Buffered Coordination Modulation as a Means of Controlling Crystal Morphology and Molecular Diffusion in an Anisotropic Metal-Organic Framework

Significant advances have been made in the synthesis of chemically selective environments within metal-organic frameworks, yet materials development and industrial implementation have been hindered by the inability to predictively control crystallite size and shape. One common strategy to control crystal growth is the inclusion of coordination modulators, which are molecular species designed to compete with the linker for metal coordination during synthesis. However, these modulators can simultaneously alter the pH of the reaction solution, an effect that can also significantly influence crystal morphology. Herein, noncoordinating buffers are used to independently control reaction pH during metal-organic framework synthesis, enabling direct interrogation of the role of the coordinating species on crystal growth. We demonstrate the efficacy of this strategy in the synthesis of low-dispersity single-crystals of the framework Co₂(dobdc) (dobdc^4-= 2,5-dioxido-1,4-benzenedicarboxylate) in a pH 7-buffered solution using cobalt(II) acetate as the metal source. Density functional theory calculations reveal that acetate competitively binds to Co during crystallization, and by using a series of cobalt(II) salts with carboxylate anions of varying coordination strength, it is possible to control crystal growth along the c-direction. Finally, we use zero length column chromatography to show that crystal morphology has a direct impact on guest diffusional path length for the industrially important hydrocarbon m-xylene. Together, these results provide molecular-level insight into the use of modulators in governing crystallite morphology and a powerful strategy for the control of molecular diffusion rates within metal-organic frameworks.

Negative cooperativity upon hydrogen bond-stabilized O2 adsorption in a redox-active metal-organic framework

The design of stable adsorbents capable of selectively capturing dioxygen with a high reversible capacity is a crucial goal in functional materials development. Drawing inspiration from biological O2 carriers, we demonstrate that coupling metal-based electron transfer with secondary coordination sphere effects in the metal-organic framework Co2(OH)2(bbta) (H2bbta = 1H,5H-benzo(1,2-d:4,5-d')bistriazole) leads to strong and reversible adsorption of O2. In particular, moderate-strength hydrogen bonding stabilizes a cobalt(III)-superoxo species formed upon O2 adsorption. Notably, O2-binding in this material weakens as a function of loading, as a result of negative cooperativity arising from electronic effects within the extended framework lattice. This unprecedented behavior extends the tunable properties that can be used to design metal-organic frameworks for adsorption-based applications.

Water Enables Efficient CO2 Capture from Natural Gas Flue Emissions in an Oxidation-Resistant Diamine-Appended Metal-Organic Framework

Supported by increasingly available reserves, natural gas is achieving greater adoption as a cleaner-burning alternative to coal in the power sector. As a result, carbon capture and sequestration from natural gas-fired power plants is an attractive strategy to mitigate global anthropogenic CO₂ emissions. However, the separation of CO₂ from other components in the flue streams of gas-fired power plants is particularly challenging due to the low CO₂ partial pressure (∼40 mbar), which necessitates that candidate separation materials bind CO₂ strongly at low partial pressures (≤4 mbar) to capture ≥90% of the emitted CO₂. High partial pressures of O₂ (120 mbar) and water (80 mbar) in these flue streams have also presented significant barriers to the deployment of new technologies for CO₂ capture from gas-fired power plants. Here, we demonstrate that functionalization of the metal-organic framework Mg₂(dobpdc) (dobpdc^4- = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate) with the cyclic diamine 2-(aminomethyl)piperidine (2-ampd) produces an adsorbent that is capable of ≥90% CO₂ capture from a humid natural gas flue emission stream, as confirmed by breakthrough measurements. This material captures CO₂ by a cooperative mechanism that enables access to a large CO₂ cycling capacity with a small temperature swing (2.4 mmol CO₂/g with ΔT = 100 °C). Significantly, multicomponent adsorption experiments, infrared spectroscopy, magic angle spinning solid-state NMR spectroscopy, and van der Waals-corrected density functional theory studies suggest that water enhances CO₂ capture in 2-ampd-Mg₂(dobpdc) through hydrogen-bonding interactions with the carbamate groups of the ammonium carbamate chains formed upon CO₂ adsorption, thereby increasing the thermodynamic driving force for CO₂ binding. In light of the exceptional thermal and oxidative stability of 2-ampd-Mg₂(dobpdc), its high CO₂ adsorption capacity, and its high CO₂ capture rate from a simulated natural gas flue emission stream, this material is one of the most promising adsorbents to date for this important separation.

Functionalized Porous Aromatic Frameworks as High-Performance Adsorbents for the Rapid Removal of Boric Acid from Water

This study demonstrates that functionalized, highly porous polymers are promising for the adsorptive capture of boric acid, a neutral contaminant that is difficult to remove from seawater using conventional reverse osmosis membranes. Appending N-methyl-d-glucamine (NMDG) to the pore walls of high-surface-area porous aromatic frameworks (PAFs) yields the adsorbents PAF-1-NMDG and P2-NMDG in a simple two-step synthesis. The boron-selective PAFs demonstrate adsorption capacities that are up to 70% higher than those of a commercial boron-selective resin, Amberlite IRA743, and markedly faster adsorption rates, owing to their higher NMDG loadings and greater porosities relative to the resin. Remarkably, PAF-1-NMDG is able to reduce the boron concentration in synthetic seawater from 2.91 to <0.5 ppm in less than 3 min at an adsorbent loading of only 0.3 mg mL^-1 . The boron adsorption rate constants of both frameworks, determined via a pseudo-second-order rate model, represent the highest values reported in the literature-in most cases orders of magnitude higher than those of other boron-selective adsorbents. The frameworks can also be readily regenerated via mild acid/base treatment and maintain constant boron adsorption capacities for at least 10 regeneration cycles. These results highlight the numerous advantages of PAFs over traditional porous polymers in water treatment applications.

Enantioselective Recognition of Ammonium Carbamates in a Chiral Metal-Organic Framework

Chiral metal-organic frameworks have attracted interest for enantioselective separations and catalysis because of their high crystallinity and pores with tunable shapes, sizes, and chemical environments. Chiral frameworks of the type M2(dobpdc) (M = Mg, Mn, Fe, Co, Ni, Zn; dobpdc4- = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate) seem particularly promising for potential applications because of their excellent stability, high internal surface areas, and strongly polarizing open metal coordination sites within the channels, but to date these materials have been isolated only in racemic form. Here, we demonstrate that when appended with the chiral diamine trans-1,2-diaminocyclohexane (dach), Mg2(dobpdc) adsorbs carbon dioxide cooperatively to form ammonium carbamate chains, and the thermodynamics of CO2 capture are strongly influenced by enantioselective interactions within the chiral pores of the framework. We further show that it is possible to access both enantiomers of Mg2(dobpdc) with high enantiopurity (≥90%) via framework synthesis in the presence of varying quantities of d-panthenol, an inexpensive chiral induction agent. Investigation of dach-M2(dobpdc) samples following CO2 adsorption-using single-crystal and powder X-ray diffraction, solid-state nuclear magnetic resonance spectroscopy, and density functional theory calculations-revealed that the ammonium carbamate chains interact extensively with each other and with the chiral M2(dobpdc) pore walls. Subtle differences in the non-covalent interactions accessible in each diastereomeric phase dramatically impact the thermodynamics of CO2 adsorption.

Calcium Coordination Solids for pH-Triggered Release of Olsalazine

Calcium coordination solids were synthesized and evaluated for delivery of olsalazine (H₄ olz), an anti-inflammatory compound used for treatment of ulcerative colitis. The materials include one-dimensional Ca(H₂ olz)⋅4 H₂ O chains, two-dimensional Ca(H₂ olz)⋅2 H₂ O sheets, and a three-dimensional metal-organic framework Ca(H₂ olz)⋅2DMF (DMF=N,N-dimethylformamide). The framework undergoes structural changes in response to solvent, forming a dense Ca(H₂ olz) phase when exposed to aqueous HCl. The compounds Ca(H₂ olz)⋅x H₂ O (x=0, 2, 4) were each pressed into pellets and exposed to simulated gastrointestinal fluids to mimic the passage of a pill from the acidic stomach to the pH-neutral intestines. All three calcium materials exhibited a delayed release of olsalazine relative to Na₂ (H₂ olz), the commercial formulation, illustrating how formulation of a drug within an extended coordination solid can serve to tune its solubility and performance.

A Microporous Amic Acid Polymer for Enhanced Ammonia Capture

Amic acids, consisting of carboxylic acids and amides, are often utilized as intermediates that can further undergo a dehydration-cyclization step to yield polymeric cyclic imides. Compared with imide-based materials, the presence of Brønsted acidic groups and multiple hydrogen-bond donors and acceptors in materials incorporating amic acids opens up the possibility for a variety of host-guest interactions. Here we report a facile and catalyst-free synthesis of a Brønsted acidic porous poly(amic acid) (PAA) and present its NH₃ uptake properties using gas adsorption and breakthrough measurements. Simple addition of water as a cosolvent to a mixture of tetrakis(4-aminophenyl)methane and pyromellitic anhydride resulted in the formation of PAA in almost quantitative yield. Further mechanistic studies with model compounds revealed the importance of additive water to generate amic acid species selectively without forming cyclic imides at high temperatures. Gas adsorption isotherms and breakthrough curves obtained under dry and humid conditions demonstrate the enhanced NH₃ uptake in the case of PAA compared with the related polycyclic imide at both low and high pressures. Furthermore, the results of adsorption/desorption cycling experiments provide insights into the strength of the interaction between ammonia and the polymers.

Highly effective ammonia removal in a series of Brønsted acidic porous polymers: investigation of chemical and structural variations

Efficient removal of ammonia from air is demonstrated in a series of Brønsted acidic porous polymers under dry and humid conditions. The impact of acidic group strength and their spatial distribution on the ammonia uptake is investigated systematically.

Although a widely used and important industrial gas, ammonia (NH₃) is also highly toxic and presents a substantial health and environmental hazard. The development of new materials for the effective capture and removal of ammonia is thus of significant interest. The capture of ammonia at ppm-level concentrations relies on strong interactions between the adsorbent and the gas, as demonstrated in a number of zeolites and metal–organic frameworks with Lewis acidic open metal sites. However, these adsorbents typically exhibit diminished capacity for ammonia in the presence of moisture due to competitive adsorption of water and/or reduced structural stability. In an effort to overcome these challenges, we are investigating the performance of porous polymers functionalized with Brønsted acidic groups, which should possess inherent structural stability and enhanced reactivity towards ammonia in the presence of moisture. Herein, we report the syntheses of six different Brønsted acidic porous polymers exhibiting –NH₃Cl, –CO₂H, –SO₃H, and –PO₃H₂ groups and featuring two different network structures with respect to interpenetration. We further report the low- and high-pressure NH₃ uptake in these materials, as determined under dry and humid conditions using gas adsorption and breakthrough measurements. Under dry conditions, it is possible to achieve NH₃ capacities as high as 2 mmol g^–1 at 0.05 mbar (50 ppm) equilibrium pressure, while breakthrough saturation capacities of greater than 7 mmol g^–1 are attainable under humid conditions. Chemical and structural variations deduced from these measurements also revealed an important interplay between acidic group spatial arrangement and NH₃ uptake, in particular that interpenetration can promote strong adsorption even for weaker Brønsted acidic functionalities. In situ infrared spectroscopy provided further insights into the mechanism of NH₃ adsorption, revealing a proton transfer between ammonia and acidic sites as well as strong hydrogen bonding interactions in the case of the weaker carboxylic acid-functionalized polymer. These findings highlight that an increase of acidity or porosity does not necessarily correspond directly to increased NH₃ capacity and advocate for the development of more fine-tuned design principles for efficient NH₃ capture under a range of concentrations and conditions.

Increasing BCI communication rates with dynamic stopping towards more practical use: an ALS study

OBJECTIVE

The P300 speller is a brain-computer interface (BCI) that can possibly restore communication abilities to individuals with severe neuromuscular disabilities, such as amyotrophic lateral sclerosis (ALS), by exploiting elicited brain signals in electroencephalography (EEG) data. However, accurate spelling with BCIs is slow due to the need to average data over multiple trials to increase the signal-to-noise ratio (SNR) of the elicited brain signals. Probabilistic approaches to dynamically control data collection have shown improved performance in non-disabled populations; however, validation of these approaches in a target BCI user population has not occurred.

APPROACH

We have developed a data-driven algorithm for the P300 speller based on Bayesian inference that improves spelling time by adaptively selecting the number of trials based on the acute SNR of a user's EEG data. We further enhanced the algorithm by incorporating information about the user's language. In this current study, we test and validate the algorithms online in a target BCI user population, by comparing the performance of the dynamic stopping (DS) (or early stopping) algorithms against the current state-of-the-art method, static data collection, where the amount of data collected is fixed prior to online operation.

MAIN RESULTS

Results from online testing of the DS algorithms in participants with ALS demonstrate a significant increase in communication rate as measured in bits/min (100-300%), and theoretical bit rate (100-550%), while maintaining selection accuracy. Participants also overwhelmingly preferred the DS algorithms.

SIGNIFICANCE

We have developed a viable BCI algorithm that has been tested in a target BCI population which has the potential for translation to improve BCI speller performance towards more practical use for communication.

Channel selection methods for the P300 Speller

The P300 Speller brain-computer interface (BCI) allows a user to communicate without muscle activity by reading electrical signals on the scalp via electroencephalogram. Modern BCI systems use multiple electrodes ("channels") to collect data, which has been shown to improve speller accuracy; however, system cost and setup time can increase substantially with the number of channels in use, so it is in the user's interest to use a channel set of modest size. This constraint increases the importance of using an effective channel set, but current systems typically utilize the same channel montage for each user. We examine the effect of active channel selection for individuals on speller performance, using generalized standard feature-selection methods, and present a new channel selection method, termed jumpwise regression, that extends the Stepwise Linear Discriminant Analysis classifier. Simulating the selections of each method on real P300 Speller data, we obtain results demonstrating that active channel selection can improve speller accuracy for most users relative to a standard channel set, with particular benefit for users who experience low performance using the standard set. Of the methods tested, jumpwise regression offers accuracy gains similar to the best-performing feature-selection methods, and is robust enough for online use.

Abbreviated endometriosis-associated infertility correlates with in vitro fertilization success

The utility of in vitro fertilization (IVF) for refractory infertility associated with endometriosis was studied by reviewing the 6-year experience with IVF and pregnancy follow-up at University Hospital, London, Ontario. Two hundred forty cycles were begun in 124 couples in whom endometriosis was the sole identified cause of infertility. In a program employing predominantly ultrasound-guided transvaginal oocyte retrieval, live birth rates were not reduced with advanced degrees of endometriosis. Live births were positively correlated with a shorter infertility duration.

Elevation of serum progesterone with oral micronized progesterone after in vitro fertilization. A randomized, controlled trial

In a randomized, controlled trial, oral micronized progesterone (P4) supplementation effectively elevated luteal phase serum P4 levels after in vitro fertilization (IVF). Of 34 nonconception IVF cycles, 12 were supplemented with oral micronized P4, 200 mg four times daily, beginning the day of oocyte retrieval, while 22 control cycles did not receive supplementation. With oral micronized P4 supplementation the P4 levels were higher (P less than .001) and the luteal phase longer (P less than .05). Oral micronized P4 supplementation appears to be a convenient method of supporting serum P4 levels during the luteal phase after IVF.

MMPI study of identical twins: cancer patients and bone marrow donors

23 identical twin pairs, one with a hematologic malignancy, the other a bone marrow donor, completed the MMPI while in the hospital. The validity, clinical, and Repression-Sensitization scales were scored. Paired t tests for the entire group (aged 16 to 67 yr., M = 44 yr.) showed significant differences on Hs, D, and Hy. Males ( n = 12 pairs) had no significant differences, while females ( n = 11 pairs) had significant differences on Hs, D, Hy, Pa, and R-S. Female patients scored higher on Hs, D, Hy, lower on Pa and were repressors. These findings are congruent with previous research that has yielded psychological differences in people who develop malignancies and those who do not.