Self-association of daunomycin antibiotic in various buffer solutions

The self-association of an antitumor antibiotic, daunomycin (DAU), in various buffer solutions, including water-salt solutions, phosphate buffer, HEPES, and TRIS, was studied by 1D and 2D ¹H NMR spectroscopy at 500 MHz. The two-dimensional NOESY spectra and the concentration and temperature dependences of the chemical shifts of antibiotic protons in the solvents studied showed that the self-association parameters of DAU were independent of the type of buffer solutions. The most probable two spatial structures of the dimer of DAU in solution were constructed by the method of molecular mechanics. The mutual orientation of the chromophores was parallel in one structure and antiparallel in the other.     

Glass forming ability and thermal stability in the system ZrF46BaF26PrF3

New glasses have been synthesized in the system ZrF₄6BaF₂6PrF₃. Glasses were prepared by conventional fusion method and the vitreous domain was established. For vitreous samples the thermal stability parameters were determined, so that the best compositions could be selected according to a compromise between high glass forming ability and thermal stability vs. crystallization.     

Diels—Alder reaction. Effect of internal and external factors on the reactivity of diene—dienophile systems

The key factors influencing the Diels—Alder reaction rate at ambient and elevated pressures were elucidated using data on the reactivity of various diene—dienophile systems in usual and Lewis acid-catalyzed Diels—Alder reactions, the reaction enthalpy, complex formation, dissolution, and solvation, and the donor-acceptor properties of the reactants. It was found that taking account of both the orbital interaction energy and the balance of bond rupture and formation energies allows correct prediction of the reaction rate in the absence or in the presence of Lewis acids.     

Experimental and theoretical study of vibrational spectra and structure of dihalogermylene and dihalostannylene complexes with 1,4-dioxane and triphenylphosphine

Vibrational (Raman and IR) spectra of the 1:1 complexes of dihalogermylene and dihalostannylene with 1,4-dioxane and PPh₃ have been reported, the structures of the complexes Cl₂Ge·C₄H₈O₂ and Cl₂Ge·PPh₃ updated using high-resolution X-ray method. Quantum-chemistry calculations of the geometry and normal mode frequencies and eigenvectors were carried out for some of the complexes. The results show that in the structure of the polymeric solid complexes of X₂M with 1,4-dioxane, intermolecular coordination XM plays a prominent role, whereas the corresponding complexes with PPh₃ are monomeric. In the vibrational spectra of all the complexes, an inversion of symmetric and antisymmetric stretching νXM (X=Cl, Br; M=Ge, Sn) frequencies, found for ‘free’ X₂M^II particles, still persists, suggesting that the X₂M moieties preserve their specifity as carbene analogues also in the complexes.     

Isolation,purification, and characterization of two forms of lipase from the fungusMucor miehei

Two forms of lipases (A and B) have been isolated from the fungusMucor miehei UzLT-3 and purified to the homogeneous state, and molecular masses of 43 and 40 kDa have been established for them from the results of disk electrophoresis and gel filtration. The isoelectric points of the lipases are 4.7 for form A and 4.9 for form B. Institute of Microbiology, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax 41 71 29. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 673–676, September–October, 1994.     

Determination of flux from a saddle field fast-atom bombardment gun

The flux or beam density (equivalent current/area) of xenon atoms striking the sample target from a saddle field fast-atom bombardment (FAB) gun has been compared with that from a cesium ion gun mounted on the same instrument. A shielded Faraday cup mounted on the end of a solids probe was used to measure directly the flux of the Cs⁺ beam. Samples of methylene blue in glycerol solution were then exposed to the ion beam at different fluxes and the extents of reduction were measured. The extent of reduction varied linearly with flux up to a value of about 1.16 × 10¹³ particles s^?1 cm^?2 (1.85 μ cm^?2); above this level, the reduction effect appeared to saturate. FAB spectra were obtained from the same dye solution by using varying settings of the FAB gun. By comparing the extents of reduction of the dye from the two guns, the flux from the atom gun could be estimated. Observation of luminescence from a CsI-coated target allowed estimation of the area of the atom beam. The atom beam “equivalent current” could then be calculated by multiplying the flux times the area. It was noted that for given settings, the flux from the atom gun depended on the physical condition of the gun electrodes. With new electrodes, a flux ≥ 1.16 × 10¹³ particles s^?1 cm^?2 was obtained with nominal gun emission currents of 0.60–1.0 mA. Electrodes used extensively, but freshly cleaned, provided a flux of ～ 8 × 10¹² particles s^?1 cm^?2 at nominal emission currents of 0.40–1.0 mA. With dirty electrodes this flux could only be achieved at the highest (1.0 mA) emission current. This decline in performance occurs over a matter of months as a result of contamination and erosion of the electrodes during use. Such behavior can adversely affect spectral reproducibility even when nominal FAB gun voltage and emission current are carefully reproduced.     

Separation of dideoxyribonucleosides in trace amounts by automated liquid chromatography and capillary electrophoresis.

No satisfactory high-performance liquid chromatographic (HPLC) method is currently available for the separation of the major dideoxyribonucleosides (ddNs) and their derivatives. A method involving HPLC has been developed for the separation of five major ddNs [ddA, ddC, ddI, azT and 2',3'-dideoxy-2',3'-didehydrothymidine (d4T)]. Elution of the common and modified components of DNA was also examined under the selected separation conditions of HPLC. The elution characteristics of these compounds were studied using serum plasma samples spiked with ddN derivatives. In addition, capillary electrophoresis (CE) was investigated for the separation of ddNs and their derivatives. Picomolar amounts of the five major ddNs and the metabolic product of azT [5'-O-glucuronide-3'-azido-3'-deoxythymidine (Glo-azT)] were satisfactorily resolved in 10 min by using a modification of CE. The spectral properties of the ddNs were characterized under different pH conditions and compared with those of their parent deoxyribonucleosides (dNs) because these compounds are commonly measured in HPLC by their spectral properties. The spectra of ddC and ddT derivatives resemble very closely those of dC and dT, but those of ddA and ddI differ to some extent from their parent dNs. The HPLC method was extensively examined for satisfactory resolutions of these compounds. For example, an isocratic elution method, although simple, failed to resolve these compounds and ion-pair chromatography did not offer any advantage. Gradient elution involving buffered solutions and increasing amounts of an organic modifier yielded satisfactory results. Methanol appeared to be the organic modifier of choice. A reversed-phase matrix with smaller than octadecyl alkyl chains did not produce the necessary interactions. Uniform spherical beads of smaller diameter produced superior resolutions. The separation of these compounds on three commercially available columns is discussed. The separation of human plasma samples spiked with dideoxynucleoside derivatives by HPLC was accomplished in ca. 16 min. The presence of the dNs did not interfere in their separations.     

DMC: A multifunctional hybrid dynamics/Monte Carlo simulation algorithm for the evaluation of conformational space

A hybrid conformational search algorithm (DMC) is described that combines a modified form of molecular dynamics with Metropolis Monte Carlo sampling, using the COSMIC(90) force field. Trial configurations are generated by short bursts of high-temperature dynamics in which the initial kinetic energy is focused into single bond rotations or alternatively into “corner-flapping” motions in ring systems. Constant temperature and simulated annealing search protocols have been applied to the conformational analysis of several model hydrocarbons (cyclopentane, cyclohexane, cycloheptane, cyclooctane, cycloheptadecane, decane, and tetradecane), and the performance compared with conventional molecular dynamics and Monte Carlo sampling methods. Optimum Metropolis sampling temperatures have been determined and range from 1000–2000 K for acyclic molecules to 3000 K for cyclic systems. Simulated annealing runs are most successful at locating the global minimum when cooling slowing from these optimum temperatures.     

Preparation de membranes echangeuses de cations par photogreffage d'ethers allyliques du poly (alcool vinylique). Etude de certaines de leurs proprietes—II: Photogreffage des poly (alcools vinyliques) allyles

Poly(vinyl alcohols) partially allylated have been grafted with sulphonic acid. The influence of experimental parameters (vinyl sulphonic acid concentration, swelling before grafting, photoinitiator concentration, grafting temperature and duration of the irradiation) have been studied in detail.     

THE PHOTOMORPHOGENETIC CONTROL OF THE DEVELOPMENT OF PLASTID GLYCERALDEHYDE-PHOSPHATE DEHYDROGENASE AND PHOSPHORIBULOKINASE ACTIVITIES IN COTYLEDONS OF MUSTARD SEEDLINGS

The plastid glyceraldehyde-phosphate dehydrogenase and phosphoribulokinase of mustard cotyledon extracts were activated by preincubation with ATP and with ATP and dithiothreitol respectively. By in vitro activation prior to assay, it was possible to determine the potential activities, which appear to have been directly proportional to the amount of each enzyme protein present. In this way it was possible to deduce the net synthesis of these two enzymes. The induction of synthesis of glyceraldehyde-phosphate dehydrogenase and phosphoribulokinase, by continuous far red or white light were similar hut net synthesis in continuous far red continued longer for glyceraldehyde-phosphate dehydrogenase than for phosphoribulokinase. The kinetics of the development of the glyceraldehyde-phosphate dehydrogenase potential activity were very close to those reported by Bruning et al. (1975) for this enzyme. The data do not permit elimination of either the single switch or multiple switches hypotheses for the action of phytochrome. Continuous white illumination gave results similar to those for continous far red for the net synthesis of the two enzymes but it was more effective than far-red in bringing about enzyme activation in vivo.