High resolution and tandem fourier-transform mass spectrometry with californium-252 plasma desorption

For ions formed by plasma desorption (PD) in a Fourier-transform mass spectrometer, high resolution measurements are demonstrated, such as 65,000 (FWHH) for the protonated molecular ion of gramicidin S (MW 1140.7). Resolution is substantially improved by delaying measurements until a significant ion concentration has built up in the cell, and by collisionally deactivating the orbital kinetic energy of the ions. This also makes the ions available for subsequent dissociation steps, so that tandem mass spectrometry can be demonstrated for PD ions. With this for larger ions, collisionally activated dissociation (CAD) is affected with> 85% efficiency. The CAD spectra of (M + Na)⁺ and of fragment ions from the PD of gramicidin S provide structurally useful information.     

Entropy drives an attached water molecule from the C- to N-terminus on protonated proline

Results from infrared photodissociation (IRPD) spectroscopy and kinetics of singly hydrated, protonated proline indicate that the water molecule hydrogen bonds preferentially to the formally neutral carboxylic acid at low temperatures and at higher temperatures to the protonated N-terminus, which bears the formal charge. Hydration isomer populations obtained from IRPD kinetic data as a function of temperature are used to generate a van't Hoff plot that reveals that C-terminal binding is enthalpically favored by 4.2-6.4 kJ/mol, whereas N-terminal binding is entropically favored by 31-43 J/(mol K), consistent with a higher calculated barrier for water molecule rotation at the C-terminus.     

Zn2+ has a primary hydration sphere of five: IR action spectroscopy and theoretical studies of hydrated Zn2+ complexes in the gas phase

Complexes of Zn(2+)(H(2)O)(n), where n = 6-12, are examined using infrared photodissociation (IRPD) spectroscopy, blackbody infrared radiative dissociation (BIRD), and theory. Geometry optimizations and frequency calculations are performed at the B3LYP/6-311+G(d,p) level along with single point energy calculations for relative energetics at the B3LYP, B3P86, and MP2(full) levels with a 6-311+G(2d,2p) basis set. The IRPD spectrum of Zn(2+)(H(2)O)(8) is most consistent with the calculated spectrum of the five-coordinate MP2(full) ground-state (GS) species. Results from larger complexes also point toward a coordination number of five, although contributions from six-coordinate species cannot be ruled out. For n = 6 and 7, comparisons of the individual IRPD spectra with calculated spectra are less conclusive. However, in combination with the BIRD and laser photodissociation kinetics as well as a comparison to hydrated Cu(2+) and Ca(2+), the presence of five-coordinate species with some contribution from six-coordinate species seems likely. Additionally, the BIRD rate constants show that Zn(2+)(H(2)O)(6) and Zn(2+)(H(2)O)(7) complexes are less stable than Zn(2+)(H(2)O)(8). This trend is consistent with previous work that demonstrates the enthalpic favorability of the charge separation process forming singly charged hydrated metal hydroxide and protonated water complexes versus loss of a water molecule for complexes of n ≤ 7. Overall, these results are most consistent with the lowest-energy structures calculated at the MP2(full) level of theory and disagree with those calculated at B3LYP and B3P86 levels.     

A Variational Finite Element Discretization of Compressible Flow

Foundations of Computational Mathematics - We present a finite element variational integrator for compressible flows. The numerical scheme is derived by discretizing, in a structure-preserving way,...     

1‐Hydroxy‐1H‐benzo[d][1,2,6]oxazaborinin‐4(3H)‐one

The structure of the title compound, C₇H₆BNO₃, a new boron heterocycle, prepared by the condensation of (2‐ethoxycarbonylphenyl)boronic acid and hydroxylamine, reveals the specific mode of intramolecular condensation between a phenylboronic acid and an ortho hydroxamic acid substituent. The crystal structure shows that dehydration occurs to form a planar oxazaborinine ring possessing both phenol‐like B—O—H and lactam functional groups. In the extended structure, intermolecular hydrogen bonding generates a 14‐membered ring. To our knowledge, this is the first crystal structure determination involving a six‐membered ring that exhibits consecutive B—OH, O, NH, and C=O functional groups.     

Symmetric Functions and Generating Functions for Descents and Major Indices in Compositions

In [18], Mendes and Remmel showed how Gessel’s generating function for the distributions of the number of descents, the major index, and the number of inversions of permutations in the symmetric group could be derived by applying a ring homomorphism defined on the ring of symmetric functions to a simple symmetric function identity. We show how similar methods may be used to prove analogues of that generating function for compositions.