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Prevention programs should address relationship context in contraceptive decision making, perhaps by combining relationship and sex education curricula to foster communication and negotiation skills.

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Picosecond mid-IR pump-probe measurements of vibrational relaxation (VR) of CO bound to the active sites of wild-type and mutant myoglobins (Mb) reveal that an approximately linear relationship exists between the protein matrix-induced CO frequency shift and the VR rate. This relation parallels a similar linear relationship seen in a series of heme model compounds where Fe was replaced by Ru and Os. The VR rate of CO in the Mb is sensitive only to the magnitude of protein-induced carbonyl frequency shifts and apparently is not sensitive to the specific details of how the shift is induced, e.g., hydrogen bonding to CO or electrostatic interactions in the heme pocket. CO VR is insensitive to substantial changes in protein structure that do not affect the CO vibrational frequency. These observations suggest that the mechanism of carbon monoxide VR in heme proteins such as Mb occurs by through-π-bond anharmonic coupling, which, as shown in prior work, is also the dominant coupling in the model compounds. The experiments indicate that differing protein structures influence VR of CO bound at the active site not by opening and closing channels for vibrational energy flow from CO to the protein but by affecting the rate of energy flow from CO to heme. The rates are determined by the extent of back-bonding, which determines the magnitude of through-π-bond anharmonic coupling between CO and heme. The back-bonding and, therefore, the extent of anharmonic coupling are influenced by the electric fields in the heme pocket, which likely differ in the proteins studied here.

A Michelson-type spectral interferometer that uses a common beam path for the reference and the sample arms is described. This optical arrangement is more compact and stable than the more commonly used dual-arm interferometer and is well suited for frequency-domain optical coherence tomography of biological samples. With a 16-bit CCD camera, the instrument has sufficient dynamic range and resolution for imaging to depths of 2 mm in scattering biological materials. Images obtained with this spectral interferometer are presented, including cross-sectional images in a Xenopus laevis tadpole.