Atomic Scale Investigation Of Xanthine-copper Complex On Cu(111)

As one of the major global challenges,cancer and genetic diseases are seriously endangering human life and health.Previous studies have shown that metal elements can open the hydrogen bond between guanine and cytosine,or selectively cut off the DNA sequence,so as to inhibit its replication and synthesis,so that cancer cells can not divide and play an anti-cancer role.Among them,copper has been proved to play a significant role in the invasion and migration of cancer and has potential anti-cancer applications.DNA tetrads based on guanine tetrad structure exist in cell telomeres,which play an important role in chromosome stability,telomere length maintenance,gene modulation and so on.Xanthine,as a typical purine molecule,is one of the precursors of original nucleic acids.It not only exists in human tissues and body fluids,but also participates in various important physiological functions of human body.It has been proved that it can form stable tetrad instead of guanine to form a new artificial tetrad.In view of the important biochemical functions of copper and xanthine,it is of great significance to understand the interaction between them.Based on this,the formation,structural properties of xanthine-copper complex on the surface of Cu(111)and the influence of different preparation conditions on the composite were studied by using STM and DFT.The formation of xanthine-copper complex on the surface of Cu(111)was studied by changing the substrate temperature,annealing temperature and molecular coverage.The results show that the molecular deposition temperature and post annealing tempera ture can effectively change the structure of Cu(111)surface and the chirality of the obtained structure.The geometry and energy of different structures of xanthine-copper complex formed on the surface of Cu(111)were analyzed by density functional theo ry.The theoretical results show that the dimer structure is the basic unit of different surface complexes.There are five different dimer structures on the surface,and all of them are composed of the same chiral xanthine molecules.When the substrate temperature is 255 K,all the surface dense structures are composed of left-handed dimers.When the substrate temperature is 298 K,all the surface dense stru ctures are composed of right-handed dimers and left-handed dimers.The dimers are connected by three different double hydrogen bonds(N3-H···O2;N9-H···O6;N1-H···O6).The N7 position of the xanthine molecule in the dimers can interact with the free copper atoms on the surface of the substrate to form a complex structure which is further stable.It is proved by theoretical calculation that different preparation conditions can not only produce different complex structures,but also control the chirality of the structural phase: the low substrate temperature is more likely to form a single chiral close packed structure,that is,the structural phase is composed of the same chiral xanthine dimer;when the substrate temperature is increased,irregular and regular network structures can be generated,and the network contains different hands Xanthine dimer of sex.All structural phases are formed by intermolecular hydrogen bonds and molecular copper coordination bonds.