Regioselective synthesis of antiparallel loops on a macrocyclic scaffold constrained by oxazoles and thiazoles

The regioselective syntheses and structures are reported for two tris-macrocylic compounds, each possessing two antiparallel loops on a macrocyclic scaffold constrained by two oxazoles and two thiazoles. NMR solution structures show the loops projecting from the same face of the macrocycle. Such molecules are shown to be prototypes for mimicking multiple loops of proteins.[structure: see text]     

A diatropic ring current in a fluorofullerene trannulene

Ipsocentric current-density maps for a fluorofullerene derivative, C60F15H3, modelling the addition pattern of the experimentally characterised C60F15[CBr(CO2Et)2]3 which contains an [18]trans-annulene system, reveal a diamagnetic ring current dominated by the contribution of the four HOMO electrons, as in a classical (4n + 2) aromatic annulene.     

On the first excited state of137Ba

The first excited state of¹³⁷Ba has been excited by the inelastic scattering of accelerator-produced neutrons. The energy of this state at 283.5 keV is not in agreement with the generally accepted value of 279.2 keV, but is in accord with other recent measurements. No evidence for a doublet of states near this energy is found.     

Application of solution techniques for rapid growth of organic crystals

Single crystals of a pure hydrocarbon, 1,3,5-triphenylbenzene, with properties suitable for high-energy neutron detection were grown from toluene solutions using slow evaporation and temperature reduction methods with growth rates up to 10 mm/day. Application of the rapid growth technique developed earlier for growth of large water-soluble crystals shows that crystals of aromatic compounds can be successfully grown from solutions in large volumes required for their use as scintillator materials for radiation detection.     

Influence of Equilibration Time in Solution on the Inclusion/Exclusion Topology Ratio of Host–Guest Complexes Probed by Ion Mobility and Collision‐Induced Dissociation

Host–guest complexes are formed by the creation of multiple noncovalent bonds between a large molecule (the host) and smaller molecule(s) or ion(s) (the guest(s)). Ion‐mobility separation coupled with mass spectrometry nowadays represents an ideal tool to assess whether the host–guest complexes, when transferred to the gas phase upon electrospray ionization, possess an exclusion or inclusion nature. Nevertheless, the influence of the solution conditions on the nature of the observed gas‐phase ions is often not considered. In the specific case of inclusion complexes, kinetic considerations must be taken into account beside thermodynamics; the guest ingression within the host cavity can be characterized by slow kinetics, which makes the complexation reaction kinetically driven on the timescale of the experiment. This is particularly the case for the cucurbituril family of macrocyclic host molecules. Herein, we selected para‐phenylenediamine and cucurbit[6]uril as a model system to demonstrate, by means of ion mobility and collision‐induced dissociation measurements, that the inclusion/exclusion topology ratio varies as a function of the equilibration time in solution prior to the electrospray process.     

NMR elucidation of a novel (S)-pentacyclo-undecane bis-(4-phenyloxazoline) ligand and related derivatives

The NMR elucidation of a novel ligand (S)-pentacyclo-undecane bis-(4-phenyloxazoline) and related pentacyclo-undecane (PCU) derivatives is reported. Two-dimensional NMR proved to be a powerful technique in overcoming the difficulties associated with the elucidation of these compounds when only one-dimensional NMR data is utilized. A chiral substituent was introduced to both 'arms' of the PCU skeleton to produce derivatives 1-3. These derivatives display C(1) symmetry with all thecage atoms being nonequivalent. Owing to overlapping of peaks in the (1)H spectra, identification of these diastereomeric protons was very difficult. The (13)C spectra gave rise to clear splitting of the nonequivalent carbons. This is unusual compared to similar PCU derivatives with chiral substituents as splitting of all the diastereomeric cage carbons has not yet been reported. Nuclear Overhauser enhancement spectroscopy (NOESY) correlations of derivatives 1-3 confirm the different conformations of the molecule in which the side 'arms' occupy different orientations with respect to cage moiety.     

New synthetic routes to a disulfidodinickel(II) complex: characterization and reactivity of a Ni2(mu-eta2:eta2-S2) core

Activation of elemental sulfur by the monovalent nickel complex [PhTt (tBu)]Ni(CO) [PhTt(tBu)=phenyl{tris[(tert-butylmethyl)thio]methyl}borate] generates the disulfidodinickel(II) complex 2. This species is alternatively accessible via thermal decomposition of [PhTt (tBu)]Ni(SCPh3). Spectroscopic, magnetic, and X-ray diffraction studies establish that 2 contains a mu-eta(2):eta(2)-S2 ligand that fosters antiferromagnetic exchange coupling between the Ni (II) ions. This observation is in contrast to the lighter congener, oxygen, which strongly favors the bis(mu-oxo)dinickel(III) structure. 2 oxidizes PPh 3 to SPPh3 and reacts with O2, generating several products, one of which has been identified as [(PhTt (tBu))Ni]2(mu-S) (3).     

Interactions and dynamics in ionic liquids

Precise dielectric spectra have been determined at 25 degrees C over the exceptionally broad frequency range of 0.1 相似文献   

Nature of the pygmy resonance in continuous <Emphasis Type="Italic">γ</Emphasis> spectra

Two-step-cascade spectra of the ¹⁷¹Yb(n, γγ)¹⁷²Yb reaction have been measured using thermal neutrons. They are compared to calculations based on experimental values of the level density and radiative strength function obtained from the ¹⁷³Yb(³He, aγ)¹⁷²Yb reaction. The multipolarity of a 6.5(15) μ _N ² resonance at 3.3(1) MeV in the strength function is determined to be M1 by this comparison.