Visualizing Molecular-Scale Adsorption Structures of Anti-freezing Surfactants on Sapphire (0001) Surfaces at Different Concentrations by 3D Scanning Force Microscopy

Anti-freezing surfactants form an adsorption layer at the solid-water interface to inhibit the nucleation and growth of ice. However, this mechanism has not been elucidated at the molecular scale because of the difficulties in visualizing such adsorption structures. In this study, we overcome this limitation by directly visualizing the three-dimensional (3D) adsorption structures of anti-freezing surfactants, hexadecyltrimethylammonium bromide (C₁₆TABs), on sapphire (0001) surfaces through 3D scanning force microscopy. We present molecularly resolved two-dimensional/3D images of the adsorption structures in solutions of 1, 10, and 100 ppm. At 1 ppm, the molecules form a monolayer with a flat-lying configuration. At 10 ppm, the molecular orientation is closer to the upright configuration, with a relatively large tilt angle. At 100 ppm, the molecules form a bilayer with almost upright configurations, providing excellent screening of the sapphire surface from water. Owing to the steric and electrostatic repulsion between adjacent molecular head groups, the surface of the bilayer exhibits relatively large fluctuations, inhibiting the formation of stable ice-like structures. The understanding of molecular-level mechanisms provides important guidelines for improving the design of anti-freezing surfactants for practical applications such as car coolants.

Unintentional Ethylene Glycol Poisoning in an Adolescent

The differential diagnosis is broad when a patient presents with an altered mental status. Ethylene glycol poisoning, a life-threatening condition, can occur as an intentional self-harm attempt or unintentional consumption. It is metabolized in the liver by a series of enzymes, and the metabolites so formed are responsible for the majority of clinical effects. The diverse range of clinical effects includes central nervous system (CNS), gastrointestinal, cardiovascular system (CVS), pulmonary as well as renal effects. The evidence of metabolic acidosis, elevated anion gap, high osmolal gap, and calcium oxalate crystals in laboratory analysis strongly suggests ethylene glycol poisoning. The treatment traditionally consists of alcohol dehydrogenase inhibitors such as fomepizole or ethanol, and in some cases, hemodialysis is needed as well.