How deviations in the elemental profile of Humulus lupulus grown throughout the U.S. and Germany influence hop and beer quality.

Recently studies based on limited sample sizes procured from minor hop growing regions have speculated that the elemental profile of hops can possibly be used to authenticate the origin of a hop because changes in hop elemental profiles were realted to growing region and that these changes might also be related to beer quality. To explore this further, 205 hop samples (i.e. 203 whole cone hops and 2 pelletized samples) compromised of 19 varieties were procured from the major hop growing regions (i.e. the U.S. and Germany). These hops were digested with microwave digestion and analyzed for 25 elements using ICP-MS. Hops from most of the U.S. regions (mainly WA) had vastly different elemental profiles than hops from Germany. German hops had significantly lower concentrations for most of the elements except for Cu and K. Interestingly, high alpha varieties had significantly different elemental profiles than varieties bred for aroma purposes. Dry-hopping trials were then performed in an ale and a lager with the hops that had significantly different elemental profiles. Although heavy metals were extracted from hops into beer, at the 5 g/L dry-hopping load used in this study, beer concentrations of these elements remained below regulated water quality standards set by Germany, the U.S., and Canada. Based on electron paramagnetic resonance, dry-hopping had an antioxidant impact on beer regardless of the original elemental profile of the hops which was correlated to hop polyphenol and α/ ß - acid concentrations. Overall these results highlight that many factors including location have the potential to influence the elemental profile of hops and that changes in the elemental profiles of hops can be related to beer quality.

Ion Mobility Spectrometry Characterization of the Intermediate Hydrogen-Containing Gold Cluster Au7(PPh3)7H52.

We employ ion mobility spectrometry and density functional theory to determine the structure of Au7(PPh3)7H52+ (PPh3 = triphenylphosphine), which was recently identified by high mass resolution mass spectrometry. Experimental ion-neutral collision cross sections represent the momentum transfer between the ionic clusters and gas molecules averaged over the relative thermal velocities of the colliding pair, thereby providing structural insights. Theoretical calculations indicate the geometry of Au7(PPh3)7H52+ is similar to Au7(PPh3)7+, with three hydrogen atoms bridging two gold atoms and two hydrogen atoms forming single Au-H bonds. Collision-induced dissociation products observed during IMS experiments reveal that smaller hydrogen-containing clusters may be produced through fragmentation of Au7(PPh3)7H52+. Our findings indicate that hydrogen-containing species like Au7(PPh3)7H52+ act as intermediates in the formation of larger phosphine ligated gold clusters. These results advance the understanding and ability to control the mechanisms of size-selective cluster formation, which is necessary for scalable synthesis of clusters with tailored properties.

SLIM Ultrahigh Resolution Ion Mobility Spectrometry Separations of Isotopologues and Isotopomers Reveal Mobility Shifts due to Mass Distribution Changes.

We report on separations of ion isotopologues and isotopomers using ultrahigh-resolution traveling wave-based Structures for Lossless Ion Manipulations with serpentine ultralong path and extended routing ion mobility spectrometry coupled to mass spectrometry (SLIM SUPER IMS-MS). Mobility separations of ions from the naturally occurring ion isotopic envelopes (e.g., [M], [M+1], [M+2], ... ions) showed the first and second isotopic peaks (i.e., [M+1] and [M+2]) for various tetraalkylammonium ions could be resolved from their respective monoisotopic ion peak ([M]) after SLIM SUPER IMS with resolving powers of ∼400-600. Similar separations were obtained for other compounds (e.g., tetrapeptide ions). Greater separation was obtained using argon versus helium drift gas, as expected from the greater reduced mass contribution to ion mobility described by the Mason-Schamp relationship. To more directly explore the role of isotopic substitutions, we studied a mixture of specific isotopically substituted (15N, 13C, and 2H) protonated arginine isotopologues. While the separations in nitrogen were primarily due to their reduced mass differences, similar to the naturally occurring isotopologues, their separations in helium, where higher resolving powers could also be achieved, revealed distinct additional relative mobility shifts. These shifts appeared correlated, after correction for the reduced mass contribution, with changes in the ion center of mass due to the different locations of heavy atom substitutions. The origin of these apparent mass distribution-induced mobility shifts was then further explored using a mixture of Iodoacetyl Tandem Mass Tag (iodoTMT) isotopomers (i.e., each having the same exact mass, but with different isotopic substitution sites). Again, the observed mobility shifts appeared correlated with changes in the ion center of mass leading to multiple monoisotopic mobilities being observed for some isotopomers (up to a ∼0.04% difference in mobility). These mobility shifts thus appear to reflect details of the ion structure, derived from the changes due to ion rotation impacting collision frequency or momentum transfer, and highlight the potential for new approaches for ion structural characterization.

Role of sterics in phosphine-ligated gold clusters.

This study examined the solution-phase exchange reactions of triphenylphosphine (PPh3) ligands on Au8L72+ (L = PPh3) gold clusters with three different tolyl ligands using electrospray ionization mass spectrometry to provide insight into how steric differences in the phosphines influence the extent of ligand exchange and the stability of the resulting mixed-phosphine clusters. The size distributions of tolyl-exchanged gold clusters were found to depend on the position of the methyl group in the tri(tolyl)phosphine ligands (-ortho, -meta, and -para). Due to different sterics, the tri(m-tolyl)phosphine (TMTP) and tri(p-tolyl)phosphine (TPTP) ligands exchanged efficiently onto the Au8L72+ (L = PPh3) clusters while the tri(o-tolyl)phosphine ligands did not exchange. In addition, while TPTP fully exchanged with all seven PPh3 on the Au8L72+ cluster, TMTP exchanged with only six PPh3 ligands. Employing collision-induced dissociation, the tolyl-exchanged mixed-ligand clusters were demonstrated to fragment through loss of neutral ligands and AuL2+. Comparison of the relative fragmentation yields of PPh3vs. TMTP and TPTP from the mixed-ligand clusters indicated that these tolyl ligands are more strongly bonded to the Au82+ gold core than PPh3. To provide molecular-level insight into the experimental results we also performed complementary electronic structure calculations using density functional theory at the B3LYP-D3/SDD level of theory on representative model systems. These computations revealed that steric interactions of the CH3 group on the tri(o-tolyl)phosphine ligand are responsible for the lack of ligand exchange in solution with PPh3. Our joint experimental and theoretical findings demonstrate the subtle interplay of steric and electronic factors that determine the size distribution, stability, and dissociation pathways of phosphine ligated gold clusters.

Ligand induced structural isomerism in phosphine coordinated gold clusters revealed by ion mobility mass spectrometry.

Structural isomerism in ligated gold clusters is revealed using electrospray ionization ion mobility spectrometry mass spectrometry. Phosphine ligated Au8 clusters are shown to adopt more extended type structures with increasing exchange of methyldiphenylphosphine (MePPh2) for triphenylphosphine (PPh3). These ligand-dependant structure-property relationships are critical to theoretical modeling of clusters as well as their applications in catalysis and photovoltaics.

Observing the real time formation of phosphine-ligated gold clusters by electrospray ionization mass spectrometry.

The early stages of reduction and nucleation of ligated gold clusters in solution are largely unknown due, in part, to high reaction rates and the inherent complexity of the process. This study demonstrates that the addition of a diphosphine ligand, 1-4-bis(diphenylphosphino)butane (L4) to a methanolic solution of the gold precursor, chloro(triphenylphosphine)gold(I) (Au(PPh3)Cl), results in the initial formation of organometallic complexes of the type [Au(L4)x(L4O)y(PPh3)z]+. These initial complexes lower the rate of gold reduction so that the reaction can be directly monitored over time from 1 min to over an hour using on-line electrospray ionization mass spectrometry (ESI-MS). The results indicate that the formation of cationic Au8(L4)42+, Au9(L4)4H2+ and Au10(L4)52+ clusters occurs through specific reaction pathways that may be kinetically controlled by varying either the concentration of reducing agent or the extent of L4 oxidation. Comparison of selected ion chronograms indicates that Au2(L4)2H+ may be an intermediate in the formation of Au8(L4)42+ and Au10(L4)52+ while a variety of chlorinated clusters may be involved in the formation of Au9(L4)4H2+. Additionally, high resolution mass spectrometry enabled the identification of 53 new gold containing species produced under highly oxidative conditions. New intermediate species were identified which aid the understanding of how different size gold clusters may be stabilized during the growth process.

Direct Analysis of Xanthine Stimulants in Archaeological Vessels by Laser Desorption Resonance Enhanced Multiphoton Ionization.

Resonance enhanced multiphoton ionization spectroscopy (REMPI) generates simultaneous vibronic spectroscopy and fragment free mass spectrometry to identify molecules within a complex matrix. We combined laser desorption with REMPI spectroscopy to study organic residues within pottery sherds from Maya vessels (600-900 CE) and Mississippian vessels (1100-1200 CE), successfully detecting three molecular markers, caffeine, theobromine, and theophylline, associated with the use of cacao. This analytical approach provides a high molecular specificity, based on both wavelength and mass identification. At the same time, the high detection limit allows for direct laser desorption from sherd scrapings, avoiding the need for extracting organic constituents from the sherd matrix.

Resonant Infrared Multiple Photon Dissociation Spectroscopy of Anionic Nucleotide Monophosphate Clusters.

We report mid-infrared spectra and potential energy surfaces of four anionic, 2'-deoxynucleotide-5'-monophosphates (dNMPs) and the ionic DNA pairs [dGMP-dCMP-H](1-), [dAMP-dTMP-H](1-) with a total charge of the complex equal to -1. We recorded IR action spectra by resonant IR multiple-photon dissociation (IRMPD) using the FELIX free electron laser. The potential energy surface study employed an on-the-fly molecular dynamics quenching method (MD/Q), using a semiempirical AM1 method, followed by an optimization of the most stable structures using density functional theory. By employing infrared multiple-photon dissociation (IRMPD) spectroscopy in combination with high-level computational methods, we aim at a better understanding of the hydrogen bonding competition between the phosphate moieties and the nucleobases. We find that, unlike in multimer double stranded DNA structures, the hydrogen bonds in these isolated nucleotide pairs are predominantly formed between the phosphate groups. This intermolecular interaction appears to exceed the stabilization energy resulting from base pairing and directs the overall cluster structure and alignment.