Steric effects composite model

The use of sterlo parameters such as and of methods such as the branching equations to represent sterlo effects on bio-activity Is Justified. Transport parameters are composite they are a function of differences In Intermolecular forces. The function of bulk and area parameters Is to provide the proper mix of Intennol-eoular forces required by a particular mode of bloaotlvlty. In the absence of parabolic or bilinear behavior bloactlv-Ity can be modeled by an equation based on Intermolecular forces and steric effects. 

In a human tumor xenograft model, Kong et al.21 compared the antitumor effect of doxorubicin encapsulated in three types of liposome formulations, a nonthermosensitive liposome (NTSL), a traditional thermosensitive liposome (TTSL), and a low-temperature-sensitive liposome (LTSL). All three liposomes are sterically stabilized with PEG grafted on their surface. All the liposomes have a long circulation time and can accumulate selectively in tumor tissue. However, the lipid compositions of the three formulations are different. The NTSL was composed of saturated long-chain lipids such as hydrogenated soybean... 

Studies by HeEsing have provided support for the steric exclusion model and have demonstrated that (1) the composition of the immune complex formed is not affected by the presence of a polymer (2) there is no complex formed between the polymer and the antigen, antibody, or immune complex (3) the polymer effect is dependent on the molecular weight of both antigen and polymer (4) and the use of polymer in a reaction mixture can increase the precipitation of immune complex with low-avidity antibody. Addition of polymer to a mixture of antigen and antibody causes a notable increase in the rate of immune complex growth, especially during the early phase of the reaction. ... 

Brooks and Cramer [91] extended this work on the single-component mass action model to competitive isotherms. The steric factor (tr) that they introduced to accoimt for this effect depends on the nature of the resin e.g., density of ions), the ionic strength and composition of the solution (which control the molecular structure of the protein), and the nature of the protein and its concentration (most proteins will probably have a larger apparent footprint at high dilution than at high concentration). Thus, the steric factor appears as an additional but empirical... 

Conformation and Chemical Shifts.—Chemical shifts have been correlated with conformation for H shifts in polystyrene and poly(vinyl chloride) and C shifts in model compounds of polypropylene. In all these papers, the chemical shift is related empirically to the occurrence of three- and four-bond steric interactions, similar to those used in the rotational isomeric state treatment of polymer statistical mechanics, " and the shift is expressed as a sum of compositional and conformational increments. The origin of the shielding contributions (magnetic anisotropy, electric field effects, etc.) is not stated, except for polystyrene in which the magnetic anistropy of the aromatic rings are incorporated... 

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