Surface chemical heterogeneity of bacteriogenic iron oxides from a subterranean environment

This study quantifies the surface chemical heterogeneity of bacteriogenic iron oxides (BIOS) and its end-members (2-line ferrihydrite and intermixed intact and fragmented bacteria). On a dry weight basis, BIOS consisted of 64.5 +/- 1.8% ferrihydrite and 34.5 +/- 1.8% organic matter. Enrichment of Al, Cu, Cr, Mn, Sr, and Zn was shown in the solid versus the aqueous phase (1.9 < log Kd < 4.2). Within the solid-phase Al (69.5%), Cu (78.7%), and Zn (77.9%) were associated with the bacteria, whereas Cr (59.8%), Mn (99.8%), and Sr (79.4%) preferred ferrihydrite. Acid-base titration data from the BIOS and bacteria were fitted using FOCUS pKa spectroscopy. The bacteria spectrum with pKa's of 4.18 +/- 0.37, 4.80 +/- 0.54, 6.98 +/- 0.45, and 9.75 +/- 0.68 was similar to discrete and continuous spectra for intact and fragmented bacteria. The BIOS spectrum recorded pKa's of 4.27 +/- 0.51, 6.61 +/- 0.51, 7.89 +/- 1.10, and 9.65 +/- 0.66 and was deconvoluted to remove overlapping binding site contributions from the bacteria. The resulting residual iron oxide spectrum coincided with discrete MUSIC spectra for goethite and lepidocrocite with pKa values of 4.10 +/- 0.43, 6.53 +/- 0.45, 7.81 +/- 0.76, and 9.51 +/- 0.68. Surface site density analysis showed that acidic sites (pKa < 6) were contributed by the bacteria (37%), whereas neutral sites (6 < pKa < 8) were characteristic of the iron oxide fraction (35%). Basic sites (8 < pKa) were higher in the bacteria (57%), than in the BIOS (44%) or iron oxide fractions (47%). This analysis suggested a high degree of bacterial group masking and a similarity between the BIOS and goethite surface reactivity. An understanding of the BIOS surface chemical heterogeneity and inherent proton and metal binding capacity was obtained through the use of FOCUS apparent pKa spectroscopy.     

Effect of mandibular and tongue protrusion on upper airway size during wakefulness

Oral appliances for the treatment of obstructive sleep apnea (OSA) produce either mandibular or tongue protrusion, and are thought to enlarge the upper airway (UA). We used videoendoscopy to measure UA cross-sectional area (CSA) and shape in the hypopharynx, oropharynx, and velopharynx during various stages of active mandibular and tongue protrusion during wakefulness in 10 patients with OSA and nine control subjects. Measurements were made in the supine position at end-tidal expiration, and were normalized to the CSA in the normal bite position. Airway shape was expressed as the anteroposterior/lateral (AP/L) diameter ratio. There were no differences between OSA patients and controls in the effects of mandibular and tongue protrusion on UA caliber. Both mandibular and tongue protrusion increased CSA in the hypopharynx and oropharynx (p < 0.001), whereas only tongue protrusion increased CSA in the velopharynx (p < 0.001). Tongue protrusion caused a greater increase in oropharyngeal and velopharyngeal CSA than did mandibular protrusion (p < 0.05). Mandibular protrusion caused a greater increase in CSA in the hypopharynx than in the oropharynx or velopharynx (p < 0.05). Obese patients had a larger relative increase in oropharyngeal CSA with mandibular and tongue protrusion than did subjects of normal weight. Tongue protrusion increased the AP/L diameter ratio in the oropharynx and velopharynx (p < 0.001), and mandibular protrusion did so to a lesser extent in the oropharynx (p < 0.01), resulting in a more circular airway shape. We conclude that mandibular and tongue protrusion increase the CSA and alter the shape of the UA during wakefulness.     

The material basis for reduced mechanical properties in oim mice bones

Osteogenesis imperfecta (OI), a heritable disease caused by molecular defects in type I collagen, is characterized by skeletal deformities and brittle bones. The heterozygous and homozygous oim mice (oim/+ and oim/oim) exhibit mild and severe OI phenotypes, respectively, serving as controlled animal models of this disease. In the current study, bone geometry, mechanics, and material properties of 1-year-old mice were evaluated to determine factors that influence the severity of phenotype in OI. The oim/oim mice exhibited significantly smaller body size, femur length, and moment of area compared with oim/+ and wild-type (+/+) controls. The oim/oim femur mechanical properties of failure torque and stiffness were 40% and 30%, respectively, of the +/+ values, and 53% and 36% of the oim/+ values. Collagen content was reduced by 20% in the oim/oim compared with +/+ bone and tended to be intermediate to these values for the oim/+. Mineral content was not significantly different between the oim/oim and +/+ bones. However, the oim/oim ash content was significantly reduced compared with that of the oim/+. Mineral carbonate content was reduced by 23% in the oim/oim bone compared with controls. Mineral crystallinity was reduced in the oim/oim and oim/+ bone compared with controls. Overall, for the majority of parameters examined (geometrical, mechanical, and material), the oim/+ values were intermediate to those of the oim/oim and +/+, a finding that parallels the phenotypes of the mice. This provides evidence that specific material properties, such as mineral crystallinity and collagen content, are indicative and possibly predictive of bone fragility in this mouse model, and by analogy in human OI.