High‐resolution X‐ray diffraction experiments, theoretical calculations and atom‐specific X‐ray absorption experiments were used to investigate two nickel complexes, (MePh3P)2NiII(bdtCl2)2·2(CH3)2SO ...complex (1) and (MePh3P)NiIII(bdtCl2)2 complex (2). Combining the techniques of nickel K‐ and sulfur K‐edge X‐ray absorption spectroscopy with high‐resolution X‐ray charge density modeling, together with theoretical calculations, the actual oxidation states of the central Ni atoms in these two complexes are investigated. Ni ions in two complexes are clearly in different oxidation states: the Ni ion of complex (1) is formally NiII; that of complex (2) should be formally NiIII, yet it is best described as a combination of Ni2+ and Ni3+, due to the involvement of the non‐innocent ligand in the Ni—L bond. A detailed description of Ni—S bond character (σ,π) is presented.
Differences between the formal oxidation states of two nickel(II/III) coordination compounds with a non‐innocent ligand were studied. There are differences between the theoretical calculations as well as between various experimental results.
Charge density study of a mixed-valence tri-cobalt compound, Co3(μ-admtrz)4(μ-OH)2(CN)6·2H2O (1) (admtrz = 3,5-dimethyl-4-amino-1,2,4-triazole), is investigated based on high resolution X-ray ...diffraction data and density functional theory (DFT) calculations. The molecular structure of this compound contains three cobalt atoms in a linear fashion, where two terminal ones are CoIII at a low-spin (LS) state and a central one is CoII at a high-spin (HS) state with a total spin quantum number, S total, of 3/2. It is centrosymmetric with the center of inversion located at the central Co atom (Co2). The Co2 ion is linked with each terminal cobalt (Co1) ion through two μ-admtrz ligands and a μ-OH ligand in a CoN4O2 coordination, where the Co1 is bonded additionally to three CN ligands with CoN2OC3 coordination. The combined experimental and theoretical charge density study identifies the different characters of two types of cobalt ions; more pronounced charge concentration and depletion features in the valence shell charge concentration (VSCC) are found in the CoIII ion than in the CoII ion, and d-orbital populations also show the difference. According to topological properties associated with the bond critical point (BCP), the Co1–C(N) bond is the strongest among all the Co-ligand bonds in this compound; the Co–O is stronger than Co–N bond. Again Co1–O is stronger than Co2–O, so as the Co1–N being stronger than Co2–N bond. The electronic configuration of each type of Co atom is further characterized through magnetic measurement, Co-specific X-ray absorption near edge spectroscopy (XANES), and X-ray emission spectra (XES).
The C-O coupling reaction between 2,4-dimethylphenol and 4-bromotoluene catalyzed by the CuI/K2CO3/phen system can be inhibited by the radical scavenger cumene. Complexes ...Cu(i)(phen)(1-(2,4-dimethylphenoxy)-4-methylbenzene)(+) (denoted as A), {HCu(i)(phen)(2,4-dimethylphenoxy)}(+) and Cu(i)(2,4-dimethylphenoxy)2(-) (denoted as B) were observed by in situ electrospray ionization mass spectrometry (ESI-MS) analysis of the copper(i)-catalyzed C-O coupling reaction under the catalytic reaction conditions indicating that they could be intermediates in the reaction. The in situ EPR study of the reaction solution detected the Cu(ii) species with a fitted g value of 2.188. A catalytic cycle with a single electron transfer (SET) step was proposed based on these observations.
This manuscript describes the interaction of low-molecular-weight DNICs with short peptides designed to explore the stability and structure of DNIC–peptide/RRE–peptide constructs. Although ...characterization of protein-bound and low-molecular-weight DNICs is possible via EPR, XAS, and NRVS, this study demonstrates that the combination of aqueous IR νNO and UV–vis spectra can serve as an efficient tool to characterize and discriminate peptide-bound DNICs and RREs. The de novo chelate-cysteine-containing peptides KC(A) n CK-bound (n = 1–4) dinitrosyliron complexes KC(A) n CK-DNIC (CnA-DNIC) and monodentate-cysteine-containing peptides KCAAK-/KCAAHK-bound Roussin’s red esters (RREs) KCAAK-RRE/KCAAHK-RRE were synthesized and characterized by aqueous IR, UV–vis, EPR, CD, XAS, and ESI-MS. In contrast to the inertness of chelate-cysteine-containing peptide-bound DNICs toward KCAAK/KCAAHK, transformation of KCAAK-RRE/KCAAHK-RRE into CnA-DNIC triggered by CnA and reversible transformation between CnA-DNIC and CnA-RRE via {Fe(NO)2}9-{Fe(NO)2}10 reduced-form peptide-bound RREs demonstrate that the {Fe(NO)2}9 motif displays a preference for chelate-cysteine-containing peptides over monodentate-cysteine-containing peptides. Also, this study may signify that nitrosylation of Fe–S proteins generating protein-bound RREs, reduced protein-bound RREs, or protein-bound DNICs are modulated by both the oxidation state of iron and the chelating effect of the bound proteins of Fe–S clusters.
Thiathiophthene (TTP), a planar molecule with two fused heterocyclic five-membered rings and an essentially linear S–S–S bond, is a molecule of great interest due to its unique chemical bondings. To ...elucidate the remarkable bonding nature, a combined experimental and theoretical study on the electron density distribution of 2,5-dimethyl-3,4-trimethylene-6a-TTP (1) is investigated based on a multipole model through high-resolution X-ray diffraction data experimentally and on the density functional calculations (DFT) theoretically. In addition, S K-edge X-ray absorption spectroscopy (XAS) is measured to verify the chemical bonding concerning the sulfur atoms. The molecule can be firmly described as 10π electron with aromatic character among the eight atoms, S3C5, of the two fused five-membered rings plus three-center four-electron σ character along the S–S–S bond. Such bonding description is verified with the calculated XAS spectrum, where the pre-edge absorption for transitions from S 1s to π* and σ* are located. The three-center four-electron S–S–S σ bond makes the terminal S atoms richer in electron density than the central one.
Novel multifunctional fluorescent electrospun (ES) nanofibers exhibiting high sensitivity for various metal ions were prepared from binary blends of poly(2-hydroxyethyl ...methacrylate-co-N-methylolacrylamide) (poly(HEMA-co-NMA)) and 9,9-dihexylfluorene-2,7-bipyridine (bpy-F-bpy) by using a single-capillary spinneret. Different compositions of poly(HEMA-co-NMA) were synthesized through free-radical polymerization. The HEMA moieties were designed to exhibit hydrophilic properties, and the NMA content substantially affected the stability of the ES nanofibers in water. Experimental optical spectra and simulation results demonstrated that the fluorescent sensing probe bpy-polyfluorene-bpy could detect various metal ions. ES nanofibers prepared from copolymers with a 77:23 HEMA:NMA ratio blended with 5% bpy-F-bpy (P2-5) exhibited apparent color change from blue to green, color change from blue to blue-green and fluorescence quenching when detecting Zn2+ , Hg2+ and Cu2+ , respectively. The P2-5 ES nanofibers exhibited ultrasensitivity for Zn2+ (10-7 -10-3 m) because of the 70 nm red shift of the emission maximum, and high reversibility because of their on-off switchable fluorescence emission upon the sequential addition of Zn2+ and ethylenediaminetetraacetic acid cycled several times. These results and a microfluidics system study indicated that the nanofibers, which have a high surface-to-volume ratio, can be used as 'naked eye' sensors for sensing various metal ions and as efficient multifunctional chemosensor-filtering devices.
Reaction of hydrido5,10,15,20-tetrakis(p-tolyl)porphyrinatoiridium(III) (Ir(ttp)H) (1) with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) (2) at room temperature gave a 90% yield of the unsupported ...iridium(II) porphyrin dimer, IrII 2(ttp)2 (3). Kinetic measurements revealed that the oxidation followed overall second-order kinetics: rate = kIr(ttp)HTEMPO, k(25 °C) = 6.65 × 10−4 M−1. The entropy of activation (ΔS ‡ = −25.3 ± 2.5 cal mol−1 K−1) and the kinetic isotope effect of 7.2 supported a bimolecular associative mechanism in the rate-determining hydrogen atom transfer from Ir(ttp)H to TEMPO.
Double-stranded polymeric ladderphane 1 using HBC as linkers and the single-stranded comblike polynorbornene 2 with HBC pendants are synthesized by the ring-opening metathesis polymerization using ...the first-generation Grubbs catalyst. The photophysical properties of these HBC-incorporated polymers indicate significant interactions between adjacent polynuclear aromatic chromophores which are comparable with those of aggregated forms of the HBC cores. No liquid crystal properties, however, are observed in these polymers. The STM images of 1 and 2 demonstrate the unique properties of polynorbornene derivatives having N-aryl-5,6-endopyrrolidene pendants or linkers where the polymers are self-assembled to form ordered two-dimensional arrays on the HOPG surface.
Novel π–extended conjugated amphiphiles composed of a hydrophilic section of two quaternary ammonium groups and p-phenylene ethynylene with adjustable alkyl chain hydrophobic section were prepared by ...a multistep synthesis. These dicationic amphiphiles showed good water solubility and formed a tubular assembly in water. The evidence for the nanotubular comes from direct optical and TEM observations. A strong π–π stacking interaction between neighboring molecules, as evidenced by the red-shift and self-quenching in fluorescence, is proposed for the self-assembly. At the same time, dehydration of the bromide led to strong counterion condensation in headgroups, which resulted in the small curvature structure of the nanotubes. A bilayer lamellar structural model for the organic nanotube is proposed, and a reasonable structural model based on the experimental XRD pattern, as well as cell constants, is proposed.
Four series of simple and rodlike racemic biphenyl mesogens possessing a 2-octyloxy tail and different substituents at the inner-core position of the phenyl ring were easily prepared. The mesophases ...of these racemic biphenyl mesogens were confirmed by variable-temperature XRD and the characteristic texture of POM. In general, cubic BPs can be induced by adding an appropriate ratio of chiral additive S811 or ISO(6OBA)2 into these racemic biphenyl mesogens during the heating and cooling processes. Interestingly, BPIII (5–6 K) easily dominates in highly chiral conditions for the blended mixture composed of mono-substituted biphenyl mesogens and chiral dopant S811 . In addition, the formation temperature of BPIII is near room temperature (36 °C) when compound C6OBiPhI-OH is blended with 35 wt% S811 during the cooling process. Stable BPs with more than 20 K present in the blended mixture system were composed of chiral dopant ISO(6OBA)2 and no substituted biphenyl mesogens CnOBiPhI-H or difluoro substituted CnOBiPhI-FF . Notably, the widest temperature range of BP (∼34 K) can be induced by adding only 10 wt% chiral dopant ISO(6OBA)2 with high HTP into the biphenyl compound C6OBiPhI-H . The properties of the BPs were characterized by POM, DSC and reflection spectra. On the basis of our experimental results and molecular modeling, we demonstrated that the appearance and temperature range of BPs in this simple type of biphenyl mesogen with 2-octyloxy tail are affected by the molecular dipole moment and biaxiality.
PDF
