HS Fraction Research Articles

Light-induced spin-state switching in Fe(II) spin-crossover complexes with thiazole-based chelating ligands.

Homoleptic complexes [Fe(4bt)3](ClO4)2 (1), [Fe(2bt)3](ClO4)2 (2), and [Fe(3tpH)3](ClO4)2 (3) were obtained by a reaction between the Fe(II) precursor salt and the corresponding thiazole-based bidentate ligand (L = 4bt = 4,4'-bithiazole, 2bt = 2,2'-bithiazole, 3tpH = 3-(thiazol-2-yl)pyrazole). X-ray crystal structure determination revealed crystallization of solvent-free complex 1, a solvate 2·MeOH, and a co-crystal 3·2(3tpH). The crystal packing of all these complexes is dominated by one-dimensional interactions between the [Fe(L)3]2+ cations. These interactions are stronger in 2·MeOH and 3·2(3tpH), leading to cooperative and slightly hysteretic transitions between the high-spin and low-spin electronic configurations at ∼235 K and 159 K, respectively. In contrast, weaker intermolecular interactions in 1 result in a gradual spin crossover above 300 K, with the maximum fraction of the HS state ∼25% achieved at 400 K. Complexes 2 and 3·2(3tpH) exhibit light-induced excited spin state trapping (LIESST) under irradiation with white light or a 532 nm laser at 5 K. After the photoexcitation, the trapped metastable HS state relaxes to the ground LS state with the average relaxation temperature of 81 K and 68 K, respectively. Examination of the relaxation dynamics by optical absorption spectroscopy on a single crystal of 3·2(3tpH) revealed the sigmoidal shape of the relaxation curves at lower temperatures, attributed to cooperative effects, as well as a plateau at ∼10% of the HS fraction at intermediate temperatures, hinting at a more complex mechanism for the relaxation of the LIESST phase in this material.

Electrochemical oxidation treatment of reverse osmosis concentrated landfill leachate: Effect of operation parameters and evolution of dissolved organic matter

Electrochemical oxidation (EO) is a viable option for the advanced treatment of reverse osmosis concentrated landfill leachate (ROCLL). This work characterized dissolved organic matter (DOM) in ROCLL with size exclusion chromatography (SEC) and then investigated the impact of operating parameters on the removal of DOM fractions with response surface methodology (RSM). The SEC chromatograms revealed that the DOM fractions in ROCLL comprised of biopolymers (BP, > 18 kDa), humic substances (HS, 0.45–18 kDa) and low molecular weight substances (LMWS, < 0.45 kDa). For the EO configuration with different anodes, the BDD film anode showed the highest removal efficiency for DOM in terms of COD, DOC, UVA254 and fluorescence indices, followed by Ti, graphite, Ti/RuO2-IrO2 and Ti/SnO2-Sb2O5 anodes. The RSM experiments suggested that pH was the most critical factor to enhance the removal of all DOM fractions, and acidification pretreatment could remove approximately 50% BP and 30% HS fractions due to the pH-induced precipitation. The DOC removal kinetics of DOM fractions could be described by pseudo-zero kinetic model with rates in the order of HS > LMWS > BP, which were controlled by charge transfer process. Differently, the elimination of chromophores and fluorophores followed pseudo-first kinetics, which was limited by mass transport process. Via nonnegativity matrix factorization (NMF) deconvolution of the SEC-OCD chromatograms, BP-C1, HS-C2 and LMWS-C1 subfractions required to be removed through further treatment after EO process. This work demonstrates the potential for SEC analysis coupled with mathematical approaches to give informative insights into the evolution of DOM and provide optimization strategies for the EO treatment of complex ROCLL.

Observation of Two-Step Spin Transition in Graphene Oxide-Based Hybrids with Iron(II) 4-amino-1,2,4-triazole Spin Crossover Nanoparticles.

A novel experimental protocol based on a reverse micellar method is presented for the synthesis of graphene oxide (GO)-based hybrids with spin crossover nanoparticles (SCO NPs) of the 1D iron(II) coordination polymer with the formula [Fe(NH2trz)3](Br2). By introducing different quantities of 0.5% and 1.0% of GO (according to iron(II)) into the aqueous phase, two hybrids, NP4 and NP5, were synthesized, respectively. The morphological homogeneity of the NPs on the surface of the GO flakes is greatly improved in comparison to the pristine [Fe(NH2trz)3](Br2) NPs. From the magnetic point of view and at a low magnetic sweep rate of 1 K/min, a two-step hysteretic behavior is observed for NP4 and NP5, where the onset of the low-temperature second step appeared at 40% and 30% of the HS fraction, respectively. For faster sweep rates of 5-10 K/min, the two steps from the cooling branch are progressively smeared out, and the critical temperatures observed are T1/2↑ = 343 K and T1/2↓ = 288 K, with a thermal width of 55 K for both NP4 and NP5. A Raman laser power-assisted protocol was used to monitor the thermal tolerance of the hybrids, while XPS analysis revealed electronic interactions between the SCO NPs and the GO flakes.

Hydro-liquefaction of the ashless coal from de-polymerization of Shengli lignite

This work performed de-polymerization of Shengli lignite (SL) to remove minerals, and the resultant product (denoted as SDP) was subjected to hydro-liquefaction to prepare value-added aromatic products, especially n-hexane soluble fractions (HS for abbreviation). Compared with raw lignite, SDP is easily converted to light products (HS) with low H2 consumption due to its small molecular weight and less free radicals generated during hydro-liquefaction. Appropriate temperatures (e.g., 400 °C) are required for efficient conversion of SDP into HS fractions. Ni-Mo-S/Al2O3 catalyst effectively promotes hydrogenation of SDP into HS during the reaction, moreover, the condensation reaction is effectively reduced. The yield of HS (YHS) reaches to 73.7% and the yield of THFI (YTHFI) is only 2% with the use of Ni-Mo-S/Al2O3 at 400 °C. The Aromatic fractions in the solvent effectively reduce YTHFI through suppression of condensation reaction, and the hydrogen donor solvents remarkably increase YHS. The HS fractions primarily consist of aromatic hydrocarbons with 1–3 rings and aromatic derivatives containing alkyl as well as various oxygen-containing functional groups.

Three-dimensional electroelastic modeling of the nucleation and propagation of the spin domains in spin-crossover materials

A three-dimensional version of the electroelastic model allowing the description of spin-crossover (SCO) materials taking into account for the volume change at the transition between the LS and the HS spin states is developed. The investigations are realized on a rectangular parallelepiped lattice with cubic symmetry. The SCO units are modeled by two-states fictitious spins coupled by springs whose equilibrium distances depend on the spin states. We implemented massive parallel simulations using CUDA (Compute Unified Device Architecture) programming where the spin states are updated using the Monte Carlo Metropolis algorithm, while the mechanical relaxation (lattice position) is performed by molecular dynamics. In this work, we investigated (i) the case of the thermal spin transition showing the macroscopic deformation of the parallelepiped accompanying the propagation of single domains and (ii) the isothermal relaxation of the photoinduced metastable HS fraction at low temperature. In both cases, the interplay between the electronic and the structural aspects of these transformations is analyzed and discussed in relation with the model parameters.

Magnetic properties of the mononuclear iron (III) complexes with biphenyl‐disubstituted Schiff base ligand: EPR and SQUID study

The magnetic features of the mononuclear iron (III) complexes [Fe(L)2]+X−with tridentate Schiff base ligands [where L is 4‐(4‐diphenylcarboxy)‐2′‐oxysalicylidene‐N′‐ethylene‐N‐ethylene‐2′‐amine‐(carboxy‐4‐diphenyl) and X− = Cl−(1), PF6−(2) and NO3−(3) counter‐ions] have been studied by electron paramagnetic resonance (EPR) spectroscopy, SQUID (superconducting quantum interference device) magnetometry (solid), and Evans1H nuclear magnetic resonance method (solution). EPR established that compounds (1) and (2) consist of two types high‐spin (HS, S = 5/2) centers with weak distorted and strong low‐symmetry octahedral crystal fields. The signals from low‐spin centers (LS, S = 1/2) of Fe (III) are observed in the spectra of compounds2and3. SQUID revealed permanent HS behavior in (1) and mixed LS + HS in (2), (3) in wide temperature range, while solution method—only HS. Magnetic measurements allowed to estimate part of HS and LS fractions and detected antiferromagnetic exchange interactions between the neighboring Fe (III) ions in complexes.“

The Branched Schiff Base Cationic Complexes of Iron(III) with Different Counter-Ions

The Fe(III) complexes of branched asymmetric dendrimers were obtained by a one-step reaction as the second-generation architectures. Mesomorphic behavior was found for complexes with PF6− and BF4− counter-ions. To obtain knowledge about the existence of HS and LS fractions of iron(III) ion and their evolution with temperature, EPR methods were used. It was demonstrated that compounds contain one low-spin (LS, S = 1/2) and two HS-spin (HS, S = 5/2) of Fe(III) centers and are packed into two magnetic sub-lattices. A floating layers of Fe(III) complexes and Langmuir–Blodgett films on their base were formed and investigated in the presence of a magnetic field.

Large cooperative effects in tunneling rates across van der Waals coupled binary self-assembled monolayers

This paper describes large positive cooperative effects of two orders of magnitude in the tunneling rates across molecular junctions of mixed self-assembled monolayers (SAMs) of rectifying (ferrocenyl undecanethiol HS(CH2)11Fc) and non-rectifying molecules with different terminal groups (11-undecanethiol and its derivatives, denoted as HS(CH2)11X, where X = -H, -NH2 or -NO2). By gradually diluting the surface fraction of HS(CH2)11Fc in the mixed SAM, it is found that the large positive cooperative effect is only important in the coherent tunneling regime but not in the incoherent tunneling regime. Density functional theory (DFT) shows that the measured cooperative effects in the tunneling rates in these binary systems are caused by Fc---X van der Waals interactions which increase in the order of -H< -NH2< -NO2. These strong cooperative effects dramatically alter the operation of a molecular diode, further highlighting the importance of taking cooperative effects into account, in this case driven by van der Waals interactions, in the rational design of electronic devices working at tunneling regime.

Chemical composition and chemosystematic evaluation of the fruit and root headspace fractions of selected Heracleum taxa from southeastern Europe

This work is focused on nine Heracleum taxa (Apiaceae): H. sphondylium, H. sibiricum, H. montanum, H. ternatum, H. pyrenaicum subsp. pollinianum, H. pyrenaicum subsp. orsinii and H. verticillatum, belonging to the H. sphondylium group, and H. orphanidis, all from sect. Heracleum, as well as H. austriacum subsp. siifolium from sect. Wendia. The aim was to isolate the headspace (HS) fractions from 17 fruit samples (collected from all nine Heracleum taxa) and 13 root samples (collected from all eight taxa belonging to sect. Heracleum), to investigate their composition and chemosystematic significance, as well as to compare these results with those previously obtained for the essential oils isolated by hydrodistillation from the same fruit and root samples. The HS fractions were isolated using an automatic static HS sampler and analysed by GC-FID and GC-MS. The fruit HS fractions were dominated by octyl acetate and/or ?-pinene (the taxa from the sect. Heracleum), or n-octanol (H. austriacum), whereas the root HS fractions mainly contained ?-pinene and/or (Z)-?-ocimene (the taxa from the H. sphondylium group), or n-nonane (H. orphanidis). The chemosystematic significance was evaluated using multivariate statistical methods: principal component analysis (PCA), non-metric multidimensional scaling (nMDS) and agglomerative hierarchical clustering based on the unweighted pair-group arithmetic average (UPGMA) algorithm. As in the case of previously investigated essential oils, the statistical analysis of the fruit and root HS fractions generally resulted in the grouping of the investigated H. sphondylium group representatives, and within this group, the grouping of morphologically related H. sphondylium and H. montanum and the isolated position of H. verticillatum. The statistical analysis of the root HS fractions resulted in better separation of the taxa (even compared to previous analysis of the essential oils), i.e. isolated positions of H. ternatum and H. pyrenaicum were observed.

The effects of humic substances on DNA isolation from soils.

BackgroundHumic substances (HS) are compounds with a complicated structure, present in the humus soil layer, water, lake sediments, peat, brown coal and shales. Due to their similar physicochemical properties to DNA, they may have an adverse effect on the subsequent use of the isolated material. The main aim of this research was to examine the effect of HS on DNA isolation depending on the soil type and land use, taking into account the spectroscopic full characteristics of HS fractions.MethodsThe research was conducted on eight types of soil sample. Soils represented the most important Soil Reference Groups for temperate climates: Fluvisols, Regosols, Cambisols, Arenosols, Histosols and Luvisols. Soil samples were also collected from areas diversified in terms of use: arable land, grassland and forest. The extraction of HS fractions was performed using the procedure recommended by the International HS Society. The fractional composition of HS was characterized by UV–Vis and fluorescence methods. Soil DNA is extracted by direct cell lysis in the using a CTAB-based method with a commonly-used commercial soil DNA isolation kit. The basis for assessing the quantity and quality of extracted DNA was the Polymerase chain reaction (PCR) reaction since the analysis of soil DNA often relies on the use of PCR to study soil microorganisms.ResultsBased on the results, it can be concluded that in the presence of a high concentration of HS, the isolated DNA was low quality and the additional purification procedure was necessary. Despite the differentiation of the internal structure of HS fractions, the decisive factor in the efficiency of DNA isolation from soil samples was the total carbon content in HS. Reduced DNA yields can significantly constrain PCR detection limits to levels inadequate for metagenomic analysis, especially from humus-rich soils.

P0105THE ROLE OF PROTEOGLYCANS IN GLOMERULAR PHYSIOLOGY AND PATHOPHYSIOLOGY

Abstract Background and Aims Damage to the filtration barrier in the kidney may result in proteinuria, a hallmark of kidney disease. The glomerular filtration barrier consist of 3 layers: the endothelial cells with their endothelial surface layer (ESL), the glomerular basement membrane and podocytes. The ESL is rich in negatively charged molecules, such as proteoglycans (PGs). The negatively charged molecules restrain the flow of charged molecules, as albumin, over the barrier. Loss of ESL has been shown to lead to proteinuria without damage to the other structures of the filtration barrier. In order to gain further knowledge about the function and composition of the glomerular ESL we eluted the glomerular ESL from rats and analyzed the PG content as well as the effect of loss of the ESL on the function of the glomerular filtration. Method The basic principles of ion exchange chromatography were applied in this study. In order to elute highly negatively charged proteoglycans of the ESL, we used 1 M NaCl solution (HS). 1 M mannitol (HO) was included to evaluate osmotic effects. A control fraction was eluted with normal saline solution (0,15 M NaCl) (NS). Solutions were introduced intraarterially to rat kidneys under anesthesia in vivo. Venous effluent was collected and analyzed using proteomics and mass spectrometry. Fractional clearance of albumin was measured as well as GFR. Electron microscopy (EM) was used to investigate changes to the filtration barrier and the thickness of the glomerular ESL. Immunohistochemistry was used to confirm the presence of identified PGs in human tissue. Results We identified 15 PGs and PG candidates in ESL as well as hyaluronan. The most abundant PGs were lumican, glypican-1, syndecan-4, perlecan, podocan, decorin, serglycan, agrin and biglycan. In general, PGs were found in in all HS, NS and HO fractions, but in higher yields in the HS samples. EM demonstrated that the glomerular ESL thickness was significantly reduced in HS perfused rats – 28% (p&amp;lt;0.05) compared to rats perfused with NS. Rats perfused with HS also had increased fractional clearance of albumin compared to NS and HO, and a large reduction of GFR 10 minutes after perfusion. Conclusion The ESL itself represents a dynamic structure with significant molecular turnover and is formed by PGs, glycosaminoglycans, glycoproteins and soluble proteins. In our study, we identified several PGs in the glomerular endothelial ESL. We show that loss of ESL leads to increased albumin fractional clearance and reduction in GFR after perfusion, strongly suggesting that the ESL is important for preventing proteinuria. Characterizing the composition of the glomerular ESL is therefore of great importance, and can give new possible targets for treatment of proteinuria.

Sequential Extraction of Coal Tar Pitch and Structural Characterization of Enriched Large Polycyclic Aromatic Hydrocarbons

AbstractFour fractions separated sequentially from a coal tar pitch by two different methods are examined by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI TOF‐MS) and 50/24 matrix analysis, to evaluate both separation effectiveness and characteristics of large polycyclic aromatic hydrocarbons (PAHs) in variable fractions. Both Soxhlet extraction and anti‐solvent precipitation can sequentially produce four fractions that have narrower molecular mass distribution with specific structural features of PAHs. The results show that the overall molecular mass (MM) and ring size of large PAHs abundant in the fractions gradually shift to higher values as solvent strength increases, with some overlap between two adjacent fractions. A broad range of peaks in MS spectra has been resolved as 4‐ to about 25‐ ring PAHs by 50/24 matrix analysis, with some detailed molecular structure elucidated. For example, the PAHs in the light HS fraction include 4 to 11‐ring aromatics with more ortho‐condensed structure. On the other hand, heavier fractions contain more aromatic rings fused by bay‐condensations that result in quaternary aromatic carbons. Besides structural insights, SEM morphologically reveals differences in the extraction effectiveness between Soxhlet and anti‐solvent, due to mass transfer and diffusion limitations in bituminous material.

Evolution of Spin-Crossover Transition in Hybrid Crystals Involving Cationic Iron Complexes [Fe(III)(3-OMesal2-trien)]+ and Anionic Gold Bis(dithiolene) Complexes Au(dmit)2 and Au(dddt)2

Hybrid ion-pair crystals involving hexadentate [Fe(III)(3-OMesal2-trien)]+ spin-crossover (SCO) cationic complexes and anionic gold complexes [Au(dmit)2]− (1) (dmit = 4,5-dithiolato-1,3-dithiole-2-thione) and [Au(dddt)2]− (2) (dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate) were synthesized and studied by single-crystal X-ray diffraction, P-XRD, and SQUID magnetometry. Our study shows that both complexes have similar 1:1 stoichiometry but different symmetry and crystal packing. Complex 1 has a rigid structure in which the SCO cations are engaged in strong π-interplay with molecular surrounding and does not show SCO transition while 2 demonstrates a reversible transition at Tsco = 118 K in a much “softer”, hydrogen-bonded structure. A new structural indicator of spin state in [Fe(sal2-trien)]+ complexes based on conformational analysis has been proposed. Aging and thermocycling ruined the SCO transition increasing the residual HS fraction from 14 to 41%. Magnetic response of 1 is explained by the AFM coupled dimers S = 5/2 with J1 = −0.18 cm−1. Residual high-spin fraction of 2, apart from a contribution of the weak dimers with J12 = J34 = −0.29 cm−1, is characterized by a stronger interdimer coupling of J23 = −1.69 cm−1, which is discussed in terms of possible involvement of neutral radicals [Au(dddt)2].

Numerical simulation of a device with two spin crossover complexes: application for temperature and pressure sensors

The spin-crossover (SCO) phenomenon is related to the ability of a transition metal to change its spin state vs. a given perturbation. For an iron(II) SCO complexes the reversible changes involve the diamagnetic low-spin (S = 0) and the paramagnetic high-spin (HS S = 2) states [1,2,3]. In this contribution we simulate the HS Fraction (nHS) for different set values of temperature and pressure for a device using two SCO complexes with weak elastic interactions. We improve the calculation given by Linares et al. [4], taking also into account different volume (VHS, VLS) changes of the SCO. We perform all the calculation in the frame work of an Ising-like model solved in the mean-field approximation. The two SCO show in the case of “weak elastic interactions”, gradual spin transitions such that both temperature and pressure values can be obtained from the optical observation in the light of calculations discussed in this article.

Antibacterial, Anti-Diarrhoeal, Analgesic, Cytotoxic Activities, and GC-MS Profiling of Sonneratia apetala (Buch.-Ham.) Seed.

Fruits of Sonneratia apetala (Buch.-Ham.), (English: mangrove apple, Bengali: keora) both seeds and pericarps, are largely consumed as food besides their enormous medicinal application. The fruit seeds have high content of nutrients and bioactive components. The seeds powder of S. apetala was successively fractionated using n-hexane, diethyl ether, chloroform, ethyl acetate, and methanol. The fractions were used to evaluate antibacterial, anti-diarrhoeal, analgesic, and cytotoxic activities. Methanol fraction of seeds (MeS) stronly inhibited Escherichia coli strains, Salmonella Paratyphi A, Salmonella Typhi, Shigella dysenteriae, and Staphylococcus aureus except Vibrio cholerae at 500 μg/disc. All the fractions strongly inhibited castor oil induced diarrhoeal episodes and onset time in mice at 500 mg extract/kg body weight (P<0.001). At the same concentration, MeS had the strongest inhibitory activity on diarrhoeal episodes, whereas the n-hexane fraction (HS) significantly (P<0.05) prolonged diarrhoeal onset time as compared to positive control. Similarly, HS (P<0.005) inhibited acetic acid induced writhing in mice at 500 mg extract/kg, more than any other fraction. HS and diethyl ether fractions of seed strongly increased reaction time of mice in hot plate test at 500 mg extract/kg. All the fractions showed strong cytotoxic effects in brine shrimp lethality tests. Gas chromatography-mass spectrometry analysis of HS led to the identification of 23 compounds. Linoleic acid (29.9%), palmitic acid (23.2%), ascorbyl palmitate (21.2%), and stearic acid (10.5%) were the major compounds in HS. These results suggest that seeds of S. apetala could be of great use as nutraceuticals.

Direct Optical Microscopy Observation of Photo-Induced Effects and Thermal Relaxation in a Spin Crossover Single Crystal

Background: Spin crossover (SC) compounds are among the most fascinating molecular solids exhibiting thermal and photo-switching. The spin crossover phenomenon manifests, generally, in iron (II) complexes in octahedral symmetry, surrounded by nitrogen atoms. The splitting of the energy of the d orbitals into the t2g (ground state) and eg (excited state) allows the existence of two possible electronic states, namely high-spin (HS, S=2) and low-spin (LS, S=0) for weak and strong ligand-field configurations, respectively. At the solid state, the switching between these two electronic states is possible with temperature, light, pressure, etc. and may lead to gradual or first-order transitions, accompanied with a thermal hysteresis loop. In addition, SC materials exhibit interesting non-equilibrium phenomena, like photo-induced metastable states at low-temperature and their non-linear thermally-induced relaxation, which will be investigated in the current work. Methods: Optical microscopy technique is used here to visualize the first-order thermal spin transition in the single crystal [{Fe(NCSe)(py)2}2 (m-bpypz)], where py = pyridine and bpypz= 3,5-bis(2-pyridyl)-pyrazolate, hereafter abbreviated Fe(NCSe). The experimental set-up was also adapted to include a photo-excitation through the objective of the microscope. We then succeeded in imaging, the spatiotemporal transformation of the SC single crystal under light at very low temperature, ~20K. Image processing allowed to furnish quantitative data on this transformation. Results: This report focusses on the first direct visualization by optical microscopy of the photo-transformation of the SC single crystal under light. The phenomenon behind this process, called LIESST effect (Light-induced Excited Spin State Trapping) is well known in the SC topic, and was studied in the past using magnetic and optical absorption techniques, but not yet visualized. Our results show that the transformation from LS to HS under light proceeds in a homogeneous way, without any presence of domain coarsening (at the resolution of the optical microscopy, ~500 nm), in good agreement with the general admitted idea that the LIESST effect is a non-cooperative process. We have also followed the spatiotemporal transformation (at higher temperature, T~60K) of the crystal during its thermal relaxation from the photo-induced metastable HS state to the stable LS state. We could derive the time dependence of the HS fraction which was found to follow the usual sigmoidal shape, in excellent agreement with previous magnetic data, thus confirming the cooperative character of this relaxation. As for the photo-excitation, our data demonstrated that the relaxation process from HS to LS proceeds without any domain formation: the crystal remains in the homogeneous state during the overall relaxation process. From the theoretical view point, the photoexcitation and the relaxation processes are described by the kinetic mean field model whose all parameters were derived from the experiment. Conclusion: We presented optical microscopy studies on the single crystal Fe(NCSe) which included the visualization of the first-order thermal transition and also the photo-excitation and the relaxation of one single crystal Fe(NCSe) under light. The thermal equilibrium transition, that is the first-order transition observed at ~112K, proceeds via the formation of a single domain which propagates overall the crystal. In contrast, the photoexcitation process and the subsequent thermal relaxation of the photo-induced HS state, did not show any domain formation. These two last processes take place through homogenous transformations of the crystal. The analysis of our optical microscopy data of photoexcitation/relaxation, in the frame of a kinetic mean-field description, allowed to derive all thermodynamic parameters of the model, such as the interaction parameter and the effective energy barriers. The current observations underline the role of the lattice dynamics and its crucial temperature dependence, in the conditions of occurrence of domains formation. In general, the existence of macroscopic domains requires the presence of an instability. Keywords: Mean-field kinetics, optical microscopy, photo-excitation, relaxation, spin-crossover, visualization.

Interplay between elastic interactions in a core-shell model for spin-crossover nanoparticles

A coupled spin deformation model for spin-crossover (SC) materials, consisting of distortable 2D square-shaped lattices, whose sites may be occupied by high-spin $(\mathrm{HS})$ or low-spin $(\mathrm{LS})$ atoms, is studied by Monte Carlo simulations. To be consistent with the experimental studies, we have studied shell-free and core-shell nanoparticles. In the case of shell-free nanoparticles, we constrained the surface of the nanoparticle (one layer) to be in the $\mathrm{HS}$ state from the electronic and the elastic point of view because the surface atoms have weaker ligand-field energy than those of the bulk. We then investigated the size effects and found that the thermal hysteresis width $\ensuremath{\Delta}T$ and the transition temperature ${T}_{\mathrm{eq}}$ follow the respective universal laws, $\ensuremath{\Delta}T\ensuremath{\propto}\sqrt{(L\ensuremath{-}{L}_{0})}$ and ${T}_{\mathrm{eq}}\ensuremath{\propto}\sqrt{\mathrm{ln}(L\ensuremath{-}{L}_{c})}$, where $L$ is the nanoparticle size. These laws hold independently of the sweeping rate of temperature. In a second stage, we studied the effect of a soft shell on the thermal properties of the core shell nanoparticle for which we have investigated the thermodynamic properties at various sizes of the shell. We find that the thermal hysteresis shifts downwards and the corresponding width increases; a result that contrasts with that of shell-free nanoparticles. In addition, we have observed that large shell size widths hinder the domain formation upon the first-order transition, although the transition is still of first order. These behaviors originate from the elastic stress produced by the shell on the bulk of the nanoparticle, and are identified through the spatial distribution of the internal stress upon the thermal transition. Moreover, we studied the effect of the shell size on the relaxation of the photoinduced metastable HS fraction at low temperature. At this end, a preliminary optimization of the structure of the nanoparticle is performed. We then evidenced that increasing the size of the shell results in an acceleration of the relaxation process. This behavior is in excellent agreement with recent data reported on core shell nanoparticles of Prussian Blue analogs.

Natural organic matter removal by ion exchange at different positions in the drinking water treatment lane

Abstract. To guarantee a good water quality at the customers tap, natural organic matter (NOM) should be (partly) removed during drinking water treatment. The objective of this research was to improve the biological stability of the produced water by incorporating anion exchange (IEX) for NOM removal. Different placement positions of IEX in the treatment lane (IEX positioned before coagulation, before ozonation or after slow sand filtration) and two IEX configurations (MIEX® and fluidized IEX (FIX)) were compared on water quality as well as costs. For this purpose the pre-treatment plant at Loenderveen and production plant Weesperkarspel of Waternet were used as a case study. Both, MIEX® and FIX were able to remove NOM (mainly the HS fraction) to a high extent. NOM removal can be done efficiently before ozonation and after slow sand filtration. The biological stability, in terms of assimilable organic carbon, biofilm formation rate and dissolved organic carbon, was improved by incorporating IEX for NOM removal. The operational costs were assumed to be directly dependent of the NOM removal rate and determined the difference between the IEX positions. The total costs for IEX for the three positions were approximately equal (0.0631 € m−3), however the savings on following treatment processes caused a cost reduction for the IEX positions before coagulation and before ozonation compared to IEX positioned after slow sand filtration. IEX positioned before ozonation was most cost effective and improved the biological stability of the treated water.

Vibration-driven thermal transition in binuclear spin crossover complexes

An Ising-like model including the effect of intramolecular vibrations is proposed to investigate Fe(II) binuclear spin crossover complexes, especially in the situation where it allows the assessment of the conditions under which cooperative exchange interactions are weak enough to favor a vibration-driven mechanism for the thermal transition. In particular, two spin states (LS-LS, LS-HS or HS-HS where LS and HS stand for low-spin and high-spin respectively) must be quasi-degenerate. Whatever the equi-energy scenario, the effect of molecular vibrations on the groundstate appears in the low temperature region, where a deviation from the low frequency approximation of the standard Ising-like model is observed. Thirteen quasi-equi-energy situations lead to three possible vibronic groundstates at T = 0 K, from which the thermal evolution of the HS fraction presents a similar trend as mononuclear systems. However, binuclear systems permit to generate a HS-LS vibronic groundstate. For this latter case the application of pressure, known to drastically affect the spin transition, is suggested to reveal a two-step behavior according to a LS-LS, HS-LS HS-HS scheme. Intramolecular coupling between the two metallic centres and intermolecular cooperativity few influence the spin transition curves due to a difference of the temperature ranges between the effects of molecular vibrations and spin crossover phenomenon.

FeIII Spin‐Crossover Complexes with Photoisomerizable Ligands: Experimental and Theoretical Studies on the Ligand‐Driven Light‐Induced Spin Change Effect

AbstractConflicting results have been reported with respect to the photoinduced switching of the magnetic properties of [FeIII(salten)]+ complexes [salten = 4‐azaheptamethylene‐1,7‐bis(salicylideneiminate)] coordinated by photoisomerizable ligands. In order to address this problem, two FeIII complexes [Fe(salten)(3‐azpy)]BPh4 (1) and [Fe(salten)(4‐azpy)]BPh4 (2) have been synthesized and characterized by various physicochemical methods (azpy = phenylazopyridine). Both 1 and 2 exhibit a low spin (S = 1/2) to high spin (HS, S = 5/2) transition in the solid state. In solution at room temperature both complexes are predominantly HS. Upon exposure to 310 (trans → cis) and 440 nm radiation (cis → trans) the free and coordinated 3‐ and 4‐azpy ligands undergo a reversible cis–trans isomerization. For 2 a corresponding reduction of the HS fraction 2 % is observed, whereas in 1 no effect is observed. Extensive DFT calculations, which employ different functionals and basis sets, explain this experimental result. The consequences of these findings with respect to the design of spin‐switchable iron(III) complexes with photoactive ligands are discussed.