Crystal structure of 2,8,14,20-tetranaphthylpyrogallol[4]arene

The aromatic derivative 2,8,14,20-tetranaphthylpyrogallol[4]arene was synthesized by the acid catalyzed condensation of 2-naphthaldehyde and pyrogallol in refluxing aqueous ethanol. Single crystal X-ray analysis revealed that the molecule crystallizes in a triclinic space group P1(bar) No. 2, with a = 11.3396(7) Å, b = 15.9942(10) Å, c = 26.3653(17) Å, α = 94.309(2)°, β = 91.765(2)°, γ = 93.892(2)°, D _calc = 1.298 g/m³ for Z = 1. Within the unit cell, six methanol molecules of crystallization plus one molecule of pyrazine were found to accompany the pyrogallol macrocycle. In the solid state, the macrocycle is found to adopt the chair conformation.     

An explicit semi-factorial compactification of the Néron model

C. Pépin recently constructed a semi-factorial compactification of the Néron model of an Abelian variety using the flattening technique of Raynaud–Gruson. Here we prove that an explicit semi-factorial compactification is a certain moduli space of sheaves — the family of compactified Jacobians.     

Efficient generation of FIR radiation by optical pumping of D2 18O

In this paper we show that D₂ ¹⁸O vapour, optically pumped with a continuously tunable high pressure CO₂ laser, is an excellent source for far infrared radiation. Both high photon conversion coefficients and broad Raman gain regions were found for a large number of new laser transitions spread over the frequency range from 25 cm^–1 to 240 cm^–1. We demonstrate that these Raman gain regions can be used to generate far infrared laser pulses with high intensity and durations of about 100 ps.     

Structural disorder of the CD3zeta transmembrane domain studied with 2D IR spectroscopy and molecular dynamics simulations

In a recently reported study [Mukherjee, et al. Proc. Natl. Acad. Sci. U.S.A. 2006, 103, 3528] we used 2D IR spectroscopy and 1-(13)C=(18)O isotope labeling to measure the vibrational dynamics of 11 amide I modes in the CD3zeta transmembrane domain. We found that the homogeneous line widths and population relaxation times were all nearly identical, but that the amount of inhomogeneous broadening correlated with the position of the amide group inside the membrane. In this study, we use molecular dynamics simulations to investigate the structural and dynamical origins of these experimental observations. We use two models to convert the simulations to frequency trajectories from which the mean frequencies, standard deviations, frequency correlation functions, and 2D IR spectra are calculated. Model 1 correlates the hydrogen-bond length to the amide I frequency, whereas model 2 uses an ab initio-based electrostatic model. We find that the structural distributions of the peptidic groups and their environment are reflected in the vibrational dynamics of the amide I modes. Environmental forces from the water and lipid headgroups partially denature the helices, shifting the infrared frequencies and creating larger inhomogeneous distributions for residues near the ends. The least inhomogeneously broadened residues are those located in the middle of the membrane where environmental electrostatic forces are weakest and the helices are most ordered. Comparison of the simulations to experiment confirms that the amide I modes near the C-terminal are larger than at the N-terminal because of the asymmetric structure of the peptide bundle in the membrane. The comparison also reveals that residues at a kink in the alpha-helices have broader line widths than more helical parts of the peptide because the peptide backbone at the kink exhibits a larger amount of structural disorder. Taken together, the simulations and experiments reveal that infrared line shapes are sensitive probes of membrane protein structural and environmental heterogeneity.     

Gas‐Phase versus Liquid‐Phase Structures by Electrospray Ionization Mass Spectrometry

Preferred protonation : Does electrospray ionization mass spectrometry produce gas‐phase or liquid‐phase structures? The preferred protonation site in p‐aminobenzoic acid depends upon the medium, and the structure of its conjugate acid varies with the solvent used during spraying.