Monday, January 10, 2011

J. Phys. Chem. A

Crystal Structure Based Design of Signal Enhancement Schemes for Solid-State NMR of Insensitive Half-Integer Quadrupolar Nuclei

Luke A. O’Dell* and Christopher I. Ratcliffe

J. Phys. Chem. A, Article ASAP
DOI: 10.1021/jp111531e
Publication Date (Web): December 21, 2010

A combination of density functional and optimal control theory has been used to generate amplitude- and phase-modulated excitation pulses tailored specifically for the 33S nuclei in taurine, based on one of several reported crystal structures. The pulses resulted in significant signal enhancement (stemming from population transfer from the satellite transitions) without the need for any experimental optimization. This allowed an accurate determination of the 33S NMR interaction parameters at natural abundance and at a moderate magnetic field strength (11.7 T). The 33S NMR parameters, along with those measured from 14N using frequency-swept pulses, were then used to assess the accuracy of various proposed crystal structures.


Interactions of Volatile Organic Compounds with Syndiotactic Polystyrene Crystalline Nanocavities
Alexandra R. Albunia*, Patrizia Oliva, and Alfonso Grassi

J. Phys. Chem. A, Article ASAP
DOI: 10.1021/jp1090608
Publication Date (Web): December 17, 2010

The interaction of some volatile organic compounds, namely, 1,2-dichloroethane, 1,2-dibromoethane, and 1,1,2,2-tetrachloroethane, included in the δ crystalline phase of syndiotactic polystyrene (sPS) has been studied in terms of conformation, orientation, and dynamical behavior. By combination of X-ray diffraction (XRD), Fourier-transform infrared (FTIR), and solid-state 2H NMR analyses, it has been shown that despite the differences in guest molecular properties (mass, boiling temperature, and volume), stable sPS/guest δ-clathrate cocrystals are formed since the nanoporous δ crystalline form has a flexible structure able to adapt itself to the guest molecule. As a consequence of inclusion, it has been shown that the guest diffusivity is strongly reduced and the dynamical processes are constrained, particularly when these guests are in trans
conformation. This suggests the nanoporous sPS δ form to be an efficient tool for water and air purification through volatile organic compound absorption.

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