MALDI-MS Imaging Analysis of Noninflammatory Type III Rotaxane Dendrimers.

Rotaxane dendrimers with hyperbranched macromolecular interlocked structures and size modulation capacity demonstrate drug binding and release ability upon external stimuli. Mass spectrometry imaging (MSI) can offer the high-throughput screening of endogenous/exogenous compounds. Herein, we reported a novel method to display the in situ spatial distribution of label-free monodispersed type III rotaxane dendrimers (RDs) G1 (first generation, size ∼1.5 nm) and G2 (second generation, size ∼5 nm) that were explored as potential drug vehicles in spleen tissue by using matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-MSI). Experimental results indicated that the trans-2-[3-(4-tert-butylphenyl)-2-methyl-2-propenylidene]malononitrile (DCTB) matrix exhibited the best performance for monodispersed type III RDs G1 and G2. The optimized method was successfully applied to map the in vivo spatial distribution of type III RDs G1 and G2 in the spleen from intraperitoneally injected mice. The MALDI-MSI images revealed that RDs G1 and G2 were relatively stable in the spleen within 24 h after administration. It was found that the identified type III RDs G1 and G2 penetrated through the tunica serosa and were predominantly localized in red pulp regions of spleens. They were also mapped in a marginal zone of spleens simultaneously. There was almost no toxicity of type III RDs G1 and G2 to mice spleens from the H&E results. Furthermore, the type III RDs did not induce the expression of inflammatory cytokines from peripheral blood mononuclear cells (PBMCs) or THP-1 monocytes. The MSI analysis not only demonstrated its ability to image select rotaxane dendrimers in a rapid and efficient manner but also provided tremendous assistance on the applications of the further treatment of cancerous tissue as safe drug carriers. Furthermore, the new strategy demonstrated in this study could be applied on other label-free mechanically interlocked molecules, molecular machines, and macromolecules, which opened a new path to evaluate the toxicological and pharmacokinetic characteristics of these novel materials at the suborgan level.

Analysis of a polydisperse polyrotaxane based on poly(ethylene oxide) and α-cyclodextrins using nanoelectrospray and LTQ-Orbitrap.

Polyrotaxanes (PR) are among the most studied interlocked molecules in the field of supramolecular chemistry. Cyclodextrin based polyrotaxanes (CD based PRs) are well-known to be difficult to analyze by mass spectrometry (MS). Nanoelectrospray (nanoESI) employed during mass spectrometry (MS) and tandem mass spectrometry (MS/MS) experiments turns out to be particularly useful to analyze these noncovalent assemblies. While ESI/nanoESI based spectra usually contain multicharged species which greatly complicate the interpretation, particularly for such complex mixtures analysis, the hyphenation with a high resolution analyzer such as Orbitrap could overcome this limitation. This Article reports efforts to achieve a detailed structural deciphering by nanoESI-MS and nanoESI-MS/MS of CD based PRs constituted of αCDs, unmodified or surrounded by 1 or 2 sulfation(s), which were threaded along polydisperse poly(ethylene oxide) α,ω-dipyrenyl chains. The described method is more sensitive and less sample consuming than a typical NMR experiment and in good agreement with size-exclusion chromatography (SEC) results. Moreover, as compared to MALDI-TOF MS analysis, all populations were presumably elucidated without discrimination effect. Therefore, this MS development allowed us to estimate the PR sample content with 16 to 35 ethylene oxide units, 1 to 5 αCDs threaded, and 0 to 10 sulfo groups grafted on the overall CDs. Finally, the method afforded the possibility to unambiguously attribute supramolecular architectures from 2276.0278 to 7767.8342 g·mol(-1) corresponding to poly[2]- to poly[6]rotaxanes.

Thermal properties and microstructures of methylated polyrotaxane solutions.

Aqueous solutions of polyrotaxanes consisting of poly(ethylene glycol) and methylated alpha-cyclodextrins (alpha-CD) were studied by means of differential scanning calorimetry (DSC), dynamic light scattering, and X-ray diffraction in order to investigate the effect of the degree of methylation on thermoresponsive behavior. Polyrotaxanes with a degree of methylation higher than 50% had a lower critical solution temperature (LCST) and showed reversible associations and dissociations in water. In the transmittance measurements, the cloud point of methylated polyrotaxanes (MePR) shifted to a lower temperature with an increase in the degree of methylation. The heating curve obtained by DSC for the nearly permethylated polyrotaxane showed one broad endothermic peak that was associated with the microcrystallization of methylated CDs by hydrophobic interactions. On the other hand, the DSC profiles for partially methylated polyrotaxanes had several endothermic peaks, indicating multiple phase transitions of the MePR solutions. The results imply that the thermal properties of the MePR-water system are significantly affected by not only the methyl groups on alpha-CDs but also by the remaining hydroxyl groups.

Monitoring cyclodextrin-polyviologen pseudopolyrotaxanes with the Bradford assay.

Self-assembled multivalent pseudopolyrotaxanes, composed of lactoside-bearing cyclodextrin (CD) rings threaded on linear polyviologen polymers, have been introduced recently as flexible and dynamic neoglycoconjugates. In the course of this research, it was found that polyviologens are responsive to the Bradford assay, which is traditionally highly selective for proteins. The response of the pseudopolyrotaxanes to the Bradford assay was dependant on, and thus indicative of, the degree of threading of the CD rings onto the polyelectrolyte. The assay was then used to report on the threading and dethreading of native and lactoside-bearing alpha-CD rings onto and off of polyviologen chains, a phenomenon which demonstrates the utility of biochemical assays to address problems unique to supramolecular chemistry.

Macroscopic transport by synthetic molecular machines.

Nature uses molecular motors and machines in virtually every significant biological process, but demonstrating that simpler artificial structures operating through the same gross mechanisms can be interfaced with-and perform physical tasks in-the macroscopic world represents a significant hurdle for molecular nanotechnology. Here we describe a wholly synthetic molecular system that converts an external energy source (light) into biased brownian motion to transport a macroscopic cargo and do measurable work. The millimetre-scale directional transport of a liquid on a surface is achieved by using the biased brownian motion of stimuli-responsive rotaxanes ('molecular shuttles') to expose or conceal fluoroalkane residues and thereby modify surface tension. The collective operation of a monolayer of the molecular shuttles is sufficient to power the movement of a microlitre droplet of diiodomethane up a twelve-degree incline.

Halide anion directed assembly of luminescent pseudorotaxanes.

A series of new photo-active rhenium(i) bipyridyl based pseudorotaxane complexes is assembled via halide anion templation.