Enhanced optical limiting in derivatized fullerenes.

We have observed enhanced optical limiting behavior in solutions of a derivatized fullerene (phenyl-C(61)-butyric acid cholesteryl ester) from 532 to 700 nm. Transient absorption measurements determined the spectral and temporal regions of interest for optical limiting in C(60) and in C(60) derivatives that are due to a reverse saturable absorption mechanism and predicted enhanced limiting at longer wavelengths. Intensity-dependent transmission measurements made at several wavelengths confirmed these results. The increased solubility and the broadened ground-state absorption of the functionalized C(60) make it suitable for use as an optical limiter in the red and the near infrared.

Conjugated polymer films for gas separations.

Permeabilities for a series of gases through free-standing films of the conjugated polymer polyaniline are reported. A remarkable selectivity has been achieved for important gas pairs incuding hydrogen-nitrogen, oxygen-nitrogen, and carbon dioxide-methane. The selectivity values of 3590 for H(2)/N(2), 30 for O(2)/N(2), and 336 for CO(2)/CH(4) surpass the highest previously reported values of 313, 16, and 60 for the nonconjugated polymers poly(trifluorochloroethylene), cellulose nitrate, and a fluorinated polyimide, respectively. The process for tailoring gas selectivity of a polyaniline membrane involves first enhancing the permeabilities of gases with small diameters [<3.5 angstroms (A)] by doping and undoping the polymer film with counterions of an appropriate size. High selectivities are then achieved by decreasing the permeabilities of larger gases (>3.5 A diameter) through controlled redoping of the polymer. The permanent morphological changes induced in this conjugated polymer system and others indicate the potential for development of universal membranes for gas separations.

Carbon/nutrient balance as a predictor of plant defense in Alaskan balsam poplar: Potential importance of metabolite turnover.

The carbon/nutrient balance hypothesis fails to correctly predict effects of fertilization and shading on concentrations of defensive metabolites in Alaskan balsam poplar (Populus balsamifera). Of six metabolites analyzed, only one responded in the predicted fashion to fertilization and one to shading. These results and those of other similar studies suggest that while the carbon/nutrient balance hypothesis may correctly predict the effects of fertilization and shading on the concentrations of metabolic "end products", it fails for many metabolites because of the dynamics associated with their production and turnover. In metabolites that turn over, static concentration is a poor predictor of defensive investment.

Winter chemical defense of Alaskan balsam poplar against snowshoe hares.

Palatabilities of parts and growth stages of balsam poplar (Populus balsamifera) to snowshoe hares (Lepus americanus) are related to concentrations of specific plant metabolites that act as antifeedants. Buds are defended from hares by cineol, benzyl alcohol, and (+)-α-bisabolol. Internodes are defended by 6-hydroxycylohexenone (6-HCH) and salicaldehyde. Although defense of interaodes depends upon both compounds, the defense of juvenile internodes is principally related to salicaldehyde concentration; the defense of internode current annual growth is principally related to 6-HCH concentration. The concentration of 6-HCH can be supplemented by the hydrolysis of phenol glycosides when plant tissue is disrupted, raising the possibility of a dynamic element of the chemical defense of poplar.