Inorganic and Organozinc Fluorocarboxylates: Synthesis, Structure and Materials Chemistry

The organozinc fluorocarboxylates RZnO₂CR_f and RZnO₂CR_f·TMEDA, along with Zn­(O₂CR_f)₂·TMEDA (R = Me, Et; R_f = C₂F₅, C₃F₇) have been synthesized. The structures of EtZnO₂C₂F₅ (<b>5</b>), EtZnO₂C₃F₇ (<b>7</b>), Et­Zn­O₂C₂F₅·TMEDA (<b>11</b>), Zn­(O₂C₂F₅)₂·TMEDA (<b>13</b>), along with products from the adventitious reaction with either O₂ or H₂O, Zn₁₀Me₄(OMe)₄(O₂CC₂F₅)₁₂ (<b>2</b>), Zn₉­Et₂­(O₂­CC₂F₅)₁₂(O)₂ (<b>6</b>), Zn₈Et₄(OEt)₄(O₂CC₃F₇)₆(O) (<b>8</b>), [Zn­(O₂CC₃F₇)₂·TMEDA]₂·H₂O (<b>15</b>) have been determined. Thin films of oriented ZnO have been deposited on glass substrates by low-pressure chemical vapor deposition (LPCVD) using <b>3</b> and <b>10</b> as precursors, though no fluorine incorporation in the films was noted. LPCVD using <b>13</b> as precursor also yielded fluorine-free ZnO, but lacking the oriented growth observed using <b>3</b>, <b>10</b>. However, <b>5</b>, which exhibits short intermolecular Zn···F contacts in the solid state, thermally decomposes to bulk ZnF₂

Unnatural Amino Acid Mutagenesis Reveals Dimerization As a Negative Regulatory Mechanism of VHR’s Phosphatase Activity

<i>Vaccinia</i> H1-related (VHR) phosphatase is a dual specificity phosphatase that is required for cell-cycle progression and plays a role in cell growth of certain cancers. Therefore, it represents a potential drug target. VHR is structurally and biochemically well characterized, yet its regulatory principles are still poorly understood. Understanding its regulation is important, not only to comprehend VHR’s biological mechanisms and roles but also to determine its potential and druggability as a target in cancer. Here, we investigated the functional role of the unique “variable insert” region in VHR by selectively introducing the photo-cross-linkable amino acid <i>para-</i>benzoylphenylalanine (<i>p</i>BPA) using the amber suppression method. This approach led to the discovery of VHR dimerization, which was further confirmed using traditional chemical cross-linkers. Phe68 in VHR was discovered as a residue involved in the dimerization. We demonstrate that VHR can dimerize inside cells, and that VHR catalytic activity is reduced upon dimerization. Our results suggest that dimerization could occlude the active site of VHR, thereby blocking its accessibility to substrates. These findings indicate that the previously unknown transient self-association of VHR acts as a means for the negative regulation of its catalytic activity

How To Arrive at Accurate Benchmark Values for Transition Metal Compounds: Computation or Experiment?

With the objective of analyzing which kind of reference data is appropriate for benchmarking quantum chemical approaches for transition metal compounds, we present the following, (a) a collection of 60 transition metal diatomic molecules for which experimentally derived dissociation energies, equilibrium distances, and harmonic vibrational frequencies are known and (b) a composite computational approach based on coupled-cluster theory with basis set extrapolation, inclusion of core–valence correlation, and corrections for relativistic and multireference effects. The latter correction was obtained from internally contracted multireference coupled-cluster (icMRCC) theory. This composite approach has been used to obtain the dissociation energies and spectroscopic constants for the 60 molecules in our data set. In accordance with previous studies on a subset of molecules, we find that multireference corrections are rather small in many cases and CCSD­(T) can provide accurate reference values, if the complete basis set limit is explored. In addition, the multireference correction improves the results in cases where CCSD­(T) is not a good approximation. For a few cases, however, strong deviations from experiment persist, which cannot be explained by the remaining error in the computational approach. We suggest that these experimentally derived values require careful revision. This also shows that reliable reference values for benchmarking approximate computational methods are not always easily accessible via experiment and accurate computations may provide an alternative way to access them. In order to assess how the choice of reference data affects benchmark studies, we tested 10 DFT functionals for the molecules in the present data set against experimental and calculated reference values. Despite the differences between these two sets of reference values, we found that the ranking of the relative performance of the DFT functionals is nearly independent of the chosen reference

Intramolecular Charge-Transfer Excited-State Processes in 4‑(<i>N</i>,<i>N</i>‑Dimethylamino)benzonitrile: The Role of Twisting and the πσ* State

The structural processes leading to dual fluorescence of 4-(di­methyl­amino)­benzo­nitrile in the gas phase and in acetonitrile solvent were investigated using a combination of multireference configuration interaction (MRCI) and the second-order algebraic diagrammatic construction (ADC(2)) methods. Solvent effects were included on the basis of the conductor-like screening model. The MRCI method was used for computing the nonadiabatic interaction between the two lowest excited ππ* states (S₂(L_a, CT) and S₁(L_b, LE)) and the corresponding minimum on the crossing seam (MXS) whereas the ADC(2) calculations were dedicated to assessing the role of the πσ* state. The MXS structure was found to have a twisting angle of ∼50°. The branching space does not contain the twisting motion of the di­methyl­amino group and thus is not directly involved in the deactivation process from S₂ to S₁. Polar solvent effects are not found to have a significant influence on this situation. Applying <i>C_s</i> symmetry restrictions, the ADC(2) calculations show that CCN bending leads to a strong stabilization and to significant charge transfer (CT). Nevertheless, this structure is not a minimum but converts to the local excitation (LE) structure on releasing the symmetry constraint. These findings suggest that the main role in the dynamics is played by the nonadiabatic interaction of the LE and CT states and that the main source for the dual fluorescence is the twisted internal charge-transfer state in addition to the LE state

New Polymorphs of Perylene:Tetracyanoquinodimethane Charge Transfer Cocrystals

We report two hitherto unknown polymorphs of the charge transfer (CT) cocrystal perylene:tetracyanoquinodimethane (TCNQ) grown by physical vapor transport (PVT) in argon atmosphere. One of the polymorphs, named β, has stoichiometry 1:1 and adds to the three known structures with stoichiometry 1:1 (α), 2:1, and 3:1. Interestingly, below (280 ± 10) K the β structure undergoes a phase transition to what we refer to as the γ polymorph, with halving of the unit cell and reduction of symmetry from monoclinic to triclinic. Both new crystal structures present two alternating stacks with different intermolecular and intramolecular geometries. In stack S–I the perylene molecules show substantial deviations from planarity, with the angle between the naphthalene intramolecular moieties of 6.69°, and with the perylene and TCNQ molecular centroids shifted by 1.95 Å. In the second stack, S-II, the perylene is planar, and the centroids almost coincident. Structural investigations on bond length complemented by vibrational IR spectroscopy indicate that in the new polymorphs the degree of charge transfer, ρ, can be 0 or 0.12. The higher value of ionicity to be due to donor–acceptor pairs in the S-II, while molecules in S-I are closer to neutrality. Thus, the ionicity of the donor–acceptor pair depends on the stack and is comparable to that of the α polymorph which we redetermined as ρ = 0.15 ± 0.05

Experimental Basicities of Phosphazene, Guanidinophosphazene, and Proton Sponge Superbases in the Gas Phase and Solution

Experimental gas-phase superbasicity scale spanning 20 orders of magnitude and ranging from bicyclic guanidine 7-methyl-1,5,7-triazabicyclo[4.4.0]­dec-5-ene to triguanidinophosphazenes and P₃ phosphazenes is presented together with solution basicity data in acetonitrile and tetrahydrofuran. The most basic compound in the scaletriguanidinophosphazene Et–NP­[NC­(NMe₂)₂]₃has the highest experimental gas-phase basicity of an organic base ever reported: 273.9 kcal mol^–1. The scale includes besides the higher homologues of classical superbasic phosphazenes and several guanidino-substituted phosphazenes also a number of recently introduced bisphosphazene and bis-guanidino proton sponges. This advancement was made possible by a newly designed Fourier transform ion cyclotron resonance (ICR) mass spectrometry setup with the unique ability to generate and control in the ICR cell sufficient vapor pressures of two delicate compounds having low volatility, which enables determining their basicity difference. The obtained experimental gas-phase and solution basicity data are analyzed in terms of structural and solvent effects and compared with data from theoretical calculations