

Synthesis and characterization of a novel, multifunctional, solvent‐free room‐temperature liquid based on alkylated double‐decker lutetium(III) phthalocyanine (Pc₂Lu) are described. Lowering of the melting point and viscosity of intrinsically solid Pc₂Lu compounds has been achieved through the attachment of flexible, bulky, and long branched‐alkyl chains, that is, thio‐2‐octyldodecyl, to the periphery of the Pc₂Lu unit. The embedded Pc₂Lu unit maintains its inherent molecular functions, such as spin‐active nature and electrochromic behavior in the liquid state. Comparison of the properties with a solid‐like Pc₂Lu derivative, functionalized with shorter alkyl chains, that is, thio‐2‐ethylhexyl, underlines the importance of the hampering effect on the π–π interactions of neighboring Pc₂Lu molecules by bulkier and longer branched‐alkyl chains. This study could possibly pave the way for novel multifunctional liquids whose spin‐activities are associated with their rheological or optoelectronic properties.     

Linear Independence of Time-Frequency Translates in $$\mathbb {R}^d$$

We establish the linear independence of time-frequency translates for functions \(f\) on \(\mathbb {R}^d\) having one-sided decay \(\lim _{x \in H,\ |x|\rightarrow \infty } |f(x)| e^{c|x| \log |x|} = 0\) for all \(c>0\), which do not vanish on an affine half-space \(H \subset \mathbb {R}^d\).     

Simultaneous speciation analysis of inorganic nitrogen with the use of ion chromatography in highly salinated environmental samples

We present the development of a method for the simultaneous determination of inorganic nitrogen species in oxidized (NO₂^–, NO₃^–) and reduced (NH₄⁺) forms using ion chromatography with diode‐array detection (205, 208, and 425 nm, respectively). The oxidized forms were determined directly after the separation in the anion exchanger, while the reduced form was determined in the column hold‐up time after derivatization with the Nessler reagent. The use of an appropriate modifier (Seignette reagent) and mobile phase (NaCl) enabled the determination of inorganic nitrogen species in highly salinated environmental samples (water, sediments). Moreover, low detection limits were obtained of 0.04 mg/L for NH₄⁺ and 0.006 and 0.005 mg/L for NO₂^– and NO₃^–, respectively. The analysis of environmental samples indicated NH₄⁺ contents of up to 1161 ± 47 mg/kg and NO₃^– of up to 148 ± 6 mg/kg for sediment samples, as well as the NH₄⁺ concentrations of up to 0.98 ± 0.10 mg/L, NO₂^– of up to 24 ± 1 mg/L and NO₃^– of up to 20 ± 1 mg/L for water samples.     

Poly(3-octylthiophene) as solid contact for ion-selective electrodes: contradictions and possibilities

The hydrophobic conductive polymer, poly(3-octylthiophene) (POT), is considered as uniquely suited to be used as an ion-to-electron transducer in solid contact (SC) ion-selective electrodes (ISEs). However, the reports on the performance characteristics of POT-based SC ISEs are quite conflicting. In this study, the potential sources of the contradicting results on the ambiguous drift and poor potential reproducibility of POT-based ISEs are compiled, and different approaches to minimize the drift and the differences in the standard potentials of POT-based SC ISEs are shown. To set the potential of the POT film, it has been loaded with a 7,7,8,8-tetracyanoquinodimethane (TCNQ/TCNQ^·?) redox couple. An approximately 1:1 TCNQ/TCNQ^·?ratio in the POT film has been achieved through potentiostatic control of the potential of the redox couple-loaded conductive polymer. It is hypothesized that once the POT film has a stable, highly reproducible redox potential, it will provide similarly stable and reproducible interfacial potentials between the POT film and the electron-conducting substrate and result in SC ISEs with excellent reproducibility and potential stability. Towards this goal, the potentials of Au, GC, and Pt electrodes with drop-cast POT film coatings were recorded in KCl solutions as a function of time. Some of the POT films were loaded with TCNQ and coated with a K⁺-selective membrane. The improvement in the potential stabilities and sensor-to-sensor reproducibility as a consequence of the incorporation of TCNQ in the POT film and the potentiostatic control of the TCNQ/TCNQ^·?ratio is reported.