Rhenium oxo complexes of a chelating diyne ligand. Synthesis and study of the kinetics of protonation.

A series of oxo complexes, Re(O)X(diyne) (X = I, Me, Et), have been prepared from 2,7-nonadiyne and Re(O)I(3)(PPh(3))(2). Addition of B(C(6)F(5))(3) to Re(O)I(2,7-nonadiyne) (5) results in coordination of the oxo ligand to the boron. The protonation of Re(O)(X)(2-butyne)(2) and Re(O)(X)(2,7-nonadiyne)(2) with a variety of acids has been examined. With 5 and HBF(4)/Et(2)O, the ultimate product was [Re(CH(3)CN)(3)(I)(2,7-nonadiyne)](2+) (7). The conversion of 5 to 7 changes the conformation of the diyne ligand from a "chair" to a "boat" and shifts its propargylic protons considerably downfield in the (1)H NMR. The kinetics of the protonation of Re(O)I(2,7-nonadiyne) (5) by CF(3)SO(3)H in CH(3)CN have been monitored by visible spectroscopy, in a stopped-flow apparatus, and by low temperature (1)H NMR. Two second-order rate constants, presumably successive protonations, were observed in the stopped-flow, k(1) = 11.9 M(-)(1) s(-)(1) and k(2) = 3.8 M(-)(1) s(-)(1). Low temperature (1)H NMR spectroscopy indicated that the resulting solution contained a mixture of two doubly protonated intermediates X and Y, each of which slowly formed the product 7 via an acid-independent process.

Ciprofloxacin plus piperacillin is an equally effective regimen for empiric therapy in febrile neutropenic patients compared with standard therapy.

The purpose of this study was to test the comparative efficacy and toxicity of empiric gentamicin and ciprofloxacin, in combination with piperacillin, in febrile patients with treatment-induced neutropenia. Fifty patients were prospectively randomized to receive piperacillin plus gentamicin (PG), and 46 were randomized to receive piperacillin plus ciprofloxacin (PC). The groups were similar in age, sex, diagnosis, duration of neutropenia, and incidence of positive cultures. The two antibiotic regimens were associated with comparable rates of defervescence in the patients with gram-positive bacteremia. In the patients with gram-negative bacteremia and those with negative cultures, however, defervescence was more prompt in the PC group. In particular, 27% of the culture-negative patients on PC, compared to only 5% of those on PG, defervesced within 72 hr (P = 0.015). Because of the more prompt defervescence in the PC group, amphotericin B was used less frequently; 78% of the patients on PG compared with only 56% of those on PC were started on amphotericin B (P = 0.025). PC is an effective alternative to the more traditional PG for treatment of febrile neutropenic hosts who have not been given prophylactic quinolones. More important, PC appears to hasten defervescence compared with PG, especially in culture-negative patients and those with gram-negative bacteremia, and may decrease the necessity of additional antimicrobial agents such as amphotericin B.

Measurement of arterial oxygen-haemoglobin saturation in newborn lambs by pulse oximetry.

Percentage arterial oxygen saturation (SpO2) was measured in 69 neonatal lambs at one, five and 10 minutes after birth using a pulse oximeter applied to the tail. The lambs were given a subjective vitality score from 1 to 4, with 1 being normal and 4 being stillborn. Of the 42 lambs born after a normal parturition, 19 were measured after one minute, 29 after five minutes and 24 after 10 minutes; the mean (sd) SpO2 values of these groups were 67 (15) per cent, 84 (9) per cent and 83 (9) per cent, respectively. Of the 27 lambs born after dystocia, 16 were measured after one minute, 18 after five minutes and 12 after 10 minutes; the mean (sd) SpO2 values of these groups were 61 (15) per cent, 69 (16) per cent and 69 (19) per cent, respectively. The values measured in the lambs born after dystocia were significantly lower than those in the lambs born normally at five and 10 minutes (P < 0.005 and P < 0.05, respectively). Of the lambs born with a vitality score of 1, 24 were measured after one minute, 33 after five minutes and 26 after 10 minutes; they had mean SpO2 values of 72 (11), 82 (10) and 81 (12) per cent, respectively. Of the lambs born with vitality scores of 2 or 3, 11 were measured after one minute, 14 after five minutes and 10 after 10 minutes; they had mean SpO2 values of 48 (6), 68 (17) and 72 (20) per cent, respectively. The SpO2 values of the lambs with vitality scores of 2 or 3 were significantly lower than those of the lambs with a vitality score of 1 at one and five minutes after birth (P < 0.0001 and P < 0.05, respectively).

Calf RTH-1 nuclease can remove the initiator RNAs of Okazaki fragments by endonuclease activity.

In eukaryotes, the endonucleolytic activity of the calf RTH-1 class 5'- to 3'-exo/endonuclease can function without RNase H1 to remove initiator RNA from Okazaki fragments. Cleavage requires that the RNA be displaced to form an unannealed single-stranded 5'-tail or flap structure. On substrates with RNA-initiated primers, DNA oligomers that competed with the RNA for template binding simulated strand displacement synthesis from an upstream Okazaki fragment. This allowed cutting of displaced RNA segments by RTH-1 nuclease. Requirements for the reaction also were examined on substrates in which the tail was unannealed because it was intentionally mispaired. On both types of substrate, the nuclease slides over the RNA region from the 5'-end and cleaves at the beginning of the annealed region, irrespective of whether ribo- or deoxyribonucleotides are at the cleavage site. Presence of a triphosphate or a 7-methyl 3'G5'ppp5' G cap structure at the 5'-end of the RNA does not affect cleavage. The previously reported stimulation of the nuclease by an upstream primer was not always observed, suggesting that not every site in the downstream Okazaki fragment is equally susceptible to cleavage during displacement synthesis in vivo. The biological role of the endonuclease activity of RTH-1 nuclease in Okazaki fragment processing is discussed.

Long-term performance of precision crystal oscillators in a near-Earth orbital environment.

The Navy Navigation Satellite System (NNSS) uses precision quartz crystal oscillators to provide time and frequency in the orbiting spacecraft. The frequency changes for multiple oscillators, which were observed for 28 years of operational service in the orbital environment, are discussed. The primary frequency changes are believed to be caused by mass transfer to and from the resonator, stress relief in the resonator mounting structure and electrodes, and ionizing radiation of the quartz resonator. Observations to a resolution of 10- 13 have been made from 1963 to 1991 on 20 operational satellites in near-Earth orbit. No oscillator failures have occurred during the entire program life of nearly 30 years. One oscillator provided continuous operational service for over 21 years, and several have served more than 15 years. No oscillator changed frequency more than two parts in 107 while in operational service. One of the best performing oscillators had a predictable drift rate of 9x10(-13)+/-1x10(-13) per day after three years of service.

Mechanism of assembly of the tyrosyl radical-dinuclear iron cluster cofactor of ribonucleotide reductase.

Incubation of the apoB2 subunit of Escherichia coli ribonucleotide reductase with Fe2+ and O2 produces native B2, which contains the tyrosyl radical-dinuclear iron cluster cofactor required for nucleotide reduction. The chemical mechanism of this reconstitution reaction was investigated by stopped-flow absorption spectroscopy and by rapid freeze-quench EPR (electron paramagnetic resonance) spectroscopy. Two novel intermediates have been detected in the reaction. The first exhibits a broad absorption band centered at 565 nanometers. Based on known model chemistry, this intermediate is proposed to be a mu-peroxodiferric complex. The second intermediate exhibits a broad absorption band centered at 360 nanometers and a sharp, isotropic EPR signal with g = 2.00. When the reaction is carried out with 57Fe2+, this EPR signal is broadened, demonstrating that the intermediate is an iron-coupled radical. Variation of the ratio of Fe2+ to B2 in the reaction and comparison of the rates of formation and decay of the intermediates to the rate of formation of the tyrosyl radical (.Y122) suggest that both intermediates can generate .Y122. This conclusion is supported by the fact that both intermediates exhibit an increased lifetime in a mutant B2 subunit (B2-Y122F) lacking the oxidizable Y122. Based on these kinetic and spectroscopic data, a mechanism for the reaction is proposed. Unlike reactions catalyzed by heme-iron peroxidases, oxygenases, and model complexes, the reconstitution reaction appears not to involve high-valent iron intermediates.