Polarographic analysis for corticosteroids: Part 4. Determination of Corticosteroids in Multicomponent and Complex Pharmaceutical Preparations

Differential pulse polarographic methods for determination of corticosteroids in multicomponent and complex pharmaceutical preparations are described. The influence of other reducible common components of such preparations and excipients on the height of the reduction peaks of corticosteroids and the accuracy of the results was investigated, as well as the interference of excipients by adsorption processes at the electrode or at solid particles of the preparations. In the procedures developed, variations in composition of the supporting electrolyte according to the lipophilicity of the preparation, and the use of standard additions, produce results quickly and reliably. Standard deviations vary from 0.8 to 2.8%.     

Photophysical properties of borondipyrromethene analogues in solution

The photophysical properties of seven new 8-(p-substituted)phenyl analogues of 4,4-difluoro-3,5-dimethyl-8-(aryl)-4-bora-3a,4a-diaza-s-indacene (derivatives of the well-known fluorophore BODIPY) in several solvents have been studied by means of absorption and steady-state and time-resolved fluorimetry. For each compound, the fluorescence quantum yield and lifetime are lower in solvents with higher polarity owing to an increase in the rate of nonradiative deactivation. Increasing the electron withdrawing strength of the p-substituent on the phenyl group in position 8 also leads to lower fluorescence quantum yields and lifetimes. When the p-substituent on the phenyl group in position 8 is a tertiary amine [8-(4-piperidinophenyl), 8-(4-N,N-dimethylaminophenyl), and 8-(4-morpholinophenyl)], the low quantum yields of these compounds in more polar solvents can be rationalized by the inversion of the energy levels of an apolar, highly fluorescent and a polar, nonfluorescent excited state, where charge transfer from the tertiary amine to the BODIPY unit occurs. These amine analogues can be protonated at low pH in aqueous solution. Fluorescence titrations yielded pK(a) values of their conjugate ammonium salts which are in agreement with the electron donating tendency of the amine group: piperidino (4.15) > dimethylamino (2.37) > morpholino (1.47), with the pK(a) values in parentheses. The rate constant of radiative deactivation (k(f)) is the same for all compounds in all solvents studied (k(f) = 1.4 x 10(8) s(-1)).     

Synthesis of dityrosine cross-linked peptide dimers using the Miyaura-Suzuki reaction

[reaction: see text] Since peroxidase-catalyzed dityrosine formation is inefficient for peptides, we have developed alternative conditions for intermolecular dityrosine formation using the Miyaura-Suzuki reaction. A one-pot reaction is effective for cross-linking short peptides, but longer peptides inhibit the Suzuki step, mandating a traditional two-step procedure using potassium acetate for the Miyaura reaction and potassium carbonate for the Suzuki coupling. These palladium-based methods are complementary to the well-established peroxidase-catalyzed oxidative phenolic coupling of full-length proteins.     

Spontaneous Liquid/Liquid Displacement in a Capillary

When a two-phase column consisting of paraffin oil and silicon oil is placed in an otherwise air-filled, horizontal glass capillary, the column starts moving spontaneously. Silicon oil displaces paraffin oil, which in its turn displaces air at atmospheric conditions; a stable film of silicon oil is left at the receding silicon oil/air meniscus. The driving force for the motion is the difference in capillary pressure at the free interfaces. However, the column moves considerably more slowly than predicted by the driving forces; it appears that the forces resisting the motion at the moving liquid/liquid/solid line are much larger than one would expect on the basis of the interfacial tension and the viscosities of the two phase system. Some considerations are made on the relationship of the theory of Fowkes to our system. Also, a method for measuring low interfacial tensions between immiscible liquids is proposed.     

Cumulated double bond systems as ligands : X. N-sulfinylaniline complexes of rhodium(I) and iridium(I) of the type [MCl(PR3)2L] in which L is coordinated via the π-NS and via the sulfur atom respectively; crystal and molecular structure of [RhCl(P-i-Pr3)2(4-MeC6H4NSO)]; determination of the 1J(103Rh15N) by 15N NMR spectroscopy

Each of the compounds [MCl(Pr₃)₂(ArylNSO)] (M = Rh^I, Ir^I; R = i-Pr, Cy: Aryl = C₆H₅, 4-MeC₆H₄, 4-ClC₆H₄, 2,4,6-Me₃C₆H₂ appears to exist as two isomers both in the solid state and in solution. The molecular and single crystal structure of one of the isomers of [RhCl(P-i-Pr)₃)₂(4-Me₆H₄NSO)] shows that the N-sulfinylaniline ligand is in the cis-configuration and coordinated to the rhodium atom via the sulfur-atom. The ligand lies in a plane which includes the rhodium atom and is in agreement with the Rh-S distance of 2.10 Å. IR results of the compounds (solid and solutions), ²¹P NMR data and ¹⁵N NMR of a ¹⁵N labelled compound, which yielded a ¹⁰³Rh¹⁵N coupling constant of 15.5 Hz, show that in the second isomer the N-sulfinylaniline ligand is probably bonded to the metal atom via the π-NS bond.The ratio of the metal-π-NS bonded isomer and the metal-S bonded isomer decreases in the order Aryl = 4-ClC₆H₄ > C₆H₅ > 4-MeC₆H₄; R = i-Pr > Cy and M = Rh > Ir. The interconversion of the two isomers is intramolecular and becomes observable on the ³¹P NMR time scale at about 40° C for M = Rh.In the case of [Ir(P-i-Pr₃)₂(4-MeC₆H₄NSO)], cyclometallation of the sul- finylaniline is observed via the ortho-carbon atom, whereas cyclometallation via P-i-Pr₃ is observed when the ortho-positions are blocked by methyl groups, e.g. when L = 2,4,6-Me₃C₆H₂NSO.     

Systematic computer-aided interpretation of vibrational spectra

The diagnostic value of an interpretation system for vibrational spectra has been investigated in relation to the number of structural units the system can cope with. For five structural units the correlated wavenumber intervals are derived from three infrared and three Raman files by the CRISE program. The interpretative value of each interval in relation to the intensity threshold is discussed. For most intervals a decrease is found on increasing the number of structural units.     

The lowest triplet state of benzene: Differences in electronic structure in two crystalline modifications of a cyclohexane host

Microwave induced delayed phosphorescence (MIDP) measurements have been performed in the 00 bands of the phosphorescence spectrum of benzene dissolved in two phases of cyclohexane. From the relative radiative rates for decay of the three zero-field levels it is concluded that on the average the symmetry of the electronic structure is lower than D_2h. In the monoclinic low temperature stable phase of cyclohexane (phase II) the structure is approximately antiquinoidal, and in the metastable phase III it is approximately quinoidal.     

Gas-phase ion/molecule reactions between dimethoxyphosphonium ions and aromatic hydrocarbons

Ion/molecule reactions between O=P(OCH(3))(2)(+) phosphonium ions and six aromatic hydrocarbons (benzene, toluene, 1,2,4-trimethylbenzene, naphthalene, acenaphthylene and fluorene) were performed in a quadrupole ion trap mass spectrometer. The O=P(OCH(3))(2)(+) phosphonium ions, formed by electron impact from neutral trimethyl phosphite, were found to react with aromatic hydrocarbons (ArHs) to give (i) an adduct [ArH, O=P(OCH(3))(2)](+) and (ii) for ArHs which have an ionization energy below or equal to 8.14 eV, a radical cation ArH(+ *) by charge transfer reaction. Collision-induced dissociation experiments, which produce fragment ions other than the O=P(OCH(3))(2)(+) ions, indicate that the adduct ions are covalent species. Isotope-labeled ArHs were used to elucidate fragmentation mechanisms. The charge transfer reactions were investigated using density functional theory at the B3LYP/6-311 + G(3df,2p)//B3LYP/6-31G(d,p) level of theory. The potential energy surface obtained from B3LYP/6-31G(d,p) calculations for the reaction between O=P(OCH(3))(2)(+) and benzene is described.     

DNA electrophoresis in agarose gels: a simple relation describing the length dependence of mobility

Electrophoretic mobilities of DNA molecules ranging in length from 100 to 10 000 base pairs (bp) were measured in gels of eleven concentrations of agarose from 0.5 to 1.5%. Excellent fits of the dependence of mobility on DNA length were obtained with the relationship [equation: see text] showing an e(-L/gamma) crossover, where L is the length of a DNA fragment and gamma is a crossover length ranging from 8000 to 12000 bp. The other parameters in the fit are mu(s) the mobility of short DNA with unit charge in the limit as length is extrapolated to zero, and muI, the mobility of long DNA as length is extrapolated to infinity. This exponential relationship should be a useful interpolation function for determining DNA lengths over a wide range. The simplicity of this relationship may be of more fundamental significance and suggests that some common feature dominates the electrophoresis of double stranded DNA fragments in agarose gels, regardless of length.