DMAE AND DMAE BITARTRATE IN COSMETICS 273 Nuclear magnetic resonance. The 1H-NMR spectra were recorded with Varian Direct drive (400 MHz) spectrometers for solutions in D2O. RESULTS AND DISCUSSION DIFFERENTIAL SCANNING CALORIMETRY Figure 2 shows the thermogram of DMAE bitartrate at room temperature. Two endother- mal peaks were evident: one at 67.1°C and a larger peak at 113.6°C that marked the melt- ing point (melting range: 112.7°–118.2°C). The heat exchanges for these peaks were 55 J/g and 114 J/g. The basal heat curve showed signs of shift between 200°C and 212°C. Stability was evaluated by comparing the DSC thermograms obtained at room tempera- ture with those recorded at 40°C and 60°C. Figure 3 shows the results for DMAE bitar- trate at each temperature. The endothermal peak at 67.1°C was no longer evident, although large peaks were seen at 114.5°C (40°C) and 115.1°C (60°C). Disappearance of the smaller endothermal peak may indicate loss of occluded water due to crystallization as a result of evaporation after storage of the samples at a the two higher temperatures. Figures 4 and 5 compare the stability of DMAE bitartrate at different times in samples kept at room temperature versus 40°C or 60°C. The behavior at days 7, 14, and 30 was similar to that of the room-temperature samples, and the endothermal peak remained unchanged. Calorimetric tests thus detected no changes in any of the samples kept at 25°C, 40°C, or 60°C for different periods. All curves showed the characteristic melting point for DMAE bitartrate. ULTRAVIOLET SPECTROSCOPY The spectra showed no clear peaks for maximal absorbance, and so the UV spectros- copy results were uninformative for the purposes of characterizing DMAE and DMAE bitartrate. Figure 7. FTIR spectra of DMAE bitartrate.
JOURNAL OF COSMETIC SCIENCE 274 Figure 8. 1HNMR spectra of DMAE at 25°C (A), 40°C (B), and 60°C (C). INFRARED SPECTROSCOPY We used IR spectroscopy to look for possible structural changes in DMAE and DMAE bitartrate after storage at different temperatures. Figures 6 and 7 show the positions of
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