Probing Structural Defects in MOFs Using Water Stability

Defects in the crystal structures of metal-organic frameworks (MOFs), whether present intrinsically or introduced via so-called defect engineering, can play strong roles in the properties of MOFs for various applications. Unfortunately, direct experimental detection and characterization of defects in MOFs are very challenging. We show that in many cases, the differences between experimentally observed and computationally predicted water stabilities of MOFs can be used to deduce information on the presence of point defects in real materials. Most computational studies of MOFs consider these materials to be defect-free, and in many cases, the resulting structures are predicted to be hydrophobic. Systematic experimental studies, however, have shown that many MOFs are hydrophilic. We show that the existence of chemically plausible point defects can often account for this discrepancy and use this observation in combination with detailed molecular simulations to assess the impact of local defects and flexibility in a variety of MOFs for which defects had not been considered previously.

Structural and Adsorption Properties of ZIF-8-7 Hybrid Materials Synthesized by Acid Gas-Assisted and De Novo Routes

The tuning of micropore environments in zeolitic imidazolate frameworks (ZIFs) by mixed-linker synthesis has the potential for enabling new molecular separation properties. However, de novo synthesis of mixed-linker (hybrid) ZIFs is often challenging due to the disparate chemical properties of the different linkers. Here, we elucidate the structure and properties of an unconventional ZIF-8-7 hybrid material synthesized via a controlled-acid-gas-assisted degradation and reconstruction (solvent-assisted crystal redemption, SACRed) strategy. Selective insertion of benzimidazole (ZIF-7 linker) into ZIF-8 using SACRed is used as a facile method to generate a ZIF-8-7 hybrid material that is otherwise difficult to synthesize by de novo methods. Detailed crystal structure and textural characterizations clarify the significant differences in the microstructure of the SACRed-derived ZIF-8-7 hybrid material relative to a de novo synthesized hybrid of the same overall linker composition as well as the parent ZIF-8 material. Unary and binary adsorption measurements reveal the tunability of adsorption characteristics as well as the prevalence of nonideal cooperative mixture adsorption effects that lead to large deviations from predictions made with ideal adsorbed solution theory.

Hierarchical ZIF-8 Materials via Acid Gas-Induced Defect Sites: Synthesis, Characterization, and Functional Properties

Microporous metal-organic frameworks (MOFs) have been widely studied for molecular separation and catalysis. The uniform micropores of MOFs (<2 nm) can introduce diffusion limitations and render the interiors of the crystal inaccessible to target molecules. The introduction of hierarchical porosity (interconnected micro and mesopores) can enhance intra-crystalline diffusion while maintaining the separation/catalytic selectivity. Conventional hierarchical MOF synthesis involves complex strategies such as elongated linkers, soft templating, and sacrificial templates. Here, we demonstrate a more general approach using our controlled acid gas-enabled degradation and reconstruction (Solvent-Assisted Crystal Redemption) strategy. Selective linker labilization of ZIF-8 is shown to generate a hierarchical pore structure with mesoporous cages (∼50 nm) while maintaining microporosity. Detailed structural and spectroscopic characterization of the controlled degradation, linker insertion, and subsequent linker thermolysis is presented to show the clustering of acid gas-induced defects and the generation of mesopores. These findings indicate the generality of controlled degradation and reconstruction as a means for linker insertion in a wider variety of MOFs and creating hierarchical porosity. Enhanced molecular diffusion and catalytic activity in the hierarchical ZIF-8 are demonstrated by the adsorption kinetics of 1-butanol and a Knoevenagel condensation reaction.

How Reproducible are Surface Areas Calculated from the BET Equation?

Porosity and surface area analysis play a prominent role in modern materials science. At the heart of this sits the Brunauer-Emmett-Teller (BET) theory, which has been a remarkably successful contribution to the field of materials science. The BET method was developed in the 1930s for open surfaces but is now the most widely used metric for the estimation of surface areas of micro- and mesoporous materials. Despite its widespread use, the calculation of BET surface areas causes a spread in reported areas, resulting in reproducibility problems in both academia and industry. To prove this, for this analysis, 18 already-measured raw adsorption isotherms were provided to sixty-one labs, who were asked to calculate the corresponding BET areas. This round-robin exercise resulted in a wide range of values. Here, the reproducibility of BET area determination from identical isotherms is demonstrated to be a largely ignored issue, raising critical concerns over the reliability of reported BET areas. To solve this major issue, a new computational approach to accurately and systematically determine the BET area of nanoporous materials is developed. The software, called "BET surface identification" (BETSI), expands on the well-known Rouquerol criteria and makes an unambiguous BET area assignment possible.

Transport of microorganisms into cellulose nanofiber mats

Electrospun cellulose nanofiber mat “sponges” are a green platform technology that has the potential to remove detrimental microorganisms from wounds, trap bacteria within a protective military textile, or remediate contaminated water.

Multidrug-resistant Acinetobacter baumannii: an emerging pathogen among older adults in community hospitals and nursing homes

BACKGROUND

Drug-resistant Acinetobacter species are problematic in tertiary-care hospitals. We describe the epidemiology, resistance patterns, and outcomes of older adults with Acinetobacter infection in community hospitals.

METHODS

We queried the microbiology databases of the Oakwood Healthcare System (4 hospitals with 632, 259, 199, and 168 beds) for clinical Acinetobacter cultures obtained in 2003-2008. Patients aged 60 years who were admitted from home or nursing homes were included. We recorded the initial Acinetobacter isolate and susceptibility to 8 antibiotics. Cultures obtained 48 h after hospitalization were categorized as "nosocomial." Administrative databases provided patients' origins (home or nursing home) and discharge destinations (home, nursing home, long-term acute-care facility, another hospital, or hospice care or death).

RESULTS

During the 6-year period, 560 community-dwelling (mean age +/- standard deviation, 74 +/- 8.6 years) and 280 nursing home-dwelling (78 +/- 9.1 years) patients had Acinetobacter isolated. During this period, Acinetobacter prevalence increased 25% (P<.001, by trend test). In comparison of 2003 with 2008, Acinetobacter resistance to imipenem and ampicillin/sulbactam increased (from 1.8% to 33.1%; P<.001), as did "panresistance" (ie, resistance to all 8 antibiotics; increase from 0.0% to 13.6%; P<.001). Although resistance was stable in community-acquired isolates (resistance to approximately 4.2 antibiotics), resistance increased among nursing home-acquired and nosocomial-acquired isolates (from 4.5 to 5.7 and from 5.0 to 6.0 antibiotics, respectively; P<.01). At discharge, only 25% of community-dwelling and 50% of nursing home-dwelling patients returned to their place of origin; the remainder required higher levels of care or died. After adjustment for age, length of stay, and origin, resistance to each additional antibiotic predicted a >20% increased risk for discharge to higher levels of care or death (odds ratio, 1.23; 95% confidence interval, 1.11-1.36).

CONCLUSIONS

The prevalence and resistance of Acinetobacter species are increasing in the community. Patients with resistant isolates are selectively discharged to nursing homes and long-term acute-care facilities, introducing resistance to new facilities.

Effect of chronic treatment of ethanol on benzodiazepine and picrotoxin sites on the GABA receptor complex in regions of the brain of the rat

Ethanol has been shown to enhance gamma-aminobutyric acid (GABA)ergic transmission. In this study an examination was made of the effect of chronic treatment with ethanol and its withdrawal at 24 h on the binding of [3H]flunitrazepam and [35S]t-butylbicyclophosphorothionate (TBPS) to brain regions in rat. Rats were rendered tolerant to, and dependent on, ethanol by an intragastric intubation method. The affinity (KD) or the binding capacity (Bmax) of [3H]flunitrazepam or [35S]TBPS was not altered by chronic treatment with ethanol or during withdrawal from ethanol. Neither the enhancing effect of GABA on the binding of [3H]flunitrazepam nor its inhibitory effect on the binding of [35S]TBPS were affected by chronic treatment with ethanol or its withdrawal at 24 h. These results suggest that the sensitivity of benzodiazepine and picrotoxin sites on the oligomeric GABA receptor complex is not affected during tolerance to, or withdrawal from ethanol. It is suggested that the effects of ethanol on GABAergic transmission may be produced at the level of coupled chloride ion channels.

The effect of in vitro and in vivo ethanol administration on [35S]t-butylbicyclophosphorothionate binding in C57 mice

Previous studies have shown that ethanol may produce some of its effects by facilitation of GABAergic transmission. One of the potential sites of drug action at the GABA receptor complex is the picrotoxin site, which can be studied with [35S]t-butylbicyclophosphorothionate (TBPS). Ethanol inhibited the binding of [35S]TBPS to C57 mice brain regions in vitro. This inhibition appears to be noncompetitive since ethanol decreased the Bmax and not the KD value of [35S]TBPS. C57 mice were chronically treated with ethanol in liquid diet to determine if the sensitivity of TBPS binding is altered following chronic treatment or during withdrawal. Chronic treatment with ethanol and during withdrawal did not alter the KD or Bmax values of [35S]TBPS binding in C57 mice brain regions. It is suggested that the sensitivity of picrotoxin site on the oligomeric GABA receptor complex is not altered during ethanol tolerance or withdrawal. The effects of ethanol on GABA system may be mediated by its interaction with the coupling mechanism(s) or a direct effect on the chloride channels.

GABA and benzodiazepine binding sites in spontaneously hypertensive rat

The binding of GABA to its central receptor sites and of benzodiazepines to central and peripheral types of binding sites was compared in age-matched spontaneously hypertensive rat (SHR) and normotensive (WKY) rat. The KD and Bmax values of GABA agonist binding were not significantly different between SHR and WKY rat in the forebrain, cerebellum or pons-medulla. The binding of [3H]flunitrazepam to central types of binding sites was also not different in 12 week-old SHR and WKY rat. However, the binding of [3H]flunitrazepam and [3H]RO5-4864 was significantly lower in the SHR kidney, as compared to WKY rat kidney. This decrease was due to a lower Bmax in SHR kidney. In contrast, the binding of these radioligands in the hearts of the two strains was not different. These results indicate that the SHR has lower peripheral benzodiazepine binding sites in the kidney as compared to age-matched normotensive WKY rat kidney.

Enhancement of diazepam and gamma-aminobutyric acid binding by (+)etomidate and pentobarbital

(+)Etomidate and pentobarbital enhance [3H]diazepam and [3H]gamma-aminobutyric acid [( 3H]GABA) binding to cerebral cortex membranes. Both (+)etomidate and pentobarbital increase the affinity of [3H]diazepam for its binding sites. In contrast, they increase the Bmax of both the high- and low-affinity GABA receptor sites. The enhancement of [3H]diazepam and [3H]GABA by (+)etomidate and pentobarbital is blocked by GABA antagonists. These results indicate that hypnotic drugs such as (+)etomidate and pentobarbital, which are not structurally related, modulate diazepam and GABA binding sites via similar mechanisms.

Group-selective reagent modification of the benzodiazepine-gamma-aminobutyric acid receptor-ionophore complex reveals that low-affinity gamma-aminobutyric acid receptors stimulate benzodiazepine binding

The modification of membrane proteins with diethylpyrocarbonate (DEP) and diazotized sulfanilate was investigated on the binding of three benzodiazepine radioligands in three brain regions. Both of these reagents produced a dose-dependent inactivation of [3H] diazepam, [3H]flunitrazepam, and [3H]propyl beta-carboline-3-carboxylate binding to cortex, cerebellum, and hippocampus. Both DEP and diazotized sulfanilate decrease the Bmax of the benzodiazepine binding sites without altering the KD. The ability of muscimol and pentobarbital to enhance [3H]diazepam binding was not altered by DEP pretreatment in any of the three regions. Scatchard analysis indicated that, following the inactivation of 40-50% of [3H]diazepam binding by 1 mM DEP, pentobarbital and muscimol were still able to increase the affinity of [3H]diazepam binding in cortex, cerebellum, and hippocampus. In contrast, diazotized sulfanilate pretreatment abolishes the ability of muscimol and pentobarbital to enhance [3H]diazepam binding in these three regions. The effects of these reagents on [3H] gamma-aminobutyric acid (GABA) binding revealed that sulfanilate but not DEP eliminates the low-affinity GABA receptor sites in cortex and cerebellum. Thus, while both DEP and sulfanilate inactivate benzodiazepine binding sites, only sulfanilate abolishes the low-affinity GABA binding sites and the ability of the GABA agonists to enhance [3H]diazepam binding. These results suggest that the stimulation of benzodiazepine binding appears to be mediated by the low-affinity GABA receptors.