scholarly journals Mathematical modelling of thermal microexplosion in a catalyst granule with point sources of heat release

2022 ◽  
Vol 2150 (1) ◽  
pp. 012027
Author(s):  
I V Derevich ◽  
A Yu Fokina
Keyword(s):  
Porous Ceramic ◽  
Homogeneous Model ◽  
Point Sources ◽  
Active Centre ◽  
Transfer Processes ◽  
Catalyst Granule ◽  
Reactor Temperature ◽  
Synthesis Reactions ◽  
Spherical Catalyst ◽  
Active Centres

Abstract A mathematical model of heat and mass transfer in a spherical catalyst granule is proposed. Exothermic synthesis reactions are carried out on point active centres located inside a porous ceramic granule. From the surface of the granule the heat of catalytic reactions is removed into liquid synthesis products. The rate of a chemical reaction is modelled by a modified Arrhenius law. In contrast to the homogeneous model of a catalytic granule methods for calculating heat transfer processes in a system of point, active centres do not develop. An iterative procedure is suggested to calculate the unknown temperature and concentration of the reagent at the active centre. It is shown that the temperature of the active centres is significantly higher than in the volume of the granule. The results of modelling a thermal explosion with increasing granule size and reactor temperature are presented.

scholarly journals Evidence that the active centre of chymopapain A is different from the active centres of some other cysteine proteinases and that the Brønsted coefficient (βnuc.) for the reactions of thiolate anions with 2,2′-dipyridyl disulphide may be decreased by reagent protonation

1980 ◽  
Vol 189 (1) ◽  
pp. 189-192 ◽  
Author(s):  
K Brocklehurst ◽  
B S Baines ◽  
M S Mushiri
Keyword(s):  
Carica Papaya ◽  
Cysteine Proteinases ◽  
Active Centre ◽  
Pka Values ◽  
Nitrobenzoic Acid ◽  
Specific Reactivity ◽  
Ph Range ◽  
Thiolate Anions ◽  
Active Centres

The active centres of chymopapains A and B (jointly designated EC 3.4.22.6) and papaya (Carica papaya L.) peptidase A were investigated by using 2,2′-dipyridyl disulphide and 5,5′-dithiobis-(2-nitrobenzoic acid) as thiol-specific reactivity probes. Whereas the first active-centre pKa values for chymopapain B and papaya peptidase A are less than 5, is as the case for papain (EC 3.4.22.2) and ficin (EC 3.4.22.3), that for chymopapain A is about 6.8. The reason why the reactions of thiols of pKa approx. 6.5 with 2.2′-dipyridyl disulphide are essentially pH-independent in the pH range around the thiol pKa is delineated. The value of the Brønsted coefficient (beta nuc.) for the reactions of thiolate ions with the 2,2′-dipyridyl disulphide monocation appears to be smaller than its value for the corresponding reactions with the neutral disulphide.

scholarly journals Assembly and Redox-Rich Hydride Chemistry of an Asymmetric Mo2S2 Platform

Molecules ◽  
2020 ◽  
Vol 25 (13) ◽  
pp. 3090
Author(s):  
Alex McSkimming ◽  
Jordan W. Taylor ◽  
W. Hill Harman
Keyword(s):  
Electron Transfer ◽  
Solid State ◽  
Dft Calculations ◽  
Spectroscopic Properties ◽  
Molybdenum Sulfide ◽  
Proton Reduction ◽  
Hydride Complex ◽  
Transfer Processes ◽  
Electron Transfer Processes ◽  
Synthesis Reactions

Although molybdenum sulfide materials show promise as electrocatalysts for proton reduction, the hydrido species proposed as intermediates remain poorly characterized. We report herein the synthesis, reactions and spectroscopic properties of a molybdenum-hydride complex featuring an asymmetric Mo2S2 core. This molecule displays rich redox chemistry with electrochemical couples at E½ = −0.45, −0.78 and −1.99 V vs. Fc/Fc+. The corresponding hydrido-complexes for all three redox levels were isolated and characterized crystallographically. Through an analysis of solid-state bond metrics and DFT calculations, we show that the electron-transfer processes for the two more positive couples are centered predominantly on the pyridinediimine supporting ligand, whereas for the most negative couple electron-transfer is mostly Mo-localized.

scholarly journals The chemical reactions of the haemagglutinins and neuraminidases of different strains of influenza viruses: I. Effect of reagents reacting with amino acids in the active centres

1969 ◽  
Vol 67 (2) ◽  
pp. 289-299 ◽  
Author(s):  
L. Hoyle
Keyword(s):  
Chemical Reactions ◽  
Protein Molecule ◽  
Enzymic Activity ◽  
Amide Group ◽  
Influenza Viruses ◽  
Active Centre ◽  
Neuraminidase Activity ◽  
Sh Group ◽  
Different Strains ◽  
Active Centres

SUMMARYStudies of the chemical reactions of the haemagglutinins and neuraminidases of eight strains of influenza viruses have been made by the use of chemical reagents reacting with chemically active groups in the protein molecule. The results indicate a close resemblance between the active centres of the haemagglutinins and neuraminidases in all the strains tested. In all cases the activities were unaffected by reagents reacting with the —SH group of cysteine, the —CH3S group of methionine, the amino group of lysine, the guanidyl group of arginine, or the indole ring of tryptophan. In all cases both the haemagglutinating and enzymic activities were reduced or destroyed by agents reacting with amide groups or reacting with both tyrosine and histidine.By the use of iodine under conditions in which tyrosine reacts but not histidine, and fluorodinitrobenzene under conditions in which histidine reacts more strongly than tyrosine, it was possible to detect a number of different active centres.(1) An active centre containing histidine and an amide group but not containing tyrosine was present in all the virus strains and was the only centre detectable in A1 and A2 strains. This type of centre appeared to possess both haemagglutinating and neuraminidase activity.(2) Active centres containing tyrosine and an amide group were detected in strains of A and B viruses. There was some evidence suggesting that tyrosine-containing centres were of two types: one possessing both haemagglutinating and enzymic activity while the other was a haemagglutinin without neuraminidase activity.The results could be explained by supposing that the presence of histidine in the active centre was essential for neuraminidase activity and that enzymically active tyrosine-containing centres also contained histidine, but that tyrosine could substitute for histidine, but that tyrosine could substitute for histidine in haemagglutinating centres.

scholarly journals Differences in the interaction of the catalytic groups of the active centres of actinidin and papain Rapid purification of fully active actinidin by covalent chromatography and characterization of its active centre by use of two-protonic-state reactivity probes

1981 ◽  
Vol 197 (3) ◽  
pp. 739-746 ◽  
Author(s):  
K Brocklehurst ◽  
B S Baines ◽  
J P Malthouse
Keyword(s):  
Cysteine Proteinase ◽  
Thiol Group ◽  
Interactive System ◽  
Active Centre ◽  
Ph Values ◽  
Hydrophobic Binding ◽  
Rapid Purification ◽  
Active Centres ◽  
Covalent Chromatography

1. A rapid method of isolation of fully active actinidin, the cysteine proteinase from Actinidia chinensis (Chinese gooseberry or kiwifruit), by covalent chromatography, was devised. 2. The active centre of actinidin was investigated by using n-propyl 2-pyridyl disulphide, 4-(N-aminoethyl 2′-pyridyl disulphide)-7-nitrobenzo-2-oxa-1,3-diazole and 4-chloro-7-nitrobenzofurazan as reactivity probes. 3. The presence in actinidin in weakly acidic media of an interactive system containing a nucleophilic sulphur atom was demonstrated. 4. The pKa values (3.1 and 9.6) that characterize this interactive system are more widely separated than those that characterize the interactive active centre systems of ficin (EC 3.4.22.3) and papain (EC 3.4.22.2) (3.8 and 8.6, and 3.9 and 8.8 respectively). 5. Actinidin was shown to resemble ficin rather than papain in (i) the disposition of the active-centre imidazole group with respect to hydrophobic binding areas, and (ii) the inability of the active-centre aspartic acid carboxy group to influence the reactivity of the active-centre thiol group at pH values of about 4. 6. The implications of the results for one-state and two-state mechanisms for cysteine-proteinase catalysis are discussed.

scholarly journals Multiple personalities of the RNA polymerase active centre

Microbiology ◽  
2014 ◽  
Vol 160 (7) ◽  
pp. 1316-1320 ◽  
Author(s):  
Nikolay Zenkin
Keyword(s):  
Rna Synthesis ◽  
Catalytic Properties ◽  
Amino Acid Content ◽  
Annual Conference ◽  
Active Centre ◽  
Catalytic Activities ◽  
Trigger Loop ◽  
Living Organisms ◽  
Unique Ability ◽  
Active Centres

Transcription in all living organisms is accomplished by highly conserved multi-subunit RNA polymerases (RNAPs). Our understanding of the functioning of the active centre of RNAPs has transformed recently with the finding that a conserved flexible domain near the active centre, the trigger loop (TL), participates directly in the catalysis of RNA synthesis and serves as a major determinant for fidelity of transcription. It also appears that the TL is involved in the unique ability of RNAPs to exchange catalytic activities of the active centre. In this phenomenon the TL is replaced by a transcription factor which changes the amino acid content and, as a result, the catalytic properties of the active centre. The existence of a number of transcription factors that act through substitution of the TL suggests that the RNAP has several different active centres to choose from in response to external or internal signals. A video of this Prize Lecture, presented at the Society for General Microbiology Annual Conference 2014, can be viewed via this link: https://www.youtube.com/watch?v=79Z7iXVEPo4

Investigation of a Steam Reforming System of Methane Integrated With a Combustion Burner

2008 ◽  
Author(s):  
Joonguen Park ◽  
Shinku Lee ◽  
Joongmyeon Bae ◽  
Myungjun Kim
Keyword(s):  
Steam Reforming ◽  
Homogeneous Model ◽  
Operating Parameter ◽  
Feed Ratio ◽  
Steam Reformer ◽  
Combustion Gas ◽  
Transfer Rates ◽  
Fuel Feed ◽  
Combustion Gases ◽  
Reactor Temperature

The objective of this study is to analyze the steam reforming system using numerical method. The system consists of a cylindrical-type steam reformer and a combustion burner. Heat is supplied to the endothermic steam reformer by the combustion gases which flow around the reformer. Eddy Break-Up (EBU) model is incorporated for the combustion reaction, and pseudo-homogeneous model is used for the steam reforming reaction. The temperature at the reformer center and the concentration of species at the outlet are compared with the measured data for code validation. The correlation between the performances and the shapes of the system has been studied by using two different configurations. One has the flame guide between the combustion burner and the steam reformer, and the other does not. The flame guide makes the flow of the combustion gas changed. The operating parameters are reactant flow rates which are supplied to the steam reformer and the combustion burner. Reactor temperature profiles, heat transfer rates, fuel conversion, and the hydrogen yields are calculated as the numerical results. Moreover, fuel feed ratio between the burner and the reformer is also manipulated as an operating parameter to discuss about efficiency.

scholarly journals Studies on the active centre of Rhodotorula gracilisd-amino acid oxidase and comparison with pig kidney enzyme

1992 ◽  
Vol 286 (2) ◽  
pp. 389-394 ◽  
Author(s):  
L Pollegioni ◽  
S Ghisla ◽  
M S Pilone
Keyword(s):  
Amino Acid ◽  
Solvent Accessibility ◽  
Alkylating Agents ◽  
Fine Tuning ◽  
Acid Oxidase ◽  
Amino Acid Oxidase ◽  
Active Centre ◽  
Pig Kidney ◽  
Mammalian Enzyme ◽  
Active Centres

D-Amino acid oxidase (EC 1.4.3.3) from Rhodotorula gracilis has been reconstituted with 8-chloro-, 8-mercapto-, 6-hydroxy-, 2-thio-, 5-deaza- and 1-deaza-FAD, and the properties of the resulting complexes have been studied and compared with those of the correspondingly modified pig kidney D-amino acid oxidases. Binding appears to be tight for most analogues, at least as tight as for native FAD (approximately 10(-8) M). 8-Mercapto- and 6-hydroxy-FAD bind in their para- and ortho-quinoid forms respectively to yeast D-amino acid oxidase, inferring the presence of a positive charge near the flavin N(1) position, as in the case of the mammalian enzyme. On the other hand, important differences in active-site microenvironment emerge: solvent accessibility to flavin position 8 is drastically restricted in yeast D-amino acid oxidase as indicated by the unreactivity of 8-chloro- and 8-mercapto-FAD enzyme with thiolates and alkylating agents. Significantly different microenvironments are also likely to occur around the flavin positions N(1)-C(2) = 0, N(3)-H and N(5). This is deduced from the differences in interaction of the two proteins with 1-deaza-FAD, 5-deaza-FAD and 2-thio-FAD and from the properties of the respective complexes. The same re-side flavin stereospecificity as shown by the mammalian enzyme was determined for the yeast enzyme using 8-hydroxy-5-deaza-FAD. Thus we can deduce the presence of a similar pattern of functional groups at the active centres of the two enzymes, while the fine tuning of specificity and regulation correlate with environmental differences at specific flavin loci.

scholarly journals Characterization of the papain active centre by using two-protonic-state electrophiles as reactivity probes. Evidence for nucleophilic reactivity in the un-interrupted cysteine-25-histidine-159 interactive system

1978 ◽  
Vol 171 (2) ◽  
pp. 385-401 ◽  
Author(s):  
M Shipton ◽  
K Brochlehurst
Keyword(s):  
Thiol Group ◽  
Interactive System ◽  
Pyridyl Ring ◽  
Thiol Groups ◽  
Sulphur Atom ◽  
Active Centre ◽  
Nucleophilic Reactivity ◽  
Imidazolium Ion ◽  
Active Centres

1.2,2′-Dipyridyl disulphide (2-Py-S-S-2-Py) and n-propyl 2-pyridyl disulphide (propyl-S-S-2-Py) were used as two-protonic-state reactivity probes to investigate the active centre of papain (EC 3.4.22.2).2. The existence of a striking rate optimum at pH approx. 4 in the reaction of papain not only with the symmetrical probe but also with the unsymmetrical probe is shown to constitute compelling evidence that the thiolate ion component of the cysteine-25-histidine-159 interactive system of papain possesses appreciable nucleophilic character. It is not a necessary requirement that the probe reagent should engage the imidazolium ion of histidine-159 in hydrogen-bonding for the sulphur atom of the interactive system to display nucleophilic character. The single proton-binding site of propyl-S-S-2-Py cannot simultaneously interrupt the active-centre ion pair and provide for rate enhancement as the pH is lowered towards 4. The possible implication of this for the mechanism of papain-catalysed hydrolysis is discussed. 3. The suspected difference in the active centres of papain and ficin (EC 3.4.22.3), which could be a lack in ficin of a carboxy group conformationally equivalent to that of aspartic acid-158 of papain is confirmed. The reactivity of the papain thiol group towards both probe reagents is controlled by two ionizations with pKa close to 4 that are positively co-operative. 4. In the reaction of papain with 2-Py-S-S-2-Py. the reactivity appears to be controlled also by an addition ionization with pKa approx. 5. Possible origins of this additional ionization are discussed. K. The spectral and ionization characteristics of propyl-S-S-2-Py are reported. 6. The reagent reacts rapidly with thiol groups at the sulphur atom distal from the pyridyl ring to provide, at pH values below 9, stoicheiometric release of 2-thiopyridone. This property, together with the ability of the reagent markedly to increase its electrophilicity consequent on protonation, suggests alkyl-2-pyridyl disulphides in general as valuable two-protonic-state reactivity probes with exceptional specificity for thiol groups.

Effect of Hg in Jiaozhou Bay Waters - Aquatic Transfer Process

2014 ◽  
Vol 955-959 ◽  
pp. 2491-2495 ◽  
Author(s):  
Yu Chen ◽  
Yan Feng Qu ◽  
Ren Lin Pei ◽  
Dong Fang Yang
Keyword(s):  
Jiaozhou Bay ◽  
Pollution Prevention ◽  
Point Sources ◽  
Environmental Capacity ◽  
Transfer Processes ◽  
Water Environmental Capacity ◽  
Vertical Distributions ◽  
Different Seasons ◽  
Cyclic Utilization ◽  
Bottom Waters

Based on the investigation data of Hg in Jiaozhou Bay waters in April, July and October 1986, this paper tried to analysis the horizontal, vertical and seasonal distributions of Hg in Jiaozhou Bay, and to reveal the pollution sources and transfer processes of Hg. Results showed that Jiaozhou Bay had been heavily polluted by Hg, whatever in different seasons. Hg in Jiaozhou Bay was mainly from point sources such as industrial waste and sewage runoff. The horizonal and vertical distributions of Hg content showed the transfer processes as, from estuaries to their outside and the bay mouth, and form surface waters to bottom waters, respectively. The water environmental capacity of Hg in Jiaozhou Bay had been unable to carry the emission load of Hg, and therefore the reduction of emission as well as the improvement of cyclic utilization ratio were the primary processes for Hg pollution prevention and reduction.

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