Sugar Acetates as CO₂-philes: Molecular Interactions and Structure Aspects from Absorption Measurement Using Quartz Crystal Microbalance

Abstract

Sugar acetates, recognized as attractive CO(2)-philic compounds, have potential uses as pharmaceutical excipients, controlled release agents, and surfactants for microemulsion systems in CO(2)-based processes. This study focuses on the quantitative examination of absorption of high pressure CO(2) into these sugar derivatives using quartz crystal microbalance (QCM) as a detector. In addition to the absorption measurement, the QCM is initially found to be able to detect the CO(2)-induced deliquescence of sugar acetates, and the CO(2) pressure at which the deliquescence happens depends on several influencing factors such as the temperature and thickness of the film. The CO(2) absorption in alpha-D-glucose pentaacetate (Ac-alpha-GLU) is revealed to be of an order of magnitude larger in comparison with its anomer Ac-beta-GLU, whereas alpha-D-galactose pentaacetate (Ac-alpha-GAL) absorbs CO(2) less than Ac-alpha-GLU due to the steric-hindrance between the acetyl groups on the anomeric and C4 carbons, implying the significant importance of the molecular structure and configuration of sugar acetates on the absorption. The effects of molecular size and acetyl number of sugar acetates on the CO(2) absorption are evaluated and the results indicate that the conformation and packing of crystalline sugar acetate as well as the accessibility of the acetyls are also vital for the absorption of CO(2). It is additionally found that a CO(2)-induced change in the structure from a crystalline system to an amorphous system results in an order of magnitude increase in CO(2) absorption. Further investigation illustrates the interaction strength between sugar acetates and CO(2) by calculating the thermodynamic parameters such as Henry's law constant, enthalpy and entropy of dissolution from the determined CO(2) absorption. Experiments and calculations demonstrate that sugar acetates exhibit high CO(2) absorption, as at least comparable to ionic liquids. Since the ionic liquids have potential uses in the separation of acidic gases, it is evident from this study that sugar acetates could be used as possible materials for CO(2) separation.

Shape Modification of Water-in-CO2 Microemulsion Droplets through Mixing of Hydrocarbon and Fluorocarbon Amphiphiles

“…However, such a fluorine-rich molecular design has significant disadvantages for industrial scale applications due to economic and environmental concerns [17,18,19,20]. On the other hand, despite only a few successful examples of stable dispersions with hydrocarbon (HC) surfactants in scCO2 [20,21,22 ], development of efficient CO2-philic surfactants with minimum fluorine content still presents a great challenge, requiring a deeper insight to understand the general behaviour of surfactants in water/CO2 systems.…”

A Survey of the 2010 Quartz Crystal Microbalance Literature

“…The partitioning of drug molecules between super critical carbon dioxide and poly(lactic acid) surfaces was investigated by QCM (Ma et al ., ). Furthermore, the adsorption of carbon dioxide on sugar acetate surfaces showed a high dependence on the molecular structure of the film and it was suggested that sugar acetates could find application in the separation of carbon dioxide (Ma et al ., ). Of biological relevance, the anaesthetic enflurane was detected on a dipalmitoyl phosphatidyl choline monolayer in order to further probe the mechanism of action (Yamamoto et al ., ).…”

Imidazole Promoted Efficient Anomerization of β-D-Glucose Pentaacetate in Organic Solutions and Solid State

“…D-Glucose pentaacetate is an important intermediate for synthesis of different types of glycosides. 1,6 During glycosylation, although β-D-glucose pentaacetate was found to react faster with nucleophiles in the presence of Lewis acids, 6b its α anomer showed better performance in more applications like CO2 absorption 7 and stimulation of insulin release 8 . α-D-Glucose pentaacetate was usually prepared from acetylation of D-glucose, or anomerization of β-anomer with acetyl anhydride catalyzed by Lewis acids.…”