Cu(II) and Ni(II) complexes of n (2 hydroxybenzyl) amino acid ligands synthesis, structures, properties and catecholase activity

Chapter 1 Introduction 1-3 CopperII complexes of Schiff base ligands 4 1-4 CopperII complexes with reduced Schiff base ligands 11 1-5 NiII complexes with Schiff base and reduced Schiff

SYNTHESIS, STRUCTURES, PROPERTIES AND

CATECHOLASE ACTIVITY

BELLAM SREENIVASULU

(M Sc., S K University, A P India)

A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY

DEPARTMENT OF CHEMISTRY NATIONAL UNIVERSITY OF SINGAPORE

2006

Dedicated to my beloved parents especially

To My Father

ACKNOWLEDGEMENTS

I am greatly indebted to my advisor, Dr Jagadese J Vittal for his invaluable guidance, positive criticism, enlightening discussions and constructive suggestions throughout the candidature which immensely helped me in attaining the scientific and scholarly attitude of a researcher I greatly admire his guidance and wish to express

my sincere gratitude for his constant support, patience and supervision at each and every stage of my PhD life

Many thanks to Prof Song Gao, Peking University, China for low temperature magnetic measurements and calculations Also, many thanks to the all technicians and staff from EA, NMR, IR, TGA, XRD, micro analytical, analytical and honours laboratories at the Department of Chemistry, NUS Particularly, I am thankful to Dr Jagadese J Vittal for single crystal X-ray data collection, structure solution and refinements of the crystal structures presented in this thesis

I am grateful to my mother, brothers, sisters and all family members for their kind support Especially, I am thankful to my eldest brother, B Ravi Kumar for his guardianship, moral support and encouragement all the times I also express my sincere thanks to the past and present members of our research group and all my friends who have shown their support for their invaluable and helpful discussions I

am also thankful to Dr Srinivasa Buddudu and Dr W Rajendra for their encouragement

I also deeply appreciate National University of Singapore for awarding me a Research Fellowship for my PhD

i

Declaration

This work described in this thesis was carried at the Department of Chemistry, National University of Singapore from 7th Jan 2002 to 30th Mar

2006 under the supervision of Associate Professor Jagadese J Vittal

All the work described herein is my own, unless stated to the contrary, and

it has not been submitted previously for a degree at this or any other university

Bellam Sreenivasulu

2006

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Chapter 1 Introduction

1-3 Copper(II) complexes of Schiff base ligands 4

1-4 Copper(II) complexes with reduced Schiff base ligands 11 1-5 Ni(II) complexes with Schiff base and reduced Schiff base ligands 15 1-6 Solid-state supramolecular transformations by thermal dehydration 18 1-7 Effect of C=O···π interactions on thermal dehydration 19

1-12 Potential applications of Schiff base and reduced Schiff base complexes 28

Chapter 2 Dinuclear Copper(II) Complexes as Functional Models for the

Catechol Oxidase

Part-A Synthesis, Characterization, Structural Properties and

Catecholase Activity of Dicopper(II) Complexes of reduced Schiff base Ligands

2-A-2-2-1 [Cu2 (Scp11)2(MeOH) 2], IIA-1a 64

2-A-2-2-2 [Cu2 (ClScp11)2(DMF)(H2O)] MeCN, IIA-2a 66 2-A-2-2-3 [Cu2 (MeScp11)2 (MeOH)2].2MeOH, IIA-3a 68

2-A-2-2-4 [Cu2(OHScp11)2(H2O)2], IIA-4 70 2-A-2-2-5 [Cu2(ClSch11)2(MeOH)2].2MeOH, IIA-6a 73 2-A-2-2-6 [{Cu2(Sch12)2}2⋅Cu2(Sch12)2(H2O)2].4H2O, IIA-8 75

2-A-2-2-7 [Cu2(ClSch12)2].2MeOH, IIA-9a 78

2-A-2-2-8 [Cu2(Diala4)2(DMSO)2]⋅2DMSO⋅2Acetone, IIA-12a 79

iv

2-A-3-4 Thermogravimetric studies 87 2-A-3-5 Magnetic studies of [{Cu2(Sch12)2}2Cu2(Sch12)2(H2O)2].4H2O, IIA-8 89

2-A-6-3 Catecholase activity and kinetics measurements 107

Part-B Dicopper(II) Complexes as Functional Models for the Catecholase

Activity: Influence of Weakly Coordinating Sulfonate Group on the Oxidation of 3,5-DTBC

2-B-2-2-2 [Cu2(Saes)2(H2O)2].2H2O, IIB-3 116

2-B-2-2-3 [Cu2(Sae)2].2H2O, IIB-4 119 2-B-2-2-4 [Cu2(Sae)2(DMF)2].2DMF, IIB-5 122

Part-C 3D Coordination Polymer with Hexagonal Diamondoid Topology

displaying Star-like Channels

Part-D Experimental Section

2D-12 Single crystal X-ray crystallography 173

Chapter 3 Cu(II) and Ni(II) Complexes of reduced Schiff base Ligands

containing Additional Functional Groups in the Amino Acid side chain

3-2-1-1 [Cu(HSglu)(H2O)].H2O, III-2 178

3-2-1-2 [Cu(HMeSglu)(H2O)].2H2O, III-3 181

3-2-1-4 [Ni2(Smet)2(H2O)2], III-6 188

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Chapter 4 Ni(II) Helical Staircase Coordination Polymer Encapsulating

Helical Water Molecules

4-3-1 Crystal structure of [(H2O)2⊂{Ni(HSglu)(H2O)2}]⋅ H2O, IV-1 215

4-6-3 X-ray crystallography 225

Suggestions for Future work 236

Appendix (provided in the CD ROM attached)

A-3 Thermo gravimetric curves of IIA-1 – IIA-13 S7

A-4 UV-Vis spectra of oxidation of 3,5-DTBC by IIA-1 – IIA-13 S11

A-6 Thermogravimetric curves of IIB-1 – IIB-4 S15

A-7 UV-Vis spectra of oxidation of 3,5-DTBC by IIB-2 and IIB-4 S16

A-9 Thermo gravimetric curves of III-1 – III-7 S17 CIF files of all the crystal structures

ix

EPR electron paramagnetic resonance

e.s.d estimated standard deviation (standarduncertainty parameter)

ESI-MS electrospray ionization mass spectroscopy

ESR electron spin resonance

x

H2ClScp11 N-(2-hydroxy-5-chlorobenzyl)-1-aminocyclopentatecarboxylic acid

H2MeScp11 N-(2-hydroxy-5-methylbenzyl)-1-aminocyclopentatecarboxylic acid

H2OHScp11 N-(2,5-dihydroxybenzyl)-1-aminocyclopentatecarboxylic acid

H2Sams N-(2-hydroxysalicylidene)-aminomethanesulfonic acid

H2Saes N-(2-hydroxysalicylidene)-aminoethanesulfonic acid

H2Sam N-(2-hydroxybenzyl)-aminomethanesulfonic acid

H2Sae N-(2-hydroxybenzyl)-aminoethanesulfonic acid

H2Sas N -(2-hydroxybenzyl)-L-aspartic acid

H3Sglu N -(2-hydroxybenzyl)-L-glutamic acid

H3MeSglu N-(2-hydroxy-5-methylbenzyl)-L-glutamic acid

Hz hertz

Ind Reflns independent reflections

JA-B coupling constant between nuclei A and B

LMCT ligand to metal charge transfer

Copyrights Permission

I sincerely acknowledge the publishers of American Chemical Society (ACS), VCH Verlag GmbH & Co KG, Royal Society of Chemistry (RSC) and Elsevier B V (ScienceDirect) for granting copyrights permission to reproduce the figures from the respective journals as below Permission has been granted for using the following list

Wiley-of figures from various journals Wiley-of the above mentioned publishers (citations have also been mentioned in the figure captions appropriately)

Copyrights permission from American Chemical Society

Figure 1-9 Reprinted with permission from Inorg Chem 2005, 44, 1302

Figure 1-12 Reprinted with permission from Cryst Growth Des 2005, 5, 41

Figure 1-13 Reprinted with permission from Cryst Growth Des 2004, 3, 781 Figure 1-14 Reprinted with permission from Inorg Chem 2001, 40, 5934

Figure 2-2 Reprinted with permission from Acc Chem Res 2002, 35, 183

Figure 2-4 Reprinted with permission from Acc Chem Res 2002, 35, 183

Figure 2-6 Reprinted with permission from Inorg Chem 1996, 35, 3409

Figure 2-11 Reprinted with permission from Inorg Chem 2002, 41, 1788

Figure 2-12 Reprinted with permission from Inorg Chem 2002, 41, 3983

Copyrights permission from Wiley-VCH Verlag GmbH & Co KG

Figure 1-2 Taken from Angew.Chem Int Ed Engl 2004, 43, 87

Figure 1-8 Taken from Angew Chem Int Ed Engl 2003, 42, 1940

Figure 2-8 Taken from Chem Eur J 2002, 8, 247

Figure 2-9 (right).Taken from Chem Eur J 2001, 7, 2143

Figure 2-10 Taken from Chem Eur J 2001, 7, 2143

Figure 4-1 Taken from Angew.Chem Int Ed Engl 2005, 44, 5720

Figure 4-3 Taken from Eur J Inorg Chem 2005, 3214

Copyrights permission from Royal Society of Chemistry

Figure 4-2 Chem Commun 2004, 716 (Reprinted with permission of The Royal

Society of Chemistry)

Figure 4-4 Chem Commun 2005, 3024 (Reprinted with permission of The Royal

Society of Chemistry)

Copyrights permission from Elsevier B.V (ScienceDirect)

Figure 2-9 (left) Taken from Inorg Chim Acta 2002, 337, 429

xiv

Summary

This research work presents the synthesis, characterization and structural studies of

different series of Cu(II) and Ni(II) complexes of

N-(2-hydroxy-5-substituted-benzyl)-amino acids which includes various natural/unnatural N-(2-hydroxy-5-substituted-benzyl)-amino acids The unnatural amino acids employed to synthesize these ligands are aminocyclopentane/hexanecarboxylic acids and aminomethane/ethanesulfonic acids containing carboxylate and sulfonate donors respectively The objective of the present study is to investigate the coordination chemistry of these ligands with Cu(II) and Ni(II) and explore the Cu(II) complexes as functional models for the enzyme, catechol oxidase

While utilizing the unnatural amino acids such as 1- and/or aminoclopentane/hexanecarboxylic acids, and commercially available salicylaldehydes with para-substituents such as H, Me, Cl and OH, various reduced

2-Schiff base ligands, N-(2-hydroxy-5-substituted-benzyl)-amino acids are synthesized

On the other hand, commercially available L-alanine and different hydroxy

substituted salicylaldehydes are utilized for the synthesis of 3-, 4- and 5- hydroxy

substituted N-(2-hydroxybenzyl)-L-alanine ligands A new series of closely related yet

distinct dinuclear Cu(II) complexes, obtained upon subsequent complexation with all these ligands, are investigated for their structural properties and for their ability to mimic catechol oxidase as functional models These activity studies are mainly focused on evaluating the effect of various substituents such as OH, Cl and –CH3, present at the 5th position of the phenyl ring of the ligands on the oxidation of 3,5-DTBC (catecholase activity) A detailed account of these findings is given in Part-A

in Chapter 2 Further, the catecholase activities observed in these complexes, under

xv

the similar experimental conditions, are compared with that of the related dicopper(II) complexes previously studied by our research group

Another series of dicopper(II) complexes of the reduced Schiff base ligands,

N-(2-hydroxybenzyl)-aminomethane/ethanesulfonic acids, containing weakly coordinating sulfonate donor group instead of carboxylate group in the amino acid side arm are investigated to evaluate the role of sulfonate donor on the structures as well as on catecholase activity In this case the Schiff base complexes are also studied These results demonstrating the effect of weakly coordinating sulfonate donors on both the structures and catecholase activity are also systematically compared with the related and analogous complexes containing carboxylate donors Details of these findings are given as Part-B in Chapter 2

The reactivity of H2Scp11 ligand towards Cu(II) ion under different crystallization conditions and the interesting structural features of the resulting Cu(II) complexes are presented in Part-C in Chapter 2

Further investigations on the coordination chemistry of reduced Schiff base ligands are made by incorporating additional reactive functional groups in the amino acid side arm such as –COO-, -SCH3, -CONH2 with a view that these additional functional groups may show interesting connectivity upon complexation with metal ions such as Cu(II) and Ni(II) The results are described in Chapter 3

xvi

A Ni(II) complex of H3Sglu (N-(2-hydroxybenzyl)-L-glutamic acid) ligand, with a

novel display of spiral coordination polymeric structure with a fascinating encapsulation of hydrogen bonded helical water molecules is described in Chapter 4

xvii

List of Compounds Synthesized

IIA-2a [Cu2(ClScp11)2(DMF)(H2O)].MeCN*

IIA-3 [Cu2(MeScp11)2(H2O)2]

IIA-3a [Cu2(MeScp11)2(MeOH)2].2MeOH*

IIA-4 [Cu2(OHScp11)2(H2O)2]*

xix

IIA-6a [Cu 2 (ClSch11) 2 (MeOH) 2 ].2MeOH*

IIA-7 [Cu2(MeSch11)2(H2O)2]

xx

IIA-9a [Cu2(ClSch12)2].2MeOH*

IIA-10 [Cu2(MeSch12)2(H2O)2]

xxi

H3Diala3 N-(2,3-dihydroxybenzyl)-L-alanine

H 3 Diala4 N-(2,4-dihydroxybenzyl)-L-alanine

H 3 Diala5 N-(2,5-dihydroxybenzyl)-L-alanine

IIA-11 [Cu 2 (Diala5) 2 (H 2 O) 2 ].H 2O

IIA-12 [Cu 2 (Diala4) 2 (H 2 O) 2 ].H 2O

IIA-12a [Cu2(Diala4)2(DMSO)2]⋅2DMSO⋅2Acetone *

xxii

IIA-13 [Cu2(Diala3 )2(H2O)2].H2O

IIB-1 [Cu2(Sams)2(H2O)2]*

IIB-2 [Cu 2 (Sam) 2 (H 2 O) 2 ].H 2 O

xxiii

IIB-3 [Cu2(Saes)2(H2O)2].2H2O*

IIB-4 [Cu 2 (Sae) 2 ].2H 2 O*

IIB-5 [Cu 2 (Sae) 2 (DMF) 2 ].2DMF*

IIC-1 [Cu2(Scp11)2].H2O*

IIC-2 [Cu2(Scp11)2(H2O)2]·2Me2CO*

H3Sas N-(2-hydroxybenzyl)-L-aspartic acid

xxiv

H3Sglu N-(2-hydroxybenzyl)-L-glutamic acid

III-2 [Cu(HSglu)(H2O)].H2O*

III- 3 [Cu(HMeSglu)(H 2 O)].2H 2O*

xxv

III-4 [Cu2(Smet)2]*

III-5 [Ni(HSas)(H2O)]*

III-6 [Ni2(Smet)2(H2O)2]*

III-7 [Ni(HSapg) 2]*

IV-1 [(H2O)2⊂{Ni(HSglu)(H 2 O)2}]⋅H 2 O*

* Crystal structure determined

xxvi

List of Figures Chapter 1

Page

Figure 1-2 Formation of mixed CuII12CuI2 clusters from [{Cu(HL)}4] units via

Figure 1-4 Various ternary Schiff base Cu(II) complexes employed for DNA

Figure 1-5 Scheme of 2-imidazolecaboxaldehyde, and 2-pyridinecarbox-

Figure 1-7 Ligands suitable for the complexes with cytotoxic and antitumour

Figure 1-8 Molecular structure of [Cu8L8Py10].Py.3MeOH.(C2H5)2O showing

the trapped pyridine molecules (the solvent molecules are excluded

Figure 1-9 Diagrammatic illustration of thermal dehydration creating empty

channel and filling I2 inside the channels 14

Figure 1-10 Some of the reduced Schiff base-amino acid ligands investigated

Figure 1-11 Schematic illustration of interconversion from 3D H-bonded

network to a coordination polymeric network via thermal

Figure 1-12 (Left) Interactions between the carboxyl group and the phenyl

ring in [Cu2(Sgly)2(H2O)].H2O and [Cu2(Sala)2(H2O)]n (Right) Schematic of C=O···π interaction between the carboxylate

Figure 1-14 Schematic diagram illustrating the pH-dependent

Figure 1-15 Schematic illustration of the interconversion of the

Figure 1-16 2-pyridylmethyl derivatives of reduced Schiff base ligands 24

Figure 1-17 CPK models of various 1D polymers derived from Hpgly and

Figure 1-18 Diagrammatic illustration of formation of complexes

Figure 1-20 Ligands containing aminocyclopentane/cyclohexanecarboxylic

Chapter 2

Figure 2-2 Overall structure of catechol oxidase from sweet potato (ipomoea

batatas) Copper atoms are shown in orange, α helices in blue,

xxvii

β sheets in green 50

Figure 2-3 Oxy and met forms of the during the activity of tyrosinase and/or

Figure 2-4 Coordination sphere of the dinuclear copper center in the met state 52

Figure 2-5 Biomimetic oxidation of 3,5-DTBC catalyzed by dicopper(II)

Figure 2-6 Formation of 3,5-DTBQ band after during the oxidation of

3,5-DTBC catalyzed by [Cu2bbpen2](ClO4)2·3MeOH in MeOH

The spectra are recorded every 10 min The inset shows the course

of the absorption maximum at 405 nm with time for 10 and 100

Figure 2-7 Proposed steric match and binding of substrate with complex 54

Figure 2-8 TCBQ complexes, [HL3Cu2(TCC)(H2O)2]2.ClO4 (left) and

[HL4Cu2(TCC)(H2O)]2.ClO4 (right) as models for substrate binding 54

Figure 2-9 Dicopper(II) complexes studied by Mukherjee et al and

Figure 2-10 Possible mechanism of 3,5-DTBC oxidation catalyzed by dinuclear

Figure 2-11 Proposed mechanism for the pH dependent oxidation of 3,5-DTBC

by acetate bridged complex, [Cu2(H2bbppnol)(µOAc)(H2O)2]Cl2.2H2O 57

Figure 2-12 Proposed mechanism for the interaction between dinuclear copper(II)

µ-OH complexes and the 3,5-DTBC Insert: (A) intermediate proposed

by Krebs; (B) intermediate proposed by Solomon 58

Figure 2-13 Schematic representation of dicopper(II) complexes 63

Figure 2-15 A view showing a portion of the 1D hydrogen-bonded structure

Figure 2-16 A perspective view of the unit cell contents of IIA-2a 66

Figure 2-22 A segment of H-bonded 3D network in IIA-4 72

Figure 2-25 Perspective view of the unit cell contents in IIA-8 The lattice

water molecules are omitted for clarity 76

Figure 2-26 Portion of packing diagram of IIA-8 showing the 2D connectivity

The hydrogen atoms and lattice water molecules have been omitted

Figure 2-28 A portion of the 1D structure formed between IIA-9 and methanol

xxviii

Figure 2-33 The temperature dependences of χm and χmT in the range of

2-350 K for IIA-8 The solid lines are fittings using a Cu2

Figure 2-34 Oxidation of 3,5-DTBC by IIA-8 monitored by UV-Vis

spectroscopy Higher concentrations were used only to emphasize

Figure 2-35 (a) Typical plot for Absorption Vs Time during kinetic studies

Curve ‘a’ at the starting concentration of the substrate (1.0x10-3 M) and curve ‘e’ at the final concentration of the substrate

(1.3x10-2 M) (b) Lineweaver-Burk plot for IIA-8 92

Figure 2-37 Hydrogen bonded 2D sheet structure of IIB-1 in ac-plane 116

Figure 2-41 A portion of the 2D structure in IIB-4 121

Figure 2-44 The temperature dependences of χm and χmT in the range of

2-350 K for IIB-1 (a), IIB-3 (b) and IIB-4 (c) The solid lines are

fittings using a Cu2dimer model 129

Figure 2-45 (a)Oxidation of 3,5-DTBC by IIB-4 monitored by UV-Vis

spectroscopy Higher concentrations were used only to emphasize

the bands for the oxidation process (b) Typical plot for Absorption

vs Time during kinetic studies Curve ‘a’ at the starting concentration

of the substrate (1.0x10-3 M) and curve ‘e’ at the final concentration

of the substrate (1.3x10-2 M) (c) Lineweaver-Burk plot for catalysis

by IIB-4 130

Figure 2-49 Simplified diagram showing hexagonal diamondoid connectivity

in IIC-1 (only atoms involved in the connectivity are shown for

Figure 2-50 A segment of 3D network architecture with star-shaped channels

view along [111] IIC-1 (The oxygen atoms of the disordered

lattice water molecules and the hydrogens are omitted for clarity) 157

Figure 2-51 3D coordination polymeric network in IIC-1 displaying star-like

Figure 2-56 SEM image showing microtubular structure in IIA-1 162 Figure 2-57 Single-pot crystallization of IIA-1 furnishing IIC-1 and IIC-2 163

Chapter 3

xxix

Figure 3-2 Perspective view of the repeating unit in III-2 179

Figure 3-3 A segment of 1D polymeric structure propagating along c axis in

Figure 3-4 View of the portion of 2D hydrogen bonded sheets along c axis in

III-2 (The C-H hydrogen bonds are omitted for clarity) 181

Figure 3-6 Portion of 1D polymeric structure propagating along c axis in III-3

Figure 3-9 Perspective view of III-5 showing the connectivity between the

Figure 3-13 Hydrogen bonded 1D polymeric strand in III-6 along a axis 189

Figure 3-14 A portion of 2D sheet structure in III-6 sustained by C-H…S

Figure 3-15 2D hydrogen bonded sheets in III-6 along c axis showing C-H···S

Figure 3-17 (Top) Hydrogen bonded 3D network structure in III-7 viewed

from b axis (Bottom) A segment of hydrogen bonded 3D network

showing the connectivity via hydrogen bonding by –CONH2

Chapter 4

Figure 4-1 Schematic representation of water transport in aquaporin

proteins 211

Figure 4-2 1D helical water chain constructed by alternate water molecules

anchoring the supramolecular Cu(II) complex 212

Figure 4-3 Left handed 1D helical water chain observed by Hong et al 213

Figure 4-4 (Left) Ow–HOw hydrogen bonding in a water helix of ClPHG.(H2O)3

(disordered protons are shown) (Right) along with the spiral assembly of host molecules (green, blue) around the right-handed

Figure 4-6 (Left) Display of helical water chain encapsulated in IV-1,

(Right) Top view of the staircase polymer without helical water

Figure 4-7 (Left) Top view of IV-1 showing water filled helical channel

(Right) Hydrogen bonded helical water chain with space filling

Figure 4-8 Packing of the staircase polymer IV-1 viewed along b axis

showing chiral channel The water molecules in the channels are

Figure 4-10 (Left) Single crystals of IV-1 at RT before heating (Right) Single

crystals of IV-1 after heating to 150 ºC 223

xxx

List of Tables Chapter 2

Table 2-1 Selected bond distances (Å) and bond angles (º) for IIA-1a 65

Table 2-3 Selected bond distances (Å) and bond angles (º) for IIA-2a 67

Table 2-5 Selected bond distances (Å) and bond angles (º) for IIA-3a 69

Table 2-6 Hydrogen bond distances (Å) and angles (º) for IIA-3a 69

Table 2-7 Selected bond distances (Å) and bond angles (º) for IIA-4 71

Table 2-9 Selected bond distances (Å) and bond angles (º) for IIA-6a 74

Table 2-10 Hydrogen bond distances (Å) and angles (º) for IIA-6a 75 Table 2-11 Selected bond distances (Å) and bond angles (º) for IIA-8 77

Table 2-12 Hydrogen bond distances (Å) and angles (º) for IIA-8 77

Table 2-13 Selected bond distances (Å) and bond angles (º) for IIA-9a 78

Table 2-14 Hydrogen bond distances (Å) and angles (º) for IIA-9a 79

Table 2-15 Selected bond distances (Å) and bond angles (º) for IIA-12a 81

Table 2-16 Hydrogen bond distances (Å) and angles (º) for IIA-12a 82

Table 2-34 Kinetic parameters for the activity of IIB-2 - IIB-4 131

Table 2-38 Hydrogen bond lengths (Å) and bond angles (º) in IIC-2 160

Table 2-39 Crystallographic data and structure refinement details 166

Chapter 3

Table 3-2 Hydrogen bond lengths (Å) and bond angles (º) in III-2 181

Table 3-4 Hydrogen bond lengths (Å) and bond angles (º) in III-3 185

xxxi

Table 3-5 Selected bond lengths (Å) and angles (º) for III-5 186

Table 3-6 Hydrogen bond lengths (Å) and bond angles (º) in III-5 188

Table 3-7 Selected bond lengths (Å) and bond angles (º) for III-6 189

Table 3-8 Hydrogen bond lengths (Å) and bond angles (º) in III-6 191

Table 3-11 Selected IR absorption bands (cm-1) in III-1 - III-7 196

Table 3-14 Crystallographic data and structure refinement details 205

Chapter 4

Table 4-2 Hydrogen bond lengths (Å) and bond angles (º) in IV-1 219

Table 4-3 Crystallographic data and structure refinement details 226

xxxii

Publications and Presentations

Angew Chem Intl Ed Engl 2004, 43, 5769-5772

3 Bellam Sreenivasulu, Muthalagu Vetrichelvan, Feng Zao, Song Gao, Jagadese

J Vittal, “Cu(II) complexes of Schiff base and Reduced Schiff base ligands: Influence of weakly coordinating sulfonate group on the structures and

oxidation of 3,5-DTBC” Eur J Inorg Chem 2005, 4635-4645

4 Bellam Sreenivasulu, Feng Zao, Song Gao, Jagadese J Vittal, “Synthesis, Structures and Catecholase Activity of a New Series of Dicopper(II)

Complexes of Reduced Schiff Base Ligands” Eur J Inorg Chem, 2006,

2656-2670

5 Bellam Sreenivasulu, Jagadese J Vittal, “Cu(II) and Ni(II) Complexes of reduced Schiff base Ligands containing Reactive Functional Groups in the Amino Acid side chain” (Manuscript to be submitted)

Conference presentations

1 Bellam Sreenivasulu, Jagadese J Vittal, “Hollow Helical Coordination Polymer as a Model for Molecular Water Tube” International Conference on

Materials for Advanced Technologies (ICMAT-03, 7-12 Dec-2003),

Singapore (Won RSC’s CrystEnggCom Best Poster award)

xxxiii

2 Bellam Sreenivasulu, Muthalagu Vetrichelvan, Jagadese J Vittal, “Cu(II) complexes of Schiff base and reduced Schiff base ligands: Influence of weakly ligating sulfonate group on the structures and catecholase activity.”

International Conference on Biological Inorganic Chemistry (ICBIC-12, 31 st

July – 5 th Aug 2005), University of Michigan, Ann Arbor, Michigan, USA.

3 Bellam Sreenivasulu and Jagadese J Vittal, "A Staircase Coordination Polymer Encapsulating Helical Water Chain: A Model for Aquaporin Water

Channel" First Graduate Congress (21st Sept 2005) Faculty of Science,

NUS, Singapore (Won Best Poster award)

4 Bellam Sreenivasulu and Jagadese J Vittal, “Synthesis, Structures and Catecholase activity of new series of dinuclear Cu(II) complexes of reduced

Schiff base ligands” Singapore International Chemical Conference (SICC-4,

Chapter 1 Introduction

1

1-1 General Introduction

Various transition metals, Fe, Cu, Zn, Mn, Mo, Co, Ni and V etc., in the form of metalloenzymes are known to involve in many essential life processes such as growth and metabolism.1 Copper has been found to be an essential trace element in living systems Metalloenzymes containing copper involve mainly in diverse array of redox activity due to the existence of +1 (Cu(I)) and +2 (Cu(II)) oxidation states that are readily accessible and interconvertible with the typical ligand donors found in protein environments.2 Thus, the active site copper ions perform the functions of electron transfer, reversible O2-binding, mono- or dioxygenation of organic substrates

(oxygenases), oxidation of ortho-diphenols to ortho-diquinones and O2-reduction to either water or hydrogen peroxide (oxidases), or reduction of NOx species such as nitrite to nitrous oxide 3

Another transition metal of considerable interest is nickel which has been shown to sustain certain life forms by catalyzing reactions that are crucial in growth processes.4Various Ni-promoted biological reactions are more complex, and involve redox changes at a Ni site which will act either alone or spin-coupled to other redox active components (e.g Fe-S clusters).5 As a component of Ni-Fe and Ni-Fe-Se in the metalloenzyme hydrogenase, Ni facilitates the transfer of H+ or from H2 Further, the Ni-containing metalloenzyme, methyl-coenzyme M reductase assists in generating cellular energy by helping in the conversion of CO2 to CH4 in methanogenic bacteria Carbon monoxide dehydrogenase (CODH), a Ni-containing Fe-S protein, helps to assemble acetic acid and fix CO2 in acetogenic bacteria.6

2

In view of the variety of bioinorganic functions mediated by metals ions, particularly, Cu- and Ni-containing metalloenzymes, there has been increased emphasis on functional modeling of metalloproteins While such modeling of the metalloprotein active sites is an important and ongoing endeavor, the knowledge of the structures and underlying coordination chemistry of the metals, and their physicochemical characterizations appear highly essential.7

1-2 Coordination preferences of Cu and Ni

Owing to the relatively simple d 9 configuration and formation of a wide variety of compound, and stereochemistry displayed, Cu(II) ion, in its most common oxidation state, is one of the most studied metal ions Further, based on the compounds formed, the magnetic properties associated with mono and polynuclear species are considerably varied from paramagnetic to antiferromagnetic to ferromagnetic behavior.8 Like the other transition metal(II) cations in 3d series, copper(II) tends to

readily form the coordination complexes displaying various geometries such as square planar, square pyramidal and/or trigonal bipyramidal, and octahedral with the coordination number of four, five and six respectively.2 The possible intermediate square pyramidal or trigonal bipyramidal geometry for the five coordinated Cu(II) centers can be judged based on the τ value (τ = β-α/60, where β and α are the two planar angels > 90º) introduced by Reedjik and co-workers.9 The τ value of 0 and 1 stands respectively for the perfect square pyramid and perfect trigonal bipyramid geometry around Cu(II) ion in an ideal situation, which is quite rare.10 The parameter

τ provides a convenient way for comparing structures of similar five coordinated structures.11

3

Ni+2 ions represent the most common oxidation state of nickel An excellent and

discussion of the coordination chemistry of nickel has been presented by Wilkinson et

al.12 and Cotton and Wilkinson.13 Nickel(II) ion is characterized by the formation of nearly regular octahedral and tetrahedral geometries in addition to the square planar geometry.14 In five coordinated geometry, unlike copper(II) showing distortion between square pyramid to trigonal bipyramid, Ni(II) ion forms mainly regular structures.12 As nickel is considered to be at the borderline between hard and soft metals, it can interact with a wide variety of ligands containing both hard and soft donor atoms.5 As with other transition metals like copper(II), the electronic spectra of nickel compounds can provide a wealth of information about the ligand type and geometry.15 Henceforth, the chemistry of the metal complexes of Schiff base and reduced Schiff bases are reviewed

1-3 Copper(II) complexes of Schiff base ligands

Pyridoxal 5’-phosphate (PLP) is one of the most important pyridoxal (Vitamin B6) analogue and the enzymes containing PLP catalyze many reactions such as transamination, decarboxylation, β-elimination and racemization involving the primary amino acids.16 Schiff bases derived from natural amino acids act as intermediates in studying transformations in enzymatic and non-enzymatic reactions with pyridoxal participation.16 Many of these reactions are related to non-enzymatic model reactions in which pyridoxal is the catalyst and a metal ion replaces the apoenzymatic protein.17 Catalytic activities are also observed with derivatives of salicylaldehyde18 and comparative studies have also been made where salicylaldehyde has been replaced by pyruvate and camphor, with the aim of elucidating the mechanism of action of vitamin B6 containing enzymes Schiff base ligands can be

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