Infrared Photodissociation Spectroscopic and Theoretical Study of [Co（CO2）n]+ Clusters

The mass-selected infrared photodissociation (IRPD) spectroscopy was utilized to investigate the interactions of cationic cobalt with carbon dioxide molecules. Quantum chemical calculations were performed on the [Co(CO2)n]^+ clusters to identify the structures of the low-lying isomers and to assign the observed spectral features. All the [Co(CO2)n]^+(n=2-6) clusters studied here show resonances near the CO2 asymmetric stretch of free CO2 molecule. Experimental and calculated results indicate that the CO2 molecules are weakly bound to the Co+ cations in an end-on con guration via a charge-quadrupole electrostatic interaction. The present IRPD spectra of [Co(CO2)n]^+ clusters have been compared to those of Ar-tagged species ([Co(CO2)n]^+-Ar), which would provide insights into the tagging effect of rare gas on the weakly-bounded clusters.

Infrared Spectroscopy of CO2 Transformation by Group Ⅲ Metal Monoxide Cations

Infrared photodissociation spectroscopy of mass-selected[MO(CO2)n]^+(M=Sc,Y,La)complexes indicates that the conversion from the solvated structure into carbonate one can be achieved by the ScO^+ cation at n=5 and by the YO^+ cation at n=4,while only the solvated structures are observed for the LaO^+ cation.These findings suggest that both the ScO^+ and YO^+cations are able to fix CO2 into carbonate.Quantum chemical calculations are performed on[MO(CO2)n]^+ to identify the structures of the low-lying isomers and to assign the observed spectral features.Theoretical analyses show that the[YO(CO2)n]^+ complex has the smallest barrier for the conversion from the solvated structure into carbonate one,while[LaO(CO2)n]^+ exhibits the largest conversion barrier among the three metal oxide cations.The present system affords a model in clarifying the effect of different metals in catalytic CO2 transformation at the molecular level.

Ocellatuspyrones A‒G,new antibacterial polypropionates from the Chinese mollusk Placobranchus ocellatus

Marine invertebrates serve as rich sources of secondary metabolites with intriguing chemical diversities and a wide spectrum of biological activities.Particularly,marine shell-less sacoglossan mollusks have attracted much attentions due to the fact that mollusks apply complex metabolites as chemical defense agents against to their predators.With the purpose of discovering bioactive secondary metabolites to develop marine-derived medicines from the South China Sea,we have conducted a chemical study on the photosynthetic mollusk Placobranchus ocellatus.As a result,seven newγ-pyrone polypropionates,namely(±)-ocellatuspyrone A(1),(±)-ocellatuspyrone B(2),and ocellatuspyrones C−G(5,9−12),along with fve known polypropionates,have been isolated and characterized from the South China Sea photosynthetic mollusk Placobranchus ocellatus.Extensive spectroscopic analysis,single crystal X-ray difraction analysis,modifed Mosher’s method,ECD comparison,CD exciton chirality method,TDDFT-ECD calculation,and chemical conversion were used to determine the structures and absolute confgurations of the new compounds and the stereochemistry of undefned known compounds 4,6 and 7.All these isolated polypropionates were evaluated in bioassays for their biological activities,including antibacterial,neuroprotective efect,anti-infammatory,PTP1B inhibitory,and antiviral activities.Compounds 7,8 and 11 were found for the frst time to show antibacterial activity against fsh pathogenic bacteria Streptococcus parauberis(the main pathogen causing fsh streptococcal infections and acute death)with MIC values of 35.8,34.2,and 37.4μg/mL,respectively,which might be potential novel antibacterial agents for the treatment of fsh infectious diseases.