Threading statistical

The concept of producing molecular systems linked in the above mechanical manner is not new. In fact, the construction of a catenane has been pre-empted by Nature. The occurrence of duplex circular DNA in a catenane form is well established - with the interlinking of two double stranded DNA rings being effected enzymatically.  

Schill, Catenanes, Rotaxanes and Knots, Academic Press, New York, 1971. 

Wasserman This was the first characterised catenane it was prepared by statistical threading, not self-assembly 

Other procedures - often multistep - have also been employed to obtain cate-nanes. However, although useful as a comparison, these procedures are of marginal relevance to the present discussion since they are not primarily based on self-assembly principles.  

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Figure 5. Tying a knot in the course of the cyclization reaction of a linear molecule A-B after statistical threading.

Thus it is obvious that statistical threading is not a very effective approach. However, it is still very useful because an alternative route might not exist for some specific polyrotaxanes with certain chemical compositions. And according to the model study by Joyce et al. [72], the calculated percentage of cyclic polydi-methylsiloxane threaded onto linear siloxane is between 0.2 and 0.3 for a 30-... 

After the very early achievements due to the real pioneers of chemical topology who forty years ago first acceeded to that intriguing molecule that is a catenane (by statistical threading approach Wasserman, 1960 or by a directed approach Liittringhaus and Schill, 1964), this peculiar field of research concerned with molecules whose prime feature rests without doubt on beauty and non trivial spacial arrangement, has in the beginning of the 80 s literaly exploded with the apparition of various templated approaches. 

Preparation of the first rotaxanes was also accomplished by means of statistical threading of a chain through a cycle with following attaching of bulky substituents to the loose ends of the threaded chain [5], Statistical means of molecular threading were pushed out by much more efficient covalent templation procedures developed by Schill etal. [6,7],... 

One of the earliest rotaxane syntheses was based on statistical threading (Figure 2.6).3 Harrison and Harrison coupled the 30-membered macrocycle 1 bearing a pendent carboxylic group to a Merrifield s peptide resin, forming... 

The early syntheses of catenanes and rotaxanes were mainly based on statistical threading approaches or on directed methodologies involving chemical conversion [30]. To obtain a catenated molecule, one ring must be closed in the presence of a... 

The very first rotaxanes were, however, not prepared via the template technique. In 1967, Schill and Zollenkopf [3] described a directed rotaxane synthesis (i.e. by the use of temporary, cleverly disposed covalent bonds), which was traced from the first directed catenane synthesis developed by Schill and Luttringhaus in 1964 [32]. Quite simultaneously, Harrison and Harrison published the first rotaxane synthesis by statistical threading [4]. 

The relevant thermodynamic and kinetic parameters are displayed diagrammatically in Figure 4. From the point of view of kinetics, AC is significant only in the case of slippage. From the point of view of thermodynamics, if AH° 0, the threading is controlled by entropy this is the case of the so-called statistical threading. If AH° < 0, the threading is controlled by enthalpy the threaded species is thermodynamically much more stable than the separated components. In this latter case, the equilibrium of scheme 1 can be rewritten as shown in scheme 2 ... 

One of the earliest rotaxane syntheses involved statistical threading. Harrison and Harrison [4] coupled the 30-membered macrocycle (3) bearing a pendent carboxylic group to a Merrifield s peptide resin, forming the resin adduct (4) (Figure 7). Next, a column was charged with this modified resin and treated with a solution of decane-1, 10-diol (5) and triphenylmethyl chloride (6) in a mixture of pyridine, dimethylfor-mamide and toluene. The process was repeated 70 times. After washing the column,... 

Figure 8 Statistical threading (temperature-controlled slippage). Preparation of [2]-rotaxane (10) [38],...

Quantitative but statistical threading takes place by mixing 124 and 118 with enough Cu(CH ,CN)4 for every ring and subsequently adding the siring 123. Unexpectedly, the three complexes 125, 126 and 127, obtained in the 1 1 2 statistical ratio in solution, could be separated by chromalo-... 

The first mention of synthetic rotaxanes appeared in 1967 [11]. It was based on statistical threading of an immobilized cycle by decane-1,10-diol followed by capping using a trityl ether bulky oup. Another system using statistical threading 1 to rotaxanes in relatively high yield [12]. A directed synthesis was also reported in 1969 by Schill and Zollenkopf.[13]... 

A main chain polyrotaxane, a mechanically interlocked structure that can be considered as a string of pearls, in which the strand is the polymer backbone and the pearls are the cychc species threaded onto the strand. The backbone polymer can be a polyester, polyamide, poly(ethylene oxide), or virtually any linear polymer. The cyclic species are typically crown ethers, cyclodextrins (CDs), cucurbimrils, and calix-arenes. Polyrotaxanes can be made by two different methods statistical threading or via the template approach (enthalpi-cally driven). The statistical approach utilizes le Chatelier s principle with an excess macrocycle during the polymerization. The template approach is driven by attractive interactions of the macrocyclic species with either the monomer... 

Information maintains a statistical thread throughout the atomic and molecular realm. The elements H, He, Li, and so forth are distributed on the planet with spatial frequencies dependent on the source, say, coal mined in West Virginia as opposed to water in Lake Michigan. The frequencies are by no means independent of one another. If an H atom appears in a molecule extracted from coal, odds are that C, O, or N units, and not Li, will be a spatially nearest neighbor. 

Early attempts at preparing catenanes relied on a more or less statistical threading approach. By cyclizing very long chains (with over 30 carbons) to make very large rings, there... 

The basic regularities of the statistical thesis of polyrotaxanes have been established by Agam and Zilkha They obtained polyrotaxanes by a statistical threading of crown polyesters on polyethylet glycols. Polyethylene glyccds with a molecular mass of 400, 600, and 1000 were selected as linear chains, and crown polyesters with different munbers of atoms in the cycle (30,44, and 58), as macrocycles. The reactants were mixed, heated, and an equilibrium mixture was frozen by the addition rf naphtilene-l,5-diizocyanate with the formation of polyurethane. The number of bound cycles was determined after a selective separation on silica gel. 

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