Phase transitions in Cs5(HSO4)2(H2PO4)3 crystal

The symmetry (sp. gr.I $\bar 4$ 3d) and lattice parameters have been determined for the first time for Cs₅(H₂SO₄)₂(H₂PO₄)₃ crystals in the temperature range from 172 to 390 K. The thermal and optical properties of crystals, as well as their conductivity, have been investigated at elevated temperatures. It is shown that a crystal heated to T = 365 K undergoes a phase transition with symmetry lowering to the tetragonal phase (with the parameters a = 4.965(1) Å and c = 5.016(1) Å), while at T ≈ 390 K a phase transition to the cubic phase is presumably observed. With a decrease in temperature, a phase transition without a change in symmetry occurs at T = 240 K.     

Pluronic L61 accelerates flip-flop and transbilayer doxorubicin permeation

It has recently been found that Pluronics (block copolymers of ethylene oxide, EO, and propylene oxide, PO) favor the permeability and accumulation of anthracycline antibiotics, for example doxorubicin (Dox), in tumor cells. In an effort to understand these results, the interaction of EO(2)/PO(32)/EO(2) (Pluronic L61) with unilamellar egg yolk vesicles (80-100 nm in diameter) was examined. A partition coefficient K(p)=[Pl](membrane)/[Pl](water)=45 was determined. This corresponds to adsorption of about 20 polymer molecules to the surface of each vesicle in a 20 microM polymer solution. Despite this rather weak adsorption, Pluronic has a substantial effect upon the transmembrane permeation rate of Dox and upon the phospholipid flip-flop rate within the bilayers. Thus, the Dox permeation rate increases threefold and the flip-flop rate increases sixfold in 20 microM Pluronic. The two rates increase linearly with the amount of adsorbed polymer. The obvious ability of Pluronics to increase the mobility of membrane components may have important biomedical consequences.     

New Approaches in Broadband Fiber-Optical Interferometry for Optical Coherent Tomography

We have developed new methods of IR ultrabroadband interferometry for increasing the limiting capabilities of optical coherent tomography (OCT). In particular, this permitted us to create an optical coherent microscope combining the principles of confocal microscopy and OCT. To increase the longitudinal resolution, we synthesized an ultrabroadband optical spectrum based on two superluminescent diodes with separated radiation spectra. The resulting longitudinal resolution was 3.4 m and the transverse resolution was 3.9 m. Images of the inner structure of biological tissues are obtained at the cellular level. Experimental results of a study of biological tissue by the cross-polarization OCT are described.     

The influence of the crystalline field on the distortion of the octahedral complexes of divalent iron

The analysis of the experimentally observed distortions of the impurity octahedral Fe(II) complexes in the crystalline matrices of various symmetry shows that these distortions are of the Jahn-Teller (JT) nature. The Mössbauer investigation results for the impurity complexes [Fe(H₂O)₆]²⁺ in Cu_I-xFe_xSiF₆ · 6H₂O combined with the similar data for the series of isomorphic compounds MeSiF₆ · 6H₂O (Me=Ni,Zn, Co) indicate that the value of distortion is determined by the crystalline field of the matrix. The sign of the quadrupole splitting on the ferrous nucleus (Δ E_Q < 0) obtained from the (Δ E_Q < O) -resonance measurements on Cu_I-xFe_xSiF₆ · 6H₂O (x < 0,05) in the magnetic field corresponds to the ground orbital singlet, inherent to the systems, when the JT distortion occurs. The ⁵T_2g vibronic instability calculations with the spin-orbit interaction taken into account, confirm the experimental data on the compliance of the Fe(II) octahedral complex; thus it is possible to use this complex as the probe of the intracrystalline fields.     

Calculation of transition intensities for torsional vibrations in IR and Raman spectra of dihydroxybenzenes

We present the calculated intensity distribution for bands and lines in torsional IR and Raman spectra of dihydroxybenzenes. The calculations were based on calculated matrix elements for the components of the dipole moment and the polarizability tensor. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 5, pp. 598–603, September–October, 2007.     

Large orbital moments and internal magnetic fields in lithium nitridoferrate(I)

The iron nitridometalates Li2[(Li(1-x)Fe(I)(x))N] display ferromagnetic ordering and spin freezing. Large magnetic moments up to 5.0mu(B)/Fe are found in the magnetization. In M?ssbauer effect studies huge hyperfine magnetic fields up to 696 kOe are observed at specific Fe sites. These extraordinary fields and moments originate in an unusual ligand field splitting for those Fe species leading [within local spin density approximation (LSDA)] to a localized orbitally degenerate doublet. Including spin-orbit interaction and strong intra-atomic electron correlation (LDA+SO+U) gives rise to a large orbital momentum.     

Polymorphism and Pressure Driven Thermal Spin Crossover Phenomenon in [Fe( abpt )2(NC X )2] ( X =?S, and Se): Synthesis, Structure and Magnetic Properties

Summary.  The monomeric compounds [Fe(abpt)₂(NCX)₂] (X = S (1), Se (2) and abpt = 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole) have been synthesized and characterized. They crystallize in the monoclinic P2₁/n space group with a = 11.637(2) ?, b = 9.8021(14) ?, c = 12.9838(12) ?, β = 101.126(14)°, and Z = 2 for 1, and a = 11.601(2) ?, b = 9.6666(14) ?, c = 12.883(2) ?, β = 101.449(10)°, and Z = 2 for 2. The unit cell contains a pair mononuclear [Fe(abpt)₂(NCX)₂] units related by a center of symmetry. Each iron atom, located at a molecular inversion center, is in a distorted octahedral environment. Four of the six nitrogen atoms coordinated to the Fe(II) ion belong to the pyridine-N(1) and triazole-N(2) rings of two abpt ligands. The remaining trans positions are occupied by two nitrogen atoms, N(3), belonging to the two pseudo-halide ligands. The magnetic susceptibility measurements at ambient pressure have revealed that they are in the high-spin range in the 2 K–300 K temperature range. The pressure study has revealed that compound 1 remains in high-spin as pressure is increased up to 4.4 kbar, where an incomplete thermal spin crossover appears at around T _1/2 = 65 K. Quenching experiments at 4.4 kbar have shown that the incomplete character of the conversion is a consequence of slow kinetics. Relatively sharp spin transition takes place at T _1/2 = 106, 152 and 179 K, as pressure attains 5.6, 8.6 and 10.5 kbar, respectively. Corresponding author. E-mail: jose.a.real@uv.es Received June 12, 2002; accepted July 1, 2002