Group contribution association

Interestingly, the activity of C. thermocellum in SCF ethane, SCF CO2, liquid propane, and gaseous propane does not follow the log P trends seen with liquid solvents. Thus, log P may be of limited value when applied to the correlation of metabolic activity in compressed solvents. The traditional definition of log P (25 °C and 0.1 MPa) was extended to our incubation conditions (60 °C and 7 MPa) using the group contribution associating equation of state (GCA-EOS) (48,49) to calculate the mole fraction of the dissolved compressed fluids in octanol and water. Log P logio(x,- /x,- )] correlated well with the total metabolic activity (ratio of total products formed in the treatment to the total products formed in the control) in liquid hydrocarbon solvents (Fig. 2) (37). 

The phase equilibria of the hydroformylation of hex-l-ene in supercritical CO2 was studied experimentally by Jiang et al for different degrees of conversion, involving mixtures of CO, H2, CO2, hex-l-ene and heptanal. Marteel et al conducted the reaction at r= 373 K and p = 18.6 MPa and had to use a CO2 + reactant mass ratio equal to 3 to operate within the homogenous phase. Pereda et modelled the measurements reported by Jiang et al with Group Contribution Association equation of state" " and showed the use of... 

There are three terms in the expression of the residual Helmholtz function in the Group Contribution Association equation of state, each one representing the contributions of different intermolecular forces (i), repulsive or free volume A (ii), attractive or dispersive and (iii), specific association forces The residual Helmholtz function in the Group Contribution Association equation of state is given by ... 

Neither the Group Contribution Association equation of state nor Soave-Redlich-Kwong equations of state with MHV2 mixing rules are recommended methods to prediet mixture densities. The Peng-Robinson equation of state with classical mixing rules is the more preeise model among the van der Waals family of equation of state to predict molar volumes of mixtures particularly when the volume eorrection has been used as proposed by Peneloux et... 

In this Chapter the group contribution equations of states are proposed because of their predictive capacity for components for which thermodynamic data is either limited or non-existent. MHV2 and Group Contribution Association equation of state are both suitable models to describe highly non-ideal mixtures. The use of MHV2 is more attractive due to its mathematical simplicity and wider parameter table however, Group Contribution Association equation of state is more appropriate for mixtures that have association elfects and or big size-asymmetry. In this chapter several applications of both models to reactive mixtures have been given. 

The group contribution method allows the approximate calculation of solubility by summing up fragmental values associated with substmctural units of the compounds (see Section 7.1). In a group contribution model, the aqueous solubility values are computed by Eq. (12), where log S is the logarithm of solubility, C is the number of occurrences of a substmctural group, i, in a molecule, and is the relative contribution of the fragment i. 

Enthalpy of Formation The ideal gas standard enthalpy (heat) of formation (AHJoqs) of chemical compound is the increment of enthalpy associated with the reaction of forming that compound in the ideal gas state from the constituent elements in their standard states, defined as the existing phase at a temperature of 298.15 K and one atmosphere (101.3 kPa). Sources for data are Refs. 15, 23, 24, 104, 115, and 116. The most accurate, but again complicated, estimation method is that of Benson et al. " A compromise between complexity and accuracy is based on the additive atomic group-contribution scheme of Joback his original units of kcal/mol have been converted to kj/mol by the conversion 1 kcal/mol = 4.1868 kJ/moL... 

Polar groups contribute greatly to adhesion of proteins to carbohydrates and to their cohesion. In denatured or unfolded proteins, such as animal glues, the peptide amide groups play an important role in adhesion but in the undenatured collagen, most peptide groups are associated in helical conformations. 

Evidence for intramolecular hydrolysis of the methyl ester (62) by metal hydroxide has been provided.329 Molecular models of the metal complex (63) indicate that when complexation with the imidazole nitrogen and the phenolic hydroxyl group occurs, it is not possible for coordination of the ester carbonyl group to occur. This point, taken in conjunction with the observed pH rate profile which shows that ionization of the M—OH2 group is associated with catalysis, eliminates metal ion activation of the carbonyl bond to intermolecular attack by OH- as a contributing factor. For base hydrolysis of (62) kOH = 2.7 x 10-2 M-1 s-1 at 25 °C. The specific rate constants for intramolecular hydrolysis by the M—OH species are 0.245 s-1 and 2 x 10-2 s-1 for the Co11 and Ni11 complexes respectively. 

The conformation-dependent contribution to chemical shifts that is best understood is the ring-current contribution associated with conjugated groups. Various functional forms have been tested and calibrated against observed data (41-43). The basic ideas may be found in textbooks (8) and reviews (41). The general form of ring current contributions is ... 

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