Acyclic and cyclic imines and their metal complexes: recent progress in biomaterials and corrosion applications

Abstract

This review describes the contemporary development applications on scientific areas of acyclic and cyclic Schiff bases and their complexes with an emphasis on the author's contribution to the field. After a short historical introduction, this manuscript is divided into two main parts. In the first section, Schiff bases are reviewed for their biological activities including antibacterial, antifungal, antioxidant, cytotoxic, and enzymatic activities as well as their interaction with single-stranded-DNA which have shown remarkable activities in each region of research. The second part deals with the corrosion of metal and its alloys in corrosive environments and their organic inhibitors. The main section of this part is to investigate the different chemical structures for Schiff bases used in such aggressive solution to protect metals. Knowing the maximum corrosion efficiency or bioactivity of a specific chemical structure in a specific application environment is helpful for choosing the most appropriate compound.

Scheme 1. Synthesis of Cu(ii) complexes [Cu(L₁)₂–Cu(L₄)₂].

Scheme 2. Synthesis of complexes M(L₁)PPh₃–M(L₄)PPh₃.

Scheme 3. Synthesis of Schiff base complexes (a–c).

Scheme 4. Synthesis of imines (HL₁–HL₄).

Scheme 5. Structures of the ligands and the formation of complexes 1–3.

Scheme 6. Structures of SBs (L¹ and L²).

Scheme 7. Synthesis of the copper complexes from bis(dithiocarbazate) ligands. Reagents and conditions: (a) CS₂, KOH, EtOH, 0 °C, 1 h; (b) CH₃I or PhCH₂Cl, EtOH, 0 °C, 5 h; (c) for SMHDH₂ (2,5-hexanedione, EtOH, 79 °C, 1 h), for SBHDH₂ (2,5-hexaedione, EtOH, 79 °C, 5 min) and (d) for CuSMHD [Cu(OAC)₂·H₂O, MeOH, 65 °C, 1 h], for CuSBHD [Cu(OAc)₂, acetonitrile, r.t, 1 h].

Fig. 1. Structures of Schiff bases 1a–1k and their corresponding secondary amines 3a–3k showing the numbering system used in the assignment of ¹H and ¹³C NMR spectra.

Scheme 8. Synthesis of SB ligands.

Scheme 9. Preparation of Schiff bases (SBs).

Scheme 10. (I) Synthesis route to Schiff bases of 5-substituted isatins. (II) Synthetic routes to compound 7 and Schiff bases of N-arylmethylisatin 11a–13c. Reagents and conditions: (a) phenylhydrazine, ethanol 96% (w/w), acetic acid; (b) fluorinated benzyl chlorides, K₂CO₃, KI, acetonitrile; (c) compounds 8–10, ethanol 96% (w/w), acetic acid.

Scheme 11. Synthesis of bis-Schiff from isatins.

Scheme 12. Synthetic route for SBs.

Scheme 13. Synthetic pathway for the protection of target compounds 2, 3, 4, 5, 6 and 7.

Scheme 14. Synthesis of copper complexes [Cu(L₁)₂–Cu(L₃)₂].

Scheme 15. Synthesis of Schiff bases 1–5.

Scheme 16. Synthesis of C6-Schiff bases of chitosan derivatives.

Scheme 17. Synthesis of chitosan Schiff bases (ChBs).

Scheme 18. Modification of chitosan-graft-polyacrylonitrile.

Scheme 19. Schematic representation of ionic liquid-anchored chitosan Schiff bases and their metal complexes.

Scheme 20. Synthetic route for the preparation of SBs.

Fig. 2. Molecular structure of investigated SBs (P1: X = H; P2: X = Cl; P3: X = Br).

Fig. 3. Optimized geometrical configurations of BFBT, TMBT, and FNBT.

Fig. 4. (((5-Phenyl-1,3,4-thiadiazol-2-yl)imino)quinolone-2-ol/thiol).

Fig. 5. Structures of studied Schiff bases.

Fig. 6. Chemical structure of the investigated compounds.

Fig. 7. Chemical structure of the tested SBs.

Fig. 8. Structure of inhibitor molecule.

Scheme 21. Representation procedures for the synthesis of Schiff base compounds.

Scheme 22. Synthetic route for investigated SBs.

Scheme 23. Chemical structure of Schiff base molecules S1 and S2.

Scheme 24. Synthesis of ferrocene carboxaldehyde propanoylhydrazone (fcph) and ferrocene carboxaldehyde furoylhydrazone (fcfh) Schiff bases.

Scheme 25. Reaction pathway showing the formation (E)-4-((naphthalen-2-ylimino)methyl)phenol Schiff base.

Scheme 26. Reaction route for the preparation of (a) (Z)-N-(2-chlorobenzyllidene)naphthalene-1-amine, and (b) (Z)-N-(3-nitrobenzyllidene)naphthalene-1-amine.

Scheme 27. Reaction of vanillin with isoniazid.

Fig. 9. Chemical structures of the Schiff bases.

Fig. 10. Chemical structures of the synthesized inhibitors.

Fig. 11. Chemical structure of the synthesized corrosion inhibitors: (a) N′-(4-hydroxybezylidene)nicotinic hydrazone (HBNH), and (b) N′-(4-methylbezylidene)nicotinic hydrazone (MBNH).

Fig. 12. Chemical structures of the synthesized SBs.

Fig. 13. Structure of the investigated SBs.

Fig. 14. Chemical structure of SBs.

Fig. 15. Names and structures of the investigated SBs.

Fig. 16. Synthesis route of the studied compounds: (a) 4-(dimethylamino)benzaldehyde, (b) aniline, (c) (E)-N,N-dimethyl-4-((phenylimino)methyl)aniline (E-NDPIMA), (d) diethylphosphite, and (e) diethyl ((4-(dimethylamino)phenyl)(phenylamino)methyl)phosphonate (α-APD).

Fig. 17. General structure of the investigated SBs.

Fig. 18. Schiff bases.

Fig. 19. Structure of the investigated SBs: 3-(5-nitro-2-hydroxybenzylideneamino)-2-(5-nitro-2-hydroxyphenyl)-2,3-dihydroquinazoline-4(1H)-one (NNDQ).

Fig. 20. Structure of the studied SBs.