Phosphate and Vanadate in Biological Systems: Chemical Relatives or More?

Structural and functional analogies between acid phosphatases and vanadium haloperoxidases are reflected in the conservation of the amino acid residues contributing to the active sites of these enzymes. This has interesting consequences for the research on both enzyme systems. A first example is the newly proposed structure for the active site of human glucose-6-phosphatase: The picture shows parts of six of the nine transmembrane helices as well as the amino acids (black ovals) that presumably participate in the formation of the active site.     

Functionalization of Non‐activated C?H Bonds of Alkanes: An Effective and Recyclable Catalytic System Based on Fluorinated Silver Catalysts and Solvents

The complexes F_n‐TpAg(L) (F_n‐Tp=a perfluorinated hydrotris(indazolyl) borate ligand; L=acetone or tetrahydrofuran) efficiently catalyze the functionalization of non‐activated alkanes such as hexane, 2,3‐dimethylbutane, or 2‐methylpentane by insertion of CHCO₂Et units (from N₂CHCO₂Et, ethyl diazoacetate, EDA) into their C? H bonds. The reactions are quantitative (EDA‐based), with no byproducts derived from diazo coupling being formed. In the case of hexane, the functionalization of the methyl C? H bonds has been achieved with the highest regioselectivity known to date with this diazo compound. This catalytic system also operates under biphasic conditions by using fluorous solvents such as Fomblin or perfluorophenanthrene. Several cycles of catalyst recovery and reuse have been performed, with identical chemo‐ and regioselectivities.     

Are They Linear,Bent, or Cyclic? Quantum Chemical Investigation of the Heavier Group 14 and Group 15 Homologues of HCN and HNC

The singlet potential‐energy surface (PES) of the system involving the atoms H, X, and E (the (H, X, E) system) in which X=N–Bi and E=C–Pb has been explored at the CCSD(T)/TZVPP and BP86/TZ2P+ levels of theory. The nature of the X? E bonding has been analyzed with charge‐ and energy‐partitioning methods. The calculations show that the linear isomers of the nitrogen systems lin ‐HEN and lin ‐HNE are minima on the singlet PES. The carbon compound lin ‐HCN (HCN=hydrogen cyanide) is 14.9 kcal mol^?1 lower in energy than lin ‐HNC but the heavier group 14 homologues lin ‐HEN (E=Si–Pb) are between 64.8 and 71.5 kcal mol^?1 less stable than the lin ‐HNE isomers. The phosphorous system (H, P, E) exhibits significant differences concerning the geometry and stability of the equilibrium structures compared with the nitrogen system. The linear form lin ‐HEP of the former system is much more stable than lin ‐HPE . The molecule lin ‐HCP is the only minimum on the singlet PES. It is 78.5 kcal mol^?1 lower in energy than lin ‐HPC , which is a second‐order saddle point. The heavier homologues lin ‐HPE , in which E=Si–Pb, are also second‐order saddle points, whereas the bent ‐HPE structures are the global minima on the PES. They are between 10.3 (E=Si) and 36.5 kcal mol^?1 (E=Pb) lower in energy than lin ‐HEP . The bent ‐HPE structures possess rather acute bending angles H‐P‐E between 60.1 (E=Si) and 79.7° (E=Pb). The energy differences between the heavier group 15 isomers lin ‐HEX (X=P–Bi) and the bent structures bent ‐HXE become continuously smaller. The silicon species lin ‐HSiBi is even 3.1 kcal mol^?1 lower in energy than bent ‐HBiSi . The bending angle H‐X‐E becomes more acute when X becomes heavier. The drastic energy differences between the isomers of the system (H, X, E) are explained with three factors that determine the relative stabilities of the energy minima: 1) The different bond strength between the hydrogen bonds H? X and H? E. 2) The electronic excitation energy of the fragment HE from the X ²Π ground state to the ⁴Σ^? excited state, which is required to establish a E≡X triple bond in the molecules lin ‐HEX . 3) The strength of the intrinsic X? E interactions in the molecules. The trends of the geometries and relative energies of the linear, bent, and cyclic isomers are explained with an energy‐decomposition analysis that provides deep insight into the nature of the bonding situation.     

Are Clusters Important in Understanding the Mechanisms in Atmospheric Pressure Ionization? Part 1: Reagent Ion Generation and Chemical Control of Ion Populations

It is well documented since the early days of the development of atmospheric pressure ionization methods, which operate in the gas phase, that cluster ions are ubiquitous. This holds true for atmospheric pressure chemical ionization, as well as for more recent techniques, such as atmospheric pressure photoionization, direct analysis in real time, and many more. In fact, it is well established that cluster ions are the primary carriers of the net charge generated. Nevertheless, cluster ion chemistry has only been sporadically included in the numerous proposed ionization mechanisms leading to charged target analytes, which are often protonated molecules. This paper series, consisting of two parts, attempts to highlight the role of cluster ion chemistry with regard to the generation of analyte ions. In addition, the impact of the changing reaction matrix and the non-thermal collisions of ions en route from the atmospheric pressure ion source to the high vacuum analyzer region are discussed. This work addresses such issues as extent of protonation versus deuteration, the extent of analyte fragmentation, as well as highly variable ionization efficiencies, among others. In Part 1, the nature of the reagent ion generation is examined, as well as the extent of thermodynamic versus kinetic control of the resulting ion population entering the analyzer region.

Can Variations of 1H NMR Chemical Shifts in Benzene Substituted with an Electron‐Accepting (NO2)/Donating (NH2) Group be Explained in Terms of Resonance Effects of Substituents?

The classical textbook explanation of variations of ¹H NMR chemical shifts in benzenes bearing an electron‐donating (NH₂) or an electron‐withdrawing (NO₂) group in terms of substituent resonance effects was examined by analyzing molecular orbital contributions to the total shielding. It was found that the π‐electronic system showed a more pronounced shielding effect on all ring hydrogen atoms, relative to benzene, irrespective of substituent +R/?R effects. For the latter, this was in contrast to the traditional explanations of downfield shift of nitrobenzene proton resonances, which were found to be determined by the σ‐electronic system and oxygen in‐plane lone pairs. In aniline, the +R effect of NH₂ group can be used to fully explain the upfield position of meta‐H signals and partly the upfield position of para‐H signals, the latter also being influenced by the σ‐system. The position of the lowest frequency signal of ortho‐Hs was fully determined by σ‐electrons.     

Synthesis of Coenzyme Q<Subscript>10</Subscript> and β-carotene by Yeasts Isolated from Antarctic Soil and Lichen in Response to Ultraviolet and Visible Radiations

The effect of different doses of visible (Vis), ultraviolet-А (UVA), and mixed light (UVA + Vis) upon coenzyme Q₁₀ (CoQ₁₀) and β-carotene synthesis and biomass yield by the Sporobolomyces salmonicolor AL₁, Cryptococcus albidus AS₅₅, Cryptococcus laurentii AS₅₆, and C. laurentii AS₅₈ strains isolated from Antarctic samples was investigated. The β-carotene concentration in the red strain biomass increased by 52% under irradiation with 11 J/cm² Vis, and the CoQ₁₀ concentration rose by 37% in relation to the control quantity obtained through dark cultivation. Under irradiation with 6 J/cm² UVA, the S. salmonicolor AL₁ strain synthesized 15% more β-carotene; C. albidus AS₅₅, 22%; C. laurentii AS₅₆, 44%; and C. laurentii AS₅₈, 35% in relation to the control quantity. Irradiation with a low UVА + Vis dose significantly stimulated β-carotene biosynthesis by the strains of the Cryptococcus genus (87%, 138%, and 100%), whereas S. salmonicolor AL₁ increased the β-carotene content to a smaller degree (55%). Higher doses of all three irradiation types inhibited β-carotene accumulation. Vis suppressed CoQ₁₀ biosynthesis in the Cryptococcus strains, whereas UVА and UVА + Vis inhibited it in all four strains. The S. salmonicolor AL₁ strain pre-treated with 0.02 J/cm² UVA synthesized twice as much CoQ₁₀ and β-carotene when cultivated in the presence of Vis light in an 11-J/cm² dose.     

Is the Conventional Interpretation of the Anisotropic Effects of CC Double Bonds and Aromatic Rings in NMR Spectra in Terms of the π‐Electron Shielding/Deshielding Contributions Correct?

Based on the nucleus‐independent chemical shift (NICS) concept, isotropic magnetic shielding values have been computed along the three Cartesian axes for ethene, cyclobutadiene, benzene, naphthalene, and benzocyclobutadiene, starting from the molecular/ring center up to 10 Å away. These through‐space NMR spectroscopic shielding (TSNMRS) values, which reflect the anisotropic effects, have been broken down into contributions from localized‐ and canonical molecular orbitals (LMOs and CMOs); these contributions revealed that the proton NMR spectroscopic chemical shifts of nuclei that are spatially close to the C?C double bond or the aromatic ring should not be explained in terms of the conventionally accepted π‐electron shielding/deshielding effects. In fact, these effects followed the predictions only for the antiaromatic cyclobutadiene ring.     

Determination of pharmaceuticals in environmental and biological matrices using pressurised liquid extraction—Are we developing sound extraction methods?

Pressurised liquid extraction (PLE) is now a well established and extensively applied extraction technique in environmental analysis for pollutants such as persistent organic pollutants (POPs). During the past decade, an emerging group of environmentally interesting analytes are pharmaceuticals that are continuingly released into the environment. This class is comprised with compounds of various properties. As the field of the analysis of these compounds grows, an increasing number of PLE methods for pharmaceuticals of varying quality are developed and published. This review summarises the critical PLE parameters during PLE method development and highlight them with examples from recently published papers utilising pressurised liquid extraction for the determination of pharmaceuticals in environmental and biological matrices. These recent methods are summarised and critically discussed with the aim to provide important reflections to alleviate in future PLE development for pharmaceuticals in environmental matrices.     

Structure and Bonding in First‐Row Transition‐Metal Dicarbides: Are They Related to the Stability of Met‐cars?

First-row transition-metal dicarbides MC(2) (M=Sc-Zn) have been investigated by using quantum-mechanical techniques. The competition between cyclic and linear isomers in these systems has been studied and the bonding scheme for these compounds is discussed through topological analysis of electron density. All of the systems have been found to prefer a C(2v)-symmetric arrangement, although for ZnC(2) the energy difference between this and the linear isomer is rather small. In most cases the C(2v)-symmetric structure corresponds to a T-shaped structure, with the exceptions of TiC(2), CoC(2), and NiC(2) which have been shown to be true rings. A detailed analysis of the variation of the energy of the system with geometry has been carried out. An analysis of the bonding, taking into account the main interactions between the valence orbitals of both fragments, the M atom and the C(2) molecule, has allowed the main features of these compounds to be interpreted. A clear correlation between the dissociation energies of the first-row transition-metal dicarbides and the bonding energies of the corresponding met-cars was observed.     

Comparisons of Photo‐Fries Rearrangements of 4‐Dodecylphenyl Phenylacetate and Two Structurally Related Esters in Hexane and Polyethylene Cages. How Important Are Anchoring Chains?†

Photo-Fries rearrangements of 4-dodecylphenyl phenylacetate have been investigated in polyethylene films with 0-71% crystallinity and in hexane over a range of temperatures. The results are compared to those reported previously from phenyl phenylacetate and 1-naphthyl tetradecanoate to assess the influence of a long alkyl chain on the in-cage motions of the intermediate singlet radical pairs. It is demonstrated that the reactivity and selectivity of intimate singlet radical pairs can be tuned by judicious placement of long-chain substituents and selection of a specific polyethylene type as the reaction matrix.     

Why Are Proteins Charged? Networks of Charge–Charge Interactions in Proteins Measured by Charge Ladders and Capillary Electrophoresis

Almost all proteins contain charged amino acids. While the function in catalysis or binding of individual charges in the active site can often be identified, it is less clear how to assign function to charges beyond this region. Are they necessary for solubility? For reasons other than solubility? Can manipulating these charges change the properties of proteins? A combination of capillary electrophoresis (CE) and protein charge ladders makes it possible to study the roles of charged residues on the surface of proteins outside the active site. This method involves chemical modification of those residues to generate a large number of derivatives of the protein that differ in charge. CE separates those derivatives into groups with the same number of modified charged groups. By studying the influence of charge on the properties of proteins using charge ladders, it is possible to estimate the net charge and hydrodynamic radius and to infer the role of charged residues in ligand binding and protein folding.     

Dissociation of Fumaric Acid: Spectrophotometric Investigation in Aqueous Solutions from 10 to 90 <Superscript>∘</Superscript>C and Theoretical Considerations

The dissociation constants of fumaric acid were extracted from UV-vis spectra in the 10–90 ^∘C range. These values were used to extract thermodynamic parameters that showed the temperature effects on the dissociations reactions to be dominantly driven by the solvent. The molar absorption coefficients for the fumaric acid, the bifumarate and fumarate species, can be accurately reproduced with the two-term Gauss–Lorentz equation. Deconvolution of these bands showed strong π–π^∗ transitions for all species and weaker charge-transfer-to-solvent transitions for the charged species. TD-DFT calculations were used to identify the most important molecular orbitals involved in the vertical excitations of the fumaric acid species. The electron population and their states of delocalization were also estimated with topological analyses of the electron density and of the Becke–Edgecombe Electron Localization Function.     

Composition,Enthalpy, and Vaporization Temperature Calculation of Ag‐SiO<Subscript>2</Subscript> Plasmas with Air in the Temperature Range from 1000 to 6000 K and for Pressure Included between 1 and 50 bars

With the Gibbs free energy minimization method, the molar fraction of chemical species are determined in temperature range included between 1000 and 6000 K for several proportions of air, silver and silica and for pressures included between 1 and 50 bars. The enthalpy and the vaporization temperature of liquid silver and liquid silica are studied. The key role of pressure on composition, enthalpy and the vaporization temperature is shown. The electrical neutrality is study, and the importance of ionized gaseous silver at low temperature is shown even for low amount of silver. The increase of electronegative ions (Ag^– and O^–) with pressure is shown. The vapor pressures fitting coefficients of Ag and SiO₂ are given.     

Kinetics of the Same Reaction Monitored over Nine Orders of Magnitude in Concentration: When Are Unique Subensemble and Single‐Turnover Reactivity Displayed?

Essentially no information is known about the behavior of individual molecular catalysts under reaction conditions. This is a result of the averaging inherent to traditional analytical techniques. Herein, a combined fluorescence microscopy and ¹H NMR spectroscopy study reveals that unique (that is, non‐ensemble averaged) distributions and time‐variable kinetics from molecular ruthenium catalysts within growing polynorbornene occur and are detectable between 10^?9 m and 10^?6 m of substrate, surprisingly just 1000‐fold less concentrated than a typical laboratory bench‐scale reaction. The kinetic states governing single‐turnover events are determinable by overlay of the signal arising from individual monomer insertion reactions with that from polymer growth from neighboring catalysts.     

Formation of a Cluster H<Subscript>2</Subscript>V<Subscript>10</Subscript>O<Stack><Subscript>28</Subscript><Superscript>4–</Superscript></Stack> under the Action of Brønsted Acids and Its Catalytic Activity in Oxidation of Alkylbenzenes

New method was developed for the preparation of vanadium cluster of the composition {Me₂NH₂}₄* H₂V₁₀O₂₈ from vanadyl(IV) acetylacetonate in the presence of 2-hydroxy-2-trifluoromethylchroman-4-one or its synthetic precursor, 2′-hydroxyacetophenone. The structure of the cluster was proved by X-ray diffraction (XRD) analysis. The cluster of decavanadate catalyzes oxidation of toluene and o-xylene creating promising situation for developing new catalytic materials.     

The Electronic State of Hydrogen in the α Phase of the Hydrogen‐Storage Material PdH(D)x: Does a Chemical Bond Between Palladium and Hydrogen Exist?

The palladium–hydrogen system is one of the most famous hydrogen‐storage systems. Although there has been much research on β‐phase PdH(D)_x, we comprehensively investigated the nature of the interaction between Pd and H(D) in α‐phase PdH(D)_x (x<0.03 at 303 K), and revealed the existence of Pd?H(D) chemical bond for the first time, by various in situ experimental techniques and first‐principles theoretical calculations. The lattice expansion, magnetic susceptibility, and electrical resistivity all provide evidence. In situ solid‐state ¹H and ²H NMR spectroscopy and first‐principles theoretical calculations revealed that a Pd?H(D) chemical bond exists in the α phase, but the bonding character of the Pd?H(D) bond in the α phase is quite different from that in the β phase; the nature of the Pd?H(D) bond in the α phase is a localized covalent bond whereas that in the β phase is a metallic bond.     

Are the reduction and oxidation properties of nitrocompounds dissolved in water different from those produced when adsorbed on a silica surface? A DFT M05‐2X computational study

The reduction and oxidation properties of four nitrocompounds (trinitrotoluene [TNT], 2,4‐dinitrotoluene, 2,4‐dinitroanisole, and 5‐nitro‐2,4‐dihydro‐3H‐1,2,4‐triazol‐3‐one [NTO]) dissolved in water as compared with the same properties for compounds adsorbed on a silica surface were studied. To consider the influence of adsorption, cluster models were developed at the M05/tzvp level. A hydroxylated silica (001) surface was chosen to represent a key component of soil. The PCM(Pauling) and SMD solvation models were used to model water bulk influence. The following properties were analyzed: electron affinity, ionization potential, reduction Gibbs free energy, oxidation Gibbs free energy, and reduction and oxidation potentials. It was found that adsorption and solvation decrease gas phase electron affinity, ionization potential, and Gibbs free energy of reduction and oxidation, and thus, promote redox transformation of nitrocompounds. However, in case of solvation, the changes are more significant than for adsorption. This means that nitrocompounds dissolved in water are easier to transform by reduction or oxidation than adsorbed ones. Among the considered compounds, TNT was found to be the most reactive in an electron attachment process and the least reactive for an electron detachment transformation. During ionization, a deprotonation of adsorbed NTO was found to occur. © 2015 Wiley Periodicals, Inc.     

Nickel Complexes of a Pincer Amidobis(amine) Ligand: Synthesis,Structure, and Activity in Stoichiometric and Catalytic C?C Bond‐Forming Reactions of Alkyl Halides

Get a grip! Ni^II complexes of the new pincer amidobis(amine) ligand are described. The Ni chloride complex catalyzes Kumada–Corriu–Tamao coupling of unactivated alkyl halides with alkyl Grignard reagents, as well as double C–C coupling of CH₂Cl₂ with alkyl Grignard reagents (see schemes).

     

Heteroleptic Silylamido Phenolate Complexes of Calcium and the Larger Alkaline Earth Metals: β‐Agostic Ae⋅⋅⋅Si?H Stabilization and Activity in the Ring‐Opening Polymerization of L‐Lactide

The factors governing the stability and the reactivity towards cyclic esters of heteroleptic complexes of the large alkaline earth metals (Ae) have been probed. The synthesis and stability of a family of heteroleptic silylamido and alkoxide complexes of calcium [{LOⁱ}Ca? Nu(thf)_n] supported by mono‐anionic amino ether phenolate ligands (i=1, {LO¹}^?=4‐(tert‐butyl)‐2,6‐bis(morpholinomethyl)phenolate, Nu^?=N(SiMe₂H)₂^?, n=0, 4 ; i=2, {LO²}^?=2,4‐di‐tert‐butyl‐6‐{[2‐(methoxymethyl)pyrrolidin‐1‐yl]methyl}phenolate, Nu^?=N(SiMe₂H)₂^?, n=0, 5 ; i=4, {LO⁴}^?=2‐{[bis(2‐methoxyethyl)amino]methyl}‐4,6‐di‐tert‐butylphenolate, Nu^?=N(SiMe₂H)₂^?, n=1, 6 ; Nu^?=HC?CCH₂O^?, n=0, 7 ) and those of the related [{LO³}Ae? N(SiMe₂H)₂] ({LO³}^?=2‐[(1,4,7,10‐tetraoxa‐13‐azacyclopentadecan‐13‐yl)methyl]‐4,6‐di‐tert‐butylphenolate Ae=Ca, 1 ; Sr, 2 ; Ba, 3 ) have been investigated. The molecular structures of 1 , 2 , [( 4 )₂], 6 , and [( 7 )₂] have been determined by X‐ray diffraction. These highlight Ae???H? Si internal β‐agostic interactions, which play a key role in the stabilization of [{LOⁱ}Ae? N(SiMe₂H)₂] complexes against ligand redistribution reactions, in contrast to regular [{LOⁱ}Ae? N(SiMe₃)₂]. Pulse‐gradient spin‐echo (PGSE) NMR measurements showed that 1 , 4 , 6 , and 7 are monomeric in solution. Complexes 1 – 7 mediate the ring‐opening polymerization (ROP) of L ‐lactide highly efficiently, converting up to 5000 equivalents of monomer at 25 °C in a controlled fashion. In the immortal ROP performed with up to 100 equivalents of exogenous 9‐anthracenylmethanol or benzyl or propargyl alcohols as a transfer agent, the activity of the catalyst increased with the size of the metal ( 1 < 2 < 3 ). For Ca‐based complexes, the enhanced electron‐donating ability of the ancillary ligand favored catalyst activity ( 1 > 6 > 4 ≈ 5 ). The nature of the alcohol had little effect over the activity of the binary catalyst system 1 /ROH; in all cases, both the control and end‐group fidelity were excellent. In the living ROP of L ‐LA, the HC?CCH₂O^? initiating group (as in 7 ) proved superior to N(SiMe₂H)₂^? or N(SiMe₃)₂^? (as in 6 or [{LO⁴}Ca? N(SiMe₃)₂] ( B ), respectively).