Soft-triple resonance solid-state NMR experiments for assignments of U-13C, 15N labeled peptides and proteins

The process of obtaining sequential resonance assignments for heterogeneous polypeptides and large proteins by solid-state NMR (ssNMR) is impeded by extensive spectral degeneracy in these systems. Even in these challenging cases, the cross peaks are not distributed uniformly over the entire spectral width. Instead, there exist both well-resolved single resonances and distinct groups of resonances well separated from the most crowded region of the spectrum. Here, we present a series of new triple resonance experiments that exploit the non-uniform clustering of resonances in heteronuclear correlation spectra to obtain additional resolution in the more crowded regions of a spectrum. Homonuclear and heteronuclear dipolar recoupling sequences are arranged to achieve directional transfer of coherence between neighboring residues in the peptide sequence. A frequency-selective (soft) pulse is applied to select initial polarization from a limited (and potentially) well-resolved region of the spectrum. The pre-existing resolution of one or more spins is thus utilized to obtain additional resolution in the more crowded regions of the spectrum. A new protocol to utilize these experiments for sequential resonance assignments in peptides and proteins is also demonstrated.     

Approaching a persistent favorskii zwitterion

2-Phenalanone has been synthesized via a double Curtius procedure and converted to the conjugate acid of 2-phenalenylium oxide, a potential persistent Favorskii zwitterion.     

Determining the sigma-donor ability of the cyclopropane C-C bond

The low temperature crystal structures of ester and ether derivatives of varying electron demand, derived from cyclopropylmethanol and dicyclopropylmethanol , have been determined. These structures show a very strong response of the C-OR bond distance to the electron demand of the OR substituent, demonstrating the strong sigma-donor ability of the strained C-C bonds in the cyclopropane ring.     

Passive mode-locking by use of waveguide arrays

A novel mode-locking technique is presented in which the intensity-dependent spatial coupling dynamics of a waveguide array is used to achieve temporal mode-locking in a passive optical fiber laser. By use of the discrete, nearest-neighbor spatial coupling of the waveguide array, low-intensity light can be transferred to the neighboring waveguides and ejected (attenuated) from the laser cavity. In contrast, higher-intensity light is self-focused in the waveguide and remains largely unaffected. Numerical studies of this pulse shaping mechanism (intensity discrimination) show that using current waveguide arrays and standard optical fiber technology produces stable and robust mode-locked soliton-like pulses.     

Generation of hyperentangled photon pairs

We experimentally demonstrate the first quantum system entangled in every degree of freedom (hyperentangled). Using pairs of photons produced in spontaneous parametric down-conversion, we verify entanglement by observing a Bell-type inequality violation in each degree of freedom: polarization, spatial mode, and time energy. We also produce and characterize maximally hyperentangled states and novel states simultaneously exhibiting both quantum and classical correlations. Finally, we report the tomography of a 2 x 2 x 3 x 3 system (36-dimensional Hilbert space), which we believe is the first reported photonic entangled system of this size to be so characterized.     

Long waves in streamwise varying shear flows: new mechanisms for a weakly nonlinear instability

The weakly nonlinear dynamics of long waves embedded in marginally stable shear flows that vary in the streamwise direction are shown to be governed by a variable-coefficient Boussinesq equation. Depending on the local stability characteristics of the flow, new nonmodal or modal instabilities may emerge that serve as natural mechanisms for achieving amplitude thresholds necessary for weakly nonlinear instability and the transition to fully finite-amplitude states.     

An outer-sphere ligand for uranyl carbonate

A novel supramolecular host for the uranyl carbonate complex has been designed and synthesized. The modified cyclodextrin host binds uranyl carbonate in water with a stability of 253 M(-1).     

Jason Wagoner and Nathan A. Baker, "Solvation forces on biomolecular structures: A comparison of explicit solvent and Poisson-Boltzmann models,"Journal of Computational Chemistry(2004) 25(13) 1623–1629

The article to which this Erratum refers was published in Journal of Computational Chemistry (2004) 25(13) 1623–1629     

3,6-dioxypyridazine bridged tungsten-tungsten quadruple bonds. Comparisons of electron delocalisation with oxalate bridged compounds

The preparation and characterisation of the tungsten-tungsten quadruply bonded, 3,6-dioxypyridazine bridged complex [((t)BuCO(2))(3)W(2)](2)([micro sign]-H(2)C(4)N(2)O(2)) and its single electron oxidised radical cation are reported and, when compared with related bridged dimolybdenum complexes, reveal a different mechanism of electronic coupling from that seen in related oxalate bridged systems.     

Synthetic applicability and in situ recycling of a B-methoxy oxazaborolidine catalyst derived from cis-1-amino-indan-2-ol

A procedure is described that greatly simplifies the use of an oxazaborolidine catalyst derived from (1R,2S) cis-1-amino-indan-2-ol. This B-OMe catalyst has been employed in the asymmetric reduction of a number of structurally diverse prochiral ketones, in particular the reduction of alpha-amino acetophenone and its derivatives. A method for reducing the effective catalyst loading by "in situ recycling" is also presented. [structure: see text]