Distinguishing between Structural Models of ß'-Sialons Using a Combined Solid-State NMR, Powder XRD, and Computational Approach.

ß'-Sialons (Si6-zAlzOzN8-z, where 0 ≤ z ≤ ∼4.2) are studied using a combination of 29Si and 27Al solid-state NMR, using magnetic fields of up to 20 T, powder X-ray diffraction, and density functional theory (DFT) calculations of both the structure and NMR parameters. Four different structural models have been proposed in the literature for the replacement of silicon and nitrogen by aluminum and oxygen within a ß-Si3N4-structured lattice. Experimental data are presented for the variation with composition (z) of the unit cell parameters from diffraction and the local coordination units present suggested by NMR data. The experimental data are compared to the changes with composition in the DFT calculations of the structure and the NMR parameters according to the four models, allowing the models to be distinguished. It is shown that only one of these, the domain model, is fully consistent with all of the experimental data and is, therefore, a good structural model for ß'-sialons. More speculatively, it is suggested that for the domain model, 27Al NMR data might provide a constraint on the thickness of its aluminum-rich layers.

Cis-isomerism and other chemical requirements of steroidal agonists and partial agonists acting at TRPM3 channels.

BACKGROUND AND PURPOSE: The transient receptor potential melastatin-3 (TRPM3) channel forms calcium-permeable, non-selective, cationic channels that are stimulated by pregnenolone sulphate (PregS). Here, we aimed to define chemical requirements of this acute steroid action and potentially reveal novel stimulators with physiological relevance. EXPERIMENTAL APPROACH: We used TRPM3 channels over-expressed in HEK 293 cells, with intracellular calcium measurement and whole-cell patch-clamp recording techniques. KEY RESULTS: The stimulation of TRPM3 channels was confined to PregS and closely related steroids and not mimicked by other major classes of steroids, including progesterone. Relatively potent stimulation of TRPM3-dependent calcium entry was observed. A sulphate group positioned at ring A was important for strong stimulation but more striking was the requirement for a cis (beta) configuration of the side group, revealing previously unrecognized stereo-selectivity and supporting existence of a specific binding site. A cis-oriented side group on ring A was not the only feature necessary for high activity because loss of the double bond in ring B reduced potency and loss of the acetyl group at ring D reduced efficacy and potency. Weak steroid stimulators of TRPM3 channels inhibited effects of PregS, suggesting partial agonism. In silico screening of chemical libraries for non-steroid modulators of TRPM3 channels revealed the importance of the steroid backbone for stimulatory effects. CONCLUSIONS AND IMPLICATIONS: Our data defined some of the chemical requirements for acute stimulation of TRPM3 channels by steroids, supporting the existence of a specific and unique steroid binding site. Epipregnanolone sulphate was identified as a novel TRPM3 channel stimulator.

A prospective clinical study to investigate the microbial contamination ofa needleless connector.

Needleless connectors, which allow direct access to intravascular catheters, are widely used in clinical practice. The benefits of these devices to healthcare workers are well documented; however, the potential risk of microbial contamination and associated infection is unclear. This clinical study evaluated microbial contamination rates for a needleless connector, Connecta Clave(R) (CC(R)), as compared to a conventional three-way tap, which was connected to the hubs of central venous catheters (CVC) immediately following insertion. Patients in the study group had CC(R) attached to the three-way taps, whereas the control group had standard entry port caps. On removal (up to 72 h) the connectors were studied for microbial contamination. There was no significant difference between the number of three-way taps contaminated on the internal surface with micro-organisms in the control group with entry port caps (19/132, 14%) compared to the group with CC(R) (18/105, 17%). Sixteen percent (27/173) of the CC(R) were contaminated with micro-organisms on the internal surfaces. The external surface of 33% (27/82) of the CC(R) silicone seals were contaminated after clinical use. Micro-organisms were also isolated from 9% (8/91) of the silicone seals after disinfection. The use of this needleless connector, compared to standard caps therefore does not appear to increase the risk of infection via the internal lumen of three-way taps.

Foliage damage in coniferous trees following volcanic ashfall from Mt. St. Helens.

The foliage of coniferous plants in the area to the northeast of Mt. St. Helens, Washington State, was exposed to heavy ashfall during the May 18, 1980 eruption of the volcano. Significant damage to the pre-1980 foliage occurred after the eruption and continued through the summer. The amount of damage seen on the needles was significantly related to the amount of ash on the foliage.Elevated temperatures caused the foliage damage. The presence of ash on the foliage increased the dimensions of the shoot, thus increasing the boundary layer resistance. In turn this change in geometry elevated needle temperatures. Typical maximum needle temperatures for ash-laden foliage of Abies amabilis were in the range of 35° to 45° C and were 10° C above those of plants without ash. Damage occurred to needles at 40° C after a short growth-chamber exposure. Temperatures within the ash on the foliage also exceeded 40 degrees C.Neither chemical nor mechanical (abrasion) damage occurred. There was no melting of the cuticle. The plants with ash-covered foliage did not experience lower water potentials than those of control plants. The total radiation reflected from the needles was similar for foliage with and without ash.

Low proton conductance of plant cuticles and its relevance to the Acid-growth theory.

Evidence obtained on the relation between the pH of the medium and the growth of intact stem sections is compatible with the acid-growth theory only if the proton conductance of the cuticle is so low that the cuticle is an effective barrier to the entry or exit of protons from the tissue. By measuring the rate at which protons cross frozen-thawed epidermal strips of sunflower (Helianthus annuus L.) and soybean hypocotyls (Glycine max Morr.) and enzymically isolated cuticles of Berberis aquifolium Persh. and tomato (Lycopersicum esculentum Mill.) fruit, we have now demonstrated the low proton conductance of the cuticular layer. Unless the conductance is enhanced by abrasion of the cuticle or by removal of the cuticular waxes, proton movement into and out of a tissue across the cuticle will be significant only over long time periods.