Stability of Aliphatic Dithiocarboxylic Acid Self-Assembled Monolayers on Gold

Self-assembled monolayers (SAMs) were prepared by the adsorption of aliphatic dithiocarboxylic acids (ADTCAs) onto the surface of gold. The films were characterized using a variety of analytical techniques: ellipsometry, contact angle goniometry, polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS), and X-ray photoelectron spectroscopy (XPS). These studies found that the ADTCAs attach to the surface of gold via equivalent binding of both sulfur moieties in the dithiocarboxylic acid headgroup. The stability of these highly orientated SAMs was examined at room temperature under a variety of atmospheric conditions (i.e., under argon, oxygen, air, and humid air) and compared to the stability of related SAMs derived from n-alkanethiols. The ADTCA-based SAMs were observed to decompose relatively rapidly via oxidation of the sulfur headgroups, as judged by XPS. The rate of desorption of the SAMs was observed to vary as a function of the atmospheric conditions as well as the chain length of the ADTCA adsorbates

Worldwide trends in underweight and obesity from 1990 to 2022: a pooled analysis of 3663 population-representative studies with 222 million children, adolescents, and adults

Background Underweight and obesity are associated with adverse health outcomes throughout the life course. We estimated the individual and combined prevalence of underweight or thinness and obesity, and their changes, from 1990 to 2022 for adults and school-aged children and adolescents in 200 countries and territories. Methods We used data from 3663 population-based studies with 222 million participants that measured height and weight in representative samples of the general population. We used a Bayesian hierarchical model to estimate trends in the prevalence of different BMI categories, separately for adults (age ≥20 years) and school-aged children and adolescents (age 5–19 years), from 1990 to 2022 for 200 countries and territories. For adults, we report the individual and combined prevalence of underweight (BMI <18·5 kg/m2) and obesity (BMI ≥30 kg/m2). For schoolaged children and adolescents, we report thinness (BMI <2 SD below the median of the WHO growth reference) and obesity (BMI >2 SD above the median). Findings From 1990 to 2022, the combined prevalence of underweight and obesity in adults decreased in 11 countries (6%) for women and 17 (9%) for men with a posterior probability of at least 0·80 that the observed changes were true decreases. The combined prevalence increased in 162 countries (81%) for women and 140 countries (70%) for men with a posterior probability of at least 0·80. In 2022, the combined prevalence of underweight and obesity was highest in island nations in the Caribbean and Polynesia and Micronesia, and countries in the Middle East and north Africa. Obesity prevalence was higher than underweight with posterior probability of at least 0·80 in 177 countries (89%) for women and 145 (73%) for men in 2022, whereas the converse was true in 16 countries (8%) for women, and 39 (20%) for men. From 1990 to 2022, the combined prevalence of thinness and obesity decreased among girls in five countries (3%) and among boys in 15 countries (8%) with a posterior probability of at least 0·80, and increased among girls in 140 countries (70%) and boys in 137 countries (69%) with a posterior probability of at least 0·80. The countries with highest combined prevalence of thinness and obesity in school-aged children and adolescents in 2022 were in Polynesia and Micronesia and the Caribbean for both sexes, and Chile and Qatar for boys. Combined prevalence was also high in some countries in south Asia, such as India and Pakistan, where thinness remained prevalent despite having declined. In 2022, obesity in school-aged children and adolescents was more prevalent than thinness with a posterior probability of at least 0·80 among girls in 133 countries (67%) and boys in 125 countries (63%), whereas the converse was true in 35 countries (18%) and 42 countries (21%), respectively. In almost all countries for both adults and school-aged children and adolescents, the increases in double burden were driven by increases in obesity, and decreases in double burden by declining underweight or thinness. Interpretation The combined burden of underweight and obesity has increased in most countries, driven by an increase in obesity, while underweight and thinness remain prevalent in south Asia and parts of Africa. A healthy nutrition transition that enhances access to nutritious foods is needed to address the remaining burden of underweight while curbing and reversing the increase in obesit

Physical organic probes of interfacial wettability reveal the importance of surface dipole effects

ABSTRACT: The interfacial wettabilities of self-assembled monolayers (SAMs) on gold generated from trifluoromethyl-and methyl-terminated alkanethiols were evaluated using a combination of non-polar, polar protic and polar aprotic contacting liquids. The wettabilities for the non-polar hydrocarbon liquids indicate that the fluorinated films are wet less than the hydrocarbon films, demonstrating the non-ideal nature of dispersive interactions between hydrocarbons and fluorocarbons. In contrast, the wettabilities for the polar liquids revealed that the fluorinated films were wet more than the hydrocarbon films. The presence of interactions between the dipoles of the liquid molecules and oriented CF 3 -CH 2 dipoles at the monolayer surface was proposed to rationalize the observed trends. Furthermore, the wettabilities of the polar aprotic liquids exhibited an inverse odd-even trend that supports the existence of oriented dipole effects upon wettability. The influence of the dipoles on the interfacial wettabilities was further examined using a series of SAMs generated from terminally fluorinated hexadecanethiols having an increasing degree of fluorination. As the dipoles were buried further into the monolayer surface, their influence on the wettabilities decreased. The interfacial energies of wetting for these films were evaluated in terms of their works of adhesion. These analyses provided evidence for the contribution of oriented dipoles to the interfacial interactions of organic thin films, in addition to the commonly recognized contributions of dispersive and acid-base interactions