NMR studies into colloidal stability and magnetic order in fatty acid stabilised aqueous magnetic fluids

We report the physico-chemical characterisation of fatty acid stabilised aqueous magnetic fluids, which are ideal systems for studying the influence of nanoparticle aggregation on the emergent magnetic resonance properties of the suspensions. Stable colloids of superparamagnetic magnetite, Fe(3)O(4), nanoparticle clusters in the 80 to 100 nm size range were produced by in situ nanoparticle growth and stabilisation, and by suspending pre-formed nanoparticles. NMR relaxation analysis shows that the magnetic resonance properties of the two types of suspension differ substantially and provides new insights into how the relaxation mechanisms are determined by the organisation of the nanoparticles within the clusters.     

Insights into the mechanism of O₂ formation and release from the Mn₄O₄L₆ "cubane" cluster

To probe photoinduced water oxidation catalyzed by the Mn?O?L? cubane clusters, we have computationally studied the mechanism and controlling factors of the O? formation from the [Mn?O?L?] catalyst, 6. It was demonstrated that dissociation of an L = H?PO?? ligand from 6 facilitates the direct O-O bond formation that proceeds with a 28.3 (33.4) kcal/mol rate-determining energy barrier at the transition state TS1. This step (the O-O single bond formation) of the reaction is a two-electron oxidation/reduction process, during which two oxo ligands are transformed into to μ2:η2-O?2? unit, and two ("distal") Mn centers are reduced from the 4+ to the 3+ oxidation state. Next two-electron oxidation/reduction occurs by "dancing" of the resulted O?2? fragment between the Mn1 and Mn2/Mn(2')-centers, keeping its strong coordination to the Mn(1')-center. As a result of this four-electron oxidation/reduction process Mn centers of the Mn?-core of I transform from {Mn1(III)-Mn(1')(III)-Mn2(IV)-Mn(2')(IV)} to {Mn1(II)-Mn(1')(II)-Mn2(III)-Mn(2')(III)} in IV. In other words, upon O? formation in cationic complex [Mn?O?L?](+), I, all four Mn-centers are reduced by one electron each. The overall reaction I → TS1 → II → III → TS2 → IV → TS3 → V → VI + O? is found to be exothermic by 15.4 (10.5) kcal/mol. We analyze the lowest spin states and geometries of all reactants, intermediates, transition states, and products of the targeted reaction.     

The aza Arndt–Eistert reaction based on N-trifluoromethylsulfonylarenecarboximidoyl chlorides

The aza analogues of carboxylic acids chlorides containing the NSO₂CF₃ and NSO₂CH₃ groups instead of oxygen atom were used in the Arndt–Eistert reaction. It was found that N-trifluoromethylsulfonyl-(4-fluorophenyl)-carboximidoyl chloride 1 reacts with diazomethane vigorously even at ?70 °C with formation of 1-trifluoromethylsulfonylamino-2-(4-fluorophenyl)-2,3-dimorpholine-4-yl-propane 3, 2-trifluoromethylsulfonylamino-2-(4-fluorobenzyl)-7-oxa-4-azonia-spiro[3.5]nonane 4, 2-trifluoromethylsulfonylamino-2-(4-fluorobenzyl)-1,3-dimorpholine-4-yl-propane 5 and 1-trifluoromethylsulfonylamino-2-(4-fluorobenzyl)-2,3-dimorpholine-4-yl-propane 6. Reaction of N-methylsulfonylbenzcarboximidoyl chloride 8 with diazomethane proceeds at ?15 °C yielding 4-chloro-4-methylsulfonylaminomethyl-3-phenyl-4,5-dihydro-1H-pyrazoline 9.     

Model for the dynamics of two interacting axisymmetric spherical bubbles undergoing small shape oscillations

Interaction between acoustically driven or laser-generated bubbles causes the bubble surfaces to deform. Dynamical equations describing the motion of two translating, nominally spherical bubbles undergoing small shape oscillations in a viscous liquid are derived using Lagrangian mechanics. Deformation of the bubble surfaces is taken into account by including quadrupole and octupole perturbations in the spherical-harmonic expansion of the boundary conditions on the bubbles. Quadratic terms in the quadrupole and octupole amplitudes are retained, and surface tension and shear viscosity are included in a consistent manner. A set of eight coupled second-order ordinary differential equations is obtained. Simulation results, obtained by numerical integration of the model equations, exhibit qualitative agreement with experimental observations by predicting the formation of liquid jets. Simulations also suggest that bubble-bubble interactions act to enhance surface mode instability.     

Transannular additions of selectfluor and xenon difluoride: regioselectivity and mechanism

The addition of 1‐chloromethyl‐4‐fluoro‐1,4‐diazoniabicyclo[2.2.2]octane bis‐tetrafluoroborate (F‐TEDA) to unsaturated systems was modelled computationally at the ab initio levels and studied experimentally. The reaction of olefins with F‐TEDA is driven exclusively by charge transfer and displays the antibonding orbital picture in the transition structure for F‐transfer, similarly to that for the reactions of olefins with F‐radical. In contrast, the electrophilic and concerted fluorinations, respectively with H₂O???F⁺ complex and with F₂, show strong bonding interactions between the fluorine and olefin moieties in the transition structures. The reaction with F‐TEDA involves an initial formation of highly delocalized charge‐transfer complexes in the first step with further low‐barrier (ca 4 kcal) migration of fluorine and is best described as an inner‐sphere electron transfer. This nonelectrophilic mechanism is operative for the transannular addition of F‐TEDA to 3‐methylene‐7‐ethylidenebicyclo[3.3.1]nonane studied experimentally. The addition mode is determined by the formation of a more stable complex via the ethylidene fragment and demonstrates selectivities that differ from conventional electrophilic additions. This mechanistic scenario may be extended to the fluorination with xenon difluoride where similar products are formed in high yields. Copyright © 2010 John Wiley & Sons, Ltd.     

EPR evidence of antiferromagnetic ordering in single‐layer graphene

We report electron paramagnetic resonance (EPR) evidence of the antiferromagnetic ordering in pristine single‐layer graphene. Temperature dependences of the parameters of EPR spectra obtained for vacuum‐processed samples were studied within the temperature range of 4.2–300 K. Our experiment has confirmed recent theoretical predictions that in single‐layer graphene the carrier‐mediated exchange interaction leads to antiferromagnetic coupling. We note some quantitative discrepancies between the theory and experimental findings and discuss their origins. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Spatial condensation of trapped polaritons in graphene and semiconductor structures

The theoretical and experimental status of the Bose–Einstein Condensation (BEC) of trapped quantum well (QW) polaritons in a microcavity is presented. The results of recent experiments that have shown the possibility to create an in-plane harmonic potential trap for a two-dimensional (2D) exciton polaritons in a cavity are discussed. We report the theory of BEC and of the trapped QW exciton polaritons in a microcavity. In addition, we study the BEC of trapped magnetoexciton polaritons in a graphene layer (GL) embedded in an optical microcavity in high magnetic field. In both cases the polaritons are considered to be in a harmonic potential trap. We compare the theoretical results with the existing experiments and discuss the experimental observation of predicted phenomena.     

Cichoń’s diagram,regularity properties and {\varvec{\Delta}^1_3} sets of reals

We study regularity properties related to Cohen, random, Laver, Miller and Sacks forcing, for sets of real numbers on the \({\varvec{\Delta}^1_3}\) level of the projective hieararchy. For \({\varvec{\Delta}^1_2}\) and \({\varvec{\Sigma}^1_2}\) sets, the relationships between these properties follows the pattern of the well-known Cichoń diagram for cardinal characteristics of the continuum. It is known that assuming suitable large cardinals, the same relationships lift to higher projective levels, but the questions become more challenging without such assumptions. Consequently, all our results are proved on the basis of ZFC alone or ZFC with an inaccessible cardinal. We also prove partial results concerning \({\varvec{\Sigma}^1_3}\) and \({\varvec{\Delta}^1_4}\) sets.