Study Of R-S/Se…N/O Chalcogen Bond In Organic Molecules Containing Sulfur/Selenium

In recent years,chalcogen bond has been received more and more attentions as a novel intermolecular weak interaction by science researchers.Similar to hydrogen bond and halogen bond,chalcogen bond refers to the net attractive interaction between an electrophilic region associated with a chalcogen atom in a molecular entity and a nucleophilic region in another,or the same,molecular entity.More specifically,it can be named as sulfur bond,selenium bond and tellurium bond.At present,chalcogen bond has been paid more and more attentions in the fields of crystal engineering,anion recognition,pharmaceutical chemistry,catalysis;and even played a critical role in protein folding.In this dissertation,the research of chalcogen bonding properties in crystal assembly and pharmaceutical chemistry are explored by experimental and theoretical methods.First,the X-ray single crystal diffraction reveals that polymorphic ortho-nitrophenyl selenocyanate(o-NSC,crystal 1a and 1b)and monomorphic para-nitrophenyl selenocyante(p-NSC,crystal 2)crystals are all stabilized mainly by the intermolecular and very strong intramolecular C-Se…O/N chalcogen bonds with other different interactions.The thermogravimetric and differential scanning calorimetry thermogram analyses show that the starting decomposed temperature and melting points of three crystals are different,following the order of 1b>1a>2,which is well consistent with the structural characters of crystals.In addition,atoms in molecules(AIM),natural bond orbital(NBO)and reduced density gradient(RDG)analyses indicate that the total strengths of C-Se…O and C-Se…N chalcogen bonds decrease in the order 1b>1a>2.This study could be significant for engineering functional crystals based on the robust C-Se…O and C-Se…N chalcogen bonds,and for designing drugs containing selenium as well as understanding their interaction in biosystems.Second,three organoselenium isomers(o-NSC,m-NSC,p-NSC)and two simple amino acid molecules(Gly,Ala)are selected as study objects,and the geometry optimization,energy calculation,topological analysis of electronic structure,NBO and RDG analyses are carried out using computational chemistry method.The calculations suggest that one type of complex(configuration I)is formed by intramolecular,intermolecular C-Se…O selenium bond and O-H…N hydrogen bond in o-NSC…Gly/Ala interaction system,in which the benzene ring plane of o-NSC and molecular skeleton of Gly/Ala are located in the same plane.While two types of complexes are formed by intermolecular C-Se…O selenium bond and C-H…p-hole contact in m-NSC/p-NSC…Gly/Ala interaction system.Of which one(configuration I)is similar with that o-NSC…Gly/Ala complex,the other(configuration II)is that Gly/Ala molecule stands above the benzene ring plane of m-NSC/p-NSC.The bonding length,AIM and RDG results indicated that m-NSC…Gly/Ala complex is the most stable in the same type of complexes,and the intermolecular C-Se…O selenium bonds in these complexes are the strongest.In addition,AIM analysis shows that the intermolecular C-Se…O selenium bond belongs to the closed-shell interaction,the larger the electron density is,the greater the interaction energy is,and the more stable the complex is.This study could be helpful for understanding the interaction between organoselenium molecules and proteins from a theoretical angle,and also provides certain theoretical basis for the pharmacological mechanism of organoselenium drug molecules.At last,based on the traditional solvent evaporation method,the single crystals of4,7-Dibromo-2,1,3-Benzothidiazole(Br₂S) and 4,7-Dibromo-2,1,3-Benzoselenadiazole(Br₂Se)are self-assembled using N-S/Se…N chalcogen bond,C-Br…Br-C halogen bond and other assistant interactions(i.e.,p-hole bond and hydrogen bond).The relative strength of sulfur bond,selenium bond and halogen bond is analyzed by AIM,NBO and RDG methods.The results indicated that strength of sulfur bond and selenium bond follow the order of N-Se…N>N-S…N in two single crystals,and the strength of N-S/Se…N is greater than that of C-Br…Br-C halogen bond.This study could provide certain throretical basis for the design of novel host molecules to recognize anion selectively based on the competitive or cooperation of sulfur bond,selenium bond and halogen bond.