Macroscopic and spectroscopic characterization of selenate, selenite, and chromate adsorption at the solid–water interface of γ-Al2O3

The interaction of selenate, selenite, and chromate with the hydrated surface of γ-Al₂O₃ was studied using a combination of macroscopic pH edge data, electrophoretic mobility measurements, and X-ray absorption spectroscopic analyses. The pH edge data show generally increased oxyanion adsorption with decreasing pH, and indicate ionic strength-(in)dependent adsorption of chromate and selenate across the pH range 4–9, and ionic strength-(in)dependent adsorption of selenite in this pH range. The adsorption of chromate peaks at pH 5.0, whereas for selenate and selenite no pH adsorption maxima are observed. Electrophoretic mobility measurements show that all three oxyanions decrease the zeta potential of γ-Al₂O₃ upon adsorption; however, only selenite decreased the pH_PZC of the γ-Al₂O₃ sorbent. EXAFS data indicate that selenite ions are coordinated in a bridging bidentate fashion to surface AlO₆ octahedra, whereas no second-neighbor Al scattering was observed for adsorbed selenate ions. Combined, the results presented here show that pH is a major factor in determining the extent of adsorption of selenate, selenite, and chromate on hydrated γ-Al₂O₃. The results point to substantial differences between these anions as to the mode of adsorption at the hydrated γ-Al₂O₃ surface, with selenate adsorbing as nonprotonated outer-sphere complexes, chromate forming a mixture of monoprotonated and nonprotonated outer-sphere adsorption complexes, and selenite coordinating as inner-sphere surface complexes in bridging configuration.     

Stereoselective synthesis of a MCHr1 antagonist

Melanin-concentrating hormone (MCH) is implicated in the feeding behavior in mammals affording a potential target to control overeating in people. Compound 1 (AMG 076) has been identified as a potent MCHr1 antagonist for the treatment of obesity. A synthesis suitable for the large-scale preparation of this lead candidate was developed to support preclinical studies. A Robinson annulation of benzylpiperidone and resolution of the desired enone from a mixture of the diastereomers afforded key intermediate 6 after a stereoselective hydrogenation. Subsequent Fischer indole synthesis with hydrazine 5 then provided the advanced intermediate, indole 2. Two complementary reductive amination strategies employing either aldehyde 3 or lactol 4 led to the synthesis of title compound 1.     

Trimerization of the HIV Transmembrane Domain in Lipid Bilayers Modulates Broadly Neutralizing Antibody Binding

The membrane‐proximal external region (MPER) of HIV gp41 is an established target of antibodies that neutralize a broad range of HIV isolates. To evaluate the role of the transmembrane (TM) domain, synthetic MPER‐derived peptides were incorporated into lipid nanoparticles using natural and designed TM domains, and antibody affinity was measured using immobilized and solution‐based techniques. Peptides incorporating the native HIV TM domain exhibit significantly stronger interactions with neutralizing antibodies than peptides with a monomeric TM domain. Furthermore, a peptide with a trimeric, three‐helix bundle TM domain recapitulates the binding profile of the native sequence. These studies suggest that neutralizing antibodies can bind the MPER when the TM domain is a three‐helix bundle and this presentation could influence the binding of neutralizing antibodies to the virus. Lipid‐bilayer presentation of viral antigens in Nanodiscs is a new platform for evaluating neutralizing antibodies.     

Heterologous Production of Fungal Maleidrides Reveals the Cryptic Cyclization Involved in their Biosynthesis

Fungal maleidrides are an important family of bioactive secondary metabolites that consist of 7, 8, or 9‐membered carbocycles with one or two fused maleic anhydride moieties. The biosynthesis of byssochlamic acid (a nonadride) and agnestadride A (a heptadride) was investigated through gene disruption and heterologous expression experiments. The results reveal that the precursors for cyclization are formed by an iterative highly reducing fungal polyketide synthase supported by a hydrolase, together with two citrate‐processing enzymes. The enigmatic ring formation is catalyzed by two proteins with homology to ketosteroid isomerases, and assisted by two proteins with homology to phosphatidylethanolamine‐binding proteins.     

A Simple Primary Amide for the Selective Recovery of Gold from Secondary Resources

Waste electrical and electronic equipment (WEEE) such as mobile phones contains a plethora of metals of which gold is by far the most valuable. Herein a simple primary amide is described that achieves the selective separation of gold from a mixture of metals typically found in mobile phones by extraction into toluene from an aqueous HCl solution; unlike current processes, reverse phase transfer is achieved simply using water. Phase transfer occurs by dynamic assembly of protonated and neutral amides with [AuCl₄]^? ions through hydrogen bonding in the organic phase, as shown by EXAFS, mass spectrometry measurements, and computational calculations, and supported by distribution coefficient analysis. The fundamental chemical understanding gained herein should be integral to the development of metal‐recovery processes, in particular through the use of dynamic assembly processes to build complexity from simplicity.     

Nitrosylation of Nitric‐Oxide‐Sensing Regulatory Proteins Containing [4Fe‐4S] Clusters Gives Rise to Multiple Iron–Nitrosyl Complexes

The reaction of protein‐bound iron–sulfur (Fe‐S) clusters with nitric oxide (NO) plays key roles in NO‐mediated toxicity and signaling. Elucidation of the mechanism of the reaction of NO with DNA regulatory proteins that contain Fe‐S clusters has been hampered by a lack of information about the nature of the iron‐nitrosyl products formed. Herein, we report nuclear resonance vibrational spectroscopy (NRVS) and density functional theory (DFT) calculations that identify NO reaction products in WhiD and NsrR, regulatory proteins that use a [4Fe‐4S] cluster to sense NO. This work reveals that nitrosylation yields multiple products structurally related to Roussin's Red Ester (RRE, [Fe₂(NO)₄(Cys)₂]) and Roussin's Black Salt (RBS, [Fe₄(NO)₇S₃]. In the latter case, the absence of ³²S/³⁴S shifts in the Fe?S region of the NRVS spectra suggest that a new species, Roussin's Black Ester (RBE), may be formed, in which one or more of the sulfide ligands is replaced by Cys thiolates.     

Effect of temperature on gradient reequilibration in reversed-phase liquid chromatography

The effect of mobile phase modifier and temperature on gradient reequilibration is examined using three different stationary phases. The stationary phases studied are a traditional C18 phase, a polar endcapped C18 phase, and an alkyl phase with a polar embedded group. It was observed that both temperature and choice of mobile phase organic modifier had an effect on gradient reequilibration volume on both the traditional C18 stationary phase and the polar endcapped phase. On both these phases, at any given temperature, the reequilibration volume was generally smaller when methanol was used as the mobile phase modifier as compared to acetonitrile. As the temperature is increased from 10 to 50 degrees C, significant reductions in reequilibration volume were observed with both mobile phase modifiers. In contrast, neither temperature nor choice of modifier appeared to have much effect on reequilibration volume when the polar embedded group stationary phase was considered.     

Characterisation of nicotine and related compounds using electrospray ionisation with ion trap mass spectrometry and with quadrupole time-of-flight mass spectrometry and their detection by liquid chromatography/electrospray ionisation mass spectrometry

Electrospray ionisation ion trap mass spectrometry (ESI-MS(n)) has been used to study the fragmentation patterns of nicotine and nine of its related compounds. From this study certain characteristic fragmentations are apparent with generally the pyrrolidine or piperidine ring being subject to chemical modifications. The structures of the product ions proposed for the ESI-MS(n) study have been supported by results from electrospray ionisation quadrupole time-of-flight mass spectrometry (ESI-QTOF-MS). Compounds with pyrrolidine and piperidine rings that possess an unsubstituted N atom have been shown to lose NH(3) at the MS(2) stage. Those compounds with N-methyl groups lose CH(3)NH(2) at the MS(2) stage. The loss of NH(3) or CH(3)NH(2) leaves the corresponding rings opened and this is followed by ring closure at the pyridine-2 carbon atom. Mono-N-oxides fragment in a similar way but the di-N-oxide can also fragment by cleavage of the bond between the pyridine and pyrrolidine rings. Cotinine also can undergo cleavage of this bond between the rings.This data therefore provides useful information on how substituents and the nature of the non-pyridine ring can affect the fragmentation patterns of nicotine and its related compounds. This information can be used in the characterisation of these compounds by liquid chromatography/electrospray ionization mass spectrometry (LC/ESI-MS) which results in the separation of nicotine and its related compounds with limits of detection (LODs) ranging from 15 to 105 ng/mL. The use of LC/ESI-MS to study nicotine-containing samples resulted in the simultaneous and unambiguous identification of seven of the compounds discussed in this paper: cotinine identified at retention time 12.5 min (with its [M+H](+) ion at m/z 177), nornicotine 16.0 min (m/z 149), anatabine 18.0 min (m/z 161), myosmine 18.5 min (m/z 147), anabasine 20.4 min (m/z 163), nicotine 22.2 min (m/z 163), and nicotyrine 31.4 min (m/z 159). For quality control of nicotine replacement therapy products, these nicotine impurities can be readily identified and determined at levels up to 0.3% for single impurities and up to 1.0% for total impurities.