Crown ethers at the aqueous solution-air interface: 1. Assignments and surface spectroscopy

The surface of aqueous solutions of 4-Nitro Benzo-15-Crown-5 (NB15C5) and Benzo-15-Crown-5 (B15C5) has been studied using the surface sensitive technique vibrational sum frequency spectroscopy (VSFS). The NO, CN, COC and CH vibrational modes of these compounds at the air-water interface as well as OH vibrational modes of the surface water hydrating this compound have been targeted in order to obtain molecular information about arrangement and conformation of the adsorbed crown ether molecules at the air-water interface. The CH(2) vibrational modes of crown ethers have been identified and found to be split due to interaction with ether oxygen. The spectra provide evidence for the existence of a protonated crown complex moiety at the surface leading to the appearance of strongly ordered water species. The interfacial water species are influenced by the resulting charged interface and by the strong Zundel polarizability due to tunneling of the proton species between equivalent sites within the crown ring.     

Multiple solutions for Neumann and periodic problems with singular ?-Laplacian

We use the critical point theory for convex, lower semicontinuous perturbations of C¹-functionals to establish existence of multiple radial solutions for some one parameter Neumann problems involving the operator . Similar results for periodic problems are also provided.     

Closely embedded Kre?n spaces and applications to Dirac operators

Motivated by energy space representation of Dirac operators, in the sense of K. Friedrichs, we recently introduced the notion of closely embedded Kre?n spaces. These spaces are associated to unbounded selfadjoint operators that play the role of kernel operators, in the sense of L. Schwartz, and they are special representations of induced Kre?n spaces. In this article we present a canonical representation of closely embedded Kre?n spaces in terms of a generalization of the notion of operator range and obtain a characterization of uniqueness. When applied to Dirac operators, the results differ according to a mass or a massless particle in a dramatic way: in the case of a particle with a nontrivial mass we obtain a dual of a Sobolev type space and we have uniqueness, while in the case of a massless particle we obtain a dual of a homogenous Sobolev type space and we lose uniqueness.     

A metrological approach for the assessment of selenium status in human serum

This work addresses a metrological approach for the assessment of Se status in humans in terms of serum selenomethionine (SeMet). The quantification of SeMet was carried out using a primary method of chemical analysis, namely species-specific isotope dilution (SSID) in combination with HPLC coupled to collision/reaction cell inductively coupled plasma-mass spectrometry. SeMet was released from the serum selenoalbumin (a seleno-containing protein where SeMet is randomly incorporated) by enzymatic hydrolysis of the whole serum. This study is a follow-up of the analytical method development reported previously, and it focuses primarily on the evaluation of the uncertainty budget and the main uncertainty sources for SeMet determination in three commercial serums, namely BCR-637 (certified for total Se) and two serum standards, SERONORM level 1 (SERO-L1) and 2 (SERO-L2) (with indicative concentrations of total Se). The metrological approach reported here could be considered as a pilot study in terms of metrological determination of SeMet in human serum, hence being suitable for method validation and inter-laboratory comparison.     

Analysis of human blood plasma and hen egg white by chiroptical spectroscopic methods (ECD, VCD, ROA)

Chiroptical methods are widely used in structural and conformational analyses of biopolymers. The application of these methods to investigations of biofluids would provide new avenues for the molecular diagnosis of protein-misfolding diseases. In this work, samples of human blood plasma and hen egg white were analyzed using a combination of conventional and chiroptical methods: ultraviolet absorption/electronic circular dichroism (UV/ECD), Fourier transform infrared absorption/vibrational circular dichroism (FTIR/VCD), and Raman scattering/Raman optical activity (Raman/ROA). For comparison, the main components of these substances—human serum albumin (HSA) and ovalbumin (Ova)—were also analyzed by these methods. The ultraviolet region of the ECD spectrum was analyzed using the CDNN CD software package to evaluate the secondary structures of the proteins. The UV/ECD, FTIR/VCD, and Raman/ROA spectra of the substances were quite similar to those of the corresponding major proteins, while some differences were also detected and explained. The conclusions drawn from the FTIR/VCD and Raman/ROA data were in good agreement with the secondary structures calculated from ECD. The results obtained in this work demonstrate that the chiroptical methods used here can be applied to analyze not only pure protein solutions but also more complex systems, such as biological fluids.

Bimetallic Anionic Organic Frameworks with Solid-State Cation Conduction for Charge Storage Applications

A new phosphonate-based anionic bimetallic organic framework, with the general formula of A₄−Zn−DOBDP (wherein A is Li⁺ or Na⁺, and DOBDP⁶⁻ is the 2,5-dioxido-1,4-benzenediphosphate ligand) is prepared and characterized for energy storage applications. With four alkali cations per formula unit, the A₄−Zn−DOBDP MOF is found to be the first example of non-solvated cation conducting MOF with measured conductivities of 5.4×10⁻⁸ S cm⁻¹ and 3.4×10⁻⁸ S cm⁻¹ for Li₄- and Na₄- phases, indicating phase and composition effects of Li⁺ and Na⁺ shuttling through the channels. Three orders of magnitude increase in ionic conductivity is further attained upon solvation with propylene carbonate, placing this system among the best MOF ionic conductors at room temperature. As positive electrode material, Li₄−Zn−DOBDP delivers a specific capacity of 140 mAh g⁻¹ at a high average discharge potential of 3.2 V (vs. Li⁺/Li) with 90 % of capacity retention over 100 cycles. The significance of this research extends from the development of a new family of electroactive phosphonate-based MOFs with inherent ionic conductivity and reversible cation storage, to providing elementary insights into the development of highly sought yet still evasive MOFs with mixed-ion and electron conduction for energy storage applications.     

Simultaneous speciation analysis of glutathione peroxidase,selenoprotein P and selenoalbumin in human serum by tandem anion exchange-affinity HPLC and on-line isotope dilution ICP-quadrupole MS

A method based on anion exchange (AE) and affinity (AF)-HPLC (AE-AF-HPLC) hyphenated to inductively coupled plasma-(quadrupole) mass spectrometry (ICP-QMS) was developed for the speciation analysis of selenoprotein P (SelP), glutathione peroxidase (GPx) and selenoalbumin (SeAlb) in human serum. AE-HPLC is proposed here for the on-line alleviation of Cl and Br spectral interferences on ⁷⁷Se (⁴⁰Ar³⁷Cl) and ⁸²Se (⁸¹Br¹H). Separation of GPx, SelP and SeAlb by AE-AF-HPLC was obtained within a total chromatographic runtime of <20 min. On-line (post-column) isotope dilution (ON-ID) and on-line external calibration (ON-EC)-ICP-QMS were used for the quantification of Se in GPx, SelP and SeAlb. ON-EC using a Se-L-cystine standard was shown to be a suitable approach for the routine simultaneous speciation analysis of serum GPx, SelP and SeAlb. The method validation was carried out by direct ICP-sector field MS determination of Se in GPx, SelP and SeAlb fractions collected after AE-AF-HPLC separation. In addition, the method accuracy for the determination of total protein-bound Se was assessed by analyzing a human serum reference material (BCR-637) certified for total Se content. Figure A methodology for the alleviation of Cl and Br interferences in the accurate simultaneous speciation analysis of glutathione peroxidase, selenoprotein P and selenoalbumin in human serum by affinity HPLC coupled on-line with ICP-quadrupole MS is proposed. This approach may be particularly useful for clinical laboratories that only have an ICP-quadrupole MS without a collision cell, or that lack an expensive ICP-SFMS (high-resolution) instrument     

Structure of sodiated polyglycines

The intrinsic folding of peptides about a sodium ion has been investigated in detail by using infrared multiple photon dissociation (IRMPD) spectroscopy and a combination of theoretical methods. IRMPD spectroscopy was carried out on sodiated polyglycines G(n)-Na(+) (n=2-8), in both the fingerprint and N-H/O-H stretching regions. Interplay between experimental and computational approaches (classical and quantum) enables us to decipher most structural details. The most stable structures of the small peptides up to G(6)-Na(+) maximize metal-peptide interactions with all peptidic C=O groups bound to sodium. In addition, direct interactions between peptide termini are possible for G(6)-Na(+) and larger polyglycines. The increased flexibility of larger peptides leads to more complex folding and internal peptide structuration through γ or β turns. A structural transition is found to occur between G(6)-Na(+) and G(7)-Na(+), leading to a structure with sodium coordination that becomes tri-dimensional for the latter. This transition was confirmed by H/D exchange experiments on G(n)-Na(+) (n=3-8). The most favorable hydrogen-bonding pattern in G(8)-Na(+) involves direct interactions between the peptide termini and opens the way to salt-bridge formation; however, there is only good agreement between experimental and computational data over the entire spectral range for the charge solvation isomer.     

Spectroscopic properties and ab initio calculations on the structure of erbium–zinc-borate glasses and glass ceramics

Glasses in the (Er₂O₃)_x·(B₂O₃)_(60 ? x)·(ZnO)₄₀ system (0 ≤ x ≤ 15 mol%) have been prepared by the melt quenching technique. X-ray diffraction, FTIR spectroscopy, UV-VIS spectroscopy and ab initio calculations studies have been employed to study the role of Er₂O₃ content on the structure of the investigated glass system.X-ray diffraction and infrared spectra of the glasses reveal that the B–O–B bonds may be broken with the creation of new non-bridging oxygen ions facilitating the formation of Er–O–B linkages. The excess of oxygen can be accommodated in the network by the conversion of sp² planar [BO₃] units to the more stable sp³ [BO₄] tetrahedral structural units. The linkages of the [BO₄] structural units can polymerize in [B₃O₉]^? 9 cyclic trimeric ions which will produce the ErBO₃ crystalline phase. An increase of the efficiency corresponding to the ⁴I_15/2 state to ⁴I_11/2 state (4f–4f) transitions of Er^+ 3 ions was observed for the erbium oxide richest glasses.Ab initio calculations on the structure of the matrix network show the thermodynamic instability of the [BO₄], [ZnO₄] and [Zn₄O] structural units. Formation of three-coordination oxygens was necessary to compensate shortage of oxygens from zinc ions.