- Characterization of the molecular packing, thermotropic phase behaviour and critical micellar concentration of a homologous series of N-acyltaurines (n = 9–18). PXRD, DSC and fluorescence spectroscopic studies
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N-acyltaurines (NATs) are amides of fatty acids that can be structurally related to endocannabinoids. They show interesting physiological and pharmacological properties. We have synthesized a homologous series of NATs with saturated acyl chains (n = 9–18) and investigated their supramolecular structure and thermotropic phase transitions by powder X-ray diffraction (PXRD) and differential scanning calorimetry (DSC). The d-spacings obtained from PXRD increase linearly with chain length with an increment of ~0.847 ? per additional CH2 moiety suggesting that NATs adopt a tilted bilayer structure with similar packing in crystal lattice. Results obtained from DSC studies indicate that the endothermic transition temperature (Tt) of NATs showed a gradually increasing trend with increasing acyl chain length. The enthalpy (ΔHt) and entropy (ΔSt) of transition show odd-even alternations with odd-chain compounds having higher values than the even-chain compounds. The critical micellar concentration (CMC) of NATs was determined in water at room temperature by fluorescence spectroscopy by monitoring the spectral changes of 8-anilinonaphthalene-1-sulfonic acid (ANS). The CMCs of NATs were found to decrease with increase in acyl chain length. The present results provide a thermodynamic and structural basis for investigating the interaction of NATs with other membrane lipids and proteins, which in turn can shed light in understanding how they function in vivo (in biological membranes).
- Arul Prakash, Sukanya,Kamlekar, Ravi Kanth
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- Synthesis, characterization, and determination of critical micellar concentration and thermotropic phase transition of taurolipids
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Taurolipids (NAT) are a newer class of fatty acid amides (FAA) identified in the central nervous system, liver, and kidney of fatty acid amide hydrolase knockout mice. In this study, we reported a convenient method to synthesize NATs in fair yield and characterized using FTIR, 1H NMR and 13C NMR. Fluorescence spectroscopy study showed that NATs form micelles in an aqueous environment and the critical micellar concentration (CMC) follows a linear trend with respect to fatty acid acyl chain length. Differential scanning calorimetry reveals that NATs undergoes broad endothermic transition with transition temperatures increases with increasing fatty acid acyl chain length though the magnitude of change from one chain length to another chain length decreases as the acyl chain length increase. The transition enthalpy (ΔHt) and transition entropy (ΔSt) corresponding to the chain-melting phase transition depends linearly on the acyl chain length and fitted to a linear equation, which yielded the incremental values, ΔHinc (1.09?±?0.03?kcal·mol??1) and ΔSinc (2.96?±?0.16?cal·mol??1·K??1), contributed by each methylene unit to ΔHt and ΔSt. The end contributions arising from the head group and the terminal methyl group were calculated to be ΔH0?=???7.28?±?0.46?kcal·mol??1 and ΔS0?=???17.36?±?2.11?cal·mol??1·K??1. Thermodynamic parameters, incremental values of ΔHinc and ΔSinc suggest that the acyl chains in NATs are tightly packed and the obtained larger negative ΔS0 suggest that the hydration of polar sulfonate group of NATs also play an important role in the self-assembly of NATs.
- Megarajan, Sengan,Vairaprakash, Pothiappan,Anbazhagan, Veerappan
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p. 104 - 110
(2017/03/31)
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