Polymeric cobalt(II) thiolato complexes-syntheses, structures and properties of ¹∞[Co(SMes)₂] and ¹∞[Co(SPh)₂NH₃]

Reactions of [Co(N(SiMe3)2)2thf] with 2.1 equiv. of MesSH (Mes = C6H2-2,4,6-(CH3)3) yield dark brown crystals of the one dimensional chain compound 1∞[Co(SMes)2]. In contrast reactions of [Co(N(SiMe3)2)2thf] with 2.1 equiv. of PhSH result in the formation of a dark brown almost X-ray amorphous powder of ‘Co(SPh)2’. Addition of aliquots of CH3OH to the latter reaction resulted in the almost quantitative formation of crystalline ammonia thiolato complexes either [Co(SPh)2(NH3)2] or 1∞[Co(SPh)2NH3]. Single crystal XRD reveals that 1∞[Co(SPh)2NH3] forms one-dimensional chains in the crystal via μ2-SPh bridges whereas [Co(SPh)2(NH3)2] consists at a first glance of isolated distorted tetrahedral units. Magnetic measurements suggest strong antiferromagnetic coupling for the two chain compounds 1∞[Co(SMes)2] (J = −38.6 cm−1) and 1∞[Co(SPh)2NH3] (J = −27.1 cm−1). Interestingly, also the temperature dependence of the susceptibility of tetrahedral [Co(SPh)2(NH3)2] shows an antiferromagnetic transition at around 6 K. UV-Vis-NIR spectra display d–d bands in the NIR region between 500 and 2250 nm. Thermal gravimetric analysis of [Co(SPh)2(NH3)2] and 1∞[Co(SPh)2NH3] reveals two well separated cleavage processes for NH3 and SPh2 upon heating accompanied by the stepwise formation of ‘Co(SPh)2’ and cobalt sulfide

SMM behaviour and magnetocaloric effect in heterometallic 3d-4f coordination clusters with high azide : metal ratios

We present the synthesis and characterization of heterometallic compounds with a very large azide to metal ratio and fascinating magnetic properties

Membrane Thinning and Thickening Induced by Membrane-Active Amphipathic Peptides

Membrane thinning has been discussed as a fundamental mechanism by which antimicrobial peptides can perturb cellular membranes. To understand which factors play a role in this process, we compared several amphipathic peptides with different structures, sizes and functions in their influence on the lipid bilayer thickness. PGLa and magainin 2 from X. laevis were studied as typical representatives of antimicrobial cationic amphipathic α-helices. A 1:1 mixture of these peptides, which is known to possess synergistically enhanced activity, allowed us to evaluate whether and how this synergistic interaction correlates with changes in membrane thickness. Other systems investigated here include the α-helical stress-response peptide TisB from E. coli (which forms membrane-spanning dimers), as well as gramicidin S from A. migulanus (a natural antibiotic), and BP100 (designer-made antimicrobial and cell penetrating peptide). The latter two are very short, with a circular β-pleated and a compact α-helical structure, respectively. Solid-state 2H-NMR and grazing incidence small angle X-ray scattering (GISAXS) on oriented phospholipid bilayers were used as complementary techniques to access the hydrophobic thickness as well as the bilayer-bilayer repeat distance including the water layer in between. This way, we found that magainin 2, gramicidin S, and BP100 induced membrane thinning, as expected for amphiphilic peptides residing in the polar/apolar interface of the bilayer. PGLa, on the other hand, decreased the hydrophobic thickness only at very high peptide:lipid ratios, and did not change the bilayer-bilayer repeat distance. TisB even caused an increase in the hydrophobic thickness and repeat distance. When reconstituted as a mixture, PGLa and magainin 2 showed a moderate thinning effect which was less than that of magainin 2 alone, hence their synergistically enhanced activity does not seem to correlate with a modulation of membrane thickness. Overall, the absence of a typical thinning response in the case of PGLa, and the increase in the repeat distance and membrane thickening observed for TisB, demonstrate that the concept of peptide-induced membrane thinning cannot be generalized. Instead, these results suggest that different factors contribute to the resulting changes in membrane thickness, such as the peptide orientation in the bilayer, and/or bilayer adaptation to hydrophobic mismatch

High spin cycles: topping the spin record for a single molecule verging on quantum criticality

The cyclisation of a short chain into a ring provides fascinating scenarios in terms of transforming a finite array of spins into a quasiinfinite structure. If frustration is present, theory predicts interesting quantum critical points, where the ground state and thus lowtemperature properties of a material change drastically upon even a small variation of appropriate external parameters. This can be visualised as achieving a very high and pointed summit where the way down has an infinity of possibilities, which by any parameter change will be rapidly chosen, in order to reach the final ground state. Here we report a mixed 3d/4f cyclic coordination cluster that turns out to be very near or even at such a quantum critical point. It has a ground state spin of S = 60, the largest ever observed for a molecule (120 times that of a single electron). [Fe10Gd10(Me-tea)10(Me-teaH)10(NO3)10]\ub720MeCN forms a nano-torus with alternating gadolinium and iron ions with a nearest neighbour Fe\u2013Gd coupling and a frustrating next-nearest neighbour Fe\u2013Fe coupling. Such a spin arrangement corresponds to a cyclic delta or saw-tooth chain, which can exhibit unusual frustration effects. In the present case, the quantum critical point bears a \u2018flatland\u2019 of tens of thousands of energetically degenerate states between which transitions are possible at no energy costs with profound caloric consequences. Entropy-wise the energy flatland translates into the pointed summit overlooking the entropy landscape. Going downhill several target states can be reached depending on the applied physical procedure which offers new prospects for addressability

Beamline diagnostics for protein crystallography using synchrotron radiation

Beam diagnostics devices are described for the monitoring of all basic parameters relevant to protein data collection using synchrotron radiation. The parameters include the total power in the white beam, the positions and directions of the incident white and monochromatic beams, and the intensity, wavelength, and polarization in the incident monochromatic beam. Such devices have been installed on a doubly focusing wiggler beamline, BW6, at DORIS. They assure high quality in protein data collection despite fluctuations in the beam, facilitate rapid alignment of the entire beamline, and provide a basis for automatic realignment of the diffraction setup and the x‐ray optics

Pharmaceutical hydrates under ambient conditions from high-pressure seeds:A case study of GABA monohydrate

A monohydrate form of the neurotransmitter γ-amino butyric acid (GABA) has been crystallised in the 0.4–0.8 GPa pressure range, recovered to ambient pressure and then used as a seed. Theoretical calculations have been used to rationalise the experimental observations and gain an insight into thermodynamic stability.</p

Homoleptic 1-D Iron Selenolate Complexes — Synthesis, Structure, Magnetic and Thermal Behaviour of 1•[Fe(SeR)2] (R = Ph, Mes)

The first examples of polymeric homoleptic iron chalcogenolato complexes 1 [Fe(SePh)2] and [Fe(SeMes)2] (Ph = phenyl = C6H5, Mes = mesityl = C6H2-2,4,6-(CH3)3) have been both prepared by reaction of [Fe(N(SiMe3)2)2] with two equivalents of HSeR (R = Ph, Mes) while 1 1[Fe(SePh)2] was found to be also easily accessible through reactions of either FeCl2, Fe(OOCCH3)2 or FeCl3 with PhSeSiMe3 in THF. In the crystal, the two compounds form one-dimensional chains with bridging selenolate ligands comprising distinctly different Fe–Se–Fe bridging angles, namely 71.15–72.57◦ in 1 [Fe(SePh)2] and 91.80◦ in 1 [Fe(SeMes)2]. Magnetic measurements supported by DFT calculations reveal that this geometrical change has a pronounced influence on the antiferromagnetic exchange interactions of the unpaired electrons along the chains in the two different compounds with a calculated magnetic exchange coupling constant of J = -137 cm-1 in 1 [Fe(SePh)2] and J = -20 cm-1 in 1 [Fe(SeMes)2]. In addition we were able to show that the ring molecule [Fe(SePh)2]12 which is a structural isomer of [Fe(SePh)2] behaves magnetically similar to the latter one. Investigations by powder XRD reveal that the ring molecule is only a metastable intermediate which converts in THF completely to form [Fe(SePh)2]. Thermal gravimetric analysis of 1 [Fe(SePh)2] under vacuum conditions shows that the compound is thermally labile and already starts to decompose above 30 ◦C in a two step process under cleavage of SePh2 to finally form at 250 ◦C tetragonal PbO-type FeSe. The reaction of [Fe(SePh)2] with the Lewis base 1,10-phenanthroline yielded, depending on the conditions, the octahedral monomeric complexes [Fe(SePh)2(1,10-phen)2] and [Fe(1,10-phen)3][Fe(SePh)4].JRC.DDG.F.2-Cleaner energ