Hydrazone

Abstract: [reaction: see text] A new fluorescent probe, salicylaldehyde rhodamine B hydrazone (1), was synthesized and displayed selective Cu(II)-amplified absorbance and fluorescence emission above 500 nm in neutral buffered media. Upon the addition of Cu(II), the spirolactam ring of 1 was opened and a 1:1 metal-ligand complex was formed. The detection of Cu(II) by 1 at a lower micromolar level was successful even in buffered water.

Abstract: Hydrazones and oximes are common conjugates, but are labile to hydrolysis. The hydrolytic stability of isostructural hydrazones and an oxime have been determined at pD 5.0–9.0. The hydrolysis of each adduct was catalyzed by acid. Rate constants for oxime hydrolysis were nearly 103-fold lower than those for simple hydrazones; a trialkylhydrazonium ion (formed after condensation) was even more stable than the oxime. The data suggest a general mechanism for conjugate hydrolysis.

Abstract: The hydrazone functional group has been extensively studied and used in the context of supramolecular chemistry. Its pervasiveness and versatility can be attributed to its ease of synthesis, modularity, and most importantly unique structural properties, which enable its integration in different applications. This review provides an overview of the utilization of hydrazones in three supramolecular chemistry related areas: molecular switches, metallo-assemblies and sensors. These topics were chosen because they highlight the diversity of hydrazones, and emphasize their uniqueness vis-a-vis the imine functional group. Discussion entails (i) chemical and light activated switching of hydrazones, and how this can be used in controlling the properties of self-assembled systems, (ii) the use of hydrazones in the formation of dynamic and stimuli responsive metallogrids, and (iii) the use of hydrazones in detecting metal cations (Zn2+, Cu2+, Hg2+, etc.), anions (F−, CN−, P2O74−, etc.) and neutral molecules (amines, water, Cys, etc.).

Abstract: A general approach for forming peptide dendrimers with oxime, hydrazone, and thiazolidine linkages was developed using unprotected peptides as building blocks and selective ligation between an aldehyde and a weak base. To illustrate the generality of this approach, a branched lysine core matrix with an aldehyde was used to ligate four copies of unprotected peptides containing a weak nucleophilic base such as aminooxy, hydrazide, or cysteine 1,2-aminothiol groups at their N-termini to form synthetic branched proteins. Various parameters affecting the ligations were studied, and optimal conditions gave 12-27-fold rate increases and shortened the reaction time from 24-60 to 2-8 h. Among the three reactions studied, ligation by thiazolidine appeared to be superior to ligation by oxime or hydrazone in reaction rate and product stability. The purified dendrimeric products gave single peaks on reverse phase HPLC and size exclusion HPLC. Their macromolecular structures were also characterized by mass spectrometry and amino acid analysis. Circular dichroism spectra of the dendrimers showed that they have an increased ordered helical structure. Ligation reactions using a mutually reactive weak base and aldehyde pair should provide a useful approach for the synthesis of peptide dendrimers and artificial proteins.