Precursor Cation Research Articles

Insight into a novel cobalt complex with promising electric energy stocker properties: A combined DFT and experimental study

A new [Co(SCN)4]·2(C5H14N2)·2(CNS), synthesized from a thiocyanic cobalt precursor and homopiperazinium organic cation in EtOH under hot and basic conditions. X-ray diffraction DATA showed that the compound is composed of one Co cation, located on a center of inversion and four thiocyanates anion, and two homopiperazinium co-ligands add to two thiocyanate ions crystallographically independent in a monoclinic unit cell with P21/c space group. N-H∙∙∙S and N-H∙∙∙N interactions form a distinctive ring–like pattern that links units in crystal packing. This work demonstrates an easy fabrication of a new compound with excellent dielectric properties. Additionally, Fourier Transform Infrared (FT-IR) spectroscopy studies the different functional groups. The dielectric study shows that the developed material has a huge dielectric constant εr≈1010. The resulting material also exhibits a reasonably low loss (tang δ < 1) at low frequencies. Hirshfeld surface (HS) was carried out to study the elemental contact of molecules in crystal packing. Theoretical investigations were performed by using DFT-B3LYP functional. The frontier molecular orbital (FMO) and natural bonding orbitals (NBO) analysis are evident for excellent reactivity and charge transfer within the complex. The global reactivity descriptors were calculated to get deep insight into the reactivity and electronic properties of the complex. For the optical and nonlinear optical (NLO) properties, the static polarizability (αo) and hyperpolarizability (βo) were calculated at the same method. The observed remarkable βo value of 58737.93 au is indicating its excellent NLO properties.

Sulfurization of co-evaporated Cu2ZnGeSe4 layers: Influence of the precursor cation's ratios on the properties of Cu2ZnGe(S,Se)4 thin films

Sulfurization of co-evaporated Cu2ZnGeSe4 layers: Influence of the precursor cation's ratios on the properties of Cu2ZnGe(S,Se)4 thin films

Sulfurization of co-evaporated Cu2ZnGeSe4 layers: Influence of the precursor cation's ratios on the properties of Cu2ZnGe(S,Se)4 thin films

Sulfurization of co-evaporated Cu2ZnGeSe4 layers: Influence of the precursor cation's ratios on the properties of Cu2ZnGe(S,Se)4 thin films

Boroxine benzaldehyde complex for pharmaceutical applications probed by electron interactions.

2,4,6-Tris(4-formylphenyl)boroxine (TFPB) is a substituted boroxine containing a benzaldehyde molecule bonded to each boron atom. Boroxine cages are an emerging class of functional nanostructures used in host-guest chemistry, and benzaldehyde is a potential radiosensitizer. Reactions initiated by low-energy electrons with such complexes may dictate and bring new fundamental knowledge for biomedical and pharmaceutical applications. The electron ionization properties of TFPB are investigated using a gas-phase electron-molecule crossed beam apparatus coupled with a reflectron time-of-flight mass spectrometer in an orthogonal geometry. Ionization and threshold energies are experimentally determined by mass spectra acquisition as a function of the electron energy. The abundance of the molecular precursor cation in the mass spectrum at 70 eV is significantly lower than that of the most abundant fragment C7 H5 O+ . Twenty-nine cationic fragments with relative intensities >2% are detected and identified. The appearance energies of six fragment cations are reported, and the experimental first ionization potential is found at eV. Moreover, eight double cations are identified. The present results are supported by quantum chemical calculations based on bound state techniques, electron ionization models and thermodynamic thresholds. According to these results, the TPFB properties may combine the potential radiosensitizer effect of benzaldehyde with the stability of the boroxine ring.

Integrating structure-based machine learning and co-evolution to investigate specificity in plant sesquiterpene synthases.

Sesquiterpene synthases (STSs) catalyze the formation of a large class of plant volatiles called sesquiterpenes. While thousands of putative STS sequences from diverse plant species are available, only a small number of them have been functionally characterized. Sequence identity-based screening for desired enzymes, often used in biotechnological applications, is difficult to apply here as STS sequence similarity is strongly affected by species. This calls for more sophisticated computational methods for functionality prediction. We investigate the specificity of precursor cation formation in these elusive enzymes. By inspecting multi-product STSs, we demonstrate that STSs have a strong selectivity towards one precursor cation. We use a machine learning approach combining sequence and structure information to accurately predict precursor cation specificity for STSs across all plant species. We combine this with a co-evolutionary analysis on the wealth of uncharacterized putative STS sequences, to pinpoint residues and distant functional contacts influencing cation formation and reaction pathway selection. These structural factors can be used to predict and engineer enzymes with specific functions, as we demonstrate by predicting and characterizing two novel STSs from Citrus bergamia.

Evidence of the presence of minor tautomeric forms in selected nitroanilines.

RationaleNitroanilines can exist in several tautomeric forms: nitro‐amino, nitro‐imino, and aci‐imino. The importance of evaluating minor tautomeric species comes from the fact that even less abundant tautomers have been proved to play important roles in reaction mechanisms.MethodsElectron ionization mass spectra of the pesticide Pendimethalin and four related nitroanilines were recorded at 70 eV to find information about the presence of minor tautomeric forms in the gas phase. The existence of the possible tautomers was evaluated by studying specific fragmentation pathways, which were confirmed by tandem mass spectrometry (MS/MS) experiments. Further supporting information was obtained by studying the structures of some intermediate compounds by theoretical calculations at the B3LYP 6‐311++G(d,p) level.ResultsThe mass spectrum of Pendimethalin suggests the coexistence of the nitro‐amine tautomer (the most stable form) with four possible less stable tautomers in equilibrium. The fragmentation routes were used to explain analogous peaks in two related compounds. However, the spectra of two other related compounds that cannot follow the proposed route of fragmentation for nitro‐imine tautomers do not show the analogous peak. Theoretical calculations were used to correlate the precursor cation with the proposed fragmentation pathway.ConclusionsBy the study of mass spectra and proposed fragmentation pathways it can be concluded that, although the nitro‐amine is the most abundant species within the system, minor tautomers (nitro‐imine and aci‐imine) coexist in the gas phase.

Synergistic effect of Co + Mo codoping on the photocatalytic performance of titania thin films

Thin films of anatase codoped with 0.01 mol% Co and 0.01 mol% Mo up to 5.00 mol% Co and 5.00 mol% Mo were fabricated by spin coating on soda-lime-silica glass substrates. The films subsequently were calcined in air at 450 °C for 2 h. The mineralogical, chemical, morphological, topographical, optical, and photocatalytic properties of the films were investigated in order to assess the factors and mechanisms affecting the photocatalytic properties. The analytical techniques included glancing angle X-ray diffraction, X-ray photoelectron spectrometry, atomic force microscopy, UV–Vis spectrophotometry, and methylene blue photodegradation. A key determinant of the data was the solubility limit of the dopants, particularly Co. When this was exceeded (≥0.30 mol%), the formation of undetectable precipitates commenced blockage of the active sites, thereby reducing the photocatalytic performance. The initial precursor cation valences altered from Co2+ and Mo5+ to Co2+/Co3+ and Mo4+/Mo5+ upon interstitial solid solution. The absence of charge-compensating Ti3+/Ti4+ redox indicates that charge compensation for the codoping was by IVCT through the reaction Co2+ + Mo5+ ↔ Co3+ + Mo4+. While the three dominant factors affecting the band gap were crystallinity, grain size, and precipitation, the band gap did not dominate the photocatalytic performance or its kinetics. These were reduced by blockage of the active sites by dopant precipitates and, to a lesser extent, from contamination from the cations from the substrate. These phases were the dominant factor in decreasing the optical transmission and thus increasing the band gap through the absorption, reflection, and scattering mechanisms of these grains; the crystallinity and grain size were of secondary importance.

Fundamental Studies on Poly(2-oxazoline) Side Chain Isomers Using Tandem Mass Spectrometry and Ion Mobility-Mass Spectrometry.

When polymer mixtures become increasingly complex, the conventional analysis techniques become insufficient for complete characterization. Mass spectrometric techniques can satisfy this increasing demand for detailed sample characterization. Even though isobaric polymers are indistinguishable using simple mass spectrometry (MS) analyses, more advanced techniques such as tandem MS (MS/MS) or ion mobility (IM) can be used. Here, we report proof of concept for characterizing isomeric polymers, namely poly(2-n-propyl-2-oxazoline) (Pn-PrOx) and poly(2-isopropyl-2-oxazoline) (Pi-PrOx), using MS/MS and IM-MS. Pi-PrOx ions lose in intensity at higher accelerating voltages than Pn-PrOx ions during collision-induced dissociation (CID) MS/MS experiments. A Pn/i-PrOx mixture could also be titrated using survival yield calculations of either precursor ions or cation ejection species. IM-MS yielded shape differences in the degree of polymerization (DP) regions showing the structural rearrangements. Combined MS techniques are thus able to identify and deconvolute the molar mass distributions of the two isomers in a mixture. Finally, the MS/MS and IM-MS behaviors are compared for interpretation. Graphical Abstract .

Fabrication and Characterization of Perovskite Solar Cells: An Integrated Laboratory Experience

Perovskite solar cells have garnered exponential research interest due to their facile fabrication, solution processability, and low cost. However, there have been limited efforts to integrate this class of materials into the undergraduate laboratory curriculum. Therefore, we designed an integrated laboratory experiment in our upper-division integrated laboratory sequence to teach students about research procedures and tools used in physical, organic, inorganic, and materials chemistry. This laboratory sequence involves conversion of sunlight to electricity, which is one of the most challenging renewable energy issues we are facing as a society. In this work, upper-level undergraduates study four variables affecting the morphology and optical properties of perovskites: solvent treatment, percent of water added to a precursor mixture, cation substitution, and precursor temperature. To do so, students deposit uniform films of the material using spin-coating and annealing, and then probe the resulting film p...

Unimolecular reaction energies for polycyclic aromatic hydrocarbon ions.

Imaging photoelectron photoion coincidence spectroscopy was employed to explore the unimolecular dissociation of the ionized polycyclic aromatic hydrocarbons (PAHs) acenaphthylene, fluorene, cyclopenta[d,e,f]phenanthrene, pyrene, perylene, fluoranthene, dibenzo[a,e]pyrene, dibenzo[a,l]pyrene, coronene and corannulene. The primary reaction is always hydrogen atom loss, with the smaller species also exhibiting loss of C2H2 to varying extents. Combined with previous work on smaller PAH ions, trends in the reaction energies (E0) for loss of H from sp2-C and sp3-C centres, along with hydrocarbon molecule loss were found as a function of the number of carbon atoms in the ionized PAHs ranging in size from naphthalene to coronene. In the case of molecules which possessed at least one sp3-C centre, the activation energy for the loss of an H atom from this site was 2.34 eV, with the exception of cyclopenta[d,e,f]phenanthrene (CPP) ions, for which the E0 was 3.44 ± 0.86 eV due to steric constraints. The hydrogen loss from PAH cations and from their H-loss fragments exhibits two trends, depending on the number of unpaired electrons. For the loss of the first hydrogen atom, the energy is consistently ca. 4.40 eV, while the threshold to lose the second hydrogen atom is much lower at ca. 3.16 eV. The only exception was for the dibenzo[a,l]pyrene cation, which has a unique structure due to steric constraints, resulting in a low H loss reaction energy of 2.85 eV. If C2H2 is lost directly from the precursor cation, the energy required for this dissociation is 4.16 eV. No other fragmentation channels were observed over a large enough sample set for trends to be extrapolated, though data on CH3 and C4H2 loss obtained in previous studies is included for completeness. The dissociation reactions were also studied by collision induced dissociation after ionization by atmospheric pressure chemical ionization. When modeled with a simple temperature-based theory for the post-collision internal energy distribution, there was reasonable agreement between the two sets of data.

Photoelectron Spectrum and Energetics of the meta-Xylylene Diradical.

The meta-xylylene diradical m-C8H8 is a prototypical organic triplet that represents a building block for organic molecule-based magnets and also serves as a model compound for test and refinement of quantum chemical calculations. Flash vacuum pyrolysis of 1,3-bis-iodomethyl-benzene (m-C8H8I2) produces m-C8H8 in gas phase; we used photoelectron spectroscopy to probe the first two electronic states of the radical cation, and resolve the vibrational fine structure of the ground state band. The determined adiabatic ionization energy of m-C8H8 is (7.27 ± 0.01) eV. Heat of formation of the diradical was established measuring C-I bond dissociation thresholds in the precursor cation and utilizing a thermochemical cycle to yield ΔHf,298K = (325 ± 8) kJ mol-1, ca. 10 kJ mol-1 below the previous value.

Influence of electronic and molecular structure on the fragmentation dynamic of even-electron carbocationic triangulenes and helicenes in the gas phase.

Stable, long-lived organic cations are directly transferred by electrospray ionization (ESI) from solution into the gas phase where their collision-induced dissociations (CID) are studied by tandem mass spectrometry. Three related types of triphenyl carbenium ions are investigated, in which the meta positions are either substituted by methoxy groups or tertiary nitrogen bridges, including tetramethoxyphenylacridinium (TMPA+ ), dimethoxyquinacridinium (DMQA+ ), and triazatriangulenium (TATA+ ) cations. These ions are triangular in shape with increasing degrees of planarity. Fragmentation occurs at the periphery of the triangular molecule, involving the methoxy groups and the substituent of the nitrogen bridge. Each initial precursor cation is an even electron (EE) system and shows competing dissociations into both even (EE) and odd electron (OE) fragment ions. The latter reaction is a breach of the classic 'even-electron rule' in mass spectrometry. While the EE fragment dissociates similar to the precursor, the OE fragment ion shows a rich radical-induced fragmentation pattern. Two driving forces direct the fragmentation of the EE precursor ion toward OE fragment ions, including the release of stabilized radicals and the extension of the π-system by increasing planarization of the triangulene core. Copyright © 2017 John Wiley & Sons, Ltd.

Ground Electronic State of Peptide Cation Radicals: A Delocalized Unpaired Electron?

Electron capture and electron transfer dissociations are bioanalytical methods for fragmenting cations after reduction by an electron. Previous computational studies based on conventional DFT schemes have concluded that the first step of these processes, the attachment of the electron, leads to extensive delocalization of the spin density in the intermediate radical cation. Here we show that most DFT methods produce unphysical results when studying single electron reduction of a dicationic peptide. This is not the case for post-HF methods and long-range corrected functionals that show satisfying electron affinities, intermolecular interaction energies, and spin density trends. Our results suggest that the charged group with the highest electron affinity on the precursor cation is also the site of spin density in the electronic ground state after electron attachment. These findings have important implications for the interpretation of experimental data from electron-based processes in biomolecules and may ...

An experimental and computational study on the dissociation behavior of hydroxypyridine N‐oxides in atmospheric pressure ionization mass spectrometry

A tandem mass spectrometric study of protonated isomeric hydroxypyridine N-oxides was carried out with a hybrid quadrupole/time-of-flight mass spectrometer coupled with different atmospheric pressure ionization sources. The behavior observed in the collision-induced dissociation (CID) mass spectra of the parent cations, was similar irrespective of the source employed. However, there were intrinsic differences in the intensities of the two fragments observed for each isomer. The major fragment because of elimination of a hydroxyl radical, dominated the CID spectra (in contrast with weaker water loss) at different energy thresholds. Therefore, it was possible to differentiate both isomers at collision energies above 13 eV by comparing the ratio of intensities of the major fragment relative to the precursor cation. In addition, quantum chemical calculations at the B3LYP/6-31 + + G(d,p) level of theory were performed for the protonated isomers of hydroxypyridine N-oxide and their radical cation products in order to gain insight into the major routes of dissociation. The results suggest that dissociation from the lowest triplet excited state of the protonated species would provide a reasonable rationalization for the difference in behavior of both isomers.

Density functional theory study on the –SO3H functionalized acidic ionic liquids

In this work, the structures of the –SO3H functionalized acidic ionic liquid 1-(3-sulfonic acid) propyl-3-methylimidazolium hydrogen sulfate ([C3SO3Hmim]HSO4), including its precursor compound (zwitterion), cation, and cation–anion ion-pairs, were optimized systematically by the DFT theory at B3LYP/6-311++G** level, and their most stable geometries were obtained. The calculation results indicated that a great tendency to form strong intramolecular hydrogen bonds was present in the zwitterion, and this tendency was weakened in the cation that was the protonation product of zwitterion. The intramolecular hydrogen bonds and intermolecular hydrogen bonds coexisted in the ionic liquid, and they played an important role in the stability of the systems. The strongest interaction in the ionic liquid was found between the anion and the functional group. The transition state research and the intrinsic reaction coordinate analysis of the hydrogen transfer reaction showed that, when the cation and the anion interacted near the functional group by double O–H···O hydrogen bonds, the ionic liquid was inclined to exist in a form of the zwitterion and H2SO4.

Design of Multilayered Nanostructures and Donor–Acceptor Interfaces in Solution‐Processed Thin‐Film Organic Solar Cells

AbstractMultilayered polymer thin‐film solar cells have been fabricated by wet processes such as spin‐coating and layer‐by‐layer deposition. Hole‐ and electron‐transporting layers were prepared by spin‐coating with poly(3,4‐ethylenedioxythiophene) oxidized with poly(4‐styrenesulfonate) (PEDOT:PSS) and fullerene (C60), respectively. The light‐harvesting layer of poly‐(p‐phenylenevinylene) (PPV) was fabricated by layer‐by‐layer deposition of the PPV precursor cation and poly(sodium 4‐styrenesulfonate) (PSS). The layer‐by‐layer technique enables us to control the layer thickness with nanometer precision and select the interfacial material at the donor–acceptor heterojunction. Optimizing the layered nanostructures, we obtained the best‐performance device with a triple‐layered structure of PEDOT:PSS|PPV|C60, where the thickness of the PPV layer was 11 nm, comparable to the diffusion length of the PPV singlet exciton. The external quantum efficiency spectrum was maximum (ca. 20%) around the absorption peak of PPV and the internal quantum efficiency was estimated to be as high as ca. 50% from a saturated photocurrent at a reverse bias of −3 V. The power conversion efficiency of the triple‐layer solar cell was 0.26% under AM1.5G simulated solar illumination with 100 mW cm−2 in air.

Microstructure of metal-organic deposited YBa2Cu3O7−δ wires with Dy and Zr additions observed by TEM

Abstract The improvement of critical current densities of superconducting wires is essential for commercial applications. Many approaches have been demonstrated to enhance flux pinning of YBa2Cu3O7−δ (YBCO) second-generation (2G) superconducting wires and therefore to increase critical current densities of the materials. In this work, we study the microstructures which lead to enhanced critical current density through flux pinning by nanoparticles in metal-organic deposited (MOD) YBCO films with Dy or Zr additions. Transmission electron microscopy (TEM) observation revealed that large densities of nanoparticles can be formed in YBCO films through altering the precursor stoichiometry and cation additions. Most of these nanoparticles are in the range of 10–50 nm, and are well dispersed, making them ideal for flux pinning in YBCO 2G wires. The effects on critical current of these nanoparticles acting as flux pinning centers are investigated.

Performance Characteristics of Electron Transfer Dissociation Mass Spectrometry

We performed a large scale study of electron transfer dissociation (ETD) performance, as compared with ion trap collision-activated dissociation (CAD), for peptides ranging from approximately 1000 to 5000 Da (n approximately 4000). These data indicate relatively little overlap in peptide identifications between the two methods ( approximately 12%). ETD outperformed CAD for all charge states greater than 2; however, regardless of precursor charge a linear decrease in percent fragmentation, as a function of increasing precursor m/z, was observed with ETD fragmentation. We postulate that several precursor cation attributes, including peptide length, charge distribution, and total mass, could be relevant players. To examine these parameters unique ETD-identified peptides were sorted by length, and the ratio of amino acid residues per precursor charge (residues/charge) was calculated. We observed excellent correlation between the ratio of residues/charge and percent fragmentation. For peptides of a given residue/charge ratio, there is no correlation between peptide mass and percent fragmentation; instead we conclude that the ratio of residues/charge is the main factor in determining a successful ETD outcome. As charge density decreases so does the probability of non-covalent interactions that can bind a newly formed c/z-type ion pair. Recently we have described a supplemental activation approach (ETcaD) to convert these non-dissociative electron transfer product ions to useful c- and z-type ions. Automated implementation of such methods should remove this apparent precursor m/z ceiling. Finally, we evaluated the role of ion density (both anionic and cationic) and reaction duration for an ETD experiment. These data indicate that the best performance is achieved when the ion trap is filled to its space charge limit with anionic reagents. In this largest scale study of ETD to date, ETD continues to show great promise to propel the field of proteomics and, for small- to medium-sized peptides, is highly complementary to ion trap CAD.

Synthesis, Rheological Behavior and Mechanical Characterization of Structural Fast-Setting Geopolymers

Geopolymers are inorganic materials with ceramic characteristics that can be synthesized at room temperature from the setting of slurries. Their structure consists of aluminosilicate units that polymerize in alkaline environment. The setting rate and mechanical behavior of geopolymers strongly depends on the SiO2:Al2O3 molar ratio, polymeric precursor and polymerization cation. The present work reports the synthesis and characterization of 3.5:1 (SiO2:Al2O3) structural geopolymers prepared using either metakaolin (GPMK) or kaolin (GPK) as geopolymeric precursor in potassium hydroxide solution. GPMK depicted quick setting whereas GPK set only after 4 hours. The rheological characterization of the slurries revealed that plastic viscosity and yield point of GPK were 0.40 Pa.s and 14.2 Pa, respectively, whereas GPMK set instantly. The compressive strength of both geopolymers were measured after 24 hours and resulted in similar results, i.e., 4.6 MPa for GPMK and 4.4 MPa for GPK. The strength of both geopolymers was compatible to values typical of structural materials.

Anion of Tetrachloroethane (Tetra): Fragmentation and Geminate Ion Kinetics in Liquid Methylcyclohexane (MCH)

In the context of studies on the influence of the anion lifetime on the geminate ion kinetics, 1,1,1,2- and 1,1,2,2-tetrachloroethane (1112-Tetra and 1122-Tetra) were studied as solutes in liquid methylcyclohexane (MCH) at low temperatures (133−183 K). The two isomers serve as examples of long anion lifetime. The analysis of the pulse radiolysis data was based on the t-0.6 semiempirical law for geminate ion kinetics. The visible band with λmax = 450 or 430 nm is shown to be due to the anion of 1112-Tetra or 1122-Tetra, respectively. Its kinetics relates to three consecutive geminate pairs of ions, due to two ionic reactions: (a) The fast process represents the cationic mechanism: the precursor cation M+* relaxes (or isomerizes) to the high mobility ion MCH+ (kr) and simultaneously fragments (kf) to a diffusional methylcyclohexene+ (MCHene+). The total M+* decay (ktot = kr + kf) produces mixed cations (MCH+,MCHene+). (b) The slow process is due to the anion fragmentation (k-) from Tetra- to Cl- + R•, with τ- = 13.7 or 20.0 μs (143 K) for 1112- or 1122-Tetra, respectively. The fragment radical R• is freed too late to allow scavenging of positive charge. The three geminate pairs of ions are (M+*/Tetra-), (MCH +,MCHene+/Tetra-), and (MCH+,MCHene+/Cl-). All ions (except Cl-) contribute to the optical absorption. The rate constants ktot and k- are both independent of the concentration of Tetra. For ktot this means that M+* decays in a fixed ratio of kf to kr. This is in contrast to previous findings with N2O or CHCl3 but corresponds to our recent proposal that M+* appears to represent some isomer of MCH+ in a higher energy state (or of higher ionization potential). The anion fragmentation rate for 1112-Tetra is k-(143 K) = (7.3 ± 0.6) × 104 s-1 with Eact = 17.8 kJ/mol and log A = 11.2. For 1122-Tetra it is k-(143 K) = (5.0 ± 1.0) × 104 s-1 with Eact = 16.9 kJ/mol and log A = 10.9. The free ion intercepts, from the t-0.6-simulations, reveal for all geminate pairs with Tetra- a strong dependence on the Tetra concentration [T], eventhough complete electron scavenging was ascertained. This is explained by the formation of dimer anions through an equilibrium T- + T ⇌ . The absorption at 450 nm (or 430 nm) then is due to (most likely a charge resonance transition (T ← T-)). For the initial geminate pair (M+*/Tetra-), the free ion intercept was smaller than the one for Tetra- alone (actually ). As this result was based on the assumption that M+* and MCH+ have the same mobility, this now reveals that the precursor cation M+* must have at least a 9 times higher mobility than MCH+.