The optical rotatory dispersion (ORD), electronic circular dichroism (ECD), and vibrational circular dichroism (VCD) spectra of (+)-garcinia acid dimethyl ester have been measured and analyzed by comparison with the corresponding spectra predicted by quantum chemical methods for (2S,3S)-garcinia acid dimethyl ester. For solution-phase calculations the recently developed continuous surface charge polarizable continuum model (PCM) has been used. It is found that gas-phase predictions and PCM predictions at the B3LYP/aug-cc-pVDZ level yield nearly mirror-image ECD spectra in the 190–250 nm region for the same absolute configuration and that gas-phase ECD predictions lead to incorrect absolute configuration. At the CAM-B3LYP/aug-cc-pVDZ level, however, gas-phase predictions and PCM predictions of ECD in the 190–250 nm region are not so different, but PCM predictions provide better agreement with the experimental observations. For carbonyl stretching vibrations, the vibrational band positions predicted at the B3LYP/aug-cc-pVDZ level in gas-phase calculations differ significantly from the corresponding experimentally observed band positions, and this discrepancy has also been corrected by the use of PCM. In addition, the solution-phase VCD predictions provided better agreement (with experimental VCD observations) than gas-phase VCD predictions. These observations underscore the importance of including solvent effects in quantum chemical calculations of chiroptical spectroscopic properties.
A detailed investigation on the effect of preparation method on the structural, magnetic, and acidic properties of cobalt ferrite nanoparticles prepared by sol-gel and co-precipitation is presented. Citric acid and ethylene glycol were used as gelling agents, while sodium hydroxide and aqueous ammonia were used as precipitating agents. The resulting ferrites were calcined at 450 ℃ and 750 ℃. Sharper X-ray diffraction (XRD) peaks were observed for the samples calcined at 750 ℃, indicating greater crystallinity of the samples calcined at higher temperature. Average crystallite sizes fell in the ranges of 7.1-21.1 nm and 30.4-42.1 nm for the samples calcined at 450 ℃ and 750 ℃, respectively. The infrared spectra revealed two main absorption bands, the high frequency band ν 1 around 600 cm 1 and the low frequency band ν 2 around 400 cm 1 arising from stretching vibrations of the oxygen bond with the metal in the tetrahedral (A) and octahedral (B) sites in the spinel lattice. Agglomeration of particles was observed in the scanning electron microscopy (SEM) images. Magnetic parameters of CoFe 2 O 4 nanoparticles greatly depended on calcination temperature and preparation techniques. Ammonia temperature programmed desorption (TPD) measurements indicated that weak acid sites predominate medium strength sites, while the number of strong acid sites is the least. Cumulative acidity decreased for the samples calcined at higher temperature. The results underline the effect of preparation conditions on the morphology, crystallite size, and magnetic properties of nano ferrites.
Determination of the absolute configurations and predominant conformations of chiral natural products, occurring as carboxylic acids, using chiroptical spectroscopic methods becomes challenging due to the formation of solute aggregates (in the form of dimers, etc.) and/or solute-solvent complexes resulting from intermolecular hydrogen bonding with solvent. A hypothesis that such aggregation effects can be avoided by using corresponding sodium salts or acid anhydrides for chiroptical spectroscopic measurements has been tested. For this purpose, vibrational circular dichroism, electronic circular dichroism, and optical rotatory dispersion spectra for disodium salts of two natural products, hibiscus acid and garcinia acid, and the anhydride of acetylated garcinia acid have been measured. These experimental spectra are analyzed in combination with quantum chemical calculations of corresponding spectra. The spectral analysis for sodium salts and anhydride turned out to be simpler, suggesting that the conversion of carboxylic acids to corresponding salts or anhydride can be advantageous for the application of chiroptical spectroscopy.
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