The concept of a spatial-velocity hodograph is introduced to describe quantitatively the extrusion of a carbon tubule from a catalytic particle. The conditions under which a continuous tubular surface can be generated are discussed in terms of this hodograph, the shape of which determines the geometry of the initial nanotube. The model is consistent with all observed tubular shapes and explains why the formation process induces stresses that may lead to "spontaneous" plastic deformation of the tubule. This result is due to the violation of the continuity condition, that is, to the mismatch between the extrusion velocity by the catalytic particle, required to generate a continuous tubular surface, and the rate of carbon deposition.

Prenylated flavonoids found in hops and beer, i.e., prenylchalcones and prenylflavanones, were examined for their ability to inhibit in vitro oxidation of human low-density lipoprotein (LDL). The oxidation of LDL was assessed by the formation of conjugated dienes and thiobarbituric acid-reactive substances (TBARS) and the loss of tryptophan fluorescence. At concentrations of 5 and 25 microM, all of the prenylchalcones tested inhibited the oxidation of LDL (50 microg protein/ml) induced by 2 microM copper sulfate. The prenylflavanones showed less antioxidant activity than the prenylchalcones, both at 5 and 25 microM. At 25 microM, the nonprenylated chalcone, chalconaringenin (CN), and the nonprenylated flavanone, naringenin (NG), exerted prooxidant effects on LDL oxidation, based on TBARS formation. Xanthohumol (XN), the major prenylchalcone in hops and beer, showed high antioxidant activity in inhibiting LDL oxidation, higher than alpha-tocopherol and the isoflavone genistein but lower than the flavonol quercetin. When combined, XN and alpha-tocopherol completely inhibited copper-mediated LDL oxidation. These findings suggest that prenylchalcones and prenylflavanones found in hops and beer protect human LDL from oxidation and that prenylation antagonizes the prooxidant effects of the chalcone, CN, and the flavanone, NG.

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Background-Moderate red wine consumption is inversely associated with coronary ischemia, and both red wine and purple grape juice (PGJ) contain flavonoids with antioxidant and antiplatelet properties believed to be protective against cardiovascular events. Acute cardiac events are also associated with decreased platelet-derived nitric oxide (NO) release. In this study, the effects of PGJ and PGJ-derived flavonoids on platelet function and platelet NO production were determined. Methods and Results-Incubation of platelets with dilute PGJ led to inhibition of aggregation, enhanced release of platelet-derived NO, and decreased superoxide production. To confirm the in vivo relevance of these findings, 20 healthy subjects consumed 7 mL · kg Ϫ1 · d Ϫ1 of PGJ for 14 days. Platelet aggregation was inhibited after PGJ supplementation, platelet-derived NO production increased from 3.5Ϯ1.2 to 6.0Ϯ1.5 pmol/10 8 platelets, and superoxide release decreased from 29.5Ϯ5.0 to 19.2Ϯ3.1 arbitrary units (PϽ0.007 and PϽ0.05, respectively). ␣-Tocopherol levels increased significantly after PGJ consumption (from 15.6Ϯ0.7 to 17.6Ϯ0.9 mol/L; PϽ0.009), and the plasma protein-independent antioxidant activity increased by 50.0% (PϽ0.05). Last, incubation of platelets with select flavonoid fractions isolated from PGJ consistently attenuated superoxide levels but had variable effects on whole-blood aggregation, platelet aggregation, and NO release. Conclusions-Both in vitro incubation and oral supplementation with PGJ decrease platelet aggregation, increase platelet-derived NO release, and decrease superoxide production. These findings may be a result of antioxidant-sparing and/or direct effects of select flavonoids found in PGJ. The suppression of platelet-mediated thrombosis represents a potential mechanism for the beneficial effects of purple grape products, independent of alcohol consumption, in cardiovascular disease. (Circulation. 2001;103:2792-2798.)