Carmelo Sgarlata

External and Internal Guest Binding of a Highly Charged Supramolecular Host in Water: Deconvoluting the Very Different Thermodynamics

NMR, UV-vis, and isothermal titration calorimetry (ITC) measurements probe different aspects of competing host-guest equilibria as simple alkylammonium guest molecules interact with both the exterior (ion-association) and interior (encapsulation) of the [Ga(4)L(6)](12-) supramolecular assembly in water. Data obtained by each independent technique measure different components of the host-guest equilibria and only when analyzed together does a complete picture of the solution thermodynamics emerge. Striking differences between the internal and external guest binding are found. External binding is enthalpy driven and mainly due to attractive interactions between the guests and the exterior surface of the assembly while encapsulation is entropy driven as a result of desolvation and release of solvent molecules from the host cavity.

New Cyclodextrin‐Bearing 8‐Hydroxyquinoline Ligands as Multifunctional Molecules

Recent investigations have rekindled interest in 8-hydroxyquinolines as therapeutic agents for cancer, Alzheimers disease, and other neurodegenerative disorders. Three new β-cyclodextrin conjugates of 8-hydroxyquinolines and their copper(II) and zinc(II) complexes have been synthesized and characterized spectroscopically. In addition to improving aqueous solubility, due to the presence of the cyclodextrin moiety, the hybrid systems have interesting characteristics including antioxidant activity, and their copper(II) complexes are efficient superoxide dismutase (SOD) mimics. The ligands and their copper(II) complexes show low cytotoxicity, attributed to the presence of the cyclodextrin moiety. These compounds have potential as therapeutic agents in diseases related both to metal dyshomeostasis and oxidative stress.

Synthesis, characterization of a novel calixarene having dipyridyl pendants and study of its complexes with Cu(II) and Co(II)

Abstract Two dipyridyl pendants were attached to the 1,3 positions of a calix[4]arene, with the purpose of having a ligand able to complex Cu(II) and Co(II). Indeed, the new ligand, fixed in its 1,3-alternate conformation, forms stable complexes with both Co(II) and Cu(II), as shown by UV–vis titrations carried out in acetonitrile. However, the data analysis clearly shows that the ligand forms with the two metal ions complexes having different stoichiometries.

Conditions for calibration of an isothermal titration calorimeter using chemical reactions.

The reaction of protonation of 2-amino-2-(hydroxymethyl)-1,3-propanediol (TRIS) is a suitable one for the calibration of isothermal titration calorimeter (ITC), providing that experimental conditions are appropriately chosen. The conditions and methods for handling experimental data from a nanowatt-ITC are discussed. Also, the binding of Ba2+ to 18-Crown-6 is successfully used to check the accuracy and precision of the chemical calibration performed with TRIS. This latter reaction has the additional advantage that the data can also be used for a check on the determination of the value of a binding constant. The anomaly of the first injection in ITC is analyzed and, by combining calorimetric and spectroscopic measurements, it is shown that it mainly results from a backlash effect of the syringe plunger rather than from a diffusion effect.

Multifunctional 8‐Hydroxyquinoline‐Appended Cyclodextrins as New Inhibitors of Metal‐Induced Protein Aggregation

Mounting evidence suggests a pivotal role of metal imbalances in protein misfolding and amyloid diseases. As such, metal ions represent a promising therapeutic target. In this context, the synthesis of chelators that also contain complementary functionalities to combat the multifactorial nature of neurodegenerative diseases is a highly topical issue. We report two new 8-hydroxyquinoline-appended cyclodextrins and highlight their multifunctional properties, including their Cu(II) and Zn(II) binding abilities, and capacity to act as antioxidants and metal-induced antiaggregants. In particular, the latter property has been applied in the development of an effective assay that exploits the formation of amyloid fibrils when β-lactoglobulin A is heated in the presence of metal ions.

A gemini guest triggers the self-assembly of a calixarene capsule in water at neutral pH

A gemini guest having both aromatic units and negative charges induces the self-assembling of a homodimeric capsule when interacting with a positively charged calixarene at pH 7.

Guest-induced capsule formation based on concerted interactions in water at neutral pH

The interaction of a tetracationic calixarene (TAC4) with dianionic guest (BS) in water was studied with NMR, nano-ITC and ESI-MS experiments; the convergent evidence provided by these different techniques shows that the addition of a suitable guest molecule triggers the formation of a homodimeric capsule in aqueous neutral solution.

Ratiometric fluorescence sensing and cellular imaging of Cu2+ by a new water soluble trehalose-naphthalimide based chemosensor

A new turn-on Cu2+ fluorescent sensor (CST) having a trehalose moiety, which confers a relatively large solubility in water, has been synthesized. The chemosensor is therefore suitable for studies in aqueous solution. Full potentiometric and UV-vis characterization evidence that at physiological pH CST forms with Cu2+ a species with a 1:1 stoichiometry allowing for a straightforward correlation between CST response and copper(II) concentration. The presence of the trehalose unit does not negatively affect the selectivity of CST for Cu2+ over a series of metal ions of interest as proven by fluorescence measurements. The novel chemosensor, tested in differentiated neuroblastoma SH-SY5Y cells, is able to detect Cu2+ in the extracellular region, as well as to track copper transfer processes upon cell stimulation induced by cellular depolarization.

Self-assembling, patterning and SPR imaging of a 1,3 alternate bis(dipyridyl)calix[4]arene derivative-Cu2+ complex immobilized on to Au(111) surfaces.

The electrochemically switchable Cu(2+) complex of a 1,3 alternate bis(dipyridyl)calix[4]arene derivative forms self-assembled monolayers on Au(111) surfaces. The receptor is patterned on the surface by using microcontact printing procedures and the resulting surface is imaged via SPR.

Complexation of biologically active amines by a water-soluble calix[5]arene

Host–guest complexes of an amphiphilic water-soluble p-tert-butylcalix[5]arene bearing 4-sulphonatobutoxy groups at the narrow rim with trace amines (2-phenylethylamine and tyramine) and a neurotransmitter (dopamine), originally investigated via 1H NMR, have been re-examined via ITC in order to double check the reliability of the values obtained through a van’t Hoff analysis of the NMR data. The calorimetrically determined data confirm the existence of a 1:1 host–guest species; however, there are inconsistencies between the van’t Hoff derived values and the values determined via direct calorimetry. These discrepancies do not result from proton displacement due to inclusion, but rather result from the temperature dependence of the van’t Hoff enthalpies.