A Macrocyclic Ligand Framework That Improves Both the Stability and T1-Weighted MRI Response of Quinol-Containing H2O2 Sensors

2021 ◽  
Author(s):  
Sana Karbalaei ◽  
Erik Knecht ◽  
Alicja Franke ◽  
Achim Zahl ◽  
Alexander C. Saunders ◽  
...  
Keyword(s):  
Macrocyclic Ligand ◽  
The Stability

scholarly journals Iron-TAML Complexes: A Computational Approach to Improving Stability

2021 ◽  
Author(s):  
◽  
Kevin Tuano
Keyword(s):  
Water Oxidation ◽  
Density Functional ◽  
Prolonged Exposure ◽  
Computational Study ◽  
Macrocyclic Ligand ◽  
Oxidation Mechanism ◽  
Nucleophilic Attack ◽  
Functional Theory ◽  
The Stability ◽  
Oxidation Chemistry

<p>Researchers at the Institute for Green Oxidation Chemistry of the Carnegie Mellon University developed a group of catalysts called tetra amido macrocyclic ligand (TAML) activators. The purpose of that research was that TAML activators would breakdown pollutants in the presence of a sacrificial oxidant. Furthermore, the catalyst was designed to decompose on a required timescale, as to not damage the environment by prolonged exposure. Since the initial designs from the 1980’s, the TAML structure has undergone significant changes to increase efficiency or selectivity. Other uses of this group of catalysts have been explored, namely, the oxidation of water to molecular oxygen.  This work presents a computational study using Density Functional Theory (DFT) which addresses the issue regarding the stability of certain iron-TAML intermediates in the water oxidation mechanism. Hence, the work seeks to explore how changing certain groups on the TAML ring can affect the stability of the reactive intermediates and the activation energy of the nucleophilic attack within the mechanism. The work highlights the importance of the fluorinated tail of the TAML structure in the accessibility of the desired transition state.</p>

scholarly journals Iron-TAML Complexes: A Computational Approach to Improving Stability

2021 ◽  
Author(s):  
◽  
Kevin Tuano
Keyword(s):  
Water Oxidation ◽  
Density Functional ◽  
Prolonged Exposure ◽  
Computational Study ◽  
Macrocyclic Ligand ◽  
Oxidation Mechanism ◽  
Nucleophilic Attack ◽  
Functional Theory ◽  
The Stability ◽  
Oxidation Chemistry

<p>Researchers at the Institute for Green Oxidation Chemistry of the Carnegie Mellon University developed a group of catalysts called tetra amido macrocyclic ligand (TAML) activators. The purpose of that research was that TAML activators would breakdown pollutants in the presence of a sacrificial oxidant. Furthermore, the catalyst was designed to decompose on a required timescale, as to not damage the environment by prolonged exposure. Since the initial designs from the 1980’s, the TAML structure has undergone significant changes to increase efficiency or selectivity. Other uses of this group of catalysts have been explored, namely, the oxidation of water to molecular oxygen.  This work presents a computational study using Density Functional Theory (DFT) which addresses the issue regarding the stability of certain iron-TAML intermediates in the water oxidation mechanism. Hence, the work seeks to explore how changing certain groups on the TAML ring can affect the stability of the reactive intermediates and the activation energy of the nucleophilic attack within the mechanism. The work highlights the importance of the fluorinated tail of the TAML structure in the accessibility of the desired transition state.</p>

scholarly journals Solvents Influence On Thermodynamics Of Complexation Between Dibenzo 18-Crown-6 With Tl+, Cs+ And Uo22+ Cations In Pure Acetonitrile, Pure Dimethylesulfoxide And Acetonitrile-Dimethylesulfoxide Binary Mixtures By Conductometric Method

2019 ◽  
pp. 63-74
Author(s):  
Naresh Desai ◽  
Dhruvi Mehta ◽  
Raviprakash Chandra ◽  
M. M. Maisuria
Keyword(s):  
Binary Mixtures ◽  
Stability Constants ◽  
Standard Enthalpy ◽  
Macrocyclic Ligand ◽  
Standard Entropy ◽  
Free Energies ◽  
Thermodynamics Of Complexation ◽  
Enthalpy Changes ◽  
The Stability ◽  
Complexation Reactions

The stability constants of 1:1 (M-L) complexes of Dibenzo-18-crown-6 (DB18C6) with Tl+, Cs+ and UO22+ cations have been determined conductometrically. The conductance data show that the stoichiometry of the complexes formed between the macrocyclic ligand and Tl+, Cs+ and UO22+ cations is 1:1 (M:L). GENPLOT computer program used to find the stability constants of the complexes were obtained from fitting of molar conductivity curves. The selectivity order of DB18C6 for the metal cations changes with the nature and composition of the binary mixed solvent. We also determined the Gibbs standard free energies (∆G0), the standard enthalpy changes (∆H0) and standard entropy changes (∆S0) for formation of these complexes in acetonitrile – dimethylesulfoxide (AN-DMSO) binary mixtures for the complexation. The values of standard enthalpy changes (∆H0 ) for complexation reactions were obtained from the slope of the van’t Hoff plots and the changes in standard entropy (∆S0) were calculated from the relationship ∆G0298.15 = ∆H0 - 298.15 ∆S0.

scholarly journals Thermodynamic investigations of complexation between dibenzo 18-crown-6 with Ni2+, Zn2+ and Cd2+ cations in pure acetonitrile, pure dimethylesulfoxide and acetonitrile-dimethylesulfoxide binary mixtures using conductometric method

2019 ◽  
pp. 43-53
Author(s):  
Naresh Desai ◽  
Dhruvi Mehta ◽  
Raviprakash Chandrab ◽  
M.M. Maisuria
Keyword(s):  
Binary Mixtures ◽  
Stability Constants ◽  
Standard Enthalpy ◽  
Macrocyclic Ligand ◽  
Standard Entropy ◽  
Free Energies ◽  
Enthalpy Changes ◽  
Conductance Data ◽  
The Stability ◽  
Complexation Reactions

The stability constants of 1:1 (M-L) complexes of Dibenzo-18-crown-6 (DB18C6) with Ni2+, Zn2+ and Cd2+ cations have been determined conductometrically. The conductance data show that the stoichiometry of the complexes formed between the macrocyclic ligand and Ni2+, Zn2+ and Cd2+ cations is 1:1 (M:L). GENPLOT computer program used to find the stability constants of the complexes were obtained from fitting of molar conductivity curves. The selectivity order of DB18C6 for the metal cations changes with the nature and composition of the binary mixed solvent. We also determined the Gibbs standard free energies (∆G0), the standard enthalpy changes (∆H0) and standard entropy changes (∆S0) for formation of these complexes in acetonitrile – dimethylesulfoxide (AN-DMSO) binary mixtures for the complexation. The values of standard enthalpy changes (∆H0 ) for complexation reactions were obtained from the slope of the van’t Hoff plots and the changes in standard entropy (∆S0) were calculated from the relationship ∆G0298.15 = ∆H0 - 298.15 ∆S0.

Mercury(II) and Lead(II) Complexes of 1-Oxa-7-thia-4,10-diazacyclododecane ([12]aneN2OS)

1999 ◽  
Vol 52 (1) ◽  
pp. 1 ◽  
Author(s):  
Trevor W. Hambley ◽  
Shahara Afshar ◽  
Sebastian T. Marcus ◽  
Lawrence R. Gahan
Keyword(s):  
Stability Constants ◽  
Macrocyclic Ligand ◽  
Protonation Constants ◽  
Secondary Amines ◽  
Monoclinic Space Group ◽  
Space Group ◽  
X Ray ◽  
X Ray Crystallography ◽  
The Stability ◽  
Lead Complex

The mixed donor 12-membered macrocyclic ligand 1-oxa-7-thia-4,10-diazacyclododecane ([12]aneN2OS) has been synthesized and the mercury(II) and lead(II) complexes, [Hg([12]aneN2OS)(NO3)2] and [Pb([12]aneN2OS)(NO3)2], have been isolated and characterized by X-ray crystallography. Crystals of the mercury complex are monoclinic, space group P 21/c, a 9·576(2), b 10·757(2), c 14·789(4) Å, β 93·58(2)°, whilst crystals of the lead complex are monoclinic, space group P 21/n, a 19·490(7), b 8·010(2), c 19·576(6) Å, β 109·90(2)°. The protonation constants and stability constants have been determined potentiometrically in aqueous solution. The protonation constants for [12]aneN2OS (log KHL 9·13; log K H2L 6·85) appear typical for secondary amines in similar trans-substituted 12-membered macrocycles. The magnitudes of the stability constants (HgII, log KHgL 10·5; PbII, log KPbL 6·6) are consistent with trends observed previously for macrocyclic ligands as secondary amine donors are replaced with oxygen and thioether donors.

scholarly journals CONDUCTOMETRIC STUDY OF LIGAND STRUCTURE INFLUENCE ON THE Pb(II) COMPLEXATION WITH CROWN ETHERS

STED JOURNAL ◽  
2020 ◽  
Vol 2 (2) ◽  
Author(s):  
Edita Bjelić ◽  
Mersiha Suljkanović ◽  
Jasmin Suljagić ◽  
Azra Kovačević
Keyword(s):  
Crown Ethers ◽  
Metal Ion ◽  
Macrocyclic Ligand ◽  
Complexation Reaction ◽  
Stoichiometric Ratio ◽  
Ligand Structure ◽  
Conductance Data ◽  
Conductometric Study ◽  
The Stability ◽  
Triton X

The conductometric study of ligand structure influence on the Pb(II) complexation with crown ethers in different solvents has been investigated. In this paper, the complexation reaction of macrocyclic ligand, 18-crown-6 (18C6), dibenzo-18-crown-6 (DB18C6), and Pb(II) cation was studied in different solvents: dichloromethane (DCM) and 1,2- dichloroethane (1,2-DCE). The effects of surfactant structure (Triton X-100 and Triton X-45) on the conductivity of the Pb(II) complex with 18-crown-6 and dibenzo-18-crown-6 ether have been investigated. The conductance data showed that the stoichiometry of the complexes in most cases is 1:1(ML). It is also demonstrated that the influence of crown ethers is deeply affected by the organic solvent used. In the solvents studied, the stability of the resulting complexes showed higher stability in dichloromethane comparing with 1,2- dichloroethane. Macrocyclic ligand 18-crown-6 showed more suitable for complexation of Pb(II) ions compared to dibenzo-18-crown-6. Adding a surfactant affected the higher absolute values of the conductivity of systems, but not the change in the stoichiometric ratio between a metal ion and macrocyclic ligand.

Open discussion

1982 ◽  
Vol 99 ◽  
pp. 605-613
Author(s):  
P. S. Conti
Keyword(s):  
Buenos Aires ◽  
Large Mass ◽  
List Type ◽  
Common Phenomenon ◽  
Open Discussion ◽  
The Stability ◽  
Ring Nebulae

Conti: One of the main conclusions of the Wolf-Rayet symposium in Buenos Aires was that Wolf-Rayet stars are evolutionary products of massive objects. Some questions:–Do hot helium-rich stars, that are not Wolf-Rayet stars, exist?–What about the stability of helium rich stars of large mass? We know a helium rich star of ∼40 MO. Has the stability something to do with the wind?–Ring nebulae and bubbles : this seems to be a much more common phenomenon than we thought of some years age.–What is the origin of the subtypes? This is important to find a possible matching of scenarios to subtypes.

Symmetric Multistep Methods Revisited: II. Numerical Experiments

1999 ◽  
Vol 173 ◽  
pp. 309-314 ◽  
Author(s):  
T. Fukushima
Keyword(s):  
Multistep Methods ◽  
Computational Time ◽  
Integration Time ◽  
Implicit Methods ◽  
Symmetric Methods ◽  
Celestial Bodies ◽  
The Stability ◽  
Predictor Corrector ◽  
Symmetric Multistep Methods ◽  
Integration Errors

AbstractBy using the stability condition and general formulas developed by Fukushima (1998 = Paper I) we discovered that, just as in the case of the explicit symmetric multistep methods (Quinlan and Tremaine, 1990), when integrating orbital motions of celestial bodies, the implicit symmetric multistep methods used in the predictor-corrector manner lead to integration errors in position which grow linearly with the integration time if the stepsizes adopted are sufficiently small and if the number of corrections is sufficiently large, say two or three. We confirmed also that the symmetric methods (explicit or implicit) would produce the stepsize-dependent instabilities/resonances, which was discovered by A. Toomre in 1991 and confirmed by G.D. Quinlan for some high order explicit methods. Although the implicit methods require twice or more computational time for the same stepsize than the explicit symmetric ones do, they seem to be preferable since they reduce these undesirable features significantly.

Uniformity of Magnification from Different Electron Microscopes

1967 ◽  
Vol 25 ◽  
pp. 32-33
Author(s):  
Godfrey C. Hoskins ◽  
V. Williams ◽  
V. Allison
Keyword(s):  
Diffraction Grating ◽  
The Other ◽  
Carbon Replica ◽  
Electron Microscopes ◽  
The Stability

The method demonstrated is an adaptation of a proven procedure for accurately determining the magnification of light photomicrographs. Because of the stability of modern electrical lenses, the method is shown to be directly applicable for providing precise reproducibility of magnification in various models of electron microscopes.A readily recognizable area of a carbon replica of a crossed-line diffraction grating is used as a standard. The same area of the standard was photographed in Phillips EM 200, Hitachi HU-11B2, and RCA EMU 3F electron microscopes at taps representative of the range of magnification of each. Negatives from one microscope were selected as guides and printed at convenient magnifications; then negatives from each of the other microscopes were projected to register with these prints. By deferring measurement to the print rather than comparing negatives, correspondence of magnification of the specimen in the three microscopes could be brought to within 2%.

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