ISSN:
1572-8927
Keywords:
DNA binding
;
intercalation
;
enthalpy and entropy changes
;
calorimetric
;
small molecules
;
substituted naphthalene monoimides
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Abstract Calorimetric studies have been performed on the intercalation of a series of nitro and amino substituted naphthalene monoimide cations to calf thymus DNA. For comparison, we also included in the study the unsubstituted naphthalene diimide dication. All of the substituted naphthalene monoimides formed dimers at the concentrations used in the calorimetric titrations, and dimerization constants for these compounds were derived from spectroscopic studies and used in calculating the ΔH B o parameters from the calorimetric data. The dimerization constants increase in the order 3-NO2MI=4-NO2MI〉3-NH2MI〉4-NH2MI. For the unsubstituted naphthalene monoimide and 3-NO2MI and 4-NO2MI, the ΔH B o parameters are within experimental error equal to that found for the naphthalene diimide, i.e., −4.3 kcal-mol−1. Thus, changes in entropy cause the K B for the diimide to be 40 times larger than that for the monoimide. This observation is consistent with the current electrostatic theory for counterion binding to DNA: a dication should cause the release of more counterions than a monocation and produce a more positive ΔS B o . For the amino substituted naphthalene monoimides, the K B values are similar to the other monoimides, but ΔH B o =−6.7 kcal-mol−1. We propose that a hydrogen bond is responsible for the unusual enthalpy and entropy effects seen for 3-NH2MI and 4-NH2MI.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00645811
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