ABSTRACT
Molecular transport is an important aspect in metal-organic frameworks (MOFs) as it affects many of their applications, such as adsorption/separation, drug delivery and catalysis. Yet probing the fundamental diffusion mechanisms in MOFs is challenging, and the interplay between the MOF's features (such as the pore structure and linker dynamics) and molecular transport remains mostly unexplored. Here, the pulsed-field gradient nuclear magnetic resonance (PFG NMR) technique is used to probe the diffusion of several probe molecules, i.e., water, xylenes and 1,3,5-triisopropylbenzene (TIPB), within the UiO-66 MOF and its derivatives (UiO-66NH2 and UiO-66Br). Exploiting differences in the size of probe molecules we were able to probe the diffusion rate selectively in the different pore environments of the MOFs. In particular, when relatively small molecules, such as water and small hydrocarbons, were used as probes, the PFG NMR log attenuation plots were non-linear with two distinctive diffusion regions, suggesting faster diffusion in the inter-crystalline space and slower diffusion within crystal aggregates, the latter occurring mostly inside the framework of the MOFs. Conversely, experiments with a larger probe molecule, i.e., TIPB, with a kinetic diameter of 0.95 nm, which makes it unable to access the framework windows of the MOF crystals, showed linear PFG NMR log attenuation plots, which indicates diffusion occurring in a single environment, most likely in the inter-crystalline space. Analysis of the apparent tortuosity values of the systems under investigation highlights the role of linker functionalisation in influencing the molecular diffusion of the probe molecules, which affects both intra-molecular interactions and pore accessibility within the MOF crystals. The findings of this work demonstrate that the diffusion behaviour of probe molecules within MOFs is influenced by the pore size, structure, functionalisation of the MOF linker and molecular interactions. Our study contributes to further advance the understanding of mass transport in MOFs by PFG NMR and provides insights that can inform the design and optimisation of MOF-based materials for various applications.
ABSTRACT
BACKGROUND: Early detection for tuberculosis (TB) and rifampicin-resistant TB (RRTB) is crucial for proper control of this disease. WHO recommended the use of the GeneXpert assay at district level to cover these two public health demands? A study evaluated the diagnostic impact of the GeneXpert assay in detecting TB and RRTB. Odd results were observed in this study in the form of discordance between the GeneXpert assay and the conventional culture and drug-susceptibility testing (DST). AIM OF THE STUDY: To assess the molecular diagnostic validity of the GeneXpert assay when results do not match phenotypic results given by DST. METHODS: Pulmonary TB patients with recently detected sputum positive for acid-fast bacilli (AFB) were recruited from random geographical clusters (18 out of 36 primary healthcare districts in the middle five governorates in Iraq) during a 1-year period (November 2013-October 2014). Sputum samples from all enrolled patients were sent for GeneXpert assay testing, culture, and DST. Genotype mycobacterium (GM) from Hain Lifescience (Nehren, Germany) was used to detect non-tuberculosis mycobacteria (NTM) whenever suspected. Those with discordant results regarding the status of RRTB between GeneXpert assay and DST were retested with the line probe assay (LPA). Simple frequency distribution was used to describe study results. RESULTS: Four-hundred ten patients were enrolled, all of whom were culture positive. Only two patients were found negative for TB on GeneXpert assay who were then diagnosed as NTM by LPA (GM). Out of the 408 patients, discordance between GeneXpert and DST regarding the status of rifampicin susceptibility was observed in 17 cases (4%). Nine patients were RR on GeneXpert but rifampicin susceptible (RS) on DST. LPA agreed with GeneXpert assay for all nine cases. Eight patients were RS on GeneXpert but RR on DST. Here, LPA disagreed with GeneXpert assay only in one patient who was found to be RR by LPA. CONCLUSION: GeneXpert assay is a valid molecular test for TB and RRTB regardless of its discordance with conventional culture and DST.
ABSTRACT
OBJECTIVE/BACKGROUND: Nontuberculosis mycobacteria (NTM), defined as any mycobacterial strain other than Mycobacterium tuberculosis complex, are a diverse group of pathogens that cause a substantive, but often unappreciated worldwide burden of illness. NTM cause illness similar to M. tuberculosis, but generally do not respond to classic tuberculosis (TB) drug regimens. Here, we evaluated GenoType Mycobacterium CM/AS (Hain Lifesciences) for rapid identification of NTM and compared its results with those of other biochemical tests. METHODS: During the study interval from February 2015 to August 2015, samples were tested by GenoType Mycobacterium tuberculosis complex (MTBC) for differentiation of MTB complex, and NTM isolates obtained from patients were analyzed with the GenoType Mycobacterium CM assays for common mycobacteria. RESULTS: All samples tested were M. tuberculosis (typical), except samples from sputum that was negative according to Geno Type MTBC results. All isolates were analyzed with the Geno Type Mycobacterium CM (for common mycobacteria) assays, which correctly identified the species as Mycobacterium chelonae, Mycobacterium intracellulare, Mycobacterium kansasii, and Mycobacterium simiae. CONCLUSION: GenoType testing of Mycobacteria species using GenoType MTBC and GenoType Mycobacterium CM constitutes a reliable, rapid, simple, and easy-to-interpret assay. Moreover, it appears suitable for use in our region, since it identified all mycobacterial species.
