Molecular state and distribution of fullerenes entrapped in sol-gel samples.

A novel synthetic method that can encapsulate fullerene molecules (pure C60, pure C70, or their mixture) over a wide range of concentrations ranging from micromolar to millimolar in hybrid glass by a sol-gel method without any time-consuming, complicated, and unwanted extra steps (e.g., addition of a surfactant or derivatization of the fullerenes) has been successfully developed. The molecular state and distribution of encapsulated fullerene molecules in these sol-gel samples were unequivocally characterized using newly developed multispectral imaging techniques. The high sensitivity (single-pixel resolution) and ability of these instruments to record multispectral images at different spatial resolutions (approximately 10 microm with the macroscopic instrument and approximately 0.8 microm with the microscopic instrument) make them uniquely suited for this task. Specifically, the imaging instruments can be used to simultaneously measure multispectral images of sol-gel-encapsulated C60 and C70 molecules at many different positions within a sol-gel sample in an area either as large as 3 mm x 4 mm (with the macroscopic imaging instrument) or as small as 0.8 microm x 0.8 microm (with the microscopic instrument). The absorption spectrum of the fullerene molecule at each position can then be calculated either by averaging the intensity of a 15 x 15 square of pixels (which corresponds to an area of 3 mm x 4 mm) or from the intensity of a single pixel (i.e., an area of about 0.8 microm x 0.8 microm), respectively. The molecular state and distribution of fullerene molecules within sol-gel samples can then be determined from the calculated spectra. It was found that spectra of encapsulated C60 and C70 measured at five different positions within a sol-gel sample were similar not only to one another but also to spectra measured at six different times during the sol-gel reaction process (from t = 0 to 10 days). Furthermore, these spectra are similar to the corresponding spectra of monomeric C60 or C70 molecules in solution. Similarly, spectra of sol-gel samples containing a mixture of C60 and C70 were found to be the same at five different positions, as well as similar to spectra calculated from an average of the spectra of C60 and C70 either encapsulated in a sol-gel or in solution. It is evident from these results that C60 and C70 molecules do not undergo aggregation upon encapsulation into a sol-gel but rather remain in their monomeric state. Furthermore, entrapped C60 and C70 molecules in their monomeric state were distributed homogeneously throughout the entire sol-gel samples. Such a conclusion can be readily, quickly, and easily obtained, not with traditional spectroscopic techniques based on the use of a single-channel detector (absorption, fluorescence, infrared, Raman) but rather with the newly developed multispectral imaging technique. More importantly, the novel synthetic method reported here makes it possible, for the first time, to homogenously entrap monomeric fullerene molecules (C60, C70, or their mixture) in a sol-gel at various concentrations ranging from as low as 2.2 mM C60 (or 190 microM C70) to as high as 4.2 mM C60 (or 360 microM C70).

Nanodiamond particles forming photonic structures.

Colloid suspensions of irregularly shaped, highly charged detonation nanodiamond particles are found to have unexpected optical properties, similar to those of photonic crystals. This finding is all the more surprising since the particles used in this work are far more polydisperse than those typically forming photonic crystals. Intensely iridescent structures have been fabricated using the centrifugation of aqueous suspensions of nanodiamonds.

Near-infrared spectrophotometric determination of compositions of fullerene samples.

A novel method has been developed for the sensitive and accurate determination of compositions of fullerene samples. The method is based on the synergistic use of spectrophotometric measurements and partial least square method. The method is not only simple, inexpensive and fast but also is non-destructive. Compositions of various fullerene samples including fullerite which is the precursor to C(60) and C(70), can be directly and non-destructively determined by this method without any time-consuming separation step as in the HPLC method or destruction as in the MS method.

Determination of enantiomeric compositions of pharmaceutical products by near-infrared spectrometry.

A new method for the determination of enantiomeric compositions of a variety of drugs including propranolol, atenolol, and ibuprofen has been developed. The method is based on the use of the near-infrared technique to measure diastereomeric interactions between an added carbohydrate compound and both enantiomeric forms of a drug followed by evaluation of the data by partial least square analysis. The fact that the method works well with all three macrocyclic carbohydrates with different cavity sizes (i.e., alpha-, beta-, and gamma-cyclodextrin) and with sucrose, which is a linear carbohydrate, clearly demonstrates that it is not necessary to have inclusion complex formation to produce effective diastereomeric interactions. Rather a simple adsorption of the drug onto a carbohydrate is sufficient. Since inclusion complex formation is not a requisite, this method is not limited to the three drugs evaluated in this study but is rather universal as it can, in principle, be used for the sensitive and accurate determination of enantiomeric compositions of many different types of drugs with only about 1.5mg/mL concentration and enantiomeric excess as low as 0.80%, in water or in a mixture of water with organic solvent. Furthermore, it does not rely on the use of rather expensive carbohydrates such as cyclodextrins but is equally as effective even with a simple and inexpensive carbohydrate such as sucrose.

Determination of enantiomeric compositions of amino acids by near-infrared spectrometry through complexation with carbohydrate.

A new method has been developed for the determination of enantiomeric compositions of a variety of compounds. The method is based on the use of the near-infrared technique to measure diastereomeric interactions between an added carbohydrate compound with both enantiomeric forms of an analyte followed by partial least-squares analysis of the data. The fact that the method works well with all three macrocyclic carbohydrates with different cavity size (i.e., alpha-, beta-, and gamma-cyclodextrin) as well as with sucrose, which is a linear carbohydrate, clearly demonstrates that it is not necessary to have inclusion complex formation in order to produce effective diastereomeric interactions. Rather, a simple adsorption of the analyte onto a carbohydrate is sufficient. Since inclusion complex formation is not a requisite, this method is not limited to the amino acid studies here but is rather universal and sensitive as it can, in principle, be used to determine enantiomeric compositions for all types of compounds with only microgram concentration and enantiomeric excess as low as 1.5%, in water or in a mixture of water and organic solvent. Furthermore, it does not rely on the use of rather expensive carbohydrates such as cyclodextrins but is equally as effective even with a simple and inexpensive carbohydrate such as sucrose.

Enhancement of the thermal lens signal induced by sample matrix absorption of the probe laser beam.

The effect of the absorption of the probe laser beam by the sample matrix on the thermal lens signal of a solute was investigated for aqueous solutions of Tb(III), Yb(III), and Nd(III). The measurements were performed with a thermal lens instrument in which the pump and the probe beam were derived from a tunable Ti:sapphire laser. Thermal lens signals were found to be enhanced in the region where the probe beam overlapped with the absorption band of the sample matrix. The observed enhancement was confirmed further with samples of the same solutes (lanthanide ions) but in D20, which does not absorb in the same spectral region as water. The enhancement may be due to the fact that absorption by the sample matrix led to a change in its refractive index and the production of a temperature gradient. In addition to fundamental importance, the observed enhancement can be used to improve the sensitivity of the thermal lens measurements by judiciously selecting a solvent that absorbs the probe laser beam.