Self-assembly dynamics of a cylindrical capsule monitored by fluorescence resonance energy transfer

The constituent cavitands of a cylindrical capsule were labeled with donor and acceptor fluorophores, and fluorescence resonance energy transfer (FRET) was employed as a tool to study the dynamics of self-assembly. When donor and acceptor dyes are present in the same capsular assembly, they are brought within 25 A of each other, a distance suitable for efficient energy transfer to occur between them. This allowed for the study of interacting species at nanomolar concentrations providing information unattainable from NMR experiments. The kinetic stability of the capsule in the presence of various guest molecules was investigated which revealed a range of more than 4 orders of magnitude in the rates of cylindrical capsule exchange. While the thermodynamic stability of the capsule generally dictates the self-assembly dynamics, it was discovered that longer rigid guests can impart a significant kinetic barrier to monomer exchange.     

Profiling of amine metabolites in human biofluids by micellar electrokinetic chromatography with laser-induced fluorescence detection

A rapid and sensitive capillary electrophoresis (CE) method has been developed for profiling organic metabolites containing amine functional groups in mammalian biofluids. Metabolites containing an amine group were derivatized with 4-fluoro-7-nitrobenzo-2,1,3-oxadiazol (NBD-F), separated by micellar electrokinetic chromatography (MEKC), and detected by argon-ion (488 nm) laser-induced fluorescence detection. The optimized MEKC background electrolyte conditions were: 50 mmol L⁻¹ sodium cholate, 5 mmol L⁻¹ β-cyclodextrin, and 20 mmol L⁻¹ Brij 35 in 20 mmol L⁻¹ aqueous borate buffer, pH 9.3, containing 7% methanol. Under these conditions all the amine compounds in mammalian biofluids, for example plasma, saliva, and urine, were derivatized directly, without extraction, in a minimum volume of 100 nL and the derivatives could be separated within 16 min. Up to 90% of the amine-containing metabolites in plasma and saliva could be identified by reference to standard compounds. For twenty amine standards linearity of calibration was better than R ² = 0.99. Migration-time and peak-area reproducibility were better than RSD 1.5% and 15% respectively. In replicate analysis of human plasma bioanalytical precision ranged between 0.7 and 3.8 RSD% for a 5.0-μL volume and between 1.7 and 5.5 RSD% for 100-nL volume. The concentrations measured were found to be in agreement with literature values.     

Mixed-valence states formation in conformationally flexible metal-free 5,10,15,20-tetraferrocenylporphyrin and 5,10-bisferrocenyl-15,20-bisphenylporphyrin

Metal-free 5,10,15,20-tetraferrocenylporphyrin and 5,10-bisferrocenyl-15,20-bisphenylporphyrin have been prepared and characterized by UV-Vis, MCD, (1)H, (13)C, and variable-temperature NMR, APCI- and ESI-MS, and M?ssbauer spectroscopy, while their redox properties were investigated using electrochemical (cyclic voltammetry and differential pulse voltammetry), spectroelectrochemical, and chemical oxidation approaches. The electronic structure calculations at Density Functional Theory level reveal that both compounds adopt saddle conformations and the HOMOs in both complexes are predominantly metal-centered, while the LUMOs predominantly consist of porphyrin pi* orbitals. In spite of the rotational freedom of ferrocenyl substituents at room temperature, both metal-free 5,10,15,20-tetraferrocenylporphyrin and 5,10-bisferrocenyl-15,20-bisphenylporphyrin are able to form mixed-valence states upon the successive ferrocene-based two- and one-electron oxidations, respectively, as confirmed by UV-Vis, MCD, M?ssbauer, electro-, and spectroelectrochemical methods, and thus, the earlier suggested (Boyd et al. Chem. Commun., 1999, 637) requirements for the formation of mixed-valence states in ferrocene-containing porphyrins should be revised.     

Total syntheses of angelicoin A, hericenone J, and hericenol A via migratory prenyl- and geranylation-aromatization sequences

A five-step synthesis of the natural product angelicoin A using a late stage highly regioselective palladium(0)-catalyzed decarboxylative prenyl migration and aromatization sequence as the key step is reported. The method was extended with geranyl migration in eight-step total syntheses of hericenone J and hericenol A from geraniol.     

A continuum calculation for the giant dipole resonance in28Si including the effect of collective correlations

Continuum shell model calculations for the giant dipole resonance in²⁸Si based on both the 1p 1h model and the collective correlation model are described and the results compared with experiment. The eigenchannel theory of nuclear reactions has been used to include the effect of the particle continuum.     

M1 transition strength in the SU(3) limit of the generalized IBM-2

We generalize the SU(3) limit of the standard IBM-2 formalism of sd bosons to sdg…λ bosons, where λ denotes a boson of arbitrarily large, even angular momentum λ, and investigate the effect on the B(M1, 0₁⁺ → 1⁺) transition strength. In the SU(3) limit, all the M1 transition strength resides in a single 1⁺ state and is proportional to λ.     

Electronic surface states of Cu(1 1 0) surface

Surface states are a unique and important class of quantum states that shave an important effect on the electronic properties of Cu(1 1 0) surface. The Cu(1 1 0) surface has been studied using ultraviolet photoemission spectroscopy (PES), inverse photoemission spectroscopy (IPES), and reflection anisotropy spectroscopy (RAS), and shows a resonance in the RAS spectra at 2.1 eV due to a transition between occupied and unoccupied surface states. The unoccupied surface state involved in the RAS transition at an energy of 1.7 eV at the point of the surface Brillouin zone has been investigated using IPES and the occupied surface state is seen in PES spectra at 0.45 eV below the Fermi level. The energy difference of the surface states, 2.15 eV, is a good match to the transition energy found in the RAS experiments.