We report the vibrational spectra of the hydronium and methylammonium ions captured in the C 3v binding pocket of the 18-crown-6 ether ionophore. Although the NH stretching bands of the CH 3 NH 3 + ion are consistent with harmonic expectations, the OH stretching bands of H 3 O + are surprisingly broad, appearing as a diffuse background absorption with little intensity modulation over 800 cm −1 with an onset ∼400 cm −1 below the harmonic prediction. This structure persists even when only a single OH group is present in the HD 2 O + isotopologue, while the OD stretching region displays a regular progression involving a soft mode at about 85 cm −1. These results are rationalized in a vibrationally adiabatic (VA) model in which the motion of the H 3 O + ion in the crown pocket is strongly coupled with its OH stretches. In this picture, H 3 O + resides in the center of the crown in the vibrational zeropoint level, while the minima in the VA potentials associated with the excited OH vibrational states are shifted away from the symmetrical configuration displayed by the ground state. Infrared excitation between these strongly H/D isotope-dependent VA potentials then accounts for most of the broadening in the OH stretching manifold. Specifically, low-frequency motions involving concerted motions of the crown scaffold and the H 3 O + ion are driven by a Franck-Condon-like mechanism. In essence, vibrational spectroscopy of these systems can be viewed from the perspective of photochemical interconversion between transient, isomeric forms of the complexes corresponding to the initial stage of intermolecular proton transfer.vibrational spectroscopy | hydrogen bonding | vibrationally adiabatic | proton transfer

We describe a systematic method for the preparation and spectroscopic characterization of a CO2 molecule coordinated to an activated bisphenoidal nickel(I) compound containing a tetraazamacrocyclic ligand in the gas phase. The resulting complex was then structurally characterized by using mass-selected vibrational predissociation spectroscopy. The results indicate that a highly distorted CO2 molecule is bound to the metal center in an η(2)-C,O coordination mode, thus establishing an efficient and rational method for the preparation of metal-activated CO2 for further studies using ion chemistry techniques.

Gas-phase ion chemistry methods that capture and characterize the degree of activation of small molecules in the active sites of homogeneous catalysts form a powerful new tool to unravel how ligand environments affect reactivity. A key roadblock in this development, however, is the ability to generate the fragile metal oxidation states that are essential for catalytic activity. Here we demonstrate the preparation of the key Ni(I) center in the widely used cyclam scaffold using ion–ion recombination as a gas-phase alternative to electrochemical reduction. The singly charged Ni+(cyclam) coordination complex is generated by electron transfer from fluoranthene and azobenzene anions to doubly charged Ni2+(cyclam), using the electron-transfer dissociation protocol in a commercial quadrupole ion trap instrument and in a custom-built octopole RF ion trap. The successful preparation of the Ni+(cyclam) cation is verified through analysis of its vibrational spectrum obtained using the infrared free electron laser FELIX.

The accumulation of independent mutations over time in two populations often leads to reproductive isolation. Reproductive isolation between diverging populations may be reinforced by barriers that occur either pre- or postzygotically. Hybrid sterility is the most common form of postzygotic isolation in plants. Four postzygotic sterility loci, comprising three hybrid sterility systems (Sa, s5, DPL), have been recently identified in Oryza sativa. These loci explain, in part, the limited hybridization that occurs between the domesticated cultivated rice varieties, O. sativa spp. japonica and O. sativa spp. indica. In the United States, cultivated fields of japonica rice are often invaded by conspecific weeds that have been shown to be of indica origin. Crop-weed hybrids have been identified in crop fields, but at low frequencies. Here we examined the possible role of these hybrid incompatibility loci in the interaction between cultivated and weedy rice. We identified a novel allele at Sa that seemingly prevents loss of fertility in hybrids. Additionally, we found wide-compatibility type alleles at strikingly high frequencies at the Sa and s5 loci in weed groups, and a general lack of incompatible alleles between crops and weeds at the DPL loci. Our results suggest that weedy individuals, particularly those of the SH and BRH groups, should be able to freely hybridize with the local japonica crop, and that prezygotic factors, such as differences in flowering time, have been more important in limiting weed-crop gene flow in the past. As the selective landscape for weedy rice changes due to increased use of herbicide resistant strains of cultivated rice, the genetic barriers that hinder indica-japonica hybridization cannot be counted on to limit the flow of favorable crop genes into weeds.

Formation of N-H and N-C bonds from functionalization of N2 is a potential route to utilization of this abundant resource. One of the key challenges is to make the products of N2 activation reactive enough to undergo further reactions under mild conditions. This paper explores the strategy of "alkali control," where the presence of an alkali metal cation enables the reduction of N2 under mild conditions, and then chelation of the alkali metal cation uncovers a highly reactive species that can break benzylic C-H bonds to give new N-H and Fe-C bonds. The ability to "turn on" this C-H activation pathway with 18-crown-6 is demonstrated with three different N2 reduction products of N2 cleavage in an iron-potassium system. The alkali control strategy can also turn on an intermolecular reaction of an N2-derived nitride with methyl tosylate that gives a new N-C bond. Since the transient K+-free intermediate reacts with this electrophile but not with the weak C-H bonds in 1,4-cyclohexadiene, it is proposed that the C-H cleavage occurs by a deprotonation mechanism. The combined results demonstrate that a K+ ion can mask the latent nucleophilicity of N2-derived nitride and imide ligands within a trimetallic iron system, and points a way toward control over N2 functionalization.

There is great interest in developing Mn water‐splitting catalysts due to their low cost, abundance, and relevance to the oxygen‐evolving complex (OEC). Three ligands with highly donating pyridine alkoxide moieties, including 2‐(pyridin‐2‐yl)propan‐2‐ol (pyalkH), 2,2′‐(pyridine‐2,6‐diyl)bis(propan‐2‐ol) (py‐dialkH2), and 2‐[(2,2′‐bipyridin)‐6‐yl]propan‐2‐ol (bipy‐alkH), have been screened with Mn for oxygen‐evolution catalysis. Complexes with the ligand bipy‐alkH were shown to evolve O2 when driven by Oxone (potassium peroxymonosulfate). The catalytic mixture generated from the precursor complex [Mn(bipy‐alkH)Cl2] retained activity in unbuffered solution beyond 160 h.

Recent advances in the coupling of vibrational spectroscopy with mass spectrometry create new opportunities for the structural characterization of metabolites with great sensitivity. Previous studies have demonstrated this scheme on 300 K ions using very high power free electron lasers in the fingerprint region of the infrared. Here we extend the scope of this approach to a single investigator scale as well as extend the spectral range to include the OH stretching fundamentals. This is accomplished by detecting the IR absorptions in a linear action regime by photodissociation of weakly bound N molecules, which are attached to the target ions in a cryogenically cooled, rf ion trap. We consider the specific case of the widely used drug Valsartan and two isomeric forms of its metabolite. Advantages and challenges of the cold ion approach are discussed, including disentangling the role of conformers and the strategic choices involved in the selection of the charging mechanism that optimize spectral differentiation among candidate structural isomers. In this case, the Na complexes are observed to yield sharp resonances in the high frequency NH and OH stretching regions, which can be used to easily differentiate between two isomers of the metabolite. Graphical Abstract ᅟ.

We address the molecular level origins of the dramatic difference in the catalytic mechanisms of CO activation by the seemingly similar molecules pyridine (Py) and imidazole (Im). This is accomplished by comparing the fundamental interactions of CO radical anions with Py and Im in the isolated, gas phase PyCO and ImCO complexes. These species are prepared by condensation of the neutral compounds onto a (CO) cluster ion beam by entrainment in a supersonic jet ion source. The structures of the anionic complexes are determined by theoretical analysis of their vibrational spectra, obtained by IR photodissociation of weakly bound CO molecules in a photofragmentation mass spectrometer. Although the radical PyCO system adopts a carbamate-like configuration corresponding to formation of an N-C covalent bond, the ImCO species is revealed to be best described as an ion-molecule complex in which an oxygen atom in the CO radical anion is H-bonded to the NH group. Species that feature a covalent N-C interaction in ImCO are calculated to be locally stable structures, but are much higher in energy than the largely electrostatically bound ion-molecule complex. These results support the suggestion from solution phase electrochemical studies (Bocarsly et al. ACS Catal. 2012, 2, 1684-1692) that the N atoms are not directly involved in the catalytic activation of CO by Im.