Polarization switching of crystal structure in the nonphotochemical laser-induced nucleation of supersaturated aqueous L-histidine

Polarization switching of polymorphs has been observed in the nonphotochemical laser-induced nucleation of aqueous L-histidine in the supersaturation range 1.40-1.60. Exposure of solutions to 0.24 GW/cm(2), 7 ns pulses of 532 nm light induced the nucleation of different polymorphs of L-histidine depending on polarization state of the light. Circularly polarized laser pulses tended to nucleate the orthorhombic A polymorph, whereas linearly polarized pulses tended to nucleate a mixture of the orthorhombic A and monoclinic B polymorphs. Higher supersaturation also favors the formation of mixed polymorphs. These observations support the hypothesis that the laser is organizing hydrogen-bonded groups of histidine molecules through an optical Kerr alignment.