Synthesis efficiency

A spin column from the kit is inserted into a 2-mL collection tube, and the sample is pipeted onto the column. The column is centrifuged at 1 l,000g for 1 min, and the flowthrough is saved to evaluate the cDNA synthesis efficiency. The collection tube is discarded in an appropriate container for radioactive waste. 

The Marshall Unker [23] has been widely used to synthesize compounds that can be cleaved by primary and secondary amines to afford the corresponding amides. Marshall linker was used in the synthesis of three or more diversity-site hbraries because it allowed the addition of one more diversity element at the cleavage step. While the original reported linker [23] involved the oxidation of the Unker before cleavage, the efficient release of the resin-bound compounds using nucleophiles from the unoxidized linker has been reported [16, 24]. Similarly to the acid-labile linkers, the kinetics of the cleavage reaction and time required for this reaction directly affect the synthesis efficiency, purity and yield of the final products. A cleavage study was carried out on seven resin-bound thiophenol esters (34—40) on Marshall Unker with 3 amines (41-43) (Scheme 12.11 and Tab. 12.4). 

Because vicinal diamines and 2-aminoalcohols are important components of natural products and medicinal agents, and used as ligands for metal-catalyzed reactions, especially in asymmetric synthesis, efficient methods for the compounds have been extensively investigated over the past decade. " ... 

Many transformations that were inaccessible by traditional organic chemistry are now possible and thus significantly increase synthesis efficiency. In just one step, catalysts enable certain transformations that increase the complexity of the molecules in such a way that it is difficult to recognize the relationship between the product and the starting material. 

It is noted that several of the filtering steps have the added consequence of removing the purely combinatorial-based form to the library. One has to balance two competing priorities synthesis efficiency and screening value. The former makes it easy to generate large libraries, while the latter takes a more accurate measure of molecular properties by eliminating inappropriate product molecules and thus facilitates the specification of a better library. 

Because the decomposition rates are relatively insensitive to temperature, Eq. (18.3) is operated at 130°C to 150°C and 3.0 MPa132 to speed up the ratedetermining step. Excess ammonia, at a ratio of 40 1, is used to minimize the hydrazine-chlorine decomposition. Synthesis efficiency favors a dilute system although the increase in operating cost due to the low concentration may ultimately become inhibiting. The Raschig process is shown in Figure 18.1132. 

Table II. Chemical conpceition, synthesis efficiency, pore filling and framework charge balance of seme pure Nu-10 sarples, synthesized under various experimental...

Sarrple Unit cell conpceiticn of Synthesis efficiency Pore filling Framework charge balance ... 

The chemical analysis allows to calculate the synthesis efficiency in terms of A1 incorporation for all samples. In 8 cases, Nu-10 was prepared with nearly 100% efficiency, while 5 other samples show a more important lattice A1 incorporation than that predicted from the gel composition (Figure 1). 

The next remarkable observation was the close correlation between the synthesis efficiency and the pore filling by the organics incorporated during synthesis. The filling of each sample was calculated from host and guest geometries as follows. 

Note that the presence of cristobalite as side phase does not influence this behavior (samples 4 and 9). The only consequence due to its formation (probably induced by other variables) is the decrease of the overall Si content in the gel. This does not seem to affect the Nu-10 synthesis efficiency, provided the gel composition is recalculated adequately (Table II). 

The other situation supposes the formation of stable rings that contain the maximum number of A1 atoms, from a Si-rich gel. This can be a slow process, kinetically limited by the slow A1 incorporation stemming from A1 poor gel phases. Such a system will yield a limited number of Al-rich zeolite nuclei with a fairly low rate. In such a case, a poor "synthesis efficiency", i.e. poor correlation between the Si/Al atomic ratio in the gel and that of the final zeolite, is observed (52) "Figure 5". 

Fig 5 Relationship between Si/Al ratio in the gel and in a series of faujasite zeolite samples crystallized from it example of poor synthesis efficiency (adapted from ref. 53) ... 

Formation of taurine chloramines and of other small-molecular-weight amines accounts for 90% of all chloramine output in stimulated PMNs (G24). Chloramine synthesis efficiency approaches 100% of the stoichiometic amount of HOC1 employed (W5). Though HOC1 reacts spontaneously, with taurine as a chlorine donor, taurine chloramine production in the presence of MPO is one order of magnitude faster than the spontaneous one (k = 4.4 x 105 versus k = 2.8 x 106 M-1s-1). This indicates that the MPO-mediated taurine chlorination reaction may involve an enzyme intermediate species rather then free HOC1. 

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