WILLIAM HENRY BRAGG (1862-1942) WILLIAM LAWRENCE BRAGG (1890-1971)

1912 – England

X-rays scattered from a crystal will show constructive interference provided their wavelength ( λ ) fits the equation

2d sin θ = n λ 

where d is the spacing between atoms of the crystal, θ the angle through which the rays have scattered and n is any whole number

This is the cornerstone of the science of X-ray crystallography.

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Symmetrically spaced atoms cause re-radiated X...

Symmetrically spaced atoms cause re-radiated X-rays to reinforce each other in the specific directions where their path-length difference, 2d sin θ, equals an integer multiple of the wavelength λ (Photo credit: Wikipedia)

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DOROTHY CROWFOOT HODGKIN (1910- 94)

1934 – England

Photograph of Dorothy Mary Hodgkin OM, FRS (12 May 1910 – 29 July 1994), née Crowfoot,  a British chemist, credited with the development of protein crystallography. Dorothy Crowfoot was born in Cairo on May 12th, 1910 where her father, John Winter Crowfoot was working in the Egyptian Education Service. ©

DOROTHY CROWFOOT HODGKIN

‘X-ray diffraction’

X-ray crystallography. X-rays are unique in that their wavelength is about the length of bonds within molecules. When X-rays hit a crystallized molecule, the electrons surrounding each atom cause the beam to bend. Because there are many atoms the result is that when the X-rays exit the crystal and fall onto a photographic plate, they produce a series of light and dark patches. Measuring the intensity and relative position of each patch indicates the relative positions of atoms within the crystal.

photo of Dorothy Hodgkin ©

With her co-worker John Desmond Bernal (1901-1971) Hodgkin produced the first diffraction patterns for proteins.

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NEXT button - X-RAY CRYSTALLOGRAPHYX-RAY CRYSTALLOGRAPHY

ROSALIND FRANKLIN (1920- 58)

1952 – London, England

‘Description of the basic helical structure of the DNA molecule’

dna_overview

DNA overview

Photograph of young ROSALIND FRANKLIN &copy:

ROSALIND FRANKLIN

Her work is used, unaccredited, in Watson & Crick’s Nobel Prize-winning paper, from information ‘secretly’ leaked from Maurice Hugh Frederick Wilkins.

Through her work on X-ray diffraction, she realised that the ‘backbone’ of the DNA molecule was on the outside.

By 1952, Franklin had taken the clearest pictures of the molecules to date, which provided evidence of a helical, or spiral structure.
Watson & Crick would eventually articulate a ‘double-helix’ construction.

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