Inclusional Complexation by Cyclodextrin−Polymer Conjugates in Organic Solvents

Targeted biodegradable dendritic MRI contrast agent for enhanced tumor imaging

Highly sensitive and safe contrast agents (CAs) are essential for magnetic resonance imaging (MRI) to achieve accurate tumor detection and imaging. Dendrimer-based macromolecular MRI contrast agents are advantageous owing to their tumor-targeting ability, enhanced imaging contrast and enlarged imaging window. However, most of them have drawbacks of non-degradability and thereby long-term retention in body and toxicity. Herein, a tumor-targeting biodegradable dendritic CA (DCA) (FA-PEG-G2-DTPA-Gd) was prepared from a polyester dendrimer conjugated with gadolinium (Gd) chelates and PEG chains with distal folic acid. The DCA had a high longitudinal relaxivity up to 17.1mM(-1)s(-1), 4 times higher than the clinically used CA Magnevist. The MRI contrasted by FA-PEG-G2-DTPA-Gd outlined the inoculated tumor more clearly, and had much higher contrast enhancement for a much longer time than Magnevist. More importantly, the biodegradable FA-PEG-G2-DTPA-Gd gave much less Gd retentions in all the organs or tissues than non-degradable DCAs. Thus, the high efficiency in MRI contrast enhancement and low Gd retention merit it a promising CA for contrast enhanced tumor MRI.

Self-oriented glucose-modified infrared sensor for the detection of compounds bearing carboxylic acid groups

To explore the interactions of self-oriented glucose toward organic species, we prepared a glucose-modified infrared (IR) chemical sensor and examined its performance in the detection of compounds bearing carboxylic acid functional groups. Using a two-layer modification method, we chemically bonded glucose to the surface of an IR sensing element. The immobilized glucose moieties exhibited the ability to assemble into a chemical form similar to that of the cyclodextrins (CDs) such that they could trap targeted molecules. This modified sensing phase displayed an analysis capability similar to that of CDs, but without the problems encountered attempting to maintain the activity of the latter. From a systematic examination of three classes of structural analogs of acids, we found that the behavior of the glucose-modified sensing phase was similar to that of a CD-modified sensing phase. In terms of quantitative detection, we obtained an average regression coefficient of approximately 0.996 for the analytical signals of the examined compounds at concentrations less than 20 mg/L. The linearity of the standard curves was related to the detection time: the shorter the detection time, the greater the linearity. Defined as three times the noise level, we obtained detection limits of a few hundred parts per billion (microg/L) for the determination of high-polarity compounds using our glucose-modified sensing phase.

Orientational effect of surface-confined cyclodextrin on the inclusion of bisphenols

The molecular recognition of various kinds of bisphenols (BPs) and a bisphenol A-polymer conjugate (BPA-polymer) by a self-assembled monolayer (SAM) of thiolated beta-cyclodextrin (CD) on a gold electrode was examined using cyclic voltammetry (CV). Based on the inhibitory effect of BPs on the inclusion of hydroquinone (HQ) as a probe by the surface-confined CD, the association constants (K(assoc)) of BPs with the immobilized beta-CD were estimated. The K(assoc) values for BPs with the SAM of 3-dithiobis(undecanoylamido)-3-deoxy-beta-cyclodextrin (DTUA-beta-CD) were smaller than those in the free beta-CD system reported previously. A similar tendency was obtained when 6-(lipoylamido)-6-deoxy-beta-cyclodextrin (LP-beta-CD) was used in place of DTUA-beta-CD. The K(assoc) values for all the BPs except for bisphenol B with the SAM of LP-beta-CD were always larger than those with the SAM of DTUA-beta-CD, due to a difference in the orientation of the beta-CD moiety in the SAMs. Furthermore, adsorption and desorption processes of the BPA-polymer from the surface-confined beta-CD was followed using local surface plasmon resonance spectroscopy.

Inclusion of phthalate esters by a self-assembled monolayer of thiolated cyclodextrin on a gold electrode

Complexation of phthalic acid esters (PAEs) by a self-assembled monolayer (SAM) of thiolated alpha-cyclodextrin (6-(2-mercaptoethylamino)-6-deoxy-alpha-cyclodextrin, MEA-alpha-CD) on a gold electrode was examined by a cyclic voltammetry using hydroquinone (HQ) as a probe. From the inhibitory effect of the phthalate esters on the inclusion of HQ by the surface-confined cyclodextrin (CD), the association constants (Kasn) of the esters with the immobilized CD were estimated. For comparison, the association of PAEs with free alpha-CD was examined spectrophotometrically using methyl orange as a probe. It was concluded that, in both free and surface-confined CD systems, the Kasn value increased with an increase in the length of aliphatic alcohols conjugated to phthalic acid. Furthermore, the Kasn values for PAEs in the SAM system were much larger than those in a free CD system. This could be intuitively ascribed to the steric factor for the PAEs to come out from the cavity of surface-confined CD, whose rim was in contact with the PAEs. Thermodynamic parameters indicated that the inclusion of PAEs in the SAM system was entropy-driven, which is different from the free CD system where the inclusion was favored by both enthalpy and entropy. This is partly due to the difficulties in cancellation of strain energy by the inclusion into the cavity of the densely fixed CD (97% of the calculated maximum) and partly due to the reduction of hydrogen bonding between the PAEs and the surface-confined CD. Desolvation of the PAEs and CD by the friction at the penetration into the cavity of CD, which was rigidly fixed to the electrode, might also contribute to the positive entropy change. These factors might emphasize the apolar factor of binding to be characterized by a favorable entropy change in the immobilized CD system.