Steric capture

A molecule of AMG contains four identical polypeptide chains, present as a pair of dimer subunits. The dimers are covalently linked by disulfide bonds, whereas the pairs are held together by noncovalent bonds. The dimer is the active unit one molecule of AMG can therefore bind up to two protease molecules. Each monomer contains both the thiol ester mentioned previously and a bait site, both of which are essential for inhibitory activity. After the bait site reacts with a protease, the thiol ester is activated and may form covalent bonds with lysine residues on the protease, thus immobilizing it. However, covalent binding is not essential for steric capture and inhibition of proteases. ... 

Figure 9 The schematical representation of dispersion polymerization process, (a) initially homogeneous dispersion medium (b) particle formation and stabilizer adsorption onto the nucleated macroradicals (c) capturing of radicals generated in the continuous medium by the forming particles and monomer diffusion to the forming particles (d) polymerization within the monomer swollen latex particles, (e) latex particle stabilized by steric stabilizer and graft copolymer molecules (f) list of symbols.

This difference between NHCs and phosphines was acknowledged early, and the so-called fence model, see Fig. 1.16, was proposed [79], In this model the NHC is seen as a fence , with a length and a height . These quantities were initially used to quantify the steric effect of NHCs. However, this model showed some limitations in properly capturing the behaviour of some common NHCs, such as ICy, and was thus abandoned [79]. 

The measurement of these angles for a series of [PdClj(NHC) P(OR)3 ] complexes permitted to evidence the remarkable flexibility of NHCs due to rotations aronnd the iV-substituent bonds [82]. This flexibility, captured by the allows NHCs to respond actively to the steric requirements of co-ligands. This is further confirmed by ab initio molecular dynamics simulations aimed at understanding the variability of ( )j and in a series of NHCs containing Ru-complexes relevant to olefin metathesis [83]. 

Although additional experiments and simulations are needed to determine how much of reality is captured in this model, it does explain one important property of proteins their rapid rate of refolding, which is independent of denaturation conditions. If the polypeptide chain is unable to escape from this steric trap and access conformations with the wrong topology, it could never wander far from the folded conformation and thereby avoid incorrect side chain/side chain interactions. 

Among the three subcategories, boronate compounds seemed to be the most efficient in coordinating with anions and enhancing lithium ion stability, although the number of electron-withdrawing substituents in boronate is only two. The authors thus inferred that the ability of these anion receptors to capture an anion depends not only on the electron-deficiency of the core atom but perhaps also on the steric hindrance presented by these substituents on the core. With only two substituents, the core of the boronates is obviously more exposed and therefore more easily accessible for an anion. The higher ion conductivity achieved by boronate additive therefore comes from the better balance between the electron-deficiency and steric openness of this compound as... 

Radical cations as well as cations are good electrophiles dependent on steric and electronic effects and, therefore, potent targets for nucleophilic capture. 

SAMs of thiols (and thiol-modified ONDs) can be highly ordered and densely packed, improving the availability of active surface groups (and capture probes) for binding and hybridization. However, dense packing may not always be advantageous in DNA hybrid capture. Steric hindrance effects can occur if the immobilized capture probes are too close together. 

Self (S4) first proposed the concept of noncompetitive assay for haptens utilizing an adequate combination of an a-type and a jS-type anti-idiotype antibody, in which he used the term, selective antibody for the a-type antibodies. Then, Barnard and Cohen (Bl) applied this assay principle for the determination of serum E2, naming the assay system an idiometric assay. Figure 12A illustrates the assay procedure of the idiometric assay of E2. The target hapten is captured by excess anti-E2 antibody immobilized on microtiter strips by incubation at room temperature for 1 h (step i). After washing the strips, the /3-type anti-idiotype antibody was added in order to saturate (or block) the unoccupied paratope of the anti-E2 antibody (incubation, room temperature for 30 min) (step ii). The a-type anti-idiotype antibody, which has been labeled with a europium chelate (H4), was then added to the plate and incubated at room temperature for a further 2 h (step iii). Finally, fluorescence intensity due to bound europium was measured with a time-resolved fluorometer. Because of large steric hindrance around the bound jS-type antibody (MW 150,000), the labeled a-type antibody would. 

The nucleophilic capture of tricyclane radical cations 115 " and 117 " supports the role of conventional steric hindrance 115 reacts at the 3° carbon ( 116 ), whereas the chiral isomer 117 + is captured by backside attack at the less hindered 3° carbon ( 118 ). " Both reactions are regio- and stereospecific and avoid attack at the neopentyl-type carbon (denoted by an asterisk). 

Several approaches have been used to enhance the sensitivity of PMMA, (45) either by introducing chemical and/or steric configurations which tend to weaken the main chain stability of the polymer (Table V), or by substitution on the quarternary carbon with polar electronegative substituents (Table VI) which also has the effect of weakening the main chain. The -substituents are believed to enhance the capture of secondary electrons followed by resonance dissociation (57). 

The method of RNA catalyst capture really depends on the properties of the tethered product. Another method for selective partitioning is by chromatographic (HPLC) methods based on the properties of products that do not contain an affinity tag such as biotin. If the overall electrostatic or steric properties of the RNA product are significantly changed so that they are much different than those of the unreactecl RNA, chromatographic methods can be used to separate and recover the products and obtain their sequence information [14]. 

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