Kinetics and mechanisms, in solution

Fig. 3.6 Some of the experimental methods available for the study of kinetics and mechanisms in solution, classified according to their approximate time resolution.

We will first describe some of the theoretical aspects for cocrystal design, followed by a summary of the pharmaceutical properties of cocrystals, including their solubility dependence on cocrystal component concentration and in some cases on solution pH. Processes for cocrystal formation will be presented by considering the factors that control cocrystallization kinetics and mechanisms in solution and in solid-state mediated processes. This article will be useful to the reader who wishes to anticipate cocrystal formation during pharmaceutical processes and storage and to those who wish to proactively discover new phases. 

In this volume, the format, coverage, and approach in dealing with various aspects of Inorganic Reaction Mechanisms are similar to those adopted for the previous volumes of the series. Once again, rather than make an attempt at cataloguing all the articles in which mention is made of mechanism, we have chosen (with an eye on volume size and cost ) to concentrate on papers in which kinetics and mechanisms in solution form the principal interest. This policy inevitably leads to mention of some papers being cursory with a consequent loss of subtlety. It is our hope, however, that any resultant oversimplification or misrepresentation is minimal. Review articles cited are those which should be accessible to the great majority of readers. 

ABSTRACT E QcXnc field effects in macromolecular organizations such as proteins, nucleic acids, and membranes frequently involve both chemical-conformational changes and physical-orientational displacements of molecular subgroups. Electro-optic techniques in conjunction with relaxation kinetics in high electric fields provide a tool for the investigation of the complex processes encountered in bioelectric phenomena on the level of macromolecules, membrane fragments, and other cellular units. Whereas Part I covers the thermodynamics of electric field effects, this part deals with practical and theoretical aspects of kinetics and mechanisms in aqueous solutions of macromolecules and membranes. 

VIL Villetti, M.A., Soldi, V., Rochas, C., and Borsali, R., Phase-separation kinetics and mechanism in a methylcellulose/salt aqueous solution studied by time-resolved small-angle light scattering (SALS), Macro/wo/. Chem. Phys., 212, 1063, 2011. 

The differenee in reaction rates of the amino alcohols to isobutyraldehyde and the secondary amine in strong acidic solutions is determined by the reactivity as well as the concentration of the intermediate zwitterions [Fig. 2, Eq. (10)]. Since several of the equilibrium constants of the foregoing reactions are unknown, an estimate of the relative concentrations of these dipolar species is difficult. As far as the reactivity is concerned, the rate of decomposition is expected to be higher, according as the basicity of the secondary amines is lower, since the necessary driving force to expel the amine will increase with increasing basicity of the secondary amine. The kinetics and mechanism of the hydrolysis of enamines demonstrate that not only resonance in the starting material is an important factor [e.g., if... 

This review is devoted to the study of the kinetics and mechanisms of the direct esterification of carboxylic adds with alcohols. The results which are analyzed here concern esterifications and linear polyesterifications between small molecules or oligomers in solution or in bulk. We will examine the following points ... 

The kinetics and mechanism of formation of 2,3-naphthotriazole (6.49) were studied by Oh and Williams (1989). In aqueous solutions of 0.2-1.0 m HC104 the dependence of the reaction on acidity indicated simultaneous involvement of the protonated and unprotonated substrates (6.47 and 6.48 respectively). The unproton-ated form of 2,3-diaminonaphthalen (6.48) reacts with the nitrosyl ion (NO+) on encounter (rate constant k ). The 2-NH3 substituent reduces the reactivity of 6.47 by a factor of about 800 (ki/k2). The rate-limiting formation of the diazonium ion (Scheme 6-33) is followed by a rapid cyclization (Scheme 6-34). 

Kinetics and mechanism of alkali ion complex formation in solution. R. Winkler, Struct. Bonding (Berlin), 1972,10,1-24 (38). 

Winkler R (1972) Kinetics and Mechanism of Alkali Ion Complex Formation in Solution. W 1-24... 

The kinetics and mechanism of the growth of anodic silver sulfide films on silver metal in aqueous sulfide solutions has been studied under potentiodynamic conditions [162], The Ag2S film formation was presumed to proceed as... 

K. W. Sykes, in Kinetics and Mechanism of Inorganic Reactions in Solution, Chemical Society, London, 1954, p. 64. 

Photoemission phenomena are of great value for a number of areas in electrochemistry. In particnlar, they can be used to study the kinetics and mechanism of electrochemical processes involving free radicals as intermediates. Photoemission measurements can be also used to study electric double-layer structure at electrode surfaces. For instance by measuring the photoemission current in dilute solution and under identical conditions in concentrated solutions (where we know that / = 0), we can find the value of / in the dilute solution by simple calculations using Eq. (29.9). 

Chiang, Y. Kresge, A. J. Hellrung, B. Schunemann, P Wirz J. Flash photolysis of 5-methy 1-1,4-naphthoquinone in aqueous solution kinetics and mechanism of photoenoli-zation and of enol trapping. Helv. Chim. Acta 1997, 80, 1106-1121. 

Mandich, N.V. and Vyazovikina, N.V., Kinetics and mechanisms of the chromium anodic dissolution in the chromium plating solution in the transpassive range, 47th Meeting of International Society for Electrochemistry, Veszprem, Hungary, September 1996. 

The nature of Agn in solution and the kinetics and mechanisms of Ag11 oxidations of a variety of inorganic and organic substrates have been studied, complexes [Ag(Py)4]2+ and [Ag(bipy)2]2+ are typical examples.212-215... 

Tang WZ, An H (1995) Photocatalytic degradation kinetics and mechanism of acid blue 40 by UV/Ti02 in aqueous solution. Chemosphere 31 4171-4183... 

The kinetics and mechanisms of the C —> G transition in a concentrated solution of PS-fr-PI in the PS-selective solvent di-n-butyl phthalate was studied [137,149]. An epitaxially transformation of the shear-oriented C phase to G, as previously established in melts [13,50,150], was observed. For shallow quenches into G, the transition proceeds directly by a nucleation and growth process. For deeper quenches, a metastable intermediate structure appears, with scattering and rheological features consistent with the hexag-onally perforated layer (PL) state. The C -> G transition follows the same pathways, and at approximately the same rates, even when the initial C phase is not shear-oriented. 

---