title: Spectroscopy and microscopy studies of the recognition of amino acids and aggregation of proteins by Zn(II) complex of lower rim naphthylidene conjugate of calix[4]arene.
abstract: A lower rim naphthylidene conjugate of calix[4]arene [L] has been synthesized and characterized, and the structure has been established on the basis of single crystal XRD. The L has been found to be selective toward Zn(2+), which induces appropriate changes in the arms of L so that the N(2)O(2) coordination results in the formation of a tetrahedral complex; namely, [ZnL]. [ZnL] recognizes Asp, Cys, His, and Glu from among the naturally occurring amino acids owing to the protonation and chelating ability of the amino acid and the pi-pi interaction ability of the side chain of the amino acid with [ZnL]. All of these features have been demonstrated on the basis of fluorescence, absorption, and lifetime measurements. The rechelation of Zn(2+) by the amino acid used in the titration has been demonstrated on the basis of ESI-MS studies in the case of Cys to result in a Zn(2+) complex having either 5- or 6-coordination. [ZnL] has also been shown to be selective toward glutathione and glutathione oxidized. The amino acids present in the proteins also interact with [ZnL], resulting in dechelation of [ZnL] as well as aggregation of the protein, as demonstrated on the basis of absorption and fluorescence spectroscopy and atomic force microscopy. The alpha-helical proteins (namely, albumins) exhibit greater conformational changes, as compared to the beta-sheet proteins (namely, lectins), as studied on the basis of CD spectroscopy. The aggregation of the proteins when treated with [ZnL] follows a trend: peanut agglutinin < bovine serum albumin < jacalin < human serum albumin. The present studies clearly demonstrated the recognition features of [ZnL] toward Asp, Cys, His, and Glu, and the peptides and proteins containing these by spectroscopy and microscopy studies.
authors.affiliation: Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, India.
authors.forename: Jugun Prakash
authors.initials: JP
authors.lastname: Chinta
authors.forename: Amitabha
authors.initials: A
authors.lastname: Acharya
authors.forename: Amit
authors.initials: A
authors.lastname: Kumar
authors.forename: Chebrolu P
authors.initials: CP
authors.lastname: Rao
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D000818:Animals; D047250:Calixarenes / Q000737:chemistry*; D002417:Cattle; D008853:Microscopy / Q000379:methods; D018625:Microscopy, Atomic Force / Q000379:methods; D009281:Naphthalenes / Q000737:chemistry*; D010455:Peptides / Q000737:chemistry; D010636:Phenols / Q000737:chemistry*; D011485:Protein Binding; D017433:Protein Structure, Secondary; D011506:Proteins / Q000737:chemistry; D012709:Serum Albumin / Q000737:chemistry; D013050:Spectrometry, Fluorescence / Q000379:methods; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods; D015032:Zinc / Q000737:chemistry*
chemical_list: D000596:Amino Acids; D009281:Naphthalenes; D010455:Peptides; D010636:Phenols; D011506:Proteins; D012709:Serum Albumin; C121325:calix(4)arene; D047250:Calixarenes; D015032:Zinc