Schiff’s Base, Formation

Back in 1937, Braunstein and Kritzman and, independently, Herbst, had proposed transamination might proceed via a Schiff s base formation. The essential lability of the H atom on the a-C atom was shown with deuterium labelling (1942). a-2H alanine released 2H into the medium during transamination. The label did not appear in glutamate, the end-product. 

Fig.1 Schematic illustration of the immobilization of penicillin G acylase on glutamate-pillared LDHs. Reaction of the primary amino groups of the intercalated glutamate ions with glutaraldehyde through Schiff s base formation is followed by covalent coupling of the residual aldehyde groups with the free amino groups of the enzyme...

Seong (2002) compared silylated (aldehyde) and silanated (amine and epoxy) compounds from several commercial sources to the performance of an antigen (IgG) microarray. In addition, the efficiency of phosphate-buffered saline (PBS) (pH 7.4) and carbonate (pH 9.6) printing buffers were compared. While the various slides and surface chemistries showed differences in their binding isotherms, they ultimately reached similar levels of saturation. Silylated (aldehyde) slides showed comparable loading in both buffer systems. Apparently, tethering of antibody to the surface by Schiff s base formation of the surface aldehyde and lysine residues on the protein was applicable over a broad pH. However, carbonate buffer increased binding of proteins on silanated surfaces. 

In our development studies, Endeavor (5 mL) and Buchi (IL) reactor systems were used to screen catalysts and to evaluate the impurity profile under various process conditions. Elydrogenation kinetic studies were carried out using a 100 mL EZ-seal autoclave with an automatic data acquisition system to monitor the hydrogen uptake and to collect samples for HPLC analysis. Standard conditions of 5 g of aldehyde in 25 mL ethyl acetate and 25 mL methanol with 0.5 g of 5%Pd/C Engelhard Escat 142 were used in this investigation. For the Schiff s base formation and subsequent hydrogenation, inline FTTR was used to follow the kinetics of the Schiff s base formation under different conditions. Tables 1 and 2 show the changes in the substrate concentration under different conditions. Both experiments were carried without any limitations of gas-liquid mass transfer. 

Schiff s base formation occurs by condensation of the free amine base with aldehyde A in EtOAc/MeOff. The free amine base solution of glycine methyl ester in methanol is generated from the corresponding hydrochloride and triethylamine. Table 4 shows the reaction concentration profiles at 20-25°C. The Schiffs base formation is second order with respect to both the aldehyde and glycine ester. The equilibrium constant (ratio k(forward)/ k(reverse)) is calculated to be 67. 

Structures of catalytic intermediates in pyridoxal-phosphate-dependent reactions. The initial aldimine intermediate resulting from Schiff s base formation between the coenzyme and the a-amino group of an amino acid (a). This aldimine is converted to the resonance-stabilized... 

Pittner, F., and Hoffmann Ostenhof, O., 1978, Studies on the biosynthesis of cyclitols, XXXVII. On mechanism and function of Schiff s base formation as an intermediary reaction step of myo-inositol-1-phosphate synthase from rat testicles. Hoppe Seylers Z. Physiol. Chem. 359 1395-1400. 

The Amadori product from D-glucose 33 and L-proline decomposes at 130 °C in DMF to afford 33 and D-Mannose 54, indicating the reversibility of the Amadori reaction. A kinetic study using 33 and phenylalanine indicates that the Schiff s base formation is the rate-determining step of the Maillard reaction [275,276]. 

O o Schiff s base formation pyrroles, cross-linking... 

Simple peptides [M + H]+ Identification of N-terminus via Schiff s base formation 61... 

Thiourea formation Schiff s base formation Carbamate formation Alkylation... 

The Schiff s base formation between AdoMet and the pyridoxal phosphate-enzyme complex leads to elimination of a proton at a-C of AdoMet to generate a carbanion. The positive sulfonium ion of AdoMet activates the methylene at 7-C and facilitates the intramolecular y-displacement reaction by the carbanion, generating ACC and MTA. The direct 7-displacement was demonstrated by Ramalingam et al. [78]. 

A prerequisite that the mechanism in a series should be the same is a linear free-energy correlation if a member of the series takes a different pathway then the alternative mechanism will be more favourable, will predominate over the normal and will be diagnosed as a positive deviant point. An example of this behaviour is the demonstration that general acid catalysis by primary amines of the iodination of acetone differs from that by carboxylic acids (Fig. 24) [3a] simple proton transfer is identified with the carboxylic acid catalysis and it is thought that amines utihse Schiff s base formation (Eqn. 116) leading to a more favourable path. 

Hardening of gelatin with low molecular weight aldehydes is well documented in the literatureCrosslinking is predominantly due to Schiff s base formation by condensation of the formil group and the e-amino groups present in lysine and hydroxylysine residues. 

The most important feature of the NBP test is that it provides a rationalistic criterium for evaluating fish toxicity data for certain classes of organic micropollutants that have an enhanced toxicity compared to those compounds whose mode of toxic action is based on a narcosis mechanism (minimal toxicity). Applicability of the NBP test is restricted to those classes of compounds that are directly reactive in nucleophilic displacement reactions (SN reactions) like, e.g., alkylhalides, epoxides, -lactones, etc. The NBP test is not applicable to those compounds that are bioactivated in vivo to reactive intermediates. Lipnick (1985) has used, referring to this phenomena, the term pro-electrophiles. For those kinds of compounds, descriptors representing the degree of bioactivation, should be incorporated. The NBP test is, of course, not suitable for compounds that act as electrophiles by other reaction mechanisms like, e.g., the Schiff s base formation of aldehydes. 

Any Schiff s base formation in a perfume itself is brought about by the deliberate inclusion of methyl anthranilate in the mixture. Work published almost 50 years ago by Wells [13] reviews some interesting Schiff s compounds of use to the perfumer. For the chemist, it is important to note that the formation of a Schiff s base can be quite slow and the compounds can be highly colored. Perfume oils delivered to a detergent manufacturer will be stable and matured, such that the consequences of the reactions reviewed in this section should be somewhat academic. However, autooxidation reactions such as... 

The dehydration nd deamination may be effected through a Schiff s base formation with pyridoxal phosphate. Such a mechanism has been postulated by Metzler and Snell SS9). It will be noted in the discussion below that many of the dehydrases studied require pyridoxal-5-phosphate. Replacement of the hydroxyl-hydrogen atom of the substrate prevents deamination. 

In the case of PAM, oligoglycine was first fixed to the carrier surface through Schiff s base formation, followed by reduction. After that, the enzymes were bound to the carboxyl end group of the spacer by using l-ethyl-3- (3-dimethylaminopropyl)-carbodiimide, a water-soluble activator. The enzymes were fixed to the ChB through the iminosuccinic anhyride present at the end of the oligonylon spacers. 

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