Branched-cyclodextrin

This strategy was based on the supramolecular immobilization of alternating layers of HRP (either modified with 1-adamantane or P-cyclodextrin-branched carboxymethylcellulose residues) on Au electrodes coated with polythiolated P-cyclodextrin polymer. Fragoso et al. adopted a similar strategy by the immobilization of a first layer of thiolated cyclodextrin polymer on a gold electrode followed by the supramolecular capture of adamantane-modified HRP (Fig. 6)... 

Figures 4 and 5 show the plots of log 1/Kd vs. log Pe for branched or cyclic alcohol-cyclodextrin systems. Both of the plots showed considerable scatter in contrast to the plots for 1-alkanol systems (solid lines). However, a remarkable trend was found by comparing both plots. Most of the plots for an a-cyclodextrin system (Fig. 4) are located below the straight line due to Eq. 5, whereas those for a P-cyclodextrin system (Fig. 5) are located above the straight line given by Eq. 6. This shows that it is general for a bulky alcohol to associate with a-cyclodextrin less strongly and with P-cyclodextrin more strongly than a rod-like 1-alkanol if the log Pe values are the...

Fig. 4. Plots of log 1 /Kd vs. log Pe for complexes of a-cyclodextrin with branched alkanols (O) and cycloalkanols ( ). The solid line was given by the plots for an a-cyclodextrin-1-alkanol system. Numbers shown refer to the numbers in the first column of Table 2. Reproduced with permission from the Chemical Society of Japan...

Matsui75) has computed energies (Emin) which correspond to the minimal values of Evdw in Eq. 1 for cyclodextrin-alcohol systems (Table 2). Besides normal and branched alkanols, some diols, cellosolves, and haloalkanols were involved in the calculations. The Emi values obtained were adopted as a parameter representing the London dispersion force in place of Es. Regression analysis gave Eqs. 9 and 10 for a- and P-cyclodextrin systems respectively. 

Upon formulating these relationships, phenols with branched alkyl substituents were not included in the data of a-cyclodextrin systems, though they were included in (3-cyclodextrin systems. In all the above equations, the n term was statistically significant at the 99.5 % level of confidence, indicating that the hydrophobic interaction plays a decisive role in the complexation of cyclodextrin with phenols. The Ibrnch term was statistically significant at the 99.5% level of confidence for (3-cyclo-dextrin complexes with m- and p-substituted phenols. The stability of the complexes increases with an increasing number of branches in substituents. This was ascribed to the attractive van der Waals interaction due to the close fitness of the branched substituents to the (3-cyclodextrin cavity. The steric effect of substituents was also observed for a-cyclodextrin complexes with p-substituted phenols (Eq. 22). In this case, the B parameter was used in place of Ibmch, since no phenol with a branched... 

In order to keep the mild conditions, hydroxycarbonylation has been performed in biphasic media, maintaining the catalyst in the aqueous phase thanks to water-soluble mono- or diphosphine ligands. In the presence of the sodium salt of trisulfonated triphenylphosphine (TPPTS), palladium was shown to carbonylate efficiently acrylic ester [19], propene and light alkenes [20,21] in acidic media. For heavy alkenes the reduced activity due to the mass transfer problems between the aqueous and organic phases can be overcome by introducing an inverse phase transfer agent, and particularly dimeihyl-/-i-cyclodextrin [22,23]. Moreover, a dicationic palladium center coordinated by the bidentate diphosphine ligand 2,7-bis(sulfonato)xantphos (Fig. 2) catalyzes, in the presence of tolylsulfonic acid for stability reasons, the hydroxycarbonylation of ethylene, propene and styrene and provides a ca. 0.34 0.66 molar ratio for the two linear and branched acids [24],... 

With increasing concentration of methylated /1-cyclodextrin the selectivity to n-nonanal increases from 64% to 72%, while the conversion of the olefin is constantly as high as 97%. Obviously the addition of the methylated /i-cyclodextrin has only a moderate influence on the isomerizing hydroformylation of trans-4-octene to n-nonanal. The addition of only 0.2 mol.-% of methylated /3-cyclodextrin lowers the isomerization rate which results in the formation of slightly more branched aldehydes. In pharmacy j6-cyclodextrins are established as solvation mediators between polar and less polar solvents. This is one possible explanation for the rise in selectivity to n-nonanal with an increasing j6-cyclodextrin concentration. At higher con-... 

U Holzgrabe, H Mallwitz, SK Branch, TM Jefferies, M Wiese. Chiral discrimination by NMR spectroscopy of ephedrine and JV-methylephedrine induced by /3-cyclodextrin, heptakis(2,3-di-0-acetyl)-/3-cyclodextrin and hep-takis-(6-0-acetyl)-/3-cyclodextrin. Chirality 9 211-219, 1997. 

Tosylcyclomaltoheptaose (15 a) treated with 2 eq of the sodium salt of either 1-thio-a- (16a) or l-thio- -n-glucopyranose (16b) in DMPU at 70 °C for 5 h afforded the expected branched cyclodextrins (17a, 17b) in 66 and 60% yield respectively [23] (Scheme 6). 

The branched cyclodextrins (CDs, 17 a, 17 b) and their analogues with D-galactosyl and a-D-mannosyl residues (17c, 17d) have also been prepared under mild conditions by the approach depicted in Scheme 6 [24,25]. Selective in situ S-deacetylation and activation was obtained by treatment of peracetylated 1-thioglycoses (10a, 8e, 8g) by cysteamine in the presence of diAioerythritol in HMPA [26]. This method was very efficient for ffie synthesis of branched CDs (17a) (80%), (17b) (60%), and (17c) (85%) when the acceptor molecule (15b) bearing primary iodide was used. However, peracetylated 1-thioa-D-mannose (8f) failed as a donor under these conditions, but tetra-O-acetyl-l-thio-a-mannose (8 b) afforded the expected CD (17d) in high yield (83%). 

Bender, H., Siebert, R., Stadler-Szoke, A. (1982). Can cyclodextrin glycosyltransferase be useful for the investigation of the fine structure ofamylopectins Characterisation of highly branched clusters isolated from digests with potato and maize starches. Carbohydr. Res., 110,245-259. 

It should be stressed that there is not alwaysjustice in reseach evaluation. The selective formation of inclusion complexes by cyclodextrins (such as 11) was established by Cramer [6] at least 15 years earlier than that by crown ethers. However, cyclodextrin studies forming an independent branch of host-guest chemistry seem underestimated in spite of their considerably greater practical importance at present than that of other host macrocycles (crown ethers 17, calixarenes 18, etc.). Sometimes they are even totally neglected by discussing inclusion phenomena [7]. 

Stereoanalysis of 2-alkyl-branched acids, esters and alcohols in apple aroma concentrate Restriction capillary (25 m X 0.23 mm i.d.) coupled to a glass capillary column, (25 m X 0.32 mm i.d.) coated with a 18.8% solution of PS-255 and 1.5% dicumyl peroxide. Glass capillary column (38 m X 0.23 mm i.d.) coated with heptakis (2,3,6-tri-0-ethyl)-/3-cyclodextrin (33% in OV-1701-vinyl) 6... 

Amino acid sequence relationships between that of branching enzyme (BE) and amy-lolytic enzymes, such as a-amylase, pullulanase, glucosyltransferase and cyclodextrin glucanotransferase, especially at those amino acids believed to be contacts between the substrate and the amylase family enzymes, were first reported by Romeo et al.283 Baba et al.284 reported that there was a marked conservation in the amino acid sequence of the four catalytic regions of amylolytic enzymes in maize endosperm BEI. As shown in Table 4.12, four regions that putatively constitute the catalytic... 

Branched cydodextrins are also used to increase the solubility of complexes. Two methods are used to make branched cydodextrins, an enzymic method and a pyrolytic method. In the enzymic method, a starch debranching enzyme, such as pul-lulanase, is added to a solution of cyclodextrin and a large excess of D-glucose or maltose to force the reaction to proceed in the reverse direction, i.e. to add rather than remove a branch.69 Since the equilibrium favors the debranching reaction, yields are low and the product typically contains —15% branched cyclodextrin and —85% glucose or maltose. Purification is difficult because of the high solubility of both the glucose or maltose and the branched cyclodextrin, but much of the unreacted cyclodextrin can be removed by crystallization. 

Branched cydodextrins can also be formed by heating dry cyclodextrin in the presence of a small amount of hydrogen chloride.70 The pyrolysis product is dissolved in a small amount of water to dissolve the branched cyclodextrin, leaving behind most of the (3-cyclodextrin which has limited solubility. 

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