A new FeIII^{III} substituted arsenotungstate [FeIII^{III} 2_{2}2(AsIII^{III}W6_{6}O23_{23})2_{2}(AsIII^{III}O3_{3}H)2_{2}]12−^{12-}: Synthesis, structure, characterization and magnetic properties

The iron(III)-containing arsenotungstate [Fe$^{III}$ $_{2}$2(As$^{III}$W$_{6}$O$_{23}$)$_{2}$(As$^{III}$O$_{3}$H)$_{2}$]$^{12-}$ (1) was prepared via a simple, one-pot reaction in aqueous basic medium. The compound was isolated as its sodium salt, and structurally-characterized by Single Crystal X-ray Diffraction (SCXRD), Powder X-ray Diffraction (PXRD), Fourier-Transform Infrared (FT-IR) spectroscopy, Thermogravimetric Analysis (TGA) and elemental analysis. Its magnetic properties are reported; the antiferromagnetic coupling between the two FeIII centers is unusually weak as a result of the bridging geometry imposed by the rigid arsenotungstate metalloligands

The Influence of Halide Substituents on the Structural and Magnetic Properties of Fe6_{6}Dy3_{3} Rings

We report the synthesis and magnetic properties of three new nine-membered Fe(III)-Dy(III) cyclic coordination clusters (CCCs), with a core motif of [Fe$_{6}$Dy$_{3}$(μ-OMe)$_{9}$(vanox)$_{6}$(X-benz)$_{6}$] where the benzoate ligands are substituted in the para-position with X = F (1), Cl (2), Br (3). Single crystal X-ray diffraction structure analyses show that for the smaller fluorine or chlorine substituents the resulting structures exhibit an isostructural Fe$_{6}$Dy$_{3}$ core, whilst the 4-bromobenzoate ligand leads to structural distortions which affect the dynamic magnetic behavior. The magnetic susceptibility and magnetization of 1-3 were investigated and show similar behavior in the dc (direct current) magnetic data. Additional ac (alternating current) magnetic measurements show that all compounds exhibit frequency-dependent and temperature-dependent signals in the in-phase and out-of-phase component of the susceptibility and can therefore be described as field-induced SMMs. The fluoro-substituted benzoate cluster 1 shows a magnetic behavior closely similar to that of the corresponding unsubstituted Fe$_{6}$Dy$_{3}$ cluster, with U$_{eff}$ = 21.3 K within the Orbach process. By increasing the size of the substituent toward 4-chlorobenzoate within 2, an increase of the energy barrier to U$_{eff}$ = 36.1 K was observed. While the energy barrier becomes higher from 1 to 2, highlighting that the introduction of different substituents on the benzoate ligand in the para-position has an impact on the magnetic properties, cluster 3 shows a significantly different SMM behavior where U$_{eff}$ is reduced in the Orbach regime to only 4.9 K

Synthesis of N-(2,4-dinitrophenyl) derivatives of D-ribosylamines; unexpected reaction and hydrolysis products

Reaction of 2,3-O-isopropylidene-d-ribofuranosylamine with 2,4-dinitrofluorobenzene afforded the crystalline 2,3-O-isopropylidene-N-(2,4-dinitrophenyl)-β-d-ribofuranosylamine (3) and a 1:1 crystalline complex of 2,3-O-isopropylidene-N-(2,4-dinitrophenyl-α-d-ribofuranosylamine and 2,3-O-isopropylidene-β-d-ribofuranose; controlled acidic hydrolysis of 3 afforded N-(2,4-dinitrophenyl-α-d-ribopyranosylamine and not the expected β-d-furanosylamine derivative. The structures of the new compounds were confirmed by NMR spectroscopy and X-ray crystallography

Identification of amino acid residues of the NR2A subunit that control glutamate potency in recombinant NR1/NR2A NMDA receptors

The NMDA type of ligand-gated glutamate receptor requires the presence of both glutamate and glycine for gating. These receptors are hetero-oligomers of NR1 and NR2 subunits. Previously it was thought that the binding sites for glycine and glutamate were formed by residues on the NR1 subunit. Indeed, it has been shown that the effects of glycine are controlled by residues on the NR1 subunit, and a “Venus flytrap” model for the glycine binding site has been suggested by analogy with bacterial periplasmic amino acid binding proteins. By analysis of 10 mutant NMDA receptors, we now show that residues on the NR2A subunit control glutamate potency in recombinant NR1/NR2A receptors, without affecting glycine potency. Furthermore, we provide evidence that, at least for some mutated residues, the reduced potency of glutamate cannot be explained by alteration of gating but has to be caused primarily by impairing the binding of the agonist to the resting state of the receptor. One NR2A mutant, NR2A(T671A), had anEC50for glutamate 1000-fold greater than wild type and a 255-fold reduced affinity for APV, yet it had single-channel openings very similar to those of wild type. Therefore we propose that the glutamate binding site is located on NR2 subunits and (taking our data together with previous work) is not on the NR1 subunit. Our data further imply that each NMDA receptor subunit possesses a binding site for an agonist (glutamate or glycine).</jats:p

Mechanism of magnetisation relaxation in M III 2 Dy III 2 (M = Cr, Mn, Fe, Al) “butterfly” complexes: How important are the transition metal ions here?

We describe the synthesis, characterisation and magnetic studies of four tetranuclear, isostructural “butterfly” heterometallic complexes: [MIII 2 LnIII 2 (m3-OH)2(p-Me-PhCO2)6(L)2] (H2 L ¼ 2,20-((pyridin-2-ylmethyl)azanediyl)bis(ethan-1-ol), M ¼ Cr, Ln ¼ Dy (1), Y (2), M ¼ Mn, Ln ¼ Dy (3), Y (4)), which extend our previous study on the analogous 5 {Fe2Dy2}, 6 {Fe2Y2} and 7 {Al2Dy2} compounds. We also present data on the yttrium diluted 7 {Al2Dy2}: 8 {Al2Dy0.18Y1.82}. Compounds dc and ac magnetic susceptibility data reveal single-molecule magnet (SMM) behaviour for complex 3 {Mn2Dy2}, in the absence of an external magnetic field, with an anisotropy barrier Ueff of 19.2 K, while complex 1 {Cr2Dy2}, shows no ac signals even under applied dc field, indicating absence of SMM behaviour. The diluted sample 8 {Al2Dy0.18Y1.82} shows field induced SMM behaviour with an anisotropy barrier Ueff of 69.3 K. Furthermore, the theoretical magnetic properties of [MIII 2 LnIII 2 (m3-OH)2(p-Me-PhCO2)6(L)2] (M ¼ Cr, 1 or Mn, 3) and their isostructural complexes: [MIII 2 DyIII 2 (m3-OH)2(p-Me-PhCO2)6(L)2] (M ¼ Fe, 5 or Al, 7) are discussed and compared. To understand the experimental observations for this family, DFT and ab initio CASSCF + RASSI-SO calculations were performed. The experimental and theoretical calculations suggest that altering the 3dIII ions can affect the single-ion properties and the nature and the magnitude of the 3dIII–3dIII, 3dIII–DyIII and DyIII–DyIII magnetic coupling, thus quenching the quantum tunneling of magnetisation (QTM) significantly, thereby improving the SMM properties within this motif. This is the first systematic study looking at variation and therefore role of trivalent transition metal ions, as well as the diamgnetic AlIII ion, on slow relaxation of magnetisation within a series of isostructural 3d–4f butterfly compounds

Rapid detection of trace bacteria in biofluids using porous monoliths in microchannels

We present advancements in microfluidic technology for rapid detection of as few as 10 rickettsial organisms in complex biological samples. An immuno-reactive filter, macroporous polyacrylamide monolith (PAM), fabricated within a microfluidic channel enhances solid-phase immuno-capture, staining and detection of targeted bacteria. Bacterial cells in samples flowing through the channel are forced to interact with the PAM filter surface due to size exclusion, overcoming common transport and kinetic limitations for rapid (min), high-efficiency (~100%) capture. In the process, targeted cells in sample volumes of 10 ?l to >100 ?l are concentrated within a sub-50 nl region at the PAM filter edge in the microchannel, thus concentrating them over 1000-fold. This significantly increases sensitivity, as the hydrophilic PAM also yields low non-specific immuno-fluorescence backgrounds with samples including serum, blood and non-targeted bacteria. The concentrated target cells are detected using fluorescently-labeled antibodies. With a single 2.0�0�3 mm PAM filter, as few as 10 rickettsial organisms per 100 祃 of lysed blood sample can be analyzed within 60 min, as compared to hours or even days needed for conventional detection methods. This method is highly relevant to rapid, multiplexed, low-cost point of care diagnostics at early stages of infection where diagnostics providing more immediate and actionable test results are needed to improve patient outcomes and mitigate potential natural and non-natural outbreaks or epidemics of rickettsial diseases

Assisted Self-Assembly to Target Heterometallic Mn-Nd and Mn-Sm SMMs: Synthesis and Magnetic Characterisation of [Mn7_{7}Ln3_{3}(O)4_{4}(OH)4_{4}(mdea)3_{3}(piv)9_{9}(NO3_{3})3_{3}] (Ln=Nd, Sm, Eu, Gd)**

Assisted self-assembly by using a preformed [Mn$_{6}$O$_{2}$(piv)$_{10}$(4-Me-py)$_{2}$(pivH)$_{2}$] (1) (pivH=pivalic acid) cluster leads to 3 different outcomes of the reaction with Ln(NO$_{3}$)$_{3}$ ⋅ xH$_{2}$O (Ln=Pr−Ho and Y): Mn$_{7}$Ln$_{3}$ and in some cases the inverse butterfly Mn$_{2}$Ln$_{2}$ for Ln=Pr−Eu, Mn$_{5}$Ln$_{4}$ for Ln=Tb-Ho and in the special case of Gd all three possibilities can form. Whilst the magnetic properties for the Mn$_{5}$Ln$_{4}$ systems show the expected known SMM properties, for Mn$_{7}$Ln$_{3}$ two new examples of Nd- and Sm-containing SMMs have been discovered. in an assisted self-assembly approach starting from the [Mn$_{6}$O$_{2}$(piv)$_{10}$(4-Me-py)$_{2}$(pivH)$_{2}$] cluster a family of Mn−Ln compounds (Ln=Pr−Yb) was synthesised. The reaction of [Mn$_{6}$O$_{2}$(piv)$_{10}$(4-Me-py)$_{2}$(pivH)$_{2}$] (1) with N-methyldiethanolamine (mdeaH$_{2}$) and Ln(NO$_{3}$)$_{3}$ ⋅ 6H$_{2}$O in MeCN generally yields two main structure types: for Ln=Tb−Yb a previously reported Mn$_{5}$Ln$_{4}$ motif is obtained, whereas for Ln=Pr−Eu a series of Mn$_{7}$Ln$_{3}$ clusters is obtained. Within this series the Gd$^{III}$ analogue represents a special case because it shows both structural types as well as a third Mn$_{2}$Ln$_{2}$ inverse butterfly motif. Variation in reaction conditions allows access to different structure types across the whole series. This prompts further studies into the reaction mechanism of this cluster assisted self-assembly approach. For the Mn$_{7}$Ln$_{3}$ analogues reported here variable-temperature magnetic susceptibility measurements suggest that antiferromagnetic interactions between the spin carriers are dominant. Compounds incorporating Ln=Nd$^{III}$(2), Sm$^{III}$(3) and Gd$^{III}$ (5) display SMM behaviour. The slow relaxation of the magnetisation for these compounds was confirmed by ac measurements above 1.8 K

Inorganic Approach to Stabilizing Nanoscale Toroidicity in a Tetraicosanuclear Fe18_{18}Dy6_{6} Single Molecule Magnet

Cyclic coordination clusters (CCCs) are proving to provide an extra dimension in terms of exotic magnetic behavior as a result of their finite but cyclized chain structures. The Fe$_{18}$Dy$_{6}$ CCC is a Single Molecule Magnet with the highest nuclearity among Ln containing clusters. The three isostructural compounds [Fe$_{18}$Ln$_{6}$(μ-OH)$_{6}$(ampd)$_{12}$(Hampd)$_{12}$(PhCO$_{2}$)$_{24}$](NO$_{3}$)$_{6}$·38MeCN for Ln = Dy$^{III}$ (1), Lu$^{III}$ (2), or Y$^{III}$ (3), where H$_{2}^{-}$ampd = 2-amino-2-methyl-1,3-propanediol, are reported. These can be described in terms of the cyclization of six {Fe$_{3}$Ln(μOH)(ampd)$_{2}$(Hampd)$_{2}$(PhCO$_{2}$)$_{4}$}$^{+}$ units with six nitrate counterions to give the neutral cluster. The overall structure consists of two giant Dy$_{3}$ triangles sandwiching a strongly antiferromagnetically coupled Fe$_{18}$ ring, leading to a toroidal arrangement of the anisotropy axis of the Dy ions, making this the biggest toroidal arrangement on a molecular level known so far

A Method of Measuring Rates of Corrosion of Iron in the Presence of Carbon Dioxide and Air and the Influence of Electrical Potentials on Such Rates

The method consists in subjecting cylindrical samples of 4ft. by 1/10 ft. wrought iron to the action of water saturated with the gas mixture. The water and gas are passed through the cell at such a rate as to insure a constant and known composition. A precision of 5% is obtained in runs of 48 hours duration. 4% CO2 mixed with air dissolves 1 gram of iron per square centimeter of exposed surface in 735 days while it required 1927 days with air alone. A fall of 25/100 millivolt per centimeter increased the rate of corrosion 28%. 25/1000 millivolt per centimeter had no appreciable effect upon the rate. The conclusion is reached that a fall of more than 25/100 millivolt is necessary. Methods of eliminating corrosion of this type are given