Intercalation and dynamics of hydrated Fe<Superscript>2+</Superscript> in the vermiculites from Santa Olalla and Ojén

Although the intercalation of Fe³⁺ into layered phyllosicilicates—especially into smectites—attracted much attention in the past two decades, the information about Fe²⁺ loaded phyllosilicates is sparse. Here we present an investigation of the Fe²⁺ exchanged vermiculites from Santa Olalla and Ojén (Andalusia, Spain) by means of Mössbauer spectroscopy. The room temperature Mössbauer spectra are very similar to those of the starting compounds (Na forms) except for a decrease of the contribution of structural Fe³⁺ and a concomitant increase of the contribution of Fe²⁺ sites, indicating an internal redox process. The extent of this redox reaction is different for the two vermiculites. Thus, the intercalated Fe²⁺ acts as an electron mediator from the external medium to the structural Fe³⁺ ions. A new component attributable to intercalated Fe²⁺ is practically invisible in the room temperature Mössbauer spectra, but increases strongly and continuously during cooling to 4.2 K, where it is the dominant feature of the Mössbauer patterns. At 4.2 K, its quadruple splitting amounts to 3.31 mm/s, which is in excellent agreement with the quadrupole slitting of Fe²⁺ coordinated to six water molecules in a highly symmetric octahedral arrangement. The strong decrease of the Mössbauer–Lamb factor of this component with increasing temperature indicates a weak bonding of the Fe²⁺ in the interlayer space.     

Kinetic stability of water-dispersed oil droplets encapsulated in a polyelectrolyte multilayer shell

The original theoretical model of polyelectrolyte adsorption onto water-dispersed colloid particles is extended to the system of polydisperse droplets of sunflower oil. Polycation (poly(allylamine hydrochloride)) and polyanion (poly(sodium 4-styrenesulfonate)) are taken in the theoretically projected concentrations to perform Layer-by-Layer assembly of a multilayer shell on the surface of oil droplets preliminary stabilized with a protein emulsifier (bovine serum albumin). The velocity of gravitational separation in suspension of encapsulated oil droplets is theoretically predicted and experimentally measured depending on the coating shell's thickness, aiming to clarify the mechanism to control over the separation process. Combining the theory and experimental data, the mass density of a polyelectrolyte multilayer shell assembled in a Layer-by-Layer fashion is obtained. Polyelectrolyte multilayer coated oil droplets are characterized by means of ζ-potential, and particle size measurements, and visualized by scanning electron microscopy.     

Characterization of low-frequency modes in aqueous peptides using far-infrared spectroscopy and molecular dynamics simulation

Far-infrared spectroscopy was used to study the dynamics of three aqueous peptides having varied helicity. Experimental data were compared to the molecular dynamics simulated far-infrared absorbance spectrum derived from the dipole time correlation function. Vibrational density of state (VDOS) simulation was then used to analyze the contribution of different structural elements to the bands. Frozen aqueous peptide samples were studied in the frequency range between 325 and 540 cm(-1) where the ice absorbance is low. Three resonances were identified; band I centered at approximately 333 cm(-1), band II centered at approximately 380 cm(-1), and band III comprising two constituent bands at approximately 519 and 528 cm(-1). The peak height and frequency of the maximum absorbance of bands I and II varied depending on the helicity of the peptide. VDOS of the far-infrared absorbance spectrum confirmed that bands I and II were associated with the peptide backbone and that band III had both potential backbone and side chain components.     

Selective and cell-active inhibitors of the USP1/ UAF1 deubiquitinase complex reverse cisplatin resistance in non-small cell lung cancer cells

Ubiquitin-specific proteases (USPs) have in recent years emerged as a promising therapeutic target class. We identified selective small-molecule inhibitors against a deubiquitinase complex, the human USP1/UAF1, through quantitative high throughput screening (qHTS) of a collection of bioactive molecules. The top inhibitors, pimozide and GW7647, inhibited USP1/UAF1 noncompetitively with a K(i) of 0.5 and 0.7?μM, respectively, and displayed selectivity against a number of deubiquitinases, deSUMOylase, and cysteine proteases. The USP1/UAF1 inhibitors act synergistically with cisplatin in inhibiting cisplatin-resistant non-small cell lung cancer (NSCLC) cell proliferation. USP1/UAF1 represents a promising target for drug intervention because of its involvement in translesion synthesis and Fanconi anemia pathway?important for normal DNA damage response. Our results support USP1/UAF1 as a potential therapeutic target and provide an example of targeting the USP/WD40 repeat protein complex for inhibitor discovery.     

Interaction of 1,2,5-chalcogenadiazole derivatives with thiophenolate: hypercoordination with formation of interchalcogen bond versus reduction to radical anion

According to the DFT calculations, [1,2,5]thiadiazolo[3,4-c][1,2,5]thiadiazole (4), [1,2,5]selenadiazolo[3,4-c][1,2,5]thiadiazole (5), 3,4-dicyano-1,2,5-thiadiazole (6), and 3,4-dicyano-1,2,5-selenadiazole (7) have nearly the same positive electron affinity (EA). Under the CV conditions they readily produce long-lived π-delocalized radical anions (π-RAs) characterized by EPR. Whereas 4 and 5 were chemically reduced into the π-RAs with thiophenolate (PhS(-)), 6 did not react and 7 formed a product of hypercoordination at the Se center (9) isolated in the form of the thermally stable salt [K(18-crown-6)][9] (10). The latter type of reactivity has never been observed previously for any 1,2,5-chalcogenadiazole derivatives. The X-ray structure of salt 10 revealed that the Se-S distance in the anion 9 (2.722 ?) is ca. 0.5 ? longer than the sum of the covalent radii of these atoms but ca. 1 ? shorter than the sum of their van der Waals radii. According to the QTAIM and NBO analysis, the Se-S bond in 9 can be considered a donor-acceptor bond whose formation leads to transfer of ca. 40% of negative charge from PhS(-) onto the heterocycle. For various PhS(-)/1,2,5-chalcogenadiazole reaction systems, thermodynamics and kinetics were theoretically studied to rationalize the interchalcogen hypercoordination vs reduction to π-RA dichotomy. It is predicted that interaction between PhS(-) and 3,4-dicyano-1,2,5-telluradiazole (12), whose EA slightly exceeds that of 6 and 7, will lead to hypercoordinate anion (17) with the interchalcogen Te-S bond being stronger than the Se-S bond observed in anion 9.     

Quantitative and confirmative performance of liquid chromatography coupled to high-resolution mass spectrometry compared to tandem mass spectrometry

The quantitative and confirmative performance of two different mass spectrometry (MS) techniques (high-resolution MS and tandem MS) was critically compared. Evaluated was a new extraction and clean-up protocol which was developed to cover more than 100 different veterinary drugs at trace levels in a number of animal tissues and honey matrices. Both detection techniques, high-resolution mass spectrometry (HRMS) (single-stage Orbitrap instrument operated at 50 000 full width at half maximum) and tandem mass spectrometry (MS/MS) (quadrupole technology) were used to validate the method according to the EU Commission Decision 2002/657/EEC. Equal or even a slightly better quantitative performance was observed for the HRMS-based approach. Sensitivity is higher for unit mass resolution MS/MS if only a subset of the 100 compounds has to be monitored. Confirmation of suspected positive findings can be done by evaluating the intensity ratio between different MS/MS transitions, or by accurate mass based product ion traces (no precursor selection applied). MS/MS relies on compound-specific optimized transitions; hence the second, confirmatory transition generally shows relatively high ion abundance (fragmentation efficacy). This is often not the case in single-stage HRMS, since a generic (not compound-optimized) collision energy is applied. Hence, confirmation of analytes present at low levels is superior when performed by MS/MS. Slightly better precision, but poorer accuracy (fortified matrix extracts versus pure standard solution) of ion ratios were observed when comparing data obtained by HRMS versus MS/MS.     

Mass spectrometric stereoisomeric differentiation between α- and β-ascorbic acid 2-O-glucosides. Experimental and density functional theory study

L-Ascorbic acid and two distinct anomers, namely the α-D-glucopyranosyl and β-D-glucopyranosyl-(1→2)-L-ascorbic acid (stereoisomers), were studied within the scope of collision-induced dissociation (CID) experiments, performed by linear ion acceleration and collision with argon atoms inside a hexapole quadrupole hexapole ion beam guide, which is coupled to an ion cyclotron resonance (ICR) cell with a 12 Tesla magnet for high-resolution measurements. Loss of C(2)H(4)O(2) neutral from the [M-H](-) anion of L-ascorbic acid was observed. Density functional theory (DFT) calculations on the 6-311+G(2d,p)//6-31+G(d) level of theory reveal a new concerted mechanism for an intramolecular gas-phase rearrangement, through which the observed ejected neutral C(2)H(4)O(2) can take place. A similar rearrangement also occurs in the case of α- and β-D-glucopyranosyl-(1→2)-L-ascorbic acid. For the α isomer, only homolytic glycoside fragmentation was observed. For the β isomer, both homolytic and heterolytic glycoside cleavages were possible. The mechanisms behind all observed fragmentation pathways were fully understood by the implementation of accurate DFT calculations. Stereoisomeric differentiation between α and β isomers of the L-ascorbic acid-2-O-glucoside could be revealed by tandem mass spectrometry (MS/MS) experiments and were explained theoretically.     

Self-assembling zeolite crystals into uniformly oriented layers

We report important progress made in the synthesis of oriented functional layers of nanochannel materials by using coordination chemistry as a tool. Zeolite L (ZL) crystals have been arranged into oriented layers through the coordinative interactions between a functional organic linker (L) and metal cations used for connecting the different parts. As organic linker we used a terpyridyl ligand bearing a urea group and a reactive siloxane part. Two strategies that lead to monolayers with different properties are described. The first consists of reacting the siloxane group of ligand L with OH groups of the substrate (S), and selectively reacting the siloxane group of L with OH groups located at the base of the ZL crystals. Next, metal cations M(n+), for example, Zn(2+) or Cu(2+), are coordinated to the terpy group on the modified substrate. To this the modified ZL is added and coordinatively bound by the terpy(Mn(n+))terpy interaction, leading to oriented ZL layers. The second method consists of reacting substrate S and ligand L in the presence of a metal cation. A layer with reactive siloxane groups is formed on S to which the ZL crystals are bound by the reaction of the hydroxyl groups of their base. Zn(2+), Cu(2+), and lanthanide ions Eu(3+) and Tb(3+)have been tested successfully, all of them leading to high-quality ZL monolayers with open channels, accessible for accepting guests, oriented perpendicularly with respect to the surface of S.