Dissociation kinetics of macrocyclic trivalent lanthanide complexes of 1-oxa-4,7,10-triazacyclododecane-4,10-diacetic acid (H₂ODO2A)

<div><p>The dissociation kinetics of selected trivalent lanthanide (Ln³⁺, Ln=La, Pr, Eu, Er, Lu) complexes of the macrocyclic ligand H₂ODO2A (1-oxa-4,7,10-triazacyclododecane-4,10-diacetic acid), LnODO2A⁺, were studied in the [H⁺] range (0.1–2.4) × 10⁻⁴ M in the temperature range 15–45 °C. Excess Cu²⁺ ions were used as the scavenger for the ligand in acetate–acetic acid buffer medium. The dissociation reactions are independent of [Cu²⁺] and follow the rate law <i>k</i>_obs = <i>k</i>_d + <i>k</i>_AC[Acetate] + K′<i>k</i>_lim[H⁺]/(1 + K′[H⁺]), where <i>k</i>_d, <i>k</i>_AC, and <i>k</i>_lim are the respective dissociation rate constants for the [H⁺]-independent, acetate-assisted, and the [H⁺]-dependent limiting pathways; K′ is the equilibrium constant for the protonation reaction LnODO2A⁺ + H⁺ LnODO2AH²⁺. The dissociation rates of LnODO2A⁺ complexes are all faster than those of the corresponding LnDO2A⁺ complexes (DO2A²⁻ is the fully deprotonated dianion of the ligand H₂DO2A, 1,4,7,10-tetrazacyclo-dodecane-1,7-diacetic acid), consistent with the notion that LnODO2A⁺ complexes are kinetically more labile and thermodynamically less stable than the corresponding LnDO2A⁺ complexes, and H₂ODO2A is not pre-organized for Ln³⁺ ion complexation but H₂DO2A is.</p></div

Differences of Typical Wuyi Rock Tea in Taste and Nonvolatiles Profile Revealed by Multisensory Analysis and LC–MS-Based Metabolomics

Wuyi Rock tea, specifically Shuixian and Rougui, exhibits distinct sensory characteristics. In this study, we investigated the sensory and metabolite differences between Shuixian and Rougui. Quantitative description analysis revealed that Rougui exhibited higher intensity in bitter, thick, harsh, and numb tastes, while Shuixian had stronger salty and umami tastes. Nontargeted metabolomics identified 151 compounds with 66 compounds identified as key differential metabolites responsible for metabolic discrimination. Most of the catechins and flavonoids were enriched in Rougui tea, while epigallocatechin-3,3′-di-O-gallate, epigallocatechin-3,5-di-O-gallate, gallocatechin-3,5-di-O-gallate, isovitexin, and theaflavanoside I were enriched in Shuixian tea. Catechins, kaempferol, quercetin, and myricetin derivatives were positively correlated with bitter taste and numb sensation. Sour taste was positively correlated to organic acids. Amino acids potentially contributed to salty and umami tastes. These results provide further insights into the taste characteristics and the relationship between taste attributes and specific metabolites in Wuyi Rock tea

Atomic-Scale Interfacial Band Mapping across Vertically Phased-Separated Polymer/Fullerene Hybrid Solar Cells

Using cross-sectional scanning tunneling microscope (XSTM) with samples cleaved in situ in an ultrahigh vacuum chamber, this study demonstrates the direct visualization of high-resolution interfacial band mapping images across the film thickness in an optimized bulk heterojunction polymer solar cell consisting of nanoscale phase segregated blends of poly­(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM). We were able to achieve the direct observation of the interfacial band alignments at the donor (P3HT)-acceptor (PCBM) interfaces and at the interfaces between the photoactive P3HT:PCBM blends and the poly­(3,4-ethylenedioxythiophene) poly­(styrenesulfonate) (PEDOT:PSS) anode modification layer with an atomic-scale spatial resolution. The unique advantage of using XSTM to characterize polymer/fullerene bulk heterojunction solar cells allows us to explore simultaneously the quantitative link between the vertical morphologies and their corresponding local electronic properties. This provides an atomic insight of interfacial band alignments between the two opposite electrodes, which will be crucial for improving the efficiencies of the charge generation, transport, and collection and the corresponding device performance of polymer solar cells

On-Chip Thin Film Zernike Phase Plate for In-Focus Transmission Electron Microscopy Imaging of Organic Materials

Transmission electron microscopy (TEM) is a powerful tool for imaging nanostructures, yet its capability is limited with respect to the imaging of organic materials because of the intrinsic low contrast problem. TEM phase plates have been in development for decades, yet a reliable phase plate technique has not been available because the performance of TEM phase plates deteriorates too quickly. Such an obstacle prohibits in-focus TEM phase imaging to be routinely achievable, thus limiting the technique being used in practical applications. Here we present an on-chip thin film Zernike phase plate which can effectively release charging and allow reliable in-focus TEM images of organic materials with enhanced contrast to be routinely obtained. With this stable system, we were able to characterize many polymer solar cell specimens and consequently identified and verified the existence of an unexpected nanoparticle phase. Furthermore, we were also able to observe the fine structures of an Escherichia coli specimen, without staining, using this on-chip thin film phase plate. Our system, which can be installed on a commercial TEM, opens up exciting possibilities for TEM to characterize organic materials

Self-Encapsulated Doping of n-Type Graphene Transistors with Extended Air Stability

This paper presents an innovative approach to fabricating controllable n-type doping graphene transistors with extended air stability by using self-encapsulated doping layers of titanium suboxide (TiOx) thin films, which are an amorphous phase of crystalline TiO₂ and can be solution processed. The nonstoichiometry TiOx thin films consisting of a large number of oxygen vacancies exhibit several unique functions simultaneously in the n-type doping of graphene as an efficient electron-donating agent, an effective dielectric screening medium, and also an encapsulated layer. A novel device structure consisting of both top and bottom coverage of TiOx thin layers on a graphene transistor exhibited strong n-type transport characteristics with its Dirac point shifted up to −80 V and an enhanced electron mobility with doping. Most interestingly, an extended stability of the device without rapid degradation after doping was observed when it was exposed to ambient air for several days, which is not usually observed in other n-type doping methods in graphene. Density functional theory calculations were also employed to explain the observed unique n-type doping characteristics of graphene using TiOx thin films. The technique of using an “active” encapsulated layer with controllable and substantial electron doping on graphene provides a new route to modulate electronic transport behavior of graphene and has considerable potential for the future development of air-stable and large-area graphene-based nanoelectronics

Dependence of Nanocrystal Dimensionality on the Polymer Nanomorphology, Anisotropic Optical Absorption, and Carrier Transport in P3HT:TiO₂ Bulk Heterojunctions

It is known that the nanoscale morphological organization of donors or acceptors in bulk heterojunction (BHJ) solar cells is critical to device performance and strongly affects carrier generation, transporting, and collection. This work demonstrates the dependence of nanocrystal dimensionality and organization on the polymer nanomorphology in P3HT:TiO₂ hybrid bulk heterojunctions, which were revealed using grazing-incidence X-ray diffraction (GIXRD) using a synchrotron X-ray beam and electron tomography. We further performed a multiscale molecular dynamic simulation to understand the morphological orientation of a polymer blended with TiO₂ nanoparticles (NPs) or nanorods (NRs). The correlation between polymer nanoscale morphology and the dimensionality and anisotropy of nanocrystals in P3HT:TiO₂ hybrids clearly explains the observation of different optical absorption and carrier transport behaviors in directions perpendicular or parallel to the film substrate. Our results provide crucial information toward understanding the interplay between nanocrystal dimensionality and polymer morphology in developing organic/inorganic hybrid electronic devices such as thin film transistors (TFTs) or photovoltaics (PVs)