Unravelling surface and interfacial structures of a metal–organic framework by transmission electron microscopy

Metal-organic frameworks (MOFs) are crystalline porous materials with designable topology, porosity and functionality, having promising applications in gas storage and separation, ion conduction and catalysis. It is challenging to observe MOFs with transmission electron microscopy (TEM) due to the extreme instability of MOFs upon electron beam irradiation. Here, we use a direct-detection electron-counting camera to acquire TEM images of the MOF ZIF-8 with an ultralow dose of 4.1 electrons per square ångström to retain the structural integrity. The obtained image involves structural information transferred up to 2.1 Å, allowing the resolution of individual atomic columns of Zn and organic linkers in the framework. Furthermore, TEM reveals important local structural features of ZIF-8 crystals that cannot be identified by diffraction techniques, including armchair-type surface terminations and coherent interfaces between assembled crystals. These observations allow us to understand how ZIF-8 crystals self-assemble and the subsequent influence of interfacial cavities on mass transport of guest molecules

Influence of glycemic control on the levels of subgingival periodontal pathogens in patients with generalized chronic periodontitis and type 2 diabetes

Abstract Objective This study evaluated the influence of glycemic control on the levels and frequency of subgingival periodontal pathogens in patients with type 2 diabetes mellitus (DM) and generalized chronic periodontitis (ChP). Material and Methods Fifty-six patients with generalized ChP and type 2 DM were assigned according to the levels of glycated hemoglobin (HbA1c) into one of the following groups: HbA1c<8% (n=28) or HbA1c&#8805;8% (n=28). Three subgingival biofilm samples from sites with probing depth (PD)<5 mm and three samples from sites with PD&#8805;5 mm were analyzed by quantitative Polymerase Chain Reaction (PCR) for the presence and levels of Porphyromonas gingivalis, Tannerella forsythia, Treponema denticola, Eubacterium nodatum, Parvimona micra, Fusobacterium nucleatum ssp. and Prevotella intermedia. Results The mean counts of F. nucleatum ssp. were statistically significantly higher in the sites with PD&#8805;5 mm of the HbA1c&#8805;8% group (p<0.05). Frequencies of detection of T. forsythia, E. nodatum, P. micra and F. nucleatum ssp. were all higher in the sites with PD&#8805;5 mm of the patients with HbA1c&#8805;8%, compared with those of patients with HbA1c<8% (p<0.05). Frequency of detection of P. intermedia was higher in the sites with PD<5 mm of the patients with HbA1c&#8805;8% than those of the patients with HbA1c<8% (p<0.05). Conclusions Poor glycemic control, as indicated by HbA1c&#8805;8%, is associated with increased levels and frequencies of periodontal pathogens in the subgingival biofilm of subjects with type 2 DM and ChP