Marcus Mortimer Sundle
Ontology highlight
ABSTRACT:
SUBMITTER: Saperia J
PROVIDER: S-EPMC544479 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description: Not available
| S-EPMC1125904 | biostudies-literature
Project description:Two forms of the equation for expression of the rate constant for electron transfer through a Marcus-type treatment are discussed. In the first (exergonic) form, the Arrhenius exponential term was replaced by its classical Marcus term; in the second (endergonic) form, the forward rate constant was replaced by the reverse rate constant (the forward rate constant in the exergonic direction), which was expanded to an equivalent Marcus term and multiplied by the equilibrium constant. When the classical Marcus treatment was used, these two forms of the rate equation give identical curves relating the logarithm of the rate constant to the driving force. The Marcus term for the relation between activation free-energy, DeltaG#, reorganization energy, lambda, and driving force, DeltaG(o), derived from parabolas for the reactant and product states, was identical when starting from exergonic or endergonic parabolas. Moser and colleagues introduced a quantum mechanical correction factor to the Marcus term in order to fit experimental data. When the same correction factor was applied in the treatment for the endergonic direction by Page and colleagues, a different curve was obtained from that found with the exergonic form. We show that the difference resulted from an algebraic error in development of the endergonic equation.
| S-EPMC2238675 | biostudies-literature
Project description:This report highlights the importance for neonatologists/pediatricians of considering Marcus Gunn jaw-winking syndrome among differential diagnoses of ptosis. A detailed clinical assessment is crucial to promptly recognize and appropriately manage it.
| S-EPMC7869362 | biostudies-literature
Project description:Electron transfer reactions slow down when they become very thermodynamically favorable, a counterintuitive interplay of kinetics and thermodynamics termed the inverted region in Marcus theory. Here we report inverted region behavior for proton-coupled electron transfer (PCET). Photochemical studies of anthracene-phenol-pyridine triads give rate constants for PCET charge recombination that are slower for the more thermodynamically favorable reactions. Photoexcitation forms an anthracene excited state that undergoes PCET to create a charge-separated state. The rate constants for return charge recombination show an inverted dependence on the driving force upon changing pyridine substituents and the solvent. Calculations using vibronically nonadiabatic PCET theory yield rate constants for simultaneous tunneling of the electron and proton that account for the results.
| S-EPMC6681808 | biostudies-literature
Project description:RationaleThis case report describes the Marcus Gunn phenomenon (MGP), an infrequent type of congenital unwanted contractions of facial muscles that occurs in 4%-6% of patients with congenital ptosis. The defining characteristic of MGP is the affected eyelid lifting in a manner similar to the opening of the mouth.Patient concernsIt addresses a 45-year-old man who was examined in the dental clinic with a severely decayed tooth. He exhibited evidence of normal vision and synchronous movement of his lips and eyelid.DiagnosisThe conditions matched those of the autosomal dominant disorder with incomplete penetration, the MGP. The carious tooth was restored without the necessity for any surgical intervention.TreatmentThe patient was given appropriate dental treatment without any surgical intervention for Marcus Gunn Syndrome.OutcomeAfter receiving routine fillings to treat dental caries, the patient stopped complaining of pain.Take-away lessonThis case report reveals insight into a situation that has been speculated to be an example of neural redirection syndrome, in which impulses from the trigeminal nerve's motor unit are naturally redirected into the levator palpebrae superioris muscles of the upper eyelid and the superior pterygoid muscle.
| S-EPMC11340846 | biostudies-literature
Project description:A key process underlying the application of low-dimensional, quantum-confined semiconductors in energy conversion is charge transfer from these materials, which, however, has not been fully understood yet. Extensive studies of charge transfer from colloidal quantum dots reported rates increasing monotonically with driving forces, never displaying an inverted region predicted by the Marcus theory. The inverted region is likely bypassed by an Auger-like process whereby the excessive driving force is used to excite another Coulomb-coupled charge. Herein, instead of measuring charge transfer from excitonic states (coupled electron-hole pairs), we build a unique model system using zero-dimensional quantum dots or two-dimensional nanoplatelets and surface-adsorbed molecules that allows for measuring charge transfer from transiently-populated, single-charge states. The Marcus inverted region is clearly revealed in these systems. Thus, charge transfer from excitonic and single-charge states follows the Auger-assisted and conventional Marcus charge transfer models, respectively. This knowledge should enable rational design of energetics for efficient charge extraction from low-dimensional semiconductor materials as well as suppression of the associated energy-wasting charge recombination.
| S-EPMC8566515 | biostudies-literature
Project description:Chemical reactions that involve net hydrogen atom transfer (HAT) are ubiquitous in chemistry and biology, from the action of antioxidants to industrial and metalloenzyme catalysis. This report develops and validates a procedure to predict rate constants for HAT reactions of oxyl radicals (RO(*)) in various media. Our procedure uses the Marcus cross relation (CR) and includes adjustments for solvent hydrogen-bonding effects on both the kinetics and thermodynamics of the reactions. Kinetic solvent effects (KSEs) are included by using Ingold's model, and thermodynamic solvent effects are accounted for by using an empirical model developed by Abraham. These adjustments are shown to be critical to the success of our combined model, referred to as the CR/KSE model. As an initial test of the CR/KSE model we measured self-exchange and cross rate constants in different solvents for reactions of the 2,4,6-tri-tert-butylphenoxyl radical and the hydroxylamine 2,2'-6,6'-tetramethyl-piperidin-1-ol. Excellent agreement is observed between the calculated and directly determined cross rate constants. We then extend the model to over 30 known HAT reactions of oxyl radicals with OH or CH bonds, including biologically relevant reactions of ascorbate, peroxyl radicals, and alpha-tocopherol. The CR/KSE model shows remarkable predictive power, predicting rate constants to within a factor of 5 for almost all of the surveyed HAT reactions.
| S-EPMC2851756 | biostudies-literature
Project description:Marcus Gunn jaw winking synkinesis (MGJWS) is caused by congenital miswiring of a branch of the fifth cranial nerve into the branch of the third cranial nerve supplying the levator muscle. It has been observed in 2-13% of patients with congenital ptosis. Although bilateral cases were reported, most were unilateral and occurred more frequently on the left side than the right. We report two cases of children who presented with ptosis and were diagnosed with MGJWS.
| S-EPMC3618604 | biostudies-other
Project description:The Marcus model forms the foundation for all modern discussion of electron transfer (ET). In this model, ET results in a change in diabatic potential energy surfaces, separated along an ET nuclear coordinate. This coordinate accounts for all nuclear motion that promotes electron transfer. It is usually assumed to be dominated by a collective asymmetric vibrational motion of the redox sites involved in the ET. However, this coordinate is rarely quantitatively specified. Instead, it remains a nebulous concept, rather than a tool for gaining true insight into the ET pathway. Herein, we describe an ab initio approach for quantifying the ET coordinate and demonstrate it for a series of dinitroradical anions. Using sampling methods at finite temperature combined with density functional theory calculations, we find that the electron transfer can be followed using the energy separation between potential energy surfaces and the extent of electron localization. The precise nuclear motion that leads to electron transfer is then obtained as a linear combination of normal modes. Once the coordinate is identified, we find that evolution along it results in a change in diabatic state and optical excitation energy, as predicted by the Marcus model. Thus, we conclude that a single dimension of the electron transfer described in Marcus–Hush theory can be described as a well-defined nuclear motion. Importantly, our approach allows the separation of the intrinsic electron transfer coordinate from other structural relaxations and environmental influences. Furthermore, the barrier separating the adiabatic minima was found to be sufficiently thin to enable heavy-atom tunneling in the ET process. The electron transfer coordinate of the Marcus–Hush model is recovered from ab initio calculations.
| S-EPMC10466304 | biostudies-literature