Uranyl Formate Research Articles

Reactions of gas-phase uranyl formate/acetate anions: reduction of carboxylate ligands to aldehydes by intra-complex hydride attack.

In a previous study, electrospray ionization, collision-induced dissociation (CID), and gas-phase ion-molecule reactions were used to create and characterize ions derived from homogeneous precursors composed of a uranyl cation (UVIO22+) coordinated by either formate or acetate ligands [E. Perez, C. Hanley, S. Koehler, J. Pestok, N. Polonsky and M. Van Stipdonk, Gas phase reactions of ions derived from anionic uranyl formate and uranyl acetate complexes, J. Am. Soc. Mass Spectrom., 2016, 27, 1989-1998]. Here, we describe a follow-up study of anionic complexes that contain a mix of formate and acetate ligands, namely [UO2(O2C-CH3)2(O2C-H)]- and [UO2(O2C-CH3)(O2C-H)2]-. Initial CID of either anion causes decarboxylation of a formate ligand to create carboxylate-coordinated U-hydride product ions. Subsequent CID of the hydride species causes elimination of acetaldehyde or formaldehyde, consistent with reactions that include intra-complex hydride attack upon bound acetate or formate ligands, respectively. Density functional theory (DFT) calculations reproduce the experimental observations, including the favored elimination of formaldehyde over acetaldehyde by hydride attack during CID of [UO2(H)(O2C-CH3)(O2C-H)]-. We also discovered that MSn CID of the acetate-formate complexes leads to generation of the oxyl-methide species, [UO2(O)(CH3)]-, which reacts with H2O to generate [UO2(O)(OH)]-. DFT calculations support the observation that formation of [UO2(O)(OH)]- by elimination of CH4 is favored over H2O addition and rearrangement to create [UO2(OH)2(CH3)]-.

Visualization of Necroptotic Cell Death through Transmission Electron Microscopy.

Transmission electron microscopy (TEM) is an all-in-one tool to visualize the complex systems of any specimen that is 1nm in size or smaller. The current chapter provides detailed guidelines for imaging morphological changes during programmed cell necrosis using TEM as a single-step methodology. In this protocol, a novel aldehyde dehydrogenase inhibitor is used to induce cell programmed necrosis in ovarian cancer cell lines (A2780 and SKOV3). This process is followed by gradient dehydration with ethanol, chemical fixation, sampled grid preparation, and staining with 0.75% uranyl formate. Following fixation and grid preparation, cells are imaged using TEM. The resulting images reveal morphological changes consistent with necrotic morphology, including swelling of cells and organelles, appearance of vacuoles, and plasma membrane rupture followed by leakage of cellular contents. The current approach allows a single-step methodology for characterization of cell-programmed necrosis in cells based on morphology.

Can uranyl complexes encapsulate to carbon nanotubes? A periodic DFT study

Periodic density functional theory (DFT)-based calculations were carried out on a series of uranyl complexes encapsulated within single walled (SW)-CNT to understand their encapsulation affinities. We find that uranyl-aqua complex $$([\hbox {UO}_{2}(\hbox {H}_{2}\hbox {O})_{5}]^{2+}$$ ) binds stronger as compared to uranyl-hydroxo-complex $$([\hbox {UO}_{2}(\hbox {OH})_{4}]^{2-}$$ ) due to the variable overall charge of the complex. Further, binding affinities of uranyl formate complexes with different formate stoichiometries (1:1, 1:2 and 1:3) with SW-CNT are considered. Here again, due to variable charges, cationic mono-‘formate-uranyl $$([\hbox {UO}_{2}(\hbox {FM})(\hbox {H}_{2}\hbox {O})_{3}]^{1+})$$ complex binds stronger as compared to anionic tri-formate uranyl $$([\hbox {UO}_{2}(\hbox {FM})_{3}]^{1-})$$ . Further, due to the very weak binding commonly found in $$[\hbox {UO}_{2}(\hbox {FM})_{3}]^{1-}$$ to CNT, the tubular ends of SW-CNT are sealed with functionalized $$\hbox {C}_{36}$$ fullerene. The binding affinity of uranyl complex is not improved when $$\hbox {C}_{36}$$ fullerene is used to seal to the SW-CNT as compared to its unsealed counterpart. However, upon functionalizing (at the hub carbon) the $$\hbox {C}_{36}$$ cork, the binding affinity of $$[\hbox {UO}_{2}(\hbox {FM})_{3}]^{1-}$$ is larger inside the CNT due to favorable hydrogen bonding interactions with the uranyl oxygens. Our findings are consistent with the experimental observations which will help to design novel nanomaterials for nuclear waste management processes. The use of functionalized fullerene as removable corks which can seal single walled carbon nanotubes has the ability to bind uranyl complexes very efficiently is revealed through density functional theory based calculations.

Negative Staining and Transmission Electron Microscopy of Bacterial Surface Structures.

Negative staining is an essential and versatile staining technique in transmission electron microscopy that can be employed for visualizing bacterial cell morphology, size, and surface architecture at high resolution. Bacteria are usually transferred by passive electrostatic adsorption from suspensions in physiological saline onto suitable hydrophilic support films on electron microscopic grids. There they are contrasted, or "stained," by heavy metal ions in solution such as tungsten, uranyl, molybdate, or vanadate compounds. Here, I describe how to visualize the interaction between the bacterial M1 protein and complement factors C1q and C3 on the surface of group A streptococcus by negative staining with uranyl formate on carbon support films. The methodology should be generally applicable to the study of a large number of other bacteria-protein interactions.

Gas Phase Reactions of Ions Derived from Anionic Uranyl Formate and Uranyl Acetate Complexes.

The speciation and reactivity of uranium are topics of sustained interest because of their importance to the development of nuclear fuel processing methods, and a more complete understanding of the factors that govern the mobility and fate of the element in the environment. Tandem mass spectrometry can be used to examine the intrinsic reactivity (i.e., free from influence of solvent and other condensed phase effects) of a wide range of metal ion complexes in a species-specific fashion. Here, electrospray ionization, collision-induced dissociation, and gas-phase ion-molecule reactions were used to create and characterize ions derived from precursors composed of uranyl cation (UVIO22+) coordinated by formate or acetate ligands. Anionic complexes containing UVIO22+ and formate ligands fragment by decarboxylation and elimination of CH2=O, ultimately to produce an oxo-hydride species [UVIO2(O)(H)]-. Cationic species ultimately dissociate to make [UVIO2(OH)]+. Anionic complexes containing acetate ligands exhibit an initial loss of acetyloxyl radical, CH3CO2•, with associated reduction of uranyl to UVO2+. Subsequent CID steps cause elimination of CO2 and CH4, ultimately to produce [UVO2(O)]-. Loss of CH4 occurs by an intra-complex H+ transfer process that leaves UVO2+ coordinated by acetate and acetate enolate ligands. A subsequent dissociation step causes elimination of CH2=C=O to leave [UVO2(O)]-. Elimination of CH4 is also observed as a result of hydrolysis caused by ion-molecule reaction with H2O. The reactions of other anionic species with gas-phase H2O create hydroxyl products, presumably through the elimination of H2. Graphical Abstract ᅟ.

Structural Studies Reveal the Functional Modularity of the Scc2-Scc4 Cohesin Loader.

The remarkable accuracy of eukaryotic cell division is partly maintained by the cohesin complex acting as a molecular glue to prevent premature sister chromatid separation. The loading of cohesin onto chromosomes is catalyzed by the Scc2-Scc4 loader complex. Here, we report the crystal structure of Scc4 bound to the N terminus of Scc2 and show that Scc4 is a tetratricopeptide repeat (TPR) superhelix. The Scc2 N terminus adopts an extended conformation and is entrapped by the core of the Scc4 superhelix. Electron microscopy (EM) analysis reveals that the Scc2-Scc4 loader complex comprises three domains: a head, body, and hook. Deletion studies unambiguously assign the Scc2N-Scc4 as the globular head domain, whereas in vitro cohesin loading assays show that the central body and the hook domains are sufficient to catalyze cohesin loading onto circular DNA, but not chromatinized DNA in vivo, suggesting a possible role for Scc4 as a chromatin adaptor.

(C2H5)4N][U2O4(HCOO)5], an ammonium uranyl formate framework showing para- to ferro-electric transition: synthesis, structures, and properties.

We report an ammonium uranyl formate framework of formula [(C2H5)4N][U2O4(HCOO)5], prepared by using components of tetraethylammonium, uranyl, and formate. The compound possesses a layered structure of anionic uranyl-formate wavy sheets and intercalated (C2H5)4N(+) cations. The sheet consists of pentagonal bipyramidal uranyl cations connected by equatorial anti-anti and anti-syn HCOO(-) bridges, and it has a topology of 3(3)·4(3)·5(4) made of edge-sharing square and triangle grids. The high-temperature (HT) phase belongs to the chiral but nonpolar tetragonal space group P42(1)m. In the structure, one HCOO(-) is 2-fold disordered, showing a flip motion between the two anti-syn orientations. On cooling, this flip motion slowed and finally froze, leading to a phase transition at ∼200 K. The low-temperature (LT) structure is monoclinic and polar in space group P2(1); the cations shift, and the layers slide. Especially, the concerted and net shifts of the ammonium cations toward the -b direction, with respect to the anionic sheets, result in an estimated spontaneous polarization of 0.86 μC cm(-2) in LT. The phase transition is thus para- to ferro-electric, in Aizu notation 42mF2, accompanied by significant, anisotropic dielectric anomalies, with a quite significant thermal hysteresis. Variable-temperature luminescent spectroscopy and differential scanning calorimetry confirmed the transition and provided further information. The structure-property relationship is established.

Formic acid interaction with the uranyl(vi) ion: structural and photochemical characterization

Complex formation between the uranyl(VI) ion and formic acid was studied by infrared absorption (IR) and X-ray absorption (EXAFS) spectroscopy as well as density functional theory (DFT) calculations. In contrast to the acetate ion which forms exclusively a bidentate complex with uranyl(VI), the formate ion binds to uranyl(VI) in a unidentate fashion. The photochemistry of the uranyl(VI)-formic acid system was explored by DFT calculations and photoreduction of uranyl(VI) in the presence of formic acid was found to occur via an intermolecular process, that is, hydrogen abstraction from hydrogenformate by the photo-excited uranyl(VI). There is no photo-induced decarboxylation of uranyl(VI) formate via an intramolecular process, presumably due to lack of a C=C double bond.

The fibrillogenic L178H variant of apolipoprotein A-I forms helical fibrils

A number of amyloidogenic variants of apoA-I have been discovered but most have not been analyzed. Previously, we showed that the G26R mutation of apoA-I leads to increased β-strand structure, increased N-terminal protease susceptibility, and increased fibril formation after several days of incubation. In vivo, this and other variants mutated in the N-terminal domain (residues 26 to ∼90) lead to renal and hepatic accumulation. In contrast, several mutations identified within residues 170 to 178 lead to cardiac, laryngeal, and cutaneous protein deposition. Here, we describe the structural changes in the fibrillogenic variant L178H. Like G26R, the initial structure of the protein exhibits altered tertiary conformation relative to wild-type protein along with decreased stability and an altered lipid binding profile. However, in contrast to G26R, L178H undergoes an increase in helical structure upon incubation at 37°C with a half time (t1/2) of about 12 days. Upon prolonged incubation, the L178H mutant forms fibrils of a diameter of 10 nm that ranges in length from 30 to 120 nm. These results show that apoA-I, known for its dynamic properties, has the ability to form multiple fibrillar conformations, which may play a role in the tissue-specific deposition of the individual variants.

Funnel-like Hexameric Assembly of the Periplasmic Adapter Protein in the Tripartite Multidrug Efflux Pump in Gram-negative Bacteria

Gram-negative bacteria expel diverse toxic chemicals through the tripartite efflux pumps spanning both the inner and outer membranes. The Escherichia coli AcrAB-TolC pump is the principal multidrug exporter that confers intrinsic drug tolerance to the bacteria. The inner membrane transporter AcrB requires the outer membrane factor TolC and the periplasmic adapter protein AcrA. However, it remains ambiguous how the three proteins are assembled. In this study, a hexameric model of the adapter protein was generated based on the propensity for trimerization of a dimeric unit, and this model was further validated by presenting its channel-forming property that determines the substrate specificity. Genetic, in vitro complementation, and electron microscopic studies provided evidence for the binding of the hexameric adapter protein to the outer membrane factor in an intermeshing cogwheel manner. Structural analyses suggested that the adapter covers the periplasmic region of the inner membrane transporter. Taken together, we propose an adapter bridging model for the assembly of the tripartite pump, where the adapter protein provides a bridging channel and induces the channel opening of the outer membrane factor in the intermeshing tip-to-tip manner.

Morphology and structure of lipoproteins revealed by an optimized negative-staining protocol of electron microscopy

Plasma lipoprotein levels are predictors of risk for coronary artery disease. Lipoprotein structure-function relationships provide important clues that help identify the role of lipoproteins in cardiovascular disease. The compositional and conformational heterogeneity of lipoproteins are major barriers to the identification of their structures, as discovered using traditional approaches. Although electron microscopy (EM) is an alternative approach, conventional negative staining (NS) produces rouleau artifacts. In a previous study of apolipoprotein (apo)E4-containing reconstituted HDL (rHDL) particles, we optimized the NS method in a way that eliminated rouleaux. Here we report that phosphotungstic acid at high buffer salt concentrations plays a key role in rouleau formation. We also validate our protocol for analyzing the major plasma lipoprotein classes HDL, LDL, IDL, and VLDL, as well as homogeneously prepared apoA-I-containing rHDL. High-contrast EM images revealed morphology and detailed structures of lipoproteins, especially apoA-I-containing rHDL, that are amenable to three-dimensional reconstruction by single-particle analysis and electron tomography.

Actin Binding by Hip1 (Huntingtin-interacting Protein 1) and Hip1R (Hip1-related Protein) Is Regulated by Clathrin Light Chain

The huntingtin-interacting protein family members (Hip1 and Hip1R in mammals and Sla2p in yeast) link clathrin-mediated membrane traffic to actin cytoskeleton dynamics. Genetic data in yeast have implicated the light chain subunit of clathrin in regulating this link. To test this hypothesis, the biophysical properties of mammalian Hip1 and Hip1R and their interaction with clathrin light chain and actin were analyzed. The coiled-coil domains (clathrin light chain-binding) of Hip1 and Hip1R were found to be stable homodimers with no propensity to heterodimerize in vitro. Homodimers were also predominant in vivo, accounting for cellular segregation of Hip1 and Hip1R functions. Coiled-coil domains of Hip1 and Hip1R differed in their stability and flexibility, correlating with slightly different affinities for clathrin light chain and more markedly with effects of clathrin light chain binding on Hip protein-actin interactions. Clathrin light chain binding induced a compact conformation of both Hip1 and Hip1R and significantly reduced actin binding by their THATCH domains. Thus, clathrin is a negative regulator of Hip-actin interactions. These observations necessarily change models proposed for Hip protein function.

Trace detection and differentiation of uranyl(VI) ion cast films utilizing aligned Ag nanorod SERS substrates

Aligned Ag nanorod arrays prepared by oblique angle vapor deposition (OAD) were utilized to observe the SERS response for cast films of adsorbed uranyl ion complexes. These nanorod arrays consisted of preferentially aligned and tilted cylindrically shaped nanorods (average nanorod length = 858 nm). Routine SERS spectra of cast films of uranyl nitrate resulted in 0.87 pg of material analyzed with a detection limit estimated at 0.87 fg of adsorbed uranyl nitrate. The main spectral feature observed was a strong, broad peak centered at 700 cm −1 assigned to the ν 1 symmetric stretch of the uranyl ion, ν s(UO 2). The complex shape of this band is attributed to multiple uranyl complexes adsorbed onto the Ag surface. Uranyl nitrate cast films formed from ethanol solutions were more uniform and had stronger adsorption to the Ag surface compared to films formed from aqueous solutions. Differentiation of uranyl ion cast films formed from four different uranyl systems (i.e., uranyl nitrate hexahydrate, uranyl acetate dihydrate, uranyl formate monohydrate, and uranyl chloride trihydrate) was accomplished using univariate spectral analysis as well as Partial Least Squares Discriminant Analysis (PLSDA). A simple PLSDA calibration was able to correctly classify 27 SERS spectra of unknown uranyl ion cast films based on the type of anionic ligand present.

Parametric Investigation of Laser-Induced Fluorescence of Solid-State Uranyl Compounds

The combination of remote/standoff sensing and laser-induced fluorescence (LIF) spectroscopy shows potential for detection of uranyl (UO2(2+)) compounds. Uranyl compounds exhibit characteristic emission in the 450-600 nm (22,200 to 16,700 cm(-1)) spectral region when excited by wavelengths in the ultraviolet or in the short-wavelength portion of the visible spectrum. We report a parametric study of the effects of excitation wavelength [including 532 nm (18,797 cm(-1)), 355 nm (28,169 cm(-1)), and 266 nm (37,594 cm(-1))] and excitation laser power on solid-state uranium compounds. The uranium compounds investigated include uranyl nitrate, uranyl sulfate, uranyl oxalate, uranium dioxide, triuranium octaoxide, uranyl acetate, uranyl formate, zinc uranyl acetate, and uranyl phosphate. We observed the characteristic uranyl fluorescence spectrum from the uranium compounds except for uranium oxide compounds (which do not contain the uranyl moiety) and for uranyl formate, which has a low fluorescence quantum yield. Relative uranyl fluorescence intensity is greatest for 355 nm excitation, and the order of decreasing fluorescence intensity with excitation wavelength (relative intensity/laser output) is 355 nm > 266 nm > 532 nm. For 532 nm excitation, the emission spectrum is produced by two-photon excitation. Uranyl fluorescence intensity increases linearly with increasing laser power, but the rate of fluorescence intensity increase is different for different emission bands.

Two uranyl-organic frameworks with formic acid. A novel example of a uranyl-based nanotubular assemblage

Reaction of uranyl nitrate with formic acid in the presence of DABCO or NMe4OH under hydrothermal conditions gave two novel uranyl-organic frameworks. When templated by H-DABCO+ counter-ions, uranyl formate crystallizes as ribbons including μ3-oxo and μ2- and μ3-hydroxo ions. In one experiment with NMe4OH, a nanotubular material was obtained instead of the more usual two- or three-dimensional uranyl formates, with an inner tubule diameter of ca. 6Å.

Kinetics and electrochemical studies of uranium in acetate and formate media by cyclic voltammetry

SummaryThe cyclic voltammetric behavior of uranyl ion was investigated at hanging mercury drop electrode in perchlorate supporting electrolyte. The standard heterogeneous electron transfer rate constant “ks” for the reduction of uranyl ion in perchlorate medium was (2.74±0.03)×10−3cm s−1while in acetate and formate medium the value ofkswas (2.83±0.02)×10−3and (2.66±0.02)×10−3cm s−1, respectively. The effect of temperature on the values ofkswas investigated and thermodynamic constants ΔH*, ΔS* and ΔG298* were evaluated. The values of ΔH*, ΔS*; and ΔG298* were 8.06±0.03 kJ mol−1, −23.42±0.05 J mol−1K−1and 15.02±0.07 kJ mol−1in simple perchlorate medium and 3.67±0.02 kJ mol−1, −38.04±0.05 J mol−1K−1, and 15.01±0.03 kJ mol−1in acetate medium and 0.79±0.02 kJ mol−1, −48.24±0.04 J mol−1K−1and 15.17±0.02 kJ mol−1in formate medium, respectively. The thermodynamic data showed that the process of reduction of uranyl ion at hanging mercury drop electrode was endothermic and non-spontaneous. The stability constants of uranyl acetate and uranyl formate were calculated from an analysis of the shift in peak potential data. The logβ1and logβ2values for 1:1 and 1:2 uranyl acetate complexes were 2.67±0.04 and 4.71±0.01, respectively. The values of logβ1and logβ2of uranyl formate complex were 1.61±0.02 and 2.57±0.01, respectively, which are reported for the first time.

COMP Acts as a Catalyst in Collagen Fibrillogenesis

We have previously reported that COMP (cartilage oligomeric matrix protein) is prominent in cartilage but is also present in tendon and binds to collagens I and II with high affinity. Here we show that COMP influences the fibril formation of these collagens. Fibril formation in the presence of pentameric COMP was much faster, and the amount of collagen in fibrillar form was markedly increased. Monomeric COMP, lacking the N-terminal coiled-coil linker domain, decelerated fibrillogenesis. The data show that stimulation of collagen fibrillogenesis depends on the pentameric nature of COMP and not only on collagen binding. COMP interacts primarily with free collagen I and II molecules, bringing several molecules to close proximity, apparently promoting further assembly. These assemblies further join in discrete steps to a narrow distribution of completed fibril diameters of 149 +/- 16 nm with a banding pattern of 67 nm. COMP is not found associated with the mature fibril and dissociates from the collagen molecules or their early assemblies. However, a few COMP molecules are found bound to more loosely associated molecules at the tip/end of the growing fibril. Thus, COMP appears to catalyze the fibril formation by promoting early association of collagen molecules leading to increased rate of fibrillogenesis and more distinct organization of the fibrils.

Functional and Structural Characterization of a Prokaryotic Peptide Transporter with Features Similar to Mammalian PEPT1

The ydgR gene of Escherichia coli encodes a protein of the proton-dependent oligopeptide transporter (POT) family. We cloned YdgR and overexpressed the His-tagged fusion protein in E. coli BL21 cells. Bacterial growth inhibition in the presence of the toxic phosphonopeptide alafosfalin established YgdR functionality. Transport was abolished in the presence of the proton ionophore carbonyl cyanide p-chlorophenylhydrazone, suggesting a proton-coupled transport mechanism. YdgR transports selectively only di- and tripeptides and structurally related peptidomimetics (such as aminocephalosporins) with a substrate recognition pattern almost identical to the mammalian peptide transporter PEPT1. The YdgR protein was purified to homogeneity from E. coli membranes. Blue native-polyacrylamide gel electrophoresis and transmission electron microscopy of detergent-solubilized YdgR suggest that it exists in monomeric form. Transmission electron microscopy revealed a crown-like structure with a diameter of approximately 8 nm and a central density. These are the first structural data obtained from a proton-dependent peptide transporter, and the YgdR protein seems an excellent model for studies on substrate and inhibitor interactions as well as on the molecular architecture of cell membrane peptide transporters.

Nonribosomal Synthesis of Fengycin on an Enzyme Complex Formed by Fengycin Synthetases

Fengycin, a lipopeptidic antibiotic, is synthesized nonribosomally by five fengycin synthetases (FenC, FenD, FenE, FenA, and FenB) in Bacillus subtilis F29-3. This work demonstrates that these fengycin synthetases interlock to form a chain, which coils into a 14.5-nm structure. In this chain, fengycin synthetases are linked in the order FenC-FenD-FenE-FenA-FenB by interactions between the C-terminal region of an upstream enzyme and the N-terminal region of its downstream partner enzyme, with their amino acid activation modules arranged colinearly with the amino acids in fengycin. This work also reveals that fengycin is synthesized on this fengycin synthetase chain, explaining how fengycin is synthesized efficiently and accurately. The results from this investigation demonstrate that forming a peptide synthetase complex is crucial to nonribosomal peptide synthesis.

Acceleration of Amyloid β-Peptide Aggregation by Physiological Concentrations of Calcium

Alzheimer disease is characterized by the accumulation of aggregated amyloid beta-peptide (Abeta) in the brain. The physiological mechanisms and factors that predispose to Abeta aggregation and deposition are not well understood. In this report, we show that calcium can predispose to Abeta aggregation and fibril formation. Calcium increased the aggregation of early forming protofibrillar structures and markedly increased conversion of protofibrils to mature amyloid fibrils. This occurred at levels 20-fold below the calcium concentration in the extracellular space of the brain, the site at which amyloid plaque deposition occurs. In the absence of calcium, protofibrils can remain stable in vitro for several days. Using this approach, we directly compared the neurotoxicity of protofibrils and mature amyloid fibrils and demonstrate that both species are inherently toxic to neurons in culture. Thus, calcium may be an important predisposing factor for Abeta aggregation and toxicity. The high extracellular concentration of calcium in the brain, together with impaired intraneuronal calcium regulation in the aging brain and Alzheimer disease, may play an important role in the onset of amyloid-related pathology.