Reversible Sorptive Preconcentration of Noble Metals Followed by FI-ICP-MS Determination.

In this paper, we propose the combined procedure of noble metal (NM) determination, including fire assay, acid digestion, and reversible dynamic sorptive preconcentration, followed by flow-injection ICP-MS. Reversible preconcentration of all NMs was carried out using micro-column packed new PVBC-VP sorbent and elution with a mixture of thiourea, potassium thiocyanate, and HCl, which recovers Pd, Ir, Pt, and Au by 95% and Ru, and Rh by 90%. The proposed procedure was approved using certified reference materials.

50 years of chiral liquid Chromatography. How it started.

The birth of modern chiral liquid chromatography can be traced back to the years 1968-71 when the first complete resolution of a racemic amino acid was obtained and presented in the literature. Extreme enantioselectivity was achieved due to the introduction of ligand exchange principle, i.e. participation of a copper ion in the solute-sorbent interactions. Simultaneously, first microporous (hypercrosslinked) polymeric matrixes were introduced, thus enhancing the chromatographic efficiency of the process.

Trace enrichment of phenylcarboxylic acids from a model biological fluid and serum of human blood.

The study was focused on the development of a solid-phase extraction protocol for seven phenylcarboxylic acids from albumin solutions by using unmodified hyper-cross-linked polystyrene restricted access materials with crosslinking degrees varying from 100 to 400% (four of the acids are known to be markers of sepsis). The breakthrough volume of the most hydrophilic 3,4-dihydroxybenzoic acid rises as the sorbent bridging extent grows. Inversely, the breakthrough volume of the most hydrophobic 3-phenylpropionic acid was found to decrease considerably when the degree of crosslinking exceeds 200%. This unusual pattern is because of the superposition of two opposite tendencies. Increasing substitution extent of phenyls facilitates their π-π-interactions with polar compounds whereas rising density of the network reduces the accessibility of sorption sites to all solutes. Mini-cartridges containing 30 mg of an optimal sorbent take up the acids completely and reversibly, the recoveries being close to 100% even in the presence of high concentrations of albumin. By coupling the developed solid-phase extraction with high-performance liquid chromatography and diode array detection technique, we managed to determine quantitatively phenylcarboxylic acids in the serum of a healthy patient blood, and the recoveries varied from 93 to 100% while the limit of quantification was (4-9) × 10-7  M.

Hypercrosslinked polymeric restricted access materials for analysis of biological fluids.

New restricted access materials based on microporous hypercrosslinked polystyrene have been developed. The materials are aimed to use as packings for solid-phase extraction cartridges to isolate low-molecular-weight analytes from biological fluids (for instance, blood plasma or serum). Two features distinguish these polymers from all known restricted access materials. The first one consists of the microporous hypercrosslinked polystyrene that not only exclude proteins from the sorbent phase but also do not adsorb them on the bead outer surface, and so they do not cause coagulation of blood protein components. Therefore, these materials do not require any chemical modification. The second distinguishing feature is the ability of hypercrosslinked sorbents to take up a wide variety of polar and nonpolar organic compounds. The sorbents were obtained in the form of beads of 60-70 µm in diameter by cross-linking styrene copolymers with 1, 2, and 3% divinylbenzene with monochlorodimethyl ether to 100, 150, and 200% cross-linking degree. The sorbents exhibit all typical properties of hypercrosslinked networks. They do not take up albumin, the major blood protein, and cytochrome C, representative of smaller protein molecules, but are capable of adsorbing drugs, vitamins, and phenyl carboxylic acids (markers of sepsis) from model aqueous solutions.

Enantiomeric-Enriched Ferrocenes: Synthesis, Chiral Resolution, and Mathematic Evaluation of CD-chiral Selector Energies with Ferrocene-Conjugates.

Enantiomeric-enriched ferrocene-modified pyrazoles were synthesized via the reaction of the ferrocene alcohol, (S)-FcCH(OH)CH3 (Fc = ferrocenyl), with various pyrazoles in acidic conditions at room temperature within several minutes. X-ray structural data for racemic (R,S)-1N-(3,5-dimethyl pyrazolyl)ethyl ferrocene (1) and its (S)-enantiomer (S)-1 were determined. A series of racemic pyrazolylalkyl ferrocenes was separated into enantiomers by analytical HPLC on ß- and γ-cyclodextrins (CD) chiral stationary phases. The quantum chemical calculations of interaction energies of ß-CD were carried out for both (R)- and (S)-enantiomers. A high correlation between experimental HPLC data and calculated interaction energies values was obtained.

Physicochemical and adsorption properties of hypercross-linked polystyrene with ultimate cross-linking density.

The paper describes unexpected properties of hypercross-linked polystyrenes with ultimate cross-linking degrees of 300, 400, and 500%, where three, four, or five methylene links, respectively, could bind each polystyrene phenyl ring to its spacious neighbors. The polymers exhibit a strong electron spin resonance signal, unusual spectra in IR, UV, and visible ranges, and they are not typical dielectrics. The nonfunctionalized hypercross-linked polymers absorb significant amounts of inorganic acids, salts, and bases due to interactions of protons or other cations with electron-donating fragments of the aromatic network with the high extent of mutual connectivity and also due to dispersion interactions of anions with the polymer matrix.

The use of phosphite-type ligands in the Ir-catalyzed asymmetric hydrogenation of heterocyclic compounds.

A series of chiral phosphite-type ligands was tested in asymmetric Ir-catalyzed hydrogenation of quinolines and 2,4,5,6-tetrahydro-1H-pyrazino(3,2,1-j,k)carbazole. Hydrogenation of quinaldine hydrochloride provided superior enantioselectivity up to 65% ee compared to quinaldine free base. The ligands were tested for the first time in the asymmetric Ir-Ircatalyzed hydrogenation of 2,4,5,6-tetrahydro-1H-pyrazino(3,2,1-j,k)carbazole yielding the antidepressant drug, pirlindole.

Paradoxes of thermodynamics of swelling equilibria of polymers in liquids and vapors.

An automatic registration of the changing size of a single spherical microbead of a cross-linked polymer was applied for studying the swelling process of the bead by the sorption of vapors and/or liquids. Many representatives of all three basic types of polymeric networks, gel-type, hypercrosslinked, and macroporous, were examined. Only the first two display large volume changes and prove suitable for following the kinetics and extent of swelling by the above dilatometric technique. The results unambiguously prove that swelling of all polymeric networks in liquids is always higher than in corresponding saturated vapors (Schroeder's paradox). The general nature of this phenomenon implies that the absolute activity of any sorbate in its liquid form is always larger than in the form of its saturated vapor. Surprisingly, gels with any solvent contents, which fall into the broad range between the vapor-equilibrated and liquid-equilibrated extreme contents, retain their volumes constant in the saturated vapor atmosphere. This paradox of a wide range of gels swollen to a different extent and, nevertheless, standing in equilibrium with saturated vapor is explained by the specificity of the network polymers, namely, that the energy of the solvent-polymer interactions is easily compensated by the energy of remaining between-chain interactions at any solvent content in the above range. Therefore, the strain-free swollen gels do not generate enhanced vapor pressure, but neither display the ability to take up more sorbate from its vapor.

Carborane complexes of ruthenium(III): studies on thermal reaction chemistry and the catalyst design for atom transfer radical polymerization of methyl methacrylate.

The heating of the 18-electron complex [3,3-(dppb)-3-H-3-Cl-closo-3,1,2-RuC(2)B(9)H(11)] (3) in benzene at 80 °C in the presence of a small amount of CCl(4) as initiator afforded paramagnetic 17-electron species [3,3-(dppb)-3-Cl-closo-3,1,2-RuC(2)B(9)H(11)] (4) along with minor amounts of two P-phenylene ortho-cycloboronated derivatives [3-Cl-3,3,8-{Ph(2)P(CH(2))(4)PPh-µ-(C(6)H(4)-ortho)}-closo-3,1,2-RuC(2)B(9)H(10)] (5) and [3,7-Cl(2)-3,3,8-{Ph(2)P(CH(2))(4)PPh-µ-(C(6)H(4)-ortho)}-closo-3,1,2-RuC(2)B(9)H(10)] (6) in total yield of ca. 80%. The heating of either 3 or 4 in toluene at 95 °C in the absence of CCl(4) led to the selective formation of 5, which was isolated in 64% and 46% yield, respectively. Thermolysis of 3 at higher temperatures (boiling toluene, 110 °C) gives novel paramagnetic species [3-Cl-3,3,7,8-{Ph(2)P(CH(2))(4)P-µ-(C(6)H(4)-ortho)(2)}-closo-3,1,2-RuC(2)B(9)H(9)] (7) featuring bis(ortho-cycloboronation) of both P-phenyl groups at the same phosphorus atom of the ruthenium-bound dppb ligand. All new paramagnetic complexes 4-7, as well as starting diamagnetic species 3, were characterized by single-crystal X-ray diffraction and, in addition, by EPR spectroscopic studies of odd-electron complexes. Ruthenacarboranes 3-5 and 7 all display high efficiency as catalysts for the atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA). Complex 5 gave the best catalyst performance in terms of polydispersity; the PDI (M(w)/M(n)) of the polymer samples is as low as 1.15.

Application of a new amidophosphite ligand to Rh-catalyzed asymmetric hydrogenation of ß-dehydroamino acid derivatives in supercritical carbon dioxide: activation effect of protic Co-solvents.

New chiral amidophosphite ligand was synthesized and tested in the Rh-catalyzed asymmetric hydrogenation of (Z)-ß-(acylamino)acrylates in protic solvents and supercritical carbon dioxide (scCO(2) ) The catalytic performance is affected greatly by the acidity of the solvents. Better enantioselectivity (up to 88% ee) was achieved in scCO(2) containing 1,1,1,3,3,3-hexafluoro-2-propanol, compared to neat protic solvents.

(S)-6-Bromo-BINOL-based phosphoramidite ligand with C(1) symmetry for enantioselective hydrogenation and allylic substitution.

(S)-6-Br-BINOL-derived phosphoramidite, a simple monodentate ligand with a stereogenic center at the phosphorus atom, was synthesized for the first time. This stereoselector generated a high level of enantioselectivity (80-95% ee) in the rhodium-catalyzed hydrogenation of alpha-dehydrocarboxylic acid esters and was also successfully employed in the asymmetric palladium-catalyzed allylic substitution of (E)-1,3-diphenylallyl acetate. The optical yield also showed significant dependence with reaction type: up to 70% ee for allylic amination, up to 75% ee for allylic sulfonylation, and up to 90% ee for allylic alkylation.

Chiral phosphites derived from carboranes: electronic effect in catalytic asymmetric hydrogenation.

A series of new fine-tunable monodentate phosphite and phosphoramidite ligands based on carboranes have been synthesized and used for asymmetric Rh-catalyzed hydrogenation of prochiral olefins with the result of up to 99.8% ee. Dependence of the enantioselectivity on the electron-withdrawing or electron-donating properties of the carboranyl substituent has been studied.

Novel P,N-bidentate phosphite ligands in asymmetric catalysis.

Results achieved by the authors in the synthesis of chiral P,N-phosphite ligands are summarized. Three groups of new chiral P,N-phosphites are discussed, namely, ligands derived from 1,1'-bi-2-naphthol, ligands possessing an acyclic phosphorus center, and P*-chiral ligands derived from (S)-2-anilinomethylpyrrolidine. An overview of complexation of the ligands with Rh(I) and Pd(II) precursors is given. Accessibility and stability of chiral phosphite ligands possessing acyclic phosphorus was analyzed for the first time along with their efficiency in terms of stereoselectivity. The title ligands are shown to be highly efficient in the Pd-catalyzed allylic alkylation (up to 85% ee) and, especially, allylic sulfonylation (up to 97% ee) reactions in certain cases outperformed all known catalytic systems.

Enantioselective ligand exchange in modern separation techniques.

As a follow-up to a series of review articles on enantioselective ligand exchange chromatography, the present contribution critically evaluates achievements in this area of active and successful research which have been reported in the scientific since 1992. Also discussed is enantioselective ligand exchange in electromigration techniques which have developed especially fruitfully during the last decade.