Characterisation by rotational spectroscopy of a hydrogen-bonded dimer formed between H2O and HCN

The rotational spectra in the vibrational ground states of (H₂O, HC¹⁴N) and (H₂O, HC¹⁵N) have been assigned in the frequency range 6–19 GHz. Values of rotational constants (B_O, C_O) and centrifugal distortion constants (Δ_J, Δ_JK) have been determined for both species, while the ¹⁴N-nuclear quadrupole coupling constants x_aa and x_bb have been established for the first. Observations concerning additional hyperfine structure arising from H,H nuclear spin-nuclear spin coupling in the H₂O subunit suggest that (H₂O,HCN) has a pair of equivalent protons and is effectively planar in the zero-point state. Observed spectroscopic constants are consistent only with the arrangement H₂O…HCN, with r(O…C) = 3.1387 Å.     

Structural and electronic properties of the charge-transfer complex H3P...Br2 determined by Fourier transform microwave spectroscopy

The ground-state rotational spectra of six isotopomers of the symmetric-top complex H3P...Br2 have been measured by the technique of pulsed-nozzle, Fourier transform microwave spectroscopy. The spectroscopic constants B0, DJ, DJK, chiaa(Brx) and Mbb(Brx), x=i (inner) or o (outer) bromine atom, were obtained from analysis of the spectra. Interpretation of these constants with the aid of models revealed that the pre-reactive complex has an intermolecular bond of length r(P...Br) = 3.0440(4) A between the P atom of PH3 and one Br atom of Br2 and that this bond is a relatively strong one, as measured by the intermolecular stretching force constant ksigma-9.8 Nm(-1). The complex was discovered to have a significant contribution from charge transfer in the ground state by establishing the fraction of intermolecular charge transferred from P to Bri[sigmai = 0.077(23)] and the fraction of intramolecular charge transferred from Bri to Bro [sigmap(Br)=0.11(1)].     

The chaotic behaviour of search algorithms

Certain search algorithms produce a sequence of decreasing regions converging to a pointx ^*. After renormalizing to a standard region at each iteration, the renormalized location ofx ^*, sayx _x, may obey a dynamic process. In this case, simple ergodic theory might be used to compute asymptotic rates. The family of second-order line search algorithms which contains the Golden Section (GS) method have this property. The paper exhibits several alternatives to GS which have better almost sure ergodic rates of convergence for symmetric functions despite the fact that GS is asymptotically minimax. The discussion in the last section includes weakening of the symmetry conditions and announces a backtracking bifurcation algorithm with optimum asymptotic rate.     

83 Kr Nuclear quadrupole coupling in KrHF: evidence for charge transfer

The ⁸³Kr nuclear quadrupole coupling constant in KrHF has been measured to be x = 10.227(71) MHz. Using the known ⁸³Kr nuclear quadrupole moment, the field gradient at the Kr nucleus is evaluated and interpreted in terms of charge transfer in the weak Kr-HF van der Waals bond. Rotational assignments are reported for ⁸²Kr, ⁸³Kr, ⁸⁴Kr, and ⁸⁶Kr isotopic KrHF.     

Local Structure of Glassy Lithium Phosphorus Oxynitride Thin Films: A Combined Experimental and Ab Initio Approach

Lithium phosphorus oxynitride (LiPON) is an amorphous solid-state lithium ion conductor displaying exemplary cyclability against lithium metal anodes. There is no definitive explanation for this stability due to the limited understanding of the structure of LiPON. Herein, we provide a structural model of RF-sputtered LiPON. Information about the short-range structure results from 1D and 2D solid-state NMR experiments. These results are compared with first principles chemical shielding calculations of Li-P-O/N crystals and ab initio molecular dynamics-generated amorphous LiPON models to unequivocally identify the glassy structure as primarily isolated phosphate monomers with N incorporated in both apical and as bridging sites in phosphate dimers. Structural results suggest LiPON′s stability is a result of its glassy character. Free-standing LiPON films are produced that exhibit a high degree of flexibility, highlighting the unique mechanical properties of glassy materials.     

Rapid method for quantifying the extent of methionine oxidation in intact calmodulin

We have developed a method for rapidly quantifying the extent to which the functionally important Met¹⁴⁴ and Met¹⁴⁵ residues near the C-terminus of calmodulin (CaM) are converted to the corresponding sulfoxides, Met(O). The method utilizes a whole protein collision-induced dissociation (CID) approach on an electrospray ionization quadrupole time-of-flight (ESI-Q-TOF) mass spectrometer. Using standards of CaM oxidized by hydrogen peroxide (H₂O₂) or peroxynitrite (ONOO⁻), we demonstrated that CID fragmentation of the protein ions resulted in a series of C-terminal singly charged y₁–y₁₅ ions. Fragments larger than y₄ exhibited mass shifts of +16 or +32 Da, corresponding to oxidation of one or two methionines, respectively. To assess the extent of oxidative modification for Met¹⁴⁴ and Met¹⁴⁵ to Met(O), we averaged the ratio of intensities for y _n , y _n + 16, and y _n + 32 ions, where n = 6–9. By alternating MS and CID scans at low and high collision energies, this technique allowed us to rapidly determine both the distribution of intact CaM oxiforms and the extent of oxidative modification in the C-terminal region of the protein in a single run. We have applied the method to studies of the repair of fully oxidized CaM by methionine sulfoxide reductases (MsrA and MsrB), which normally function in concert to reduce the S and R stereoisomers of methionine sulfoxide. We found that repair of Met(O)¹⁴⁴ and Met(O)¹⁴⁵ did not go to completion, but was more efficient than average Met repair. Absence of complete repair is consistent with previous studies showing that accumulation of methionine sulfoxide in CaM can occur during aging (Gao, J.; Yin, D.; Yao, Y.; Williams, T. D.; Squier, T. C. Biochemistry 1998, 37, 9536–9548).     

Impact of multiple re-use of anion-exchange chromatography media on virus removal

We evaluated viral clearance in multiply-cycled anion-exchange media run in flow-through mode. We found that anion-exchange columns do not lose viral clearance capacity after extensive re-use, if they are cleaned with recommended buffers that do not chemically degrade the media. In contrast, anion-exchange (AEX) columns that are not cleaned or are cleaned with buffers that chemically degrade the media lost viral clearance capacity after extended use. In these cases, other performance attributes that changed at the same time were increased band spreading, decreased DNA clearance and accumulating backpressure that prevented re-use past 80-120 cycles. Thus, our data suggests that flow through mode anion-exchange columns that are cleaned with recommended cleaning buffers, and periodically monitored for band spreading, DNA clearance and/or backpressure need not be re-evaluated for viral clearance at the end of the validated media lifetime.