Template ratios

These amounts may need to be altered if the reaction is not successful using these guidelines. The optimum reaction conditions may require different primer/template ratios and these can only be determined empirically... 

Fig. 1 Influence of aniline to template ratio on conductivity for enzymatic PANI/DODD (diamonds) and enzymatic PANI/DBSA (squares). (Reprinted with permission from Rumbau et al. [38], (g) 2007, Elsevier)...

Experimental results (Fig. 1) show that for PANI/DODD and PANI/DBSA synthesized under the same conditions, the conductivity of the PANI/DODD complex is indeed higher than that of the PANI/DBSA. Furthermore, the DODD template allows the use of a higher aniline to template ratio before precipitation occurs. PANI/DBSA complexes show precipitation at ratios close to 2.5 1 whereas PANI/DODD complexes remain in solution even at a ratio of 4 1. 

Combinatorial MIP development can be speeded up considerably by using experimental design approaches [27-31]. These allow one to identify the most significant factors determining the performance of imprinted polymers (for example the degree of cross-linking, the monomer template ratio, the initiator... 

Moreover, high enantioselectivity has been reported for an MIP that was selective for Z-glutamate [33]. Here, changes in the UV-vis absorbance of the l-(4-styryl)-3-(3-nitrophenyl)urea monomer were monitored, as opposed to the previous studies where the intrinsic absorbance of the template was measured. The UV-vis spectroscopy titration of the functional monomer with different concentrations of the template in solution led to a bathochromic shift from 349 to 364 nm. The colour change of both the solution and the resulting bulk polymer upon addition of Z-glutamate was visible even to the naked eye, with a 1 1 monomer-to-template ratio demonstrated. 

The preparation of imprinted polymers based on imidazole was also recently reported by Li et al. [41], who used essentially the same system as Mosbach to investigate the effect of the monomer-template ratio on catalytic specificity. 

Table 6.10 Template ratios for the formation of 6.98 (n = 1, R = CH2CH2Ph) by a variety of guest species, and relative stabilities of the resulting carceplexes in nitrobenzene

From your reading of Section 6.7, guess possible values for the template ratios for the synthesis of 6.98 in NMP in the presence of the following guests. Consider the influence of molecular size and shape, as well as host-guest interactions such as C— FI hydrogen bonds, n-nstacking etc. 

Table 3 Template ratios were obtained from a series of competition experiments whereby the conversion of 13 into [14 guest1] and [14 guest2] was monitored in NMP solvent at 60°C...

Templating molecule Template ratio Guest volume (A3) Packing coefficient (%)... 

Fig. 9 An excellent linear relationship (R2 = 0.99) between template ratios TRn for obtaining [14 guest] from resorcinarene 13 and monobridged A-[14] intermediate is evident from the plot.85...

Table 4 Relative thermodynamic stabilities (log A rel at 298 K) of [132 guest] and template ratios (TRU at 333 K) for the formation of [14 guest] were determined and normalized to NMP88...

Fig. 10 Apparently, there existed a good linear relationship between template ratios (TRi 1) for obtaining [14 guest] and relative thermodynamic stabilities log Km of [132 guest].

Table 5 Template ratios TRn were for guests 17-22 measured in IV-formylpiperidine (NFP) at 343.0 K...

Table 6 Template ratios TR13 were for tris-acetylene 17, competing with multiple solvent molecules for templating the formation of capsule 15, measured in various solvents at different temperatures95...

Guesti Guest2 Template ratio, TRi3 (M2) Solvent Temperature (K)... 

Bulk imprinted polymers [38] Various combinations of porogens, functional monomers (MAA and DEAEMA) and functional monomer/template ratios were compared and the most selective MIP was that obtained using a mixture of DEAEMA, CAP (functional monomer template ratio 2 1) and EDM A in THF. The mixture was polymerised, washed and particles sized to 25-63 m in diameter were packed into HPLC columns. 

In situ-imprinted polymers [39] To further simplify construction of such sensors we investigated the use of in situ or rod imprinted polymers using the technique pioneered by Matsui et al. (see Chapter 13). Solutions of template, either DEAEMA or AA as functional monomers, EDMA and initiator in the porogen (4 1 octanohdodecanol, w/w) were introduced into 100 x 4.6 mm (i.d.) HPLC columns and polymerised in situ at either 50 or 70°C. These rods were then flushed with MeCN until a stable absorbance and back pressure were obtained. The most selective polymers were those polymerised at 50°C using DEAEMA as the functional monomer, with a functional monomer/template ratio of either 2 1 or 4 1. The latter was chosen for use in the sensor so as to directly compare the results obtained using bulk and in situ imprinted polymers. 

Organic Molecularly imprinted polymers Functional monomer(s) Template concentration Cross-linker Porogen Monomer(s)/template ratio Physical conditions during polymerization... 

The next step in the protocol is the computation of monomer-template ratio performed by simulated annealing using a molecular dynamics approach (for detailed description see Sect. 2.2). 

Other variables in the imprinting process are stoichiometry and temperature, which are particularly important in the cases of noncovalent imprinted polymers. Lower temperatures and higher functional monomer to template ratios stabilize noncovalent prepolymerization complexes, resulting in noncovalent MIPs with higher capacities and selectivities. The imprinting process can be carried out at lower temperatures by either UV initiated radical polymerizations or by using azo-based radical initiators. 

Fish WP, Ferreira J, Sheardy RD, Snow NH, O Brien TP (2005) Rational design of an imprinted polymer maximizing selectivity by optimizing the monomer-template ratio for a cinchonidine MIP, prior to polymerization, using microcalorimetry. J Liquid Chromatogr. Related Technol 28(1) 1—15... 

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