Semi-empirical conformational energy calculations were performed for the mononucleotides 59-AMP, NMN+ and 39-AMP. Only intramolecular forces are considered. Essentially all conformational states were explored to investigate the population distribution likely to be found in a non-crystalline environment. The calculations suggest that 59-AMP and 39-AMP are relatively flexible and a mixture of conformational states is expected. In contrast, the results for NMN+ suggest that a strong electrostatic interaction between the positively charged nicotinamide nitrogen atom and negatively charged phosphate oxygen is possible, stabilizing a few specific states. This interaction will be most significant in a solvent-free situation or an apolar environment.
