Biphasic inverted

The lipases demonstrated very high stability in media partially or totally composed of organic solvent. In such media, the lipases catalyze esterification, transesterification, and resolution of enantiomers [19,45,75,97-100]. Nevertheless, several biphasic systems (organic-aqueous) are used for hydrolysis of lipid and fats [7,34,101]. Kinetic studies in biphase media or in inverted micelles demonstrate that the lipase behavior is different... 

Scheme 8.5. Hydroformylation of polar substrates in an inverted biphasic SCCO2/H2O system...

Biphasic systems that contain the catalyst in the supercritical phase and the substrates/products in a second liquid phase can also be implemented. With water as the polar phase, these inverted systems are particularly attractive for the conversion of highly polar and/or low-volatile hydrophilic substrates with limited solubility in typical SCFs such as scC02. 

Scheme 4 Hydroformylation of 14 with scC02-soluble Rh catalyst in an inverted biphasic system SCCO2/H2O...

Figure 4.8 Inverted scC02-aqueous biphasic enantioselective hydrogenation reaction.

Most examples so far have concentrated on SCCO2 as the phase containing substrates and/or products, corresponding to the mobile phase in continuous flow operation. More recently, the reverse situation, where the catalyst is retained in the SCCO2 phase, has also found increasing interest. These systems have been referred to as inverted biphasic catalysis. 

Figure 26.1. Hormesis may be defined as a dose-response relationship that is characterized by a biphasic (J- or inverted U-shaped) response. The quantitative features of the typical hermetic responses are similar, with the magnitude of the maximum stimulatory response typically being 30-60% greater than controls, the width of the stimulatory or hermetic zone averaging approximately 10-fold, and the interval from the zero equivalent point to the maximum stimulation averaging four- to fivefold (Calabrese and Blain 2005). [Figure adapted from Nascarella et al. (2009).]...

An inverted scC02-aqueous biphasic system has been used as reaction medium for Rh-catalyzed hydrogenation of polar substrates (Equation 4.36). Chiral and achiral C02-philic catalysts were efficiently dissolved and immobilized in scC02 as the (upper) stationary phase, while water, as the mobile phase, contained the polar substrates and products. Notably, product separation and catalyst recycling were conducted by maintaining the pressure in the reaction vessel. The catalyst phase was reused several times with high conversion and product yields of more than 85% [70]. 

USA biphasic insulin lispro insulin Humalog MIX Recombinant human insulin where the B chain amino acids at 28 and 29 are inverted with different proportions of a protamine suspension Diabetes... 

From the standpoint of solvents and their environmental friendliness and nontoxicity one can image a hybrid process comprising an inverted aqueous biphasic catalysis where the catalyst is immobilized in the organic phase and the polar substrates and products reside in the aqueous phase [10] - but there is no indication for serious industrial research work. 

As noted in Section 6.3.1, supercritical CO2 offers three fundamentally different procedures, each of which can be carried out in conventional or inverted biphasic systems. Concentrating initially on methods using SCCO2 as the product stream... 

As outlined in general in Section 6.3, two distinct engineering concepts can be envisaged for transition metal catalysis in scC02-based biphasic systems. In one case the compressed CO2 phase is used as the compartment for substrates and/or products, whereas the catalyst is contained in the liquid phase, in the present case water. We will refer to this scenario as H2O/SCCO2 biphasic catalysis and examples are discussed in this section. In the other case, carbon dioxide is used as the catalyst-containing phase, whereas substrates and products are retained in the polar aqueous phase. We refer to this system as inverted biphasic catalysis , denoted as SCCO2/ H2O, and it will be subject of the discussion in Section 6.4.4.4. 

Catalysis in Inverted Biphasic Systems of Type scCOj/HjO... 

Figure Laboratory-scale setup for catalysis in inverted scCOj/HjO biphasic systems.

Figures Macroscopic separation inverted phase transition for (hydroxypropyi)ceiiuiose in H2O. An isotropic soiution with poiymer voiume fraction >0.05 produces a biphasic (isotropic + iiquid-crystaiiine) mixture at T > 42°C. The condition 7 = (x 0.5) occurs at T = 41 °C. (From C.V. Larez, V. Crescenzi, and A. Ciferri. Macromolecules 28 5280, 1995. Copyright 1995 ACS.)...

To form stable MLO-based EMEs, the following important requirements need to be fulfilled (1) the system should be biphasic (Winsor-II-type system), i.e., the inverted type microemulsion systems should coexist with excess water, (2) the presence of an efficient stabilizer covering the outer surface of the kinetically stabifized droplets containing the internal W/O microemulsion system is needed, and (3) this internal microemulsion sfiucture should be preserved after the dispersing procedure. It should here be pointed out that microemulsions are, at a certain temperature, known to be sensitive systems with respect to any changes in their composition that may lead to the loss of their thermodynamic stability. Such a loss would in turn cause the formation of normal emulsions or, in a worst case scenario, a phase separation into oleic- and aqueous-rich phases. 

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