Diamond-related materials as potential new media in separation science

Recent progress in the development of various diamond-related materials (DRMs) has induced a strong interest in their use as a stationary phase in various separation techniques. DRMs meet many requirements for use as a stationary phase in chromatography, including excellent mechanical and chemical stability, high thermal stability, low chemical reactivity of the surface, and biocompatibility. The general physicochemical properties of diamond and the preparation of different types of DRMs are reviewed, and an overview is provided of current and possible future applications in solid-phase extraction and various separation technologies.     

Amino acids as suitable N-nucleophiles for the aza-Michael reaction of vinylphosphoryl compounds in water

Application of water as a sole solvent promotes the aza-Michael reaction of diethyl vinylphosphonate and diphenylvinylphosphine oxide with α-substituted amino acid sodium salts generated in situ to afford the corresponding β-aminophosphonates and β-aminophosphine oxides in excellent yields and of high purity. The approach is equally suitable for the synthesis of both racemic and optically active compounds. In the case of glycine, the mono and bis(phosphonoethyl)-substituted products are formed in 6:4 ratio and when using a stoichiometric amount of the reactants, N,N-bis[2-(diethoxyphosphoryl)ethyl]glycine was the only product. In contrast, to perform the double phosphonoethylation of d,l-alanine, prolonged heating of the reaction mixture was required.     

Crystal structures of lanthanide(III) complexes with cyclen derivative bearing three acetate and one methylphosphonate pendants

A series of lanthanide(III) complexes formulated as M[Ln(Hdo3ap)].xH(2)O (M = Li or H and Ln = Tb, Dy, Er, Lu, and Y) with the monophosphonate analogue of H(4)dota, 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic-10-methylphosphonic acid (H(5)do3ap), was prepared in the solid state and studied using X-ray crystallography. All of the structures show that the (Hdo3ap)(4-) anion is octadentate coordinated to a lanthanide(III) ion similarly to the other H(4)dota-like ligands, i.e., forming O(4) and N(4) planes that are parallel and have mutual angle smaller than 3 degrees . The lanthanide(III) ions lie between these planes, closer to the O(4) base than to the N(4) plane. All of the structures present the lanthanide(III) complexes in their twisted-square-antiprismatic (TSA) configuration. Twist angles of the pendants vary in the range between -24 and -30 degrees, and for each complex, they lie in a very narrow region of 1 degree. The coordinated phosphonate oxygen is located slightly above (0.02-0.19 Angstroms) the O(3) plane formed with the coordinated acetates. A water molecule was found to be coordinated only in the terbium(III) and neodymium(III) complexes. The bond distance Tb-O(w) is unusually long (2.678 Angstroms). The O-Ln-O angles decrease from 140 degrees [Nd(III)] to 121 degrees [Lu(III)], thus confirming the increasing steric crowding around the water binding site. A comparison of a number of structures of Ln(III) complexes with DOTA-like ligands shows that the TSA arrangement is flexible. On the other hand, the SA arrangement is rigid, and the derived structural parameters are almost identical for different ligands and lanthanide(III) ions.     

Vibrations in the B4 rhombic structure

A double minimum six-dimensional potential energy surface (PES) is determined in symmetry coordinates for the most stable rhombic (D2h) B4 isomer in its 1Ag electronic ground state by fitting to energies calculated ab initio. The PES exhibits a barrier to the D4h square structure of 255 cm(-1). The vibrational levels (J=0) are calculated variationally using an approach which involves the Watson kinetic energy operator expressed in normal coordinates. The pattern of about 65 vibrational levels up to 1600 cm(-1) for all stable isotopomers is analyzed. Analogous to the inversion in ammonia-like molecules, the rhombus rearrangements lead to splittings of the vibrational levels. In B4 it is the B1g (D4h) mode which distorts the square molecule to its planar rhombic form. The anharmonic fundamental vibrational transitions of 11B4 are calculated to be (splittings in parentheses): G(0)=2352(22) cm(-1), nu1(A1g)=1136(24) cm(-1), nu2(B1g)=209(144) cm(-1), nu3(B2g)=1198(19) cm(-1), nu4(B2u)=271(24) cm(-1), and nu5(Eu)=1030(166) cm(-1) (D4h notation). Their variations in all stable isotopomers were investigated. Due to the presence of strong anharmonic resonances between the B1g in-plane distortion and the B2u out-of-plane bending modes, the higher overtones and combination levels are difficult to assign unequivocally.     

Molecular dynamics in nanostructured polyimide-silica hybrid materials and their thermal stability

Molecular motion and thermal stability in two series of nanophase-separated polyimide-silica (PI-SiO₂) hybrid networks with chemically bound components were studied. The hybrids were prepared via a sol-gel process and differed in PI structure and chain length, and in SiO₂ content ranging from 10 to 50 wt.%. Differential scanning calorimetry, laser-interferometric creep rate spectroscopy, dielectric relaxation spectroscopy, thermally stimulated depolarization current techniques, and thermogravimetry were used covering, on the whole, the ranges of 100–900 K and 10⁻³-10⁹ Hz. Silica domains influenced PI dynamics in two opposite directions. Loosened segmental packing in chains confined to nanovolumes resulted mainly in rise of small-scale motion below β-relaxation region, while anchoring of chain ends to ‘rigid walls’ caused, contrarily, a partial or total suppression of segmental motion above T_β, especially drastically at the temperatures close to and within glass transition. The latter resulted in a large change in thermal stability, e.g., 2.5-fold increasing of the apparent activation energy of thermooxidative degradation, and more than 100° rise of predicted long-term thermal stability for the hybrids as compared to that for PI.     

Synthesis and reactivity of 1,2,4-triazolo[1,5-c]quinazolines

The preparation of 1,2,4-triazolo[1,5-c]quinazolines 4a-d , 5 , 8a-d by cyclocondensation of 1a-c with carboxylic acids and carboxylic anhydrides, respectively, is described. By different pathways, the 5-thioxo-5,6-dihydro-1,2,4-triazolo[1,5-c]quinazolines 4a-d react with hydrazine hydrate or amines with the formation of 5-substituted 1,2,4-triazolo[1,5-c]quinazolines 9 and 10a-d . Cyclocondensation of 9 with carboxylic acids, carboxylic anhydrides, and nitrous acid, respectively, leads to the new anellated heterocycles bis-1,2,4-triazolo[4,3-a:1,5-c]quinazoline 13 and tetrazolo [1,5-a]-1,2,4-triazolo[1,5-c]quinazoline ( 14 ).