On the crystal structures and phase transitions of hydrates in the binary dimethyl sulfoxide-water system.

Neutron powder diffraction data have been collected from a series of flash-frozen aqueous solutions of dimethyl sulfoxide (DMSO) with concentrations between 25 and 66.7 mol% DMSO. These reveal the existence of three stoichiometric hydrates, which crystallize on warming between 175 and 195 K. DMSO trihydrate crystallizes in the monoclinic space group P21/c, with unit-cell parameters at 195 K of a = 10.26619 (3), b = 7.01113 (2), c = 10.06897 (3) Å, ß = 101.5030 (2)° and V = 710.183 (3) Å3 (Z = 4). Two of the symmetry-inequivalent water molecules form a sheet of tiled four- and eight-sided rings; the DMSO molecules are sandwiched between these sheets and linked along the b axis by the third water molecule to generate water-DMSO-water tapes. Two different polymorphs of DMSO dihydrate have been identified. The α phase is monoclinic (space group P21/c), with unit-cell parameters at 175 K of a = 6.30304 (4), b = 9.05700 (5), c = 11.22013 (7) Å, ß = 105.9691 (4)° and V = 615.802 (4) Å3 (Z = 4). Its structure contains water-DMSO-water chains, but these are polymerized in such a manner as to form sheets of reniform eight-sided rings, with the methyl groups extending on either side of the sheet. On warming above 198 K, α-DMSO·2H2O undergoes a solid-state transformation to a mixture of DMSO·3H2O + anhydrous DMSO, and there is then a stable eutectic between these two phases at ∼203 K. The ß-phase of DMSO dihydrate has been observed in a rapidly frozen eutectic melt and in very DMSO-rich mixtures. It is observed to be unstable with respect to the α-phase; above ∼180 K, ß-DMSO·2H2O converts irreversibly to α-DMSO·2H2O. At 175 K, the lattice parameters of ß-DMSO·2H2O are a = 6.17448 (10), b = 11.61635 (16), c = 8.66530 (12) Å, ß = 101.663 (1)° and V = 608.684 (10) Å3 (Z = 4), hence this polymorph is just 1.16% denser than the α-phase under identical conditions. Like the other two hydrates, the space group appears likely, on the basis of systematic absences, to be P21/c, but the structure has not yet been determined. Our results reconcile 60 years of contradictory interpretations of the phase relations in the binary DMSO-water system, particularly between mole fractions of 0.25-0.50, and confirm empirical and theoretical studies of the liquid structure around the eutectic composition (33.33 mol% DMSO).

Muscle fatigue examined at different temperatures in experiments on intact mammalian (rat) muscle fibers.

In experiments on small bundles of intact fibers from a rat fast muscle, in vitro, we examined the decline in force in repeated tetanic contractions; the aim was to characterize the effect of shortening and of temperature on the initial phase of muscle fatigue. Short tetanic contractions were elicited at a control repetition rate of 1/60 s, and fatigue was induced by raising the rate to 1/5 s for 2-3 min, both in isometric mode (no shortening) and in shortening mode, in which each tetanic contraction included a ramp shortening at a standard velocity. In experiments at 20 degrees C (n = 12), the force decline during a fatigue run was 25% in the isometric mode but was significantly higher (35%) in the shortening mode. In experiments at different temperatures (10-30 degrees C, n = 11), the tetanic frequency and duration were adjusted as appropriate, and for shortening mode, the velocity was adjusted for maximum power output. In isometric mode, fatigue of force was significantly less at 30 degrees C ( approximately 20%) than at 10 degrees C ( approximately 30%); the power output (force x velocity) was >10x higher at 30 degrees C than at 10 degrees C, and power decline during a fatigue run was less at 30 degrees C ( approximately 20-30%) than at 10 degrees C ( approximately 50%). The finding that the extent of fatigue is increased with shortening contractions and is lower at higher temperatures is consistent with the view that force depression by inorganic phosphate, which accumulates within fibers during activity, may be a primary cause of initial muscle fatigue.

Nosocomial infection following cardiovascular surgery: comparison of two periods, 1987 vs. 1992.

OBJECTIVE: To evaluate whether changes have occurred at our center in the rate of nosocomial infections and in the infectious organisms consequent to changes in policy and procedure as of 1987. SETTING: Multidisciplinary pediatric intensive care unit (PICU) in a major tertiary care center. DESIGN: Prospective comparative study. PATIENTS: Four-hundred and fifty-five consecutive patients who underwent cardiac surgery within a 10-month period. INTERVENTIONS: Changes related to antibiotic use and invasive device management were introduced after the 1987 survey. To determine the effect of these changes, all patients undergoing cardiac surgery between July 1991 and April 1992 were followed daily from PICU admission to 2 months after hospital discharge for signs of infection. Each infectious episode was reviewed by the nosocomial infection control committee. A weighted scoring system was used to determine risk. MEASUREMENTS AND MAIN RESULTS: In the 1987 study, 40 of 310 patients had 78 infections for a nosocomial infection ratio (NIR) of 25.2. Of the 455 patients surveyed in 1992, 72 had 91 episodes of infection. The nosocomially infected patient rate was 15.8 and the NIR was 20. The frequency of wound infection decreased from 7% in 1987 to 4.3% in this study, and no episode of mediastinitis was observed. In the bacteriological spectrum, the absence of candidal infection was significant, and there was a decrease in the proportional frequency of pseudomonas infection from 21% to 15%. CONCLUSION: The comparison between the two time periods demonstrates that an aggressive approach to managing intravascular catheters and urinary catheters and limiting the use of antibiotics probably affects the spectrum of nosocomial infections.