Developing New Assembly Systems And New Characterization Method:Face-rotating Molecular Polyhedra And Micro-fluidic NMR Technology

Supramolecular chemistry is defined as "chemistry beyond the molecule",its main focus is molecular assemblies through non-covalent interactions or dynamic covalent bond.Those interactions are also essential in biological molecular assemblies such as DNA or protein,which exhibit sophisticated structures and functionalities.To give deep understanding of interactions,mimic structures and increase out undertstnad of life,chemists use supramolecular chemistry to study the nature of those interactions,the physicochemical properties of the assembly process and the mechanism of assembling process.There are two fundamental questions in molecular assembly:how to construct complex assembly systems and how to characterize them.This dissertation contributes from two aspects:new molecular assembly strategy and new characterization method.In the first section of this dissertation,molecular face-rotating polyhedra were assembled using truxene derivatives as facial building blocks.The C3 symmetric truxene(facial building blocks)and C2 vertex linkers(vertexes building blocks)were assembled into[4+6]polyhedra using dynamic covalent bond.Three sp3 carbons in truxene skeleton exhibit certain directionality,forming either clockwise(C)or anti-clockwise(A)patterns.Truxene derivatives thus possess 2D chirality but no 3D chirality in solution due to free rotation.Because rotational pattern of each face of polyhedra can be either C or A,there are five possible dia stereoisomers for[4+6]octahedra:AAAA,CAAA,CCAA,CCCA and CCCC.Assembly of achrial vertexes ethylenediamine with truxene derivatives give only CCCC and AAAA conformation,confirmed by nuclear magnetic resonance(NMR)spectra,chiral separation,single crystal structure and circular dichroism spectra.Interestingly,the CCCC or AAAA exhibit the highest molar ellipticity ever reported.Assembly of chiral vertexes,e.g.(R,R)-cyclohexanediamine,with truxene derivatives at high temperature give only AAAA,whereas reactions at room temperature give kinetic products.Both experiments and calculations results showed that van der Waals forces among alkyl groups of different faces are key to diastereoisomer selectivity.When racemic diamine and truxene were assembled into polyhedra,the reaction underwent narcissistic chiral self-sorting process and gave only homo-chiral,homo-directional molecular polyhedra.Assembly of D3h symmetric facial building blocks with racemic diamine exhibit no selectivity and gave products of mixture of homo-chiral and hetero-chiral polyhedra.The second section of this dissertation is developing high resolution micro-fluidic NMR techniques for in-situ characterization of complex assembly system.The micro-fluidic chips including channels and NMR sample chamber were cut from thin polymethylmethacrylate(PDMS)board by CO2 laser cutter,the total thickness of micro-fluidic chips were less than 1 mm.Microstripline were used as radio frequency coil and soldered to the circuits of commercial NMR probes.This device can take high resolution NMR spectra from 2 μL sample volume.