Kinetic roughening and energetics of tetragonal lysozyme crystal growth

Lysozyme crystal growth rates over 5 orders of magnitude in range can be described using a layer-by-layer model in which growth occurs by 2D nucleation on the crystal surface. Upon the basis of the 2D nucleation model of layer growth, the effective barrier for growth was determined to be gamma = 1.3 +/- 0.3 x 10(-13) erg/molecule, corresponding to a barrier of 3.2 +/- 0.7 k(B)T, at 22 degreesC. For solution supersaturation, In c/c(eq) greater than or equal to 1.9 +/- 0.2, the nucleation model would not predict or consistently estimate the highest observable crystal growth rates. As such, a kinetic roughening hypothesis in which crystal growth occurs by a continuous mode was implemented for all growth rate data obtained above In c(r)/c(eq) greater than or equal to 2. That is, independent of the solution conditions that vary with buffer pH, temperature, or precipitant concentration, crystal growth occurs by the continuous addition of molecules anywhere on the crystal surface, above a roughening solution supersaturation. The energy barrier, E-c for the continuous growth process is 6.1 +/- 0.4 x 10(-13) erg/molecule or 15 +/- 11 kBT at 22 degreesC).