Model of Controlled Synthesis of Uniform Colloid Particles: Cadmium Sulfide

The recently developed two-stage growth model of synthesis of monodispersed polycrystalline colloidal particles is utilized and improved to explain growth of uniform cadmium sulfide spheres. The model accounts for the coupled processes of nucleation, which yields nanocrystalline precursors, and aggregation of these subunits to form the final particles. The key parameters have been identified that control the size selection and uniformity of the CdS spheres, as well as the dynamics of the process. This approach can be used to generally describe the formation of monodispersed colloids by precipitation from homogeneous solutions.Comment: 20 pages in PD

Formation of Monodispersed Cadmium Sulfide Particles by Aggregation of Nanosize Precursors

Monodispersed spherical cadmium sulfide particles were used as a model system in order to explain the size selection in the formation of colloids by aggregation of nanosize subunits. Several procedures of mixing the reactants were employed to precipitate these solids and follow the kinetics of particle growth. Efficient numerical simulation techniques for the model rate equations were developed to fit the experimental results. Our results have confirmed the recently proposed mechanism of two-stage growth by nucleation of nanosize crystalline primary particles and their subsequent aggregation into polycrystalline secondary colloids.Comment: 18 pages (with 6 figures) in PD

Rapamycin-mediated mouse lifespan extension: Late-life dosage regimes with sex-specific effects.

To see if variations in timing of rapamycin (Rapa), administered to middle aged mice starting at 20 months, would lead to different survival outcomes, we compared three dosing regimens. Initiation of Rapa at 42 ppm increased survival significantly in both male and female mice. Exposure to Rapa for a 3-month period led to significant longevity benefit in males only. Protocols in which each month of Rapa treatment was followed by a month without Rapa exposure were also effective in both sexes, though this approach was less effective than continuous exposure in female mice. Interpretation of these results is made more complicated by unanticipated variation in patterns of weight gain, prior to the initiation of the Rapa treatment, presumably due to the use of drug-free food from two different suppliers. The experimental design included tests of four other drugs, minocycline, β-guanidinopropionic acid, MitoQ, and 17-dimethylaminoethylamino-17-demethoxygeldanamycin (17-DMAG), but none of these led to a change in survival in either sex

Rapamycin-mediated mouse lifespan extension: Late-life dosage regimes with sex-specific effects.

To see if variations in timing of rapamycin (Rapa), administered to middle aged mice starting at 20 months, would lead to different survival outcomes, we compared three dosing regimens. Initiation of Rapa at 42 ppm increased survival significantly in both male and female mice. Exposure to Rapa for a 3-month period led to significant longevity benefit in males only. Protocols in which each month of Rapa treatment was followed by a month without Rapa exposure were also effective in both sexes, though this approach was less effective than continuous exposure in female mice. Interpretation of these results is made more complicated by unanticipated variation in patterns of weight gain, prior to the initiation of the Rapa treatment, presumably due to the use of drug-free food from two different suppliers. The experimental design included tests of four other drugs, minocycline, β-guanidinopropionic acid, MitoQ, and 17-dimethylaminoethylamino-17-demethoxygeldanamycin (17-DMAG), but none of these led to a change in survival in either sex

Metabolic and Neuropsychiatric Effects of Calorie Restriction and Sirtuins

Most living organisms, including humans, age. Over time the ability to do physical and intellectual work deteriorates, and susceptibility to infectious, metabolic, and neurodegenerative diseases increases, which leads to general fitness decline and ultimately to death. Work in model organisms has demonstrated that genetic and environmental manipulations can prevent numerous age-associated diseases, improve health at advanced age, and increase life span. Calorie restriction (CR) (consumption of a diet with fewer calories but containing all the essential nutrients) is the most robust manipulation, genetic or environmental, to extend longevity and improve health parameters in laboratory animals. However, outside of the protected laboratory environment, the effects of CR are much less certain. Understanding the molecular mechanisms of CR may lead to the development of novel therapies to combat diseases of aging and to improve the quality of life. Sirtuins, a family of NAD+-dependent enzymes, mediate a number of metabolic and behavioral responses to CR and are intriguing targets for pharmaceutical interventions. We review the molecular understanding of CR; the role of sirtuins in CR; and the effects of sirtuins on physiology, mood, and behavior.Paul F. Glenn FoundationNational Institutes of Health (U.S.