A Cyclodextrin Polymer as Supramolecular Matrix for Scalable Green Photooxygenation of Hydrophobic Substrates in Homogeneous Phase.

In the quest for new therapies targeting hypoxia, aromatic endoperoxides have intriguing potential as oxygen releasing agents (ORAs) able to free O2 in tissues upon suitable trigger. Four aromatic substrates were synthesized and the formation of their corresponding endoperoxides was optimized in organic solvent upon selective irradiation of Methylene Blue, a low-cost photocatalyst, producing the reactive singlet oxygen species. Complexation of the hydrophobic substrates within a hydrophilic cyclodextrin (CyD) polymer allowed their photooxygenation in homogeneous aqueous environment using the same optimized protocol upon dissolution in water of the three readily accessible reagents. Notably, reaction rates were comparable in buffered D2 O and organic solvent and, for the first time, the photooxygenation of highly hydrophobic substrates was achieved for millimolar solutions in non-deuterated water. Quantitative conversion of the substrates, straightforward isolation of the endoperoxides and recovery of the polymeric matrix were achieved. Cycloreversion of one ORA to the original aromatic substrate was observed upon thermolysis. These results hold great potential for the launch of CyD polymers both as reaction vessels for green, homogeneous photocatalysis and as carrier for the delivery of ORAs in tissues.

Silylated-Acetylated Cyclodextrins as Chiral Sensors for the Enantiodiscrimination of Fluorinated Anesthetics.

Silylated-acetylated cyclodextrin (CD) derivatives have recently been investigated, via nuclear magnetic resonance (NMR) spectroscopy, as chiral sensors for substrates that are endowed and devoid of fluorine atoms, and the importance of Si-F interaction in the discrimination phenomena has been assessed. Here, the contributions of both superficial interactions and inclusion processes were further evaluated by extending the records to other chiral fluorinated substrates of interest for pharmaceutical applications. Non-equivalences were measured for both the 1H and 19F resonances in equimolar mixtures with the CDs; the promising results also supported the use of chiral sensors in sub-stoichiometric amounts. Finally, the occurrence of inclusion processes was evaluated by analyzing the intermolecular dipolar interactions by means of ROESY (Rotating-frame Overhauser Enhancement Spectroscopy) experiments. The study confirmed that the γCD derivative is the best chiral solvating agent for the fluorinated substrates investigated, likely due to the higher number of silyl moieties that can be involved in Si-F interactions. The contribution of inclusion processes to the enantiodiscrimination was also confirmed by comparison with the α- and ß-analogues. Overall, the CD derivatives proved to be able to discriminate fluorinated substrates even when used in sub-stoichiometric amounts.

Sulfobutylation of Beta-Cyclodextrin Enhances the Complex Formation with Mitragynine: An NMR and Chiroptical Study.

Mitragynine (MTR), the main indole alkaloid of the well-known plant kratom (Mitragyna speciosa), is one of the most studied natural products nowadays, due to its remarkable biological effects. It is a partial agonist on the opioid receptors, and as such relieves pain without the well-known side-effects of the opioids applied in the clinical practice. MTR and its derivatives therefore became novel candidates for drug development. The poor aqueous solubility and low bioavailability of drugs are often improved by cyclodextrins (CyDs) as excipients through host-guest type complex formation. Among the wide variety of CyDs, sulfobutylether-beta-cyclodextrin (SBEßCyD) is frequently used and official in the European and U.S. Pharmacopoeia. Herein, the host-guest complexation of MTR with ßCyD and SBEßCyD was studied using chiroptical and NMR spectroscopy. It was found by NMR measurements that MTR forms a rather weak (logß11 = 0.8) 1:1 host-guest complex with ßCyD, while the co-existence of the 2MTR∙SBEßCyD and MTR∙SBEßCyD species was deducted from 1H NMR titrations in the millimolar MTR concentration range. Sulfobutylation of ßCyD significantly enhanced the affinity towards MTR. The structure of the formed inclusion complex was extensively studied by circular dichroism spectroscopy and 2D ROESY NMR. The insertion of the indole moiety was confirmed by both techniques.

Fully Symmetric Cyclodextrin Polycarboxylates: How to Determine Reliable Protonation Constants from NMR Titration Data.

Acid-base properties of cyclodextrins (CDs), persubstituted at C-6 by 3-mercaptopropionic acid, sualphadex (Suα-CD), subetadex (Suß-CD) and sugammadex (Suγ-CD, the antidote of neuromuscular blocking steroids) were studied by 1H NMR-pH titrations. For each CD, the severe overlap in protonation steps prevented the calculation of macroscopic pKa values using the standard data fitting model. Considering the full symmetry of polycarboxylate structures, we reduced the number of unknown NMR parameters in the "Q-fitting" or the novel "equidistant macroscopic" evaluation approaches. These models already provided pKa values, but some of them proved to be physically unrealistic, deceptively suggesting cooperativity in carboxylate protonations. The latter problem could be circumvented by adapting the microscopic site-binding (cluster expansion) model by Borkovec, which applies pairwise interactivity parameters to quantify the mutual basicity-decreasing effect of carboxylate protonations. Surprisingly, only a single averaged interactivity parameter could be calculated reliably besides the carboxylate 'core' microconstant for each CD derivative. The speciation of protonation isomers hence could not be resolved, but the optimized microscopic basicity parameters could be converted to the following sets of macroscopic pKa values: 3.84, 4.35, 4.81, 5.31, 5.78, 6.28 for Suα-CD; 3.82, 4.31, 4.73, 5.18, 5.64, 6.06, 6.54 for Suß-CD and 3.83, 4.28, 4.65, 5.03, 5.43, 5.81, 6.18, 6.64 for Suγ-CD. The pH-dependent charge of these compounds can now be accurately calculated, in support of designing new analytical methods to exploit their charge-dependent molecular recognition such as in cyclodextrin-aided chiral capillary electrophoresis.

Enhancing the Anticancer Activity of Sorafenib through Its Combination with a Nitric Oxide Photodelivering ß-Cyclodextrin Polymer.

In this contribution, we report a strategy to enhance the therapeutic action of the chemotherapeutic Sorafenib (SRB) through its combination with a multifunctional ß-cyclodextrin-based polymer able to deliver nitric oxide (NO) and emit green fluorescence upon visible light excitation (PolyCDNO). The basically water-insoluble SRB is effectively encapsulated in the polymeric host (1 mg mL-1) up to a concentration of 18 µg mL-1. The resulting host-guest supramolecular complex is able to release SRB in sink conditions and to preserve very well the photophysical and photochemical properties of the free PolyCDNO, as demonstrated by the similar values of the NO release and fluorescence emission quantum efficiencies found. The complex PolyCDNO/SRB internalizes in HEP-G2 hepatocarcinoma, MCF-7 breast cancer and ACHN kidney adenocarcinoma cells, localizing in all cases mainly at the cytoplasmic level. Biological experiments have been performed at SRB concentrations below the IC50 and with light doses producing NO at nontoxic concentrations. The results demonstrate exceptional mortality levels for PolyCDNO/SRB upon visible light irradiation in all the different cell lines tested, indicating a clear synergistic action between the chemotherapeutic drug and the NO. These findings can open up exciting avenues to potentiate the anticancer action of SRB and, in principle, to reduce its side effects through its use at low dosages when in combination with the photo-regulated release of NO.

Cellular Effects of Cyclodextrins: Studies on HeLa Cells.

Cyclodextrins are high molecular weight, hydrophilic, cyclic, non-reducing oligosaccharides, applied as excipients for the improvement of the solubility and permeability of insoluble active pharmaceutical ingredients. On the other hand, beta-cyclodextrins are used as cholesterol sequestering agents in life sciences. Recently, we demonstrated the cellular internalization and intracellular effects of cyclodextrins on Caco-2 cells. In this study, we aimed to further investigate the endocytosis of (2-hydroxylpropyl)-beta-(HPBCD) and random methylated-beta-cyclodextrin (RAMEB) to test their cytotoxicity, NF-kappa B pathway induction, autophagy, and lysosome formation on HeLa cells. These derivatives were able to enter the cells; however, major differences were revealed in the inhibition of their endocytosis compared to Caco-2 cells. NF-kappa B p65 translocation was not detected in the cell nuclei after HPBCD or RAMEB pre-treatment and cyclodextrin treatment did not enhance the formation of autophagosomes. These cyclodextrin derivates were partially localized in lysosomes after internalization.

Enantioseparation of solriamfetol and its major impurity phenylalaninol by capillary electrophoresis using sulfated gamma cyclodextrin.

R-solriamfetol is a recently approved drug used for the treatment of excessive sleepiness associated with narcolepsy and sleep apnea. Herein, a capillary electrophoretic method was developed, enabling the simultaneous analysis of the API and its S-enantiomer in addition to the enantiomers of its major impurity phenylalaninol. Twenty-nine different cyclodextrins (CDs), including native, neutral, and charged ones were screened as potential chiral selectors, and the best results were obtained with sulfated CDs. Randomly sulfated-ß-CD exhibited outstanding enantioresolution, the peaks of phenylalaninol enantiomers inserted between the two peaks of solriamfetol enantiomers, while sulfated-γ-CD (S-γ-CD) showed remarkable resolution values in a much shorter analysis time with the optimal enantiomer migration order. Among the single isomer sulfated CD derivatives, substituent dependent enantiomer migration order reversal could also be observed in the case of heptakis(6-O-sulfo)-ß-CD (HS-ß-CD) or heptakis(2,3-O-dimethyl-6-O-sulfo)-ß-CD (HDMS-ß-CD) with R-,S-solriamfetol, and heptakis(2,3-O-diacetyl-6-O-sulfo)-ß-CD (HDAS-ß-CD) resulting S-,R-solriamfetol migration order. The sulfated-γ-CD system was chosen for method optimization applying orthogonal experimental design. The optimized method (45 mM Tris-acetate buffer, pH 4.5, 4 mM S-γ-CD, 21°C, +19.5 kV) was capable for the baseline separation of solriamfetol and phenylalaninol enantiomers within 7 min. The optimized method was validated according to the ICH guidelines and successfully applied for the analysis of pharmaceutical preparation (Sunosi® 75 mg tablet), thus it may serve as a routine procedure for the laboratories of regulatory authorities as well as in Pharmacopoeias.

Single Isomer N-Heterocyclic Cyclodextrin Derivatives as Chiral Selectors in Capillary Electrophoresis.

In order to better understand the chiral recognition mechanisms of positively charged cyclodextrin (CD) derivatives, the synthesis, the pKa determination by 1H nuclear magnetic resonance (NMR)-pH titration and a comparative chiral capillary electrophoretic (CE) study were performed with two series of mono-substituted cationic single isomer CDs. The first series of selectors were mono-(6-N-pyrrolidine-6-deoxy)-ß-CD (PYR-ß-CD), mono-(6-N-piperidine-6-deoxy)-ß-CD (PIP-ß-CD), mono-(6-N-morpholine-6-deoxy)-ß-CD (MO-ß-CD) and mono-(6-N-piperazine-6-deoxy)-ß-CD (PIPA-ß-CD), carrying a pH-adjustable moiety at the narrower rim of the cavity, while the second set represented by their quaternarized, permanently cationic counterparts: mono-(6-N-(N-methyl-pyrrolidine)-6-deoxy)-ß-CD (MePYR-ß-CD), mono-(6-N-(N-methyl-piperidine)-6-deoxy)-ß-CD (MePIP-ß-CD), mono-(6-N-(N-methyl-morpholine)-6-deoxy)-ß-CD (MeMO-ß-CD) and mono-(6-N-(4,4-N,N-dimethyl-piperazine)-ß-CD (diMePIPA-ß-CD). Based on pH-dependent and selector concentration-dependent comparative studies of these single isomer N-heterocyclic CDs presented herein, it can be concluded that all CDs could successfully be applied as chiral selectors for the enantiodiscrimination of several negatively charged and zwitterionic model racemates. The substituent-dependent enantiomer migration order reversal of dansylated-valine using PIP-ß-CD contrary to PYP-ß-CD, MO-ß-CD and PIPA-ß-CD was also studied by 1H- and 2D ROESY NMR experiments.

Synthesis of the chiral selector heptakis(6-O-methyl)-ß-cyclodextrin by phase-transfer catalysis and hydrazine-mediated transfer-hydrogenation.

The exhaustive primary-side alkylation of cyclodextrins has never been achieved directly. The undesired and simultaneous derivatization of the secondary hydroxyl moieties generates intricate isomeric mixtures that are challenging to purify, analyse and characterize. The aim of this study was to develop a chromatography-free and up-scalable strategy towards the preparation of per-6-O-methylated cyclodextrin and to test the compound as potential chiral selector. The target molecule was prepared according to a five-step synthesis by using methyltriphenylphosphonium bromide as catalyst under heterogeneous conditions. The removal of benzyl moieties, used as temporary secondary-side protecting groups, was attained by applying hydrazine-carbonate in the presence of Pd/C. All the intermediates were obtained in high yields, thoroughly characterized and their purity was assessed by ad-hoc developed HPLC methods. The per-6-O-methylated ß-cyclodextrin showed promising chiral recognition ability as background electrolyte additive in cyclodextrin-modified capillary electrophoresis using the recreational drug methylene-dioxypyrovalerone as model compound. Additionally, a model for the inclusion geometry between the single isomer host and the selected drug was developed based on the extensive 2D NMR analysis. The versatility of the proposed synthetic strategy opens the way to the industrial production of homogeneously primary-alkylated cyclodextrins and to their wide application in chiral separation of various drugs.

Comparative analysis of the full set of methylated ß-cyclodextrins as chiral selectors in capillary electrophoresis.

The chiral separation ability of the full library of methylated-ß-cyclodextrins towards pharmacologically significant racemic drugs including basic compounds was studied by chiral CE. The syntheses of all the methylated, single isomer ß-cyclodextrins were revised and optimized and the aqueous solubility of the derivatives was unambiguously established. The three most relevant commercially available methylated isomeric mixtures were also included in the screening, so a total of ten various methylated CDs were investigated. The effects of the selector concentration on the enantiorecognition properties at acidic pH were investigated. Among the dimethylated ß-cyclodextrins, the heptakis (2,6-di-O-methyl)-ß-cyclodextrin isomer (2,6-DIMEB) resulted to be the most versatile chiral selector. Terbutaline was selected as a model compound for the in-depth investigation of host-guest enantiodiscrimination ability. The association constants between the two terbutaline enantiomers and 2,6-DIMEB were determined in order to support that the enantioseparation is driven by differences is host-guest binding. The migration order of the enantiomers was confirmed by performing spiking experiments with the pure enantiomers. 1D and 2D NMR spectroscopy was applied to the 2,3-, and 2,6-DIMEB/terbutaline systems to rationalize at molecular level the different enantioseparation ability of the dimethylated ß-cyclodextrin selectors.

A Three-Color Fluorescent Supramolecular Nanoassembly of Phototherapeutics Activable by Two-Photon Excitation with Near-Infrared Light.

A supramolecular nanoassembly, of about 30 nm in diameter, that consists of a green-fluorescent, ß-cyclodextrin-based, branched polymer co-encapsulating a red-emitting singlet oxygen (1 O2 ) photosensitizer and a nitric oxide (NO) photoreleaser, which comprises a blue fluorescent reporter, is here reported. The system exhibits "five-in-one" photofunctionalities. All components can be simultaneously excited in the phototherapeutic window with two-photons by using near-infrared light at 740 nm and despite their close proximity, behave as independent units. This allows for their in vitro visualization in carcinoma cancer cells, due to their distinct green, red, and blue fluorescence, and for the production of both cytotoxic 1 O2 and biofunctional NO.

Homo- and hetero-difunctionalized ß-cyclodextrins: Short direct synthesis in gram scale and analysis of regiochemistry.

The regioselective difunctionalization of cyclodextrins (CDs) leading to derivatives amenable to further transformations is a daunting task due to challenging purification and unambiguous characterization of the obtained regioisomers with similar physicochemical properties. The primary-side homo-difunctionalization of ß-CD can lead to three regioisomers, while the hetero-difunctionalization can generate three pairs of pseudoenantiomers. Previously, approaches with several synthetic steps, expensive reagents, high purification demands and low yields of the products have been employed. Herein we present direct, short and efficient primary-side difunctionalization strategies featuring reproducibility, ease of product purification, scalability of the reactions and versatility of the substituents introduced. Specifically, the prepared ditosylated ß-CDs were separated using preparative reversed-phase column chromatography and their structures were elucidated by NMR experiments. Azidation led to the corresponding pure diazido regioisomers. Direct monotosylation of 6-monoazido-ß-CD or monoazidation of the single regioisomers 6A,6X-ditosyl-ß-CDs afforded hetero-difunctionalized 6A-monoazido-6X-tosyl-ß-CDs in significant yields. Overall, the single regioisomers, 6A,6X-ditosyl-, 6A,6X-diazido- and 6A-monoazido-6X-monotosyl-ß-CD were prepared in one or two steps and purified in multigram scale thus opening the way towards further selective and orthogonal functionalizations of ß-CD hosts.

Widening the Therapeutic Perspectives of Clofazimine by Its Loading in Sulfobutylether ß-Cyclodextrin Nanocarriers: Nanomolar IC50 Values against MDR S. epidermidis.

Clofazimine (CLZ) is an antibiotic with a promising behavior against Gram-positive bacteria; however, the drug is completely insoluble in water and accumulates in fat tissues. We explored nanocarriers, labeled and not labeled with rhodamine, consisting of negatively charged sulfobutylether-ß-cyclodextrins for CLZ loading. A new oligomeric carrier was obtained cross-linking ßCyD with epichlorohydrin followed by sulfonation in a strongly alkaline aqueous medium. The oligomeric carrier has a MW of 53 kDa and forms small nanoparticles of a few tens of nm. With aqueous solutions containing a 25 mg/mL oligomeric carrier, we loaded up to 0.5 mg/mL of drug. The oligomers exhibited a 10-fold better loading capacity compared to monomers and formed nanoparticles with a size in the 20-60 nm range after drug loading. Circular dichroism confirmed encapsulation of the CLZ in the nanocarriers. All carriers with or without CLZ are not cytotoxic up to 1 µM, while CLZ alone is highly cytotoxic at the same concentration. The drug has IC50 values below 100 nM against S. epidermidis. The same holds true also for clinical isolates of S. epidermidis, some displaying MDR. So, the selectivity index significantly increased for CLZ/carrier systems compared to the drug alone. Taken all together, our results open new avenues for the clinical application of this antibiotic.

Enhanced single-isomer separation and pseudoenantiomer resolution of new primary rim heterobifunctionalized α-cyclodextrin derivatives.

The synthesis of batch-to-batch reproducible cyclodextrin (CD) derivatives often requires functionalization at specific positions of the CD skeleton. However, the regioselective preparation of this type of CD derivatives remains a challenge in synthetic chemistry. Thus, the present study aimed to prepare all positional regioisomers on the primary rim of homobifunctionalized diazido-α-CDs by selective substitution on the primary rim. Specifically, three positional regioisomers 6A,6B-, 6A,6C-, and 6A,6D-diazido-α-CDs were prepared via different intermediates (using sulfonylation with capping agents, bromination and tosylation). Furthermore, heterobifunctionalized 6A-azido-6X-mesitylenesulfonyl-α-CDs were also synthesized, and all regioisomers were successfully separated by HPLC. Moreover, the heterobifunctionalized α-CD regioisomers were isolated in gram-scale quantities, isomers AB and AC in the form of a pseudoenantiomeric mixture. The pseudoenantiomers AC/CA and AB/BA were resolved on an analytical scale by HPLC-MS at 10 °C. Thus, the presented synthetic and analytical methods for homo- and heterodisubstituted α-CDs are efficient and reproducible for the preparation of various pure regioisomeric CD derivatives. Accordingly, our findings indicate, (i) the versatility of selectively modified azido and mesitylene CD skeletons in preparing new types of α-CD derivatives and (ii) the potential of using resolved α-CD pseudoenantiomers in other research fields such as organocatalysis.

Characterization of a single-isomer carboxymethyl-beta-cyclodextrin in chiral capillary electrophoresis.

In this work, the synthesis, characterization, and chiral capillary electrophoretic study of heptakis-(2,3-di-O-methyl-6-O-carboxymethyl)-ß-CD (HDMCM), a single-isomer carboxymethylated CD, are presented. The pH-dependent and selector concentration-dependent enantiorecognition properties of HDMCM were investigated and discussed herein. The enantioseparation was assessed applying a structurally diverse set of noncharged, basic, and zwitterionic racemates. The increase in the selector concentration and gross negative charge of HDMCM improved the enantioseparation that could be observed in the majority of the cases. HDMCM was also successfully applied as BGE additive in NACE using a methanol-based system in order to prove the separation selectivity features and to highlight the broad applicability of HDMCM. Over 25 racemates showed partial or baseline separation with HDMCM under the conditions investigated, among which optimal enantiomer migration order was found for the four stereoisomers of tadalafil, tapentadol, and dapoxetine, offering the possibility of a chiral CE method development for chiral purity profiling of these drugs.

A non-covalent "click chemistry" strategy to efficiently coat highly porous MOF nanoparticles with a stable polymeric shell.

BACKGROUND: Metal-organic framework nanoparticles (nanoMOFs) are biodegradable highly porous materials with a remarkable ability to load therapeutic agents with a wide range of physico-chemical properties. Engineering the nanoMOFs surface may provide nanoparticles with higher stability, controlled release, and targeting abilities. Designing postsynthetic, non-covalent self-assembling shells for nanoMOFs is especially appealing due to their simplicity, versatility, absence of toxic byproducts and minimum impact on the original host-guest ability. METHODS: In this study, several ß-cyclodextrin-based monomers and polymers appended with mannose or rhodamine were randomly phosphorylated, and tested as self-assembling coating building blocks for iron trimesate MIL-100(Fe) nanoMOFs. The shell formation and stability were studied by isothermal titration calorimetry (ITC), spectrofluorometry and confocal imaging. The effect of the coating on tritium-labeled AZT-PT drug release was estimated by scintillation counting. RESULTS: Shell formation was conveniently achieved by soaking the nanoparticles in self-assembling agent aqueous solutions. The grafted phosphate moieties enabled a firm anchorage of the coating to the nanoMOFs. Coating stability was directly related to the density of grafted phosphate groups, and did not alter nanoMOFs morphology or drug release kinetics. CONCLUSION: An easy, fast and reproducible non-covalent functionalization of MIL-100(Fe) nanoMOFs surface based on the interaction between phosphate groups appended to ß-cyclodextrin derivatives and iron(III) atoms is presented. GENERAL SIGNIFICANCE: This study proved that discrete and polymeric phosphate ß-cyclodextrin derivatives can conform non-covalent shells on iron(III)-based nanoMOFs. The flexibility of the ß-cyclodextrin to be decorated with different motifs open the way towards nanoMOFs modifications for drug delivery, catalysis, separation, imaging and sensing. This article is part of a Special Issue entitled "Recent Advances in Bionanomaterials" Guest Editors: Dr. Marie-Louise Saboungi and Dr. Samuel D. Bader.

Novel ß-cyclodextrin-eosin conjugates.

Eosin B (EoB) and eosin Y (EoY), two xanthene dye derivatives with photosensitizing ability were prepared in high purity through an improved synthetic route. The dyes were grafted to a 6-monoamino-ß-cyclodextrin scaffold under mild reaction conditions through a stable amide linkage using the coupling agent 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride. The molecular conjugates, well soluble in aqueous medium, were extensively characterized by 1D and 2D NMR spectroscopy and mass spectrometry. Preliminary spectroscopic investigations showed that the ß-cyclodextrin-EoY conjugate retains both the fluorescence properties and the capability to photogenerate singlet oxygen of the unbound chromophore. In contrast, the corresponding ß-cyclodextrin-EoB conjugate did not show either relevant emission or photosensitizing activity probably due to aggregation in aqueous medium, which precludes any response to light excitation.

New synthetic strategies for xanthene-dye-appended cyclodextrins.

Xanthene dyes can be appended to cyclodextrins via an ester or amide bridge in order to switch the fluorescence on or off. This is made possible through the formation of nonfluorescent lactones or lactams as the fluorophore can reversibly cyclize. In this context we report a green approach for the synthesis of switchable xanthene-dye-appended cyclodextrins based on the coupling agent 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMT-MM). By using 6-monoamino-ß-cyclodextrin and commercially available inexpensive dyes, we prepared rhodamine- and fluorescein-appended cyclodextrins. The compounds were characterized by NMR and IR spectroscopy and MS spectrometry, their UV-vis spectra were recorded at various pH, and their purity was determined by capillary electrophoresis. Two potential models for the supramolecular assembly of the xanthene-dye-appended cyclodextrins were developed based on the set of data collected by the extensive NMR characterization.

Supramolecular structures based on regioisomers of cinnamyl-α-cyclodextrins - new media for capillary separation techniques.

This work focuses on the preparation and application of supramolecular structures based on mono-cinnamyl-α-cyclodextrins (Cin-α-CD). Pure regioisomers of Cin-α-CD having the cinnamyl moiety at the 2-O- or at the 3-O-position, respectively, were prepared, characterized and applied in capillary electrophoresis as additives to the background electrolyte. These new monomer units with a potential to self-organize into supramolecular structures were synthesized via a straightforward one-step synthetic procedure and purified using preparative reversed-phase chromatography allowing a large scale separation of the regioisomers. The ability of the monomers to self-assemble was proved by various methods including NMR spectroscopy and dynamic light scattering (DLS). The light scattering experiments showed that the monomer units have distinguishable ability to form supramolecular structures in different solvents and the size distribution of the aggregates in water can be easily modulated using different external stimuli, such as temperature or competitive guest molecules. The obtained results indicated that the two regioisomers of Cin-α-CD formed different supramolecular assemblies highlighting the fact that the position of the cinnamyl group plays an important role in the intermolecular complex formation.

Synthetic strategies for the fluorescent labeling of epichlorohydrin-branched cyclodextrin polymers.

The fluorescent tagging of cyclodextrin derivatives enlarges their spectroscopic properties thus generating chemosensors, biological tools for visualization and sophisticated photoresponsive devices. Cyclodextrin polymers, due to the cooperative interactions, exhibit additional properties compared to their monomeric counterpart. These macromolecules can be prepared either in well water-soluble form or as gels of high swelling. Two versatile synthetic strategies for introducing a fluorescent tag (rhodamine, fluorescein, nitrobenzofuran or coumarin) into the water-soluble epichlorohydrin branched cyclodextrin polymers were worked out and compared. The fluorescent labeling was realized in three steps: 1) building in azido moieties, 2) transforming the azido groups into amino groups and 3) coupling the proper fluorescent compound to the amino groups. The other strategy started by functionalization of the monomer prior to the branching. Either the fluorescent-labeled monomer or the intermediate azido derivative of the monomer was branched. Further tuning of the properties of the polymer was achieved via branching of the methylated cyclodextrin derivative. The key intermediates and the fluorescent final products were characterized by various spectroscopic techniques and capillary electrophoresis. The applied synthetic routes were evaluated based on the molecular weight, cyclodextrin content of the products and the efficiency of labeling.