Organic phase coupling method

Table I. Coupling efficiency of immobilized OPH enzymes by organic phase and aqueous phase coupling methods.

Mobile phase options are quite restricted, as only volatile buffers are suitable for LC-MS. In addition, ion-pairing agents traditionally used in LC to improve peak shape and retention time such as trifluoroacetic acid (TFA), have shown to produce ion suppression, and they are not recommended for LC-MS analysis [21]. Therefore, although few applications for specific antidepressants employ TFA or its ammonium salt due to sensitivity enhancement [48, 81-85], aqueous phases in most LC-MS analytical methods are composed by formic or acetic acid in water, or its ammonium buffers. Although acid mobile phases are by far the most common, basic aqueous mobile phases (pH ranging from 8 to 10) have been used for specific applications in order to increase antidepressant retention time or to couple the online SPE elution to chromatographic analysis [57, 72, 86, 87], Organic phase composition was typically ACN and/or MeOH. 

The problem of determining AG° for organic redox couples can usually be attacked experimentally by either electrochemical methods or gas-phase measurements of ionization potentials and electron affinities. In both approaches, we can in principle determine thermochemical parameters for one-electron oxidation (83) and reduction (84) of an organic species. 

The controlled formation of the amide bond requires activation of the carboxylic group prior to reaction with the amino component. Another important feature present in many organic compounds is an ester bond, which is typically constructed via activation of a carboxylic acid followed by reaction with an alcohol function. In this chapter coupling methods primarily based on the activation of a carboxylic acid leading to the formation of amides or esters on a solid phase are discussed. Other methods based on the formation of esters via the displacement of halides or activated alcohol moi-... 

Diosynth Rapid Solution Synthesis of Peptides (DioRaSSP), a method for repetitive peptide synthesis in solution without isolation of intermediates. EspedaUy developed for the large-scale manufacture of peptides consisting of repetitive cycles of coupling by water-soluble carbodiimides and deprotection in a permanent organic phase [I. F. Eggen etal.,/. Peptide Sci. 2005,11,633 I. F. Eggen et al., Org. Process Res. Dev. 2005, 9, 98]. 

---