本研究利用實驗及理論計算的方法，來探討薑黃素及去二甲氧基薑黃素與β-環糊精的交互作用力及鍵結機制。螢光光譜滴定法測定發現其結合常數為薑黃素112 M-1，去二甲氧基薑黃素327 M-1，顯示去二甲氧基薑黃素與β-環糊精結合力比薑黃素高。
固態紅外線光譜比較混合前與後光譜訊號的位置，發現在β-環糊精上的O‒H鍵伸縮振動區域(3550-3200 cm-1)產生紅位移，及一級與二級碳上的C‒H鍵形變振動(deformation vibrations)區域(1400-1200 cm-1)產生藍位移。理論計算發現β-環糊精上C‒H鍵之∆S%(C‒H鍵上碳的s混成變化)值增加，顯示出此增加是由於C‒H鍵之非典型氫鍵作用造成。
從二維ROESY核磁共振光譜的結果顯示，薑黃素苯環上的氫和β-環糊精內部的氫(H5)產生空間上的偶合作用(Trough Space Nuclear Overhauser effect)，去二甲氧基薑黃素的酚上OH與β-環糊精六號碳上OH (6-OH)有NOE作用。在一維1H NMR中，薑黃素與去二甲氧基薑黃素1H NMR圖譜在複合物與未加入β-環糊精前具有相同的型態(pattern)，此結果顯示出薑黃素或去二甲氧基薑黃素與β-環糊精結合比例為1:2；另外去二甲氧基薑黃素OH訊號幾乎消失，推測這是一種經由酸鹼作用，使酚上的OH之氫轉移至β-環糊精6-OH上，但高斯計算(HF/6-31g(d))得到的最穩定的結構中，去二甲氧基薑黃素酚上的氫並未轉移至β-環糊精上，因此推測可能轉移至溶液中的二甲基亞碸上(NMR量測溶液)。再由NBO的E(2)值判斷兩者生成的複合物中，結合的作用力除了氫鍵與凡得瓦力，還包含了非典型氫鍵存在(在紅外線光譜中也可看到)，且發現到非典型氫鍵作用力在去二甲氧基薑黃素所佔比例高於薑黃素，推測是去二甲氧基薑黃素間位(Meta)的OH酸性高於薑黃素對位(Para)的OH，導致兩複合物結合的氫鍵作用力的性質不同。

Adduct of curcumin/β-cyclodextrin (CCM/β-CD) plays an important role in advanced biomedical domain. To confirm the biomedical activities exhibited by the didemethylated curcumin (DCCM) molecule in a comparative manner compared to CCM, fluorescence titration method, FTIR, NMR spectrum and theoretical calculation were performed.
The relative values of binding constants of CCM and DCCM with β-CD obtained by fluorescence titration method were 112 M-1 and 327 M-1, respectively, indicating that the DCCM had about 3 times higher binding capability with β-CD compared to CCM. IR spectra were conducted for further verification of the better DCCM binding capability with β-CD and show that both blue shifts in 1400-1200 cm-1 and red shifts in 3550-3200 cm-1、950-700 cm-1 were found by comparing the variations of vibration frequencies in this studies.
ROESY-NMR experiments showed the binding mechanisms for both CCM/β-CD and DCCM/β-CD complexes showed NOE interactions between the phenyl ring protons (Hc、Hf) in CCM and phenolic protons (Hh、Hg) in DCCM with the protons of H5 and 6-OH in β-CD, respectively. Indicating both the CCM and DCCM entered the cavity of β-CD. The 1H-NMR spectra of the complexes showed that the resonance patterns of CCM and DCCM moieties were the same as that of free CCM and DCCM, indicating that one CCM or DCCM molecule could bind with two β-CD molecules since CCM and DCCM both possess a symmetric plane. Furthermore, both resonance signals and peak intensity of the phenolic protons almost disappeared in the DCCM/β-CD adduct compared to the free DCCM, revealing that the phenolic protons of the DCCM in its complex became more acidic.
Molecular calculations using HF/6-31g (d) method have been carried out. And found that the decreasing intensities of the phenolic protons in DCCM/β-CD was probably due to the acid-base interaction with the DMSO-d6 NMR locking solvent because that the optimized stable complex conformation did not show the protonation hydroxyl group of β-CD. The E(2)-analysis of donors/acceptors involved in the binding sites obtained by the natural bond orbital (NBO) method showed the effects of hyperconjugation were in good accordance with the close-contact bond. Analysis of C-H bond orbitals revealed significantly IR blue shifts (termed improper H-bonding) in both adducts, indicating that re-hybridization effects outweigh the hyperconjugation effects.

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