Sticky terminals

Much larger planar periodic structures have been obtained by symmetrised interactions of DX-type sticky DNA stars. Figure 16a, d shows three-arm [72] and four-arm [73] DNA stars constructed by paired double helices both with N = 22 long arms and N = 4 long sticky terminals. These structures are symmetric for, respectively, threefold and fourfold rotations but they are not mirror-symmetric. The lack of mirror symmetry favors deviations of the constructs from perfect flatness the center of the star may not be in the same plane as the arm tips. For this reason, in both cases the DNA constructs have been designed so that their arms stick end-to-end in such a way that each star interacts only with stars turned upside... 

As the second educt (B), the plasmid ONA with complementary sticky ends is prepared separately. In the first step the isolated plasmid DNA is cut open by a special type of enzyme called restriction endonuclease. It scans along the thread of DNA and recognizes short nucleotide sequences, e.g., CTGCAG, which ate cleaved at a specific site, e.g., between A and G. Some 50 of such enzymes are known and many are commercially available. The ends are then again extended witfa he aid of a terminal transferase by a short sequence of identical nucleotides complementary to the sticky ends of educt (A). 

Figure 6-11. Representation of the sticky patch (A) on hemoglobin S and its "receptor" (A) on deoxyhemoglobin A and deoxyhemoglobin S. The complementary surfaces allow deoxyhemoglobin S to polymerize into a fibrous structure, but the presence of deoxyhemoglobin A will terminate the polymerization by failing to provide sticky patches. (Modified and reproduced, with permission, from Stryer L Biochemistry, 4th ed. Freeman, 1995.)...

After an iPP particle reached the FBR, co-polymerization of ethylene-propylene starts preferrably inside the porous PP matrix. Depending on the individual residence time, the particle will be filled with a certain amount of ethylene-propylene rubber, EPR, that improves the impact properties of the HIPP. It is important to keep the sticky EPR inside the preformed iPP matrix to avoid particle agglomeration that could lead to wall sheeting and termination of the reactor operation. Ideally a "two phase" structure, see Fig.5.4-3, is produced. Finally, a "super-high impact" PP results that contains up to 70% EPR. How much EPR is formed per particle depends on three factors catalyst activity in the FBR, individual particle porosity, and individual particle residence time in the FBR. All particle properties are therefore influenced by the residence time distribution, and finally, a mix of particles with different relative amounts of EPR is produced - a so called "chemical distribution" see, for example, [6]. 

Note. The results presented in Table I were obtained using solutions of 5g PAA of molecular weight 1 x 10 in 500 cm ethanol and 280 cm water containing lg BzP. All of the polymerisations were performed at 78 C. Conversions to PST in the 8 hours allowed for the experiments was 100% in all cases except that using the highest styrene concentration. In this case a sticky precipitate was produced instead of a latex and the experiment was terminated after 1 hour). 

Fig. 8 Schematic representation of DNA junctions and crossover tiles. Motif 1 is a branched DNA junction with three arms and motif 2 with four arms. Every terminal in the arm is an unpaired ssDNA. The ssDNA acts as sticky ends , which may pair with another complementary strand. The two motifs 3 and 4 are two different antiparallel double-crossover molecules containing an even number of half-helical turns between branch points (DAE) or an odd number (DAO). They are more stable and thus usually applied. Oligonucleotide strands are individually represented with different colors...

After treatment with water to dissolve out the magnesium salts, and after evaporation of the ether which generally is used as solvent, sticky resinous polymers are left. Their rather low melting point (about 100°) suggests that the phenylene-silicon chains are rather short, and probably they are terminated by methyl groups or by phenyl groups derived from the hydrolysis of structures like Si—CeH4MgBr. 

Macroscopic solvent effects can be described by the dielectric constant of a medium, whereas the effects of polarization, induced dipoles, and specific solvation are examples of microscopic solvent effects. Carbenium ions are very strong electrophiles that interact reversibly with several components of the reaction mixture in addition to undergoing initiation, propagation, transfer, and termination. These interactions may be relatively weak as in dispersive interactions, which last less than it takes for a bond vibration (<10 14 sec), and are thus considered to involve "sticky collisions. Stronger interactions lead to long-lived intermediates and/or complex formation, often with a change of hybridization. For example, onium ions are formed with -donors. Even stable trityl ions react very rapidly with amines to form ammonium ions [41], and with water, alcohol, ethers, and esters to form oxonium ions. Onium ion formation is reversible, with the equilibrium constant depending on the nucleophile, cation, solvent, and temperature (cf., Section IV.C.3). 

Note that the insert and plasmid need to be specially modified to link together. "Sticky ends" must first be attached to the insert and the plasmid. The sticky ends attached to the linear insert consist of stretches of deoxycy tidy lie acid (CCCCCCC), The sticky ends attached to the linear plasmid consist of stretches of deoxyguanidylie acid (GGGGGGGG) The sticky ends consisting of "CCCCCCC" can hybridize with those consisting of "GGGGGGGG." The result is a closed, circular dsDNA. The sticky ends are attached to the insert and plasmid by terminal transferase. Terminal transferase catalyzes the attachment of nucleohdes to one end of a linear DNA molecule. 

Tails of poly dC are added to the ds DNA. Terminal transferase is used to catalyze the addition of poly dC sticky ends to the insert. 

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