Molecular recognition inside of multifunctionalized mesoporous silicas: toward selective fluorescence detection of dopamine and glucosamine

Infrared-Activated Bactericide: Rhenium Disulfide (ReS2)-Functionalized Mesoporous Silica Nanoparticles

An attractive strategy for treating bacterial infection is the combination of antibiotic chemotherapy with photothermal therapy (PTT), which could be implemented using multifunctional nanomaterials. In this work, the intrinsic photothermal efficiency of two-dimensional (2D) rhenium disulfide (ReS₂) nanosheets is enhanced by their coating on mesoporous silica nanoparticles (MSNs) to realize a highly efficient light-responsive nanoparticle endowed with controlled-release drug delivery capability, denoted as MSN-ReS₂. The MSN component of the hybrid nanoparticle features augmented pore size toward facilitating increased loading of antibacterial drugs. The ReS₂ synthesis is conducted in the presence of MSNs through an in situ hydrothermal reaction and leads to a uniform surface coating of the nanosphere. The MSN-ReS₂ bactericide testing showed more than 99% bacterial killing efficiency in both Gram-negative bacteria (Escherichia coli) and Gram-positive bacteria (Staphylococcus aureus) upon laser irradiation. A cooperative effect that led to a 100% bactericide effect on Gram-negative bacteria (E. coli) was observed when tetracycline hydrochloride was loaded in the carrier. The results show the potential of MSN-ReS₂ to be used as a wound-healing therapeutic with a synergistic bactericide role.

Simultaneous Determination of Dopamine and Uric Acid in Real Samples Using a Voltammetric Nanosensor Based on Co-MOF, Graphene Oxide, and 1-Methyl-3-butylimidazolium Bromide

A chemically modified carbon paste electrode, based on a CoMOF-graphene oxide (GO) and an ionic liquid of 1-methyl-3-butylimidazolium bromide (CoMOF-GO/1-M,3-BB/CPE), was fabricated for the simultaneous determination of dopamine (DA) and uric acid (UA). The prepared CoMOF/GO nanocomposite was characterized by field emission-scanning electron microscopy (FE-SEM), the X-ray diffraction (XRD) method, a N₂ adsorption-desorption isotherm, and an energy dispersive spectrometer (EDS). The electrochemical sensor clearly illustrated catalytic activity towards the redox reaction of dopamine (DA), which can be authenticated by comparing the increased oxidation peak current with the bare carbon paste electrode. The CoMOF-GO/1-M,3-BB/CPE exhibits a wide linear response for DA in the concentration range of 0.1 to 300.0 µM, with a detection limit of 0.04 µM. The oxidation peaks' potential for DA and uric acid (UA) were separated well in the mixture containing the two compounds. This study demonstrated a simple and effective method for detecting DA and UA in real samples.

Engineering mesoporous silica nanoparticles for drug delivery: where are we after two decades?

The present review details a chronological description of the events that took place during the development of mesoporous materials, their different synthetic routes and their use as drug delivery systems. The outstanding textural properties of these materials quickly inspired their translation to the nanoscale dimension leading to mesoporous silica nanoparticles (MSNs). The different aspects of introducing pharmaceutical agents into the pores of these nanocarriers, together with their possible biodistribution and clearance routes, would be described here. The development of smart nanocarriers that are able to release a high local concentration of the therapeutic cargo on-demand after the application of certain stimuli would be reviewed here, together with their ability to deliver the therapeutic cargo to precise locations in the body. The huge progress in the design and development of MSNs for biomedical applications, including the potential treatment of different diseases, during the last 20 years will be collated here, together with the required work that still needs to be done to achieve the clinical translation of these materials. This review was conceived to stand out from past reports since it aims to tell the story of the development of mesoporous materials and their use as drug delivery systems by some of the story makers, who could be considered to be among the pioneers in this area.

Molecular Probes, Chemosensors, and Nanosensors for Optical Detection of Biorelevant Molecules and Ions in Aqueous Media and Biofluids

Synthetic molecular probes, chemosensors, and nanosensors used in combination with innovative assay protocols hold great potential for the development of robust, low-cost, and fast-responding sensors that are applicable in biofluids (urine, blood, and saliva). Particularly, the development of sensors for metabolites, neurotransmitters, drugs, and inorganic ions is highly desirable due to a lack of suitable biosensors. In addition, the monitoring and analysis of metabolic and signaling networks in cells and organisms by optical probes and chemosensors is becoming increasingly important in molecular biology and medicine. Thus, new perspectives for personalized diagnostics, theranostics, and biochemical/medical research will be unlocked when standing limitations of artificial binders and receptors are overcome. In this review, we survey synthetic sensing systems that have promising (future) application potential for the detection of small molecules, cations, and anions in aqueous media and biofluids. Special attention was given to sensing systems that provide a readily measurable optical signal through dynamic covalent chemistry, supramolecular host-guest interactions, or nanoparticles featuring plasmonic effects. This review shall also enable the reader to evaluate the current performance of molecular probes, chemosensors, and nanosensors in terms of sensitivity and selectivity with respect to practical requirement, and thereby inspiring new ideas for the development of further advanced systems.

Hybrid carbon nanotubes modified glassy carbon electrode for selective, sensitive and simultaneous detection of dopamine and uric acid

Based on a hybrid carbon nanotube composite, a novel electrochemical sensor with high sensitivity and selectivity was designed for the simultaneous determination of dopamine (DA) and uric acid (UA). The hybrid carbon nanotube composite was prepared by ultrasonic assembly of carboxylated multi-walled carbon nanotube (MWCNT-COOH) and hydroxylated single-walled carbon nanotube (SWCNT-OH). And the hybrid (MWCNT-COOH/SWCNT-OH) composite was characterized by field emission scanning electron microscopy (FE-SEM) and Fourier transform infrared (FT-IR) spectroscopy. The electrochemical performances of MWCNT-COOH/SWCNT-OH composite modified glassy carbon electrode (MWCNT-COOH/SWCNT-OH/GCE) were analyzed by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV). Under the optimum experimental conditions, the as-prepared sensor showed high sensitivity and selectivity for DA and UA. The calibration curves obtained were linear for the currents versus DA and UA concentrations in the range 2-150 μM, and limits of detection (LODs) were calculated to be 0.37 μM and 0.61 μM (signal-to-noise ratio of 3, S/N = 3), respectively. The recoveries of DA and UA in bovine serum samples at MWCNT-COOH/SWCNT-OH/GCE were in the range 96.18-105.02%, and relative standard deviations (RSDs) were 3.34-7.27%. The proposed electrochemical sensor showed good anti-interference ability, excellent reproducibility and stability, as well as high selectivity, which might provide a promising platform for determination of DA and UA.

Development of an Approach of High Sensitive Chemiluminescent Assay for Cystatin C Using a Nanoparticle Carrier

Cystatin C is an important cysteine protease inhibitor in the human body and is proposed as a new indicator of glomerular filtration rate for the detection of kidney damage. In this article, we report an ultra-sensitive, simple, and rapid chemiluminescence immunoassay method for cystatin C detection using functionalized mesoporous silica nanoparticles. After a three step hydrolysis, the amino-functionalized MSN encapsulating dye resulted in a hydrophobic environment for fixing the dye and amino groups for biological modification. The NaIO₄ immobilization method maintained the activity of the antibody notably well. The sandwich immunoassay using two monoclonal antibodies was chosen for its selectivity. The analysis demonstrated that the detection upper was 0.0029 ng/mL and linear relationship within the range of 0.0035-0.5 ng/mL (R ² = 0.9936). The relative standard deviation (RSD) for 11 parallel measurements of 0.25 ng/mL CysC was 4.7%. The automated chemiluminescence analyzer could detect 96 wells continuously. The results demonstrated that this method is ultra-sensitive, simple, and rapid for detecting cystatin C.

Highly Selective and Sensitive Detection of Biogenic Defense Phytohormone Salicylic Acid in Living Cells and Plants Using a Novel and Viable Rhodamine-Functionalized Fluorescent Probe

Detecting plant-derived signal molecules using fluorescent probes is a key topic and a huge challenge for scientists. Salicylic acid (SA), a vital plant-derived defense hormone, can activate global transcriptional reprogramming to systemically express a network of prominent pathogenesis-related proteins against invasive microorganisms. This strategy is called systemic acquired resistance (SAR). Therefore, monitoring the dynamic fluctuations of SA in subcellular microenvironments can advance our understanding of different physiological and pathological functions during the SA-induced SAR mechanism, thus benefiting the discovery and development of novel immune activators that contribute to crop protection. Here, detection of signaling molecule SA in plant callus tissues was first reported and conducted by a simple non-fluorescent rhodamine-tagged architecture bearing a flexible 2-amino-N,N-dimethylacetamide pattern. This study can markedly advance and promote the usage of fluorescent SA probes for distinguishing SA in the plant kingdom.

New insights into the structure-performance relationships of mesoporous materials in analytical science

Mesoporous materials are ideal carriers for guest molecules and they have been widely used in analytical science. The unique mesoporous structure provides special properties including large specific surface area, tunable pore size, and excellent pore connectivity. The structural properties of mesoporous materials have been largely made use of to improve the performance of analytical methods. For instance, the large specific surface area of mesoporous materials can provide abundant active sites and increase the probability of contact between analytes and active sites to produce stronger signals, thus leading to the improvement of detection sensitivity. The connections between analytical performances and the structural properties of mesoporous materials have not been discussed previously. Understanding the "structure-performance relationship" is highly important for the development of analytical methods with excellent performance based on mesoporous materials. In this review, we discuss the structural properties of mesoporous materials that can be optimized to improve the analytical performance. The discussion is divided into five sections according to the analytical performances: (i) selectivity-related structural properties, (ii) sensitivity-related structural properties, (iii) response time-related structural properties, (iv) stability-related structural properties, and (v) recovery time-related structural properties.

Fluorogenic Detection of Monoamine Neurotransmitters in Live Cells

Monoamine neurotransmission is key to neuromodulation, but imaging monoamines in live neurons has remained a challenge. Here we show that externally added ortho-phthalaldehyde (OPA) can permeate live cells and form bright fluorogenic adducts with intracellular monoamines (e.g., serotonin, dopamine, and norepinephrine) and with L-DOPA, which can be imaged sensitively using conventional single-photon excitation in a fluorescence microscope. The peak excitation and emission wavelengths (λ_ex = 401 nm and λ_em = 490 nm for serotonin; λ_ex = 446 nm and λ_em = 557 nm for dopamine; and λ_ex = 446 nm and λ_em = 544 nm for norepinephrine, respectively) are accessible to most modern confocal imaging instruments. The identity of monoamine containing structures (possibly neurotransmitter vesicles) in serotonergic RN46A cells is established by quasi-simultaneous imaging of serotonin using three-photon excitation microscopy. Mass spectrometry of cell extracts and of in vitro solutions helps us identify the chemical nature of the adducts and establishes the reaction mechanisms. Our method has low toxicity, high selectivity, and the ability to directly report the location and concentration of monoamines in live cells.

One-Step Electrochemical Fabrication of Reduced Graphene Oxide/Gold Nanoparticles Nanocomposite-Modified Electrode for Simultaneous Detection of Dopamine, Ascorbic Acid, and Uric Acid

Here, we introduce the preparation of the hybrid nanocomposite-modified electrode consisting of reduced graphene oxide (RGO) and gold nanoparticles (AuNPs) using the one-step electrochemical method, allowing for the simultaneous and individual detection of dopamine (DA), ascorbic acid (AA), and uric acid (UA). RGO/AuNPs nanocomposite was formed on a glassy carbon electrode by the co-reduction of GO and Au3+ using the potentiodynamic method. The RGO/AuNPs nanocomposite-modified electrode was produced by subjecting a mixed solution of GO and Au3+ to cyclic sweeping from -1.5 V to 0.8 V (vs. Ag/AgCl) at a scan rate 10 mV/s for 3 cycles. The modified electrode was characterized by scanning electron microscopy, Raman spectroscopy, contact angle measurement, electrochemical impedance spectroscopy, and cyclic voltammetry. Voltammetry results confirm that the RGO/AuNPs nanocomposite-modified electrode has high catalytic activity and good resolution for the detection of DA, AA, and UA. The RGO/AuNPs nanocomposite-modified electrode exhibits stable amperometric responses for DA, AA, and UA, respectively, and its detection limits were estimated to be 0.14, 9.5, and 25 μM. The modified electrode shows high selectivity towards the determination of DA, AA, or UA in the presence of potentially active bioelements. In addition, the resulting sensor exhibits many advantages such as fast amperometric response, excellent operational stability, and appropriate practicality.

Controlled release of silyl ether camptothecin from thiol-ene click chemistry-functionalized mesoporous silica nanoparticles

As efficient drug carriers, stimuli-responsive mesoporous silica nanoparticles are at the forefront of research on drug delivery systems. An acid-responsive system based on silyl ether has been applied to deliver a hybrid prodrug. Thiol-ene click chemistry has been successfully utilized for tethering this prodrug to mesoporous silica nanoparticles. Here, by altering the steric bulk of the substituent on the silicon atom, the release rate of a model drug, camptothecin, was controlled. The synthesized drug delivery system was investigated by analytical methods to confirm the functionalization and conjugation of the mesoporous silica nanoparticles. Herein, trimethyl silyl ether and triethyl silyl ether were selected to regulate the release rate. Under normal plasma conditions (pH 7.4), both types of camptothecin-loaded mesoporous silica nanoparticles (i.e., MSN-Me-CPT and MSN-Et-CPT) did not release the model drug. However, under in vitro acidic conditions (pH 4.0), based on a comparison of the release rates, camptothecin was released from MSN-Me-CPT more rapidly than from MSN-Et-CPT. To determine the biocompatibility of the modified mesoporous silica nanoparticles and the in vivo camptothecin uptake behavior, MTT assays with cancer cells and confocal microscopy observations were conducted, with positive results. These functionalized nanoparticles could be useful in clinical treatments requiring controlled drug release.

STATEMENT OF SIGNIFICANCE

As the release rate of drug from drug-carrier plays important role in therapy effects, trimethyl silyl ether (TMS) and triethyl silyl ether (TES) were selected as acid-sensitive silanes to control the release rates of model drugs conjugated from MSNs by thiol-ene click chemistry. The kinetic profiles of TMS and TES materials have been studied. At pH 4.0, the release of camptothecin from MSN-Et-CPT occurred after 2h, whereas MSN-Me-CPT showed immediate drug release. The results showed that silyl ether could be used to control release rates of drugs from MSNs under acid environment, which could be useful in clinical treatments requiring controlled drug release.

Mimicking multivalent protein–carbohydrate interactions for monitoring the glucosamine level in biological fluids and pharmaceutical tablets

Easily synthesizable ESIPT probe for dual mode sensing of glucosamine in pure water.

A highly selective turn-on fluorescent sensor for glucosamine from amidoquinoline-napthalimide dyads

Three amidoquinoline-naphthalimide dyads are designed and synthesized in 67-73% overall yields in 3 steps from commercially available starting materials. Compounds with unsubstituted and nitro naphthalimide (1 and 2) show excellent selective fluorescent responses towards glucosamine with the enhancement of fluorescence quantum yields by 14 folds. The determination of HOMO-LUMO levels by linear sweep voltammetry suggests that the sensing mechanism likely involves the inhibition of photo-induced electron transfer (PET) between the aminoquinoline and naphthalimide moieties by glucosamine. The association constants of 1.55×10(4) and 1.45×10(4)M(-)(1), along with the glucosamine detection limits of 1.06 and 0.29µM are determined for 1 and 2, respectively. The application of 2 as a fluorescent probe for real-time detection of cellular glucosamine at micromolar level in living Caco-2 cells is also demonstrated.

Dopamine modulated ionic permeability in mesoporous silica sphere based biomimetic compartment

The building of artificial systems with similar structure and function as cellular compartments will expand our understanding of compartmentalization related biological process and facilitate the construction of biomimetic highly functional structures. Herein, surface phenylboronic acid functionalized mesoporous silica sphere was developed as a biomimetic dopamine gated compartment, in which the ionic permeability can be well modulated through the dopamine-binding induced charge reversal. As the phenylboronic acid is negatively charged, the negatively charged 1, 3, 6, 8-pyrenetetrasulfonic acid (TPSA) was hindered from permeation into the biomimetic compartment. However, the presence of dopamine and its binding with phenylboronic acid reversed the gatekeeper shell from negative to positive charged and gated the permeation of TPSA into the interior. The dopamine gated permeation phenomenon resembles that in biological system, and thus the phenylboronic acid functionalized mesoporous silica sphere was taken as a simple model for dopamine gated ion channel decorated biological compartment. It will also contribute to the development of artificial cell and responsive nanoreactor.

Selective electrochemical detection of dopamine in the presence of uric acid and ascorbic acid based on a composite film modified electrode

An electrochemical dopamine sensor based on vanadium-substituted polyoxometalates, copper oxide and chitosan–palladium was fabricated by the LBL technique.

In-depth study on the gene silencing capability of silica nanoparticles with different pore sizes: degree and duration of RNA interference

The mesoporous silica nanoparticles (MSN) having different pore sizes were synthesized and utilized for siRNA delivery system capable of controlling kinetics of RNA interference.

Antibacterial activity of vinyl imidazole(vi) functionalized silica polymer nanocomposites (SBA/VI) against Gram negative and Gram positive bacteria

Vinyl imidazole functionalized mesoporous silica (SBA/VI) nanocomposites for antibacterial activity.

A three dimensional nanowall of calcein/layered double hydroxide as an electrogenerated chemiluminescence sensor

This paper reports fabrication of a 3D nanowall structure with calcein intercalated into a layered double hydroxide, and explores its electrogenerated chemiluminescence property.

Highly promising discrimination of various catecholamines using ratiometric fluorescence probes with intermolecular self-association of two sensing elements

Two sensing elements based on fluorescence probes have been employed as a promising discriminating sensor of two catecholamines, dopamine (DA) and norepinephrine (NE), acting as a guest linker between two self-recognition sensing components.

Influence of the structural and textural properties of ordered mesoporous materials and hierarchical zeolitic supports on the controlled release of methylprednisolone hemisuccinate

To alleviate the chronic inflammation, nasal obstruction, and loss of sense of smell that produces the rhinosinusitis disease, ordered mesoporous materials and hierarchical zeolites could be used for slow and sustained corticoid (methylprednisolone hemisuccinate conjugate) release. The correlations between the delivery performance of methylprednisolone hemisuccinate and the physicochemical properties of carriers' release systems, including pore mesostructure, texture and size, and surface chemistry, have been well established. Different two-dimensional (2-D) and three-dimensional (3-D) mesostructured materials (MCM-41, SBA-15, expanded SBA-15, FDU-12, and SBA-16) were employed. In addition, for the first time to the best of our knowledge, materials based on hierarchical zeolites with additional mesoporosity (h-ZSM-5 and h-BETA zeolites) were also tested. In particular, two materials (3-D cubic mesoporous silica SBA-16 and hierarchical Beta zeolite) have been probed to be potential candidates, exhibiting high drug adsorption capacities and slow drug release rates, which is the most favourable way of drug release in the particular rhinosinusitis application. Solid-state ¹H-²⁹Si HETCOR NMR analyses confirm the strong interactions of the drug with the surface of h-BETA and 3-D SBA-16 materials, via hydrogen bonding of carboxylic, ketone, and aliphatic moieties of the methylprednisolone hemisuccinate at surface silanol sites. Because of the remarkable release performance, it is expected that 3-D mesoporous silica SBA-16 and hierarchical Beta zeolite can be attractive candidates for current applications in nasal inflammation treatments. The drug release rate can be further retarded by decreasing the pH to around 4.6; at this point more attraction forces were detected as proved by zeta-potential measurements. Therefore, a slower delivery trend of methylprednisolone hemisuccinate has been observed for all the materials, which is more pronounced in the case of SBA-15 and SBA-16.

Chemical sensing of neurotransmitters

This review focuses on the chemosensors for neurotransmitters published for the last 12 years, covering biogenic amines (dopamine, epinephrine, norepinephrine, serotonin, histamine and acetylcholine), amino acids (glutamate, aspartate, GABA, glycine and tyrosine), and adenosine.

A label-free electrochemical biosensor based on a DNA aptamer against codeine

In order to develop a sensor for opium alkaloid codeine detection, DNA aptamers against codeine were generated by SELEX (systematic evolution of ligands by exponential enrichment) technique. An aptamer HL7-14, which is a 37-mer sequence with Kd values of 0.91 μM, was optimized by the truncation-mutation assay. The specificity investigation shows that HL7-14 exhibits high specificity to codeine over morphine, and almost cannot bind to other small molecule. With this new selected aptamer, a novel electrochemical label-free codeine aptamer biosensor based on Au-mesoporous silica nanoparticles (Au-MSN) as immobilized substrate has been proposed using [Fe(CN)6](3-/4-) as electroactive redox probe. The linear range covered from 10 pM to 100 nM with correlation coefficient of 0.9979 and the detection limit was 3 pM. Our study demonstrates that the biosensor has good specificity, stability and well regeneration. It can be used to detect codeine.

A fluorescent and chemiluminescent difunctional mesoporous silica nanoparticle as a label for the ultrasensitive detection of cancer cells

A new kind of ultrabright fluorescent and chemiluminescent difunctional mesoporous silica nanoparticle (FCMSN) is reported. A luminescent dye, Rhodamine 6G or tris(2,2'-bipyridyl)dichlororuthenium(II) hexahydrate (Rubpy), is doped inside nanochannels of a silica matrix. The hydrophobic groups in the silica matrix avoid the leakage of dye from open channels. The amines groups on the surface of the FCMSN improve the modification performance of the nanoparticle. Because the nanochannels are isolated by a network skeleton of silica, fluorescence quenching based on the inner filter effect of the fluorescent dyes immobilized in nanochannels is weakened effectively. The Quantum Yield of obtained 90 nm silica particles was about 61%. Compared with the fluorescent core-shell nanoparticle, the chemiluminescence reagents can freely enter the nanoparticles to react with fluorescent dyes to create chemiluminescence. The results show that the FCMSN are both fluorescent labels and chemiluminescent labels. In biological applications, the NaIO(4) oxidation method was proven to be superior to the glutaraldehyde method. The amount of amino could affect the specificity of the FCMSN. The fluorescence microscopy imaging demonstrated that the FCMSN is viable for biological applications.

A dual fluorometric and colorimetric sensor for dopamine based on BSA-stabilized Au nanoclusters

An easy prepared fluorometric and colorimetric dual channel probe is developed for dopamine (DA) detection with high sensitivity and selectivity by use of BSA-stabilized Au nanoclusters (BSA-AuNCs). The BSA-AuNCs exhibit strong fluorescence emission, while upon addition of DA, the AuNCs show a dramatic decrease of the fluorescence intensity as a result of the photo-induced electron transfer process from the electrostatically attached DA to the BSA-AuNCs. The detection limit of DA can be as low as 10 nM. In addition, the assay for DA can also be easy to implement for visual detection due to the observed inhibition of the peroxidase-like activity of AuNCs in the presence of DA, with a detection limit of 10 nM. Both fluorometric and colorimetric methods exhibit excellent selectivity toward DA over interfering substances. Furthermore, we demonstrate the application of the present approach in hydrochloride injection sample, human serum sample and PC12 cells, which suggests its great potential for diagnostic purposes.

Functional mesoporous silica nanoparticles for the selective sequestration of free fatty acids from microalgal oil

A series of 2d-hexagonally packed mesoporous silica nanoparticle material with 10 nm pore diameter (MSN-10) covalently functionalized with organic surface modifiers have been synthesized via a post-synthesis grafting method. The material structure has been characterized by powder X-ray diffraction, electron microscopy, and nitrogen sorption analyses, and the free fatty acid (FFA) sequestration capacity and selectivity was investigated and quantified by thermogravimetric and GC/MS analysis. We discovered that aminopropyl functionalized 10 nm pore mesoporous silica nanoparticle material (AP-MSN-10) sequestered all available FFAs and left nearly all other molecules in solution from a simulated microalgal extract containing FFAs, sterols, terpenes, and triacylglycerides. We also demonstrated selective FFA sequestration from commercially available microalgal oil.

Noncovalent complexation of monoamine neurotransmitters and related ammonium ions by tetramethoxy tetraglucosylcalix[4]arene

The noncovalent complexation of monoamine neurotransmitters and related ammonium and quaternary ammonium ions by a conformationally flexible tetramethoxy glucosylcalix[4]arene was studied by electrospray ionization Fourier transform ion cyclotron resonance (ESI-FTICR) mass spectrometry. The glucosylcalixarene exhibited highest binding affinity towards serotonin, norepinephrine, epinephrine, and dopamine. Structural properties of the guests, such as the number, location, and type of hydrogen bonding groups, length of the alkyl spacer between the ammonium head-group and the aromatic ring structure, and the degree of nitrogen substitution affected the complexation. Competition experiments and guest-exchange reactions indicated that the hydroxyl groups of guests participate in intermolecular hydrogen bonding with the glucocalixarene.