Identification of parameters through which surface chemistry determines the lifetimes of hot electrons in small Au nanoparticles

This paper describes measurements of the dynamics of hot electron cooling in photoexcited gold nanoparticles (Au NPs) with diameters of ∼3.5 nm, and passivated with either a hexadecylamine or hexadecanethiolate adlayer, using ultrafast transient absorption spectroscopy. Fits of these dynamics with temperature-dependent Mie theory reveal that both the electronic heat capacity and the electron–phonon coupling constant are larger for the thiolated NPs than for the aminated NPs, by 40% and 30%, respectively. Density functional theory calculations on ligand-functionalized Au slabs show that the increase in these quantities is due to an increased electronic density of states near the Fermi level upon ligand exchange from amines to thiolates. The lifetime of hot electrons, which have thermalized from the initial plasmon excitation, increases with increasing electronic heat capacity, but decreases with increasing electron–phonon coupling, so the effects of changing surface chemistry on these two quantities partially cancel to yield a hot electron lifetime of thiolated NPs that is only 20% longer than that of aminated NPs. This analysis also reveals that incorporation of a temperature-dependent electron–phonon coupling constant is necessary to adequately fit the dynamics of electron cooling.     

Categorization of fragrance contact allergens for prioritization of preventive measures: clinical and experimental data and consideration of structure–activity relationships

Contact allergy to fragrances is still relatively common, affecting ～ 16% of patients patch tested for suspected allergic contact dermatitis, considering all current screening allergens. The objective of the review is to systematically retrieve, evaluate and classify evidence on contact allergy to fragrances, in order to arrive at recommendations for targeting of primary and secondary prevention. Besides published evidence on contact allergy in humans, animal data (local lymph node assay), annual use volumes and structure–activity relationships (SARs) were considered for an algorithmic categorization of substances as contact allergens. A total of 54 individual chemicals and 28 natural extracts (essential oils) can be categorized as established contact allergens in humans, including all 26 substances previously identified as contact allergens (SCCNFP/0017/98). Twelve of the 54 individual chemicals are considered to be of special concern, owing to the high absolute number of reported cases of contact allergy (> 100). Additionally, 18 single substances and one natural mixture are categorized as established contact allergens in animals. SARs, combined with limited human evidence, contributed to the categorization of a further 26 substances as likely contact allergens. In conclusion, the presence of 127 single fragrance substances and natural mixtures should, owing to their skin sensitizing properties, be disclosed, for example on the label. As an additional preventive measure, the maximum use concentration of 11 substances of special concern should be limited to 100 ppm. The substance hydroxyisohexyl 3‐cyclohexene carboxaldehyde and the two ingredients chloroatranol and atranol in the natural extracts Evernia prunastri and Evernia furfuracea should not be present in cosmetic products.     

A Randomized Control Trial for Evaluating Efficacies of Two Online Cognitive Interventions With and Without Fear-Appeal Imagery Approaches in Preventing Unprotected Anal Sex Among Chinese Men Who Have Sex with Men

Fear appeal approach has been used in health promotion, but its effectiveness has been mixed. It has not been well applied to HIV prevention among men who have sex with men (MSM). The present study developed and evaluated the relative efficacy of three online interventions (SC: STD-related cognitive approach, SCFI: STD-related cognitive plus fear appeal imagery approach, Control: HIV-related information based approach) in reducing prevalence of unprotected anal intercourse (UAI) among 396 MSM using a randomized controlled trial design. Participants’ levels of fear-related emotions immediately after watching the assigned intervention materials were also assessed. Participants were evaluated at baseline and 3 months after the intervention. Results showed that participants in the SCFI scored significantly higher in the instrument assessing fear after the watching the intervention materials. However, no statistically significant differences were found across the three groups in terms of UAI at Month 3. Some significant within-group reductions in some measures of UAI were found in three groups. Further studies are warranted to test the role of fear appeal in HIV prevention.