EVALUATION OF FREEZE DRIED ALOE VERA AND NOPAL CACTUS FOR POSSIBLE HEALTH TREATMENTS BY COMPARISON OF ANTIOXIDANT PROPERTIES AND FREE RADICAL INHIBITION.

The goal of this project was to characterize the antioxidant powers of lyophilized Aloe Vera (Aloe barbadensis) and Nopal Cactus (Opuntia ficus-indica) by quantifying the phenolics content and radical scavenging abilities of preparations derived from these plants. Extracts of these lyophylized succulents were assayed for phenolic compounds by the Folin Ciocalteau method and compared for free radical scavenging capability by the DPPH method. We found that even though the Aloe lyophilizate extract contained more phenolic content, the Nopal lyophilizate exhibited better free radical scavenging ability. Aloe Vera extract contained 0.278 g/L of phenolic content and exhibited 11.1% free radical inhibition, with a free radical scavenging rate constant of 0.177±0.015 min-1. Nopal Cactus extract contained 0.174 g/L of phenolic content and exhibited 13.2% free radical inhibition, with a free radical scavenging rate constant of 0.155±0.009 min-1. These results showed Nopal to have greater antioxidant potency than Aloe.

Generalizing thermodynamic properties of bulk single-walled carbon nanotubes.

The enthalpy and Gibbs free energy thermodynamical potentials of single walled carbon nanotubes were studied of all types (armchairs, zig-zags, chirals (n>m), and chiral (n

Propagation lengths of surface plasmon polaritons on metal films with arrays of subwavelength holes by infrared imaging spectroscopy.

Metal films with arrays of subwavelength holes (mesh) exhibit extraordinary transmission resonances to which many attribute a role for surface plasmon polaritons (SPPs); others debated this point. Experimental measurements of propagation lengths are presented under conditions that pertain to the use of SPPs for surface spectroscopy. The lateral extent of electromagnetic propagation along the mesh surface is measured by recording absorption spectra of a line of latex microspheres as a function of distance away from the line along the mesh. Measurements reveal an exponential functional form for decay of absorption signal laterally from the absorption source. Results at 697 cm(-1), which are closest to the strongest transmission resonance of the mesh, reveal a 1/e propagation distance along the surface of 17.8+/-2.9 microm. This is 40% larger than the lattice spacing implicating the holes as the SPP damping mechanism, however, this is significantly shorter than smooth metal expectations.

Extraordinary transmission of metal films with arrays of subwavelength holes.

Metal films with patterns of subwavelength holes (grids or meshes) have interesting optical properties including the extraordinary transmission effect. These optically thick metal films transmit more radiation than that incident on the holes owing to the excitation of surface plasmons (SPs). Meshes present a new and simple way to excite SPs at perpendicular incidence (i.e., without the need to vary the angle of the incident beam). This represents a new opportunity to integrate SPs with experiments and devices-a new instrument in the toolbox of SP techniques that may broaden the range of SP applications. This review discusses the discovery, basic optical physics, the role of SPs, and applications of the extraordinary transmission of subwavelength hole arrays.

Interaction of an infrared surface plasmon with an excited molecular vibration.

The interaction of an infrared surface plasmon and an excited molecular vibration was investigated by using a square array of subwavelength holes in a Ni film which supports propagating, surface-plasmon-mediated, transmission resonances. The largest transmission resonance [the (1,0)(-)] was tuned through the rocking vibration of the hexadecane molecule (at 721 cm(-1)) in a hexadecane film on the mesh by varying the thickness of the film. The interaction of the rocking vibration and surface plasmon is characterized spectroscopically by an increase in the intensity of the vibrational band by more than a factor of 2, variation of the vibrational line shape relative to the spectrum on a nonmetallic surface, and shifts in vibrational peak position by as much as 3.0 cm(-1). Relationships are developed between the transmission resonance position and the thickness and dielectric properties of the coating.

Carbon chains and the (5,5) single-walled nanotube: structure and energetics versus length.

Reliable thermochemistry is computed for infinite stretches of pure-carbon materials including acetylenic and cumulenic carbon chains, graphene sheet, and single-walled carbon nanotubes (SWCNTs) by connection to the properties of finite size molecules that grow into the infinitely long systems. Using ab initio G3 theory, the infinite cumulenic chain (:C[double bond]C[double bond]C[double bond]C:) is found to be 1.9+/-0.4 kcal/mol per carbon less stable in free energy at room temperature than the acetylenic chain (.C[triple bond]C-C[triple bond]C.) which is 24.0 kcal/mol less stable than graphite. The difference between carbon-carbon triple, double, and single bond lengths (1.257, 1.279, and 1.333 A, respectively) in infinite chains is evident but much less than with small hydrocarbon molecules. These results are used to evaluate the efficacy of similar calculations with the less rigorous PM3 semiempirical method on the (5,5) SWCNT, which is too large to be studied with high-level ab initio methods. The equilibrium electronic energy change for C(g)-->C[infinite (5,5) SWCNT] is -166.7 kcal/mol, while the corresponding free energy change at room temperature is -153.3 kcal/mol (6.7 kcal/mol less stable than graphite). A threefold alternation (6.866, 6.866, and 6.823 A) in the ring diameter of the equilibrium structure of infinitely long (5,5) SWCNT is apparent, although the stability of this structure over the constant diameter structure is small compared to the zero point energy of the nanotube. In general, different (n,m) SWCNTs have different infinite tube energetics, as well as very different energetic trends that vary significantly with length, diameter, and capping.

Controlling the passage of light through metal microchannels by nanocoatings of phospholipids.

The flow of polarized light through a metal film with an array of microchannels is controlled by the phase of an optically active, phospholipid nanocoating, even though the coating does not cover the open area of the microchannels. The molecular details of the assembly (DPPC phospholipid monolayer/bilayer on a hexadecanethiol monolayer on a copper- or nickel-coated microarray) were determined using the infrared, surface-plasmon-mediated, extraordinary transmission of the metal microarrays. Infrared absorption spectra with greatly enhanced absorptions by comparison to literature were recorded and used as a diagnostic for the phase, composition, and molecular geometry of these nanocoatings. This approach presents new tools for nanoscale construction in constricted microspaces, which may ultimately be useful with individual microchannels.

Enhanced infrared absorption spectra of self-assembled alkanethiol monolayers using the extraordinary infrared transmission of metallic arrays of subwavelength apertures.

The surface-plasmon-mediated, extraordinary transmission of metallic arrays of subwavelength apertures has been used as the light source for absorption studies of self-assembled monolayers on metal. Enhanced infrared absorption spectra of a sequence of alkanethiol self-assembled monolayers on copper were recorded for carbon chain lengths varying from 8 to 18 atoms. Transition positions and intensities are presented over a large range of the infrared region. The connection between the vibrational modes of the CH(2) wagging progression and the infinite methylene chain is explored using a traditional coupled oscillator approach and a new cluster perspective.