Caerin 1.1 is one of the major antimicrobial peptides isolated from the skin of the Australian green tree frog, Litoria splendida. Two‐dimensional 1H‐1H and 1H‐13C NMR spectroscopy in trifluoroethanol/ H2O (50:50, by vol.) have been used to assign the 1H and 13C‐NMR spectra of this 25‐amino‐acid peptide. From an examination of these data, and using distance geometry and molecular dynamics calculations, the solution conformation of caerin 1.1 has been determined. The peptide adopts two well‐defined helices from Leu2 to Lys11 and from Val17 to His24 separated by a region of less‐defined helicity and greater flexibility. Overall, the peptide has a distinct amphipathic charge distribution. The solution structure of caerin 1.1 is compared with activity data against a variety of micro‐organisms for the parent peptide and some naturally occurring and synthetic variants of caerin 1.1. The structural and activity data are consistent with caerin 1.1 interacting with membranes in a similar manner to other antimicrobial peptides, i.e. via a carpet‐like mechanism whereby the individual peptides aggregate in a helical manner and orient themselves parallel to the membrane in a sheet‐like arrangement [Shai, Y. (1995) Trends Biochem. Sci. 20, 460–464].

In a pilot study to determine if zinc (Zn) from zinc oxide nanoparticles in sunscreen can penetrate human skin in vivo, nanoparticles (~30nm) of a stable isotope (52% (68)Zn enrichment) were incorporated into an essentially phytochemical-based formulation and applied to the backs of 3 human subjects twice daily for 5 days during the Southern Hemisphere winter. Blood and urine were collected prior to application and at regular intervals and up to 50 days. As observed in a larger outdoor trial following this pilot study but with a different formulation and with UV exposure: values of (68)Zn in blood continued to increase beyond the 5 day application phase with the highest measurement at 14 days after the first application; variable amounts of the (68)Zn tracer were observed in urine; and the amounts of extra Zn added to blood were small and indicate very low levels of absorption (minimal estimate <0.01% of the applied dose) through the skin. Reasons for differences in absorption detected in the stable isotope trials and previous investigations include: the sensitivity of the stable isotope method; the duration of the investigations; the number of applications of sunscreen formulation; in vitro methods with excised skin; lack of measurement of blood and urine; no skin flexing; and lack of UV exposure.

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3C N.m.r. chemical shifts have been assigned to 40 natural and synthetic proanthocyanidins, related flavan-3-ols, and their peracetate derivatives. These data may be used to draw structural inferences from the related spectra of proanthocyanidin polymers.

Numerous publications and reports have expressed health and safety concerns about the production and use of nanoparticles, especially in areas of exposure monitoring, personal use, and environmental fate and transport. We suggest that stable isotopic tracers, which have been used widely in the earth sciences and in metabolic and other health-related studies for several decades, could be used to address many of these issues. One such example we are pursuing is the use of stable isotopes to monitor dermal absorption of zinc and titanium oxides in sunscreen preparations and other personal care products. Other potential applications of this tracing approach are discussed.