Phase-locked stimulated photon echo:Coherent control over Liouville-space pathways

We demonstrate coherent control over interference between different Liouville-space pathways that describe the generation of the nonlinear optical polarization in a stimulated photon echo. This control was exercised by phase-locking of the excitation pulses and observed in the heterodyne detected echo signal. A theoretical analysis of the effect is presented and found to be in good agreement with the obtained results. The relation between this novel time-domain interference effect and the pressure-induced extra resonance in four-wave mixing spectroscopy is discussed.</p

Snapshot of the equilibrium dynamics of a drug bound to HIV-1 reverse transcriptase

The anti-AIDS drug rilpivirine undergoes conformational changes to bind HIV-1 reverse transcriptase and retain potency against drug-resistance mutations. Our discovery that water molecules play an essential role in the drug binding is reported. Femtosecond experiments and theory expose molecular level dynamics of rilpivirine bound to HIV-1 reverse transcriptase. The two nitrile substituents (-CN), one on each arm of the drug, have vibrational spectra consistent with their protein environments being similar in crystals and in solutions. Two-dimensional vibrational-echo spectroscopy reveals a dry environment for one nitrile while unexpectedly the other is hydrogen-bonded to a mobile water molecule, not identified in earlier X-ray structures. Ultrafast nitrile-water dynamics are confirmed by simulations. A higher (1.51 Å) resolution X-ray structure indeed reveals a water-drug interaction network. Maintenance of a crucial anchoring hydrogen bond, despite the enlargement and structural variation of the binding pocket, may help retain the potency of rilpivirine against the pocket mutations