Repetitive oligomers

Sequencing of telomeres from a dozen or so organisms, including humans, has shown that most are repetitive oligomers with a high C content in the strand with its 3 end at the end of the chromosome. The telomere repeat sequence In humans and other vertebrates is TTACCC. These simple sequences are repeated at the very termini of chromosomes for a total of a few hundred base pairs in yeasts and protozoans and a few thousand base pairs in vertebrates. The 3 end of the C-rich strand extends 12-16 nucleotides beyond the 5 end of the complementary C-rich strand. This region is bound by specific proteins that both protect the ends of... 

We succeeded in showing that recycling of the enzyme was indeed possible in our IL solvent system, though the reaction rate gradually dropped with repetition of the reaction process. Since vinyl acetate was used as acyl donor, acetaldehyde was produced hy the hpase-catalyzed transesterification. It is well known that acetaldehyde acts as an inhibitor of enzymes because it forms a Schiff base with amino residue in the enzyme. However, due to the very volatile nature of acetaldehyde, it easily escapes from the reaction mixture and therefore has no inhibitory action on the lipase. However, this drop in reactivity was assumed to be caused by the inhibitory action of acetaldehyde oligomer which had accumulated in the [bmim][PFg] solvent system. In fact, it was confirmed that the reaction was inhibited by addition of acetaldehyde trimer. =... 

If the oxo (or methano) bridges are not exclusively syn to one another in either the bis-dienophiles or bis-dienes, then the pressure-induced repetitive Diels-Alder reactions (proceeding again highly stereoselectively) produce rigid ribbon-type oligomers on a nanometer scale (Scheme 10 entry 1). Bis-diene 45 reacts less stereoselectively than bis-diene 44 and forms with bis-dienophiles such as 46 the ribbon-type oligomers 47... 

Oxidative Polymerization Reactions. Clays can initiate polymerization of unsaturated compounds through free radical mechanisms. A free radical R", which may be formed by loss of a proton and electron transfer from the organic compound to the Lewis acid site of the clay or, alternatively, a free radical cation, R+, which may be formed by electron transfer of an electron from the organic compound to the Lewis acid site of the clay, can attack a double bond or an aromatic ring in the same manner as an electrophile. The intermediate formed is relatively stable because of resonance, but can react with another aromatic ring to form a larger, but chemically very similar, species. Repetition of the process can produce oligomers (dimers, trimers) and, eventually, polymers. 

Fig. 15 Schematic drawing of the formation of amyloid fibrils, (a) Monomeric insulin having an a-helical conformation, (b) [i-sheet (arrows) rich oligomers are being formed, (c) Amyloid fibrils having a diameter around 10 nm are being formed, (d) Higher magnification of the intrinsic repetitive (S-pIcatcd sheet structure of the amyloid fibril. The pictures were taken by transmission electron microscopy (TEM)...

Oligomer molecule, the structure of which essentially comprises the repetition of a single constitutional unit with all units connected identically with respect to directional sense. 

Smallest constitutional unit, the repetition of which constitutes a regular macromolecule, a regular oligomer molecule, a regular block, or a regular chain. 

According to the IUPAC nomenclature, oligomers1 are molecules containing a few constitutional units repetitively linked to each other. This does not define any specific molecular weight or degree of polymerization. It states, however, that the physical properties of oligomers vary with the addition or removal of one or several units. 

Repetition of this work with a similar C 18 column (250x4.0 mm dQ = 6 nm dP = 5 pm) clearly showed the presence of stereoisomers in oligomers with 4-8 repeat units, separated from a PS 600 standard 14), but the resolution was not as good as in comparable work on plain silica 461, vide supra. 

AT DNA double strand oligomers with sodium counterions and a length of 20 base pairs were obtained from Biotherm, and were dissolved in water and dried on a CaF2 window at 293 K in an atmosphere of 52% relative humidity (saturated solution of NaHSC. IDO at 20° Celsius [60]). This results in DNA samples with approximately 4 to 6 water molecules per base pair [37] (sample thickness 6.5 pm). It has been reported that under these conditions AT DNA oligomers adopt the B -form [35], Femtosecond time-resolved IR pump-probe experiments were performed with two independently tunable femtosecond pulses generated by parametric conversion processes pumped by a regenerative Ti sapphire laser system (800 nm, repetition rate 1 kHz, pulse duration 100 fs) [61]. The central frequency of the pump pulse was varied from 1630 to 1760 cm-1 and the probe was centred around 1650 cm-1 or 3200... 

Repetitive coupling of acetylenes with aryl halides is an effective way to directly build hyperbranched architecture in a stepwise manner. This type of polycoupling is often catalyzed by palladium complexes in the presence of amines and has been widely used for the preparation of well-defined oligomers, linear polymers, and perfectly branched dendrimers [19,20]. 

In the next step, 3 could insert into one of the C H bonds of 1 to provide vinylacetylene (4, butenyne), a compound that is indeed generated when 1 is pyrolyzed. Repetition of the carbene formation step could then produce 5, which, by another insertion step, would lead to hexa-l,3-dien-5-yne (6, mixture of isomers). This is already an isomer of benzene, and that it can cyclize to 2 was shown by us many years ago [6]. Obviously, 6 could also be a precursor of styrene and other oligomers of 1. The mechanism proposed in Scheme 2 could also be of importance in connection with soot formation from smaller hydrocarbon fragments, and account for the formation of 2 in interfeller space. 

The two units 59 and 60 could then be coupled to give 61 and, by repetition of this sequence, oligomers such as 62 were obtained, which, in the terminating step to yield 63, were... 

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