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1.
Nat Commun ; 15(1): 5518, 2024 Jun 29.
Artículo en Inglés | MEDLINE | ID: mdl-38951539

RESUMEN

Determining short-lived intermediate structures in chemical reactions is challenging. Although ultrafast spectroscopic methods can detect the formation of transient intermediates, real-space structures cannot be determined directly from such studies. Time-resolved serial femtosecond crystallography (TR-SFX) has recently proven to be a powerful method for capturing molecular changes in proteins on femtosecond timescales. However, the methodology has been mostly applied to natural proteins/enzymes and limited to reactions promoted by synthetic molecules due to structure determination challenges. This work demonstrates the applicability of TR-SFX for investigations of chemical reaction mechanisms of synthetic metal complexes. We fix a light-induced CO-releasing Mn(CO)3 reaction center in porous hen egg white lysozyme (HEWL) microcrystals. By controlling light exposure and time, we capture the real-time formation of Mn-carbonyl intermediates during the CO release reaction. The asymmetric protein environment is found to influence the order of CO release. The experimentally-observed reaction path agrees with quantum mechanical calculations. Therefore, our demonstration offers a new approach to visualize atomic-level reactions of small molecules using TR-SFX with real-space structure determination. This advance holds the potential to facilitate design of artificial metalloenzymes with precise mechanisms, empowering design, control and development of innovative reactions.


Asunto(s)
Manganeso , Muramidasa , Muramidasa/química , Manganeso/química , Cristalografía por Rayos X , Porosidad , Complejos de Coordinación/química , Modelos Moleculares , Animales , Monóxido de Carbono/química , Factores de Tiempo , Pollos
2.
J Vasc Surg Venous Lymphat Disord ; : 101947, 2024 Jul 14.
Artículo en Inglés | MEDLINE | ID: mdl-39013516

RESUMEN

BACKGROUND: Concomitant iatrogenic proximal venous stenosis increases venous pressure and can be a risk factor for unfavorable outcomes of lymphaticovenular anastomosis (LVA) in extremities with secondary lymphedema. This study investigated the frequency and relevant factors of venous stenosis in patients diagnosed with secondary lymphedema who underwent LVA. METHODS: Patients who underwent preoperative computed tomographic venography (CTV) and LVA for secondary lymphedema of the extremities from October 2018 to March 2022 were included. The incidence of proximal venous stenosis in the affected limb on preoperative CTV and the rate of endovascular intervention were compared between upper and lower extremities. Factors affecting proximal venous stenosis were identified through multivariable analysis using independent variables, including patient age, body mass index, comorbidities, smoking history, radiation therapy, duration of lymphedema, and location of lymphedema. RESULTS: A total of 211 patients were analyzed, including 83 patients with upper extremity and 128 patients with lower extremity lymphedema. The incidence of proximal venous stenosis in the preoperative CTV was 32.5% and 7.8% in upper extremity, and lower extremity lymphedema, respectively (p < 0.001). The incidence of venous stenosis requiring endovascular intervention was significantly higher in the upper extremity compared to the lower extremity (16.9 % vs. 6.3 %, p = 0.014). In multivariable analysis, risk factors affecting incidence of venous stenosis requiring endovascular intervention was the patient age (p = 0.007) and upper extremity (p = 0.009). CONCLUSIONS: Preoperative evaluation and treatment of venous stenosis in extremities with secondary lymphedema are necessary before LVA surgery, particularly in upper extremity lymphedema.

3.
Nature ; 626(7999): 670-677, 2024 Feb.
Artículo en Inglés | MEDLINE | ID: mdl-38297122

RESUMEN

Photosystem II (PSII) catalyses the oxidation of water through a four-step cycle of Si states (i = 0-4) at the Mn4CaO5 cluster1-3, during which an extra oxygen (O6) is incorporated at the S3 state to form a possible dioxygen4-7. Structural changes of the metal cluster and its environment during the S-state transitions have been studied on the microsecond timescale. Here we use pump-probe serial femtosecond crystallography to reveal the structural dynamics of PSII from nanoseconds to milliseconds after illumination with one flash (1F) or two flashes (2F). YZ, a tyrosine residue that connects the reaction centre P680 and the Mn4CaO5 cluster, showed structural changes on a nanosecond timescale, as did its surrounding amino acid residues and water molecules, reflecting the fast transfer of electrons and protons after flash illumination. Notably, one water molecule emerged in the vicinity of Glu189 of the D1 subunit of PSII (D1-E189), and was bound to the Ca2+ ion on a sub-microsecond timescale after 2F illumination. This water molecule disappeared later with the concomitant increase of O6, suggesting that it is the origin of O6. We also observed concerted movements of water molecules in the O1, O4 and Cl-1 channels and their surrounding amino acid residues to complete the sequence of electron transfer, proton release and substrate water delivery. These results provide crucial insights into the structural dynamics of PSII during S-state transitions as well as O-O bond formation.


Asunto(s)
Oxígeno , Complejo de Proteína del Fotosistema II , Biocatálisis/efectos de la radiación , Calcio/metabolismo , Cristalografía , Transporte de Electrón/efectos de la radiación , Electrones , Manganeso/metabolismo , Oxidación-Reducción/efectos de la radiación , Oxígeno/química , Oxígeno/metabolismo , Complejo de Proteína del Fotosistema II/química , Complejo de Proteína del Fotosistema II/metabolismo , Complejo de Proteína del Fotosistema II/efectos de la radiación , Protones , Factores de Tiempo , Tirosina/metabolismo , Agua/química , Agua/metabolismo
4.
Phys Chem Chem Phys ; 25(5): 3867-3874, 2023 Feb 01.
Artículo en Inglés | MEDLINE | ID: mdl-36647600

RESUMEN

Lithium-rich disordered rocksalt-type cathode materials are promising for high-capacity and high-power lithium-ion batteries. Many of them are synthesized by mechanical milling and may have heterogeneous structures and chemical states at the nanoscale. In this study, we performed X-ray spectroscopic ptychography measurements of Li-rich disordered rocksalt-type oxide particles synthesized by mechanical milling before and after delithiation reaction at the vanadium K absorption edge, and visualized their structures and chemical state with a spatial resolution of ∼100 nm. We classified multiple domains with different chemical states via clustering analysis. A comparison of the domain distribution trends of the particles before and after the delithiation reaction revealed the presence of domains, suggesting that the delithiation reaction was suppressed.

5.
J Phys Chem Lett ; 12(24): 5781-5788, 2021 Jun 24.
Artículo en Inglés | MEDLINE | ID: mdl-34137620

RESUMEN

A heterogeneous phase/structure distribution in the bulk of spinel lithium nickel manganese oxides (LNMOs) is the key to maximizing the performance and stability of the cathode materials of lithium-ion batteries. Herein, we report the use of two-dimensional ptychographic X-ray absorption fine structure (XAFS) to visualize the density and valence maps of manganese and nickel in as-prepared LNMO particles and unsupervised learning to classify the three-phase group in terms of different elemental compositions and chemical states. The described approach may increase the supply of information for nanoscale characterization and promote the design of suitable structural domains to maximize the performance and stability of batteries.

6.
Opt Express ; 29(10): 14394-14402, 2021 May 10.
Artículo en Inglés | MEDLINE | ID: mdl-33985163

RESUMEN

Coherent diffraction imaging (CDI) is a powerful method for visualizing the structure of an object with a high spatial resolution that exceeds the performance limits of the lens. Single-frame CDI in the X-ray region has potential use for probing dynamic phenomena with a high spatiotemporal resolution. Here, we experimentally demonstrate a general method for single-frame X-ray CDI using a triangular aperture and a Fresnel zone plate. Using 5 keV synchrotron radiation X-rays, we reconstructed the object image of the locally illuminated area with a spatial resolution of higher than 50 nm and an exposure time of more than 0.1 s without prior information about the sample. After a 10 s exposure, a resolution of 17 nm was achieved. The present method opens new frontiers in the study of dynamics at the nanoscale by using next-generation synchrotron radiation X-rays/free-electron lasers as light sources.

7.
Opt Express ; 29(2): 1441-1453, 2021 Jan 18.
Artículo en Inglés | MEDLINE | ID: mdl-33726359

RESUMEN

We propose a method of single-frame coherent diffraction imaging using a triangular aperture, which can not only reconstruct the projection image of extended objects from a single-frame coherent diffraction pattern, but also improve the image of the wavefield of the probe. In this method, a plane-wave illuminates a triangular aperture. An object is placed immediately after the aperture or in the image plane of the aperture through a lens. A far-field coherent diffraction pattern is collected by a two-dimensional detector. The object image is reconstructed from the single-frame diffraction pattern using a phase retrieval algorithm without support constraints. We simulate feasible experimental setups in the hard X-ray regime and show that this method can be practical use for single-frame coherent diffraction imaging. The present method has the potential exploring dynamic phenomena in materials science and biology with high spatiotemporal resolution using synchrotron radiation/free-electron lasers.

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