Ritort F, Bustamante C, Tinoco I
Department of Physics, University of Barcelona, Diagonal 647, 08028 Barcelona, Spain.
Proc Natl Acad Sci U S A. 2002 Oct 15;99(21):13544-8. doi: 10.1073/pnas.172525099. Epub 2002 Oct 8.
We investigate the work dissipated during the irreversible unfolding of single molecules by mechanical force, using the simplest model necessary to represent experimental data. The model consists of two levels (folded and unfolded states) separated by an intermediate barrier. We compute the probability distribution for the dissipated work and give analytical expressions for the average and variance of the distribution. To first order, the amount of dissipated work is directly proportional to the rate of application of force (the loading rate) and to the relaxation time of the molecule. The model yields estimates for parameters that characterize the unfolding kinetics under force in agreement with those obtained in recent experimental results. We obtain a general equation for the minimum number of repeated experiments needed to obtain an equilibrium free energy, to within k(B)T, from nonequilibrium experiments by using the Jarzynski formula. The number of irreversible experiments grows exponentially with the ratio of the average dissipated work, W(dis) to k(B)T.
我们使用表示实验数据所需的最简单模型，研究了单分子在机械力作用下不可逆展开过程中耗散的功。该模型由两个能级（折叠态和展开态）组成，中间有一个势垒。我们计算了耗散功的概率分布，并给出了该分布的平均值和方差的解析表达式。一阶近似下，耗散功的大小与力的施加速率（加载速率）和分子的弛豫时间成正比。该模型对表征力作用下展开动力学的参数给出的估计值，与最近实验结果中获得的估计值一致。我们通过使用雅津斯基公式，得到了一个通用方程，用于计算从非平衡实验中获得平衡自由能（精确到(k_BT)）所需的最少重复实验次数。不可逆实验的次数随着平均耗散功(W_{dis})与(k_BT)的比值呈指数增长。
