X‐ray Crystallography and Vibrational Spectroscopy Reveal the Key Determinants of Biocatalytic Dihydrogen Cycling by [NiFe] Hydrogenases

[NiFe] hydrogenases are complex model enzymes for the reversible cleavage of dihydrogen (H₂). However, structural determinants of efficient H₂ binding to their [NiFe] active site are not properly understood. Here, we present crystallographic and vibrational‐spectroscopic insights into the unexplored structure of the H₂‐binding [NiFe] intermediate. Using an F₄₂₀‐reducing [NiFe]‐hydrogenase from Methanosarcina barkeri as a model enzyme, we show that the protein backbone provides a strained chelating scaffold that tunes the [NiFe] active site for efficient H₂ binding and conversion. The protein matrix also directs H₂ diffusion to the [NiFe] site via two gas channels and allows the distribution of electrons between functional protomers through a subunit‐bridging FeS cluster. Our findings emphasize the relevance of an atypical Ni coordination, thereby providing a blueprint for the design of bio‐inspired H₂‐conversion catalysts.     

SiO(x) Monolayer Overcoating Effect on the TiO(2) Photocatalytic Oxidation of Cetylpyridinium Bromide

The effect of SiO(x) monolayer coverage on the rate of TiO(2) photocatalytic oxidation of cetylpyridinium bromide (CPB) in aqueous solutions has been studied. The rate of CPB removal from the solution (5相似文献   

Dielectric loss of polyethylene below 4.2°K arising from proton tunneling

The dielectric loss of high-density polyethylene (HDPE: melt-crystallized films and single-crystal mats), low-density polyethylene (LDPE), and copolymers of ethylene and vinyl alcohol (PEVA) was measured at 1.5 to 4.2°K in the frequency range from 10 Hz to 10 kHz. Results for HDPE show dispersion curves almost corresponding to a single relaxation and are interpreted in terms of phonon-assisted tunneling of the protons of hydroxyl groups which are accidentally attached to tertiary carbons (carbons with a short branch). Dispersion curves for LDPE and PEVA are quite broad, indicating a wide distribution of relaxation times. The loss level of PEVA passes through a maximum at 7.5% vinyl alcohol, suggesting that interaction between a couple of neighboring hydroxyl groups depresses the loss. A potential calculation for the rotation of a hydroxyl group in the orthorhombic lattice of polyethylene yielded a double-minimum potential for the tunneling when the lattice is assumed to have a distortion which is acceptable from x-ray analysis. The potential quantitatively explains the observed values of relaxation time and relaxation strength of HDPE. The concentration of hydroxyl groups in HDPE, which varies among the samples, is estimated to be of the order of 10¹⁶ cm^?3.     

Development of Radiogallium-Labeled Peptides for Platelet-Derived Growth Factor Receptor β (PDGFRβ) Imaging: Influence of Different Linkers

The purpose of this study is to develop peptide-based platelet-derived growth factor receptor β (PDGFRβ) imaging probes and examine the effects of several linkers, namely un-natural amino acids (D-alanine and β-alanine) and ethylene-glycol (EG), on the properties of Ga-DOTA-(linker)-IPLPPPRRPFFK peptides. Seven radiotracers, ⁶⁷Ga-DOTA-(linker)-IPLPPPRRPFFK peptides, were designed, synthesized, and evaluated. The stability and cell uptake in PDGFRβ positive peptide cells were evaluated in vitro. The biodistribution of [⁶⁷Ga]Ga-DOTA-EG₂-IPLPPPRRPFFK ([⁶⁷Ga]27) and [⁶⁷Ga]Ga-DOTA-EG₄-IPLPPPRRPFFK ([⁶⁷Ga]28), which were selected based on in vitro stability in murine plasma and cell uptake rates, were determined in BxPC3-luc-bearing nu/nu mice. Seven ⁶⁷Ga-labeled peptides were successfully synthesized with high radiochemical yields (>85%) and purities (>99%). All evaluated radiotracers were stable in PBS (pH 7.4) at 37 °C. However, only [⁶⁷Ga]27 and [⁶⁷Ga]28 remained more than 75% after incubation in murine plasma at 37 °C for 1 h. [⁶⁷Ga]27 exhibited the highest BxPC3-luc cell uptake among the prepared radiolabeled peptides. As regards the results of the biodistribution experiments, the tumor-to-blood ratios of [⁶⁷Ga]27 and [⁶⁷Ga]28 at 1 h post-injection were 2.61 ± 0.75 and 2.05 ± 0.77, respectively. Co-injection of [⁶⁷Ga]27 and an excess amount of IPLPPPRRPFFK peptide as a blocking agent can significantly decrease this ratio. However, tumor accumulation was not considered sufficient. Therefore, further probe modification is required to assess tumor accumulation for in vivo imaging.     

Tropolone as a High‐Performance Robust Anchoring Group for Dye‐Sensitized Solar Cells

A tropolone group has been employed for the first time as an anchoring group for dye‐sensitized solar cells (DSSCs). The DSSC based on a porphyrin, YD2‐o‐C8T, with a tropolone moiety exhibited a power‐conversion efficiency of 7.7 %, which is only slightly lower than that observed for a reference porphyrin, YD2‐o‐C8 , with a conventional carboxylic group. More importantly, YD2‐o‐C8T was found to be superior to YD2‐o‐C8 with respect to DSSC durability and binding ability to TiO₂. These results unambiguously demonstrate that tropolone is a highly promising dye‐anchoring group for DSSCs in terms of device durability as well as photovoltaic performance.     

Spin coupling in the supramolecular structure of a new tetra(quinoline-TEMPO)yttrium(III) complex

The newly synthesized tetra(quinoline-TEMPO)yttrium(III) potassium salt shows interesting structural features at the molecular and supramolecular levels, revealed by the analysis of the X-ray diffraction data. The magnetic susceptibility and EPR data corroborated with structural considerations showed that the exchange and dipolar spin coupling interactions are taking place at the nodes assembling the supramolecular 2D structure. The Y(III) center shows antiprismatic octacoordination, close to the idealized D2 symmetry. The diamagnetic transition metal plays no role in mediating the radical interactions since the TEMPO-type fragments are remote from the chelating moieties of the ligand. In turn, significant interaction occurs on the nodes consisting in the quasi-rectangular coordination of potassium counterions by the spin-bearing TEMPO groups coming from four distinct complex units. The antiferromagnetic susceptibility was consistently modeled by a spin Hamiltonian based on the rectangle topology of four spins S = 1/2. The fitted exchange parameters are Ja = -5.1 cm-1 and Jb = -3.4 cm-1 for the edges, imposing Jd = 0 for the diagonal. These values are in excellent agreement with the ab initio results Ja = -4.83 cm-1, Jb = -3.44 cm-1, Jd = -0.07 cm-1 obtained in a CASSCF(12,8) calculation. Based on the reliability of the ab initio results we were able to select the presented J parameters among several versions of multiple solutions with acceptable goodness of the fit. A methodological caveat about the artifacts of the automatic use of best fit parameters, in the absence of supplementary criteria, in the context of relative blindness of magnetic susceptibility modeling, is raised. The details of the EPR spectrum at 10 K are also consistent, in the frame of dipolar approximation, with the model of four interacting spins at the nodes of the supramolecular assembling.