A Coarse-Grained Model for Free and Template-Bound Porphyrin Nanorings

David Ormrod Morley,Dmitry V Kondratuk,Marc Malfois,Nuntaporn Kamonsutthipaijit,Harry L Anderson,Mark Wilson

doi:10.1021/acs.jpca.7b05279

David Ormrod Morley, Dmitry V Kondratuk + Show 4 more

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https://doi.org/10.1021/acs.jpca.7b05279

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Abstract

Coarse-grained simulation models are developed to study both template-bound and free porphyrin nanoring systems. Key interactions are modeled with relatively simple (and physically motivated) energy functions which allow for relatively facile transfer both between different ring sizes and between the template-bound and free nanoring systems. The effects of varying the model parameters on the respective radii of gyration are determined. The effects of including different templates on the ring structure are investigated both in terms of the detailed geometry of the template and the interaction strength between the template and the metal centers in the nanorings. The role of the template-nanoring interaction strength in controlling potential "caterpillar track" rotational motion is discussed. The relationship of the model to experimental small-angle X-ray, exchange spectroscopy, and electron spin resonance results is discussed.

Highlights

The study of the chemistry of porphyrin systems has been an area of intense investigation and rapid progress over the past century
The basic structure of the porphyrin ring as a framework of four pyrroles connected by methene linkages was proposed by Küster[1,2] in 1912 and not long after when the first Nobel Prize in the field was awarded to Fischer in 1930 for the synthesis of hemein, an iron-containing porphyrin
Our aim is to develop a “bottom-up” computational model based on relatively simple potentials which allow the capacity to explore both the structure and dynamics of a wide range of porphyrin systems

Summary

Introduction

The study of the chemistry of porphyrin systems has been an area of intense investigation and rapid progress over the past century. The initial interest in these systems arose as the role of porphyrin rings as building blocks in biological macromolecules (e.g., hemoglobin and chlorophyll) was identified. The basic structure of the porphyrin ring as a framework of four pyrroles connected by methene linkages was proposed by Küster[1,2] in 1912 and not long after when the first Nobel Prize in the field was awarded to Fischer in 1930 for the synthesis of hemein, an iron-containing porphyrin. The focus of this study originates from the resolution of the crystal structure of LH2, a light harvesting complex in photosynthetic bacteria, which was shown to contain ring-like arrays of porphyrin units.[3,4] Synthetic pathways to these cyclic materials utilize a template-directed approach used initially to form a ring containing eight butadiyne linked porphyrin units (termed cP8).[5,6] Following this success, systematic modifications to the templates has led to the synthesis of a wide range of nanorings, with rings in the range c-P5 to c-P50 becoming available.[7−11]

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