scholarly journals X-ray spectroscopy for chemical and energy sciences: the case of heterogeneous catalysis

2014 ◽  
Vol 21 (5) ◽  
pp. 1084-1089 ◽  
Author(s):  
Anatoly I. Frenkel ◽  
Jeroen A. van Bokhoven
Keyword(s):  
Heterogeneous Catalysis ◽  
Active Site ◽  
Time Scale ◽  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Time Range ◽  
Bond Breaking ◽  
Single Shot ◽  
X Rays ◽  
X Ray

Heterogeneous catalysis is the enabling technology for much of the current and future processes relevant for energy conversion and chemicals synthesis. The development of new materials and processes is greatly helped by the understanding of the catalytic process at the molecular level on the macro/micro-kinetic time scale and on that of the actual bond breaking and bond making. The performance of heterogeneous catalysts is inherently the average over the ensemble of active sites. Much development aims at unravelling the structure of the active site; however, in general, these methods yield the ensemble-average structure. A benefit of X-ray-based methods is the large penetration depth of the X-rays, enablingin situandoperandomeasurements. The potential of X-ray absorption and emission spectroscopy methods (XANES, EXAFS, HERFD, RIXS and HEROS) to directly measure the structure of the catalytically active site at the single nanoparticle level using nanometer beams at diffraction-limited storage ring sources is highlighted. The use of pump–probe schemes coupled with single-shot experiments will extend the time range from the micro/macro-kinetic time domain to the time scale of bond breaking and making.

Structural study of the X-ray-induced enzymatic reaction of octahaem cytochromecnitrite reductase

2015 ◽  
Vol 71 (5) ◽  
pp. 1087-1094 ◽  
Author(s):  
A. A. Trofimov ◽  
K. M. Polyakov ◽  
V. A. Lazarenko ◽  
A. N. Popov ◽  
T. V. Tikhonova ◽  
...  
Keyword(s):  
Nitrite Reductase ◽  
Catalytic Reaction ◽  
Active Sites ◽  
Enzymatic Reaction ◽  
Absorbed Dose ◽  
Free Form ◽  
Data Sets ◽  
X Rays ◽  
X Ray ◽  
Site Water

Octahaem cytochromecnitrite reductase from the bacteriumThioalkalivibrio nitratireducenscatalyzes the reduction of nitrite to ammonium and of sulfite to sulfide. The reducing properties of X-ray radiation and the high quality of the enzyme crystals allow study of the catalytic reaction of cytochromecnitrite reductase directly in a crystal of the enzyme, with the reaction being induced by X-rays. Series of diffraction data sets with increasing absorbed dose were collected from crystals of the free form of the enzyme and its complexes with nitrite and sulfite. The corresponding structures revealed gradual changes associated with the reduction of the catalytic haems by X-rays. In the case of the nitrite complex the conversion of the nitrite ions bound in the active sites to NO species was observed, which is the beginning of the catalytic reaction. For the free form, an increase in the distance between the oxygen ligand bound to the catalytic haem and the iron ion of the haem took place. In the case of the sulfite complex no enzymatic reaction was detected, but there were changes in the arrangement of the active-site water molecules that were presumably associated with a change in the protonation state of the sulfite ions.

scholarly journals Effect of X-rays on structural, physicochemical and functional properties of gluten protein

2021 ◽  
Vol 24 ◽  
Author(s):  
Durga Chandra ◽  
Ashish Dabade ◽  
Gauri Damgude ◽  
Chetali Malhotra
Keyword(s):  
Functional Properties ◽  
Water Solubility ◽  
Stability Index ◽  
Time Range ◽  
Gluten Protein ◽  
X Rays ◽  
Net Charge ◽  
Emulsification Activity ◽  
X Ray ◽  
Sds Page

Abstract The gluten protein was exposed to the X-ray radiations for different time range, comprising 1 and 3 seconds. The objective of this study was to determine the effect of x-ray radiations on the physicochemical properties of gluten protein. Different functional properties of proteins like water and oil holding capacities, protein solubility, emulsification activity, and stability index, foaming action and stability, water solubility, protein, and moisture content, along with SDS PAGE, FTIR, Xeta potential net charge was carried out to evaluate the effect of X-ray radiation on gluten protein. Results showed that the enhancement of water holding capacity up to 38.12%, as well as oil holding capacity up to 35% could be seen, whereas a significant decrease in emulsification activity and stability index, foaming capacity and stability, even protein content could be observed in treated samples. The net charge on protein in water solution was found to increase towards the positive side. The structure of the protein remained unchanged based on no change was observed in SDS PAGE electrograph, FTIR secondary structure region. Hence, X-ray treatment can be a possible way to alter the protein structure for “tailor-made applications” in food industries.

scholarly journals Wide-field Cameras for GRB Observations in X-rays and EUV

1995 ◽  
Vol 151 ◽  
pp. 431-434
Author(s):  
Eugene Moskalenko
Keyword(s):  
Time Scale ◽  
Field Of View ◽  
Time Variability ◽  
Wide Field ◽  
Main Task ◽  
X Rays ◽  
Interstellar Absorption ◽  
X Ray ◽  
Instrumental Approaches ◽  
Stationary Sources

Recent observations of the ASCA satellite resulted in the first identification of a GB source (Murakami et al. 1994). This success confirmed the importance of simultaneous observations in different wavelength bands for GB studies. Besides the ASCA results, there were several observations of GBs in X-ray band with the Ginga (Yoshida et al,.1989), V 78/1 (Laros et al. 1984) and other satellites. It became clear that GBs emit 4 - 8% of their energy in the 2 - 10 keV range. The main task now is to have an equipment which will be able to monitor the sky in X-rays in a mode similar to that of GRO observations, i.e. the telescope should have an all-sky field-of-view (FoV) and should work continuously.A telescope with these features but operating at soft X-ray energies may directly determine the GB distance scale, due to interstellar absorption of the photons with energies less than 2 keV, as was pointed out first by Schaefer (1993). Flaring sources similar to GBs in time scale may be found also in the EUV (hundreds of angstroms) with the help of very wide-field cameras. Of course each such device - in X-ray, soft X-ray and EUV bands - will discover many transient objects, flaring events, will study time variability of bright “stationary” sources etc. In this paper we describe several instrumental approaches in these fields.

scholarly journals Multiple application X-ray imaging chamber for single-shot diffraction experiments with femtosecond X-ray laser pulses

2014 ◽  
Vol 47 (1) ◽  
pp. 188-197 ◽  
Author(s):  
Changyong Song ◽  
Kensuke Tono ◽  
Jaehyun Park ◽  
Tomio Ebisu ◽  
Sunam Kim ◽  
...  
Keyword(s):  
Free Electron ◽  
Single Pulse ◽  
Laser Pulses ◽  
Atomic Scale ◽  
Single Shot ◽  
X Rays ◽  
Structural Investigations ◽  
X Ray ◽  
Multiple Application ◽  
X Ray Imaging

X-ray free-electron lasers (XFELs) provide intense (∼1012 photons per pulse) coherent X-rays with ultra-short (∼10−14 s) pulse lengths. X-rays of such an unprecedented nature have introduced new means of atomic scale structural investigations, and discoveries are still ongoing. Effective use of XFELs would be further accelerated on a highly adaptable platform where most of the new experiments can be realized. Introduced here is the multiple-application X-ray imaging chamber (MAXIC), which is able to carry out various single-pulse diffraction experiments including single-shot imaging, nanocrystallographic data acquisition and ultra-fast pump–probe scattering for specimens in solid, liquid and gas phases. The MAXIC established at the SPring-8 ångström compact free-electron laser (SACLA) has demonstrated successful applications in the aforementioned experiments, but is not limited to them. Also introduced are recent experiments on single-shot diffraction imaging of Au nanoparticles and serial crystallographic data collection of lysozyme crystals at SACLA.

scholarly journals Designing Heterogeneous Catalysts for Renewable Catalysis Applications Using Metal Oxide Deposition

2019 ◽  
Vol 73 (9) ◽  
pp. 698-706
Author(s):  
Yuan-Peng Du ◽  
Jeremy S. Luterbacher
Keyword(s):  
Heterogeneous Catalysis ◽  
Metal Oxide ◽  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Catalyst Deactivation ◽  
High Surface ◽  
Catalyst Stability ◽  
Synthetic Control ◽  
High Oxygen Content ◽  
Oxide Deposition

Heterogeneous catalysis has long been a workhorse for the chemical industry and will likely play a key role in the emerging area of renewable chemistry. However, renewable molecule streams pose unique challenges for heterogeneous catalysis due to their high oxygen content, frequent low volatility and the near constant presence of water. These constraints can often lead to the need for catalyst operation in harsh liquid phase conditions, which has compounded traditional catalyst deactivation issues. Oxygenated molecules are also frequently more reactive than petroleum-derived molecules, which creates a need for highly selective catalysts. Synthetic control over the nanostructured environment of catalytic active sites could facilitate the creation of both more stable and selective catalysts. In this review, we discuss the use of metal oxide deposition as an emerging strategy that can be used to synthesize and/or modify heterogeneous catalysts to introduce tailored nanostructures. Several important applications are reviewed, including the synthesis of high surface area mesoporous metal oxides, the enhancement of catalyst stability, and the improvement of catalyst selectivity.

scholarly journals An Overview of the Proofreading Functions in Bacteria and in Severe Acute Respiratory Syndrome-Coronaviruses

2021 ◽  
pp. 33-62
Author(s):  
Peramachi Palanivelu
Keyword(s):  
Amino Acids ◽  
Severe Acute Respiratory Syndrome ◽  
Structure Function ◽  
Active Site ◽  
Active Sites ◽  
Dna Polymerases ◽  
Proton Acceptor ◽  
Conserved Motifs ◽  
Bacterial Dna ◽  
X Ray

Aim: To understand the structure-function relationship of the proofreading (PR) functions in eubacteria and viruses with special reference to Severe Acute Respiratory Syndrome-Coronaviruses (SARS-CoVs) and propose a plausible mechanism of action for PR exonucleases of SARS-CoVs. Study Design: Bioinformatics, biochemical, site-directed mutagenesis (SDM), X-ray crystallographic data were used to study the structure-function relationships of the PR exonucleases from bacteria and CoVs. Methodology: The protein sequences of the PR exonucleases of various DNA polymerases, and RNA polymerases of SARS, SARS-related and human CoVs (HCoVs) were obtained from PUBMED and SWISS-PROT databases. The advanced version of Clustal Omega was used for protein sequence analysis. Along with the conserved motifs identified by the bioinformatics analysis, the data already available by biochemical, SDM experiments and X-ray crystallographic analysis on these enzymes were used to arrive at the possible active amino acids in the PR exonucleases of these crucial enzymes. Results:  A complete analysis of the active sites of the PR exonucleases from various bacteria and CoVs were done. The multiple sequence alignment (MSA) analysis showed many conserved amino acids, small and large peptide regions among them. Based on the conserved motifs, the PR exonucleases are found to fit broadly into two superfamilies, viz. DEDD and polymerase-histidinol phosphatase (PHP) superfamilies. The bacterial DNA polymerases I and II, RNase D, RNase T and ε-subunit of DNA polymerases III belong to the DEDD superfamily. The PR enzymes from SARS, SARS-related CoVs and other HCoVs also essentially belong to the DEDD superfamily. The DEDD superfamily either uses an invariant Tyr or a His as proton acceptor during catalysis. Depending on the proton acceptor, they are further classified into DEDHD and DEDYD subfamilies. RNase T, ε-subunit of DNA polymerases III and the SARS, SARS-related CoVs and other HCoVs belong to DEDHD subfamily.  However, the SARS, SARS-related CoVs and other HCoVs showed additional zinc finger motifs (ZFMs) in their active sites. DNA polymerases I, II and RNase D belong to DEDYD subfamily. The bacterial DNA polymerases X, YcdX phosphoesterases and the co-editing exonuclease of DNA polymerases III belong to the PHP superfamily. Based on the MSA, X-ray crystallographic analyses and SDM experiments, the proposed active-site proton acceptor is Tyr/His in DEDDY/H subfamilies and His in PHP superfamily of PR exonucleases.  Conclusions:   Based on the similarities of active site amino acids/motifs, it may be concluded that the DEDD and PHP superfamilies of PR exonucleases should have evolved from a common ancestor but diverged very long ago. The biochemical properties of these enzymes, including the four conserved acidic amino acid residues in the catalytic core, suggest that the CoVs might have acquired the exonuclease function, possibly from a prokaryote. However, the presence of two zinc fingers in the PR active site of the SARS, SARS-related CoVs and other HCoVs sets their PR exonucleases apart from other homologues.

scholarly journals A Cobalt-Iron Double-Atom Catalyst for the Oxygen Evolution Reaction

2019 ◽  
Author(s):  
Lichen Bai ◽  
Chia-Shuo Hsu ◽  
Duncan Alexander ◽  
Hao Ming Chen ◽  
Xile Hu
Keyword(s):  
Oxygen Evolution ◽  
Active Site ◽  
Oxygen Evolution Reaction ◽  
Active Sites ◽  
Single Atom ◽  
X Ray ◽  
Highly Active ◽  
Cobalt Iron ◽  
X Ray Absorption

Single atom catalysts exhibit well-defined active sites and potentially maximum atomic efficiency. However, they are unsuitable for reactions that benefit from bimetallic promotion such as the oxygen evolution reaction (OER) in alkaline medium. Here we show that a single atom Co precatalyst can be in-situ transformed into a Co-Fe double atom catalyst for OER. This catalyst exhibits one of the highest turnover frequencies among metal oxides. Electrochemical, microscopic, and spectroscopic data including those from operando X-ray absorption spectroscopy, reveal a dimeric Co-Fe moiety as the active site of the catalyst. This work demonstrates double-atom catalysis as a promising approach for the developed of defined and highly active OER catalysts.

2D covalent organic frameworks with built-in amide active sites for efficient heterogeneous catalysis

2019 ◽  
Vol 55 (96) ◽  
pp. 14538-14541 ◽  
Author(s):  
Yang Li ◽  
Weiben Chen ◽  
Ruidong Gao ◽  
Ziqiang Zhao ◽  
Ting Zhang ◽  
...  
Keyword(s):  
Heterogeneous Catalysis ◽  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Knoevenagel Condensation ◽  
Covalent Organic Frameworks ◽  
Excellent Performance ◽  
Bottom Up

Two new amide functionalized covalent organic frameworks (COFs) were synthesized via a bottom-up strategy and used as heterogeneous catalysts toward Knoevenagel condensation with excellent performance.

Dynamic Interconversion of Metal Active Site Ensembles in Zeolite Catalysis

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Siddarth H. Krishna ◽  
Casey B. Jones ◽  
Rajamani Gounder
Keyword(s):  
Active Site ◽  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Mean Field ◽  
Future Research ◽  
Annual Review ◽  
Publication Date ◽  
Turnover Rates ◽  
Practical Applications ◽  
Structure And Motion

Catalysis science is founded on understanding the structure, number, and reactivity of active sites. Kinetic models that consider active sites to be static and noninteracting entities are routinely successful in describing the behavior of heterogeneous catalysts. Yet, active site ensembles often restructure in response to their external environment and even during steady-state catalytic turnover, sometimes requiring non-mean-field kinetic treatments to describe distance-dependent interactions among sites. Such behavior is being recognized more frequently in modern catalysis research, with the advent of experimental methods to quantify turnover rates with increasing precision, an expanding arsenal of operando characterization tools, and computational descriptions of atomic structure and motion at chemical potentials and timescales increasingly relevant to reaction conditions. This review focuses on dynamic changes to metal active site ensembles on zeolite supports, which are silica-based crystalline materials substituted with Al that generate binding sites for isolated and low-nuclearity metal site ensembles. Metal sites can become solvated and mobilized during reaction, facilitating interactions among sites that change their nuclearity and function. Such intersite communication can be regulated by the zeolite support, resulting in non-single-site and potentially non-mean-field kinetic behavior arising from mechanisms of catalytic action that combine elements of those canonically associated with homogeneous and heterogeneous catalysis. We discuss recent literature examples that document dynamic active site behavior in metal-zeolites and outline methodologies to identify and interpret such behavior. We conclude with our outlook on future research directions to develop this evolving branch of catalysis science and harness it for practical applications. Expected final online publication date for the Annual Review of Chemical and Biomolecular Engineering, Volume 12 is June 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

scholarly journals X-rays only when you want them: optimized pump–probe experiments using pseudo-single-bunch operation

2015 ◽  
Vol 22 (3) ◽  
pp. 729-735 ◽  
Author(s):  
M. P. Hertlein ◽  
A. Scholl ◽  
A. A. Cordones ◽  
J. H. Lee ◽  
K. Engelhorn ◽  
...  
Keyword(s):  
Laser Excitation ◽  
Ccd Camera ◽  
Single Shot ◽  
X Rays ◽  
Time Resolved ◽  
Pump Probe ◽  
Charge Coupled Device ◽  
X Ray ◽  
X Ray Absorption ◽  
Sample Damage

Laser pump–X-ray probe experiments require control over the X-ray pulse pattern and timing. Here, the first use of pseudo-single-bunch mode at the Advanced Light Source in picosecond time-resolved X-ray absorption experiments on solutions and solids is reported. In this mode the X-ray repetition rate is fully adjustable from single shot to 500 kHz, allowing it to be matched to typical laser excitation pulse rates. Suppressing undesired X-ray pulses considerably reduces detector noise and improves signal to noise in time-resolved experiments. In addition, dose-induced sample damage is considerably reduced, easing experimental setup and allowing the investigation of less robust samples. Single-shot X-ray exposures of a streak camera detector using a conventional non-gated charge-coupled device (CCD) camera are also demonstrated.

Sign in / Sign up

Export Citation Format

Share Document