Intermolecular vibrations of naphthalene trimer by ionization-detected stimulated Raman spectroscopy

Dynamic self-assembled meso-structures formed across a wide concentration range in aqueous solutions of propranolol hydrochloride

HYPOTHESIS

Nanoscale characterisation of the self-associated species formed by amphiphilic pharmaceuticals in aqueous solution carries relevance across their entire journey from development through to manufacture - relevant, therefore, not only as regards formulation of the drug products as medicines, but also potentially relevant to their bioavailability, activity, and clinical side effects. Such knowledge and understanding, however, can only be fully secured by applying a range of experimental and theoretical methodologies.

EXPERIMENTS

Herein, we apply a synergistic combination of solubility, surface tension, SANS, NMR and UV spectroscopic studies, together with MD simulation and QM calculations, to investigate the meso-structures of propranolol hydrochloride aggregates in bulk aqueous solutions, at concentrations spanning 2.5 mM to > 200 mM. In addition, we explore the effects of adding NaCl to mimic the ionic strength of physiological fluids, and the differences between racemate and single enantiomer.

FINDINGS

There is a continuum of particle sizes shown to exist across the entire concentration range, with molecules joining and leaving on the nanosecond timescale, and with the distributions of aggregate sizes varying with drug and salt concentration. Given that propranolol is a highly prescribed (WHO essential) medicine, disfavouring aggregators from consideration in high-throughput screening for potential new drug candidates - as many have advocated - should thus be done cautiously.

The structures of liquid pyridine and naphthalene: the effects of heteroatoms and core size on aromatic interactions

Spatial and orientational structures of liquid naphthalene and pyridine revealed using neutron scattering combined with empirical potential structure refinement.

Vibrational spectroscopy and dynamics in the CH-stretch region of fluorene by IVR-assisted, ionization-gain stimulated Raman spectroscopy

We report stimulated Raman spectra at 0.2 and 0.03 cm(-1) resolution in the CH-stretching region of jet-cooled fluorene. The results were obtained by a version of ionization-gain stimulated Raman spectroscopy in which resonant two-photon ionization probing of the state-population changes arising from stimulated Raman transitions is assisted by the process of intramolecular vibrational redistribution (IVR) in the Raman-excited molecule. The fluorene spectra reveal extensive vibrational coupling interactions involving both the aliphatic and aromatic CH-stretching first excited states with nearby background states. Results pertaining to the symmetric aliphatic CH-stretching fundamental are consistent with a tier model of IVR and point to vibrational energy flow out of the CH stretch on a approximately 1 ps time scale with subsequent redistribution on a approximately 5 ps time scale.

Structure of the Naphthalene Dimer from Rare Gas Tagging

Excitation spectra of naphthalene dimer-argonn (n = 1-3) clusters are obtained by resonance enhanced multiphoton ionization time-of-flight mass spectroscopy. The spectra are generally independent of the number of attached argon atoms and reveal sharp structures which are fitted by superimposing independent monomer spectra. It is concluded that the rare-gas tagging technique reveals the presence of a T-shaped naphthalene dimer chromophore in the molecular beam.

The World of Non-Covalent Interactions: 2006

The review focusses on the fundamental importance of non-covalent interactions in nature by illustrating specific examples from chemistry, physics and the biosciences. Laser spectroscopic methods and both ab initio and molecular modelling procedures used for the study of non-covalent interactions in molecular clusters are briefly outlined. The role of structure and geometry, stabilization energy, potential and free energy surfaces for molecular clusters is extensively discussed in the light of the most advanced ab initio computational results for the CCSD(T) method, extrapolated to the CBS limit. The most important types of non-covalent complexes are classified and several small and medium size non-covalent systems, including H-bonded and improper H-bonded complexes, nucleic acid base pairs, and peptides and proteins are discussed with some detail. Finally, we evaluate the interpretation of experimental results in comparison with state of the art theoretical models: this is illustrated for phenol...Ar, the benzene dimer and nucleic acid base pairs. A review with 270 references.

High-level ab initio computations of structures and interaction energies of naphthalene dimers: Origin of attraction and its directionality

The intermolecular interaction energies of naphthalene dimers have been calculated by using an aromatic intermolecular interaction model (a model chemistry for the evaluation of intermolecular interactions between aromatic molecules). The CCSD(T) (coupled cluster calculations with single and double substitutions with noniterative triple excitations) interaction energy at the basis set limit has been estimated from the second-order Møller-Plesset perturbation interaction energy near saturation and the CCSD(T) correction term obtained using a medium-size basis set. The estimated interaction energies of the set of geometries explored in this work show that two structures emerge as being the lowest energy, and may effectively be considered as isoenergetic on the basis of the errors inherent in out extrapolation procedure. These structures are the slipped-parallel (Ci) structure (-5.73 kcal/mol) and the cross (D2d) structure (-5.28 kcal/mol). The T-shaped (C2v) and sandwich (D2h) dimers are substantially less stable (-4.34 and -3.78 kcal/mol, respectively). The dispersion interaction is found to be the major source of attraction in the naphthalene dimer. The electrostatic interaction is substantially smaller than the dispersion interaction. The large dispersion interaction is the cause of the large binding energies of the cross and slipped-parallel dimers.