Provenance determination, general

Earlier it was stated that provenance determination is inherently more complex for pottery than for obsidian. In general, pottery itself rather than clay is used as source material to establish the composition of pottery that was made locally. 

The goals and the final quantities to be obtained determine the method to be used. As a first approach, it is always worth checking if a documented and proven method exists. Standardized methods are often the best. They are developed by experts in the field and are usually of a high quality and are well documented. Frequently no standards can be applied and generally known methods have to be relied on. Sometimes situations occur when the whole of the measurement procedure has to be tailored for the specific situation. This is a very demanding task and considerable experience is required. 

The most common measure of polarity used by chemists in general is that of dielectric constant. It has been measured for most molecular liquids and is widely available in reference texts. However, direct measurement, which requires a nonconducting medium, is not available for ionic liquids. Other methods to determine the polarities of ionic liquids have been used and are the subject of this chapter. However, these are early days and little has been reported on ionic liquids themselves. I have therefore included the literature on higher melting point organic salts, which has proven to be very informative. 

Kinetics of chemical reactions at liquid interfaces has often proven difficult to study because they include processes that occur on a variety of time scales [1]. The reactions depend on diffusion of reactants to the interface prior to reaction and diffusion of products away from the interface after the reaction. As a result, relatively little information about the interface dependent kinetic step can be gleaned because this step is usually faster than diffusion. This often leads to diffusion controlled interfacial rates. While often not the rate-determining step in interfacial chemical reactions, the dynamics at the interface still play an important and interesting role in interfacial chemical processes. Chemists interested in interfacial kinetics have devised a variety of complex reaction vessels to eliminate diffusion effects systematically and access the interfacial kinetics. However, deconvolution of two slow bulk diffusion processes to access the desired the fast interfacial kinetics, especially ultrafast processes, is generally not an effective way to measure the fast interfacial dynamics. Thus, methodology to probe the interface specifically has been developed. 

It was already assumed in Chapter 1 that readers are familiar with the methods for determining the derivatives of algebraic functions. The general rules, as proven in all basic calculus courses, can be summarized as follows. 

The Gd-H distance, /-GdH, which enters at the inverse sixth power into the expression of inner-sphere relaxivity, is a difficult parameter to obtain experimentally. It is generally estimated on the basis of Gd-coordinated water oxygen distances, determined by solid-state X-ray analysis. Solid-state distances are good estimates of the aqueous solution state, as was experimentally proven by an X-ray absorption fine-structure study on [Gd(D0TA)(H20)] and [Gd(DTPA)(H20)]2, which gave identical values for the Gd-0 distances for both complexes in solid and solution states.20... 

The efficiency of this approach could be demonstrated in a-fucosylation with donor 32a and the acceptors 19C and 33A-D (Table XXXIII). Thus, with the help of this inverse procedure, the versatile building blocks for syntheses of the Lea, Le, Ley, and H antigen determinants are readily accessible (176). Presumably, this procedure may become of general importance when reactive glycosylating agents are employed. Alternatively, the reactivity of the fucosyl donor could be decreased, as has been recently proven very successfully (177). 

We have studied several triatomic compounds of general formula XUY, where X, Y = C, N, O, and U is the uranium atom in the formal oxidation state 4+, 5+, or 6+. We have determined the vibrational frequencies for the electronic ground state of NUN, NUO+, NUO, 0U02+, and OUO+61 and have compared them with the experimental measurements performed by Zhou and coworkers.62 The CASSCF/CASPT2 method has proven to be able to reproduce experimental results with satisfactory agreement for all these systems. 

Cobalt, as its CpCo(CO)2 complex, has proven to be especially suited to catalyze [2 + 2 + 2] cycloadditions of two alkyne units with an alkyne or alkene. These cobalt-mediated [2 + 2 + 2] cycloaddition reactions have been studied in great detail by Vollhardt337. The generally accepted mechanism for these cobalt mediated cycloadditions, and similar transition metal mediated cycloadditions in general, has been depicted in equation 166. Consecutive co-ordination of two triple bonds to CpCo(CO)2 with concomitant extrusion of two molecules of carbon monoxide leads to intermediates 578 and 579 via monoalkyne complex 577. These react with another multiple bond to form intermediate 580. The conversion of 578 to 580 is said to be kinetically favored over that of 579 to 580. Because intermediates like 580 have never been isolated, it is still unclear whether the next step is a Diels-Alder reaction to form the final product or an insertion to form 581. The exact circumstances might determine which pathway is followed. 

It was proven that microcalorimetry technique is quite well developed and very useful in providing information on the strength and distribution of acidic and basic sites of catalysts. When interpreting calorimetric data, caution needs to be exercised. In general, one must be careful to determine if the experiments are conducted under such conditions that equilibration between the probe molecules and the adsorption sites can be attained. By itself, calorimetry only provides heats of interaction. It does not provide any information about the molecular nature of the species involved. Therefore, other complementary techniques should be used to help interpreting the calorimetric data. For example, IR spectroscopy needs to be used to determine whether a basic probe molecule adsorbs on a Brpnsted or Lewis acid site. 

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