Reversible Dehydration Research Articles

Varied Carbon Content of Organic Matter in Histosols, Spodosols, and Carbonatic Soils

Soil organic carbon (OC) content is often estimated by determining organic matter (OM) content via mass loss on ignition (LOI) and assuming that there are 580 g OC kg−1 OM. We utilized thermogravimetry (TG), oven‐determined mass LOI, and the Walkley‐Black (WB) wet oxidation method to evaluate the relationship between OC and OM contents of carbonatic and organic soils from Florida and Puerto Rico and Spodosols from Florida. These soils have contrasting components and formed under different ecological settings. The OC content of OM, based on TG‐determined OM mass LOI (TG OM) and WB OC, was higher for Histosols and Spodosols than for carbonatic soils. Regression coefficients between WB OC and TG OM were high for all soils. The factor to convert OM to OC, based on TG OM and WB OC, was 0.56 ± 0.04 (±0.04 is the 95% confidence interval) (R2 = 0.93) for carbonatic soils, 0.67 ± 0.06 (R2 = 0.94) for Spodosols, and 0.69 ± 0.04 (R2 = 0.99) for Histosols. Results show that accuracy in estimating OC from OM content may be improved if the conversion equation is developed from soils within limited compositional and/or biogeochemical ranges. As such, there is no universal conversion factor between OM and OC for all soils. Loss on ignition is not a reliable OM measure if there are mass losses below 200°C that are mistakenly attributed to OM combustion, as in the case of reversible dehydration for Histosols of this study. However, TG enables detection of and accounting for such mass losses. Isothermal TG also confirmed that reversible mass loss between 105 and 200°C was energy—rather than time dependent.

Transformation of AlPO-53 to JDF-2: Reversible Dehydration of a Templated Aluminophosphate Studied by MAS NMR and Diffraction

We describe a detailed study of the aluminum phosphate AlPO-53 in both its as-made and calcined forms. In its as-made state, AlPO-53(A), the material is templated by methylammonium cations and contains occluded water molecules and also hydroxide ions that bridge pairs of aluminum atoms, increasing their coordination number to 5. Solid-state NMR experiments confirm the local environment of the aluminum and phosphorus atoms proposed in a previous structural model from powder X-ray diffraction. P-31 NMR shows the presence of four distinct resonances with an intensity ratio of 1: 1:2:2, consistent with the expected six crystallographic p Sites. Al-27 triple-quantum MAS NMR resolves five aluminum peaks, two with NMR parameters characteristic of four-coordinate Al and three of five-coordinate Al. One of these latter signals has a greater intensity than that of the others, consistent with the presence of two overlapping signals from two distinct crystallographic Al sites. First-principles calculations of NMR parameters provide a complete spectral assignment and confirm our interpretation of unresolved spectra. AlPO-53(A) is found to convert easily into a second crystalline phase on moderate heating (upon spinning in the NMR rotor for an extended period, for example), and variable-temperature powder X-ray experiments, together with TGA, suggest that this is a dehydration process yielding a second aluminophosphate, JDF-2. This is confirmed using both P-31 and Al-27 NMR, with the spectral assignment of JDF-2 supported by first-principles calculations. Calcination of AlPO-53(A) or of the dehydrated material, JDF-2, at 300 degrees C yields the microporous open-framework material AlPO-53(B), a tetrahedral network with three Al and three P sites, as confirmed by NMR and first-principles calculations. In addition to demonstrating the power of the combined use of NMR, first-principles calculations, and diffraction for detailed structural investigations, we show that the possibility of a reversible dehydration in as-made AlPO-53 and similar systems is an important consideration in structural studies and provides evidence that the published structural model for AlPO-53(A) may be incomplete.

Enantiopure and Racemic Sandwich-like Networks with Dehydration, Readsorption, and Selective Guest-Exchange Phase Transformations

The room-temperature solution reactions of R- or S-H2opa (H2opa = 2-hydroxy-2-phenylacetic acid) with freshly prepared [Ag(NH3)2](OH) in the presence of 1,3-di(4-pyridyl)propane (bpp) yielded two enantiomeric compounds, [Ag2(R-Hopa)(bpp)2](R-Hopa)·3H2O (1·3H2O) and [Ag2(S-Hopa)(bpp)2](S-Hopa)·3H2O (2·3H2O). While a similar solution reaction was carried out with racemic H2opa instead of R- or S-H2opa, a racemic compound [Ag2(R-Hopa)(S-Hopa)(bpp)2]·4H2O (3·4H2O) was formed. When bulk crystals of 3·4H2O were exposed to the air at ambient temperature, a partially dehydrated compound [Ag2(R-Hopa)(S-Hopa)(bpp)2]·H2O (4·H2O) was found, which would transform to [Ag2(R-Hopa)(S-Hopa)(bpp)2]·2MeOH (5·2MeOH) by exposing the crystals of 4·H2O in mixed MeOH−EtOH−DMF solvent or in methanol. Compounds 1−5 have characteristic hydrogen-bonding-directed sandwich-like networks consisting of Ag−bpp layers and Hopa−−ROH chains (R = H for 1−4 and Me for 5). The different structural features come from different hydrogen bonding interactions between Hopa− and the lattice water or MeOH molecules. In 1·3H2O and 2·3H2O, R-Hopa− or S-Hopa− form left-handed or right-handed helices with water molecules running in parallel to the Ag-bpp layers while in 3·4H2O, the centrosymmetric hydrogen bonding chains are composed of two enantiomers of Hopa−. Upon dehydration, the Ag···Ag dimeric units in [Ag2(bpp)2]n2n+ in 3·4H2O were broken and the positions of the Ag-bpp chains were adjusted to form new Hopa−−H2O chains between the silver layers. After absorbing methanol, the Ag-bpp chains restored to their original layer structures and 5·2MeOH is pseudopolymorphic to 3·4H2O. The reversible dehydration, readsorption, and guest-exchange among 3·4H2O, 4·H2O, and 5·2MeOH is an interesting example of phase transformation for racemic coordination polymers. The chirality of 1·3H2O and 2·3H2O was further conformed by solid-state CD spectra.

A simple aqueous metathesis reaction yields new lanthanide monothiophosphates

This paper describes the synthesis and characterization of two, new rare earth monothiophosphate materials, LaPO 3S· xH 2O and NdPO 3S· yH 2O, and their properties in comparison to the corresponding orthophosphates prepared by a similar aqueous metathesis reaction. Each of these new materials was found to exist in an amorphous phase similar to a corresponding orthophosphate mineral. The new rhabdophane-type oxythiophosphates were found to display reversible dehydration and rehydration under mild conditions. The materials were found to be thermally unstable. Disproportionation was found to occur at less than 450 °C under vacuum. Sulfur is lost during heating in air between 450 and 650 °C, according to thermogravimetric analysis (TGA) experiments, yielding the orthophosphate. The monothiophosphate hydrates display broad photoluminescence in the visible under excitation by a 325 nm laser. The compounds were also analyzed using differential thermal analysis, FT-IR and UV/vis/NIR spectroscopy.

Influence of reaction conditions on the channel shape of 3d-4f heterometallic metal–organic framework

Three structural kinds of 3d-4f metal–organic-frameworks (MOFs), {[Ln4(ox)3(Ni(IDA)2)3(H2O)6]}n·xnH2O (Type I: LnLa, Nd, Eu, Gd; IDA = iminodiacetate, ox = oxalate), {[Ln2 (ox)(Ni(IDA)2)2(H2O)2]}n·2nH2O (Type II: LnLa, Pr, Nd, Eu) and {[Dy2(ox)2Ni(IDA)2(H2O)2]}n·2nH2O (Type III), have been synthesized under hydrothermal condition. The crystal structures consist of Ln-oxalate tetramers for Type I, dimers for Type II and one-dimensional polymers for Type III bridged by the metalloligand [Ni(IDA)2]2−. While Type I contains a mixture of “Ln6Ni4-parallelogram” (A-Type) and “Ln6Ni2-parallelogram” (B-Type) channels, Type II and Type III contain only A-type and B-type channels, respectively. A fairly high stability of the MOFs is indicated by thermogravimetric analyses and reversible dehydration and rehydration of guest water molecules, which is confirmed by single crystal-to-single crystal transformation of 1 and 5.

Effect of the nature of the metal on the breathing steps in MOFs with dynamic frameworks

The thermal behaviour of the nanoporous iron(iii) terephthalate MIL-53 is in stark contrast to its chromium and aluminium analogues which show an expansion of the cell during dehydration; with iron, reversible dehydration occurs via evolution of the structure through a highly distorted metastable anhydrous phase to a more regular phase above 423 K in which pore volume remains approximately constant.

Mesaconyl-Coenzyme A Hydratase, a New Enzyme of Two Central Carbon Metabolic Pathways in Bacteria

The coenzyme A (CoA)-activated C5-dicarboxylic acids mesaconyl-CoA and beta-methylmalyl-CoA play roles in two as yet not completely resolved central carbon metabolic pathways in bacteria. First, these compounds are intermediates in the 3-hydroxypropionate cycle for autotrophic CO2 fixation in Chloroflexus aurantiacus, a phototrophic green nonsulfur bacterium. Second, mesaconyl-CoA and beta-methylmalyl-CoA are intermediates in the ethylmalonyl-CoA pathway for acetate assimilation in various bacteria, e.g., in Rhodobacter sphaeroides, Methylobacterium extorquens, and Streptomyces species. In both cases, mesaconyl-CoA hydratase was postulated to catalyze the interconversion of mesaconyl-CoA and beta-methylmalyl-CoA. The putative genes coding for this enzyme in C. aurantiacus and R. sphaeroides were cloned and heterologously expressed in Escherichia coli, and the proteins were purified and studied. The recombinant homodimeric 80-kDa proteins catalyzed the reversible dehydration of erythro-beta-methylmalyl-CoA to mesaconyl-CoA with rates of 1,300 micromol min(-1) mg protein(-1). Genes coding for similar enzymes with two (R)-enoyl-CoA hydratase domains are present in the genomes of Roseiflexus, Methylobacterium, Hyphomonas, Rhodospirillum, Xanthobacter, Caulobacter, Magnetospirillum, Jannaschia, Sagittula, Parvibaculum, Stappia, Oceanicola, Loktanella, Silicibacter, Roseobacter, Roseovarius, Dinoroseobacter, Sulfitobacter, Paracoccus, and Ralstonia species. A similar yet distinct class of enzymes containing only one hydratase domain was found in various other bacteria, such as Streptomyces species. The role of this widely distributed new enzyme is discussed.

Studies of the Mechanism of a Single-Crystal-to-Single-Crystal Reversible Dehydration of a Copper Carboxylate Framework

The open-framework copper carboxylate chloride [Cu7Cl2(THFTC)2(OH)4(H2O)2](H2O)4 (THFTC = tetrahydrofuran-2,3,4,5-tetracarboxylate) was synthesized hydrothermally and was characterized structurally and magnetically. The centrosymmetric three-dimensional framework has channels filled with water. Single crystals kept under vacuum at different temperatures (room temperature, 65 °C, and 105 °C) remain single while the structure is dehydrated in steps accompanied by distortions of the framework and repositioning of the water molecules and chlorine atoms. The dehydrated compounds are acentric and have two distinct channels with different inner environments. These single-crystal-to-single-crystal transformations are reversible evidenced by the structural studies of the dehydrated single crystals after exposure to humid air. Magnetic measurements showed antiferromagnetic coupling between the Cu2+ ions. Homometallic ferrimagnetism is observed below Tc of 2.4 and 3.4 K for the as-synthesized and the dehydrated samp...

A 3D heterometallic metal–organic framework constructed from luminescent building blocks, exhibiting reversible dehydration and rehydration procedure

A novel metal–organic framework constructed from luminescent building block, [Tb(pydc) 3] 3−, and alkaline earth ion has been designed and synthesized. It illustrates a three-dimensional (3D) structure with nano-channels, and shows reversible dehydration and rehydration behavior.

Stability of [6]-gingerol and [6]-shogaol in simulated gastric and intestinal fluids

The degradation kinetics of [6]-gingerol and [6]-shogaol were investigated in simulated gastric (pH 1) and intestinal (pH 7.4) fluids at 37 °C. Degradation products were quantitatively determined by HPLC (Lichrospher 60 RP select B column, 5 μm, 125 mm × 4 mm; mobile phase: methanol–water–acetic acid (60:39:1 v/v); flow rate: 0.6 ml/min; detection UV: 280 nm). In simulated gastric fluid (SGF) [6]-gingerol and [6]-shogaol underwent first-order reversible dehydration and hydration reactions to form [6]-shogaol and [6]-gingerol, respectively. The degradation was catalyzed by hydrogen ions and reached equilibrium at approximately 200 h. In simulated intestinal fluid (SIF) both [6]-gingerol and [6]-shogaol showed insignificant interconversion between one another. Addition of amino acids glycine, 3-amino propionic acid (β-alanine) and γ-amino butyric acid (GABA), and ammonium acetate at a range of concentrations of 0.05–0.5 mM had no effect on the rate of degradation of [6]-shogaol in SGF and 0.1 M HCl solution. However, at exceedingly high concentration (0.5 M) of ammonium acetate and glycine, significant amounts of [6]-shogaol ammonia and glycine adducts were detected. The degradation profile of [6]-gingerol and [6]-shogaol under simulated physiological conditions reported in this study will provide insight into the stability of these compounds when administered orally.

Dehydration behavior of natural cavansite: An in-situ FTIR and Raman spectroscopic study

The dehydration behavior of a natural cavansite from Poona (India) was investigated by in-situ FTIR and Raman spectroscopy. The thermal induced variations of the water molecule were followed as indicative of the dehydration process. The total mass loss (about 15.12%) occurred at least in four stages viz., 360 K (2.27%), 470 K (6.30%), 560 K (11.31%) and 760 K (15.11%). The observed spectral variations indicate that cavansite undergoes a completely reversible dehydration at about 500 K without significant structural changes. It completely dehydrates at around 775 K, above which it is in amorphous phase. Induced spectral variations also indicate that the water molecule coordinated with VO 5 group is weakly bonded and detached during early stages of dehydration.

Solution and Solid-State Preparation of 18-Crown-6 and 15-Crown-5 Adducts of Hydrogen Sulfate Salts and an Investigation of the Reversible Dehydration Processes

A new class of organic−inorganic complexes has been prepared by reaction in solution or by mechanical mixing of 15-Crown-5 or 18-Crown-6 ethers with MSO4 (M = Mn2+, Cd2+, Pb2+) and/or H2SO4 in stoichiometric amount. The complexes (15-Crown-5)[Mn(H2O)2(HSO4)2] (1), (15-Crown-5)[Cd(H2O)2(HSO4)2] (2), (15-Crown-5)[(H7O3)(HSO4)2]·H2O (3), (18-Crown-6)[Pb(HSO4)2] (4), and (18-Crown-6)[(H5O2)(HSO4)] (5) have been characterized by single-crystal X-ray diffraction. Compounds 1 and 2 undergo reversible water release−uptake processes, accompanied by a change in coordination at the metal centers; the dehydration and phase-transition processes have been investigated by DSC, TGA, and variable-temperature X-ray powder diffraction.

Facile Detection of Acyl and Peptidyl Intermediates on Thiotemplate Carrier Domains via Phosphopantetheinyl Elimination Reactions during Tandem Mass Spectrometry

With the emergence of drug resistance and the genomic revolution, there has been a renewed interest in the genes that are responsible for the generation of bioactive natural products. Secondary metabolites of one major class are biosynthesized at one or more sites by ultralarge enzymes that carry covalent intermediates on phosphopantetheine arms. Because such intermediates are difficult to characterize in vitro, we have developed a new approach for streamlined detection of substrates, intermediates, and products attached to a phosphopantetheinyl arm of the carrier site. During vibrational activation of gas-phase carrier domains, facile elimination occurs in benchtop and Fourier-transform mass spectrometers alike. Phosphopantetheinyl ejections quickly reduce >100 kDa megaenzymes to <1000 Da ions for structural assignment of intermediates at <0.007 Da mass accuracy without proteolytic digestion. This "top down" approach quickly illuminated diverse acyl intermediates on the carrier domains of the nonribosomal peptide synthetases (NRPSs) or polyketide synthases (PKSs) found in the biosynthetic pathways of prodigiosin, pyoluteorin, mycosubtilin, nikkomycin, enterobactin, gramicidin, and several proteins from the orphan pksX gene cluster from Bacillus subtilis. By focusing on just those regions undergoing covalent chemistry, the method delivered clean proof for the reversible dehydration of hydroxymethylglutaryl-S-PksL via incorporation of 2H or 18O from the buffer. The facile nature of this revised assay will allow diverse laboratories to spearhead their NRPS-PKS projects with benchtop mass spectrometers.

Supramolecular Architectures and Magnetic Properties of Coordination Polymers Based on Pyrazinedicarboxylato Ligands Showing Embedded Water Clusters

The synthesis, crystal structure, and magnetic behavior of nine transition-metal complexes based on pyrazine-2,5-dicarboxylato (pz25dc) and pyrazine-2,3-dicarboxylato (pz23dc) ligands are reported. The pz25dc ligand displays a bis-bidentate coordination mode, with the carboxylate groups almost coplanar with the pyrazine ring, to afford polymeric 1-D chains [Mn(1), Fe(2), Zn(3), and Cu(4 and 5)] and discrete dimeric entities [Mn(6)] when the 1,10-phenanthroline (phen) blocking ligand is used to avoid further polymerization. The nonplanar pz23dc ligand chelates to a unique copper center, while it bridges another one or two metal centers via the remaining carboxylate group, leading to 1-D polymeric chains (7), ladder chains (8), and sheets (9). The crystal packing of the metal-organic frameworks of compounds 4-9 generates voids which are occupied by assembled water molecules. The different water cluster patterns (tapes, four-membered discrete rings, and chains for compounds 6, 8, and 9, respectively) and their role in the cohesiveness of supramolecular architectures are analyzed. Thermogravimetric and variable-temperature X-ray powder diffraction studies have revealed the occurrence of reversible dehydration processes in compounds 6, 8, and 9. Furthermore, the magnetic behavior of these compounds has been studied in order to analyze the capability of the pyrazine ring to transmit magnetic interactions.

Synthesis, Characterization, and Separation Properties of Sn− and Ti−Silicate Umbite Membranes

Microporous stannosilicate (K2SnSi3O9·H2O) and titanosilicate (K2TiSi3O9·H2O) with an umbite structure have been prepared as continuous membranes in about 5 μm thick layers on porous α-alumina and TiO2 tubular supports by seeded hydrothermal synthesis. These membranes are able to separate H2 from N2, CO2, and propane with good selectivity. Some stability problems appeared probably related to the reversible dehydration of the membranes.

Reversible dehydration process in a novel three-dimensional covalent network based on pyrimidine-4,6-dionato bridging ligand

The novel metal-organic polymer [Zn(μ-pmdt)(H 2O)] n ( 1) ( pmdt = pyrimidine-4,6-dionate) exhibits an extended three-dimensional network with two crystallographically independent pmdt bridging ligands, one zinc(II) atom and a coordinated water molecule. The Zn(II) atoms are located at the centre of a distorted ZnN 2OOw tetrahedral chromophore. One of the pmdt ligands acts as tetradentate bridge linking four metal centers, while the other pmdt ligand shows a bidentate coordination mode bridging two metal centers. The compound shows a reversible dehydration process, involving a coordinated water molecule, to lead an amorphous anhydrous phase. This transition has been characterized by thermogravimetric and variable-temperature X-ray powder diffraction techniques.

Mild and Reversible Dehydration of Primary Amides with PdCl2 in Aqueous Acetonitrile.

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A 3D porous lanthanide–fumarate framework with water hexamer occupied cavities, exhibiting a reversible dehydration and rehydration procedure

[Sm2(fumarate)3(H2O)4] x 3 H2O, a new porous pillared layer framework with 0D cavities for the accommodation of chair-like hexameric water clusters, possesses three kinds of fumarate ligand with their two COO ends adopting different coordination modes and shows reversible de- and re-hydration behavior.

Reversible dehydration polymerization of terephthalate bridged [{Cu 2(2,2′-bpy) 2(tp)(H 2O) 3(NO 3)}·H 2O·NO 3] 2

The title compound is the first example of a molecular magnet sponge, which exhibits a carboxylate-assisted unique reversible dehydrative polymerization–rehydrative monomerization phenomenon.

Structure and Catalytic Properties of an Engineered Heterodimer of Enolase Composed of One Active and One Inactive Subunit

Enolase is a dimeric enzyme that catalyzes the interconversion of 2-phospho-D-glycerate and phosphoenolpyruvate. This reversible dehydration is effected by general acid-base catalysis that involves, principally, Lys345 and Glu211 (numbering system of enolase 1 from yeast). The crystal structure of the inactive E211Q enolase shows that the protein is properly folded. However, K345 variants have, thus far, failed to crystallize. This problem was solved by crystallization of an engineered heterodimer of enolase. The heterodimer was composed of an inactive subunit that has a K345A mutation and an active subunit that has N80D and N126D surface mutations to facilitate ion-exchange chromatographic separation of the three dimeric species. The structure of this heterodimeric variant, in complex with substrate/product, was obtained at 1.85 A resolution. The structure was compared to a new structure of wild-type enolase obtained from crystals belonging to the same space group. Asymmetric dimers having one subunit exhibiting two of the three active site loops in an open conformation and the other in a conformation having all three loops closed appear in both structures. The K345A subunit of the heterodimer is in the loop-closed conformation; its Calpha carbon atoms closely match those of the corresponding subunit of wild-type enolase (root-mean-squared deviation of 0.23 A). The kcat and kcat/Km values of the heterodimer are approximately half those of the N80D/N126D homodimer, which suggests that the subunits in solution are kinetically independent. A comparison of enolase structures obtained from crystals belonging to different space groups suggests that asymmetric dimers can be a consequence of the asymmetric positioning of the subunits within the crystal lattice.