The effect of pH and complexation on redox reactions between RS• radicals and flavins

1984 ◽  
Vol 62 (1) ◽  
pp. 171-177 ◽  
Author(s):  
Rizwan Ahmad ◽  
David A. Armstrong
Keyword(s):  
Redox Potential ◽  
Linear Function ◽  
Redox Reactions ◽  
Flavin Adenine Dinucleotide ◽  
Protonated Form ◽  
Redox Properties ◽  
The Other ◽  
Effect Of Ph ◽  
Other Hand ◽  
High Redox Potential

Elementary considerations indicate that thiol radicals, RS•, should have a high redox potential [Formula: see text][Formula: see text]However, the equilibrium [4],[Formula: see text]which is established in the presence of excess RS−, would convert RS•to [Formula: see text] which is a reducing species. Experimentally it was demonstrated that thiol radicals made by γ radiolysis of β-mercaptoethanol solutions effected two-electron oxidation of dihydroflavin FlH2 at pH 6.3 and of FlH− at pH 8. On the other hand, [Formula: see text] readily reduced Fl to FlH2 or FlH− as expected. At pH 9, photostationary states were established after a few minutes radiolysis and the ratios [FlH−]ss/[Fl]ss were a function of [Formula: see text] The main reactions occurring were:[Formula: see text]The values of k19 and k22 were both large. The ratio k19/k22 was ∼0.8 for lumiflavin and ∼0.3 for flavin adenine dinucleotide. The cyclic disulphide anions of lipoamide and dithiothreitol [Formula: see text] also effected two-electron reductions of flavins. However, the protonated form of [Formula: see text] oxidized FlH2, and the photostationary ratio [FlH−]ss/[Fl]ss was an approximate linear function of [Formula: see text]. The implications of the observed changes in redox properties of sulphur radicals on complexation with RS− and protonation were briefly considered.Des considérations élémentaires indiquent que les radicaux thiyles, RS•, doivent avoir un potentiel rédox élevé [Formula: see text][Formula: see text]

Circular dichroism and redox properties of high redox potential ferredoxins

Biochemistry ◽  
1985 ◽  
Vol 24 (10) ◽  
pp. 2542-2549 ◽  
Author(s):  
Craig T. Przysiecki ◽  
Terrance E. Meyer ◽  
Michael A. Cusanovich
Keyword(s):  
Circular Dichroism ◽  
Redox Potential ◽  
Redox Properties ◽  
Circular Dichroïsm ◽  
High Redox Potential

Influence of Ageing and Lint Accumulation on the Fastening Strength of Hook and Loop Fasteners

1992 ◽  
Vol 62 (12) ◽  
pp. 766-770 ◽  
Author(s):  
Alison R. Taylor ◽  
Nigel A. G. Johnson ◽  
Bruce Dowdell
Keyword(s):  
Linear Function ◽  
The Other ◽  
Other Hand ◽  
Opening And Closing

Two possible causes of deterioration in the fastening performance of hook and loop fasteners have been investigated. The performance, quantified by various shear and peel forces, fell by less than 20% over 5000 cycles of repeated opening and closing. On the other hand, accumulated lint caused a serious loss of performance, which was nearly a linear function of the mass of lint among the hooks.

Modeling the redox potential during the infiltration in a recharge pond located in the Llobregat river basin

2020 ◽  
Author(s):  
Paula Rodriguez-Escales ◽  
Carme Barba ◽  
Xavier Sanchez-Vila ◽  
Albert Folch
Keyword(s):  
Redox Potential ◽  
Heat Transport ◽  
The Other ◽  
Geochemical Processes ◽  
Aquifer Recharge ◽  
Non Invasive ◽  
Other Hand ◽  
Multiple Processes ◽  
A Cell ◽  
Llobregat River

<div> <p>Redox potential measurements are a sink of multiple processes and factors related to the hydrochemistry of a water.  Normally, by themselves, they do not provide enough information to describe all the processes occurring in a system and they are considered only as “an indicator” that combined with a more detailed hydrochemistry can provide information of the driving processes. There are different reasons why these measurement are not quantitatively valid. First of all, sampling plays an important role. The most common method to determine Eh in groundwater is by using an Eh probe and a cell flow, which implies, by itself, mixing of waters. On the other hand, the Eh reproducibility is also conditioned by the amount of processes considered in a numerical model. Eh depends on several geochemical processes, which at the same time, they are depending on flow and heat transport. The last achievements in sensoring science has allowed to develop sensor probes that allows the Eh measurements in a non-invasive and a continuous way.</p> </div><p>Considering this, in this work we have monitored intensively an infiltration pond (in the context of Managed Aquifer Recharge) in order to develop a proper model to reproduce the Eh. The monitoring was based in the use of non-invasive Eh probes, which registered the Eh every 15 min during a year. During that year, four hydrochemical campaigns were also developed in order to quantify the hydrochemistry of the site. On the other hand, the model considered the flow of the system, the heat transport and a set of geochemical processes which were also depending on temperature. The main processes were the generation of organic matter in the own system, the oxidation of organic carbon using different TEAPs, nitrification and different secondary geochemical processes related, specially, to iron and manganese geochemistry.</p>

Correlation between Redox Properties and Component of Multicomponent Heteropolysilicates with the Same Structure

2007 ◽  
Vol 2007 (8) ◽  
pp. 445-450
Author(s):  
Chunyan Hua ◽  
Jiang Li ◽  
Hanmin Ding ◽  
Pingang He ◽  
Yongkui Shan
Keyword(s):  
Transition Metal ◽  
Metal Ion ◽  
Redox Properties ◽  
The Other ◽  
Transition Metal Ion ◽  
Other Hand

A series of the multicomponent heteropolysilicates with the same structure has been synthesised by a controllable method. Studies on the correlation between the redox properties and composition of the polyoxometalates indicate that the character of the addenda ion has the highest influence on the oxidising ability of the heteropolyanions for a given structure, and by comparison, the effects of the number of the addenda ions and the charge of the whole heteropolyanions were not completely prominent in mixed-addenda tungstomolybdosilicate heteropolyanions. For transition metal-substituted heteropolyanions, however, the effect of the number of the addenda ions is an important factor and stronger than that of the character of the addenda ion (transition metal ion) in some cases. On the other hand, incorporation of a transition metal ion can lead to a decrease of the reversibility of redox for heteropolyanions.

EFFECT OF pH ON THE BINDING OF THYROXINE TO SERUM PROTEINS

1970 ◽  
Vol 65 (3) ◽  
pp. 409-422 ◽  
Author(s):  
Theodore Coutsoftides ◽  
Amirav Gordon
Keyword(s):  
Serum Albumin ◽  
Serum Proteins ◽  
Binding Capacity ◽  
Ph Sensitive ◽  
The Other ◽  
Rat Serum ◽  
Effect Of Ph ◽  
Thyroxine Binding Globulin ◽  
Other Hand ◽  
Maximal Binding

ABSTRACT The maximal binding capacity of human thyroxine-binding globulin (TBG) was found to decrease, and that of thyroxine-binding pre-albumin (TBPA) to increase with an increase in pH in the range of pH 7.2 to 8.2. On the other hand, the transfer of T4125I from the serum to a weak binder (Sephadex) was found to decrease with increasing pH. The same phenomena was shown to exist in mouse and rat serum, and to be blocked by DNP, a potent TBA & TBPA binding inhibitor. It is suggested that serum albumin may play a pH sensitive role in the T4 transfer to tissue.

Medicinal Chemistry Meets Electrochemistry: Redox Potential in the Role of Endpoint or Molecular Descriptor in QSAR/QSPR

2020 ◽  
Vol 20 (14) ◽  
pp. 1341-1356
Author(s):  
Karel Nesměrák
Keyword(s):  
Redox Potential ◽  
Redox Reactions ◽  
Medicinal Chemistry ◽  
Molecular Descriptor ◽  
Redox Properties ◽  
Physiological Effects ◽  
Therapeutic Activity ◽  
The Subject ◽  
The Relationship

Many biochemical reactions are based on redox reactions. Therefore, the redox potential of a chemical compound may be related to its therapeutic or physiological effects. The study of redox properties of compounds is a domain of electrochemistry. The subject of this review is the relationship between electrochemistry and medicinal chemistry, with a focus on quantifying these relationships. A summary of the relevant achievements in the correlation between redox potential and structure, therapeutic activity, resp., is presented. The first part of the review examines the applicability of QSPR for the prediction of redox properties of medically important compounds. The second part brings the exhaustive review of publications using redox potential as a molecular descriptor in QSAR of biological activity. Despite the complexity of medicinal chemistry and biological reactions, it is possible to employ redox potential in QSAR/QSPR. In many cases, this electrochemical parameter plays an essential but rarely absolute role.

Significant effect of charge microenvironment on the redox potential of [Fe4Se4(SPh)4]2− in solution and inside film

2014 ◽  
Vol 92 (7) ◽  
pp. 625-628
Author(s):  
Diganta Kumar Das ◽  
Dhanada Sarmah ◽  
Raben Ch. Roy
Keyword(s):  
Redox Potential ◽  
Electrode Surface ◽  
The Other ◽  
Positive Shift ◽  
Other Hand ◽  
Surfactant Film

Through this work, we have shown that both the nature and the compactness of charge of the microenvironment around the [Fe4Se4(SPh)4]2−/3− couple are important in determining its redox potential. The redox potential of the [Fe4Se4(SPh)4]2−/3− couple has been measured in pure dimethylformamide (DMF), DMF added with surfactants of different charges, and also in positive surfactant film on an electrode surface. The redox potential becomes 0.090 V positive when the solution microenvironment is made positive compared to that in DMF. On the other hand, if the microenvironment is made positive and static (in the form of a positive film), the positive shift in the potential is 0.265 V, and compactness of charge induced an extra 0.175 V positive shift in the potential.

A study of cometary eruptions through OH radio-lines

1999 ◽  
Vol 173 ◽  
pp. 249-254
Author(s):  
A.M. Silva ◽  
R.D. Miró
Keyword(s):  
Short Duration ◽  
Growth Curves ◽  
The Other ◽  
Initial Mass ◽  
Radio Lines ◽  
Other Hand ◽  
Sudden Rise

AbstractWe have developed a model for theH2OandOHevolution in a comet outburst, assuming that together with the gas, a distribution of icy grains is ejected. With an initial mass of icy grains of 108kg released, theH2OandOHproductions are increased up to a factor two, and the growth curves change drastically in the first two days. The model is applied to eruptions detected in theOHradio monitorings and fits well with the slow variations in the flux. On the other hand, several events of short duration appear, consisting of a sudden rise ofOHflux, followed by a sudden decay on the second day. These apparent short bursts are frequently found as precursors of a more durable eruption. We suggest that both of them are part of a unique eruption, and that the sudden decay is due to collisions that de-excite theOHmaser, when it reaches the Cometopause region located at 1.35 × 105kmfrom the nucleus.

Closing the GAP—A 5Å Scanning Microscope

1969 ◽  
Vol 27 ◽  
pp. 6-7
Author(s):  
A. V. Crewe
Keyword(s):  
Normal Form ◽  
The Other ◽  
Resolving Power ◽  
Scanning Microscope ◽  
Conventional Microscope ◽  
Other Hand ◽  
Closing The Gap ◽  
Thermal Sources ◽  
Better Than ◽  
Transmission Microscope

We have become accustomed to differentiating between the scanning microscope and the conventional transmission microscope according to the resolving power which the two instruments offer. The conventional microscope is capable of a point resolution of a few angstroms and line resolutions of periodic objects of about 1Å. On the other hand, the scanning microscope, in its normal form, is not ordinarily capable of a point resolution better than 100Å. Upon examining reasons for the 100Å limitation, it becomes clear that this is based more on tradition than reason, and in particular, it is a condition imposed upon the microscope by adherence to thermal sources of electrons.

Life Beyond 1MeV

1980 ◽  
Vol 38 ◽  
pp. 30-33
Author(s):  
K.H. Westmacott
Keyword(s):  
Electron Microscopy ◽  
Past Experience ◽  
The Other ◽  
Good Case ◽  
Other Hand ◽  
The U.S

Life beyond 1MeV – like life after 40 – is not too different unless one takes advantage of past experience and is receptive to new opportunities. At first glance, the returns on performing electron microscopy at voltages greater than 1MeV diminish rather rapidly as the curves which describe the well-known advantages of HVEM often tend towards saturation. However, in a country with a significant HVEM capability, a good case can be made for investing in instruments with a range of maximum accelerating voltages. In this regard, the 1.5MeV KRATOS HVEM being installed in Berkeley will complement the other 650KeV, 1MeV, and 1.2MeV instruments currently operating in the U.S. One other consideration suggests that 1.5MeV is an optimum voltage machine – Its additional advantages may be purchased for not much more than a 1MeV instrument. On the other hand, the 3MeV HVEM's which seem to be operated at 2MeV maximum, are much more expensive.

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