CHIRAL EXPRESSION AT THE NANOSCALE, ORIGIN AND RECOGNITION OF CHIRALITY By Anna Ewa Walkiewicz A thesis submitted to The University of Birmingham For the degree of DOCTOR OF PHILOSOPHY School of Chemistry The University of Birmingham June 2010 University of Birmingham Research Archive e-theses repository This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder. Declaration The work presented in this thesis is the original work of the author and contains no material which is result of collaboration except where otherwise stated. This dissertation is not substantially the same as any other submitted by the author for a degree or diploma or any other qualification at any other university, and no part of this work has already been or is being concurrently submitted for any such degree, diploma or other qualification. Anna E Walkiewicz June 2010 Acknowledgments Firstly, I must say words of 'thank you' to my supervisor- Professor Trevor Rayment, who gave me a lot of support and encouragement throughout my study. Also I would like to express my appreciation to the CHEXTAN- Marie Curie RTN for giving me an opportunity to work on a very interesting subject and for the financial support. Secondly I'd like to thank Dr Yitzhak Mastai from Bar Illan University for great scientific discussions, support and for NSOM measurements. The collaborators from Chextan RTN cannot go without a mention. I'd like to say thank you to the group of Professor Alan Rowan, especially to Michal Juricek and Jan 'Johny' Lauko for their amazing support in the organic synthesis. Also I would like to express my gratitude to Dr Sarah Horswell for help in PM-IRRAS measurements. Finally I would like to thank my colleagues from the Rayment group for their help and amazing support, especially to Joshua 'Reggie' Hammons for his help with programming and Richard Wiltshire for being my 'third hand' in the lab. Also I need to thank the University of Birmingham Tango Society for lifting my life a few levels up. Abstract Chirality, familiar to all chemists, is usually applied to molecules or assemblies of molecules and plays an important role in both animate and inanimate systems. It is commonly the case that chirality of a system arises from a chiral building block yet chiral systems can also emerge from achiral units. The objective of this research was to investigate the origin and recognition of chirality at the nanoscale level. To do this, self assembled monolayers made of chirally and achirally tailed molecules were used because such structures are known to form uniform surfaces, which can act as either a source of nucleation or the probing surfaces in chiral recognition. The strategy adopted in the first part of this study was to use chirally modified self assembled monolayers as a source of nucleation for crystallization of achiral compounds that can form either left or right tended forms in chiral crystallization. Such compounds, widely reviewed by Matsura, form chiral crystals even though their building blocks lack a chiral centre. This study presents experiments of induction of chirality in sodium chlorate, hippuric acid and 2,6-ditertbutyl-4-methylphenol crystals. Chiral crystallization of chosen compounds was conducted on D and L cysteine surfaces assembled on gold. The chirality of crystals grown on these surfaces was determined using polarised light microscopy, circular dichroism spectroscopy and NSOM. The small enantiomeric excess achieved in experiments was explained by the limits of chirality determination methods. It was found that crystals formed in enantiomeric excess were of opposite chirality to the SAM they were grown on. This confirms previous results presented by Mastai on crystallization of histidine on cysteine surfaces. The second part of this study presents studies of chiral recognition use of AFM technique- Force Distance Spectroscopy. Chirally and achirally modified SAMs were formed via the Cu-AAC reaction commonly called 'click chemistry'. This project investigated how the surface preparation influences chiral recognition and if the presence of the second chiral centre affects probing ability. For surface preparation, three types of linkers were used. To functionalize them two complementary compounds equipped with AlaAlaDL and AlaAlaLL dipeptide tail were used. Additional studies were carried out with hippuric acid and glutamic acid-modified SAMs. These studies showed that the way the surface is prepared plays an important role in chiral recognition. In the final recognition experiments it was found that use of molecules possessing either peptide groups or amino acid groups generates additional forces between interacting surfaces, which can be equilibrated by conducting measurements in pH close to their isoelectric point. An influence of the second chiral centre was found for the loosely packed surfaces where the molecules can freely coil. Table of Contents Table of contents List of Abbreviations ........................................................................................................................... i 1 Introduction ................................................................................................................................ 1 1.1 Project 1- chiral crystallization on surfaces-studies on origin of chirality ............................ 1 1.2 Project 2-chiral recognition at the Nanoscale ........................................................................ 2 1.3 Reference List ........................................................................................................................ 2 2 Chirality- from a molecule to a system ................................................................................. 3 2.1 Definition of chirality ............................................................................................................ 3 2.2 Formation of chiral systems .................................................................................................. 5 2.3 Chiral crystallization ............................................................................................................. 8 2.4 Chiral crystals vs achiral crystals .......................................................................................... 9 2.4.1 Generation of chirality in chiral crystals made of achiral molecules .............................. 11 2.5 Reference List ...................................................................................................................... 14 3 Preparation and characterization of chiral Self Assembled Monolayers ................... 17 3.1 Self assembly ....................................................................................................................... 17 3.2 Self assembled monolayers ................................................................................................. 17 3.2.1 Structure of self assembled monolayers .......................................................................... 20 3.2.2 Reactions, reactivity and applications of SAMs ............................................................. 27 3.3 Reference List ...................................................................................................................... 37 4 Experimental methods ............................................................................................................ 47 4.1 Preparation of substrates for gold deposition ...................................................................... 47 4.1.1 Mica ................................................................................................................................ 47 4.1.2 Glass ................................................................................................................................ 47 4.1.3 Silicon ............................................................................................................................. 48 4.2 Evaporation of gold on mica/glass/silicon ........................................................................... 48 4.3 Preparation of thiol solutions for self assembly .................................................................. 50 4.4 Preparation of SAMs ........................................................................................................... 50 4.5 Characterization methods .................................................................................................... 51 4.5.1 Ellipsometry .................................................................................................................... 51 4.5.2 Contact angle goniometry ............................................................................................... 57 4.5.3 PM-IRRAS ...................................................................................................................... 61 4.5.4 Electrochemical techniques ............................................................................................. 66 4.6 Methods for determination of crystals chirality ..................................................................