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This paper reports the chiroptical properties of thionated N‐acyl amino acid and N‐acyl dipeptide N′‐methylamide models. It was found that the optical activity of the thioamide chromophore is dominated by the chiral contribution of perturbants attached to Cα at the N‐H side of the thioamide group. The appearance of a strong negative ππ* band near 270 nm is indicative of the semiextended conformation of this residue. The ϕ ∼ −70°, ψ ⩾ 120° set of torsion angles is compatible with a type II βt‐turn or a γt‐turn conformation with the perturbing N‐H side residue in the i + 1 position of the turn. (The subscript t or tt denotes that one or both of the H‐bonded moieties is thioamide.) Earlier data show that both βt‐ and γt‐turns may be fixed by CS ⃛H‐N(CO) intramolecular H bonds. The appearance of one or two weak nπ* bands and a positive ππ* band at about 270 nm is characteristic of type II βt‐turns containing the H‐bonded thioamide group attached to the glycine residue in position i + 2. The extended conformation (ϕ ∼ −140°, ψ ∼ 140°) of a residue after the thioamide group gives rise to a negative nπ* and a positive ππ* band of comparable magnitude. Peptid1e sequences with alternating thioamide–amide–thioamide backbone tend to adopt 1t ⇆ 4t H‐bonded βtt conformations. CD studies show that type II βtt‐turns have unique chiroptical properties: the ππ* region is dominated by an exceedingly strong negative band near 260 nm (|Δε| = 19–24) accompanied by a weaker band at higher wavelength values.

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The macrolide antibiotic amphotericin B (AmB) forms an inclusion complex with gamma-cyclodextrin (gamma-CDx), resulting in a molecularly dispersed state of the drug. The state of aggregation of AmB in different solvents has been studied by absorption (uv-vis) and CD spectroscopy. While in aqueous solutions AmB forms colloid-like multimolecular aggregates, in the presence of gamma-CDx true solutions can be prepared, which show similar spectral properties as AmB dissolved in organic solvents. The AmB-gamma-CDx complex can be isolated as an amorphous, stable, water-soluble powder, indicating that gamma-CDx is a good carrier for the solubilization of this antibiotic. Using gamma-CDx as a carrier, the danger of precipitation of the drug during parenteral or intravenous administration can be largely reduced.

The complex formation of phenolphthalein and P-cyclodextrin (cyclohepta-amylose) has been investigated by spectrophotometric, c.d., and potentiometric methods. It has been shown that complexes are formed with the protonated and dissociated forms of phenolphthalein as well; the dianion is complexed in alkaline solution in a colourless form. The complexes formed have the largest stability constants among cyclodextrin complexes known up to now. The unusual stabilities and colour change can be explained by the combined effect of the accessibility of the phenolicphenolate moiety and presence of the carboxy-carboxylate group simultaneously, providing optimal space filling and the possibility for the cyclodextrin molecule to interact with three functional groups of phenolphthalein at the same time.

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