Using scanning tunnelling microscopy (STM), we demonstrate that Au-pyridyl coordination can be used to assemble two-dimensional coordination network structures on metal surfaces. The polymorphism of the coordination network structures can be manipulated at both the micro- and nanoscale. Using the same organic ligand, we assembled two distinct polymorphic network structures, which were assisted by threefold Au-pyridyl coordination on Ag(111) with predeposited Au atoms (α-network), and by twofold Au-pyridyl coordination on Au(111) (β-network), respectively. Specifically on the Au(111) surface, single-oriented β-network domains as large as ≈400 nm were selected by thermal annealing. We ascribe this global control strategy to distinct Au bonding modes tuned by molecule-substrate interactions. Using an STM tip, we succeeded in creating α-network domains (≈10 nm) locally within the homogeneous β-network domain areas on Au(111) in a controlled manner.

A self-assembled Fe-porphyrin coordination chain structure on a Au(111) surface is investigated by scanning tunneling microscopy (STM), revealing structural reconstruction resulting from an alternative change of molecular orientations and spontaneous formation of uniformly sized Fe polynuclears. The alternation of the molecular orientations is ascribed to the cooperation of the attractive coordination and the intermolecular steric repulsion as elucidated by high-resolution STM observations. Furthermore, chemical control experiments are carried out to determine the number of atoms in an Fe polynuclear, suggesting a tentative Fe dinuclear-module that serves not only as a coordination center to link porphyrin units together but also as a "dangling" site for further functionalization by a guest terpyridine ligand. The chain structure and the Fe polynuclears are stable up to 320 K as revealed by real-time STM scanning. Annealing at higher temperatures converts the chain structure into a two-dimensional coordination structure.

Fine-tuning of 2D metal–organic nanostructures is realized by alkali–pyridyl coordination.

Porcine reproductive and respiratory syndrome virus (PRRSV) has had a devastating impact on the pig industry in China, and monitoring its genetic diversity is important for epidemiological surveillance and understanding its evolution. Here, we determine the complete genome sequences of two PRRSV strains, GXYL1403 and GXNN1839. Comparative, phylogenetic, and recombination detection program analyses show that the two isolates are recombinant strains with large-fragment amino acid deletions in nsp2. GXYL1403 possesses a unique deletion region of 124 amino acids in nsp2, and GXNN1839 contains a deletion of 131 amino acids in nsp2 as compared with VR2332. Further analysis of the full-length sequence suggests that GXYL1403 is a natural recombinant between sublineages 8.1 (CH-1a like) and 8.3 (JXA1-like). The recombination site of GXYL1403 is located in nsp9–nsp12 (8961nt−11181nt). GXNN1839 is a natural recombinant between the lineage 5 (VR-2332-like) and lineage 1 (NADC30-like) strains. The recombination events occurred in nsp9 (7872nt-8162nt) and in ORF2 (12587nt−13282nt) in the genome of GXNN1839. These results provide new evidence that PRRSV strains circulating in the environment have undergone recombination among the different lineages or sublineages of field strains, and these add to our understanding of RNA combination events that occur in PRRSV.

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