Novel antibiotics: second generation macrocyclic peptides designed to trap Holliday junctions

Described are the syntheses of 15 macrocyclic peptides designed to trap Holliday junctions (HJs) in bacteria during site-specific and homologous recombination. This leads to inhibiting bacterial growth. These second generation macrocycles were based on the C-2 symmetrical HJ. They were synthesized using a strategy that permits elucidation of the amino acid role in binding HJs. The syntheses of these macrocycles are an important step in the development of a new class of antibiotics.     

Radical concentration measurements in hydrocarbon diffusion flames

Absolute OH· concentrations and relative H-atom and O-atom profiles have been measured in a laminar, co-flowing methane/air diffusion flame burning at atmospheric pressure. Laser absorption and laser-induced fluorescence methods were used to probe the A ² X ²II_itransition in OH·. The maximum OH· concentration is found to be 1.8±0.2 ×10¹⁶ cm^–3 (mole fraction =5.0×10^–3) at a temperature of 2080 K, which is twice the value calculated assuming local total equilibrium but less than half that predicted from partial equilibrium (O₂+H₂ 2OH·). Multiphoton ionization (2+1 process at 243 nm) has been used to detect H atoms, while laser-induced fluorescence at 845 nm excited by two-photon absorption at 226 nm was employed to observe O atoms. In both cases it was found that low photon intensities (2×10⁸W/cm²) and a retroreflected beam, Doppler-free geometry was required in order to avoid the photolytic production of the species of interest. For all of the concentration profile data it is necessary to correct the raw signals for variations in collisional quenching. In the case of the multiphoton ionization measurements the variation in electron detection sensitivity as a function of flame position must be accounted for as well. Establishing absolute H-atom and O-atom concentrations is discussed in terms of partial equilibrium considerations and detailed flame structure calculations.Formerly the National Bureau of Standards     

Synergies between micropreparative high-performance liquid chromatography and an instrumental optical biosensor

The recent development of an automated surface plasmon resonance technology for the measurement of biomolecular interactions (Pharmacia BIAcore) has provided new opportunities for the detection and analysis of protein-protein interactions. In the BIAcore, detection is based on changes in surface plasmon resonance which are monitored optically. Changes in surface plasmon resonance correspond to changes in surface concentration of macromolecules and can be monitored in real time.

We have found that the detection sensitivity obtainable with this technology (ng/ml concentrations of specific ligands are readily detectable for many applications) is complementary “in a bidirectional manner” to micropreparative HPLC. Thus micropreparative HPLC may be used to purify and characterise reagents for the biosensor, whilst the biosensor may be used to define chromatographic parameters such as elution conditions for affinity chromatography or serve as an affinity detector for fractions obtained during chromatographic purification.

Examples of such applications, including the potential of the biosensor to search for and monitor the purification of unknown ligands for which the target molecule has been identified, are shown. In particular, the use of the biosensor to monitor the purification of soluble epidermal growth factor receptor from A431 cell conditioned media is demonstrated.     

Assay of flurazepam in plasma by differential pulse polarography

Analytical and Bioanalytical Chemistry - A combination of differential solvent extraction based on physical chemical properties of the species involved and differential pulse polarography has been...     

The accurate calculation of dipole moments and dipole polarizabilities using Gaussian-based density functional methods

Dipole moments and static dipole polarizabilities have been calculated for a number of small molecules using the linear combination of Gaussian-type orbitals–local spin density method. The effect of augmenting standard orbital basis sets with polarization functions has been investigated. A set of optimum ζ_d, for use in calculating polarizabilities, has been derived for the first-row atoms C, N, O, and F. The results of this optimized doubly polarized double-zeta basis set compare well with results obtained using a double-zeta basis set augmented by four even-tempered ζ_d polarization functions. The results of the optimized basis set, and a basis set augmented with only a single ζ_d polarization function derived from it, compare very favorably with those obtained from Møller–Plesset perturbation theory and with experimental data. They show a marked improvement on results obtained using standard Hartree–Fock self-consistent-field molecular orbital methods where no treatment of electron-correlation is included.     

Characterisation and determination of indole alkaloids in frog-skin secretions by electrospray ionisation ion trap mass spectrometry

The characterisation of selected indole alkaloids in a quadrupole ion trap mass spectrometer is presented. Fragmentation profiles for tryptamine, 5-hydroxytryptamine (5-HT), N'-methyl 5-hydroxytryptamine (N'-methyl 5-HT), N',N'-dimethyl 5-hydroxytryptamine (bufotenine), N',N',N'-trimethyl 5-hydroxytryptamine (5-HTQ), and N',N'-dimethyl 5-methoxytryptamine (5-MeODMT) are presented with proposed structures given for each product ion observed. Such MS(n) experiments can be used to differentiate the isobaric molecular ions of the compounds 5-HTQ (M(+)) and 5-MeODMT (MH(+)). The quantitative determination of certain indole alkaloids in the skin secretions of the Australian Golden Bell frog, Litoria aurea, by LC/ESI-ion trap MS is also presented. The concentrations of 5-HT, N'-methyl 5-HT and 5-HTQ were found to be 2.68, 0.26 and 0.54 microg per mg of skin secretion, respectively.     

Multifunctional redox catalysts as selective enhancers of oxidative stress

Certain cancer cells proliferate under conditions of oxidative stress (OS) and might therefore be selectively targeted by redox catalysts. Among these catalysts, compounds containing a chalcogen and a quinone redox centre are particularly well suited to respond to the presence of OS. These catalysts combine the specific electrochemical features of quinones and chalcogens. They exhibit high selectivity and efficiency against oxidatively stressed rat PC12, human Jurkat and human Daudi cells in cell culture, where their mode of action most likely involves the catalytic activation of existent and the generation of new reactive oxygen species. The high efficiency and selectivity shown by these catalysts makes them interesting for the development of anti-cancer drugs.     

Molar mass distributions by gradient liquid chromatography: predicting and tailoring selectivity

Interactive liquid chromatography (iLC) for polymer analysis is usually applied to the characterisation of distributions other than molar mass. In particular, its use for the determination of chemical-composition, functionality-type and tacticity distributions has been demonstrated. The application of iLC for the determination of molar mass distributions (MMDs), however, has not yet been fully explored. An expanded version of the reversed-phase liquid chromatography model has been developed to describe and predict how the retention behaviour of polydisperse polystyrene samples changes with molar mass. The relationship between molar mass and the parameters of the model has been investigated in some detail and non-linear correlations were found. From the model and the relationships between the model parameters and molar mass, calibration curves (retention time versus molar mass) were constructed to predict changes in chromatographic selectivity across a given molar mass range. These calibration curves were compared to experimentally obtained curves and, in most cases, excellent agreement was found. The dramatic enhancement in selectivity that can be obtained with iLC in comparison to size-exclusion chromatography (SEC) was illustrated by measuring matrix-assisted laser desorption ionisation (MALDI) MS spectra of fractions collected during a gradient-LC separation. In the low-molar mass range, essentially monodisperse fractions were obtained. Calibration curves, predicted by the model and validated experimentally using narrow-dispersity standards and MALDI-MS spectra of fractions, were used to determine the molar mass distribution of some narrowly distributed polystyrene samples. Molar mass distributions for such standards were found to be somewhat lower than the values reported by the manufacturers. The results also deviated from those obtained by MALDI-MS.