Mechanistic studies in the reaction of 4-phenyl-1,2,4-triazoline-3,5-dione with 2,5-dimethyl-2,4-hexadiene

Secondary isotope effect measurements of methanol adducts from the reaction of 4-phenyl-1,2,4-triazoline-3,5-dione with 2,5-dimethyl-2,4-hexadiene, support the formation of an aziridinium imide intermediate rather than an open dipolar intermediate in the rate determining step.     

Optimization of a preparative capillary gas chromatography-mass spectrometry system for the isolation and harvesting of individual polycyclic aromatic hydrocarbons

Operation parameters of a preparative capillary gas chromatography (pcGC) system were optimized to facilitate clean and efficient harvesting of individual polycyclic aromatic hydrocarbons (PAHs) for subsequent compound-specific radiocarbon analysis. For PAHs, the recommended optimized settings of the specially-designed pcGC cooled injection system (CIS) and preparative fraction collector (PFC) are: 5 s CIS solvent venting time, deactivation of CIS "stop flow" injection mode, autoinjector "fast injection" mode, 60 s CIS splitless time, 340 degrees C PFC switch temperature, and 30 degrees C (ambient) trapping temperature. These optimized conditions yielded highly reproducible, pure, and efficient pcGC harvesting of six PAHs with mass recoveries of 90-100% and purity of the isolates of 97-100%.     

Efficient isolation of polyaromatic fraction from aliphatic compounds in complex extracts using dimethylformamide-pentane partitionings

A liquid-liquid partitioning method was optimized for the rapid and quantitative separation of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) from aliphatic hydrocarbons in complex primary extracts. This technique was based on the selective extraction of PAHs and PCBs from an aliphatic solvent into dimethylformamide (DMF). Partition experiments demonstrated that the optimal performance was achieved with a DMF (5% H2O)-n-pentane binary system. The optimized application of two consecutive DMF (5% H2O)-n-pentane treatments to extracts from two different polluted sediments facilitated the elimination of alkanes and unresolved complex mixture by more than 94% while the average recoveries of spiked deuterated-PAHs and 13C labeled PCBs ranged from 84 to 94 and 75 to 96%, respectively.     

Simultaneous determination of nickel(II) and cobalt(II) by square wave adsorptive stripping voltammetry on a rotating-disc bismuth-film electrode

This works reports the use of square-wave adsorptive stripping voltammetry (SWAdSV) for the simultaneous determination of Ni(II) and Co(II) on a rotating-disc bismuth-film electrode (BFE). The metal ions in the non-deoxygenated sample were complexed with dimethylglyoxime (DMG) and the complexes were accumulated by adsorption on the surface of the BFE. The stripping step was carried out by using a square-wave potential-time voltammetric excitation signal. Electrochemical cleaning of the bismuth film was employed, enabling the same bismuth film to be used for a series of measurements. The experimental variables (choice of the working electrode substrate, the presence of oxygen, the DMG concentration, the buffer concentration, the preconcentration potential, the accumulation time, the rotation speed and the SW parameters) as well as potential interferences were investigated and the figures of merit of the methods were established. Using the selected conditions, the 3σ limits of detection were 70 ng l⁻¹ for Co(II) and 100 ng l⁻¹ for Ni(II) (for 300 s of preconcentration) and the relative standard deviations were 2.3% for Co(II) and 3.9% for Ni(II) at the 2 μg l⁻¹ level (n = 8). Finally, the method was applied to the determination of nickel and cobalt in real samples with satisfactory results.     

Synthesis, pH-dependent structural characterization, and solution behavior of aqueous aluminum and gallium citrate complexes

Reactions of Al(III) and Ga(III) with citric acid in aqueous solutions, yielded the complexes (NH(4))(5)[M(C(6)H(4)O(7))(2)].2H(2)O (M(III) = Al (1), Ga (2)) at alkaline pH, and the complexes (Cat)(4)[M(C(6)H(5)O(7))(C(6)H(4)O(7))].nH(2)O (M(III) = Al (3), Ga (4), Cat. = NH(4)(+), n = 3; M(III) = Al (5), Ga (6), Cat. = K(+), n = 4) at acidic pH. All compounds were characterized by spectroscopic (FT-IR, (1)H, (13)C, and (27)Al NMR, (13)C-MAS NMR) and X-ray techniques. Complex 1 crystallizes in space group P1, with a = 9.638(5) A, b = 9.715(5) A, c = 7.237(4) A, alpha = 90.96(1) degrees, beta = 105.72(1) degrees, gamma = 119.74(1) degrees, V = 557.1(3) A(3), and Z = 1. Complex 2 crystallizes in space group P1, with a = 9.659(6) A, b = 9.762(7) A, c = 7.258(5) A, alpha = 90.95(2) degrees, beta = 105.86(2) degrees, gamma = 119.28(1) degrees, V = 564.9(7) A(3), and Z = 1. Complex 3 crystallizes in space group I2/a, with a = 19.347(3) A, b = 9.857(1) A, c = 23.412(4) A, beta = 100.549(5) degrees, V = 4389(1) A(3), and Z = 8. Complex 4 crystallizes in space group I2/a, with a = 19.275(1) A, b = 9.9697(6) A, c = 23.476(1) A, beta = 100.694(2) degrees, V = 4432.8(5) A(3), and Z = 8. Complex 5 crystallizes in space group P1, with a = 7.316(1) A, b = 9.454(2) A, c = 9.569(2) A, alpha = 64.218(4) degrees, beta = 69.872(3) degrees, gamma = 69.985(4) degrees, V = 544.9(2) A(3), and Z = 1. Complex 6 crystallizes in space group P1, with a = 7.3242(2) A, b = 9.4363(5) A, c = 9.6435(5) A, alpha = 63.751(2) degrees, beta = 70.091(2) degrees, gamma = 69.941(2) degrees, V = 547.22(4) A(3), and Z = 1. The crystal structures of 1-6 reveal mononuclear octahedral complexes of Al(III) (or Ga(III)) bound to two citrates. Solution NMR, on both 4- and 5- species, reveals rapid intramolecular exchange of the bound and unbound terminal carboxylates. Upon dissolution in water, the complexes, through a complicated reaction cascade, transform to oligonuclear 1:1 species that, in agreement with previous studies, represent the thermodynamically stable state in solution. The data provide, for the first time, structural details of low MW, mononuclear complexes of Al(III) (or Ga(III)) with citrate that are dictated, among other factors, by pH. The properties of 1-6 may provide clues relevant to their biological association with humans.     

Antibacterial Effects of Essential Oils of Seven Medicinal-Aromatic Plants Against the Fish Pathogen Aeromonas veronii bv. sobria: To Blend or Not to Blend?

Despite progress achieved, there is limited available information about the antibacterial activity of constituents of essential oils (EOs) from different medicinal-aromatic plants (MAPs) against fish pathogens and the complex interactions of blended EOs thereof. The present study aimed to investigate possible synergistic antimicrobial effects of EOs from seven Greek MAPs with strong potential against Aeromonas veronii bv. sobria, a fish pathogen associated with aquaculture disease outbreaks. The main objective was to evaluate whether blending of these EOs can lead to increased antimicrobial activity against the specific microorganism. A total of 127 combinations of EOs were prepared and their effect on A. veronii bv. sobria growth was tested in vitro. We examined both the inhibitory and bactericidal activities of the individual EOs and compared them to those of the blended EOs. The vast majority of the investigated combinations exhibited significant synergistic and additive effects, while antagonistic effects were evident only in a few cases, such as the mixtures containing EOs from rosemary, lemon balm and pennyroyal. The combination of EOs from Greek oregano and wild carrot, as well as the combinations of those two with Spanish oregano or savoury were the most promising ones. Overall, Greek oregano, savoury and Spanish oregano EOs were the most effective ones when applied either in pure form or blended with other EOs.     

Heavy-metal-ion capture, ion-exchange, and exceptional acid stability of the open-framework chalcogenide (NH(4))(4)In(12)Se(20)

The hydrothermal synthesis of the purely inorganic open-framework indium selenide (NH(4))(4)In(12)Se(20) (1) is reported. Compound 1 exhibits a unique three-dimensional open-framework structure. The framework of 1 shows an unusual, for a chalcogenide compound, rigidity arising from the unprecedented connection mode of its building blocks. Compound 1 possesses ion exchange capacity for Cs(+), Rb(+), NH(4) (+), but it has selectivity against Na(+) and Li(+). It also showed exceptional stability in relatively concentrated hydrochloric acid. Ion exchange of 1 with hydrochloric water solutions can produce its solid acid analogue H(2)(NH(4))(2)In(12)Se(20). The maximum cation-exchange capacity of 1 was found equal to two equivalents per mol, which is consistent with an exchange mechanism taking place in the 1D-channels formed by the largest cavities. In addition, 1 can do ion-exchange with heavy-metal ions like Hg(2+), Pb(2+), and Ag(+). The capacity of 1 to clean water solutions from heavy-metal ions was preliminarily investigated and found very high. Specifically, 1 can remove 99.9 % of Hg(2+), 99.8 % of Ag(+), and 94.9 % of Pb(2+) from aqueous solutions of each of these ions. Using different synthetic conditions, we isolated compound (NH(4))(2)In(12)Se(19) (2), which also has as good an acid stability as 1, but no ion-exchange properties. Overall, this work provides new hydrothermal synthetic approaches for isolation of all-inorganic open-framework chalcogenides.     

Free-field dynamic response of an inhomogeneous half-space

In this work, elastic wave propagation in the inhomogeneous half-space is solved by an analytical approach based on plane wave decomposition in conjunction with appropriate functional transformations for the displacement vector. Specifically, free-field motions are recovered at the surface of a half-space with either quadratic or exponential type of depth-dependent material parameters. The incident wave is a time harmonic, planar pressure wave and the resulting free-field motions are obtained in closed form, first for the full-space and then for the half-space by adding the reflected waves. Parametric studies show marked differences in the results when compared against the corresponding ones for a homogeneous background. Finally, sensitivities of the free-field waves on the basic characteristics of the underlying inhomogeneous material and of the incoming wave are investigated.