Ivan Bernal

Ivan Bernal
Professor
	Office: 35 Fleming Phone: (713) 743-2718 Email: ibernal@uh.edu Education B.S., Clarkson College of Technology, 1954 M.S., University of Virginia, 1956 Ph.D., Columbia University, 1963 Posdoctoral Fellow, Harvard University, 1963-64 Honors, Fellowships, etc. U.S. Senior Scientist Award, Alexander von Humboldt-Stiftung Elected Fellow, New York Academy of Sciences Elected Visiting Fellow, Australian National University Appointed Visiting Fellow, Oriel College, University of Oxford

Research Interests

We have recently investigated the cleavage of peptide bonds with Co(III) compounds of general formulae [N₄CoCl₂]Cl in water at pH ~ 7.5. N₄ is either a tetradentate amine (linear or branched), or two bidentate amines. The first two examples contain cis-dichloroCo derivatives. Results:
(1) when the amine is tren (tris-2-aminoethylamine) and the dipeptide is beta-alanine-L-histidine, the cleavage reaction carried out in a 1:1 ratio of Co:dipeptide, the products are free beta-alanine and [(tren)Co(histidine)]Cl. In the later species the Co(III) is bound by a carboxyl oxygen and the -NH2 moiety. The imidazole ring is dangling. Finally, the aminoacid is partially racemized during cleavage. Separation by chromatography of the Co complex leaves a colorless solution which contains intact beta-alanine, as shown by nmr and by crystallography of its Co derivative, [(tren)Co(beta -alanine)]Cl.
(2) when the amine is trien (1,4,7,10-tetraazadecane) and the dipeptide is beta-alanine-L-histidine, the isolated metal species is [(trien)Co(histidine)]Cl and racemization occurs partially also. Furthermore, the histidine is bound to Co by one nitrogen of imidazole and the amine moiety of the aminoacid. Therefore, the mechanism of the reaction is sensitive to the nature of the amine used.
(3) When the amine is 3,2,3-tet (1,5,8,12-tetrazadodecane) the Co complex is [trans-(3,2,3-tet)CoCl2]Cl and the dipeptide is is beta-alanine-L-histidine, the surprising product is [trans-(3,2,3-tet)Co( beta-alanine)2]Cl. This result is unique in that (a) it is the first example known of a trans-Co derivative cleaving a peptide bond (all previous experiments were failures) and (b) a single metal center broke two peptide bonds. The reaction accurs as shown below:

Recent Publications

Manas K. Saha, Ivan Bernal and Frank Fronczec, Novel room temperature, light-induced trimerisation of a simple copper(II) monomeric Schiff base complex, Chem. Commun. 84-85 (2004).

Manas K. Saha, Fransesc Lloret and Ivan Bernal, InterString Arrays of Bimetallic Assemblies with Alternative Cu²⁺-Cl-Cu²⁺ and Cu-CN-M (M=Co³⁺, Fe³⁺, Cr³⁺) Bridges: Syntheses, Crystal Structure and Magnetic Properties, Inorg. Chem., 43, 1965-1979 (2004).

Manas K. Saha, Udai Mukhopadhyay and Ivan Bernal, Co(III)-amine Complex Induced Cleavage of Dipeptides, J. Chem Soc, Dalton, 1466-1475 (2004).

U. Mukhopadyhay and I. Bernal , A Totally Unexpected Synthesis of Single Crystals of the Mineral Chalconatronite, Na₂[Cu(CO₃)₂]•3H₂O, From a Solution of a Copper Coordination Compound and Atmospheric CO₂, at Room Temperature, J. Coord. Chem., 57, 353-360 (2004).

U. Mukhopadhyay and I. Bernal, Polymorphism in Dinuclear Cu(II) Compounds—Polymorphism Caused by Different Degrees of Hydration. The Structures of [Cu(HL)]₂Cl₂•4H₂O (I), [Cu(HL)]₂Cl₂•2H₂O (II), [Cu(HL)]₂)(NO₃)₂•4H₂O (III), [Cu(HL)]₂)(NO₃)₂•2H₂O (IV) and [Cu(HL)]₂)(ClO₄)₂•2H₂O (V) (Hl = [(3-aminopropyl)-di-(2-hydroxopropyl)]amine Anion. Counterion Control of the Crystallization Pathway. Part 11, Inorg. Chim. Acta, 357, 1360-1368 (2004).

U. Mukhopadhyay, I. Bernal, D. S. Yufit, J. A. K. Howard, L. Massa, A. Gindulyte, L. Todaro and S. S. Massoud, Polymorphism in [(polyamine)Co(NO₂)x]Y Crystals Caused by Changes in Torsional Angles of the (Amine)N-Co-N-O Fragments. (x = 2, Y = NO3- : x = 3, Y = 0), Inorg. Chim. Acta, 357, 4121 (2004).

Fangfang Jian, Hailian Xiao, Pingping Sun, Udai Mukhopadhyay and Ivan Bernal, Study of the Syntheses, Structures and Thermal Properties of Three Crystalline Polymorphs of Bis(N-Phenylmethyl Benzymidazole-N) Dichloro Cobalt(II) Complex: CoCl₂(C₇H₅N₂CH₂Ph)₂, J. Coord. Chem., 57, 923 (2004).

Udai Mukhopadhyay and Ivan Bernal, Salah S. Massoud and Franz A. Mautner, Syntheses, Structures and Some Electrochemistry of Cu(II) Complexes With Tris[(2-pyridyl)methyl]amine: [Cu{N(CH₂-py)₃}(N₃)]ClO₄ (I), [Cu{N(CH₂-py)₃}(O-NO)]ClO₄ (II) and [Cu{N(CH₂-py)₃}(NCS)]ClO₄ (III), Inorg. Chim. Acta, 357, 3673-82 (2004).

Ivan Bernal, The Structure and Absolute Configuration of the More Soluble Isomer of a Compound of Composition [(S(Mo);R(C₈)-C₂₁H₁₉N₂O₂Mo]PF₆ -- A Conformational Isomer of the Compound recorded in CSD as PEPCMO. This is the Least Preferred Isomer in the Synthesis, and the Most Soluble one. Submitted to Frank Allen, at CSD, as an Electronic File, August 5, 2004. Data can be found in CCDC 246925. REFCODE = WAGXIM.

U. Mukhopadhyay, D. Choquesillo-Lazarte, J. Niclós-Gutiérrez and I. Bernal, A critical look on the nature of the intra-molecular interligand p,p-stacking interaction in mixed-ligand copper(II) complexes of aromatic side-chain amino acidates and a,a'-diimines, Crystal Engineering Communications, 6, 627-632 (2004).

Uday Mukhopadhyay and Ivan Bernal, Polymorphism and Molecular Conformations of Non-Protonated a-Aminoacids. Mendeleev, 6, 270-276 (2004).

Manas K. Saha, M. Carmen Morón, Fernando Palacio and Ivan Bernal, A New Bimetallic Intercalated 3-D Assembly Magnet [{(323-tet)Ni}₃{Fe(CN)₆}₂]n•12nH₂O (323-tet = N,N´-Bis(3-aminopropyl)ethylenediamine) : An Unprecedented Concomitant Presence of Meridional and Facial Arrangment of Ferricyanide Anion, Inorg. Chem., 44, 1354-1361 (2005).