ORIGIN OF ANOMALOUS 13-C IR ENHANCEMENT IN ANTI-PARALLEL BETA-SHEET AGGREGATES

该子项目是利用NIH/NCRR资助的中心赠款提供的资源的许多研究子项目之一。子项目和研究者（PI）可能从另一个NIH来源获得主要资金，因此可以在其他CRISP条目中表示。所列机构为中心，不一定是研究者所在机构。实验上，我们观察到反平行b折叠聚集，（Trp-Leu-Leu-Leu-*Leu-Leu）n，n=10-40，在13-C-峰中显示非常强的增强。目的是从酰胺单元在一定程度上相互偶联的角度来理解这种异常增强。这是我们的模型的基础。酰胺单元相互作用的知识是必不可少的，以获得线性IR和二维IR的结构-光谱关系以及。我们正在研究一个过渡电荷-电荷相互作用模型，其中一个过渡电荷实体被指定为每个酰胺单元。这个模型使我们能够基于蛋白质数据库中可用的原子坐标计算几乎所有中等大小二级基序的红外光谱。初步结果表明，负责观察到的13-C-峰增强的主导因素是链间和链内最近邻酰胺单元的相互作用，这是共价键或氢键。增强是依赖于聚集的长度和13-C-标记的位置，这是可以预测的。我们还细化最近邻单元的耦合强度，通过使用从头算正常模型计算，考虑到通过空间和通过键的贡献。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Experimentally we have observed that the anti-parallel b-sheet aggregates e.g., (Trp-Leu-Leu-Leu-*Leu-Leu)n, n=10-40, show very strong enhancement in 13-C-peak. The objective is to understand this anomalous enhancement from the point of view of that the amide units are coupled to each other to certain extend. It is on which our model is based. The knowledge of amide unit interactions is essential in order to obtain structure-spectrum relationship in linear IR and 2D-IR as well. We are working on a transition charge-charge interaction model, in which a transition charge entity is designated for each amide unit. This model allows us to calculate the IR spectrum of almost all the mid-sized secondary motifs based on atomic coordinates that are available at Protein Data Bank. Preliminary results showed that the dominant factors responsible for the observed 13-C-peak enhancement are the inter-chain and intra-chain nearest neighbor amide unit interactions, which are covalently bonded or hydrogen bonded. The enhancement is dependent on the length of aggregation and on the 13-C-labeling positions, which can be predicted. We are also refining the coupling strengths of the nearest neighbor units, by using the ab initio normal model calculations that take into account of both the through-space and through-bond contributions.