Synthesis of DFO derivatives and their application to fingermark detection
Abstract (Summary)1,8-diazafluoren-9-one (DFO) is one of the most common reagents used to enhance latent fingermarks on porous substrates. However, this compound is slower to react than similar reagents, and also does not always react to completion. This thesis investigated methods to address these problems. The reaction of DFO with fingermarks has been widely studied phenomenologically, but there are few studies focusing on the chemistry of the reaction. Since the accepted mechanism for the reaction of DFO with amino acids shows that DFO reacts in a 2: 1 stoichiometry with primary amino acids, linking two DFO moieties into one molecule could provide the following advantages: First, the two DFO moieties are maintained in close proximity thus increasing the chance that both can react with a single amino acid. Second, fluorescence is dependent on the overall flexibility of the molecule, so a bridged DFO dimer could lead to a more rigid product exhibiting greater fluorescence. Finally, a cyclic product should be less susceptible to hydrolysis. The synthetic route taken to synthesise DFO dimers involved five steps. The first step, synthesis of the mono-N-oxide of DFO, proceeded cleanly and in good yields. The second step involved the introduction of a halogen (chlorine and bromine) at the 2-position of the N-oxide. The 2-chloro DFO was prepared cleanly and in good yields from the N-oxide, while the 2-bromo derivative was prepared from the 2-chloro derivative via 2-amino DFO. After protection of the carbonyl functional group (using acetals) the 2-halo DFO intermediates were reacted with selected diols in basic conditions to form bridged dimers. The final step involved deprotection of the acetal to give the carbonyl functional group. Four bridged DFO dimers were synthesised. Crystal structures supporting two of these compounds were obtained, while most of the intermediate compounds in the synthetic route were characterised by NMR and mass spectrometry. Reaction of alanine with the dimer synthesised with a 2,2'-dimethyl-propane-1,3-diol bridge leads to a colour change similar to that seen with DFO. This suggests that the bridged analogues do react with amino acids and can therefore potentially be used as alternatives to DFO. Characterisation of the product with L-alanine was difficult as mass spectrometry indicated that it was polymeric. Attempted reactions at low concentrations of both the dimer and the amino acid did not lead to the formation of the desired cyclic product and in most instances, no reaction occurred. Attempts at metal ion templating also were unsuccessful, possibly since metal ions can catalyse hydrolysis of the product and intermediates during the reaction with amino acids. The products obtained from the reaction of L-alanine with a series of 2-substituted monomeric DFO compounds had similar absorbance and fluorescence spectra to the unsubstituted product, although they showed decreased fluorescence intensity in solution. Studies on porous substrates also indicated that none of the derivatives showed higher fluorescence than DFO upon reaction with fingermarks. However, the halo- derivatives appeared less susceptible to hydrolysis. The imine of DFO is stable in ethanol: acetic acid and reacts about 10 times more rapidly with L-alanine than does DFO at 60 oC and 78 oC, suggesting that the imine might allow development of fingermarks at lower temperature than required for DFO. However, when a fingermark on paper was treated with DFO and DFO imine, the DFO imine treated fingermark did not show significantly more colour or fluorescence than that with DFO treatment.
School Location:New Zealand
Source Type:Master's Thesis
Date of Publication:01/01/2008