Oxygen consumption of desert pupfish at ecologically relevant temperatures suggests a significant role for anaerobic metabolism.

Oxygen consumption is oftentimes used as a proxy for metabolic rate. However, pupfish acclimated to ecologically relevant temperatures may employ extended periods of anaerobism despite the availability of oxygen-a process we called paradoxical anaerobism. In this study, we evaluated data from pupfish exhibiting stable oxygen consumption. Routine oxygen consumption ([Formula: see text]) of a refuge population derived from Cyprinodon spp. acclimated to 28 and 33 °C was evaluated at the ecologically relevant assay temperatures of between 25 and 38 °C. Different interpretations of the data are available depending on normalization. For instance, [Formula: see text] of smaller fish, measured per fish, was remarkably stable over a wide range of assay temperatures and was not different between acclimation groups. However, when measured on a mass-specific basis, [Formula: see text] in these same smaller fish increases more predictably as temperature increased. [Formula: see text] of refuge fish and the closely related pupfish, C. nevadensis mionectes, measured near their respective acclimation temperatures, were essentially identical. However, [Formula: see text] of 28 °C acclimated fish of both species, when measured at 34 °C, was greater than that of the 33 °C acclimated fish measured at 28 °C. We suggest that this observed 'efficiency' may result from significant anaerobic metabolism use. Experiments investigating factorial aerobic scope ([Formula: see text]/[Formula: see text]) yielded values less than 1 in 21-36% of the 33 °C acclimated fish. These values indicate a substantial contribution of anaerobic metabolism to energy utilization by these fish. However, muscle lactate levels are not elevated in exercising fish-a result that is consistent with paradoxical anaerobism use.

The rotational dynamics of H2 adsorbed in covalent organic frameworks.

A combined inelastic neutron scattering (INS) and theoretical study was carried out on H2 adsorbed in two covalent organic framework (COF) materials: COF-1 and COF-102. These COFs are synthesized from self-condensation reactions of 1,4-benzenediboronic acid (BDBA) and tetra(4-(dihydroxy)borylphenyl)methane (TBPM) molecules, respectively. Molecular simulations of H2 adsorption in COF-1 revealed that the H2 molecules occupy the region between two eclipsed layers of the COF. The most favorable H2 binding site in COF-1 is located between two B3O3 clusters of the eclipsed layers. Two distinct H2 binding sites were identified in COF-102 from the simulations: the B3O3 clusters and the phenyl rings of the tetraphenylmethyl units. Two-dimensional quantum rotation calculations for H2 adsorbed at the considered sites in both COFs resulted in rotational transitions that are in good agreement with those that appear in the corresponding INS spectra. Such calculations were important for interpreting the INS spectra in these materials. Calculation of the rotational potential energy surface for H2 bound at the most favorable adsorption site in COF-1 and COF-102 revealed unusually high rotational barriers that are attributed to the nature of the B3O3 rings. The values for these barriers to rotation are greater than or comparable to those observed in some metal-organic frameworks (MOFs) that possess open-metal sites. This study demonstrates the power of using INS experiments in conjunction with theoretical calculations to gain valuable insights into the nature of the binding sites and, for the first time, the rotational dynamics of H2 adsorbed in COFs.

Exceptional ammonia uptake by a covalent organic framework.

Covalent organic frameworks (COFs) are porous crystalline materials composed of light elements linked by strong covalent bonds. A number of these materials contain a high density of Lewis acid boron sites that can strongly interact with Lewis basic guests, which makes them ideal for the storage of corrosive chemicals such as ammonia. We found that a member of the covalent organic framework family, COF-10, shows the highest uptake capacity (15 mol kg⁻¹, 298 K, 1 bar) of any porous material, including microporous 13X zeolite (9 mol kg⁻¹), Amberlyst 15 (11 mol kg⁻¹) and mesoporous silica, MCM-41 (7.9 mol kg⁻¹). Notably, ammonia can be removed from the pores of COF-10 by heating samples at 200°C under vacuum. In addition, repeated adsorption of ammonia into COF-10 causes a shift in the interlayer packing, which reduces its apparent surface area to nitrogen. However, owing to the strong Lewis acid-base interactions, the total uptake capacity of ammonia and the structural integrity of the COF are maintained after several cycles of adsorption/desorption.

A crystalline imine-linked 3-D porous covalent organic framework.

A new crystalline porous three-dimensional covalent organic framework, termed COF-300, has been synthesized and structurally characterized. Tetrahedral tetra-(4-anilyl)-methane and linear terephthaldehyde building blocks were condensed to form imine linkages in a material whose X-ray crystal structure shows five independent diamond frameworks. Despite the interpenetration, the structure has pores of 7.2 A diameter. Thus, COF-300 shows thermal stability up to 490 degrees C and permanent porosity with a surface area of 1360 m(2) g(-1).

Reticular synthesis of covalent organic borosilicate frameworks.

This paper reports the synthesis and characterization of a new crystalline 3D covalent organic framework, COF-202: [C(C6H4)4]3[B3O6 (tBuSi)2]4, formed from condensation of a divergent boronic acid, tetra(4-dihydroxyborylphenyl)methane, and tert-butylsilane triol, tBuSi(OH)3. This framework is constructed through strong covalent bonds (Si-O, B-O) that link triangular and tetrahedral building units to form a structure based on the carbon nitride topology. COF-202 demonstrates high thermal stability, low density, and high porosity with a surface area of 2690 m2 g-1. The design and synthesis of COF-202 expand the type of linkage that could be used to crystallize new materials with extended covalent organic frameworks.

Designed synthesis of 3D covalent organic frameworks.

Three-dimensional covalent organic frameworks (3D COFs) were synthesized by targeting two nets based on triangular and tetrahedral nodes: ctn and bor. The respective 3D COFs were synthesized as crystalline solids by condensation reactions of tetrahedral tetra(4-dihydroxyborylphenyl) methane or tetra(4-dihydroxyborylphenyl)silane and by co-condensation of triangular 2,3,6,7,10,11-hexahydroxytriphenylene. Because these materials are entirely constructed from strong covalent bonds (C-C, C-O, C-B, and B-O), they have high thermal stabilities (400 degrees to 500 degrees C), and they also have high surface areas (3472 and 4210 square meters per gram for COF-102 and COF-103, respectively) and extremely low densities (0.17 grams per cubic centimeter).