Water as Green Solvent for Extraction of Natural Products

Abstract

IntroductionWater is the most abundant molecule on the earth, covering 70% of its surface. Life processes on this planet are crucially dependent on the presence of water. It is often recognized that water has tremendous benefits as a green extraction solvent because it is not only inexpensive and environmentally benign but it is also nonflammable and nontoxic, providing opportunities for clean processing and pollution prevention. The water molecule contains three nuclei, one modestly heavy (oxygen), and two light ones (hydrogen). Because of water's electronic structure, the oxygen atom has a slight negative charge on it and the hydrogen atoms have a slightly positive charge [1]. When water molecules are closed together, their positive and negative regions are attracted, these attractive forces are known as hydrogen bonds. The energy associated with a hydrogen bond is 8-40 kJ/mol. The O-H bond lengths are 0.9572 Å and the average HOH bond angle is 104.52 ∘ , slightly smaller than the tetrahedral angle (109.5 ∘ ). The molecule is very small with a hard sphere diameter of 2.75 Å. The smallness of the water molecule has important consequences for the hydration of solutes. The contours of the total electron density in the HOH plane of the water molecule indicate a shape not far from spherical. The water molecule has a dipole moment of 1.85 D with two partial positive charges on the hydrogen atoms and a single zone of negative charge on the oxygen atom.It is well known that water molecules are strongly associated in the liquid phase by H-bonding. Hydrogen bonds result dominantly from electrostatic interactions with a light contribution of covalent bond formation. The H-bond interactions in liquid water constitute a 3-D H-bond network with localized and structured clustering. Therefore, the liquid structure is not determined by hard-core repulsions between the individual water molecules but rather by intermolecular and directional H-bonding. The broad variation of H-bond angles further demonstrates the noncrystalline arrangement of the water molecules and appears to indicate that some bond angle distortion in the H-bonds is rather easily allowed in the liquid. It is important to recognize that intermolecular interaction Green Extraction of Natural Products: Theory and Practice, First Edition. Edited by Farid Chemat and Jochen Strube.

Metabolomic Profile and Biological Properties of Sea Lavender (Limonium algarvense Erben) Plants Cultivated with Aquaculture Wastewaters: Implications for Its Use in Herbal Formulations and Food Additives

“…The use of water as an alternative extraction solvent has a significant advantage over organic solvents, such as ethanol, previously used in the extraction of natural compounds from sea lavender. Regardless of extracting different compounds than organic solvents, water extraction may generate higher yields of bioactive molecules, besides having a reduced environmental impact and no hazard, and require simple extraction equipment [ 34 ]. Moreover, ultrasound-assisted extraction (UAE) has been increasingly used for extracting bioactive compounds from natural products for food and pharmaceuticals, since it is considered a more sustainable technique with higher levels of efficiency (lower solvent, time, and energy consumption).…”

Alternatives for Conventional Alkane Solvents

“…They can be costly but have the advantages of nonvolatility and separability by simple gravity separations. Their structures are easily varied through synthesis, affording additional versatility and tunability. , Supercritical fluids like scCO 2 are industrially used alternative solvents and have been used in applications that range from catalyst to solvent intensive processes like extractions to commercial dry cleaning. ,− While scCO 2 requires a pressurized apparatus and depressurization/pressurization cycles in use and recycling, CO 2 has the advantage of being an abundant resource and is both recyclable and sustainable. Water is even more common as a solvent.…”

Water as Green Solvent: Methods of Solubilisation and Extraction of Natural Products—Past, Present and Future Solutions

“…The surfactant principle of action is to reduce surface tension. Different shapes of micelles are described: (classic) micelles, cylindric, layers and reverse [26]. These objects are able to solubilise non-polar NPs within their core, thus making those NPs more soluble in water (within micelles).…”

“…This consists of a temperature above which micelles are disorganised and therefore no longer water-soluble, which leads to dephasing. To purify the NPs after the extraction step, the user should bring these elements up to cloud point temperature and then add a centrifugation step to concentrate both the NPs and surfactants in the upper layer [26]. This extraction technique is called Cloud Point Extraction (CPE).…”