Chemphyschem最新文献

A polymerizable diacetylene gelator, containing urea and urethane groups, that congeals various non-polar solvents was synthesized. The gelator molecules self-assemble forming non-covalent polymers through intermolecular hydrogen bonding, as evidenced from FT-IR and concentration-dependent 1H NMR spectroscopy. The self-assembly positions the diyne units of adjacent molecules at proximity and in a geometry suitable for their topochemical polymerization. UV irradiation of the gel resulted in topochemical polymerization, transforming the non-covalent polymer to a covalent polymer, in situ, in the gel state. The polymerization was confirmed by characterizing the polydiacetylene (PDA) using UV-Vis and Raman spectroscopy. Time-dependent rheological studies revealed gradual strengthening of the gel with the duration of irradiation, suggesting that the degree of polymerization increases with the duration of irradiation. The PDA formed is a semiconductor, which might be useful for various applications.

The presence of ions in the complexation of molecules can profoundly affect the structure, resulting in changes to functionality and stability. These non-covalent interactions drive many biological processes both necessary and inimical and require extensive research to understand and predict their effects. Protonated and alkali metalated complexes of glycine (Gly) and 1-methyluracil (1-mUra) were studied using infrared multiphoton dissociation (IRMPD) spectroscopy and density functional theory (DFT) calculations. The experimental and simulated vibrational spectra were compared to help elucidate the structure of each complex. The lowest energy structure for [(Gly)(1-mUra)]H+ consists of amine protonated Gly bound to O4 of canonical 1-mUra through a single ionic hydrogen bond with another, intraglycine ionic hydrogen bond between the protonated amine group and the carbonyl oxygen. For [(Gly)(1-mUra)]Li+, [(Gly)(1-mUra)]Na+ and [(Gly)(1-mUra)]K+, the experimental spectra are most consistent with the metal cations binding in a trigonal planar geometry with 1-mUra bound to the metal cation via the O4 carbonyl. In [(Gly)(1-mUra)]Li+ and [(Gly)(1-mUra)]Na+, the metal cation is bound to canonical Gly via the carbonyl oxygen and amine nitrogen, but in [(Gly)(1-mUra)]K+, Gly is bound through both oxygens and contains an intraglycine hydrogen bond from the hydroxyl to the amine nitrogen.

2D materials have rapidly become the building blocks for the next generation of semiconducting materials and devices, with  Chemical vapor deposition (CVD) emerging as a prefered method for their synthesis. However, the predictable and reproducible growth of high quality, large 2D monolayers remains challenging. An important facet is controlling the local environment at the surface of the substrate - here, space-confinement techniques have emerged as promising candidates. We demonstrate that space-confined CVD growth using microstructured MoOx grown on Ni foam is an appealing approach for rapid growth of high quality MoS2 monolayers; a very important subset of 2D materials. This method eschews the use of powders which can be more difficult to control. By incorporation of a porous barrier in the Ni foam support, the rate of delivery of both the Mo and S source to the substrate is dampened, leading to coverage of large, high quality, mono-to-few layer triangular domains as confirmed by Raman and photoluminescence (PL) spectroscopies together with atomic force microscopy (AFM) height measurements.

Dispersing ferrofluids in liquid crystals (LCs) produces unique systems which possess magnetic functionality and novel phenomena such as droplet chaining. This work reports the formation of ferrofluid droplet chains facilitated by the topological defects within the LC director field, induced by the dispersed ferrofluid. The translational and rotational motion of these chains could be controlled via application of external magnetic fields. The process of the droplet chain formation in LCs can be stabilized by the addition of surfactants. The magnetic colloidal particles in the ferrofluid located at the interface between the ferrofluid and the LC are arranged so that a boundary layer was formed. The velocities and boundary layer thickness values of ferrofluid droplet chains in nematic 5CB (4-Cyano-4'-pentylbiphenyl) were investigated for varying average droplet sizes and number of droplets in a chain. The creation and behaviour of ferrofluid droplet chains in 5CB with the addition of the surfactant polysorbate 60 (Tween-60) and without, was comparatively investigated. The integration of liquid crystals and ferrofluids along with the incorporation of functional materials facilitates the innovative development of advanced materials for future applications.

This work presents a detailed comparative analysis of C-H activations catalyzed by three different Fe(IV)O porphyrinoid complexes. The study considers the usual heme porphyrin (complex I) as the base compound, porphyrazine (complex II), which is obtained by replacing carbon with nitrogen at the meso position, and phthalocyanine (complex III), which is obtained through the peripheral benzoannulation of porphyrazine. The focus here is to explore the impact of bridging groups and peripheral functionalization in heme systems on reactivity. Factors such as distortion energy and electron acceptor orbitals significantly affect the overall reactivity. The effect of substitution on quantum mechanical tunneling, using H/D kinetic isotope effect studies, is also included. The results reveal a fascinating reactivity order: meso nitrogen substitution enhances reactivity, while additional benzo-annulation hinders reactivity, leading to the order complex II > complex I > complex III. In comparison to the usual Cpd I, which is Fe(IV)O-porphyrin π cation radical with an -SH axial ligand, complex II was found to be more reactive. The electron affinity of the Fe(IV)O complexes and the dissociation energy of the forming Fe(IV)O-H bond aligns with observed reactivity trend. These findings support the use of accessible iron frameworks derived from porphyrin in C-H activation processes.

Herein, we propose a purely-organic donor-acceptor (D-A) molecular triad, with a light-absorbing polarized molecular wire (PMW) used as a central linkage, as a proof of concept for the possible future applications of the D-PMW-A arrangement in molecular photovoltaics. This work builds upon our earlier study on the PMW unit itself, which proved to be highly promising for the ultrafast photogeneration of free charge carriers. Quantum-chemical calculations performed for the D-PMW-A triad at a semi-empirical level of theory reveal a large electric dipole moment of the system, and show strong charge-transfer (CT) character of its lowest-energy excited electronic states, including the S1, which favours efficient dissociation of an exciton initially formed upon the absorption of light. The confirmation for this effect was found with nonadiabatic molecular dynamics simulations, revealing an ultrafast relaxation from higher, bright excited states to S1, completed on a subpicosecond timescale. The architecture of the proposed molecular triad enables its electronic coupling to the surrounding environment through chemical bonds, or noncovalent stacking interactions, which might open way for synthesis of a new class of D-PMW-A efficient molecular organic photovoltaic materials.

Cerium oxide, or ceria, (CeO2) is one of the most studied materials for its wide range of applications in heterogeneous catalysis and energy conversion technologies. The key feature of ceria is the remarkable oxygen storage capacity linked to the switch between Ce4+ and Ce3+ states, in turn creating oxygen vacancies. Changes in the electronic structure occur with oxygen removal from the lattice. Accordingly, the two valence electrons can be accommodated by the reduction of support cations where the electrons can be localized in empty f states of Ce4+ ions nearby. Quantifying the different oxidation states in situ is crucial to understand and model the reaction mechanism. Beside the different techniques to quantify Ce3+ and Ce4+ states, we discuss the use of X-ray Raman Scattering (XRS) spectroscopy as an alternative method. In particular, we show that XRS can observe the oxidation state changes of cerium directly in the bulk of the materials under realistic environmental conditions. The Hilbert++ code is used to simulate the XRS spectra and quantify accurately the Ce3+ and Ce4+ content. These results are compared to those obtained from in situ X-ray Diffraction (XRD) collected in parallel and the differences arising from the two different probes are discussed.

Earlier scanning tunneling microscopy (STM) studies have shown that nitrogen forms square c(2x2) islands on Cu(100) surfaces, the assembly of which depends on coverage. Recent calculations have revealed that adatom-adatom interactions are compatible with the formation of square c(2x2) islands. The pair distribution of these islands is a topic of the current investigation. In addition, the domain structure of islands found recently in STM experiments is discussed and explained using two types of island interactions. The potential used for the interaction between N square islands on copper is a combination of previous ab initio calculations and an updated mesoscopic interaction scheme. The 2D-BGY integral equation is extended to handle binary objects like two different types of islands. It is solved for up to a quarter island coverage using a numerical recursion algorithm. Coverage beyond half is accessible with island vacancy symmetry. The calculation predicts the formation of ordered island assemblies with increasing coverage. These results reasonably explain the previous experimental observations. The handling of binary objects also seems to be applicable to assemblies of two adatom types as found in catalysis. The assumptions and limitations of the model are discussed and open questions are formulated.

Computations based on density functional theory are carried out to examine the mechanism of photocatalytic oxidation of methane to methanol with H2O2 as oxidant and water as co-catalyst over anatase TiO2 (101) surface. The reaction proceeds with hydrogen abstraction from methane followed by the formation of surface methoxy species, which is reduced to methanol. We compare the reaction energetics for C-H dissociation in the presence and absence of surface defect, but find no discernible impact of O-vacancy on methane oxidation. In comparison, hydroxyl produced as a result of H2O2 or H2O photo-decomposition dramatically reduces the barrier for CH3-H bond cleavage. The reaction proceeds further by the reduction of surface methoxy group and is the rate-limiting step for methanol formation. Additionally, we find that methyl can also react with water to form methanol with a considerably lower barrier, suggesting an active involvement of water for methanol formation. We also study the role of water as a co-catalyst and observe significant reduction in barriers, facilitated by alternate pathway for proton transfer. The reaction pathways presented provide valuable in- sights into the mechanism of methane oxidation in the presence of H2O2 as oxidant and demonstrate the rate-enhancing role of water for these steps.

Metal nanoparticles sensitize cancers to radiotherapy however their mechanisms of action are complex. The conceptual inspiration arose from theories of physical dose deposition but various chemical and biological factors have also been identified. Interpretation of data has been limited by challenges in measuring true DNA damage compared to DNA damage repair factors. Here, we applied a new assay, STRIDE, for the first time to measure DNA double strand breaks (DSBs) in 4T1 cells as a model of triple negative breast cancer exposed to gold nanoparticles and radiation, and compared this to the common γH2AX assay for DSB repair. The STRIDE assay showed no increase in DSB detection 15 mins after irradiation for cells containing nanoparticles compared to cells without. Gold nanoparticles led to prolonged detection of DSBs after irradiation and delayed the DSB repair. The data show no evidence of increased radiation dose deposition with nanoparticles, but rather enhanced radiobiological effects resulting from nanoparticles which includes disruption of the recruitment of essential DDR machinery, thereby impairing DNA repair processes.