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Objective: To investigate the molecular characterization and antimicrobial resistance of CA-MRSA(community-associated methicillin-resistant Staphylococcus aureus) strains isolated from clinical inpatientsto provide evidence for prevention and treatment of CA-MRSA infections. Methods: Isolates of S. aureus from hospitalized patients were collected within 24 h after admission from April 2014 to Dec. 2015, and mecA gene was detected to distinguish MRSA from MSSA (methicillin-sensitive Staphylococcus aureus). Genotypic CA-MRSA strains carrying SCC mec Ⅳ/Ⅴ were obtainedfor further analysis of molecular epidemiologic characters by spa-typing and MLST（multilocus -sequence typing）. Based on the CLSI (Clinical and Laboratory Standards Istitute) guidelines, disk diffusion method was used to test drug susceptibility of CA-MRSA strains. Moreover, the presence of pvl virulence gene was detected by PCR. Results: A total of 147 strains of S. aureus including 58 MRSA strains were collected from hospitalized patients. By SCCmec typing, 9 CA-MRSA strains (SCCmec Ⅳ 3; SCCmec Ⅴ 6) were detected. All CA-MRSA strains developed resistance against different non-β-lactams, among which 8 strains developed drug-resistanceagainst aminoglycosides (mainly kanamycin) and 8 strains developed drug-resistance against erythromycin and clindamycin mediated by erm(B) mainly. Molecular typing revealed that the main CA-MRSA clone was t437-ST59, and other clones were t034-ST804, t127-ST1, t008-ST8 and t437-ST338. In addition, 5 out of 9 CA-MRSA strains were pvl gene positive. Conclusions: More pathogenic CA-MRSA strains are invading healthcare-associated settings and developing more resistance against non-β-lactams, indicating that the CA-MRSA should be closely monitored in hospitals.

The intermolecular complexes formed between imidazol-2-ylidene and its heavy-atom analogues C2H4N2X: (X = C, Si, Ge, Sn, Pb) and YH3F (Y = Si, Ge, Sn, Pb) have been optimized at the MP2/aug-cc-pVTZ level. C2H4N2X: have two electron-rich moieties, one of which is the lone pair on the X atom and the other is the 6π-electron system. Three types of binding modes (type-A, type-B and type-C) can be distinguished for C2H4N2X: according to the locations of YH3F. The type-A and type-B complexes can be located for C2H4N2C:···YH3F system, and the Eint values of the type-A complexes are much larger than those of the type-B complexes. The type-A, type-B and type-C complexes can be located for the other four systems, and the Eint values of these complexes go in the order type-B > type-C > type-A. The binding strength of the type-A complexes becomes weaker, and that of the type-B and type-C complexes becomes stronger with the increase of the X atomic number for C2H4N2X:···YH3F system, which can be clarified by the MEP maps of C2H4N2X:. The NBO, AIM and SAPT analysis was employed to explore the nature of the interactions in these complexes. [ABSTRACT FROM AUTHOR]

The dual binding behavior of the metallylenes TH2 (T = Si, Ge, Sn, Pb) with some selected Lewis acids (T'H3F, T' = Si, Ge, Sn, Pb) and bases (N2, HCN, CO, and C6H6) has been investigated by using the high-level quantum chemical method. Two types (type-A and type-B) of tetrel-bonded complexes can be formed for TH2 due to their ambiphilic character. TH2 act as Lewis bases in type-A complexes, and they act as Lewis acids in type-B ones. CO exhibits two binding modes in the type-B complexes, one of which is TH2···CO and the other is TH2···OC. The TH2···OC complexes possess a weaker binding strength than the other type-B complexes. The TH2···OC complexes are referred to as the type-B2 complexes, and the other type-B complexes are referred to as the type-B1 complexes. The type-A complexes exhibit a relatively weak binding strength with Eint (interaction energy) values ranging from –7.11 to –15.55 kJ/mol, and the type-B complexes have a broad range of Eint values ranging from −9.45 to −98.44 kJ/mol. The Eint values of the type-A and type-B1 complexes go in the order SiH2 > GeH2 > SnH2 > PbH2. The AIM (atoms in molecules) analysis suggests that the tetrel bonds in type-A complexes are purely closed-shell interactions, and those in most type-B1 complexes have a partially covalent character. The EDA (Energy decomposition analysis) results indicate that the contribution values of the three energy terms go in the order electrostatic > dispersion > induction for the type-A and type-B2 complexes, and this order is electrostatic > induction > dispersion for the type-B1 complexes. [ABSTRACT FROM AUTHOR]

Methods: The intermolecular interactions between the heavy-atom analogues of acetylene T2H2 (T = Si, Ge, Sn, Pb) and HCN have been investigated by theoretical calculations at the CCSD(T)/aug-cc-pVTZ//MP2/aug-cc-pVDZ level. Results: The global energy minimum of T2H2 is the butterfly structure A, and another energy minimum is the planar structure B. Both structures A and B exhibit the dual behavior when binding with HCN. The various hydrogen bond (HB), dihydrogen bond (DB) and tetrel bond (TB) complexes can be found according to the MEP maps of T2H2. One TB and three HB complexes formed between structure A and HCN can be located for Si2H2 and Ge2H2. One TB, two HB and one DB complexes formed between structure A and HCN can be located for Sn2H2 and Pb2H2. Four TB and one HB complexes formed between structure B and HCN can be located for all the T2H2. The geometries and binding strengths of the complexes are compared and analyzed. Conclusions: The interactions in these complexes are generally weak, and the interaction energies of these complexes range from −0.53 to −8.23 kcal/mol. The interaction energies of the TB complexes are larger than those of the corresponding HB and DB complexes for structure A···HCN systems. The relative binding strength of the four TB complexes exhibits different order for different structure B···HCN systems, which is consistent with the MEP maps of the isolated monomers. [ABSTRACT FROM AUTHOR]