scholarly journals Chirality-Matched Catalyst-Controlled Macrocyclization Reactions

2021 ◽  
Author(s):  
Jaeyeon Hwang ◽  
Brandon Q. Mercado ◽  
Scott Miller
Keyword(s):  
Transition State ◽  
Outer Sphere ◽  
Macrocyclic Compounds ◽  
Environmental Sciences ◽  
Remarkable Effect ◽  
Naturally Occurring ◽  
Additional Challenge ◽  
Intermolecular Reactions

<p>Macrocycles, formally defined as compounds that contain a ring with 12 or more atoms, continue</p><p>to attract great interest due to their important applications in physical, pharmacological and</p><p>environmental sciences. In syntheses of macrocyclic compounds, promoting intramolecular over</p><p>intermolecular reactions in the ring-closing step, is often a key challenge. Furthermore, syntheses</p><p>of macrocycles with stereogenic elements confer an additional challenge, while access to such</p><p>macrocycles are of great interest. Herein, we report the remarkable effect peptide-based catalysts</p><p>can have in promoting efficient macrocyclization reactions. We show that the chirality of the</p><p>catalyst is essential for promoting favorable, matched transition state relationships that favor</p><p>macrocyclization of substrates with pre-existing stereogenic elements; curiously, the chirality of</p><p>the catalyst is essential for successful reactions, even though no new stereogenic elements are</p><p>created. Control experiments involving either achiral variants of the catalyst, or the enantiomeric</p><p>form of the catalyst, fail to deliver the macrocycles in significant quantity in head-to-head</p><p>comparisons. The generality of the phenomenon, demonstrated here with a number of substrates,</p><p>stimulates analogies to enzymatic catalysts that produce naturally occurring macrocycles,</p><p>presumably through related, catalyst-defined outer-sphere interactions with their acyclic substrates.</p>

scholarly journals Chirality-Matched Catalyst-Controlled Macrocyclization Reactions

2021 ◽  
Author(s):  
Jaeyeon Hwang ◽  
Brandon Q. Mercado ◽  
Scott Miller
Keyword(s):  
Transition State ◽  
Outer Sphere ◽  
Macrocyclic Compounds ◽  
Environmental Sciences ◽  
Remarkable Effect ◽  
Naturally Occurring ◽  
Additional Challenge ◽  
Intermolecular Reactions

<p>Macrocycles, formally defined as compounds that contain a ring with 12 or more atoms, continue</p><p>to attract great interest due to their important applications in physical, pharmacological and</p><p>environmental sciences. In syntheses of macrocyclic compounds, promoting intramolecular over</p><p>intermolecular reactions in the ring-closing step, is often a key challenge. Furthermore, syntheses</p><p>of macrocycles with stereogenic elements confer an additional challenge, while access to such</p><p>macrocycles are of great interest. Herein, we report the remarkable effect peptide-based catalysts</p><p>can have in promoting efficient macrocyclization reactions. We show that the chirality of the</p><p>catalyst is essential for promoting favorable, matched transition state relationships that favor</p><p>macrocyclization of substrates with pre-existing stereogenic elements; curiously, the chirality of</p><p>the catalyst is essential for successful reactions, even though no new stereogenic elements are</p><p>created. Control experiments involving either achiral variants of the catalyst, or the enantiomeric</p><p>form of the catalyst, fail to deliver the macrocycles in significant quantity in head-to-head</p><p>comparisons. The generality of the phenomenon, demonstrated here with a number of substrates,</p><p>stimulates analogies to enzymatic catalysts that produce naturally occurring macrocycles,</p><p>presumably through related, catalyst-defined outer-sphere interactions with their acyclic substrates.</p>

Chirality-matched catalyst-controlled macrocyclization reactions

2021 ◽  
Vol 118 (40) ◽  
pp. e2113122118
Author(s):  
Jaeyeon Hwang ◽  
Brandon Q. Mercado ◽  
Scott J. Miller
Keyword(s):  
Transition State ◽  
Macrocyclic Compounds ◽  
Environmental Sciences ◽  
Remarkable Effect ◽  
Naturally Occurring ◽  
Additional Challenge ◽  
Intermolecular Reactions

Macrocycles, formally defined as compounds that contain a ring with 12 or more atoms, continue to attract great interest due to their important applications in physical, pharmacological, and environmental sciences. In syntheses of macrocyclic compounds, promoting intramolecular over intermolecular reactions in the ring-closing step is often a key challenge. Furthermore, syntheses of macrocycles with stereogenic elements confer an additional challenge, while access to such macrocycles are of great interest. Herein, we report the remarkable effect peptide-based catalysts can have in promoting efficient macrocyclization reactions. We show that the chirality of the catalyst is essential for promoting favorable, matched transition-state relationships that favor macrocyclization of substrates with preexisting stereogenic elements; curiously, the chirality of the catalyst is essential for successful reactions, even though no new static (i.e., not “dynamic”) stereogenic elements are created. Control experiments involving either achiral variants of the catalyst or the enantiomeric form of the catalyst fail to deliver the macrocycles in significant quantity in head-to-head comparisons. The generality of the phenomenon, demonstrated here with a number of substrates, stimulates analogies to enzymatic catalysts that produce naturally occurring macrocycles, presumably through related, catalyst-defined peripheral interactions with their acyclic substrates.

Aluminium–ligand cooperation promotes selective dehydrogenation of formic acid to H2 and CO2

2014 ◽  
Vol 5 (7) ◽  
pp. 2771-2777 ◽  
Author(s):  
T. W. Myers ◽  
L. A. Berben
Keyword(s):  
Transition State ◽  
Formic Acid ◽  
Outer Sphere ◽  
Aluminum Complex ◽  
Cooperative Interactions ◽  
Complex Metal ◽  
Selective Conversion ◽  
Hydride Abstraction ◽  
Metal Ligand

Selective conversion of formic acid to H2 and CO2 is catalysed by a molecular aluminum complex. Metal–ligand cooperative interactions stabilize a transition state for an outer-sphere β-hydride abstraction mechanism for catalysis.

scholarly journals Kinetic study of surfactant cobalt (III) complexes by [Fe(CN)6 4-]: Outer-Sphere Electron-Transfer in Ionic liquids and Liposome Vesicle

2020 ◽  
pp. 300-317
Author(s):  
Nagaraj Karuppiah ◽  
◽  
Pakkirisamy Pakkirisamy ◽  
Gunasekaran Gladwin ◽  
◽  
...  
Keyword(s):  
Phase Transition ◽  
Electron Transfer ◽  
Ionic Liquids ◽  
Transition Temperature ◽  
Transition State ◽  
Phase Transition Temperature ◽  
Outer Sphere ◽  
Complex Ions ◽  
Electron Transfer Mechanism ◽  
Outer Sphere Electron Transfer

UV-Vis., absorption spectroscopy are used to monitor the electron transfer reaction between the surfactant cobalt(III) complexes, cis-[Co(ip)2(C14H29NH2)2]3+, cis-[Co(dpq)2(C14H29NH2)2]3+ and cis-[Co(dpqc)2(C14H29NH2)2]3+ (ip = imidazo[4,5-f][1,10]phenanthroline, dpq = dipyrido[3,2-d:2’-3’-f]quinoxaline, dpqc = dipyrido[3,2-a:2’,4’-c](6,7,8,9-tetrahydro)phenazine, C14H29NH2=Tetradecylamine) and [Fe(CN)6]4- ion in liposome vesicles (DPPC) and ionic liquids ((BMIM)Br) were investigated at different temperatures under pseudo first order conditions using an excess of the reductant. The reactions were found to be second order and the electron transfer is postulated as outer-sphere. The rate constant for the electron transfer reactions were found to increase with increasing concentrations of ionic liquids. The effects of hydrophobicity of the long aliphatic double chains of these surfactant complex ions into liposome vesicles on these reactions have also been studied. Below the phase transition temperature of DPPC, the rate decreased with increasing concentration of DPPC, while above the phase transition temperature the rate increased with increasing concentration of DPPC. Kinetic data and activation parameters are interpreted in terms of an outer-sphere electron transfer mechanism. In all these media the S# values are found to be negative in direction in all the concentrations of complexes used indicative of more ordered structure of the transition state. This is consistent with a model in which the surfactant cobalt(III) complexes and Fe(CN)64- ions bind to the DPPC in the transition state. Thus, the results have been explained based on the self-aggregation, hydrophobic effect, and the reactants with opposite charge.

scholarly journals Even with nonnative interactions, the updated folding transition states of the homologs Proteins G & L are extensive and similar

2015 ◽  
Vol 112 (27) ◽  
pp. 8302-8307 ◽  
Author(s):  
Michael C. Baxa ◽  
Wookyung Yu ◽  
Aashish N. Adhikari ◽  
Liang Ge ◽  
Zhen Xia ◽  
...  
Keyword(s):  
Transition State ◽  
Triple Mutant ◽  
Homologous Proteins ◽  
Naturally Occurring ◽  
Folding Algorithm ◽  
Helical Content ◽  
State Ensemble ◽  
Transition Paths ◽  
Folding Simulations ◽  
Transition State Ensemble

Experimental and computational folding studies of Proteins L & G and NuG2 typically find that sequence differences determine which of the two hairpins is formed in the transition state ensemble (TSE). However, our recent work on Protein L finds that its TSE contains both hairpins, compelling a reassessment of the influence of sequence on the folding behavior of the other two homologs. We characterize the TSEs for Protein G and NuG2b, a triple mutant of NuG2, using ψ analysis, a method for identifying contacts in the TSE. All three homologs are found to share a common and near-native TSE topology with interactions between all four strands. However, the helical content varies in the TSE, being largely absent in Proteins G & L but partially present in NuG2b. The variability likely arises from competing propensities for the formation of nonnative β turns in the naturally occurring proteins, as observed in our TerItFix folding algorithm. All-atom folding simulations of NuG2b recapitulate the observed TSEs with four strands for 5 of 27 transition paths [Lindorff-Larsen K, Piana S, Dror RO, Shaw DE (2011) Science 334(6055):517–520]. Our data support the view that homologous proteins have similar folding mechanisms, even when nonnative interactions are present in the transition state. These findings emphasize the ongoing challenge of accurately characterizing and predicting TSEs, even for relatively simple proteins.

Kinetic solvent effects on alkaline decolorization of crystal violet in some aquo-organic solvents

1986 ◽  
Vol 64 (2) ◽  
pp. 300-307 ◽  
Author(s):  
Urmila Mandal ◽  
Sumita Sen ◽  
Kaushik Das ◽  
Kiron Kumar Kundu
Keyword(s):  
Transition State ◽  
Crystal Violet ◽  
Chemical Properties ◽  
Outer Sphere ◽  
Chloride Salt ◽  
Aqueous Mixtures ◽  
Free Energies ◽  
Initial State ◽  
Composition Profiles ◽  
Solvent Systems

Rate constants (ks) of alkaline fading of crystal violet (CV+) have been determined at 25 °C by spectrophotometric measurements in aqueous mixtures of some protic, aprotic, and dipolar aprotic cosolvents. Transfer free energies of the substrate (CV+), [Formula: see text], were also determined in some of the solvent systems from solubility measurements of the chloride salt, and by subtracting [Formula: see text] obtained earlier by use of the tetraphenylarsonium tetraphenylboron (TATB) extrathermodynamic assumption. This helped determine transfer free energies of the transition state (X≠), [Formula: see text] values of lyate ion (S−) based on the TATB assumption are already known for all of these solvent systems. The observed log (ks/kw) – composition profiles reveal that the relative solvation of the reacting species rather than the dielectric constant of the solvents dictates the complex variation of the rates of the reaction in these solvent systems. Correlation of [Formula: see text] with [Formula: see text] indicates that the reaction is largely controlled by the relative solvation of S− in most of the cases. But analysis of [Formula: see text] – composition profiles for some of the solvent systems reveals that the non-compensation of the [Formula: see text] contributions of initial-state substrate and of the transition-state complex, which may be considered to be an outer-sphere complex [CV+](S−), is also in accord with what is expected from the relative solvating characteristics of the cosolvents as guided by their respective physico-chemical properties.

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