Microcrystalline cyclodextrin

We have utilized directly these microcrystalline cyclodextrin complexes in the solid state reactions, which were carried out with gaseous halogens and hydrogen halides under air in the dark. 

In fact, at the end of the reaction of trans-cinnamic acid with chlorine under air, the sticky solid product was obtained, but with bromine no change of the solid was observed. However, when the addition of these reagents to the acid proceeded in the microcrystalline cyclodextrin matrix, there was no visual evidence of liquid phase on the crystal even in chlorination of it under microscope. 

In this reaction in cyclodextrin, the transition state should involve the ternary molecular complex composed of microcrystalline cyclodextrin complex and a fixed gaseous reagent in it. Hadjoudis, et also sug-... 

Spherical pellets containing 5% triamcinolone acetonide were prepared by Villar-Lopez and co-workers [59] by extrusion/spheronization following formulation with microcrystalline cellulose and/or a hydrophilic excipient like lactose, sodium earbox-ymethylcellulose, or P-cyclodextrin. Their suitability for coating, with a view toward colonic drug deliveiy, was assessed in terms of their size, sphericity, and dissolution test response. The best results were afforded by a 5 90 5 composition of microcrystalline cellulose, P-cyclodextrin, and triamcinolone acetonide, prepared by complex-ation of triamcinolone acetonide with P-cyclodextrin prior to the addition of microcrystalline cellulose. 

Nakai, Y., Nakajima, S., Yamamoto, K., Terada, K., and Konno, T. 1980. Effects of grinding on the physical and chemical properties of crystalline medicinals with microcrystalline cellulose V comparison with tri-O-methyl-fS-cyclodextrin ground mixturefihem. Pharm. Bull., 28 1552-1558. 

Fig. 4.3 Schematic representation of the association-dissolation of the host (cyclodextrin) and guest (p-xylene). The formed guest/host inclusion complex can be isolated as a microcrystalline powder. (From ref. [13])...

Cellulose was the first sorbent for which the resolution of racemic amino acids was demonstrated [23]. From this beginning, derivatives such as microcrystalline triacetylcellulose and /3-cyclodextrin bonded to silica were developed. The most popular sorbent for the control of optical purity is a reversed-phase silica gel impregnated with a chiral selector (a proline derivative) and copper (II) ions. Separations are possible if the analytes of interest form chelate complexes with the copper ions such as D,L-Dopa and D.L-penicillamine [24], Silica gel has also been impregnated with (-) brucine for resolving enantiomeric mixtures of amino acids [25] and a number of amino alcohol adrenergic blockers were resolved with another chiral selector [26]. A worthwhile review on enantiomer separations by TLC has been published [27],... 

Practically every type of separation that has been done by the column technique can also be carried out by thin-layer chromatography. Several papers and reviews were published on the various aspects of the technique. In addition to the books on chromatography [17,26-301, an overview of ion-exchange application of TLC was presented by Devenyi and Kalasz 311. Recent results on the separation of enantiomers have been reviewed by Mack, Hauck and Herbert (32.33) (enantiomer. separation on an RP-18 plate, impregnated with copper salt and proline derivative as chiral selectors) and Lepri, Coas and Desideri, using a microcrystalline triacetylcellulose stationary phase, or modified beta-cyclodextrins in the mobile phase 134.35). 

Direct separation of enantiomers may be performed on cellulose the use of microcrystalline cellulose is especially widely used. An other stationary phase is the microcrystalline triacetylcellulose, which is stable when using alcoholic and phenolic mobile phases however, it is unstable when glacial acetic acid and ketones are used. Optically active poly(meth)acrylate may be bound to the silica gel. and these stationary phases are widely used under the names of CHIRALPLATE or CHIR . Beta cyclodextrin can also be covalently bound to silica, and also reversed-phase plates may be used for chiral separation when the mobile phase consists of beta-cyclodextrin. 

Table 1 Rf Values of Azo Dyes on Microcrystalline Cellulose Thin Layers (Merck 557) with Various Eluent Additives at Room Temperature (CD = cyclodextrin)...

Complexes of MV+- radical cations included in cyclodextrin (CDx) were observed both in methanol/aqueous solutions and as microcrystalline powder.21 In the former situation, the spectral linewidth did not decrease monotonically with temperature, as is the case in the absence of CDx. The linewidth decrease... 

Microcrystalline cellulose triacetate, cyclodextrin- and crown ether-derived CSPs, as well as some chiral synthetic polymers, achieve enantiomer separation primarily by forming host-guest complexes with the analyte in these cases, donor-acceptor interactions are secondary. Solutes resolved on cyclodextrins and other hydrophobic cavity CSPs often have aromatic or polar substituents at a stereocenter, but these CSPs may also separate compounds that have chiral axes. Chiral crown ether CSPs resolve protonated primary amines. 

Particle size reduction can be achieved using a variety of methods. Sometimes it is helpful to carry out the particle size reduction at reduced temperatures, such as at 4°C or at liquid nitrogen temperature, -196°C. In other instances, grinding with an excipient has been employed as a means of obtaining amorphous materials. Cyclodextrins and microcrystalline cellulose have been used for this purpose. It is also possible that the use of polymeric excipients may inhibit crystal growth when the amorphous solid is dissolved in water. Table 5 contains a list of compounds that have been obtained in amorphous, or partly amorphous, form by milling. 

Mura P, Faucci MT, Parrini PL, Effects of grinding with microcrystalline cellulose and cyclodextrin on ketoprofen physicochemical properties. Drug Dev. Ind. Pharm 2001 27 119-128. 

A complementary view is given by X-ray photoelectron studies which provide evidence for hydrogen bond formation as well as preferential attachment by one or two nitrogen atoms per cyanine molecule to the hydroxyl groups in the substrates. In the thiacarbocyanine case, hydrogen bond formation was detected for microcrystalline cellulose and /S-cyclodextrin cases which involved the sulphur atom of the cyanine. 

Table 1 Values of azo dyes on microcrystalline cellulose thin layers (merck 557) with various eluent additives at room temperature (CD = cyclodextrin).

An optimum formulation of a model tablet containing furosemide (active ingredient), cyclodextrin polymer (di-sintegrant) and microcrystalline cellulose (binder) found by a computer optimization process (5) wsls investigated. 

Diffuse reflectance laser flash photolysis and laser-induced luminescence, hoth in time-resolved mode or ground-state absorption spectroscopy in the diffuse reflectance mode, are important techniques that have been used by several research groups to study opaque and crystalline systems [1—8]. These solid-state photochemical methods have been applied by us to study several organic compounds adsorbed onto different hosts such as microcrystalline cellulose [7, 8], p-tertbutylcalix[n]arenes (n = 4, 6, and 8) and their derivatives [10—12], silicalite, cyclodextrins [7, 12, 13], and silica [l4j. 

L. F. Vieira Ferreira, I. Ferreira Machado, J. P. Da Silva, and A. S. Oliveira, A diffuse reflectance comparative study of benzil inclusion within microcrystalline cellulose and P- cyclodextrin, Photochemical Photobiological Sciences, vol. 3, no. 2, pp. 174—181, 2004. 

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