Cleavable Bonds

Dithionite also is capable of cleaving oxime linkages that are formed as the result of the reaction of an aldehyde and aminoxy group (Pojer, 1979). Thus, crosslinks formed between two proteins or other molecules using this reaction strategy can be specifically broken using sodium dithionite. 

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Figure 28.5 This PIR compound contains NHS esters at both ends to capture interacting proteins through amide bond formation. It also contains MS cleavable bonds that release a central reporter group, which can be used to identify crosslinked peptides by mass spec.

A third and more recent example of where readily biodegradable surfactants have replaced surfactants that are more long-lived in the environment is the taking over of the market for textile softener surfactants by the ester quats from the stable quats. This transition is still in progress today but for several years the big soapers all base their softener formulations for the US and Western Europe markets on ester quats instead of traditional, stable quats. The change from stable quats to ester quats is probably the best example of the concept of introducing a cleavable bond in a given surfactant structure because the two types of products are very similar in structure and physical chemical charac-... 

Kratz, F., Beyer, U. and Schutte, M.T. (1999) Drug-polymer conjugates containing acid-cleavable bonds. Crit. Rev. Ther. Drug Carrier Syst., 16, 245-288. 

In contrast to photochemical or radical initiation few transfer agents have been used in thermal telomerisation of VDF (Table 3). Only two series have to be considered those which exhibit C-Br or a C-I cleavable bond and hypofluorites (see Sect. 4.1.1.5) whereas no work involving a telogen with a C-Cl bond was described in the literature. 

Thus, versatile telogens have been produced with an increased activation of the cleavable bond. It is interesting to note that, already in 1955, Haszeldine [237] observed a kind of living character of the telomerisation of CTFE according to the following reaction ... 

The bond dissociation energy of cleavable bonds of telogens appears to be a key parameter to take into account regarding reactivity. This is followed by various factors controlling the reactivity (such as energetic, electronic, polar, steric, conformational effects and role of orbital interactions) of a radical and its orientation of addition. 

Polyanhydrides have been modified by incorporating amino acids into im-ide bonds. The imide with the terminal carboxylic acids is activated with acetic anhydride and copolymerized with sebacic acid or CCP. Poly(anhydride-imides) increase the mechanical properties of the polyanhydrides. Degradation of poly(anhydride-imide)s is similar to that of polyanhydrides (i.e., surface erosion). Two different cleavable bonds (anhydride and ester) in the polymer chains have been included in polyanhydrides. Carboxylic acid-terminated e-caprolactone oligomers or carboxylic acid-terminated monomers (e.g., salicylic acid) have been polymerized with activated monomers (e.g., SA). 

The probability of any given bond within an assigned oligomer being cleaved is the same for all cleavable bonds. 

For each system of reactants, IDENTIFY-WEAKEST-BOND identifies the weakest substrate bond, and compares it with others in the system to ensure minimal global bond strength. Selected instances of bond are then appended to potentially-cleavable-bonds. 

IDENTIFY-ABSOLUTE-WEAKEST-BOND applied to potentially-cleavable-bonds bond-1... 

Since multiple bonds may reside in potentially-cleavable-bonds, each possibly leading to a micro-reaction, creates a global-... 

Drug-conjugated polymers. In these the drug is attached to a water-soluble polymer carrier by a cleavable bond. These polymers are less accessible to healthy tissues when compared with the diseased tissues. These conjugates can be used... 

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