Improving the gas sorption capacity in lantern-type metal-organic polyhedra by a scrambled cage method

The synthesis of multivariate metal-organic frameworks (MOFs) is a well-known method for increasing the complexity of porous frameworks. In these materials, the structural differences of the ligands used in the synthesis are sufficiently subtle that they can each occupy the same site in the framework. However, multivariate or ligand scrambling approaches are rarely used in the synthesis of porous metal-organic polyhedra (MOPs) - the molecular equivalent of MOFs - despite the potential to retain a unique intrinsic pore from the individual cage while varying the extrinsic porosity of the material. Herein we directly synthesise scrambled cages across two families of lantern-type MOPs and find contrasting effects on their gas sorption properties. In one family, the scrambling approach sees a gradual increase in the BET surface area with the maximum and minimum uptakes associated with the two pure homoleptic cages. In the other, the scrambled materials display improved surface areas with respect to both of the original, homoleptic cages. Through analysis of the gas sorption isotherms, we attribute this effect to the balance of micro- and mesoporosity within the materials, which varies as a result of the scrambling approach. The gas uptake of the materials presented here underscores the tunability of cages that springs from their combination of intrinsic, extrinsic, micro- and meso-porosities.

Porous Metal-Organic Cages Based on Rigid Bicyclo[2.2.2]oct-7-ene Type Ligands: Synthesis, Structure, and Gas Uptake Properties

Three new ligands containing a bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxydiimide unit have been used to assemble lantern-type metal-organic cages with the general formula [Cu4 L4 ]. Functionalisation of the backbone of the ligands leads to distinct crystal packing motifs between the three cages, as observed with single-crystal X-ray diffraction. The three cages vary in their gas sorption behaviour, and the capacity of the materials for CO2 is found to depend on the activation conditions: softer activation conditions lead to superior uptake, and one of the cages displays the highest BET surface area found for lantern-type cages so far.

Non-invasive monitoring of the growth of metal-organic frameworks (MOFs) via Raman spectroscopy

The applicability of Raman spectroscopy for phase discrimination of metal-organic frameworks (MOFs) has been demonstrated with F4_MIL-140A(Ce) and F4_UiO-66(Ce); analogues prepared from the same metal and ligand sources. Each analogue exhibits unique Raman peaks, with significant differences in the low frequency region, which is more sensitive to structural variations. Non-invasive Raman monitoring of F4_MIL-140A(Ce) synthesis indicated evolution of a unique MOF Raman peak with reaction progress; conversion of this Raman signal to extent of crystallisation was in good agreement with reported reaction kinetics determined via a synchrotron diffraction method. Additionally, Raman spectroscopy indicated initial rapid consumption of the nitric acid modulator present in the reaction coinciding with an expected high probability of nucleation. Raman spectroscopy is a promising technique for rapid screening of MOFs and can be used to study the mechanism of their formation in situ with kinetic insight into both the solution and solid phases of the reaction medium.

The Role of Cations in Resorcinol–Formaldehyde Gel Textural Characteristics

The production of resorcinol–formaldehyde xerogels has yielded insight into the gelation processes underpinning their structures. In this work, the role of the cation species from the catalyst is probed by studying the simultaneous addition of sodium carbonate and calcium carbonate to a resorcinol–formaldehyde mixture. Twenty-eight xerogels were prepared by varying the solids content, catalyst concentration, and catalyst composition, and each was analysed for its textural properties, including the surface area and average pore diameter. The results indicate that the role of the cation is linked to the stabilisation of the clusters formed within the system, and that the Group II catalyst causes the salting out of the oligomers, resulting in fewer, larger clusters, hence, an increase in pore size and a broadening of the pore size distribution. The results provide insight into how these systems can be further controlled to create tailored porous materials for a range of applications.

Multi-stimulus linear negative expansion of a breathing M(O2CR)4-node MOF

Quartz-type MOF (Me₂NH₂)₂[Cd(NO₂BDC)₂] (SHF-81) exhibits anisotropic breathing behaviour as single crystals in response to multiple stimuli.

Echocardiographic RV-E/e' for predicting right atrial pressure: a review

Right atrial pressure (RAP) is a key cardiac parameter of diagnostic and prognostic significance, yet current two-dimensional echocardiographic methods are inadequate for the accurate estimation of this haemodynamic marker. Right-heart trans-tricuspid Doppler and tissue Doppler echocardiographic techniques can be combined to calculate the right ventricular (RV) E/e′ ratio – a reflection of RV filling pressure which is a surrogate of RAP. A systematic search was undertaken which found seventeen articles that compared invasively measured RAP with RV-E/e′ estimated RAP. Results commonly concerned pulmonary hypertension or advanced heart failure/transplantation populations. Reported receiver operating characteristic analyses showed reasonable diagnostic ability of RV-E/e′ for estimating RAP in patients with coronary artery disease and RV systolic dysfunction. The diagnostic ability of RV-E/e′ was generally poor in studies of paediatrics, heart failure and mitral stenosis, whilst results were equivocal in other diseases. Bland–Altman analyses showed good accuracy but poor precision of RV-E/e′ for estimating RAP, but were limited by only being reported in seven out of seventeen articles. This suggests that RV-E/e′ may be useful at a population level but not at an individual level for clinical decision making. Very little evidence was found about how atrial fibrillation may affect the estimation of RAP from RV-E/e′, nor about the independent prognostic ability of RV-E/e′ . Recommended areas for future research concerning RV-E/e′ include; non-sinus rhythm, valvular heart disease, short and long term prognostic ability, and validation over a wide range of RAP.

Adsorption of Pb(II) ions from contaminated water by 1,2,3,4-butanetetracarboxylic acid-modified microcrystalline cellulose: Isotherms, kinetics, and thermodynamic studies

Microcrystalline cellulose (MCC) has been utilized as an adsorbent material for the removal of Pb(II) ions from aqueous solution after treatment with 1,2,3,4-butanetetracarboxylic acid (BTCA) at elevated temperature to obtain MMCC. The resulting adsorbent was characterized for point of zero point charge (pHZPC), estimation of carboxyl content, Fourier transform infrared spectroscopy (FT-IR), scan electron microscopy (SEM), and textural properties, including surface area, and subsequently utilized for the removal of Pb(II) ions from aqueous solution. The adsorption process was probed by investigating the effect of adsorbent dose, pH of solution, temperature, agitation time, and Pb(II) ion concentration. The results showed successful functionalization of MCC using BTCA, significantly improved the binding properties of the adsorbent towards Pb(II) ions. Isothermal adsorption data was analyzed using Langmuir, Freundlich and Temkin models, evaluated via nonlinear regression analysis. The maximum adsorption capacity was found to be 1155 mg/g (at pH 5 and 30 °C) from Langmuir theory, and appears independent of surface area. The Freundlich model was found to provide the best fit and the constant n was determined to be 2.69, indicating that adsorption of Pb(II) ions onto MMCC is favorable. Kinetic modelling showed good agreement for the pseudo-second order kinetic model, supporting the theory that chemisorption is involved in the adsorption process, which is promoted by a high density of active sites. Thermodynamic analysis showed that the adsorption of Pb(II) ions onto MMCC was endothermic and nonspontaneous; hence, MMCC offers an effective method of Pb(II) ion removal from aqueous solutions, with potential for water remediation processes.

Effect of S-triazine Ring Substitution on the Synthesis of Organic Resorcinol-Formaldehyde Xerogels

Resorcinol (R) and formaldehyde (F) gel synthesis has been well-studied along with alternative reagents. We present the synthesis of formaldehyde-based xerogels using chemically similar s-triazine precursors, with comparison to traditional analogues. The substitution ranges from tri-hydroxyl to tri-amine, with an intermediate species, allowing changing chemistry to be investigated. Each molecule (X) offers different acid/base properties, known to influence gel formation, as well as differences in crosslinking potential. Varying X/F ratios were selected to recreate the stoichiometry used in RF systems, where one represented higher F to match the increased reaction sites of the additives. X/C ratios were selected to probe different catalyst (C) ratios, while working within the range likely to produce viable gels. Results obtained show little impact for ammeline as an additive due to its similarity to resorcinol (activation sites and pK_a); while melamine and cyanuric acid show differing behavior depending on the level of addition. Low concentrations show melamine to have the most impact due to increased activation and competition for formaldehyde; while at high concentrations, cyanuric acid is shown to have the greatest impact as it creates a more acidic environment, which diminishes textural character, possibly attributable to larger clusters and/or weaker cross-linking of the system.

Imaging aortic valve calcification: significance, approach and implications

Aortic stenosis is the most prevalent valvular heart disease worldwide, and rates are increasing with the growing and more elderly population. Although the precise mechanisms that underpin aortic valve stenosis are incompletely understood, pathological valvular calcification has emerged as a key instigator in mediating the biomechanical stiffening that can lead to symptoms, the need for aortic valve replacement, and death if left untreated. Here, we review the currently understood processes leading to aortic valve calcification, summarise the contemporary imaging assessments of valve calcification, and highlight how these might improve patient care and accelerate our pathological understanding and the development of an effective medical therapy.

Novel hydrophilic and hydrophobic amorphous silica: Characterization and adsorption of aqueous phase organic compounds

Very few studies have investigated the adsorption performance of hydrophobic and hydrophilic silicas with dissolved organics in water, which is a required final step during produced water treatment. The cost of functionalization also hinders the use of hydrophobic materials as sorbents. Novel hydrophilic silicas, prepared at low temperature and ambient pressure, were characterised by SEM, FTIR and BET analysis, and studied for the adsorption of aqueous phase organic compounds at concentrations below their solubility limits. Adsorption capacities were found to be up to 264 mg/g for benzene and 78.8 mg/g for toluene. Direct comparison is made with the analogous hydrophobic version of one of the silica materials, demonstrating comparable uptakes for benzene concentrations lower than 50 mg/L. This finding supports the hypothesis that, at very low aqueous phase organic concentrations, hydrophobicization has no discernible effect on access of the pollutants to the internal porosity of the material.

Effects of Secondary Metal Carbonate Addition on the Porous Character of Resorcinol-Formaldehyde Xerogels

A deeper understanding of the chemistry and physics of growth, aggregation, and gelation processes involved in the formation of xerogels is key to providing greater control of the porous characteristics of such materials, increasing the range of applications for which they may be utilized. Time-resolved dynamic light scattering has been used to study the formation of resorcinol-formaldehyde gels in the presence of combinations of Group I (Na and Cs) and Group II (Ca and Ba) metal carbonates. It was found that the combined catalyst composition, including species and times of addition, is crucial in determining the end properties of the xerogels via its effect on growth of clusters involved in formation of the gel network. Combination materials have textural characteristics within the full gamut offered by each catalyst alone; however, in addition, combination materials that retain the small pores associated with sodium carbonate catalyzed xerogels exhibit a narrowing of the pore size distribution, providing an increased pore volume within an application-specific range of pore sizes. We also show evidence of pore size tunability while maintaining ionic strength, which significantly increases the potential of such systems for biological applications.

Coordination polymer flexibility leads to polymorphism and enables a crystalline solid-vapour reaction: a multi-technique mechanistic study

Despite an absence of conventional porosity, the 1D coordination polymer [Ag4 (O2 C(CF2 )2 CF3 )4 (TMP)3 ] (1; TMP=tetramethylpyrazine) can absorb small alcohols from the vapour phase, which insert into AgO bonds to yield coordination polymers [Ag4 (O2 C(CF2 )2 CF3 )4 (TMP)3 (ROH)2 ] (1-ROH; R=Me, Et, iPr). The reactions are reversible single-crystal-to-single-crystal transformations. Vapour-solid equilibria have been examined by gas-phase IR spectroscopy (K=5.68(9)×10(-5) (MeOH), 9.5(3)×10(-6) (EtOH), 6.14(5)×10(-5) (iPrOH) at 295 K, 1 bar). Thermal analyses (TGA, DSC) have enabled quantitative comparison of two-step reactions 1-ROH→1→2, in which 2 is the 2D coordination polymer [Ag4 (O2 C(CF2 )2 CF3 )4 (TMP)2 ] formed by loss of TMP ligands exclusively from singly-bridging sites. Four polymorphic forms of 1 (1-A(LT) , 1-A(HT) , 1-B(LT) and 1-B(HT) ; HT=high temperature, LT=low temperature) have been identified crystallographically. In situ powder X-ray diffraction (PXRD) studies of the 1-ROH→1→2 transformations indicate the role of the HT polymorphs in these reactions. The structural relationship between polymorphs, involving changes in conformation of perfluoroalkyl chains and a change in orientation of entire polymers (A versus B forms), suggests a mechanism for the observed reactions and a pathway for guest transport within the fluorous layers. Consistent with this pathway, optical microscopy and AFM studies on single crystals of 1-MeOH/1-A(HT) show that cracks parallel to the layers of interdigitated perfluoroalkyl chains develop during the MeOH release/uptake process.

Gelation mechanism of resorcinol-formaldehyde gels investigated by dynamic light scattering

Xerogels and porous materials for specific applications such as catalyst supports, CO2 capture, pollutant adsorption, and selective membrane design require fine control of pore structure, which in turn requires improved understanding of the chemistry and physics of growth, aggregation, and gelation processes governing nanostructure formation in these materials. We used time-resolved dynamic light scattering to study the formation of resorcinol-formaldehyde gels through a sol-gel process in the presence of Group I metal carbonates. We showed that an underlying nanoscale phase transition (independent of carbonate concentration or metal type) controls the size of primary clusters during the preaggregation phase; while the amount of carbonate determines the number concentration of clusters and, hence, the size to which clusters grow before filling space to form the gel. This novel physical insight, based on a close relationship between cluster size at the onset of gelation and average pore size in the final xerogel results in a well-defined master curve, directly linking final gel properties to process conditions, facilitating the rational design of porous gels with properties specifically tuned for particular applications. Interestingly, although results for lithium, sodium, and potassium carbonate fall on the same master curve, cesium carbonate gels have significantly larger average pore size and cluster size at gelation, providing an extended range of tunable pore size for further adsorption applications.

Metaldehyde removal from aqueous solution by adsorption and ion exchange mechanisms onto activated carbon and polymeric sorbents

Metaldehyde removal from aqueous solution was evaluated using granular activated carbon (GAC), a non-functionalised hyper-cross-linked polymer Macronet (MN200) and an ion-exchange resin (S957) with sulfonic and phosphonic functional groups. Equilibrium experimental data were successfully described by Freundlich isotherm models. The maximum adsorption capacity of S957 (7.5 g metaldehyde/g S957) exceeded those of MN200 and GAC. Thermodynamic studies showed that sorption of metaldehyde onto all sorbents is endothermic and processes are controlled by entropic rather than enthalpic changes. Kinetic experiments demonstrated that experimental data for MN200 and GAC obey pseudo-second order models with rates limited by particle diffusion. Comparatively, S957 was shown to obey a pseudo-first order model with a rate-limiting step of metaldehyde diffusion through the solid/liquid interface. Results obtained suggest that metaldehyde adsorption onto MN200 and GAC are driven by hydrophobic interactions and hydrogen bonding, as leaching tendencies were high since no degradation of metaldehyde occurred. Conversely, adsorption of metaldehyde onto S957 occurs via ion-exchange processes, where sulfonic and phosphonic functionalities degrade adsorbed metaldehyde molecules and failure to detect metaldehyde in leaching studies for S957 supports this theory. Consequently, the high adsorption capacity and absence of leaching indicate S957 is promising for metaldehyde removal from source water.

Surface interactions and quantum kinetic molecular sieving for H2 and D2 adsorption on a mixed metal-organic framework material

A rational strategy has been used to immobilize open metal sites in ultramicroporosity for stronger binding of multiple H 2 molecules per unsaturated metal site for H 2 storage applications. The synthesis and structure of a mixed zinc/copper metal-organic framework material Zn 3(BDC) 3[Cu(Pyen)] .(DMF) 5(H 2O) 5 (H 2BDC = 1,4 benzenedicarboxylic acid and PyenH 2 = 5-methyl-4-oxo-1,4-dihydro-pyridine-3-carbaldehyde) is reported. Desolvation provides a bimodal porous structure Zn 3(BDC) 3[Cu(Pyen)] (M'MOF 1) with narrow porosity (<0.56 nm) and an array of pores in the bc crystallographic plane where the adsorbate-adsorbent interactions are maximized by both the presence of open copper centers and overlap of the potential energy fields from pore walls. The H 2 and D 2 adsorption isotherms for M'MOF 1 at 77.3 and 87.3 K were reversible with virtually no hysteresis. Methods for determination of the isosteric enthalpies of H 2 and D 2 adsorption were compared. A virial model gave the best agreement (average deviation <1 standard deviation) with the isotherm data. This was used in conjunction with the van't Hoff isochore giving isosteric enthalpies at zero surface coverage of 12.29 +/- 0.53 and 12.44 +/- 0.50 kJ mol (-1) for H 2 and D 2 adsorption, respectively. This is the highest value so far observed for hydrogen adsorption on a porous material. The enthalpy of adsorption, decreases with increasing amount adsorbed to 9.5 kJ mol (-1) at approximately 1.9 mmol g (-1) (2 H 2 or D 2 molecules per Cu corresponding to adsorption on both sides of planar Cu open centers) and is virtually unchanged in the range 1.9-3.6 mmol g (-1). Virial analysis of isotherms at 87.3 K is also consistent with two H 2 or D 2 molecules being bound to each open Cu center. The adsorption kinetics follow a double exponential model, corresponding to diffusion along two types of pores, a slow component with high activation energy (13.35 +/- 0.59 kJ mol (-1)) for the narrow pores and a faster component with low activation energy (8.56 +/- 0.41 kJ mol (-1)). The D 2 adsorption kinetic constants for both components were significantly faster than the corresponding H 2 kinetics for specific pressure increments and had slightly lower activation energies than the corresponding values for H 2 adsorption. The kD 2/ kH 2 ratio for the slow component was 1.62 +/- 0.07, while the fast component was 1.38 +/- 0.04 at 77.3 K, and the corresponding ratios were smaller at 87.3 K. These observations of kinetic isotope quantum molecular sieving in porous materials are due to the larger zero-point energy for the lighter H 2, resulting in slower adsorption kinetics compared with the heavier D 2. The results show that a combination of open metal centers and confinement in ultramicroporosity leads to a high enthalpy for H 2 adsorption over a wide range of surface coverage and quantum effects influence diffusion of H 2 and D 2 in pores in M'MOF 1.

High-Capacity Hydrogen and Nitric Oxide Adsorption and Storage in a Metal−Organic Framework

Gas adsorption experiments have been carried out on a copper benzene tricarboxylate metal-organic framework material, HKUST-1. Hydrogen adsorption at 1 and 10 bar (both 77 K) gives an adsorption capacity of 11.16 mmol H2 per g of HKUST-1 (22.7 mg g(-)1, 2.27 wt %) at 1 bar and 18 mmol per g (36.28 mg g(-)1, 3.6 wt %) at 10 bar. Adsorption of D2 at 1 bar (77 K) is between 1.09 (at 1 bar) and 1.20(at <100 mbar) times the H2 values depending on the pressure, agreeing with the theoretical expectations. Gravimetric adsorption measurements of NO on HKUST-1 at 196 K (1 bar) gives a large adsorption capacity of approximately 9 mmol g(-1), which is significantly greater than any other adsorption capacity reported on a porous solid. At 298 K the adsorption capacity at 1 bar is just over 3 mmol g(-1). Infra red experiments show that the NO binds to the empty copper metal sites in HKUST-1. Chemiluminescence and platelet aggregometry experiments indicate that the amount of NO recovered on exposure of the resulting complex to water is enough to be biologically active, completely inhibiting platelet aggregation in platelet rich plasma.

Kinetic Isotope Effect for H2and D2Quantum Molecular Sieving in Adsorption/Desorption on Porous Carbon Materials

Adsorption and desorption of H(2) and D(2) from porous carbon materials, such as activated carbon at 77 K, are usually fully reversible with very rapid adsorption/desorption kinetics. The adsorption and desorption of H(2) and D(2) at 77 K on a carbon molecular sieve (Takeda 3A), where the kinetic selectivity was incorporated by carbon deposition, and a carbon, where the pore structure was modified by thermal annealing to give similar pore structure characteristics to the carbon molecular sieve substrate, were studied. The D(2) adsorption and desorption kinetics were significantly faster (up to x1.9) than the corresponding H(2) kinetics for specific pressure increments/decrements. This represents the first experimental observation of kinetic isotope quantum molecular sieving in porous materials due to the larger zero-point energy for the lighter H(2), resulting in slower adsorption/desorption kinetics compared with the heavier D(2). The results are discussed in terms of the adsorption mechanism.

Assembly of Heterometallic Clusters and Coordination Polymers by Combining Mo−S-Based Clusters with Mn2+

Addition of [Mo(V)2O2S2(edt)2]2- (edt =1,2-ethanedithiolate) to acetonitrile and/or methanol solutions of MnII containing bipyridines [4,4'-trimethylenedipyridine (TDP), 4,4'-bipyridine (4,4'-bpy), 2,2'-bipyridine (2,2'-bpy)] or 15-crown-5 produces three new heterometallic cluster coordination polymers, [Mn2[Mo2O2S2(edt)2]2(TDP)3(CH3OH)2(NCMe)2].3CH3OH.0.25MeCN (1), [Mn(TDP)2(H2O)2]2+[Mn[Mo2O2S2(edt)2)2(TDP)2]]2-.6CH3OH (2), [Mn[Mo2O2S2(edt)2](TDP)2(CH3OH)(H2O)].CH3OH (3), and three new multinuclear clusters, [Mn[Mo2O2S2(edt)2](4,4'-bpy)(CH3OH)4].0.5(4,4'-bpy) (4), [Mn[Mo2O2S2(edt)2](2,2'-bpy)2].2CH3OH (5), and (NEt4)2[Mn(15-crown-5)[Mo2O2S2(edt)2]2] (6). All compounds were characterized by X-ray crystallography. The coordination mode of Mn in these compounds depends on the ligands and the crystallization conditions. Compound 2 readily converts to 1 or 3 depending on the reaction and solvent conditions. Compounds 1 and 2 were analyzed using thermogravimetric analysis combined with mass spectroscopy (TG-MS) in the temperature range 25-500 degrees C. The room-temperature magnetic moments for compounds 1-6 were determined.

Hydrogen Adsorption on Functionalized Nanoporous Activated Carbons

There is considerable interest in hydrogen adsorption on carbon nanotubes and porous carbons as a method of storage for transport and related energy applications. This investigation has involved a systematic investigation of the role of functional groups and porous structure characteristics in determining the hydrogen adsorption characteristics of porous carbons. Suites of carbons were prepared with a wide range of nitrogen and oxygen contents and types of functional groups to investigate their effect on hydrogen adsorption. The porous structures of the carbons were characterized by nitrogen (77 K) and carbon dioxide (273 K) adsorption methods. Hydrogen adsorption isotherms were studied at 77 K and pressure up to 100 kPa. All the isotherms were Type I in the IUPAC classification scheme. Hydrogen isobars indicated that the adsorption of hydrogen is very temperature dependent with little or no hydrogen adsorption above 195 K. The isosteric enthalpies of adsorption at zero surface coverage were obtained using a virial equation, while the values at various surface coverages were obtained from the van't Hoff isochore. The values were in the range 3.9-5.2 kJ mol(-1) for the carbons studied. The thermodynamics of the adsorption process are discussed in relation to temperature limitations for hydrogen storage applications. The maximum amounts of hydrogen adsorbed correlated with the micropore volume obtained from extrapolation of the Dubinin-Radushkevich equation for carbon dioxide adsorption. Functional groups have a small detrimental effect on hydrogen adsorption, and this is related to decreased adsorbate-adsorbent and increased adsorbate-adsorbate interactions.

Hysteretic Adsorption and Desorption of Hydrogen by Nanoporous Metal-Organic Frameworks

Adsorption and desorption of hydrogen from nanoporous materials, such as activated carbon, is usually fully reversible. We have prepared nanoporous metal-organic framework materials with flexible linkers in which the pore openings, as characterized in the static structures, appear to be too small to allow H2 to pass. We observe hysteresis in their adsorption and desorption kinetics above the supercritical temperature of H2 that reflects the dynamical opening of the "windows" between pores. This behavior would allow H2 to be adsorbed at high pressures but stored at lower pressures.

Adsorption of Gases and Vapors on Nanoporous Ni2(4,4‘-Bipyridine)3(NO3)4 Metal−Organic Framework Materials Templated with Methanol and Ethanol: Structural Effects in Adsorption Kinetics

Desolvation of Ni(2)(4,4'-bipyridine)(3)(NO(3))(4).2CH(3)OH and Ni(2)(4,4'-bipyridine)(3)(NO(3))(4).2C(2)H(5)OH give flexible metal-organic porous structures M and E, respectively, which have the same stoichiometry, but subtly different structures. This study combines measurements of the thermodynamics and kinetics of carbon dioxide, methanol, and ethanol sorption on adsorbents M and E over a range of temperatures with adsorbent structural characterization at different adsorbate (guest) loadings. The adsorption kinetics for methanol and ethanol adsorption on porous structure E obey a linear driving force (LDF) mass transfer model for adsorption at low surface coverage. The corresponding adsorption kinetics for porous structure M follow a double exponential (DE) model, which is consistent with two different barriers for diffusion through the windows and along the pores in the structure. The former is a high-energy barrier due to the opening of the windows in the structure, required to allow adsorption to occur, while the latter is a lower-energy barrier for diffusion in the pore cavities. X-ray diffraction studies at various methanol and ethanol loadings showed that the host porous structures E and M underwent different scissoring motions, leading to an increase in unit cell volume with the space group remaining unchanged during adsorption. The results are discussed in terms of reversible adsorbate/adsorbent (host/guest) structural changes and the adsorption mechanism involving hydrogen-bonding interactions with specific surface sites for methanol and ethanol adsorption in relation to pore size and extent of filling. This paper contains the first evidence for individual kinetic barriers to diffusion through windows and pore cavities in flexible porous coordination polymer frameworks.

Adsorption dynamics of gases and vapors on the nanoporous metal organic framework material Ni2(4,4'-bipyridine)3(NO3)4: guest modification of host sorption behavior

This study combines measurements of the thermodynamics and kinetics of guest sorption with powder X-ray diffraction measurements of the nanoporous metal organic framework adsorbent (host) at different adsorptive (guest) loadings. The adsorption characteristics of nitrogen, argon, carbon dioxide, nitrous oxide and ethanol and methanol vapors on Ni2(4,4'-bipyridine)3(NO3)4 were studied over a range of temperatures as a function of pressure. Isotherm steps were observed for both carbon dioxide and nitrous oxide adsorption at approximately 10-20% of the total pore volume and at approximately 70% of total pore volume for methanol adsorption. The adsorption kinetics obey a linear driving force (LDF) mass transfer model for adsorption at low surface coverage. At high surface coverage, both methanol and ethanol adsorption follow a combined barrier resistance/diffusion model. The rates of adsorption in the region of both the carbon dioxide and methanol isotherm steps were significantly slower than those observed either before or after the step. X-ray diffraction studies at various methanol loadings showed that the host structure disordered initially but underwent a structural change in the region of the isotherm step. These isotherm steps are ascribed to discrete structural changes in the host adsorbent that are induced by adsorption on different sites. Isotherm steps were not observed for ethanol adsorption, which followed a Langmuir isotherm. Previous X-ray crystallography studies have shown that all the sites are equivalent for ethanol adsorption on Ni2(4,4'-bipyridine)3(NO3)4, with the host structure undergoing a scissoring motion and the space group remaining unchanged during adsorption. The activation energies and preexponential factors for methanol and ethanol adsorption were calculated for each pressure increment at which the linear driving force model was obeyed. There was a good correlation between activation energy and ln(preexponential factor), indicating a compensation effect. The results are discussed in terms of reversible adsorbate/adsorbent (guest/host) structural changes and interactions and the adsorption mechanism. The paper contains the first evidence of specific interactions between guests and functional groups leading to structural change in flexible porous coordination polymer frameworks.

A novel method for controlled and reversible long term compression of the umbilical cord in fetal sheep

1. In fetal sheep during late gestation the aims of the present study were to (1) develop a technique for inducing prolonged but reversible periods of controlled compression of the umbilical cord and (2) characterise the cardiovascular, endocrine and metabolic responses to this challenge. 2. Under 1-2 % halothane anaesthesia, 16 Welsh Mountain sheep fetuses were chronically instrumented at 118 +/- 2 days of gestation (term is ca 145 days) with an inflatable occluder cuff around the umbilical cord, amniotic and femoral vascular catheters and with transit-time flow probes around the contra-lateral femoral artery and an umbilical artery. At 125 days, umbilical blood flow was reduced by 30 % from a pre-determined 24 h baseline for 3 days by automated servo-controlled inflation of the occluder cuff (n = 8). The occluder was then deflated allowing return of umbilical blood flow to baseline. The remaining eight fetuses were used as sham-operated controls in which the occluder was not inflated throughout the protocol. Fetal cardiovascular variables were recorded at 8 s intervals and arterial blood samples taken for measurement of blood gases, glucose and lactate and plasma adrenaline, noradrenaline and vasopressin concentration throughout the study. 3. Automated servo-controlled inflation of the occluder cuff, programmed to reduce umbilical blood flow by 30 % from baseline, reduced umbilical blood flow by 30.2 +/- 1.7 %, with a coefficient of variation during compression of 6.5 +/- 1.1 %. Sustained partial compression of the umbilical cord produced falls in fetal arterial pH, P(a,O2), percentage O(2) saturation of haemoglobin, and hindlimb oxygen delivery, and increases in P(a,CO2), haemoglobin concentration, arterial blood oxygen carrying capacity and in blood glucose and lactate concentrations. While the reductions in P(a,O2), percentage saturation of haemoglobin and hindlimb oxygen delivery and the increase in P(a,CO2) were sustained throughout compression, the reduction in arterial pH and the increase in arterial oxygen carrying capacity had returned towards baseline values by 48 h compression. Fetal blood lactate concentrations reached a peak at 8 h of compression and, thereafter, were maintained at an elevated level relative to baseline. 4. Partial compression of the umbilical cord produced fetal hypertension, a reduction in femoral blood flow and, consequently, an increase in calculated fetal femoral vascular resistance for the duration of the challenge. In addition, the fall in heart rate measured in sham control fetuses by the end of the study, did not occur in cord-compressed fetuses. Cosinor analysis on 24 h rhythms of cardiovascular data indicated a significant increase in the amplitude of the 24 h rhythm in heart rate in cord-compressed fetuses relative to sham controls during the period of compression or sham-compression. Furthermore, cord compression led to an increase in fetal plasma noradrenaline, but not adrenaline and vasopressin concentrations relative to sham control fetuses. 5. In conclusion, a novel reversible method for controlled, long-term compression of the umbilical cord in sheep has been developed. The data show that sustained, partial compression of the umbilical cord produced moderate but sustained asphyxia, which resolved after the end of the compression period, and induced changes in fetal cardiovascular, endocrine and metabolic functions.

Purinergic contribution to circulatory, metabolic, and adrenergic responses to acute hypoxemia in fetal sheep

This study investigated the effects on femoral vascular resistance, blood glucose and lactate levels, and plasma catecholamine concentrations of fetal treatment with an adenosine receptor antagonist during acute hypoxemia in fetal sheep during late gestation. Under anesthesia, seven fetal sheep were instrumented between 117 and 118 days gestation (term is approximately 145 days) with vascular and amniotic catheters and an ultrasonic probe around a femoral artery. Six days after surgery, all fetuses were randomly subjected to a 3-h experiment consisting of 1 h of normoxia, 1 h of hypoxemia, and 1 h of recovery. This was done during either intravenous infusion of vehicle or the adenosine receptor antagonist [8-(p-sulfophenyl)-theophylline; 8-SPT] dissolved in vehicle. During vehicle infusion, all fetuses responded to hypoxemia with bradycardia, an increase in arterial blood pressure, and femoral vasoconstriction. Increases in blood glucose and lactate concentrations and in plasma epinephrine and norepinephrine concentrations also occurred in all fetuses during hypoxemia. Fetal treatment with 8-SPT markedly attenuated the bradycardic, hypertensive, vasoconstrictor, glycemic, and adrenergic responses to hypoxemia, but it did not affect the increase in blood lactate concentrations during hypoxemia. These data show that adenosine is involved in the mechanisms mediating fetal cardiovascular, metabolic, and adrenergic responses to hypoxemia in fetal sheep. Fetal treatment with 8-SPT mimics the effects of carotid sinus nerve section on fetal cardiovascular function during hypoxemia, suggesting a role for adenosine in mediating fetal cardiovascular chemoreflexes.

Plasma adrenocorticotropin and cortisol concentrations during acute hypoxemia after a reversible period of adverse intrauterine conditions in the ovine fetus during late gestation

The present study determined the pituitary-adrenal responses to acute hypoxemia after a period of reversible adverse intrauterine conditions produced by partial compression of the umbilical cord for 3 days in the sheep fetus during late gestation. At 118 +/- 2 days gestation (term is approximately 145 days), 12 sheep fetuses were instrumented under halothane anesthesia with an occluder cuff around the umbilical cord, amniotic and vascular catheters, and a transit-time flow probe around an umbilical artery. In 6 of the fetuses at 125 days, umbilical blood flow was reduced by about 30% from baseline for 3 days (UCC), after which the occluder was deflated. The remaining 6 fetuses acted as sham-operated controls in which the occluder was not inflated. All fetuses were then subsequently subjected to 2 periods of acute hypoxemia, elicited by reducing the maternal inspired fraction of oxygen (FiO(2)) at 2 +/- 1 and 5 +/- 2 days after the end of cord compression or sham compression. In addition, 4 fetuses from each group were subjected to an ACTH challenge 1-2 days after the final episode of acute hypoxemia. Maternal and fetal arterial blood samples were taken at appropriate intervals during cord compression, acute hypoxemia, and ACTH challenge for analyses of blood gases, pH, and plasma ACTH and cortisol concentrations. Partial compression of the umbilical cord produced reversible mild fetal asphyxia, a transient increase in fetal plasma ACTH, and a progressive increase in fetal plasma cortisol. At 5 +/- 2 days after the end of compression, despite similar blood gas status between the groups, basal plasma cortisol, but not ACTH, concentrations were significantly greater in compressed fetuses relative to sham controls. However, this dissociation did not affect a similar increment in fetal plasma ACTH and cortisol concentrations during acute hypoxemia or in the fetal plasma cortisol response to the ACTH challenge in either group. An increase in adrenocortical mass occurred in fetuses preexposed to partial compression of the umbilical cord relative to sham controls. The data suggest that fetal exposure to a reversible period of adverse intrauterine conditions produced by partial compression of the umbilical cord does not affect the magnitude of the fetal hypothalamic-pituitary-adrenal axis response to subsequent acute hypoxemia, but it leads to resetting of basal hypothalamic-pituitary-adrenal axis function in the fetus. The mechanism for this resetting may include an increase in adrenocortical steroidogenic synthetic capacity, but it is not due to a change in adrenocortical sensitivity to ACTH. Inappropriate fetal glucocorticoid exposure after reversible periods of adverse intrauterine conditions has important implications for fetal and postnatal development.

Neuropeptide Y in the sheep fetus: effects of acute hypoxemia and dexamethasone during late gestation

Plasma concentrations of neuropeptide Y (NPY) were measured in pregnant ewes and their fetuses under basal conditions and in response to acute hypoxemia during late gestation. The effects of fetal treatment with dexamethasone on these NPY responses were also examined. Under general anesthesia, 10 Welsh Mountain ewes and their fetuses were chronically instrumented between 117-120 days gestation (dGA; term is approximately 145 dGA) with vascular and amniotic catheters, and an ultrasonic probe around a femoral artery of each fetus. At 124 dGA, five fetuses were continuously infused i.v. with dexamethasone for 48 h at a rate of 1.73 +/- 0.16 microg x kg(-1) x h(-1) while the remaining five fetuses received vehicle at the same rate. At 126 dGA, 45 h from the onset of either infusion, 1 h of materno-fetal hypoxemia was induced by reducing maternal FiO2. During normoxia, maternal plasma NPY concentrations were three times those measured in fetal plasma in both groups. During hypoxemia, PaO2 fell to similar levels in the control and dexamethasone-treated groups in both mothers and fetuses. In control animals, there was a significant increase in the NPY concentration in fetal, but not maternal, plasma during hypoxemia. Fetal treatment with dexamethasone significantly enhanced the fetal NPY response to acute hypoxemia but had no effects on basal NPY levels in the fetal or maternal plasma or on the maternal response to acute hypoxemia. These data show: 1) differences between the maternal and fetal plasma NPY response to maternal inhalation hypoxia; 2) that NPY may play a role in mediating fetal defense responses to acute hypoxemia; and 3) that fetal exposure to glucocorticoids modifies the fetal plasma NPY response to acute hypoxemia.

Low doses of dexamethasone suppress pituitary-adrenal function but augment the glycemic response to acute hypoxemia in fetal sheep during late gestation

Despite the widespread use of antenatal glucocorticoid therapy in obstetric practice, little is known about the effects of synthetic glucocorticoids on the fetal capacity to respond to episodes of acute hypoxemia, such as may occur during labor and delivery. This study investigated the effects of prolonged fetal exposure to low concentrations of dexamethasone on the fetal ACTH, cortisol, and glycemic responses to an episode of acute hypoxemia during the period of dexamethasone treatment in sheep. At 118 d of gestation (term is approximately 145 d), 11 fetal sheep had catheters implanted under halothane anesthesia. From 124 d, five fetuses were infused i.v. continuously with dexamethasone (1.80 +/- 0.15 microg x kg(-1) x h(-1) in 0.9% saline at 0.5 mL/h) for 48 h, and the other six fetuses received saline solution i.v. at the same rate. At 45 h of infusion, acute hypoxemia was induced in all fetuses for 1 h by reducing the maternal inspired fraction of oxygen. During glucocorticoid treatment, fetal plasma dexamethasone concentrations increased to 3.9 +/- 0.2 nM by 24 h and remained elevated for the rest of the infusion period. During hypoxemia, a similar fall in fetal arterial PO2 occurred in both saline-infused and dexamethasone-treated fetuses. In control fetuses, significant increases in plasma ACTH and cortisol concentrations and in blood glucose concentrations occurred during hypoxemia. Dexamethasone treatment prevented the increases in fetal plasma ACTH and cortisol, and augmented the blood glucose response, induced by hypoxemia. These data indicate that prolonged fetal exposure to low concentrations of dexamethasone suppresses pituitary-adrenal function, but augments the glycemic response, to acute hypoxemia in fetal sheep during late gestation.

A comparison of the effects of intravenous tramadol, codeine, and morphine on gastric emptying in human volunteers

We compared the effects of i.v. tramadol (1.25 mg/kg), codeine (1 mg/kg), morphine (0.125 mg/kg), and saline on gastric emptying in 10 healthy human volunteers using a double-blind, randomized, cross-over design. Subjects received one treatment at each of four sessions, 2 wk apart. Gastric emptying was studied using the paracetamol absorption test. There were significant differences when comparing all treatments for concentration-time data (P = 0.002), peak serum paracetamol concentrations (Cmax; P < 0.001), times at Cmax (Tmax; P = 0.003), and areas under the curves from Time 0 to 360 min (AUC(0-360); P = 0.049). Morphine profoundly inhibited gastric emptying. Tramadol had measurable but statistically insignificant inhibitory effects on gastric emptying compared with saline (mean +/- SEM: Cmax 22.4 +/- 2.2 vs 26.8 +/- 2.5 mg/L [P = 0.19], Tmax 33 +/- 5.4 vs 19.5 +/- 2.3 min [P = 0.054] for tramadol versus saline, respectively). Compared with morphine, the Cmax (P < 0.01), Tmax, and AUC(0-360) (P < 0.05) values for tramadol were significantly different. The Tmax value for codeine (63.3 +/- 11.7) was greater than that for tramadol (P = 0.034). We conclude that tramadol has a measurable but smaller inhibitory effect on gastric emptying compared with other opioids.

IMPLICATIONS

We compared the effect of tramadol, an unconventional opioid painkiller, on stomach emptying with that of codeine and morphine in a human volunteer study. Tramadol had a measurable but smaller effect and may have clinical and economic advantages in acute pain management compared with conventional painkillers.

Influence of a changed care environment on bacterial colonization of burn wounds

This study investigated the influence of a conditioned care environment per se on bacterial colonization of burn wounds. Two cohorts of burn patients were treated in the successive years 1992 and 1993, the first group in a (permanent) purpose-designed unit and the second in wards of traditional 'open' design, during renovation of the unit. Patients who were admitted to the permanent and temporary units numbered 224 and 231 respectively, the groups being similar in features that generally influence the course and outcome of burn injuries. The principles and practice of treatment by the burn care team remained the same in both years. No significant difference in wound colonization rates was found between the two groups. We conclude that while the other known advantages of managing burn patients in purpose-designed units remain valid, a conditioned care environment per se does not influence bacterial colonization rates of burn wounds.

Glutaraldehyde concentration in the sterilization of endoscopes

Controversy over appropriate disinfection of endoscopes continues with the most commonly utilized solution in Australian hospitals, despite concern over its efficacy, being 1% glutaraldehyde (AIDAL). Review of the in-use concentrations of glutaraldehyde at Princess Alexandra Hospital has documented a significant dilutional effect in 1% glutaraldehyde by gastrointestinal endoscopes. Each hospital should determine the minimum in-use concentration acceptable for any given disinfecting solution and any given range of endoscopes. Once this level is reached, a solution change should routinely occur. Such decisions can only be made by regularly monitoring in-use concentrations of disinfectants.

Structure-function analysis of the vitamin B12 receptor of Escherichia coli by means of informational suppression

We describe a genetic analysis of the vitamin B12 receptor of Escherichia coli. Through the use of informational suppression, we have been able to generate a family of receptor variants, each identical save for a single, known substitution (Ser, Gln, Lys, Tyr, Leu, Cys, Phe) at a known site. We have studied 22 different mutants, 14 in detail, distributed throughout the length of the btuB gene. Most amino acid substitutions have a pleiotropic effect with respect to all ligands tested, the two colicins E1 and E3, the T5-like bacteriophage BF23, and vitamin B12. (The dramatic effect of a single amino acid substitution is also well exemplified by the G142A missense change which renders the receptor completely non-functional.) In some instances, however, we have been able to modify a subset of receptor functions (viz. Q62, Q150 and Q299 and the response to phage BF23). These data are summarized on a two-dimensional folding model for the BtuB protein in the outer membrane (devised using both amphipathic beta-strand analysis and sequence conservation amongst the TonB-dependent receptors). In addition, we report that the extreme C-terminus of BtuB is vital for receptor localization and provide evidence for it being a membrane-spanning beta-sheet with residue L588 situated on its hydrophobic surface. Two of the C-terminal btuB mutations are located within the region of overlap with the recently identified dga (murl) gene.

Investigation of the regulation of the Escherichia coli btuB gene using operon fusions

Operon fusions were isolated between Mu dX (lac CmR ApR) and btuB, the gene encoding the multivalent vitamin B12 outer membrane receptor. Using these fusions, vitamin B12-mediated repression of btuB in Escherichia coli was demonstrated. Mutations in metH, metE and ompR as well as exogenous methionine, membrane pertubants, high osmolar conditions and temperature had no major effect on the expression of the btuB gene.