| dc.description.abstract | Molecular modelling techniques such as PPP-MO, ZINDO and CNDO/S have been
applied to derive colour-structure relationships in a series of donor-acceptor
nitroaromatic chromogens based on diazines. Selected 2,4-disubstituted amino-5
nitropyrimidine derivatives have been synthesised and their colouristic properties
correlated with molecular modelling results. Attempts were made to synthesise the
more bathochromic predicted compounds in the pyrimidine and pyrazine series. During
the course of this investigation, IH-15N heteronuc1ear shift correlation spectra using
gHMQC and gHMBC with x-ray crystallography were used for the characterisation of
certain compounds exhibiting tautomerism.
Molecular modelling techniques have also been used to understand the chemical and
physical behaviour of colorants towards uptake by the hair fibre to assist development
of the concept of pro-pigmentation. This new technology is based on a water soluble
pigment precursor, which is converted chemically back in situ to the parent pigment
when applied to the hair fibre. A molecular modelling method has been devised and
implemented to take into account the shape and size of the molecules as a measure of
their diffusivity into the hair. Some pro-pigments which met the requirements were
selected for synthesis. Although the chemistry proved feasible with indigo, with other
pigments it was less straightforward.
A significant breakthrough was the discovery of pro-disperse dyeing. This technology
is based on the same concept as the pro-pigmentation, but using disperse dyes. The first
pro-disperse red dye was obtained. It was proved that in vitro and "in vivo" the disperse
dye was regenerated and can impart a bright red colour to the hair which withstood
more than ten shampoos. | |
