Single-chain magnet (NEt4)[Mn2(5-MeOsalen)2Fe(CN)6] Made of Mn(III)-Fe(III)-Mn(III) trinuclear single-molecule magnet with an S(T) = 9/2 spin ground state

The cyano-bridged trinuclear compound, (NEt(4))[Mn(2)(salmen)(2)(MeOH)(2)Fe(CN)(6)] (1) (salmen(2)(-) = rac-N,N'-(1-methylethylene)bis(salicylideneiminate)), reported previously by Miyasaka et al. (ref 19d) has been reinvestigated using combined ac and dc susceptibility measurements. The strong frequency dependence of the ac susceptibility and the slow relaxation of the magnetization show that 1 behaves as a single-molecule magnet with an S(T) = (9)/(2) spin ground state. Its relaxation time (tau) follows an Arrhenius law with tau(0) = 2.5 x 10(-)(7) s and Delta(eff)/k(B) = 14 K. Moreover, below 0.3 K, tau saturates around 470 s, indicating that quantum tunneling of the magnetization becomes the dominant process of relaxation. (NEt(4))[Mn(2) (5-MeOsalen)(2)Fe(CN)(6)] (2) (5-MeOsalen(2)(-) = N,N'-ethylenebis(5-methoxysalicylideneiminate)) is a heterometallic one-dimensional assembly made of the trinuclear [Mn(III)(SB)-NC-Fe(III)-CN-Mn(III)(SB)] (SB is a salen-type Schiff-base ligand) motif similar to 1. Compound 2 has two types of bridges, a cyano bridge (-NC-) and a biphenolate bridge (-(O)(2)-), connecting Mn(III) and Fe(III) ions and the two Mn(III) ions, respectively. Both bridges mediate ferromagnetic interactions, as shown by modeling the magnetic susceptibility above 10 K with g(av) = 2.03, J(Mn)(-)(Fe)/k(B) = +6.5 K, and J'/k(B) = +0.07 K, where J' is the exchange coupling between the trimer units. The dc magnetic measurements of a single crystal using micro-SQUID and Hall-probe magnetometers revealed a uniaxial anisotropy (D(T)/k(B) = -0.94 K) with an easy axis lying along the chain direction. Frequency dependence of the ac susceptibility and time dependence of the dc magnetization have been performed to study the slow relaxation of the magnetization. A mean relaxation time has been found, and its temperature dependence has been studied. Above 1.4 K, both magnetic susceptibility and relaxation time are in agreement with the dynamics described in the 1960s by R. J. Glauber for one-dimensional systems with ferromagnetically coupled Ising spins (tau(0) = 3.7 x 10(-)(10) s and Delta(1)/k(B) = 31 K). As expected, at lower temperatures below 1.4 K, the relaxation process is dominated by the finite-size chain effects (tau'(0) = 3 x 10(-)(8) s and Delta(2)/k(B) = 25 K). The detailed analysis of this single-chain magnet behavior and its two regimes is consistent with magnetic parameters independently estimated (J'and D(T)) and allows the determination of the average chain length of 60 nm (or 44 trimer units). This work illustrates nicely a new strategy to design single-chain magnets by coupling ferromagnetically single-molecule magnets in one dimension.     

The Caenorhabditis elegans DEG-3/DES-2 Channel Is a Betaine-Gated Receptor Insensitive to Monepantel

Natural plant compounds, such as betaine, are described to have nematocidal properties. Betaine also acts as a neurotransmitter in the free-living model nematode Caenorhabditis elegans, where it is required for normal motility. Worm motility is mediated by nicotinic acetylcholine receptors (nAChRs), including subunits from the nematode-specific DEG-3 group. Not all types of nAChRs in this group are associated with motility, and one of these is the DEG-3/DES-2 channel from C. elegans, which is involved in nociception and possibly chemotaxis. Interestingly, the activity of DEG-3/DES-2 channel from the parasitic nematode of ruminants, Haemonchus contortus, is modulated by monepantel and its sulfone metabolite, which belong to the amino-acetonitrile derivative anthelmintic drug class. Here, our aim was to advance the pharmacological knowledge of the DEG-3/DES-2 channel from C. elegans by functionally expressing the DEG-3/DES-2 channel in Xenopus laevis oocytes and using two-electrode voltage-clamp electrophysiology. We found that the DEG-3/DES-2 channel was more sensitive to betaine than ACh and choline, but insensitive to monepantel and monepantel sulfone when used as direct agonists and as allosteric modulators in co-application with betaine. These findings provide important insight into the pharmacology of DEG-3/DES-2 from C. elegans and highlight the pharmacological differences between non-parasitic and parasitic nematode species.     

Comparison of microwave and lower-frequency discharges for plasma polymerization

A plasma sustained by surface waves (SW) has been used to study the deposition rate R of hydrocarbon and fluorocarbon plasma polymer films as a function of excitation frequency f=/2 in the range 12–400 MHz. The SW technique allows one to vary only f while keeping constant all other parameters known to influence R, for example, power density in the plasma P. A plot of R/P at a total pressure of 200 m Torr (27 Pa) displays two plateaus, that at f<30 MHz being about five times lower than that at f100 MHz. This is attributed to the fact that electron energy distribution functions differ fundamentally at radio- (f50 MHz) and microwave (f100 MHz) frequencies, for the gas pressure range considered.     

Porphyrin derivatives having physical and chemical characteristics similar to those of the active components of hematoporphyrin derivative and with very strong photosensitizing effects

The tumour-localizing fraction of hematoporphyrin derivative (Hpd) is thought to possess an essentially diporphyrin ether structure or, alternatively, a diporphyrin ester structure, the properties of which facilitate its retention in malignant cells and its biological activity on irradiation. To elucidate this problem further, we have synthesized the dimethyl, diethyl, dipropyl, di-n-butyl and di-iso-butyl ethers of hematoporphyrin. These ethers show chromatographic properties very similar to those of the active components of Hpd. Furthermore, they are much better photosensitizers in a cellular system than are crude Hpd or Photofrin II, and, like the components of Hpd, they are taken up and retained by cells according to their degree of non-polarity.     

Investigations on the interactions between Li-TFSI and glass fibers in the ternary PP/GF/Li-TFSI composites

The polypropylene/glass fiber(PP/GF) composites with excellent antistatic performance and improved mechanical properties have been reported by incorporation of a very small amount of the organic salt, lithium bis(trifluoromethanesulfonyl)imide(Li-TFSI), into the PP/GF composites. It was considered that GF could play the role as the pathways for the movements of ions in the ternary composites. In this work, the interactions between Li-TFSI and glass fiber and the effects of such interactions on the physical properties of the composites have been systematically investigated. Three types of glass fibers with different ―OH group concentrations have been prepared in order to compare the interactions between GF and Li-TFSI. It was found that the ―OH group concentrations on the surface of glass fiber have significant effects on interactions between glass fibers and Li-TFSI. Such interactions are crucial for both the antistatic and mechanical performances of the final PP/GF/Li-TFSI composites. The investigation indicated that the GF with high ―OH group concentrations confined the movement of TFSI-, which decreased the antistatic properties of PP/GF/Li-TFSI composites. On the other hand, the GF with low ―OH group concentrations inhibited the absorption of Li-TFSI onto the GF, which also hindered the formation of Li-TFSI conductive pathway. The best antistatic performance of the ternary composites can be achieved at the intermediate ―OH concentrations on the GF.     

Synthesis of bis(amidoxime)s and evaluation of their properties as uranyl-complexing agents

Uranium pollution involves high toxicity and radioactivity and, therefore, constitutes a grave threat to human health and the environment. Chelation is an effective method for sequestering uranium. It is well known that chelators based on oxime groups are able to complex uranyl cations efficiently. To this end, various bis(amidoxime)s were synthesized by reaction of hydroxylamine with the corresponding dinitriles. In these compounds the amidoximes are separated by chains of various lengths, some including a heterocycle (pyridine or 1,3,5-triazine). The abilities of these bis(amidoxime)s to complex uranyl cation in water were evaluated by determining their affinity constants and thermodynamic parameters by means of Isothermal Titration Calorimetry (ITC). DFT calculations were also performed, to determine the optimum structures of the complexes formed between uranyl cations and the oximate groups. A tetrakis(amidoxime), also synthesized in this work, shows good affinity for uranium, and a single molecule is able chelate several uranyl cations. These results are of importance for the remediation of uranium-polluted wastewaters, and open up several perspectives for the design and synthesis of new amidoxime compounds.     

Oxydation chromique de l'adamantanone : preparation de l'acetoxy-5 adamantanone-2

chromic oxidation of adamantanone gives adamantane-2,6-dione (20%), 5-hydroxy adamantan-2-one (6%) and 5-acetoxy adamantan-2-one (36%).     

Global Solutions of the Boltzmann Equation Over {\mathbb{R}^D} Near Global Maxwellians with Small Mass

We consider the random regular k-nae- sat problem with n variables, each appearing in exactly d clauses. For all k exceeding an absolute constant \({{\it k}_0}\), we establish explicitly the satisfiability threshold \({{{d_\star} \equiv {d_\star(k)}}}\). We prove that for \({{d < d_\star}}\) the problem is satisfiable with high probability, while for \({{d > d_\star}}\) the problem is unsatisfiable with high probability. If the threshold \({{d_\star}}\) lands exactly on an integer, we show that the problem is satisfiable with probability bounded away from both zero and one. This is the first result to locate the exact satisfiability threshold in a random constraint satisfaction problem exhibiting the condensation phenomenon identified by Krz?aka?a et al. [Proc Natl Acad Sci 104(25):10318–10323, 2007]. Our proof verifies the one-step replica symmetry breaking formalism for this model. We expect our methods to be applicable to a broad range of random constraint satisfaction problems and combinatorial problems on random graphs.     

Characterisation of human hair surfaces by means of static ToF-SIMS: A comparison between Ga and C60 primary ions

This study deals with the secondary ion yield improvement induced by using C₆₀⁺ primary ions instead of Ga⁺ ones to characterize human hair surfaces by ToF-SIMS. For that purpose, a bunch of hair fibres has been analysed with both ion sources. A high improvement is observed for the detection of amino acids with C₆₀⁺ primary ions as compared to Ga⁺ ions. As an example, a yield enhancement factor greater than 3000 is found for the CNO⁻ peak. A similar gain is observed for the positive secondary ions characteristic of the amino acids. Most of the atomic ions, such as Ca⁺, O⁻ and S⁻, constitute minor peaks with C₆₀⁺ ions while they often dominate the spectrum in the case of Ga⁺ ions. However, with the C₆₀⁺ source, a series of inorganic combination peaks with the elements Ca, S and O are observed in the positive spectra (i.e. HCaSO₄⁺), while they are marginal with the Ga⁺ source. For the mass range beyond 100 m/z and in both polarities, the hair fingerprints are similar with both sources. In average, for a comparable number of primary ions per spectrum, the C₆₀⁺ ion source gives intensities between two and three orders of magnitude higher than the Ga⁺ one.