Electrochemical Behavior of the LaF3:Eu2+/Me Interface (Me = Sm,Ce, Gd,V, Ag)

The electrochemical behavior of the LaF₃ : Eu²⁺| interface (Me = Sm, Ce, Gd, V, Ag) is studied using stripping voltammetry. Current–voltage curves for cells Ag, AgCl|KCl and KF|LaF₃ : Eu²⁺|Sm (or Ce) may be viewed as background curves for analyzing solid-phase reactions with other metallic electrodes. The substrate material is found to affect properties of interfaces LaF₃ : Eu²⁺/Gd (or V), which are characterized either by solid-phase reactions involving the fluoride ion of a solid electrolyte or by reactions involving oxygen. Regularities, obtained for silver in contact with LaF₃ : Eu²⁺, link electrochemical signals of the reaction of the silver fluoride formation with the contact area.     

Coordination geometry of chromium(VI) species. The first example of cis-bridging chromate ions in helically structured catena(μ-CrO4-O,O′)[Ni(HIm)3H2O]

Nickel(II) chromate complex with imidazole (HIm) was isolated from the [Ni²⁺–HIm–CrO₄²⁻] system in various experimental conditions, i.e. reagent molar ratios and nickel(II) salts. The catena(μ-CrO₄-O,O′)[Ni(HIm)₃H₂O] (1) crystallizes in monoclinic crystal system—space group P2₁/n with cell parameters: a=11.784(2), b=8.899(2), c=13.934(3) (Å), β=95.19(3) (°). The unit cell contains two independent helixes, left- and right-handed, stabilized by intrahelical and interhelical hydrogen bonds (HB) and π–π interactions. The cis coordination of the CrO₄²⁻ anions and the HB systems appeared to be the main determinants of the helical architecture. To the best of our knowledge the cis-chromate coordination was observed for the first time. The cis coordination causes the distortion of the nickel octahedron, which was analysed by 4 K single crystal electronic spectra with D_4h symmetry approximation (gaussian resolution and crystal field parameters). This symmetry was also confirmed with the polarised electronic spectra. The magnetic properties of the complex suggest the occurrence of weak intrachain antiferromagnetic interactions between the magnetic Ni^II center. The computational DFT studies of complex 1 assuming three possible isomers mer[(HIm)₃]–cis[(CrO₄²⁻)₂], mer–trans and fac–cis suggested that the main contribution to the stability of 1 might have interhelical and intrahelical hydrogen bonds.     

Reaction of N-Acyl-α-triphenylphosphonio-α-amino Acid Esters with Organic Bases: Mechanism of the Base-Catalyzed Nucleophilic Substitution of the Triphenylphosphonium Group

Summary.  Reactions of N-acyl-α-triphenylphosphonio-α-amino acid methyl esters with organic bases (triethylamine or DBU) were investigated as the crucial step of the base-catalyzed displacement of the triphenylphosphonium group by nucleophiles. It was proved that N-acyl-α-triphenylphosphonioglycinates are transformed to an equilibrium mixture of the corresponding N-acyliminoacetates and N-acyl-α-triphenylphosphoranylidene glycinates by bases. In the case of N-acyl-α-triphenylphosphonio-α-amino acid esters with quaternary α-carbon, the α-substituted homologues of the N-acyliminoacetates were detected to be the only primary reaction product which, however, can undergo further tautomerization to the corresponding α,β-dehydro-α-amino acid derivatives. In both these cases the reaction of N-acyl-α-triphenylphosphonio-α-amino acid esters with nucleophiles proceeds via the addition of a nucleophile to the activated C=N double bond of the N-acylimino intermediate. Corresponding author. E-mail: romanm@zeus.polsl.gliwice.pl Received October 31, 2001. Accepted (revised) December 17, 2001     

X-ray absorption studies of the local strontium environments in borosilicate waste glasses

X-ray absorption spectra were collected and analyzed to characterize the strontium environments in borosilicate glass formulations developed for the immobilization of nuclear wastes. Sr can become a major constituent in some radioactive wastes because of the use of Sr-compounds in waste pretreatment processes. Data are presented for 13 borosilicate glasses that are used to simulate the anticipated waste glass compositions, where SrO concentrations range from approximately 2 to 30 wt%. The XANES data are statistically identical for all glasses investigated, and indicate divalent strontium. The EXAFS data for both crystalline standards and glasses appear to provide information only about the inner four to six coordinating oxygens that surround Sr. The data and analyses for all glasses show that the inner coordination environments around Sr have average Sr-O distances near 2.53 Å, which are statistically invariant with respect to glass composition and to various synthesis conditions. Sr-O distances determined for the glasses are within the shorter end of the range of individual Sr-O distances in the SrCO₃ and haradaite (SrVSi₂O₇) crystalline standards.     

Antiviral Effect of Nonfunctionalized Gold Nanoparticles against Herpes Simplex Virus Type-1 (HSV-1) and Possible Contribution of Near-Field Interaction Mechanism

The antiviral activity of nonfunctionalized gold nanoparticles (AuNPs) against herpes simplex virus type-1 (HSV-1) in vitro was revealed in this study. We found that AuNPs are capable of reducing the cytopathic effect (CPE) of HSV-1 in Vero cells in a dose- and time-dependent manner when used in pretreatment mode. The demonstrated antiviral activity was within the nontoxic concentration range of AuNPs. Interestingly, we noted that nanoparticles with smaller sizes reduced the CPE of HSV-1 more effectively than larger ones. The observed phenomenon can be tentatively explained by the near-field action of nanoparticles at the virus envelope. These results show that AuNPs can be considered as potential candidates for the treatment of HSV-1 infections.     

Fast excited-state intramolecular proton transfer and subnanosecond dynamic stokes shift of time-resolved fluorescence spectra of the 5-methoxysalicylic acid/diethyl ether complex

Excited-state intramolecular proton transfer (ESIPT) occurring in the salicylic acid (SA) derivative 5-methoxysalicylic acid (5-MeOSA) in an apolar solvent (cyclohexane) and in the presence of the hydrogen bond accepting agent diethyl ether (DEE) is investigated. Analysis of the directly measured subnanosecond time-resolved emission spectra (TRES) together with conventional steady-state fluorescence and time-correlated single-photon-counting (TCSPC) decays indicates that ESIPT in this system occurs much faster than fluorescence, and that the equilibrium between normal and tautomeric excited states is established before the emission from both states takes place. However, changes in time- and frequency-resolved fluorescence of the 5-MeOSA/DEE complex are observed due to structural relaxation within the complex, which is reflected in the dynamic Stokes shift of the tautomeric fluorescence band. The normal fluorescence band of 5-MeOSA/DEE does not exhibit marked changes within the investigated time range. A single-exponential relaxation time of 460 ps was determined for the dynamic Stokes shift of the tautomeric band, and it is attributed to a geometric change within the 5-MeOSA/DEE complex upon excitation. Since both tautomeric and normal emission bands are well resolved and exhibit different time-dependent behaviors, a double-well potential appears to be adequate to describe the excited state of the system studied.     

Preparation and properties of yttrium,lanthanum and lanthanideo-nitrobenzoates

The conditions of the formation of yttrium, lanthanum and lanthanideo-nitrobenzoates were studied and their quantitative composition and solubilities in water at 298 K were determined (their solubilities are of the order of 10^–2 mol dm^–3). The IR and X-ray spectra for the obtained complexes and the dehydrated rare earth elemento-nitrobenzoates were recorded; all prepared complexes are crystalline compounds. The conditions of thermal decomposition of the complexes were also studied. It was found that on heating above 523 K the complexes decompose explosively and undergo a melting process at the same time. Therefore the thermal decomposition for complexes being studied was carried out in the temperature range 273–523 K. From the results it appears that during the dehydration process or with the increase of temperature no transformation of the nitro group to nitrito occurs.

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Darstellung und Eigenschaften von Y, La und Lanthanidenorthonitrobenzoaten

Zusammenfassung Die Bedingungen zur Darstellung von Y-, La- und Lanthanidenorthonitrobenzoaten wurden untersucht. Ihre quantitative Zusammensetzung und ihre Wasserlöslichkeit bei 298 K wurde bestimmt; die Löslichkeit ist in der Größenordnung 10^–2 mol dm^–3. Die Infrarot- und Röntgenspektren der erhaltenen Komplexe sowie der Orthonitrobenzoate der seltenen Erden nach der Dehydratisierung wurden gemessen und dabei festgestellt, daß es sich um kristalline Verbindungen handelt. Das thermische Verhalten der erhaltenen Komplexe wurde festgestellt: sie zerfallen über 523 K explosiv und schmelzen zugleich. Der thermische Zerfall der erhaltenen Orthonitrobenzoate der seltenen Erden wurde im Temperaturbereich von 273–523 K untersucht. Es wurde festgestellt, daß die Y-, La- und Lanthanidenorthonitrobenzoate bei Temperaturzunahme oder im Dehydratisierungsprozeß keiner Umgruppierung in entsprechende Nitritoverbindungen unterliegen.

     

Preparation and properties of yttrium,lanthanum and lanthanide 2,4-dinitrobenzoates

Summary The conditions of the formation of rare earth 2,4-dinitrobenzoates were studied and their quantitative composition and solubilities in water at 298 K determined (their solubilities are of the order of 10^–2 mol dm^–2). The IR and X-ray spectra for the hydrated and dehydrated complexes were recorded. All complexes are crystalline compounds. The condition of thermal decomposition of the complexes were also investigated. On heating above 573 K the complexes were found to decompose explosively and undergo a melting process at the same time. Accordingly, the thermal decomposition for the complexes was carried out in the temperature range 273–573 K. The thermal stability data reveal them to dehydrate in one step and the crystallization water molecules to be bound in various ways. From the obtained results it appears that during the dehydration process no isomerisation of the nitro group to nitrito occurs.

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Herstellung und Eigenschaften von Y-, La- und Lanthaniden-2,4-Dinitrobenzoaten

Zusammenfassung Die Bedingungen zur Darstellung von Y-, La-, und Lanthaniden-2,4-dinitrobenzoaten wurden untersucht. Ihre quantitative Zusammensetzung und ihre Wasserlöslichkeit bei 298 K wurden bestimmt (die Löslichkeit ist in der Größenordnung 10^–2 mol dm^–3). Die Infrarot- und Röntgenspektren der erhaltenen Komplexe sowie der dehydratisierten wurden gemessen und dabei festgestellt, daß es sich um kristalline Verbindungen handelt. Das thermische Verhalten der Komplexe wurde ebenfalls untersucht: sie zerfallen über 573 K explosiv und schmelzen zugleich. Der thermische Zerfall der 2,4-Dinitrobenzoate wurde im Temperaturbereich von 273–573 K untersucht. Aus der thermischen Analyse ergibt sich, daß die Komplexe und die Kristallwassermoleküle in einer Stufe dehydratisiert werden und verschiedenartig gebunden sind. Es wurde festgestellt, daß die Y-, La-, und Lanthaniden-2,4-Dinitrobenzoate bei Temperaturzunahme oder im Dehydratisierungsprozeß keiner Umgruppierung in entsprechenden Nitritoverbindungen unterliegen.

     

On the spin states of μ-oxo bridged oxomolybdenum(V) dimers. A conformational analysis by the angular overlap method

The angular overlap model has been applied for the first time in a conformational study of ground state properties of coordination compounds. The existence of several triplet ground states resulting from continuous rotations about the MoOMo axis has been demonstrated for oxygen-bridged oxomolybdenum(V) dimers.     

Inhibiting effect of beta-cyclodextrin on thymine dimerization photosensitized by para-aminobenzoic acid

Beta-cyclodextrin can act as an efficient inhibitor of the photosensitized dimerization of thymine by para-aminobenzoic acid (PABA) in aqueous solution. This can be explained by considering the formation of an inclusion complex between PABA and beta-cyclodextrin.