Miyoko Suzuki

Induced circular-dichroism spectra of complexes of cyclomalto-oligosaccharides and azobenzene derivatives

Abstract The circular-dichroism spectra of the inclusion complexes of 9 types of cyclodextrin (CDs) with 6 kinds of azobenzene derivatives generally show a single peak, but sometimes form a splitting pattern in the first π → π* region. All single patterns show a positive sign; indicating that the long and slim azobenzene derivatives are incorporated into the cavity from the long-axis side. The splitting patterns change in sign and magnitude according to the substitution on the component molecules and establish the formation of various stacking modes. Plots of the lengths of the azo dyes vs. the molar circular-dichroism coefficients suggest that the substituent on the CD torus is an important factor in causing splitting and deciding the sign of the split-type Cotton effects. The foregoing splitting may arise from exciton interaction of two molecules of the chromophoric dye each in the form of a 1:1 complex and in the cyclomaltooctaose (γCD) complex.

2H NMR study of the self-assembly of an azo dye-cyclomaltooctaose (γ-cyclodextrin) complex

Abstract Orange II and γ-cyclodextrin form 2:1 and 2:2 complexes. These complexes self-associate, and microscopic viewing indicates the formation of a fibroid aggregate. The deuteron resonance (in 2 H NMR spectroscopy) from deuteron exchange and solvation between the aggregate and deuterium oxide exhibits quadrupole splitting (Δν) in the region of 0-1.2 KHz. The orientation behavior obtained from this splitting suggests the formation of a liquid-crystaloid substance. (1) The aggregate aligned by means of the super conductive and permanent magnetic fields shows a different NMR pattern and turbidity. (2) Dilution of the 0.12 M aggregate with deuterium oxide proceeds discontinuously via the nonoriented pattern to the oriented-pattern. (3) With an increase in temperature, the 2 H NMR spin-spin splitting values decrease continuously. A phase diagram that plots melting points in variable concentrations reveals separate solution and aggregate layers. (4) When the 0.06 M aggregate is diluted by deuterated solvents (water, methanol, ethanol, propanol, dimethyl sulfoxide, and acetone), increases in the amount added and the length of solvent molecules cause a regular reduction of Δν. The deuterium signal of the methyl group in dimethyl sulfoxide- d 6 exhibits a small Δν, suggesting that this solvent is included in the orientation system.

13C Nuclear Magnetic Resonance Spectra of Cyclodextrin Monomers, Derivatives and their Complexes with Methyl Orange

Low molecular mass fractions of water soluble α-, β-, and γ-cyclodextrin epichlorohydrin polymer products (cdx-Ep) were characterized by13C nuclear magnetic resonance. The derivatives proved not to be polymers, but substituted cdx having one or two glyceryl groups per one glucose at the C-2, C-3 and C-6 positions. Spectra of analogous hydroxy-propyl β-cdx indicate that the degree of substitution is rather higher at the C-6 position. Methyl orange (MO) was included into nine kinds of cdx having different inner diameters and hydrophobic torus heights; α-, β-, and γ-cdx monomers, 2, 6-dimethyl and 2, 3, 6-trimethyl β-cdx, water soluble α-, β-, and γ-cdx-Ep and ethyleneglycol-bis(epoxy-propyl) ether products. The inclusion shifts were compared with each other and with the dioxane-induced solvent shift of MO. TheN, N-dimethyl-aniline side of MO shifted to a higher field site with the increase of the inner diameter in cdx. By substituting cdx with ether groups of different length, the mechanism of inclusion formation remains substantially the same, but by lengthening the hydrophobic cavity, the hydrophobic interaction becomes stronger, as a better resemblance of inclusion shifts and solvent shifts can be observed.

Molecular dynamics of derivatives of cyclomalto-oligosaccharides and their complexes with azo dyes

Abstract The molecular motions of the inclusion complexes of several cyclomalto-oligosaccharides (CDs) and azo dyes have been studied on the basis of 13 C relaxation times. The correlation times, estimated to be of the order of 10 −10 -10 −11 s by the isotropic model, increased as the host and guest molecules became large, long, and bulky, and the increase was larger for the azo dyes than for CDs on the formation of complexes. Azo dyes rotate up to twice as fast as CDs. The motion of the azo dye with respect to the cavity of the CD indicates that the longer and more bulky azo dyes rotate slower, and that lengthening of the cavity prevents their rotation. The internal rotations of the primary alcohol, methyl, and phenyl groups were preserved in the complexes.

Induced circular-dichroism spectra of complexes of cyclomalto-oligosaccharides and azo dyes containing naphthalene nuclei☆

Abstract In the circular-dichroism spectra of inclusion complexes of 7 types of cyclodextrin (CDs) with 6 kinds of azo dyes containing the naphthalene nucleus, the direction of inclusion and the stacking mode may be elucidated from patterns in the u.v. and the first π→π * regions. The patterns in the former region indicate that the naphthalene fragment in almost all of complexes is incorporated equatorially into the cavity. Those azo dyes that have a tight fit in the CD cavity exhibit exciton interaction between two molecules of the chromophoric dye included in the complexes. The spectral pattern changes in sign according to the inclusion mode of the guest molecules and the angle between the chromophores. For example, the spectral pattern of the Orange II-cyclomaltoheptaose (β CD) complex indicates that the naphthalene nucleus is included axially, and that the angle between two molecules of the azo dye is >90°. On the other hand, the spectral pattern of the Croceine Orange-DM-β CD complex indicates equatorial inclusion and a stacking angle of

Visible and 13C nuclear magnetic resonance spectra of azo dyes and their complexes with cyclomalto-oligosaccharides

Abstract Inclusion complexes of α-, β-, and γ-cyclomalto-oligosaccharides (CDs), heptakis(2,6-di- O -methyl)- and heptakis(2,3,6-tri- O -methyl)- β CDs (Me 2 -βCD and Me 3 -βCD) with methyl orange sodium 4-[4-(dimethylamino)phenylazo]benzenesulfonate ( 3 ). tropaeolin OO sodium 4-[[4-(phenylamino)phenyl]azo]benzenesulfonate ( 1 ), metanil yellow sodium 3-[[4-(phenylamino)phenyl]azo]benzenesulfonate ( 2 ), and orange II sodium 4-[(2-hydroxy-l-napthalenyl)azo]benzenesulfonate ( 4 ) were measured by UV-vis spectrophotometry. Complex formation constants ( K ) were calculated by a non-linear least-squares method. The order of K in the 1:1 complexes is Mc 2 -βCD > Me 3 -βCD > αCD > βCD. Thus lengthening of the hydrophobic torus by substituting the CD with methyl groups exhibits a greater effect than the sizes of the inner diameter of the cavity. Since the K values correlate with the bulkiness of the hydrophobic parts of the azo dyes, these numbers suggest a direction of inclusion of the azo dye molecules (i.e., hydrophobic groups of the guest molecules associated with hydrophobic groups of the CDs) into the CD cavities. Complex formation induces a hypsochromic shift to the λ max that very closely resembles the shift induced by dioxane, suggesting that the inside of the cavity resembles this solvent. As the order of the shift is 3 > 1 , > 2 > 4 , γ CD > β CD series > α CD , and the shift scarcely appears in the complexes of 4 , the shift may be mainly derived by the inclusion of an anilino group in 1, 2 , and 3 . NMR chemical shifts, relaxation times, and rotational correlation times from the 13 C NMR studies all support the above conclusions.

The association of inclusion complexes of cyclodextrins with azo dyes

OrangeII (4) and γ cyclodextrin (CD) form 2 : 1 and 2 : 2 complexes. The complexes self-associate and microscopy indicates the formation of a fibroid aggregate. In the induced c.d. spectrum, the π → π* band of this complex appears at ∼500 nm in solution, but in the aggregate it changes to aJ-band due to the head-to-tail stacking of4 and aH-band due to its parallel stacking; this indicates that the aggregation expands not only in the direction of the symmetry axis of the CD, but also in the other two dimensions.2H-NMR spectroscopy from deuteron exchange and solvation between the aggregate and deuterium oxide exhibits quadrupole splitting in the region of 0–0.2 KHz. The orientation behavior obtained from this splitting suggests the formation of a liquid-crystaloid substance.13C-T1 NMR indicates that molecules4 and γ CD show the sameT1 values even at 333 K; this complex behaves like a single molecule. The behaviors of other azo dye-CD complexes are also discussed.

13C-n.m.r. spectra of cyclomalto-oligosaccharides (cyclodextrins), their derivatives, and complexes with azo dyes

The nature of the inclusion complexes of several cyclomalto-oligosaccharides (cyclodextrins, CDs) with azo dyes has been studied on the basis of 13C-n.m.r. chemical shifts, relaxation times, correlation times, and broadening and doubling of the n.m.r. signals. All CDs show the azo dye-induced shifts at the narrow-rim side of the CD, indicating that the azo dyes protrude from the cavity. CD-induced shifts of azo dyes depend on the hydrophobic nature of the cavity, van der Waals forces, as well as ring-current and deformation effects, and suggest inclusion essentially from the hydrophobic site. The broadening and the doubling of the 13C-n.m.r. signals, the altered relaxation and correlation times, as well as the temperature dependence for these phenomena, also provide particular information about the characteristic host-guest interactions.

Morphology and induced circular dichroism spectra on the aggregation of a cyclodextrin complex with an azo dye

Abstract Orange II (I) is easily soluble in H2O. It requires several months for the formation of needle-like crystals from a 0.16 M (saturated) aqueous solution. But when 0.03 M γ-cyclodextrin (γ-CD) is added to an equivalent of (I) at RT, the solution exhibits enhancement of the viscosity in an hour, and the microscopic viewing indicates the formation of a pine needle-like aggregate. Enough old millet jelly-like one shows well arranged stripe pattern upon rubbing. In the induced c.d. spectrum, the π→π* band of this complex appears at ∼500 nm in the solution state, but in the aggregate state, it changes to the J-band due to the head-to-tail stacking of (I) and the H-band due to parallel stacking. When MeOH is poured onto the aggregate, the latter changes colour from orange to silver-gray, but keeps the same shape. The driving force for the aggregate formation may be 1. van der Walls contact between γ-CD and two molecules of (I), 2. π-π interaction between the two molecules of (I) in γ-CD, 3. H-bonding and...

Spectroscopic Investigation of Cyclodextrin Monomers, Derivatives, Polymers and Azo Dyes (1)

Circular dichroism (CD) and visible spectra of inclusion compounds between Methyl Orange (MO) analogues and α-, β-, γ-cyclodextrin (cdx), 2,6-dimethyl-and 2,3,6-trimethyl- β-cdx, water soluble α-, β-, γ-cdx polymer products were investigated. In the CD-spectroscopic investigation, the complex with α-cdx epichlorohydrin condensate showed a large amplitude and splitting of the induced π→π*band. Fractions of glyceryl ether of less than 2000 and polymer of more than 10000 dalton molecular mass were separated. Complexes of above two fractions and MO showed the same splitting spectral pattern. Job’s plots from visible spectra showed the formation of the 1:1 complex and CD-data suggested the co-existence of the 2:1 MO-cdx complex. This splitting pattern showed the reversal of the signs when α-cdx-ethyleneglycol-bis(epoxypropyl) ether was used and disappeared when larger host molecules and azo dyes were used. The splitting was explained by exciton interaction.