Deuterium isotope effect on the dissociation of weak acids in water and deuterium oxide

Robinson, R. A.; Paabo, Maya; Bates, Roger G.

doi:10.6028/jres.073a.025

Cited by 41 publications

(42 citation statements)

References 21 publications

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“…The apparent pK a ap of 3.1 is smaller than the value determined (17) from the optical spectra (3.8). Although the optical titration was performed on solutions in H 2 O, while the present data are obtained in D 2 O, this is unlikely to be the cause of the difference, since for the present pK a ap value, determined from noncorrected pH meter readings, the variations of the pK a (D 2 O) are expected to compensate the pH readings variations (38,39) and fall within the error limits of the experiment. We ascribe the difference between the two pK a values to experimental uncertainty caused by the instability of the protein below pH 3.5.…”

Section: Dynamics Of Cu(ii) and Co(ii) M121h Azurinmentioning

confidence: 73%

The Dynamic Properties of the M121H Azurin Metal Site as Studied by NMR of the Paramagnetic Cu(II) and Co(II) Metalloderivatives

Salgado¹,

Kroes²,

Berg³

et al. 1998

Journal of Biological Chemistry

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The M121H azurin mutant in solution presents various species in equilibrium that can be detected and studied by 1 H NMR of the Cu(II) and Co(II) paramagnetic metalloderivatives. In both cases up to three species are observed in slow exchange, the proportions of which are different for the two metalloderivatives. Above pH 5 the major species displays a tetrahedral coordination in which the His 121 can be observed as a coordinated residue. Its metal site corresponds to a new type of site that is defined as a type 1.5 site. The second and third species resemble the wild type (type 1) azurin and, above pH 4.5, they are present only at a low concentration. At low pH a protonation process increases the proportion of both type 1 species at the expense of the type 1.5 species. This process, characterized by a pK a ‫؍‬ 4.3, is assigned to the protonation of His 121 . At high pH the NMR spectrum of the Co(II)-M121H azurin experiences an additional transition, which is not observed in the case of the Cu(II) protein. The dynamic properties of the M121H metal site appear to be related to changes in the coordination geometry and the strength of the axial interaction between the N ␦1 (His 121 ) and the metal.An important challenge in protein engineering is the creation or modification of metal sites in proteins (1, 2). Properties that one might wish to manipulate range from metal binding strength and metal site stability to redox potential, catalytic activity, and substrate specificity. One way to meet this task is the creation of novel metal binding sites in proteins or protein domains that in their native state have no such site (3-7). This approach depends heavily on computer-assisted modeling and automated searches for appropriate attachment sites of side chains that can act as metal ligands. The side chains must be able to attain an orientation that is favorable for strong metal binding while at the same time leaving sufficient room for possible substrate binding. The method is demanding and success is not within easy reach, but when successful the result can be spectacular (3-7).A second approach makes use of natural metalloproteins and modifies existing metal sites by applying changes in the first and second coordination shell of the metal (1, 8). The advantage of this approach is that it is relatively easy to implement and that the native site provides a solid background against which

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Section: Dynamics Of Cu(ii) and Co(ii) M121h Azurinmentioning

confidence: 73%

The Dynamic Properties of the M121H Azurin Metal Site as Studied by NMR of the Paramagnetic Cu(II) and Co(II) Metalloderivatives

Salgado¹,

Kroes²,

Berg³

et al. 1998

Journal of Biological Chemistry

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“…K, for phthalic acid and trifluoroacetic acid in D 2 0 were not available, therefore values were estimated using Rule and LaMer's law (16) and the data of Bates et al (13). In order to test the reliability of the assumptions, tests of variation in observed It0 values with changes in K, values were made.…”

Section: R + Amentioning

confidence: 99%

Neutral Solvolysis of Acyl Carbon and the Temperature Dependence of the Kinetic Solvent Isotope Effect

Rossall¹,

Robertson²

1975

Can. J. Chem.

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The temperature dependence of the rate of hydrolysis of benzoic, phthalic, and succinic anhydrides have been determined in H2O and D2O under "neutral" conditions. Corresponding data have been obtained for methyl trifluoroacetate. While both series supposedly react by the same BAc2 mechanism, remarkable differences are made obvious by this investigation. Possible sources of such differences are proposed.

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“…Ka for ionization of propionic acid in D 2 0 was estimated by interpolation of ApK, from the ApKa us. pKa (H20) plot Robinson, Paabo, and Bates (23).…”

Section: Calculationmentioning

confidence: 99%

Kinetic Solvent Isotope Effect for the Spontaneous Solvolysis Acetic and Propionic Anhydrides

Robertson¹,

Rossall²,

Redmond³

1971

Can. J. Chem.

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The large kinetic solvent isotope effects for the neutral hydrolysis of acetic and propionic anhydride show unusual temperature dependency; the former passing through a maximum at about ISo, the latter showing a minimum at 30". This unusual temperature dependency is the consequence of widely different values of the apparent ACp* in H 2 0 and D 2 0 : the value for acetic anhydride in H,O being -74 f 2 cal deg-' mol-' but -32 + 4 in D 2 0 . The corresponding values for propionic anhydride being -31 + 2 in H 2 0 but -94 f 10 in D20. The implications of these differences are discussed.L'importance des effets isotopiques cinktiques dans l'hydrolyse en milieu neutre d'anhydride acetique et propionique depend Ctrangement de la temperature; le premier passe par un maximum a environ 15" tandis que le dernier presente un minimum a 30". Cette dependance inhabituelle par rapport a la temperature est la conskquence des valeurs tres differentes du ACp* apparent dans H 2 0 et D 2 0 : la valeur pour l'anhydride acetique dans H 2 0 etant de -74 t 2 cal deg-' mol-' mais de -32 + 2 dans D20.Les valeurs correspondantes pour I'anhydride propionique sont de -31 k 2 dans H 2 0 mais -94 f 10 dans D 2 0 . Les consequences de ces differences sont discutees. Canadian Journal of Chemistry, 49, 3665 (1971) IntroductionThe spontaneous hydrolysis of carboxylic acid anhydrides have been widely studied (1-10). The reaction is characterized by large kinetic solvent isotope effects (k.s.i.e. = kHZo/kD2,) and large negative entropies of activation (AS*). Such results were interpreted as being consistent with the requirements of a general base catalyzed mechanism, BAc2, and were taken to imply (1 1) that more than one water molecule was tightly constrained in the transition state. Our interest in the effect of temperature on solvolytic rates led initially to an investigation of the temperature dependency of the large kinetic solvent isotope effect for acetic anhydride.The experimental problem simply required that we extend the careful investigation of Gold (5) over a wide temperature range and obtain a complementary set of rate data in D,O. The results were so surprising that we were led to extend our investigation to study the hydrolysis of propionic anhydride and to other anhydrides. In this paper we report our findings for the hydrolysis of acetic and propionic anhydride.

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Deuterium isotope effect on the dissociation of weak acids in water and deuterium oxide

Cited by 41 publications

References 21 publications

The Dynamic Properties of the M121H Azurin Metal Site as Studied by NMR of the Paramagnetic Cu(II) and Co(II) Metalloderivatives

The Dynamic Properties of the M121H Azurin Metal Site as Studied by NMR of the Paramagnetic Cu(II) and Co(II) Metalloderivatives

Neutral Solvolysis of Acyl Carbon and the Temperature Dependence of the Kinetic Solvent Isotope Effect

Kinetic Solvent Isotope Effect for the Spontaneous Solvolysis Acetic and Propionic Anhydrides

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