Spectroscopic and electrochemical characterization of an aqua ligand exchange and oxidatively induced deprotonation in diiron complexes

Reaction of the unsymmetrical phenol ligand 2-((bis(2-pyridylmethyl)amino)methyl)-6-(((2-pyridylmethyl)benzylamino)methyl)-4-methylphenol (HL-Bn) or its 2,6-dichlorobenzyl analogue (HL-BnCl(2)) with Fe(H(2)O)(6)(ClO(4))(2) in the presence of disodium m-phenylenedipropionate (Na(2)(mpdp)) followed by exposure to atmosphere affords the diiron(II,III) complexes [Fe(2)(L-Bn)(mpdp)(H(2)O)](ClO(4))(2) and [Fe(2)(L-BnCl(2))(mpdp)(CH(3)OH)](ClO(4))(2), respectively. The latter complex has been characterized by X-ray crystallography. It crystallizes in the monoclinic system, space group P2(1)/n, with a = 13.3095(14) A, b = 20.1073(19) A, c = 19.4997(19) A, alpha = 90 degrees, beta = 94.471(2) degrees, gamma = 90 degrees, V = 5202.6(9) A(3), and Z = 4. The structure of the compound is very similar to that of [Fe(2)(L-Bn)(mpdp)(H(2)O)](BPh(4))(2) determined earlier, except for the replacement of a water by a methanol on the ferrous site. Magnetic measurements of [Fe(2)(L-Bn)(mpdp)(H(2)O)](BPh(4))(2) reveal that the two high-spin Fe ions are moderately antiferromagnetically coupled (J = -3.2(2) cm(-)(1)). Upon dissolution in acetonitrile the terminal ligand on the ferrous site is replaced by a solvent molecule. The acetonitrile-water exchange has been investigated by various spectroscopic techniques (UV-visible, NMR, M?ssbauer) and electrochemistry. The substitution of acetonitrile by water is clearly evidenced by M?ssbauer spectroscopy by a reduction of the quadrupole splitting value from 3.14 to 2.41 mm/s. In addition, it causes a 210 mV downshift of the oxidation potential of the ferrous site and a similar reduction of the stability domain of the mixed-valence state. Exhaustive electrolysis of a solution of [Fe(2)(L-Bn)(mpdp)(H(2)O)](2+) shows that the aqua diferric species is not stable and undergoes a chemical reaction which can be partly reversed by reduction to the mixed-valent state. This and other electrochemical observations suggest that upon oxidation of the diiron center to the diferric state the aqua ligand is deprotonated to a hydroxo. This hypothesis is supported by M?ssbauer spectroscopy. Indeed, this species possesses a large quadrupole splitting value (DeltaE(Q) >or= 1.0 mm.s(-)(1)) similar to that of analogous complexes with a terminal phenolate ligand. This study illustrates the drastic effects of aqua ligand exchange and deprotonation on the electronic structure and redox potentials of diiron centers.     

DFT Simulations as Valuable Tool to Support NMR Characterization of Halide Perovskites: the Case of Pure and Mixed Halide Perovskites

Solid state NMR spectroscopy is swiftly emerging as useful tool to characterize the structure, composition and dynamic properties of lead halide perovskites. On the other hand, interpretation of solid state NMR signatures is often challenging, because of the potential presence of many overlapping signals in small range of chemical shifts, hence complicating the extraction of detailed structural features. Here, we demonstrate the reliability of periodic Density Functional Theory in providing theoretical support for the NMR characterization of halide perovskite compounds, considering nuclei with spin I=1/2. For light ¹H and ¹³C nuclei, we predict NMR chemical shifts in good agreement with experiment, further highlighting the effects of motional narrowing. Accurate prediction of the NMR response of ²⁰⁷Pb nuclei is comparably more challenging, but we successfully reproduce the downshift in frequency when changing the halide composition from pure iodine to pure bromine. Furthermore, we confirm NMR as ideal tool to study mixed halide perovskite compounds, currently at the limelight for tandem solar cells and color-tunable light emission.     

Discovery and validation of urinary exposure markers for different plant foods by untargeted metabolomics

While metabolomics is increasingly used to investigate the food metabolome and identify new markers of food exposure, limited attention has been given to the validation of such markers. The main objectives of the present study were to (1) discover potential food exposure markers (PEMs) for a range of plant foods in a study setting with a mixed dietary background and (2) validate PEMs found in a previous meal study. Three-day weighed dietary records and 24-h urine samples were collected three times during a 6-month parallel intervention study from 107 subjects randomized to two distinct dietary patterns. An untargeted UPLC-qTOF-MS metabolomics analysis was performed on the urine samples, and all features detected underwent strict data analyses, including an iterative paired t test and sensitivity and specificity analyses for foods. A total of 22 unique PEMs were identified that covered 7 out of 40 investigated food groups (strawberry, cabbages, beetroot, walnut, citrus, green beans and chocolate). The PEMs reflected foods with a distinct composition rather than foods eaten more frequently or in larger amounts. We found that 23 % of the PEMs found in a previous meal study were also valid in the present intervention study. The study demonstrates that it is possible to discover and validate PEMs for several foods and food classes in an intervention study with a mixed dietary background, despite the large variability in such a dataset. Final validation of PEMs for intake of foods should be performed by quantitative analysis.

High‐Yield Formation of Substituted Tetracyanobutadienes from Reaction of Ynamides with Tetracyanoethylene

A high‐yielding sequence of [2+2] cycloaddition–retroelectrocyclization of ynamides with tetracyanoethylene (TCNE) is described. The reaction provided tetracyanobutadiene (TCBD) species, which were characterized by various techniques. DFT and TD‐DFT calculations were also performed to complement experimental findings.     

Stability of rocksalt (111) polar surfaces: beyond the octopole

Stable polar oxide surfaces must be simultaneously electrostatically compensated and in thermodynamic equilibrium with the environment. As a paradigm, the MgO(111)-p(2x2) reconstructed surface is shown to involve combinations of Mg-covered terminations with peculiar insulating electronic structure, favored in O-poor conditions, and the O-terminated octopole, stabler in more O-rich environments. Such a picture, which could not have been foreseen by either experiments or simulations separately, goes beyond the Wolf model and reconciles the theory with the experimental data taken in variable thermodynamic conditions.     

Deposition of silica thin films formed by sol–gel method

Deposition of silica thin films on silicon wafer was investigated by in situ mass measurements with a microbalance configured for dip coating. Mass change was recorded with respect to deposition time when the substrate was fully immersed in the silica sol. Mass gain during deposition was higher than predicted from monolayer coverage of silica nano particles. This implied that deposition was facilitated by gelling of the nanoparticles on the substrate. The rate of deposition was enhanced by increasing the particle concentration in the sol and by decreasing the particle size from 12 to 5 nm. Increasing the salt concentration of the silica sol at constant pH enhanced the deposition of the silica particles. Reducing the pH of the sol from 10 to 6 decreased the deposition rate due to aggregation of the primary silica particles.     

Facetting and (n × 1) reconstructions of SrTiO3(1 1 0) surfaces

(n × 1) reconstructions and facetting of the (1 1 0) polar surface of SrTiO₃ are studied by means of a combination of shell model and density functional calculations. The polarity compensation can be achieved through the formation of {1 0 0} nano-facets, which play a crucial role in the reconstruction process. The behaviors of various possible terminations (Sr, Ti, and O) are analyzed, as well as their atomic structure and energetics. Their stability in different chemical environments is discussed, with respect to previous formulations and experimental results. The Sr-terminated surface tends to expose large facets, while the TiO and O terminations are marginally stabilized or even destabilized by (n × 1) reconstructions, respectively. Trend to facetting results from a subtle competition between the thermodynamic stability of the ideal non stoichiometric (n × 1) surfaces, and huge atomic relaxations that contribute to the lowering of the surface energy differently for each termination.     

The Cancer Genetics Network: recruitment results and pilot studies

OBJECTIVE: The National Cancer Institute established the Cancer Genetics Network (CGN) to support collaborative investigations into the genetic basis of cancer susceptibility, explore mechanisms to integrate this new knowledge into medical practice, and identify ways of addressing the associated psychosocial, ethical, legal, and public health issues. SUBJECTS AND METHODS: The CGN has developed the complex infrastructure required to support the projects, including the establishment of guidelines and policies, uniform methods, standard questionnaires to be used by all of the centers, and a standard format for submission of data to the Informatics Center. Cancer patients and their family members have been invited to enroll and be included in a pool of potential study participants. The Information Technology Group is responsible for support of the design, implementation, and maintenance of the multicenter Network-wide research protocols. RESULTS: As of January 2004, the CGN contained data on 23,995 probands (participants) and 425,798 family members. As a resource for cancer genetic studies, the CGN has a large number of probands and first-degree relatives with and without cancer and with multiple ethnicities. Different study designs can be used including case-control, case-case, and family studies. CONCLUSIONS: The unique resources of the CGN are available for studies on cancer genetic susceptibility, translational research, and behavioral research. The CGN is now at a point where approved collaborators may have access to enrolled patients and their families for special studies, as well as to the clinical, environmental and family cancer history data banked in the Informatics Center.     

Development and validation of a liquid chromatography/electrospray ionization tandem mass spectrometry method for the quantification of latanoprost free acid in rabbit aqueous humor and ciliary body

A rapid, selective and sensitive method for quantification of latanoprost free acid in rabbit aqueous humor (AH) and ciliary body (CB) using reverse phase-high performance liquid chromatography coupled with electrospray ionization (ESI)-mass spectrometry/mass spectrometry has been developed and validated. Quantification in AH and CB was achieved by stable isotope dilution employing tetra-deuterated analog of latanoprost free acid, used as internal standard. Sample preparation was based on protein precipitation with methanol in AH, and on liquid extraction with a mixture of ethyl acetate and isopropanol 60:40 (v/v) in CB. Elution was achieved on an octylsilica (C8) column, using an isocratic elution method. Detection was performed on a triple quadrupole mass spectrometer, using ESI in positive ion selected reaction monitoring mode. Calibration curves were linear in the validated concentration ranges of 10-160 ng/mL in AH and 80-1280 ng/g in CB. The accuracy and precision values, obtained from three different sets of quality control samples, each analyzed in triplicate on three different days, were within the generally accepted criteria for analytical methods (< 15%). The limit of detection was 30.66 pg/mL in AH and 237.75 pg/g in CB. The assay proved to be accurate and precise when applied to the in vivo study of latanoprost free acid in rabbit AH and CB after single administration of an eye drops containing latanoprost.