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Abstract: Through a combination of rational design and synthetic serendipity, two new structural isomers of the dithienoborepin (DTB) architecture have been realized. Unlike previous members of this family, these boron-containing [...]

Abstract: Molecular structure and vibrational spectra of acetone, acetone-[d.sub.3], and acetone-[d.sub.6] were investigated by means of ab initio and density functional theory (DFT) calculations. The harmonic and anharmonic vibrational frequencies [...]

Many proteins and proteolytic peptides incorporate the same post-translational modification (PTM) at different sites, creating multiple localization variants with different functions or activities that may coexist in cells. Current analytical methods based on liquid chromatography (LC) followed by tandem mass spectrometry (MS/MS) are challenged by such isomers that often coelute in LC and/ or produce nonunique fragment ions. The application of ion mobility spectrometry (IMS) was explored, but success has been limited by insufficient resolution. We show that high-resolution differential ion mobility spectrometry (FAIMS) employing helium-rich gases can readily separate phosphopeptides with variant modification sites. Use of He/[N.sub.2] mixtures containing up to 74% He has allowed separating to >95% three monophosphorylated peptides of identical sequence. Similar separation was achieved at 50% He, using an elevated electric field. Bisphosphorylated isomers that differ in only one modification site were separated to the same extent. We anticipate FAIMS capabilities for such separations to extend to other PTMs. 10.1021/ac101878a

Distinguishing and separating isotopic molecular variants is important across many scientific fields. However, discerning such variants, especially those producing no net mass difference, has been challenging. For example, single-stage mass spectrometry is broadly employed to analyze isotopes but is blind to isotopic isomers (isotopomers) and, except at very high resolution, species of the same nominal mass (isobars). Here, we report separation of isotopic ions, including isotopomers and isobars, using ion mobility spectrometry (IMS), specifically, the field asymmetric waveform IMS (FAIMS). The effect is not based on the different reduced masses of ion--gas molecule pairs previously theorized to cause isotopic separations in conventional IMS, but appears related to the details of energetic ion-molecule collisions in strong electric fields. The observed separation qualitatively depends on the gas composition and may be improved using gas mixtures. Isotopic shifts depend on the position of the labeled site, which allows its localization and contains information about the ion geometry, potentially enabling a new approach to molecular structure characterization. 10.1021/ac101992d

The separation of isomeric phosphorylated peptides is challenging and often impossible for multiphosphorylated isomers using chromatographic and capillary electrophoretic methods. In this study we investigated the separation of a set of single-, double-, and triple-phosphorylated peptides (corresponding to the human ????? protein) by ion-pair reversed-phase chromatography (IPRPC) and hydrophilic interaction chromatography (HILIC). In HILIC both hydroxyl and aminopropyl stationary phases were tested with aqueous acetonitrile in order to assess their separation efficiency. The hydroxyl phase separated the phosphopeptides very well from the unphosphorylated analogue, while on the aminopropyl phase even isomeric phosphopeptides attained baseline separation. Thus, up to seven phosphorylated versions of a given r domain were separated. Furthermore, the low concentration of an acidic ammonium formate buffer allowed an online analysis with electrospray ionization tandem mass spectrometry (ESI-MS/MS) to be conducted, enabling peptide sequencing and identification of phosphorylation sites. 10.1021/ac100473k

The present study describes a preparative gas chromatographic (GC) approach employed to study a series of products arising from reaction of phenylacetylene with para-substituted aryl-iodides under Sonogashira catalysis conditions. GC analysis resolves the isomers from each reaction; however, it cannot provide structural details (their MS data are virtually identical). Since classical liquid chromatography cannot resolve the isomers, preparative-scale GC is the only practical approach to provide further spectroscopic characterization of the isomers. The products are well separated by GC so a single thick-film capillary column is adequate for this case, with operation up to ~+300[degrees]C. By collection of 50+ repeat injections, sufficient material could be isolated for [sup.1]H NMR spectral analysis of the isomers, and for one isomer (isomer I) of a number of analogous related catalytic reaction mixtures, X-ray crystal structure determination enabled complete structural elucidation (absolute configuration) of the substitution pattern of the structure of this isomer. This confirmed isomer I to be the 2-para-aryl-substituted 1,3,5-triphenylbenzene product in all cases. [sup.1]H NMR spectra of isomer I products generally had similar patterns but differed markedly from the second major isomer product (isomer II). 10.1021/ac100417h

One of the alkanes found within gaseous fuel blends of interest to gas turbine applications is butane. There are two structural isomers of butane, normal butane and isobutane, and the combustion characteristics of either isomer are not well known. Of particular interest to this work are mixtures of n-butane and isobutane. A shock-tube experiment was performed to produce important ignition-delay-time data for these binary butane isomer mixtures, which are not currently well studied, with emphasis on 50-50 blends of the two isomers. These data represent the most extensive shock-tube results to date for mixtures of n-butane and isobutane. Ignition within the shock tube was determined from the sharp pressure rise measured at the end wall, which is characteristic of such exothermic reactions. Both experimental and kinetics modeling results are presented for a wide range of stoichiometries ([phi]=0.3-2.0), temperatures (1056-1598 K), and pressures (1-21 atm). The results of this work serve as a validation for the current chemical kinetics model. Correlations in the form of Arrhenius-type expressions are presented, which agree well with both the experimental results and the kinetics modeling. The results of an ignition-delay-time sensitivity analysis are provided, and key reactions are identified. The data from this study are compared with the modeling results of 100% normal butane and 100% isobutane. The 50/50 mixture of n-butane and isobutane was shown to be more readily ignitable than 100% isobutane but reacts slower than 100% n-butane only for the richer mixtures. There was little difference in ignition time between the lean mixtures. [DOI: 10.1115/1.3204654]

This paper describes a novel packing material for high selective reversed-phase high-performance liquid chromatography (RP-HPLC). The organic phase on silica is chemically designed in a way that the weak interaction sites are integrated with high orientation along the polymer main chain and high selectivity can be realized by multiple interactions with solutes. For the above purpose, we synthesized poly(octadecyl acrylate-alt-N-octadecylmaleimide)-grafted silica (Sil-poly(ODA-alt-OMI)) stationary phase. The alternating copolymerization was carried out from 3-marcaptopropytrimethoxysilane (MPS)-modified silica via surface-initiated radical-chain transfer reaction. Elemental analysis, diffuse reflectance infrared Fourier transform (DRIFT),[sup.1]H NMR, solid-state [sup.13]C cross polarization magic angle spinning (CP/MAS) NMR, and suspended-state [sup.1]H NMR were used to characterize the new organic phase. Aspects of shape selectivity was evaluated with Standard Reference Material (SRM 869b), Column Selectivity Test Mixture for Liquid Chromatography. Enhanced molecular shape selectivity was observed, that lead to the separation of SRM 1647e (16 polycyclic aromatic hydrocarbons, PAHs) in an isocratic elution. The effectiveness of this phase was also demonstrated by the separation of several [beta]-carotene and tocopherol isomers. The complete baseline separation of the tocopherol isomers was achieved using the Sil-poly(ODA-alt-OMI) phase. Chromatographic study revealed that Sil-poly(ODA-alt-OMI) has extremely high separation ability compared to monomeric and polymeric [C.sub.18] columns. Higher shape selectivity of the new RP material can be explained by a [pi]--[pi] and dipole--dipole interaction mechanism. 10.1021/ac1001178

A set of related capillary zone electrophoresis (CZE) methods have been developed for the analysis of identity, charge variants, and disulfide isoforms of IgG monoclonal antibodies (mAbs). These methods utilize an uncoated capillary column. The combined use of concentrated zwitterionic (e-amino-caproic acid) buffer and acid flushing was effective in minimizing the adsorption of protein to the inner wall of a bare capillary. Under these conditions, a selective and reproducible separation of multiple IgG1 and IgG2 monoclonal antibodies (mAbs) was obtained with a long capillary column (40 cm effective length), allowing the reliable identification of different mAbs by migration time. A rapid (~10 min) and selective separation of charged variants of IgG mAbs was attained using a short capillary column (10 cm effective length). Finally, the addition of urea in the separation buffer resulted in the separation of disulfide isoforms of IgG2 mAbs by CZE. CZE methods using an uncoated capillary column offer a versatile, generic, and economical approach to the evaluation of identity, charge heterogeneity, and disulfide isoforms of IgG antibodies. 10.1021/ac9028856

The behavior of the minimum polarizability and maximum hardness and minimum energy principles are systematically assessed to describe the two low lying isomers of nine [M.sub.4][X.su.-] bimetal clusters. The results show that, the pyramidal isomer possesses smaller polarizability and lower energy than the planar structure.

The gaseous tropolone (OH), tropolone (OD), and [sup.18.O],[sup.18.O]-tropolone9OH) exhibit Fourier transform infrared absorption (FTIR) spectra in the 800 to 300 [cm.sup.-1] spectral range. The FTIR spectra demonstrate the presence of dynamic couplings and potential function anharmonicity.

The radical rearrangement of {[2-(arylmethylene)cyclopropyl]methyl}-(phenyl)sulfanes and selanes to obtain (2-arylmethylidenebut-3-enyl)(phenyl)sulfanes and selanes as mixtures of E- and Z-isomers is demonstrated.

The synthesis and characterization of three new isomeric dipyridoannulenes which have differing conjugation pathways between the substituent alkoxy donating groups and the pyridyl acceptor groups is reported. The molecules could be used as good metal binding candidates as the pyridine moiety could act as both an electron-acceptor and a site for metal coordination.

The synthesis of a series of atropisomeric iminothiazolines is carried out by using methoxy precursors. The reaction provides insight into stereodynamics of hydrogen bond between the proton of the OH group and the nitrogen of the imino group.

Various studies are conducted to measure the values of hyperfine coupling constants (hfcs) of various methyl radical isotopomers. The negative hfcs of the muoniated radicals are found to increase in magnitude with an increase in the temperature.

Extensive semiempirical calculations are performed on the hexaanions of isolated pentagon rule (IPR) and non-IPR isomers of [C.sub.68]-[C.sub.88] and IPR isomers of [C.sub.90]-[C.sub.98], which is followed by density functional theory (DFT) calculations of the lowest energy structures. The trends in the stability of the fullerene isomers and the cluster-cage binding energies and the general rules for stability of clusterfullerenes are discussed.

The solvent-controlled helicity inversion of the various lanthanide complexes of the chiral hexaaza macrocycle and its meso-type isomer is explained. The two diastereomers of the ligand highly differ with respect to their helical twist and the configuration of amine nitrogen atoms.

High-level electronic structure calculations are used for mapping out the relevant portions of the potential energy surfaces for the release of [H.sub.2] from dimers of ammonia borane (B[H.sub.3]N[H.sub.3]) (AB). The results have shown that the neutral dimer will play a minor role in the release of [H.sub.2] from ammonia borane, with the dominant role from the ion pairs as seen in ionic liquids and the solid state.

The phase equilibria of eight binary mixtures each formed by a cyclic ether and chlorobutane isomer are described. The SAFT-VR approach predicts the phase equilibrium of the mixtures but fails to predict the azeotropic behavior exhibited by some of the mixtures.

The hole-burning (HB) spectra of phenol-[Ar.sub.n] (Ph-OH-[Ar.sub.n]) clusters with n=1, 2 were measured in molecular beam to clarify the possible existence of isomers. It was seen that two species originated from n=1 cluster and one of the species was found to originate from dissociation of n=2 cluster and presence only one isomer in the molecular beam for both n=1 and n=2 clusters was confirmed.

Geometric, electronic and vibrational properties for various topological isomers of small fullerenes were computed by the self-consistent charge density functional tight-binding (SCC-DFTB) method. The properties exhibited are C-C distance distributions which have a fingerprint area beyond the second bond partner for each isomer and IR spectra which vary greatly from species to species in overall appearance and features.

The preparation of a series of trigonal bipyramidal (TBP) cyanide-bridged complexes containing [Fe.sup.11] ions in the equatorial positions is described. The physical properties of these pentanuclear clusters are found to mimic properties measured for Persian blue (PB) and its analogues.

Quantum mechanical methods are used to investigate the geometries, harmonic vibrational frequencies, relative energetics and enthalpies of formation of (C[H.sub.3]I[O.sub.3]) isomers and the reaction C[H.sub.3][O.sub.2] + IO. Interisomerization barriers are determined along with the transition states that are involved in various pathways of the reaction C[H.sub.3][O.sub.2] + IO.

The self-assembling of tetrakis(4-hydroxyphenyl)-cavitand and terta(4-pyridyl) cavitand into a heterodimeric capsule by the four ArOH...pyridyl hydrogen bonds in CD[Cl.sub.3] with high thermodynamic stability is described. The balance among electrostatic potential repulsion, CH-[pi] interaction, in tetrakis(4-hydroxyphenyl)-cavitand and terta(4-pyridyl) cavitand-guest assembly has affected the orientational isomeric selectivity of unsymmetrical guests within tetrakis(4-hydroxyphenyl)-cavitand and terta(4-pyridyl) cavitand.

Experimental and computational were used to study the reaction of benzene-tropothione and identify three equimolar isomeric products. The findings suggest that the biradical character of the benzyne has a key role in the present reaction.

A combination of the near-IR, EPR, NMR and magnetic susceptibility measurements are employed to compare the electronic localization and the delocalization that are effectively determined by the binding of a linker in an isomer pair. The results demonstrate that the [alpha] species are electronically localized and are diradical, whereas the [beta] species are electronically delocalized and are essentially diamagnetic.

A new ligand, 8[O.sub.2] 1,4,7,10-tetraazadodecane tetraacetic acid (DOTAM), is synthesized and its lanthanide complexes are examined as potential chemical exchange saturation transfer (CEST) agents. The analysis reveals that the increasing ionic radius of the lanthanide ion leads to an increase in the extent of the distortion, thereby leading to a complete loss of symmetry in the complex.

Unbiased global optimization methods or Wulff construction and Northby lattice methods were used to study small icosahedral, decahedral and face-centered cubic (fcc) structures. The results have shown that because of the gaps in next-nearest-neighbor contacts, fcc might become energetically incomparable with strain-free close-packed (scp) at very large clusters with a pair potential.

An analysis on differential role of positional isomers of symmetric bis-2-(pyridyl)-1H-benzimidazoles as DNA binding agents was carried out. It was found that some minor chemical alterations in a set of isomeric bis-2-(n-pyridyl)-1H-benzimidazoles change their molecular structure and geometry.

Density functional theory calculations are performed to examine 12-electron reduced [alpha],[beta],[gamma],[delta] and [elipson] Keggin-like [[(Mo[O.sub.4])[Mo.sub.12][O.sub.12][S.sub.12][(OH).sub.12]].sup.2-] polyoxothiometalates (POTMs). Energy decomposition analysis shows that the enhanced stabilities of [gamma], [delta], and [elipson] isomers originate the favorable arrangements of their [Mo.sub.12][O.sub.12][S.sub.12][(OH).sub.12] shell, in which the edge-sharing [[Mo.sup.v.sub.2][([mu]-S).sub.2][O.sub.2]] fragment plays a fundamental role in stabilizing the overall structure.

An analysis of the electron density is made through natural bond orbitals (NBO), natural steric analysis (NSA), and atoms in molecules (AIM) methods and through analysis of frontier molecular orbitals (MOs). NBO shows that all compounds present through-bond interactions, but only the conformers of [2.2]-metacyclophane present significant through-space interactions.

The total syntheses of the antibiotic abyssomicin (C), together with its biologically inactive sibling abyssomicin D and its stable conformational isomer atrop-abyssomicin C, are reported. Attempted reduction of both atropisomers showed that atrop-abyssomicin C afforded abyssomicin D much more readily, which suggests that the hitherto unknown atropisomer may be synthesized by the host organism and serves as a direct precursor of abyssomicin D.

A novel parallel reaction scheme for cyclodextrin (CD) inclusion complexation, incorporating bidirectional inclusion and the formation of orientational isomers into the scheme is presented. It is shown that the thermodynamic preference of an isomer over the other is mainly due to the slow dethreading rate of isomer, thus addressing that care should be taken in interpreting the thermodynamic parameters derived from the equilibrium constants and their temperature dependence.

The electronic structure and charge transfer characteristics of two structural isomers of donor-acceptor substituted sesquifulvalene are studied by using a sufficiently high level of ab initio quantum mechanical methods. Since the chosen molecules are polar and only the dominant solute-solvent electrostatic interaction is considered, the variation of their rotational energy barriers and transition energies in solution can be interpreted and distinguished from each other in terms of the polarity difference between the ground and excited states.

The reaction of copper(I) iodine with 1,3-imidazolidine-2-thione (SC3H6N2) in a 1:2 molar ratio (M/L) has formed unusual one dimensional polymers {Cu6([mu]3-SC3H6N2)4([mu]-SC3H6N2)2([mu]-I)2I4}n and {Cu6(mu3-SC3H6N2)4([mu]-SC3H6N2)4([mu]-I)4I2}n. It is found that in the reactions of copper(I) salts with 1,3-imidazolidine-2-thione, the anions have influenced the bonding properties of the thione ligand.

A study synthesized and crystallographically characterized a pair of isomeric cyclic triads containing three quadruply bonded [Mo2] units, [[Mo2(cis-DAniF)2].sup.2+] bridged by six fluoride. For the [alpha] isomer, the three [Mo2] units are oriented in two orthogonal directions.

The influence of molecular geometry, type of exchange-correlation functional, and contraction scheme of basis set applied at the iron nuclei in the calculation of [super.57.Fe] Mossbauer isomer shifts and quadrupole splittings for a wide range of ligand types in inorganic and organometallic systems is studied. Results suggest the use of only pure exchange-correlation functionals for accurate prediction Mossbauer spectra parameters in ferrocenes.

An individualized three-step synthesis and isomer determination of 3,5-diarylisoxazoles is presented. The process helps students gain individualized experience in the characterization of reaction products by standard analytical methods and introduces students Hammett substituent constants, which are used for predicting shift effects on the [.sup.13.C] NMR signal for Cr of the isoxazole.

Vibrational sum-frequency spectroscopy and surface tensiometry are used to study the adsorption of m- and p-cyanophenol at the air-water interface. The analysis has shown that the orientation of m- and p-cyanophenol is invariant to changes in surface number density and that the cyano (CN) moiety of these isomers adopts different average orientations at the air-water interface.

The emission and excitation spectra of 2-, 3- and 4-pyridinecarboxaldehyde (2-, 2- and 4-PCA, respectively) vapors are measured at different temperatures and compared. The density functional theory (DFT) calculation has shown that the syn rotamer exists as a less stable isomer in the ground state for 2- and 3-PCA vapors.

A mechanism for the photochemical conversion of 2-vinyl-1,3-terphenyl to 8,9a-dihydrophenanthrene is presented based on ab initio restricted active space self-consistent field calculations and a molecular mechanics-valence bond dynamics simulation of a model system, the syn isomer of 2-vinylbiphenyl. An extended crossing seam between the ground and first excited electronic states was found to be largely responsible for the efficient photocyclization of the photochemically active syn isomer.

The ruthenium complexes containing 2-anilinopyridiante anionic bridging ligands substituted on the pyridyl site of the molecule are described. Reaction of the metal-metal bonded complex [Ru.sub.2]([[O.sub.2]CC[H.sub.3]).sub.4]Cl with 2-anilino-4-methylpyridine leads to the (3,1) isomer of the diruthenium (III,II) complex [Ru.sub.2][(ap-4-Me).sub.4]Cl, while the same reaction with 2-anilino-6-methylpyridine gives the monoruthenium(III) derivative, [Ru.sub.2][(ap-6-Me).sub.3].

The Pd(II) complexes of indole-containing ligands, N-(indole-3-ethyl)-[[DELTA].sup.2.11]-enaminousnic acid (IEU) and 4-[2-indol-3-ethylamino]pent-3-en-2-one (IEP) were studied to gain better understanding of metal-binding properties of lichen substances and indole ring. The results established the metal-binding properties of the indole ring and suggest that the [pi]-[pi] stacking information can be a complex factor in the formation of certain diastereomers.

New compound containing [[[O.sub.3]PC[H.sub.2]P[O.sub.3]].sup.4-] ligands {[Mo.sub.2.sup.V][O.sub.4]} units were obtained. A hexanuclear rectangular anion and octanuclaer wheels encapsulating S[O.sub.3.sup.2-] or C[O.sub.3.sup.2-] templating agents were isolated. Their structural characterization allowed a discussion on the influence of the counterions on the structure of the anions and their stability while DFT calculations confirmed the observed equilibrium between syn and anti isomers.

The amino derivative of [beta]-cyclodextrin is compounded and the formation of an intramolecular inclusion complex is explored by NMR techniques. The deprotonation/protonation of the amino group stimulates an in/out movement of the pendant side chain toward/from the cyclodextrin cavity.

The isomerization and decomposition chemistry of water-solvated acetaldehyde ions and other isomers including the carbene and vinyl alcohol ions, the structures of new fragment ions produced by [H.sub.2]O and [.sup..C][H.sub.3] loss are described. The potential energy surface (PES) describing the interconversions among water-solvated C[H.sub.3]CH[O.sup.>], C[H.sub.3]CO[H.sup.>], and C[H.sub.2]CHO[H.sup.>] is shown to involve proton-transport catalysis (PTC), catalyzed 1,2-H-transfer, and an uncatalyzed H-atom transfer mechanism, respectively.

A straightforward method for the preparation of both (Z) and (E)-alpha-fluorostilbenes was developed. The results revealed that the route to both (Z)- and (E)-alpha-fluorostilbenes was highly stereoselective, highly efficient and was suitable for scale-up preparation compared to existing methods.

The impact of urea-based surfactant molecular geometry, specifically headgroup positional isomerism, on the solubility, melting point and lyotropic phase behavior of 1- and 5-decyl urea, and 1-, 2-,4-, and 6-dodecyl urea are investigated. The surfactant-water mixtures of the urea-based surfactants have displayed three phases, such as a crystalline solid, a very dilute aqueous solution of the alkyl urea and an isotropic liquid.