Investigations of the optical and EPR spectra for VO2+ in LiKSO4 crystals

The optical spectra and EPR spectra (characterized by the spin-Hamiltonian parameters g(//), g(perpendicular), A(//) and A(perpendicular)) for the molecular ion VO2+ in LiKSO4 crystals are calculated from two microscopic theory methods, one of which is the complete diagonalization (of energy matrix) method (CDM) and the other is the perturbation theory method (PTM). The calculated three optical absorption bands and four spin-Hamiltonian parameters from the two methods are not only close to each other, but also in reasonable agreement with the experimental values. It appears that both theoretical methods are effective in the explanation of optical and EPR spectra for 3d1 ions in crystals. The negative signs of hyperfine structure constants A(//) and A(perpendicular) for VO2+ in LiKSO4 crystals are also suggested from the calculations.     

浅谈检验Fe~(2+)与Fe~(3+)的误区

空白试验证明,用浓度大于1mol/L的盐酸溶液做Fe~(3+)的提取液,或用过浓盐酸溶液酸化试液,盐酸中的Fe~(3+)都会给检验试液中的Fe~(3+)带来干扰;检验食品中的铁元素时,若铁是以Fe~(2+)形式存在,如果加入硝酸将其氧化为Fe~(3+),硝酸中Fe~(3+)会对检验试液中的Fe~(3+)带来干扰。     

Raman spectra and molecular structure of silicates

The frequencies of the strong Raman bands of silicates corresponding to the Si₂O ₅ ^2? complex anion and the SiO₂ molecule have been determined. This revealed the presence of these anions in silicates with double rings or double chains and various types of layers and the presence of SiO₂ molecules in silica modifications, feldspars, zeolites, and zircon group orthosilicates. A similarity between the Raman spectra of olivine group orthosilicates and garnet and phenacite group orthosilicates was found. This similarity was attributed to the existence of distorted tetrahedra in all of these groups, having disordered orientation in the garnet and phenacite groups.     

Theoretical investigation on the optical and EPR spectra for Cu2+-doped ZnO-CdS nanocomposites

The three optical absorption bands and EPR parameters of the [CuO₆]¹⁰⁻ center in the ZnO-CdS composite nanopowders are theoretically studied from the perturbation formulas based on the cluster approach. In the formulas, the contributions to EPR parameters arising from the ligand orbital and spin–orbit coupling interactions via covalence effect are considered. For the studied [CuO₆]¹⁰⁻ cluster, the Cu–O bond lengths are suggested to show a relative elongation ratio ρ (≈ 4.1%) along the z-axis due to Jahn–Teller effect. The defect models suggested in this work are different from the previous assumption that the impurity Cu²⁺ can replace the host Zn²⁺ site when it enters the lattices of the ΖnO and ΖnS nanocrystals, forming the tetrahedral [CuΧ₄]⁶⁻ clusters (Χ = O, S). The validity of the proposed model is discussed. The differences between the present calculations and the previous ones for the interstitial Cu²⁺ center in ZnO nanocrystals are analyzed in view of the dissimilar impurity behaviors due to the new composition CdS and distinct preparation conditions.     

Improved DFT calculation of Raman spectra of silicates

Very accurate vibrational spectra of silicates are obtained from DFT calculations if the appropriate Hamiltonian is used. Theoretical considerations suggest that the Hartree-Fock component of ACM1 hybrid functionals should be 1/6 instead of 1/4 for this class of compounds. When applied to the PBE functional this removes the scaling error of the calculated vibrational frequencies. Calculations using this PBE(n = 6) functional in combination with optimized Gaussian basis sets result in very small remaining deviations between observed and calculated Raman shifts, with standard uncertainties of ≈3.5 cm⁻¹, maximum deviations of ≈10 cm⁻¹, and no significant systematic trends. This has been confirmed for a wide range of silicate structures, for which high-quality Raman spectra have been published: forsterite α-Mg₂SiO₄ (nesosilicate), γ-Y₂Si₂O₇ (sorosilicate), K₂Ca₃Si₃O₁₀ (oligosilicate), K₂Ca₄Si₈O₂₁ (phyllosilicate), and α-quartz SiO₂ (tectosilictae).     

Interpreting conformational effects in protein nano-ESI-MS spectra

Nano-electrospray-ionization mass spectrometry (nano-ESI-MS) is employed here to describe equilibrium protein conformational transitions and to analyze the influence of instrumental settings, pH, and solvent surface tension on the charge-state distributions (CSD). A first set of experiments shows that high flow rates of N₂ as curtain gas can induce unfolding of cytochrome c (cyt c) and myoglobin (Mb), under conditions in which the stability of the native protein structure has already been reduced by acidification. However, it is possible to identify conditions under which the instrumental settings are not limiting factors for the conformational stability of the protein inside ESI droplets. Under such conditions, equilibrium unfolding transitions described by ESI-MS are comparable with those obtained by other established biophysical methods. Experiments with the very stable proteins ubiquitin (Ubq) and lysozyme (Lyz) enable testing of the influence of extreme pH changes on the ESI process, uncoupled from acid-induced unfolding. When HCl is used for acidification, Ubq and Lyz mass spectra do not change between pH~7 and pH 2.2, indicating that the CSD is highly characteristic of a given protein conformation and not directly affected by even large pH changes. Use of formic or acetic acid for acidification of Ubq solutions results in major spectral changes that can be interpreted in terms of protein unfolding as a result of the increased hydrophobicity of the solvent. On the other hand, Lyz, cyt c, and Mb enable direct comparison of protein CSD (corresponding to either the folded or the unfolded protein) in HCl or acetic acid solutions at low pH. The values of surface tension for these solutions differ significantly. Confirming indications already present in the literature, we observe very similar CSD under these solvent conditions for several proteins in either compact or disordered conformations. The same is true for comparison between water and water–acetic acid for folded cyt c and Lyz. Thus, protein CSD from water–acetic solutions do not seem to be limited by the low surface tension of acetic acid as previously suggested. This result could reflect a general lack of dependence of protein CSD on the surface tension of the solvent. However, it is also possible that the effect of acetic acid on the precursor ESI droplets is smaller than generally assumed.     

Zum System H2O2, Fe2+-, Fe3+-Ion

Ohne Zusammenfassung     

A new lawsone azo-dye for optical sensing of Fe3+ and Cu2+ and their DFT study

A new lawsone-based azo-dye 2-hydroxy-3-((pyridin-2-ylmethyl)diazenyl)naphthalene-1,4-dione (1) was synthesized and applied for sensing of metal ions. Receptor 1 showed selective fluorescent and colorimetric response for the detection of Cu²⁺ and Fe³⁺ over other tested metal ions. The fluorescence intensity of 1 was significantly quenched allowing detection of Fe³⁺ and Cu²⁺ down to 0.61 and 6.06 μM, respectively. The binding has been established by fluorescence spectroscopic method. Receptor 1 provided a 1?:?1 binding scaffold for recognition of Fe³⁺ and Cu²⁺ ions with the association constant of 3.33 × 10⁶ and 3.33 × 10⁵ M^?1, respectively. The B3LYP/6-31G/LANL2DZ method was employed for the optimization of 1 and 1·Fe³⁺ and 1·Cu²⁺.     

Simulating Nuclear subsystem rearrangement in the redox reaction between Fe2+ and Fe3+ ions

An approach that allows the numerical simulation of conformational rearrangements accompanying redox reactions in molecular systems is examined. The proposed method makes it possible on the basis of metadynamics to identify automatically the groups of atoms whose conformational motions give rise to changes in the redox properties of an investigated system. The method is used to simulate a classic model electron transfer reaction, i.e., the redox reaction between Fe²⁺ and Fe³⁺ ions in a solution. The effective activation energy of the reaction is reproduced quantitatively, and the reaction coordinate is determined. It is shown that this approach is promising for use in studying conformational changes that are associated with electron transport processes in complex molecular systems.     

Local tilting angles tau for Fe+ in Cd2+ site and Fe3+ in Si4+ site of CdSiP2 semiconductor

The EPR parameters (g factors, g(parallel), g(perdendicular) and zero-field splitting D) for Fe+ in Cd2+ site and Fe3+ in Si4+ site of CdSiP2 semiconductor are calculated from the distinct high-order perturbation formulas. From the calculations, the local tetragonal distortions and hence the local tilting angles tau (which are different from the corresponding host values) for both paramagnetic centers are estimated. The results are discussed.