MCD spectroscopy of transition metal ions in fluoride crystals

Absorption spectra of crystals of KZn _x Fe_1-x F₃ (0·006 < 1 - x < 0·07) have been measured in order to obtain information about Fe²⁺-F^--Fe²⁺ pairs. However, by means of high resolution MCD spectroscopy, it has been established that very small amounts of Fe³⁺ are present in the crystals. The absorption spectra then show features which are due to (a) Fe²⁺, (b) Fe³⁺ and (c) Fe²⁺, Fe³⁺ pairs. In addition to the characteristic Jahn-Teller split ⁵ T _2g → ⁵ E_g band of Fe²⁺, there is a weak, spin-allowed, vibronically assisted transition near 40 000 cm^-1, which is assigned to ⁵ T _2g (d⁶) → ⁵ A _1g (d⁵s). The MCD of this band is consistent with this assignment. The remainder of the visible and near ultra-violet absorption intensity is associated with Fe²⁺/Fe³⁺ pairs. Most of the bands are due to excitations localized on the Fe²⁺ though some weaker ones are assigned as excitations to ⁴ A _1g on the Fe³⁺ of the pair. There is also a strong, broad underlying absorption probably due to t _2g → t _2g charge transfer in the pair.     

Water-soluble magnetic nanoparticles with biologically active stabilizers

We present the results of the interaction of iron oxide nanoparticles with some biologically active surfactants, namely, oleic acid and cytotoxic alkanolamine derivatives. Physico-chemical properties, as magnetization, magnetite concentration and particle diameter, of the prepared magnetic samples were studied. The nanoparticle size of 11 nm for toluene magnetic fluid determined by TEM is in good agreement with the data obtained by the method of magnetogranulometry. In vitro cytotoxic effect of water-soluble nanoparticles with different iron oxide:oleic acid molar ratio were revealed against human fibrosarcoma and mouse hepatoma cells. In vivo results using a sarcoma mouse model showed observable antitumor action.     

Nonstationary mass transfer under particle magnetophoresis in diluted ferrocolloids

Nonstationary mass transfer under nanoparticle magnetophoresis in diluted ferrocolloids is experimentally investigated. Measurements performed by using the real time holography technique indicate a difference between the concentration boundary layer parameters found in the experiment and those calculated by using the approximation of nonstationary magnetodiffusion of colloidal particles. We suppose that the final stationary concentration distribution in the boundary layer is caused by a magnetic convection. Approximative calculations of concentration magnetic convection give the mass transfer relaxation time close to the exprimentally determined one.Work is supported by the European Community, Grant ERB 3510PL92-5206     

Optical spectra of synechocystis and spinach photosystem II preparations at 1.7 K: identification of the D1-pheophytin energies and stark shifts

We report and compare highly resolved, simultaneously recorded absorption and CD spectra of active Photosystem II (PSII) samples in the range 440-750 nm. From an appropriately scaled comparison of spinach membrane fragment (BBY) and PSII core spectra, we show that key features of the core spectrum are quantitatively represented in the BBY data. PSII from the cyanobacterium Synechocystis 6803 display spectral features in the Qy region of comparable width (50-70 cm(-1) fwhm) to those seen in plant PSII but the energies of the resolved features are distinctly different. A comparison of spectra taken of PSII poised in the S1QA and S2QA(-) redox states reveals electrochromic shifts largely attributable to the influence of QA(-) on Pheo(D1). This allows accurate determinations of the Pheo(D1) Qy absorption positions to be at 685.0 nm for spinach cores, 685.8 nm for BBY particles, and 683.0 nm for Synechocystis. These are discussed in terms of earlier reports of the Pheo(D1) energies in PSII. The Qx transition of Pheo(D1) undergoes a blue shift upon Q(A) reduction, and we place a lower limit of 80 cm(-1) on this shift in plant material. By comparing the magnitude of the Stark shifts of the Qx and Qy bands of Pheo(D1), the directions of the transition-induced dipole moment changes, Deltamu(x) and Deltamu(y), for this functionally important pigment could be determined, assuming normal magnitudes of the Deltamu's. Consequently, Deltamu(x) and Deltamu(y) are determined to be approximately orthogonal to the directions expected for these transitions. Low-fluence illumination experiments at 1.7 K resulted in very efficient formation of QA(-). This was accompanied by cyt b(559) oxidation in BBYs and carotenoid oxidation in cores. No chlorophyll oxidation was observed. Our data allow us to estimate the quantum efficiency of PSII at this temperature to be of the order 0.1-1. No Stark shift associated with the S1-to-S2 transition of the Mn cluster is evident in our samples. The similarity of Stark data in plants and Synechocystis points to minimal interactions of Pheo(D1) with nearby chloropyll pigments in active PSII preparations. This appears to be at variance with interpretations of experiments performed with inactive solubilized reaction-center preparations.     

A ligand-field analysis of the trensal (H(3)trensal = 2,2',2' '-tris(salicylideneimino)triethylamine) ligand. An application of the angular overlap model to lanthanides

The spectral and geometric trends of Ln(trensal) complexes (H(3)trensal = 2,2',2' '-tris(salicylideneimino)triethylamine) along the lanthanide series are analyzed. Low-temperature polarized absorption and luminescence spectra are reported for nine of the complexes with transitions suitable for analysis. Both the angular and radial geometry variations as a function of the lanthanide ion are quantified. The structural parameters are related to the trend in the ligand field found from an analysis of the f-f transitions. The ligand-field analysis is fitted globally across the whole series accounting for the contraction of the f orbitals as a function of atomic number. This study establishes the utility of describing the ligand field of f electrons within the one-electron operator approach of the angular overlap model.     

Superparamagnetic iron oxide/oleic acid nanoparticles with immobilized organosilicon derivatives of N‐(2‐hydroxyethyl)tetrahydroisoquinoline: synthesis,morphology and interaction with normal and tumour cells

Superparamagnetic iron oxide/oleic acid nanoparticles bearing lipid‐like organosilicon N‐(2‐hydroxyethyl)‐1,2,3,4‐tetrahydroisoquinoline derivatives have been synthesized with the aim of their potential biomedical application. X‐ray diffraction analysis, Dynamic light‐scattering measurements, method of magnetogranulometry and some others have been employed to investigate the morphology and properties of the nanoparticles synthesized. The magnetic core diameter of mixed covered nanoparticles ranged between 4.8 and 9.6 nm. The magnetization analyses showed that the particles are superparamagnetic at room temperature. In vitro cell cytotoxicity and intracellular NO generation caused by the water magnetic solution of nanoparticles possessing cytotoxic organosilicon heterocyclic choline analogue, namely N‐(2‐dimethyl‐n‐hexadecylsiloxyethyl)‐N‐methyl‐1,2,3,4‐tetrahydroisoquinolinium iodide, was examined in relation to monolayer human fibrosarcoma (HT‐1080) and mouse hepatoma (MG‐22A) tumour cell lines and normal mouse fibroblasts (NIH 3T3). The biological studies have revealed its selective cytotoxicity in tumour cells and strong effect on MG‐22A cell morphology. Incorporation of the synthesized nanoparticles into cells was observed. Copyright © 2013 John Wiley & Sons, Ltd.     

Cobalt-doped cadmium selenide colloidal nanowires

Co(2+)-doped CdSe colloidal nanowires with tunable size and dopant concentration have been prepared by a solution-liquid-solid (SLS) approach for the first time. These doped nanowires exhibit anomalous photoluminescence temperature dependence in comparison with undoped nanowires.     

Spectral hole-burning and magnetic circular dichroism of matrix-isolated copper phthalocyanine

Persistent spectral hole-burning in the Q-band region is reported for a concentrated (≈ 2 × 10⁻² mol l⁻¹) matrix of copper phthalocyanine in solid Ar at 1.6 K. Hole-burning occurs with a quantum efficiency of ≈ 10⁻⁶ and can be reversed by annealing at ≈ 28 K. Vibrational side holes allow determination of excited-state frequencies. A hole-burning mechanism involving triplet-state charge separation followed by rapid electron back-transfer is proposed. Temperature dependence of the MCD and the difference between MCD spectra taken before and after irradiation indicate that the excited state is split by crystal-field and spin-orbit interactions.     

Magneto-Optical Investigation of the Exchange-Coupled Dimer Cs(3)Mo(2)Br(9)

The electronic spectrum of the confacial bioctahedral complex Cs(3)Mo(2)Br(9) has been investigated by single-crystal absorption, Zeeman, and MCD spectroscopies. A total of seven distinct band regions were resolved and assigned to transitions essentially within the t(2)(2)t(2)(2) configuration that arises when the pair of t(2)(z)() orbitals in the t(2)(3)t(2)(3) configuration is decoupled by strong Mo-Mo sigma bonding. The excited state separations, and in particular the orbital g values, are sensitive to Mo-Mo pi bonding and show clearly that the pi bonding is weaker in the bromide than in the chloride complex.