Surface Complexation Modeling of Eu(III) and U(VI) Interactions with Graphene Oxide

Graphene oxide (GO) has great potential for actinide removal due to its extremely high sorption capacity, but the mechanism of sorption remains unclear. In this study, the carboxylic functional group and an unexpected sulfonate functional group on GO were characterized as the reactive surface sites and quantified via diffuse layer modeling of the GO acid/base titrations. The presence of sulfonate functional group on GO was confirmed using elemental analysis and X-ray photoelectron spectroscopy. Batch experiments of Eu­(III) and U­(VI) sorption to GO as the function of pH (1–8) and as the function of analyte concentration (10–100, 000 ppb) at a constant pH ≈ 5 were conducted; the batch sorption results were modeled simultaneously using surface complexation modeling (SCM). The SCM indicated that Eu­(III) and U­(VI) complexation to carboxylate functional group is the main mechanism for their sorption to GO; their complexation to the sulfonate site occurred at the lower pH range and the complexation of Eu­(III) to sulfonate site are more significant than that of U­(VI). Eu­(III) and U­(VI) facilitated GO aggregation was observed with high Eu­(III) and U­(VI) concentration and may be caused by surface charge neutralization of GO after sorption

The Laser-Induced Blue State of Bacteriorhodopsin: Mechanistic and Color Regulatory Roles of Protein−Protein Interactions, Protein−Lipid Interactions, and Metal Ions

In this paper we characterize the mechanistic roles of the crystalline purple membrane (PM) lattice, the earliest bacteriorhodopsin (BR) photocycle intermediates, and divalent cations in the conversion of PM to laser-induced blue membrane (LIBM; λmax = 605 nm) upon irradiation with intense 532 nm pulses by contrasting the photoconversion of PM with that of monomeric BR solubilized in reduced Triton X-100 detergent. Monomeric BR forms a previously unreported colorless monomer photoproduct which lacks a chromophore band in the visible region but manifests a new band centered near 360 nm similar to the 360 nm band in LIBM. The 360 nm band in both LIBM and colorless monomer originates from a Schiff base-reduced retinyl chromophore which remains covalently linked to bacterioopsin. Both the PM→LIBM and monomer→colorless monomer photoconversions are mediated by similar biphotonic mechanisms, indicating that the photochemistry is localized within single BR monomers and is not influenced by BR−BR interactions. The excessively large two-photon absorptivities (≥106 cm4 s molecule-1photon-1) of these photoconversions, the temporal and spectral characteristics of pulses which generate LIBM in high yield, and an action spectrum for the PM→LIBM photoconversion all indicate that the PM→LIBM and Mon→CMon photoconversions are both mediated by a sequential biphotonic mechanism in which is the intermediate which absorbs the second photon. The purple→blue color change results from subsequent conformational perturbations of the PM lattice which induce the removal of Ca2+ and Mg2+ ions from the PM surface

Trindenyl Trimolybdenum and Tritungsten Complexes: Crystal Structure of (trindenyl)[(OC)₃W–W(CO)₃]W(CO)₃Bn

Trindenyl trimolybdenum and tritungsten complexes, <i>syn,syn,anti</i>-Td­[M­(CO)₃R]₃ (Td = dihydro-1<i>H</i>-trindene trianion; M = Mo, W; R = methyl, benzyl, <i>p</i>-xylyl), have been prepared where two M­(CO)₃R groups are forced into close proximity by bonding to the same side of the trindenyl ligand. Intramolecular Mo–Mo and W–W bonds form readily either photochemically or thermally between the two <i>syn</i>-M­(CO)₃ groups of Td­[M­(CO)₃R]₃, exclusive of any intermolecular M–M bond formation. The intramolecular W–W bond-forming reaction of Td­[W­(CO)₃benzyl]₃, as enforced by the trindenyl ligand, is 148 times faster than the intermolecular W–W bond-forming reaction of (cyclopentadienyl)­W­(CO)₃benzyl. The crystal structure of the W–W product, Td­[(OC)₃W–W­(CO)₃]­W­(CO)₃benzyl, was determined: orthorhombic, <i>Pn</i>2₁<i>a</i>, <i>a</i> = 29.188(8) Å, <i>b</i> = 10.387(3) Å, <i>c</i> = 9.599(3) Å, <i>V</i> = 2910.2(15) ų, <i>Z</i> = 4, R1 = 3.93%. The W–W bond length of 3.276(2) Å is among the longest W–W bonds reported. The trindenyl ligand is twisted from planarity by 19.1°, which allows the carbonyl ligands on the adjacent tungsten atoms to be staggered

Trindenyl Trimolybdenum and Tritungsten Complexes: Crystal Structure of (trindenyl)[(OC)₃W–W(CO)₃]W(CO)₃Bn

Trindenyl trimolybdenum and tritungsten complexes, <i>syn,syn,anti</i>-Td­[M­(CO)₃R]₃ (Td = dihydro-1<i>H</i>-trindene trianion; M = Mo, W; R = methyl, benzyl, <i>p</i>-xylyl), have been prepared where two M­(CO)₃R groups are forced into close proximity by bonding to the same side of the trindenyl ligand. Intramolecular Mo–Mo and W–W bonds form readily either photochemically or thermally between the two <i>syn</i>-M­(CO)₃ groups of Td­[M­(CO)₃R]₃, exclusive of any intermolecular M–M bond formation. The intramolecular W–W bond-forming reaction of Td­[W­(CO)₃benzyl]₃, as enforced by the trindenyl ligand, is 148 times faster than the intermolecular W–W bond-forming reaction of (cyclopentadienyl)­W­(CO)₃benzyl. The crystal structure of the W–W product, Td­[(OC)₃W–W­(CO)₃]­W­(CO)₃benzyl, was determined: orthorhombic, <i>Pn</i>2₁<i>a</i>, <i>a</i> = 29.188(8) Å, <i>b</i> = 10.387(3) Å, <i>c</i> = 9.599(3) Å, <i>V</i> = 2910.2(15) ų, <i>Z</i> = 4, R1 = 3.93%. The W–W bond length of 3.276(2) Å is among the longest W–W bonds reported. The trindenyl ligand is twisted from planarity by 19.1°, which allows the carbonyl ligands on the adjacent tungsten atoms to be staggered