Template Mixtures

Leuders, T., and Friedrich, M. W. (2003). Evaluation of PGR amplification bias by terminal restriction fragment length polymorphism analysis of smaU-subunit rma and mcra genes by using defined template mixtures of methanogenic pure cultures and soil DNA extracts. Appl. Environ. Microbiol. 69, 320-326. 

To the annealed oligonucleotide/template mixture, add 10pL 10mM ATP, lOpL 25mM dNTPs, 15pL lOOmM DTT, 30 Weiss units T4 DNA ligase, 30 units T7 DNA polymerase. 

Zeolite Beta is normally prepared at high alkaline pH with a templating mixture of Et4N and Na cations which in addition are not specific for this structure [72]. This synthesis can also be carried out in F" medium H = 7-10) with diazabicyclo-octane (DABCO) [73]. While with OH" anions the size of the crystals is generally below about 0.5 pm, in the presence of F" anions and without alkali cations, crystals have a pseudo octahedral morphology with a size up to 10 im(Figure 33.). 

Despite these still-challenging issues, the fabrication of nanotubes using nanoporous hard templates is associated with several advantages beyond the possibility to align them. Readily available porous hosts such as self-ordered porous AAO have a narrow pore diameter (Dp) distribution and pores with Dp-values ranging from about 20 nm up to a few lOOnm. The pore depths (Tp) can be adjusted to values between about 1 im and several 100 xm. Therefore, it is easily possible to tailor the diameter and the aspect ratio of the nanotubes. However, the most important advantage is the possibility to control mesoscopic structure formation processes inside the pores. There are relatively few limitations regarding the materials that can be formed into nanotubes via hard templates. Mixtures, sols, semicrys-... 

The s)mthesis of zeolites is traditionally performed by crystallisation from a sol-gel mixture comprising reagents such as silica, sodium aluminate, sodium hydroxide and water. Another key component of the sol-gel mixture is a base whose main role is to regulate the pH of the mixture. If an organic base is used then a templating effect may also be observed... 

PGR amplification of a DNA sequence is faciHtated by the use of a heat-stable DNA polymerase, Taq polymerase (TM), derived from the thermostable bacterium Thermus aquaticus. The thermostable polymerase allows the repeated steps of strand separation, primer annealing, and DNA synthesis to be carried out ia a single reactioa mixture where the temperature is cycled automatically. Each cycle coasists of a high temperature step to deaature the template strands, a lower temperature annealing of the primer and template, and a higher temperature synthesis step. AH components of the reaction are present ia the same tube. 

Tlie first suggestion of a template effect which was offered in the literature was made by Greene in 1972 °. Tlie illustration of this concept is approximately that shown in Eq. (2.2), above. Greene presented several pieces of evidence in addition to the concept itself. First, he noted that when the final concentration of 18-crown-6 in a reaction mixture (MejSO) was increased from 0.04 At to 0.09 Af, the yield of crown dropped only slightly (84% to 75%). In a competition experiment, equal amounts of 18-crown-6 and 21-crown-7 were formed when one molar equivalent each of triethylene glycol and tetra-ethylene glycol were allowed to compete for triethylene glycol ditosylate (KO-t-Bu/THF). 

Because dideoxynucleotides lack 3 -OH groups, these nucleotides cannot serve as acceptors for 5 -nucleotide addition in the polymerization reaction, and thus the chain is terminated where they become incorporated. The concentrations of the four deoxynucleotides and the single dideoxynucleotide in each reaction mixture are adjusted so that the dideoxynucleotide is incorporated infrequently. Therefore, base-specific premature chain termination is only a random, occasional event, and a population of new strands of varying length is synthesized. Four reactions are run, one for each dideoxynucleotide, so that termination, although random, can occur everywhere in the sequence. In each mixture, each newly synthesized strand has a dideoxynucleotide at its 3 -end, and its presence at that position demonstrates that a base of that particular kind was specified by the template. A radioactively labeled dNTP is included in each reaction mixture to provide a tracer for the products of the polymerization process. 

Some restrictions of this molecular imprinting technique are obvious. The template must be available in preparative amounts, it must be soluble in the monomer mixture, and it must be stable and unreactive under the conditions of the polymer-... 

A number of studies have recently been devoted to membrane applications [8, 100-102], Yoshikawa and co-workers developed an imprinting technique by casting membranes from a mixture of a Merrifield resin containing a grafted tetrapeptide and of linear co-polymers of acrylonitrile and styrene in the presence of amino acid derivatives as templates [103], The membranes were cast from a tetrahydrofuran (THF) solution and the template, usually N-protected d- or 1-tryptophan, removed by washing in more polar nonsolvents for the polymer (Fig. 6-17). Membrane applications using free amino acids revealed that only the imprinted membranes showed detectable permeation. Enantioselective electrodialysis with a maximum selectivity factor of ca. 7 could be reached, although this factor depended inversely on the flux rate [7]. Also, the transport mechanism in imprinted membranes is still poorly understood. 

Simidzu et al.70) carried out template-directed synthesis using various types of templates, e. g neutral ones, 34 (PSt TCT) and PSt TCTC, and cationic ones, such as APVP, 35 (APVP PSt), UPVP PSt, ARPVP, APEI, and 36 (ARPEI). They obtained a large amount of purine-containing oligomers (dimer or trimer) as compared to pyrimidine ones by condensation of nucleotide mixture in the presence of the neutral templates containing pyrimidine bases, such as PSt TCT and PSt TCTC. The authors stated from the results that the existence of the... 

Shimidzu etaL 70 further studied polymerization by using cationic- and purine-containing templates, L e. APVP, ARFVP, APEI, etc. The experimental results are compiled in Table 5. The complementary selectivity was defined by ([pm — [pA])/([pU] + [pA]) x 100 (%) for the equimolar binary monomer mixture... 

Complexes containing encapsulated metal ions (clathrochelates ) with the formula [M(dioxime)3(BR)2] are known with iron(II) 135, cobalt(ll) 136, cobalt(III) 137, and ruthenium(ll) 138 (Fig. 37) [205-220]. Generally, these macrobicyclic complexes are prepared by template synthesis from a mixture of... 

In zeolite synthesis (ref. 2) an aqueous mixture containing a silicon source, an aluminum source, an alkali source (usually NaOH) is autoclaved and subjected to hydrothermal treatment. Hydrated Na-ions are then filling the pore system in the as-synthesized zeolite. In the case of relatively high Si/Al zeolites an organic template is required which is usually a tetraalkylammonium compound, applied as the bromide or the hydroxide. 

The template-directed preparation of cycloi is(paraquat-4,4 -biphenylene (a molecular square ) has been achieved the use of a macrocyclic hydroquinone-based polyether template incorporating an ester moiety in one polyether chain afforded a 1 1 mixture of two topologically stereoisomeric [3]catenanes <96CEJ877>. 

---