First palladium(II) and platinum(II) complexes from employment of 2,6-diacetylpyridine dioxime: synthesis, structural and spectroscopic characterization, and biological evaluation

Employment of the monoanion of 2,6-diacetylpyridine dioxime (dapdoH(2)) as a tridentate chelate in palladium(II) and platinum(II) chemistry is reported. The syntheses, crystal structures, spectroscopic and physicochemical characterization, and biological evaluation are described of [PdCl(dapdoH)] (1) and [PtCl(dapdoH)] (2). Reaction of PdCl(2) with 2 equivs of dapdoH(2) in MeOH under reflux gave 1, whereas the same reaction with PtCl(2) in place of PdCl(2) gave 2 in comparable yields (70-80%). The divalent metal center in both compounds is coordinated by a terminal chloro group and a N,N',N"-tridentate chelating (η(3)) dapdoH(-) ligand. Thus, each metal ion is four coordinate with a distorted square planar geometry. Characterization of both complexes with (1)H and (13)C NMR and UV-vis and electrospray ionization mass spectroscopies confirmed their integrity in DMSO solutions. Interaction of the complexes with human and bovine serum albumin has been studied with fluorescence spectroscopy, revealing their affinity for these proteins with relatively high values of binding constants. UV study of the interaction of the complexes with calf-thymus DNA (CT DNA) has shown that they can bind to CT DNA, and the corresponding DNA binding constants have been evaluated. Cyclic voltammograms of the complexes in the presence of CT DNA solution have shown that the interaction of the complexes with CT DNA is mainly through intercalation, which has been also shown by DNA solution viscosity measurements. Competitive studies with ethidium bromide (EB) have revealed the ability of the complexes to displace the DNA-bound EB, suggesting competition with EB. The combined work demonstrates the ability of pyridyl-dioxime chelates not only to lead to polynuclear 3d-metal complexes with impressive structural motifs and interesting magnetic properties but also to yield new, mononuclear 4d- and 5d-metal complexes with biological implications.     

Synthesis and photophysical investigation of a series of push-pull arylvinyldiazine chromophores

A new series of push-pull arylvinyldiazines has been efficiently prepared by aldol condensation between the appropriate methyldiazine and aromatic aldehyde. The optical absorption and emission properties of these chromophores were studied in different solvents and media. These compounds act as polarity sensors with a strong positive emission solvatochromism. This behavior suggests a highly polar emitting state, which is characteristic of compounds that undergo an internal charge transfer upon excitation. These molecules also exhibit halochromic properties and are potential colorimetric and luminescence pH sensors. The second-order nonlinear properties have been investigated for some of the compounds, and large and positive μβ are obtained, in particular, for pyrimidine derivatives.     

Interaction Parameters of Anhydrous Cationic Surfactant Mixtures by Inverse Gas Chromatography

The miscibility of anhydrous cationic surfactant dodecylpyridinium chloride (DPC) and hexadecylpyridinium bromide (cetylpyridinium bromide (CPB)) mixtures has been studied by using them as stationary phases in Inverse Gas Chromatography (IGC). The temperature zone of work was determined by IGC and Differential Scanning Calorimetry (DSC) techniques. Values of the interaction parameter between the surfactants obtained at four different compositions and at four temperatures showed that the miscibility depends on the overall composition and suggested that the interactions are more favorable near the center of the composition range. Results are compared with other anhydrous cationic surfactant mixtures studied by IGC, the system didodecyldimethylammonium bromide (DDAB) and dioctadecyldimethylammonium bromide (DODAB), two twin-tailed surfactants, and are interpreted in terms of the structure of the anhydrous lamellar liquid crystals compared with that of aqueous lamellar mesophases.     

Strongly correlated barriers to rotation from parametric two-electron reduced-density-matrix methods in application to the isomerization of diazene

Recently, parameterization of the two-electron reduced density matrix (2-RDM) has made possible the determination of electronic energies with greater accuracy and lower cost than traditional electron-pair theories including coupled cluster with single and double excitations [D. A. Mazziotti, Phys. Rev. Lett. 101, 253002 (2008)]. We examine the method's performance for strongly correlated barriers to rotation; in particular, we study two distinct pathways in the isomerization of diazene (N(2)H(2)) from cis to trans: (i) a strongly correlated rotational pathway and (ii) a moderately correlated inversion pathway. While single reference wavefunction methods predict that the rotational barrier is higher than the inversional barrier, the parametric 2-RDM method predicts that the rotational barrier is lower than the inversional barrier by 3.1 kcal/mol in the extrapolated basis set limit. The parametric 2-RDM results are in agreement with those from multireference methods including multireference perturbation theory and the solution to the anti-Hermitian contracted Schro?dinger equation. We report energies, optimized structures, and natural orbital occupation numbers for three diazene minima and two transition states.     

Method for determination of methyl tert-butyl ether in gasoline by gas chromatography

A simple method for the determination of methyl tert-butyl ether (MTBE) in gasoline has been developed. The separation of MTBE from other analytes was controlled by the use of gas chromatography–mass spectrometry in the full scan mode using the characteristic primary, secondary and tertiary ions m/z 73, 57 and 43. The sample mass spectrum did not show any superimposition of other analytes. The separation from the common gasoline component 2-methylpentane was sufficient for reliable quantitation. An application of the developed conditions using gas chromatography with flame ionization detection was performed by the analysis of regular, euro super, super premium unleaded and ‘Optimax’ gasoline from petrol stations in the area of Frankfurt/Main, Germany. Regular unleaded gasoline shows an average MTBE content of 0.4% (w/w), whereas the MTBE content in euro super gasoline varies between 0.4 and 4.2% (w/w). The blending of MTBE to super premium has increased from 8.2% (w/w) in 1998 to 9.8% (w/w) on average in 1999. The recently introduced gasoline ‘Optimax’ shows an average MTBE content of 11.9% (w/w). The presented method might also be used for the analysis of other ethers, such as ethyl tert-butyl ether, which requires the use of another internal standard.     

Tailor-made derivatizing agents for carbonyl compounds using liquid chromatography

A new approach for the synthesis and application of tailor-made derivatizing agents for liquid chromatography is presented. The s-triazine ring serves as the backbone for these substances. Synthesis is performed in three steps based on substitution reactions of cyanuric chloride. A chromophor or fluorophor, a reactive group and a third moiety intended to modify the polarity of the derivatizing agent are coupled to cyanuric chloride. The three groups may be selected freely from molecules which carry functional groups which might be linked to cyanuric chloride. As an example, the synthesis and application of a respective reagent for the determination of aldehydes and ketones using HPLC with fluorescence detection is carried out. Baseline separation of the derivatives and low limits of detection (1.5×10⁻⁹ mol/l for formaldehyde, 2.0×10⁻⁹ mol/l for acetaldehyde and 3.0×10⁻⁹ mol/l for p-tolualdehyde) are obtained with the new versatile reagent.     

Polymorphism in pentacene

Pentacene, C₂₂H₁₄, crystallizes in different morphologies characterized by their d(001)‐spacings of 14.1, 14.5, 15.0 and 15.4 Å. We have studied the crystal structure of the 14.1 and 14.5 Åd‐spacing morphologies grown by vapour transport and from solution. We find a close correspondence between the 14.1 Å structure reported by Holmes, Kumaraswamy, Matzeger & Vollhardt [Chem. Eur. J. (1999), 5 , 3399–3412] and the 14.5 Å structure reported by Campbell, Monteath Robertson & Trotter [Acta Cryst. (1961), 14 , 705–711]. Single crystals commonly adopt the 14.1 Åd‐spacing morphology with an inversion centre on both mol­ecules in the unit cell. Thin films grown on SiO₂ substrates above 350 K preferentially adopt the 14.5 Åd‐spacing morphology, with a slightly smaller unit‐cell volume.     

Zeta-potential measurements of OTS-covered silica samples

We have carried out zeta-potential measurements on two different OTS (octadecyl-trichlorosilane)-covered silicas (fused silica, quartz 0001) prepared under identical conditions. Streaming current measurements on the fused silica supported OTS sample indicate a well reproducible IEP of 3.5. The major part of the study focused on the quartz 0001 supported sample with an IEP lower than that of the fused silica support and in agreement with that found in a spectroscopic study. The IEP in water (on addition of HCl) was found at around pH 3, and appeared to shift to lower values in three subsequent measurements. A final measurement after a separate series in KCl media gave the same IEP as obtained in the very first measurement, suggesting that the experiments did not significantly change the interfacial properties despite a large number of experiments. In one series of measurements care was taken to exclude any cations other than protons from the measurements, such that protons are the only counter-ions to the negative net charge. While our IEPs with the quartz support agree well with recent estimates from sum frequency generation (SFG) investigations, none of the zeta-potential vs pH curves would mimic a pattern experimentally observed in the amplitude of the “ice-like” water band between pH 3.5 and 5 in that SFG study. Furthermore, our results do not indicate any significant chloride-ion adsorption in KCl systems, but instead the shift of the IEP with increasing KCl to higher pH values rather indicates specific effects of potassium ions. Under conditions more relevant to the spectroscopic study (i.e. in absence of potassium) no specific pattern reminiscent of the SFG results was found. When tested it was found that surface conductivity was negligible.