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This work explores the singular scenarios emerging from nanoscopic cavities, located in aqueous solutions, that include biomolecules and, as a consequence, the process of biomolecule hydration shell formation. The research presents a nano-scale study, performed in various systems related with protein-water solutions, using all-atoms molecular dynamics simulations. This research shows that if a protein falls within an empty nanoscopic cavity located in an aqueous solution, it will take a time, with a magnitude significant for biological processes, to rebuild its whole network of hydrogen bonds with the solvent molecules. During that protein isolation time the dynamics of the biomolecule, and therefore the corresponding bioactivity, will be seriously compromised. In the case of the protein barstar (radius of gyration of 1.17 nm) located in the centre of cavities with radius r from 2.5 to 4.5 nm, and solvent diffusion coefficients for bulk and physiologic water (2.4 and 1.5 μm2/ms, respectively), that time is found to be of the order of tens-hundreds of picoseconds, a significant temporal range concerning the dynamics and bioactivity of proteins. On the other hand, the dynamics of formation of the inner protein hydration shell has been followed using an atomic view. The required time has been found to decrease with r, as the network of water molecules approaching the biomolecule resembles that of the biological water corresponding to that biomolecule. That resemblance increases as those water molecules have previously been in close contact with the protein. The dynamics of those systems has been modelled using a two states model. Isolated bulk water is taken as reference for the computer simulations. Comparison with experimental data is also provided., This work was funded by the European Regional Development Fund (EU) together with the Government of Spain, under common Project FIS2017-87519-P. Financial support from the Government of Aragón (Aragón Research Group ‘Fenol’, E36_20R, Spain) and the European Union (Feder 2014-2020, Building Europe from Aragón) is also acknowledged.

The dynamics of the hydration shell of the inhibitor barstar is analysed at low temperature (300–243 K), through all-atom molecular dynamics simulations, and compared with that of bulk water. The relaxation of residence times of solvent molecules in the protein hydration shell follows a stretched exponential function exp[−(t/τ)β] with β = 0.48 ± 0.01, independent of temperature, showing that the decay process is mainly dominated by long-range molecular relaxation channels (short-range for bulk water). The percentage of water molecules exhibiting 4 hydrogen bonds, xHB4, is found to be a parameter essential for understanding some room and low temperature dependent properties of the protein hydration shell, suggesting an explanation for the unfreezing of protein hydration water as temperature decrease below 273 K. Moreover the dynamical transition that proteins and their hydration water exhibit at ~225 K can be explained by the decrease of ‘hydrogen bond defects’ in the protein hydration shell as temperature goes down. If most of those water molecules would present a tetrahedral arrangement (nearly no ‘hydrogen bond defects’), the bioactivity of proteins would be negligible. Comparison with experimental results is provided all along the work. Experimental data are quantitatively reproduced., This work was funded by the Ministerio de Economía, Industria y Competitividad (Spain) together with the European Regional Development Fund (European Union), under common project FIS2017-87519-P. Financial support from Gobierno de Aragón (Spain), through grant E36_17R, is also acknowledged.

The magnetic behavior of the diluted magnetic semiconductor Cd0.42Mn0.58In2S4 has been study by dc magnetization and ac susceptibility experiments. Zero field cooled and field cooled measurements reveal irreversibility below Tirr=2.60±0.15 K. Ac susceptibility data, performed as a function of the temperature and the frequency, confirm the spin-glass like behavior of the material with Tf=2.75±0.15 K. High temperature susceptibility data follow a typical Curie-Weiss law with θ=−74±1 K which suggests predominant antiferromagnetic interactions. The randomness of the magnetic ions, necessary to explain the magnetic behavior of the material, has been determined by X-ray powder diffraction experiments., This work was supported by CDCHT-ULA, FONACIT (Grant Lab-97000821), (TDA (E16/2005) and CICYT MAT2004-03395C0201.

The Mössbauer spectra of the two crystallographic forms α- and β-(NH4)2FeF5 have been studied in the temperature range 4.2-300 K. The α-form presents typical one-dimensional behavior showing a transition to magnetic ordering at Tc = (7.5±0.5) K. The spectra of the β-form indicates the presence at low temperature of two different iron sites, while the room temperature crystal structure shows only one site for the iron ions. Differential scanning calorimetry measurements evidence the presence of a reversible structural phase transition at Ts = (168.0±1) K on heating and Ts = (187.0±3) K on cooling. This form also exhibits a magnetic ordering phase transition at Tc = (13±1) K., The work in Zaragoza has been supported by grant MAT88-0174, from the Comision Interministerial de Ciencia y Tecnologia. M.C.M. is grateful for the receipt of a NATO postdoctoral fellowship. The cooperation has been partially supported by Spanish-French Integrated Action 151/90.

The low-temperature magnetic properties of MnIn2S4 have been studied using AC magnetic susceptibility and magnetization experiments. High-temperature susceptibility fits indicate the presence of antiferromagnetic interactions. Low-field magnetization data show a peak at 5.6±0.1 K, below which strong irreversibility is observed between zero-field-cooled (ZFC) and field-cooled (FC) cycles suggesting that the observed peak corresponds to a spin-glass-like transition instead of the antiferromagnetic one previously reported. Further evidence of this magnetic state comes from AC susceptibility data at different frequencies. The in-phase component χ′(T) exhibits the behavior expected of spin glasses, i.e. a shift of the cusp to higher temperatures for higher frequencies., We wish to thank CDCHT-ULA (Grant C-1395-06-05-B) and FONACIT (Grant LAB-97000821), the Spanish Government and the Diputación General de Aragón for research grants MAT2004-03395-C02-01 and DGA2005-E16, respectively.

3 pages, 4 figures.-- Proceeding of the Seventh Latin American Workshop on Magnetism, Magnetic Materials and their Applications., The magnetic properties of CoCr2S4 have been studied by DC and AC magnetization experiments in the temperature range 1.8–350 K. The temperature dependence of the DC magnetization, together with a calculated saturation magnetization per molecule of 2.73μB at 1.8 K, suggests that CoCr2S4 presents a ferrimagnetic behavior with a critical temperature of 223 K. Both the real and the imaginary parts of the AC magnetic susceptibility exhibit a sudden increase at 225 K. Between 250 and 200 K the real part of the susceptibility(χ′) is typical of a material at the phase transition from a paramagnetic to a long-range-ordered state with Tc=223±2 K. The imaginary part (χ″) presents a cusp at 120 K. An interesting behavior appears below 8 K, where χ′ is strongly reduced and simultaneously χ″ is increasing showing a maximum at 4.3 K. This particular evolution of χ″ with the temperature suggests a richer magnetic behavior for CoCr2S4 at low temperatures., Financial support from the Comisión Interministerial de Ciencia y Tecnología (CICYT-MAT2004-03395C0201), Diputación General de Aragón (E16/2005) Spain and FONACIT (Grant LAB-97000821) Venezuela is acknowledged.

6 pages, 5 figures, 1 table., Compositions of the Cd(1-x)Mn(x)In2S4 system (0.5 x 1.0) were synthesized by the melt and annealing technique and grown by the chemical vapor transport method. The magnetic cation distributions have been estimated by X-ray powder diffraction structure refinements using the Rietveld method. These alloys form a solid solution in all the range of compositions and crystallize with cubic symmetry in the space group Fd 3m. All phases show a spinel structure with a random arrangement of cations. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim), This work was supported by CDCHT-ULA(C-1395-06-05-B), FONACIT-Venezuela (Grant LAB-97000821) and Comisión Interministerial de Ciencia y Tecnología-Spain (CICYT-AT2004-03395-C0201).

Below Tc = 10.0 K undiluted Rb2FeCl5·H2O is a 3-D Heisenberg antiferromagnet possessing rather low magnetic anisotropy (α = 3.4×10-3). Dilutions of the above compound with the analogous isomorphic In derivative form a novel family of insulating spin-glasses of general formula Rb2Fe1-xInxCl5·H2O. Both in-phase (x′) and out-of-phase (x″) components of the ac magnetic susceptibility have been measured at zero (external) magnetic field and as a function of the frequency for different concentrations of the diamagnetic ion (x = 0.05, 0.1 and 0.3). Magnetization measurements after zero-field cooling and in field-cooling have also been used to characterize the spin-glass behavior of these solid solutions., The research has been supported by Grant CICYT MAT 88-0174 in Spain and by the Brazilian agencies CNPq, BID and FAPESP. The cooperative work has been supported by the “Programa de Cooperacion Cientifica Iberoamericana”.

The magnetic behavior of the ferromagnetic layered-perovskite CsMnF4 has been investigated up to pressures P of 4 GPa by using a diamond-anvil cell cooled down to 1.5 K and a SQUID vibrating magnetometer. As the pressure is increased up to 2 GPa the critical temperature TC decreases. At P≳2 GPa, however, TC is almost independent of pressure. The correlation of these results with chemical pressure effects is discussed., This work has supported by Grant No. MAT97-0951 from C.I.C.YT. (Spain), and a Grant-in-Aid for Scientific Research from Ministry of Education, Science, Sport and Culture (Japan).

The magnetic properties of a new series of diluted magnetic semiconductors Zn1-xMnxGa2Se4 with x ranging between 0 and 1 are reported from magnetization and AC magnetic susceptibility data. Antiferromagnetic as well as spin-glass-like behaviors have been detected showing a dependence with the Mn content as well as the cation distribution., Thanks are due: (i) to Dr. J. Stankiewicz for stimulating discussions, (ii) to CICYT for Grant No. MAT97-951 and (iii) to CAI and CONSI + D (DGA) for financial support from Programa Europa.

We report on the magnetic properties of the complex bimetallic compound [Cr(H2O)(NH3)5][FeCl6] studied by ac magnetic susceptibility and magnetization techniques in the range 1.5-30 K and 0-40 kOe. The crystal structure contains discrete [Cr(H2O)(NH3)5]3+ and [FeCl6]3- ions, held together by ionic forces and by a network of hydrogen bonds. At temperatures below (2.32±0.01) K the compound seems to behave as a noncollinear ferrimagnet. In addition, the experimental H-T magnetic phase diagram has been derived., The research has been supported by Grants CAICYT 3380/83 and CICYT MAT 88-0174.

Within the search for magnetic ordering in organic and metal-organic compounds, the polymeric material of formula {[Fe(C13H17N3)2]SO4·6H2O}n has been extensively studied by magnetic measurements. Our results show a basic agreement with the previous ones. Nevertheless, our study, including more data, leads to an interpretation in terms of superparamagnetism rather than metamagnetism as was previously reported., The research has been supported by grant CICYT MAT88-0174.

Magnetization and frequency dependence a.c. magnetic susceptibility measurements of the metal-organic polymers of general formula {[M(C13H17N3)2]SO4 6H2O}n, where M = Fe(II) or Co(II), are indicative of superparamagnetic behavior as a consequence of the existence of strong ferromagnetic interactions in the materials. Scanning electron microscopy and X-ray dispersive spectrometry have been used to study the homogeneity in the composition of the iron polymer.

The ferrimagnetic properties of three new Cr(III)/Fe(III) bimetallic salts, namely [Cr(NH3)5(H2O)][FeCl6], [Cr(NH3)4(H2O)2][FeCl6] and [Cr(en)3]3[FeCl6]Cl6.H2O, are reported. The respective ordering temperatures are Tc = 2.32, 2.31 and 0.91 K. The ac susceptibility data on the three compounds at temperatures above Tc can be fit to a Néel hyperbola., The research in Zaragoza and Barcelona has been supported respectively by Grants 3380/83 and 409/84, from the Comision Asesora de Investigacion Cientifica y Tecnica of the Ministerio de Educacion y Ciencia. The research in Chicago has been supported by Grant DMR-85 15224 fromthe SolidState Chemistry Program, Division of Materials Research of the National Science Foundation. Cooperative work has been supported by Grant CCB-8504/001 from the American—Spain Joint Committee for Technical and Scientific Cooperation. One of us (MCM) wants also to acknowledge a postgraduate student fellowship fromthe Ministerio de Educacion y Ciencia.

The compound [Cr(en)3][ZnCl4]Cl has been synthesized by reaction of CrCl3·6H2O, Zn and [Cr(en)3]2(SO4)3 in HCl. Its molecular and crystalline structure was determined by X-ray diffraction methods, being monoclinic, P21/c, a=21.215(3), b=12.532(2), c=13.707(2) Å, β=95.21°, V= 3629(2) Å3, Dx=1.738g cm−3, MW=474.9, Z= 8, F(000)=1928, λ(Mo Kα)=0.71069 Å, μ(Mo Kα)= 27.04 cm−1, 288 K. No significant exchange interactions between Cr(III) cations in the crystalline lattice were found. Curie-Weiss behavior was found in the three directions tested (g1=2.06±0.02,g2= 2.08±0.02,g3=2.09±0.01), T=1.2-1.4 K., The work in Barcelona has been supported by ‘Comisión Asesora de Investigación Cientifica y Técnica, (C.A.T.C.Y.T.)’ Spanish Government, Grant no. 360/81. The work in Chicago was supported by the Solid State Chemistry Program of the Division oMaterials Research of the National Science Foundation under Grant DMR 8515224. This research was also supported by the U.S.-Spain Joint Committee for Scientific and Technological Cooperation. M.C.M. also acknowledges a Doctoral Fellowship from the Spanish M.E.C.

Les deux composes du titre cristallisent dans le systeme orthorhombique avec le groupe d'espace Pnma. Affinement de la structure jusqu'a 0,020 pour les deux composes. Les anions sont des octaedres deformes