Influence of surface phase transitions on desorption kinetics: the compensation effect

Estrup, P. J.; Greene, E. F.; Cardillo, M. J.; Tully, John C.

doi:10.1021/j100408a052

Cited by 72 publications

(28 citation statements)

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“…This behavior can be viewed as an example of the well-known "compensation effect" in chemical kinetics in which the activation energy and prefactor of a reaction both change relatively abruptly in the same direction (i.e., compensate), whereas the overall reaction rate changes smoothly. In the case of desorption from a surface, this behavior has sometimes been traced to a phase transition in the substrate or adsorbate layer (15). The magnitudes of the changes in the current example, however, dwarf those of any prior report of a compensation effect of which we are aware.…”

Section: Resultsmentioning

confidence: 53%

“…The observed change in slope of the Arrhenius plot is quite abrupt. A firstorder phase transition will produce an inflection point, i.e., a discontinuity in slope (15). Although a finite-sized protein cannot exhibit a true first-order transition, the sharpness of the changeover between the two temperature regimes adds further support to the supposition that a global transformation such as melting or partial melting underlies the observations.…”

Section: Resultsmentioning

confidence: 77%

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Unusual kinetics of thermal decay of dim-light photoreceptors in vertebrate vision

Guo

Sekharan

Liu

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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We present measurements of rate constants for thermal-induced reactions of the 11-cis retinyl chromophore in vertebrate visual pigment rhodopsin, a process that produces noise and limits the sensitivity of vision in dim light. At temperatures of 52.0-64.6°C, the rate constants fit well to an Arrhenius straight line with, however, an unexpectedly large activation energy of 114 ± 8 kcal/mol, which is much larger than the 60-kcal/mol photoactivation energy at 500 nm. Moreover, we obtain an unprecedentedly large prefactor of 10 72±5 s −1 , which is roughly 60 orders of magnitude larger than typical frequencies of molecular motions! At lower temperatures, the measured Arrhenius parameters become more normal: E a = 22 ± 2 kcal/mol and A pref = 10 9±1 s −1 in the range of 37.0-44.5°C. We present a theoretical framework and supporting calculations that attribute this unusual temperature-dependent kinetics of rhodopsin to a lowering of the reaction barrier at higher temperatures due to entropy-driven partial breakup of the rigid hydrogen-bonding network that hinders the reaction at lower temperatures.non-Arrhenius | dim-light vision | transition state theory | isomerization rate R hodopsin is a vertebrate dim-light photoreceptor. Molecular studies of rhodopsin in recent decades have largely focused on its photochemistry and photoactivation (1-3). However, complete understanding of rhodopsin's function requires characterization of its thermal properties because thermal isomerization of the 11-cis retinyl chromophore can trigger the same physiological response as photo-isomerization, generating false visual signals as dark noise that jeopardizes photosensitivity (4-6). To enhance dim-light vision, rhodopsin has evolved to acquire remarkable thermal stability with a half-life of 420 y as determined by electrophysiological experiments using the outer segments of rod cells at 36°C (4). However, the molecular mechanism for the thermal stability has remained unclear. Here, we have addressed this by exploring the temperature dependence of thermal decay rate constants k(T) associated with isomerization of the retinyl chromophore and hydrolysis of the chromophore protonated Schiff-base (PSB) linkage, for temperatures ranging from the physiological temperature of 37.0°C to 64.6°C. In the upper range of temperatures from 52.0°C to 64.6°C, we find that the rate constants determined by UV-visible spectroscopy follow a linear Arrhenius model, k(T) = A pref exp(−E a /k B T), where k B is the Boltzmann constant (Fig. 1A). The slope, however, is very steep, giving an elevated activation energy, E a = 114 ± 8 kcal/mol. Surprisingly, this value is much higher than the photoactivation energy at visible wavelengths (60 kcal/mol at 500 nm). E a is also much higher than the reaction enthalpy change (32-35 kcal/mol) (7, 8) (Fig. 1B). In the lower temperature range of our rate constant measurements, 37.0-44.5°C, the slope of the Arrhenius plot decreases abruptly, as shown in Fig. 1A. Fitting a straight line through the low temperature points prod...

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Section: Resultsmentioning

confidence: 53%

Section: Resultsmentioning

confidence: 77%

Unusual kinetics of thermal decay of dim-light photoreceptors in vertebrate vision

Guo

Sekharan

Liu

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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“…Alternatively speaking, it is the strongly enhanced entropy of the mobile surface species which leads to an according quenching of the desorption rate. 46 A similar behavior has been observed for CO on Ru(0001) which likewise displays island growth and coexistence with a 2D-gas phase in the coverage range CO < 0.33 ML at elevated T. 47,48 Figure 7 shows a series of TPD spectra with 1.8-3.1 layers of NTCDA deposited onto Ag(111) at 77 K. For initial coverages in excess of 2 ML the peak at 350 K, attributed to desorption of the bilayer gradually disappears and is replaced by a peak at 375 K which does not saturate and therefore represents NTCDA multilayer desorption. As the multilayers desorb at 25 K higher temperature than the bilayer, the latter represents a metastable phase, which vanishes as soon as nuclei of the multilayer are formed.…”

Section: Thermal Desorption Spectroscopymentioning

confidence: 99%

Vibrational properties of the compressed and the relaxed 1,4,5,8-naphthalene-tetracarboxylic dianhydride monolayer on Ag(111)

Braatz

Öhl

Jakob

2012

The Journal of Chemical Physics

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Layers of 1,4,5,8-naphthalene-tetracarboxylic dianhydride (NTCDA) grown on Ag(111) at about 80 K have been investigated using Fourier transform infrared spectroscopy, spot profile analysis low-energy electron diffraction, and temperature programmed desorption. Specifically, the compressed and the relaxed monolayer, as well as the transformation between the two ordered phases have been analyzed in detail. It is found that the two monolayer phases display distinctly different vibrational spectra and can thus be discriminated with high accuracy and sensitivity. For the NTCDA/Ag(111) monolayer strong in-plane vibrational modes point at a marked dynamic charge transfer between molecule and metal substrate and provide clear evidence for an efficient electronic coupling to the Ag(111) surface in conjunction with a partially filled electronic level at the Fermi energy. The bilayer, on the other hand, is largely electronically decoupled from the substrate and, according to the vanishing infrared-active in-plane vibrational modes, is oriented parallel to the surface. On the basis of spectroscopic data the metastable nature of the bilayer phase is identified as such, leading to an improved understanding of processes encountered in the course of layer preparation and resolving inconsistencies reported in the literature.

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“…14 and 15 clarify the observed shift of the TPD spectra to low temperatures as coverage increases; it is due to the strong decrease in the activation energy for desorption with coverage. This could have been even more dramatic except that here we have a clear case of the so called compensation effect in desorption 26 : both the activation energy for desorption and the preexponent factor display similar behavior with coverage. The result is a much slower change of the overall rate of desorption with increasing coverage.…”

Section: Equilibrium Measurementsmentioning

confidence: 84%

Optical Second Harmonic Generation as a Real Time Probe of Molecule-Surface Interactions

Asscher

Rosenzweig

1995

Laser Spectroscopy and Photochemistry on Metal Surfaces

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Influence of surface phase transitions on desorption kinetics: the compensation effect

Cited by 72 publications

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Unusual kinetics of thermal decay of dim-light photoreceptors in vertebrate vision

Unusual kinetics of thermal decay of dim-light photoreceptors in vertebrate vision

Vibrational properties of the compressed and the relaxed 1,4,5,8-naphthalene-tetracarboxylic dianhydride monolayer on Ag(111)

Optical Second Harmonic Generation as a Real Time Probe of Molecule-Surface Interactions

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