Host-guest Supramolecular Complexes Research Articles

Durable organic nonlinear optical membranes for thermotolerant lightings and in vivo bioimaging

Organic nonlinear optical materials have potential in applications such as lightings and bioimaging, but tend to have low photoluminescent quantum yields and are prone to lose the nonlinear optical activity. Herein, we demonstrate to weave large-area, flexible organic nonlinear optical membranes composed of 4-N,N-dimethylamino-4ʹ-Nʹ-methyl-stilbazolium tosylate@cyclodextrin host-guest supramolecular complex. These membranes exhibited a record high photoluminescence quantum yield of 73.5%, and could continuously emit orange luminescence even being heated at 300 °C, thus enabling the fabrication of thermotolerant light-emitting diodes. The nonlinear optical property of these membranes can be well-preserved even in polar environment. The supramolecular assemblies with multiphoton absorption characteristics were used for in vivo real-time imaging of Escherichia coli at 1000 nm excitation. These findings demonstrate to achieve scalable fabrication of organic nonlinear optical materials with high photoluminescence quantum yields, and good stability against thermal stress and polar environment for high-performance, durable optoelectronic devices and humanized multiphoton bio-probes.

Cucurbituril-based Supramolecular complexes with platinum compounds influence on expression of CTLA-4 on Regulatory T cells

Tumors are a leading pathology in the population. Chemotherapy cannot provide adequately and effectively to cure patients. Some medicine, such as cytostatic, are characterized by a wide range of side effects and resistance of solid tumors to chemotherapy by these medicines. In recent research, the mechanisms of action of cytotoxic agents have been described, and the most appropriate causes of resistance have been suggested. Drug delivery system based on Cucurbit[7]uril (CB[7]) was used to minimize side effects and overcome resistance. CB[7] has ability to form host-guest supramolecular complexes with oxaliplatin and carboplatin.It is important to consider the immune system maintain to a great role, and platinum compounds are able to have an immunomodulatory effect on immunocompetent cells. There is convincing evidence about the cytotoxic response against tumor cells is also associated with immunomodulating properties. A specific immune microenvironment with high frequency of suppressor cells is made by tumors. FoxP3+ regulatory T cells are recruited by the tumor, an increased number of these cells and expression levels of CTLA-4 and PD-1 on them contribute to the progression of the tumor process. These markers correlate with recurrence and poor survival of the patients. Therefore, it is necessary that antitumor therapy agents have an effect on a subpopulation of regulatory T cells and their functional activity. This study evaluated the effects of cucurbit[7] uril, platinum compounds, and supramolecular complexes on FoxP3+ regulatory T cells and the expression of immune checkpoint molecules.In this study peripheral blood cells from volunteers (n = 8, average 29.0±2.4) were used. Mononuclear cells obtained in the standard protocol were incubated for 72 h at concentrations of 0.3 and 0.1 mM for carboplatin and oxaliplatin, respectively, as well as complexes and CB[7] in equivalent dosages. Next, the samples were labeled with monoclonal antibodies to determine the phenotype and expression of immune checkpoint molecules by flow cytometry.We obtained the following results: The CB[7]-carboplatin complex in stimulated and non-stimulated cultures significantly reduced the number of FoxP3+ regulatory T cells compared to the control. At the same time, carboplatin and the CB[7]-carboplatin complex reduced the expression of CTLA-4 in an non-stimulated culture compared to CB[7].Complexes of Cucurbit[7]urils with platinum compounds are a perspective antitumor agent with immunomodulatory properties.

Recent update on the electroactive oligopyrrolic macrocyclic hosts with a Bucky-ball heart.

Supramolecular chemistry is a multidisciplinary research area mostly associated with the investigation of host-guest interactions within intricate three-dimensional (3D) molecular architectures held together reversibly by various non-covalent interactions. Continuous efforts to develop such kinds of complex host-guest systems with designer oligopyrrolic macrocyclic receptors are a rapidly growing research domain, which is deeply involved in applied supramolecular chemistry research. These host-guest supramolecular complexes can be constructed by combining suitable electron-rich oligopyrrolic donors (as a host) with complementary electron-poor guests (as acceptors), held together by the ionic force of attraction triggered by intermolecular charge/electron transfer (CT/ET) transitions. Some of these resulting CT/ET ensembles are potential candidates for the construction of efficient optoelectronic materials, optical sensors, molecular switches, etc. In this Feature Article we aim to focus on these supramolecular ensembles composed by size and shape complementary electroactive oligopyrrolic molecular containers, which are suitable for spherical guest (e.g., buckminsterfullerene) complexation. We also provide a "state-of-the-art" overview on plausible applications of these particular host-guest systems. Our aim is to cover only specific electron-rich tetrathiafulvalene (TTF)-based oligopyrrolic receptors, e.g., TTF-calix[4]pyrroles, TTF-cryptands, TTF-porphyrins and exTTF-porphyrin-based molecular motifs reported to date, along with a brief outlining of their "functional behaviour" in materials chemistry research.

Modulation of supramolecular chirality by stepwise axial coordination in a nano-size trizinc(ii)porphyrin trimer.

Herein, we report a chiral guest's triggered spring-like contraction and extension motions coupled with unidirectional twisting in a novel flexible and 'nano-size' achiral trizinc(ii)porphyrin trimer host upon step-wise formation of 1 : 1, 1 : 2, and 1 : 4 host-guest supramolecular complexes based on the stoichiometry of the diamine guests for the first time. During these processes, porphyrin CD responses have been induced, inverted, and amplified, and reduced, respectively, in a single molecular framework due to the change in the interporphyrin interactions and helicity. Also, the sign of the CD couplets is just the opposite between R and S substrates which suggests that the chirality is dictated solely by the stereographic projection of the chiral center. Interestingly, the long-range electronic communications between the three porphyrin rings generate trisignate CD signals that provide further information about molecular structures.

Supramolecular architecture, Hirshfeld surface analysis and third-order nonlinear optical properties of crown ether with 5-nitroisophthalic acid monomethyl ester and trimesic acid

Two host-guest supramolecular complexes such as (18-crown-6)-2(5-nitroisophthalic acid monomethyl ester).2(H2O) (I) and (15-crown-6)-2(trimesic acid).2(H2O) (II), have been synthesized from ethanol-water (2:3, v/v) mixed solvent system. Crystal structures elucidated by single-crystal X-ray diffraction reveal that both belong to the triclinic system with centrosymmetric space group Pī. Inter- and intramolecular hydrogen bonding interactions and weak van der Walls forces construct the supramolecular architecture. Fingerprint plots of Hirshfeld surfaces were used to locate and analyse the percentage of hydrogen bonding interactions. The band gap energy was determined by the application of the Kubelka–Munk algorithm. The third-order nonlinear optical susceptibility (χ(3)) of the cocrystals are, 4.19 × 10−6 and 4.45 × 10−6 esu for (I) and (II) respectively.

Crystal structure, Hirshfeld surface analysis and third-order nonlinear optical properties of supramolecular complexes of 18-crown-6 with 6-hydrazinonicotinichydrazide and p-phenylenediamine

The crystal structures of the host-guest supramolecular complexes [2(6-HPCH)2+.3(18C6)].4[ClO4¯].2(H2O) (I) and [(PDA)2+.2(18C6)].2[Cl¯].10(H2O) (II) (18C6 = 18-crown-6; 6HPCH = 6-hydrazinylpyridine-1-ium-3-carbohydrazinium; PDA = p-phenylenediaminium) were determined by single-crystal X-ray diffraction analysis. Supramolecular assembly is constructed by NH···O, OH···O and C-H···O interactions. Both crystallize in the monoclinic system with centrosymmetric space group P21/n. The vibrational patterns in FT–IR are used to identify the functional groups. Direct band gap energy estimated by diffuse reflectance spectrum are, 3.42 eV for (I) and 4.78 eV for (II). Molecular interactions are analyzed by Hirshfeld surfaces, derived from single-crystal XRD data. Fingerprint plots of Hirshfeld surfaces were used to locate and analyze the percentage of hydrogen bonding interactions. A z-scan study was used to determine the third-order NLO response.

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

Tetrahydroxycalixarene methylenebisphosphonic acids: synthesis, stereochemistry, and aminoacids complexations

Interaction of the ready available monoformyl or diformyltetrahydroxycalixarenes with excess of diisopropylphosphite sodium salt gives isopropyl esters of tetrahydroxycalixarene methylenebisphosphonic acid or dimethylenebisphosphonic acid respectively with preparative yields. α-Hydroxymethylenephosphonates and phosphonyl quinon methids are formed as intermediates in the reaction. The obtained esters converts with quantitative yields into corresponding free acids by sequential treatment with trimethylbromosilane and methanol. The tetrahydroxycalixarene methylenebisphosphonic acids exist in the cone-shaped conformation and selectively form stable host-guest supramolecular complexes with aminoacids.

Long‐Range Charge Transportation Induced Organic Host–Guest Dual Color Long Persistent Luminescence

AbstractLong persistent luminescence (LPL) can store light energy in excited states and gradually release it as light. Organic host–guest systems provide a good platform for LPL, and single‐color LPL is often achieved while multicolor LPL is challengeable. Here host–guest supramolecular complexes are presented with dual LPL emissions: thermally activated delayed fluorescence (TADF) (≥100 ms) and room temperature phosphorescence (RTP). A space charge transfer from α‐cyclodextrin to diphenylacetylene (DPA) with long‐range transportation (2.32 mm) carrier along DPA strand in the supramolecular complexes is attributed to generate the TADF and RTP. Fortunately, these supramolecular complexes are readily fabricated from α‐cyclodextrin and DPA or DPA derivatives. The gradient color is observed after removing UV excitation. Furthermore, the hydrophobic property inside α‐cyclodextrin makes the LPL appear by water shedding and disappear by organic solvent infiltration, showing the character of a “switch.” This host–guest space charge transfer strategy paves a way to design LPL materials.

Pillar[5]arene-BODIPY host-guest interaction induced fluorescence enhancement and lysosomes targetable bioimaging in dilute solution

Supramolecular complex by pillar[5]arenes and BODIPY dyad through host-guest interaction was developed and showed aggregation induced emission (AIE) property. 1 H NMR titration and 2D NOESY NMR measurements were performed to evidence the host-guest interaction and the complex was formed by 1:1 M ratio. The fluorescence intensities of the BODIPY dyad were enhanced by increasing solution viscosity or and host-guest supramolecular interaction with pillar[5]arenes. Preliminary living cell imaging results demonstrated the highly emissive complex showed lysosome targetable property. • A BODIPY derivative and pillar[5]arenes formed host-guest supramolecular complexes. • The BODIPY derivative showed enhanced emission in viscous solution. • The complex showed lysosomes targetable property in living cell imaging.

A review on thermal analyses of cyclodextrins and cyclodextrin complexes

Cyclodextrins are valuable natural or synthetically modified cyclic oligosaccharides that are widely used for ameliorating properties of biologically active compounds such as food additives and ingredients or medicinal compounds. They protect these compounds against light and oxidative degradation and provide host–guest supramolecular complexes having controlled release properties by molecular encapsulation, enhancing the water solubility and bioavailability. Among many characterization methods that are applicable in both solution and solid state, thermal techniques were widely used for analysis and stability evaluation of cyclodextrins and cyclodextrin complexes. This updated review deals with the use of thermal methods for analysis of cyclodextrins and cyclodextrin complexes. Classical and modern thermal techniques used for evaluation of inclusion compound formation were reviewed. Special attention was gave for thermogravimetry–differential thermogravimetry, differential thermal analysis, differential scanning calorimetry, hot stage microscopy, as well as for the more recent techniques thermogravimetry–mass spectrometry, gas chromatography-time-of-flight-mass spectrometry and isothermal titration calorimetry. In order to evaluate the cyclodextrin complexation capability by thermal methods, we grouped for the first time the guest compound as drugs by anatomical therapeutic chemical classification (ATC), as well as odorants, essential oils and vegetable extracts, antioxidants, fatty acids, oils, fatty acid-based derivatives, other organic, organometallic and inorganic compounds. The formation of cyclodextrin inclusion complexes was emphasized by disappearance of the signal corresponding to the melting or boiling points of the guest compound and the behavior of the hydration water molecules in the complex in comparison with the raw host and guest compounds. The thermal stability of the guest compound after cyclodextrin complexation was also discussed. It was emphasized that thermal methods are some of the most valuable techniques for analyzing cyclodextrin complexes and together with other methods can complete the information related to the host–guest molecular inclusion process and the specific properties of these cyclodextrin complexes.

Visible Light-Induced Supra-Amphiphilic Switch Leads to Transition from Supramolecular Nanosphere to Nanovesicle Activated by Pillar[5]arene-Based Host-Guest Interaction.

A photoresponsive host-guest supramolecular complex (WP5⊃G) constructed by water-soluble pillar[5]arene (WP5) and spiropyran derivative (G) is presented. The spontaneous isomerization of G from spiropyran (SP) form to ring-opened merocyanine (MC) form happens either alone or in WP5⊃G in aqueous media. Irradiated by visible light, G can be converted into SP form completely and the hydrophilicity will be changed. G and WP5⊃G are both verified to self-assemble into nanospheres. Upon exposure to visible light, WP5⊃G reassemble into nanovesicles due to the change of supra-amphiphilicity, while G alone does not have this transition. Obviously, WP5 takes the key role that activates the photoinduced morphological transition.

Unexpected differences between planar and column liquid chromatographic retention of 1-acenaphthenol enantiomers controlled by supramolecular interactions involving \u03b2-cyclodextrin at subambient temperatures

We report the results of experimental work focusing on host-guest supramolecular complex creation between macrocyclic compound (β-cyclodextrin) and 1-acenaphthenol enantiomers (racemic mixture) in liquid phase composed of 35% acetonitrile in water (v/v) at different temperatures ranging from 0 to 90 °C. Experimental setup involved several analytical protocols based on classical non-forced flow planar chromatography (RP-18 TLC plates), micro-TLC (RP-18 W HPTLC plates), column chromatography (HPLC with C-18 and C-30 stationary phases), as well as UV-Vis spectrophotometry and optical microscopy. It has been found that under various planar chromatographic conditions (stationary plates type, chamber shape and volume, development mode, and saturation) non-typical retention properties (extremely high retention) of 1-acenaphthenol at subambient temperatures can be observed. To our knowledge, reported experimental results are in opposition to currently described retention models based on column chromatographic investigation of host-guest complexes (where in case of strong interaction of given analyte with macrocyclic mobile phases additive, which itself is non strongly retarded by stationary phase—close to the retention of dead volume marker, the retention of target compounds is shortened at low temperatures). To explain this TLC phenomenon that may have in our opinion a number of practical applications, especially for selective high throughput separation involving microchromatographic and/or microfluidic devices as well fractionation and extraction protocols (using, e.g., bar extraction systems), several experiments were conducted focusing on (i) acenaphthenol chromatography under different instrumental conditions, (ii) cyclodextrin retention measured as analyte or mobile phase additive, (iii) plate development time under different mobile phases and temperature settings, (iv) various column chromatographic conditions including C-30 and two C-18 stationary phases, (v) UV-Vis spectrophotometry, and (vi) microscopy inspection of precipitated CD-acenaphthenol crystals. Analysis of collected data has revealed that the most probable reasons for TLC retention behavior of 1-acenaphthenol under β-cyclodextrin additive conditions can be associated with (i) solubility changes of created host-guest complex, (ii) kinetics of solid complex precipitation, and (iii) differences in analysis time between planar and column chromatography. Because precipitation phenomenon may have a massive impact on analytes quantification involving macrocycles as the mobile phase additives, our previously reported data concerning a number of low-molecular compounds (mainly steroids and non steroidal endocrine disrupting chemicals) using HPLC methodology based on binary mobile phases without and with β-cyclodextrin and its hydroxypropyl derivative were re-examined and results discussed. Considering these data and the whole data set reported presently, the enhanced model of chromatographic retention driven by host-guest interaction was proposed.

Determination of association constant of host–guest supramolecular complex (molecular recognition of carbamazepine, antiseizure drug, with calix(4)arene)

The thermodynamic property of the host–guest, inclusion complex formed between p-t-butyl calix(4)arene which is a supramolecule, and the antiseizure drug, carbamazepine was studied. p-t-Butyl calix(4)arene has been used as a host molecule and carbamazepine as a guest molecule. Optical absorption spectral studies were carried out to investigate the molecular recognition properties of p-t-butyl calix(4)arene with carbamazepine. The stochiometry of the host–guest complexes formed and the association constant were determined. An interesting 1:2 stochiometric host–guest complex was formed. Job’s continuous method of variation and Benesi–Hildebrand expression were used for the determination of binding constant and the stochiometry of the host–guest complex formed. Molecular dimension of the host molecule plays a vital role in the formation of the host–guest stochiometric complexes.

Step-wise induction, amplification and inversion of molecular chirality through the coordination of chiral diamines with Zn(II) bisporphyrin.

For the first time, a clear and unambiguous rationalization of chirality induction, inversion and subsequent amplification process has been demonstrated for the 1 : 1 sandwich and 2 : 3 host-guest supramolecular complexes consisting of Zn(II) host and chiral diamines as guests that has so far remained the most outstanding issue for the chirogenic process.

Supramolecular interaction between a hydrophilic coumarin dye and macrocyclic hosts: spectroscopic and calorimetric study.

The photophysics of a hydrophilic molecule, 7-(diethylamino)-coumarin-3-carboxylic acid (7-DCCA), was studied in the presence of two macrocycles, (2-hydroxypropyl)-γ-cyclodextrin and cucurbit[7]uril. We have used steady-state absorption, fluorescence, and time-resolved fluorescence emission spectroscopy; Fourier transform infrared (FTIR) spectroscopy; (1)H NMR spectroscopy; and isothermal titration calorimetry (ITC) to confirm the supramolecular host-guest complex formation. The spectral properties of 7-DCCA were modulated in the presence of both macrocycles. It was assigned that 7-DCCA forms a 1:2 complex with (2-hydroxypropyl)-γ-cyclodextrin and cucurbit[7]uril. The large modulation of the emission properties of 7-DCCA in the presence of the macrocycles indicates the formation of supramolecular complexes. A significant shift in the bond vibration frequencies in the FTIR studies showed encapsulation of the dyes in the hydrophobic cavity of the macrocycles. This is further substantiated by the (1)H NMR studies, in which the upfield and downfield shifts of the protons were observed in both the aliphatic and aromatic region in the presence of macrocycles. The time-resolved anisotropy measurements further reinforce the conception of host-guest supramolecular complex formation because, in both cases, the rotational relaxation time increases significantly compared to that in water. A deeper understanding between the differences in interaction of an anionic molecule with cucurbit[7]uril and (2-hydroxypropyl)-γ-cyclodextrin will be achieved through this work. From the ITC measurement, we have formulated the forces due to complex formation.

Chameleon-like behaviour of cyclo[n]paraphenylenes in complexes with C70: on their impressive electronic and structural adaptability as probed by Raman spectroscopy

A series of four 1 : 1 host-guest supramolecular complexes of [n]CPPs and C(70) have been analyzed by Raman spectroscopy in the solid state and complemented with the analysis of their spectroscopic responses under mechanical and thermal stresses. By following the frequency behaviour of the G and RBM modes we have found that [10]CPP in the [10]CPP@C(70) complex displays a more "ordered" structure. However, in [11]CPP@C(70), the nanoring becomes oval-shaped with closer contacts with the C(70) poles and less conformational restriction in the flattened region. By mechanical and thermal stresses we are able to modify the lying conformation of [10]CPP@C(70) towards a standing orientation. [11]CPP@C(70) resists pressure changes, although it tends to shift from the standing to the lying orientation by heating. As for the crystal cell, the [n]CPPs occupy the residual empty spaces while the main crystallographic positions are reserved for C(70). These are new examples of the impressive adaptability of the [n]CPP molecules to different physico-chemical environments, a chameleon-like property which reveals the delicate equilibrium provided by cyclic conjugation and ring strain.

Transfer and control of molecular chirality in the 1 : 2 host-guest supramolecular complex consisting of Mg(II)bisporphyrin and chiral diols: the effect of H-bonding on the rationalization of chirality.

A clear rationalization of the origin of chirality transfer from an optically active diol guest to an achiral Mg(ii)bisporphyrin host in a series of 1 : 2 host-guest supramolecular complexes has been reported here that has so far remained the most outstanding issue for the chirogenic process.

Fluorescence Dynamics of Coumarin C522 as a Function of Micelle Confinement along with Cyclodextrin Supramolecular Complex Formation

Our aim is to doubly confine a molecule of coumarin C522 in a host-guest supramolecular complex with β-cyclodextrin in a reverse sodium dioctyl sulfosuccinate (AOT) micelle using nonpolar n-heptane and polar water solvents. Varying the volumes of coumarin C522 and β-cyclodextrin dissolved in water allows us to control the water-pool diameters of the reverse micelle in n-heptane with values of w=3, 5, 10, 20, and 40, where w is the ratio of water concentration to AOT concentration in n-heptane. To study the fluorescence dynamics of coumarin C522, the spectral steady-state and time-resolved dependences are compared for the two systems coumarin C522(water)/AOT(n-heptane), denoted C522/micelle, and coumarin C522/β-cyclodextrin(water)/AOT(n-heptane), referred to as C522/CD/micelle. The formation of the supramolecular host-guest complex CD-C522 is indicated by a blue shift, but in the micelle, the shift is red. However, the values of the fluorescence maxima at 520 and 515 nm are still way below the value of 535 nm representing bulk water. The interpretation of the red shift is based on two complementary processes. The first one is the confinement of CD and C522 by the micelle water pool and the second is the perturbation of the micelle by CD and C522, resulting in an increase of the water polarity. The fluorescence spectra of the C522/micelle and C522/CD/micelle systems have maxima and shoulders. The shoulder intensities at 440 nm, representing the C522 at n-heptane/AOT interface, decrease as the w values decrease. This intensity shift suggests that the small micelle provides a stronger confinement, and the presence of CD shifts the equilibrium from n-heptane towards the water pool even more. The fluorescence emission maxima of the C522/micelle and C522/CD/micelle systems for all w values clearly differentiate two trends for w=3-5, and w=10-40, suggesting different interaction in the small and large micelles. Moreover, these fluorescence maxima result in 7 and 13 nm differences for w=3 and w=5, respectively, and provide the spectral evidence to differentiate the C522 confinement in the C522/micelle and C522/CD/micelle systems as an effect of the CD molecule, which might be interpreted as a double confinement of C522 in CD within the micelle. The ultrafast decay in the case of w=3 ranges from 9.5 to 16 ps, with an average of 12.6 ps, in the case of the C522/micelle system. For C522/CD/micelle, the ultrafast decay at w=3 ranges from 9 to 14.5 ps, with an average of 11.8 ps. Increasing w values (from 10 to 40) result in a decrease of the ultrafast decay values in both cases to an average value of about 6.5 ps. The ultrafast decays of 12.6 and 11.8 ps for C522/micelle and C522/CD/micelle, respectively, are in the agreement with the observed red shift, supporting a double confinement in the C522/CD/micelle(w=3) system. The dynamics in the small and large micelles clearly show two different trends. Two slopes in the data are observed for w values of 3-5 and 10-40 in the steady-state and time-resolved data. The average ultrafast lifetimes are determined to be 12.6 and 6.5 ps for the small (w=3) and the large (w=40) micelles, respectively. To interpret the experimental solvation dynamics, a simplified model is proposed, and although the model involves a number of parameters, it satisfactory fits the dynamics and provides the gradient of permittivity in the ideal micelle for free water located in the centre (60-80) and for bound water (25-60). An attempt to map the fluorescence dynamics of the doubly confined C522/CD/micelle system is presented for the first time.

A Host–Guest Supramolecular Complex with Photoregulated Delivery of Nitric Oxide and Fluorescence Imaging Capacity in Cancer Cells

Herein we report the design, preparation, and properties of a supramolecular system based on a tailored nitric oxide (NO) photodonor and a rhodamine-labeled β-cyclodextrin conjugate. The combination of spectroscopic and photochemical experiments shows the absence of significant interchromophoric interactions between the host and the guest in the excited states. As a result, the complex is able to release NO under the exclusive control of visible light, as unambiguously demonstrated by direct detection of this transient species through an amperometric technique, and exhibits the typical red fluorescence of the rhodamine appendage. The supramolecular complex effectively internalizes in HeLa cancer cells as proven by fluorescence microscopy, shows a satisfactory biocompatibility in the dark, and induces about 50% of cell mortality upon irradiation with visible light. The convergence of all these properties in one single complex makes the present host-guest ensemble an appealing candidate for further delevopment of photoactivatable nanoscaled systems addressed to photostimulated NO-based therapy.