Spence J C H, Schmidt K, Wu J S, Hembree G, Weierstall U, Doak B, Fromme P
Department of Physics and Astronomy, Arizona State University, Tempe, AZ 85287-1504, USA.
Acta Crystallogr A. 2005 Mar;61(Pt 2):237-45. doi: 10.1107/S0108767305002710. Epub 2005 Feb 22.
The effect of the limited alignment of hydrated molecules is considered in a laser-aligned molecular beam, on diffraction patterns taken from the beam. Simulated patterns for a protein beam are inverted using the Fienup-Gerchberg-Saxton phasing algorithm, and the effect of limited alignment on the resolution of the resulting potential maps is studied. For a typical protein molecule (lysozyme) with anisotropic polarizability, it is found that up to 1 kW of continuous-wave near-infrared laser power (depending on dielectric constant), together with cooling to liquid-nitrogen temperatures, may be needed to produce sufficiently accurate alignment for direct observation of the secondary structure of proteins in the reconstructed potential or charge-density map. For a typical virus (TMV), a 50 W continuous-wave laser is adequate for subnanometre resolution at room temperature. The dependence of resolution on laser power, temperature, molecular size, shape and dielectric constant is analyzed.
研究了在激光对准的分子束中，水合分子有限排列对从该分子束获取的衍射图样的影响。使用菲纽普 - 格奇伯格 - 萨克斯顿相位算法对蛋白质束的模拟图样进行反演，并研究有限排列对所得势图分辨率的影响。对于具有各向异性极化率的典型蛋白质分子（溶菌酶），发现可能需要高达1千瓦的连续波近红外激光功率（取决于介电常数），并冷却至液氮温度，才能产生足够精确的排列，以便在重建的势图或电荷密度图中直接观察蛋白质的二级结构。对于典型病毒（烟草花叶病毒），50瓦连续波激光在室温下足以实现亚纳米分辨率。分析了分辨率对激光功率、温度、分子大小、形状和介电常数的依赖性。
