A water-based route has been demonstrated for synthesizing ZnSe and Cd-doped ZnSe (Zn(x)Cd(1-x)Se, 0 < x < 1) quantum dots (QDs) that have tunable and narrow photoluminescence (PL) peaks from the ultraviolet A (UVA) to the blue range (350-490 nm) with full-width at half-maximum (fwhm) values of 24-36 nm. Hydrazine (N(2)H(4)) was used to maintain oxygen-free conditions, allowing the reaction vessel to be open to air. The properties of the QDs were controlled using the thiol ligands, 3-mercaptopropionic acid (MPA), thiolglycolic acid (TGA), and l-glutathione (GSH). On the basis of optical spectra, linear three-carbon MPA attenuated nucleation and growth, yielding small ZnSe QDs with a high density of surface defects. In contrast, TGA and GSH produced larger ZnSe QDs with lower surface defect densities. The absorption spectra show that growth was more uniform and better controlled with linear two-carbon TGA than branched bifunctional GSH. After 20 min of growth TGA-capped ZnSe had an average diameter of 2.5 nm based on high-resolution transmission electron microscopy images; these nanocrystals had an absorbance peak maximum of approximately 340 nm (3.65 eV) and a band gap PL emission peak at 372 nm (3.34 eV). Highly fluorescent Zn(x)Cd(1-x)Se QDs were fabricated by adding a Cd-thiol complex directly to ZnSe QD solutions; PL peaks were tuned in the blue range (400-490 nm) by changing the Zn to Cd ratio. The Cd-bearing nanocrystals contained proportionally more Se based on X-ray photoelectron spectroscopy, and Cd-Se bonds had ionic character, in contrast to primarily covalent Zn-Se bonds.

Mechanical ventilation with PEEP results in longitudinal atrophy of diaphragm fibers, a response that is modulated by the elasticity of the giant sarcomeric protein titin. We postulate that longitudinal atrophy, in concert with the aforementioned cross-sectional atrophy, hampers spontaneous breathing trials in critically ill patients: during these efforts, end-expiratory lung volume is reduced, and the shortened diaphragm fibers are stretched to excessive sarcomere lengths. At these lengths, muscle fibers generate less force, and diaphragm weakness ensues.

Muscle ankyrin repeat protein 1 (MARP1) is frequently up-regulated in stressed muscle, but its effect on skeletal muscle function is poorly understood. Here, we focused on its interaction with the titin–N2A element, found in titin’s molecular spring region. We show that MARP1 binds to F-actin, and that this interaction is stronger when MARP1 forms a complex with titin–N2A. Mechanics and super-resolution microscopy revealed that MARP1 “locks” titin–N2A to the sarcomeric thin filament, causing increased extension of titin’s elastic PEVK element and, importantly, increased passive force. In support of this mechanism, removal of thin filaments abolished the effect of MARP1 on passive force. The clinical relevance of this mechanism was established in diaphragm myofibers of mechanically ventilated rats and of critically ill patients. Thus, MARP1 regulates passive force by locking titin to the thin filament. We propose that in stressed muscle, this mechanism protects the sarcomere from mechanical damage.

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