Spin Saturation Transfer Difference NMR (SSTD NMR): A New Tool to Obtain Kinetic Parameters of Chemical Exchange Processes

Quirós, M. Teresa; Macdonald, Colin; Angulo, Jesús; Muñoz, María Paz

doi:10.3791/54499

Cited by 4 publications

(4 citation statements)

References 23 publications

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“…The rates of interconversion for the isomers of 1-X were measured through spin saturation transfer difference (SSTD) , experiments (see the SI). The olefinic methine resonance was the one irradiated in these experiments (Figure S34).…”

Section: Resultsmentioning

confidence: 99%

Synthesis of Mo(IV) para-Substituted Styrene Complexes and an Exploration of Their Conversion to 1-Phenethylidene Complexes

2022

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Molybdenum(IV) styrene complexes, Mo(NAr)(p-X-styrene)(OSiPh3)2 (1-X; X = t-Bu, Me, F, Br, CF3; Ar = 2,6-i-Pr2C6H3), were synthesized and their conversion into 1-phenethylidene complexes was investigated. The two isomers of 1-X (Ph-up and Ph-down) interconvert through the rotation of the styrene about its central Mo(olefin) axis, with ΔH ‡ in the range of 13–16 kcal/mol and ΔS ‡ in the range of −7 to −16 cal/mol·K. All 1-X compounds except 1-CF 3 react slowly with a catalytic amount of PhNMe2H+ to give an equilibrium mixture of 1-X and Mo(NAr)[C(Me)(p-X-C6H4)](OSiPh3)2 (2-X) complexes. The equilibrium constants for the formation of 2-X from 1-X increase in the order of 1-Br < 1-F ∼ 1-H < 1- t -Bu < 1-Me with the range in K eq from 0.25 for 1-Br to 0.51 for 1-Me. It is proposed that the rate-limiting step is the protonation of the styrene’s CH2 group, either directly or via the addition of a proton to the Mo–CH2 bond. The rates of protonation increase in the order 1-Br < 1-H < 1- t -Bu < 1-Me, with that for 1-Me being ∼30× faster than that for 1-Br. All 1-X compounds react immediately and irreversibly with [(Et2O)2H]+ to form cationic phenethyl complexes (3-X), the intermediates in the conversion of 1-X to 2-X. X-ray structural studies were carried out for 1-X, where X = t-Bu, Me, F, Br, or CF3.

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Section: Resultsmentioning

confidence: 99%

Synthesis of Mo(IV) para-Substituted Styrene Complexes and an Exploration of Their Conversion to 1-Phenethylidene Complexes

2022

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“…It is worth noting that the temperatures required for these experiments were higher (above room temperature) than the temperatures used in the line-shape analysis of complex 1 . The calculated kinetic and thermodynamic parameters (Δ H ⧧ = 18.6 ± 0.4 kcal mol –1 ; Δ S ⧧ = −9 ± 1 Cal mol –1 K –1 ; E a (298 K) = 19.2 ± 0.4 kcal mol –1 ; Δ G ⧧ (298 K) = 21.1 ± 0.4 kcal mol –1 ) were in accordance with a slow process, as previously suggested, although the movement of the platinum is definitely happening …”

Section: Results and Discussionmentioning

confidence: 99%

“…As part of our mechanistic studies on these reactions, we sought to gather experimental evidence on the type of coordination of the platinum and the allenes, in order to understand the subtle differences in reactivities observed in platinum catalysis, and to ascertain the involvement of η 1 -coordinated allene complexes as reactive species in our catalytic cycle. As the isolation and analysis of PtCl 2 -allene complexes without stabilizing ligands is very challenging, for this study, we have selected a family of Pt-allene complexes with ancillary nitrogen-containing ligands in a four- or five-coordinated arrangement, , active catalysts in our dihydroalkoxylation reaction, and we have studied them in solid state and in solution using different NMR techniques, including our recently reported SSTD NMR method …”

Section: Introductionmentioning

confidence: 99%

“…We encountered that classic VT experiments and line-shape analysis techniques, commonly used in the analysis of fluxional processes of organometallic complexes in solution, were not suitable to study some of our complexes due to thermal instability and higher coalescence temperatures than the decomposition temperatures. Therefore, a new method was developed and applied to these challenging systems, the SSTD (Spin Saturation Transfer Difference) NMR method . This new NMR protocol combines the Spin Saturation Transfer (SST) method used for small molecules, with the Saturation Transfer Difference (STD) NMR method employed for the study of protein–ligand interactions, by measuring transient spin saturation transfer along increasing saturation times (build-up curves) in systems undergoing mutual-site exchange.…”

Section: Introductionmentioning

confidence: 99%

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Twists and Turns of Platinum-Allene Complexes: NMR Techniques for the Study of the Dynamic Behavior in Solution

et al. 2016

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Classic (dynamic exchange line-shape analysis) and novel (SSTD NMR) NMR techniques have been applied in order to obtain the kinetic and thermodynamic parameters of the three main processes occurring in the fluxional behavior of Pt-allene complexes with N-containing ligands, in four and five coordination mode, in solution. Our results show intramolecular helical and rotational movements closely related to each other, confirming η 1 -staggered structures as possible intermediates. The ligand exchange in these complexes seems to occur via a ligand-independent dissociative mechanism, where coordinating solvents might be involved in the stabilization of the intermediates. The differences observed in the interaction of allenes with other metals could be the basis to explain the divergent reactivity observed in platinum-catalyzed processes.

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Binding Moiety Mapping by Saturation Transfer Difference NMR

Brender

Krishnamoorthy²,

Ghosh

et al. 2018

Methods in Molecular Biology

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Saturation transfer difference (STD) NMR has emerged as one of the key technologies in lead optimization during drug design. Unlike most biophysical assays which report only on the binding affinity, STD NMR reports simultaneously on both the binding affinity and the structure of the binding ligand/protein complex. The STD experiment drives magnetization from a protein to a bound small molecule ligand which carries away the memory of the saturation signal when it dissociates. Since the transfer of saturation is distance dependent, STD NMR can be used to map the specific atoms on the ligand in contact with a protein receptor allowing the impact of any structural change in the binding site to be mapped directly on to the individual functional groups responsible when a suitable compound library is screened. Because the signal is detected from the free ligand and not the bound complex, it can be used on a much wider range of systems than protein-detected NMR and has the advantage of more directly reporting on distances than changes in chemical shifts alone. The STD experiment, while deceptively simple, is very sensitive to both sample conditions and acquisition parameters. We present a general protocol for setting up and STD NMR experiment with a particular focus on how choices in sample conditions and acquisition parameters affect the outcome of the experiment.

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Spin Saturation Transfer Difference NMR (SSTD NMR): A New Tool to Obtain Kinetic Parameters of Chemical Exchange Processes

Cited by 4 publications

References 23 publications

Synthesis of Mo(IV) para-Substituted Styrene Complexes and an Exploration of Their Conversion to 1-Phenethylidene Complexes

Synthesis of Mo(IV) para-Substituted Styrene Complexes and an Exploration of Their Conversion to 1-Phenethylidene Complexes

Twists and Turns of Platinum-Allene Complexes: NMR Techniques for the Study of the Dynamic Behavior in Solution

Binding Moiety Mapping by Saturation Transfer Difference NMR

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