Covalent bonding, nonspecific

CNTs can be functionalized with protein via non-covalent bond (Li et al., 2005 Kim et al., 2003 Mitchell et al., 2002). For example, (beta-lactamase I, that can be immobilized inside or outside CNTs, doesn t change enzyme s activity (Vinuesa and Goodnow, 2002). Taq enzyme can attach to the outside of CNT, and doesn t change its activity (Cui et al., 2004). Peptide with Histidine and Tryptophan can have selective affinity for CNT(Guo et al., 1998). Monoclonal antibody can attach to SWNTs. Protein-modified CNTs can be used to improve its biocompatibility and biomolecular recognition capabilities (Um et al., 2006). For example, CNTs functionalized with PEG and Triton X-100 can prevent nonspecific binding of protein and CNTs. Biotin moiety is attached to the PEG chains Streptavidin can bind specifically with biotin-CNT (Shim et al., 2002). 

Nonspecific effects can also limit the availability of solutes to undergo chemical reactions. The usual case is that the long-range electrostatic interactions between ions leads to a reduction in their availability to form ionic or covalent bonds. As with solvent-ion... 

Supramolecular chain scission differs further from covalent chain scission, because supramolecular recombination is typically the predominant fate of a ruptured chain anthropomorphically speaking, the supramolecular moieties are, by their very nature, predisposed to reassociation rather than alternative reaction pathways. This predisposition is not intrinsic to the products of covalent bond mpture, which might lead either to high-energy intermediates with nonspecific reactivity or to species that require catalyst or elevated temperature to recombine. The... 

Their approach in looking into the problem further was to find structures in which specific covalent bonding to the back side of the carbon undergoing substitution is difficult or impossible. As models for reactions at tertiary carbon they chose bridgehead substitutions. We have seen in Section 5.2 that rates in these systems are retarded, in some cases by many powers of ten, because of the increase in strain upon ionization. But the important point in the present context is that it is impossible for a solvent molecule to approach from the back side of a bridgehead carbon the only possibilities are frontside attack, known to be strongly disfavored (Section 4.2), or limiting SW1 solvolysis with nonspecific solvation. 

To analyze the surface structures, infrared spectra were studied. It was concluded from the similarities between the spectra and the deprotonated CT2- that CT forms a bidentate structure on TiOz (Martin et al., 1996). The infrared (IR) peak positions also suggest that the CT adsorbate carries a negative charge. For a purely covalent bond, the charge would be zero. This suggests that the bond formed may have a 60% ionic character and a 40% covalent character. The concentration of 4-chlorocatechol apparently determines the type of surface structure formed. At concentrations below 50 pM, 4-chlorocatechol adsorbs as a bidentate structure. At concentrations above 50 uM, 4-chlorocatechol adsorbs nonspecifically in a multilayer environment. 

To demonstrate the application of these butterfly wing SERS substrates to the problem of protein-binding detection, Garrett et al. devised a protein-binding assay. There are a variety of methods for binding proteins to a metal surface, some of which depend on the amino acid composition of the protein, others of which do not. Direct adsorption via covalent bonds between sulfur groups in proteins and metal surfaces has been used with some success [43] however, this method is unsuitable for use in Raman spectroscopy-based assays, as nonspecific binding may result in a wide variety of conformational orientations of the molecules with respect to the metal s surface. This can lead to Raman spectra that are difficult to reproduce. Not only that, but the analyte may bind to the metal as well as the antibody, which can lead to noisy spectra. 

Although much weaker than a covalent bond, the H-bond is considerably stronger than most nonspecific nonbonding interactions. To be somewhat more quantitative, H-bonds between neutral molecules, e.g., the water dimer, are generally bound by some 2-15 kcal/mol in the gas phase, relative to the separate molecules. Covalent bonds frequently exceed 100 kcal/mol in binding energy, whereas van der Waals interactions like those between two hydrocarbons are commonly less than 2 kcal/mol. 

When any two atoms approach each other closely, they create a weak, nonspecific attractive force called a van der Waals interaction. These nonspecific interactions result from the momentary random fluctuations in the distribution of the electrons of any atom, which give rise to a transient unequal distribution of electrons. If two noncovalendy bonded atoms are close enough together, electrons of one atom will perturb the electrons of the other. This perturbation generates a transient dipole in the second atom, and the two dipoles will attract each other weakly (Figure 2-8). Similarly, a polar covalent bond in one molecule will attract an oppositely oriented dipole in another. 

For immobilization studies to date, two distinct modes of immobilization have been used. The first utilizes nonspecific covalent bonding to CNBr-activated Sepharose via primary amino groups on the antibody molecule. Since there are many of these available on the antibody, this is expected to result in random orientation of antibody molecules on the support. The other method involves linkage through immobilized protein A, a protein which binds immunoglobulins in the structural F portion of the molecule. 

The two major ways in which DNA interacts with other entities can be classed as nonspecific covalent bonding via either the phosphodiesicr or sugar moieties or electrostatic dominated noncovalent bonding. Nonreversible covalent interactions are important when considering the cellular... 

The results indicate significant advantages of covalent attachment of antibodies compared to nonspecific adsorption increase of the thermodynamic stability of immobilized layer, due to covalent bond formation, and kinetic stability as a result of complications due to the slow desorption hydrolysis of Schiff bases. 

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