New types of helical canal inclusion networks

Bishop, Roger; Dance, Ian G.

doi:10.1007/3-540-19338-3_3

Cited by 62 publications

(23 citation statements)

References 200 publications

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“…[12,14] As a result, channels about 5 ä in diameter are formed that are distinctly hydrophilic in nature ( Figure 2). For brevity, we just mention that the tubular inclusion complexes of urea, [15,16] starch, [16,17] and cyclodextrines [18] have been characterized. p ± p Stacking X-ray investigations on extended p-systems such as [18]annulene, [19] kekulene, [20] or porphyrins [21] show that these systems adopt a cofacial arrangement in which the centers are offset.…”

Section: Hydrogen Bondsmentioning

confidence: 99%

A World Beyond Hydrogen Bonds?—Chalcogen–Chalcogen Interactions Yielding Tubular Structures

Gleiter

Werz

Rausch

2003

Chemistry A European J

167

120

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It is shown that tubular structures arise in the solid state through close chalcogen-chalcogen (X...X) contacts. As examples a variety of cyclic systems containing sulfur and selenium centers is presented. Common to all of them are close contacts between the chalcogen centers of neighboring stacks giving rise to a zigzag or ladder-type arrangement. In the case of cyclic systems of ring size 24-33 the resulting tubes are able to include hydrocarbons as guest molecules. For 2,7-ditelluraocta-3,5-diyne (17) the close contacts between the tellurium centers of the acyclic C(2) symmetric building blocks generate a helical arrangement in which n-hexane was included. The favored X...X contacts can be traced back to np(X)-sigma*(X[bond]C) interactions.

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Section: Hydrogen Bondsmentioning

confidence: 99%

A World Beyond Hydrogen Bonds?—Chalcogen–Chalcogen Interactions Yielding Tubular Structures

Gleiter

Werz

Rausch

2003

Chemistry A European J

167

120

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“…The best characterized inclusion complex is with iodine (I 2 /KI), which can easily be identified through its intense blue color. 26,28 It has been reported that some amylose derivatives, such as diethylaminoethylamylose and carboxymethylamylose, also form polyiodide compounds, 50 albeit only at low DS. 49 Inclusion complexes of triethylamylose with small organic molecules were observed, but xray analysis indicated a different mode of complexation where guest molecules were located in grooves between narrow amylose helices, and not actually accommodated into the V-amylose helix interior.…”

Section: 3-di-o-alkylated Amylosesmentioning

confidence: 99%

“…49 Inclusion complexes of triethylamylose with small organic molecules were observed, but xray analysis indicated a different mode of complexation where guest molecules were located in grooves between narrow amylose helices, and not actually accommodated into the V-amylose helix interior. 50 Thus, iodine staining is generally accepted as an easily applicable method to assess the ability of starch and amylose derivatives to form helical inclusion complexes. 49 The absorption maximum for these polyiodide complexes is dependent on the length of the amylose chain 28 ; the absorption maximum being ca.…”

Section: 3-di-o-alkylated Amylosesmentioning

confidence: 99%

Synthesis and characterization of 2,3‐di‐O‐alkylated amyloses: Hydrophobic substitution destabilizes helical conformation

Breitinger

2003

Biopolymers

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Amylose was selectively alkylated in the 2,3-O position of each anhydroglucose unit after trityl protection of the 6-OH groups. Alkyl iodides of varying chain length (C(2), C(5), C(8)) were coupled to amylose, and degrees of substitution (DSs) were varied between 0.3 and 1.8, as assessed by NMR analysis. Increasing amounts of methyl groups per anhydroglucose unit increased solubility in nonaqueous media, while at the same time reducing the ability of modified amylose to form a complex with iodine. The tendency to form inclusion complexes with the surfactant N-dodecyl pyridinium bromide decreased in the order beta-cyclodextrin >> amylose approximately solubilized starch, indicating that the frozen macrocycle of beta-cyclodextrin was the most efficient inclusion host. Introduction of the bulky trityl group abolished the helical amylose conformation, which is not readily reassumed in the presence of hydrophobic substitution of the C2 and C3 positions. These results indicated that a polar outer surface is necessary but not sufficient for the formation of a stable amylose helix.

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“…This, in the presence of straight-chain hydrocarbons, urea generally forms an extensively hydrogen-bonded hexagonal helical structure surrounding channels like void spaces that contain the guest molecules [6]. The host structure is remarkable in that all host molecules and inter-host hydrogen bonds project onto a hexagonal array with minimal cross-sectional area and with unusually large proportion of the projection area available to the guest species [7]. Thus, urea host channels run parallel to each other along the c-axis of the crystal without any intersections and have minimum van der Waals diameters of 5.5-5.8 Å [8].…”

mentioning

confidence: 98%

Reduction in Moisture Sensitivity/Uptake of Moisture Sensitive Drugs Through Adduction in Urea

Thakral¹,

Мадан

2008

J Pharm Innov

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In the present study, use of hexagonal urea as a means for the reduction in moisture sensitivity/uptake has been investigated using nicorandil as a model endocytic drug. Urea, a well-known adductor for linear compounds, was successfully employed for adduction of nicorandil-a substituted cyclic organic compound through recently reported technique. Formation of urea inclusion compounds was confirmed by Fourier transform infrared, differential scanning calorimetry (DSC) and X-ray diffraction. Modified Zimmerschied calorimetric method was employed for estimation of the minimum amount of rapidly adductible endocyte (RAE) required per unit weight of nicorandil for adduction in urea. Urea-nicorandil-RAE inclusion compounds containing varying proportions of guests were prepared and their thermal behavior studied by DSC. However, coinclusion of nicorandil-a normally nonadductible endocytic compound in urea-naturally resulted in distortion of narrow channels of hexagonal lattice leading to the formation of distorted hexagonal urea. Both the normal and distorted hexagonal urea revealed appreciable reduction in moisture uptake when compared to that of tetragonal urea. The distorted urea framework exhibited increased moisture uptake as compared to the non-distorted one. Study also revealed improved stability of included nicorandil upon exposure to atmosphere at higher humidity levels. The coinclusion compounds of nicorandil were found to exhibit good content uniformity. Urea inclusion compounds of nicorandil in the presence of suitable RAE can be a promising alternative for the development of stable formulations of the drug.

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New types of helical canal inclusion networks

Cited by 62 publications

References 200 publications

A World Beyond Hydrogen Bonds?—Chalcogen–Chalcogen Interactions Yielding Tubular Structures

A World Beyond Hydrogen Bonds?—Chalcogen–Chalcogen Interactions Yielding Tubular Structures

Synthesis and characterization of 2,3‐di‐O‐alkylated amyloses: Hydrophobic substitution destabilizes helical conformation

Reduction in Moisture Sensitivity/Uptake of Moisture Sensitive Drugs Through Adduction in Urea

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