Biomedical Engineering Reference
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Figure 2. Induction period value of dynamic curves of MR adsorption at air/water interface as function
of MR concentration. Temperature 25
О
С; storage time of MR solution before measurement 2 and 24
hours.
Dehydroresorcinols, as is known, may exist in three tautomeric forms in water solution
(di-enol, keto-enol and keto) [Durairaj, 2005]. This compound is also known as cyclic beta-
diketone and has been shown to exist to 95% in the keto-enol (or mono-enol) form in aqueous
solution. The pK
a
value for dehydroresorcinol is about 4.8 and, therefore it is considered an
acid and almost as strong as acetic acid. The hydroxyl groups of phenolic derivatives are
more acidic than that of aliphatic alcohols, and hence they can form stronger hydrogen bonds
as donors with suitable bonding acceptors (as in our case at pH 7.4). In certain cases, at acidic
pH values, the oxygen atom of hydroxyl group of phenol can also behave as an effective
hydrogen-bond acceptor. Generally, O − H∙∙∙O hydrogen-bonding interactions between
hydroxyl groups are strong and highly directional. It is reasonable to expect that the presence
of two O−H groups in MR would impart in intrinsic molecular and supramolecular
dimensions to MR. Apart of O − H∙∙∙O interactions, a few other intermolecular interactions
such as C−H∙∙∙O, O−H∙∙∙ˀ and O−H∙∙∙N are also important. However these interactions are
weak in nature compared to conventional hydrogen bonds [Sarmat, Baruah, 2007]. Owing to
hydrogen bonding dihydroresorcinols are able to self-assembly in aqueous solutions.
Obviously the contact times 2 hours are too short to permit the attainment of a steady state.
We choose the storage time of 24 hours for further experiments.
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