Kinetics and Mechanism. A Study of Homogeneous Chemical Reactions.

Forst, Wendell

doi:10.1021/ja01484a048

Cited by 50 publications

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“…It is well known [36] that when reactions occur between ions of unlike sign, there is generally an entropy increase in going from reactants to the activated complex, whereas reaction between ions of like sign, gives an entropy decrease. It is also reported [37] that when reaction occurs between an ion and a neutral molecule, the transition state becomes less polar than the initial state, because in the transition state the same charge is dispersed over a greater volume.…”

Section: Discussionmentioning

confidence: 99%

Kinetics of oxidation of d(+)melibiose and cellobiose by N-bromoacetamide using a rhodium(III) chloride catalyst

Singh

Srivastava

et al. 2010

Transition Met Chem

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The kinetics of oxidation of the sugars D(?)Melibiose (mel) and Cellobiose (cel) by N-bromoacetamide (NBA) in the presence of Rh(III) chloride as homogeneous catalyst in acidic medium at 45°C have been investigated. The reactions are first-order with respect to [NBA], [Rh(III)] and [substrate]. The rate is proportional to [H ? ]. No effects of [Hg(II)], [NHA] or [Cl -] on the rates were observed. Ionic strength and dielectric constant also have little effect. The observed kinetic data, available literature and spectroscopic evidence lead us to conclude that NBAH ? and [RhCl 5 (H 2 O)] 2-are the reactive species of NBA and Rh(III) chloride, respectively. The rate-determining step of the proposed reaction path common for both sugars gives an activated complex by the interaction of a charged complex species and neutral sugar molecule, which in the subsequent steps disproportionates into the reaction products with the regeneration of catalyst. The reactions have been studied at four different temperatures and with the help of first-order rate constant values, various activation parameters have been calculated. The main oxidation products of the reactions were identified as arabinonic acid, formic acid and lyxonic acid in the case of mel and arabinonic acid and formic acid in the case of cel.

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Section: Discussionmentioning

confidence: 99%

Kinetics of oxidation of d(+)melibiose and cellobiose by N-bromoacetamide using a rhodium(III) chloride catalyst

Singh

Srivastava

et al. 2010

Transition Met Chem

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“…In Table 1 Given a set of rate constants for scheme (4), we computed next the probability for a channel to occupy the two open states, 0 1 (t) and 0 2(t). For this, the set of first-order differential equations, relating the occupancies of the five states of scheme (4) to the corresponding transition rates, were solved numerically (see Frost & Pearson, 1961). Curves a in Fig.…”

Section: Ca2+ Channels In Cell-attached Patchesmentioning

confidence: 99%

Single low‐voltage‐activated calcium channels in chick and rat sensory neurones.

Carbone

Lux

1987

The Journal of Physiology

142

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SUMMARY1. Single and multiple Ca2+ channel currents were recorded from outside-out and cell-attached patches of cultured chick and rat dorsal root ganglion cells, using the patch-clamp technique.2. Outside-out patches containing a large number of Ca2+ channels revealed Ca2+ currents resembling those from the whole cell. A low-voltage-activated (l.v.a.) and a high-voltage-activated (h.v.a.) Ca2+ current similar to those described in the accompanying paper (Carbone & Lux, 1987b) could be distinguished. The h.v.a. current component subsided within 10 min following the formation of the patch, while the l.v.a. component lasted much longer.3. Unitary events related to the l.v.a. Ca2+ channel could be clearly resolved in outside-out patches formed in Na+-and K+-free media containing 5-50 mM-CaCl2.4. The amplitudes of l.v.a. channel openings were bimodally distributed, indicating the presence of two conductive states. At -40 mV, mean amplitudes of the two events were -0-29 + 0-07 pA and -0 47 + 0-085 pA in 50 mM-CaCl2, with apparent slope conductances of about 3-6 and 5-2 pS, respectively. In 5 mM-CaCl2 both slope conductances were about 3 times smaller. The mean open times were similar for both states and were fitted by a simple exponential with a time constant of about 2-5 ms at -40 mV. The time constant decreased with more-negative membrane potentials and was 0 9 ms at -100 mV. Openings frequently occurred in bursts separated by longer-lasting closures. The mean closed time during bursts was 1-33 ms at -40 mV.5. Time and amplitude distributions of elementary events were similar for chick and rat sensory neurones and with Ba2+ and Sr2+ replacing external Ca2+. 6. In the potential range examined (from -60 to -30 mV), the first-latency distribution function revealed a distinct rise to peak which occurred at considerably earlier times than peaks of macroscopic currents. The time course of macroscopic l.v.a. Ca2+ currents could be simulated in two ways: (a) by using a five-state Markov-chain model with rate constants estimated from the transition probabilities and dwell times of the channel states, and (b) by evaluating the convolution integral of the first-latency function and the burst open probability of the channel. Both approaches suggest that activation and inactivation are weakly coupled and that the l.v.a. channel of sensory neurones reopens several times before inactivating. during bursts were between 0-2 and 0 3 ms at -50 mV. These currents disappeared in the absence of external Na+. They could be blocked by 5 mM-Ni2+ or 1 mM-Cd2+ and had activation and inactivation properties similar to those of l.v.a. currents.These observations suggest that at a low [Ca2+]0, Na+ ions flow through l.v.a. channels. Increases of external, but not internal, Ca2+ concentration, from 1 x 10-9 to 1 x 10-4 M blocked the Na+ currents through l.v.a. channels with the half-block occurring at a [Ca2+]0 of 2-3 /tM.8. Several types of unitary events were resolved in cell-attached patches formed with pipettes containing 95 mM-BaCl2. At pote...

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“…[2,23], led in the direction of considering that both thermodynamic and kinetic behavior depend upon the free energy rather than on the energy or enthalpy alone. Equation (1) may be considered to be a simple, empirical version of the Eyring equation [24]:…”

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confidence: 99%

The fallacy of Meyer-Neldel temperature as a measure of disorder

Yelon

2012

Monatsh Chem

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The widespread observation of the MeyerNeldel rule has been explained as associated with large activation energies, requiring the accumulation or annihilation of a large number of excitations for a kinetic event to take place. The characteristic Meyer-Neldel or isokinetic temperature is then proportional to the energy of these excitations divided by a coupling constant. For disordered materials at low excitation energies, a similar relation has been proposed, involving the width of bandtails or of Gaussian distributions, a measure of disorder. This similarity has resulted in interpreting high activation energy results, for which it cannot be applicable, using this description. We show that this leads to contradictions with experiments as well as to logical contradictions.

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Kinetics and Mechanism. A Study of Homogeneous Chemical Reactions.

Cited by 50 publications

References 0 publications

Kinetics of oxidation of d(+)melibiose and cellobiose by N-bromoacetamide using a rhodium(III) chloride catalyst

Kinetics of oxidation of d(+)melibiose and cellobiose by N-bromoacetamide using a rhodium(III) chloride catalyst

Single low‐voltage‐activated calcium channels in chick and rat sensory neurones.

The fallacy of Meyer-Neldel temperature as a measure of disorder

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