Basis set and method dependence in quantum theory of atoms in molecules calculations for covalent bonds

The influence of various small- and medium-size basis sets used in Hartree-Fock (HF) and density functional theory (DFT)/B3LYP calculations on results of quantum theory of atoms in molecules based (QTAIM-based) analysis of bond parameters is investigated for several single, double, and triple covalent bonds. It is shown that, in general, HF and DFT/B3LYP methods give very similar QTAIM results with respect to the basis set. The smallest 6-31G basis set and DZ-quality basis sets of Dunning type lead to poor results in comparison to those obtained by the most reliable aug-cc-pVTZ. On the contrary, 6-311++G(2df,2pd) and in a somewhat lesser extent 6-311++G(3df,3pd) basis sets give satisfactory values of QTAIM parameters. It is also demonstrated that QTAIM calculations may be sensitive for the method and basis set in the case of multiple and more polarized bonds.     

Development of zinc alkyl/air systems as radical initiators for organic reactions

This paper reports a series of comparative experiments on the activity of carbon- and oxygen-centred radical species in a model reaction of the radical addition of THF to imines mediated by a series of zinc alkyl/air reaction systems. The study strongly contradicts the notion that generally R˙ radicals are the initiating species in organic reactions mediated by R_nM/air systems, and simultaneously demonstrates that oxygen-centred radical species are the key intermediates responsible for the initiation process. In addition, a new efficient RZn(L)/air initiating system for radical organic reactions exampled by a model reaction of radical addition of THF to imines is developed. Moreover, the isolation and structural characterization of the first zinc alkylperoxide supported by a carboxylate ligand, [Zn₄(μ₃-OOtBu)₃(μ₄-O)(O₂CEt)₃]₂, as well as the novel octanuclear zinc oxo(alkoxide) aggregate with entrapped O–THF species, [Zn₄(μ₄-O)(μ₃-2-O–THF)(O₂CEt)₅]₂, provide clear mechanistic signatures for the mode of function of the RZn(O₂CR′)/air system.     

A miniaturized solid-contact potentiometric multisensor platform for determination of ionic profiles in human saliva

This paper describes a miniaturized multisensor platform (MP-ISES) consisting of electrodes: a reference one (RE) and ion-selective electrodes (ISEs) for monitoring Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl⁻, and SCN⁻ ions and pH in human saliva. Gold electrode surface was modified by deposition of two layers: electrosynthesized PEDOT:PSS forming an intermediate layer, and ion-selective membrane. The developed ISEs were characterized by a wide linear range and sensitivity consistent with the Nernst model. The entire MP-ISEs are characterized by satisfactory metrological parameters demonstrating their applicability in biomedical research, in particular in measurements concerning determination of ionic profiles of saliva. Saliva samples of 18 volunteers aged from 20 to 26 participating in a month experiment had been daily collected and investigated using the MP-ISEs assigned individually to each person. Personalized profiles of ions (ionograms) in saliva, such as Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl⁻, SCN⁻, and H⁺, were obtained.

     

Design of selective molecularly imprinted sorbent for the optimized solid‐phase extraction of S‐pramipexole from the model multicomponent sample of human urine

The objective of this article was to design the selective molecularly imprinted sorbent dedicated to the solid‐phase extraction of S‐pramipexole from the complex matrix such as human urine. For that purpose, S‐2,6‐diamino‐4,5,6,7‐tetrahydrobenzothiazole was used as the template acting as the structural analog of S‐pramipexole and five various monomers were employed in the presence of ethylene glycol dimethacrylate to produce molecularly imprinted polymers. The binding capabilities of resulted polymers revealed that the highest imprinting effect was noted for polymer prepared from the itaconic acid. The comprehensive analysis of morphology and the characterization of binding sites showed not only negligible differences in the extension of surfaces of imprinted and nonimprinted polymers but also higher heterogeneity of binding sites in the imprinted material. Comprehensive optimization of the molecularly imprinted solid‐phase extraction allowed to select the most appropriate solvents for loading, washing, and elution steps. Subsequent optimization of mass of sorbent and volumes of solvents allowed to achieve satisfactory total recoveries of S‐pramipexole from the model multicomponent real sample of human urine that equals to 91.8 ± 3.2% for imprinted sorbent with comparison to only 37.1 ± 1.1% for Oasis MCX.     

Toward the preparation of the HAuF6, HAu2F11, and HAu3F16 superacids: Theoretical study

We apply the B3LYP and QCISD theoretical methods with the 6-311++G(d,p) basis set and the LANL2DZ effective core potentials to investigate the reaction paths leading to the preparation of the HAuF₆, HAu₂F₁₁, and HAu₃F₁₆ superacids. The Gibbs free energies of deprotonation of these systems are calculated to estimate their acid strength. The thermodynamic stability of the corresponding anionic precursors ((AuF₆)^–, (Au₂F₁₁)^–, and (Au₃F₁₆)^–) and their vertical excess electron detachment energies are evaluated and discussed. The suggested route of the HAu₂F₁₁ preparation involves the F^– attachment to the Au₂F₁₀ reactant which results in the formation of the (Au₂F₁₁)^– anion whose protonation yields the HAu₂F₁₁ superacid. The suggested HAuF₆ superacid preparation route is based on a qualitatively similar scheme and involves the conversion of the AuF₅ reactant into the (AuF₆)^– anion followed by its protonation. The proposed path for the HAu₃F₁₆ superacid preparation involves the attachment of AuF₅ to HAu₂F₁₁.     

Conductance of tetraalkylammonium salts in propylene carbonate at 25°C

Conductance measurements of 12 quaternary ammonium salts in propylene carbonate (PC) have been made at 25°C. The cations were either tetramethylammonium, tetraethylammonium, or tetra-n-butylammonium, and the concentrations of salt varied from about 2×10^–4 to 5×10^–3 M. The data were analyzed by the equation of Pitts. The results showed that the benzoate, nitrobenzoate, and pentachlorophenolate salts are completely dissociated. The nitrophenolate, chlorophenolate, methylsulfonate, and nitrate salts are only slightly associated (K _A from 2.5 to 6.5), while the acetate, phenylacetate, and nitrophenolate salts display somewhat more extensive association, with ionpair association constants from 17 to 45. Limiting molar conductances for the anions were derived. The factors affecting ionic mobilities in this dipolar aprotic solvent are discussed.On leave 1973–1975 from the University of Gdask, Poland.     

Thermolytic carbonates for potential 5'-hydroxyl protection of deoxyribonucleosides

Thermolytic groups structurally related to well-studied heat-sensitive phosphate/thiophosphate protecting groups have been evaluated for 5'-hydroxyl protection of deoxyribonucleosides as carbonates and for potential use in solid-phase oligonucleotide synthesis. The spatial arrangement of selected functional groups forming an asymmetric nucleosidic 5'-O-carbonic acid ester has been designed to enable heat-induced cyclodecarbonation reactions, which would result in the release of carbon dioxide and the generation of a nucleosidic 5'-hydroxyl group. The nucleosidic 5'-O-carbonates 3-8, 10-15, and 19-21 were prepared and were isolated in yields ranging from 45 to 83%. Thermolytic deprotection of these carbonates is preferably performed in aqueous organic solvent at 90 degrees C under near neutral conditions. The rates of carbonate deprotection are dependent on the nucleophilicity of the functional group involved in the postulated cyclodecarbonation reaction and on solvent polarity. Deprotection kinetics increase according to the following order: 4 < 5 < 10 < 6 < 12 < 7 < 13 < 8 < 14 congruent with 19-21 and CCl4 < dioxane < MeCN < t-BuOH < MeCN:phosphate buffer (3:1 v/v, pH 7.0) < EtOH:phosphate buffer (1:1 v/v, pH 7.0). Complete thermolytic deprotection of carbonates 7, 8, 13, and 14 is achieved within 20 min to 2 h under optimal conditions in phosphate buffer-MeCN. The 2-(2-pyridyl)amino-1-phenylethyl and 2-[N-methyl-N-(2-pyridyl)]aminoethyl groups are particularly promising for 5'-hydroxyl protection of deoxyribonucleosides as thermolytic carbonates.     

Spectroelectrochemical identity of Prussian blue films in various electrolytes: comparison of time-derivative voltabsorptometric responses with conventional cyclic voltammetry

Using Prussian blue (PB) electrodeposited on gold-covered foil as a model system, we have demonstrated the usefulness of the time-derivative measurements of absorbance versus potential (linear potential-scan voltabsorptometry) for spectroelectrochemical characterization of thin electrochromic films. The time-derivative signals were monitored for PB at 680 and 420 nm in potassium, sodium and lithium electrolytes. Information obtained from cyclic voltabsorptometry is equivalent or complementary to that from conventional cyclic voltammetry. In the case of PB films investigated in lithium electrolyte, the voltabsorptometric time-derivative peaks are better defined than the respective voltammetric peaks. The combination of voltabsorptometry with voltammetry enables molar absorptivity and/or film loading to be determined. Also, concentration changes of differently colored mixed-valence redox centers can be monitored as a function of applied potential. Received: 16 January 1997 / Accepted: 11 March 1997