Conformational properties of HO2(-)-Co(III)-bleomycin A2 (Form I) and Co(III)-bleomycin (Form II) bound to DNA oligomers offering either principal cleavage site for the drug, d(GGAAGCTTCC)2 or d(AAACGTIT)2, have been studied by NMR methods. Form I binds in slow exchange to these oligomers. It retains most of its solution nuclear Overhauser effects (NOEs) upon binding to either oligomer. Pyrimidinyl methyl protons from the metal domain of the drug make an NOE connection with a G5 2-amino proton on DNA. The bithiazole intercalates between base pairs involving either C6 and T7 or T6 and T7 of the two DNA molecules, according to NOE connections between the bithiazole protons and protons from these bases and changes in the positions of their chemical shifts. Form II also retains most of its solution NOEs upon association with the first oligomer. However, in contrast to Form I it binds to DNA in fast exchange on the NMR time scale over the temperature range of 5-35 degrees C and does not break the degeneracy of the DNA proton chemical shifts. No intermolecular NOEs between Form II and the 10-mer have been detected. Likewise, the major perturbation in chemical shift of the histidine H2 and guanine G5 protons seen in Form I-DNA adducts is absent in Form II-DNA. The association constant of Form II with d(GGAAGCTTCC)2 in 20 mM HEPES buffer at pH 7.4 and 25 degrees C is 1.7 x 10(5) M(-1), and 1.0 mol of Form II bind per mol of 10-mer.

A quantitative comparison of kinetics of seven solid-phase organic reactions on two commonly used resin supports, polystyrene (PS)- and Tentagel (TG)-based resins, is presented. The data we obtained contradict the popular presumption that reactions proceed more rapidly on “solution-like” TG resins. Our results are discussed in terms of a hypothesis in which the resin bead is viewed as another “solvent phase”. The effect of polymer backbones on the reaction kinetics is similar to the effect of solvent on a solution reaction rate. There is no single polymer support that favors all reactions. Depending on the nature of a chosen reaction, TG- or PS-based resins can be a better choice for solid-phase organic synthesis.

Co- and Fe-bleomycins (Blms) have been reacted with DNAa, d(GGAAGCTTCC)2, containing a specific site for cleavage, and DNAb, d(GGAAATTTCC)2, a closely related nonspecific 10-mer, to survey whether features of structure and reactivity of these adducts vary systematically as a function of the base sequence of the DNA oligomer. The ESR spectrum of NO-Fe(II)BlmDNAa is rhombically perturbed in comparison with that of NO-Fe(II)BlmDNAb, which is nearly identical to the spectrum of NO-Fe(II)Blm. The ESR spectrum of Fe(III)BlmDNAa in phosphate buffer is low-spin; that of Fe(III)BlmDNAb is high-spin as seen with Fe(III)Blm alone. According to absorbance spectroscopy, O2-Fe(II)BlmDNAa is stabilized in comparison with the DNAb adduct. Similar stabilization of O2-Co(II)Blm bound to DNAa but not to DNAb was also observed by ESR spectroscopy. HO2(-)-Co(III)Blm A2 binds in slow exchange on the NMR time scale to DNAa at its 5'-G-pyrimidine-3' site of cleavage. In contrast, fluorescence and NMR spectroscopy demonstrate that most of HO2(-)-Co(III)Blm A2 binds stoichiometrically in fast exchange to DNAb. The reactions of Fe(III)BlmDNAa and Fe(III)BlmDNAb with ascorbate and O2 reveal that the latter becomes activated and cleaves its 10-mer, producing base propenals, at a faster initial rate. Thus, in two series of metallobleomycins, (A) NO-Fe(II)Blm, O2-Fe(II)Blm, Fe(III)Blm in phosphate buffer, and HO2(-)-Fe(III)Blm and (B) O2-Co(II)Blm and HO2(-)-Co(III)Blm, the metal domain of each species interacts differently with DNA depending upon its base sequence.

The interactions of azide and thiocyanate with the binuclear center of oxidized cytochrome c oxidase have been characterized by Fourier transform infrared and UV-vis spectroscopy, electron paramagnetic resonance and magnetic and natural circular dichroism. Azide binds in two phases, a high-affinity phase (Kd = 64 microM) in which it is bound as a bridge to the binuclear center and a low-affinity phase (Kd = 20 mM) in which it displaces one of the axial ligands to cytochrome a. Thiocyanate also binds in two phases. The high-affinity phase (Kd = 2.7 mM) involves binding in a terminal mode to CuB; the low-affinity phase is complex and involves both CuA and cytochrome a. In contrast to the recent proposal of Yoshikawa and Caughey [(1990) J. Biol. Chem. 265, 7945-7958], we conclude that cyanide also functions as a bridge between cytochrome a3 and CuB. In the presence of cyanide, azide does not bind to its high-affinity site but thiocyanate does bind to its high-affinity site.

Abstract. A new, reproducible method is described for the preparation of highly efficient fused silica packed capillary columns using pressure programmed liquid or supercritical carbon dioxide to carry the packing material into the capillary. The method allows facile preparation of long, uniformly packed capillary columns capable of producing over 240,000 theoretical plates in SFC. Columns of up to 10 meters in length were prepared using LC packing materials of different chemical nature and particle size. The new method does not require a separate step for preparing the slurry, and it is free from the drawbacks inherent in conventional slurry-packing methods. The lower viscosity and surface tension of carbon dioxide compared to conventional slurry-forming liquids, as well as the use of ultrasonic vibration and pressure programming in the packing process, provide favorable conditions for achieving packing uniformity over greater column lengths than is achievable by other packing techniques. Proper restrictors and appropriate decompression rates during the use of these columns in SFC were found to be very important in achieving optimum column performance. In comparison to the use of open tubular columns, higher efficiencies, greater sample capacities, and faster analysis speeds can be obtained. These advantageous features make the newly developed columns suitable for trace analysis, separation of very complex mixtures, and analysis of difficult-toseparate solutes.