Organolead speciation in environmental samples: a review

The speciation of organolead in some environmental samples is reviewed. Sampling, storage and pretreatment methods for water, soil, sediment and air samples are discussed before an assessment of recent developments in analytical methods.     

Fluorescence Properties of Donor–Acceptor-Substituted Pyrazoloquinolines

The photophysical properties of three newly synthesized pyrazoloquinolines, composed of N,N-dimethylaniline as donor subunit and various substituted forms of the acceptor pyrazoloquinoline (DPPQ), were investigated by absorption as well as by stationary and time resolved fluorescence spectroscopy. These compounds show generally highly efficient emission in nonpolar and medium polar solvents; the dipole moment of the emitting state increases and the quantum yield decreases with solvent polarity. These results are explained by state reversion in polar solvents: At low polarities emission originates from a state localized on the DPPQ moiety, whereas in the high-polarity regime the next excited state of charge transfer character, in which an electron is promoted from the amino nitrogen lone pair into an excited orbital of the DPPQ moiety, becomes the fluorescent state. This view is corroborated by semiempirical calculations including the solvent reaction field, low-temperature fluorescence measurements, and the observation of effects of protonation on the spectroscopic and photophysical properties.     

Intramolecular electron-transfer excited state in 6-cyanobenzquinuclidine

6-cyanobenzquinuclidine has a rigid structure with the lone-pair orbital of the amino-group nitrogen atom and the π-orbitals of the aromatic ring mutually perpendicular. It is a model for the previously postulated twisted internal charge-transfer excited states. The fluorescent singlet state was identified as a strongly polar state with a full charge separation, observed in absorption as the ¹(n, π^*) excited state. The results strongly support the twisted internal charge-transfer state hypothesis.     

Distortion of the decavanadate polyhedron and the role of hydrogen bonding in dimethylammonium decavanadate

The dimethylammonium decavanadate, [Me₂NH₂]₆[V₁₀O₂₈] · H₂O was synthesized and its crystal structure determined by X-ray diffraction. I.r. and n.i.r. spectra were also recorded. The results, compared to the reported crystal structures of decavanadates, indicate that the deformations of isolated polyhedra and their crystal lattice packing are closely related to the anion interactions both with cations and/or water (or solvent) molecules. The i.r. spectra of the relatively strongly distorted (but unprotonated) decavanadate anion are very similar to the spectrum of protonated [Me₃CNH₃]₄[H₂V₁₀O₂₈] [1], with a different distribution of hydrogen bonds. Thus the i.r. spectra of the decavanadate salts provide no evidence for protonation. In each case, the analysis of a particular decavanadate spectrum by advanced quantum chemistry calculations is needed. The near i.r. spectra of [Me₂NH₂]₆[V₁₀O₂₈] · H₂O can be helpful in gaining a better understanding of decavanadate salts structures. These results are important because of the role of decavanadate in catalysis.     

Crystal structure and physico-chemical characterization of the nitrato complexes of copper(II) with 1-ethoxymethylimidazole

Nitrato complexes of copper(II) with 1-ethoxymethyl- imiazole (L), of general formulae CuL2(NO3)2 (1) and CuL4(NO3)2 (2) have been prepared and characterized by elemental analysis and by i.r., f.i.r., vis-n.i.r. spectral evidence, conductivity, magnetochemical measurements and single crystal X-ray analysis. Compound (1) has two 1-ethoxymethylimidazole molecules and two bidentate nitrato groups in the copper(II) co-ordination sphere. In complex (2) the immediate surroundings of copper(II) is described by a tetragonally elongated octahedron with the difference the horizontal and equatorial bond lengths of 0.462 Å.     

Determination of molybdenum in environmental samples

Molecular imprinted membrane of indole-3-ethanol (IE) was prepared by hybridization of IE imprinted polymer powder and polysulfone (PSf) membrane. The IE imprinted polymer by covalent imprinting method was synthesized with copolymerization of indole-3-ethyl methacrylate (IEMA) and divinylbenzene (DVB). The cross-linked P(IEMA-co-DVB) was ground to be powders having less than 63 μm size and then hybridized within PSf membrane by using phase inversion process. The resultant imprinted powder showed binding capacities of 1.8, 7.2, 0 and 0 μmol g⁻¹ for IE, indole, 8-hydroxyquinoline and pyrrole in aqueous solution, respectively, and after hybridization with the PSf membrane, the value was 46, 26, 0 and 0 μmol g⁻¹. As a result, it was found that the IE imprinted powder alone showed non-selectively binding to the IE, but, the hybridized powder within the PSf membrane bound selectively the IE. Evidence was presented that hydrophobic interaction of the PSf matrix caused the selective and efficient binding. We also showed separation behavior of the hybrid membranes and discussed on the binding selectivity of the IE molecule. In view point of hybrid effect of the PSf membrane and the cross-linked imprinted powder, the results of the separation of these substrates were considered.     

A Novel Approach to the Synthesis of Some 2-Aryl Alkanoic Acid Esters

A novel route to the synthesis of some 2-aryl alkanoic acid esters has been achieved. Aromatic nucleophilic substitution of various arene cyclopenta-dienyliron complexes with ethyl ethylacetoacetate and ethyl methylacetoacetate produced the complexed alkanoic acid esters. Photolysis of these complexes resulted in the liberation of the free esters in good yields.     

New trends in the electrochemical sensing of dopamine

Since the early 70s electrochemistry has been used as a powerful analytical technique for monitoring electroactive species in living organisms. In particular, after extremely rapid evolution of new micro and nanotechnology it has been established as an invaluable technique ranging from experiments in vivo to measurement of exocytosis during communication between cells under in vitro conditions. This review highlights recent advances in the development of electrochemical sensors for selective sensing of one of the most important neurotransmitters—dopamine. Dopamine is an electroactive catecholamine neurotransmitter, abundant in the mammalian central nervous system, affecting both cognitive and behavioral functions of living organisms. We have not attempted to cover a large time-span nor to be comprehensive in presenting the vast literature devoted to electrochemical dopamine sensing. Instead, we have focused on the last five years, describing recent progress as well as showing some problems and directions for future development.     

HPLC analysis of kaempherol and quercetin derivatives isolated by different extraction techniques from plant matrix

Soxhlet extraction, ultrasound extraction, and accelerated solvent extraction (ASE), followed by RP-HPLC with a photodiode array detector was used for the determination of flavonoids in fruits of Peucedanum alsaticum. Three compounds were identified: a kaempherol derivative (astragalin), and two quercetin derivatives (quercitrin and hiperoside). The highest extraction yields of the selected compounds were obtained by use of exhaustive ASE.