Structure of arginine overlayers at the aqueous gold interface: implications for nanoparticle assembly.

Adsorption of small biomolecules onto the surface of nanoparticles offers a novel route to generation of nanoparticle assemblies with predictable architectures. Previously, ligand-exchange experiments on citrate-capped gold nanoparticles with the amino acid arginine were reported to support linear nanoparticle assemblies. Here, we use a combination of atomistic modeling with experimental characterization to explore aspects of the assembly hypothesis for these systems. Using molecular simulation, we probe the structural and energetic characteristics of arginine overlayers on the Au(111) surface under aqueous conditions at both low- and high-coverage regimes. In the low-density regime, the arginines lie flat on the surface. At constant composition, these overlayers are found to be lower in energy than the densely packed films, although the latter case appears kinetically stable when arginine is adsorbed via the zwitterion group, exposing the charged guanidinium group to the solvent. Our findings suggest that zwitterion-zwitterion hydrogen bonding at the gold surface and minimization of the electrostatic repulsion between adjacent guanidinium groups play key roles in determining arginine overlayer stability at the aqueous gold interface. Ligand-exchange experiments of citrate-capped gold nanoparticles with arginine derivatives agmatine and N-methyl-l-arginine reveal that modification at the guanidinium group significantly diminishes the propensity for linear assembly of the nanoparticles.

Household composition and housing expenditures in rental-occupied and owner-occupied markets

This article examines the relationship between household compositions and housing expenditures in rental-occupied and owner-occupied markets. The author finds that renters allocate their budget proportionately between housing and nonhousing goods for an additional household member, leaving the budget share of housing expenditures unchanged. For homeowners, nevertheless, an extra member implies a reduction in housing expenditures as a share of total budget. Although age and gender compositions turn out to be significant in determining the budget share of housing expenditures for renters, they play no major role for homeowners. And although an increase in the number of working members for renters significantly reduces the share of budget spent on housing, it has no significant impact for their owner counterparts. Moreover, keeping total expenditures constant, the main income source of the head of the household does not make any difference in terms of resource allocation across housing and nonhousing goods for both renters and owners.

Intrinsic motivation in two exercise interventions: Associations with fitness and body composition

OBJECTIVE: To examine the motivational process through which increases in aerobic capacity and decreases in total body fat are achieved during high-intensity intermittent training (HIT) and moderate-intensity continuous training (MICT) interventions. METHOD: Eighty-seven physically inactive adults (65% women, age = 42 ± 12, BMI = 27.67 ± 4.99 kg/m²) took part in a 10-week randomized intervention testing group-based HIT, operationalized as repeated sprints of 15-60 s interspersed with periods of recovery cycling ≤ 25 min/session, 3 sessions/wk⁻¹, or MICT, operationalized as cycling at constant workload of ∼65% maximum aerobic capacity (VO₂max, 30-45 min/session⁻¹, 5 sessions/wk⁻¹. Assessments of VO₂max and total body fat were made pre- and postintervention. Motivation variables were assessed midintervention and class attendance was monitored throughout. Path analysis was employed, controlling for treatment arm and baseline values of VO₂max and total body fat. RESULTS: The 2 groups differed in adherence only, favoring HIT. Baseline VO₂max predicted intrinsic motivation midintervention. Intrinsic motivation predicted program adherence, which in turn predicted increases in VO2max and decreases in total body fat by the end of the study. CONCLUSION: Intrinsic motivation in HIT and MICT is positively linked to adherence to these programs, which can facilitate improvements in fitness and body composition.