Novel neutral iron(II) isocyanide maleonitrile dithiolate [Fe(S2C2(CN)2)(t-BuNC) 4] compound

FeBr2 reacts with the S2C2(CN)2(2-) ion (1:1 ratio) in the presence of an excess of t-BuNC in THF to give the mixed ligand [Fe(S2C2(CN)2)(t-BuNC) 4] compound. This neutral product with a formal oxidation state of two for the iron atom was characterized by conductivity measurements, and, i.r., Mössbauer, 13C and ¹H n.m.r. spectroscopy. There is a Fe-C pi back-donation strengthened towards isocyanide ligands, according to the data of 13C, ¹H n.m.r. and Mössbauer spectroscopy.7678Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Synthesis of the binuclear [Fe(CNBu t)(CO)4(HgSO4 )] adduct

The binuclear [Fe(CNBu t)(CO)4(HgSO4 )] adduct was obtained in the reaction of HgSO4 with [Fe(CNBu t)(CO)4] in methanol. This adduct, without a similar in the homoleptic pentacarbonyliron, was characterized by analytical and spectroscopic data. Further Mössbauer and molar conductivity studies have confirmed it's adduct nature.29930

Raft-based sphingomyelin interactions revealed by new fluorescent sphingomyelin analogs

Sphingomyelin (SM) has been proposed to form cholesterol-dependent raft domains and sphingolipid domains in the plasma membrane (PM). How SM contributes to the formation and function of these domains remains unknown, primarily because of the scarcity of suitable fluorescent SM analogs. We developed new fluorescent SM analogs by conjugating a hydrophilic fluorophore to the SM choline headgroup without eliminating its positive charge, via a hydrophilic nonaethylene glycol linker. The new analogs behaved similarly to the native SM in terms of their partitioning behaviors in artificial liquid order-disorder phase-separated membranes and detergent-resistant PM preparations. Single fluorescent molecule tracking in the live-cell PM revealed that they indirectly interact with each other in cholesterol- and sphingosine backbone–dependent manners, and that, for ∼10–50 ms, they undergo transient colocalization-codiffusion with a glycosylphosphatidylinositol (GPI)-anchored protein, CD59 (in monomers, transient-dimer rafts, and clusters), in CD59-oligomer size–, cholesterol-, and GPI anchoring–dependent manners. These results suggest that SM continually and rapidly exchanges between CD59-associated raft domains and the bulk PM

Enhancement of the Electron Spin Resonance of Single-Walled Carbon Nanotubes by Oxygen Removal

We have observed a nearly fourfold increase in the electron spin resonance (ESR) signal from an ensemble of single-walled carbon nanotubes (SWCNTs) due to oxygen desorption. By performing temperature-dependent ESR spectroscopy both before and after thermal annealing, we found that the ESR in SWCNTs can be reversibly altered via the molecular oxygen content in the samples. Independent of the presence of adsorbed oxygen, a Curie-law (spin susceptibility $\propto 1/T$) is seen from $\sim$4 K to 300 K, indicating that the probed spins are finite-level species. For both the pre-annealed and post-annealed sample conditions, the ESR linewidth decreased as the temperature was increased, a phenomenon we identify as motional narrowing. From the temperature dependence of the linewidth, we extracted an estimate of the intertube hopping frequency; for both sample conditions, we found this hopping frequency to be $\sim$100 GHz. Since the spin hopping frequency changes only slightly when oxygen is desorbed, we conclude that only the spin susceptibility, not spin transport, is affected by the presence of physisorbed molecular oxygen in SWCNT ensembles. Surprisingly, no linewidth change is observed when the amount of oxygen in the SWCNT sample is altered, contrary to other carbonaceous systems and certain 1D conducting polymers. We hypothesize that physisorbed molecular oxygen acts as an acceptor ($p$-type), compensating the donor-like ($n$-type) defects that are responsible for the ESR signal in bulk SWCNTs.Comment: 14 pages, 7 figure

Electron spin resonance study of interacting donor clusters in phosphorus-doped silicon at 100 GHz and low temperatures

ESR experiments have been performed on phosphorus-doped silicon with concentrations ranging from 1.9 x 10 17 cm-3 to 2.8 ×1018 cm-3 at 1.4-4.2 K and 100 GHz. The peak shift of the central ESR line with respect to the center of the two hyperfine lines has been investigated as a function of donor concentration, temperature, and microwave power. In general, it consists of a microwave power-dependent part and of a microwave power-independent one. The former part is interpreted in terms of the Overhauser effect ; the latter one is due to an asymmetry of the spectrum, understood on the basis of a new model proposed by one of the authors, which takes into account the clustering of nearby donors according to the exchange interaction between their electronic spins, and the hyperfine interaction with 31P nuclei.Nous avons étudié, par résonance de spin électronique à 100 GHz, à 1,4 K et 4,2 K, le silicium dopé au phosphore de la région de concentration en donneurs comprise entre 1,9 × 1017 cm-3 et 2,8 x 10 18 cm-3. Le déplacement de la raie centrale par rapport aux deux raies hyperfines a été étudié en fonction de la concentration en donneurs, de la température et de la puissance hyperfréquence. A faible puissance hyperfréquence, le déplacement de la raie centrale est dû à une asymétrie du spectre, interprétée dans un modèle proposé par un des auteurs, qui tient compte du regroupement des donneurs en amas en fonction des interactions d'échange entre leurs spins électroniques et de l'interaction hyperfine entre électrons et noyau 31P. L'augmentation du déplacement avec la puissance hyperfréquence est attribuée à une augmentation de la polarisation nucléaire par effet Overhauser