Luminescent sol–gel materials based on lanthanide aminopolycarboxylates (Ln = Nd, Eu, Tb, Yb)

Luminescent organic–inorganic hybrid materials containing immobilized lanthanide(III) complexes (Ln = Nd, Eu, Tb, Yb) with modified ethylenediaminetetraacetic and diethylenetriaminepentaacetic acid were synthesized by sol–gel method. Obtained hybrids exhibit 4f-luminescence in the visible (Eu(III) and Tb(III)) and IR-region (Nd(III) and Yb(III)). The influence of the hybrid matrix on the lanthanide luminescence was established and it was shown, that the location of resonance level of Eu(III) is optimal for efficient energy transfer from matrix, while in the case of Tb(III) energy transfer does not occur and Tb(III) is able to absorb energy only due to its own week f–f transitions. It was also established that the inorganic matrix leads to elimination of nonradiative energy losses and increase of 4f-luminescence lifetimes. Covalent binding of Ln(III) aminopolycarboxylates in the matrix allows to consider obtained materials as promising for creation of photo- and chemically-stable luminescent sensors.     

Coordination polymers of CdII and PbII with croconate show remarkable differences in coordination patterns: a structural and spectroscopic study

The croconate dianion is a highly versatile ligand with two tautomeric forms making it useful for building large superstructures in the solid state. The single‐crystal X‐ray structures of Pb^II– and Cd^II–croconate coordination polymers, namely catena‐poly[[[diaqualead(II)]‐μ‐croconato‐κ⁴O¹,O²:O³,O⁴] monohydrate], {[Pb(C₅O₅)(H₂O)₂]·H₂O}_n, 1 , and catena‐poly[[triaquacadmium(II)]‐μ‐croconato‐κ⁴O¹,O²:O³,O⁴], [Cd(C₅O₅)(H₂O)₃]_n, 2 , have been determined. Both polymers form one‐dimensional (1D) structures; 1 is a nonplanar 1D zigzag coordination polymer extended along the crystallographic b axis, whereas 2 is a planar 1D ribbon parallel to the [101] direction. In 2 , three H₂O molecules are coordinated directly to the metal atom, while in 1 , only two H₂O molecules are directly coordinated to the metal atom. A third interstitial H₂O molecule is involved in hydrogen bonding with O atoms of the croconate ligands of an adjacent layer and other H₂O molecules, resulting in stacked double layers parallel to the [105] plane. Solid‐state FT–IR and solution UV–Vis spectra also substantiate the croconate coordination.     

Effect of support nature on the efficiency of the chemisorption preconcentration of aromatic amines from air

The effect of silica gel-modifying additives on the efficiency of the chemisorption preconcentration of aniline, o-toluidine, and N,N-dimethylaniline as 5,7-dinitrobenzofurazan derivatives from atmospheric air was studied by HPLC. The recovery exhibited a maximum on unmodified silica gel, and the recovery of N,N-dimethylaniline was lower than that of primary aromatic amines. This is likely due to a decrease in the possibility of π-complex formation between an aromatic amine and silica gel after the chemical modification of the adsorbent surface. The formation of a π-complex will increase the rate of reaction between an aromatic amine and an electrophilic reagent.     

Selective determination of 4-aminobenzoic and 4-aminosalicylic acid derivatives in mixtures by flow-injection analysis

The working conditions were found for the determination of medicinal substances anesthesin (benzocaine,I), novocaine (II), novocainamide (procainamide,III), and sodium 4-aminosalicylate (IV) as their 4,6-dinitrobenzofuroxan derivatives by flow-injection analysis with spectrophotometric detection (λ 510 nm). The best conditions were attained using a mixture of ethanol (methanol) and a buffer solution of pH 6.68 (30: 70 vol %). The analytical range for the analytes was 0.08-5.0 μg/mL. The detection limits (3σ,n = 4) were 0.04 (I), 0.05 (II), 0.07 (III), and 0.03 (IV) μg/mL. Procedures for determining 4-aminobenzoic and 4-aminosalicylic acid derivatives in pharmaceuticals containing ephedrine, atropine, dimedrol, and inorganic salts and in biological fluids (protein hydrolyzate, blood plasma, and whole blood) were developed.     

Efficiency of separating amine 5,7-dinitrobenzofurazane derivatives

The influence of eluent nature and polarity, water concentration in an aqueous-organic mixture, and its pH on the retention of 5,7-dinitrobenzofurazane derivatives of a number of aromatic amines under the conditions of RP HPLC is revealed. A procedure is developed for the separation of a mixture of six aromatic amines on a column ZORBAX SB-C18.     

Dielectric relaxations of chitosan: The effect of water on the α‐relaxation and the glass transition temperature

In this work thermal relaxations of chitosan are reported by using a novel methodology that includes subtraction of the dc conductivity contribution, the exclusion of contact and interfacial polarization effects, and obtaining a condition of minimum moisture content. When all these aspects are taken into account, two relaxations are clearly revealed in the low frequency side of the impedance data. We focus on the molecular motions in neutralized and non‐neutralized chitosan analyzed by dielectric spectroscopy in the temperature range from 25 to 250 °C. Low and high frequency relaxations were fitted with the Havriliak and Negami model in the 10^?1 to 108 Hz frequency range. For the first time, the low frequency α‐relaxation associated with the glass‐rubber transition has been detected by this technique in both chitosan forms for moisture contents in the range 0.05 to 3 wt % (ca. 18–62 °C). A strong plasticizing effect of water on this primary α‐relaxation is observed by dielectric spectroscopy and is supported by dynamic mechanical analysis measurements. In the absence of water (<0.05 wt %) the α‐relaxation is obscured in the 20–70 °C temperature range by a superposition of two low frequency relaxation processes. The activation energy for the σ‐relaxation is about 80.0–89.0 kJ/mol and for β‐relaxation is about 46.0–48.5 kJ/mol and those values are in agreement with that previously reported by other authors. The non‐neutralized chitosan possess higher ion mobility than the neutralized one as determined by the frequency location of the σ‐relaxation. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2259–2271, 2009     

Electrochemical detection in high-performance liquid chromatography of organic compounds

The selectivity and sensitivity of analytical response in electrochemical (amperometric and conductometric) detection methods in the high-performance liquid chromatography of organic compounds is discussed in comparison with other detection techniques. The importance of electrode materials of different nature for extending the range of analytes is noted. Presented at the V All-Russian Conference with the Participation of CIS Countries on Electrochemical Methods of Analysis (EMA-99), Moscow, December 6–8, 1999.     

Reaction of (chloromethyl)phosphonic(-phosphinic) iso(thio)cyanates with alcohols and (α-hydroxyalkyl)phosphonates

Alcohols and α-hydroxyphosphonates undergo the addition to (chloromethyl)phosphonic(-phosphinic) iso(thio)cyanates, yielding phosphorylated (thio)urethanes. The latter undergo cyclization to form, depending on their structure, saturated or unsaturated five-membered P,N,O,S-containing heterocycles.