The handed world: 150 years of chiral molecules

19 March 2020 10:45-17:00, London, United Kingdom


Introduction

[Official registration and booking will open around the end of 2019, but expressions of interest in attending will be welcome using the Contact Information below and processed once official registration is open.]

Overview and who should attend


The meeting will review optical activity and molecular chirality from a historical perspective – beginning in the nineteenth century and ending with techniques that are used today in the latest facilities such as the Diamond Light Source, with special reference to the biological and pharmaceutical importance of chirality.  Not only those interested in history of chemistry as such but those wishing to improve their knowledge in these areas will find the meeting of value.
 

Topics covered

 
In the early nineteenth century, the rotation of polarised light was observed in in solids such as quartz, but later in liquids such as turpentine and aqueous solutions of salts of tartaric acid.   
 
From Dalton early in the century to Cannizzaro in 1860, chemists had developed a picture of molecules comprising known atoms in known numbers bound closely together.
 
These two strands of early nineteenth-century study came together in a brilliant way from Pasteur in 1860 to van’t Hoff and Le Bel in 1874.  Molecules came to be pictured in 3-dimensional space with specific geometrical arrangement of the atoms.  In particular, it was realised that when a carbon atom was bonded to four other atoms or groups, the carbon atom lay at the centre of a tetrahedron and the atoms or groups to which it was bonded lay at the corners.  Such an arrangement meant that, if the four other atoms or groups differed from each other, the molecule would exist in two non-superimposable mirror-image (“enantiomeric”) forms and that each form would rotate the plane of polarised light equally and in opposite directions.  Later, Lord Kelvin coined the word “chiral” for such “handed” molecules.
 
To arrive at such a detailed picture primarily by induction from macroscopic evidence was a great intellectual achievement, and in the twentieth century the validity of the picture was confirmed by direct investigation at the atomic level, especially by X-ray diffraction.  In due course, X-ray diffraction allowed even the determination of absolute configuration, ie which mirror image (“R” or “S”) corresponded to the dextrarotatory (“d”) enantiomer and which corresponded to the laevorotatory (“l”) enantiomer    
 
In 1895, Aimé Cotton published his discovery that chiral compounds with strong absorption of light such as transition metal tartrates displayed “optical rotatory dispersion” and “circular dichroism”.  His technique as a means of studying molecular structure has been developed greatly since the 1960s, with improved instrumentation and the availability of powerful ultraviolet light from the Diamond Light Source.  The technique can now be used, for instance, in the study of proteins in their natural biological rather than crystalline state.
 
Chirality is important because it matters to life;  molecules arising from a particular biological process are often, though not always, in just one of two chiral forms.  In Lewis Carroll’s Through the looking glass and what Alice found there, Alice speculates that “Perhaps looking-glass milk is not good to drink” – and she may be right at least in relation to the sugar lactose in the milk.  And nowadays pharmaceutical products, usually sufficiently complex molecules to exist in chiral forms, may be administered in just one form in case the other form is bad for the patient.  This has stimulated much development of chiral synthesis and of separation of enantiomers.
Speakers
Venue
The Royal Society of Chemistry

Library, The Royal Society of Chemistry, Burlington House, Piccadilly, London, W1J 0BA, United Kingdom

Committee
Organised by
RSC Historical Group
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