Metal-organic frameworks (MOFs) built up from Zr6-based nodes and multi-topic carboxylate linkers have attracted attention due to their favourable thermal and chemical stability. However, the hydrolytic stability of some of these Zr6-based MOFs has recently been questioned. Herein we demonstrate that two Zr6-based frameworks, namely UiO-67 and NU-1000, are stable towards linker hydrolysis in H2O, but collapse during activation from H2O. Importantly, this framework collapse can be overcome by utilizing solvent-exchange to solvents exhibiting lower capillary forces such as acetone.

Carbon dioxide adsorption isotherms have been computed for the metal−organic framework (MOF) Fe 2 (dobdc), where dobdc 4− = 2,5-dioxido-1,4-benzenedicarboxylate. A force field derived from quantum mechanical calculations has been used to model adsorption isotherms within a MOF. Restricted open-shell Møller−Plesset second-order perturbation theory (ROMP2) calculations have been performed to obtain interaction energy curves between a CO 2 molecule and a cluster model of Fe 2 (dobdc). The force field parameters have been optimized to best reproduced these curves and used in Monte Carlo simulations to obtain CO 2 adsorption isotherms. The experimental loading of CO 2 adsorbed within Fe 2 (dobdc) was reproduced quite accurately. This parametrization scheme could easily be utilized to predict isotherms of various guests inside this and other similar MOFs not yet synthesized.

The structure of the sodiated peptide GGGGGGGG-Na ϩ or G 8 -Na ϩ was investigated by infrared multiple photon dissociation (IRMPD) spectroscopy and a combination of theoretical methods. IRMPD was carried out in both the fingerprint and N-H/O-H stretching regions. Modeling used the polarizable force field AMOEBA in conjunction with the replica-exchange molecular dynamics (REMD) method, allowing an efficient exploration of the potential energy surface. Geometries and energetics were further refined at B3LYP-D and MP2 quantum chemical levels. The IRMPD spectra indicate that there is no free C-terminus OH and that several N-Hs are free of hydrogen bonding, while several others are bound, however not very strongly. The structure must then be either of the charge solvation (CS) type with a hydrogen-bound acidic OH, or a salt bridge (SB). Extensive REMD searches generated several low-energy structures of both types. The most stable structures of each type are computed to be very close in energy. The computed energy barrier separating these structures is small enough that G 8 -Na ϩ is likely fluxional with easy proton transfer between the two peptide termini. There is, however, good agreement between experiment and computations in the entire spectral range for the CS isomer only, which thus appears to be the most likely structure of G 8 -Na ϩ at room temperature. (J Am Soc Mass Spectrom 2010, 21, 728 -738) © 2010 American Society for Mass Spectrometry T he biological importance of sodium in performing or facilitating essential biological processes, such as neurotransmission, osmotic balance, and cellular metabolism is well documented [1][2][3]. Mass spectrometric methods have been used extensively to provide insight into peptide sequences [4,5] starting from sodium-cationized species, however with considerable debate as to the structure of the parent species and the fragmentation mechanisms [6 -8]. In this context, sodiated oligoglycines have been used in the last decade as a valuable testing ground for new experimental developments designed to obtain refined energetic and/or structural data. These include ion mobility measurements for global shape information [9,10], H/D exchange extent and kinetics for isomeric/ conformational content [11], the kinetic [12, 13] and the threshold collision induced decomposition [14] methods for thermochemical measurements, as well as infrared multiple photon dissociation (IRMPD) spectroscopy [15] for identification of functional groups and their interactions. All these studies have been complemented by extensive molecular modeling as required for translating experimental data into properties of specific molecular structures.Oligoglycines owe their value as model peptides to their relative simplicity. While the number of residues is an obvious source of conformational complexity, the absence of side chains limits the number of factors shaping their structures and energies. On the one hand, the main components of sodium-molecule interactions are electrostatic and polarization, favoring m...