Lanthanide Identity Governs Guest-Induced Dimerization in LnIII [15-MC Cu II N(L-pheHA) -5])3+ Metallacrowns.

Series of lanthanide-containing metallic coordination complexes are frequently presented as structurally analogous, due to the similar chemical and coordinative properties of the lanthanides. In the case of chiral (LnIII [15-MC Cu II N(L-pheHA) -5])3+ metallacrowns (MCs), which are well established supramolecular hosts, the formation of dimers templated by a dicarboxylate guest (muconate) in solution of neutral pH is herein shown to have a unique dependence on the identity of the MC's central lanthanide. Calorimetric data and nuclear magnetic resonance diffusion studies demonstrate that MCs containing larger or smaller lanthanides as the central metal only form monomeric host-guest complexes whereas analogues with intermediate lanthanides (for example, Eu, Gd, Dy) participate in formation of dimeric host-guest-host compartments. The driving force for the dimerization event across the series is thought to be a competition between formation of highly stable MCs (larger lanthanides) and optimally linked bridging guests (smaller lanthanides).

Different and Often Opposing Forces Drive the Encapsulation and Multiple Exterior Binding of Charged Guests to a M4 L6 Supramolecular Vessel in Water.

The supramolecular assembly [Ga4 L6 ]12- acts as a nanoscale flask to mediate the reactivity of encapsulated reactive guests and also functions as a catalyst to carry out enzyme-like chemical transformations. The guest binding to the interior cavity and exterior of this host is difficult to untangle because multiple equilibria occur in solution, and only when refining simultaneously data obtained from different techniques, such as NMR, UV/Vis, and calorimetry, can the accurate solution thermodynamics of these host-guest systems be determined. This study reports the driving forces for the inclusion and stepwise exterior guest binding of different aliphatic quaternary ammonium guests to the [Ga4 L6 ]12- assembly. Encapsulation into the host cavity was found to be an entropy-driven process, whereas exterior ion association is driven either by enthalpically favorable attractive forces or by the entropy gain due to desolvation, depending on guest size and character. The analysis of the energetics of reaction may help predicting and understanding the intimate role and contribution of the transition state in those rate-accelerated reactions involving this supramolecular assembly as an enzyme-like molecular flask.

Ubiquitin Associates with the N-Terminal Domain of Nerve Growth Factor: The Role of Copper(II) Ions.

Many biochemical pathways involving nerve growth factor (NGF), a neurotrophin with copper(II) binding abilities, are regulated by the ubiquitin (Ub) proteasome system. However, whether NGF binds Ub and the role played by copper(II) ions in modulating their interactions have not yet been investigated. Herein NMR spectroscopy, circular dichroism, ESI-MS, and titration calorimetry are employed to characterize the interactions of NGF with Ub. NGF1-14 , which is a short model peptide encompassing the first 14 N-terminal residues of NGF, binds the copper-binding regions of Ub (KD =8.6 10-5 m). Moreover, the peptide undergoes a random coil-polyproline type II helix structural conversion upon binding to Ub. Notably, copper(II) ions inhibit NGF1-14 /Ub interactions. Further experiments performed with the full-length NGF confirmed the existence of a copper(II)-dependent association between Ub and NGF and indicated that the N-terminal domain of NGF was a valuable paradigm that recapitulated many traits of the full-length protein.

Inorganic stressors of ubiquitin.

Many neurodegenerative proteinopathies are characterized by ubiquitin (Ub)-containing intraneuronal inclusion bodies. Recent reports have shown that Ub is able to bind Cu(II) and Zn(II), the dyshomeostasis of which is a hallmark of neurodegeneration. Here we use complementary techniques like potentiometry, circular dichroism-visible, and electron spin resonance to unveil the Ub/metal species that form, at neutral pH, their binding constants and structural features. Next, we show that both Zn(II) and Cu(II) ions hinder the interactions between Ub and Ub-conjugating E2 enzymes and inhibit significantly both Lys48 and Lys63 self-polyubiquitination reactions in a cell-free medium. The effects of Zn(II) and Cu(II) on Lys63 and Lys48 polyUb chain synthesis are compatible with the hypothesis that metal binding to His68 modifies the Ile44 hydrophobic patch of Ub and makes the protein less available for polyUb. These findings contribute to further arguments for a close relationship between metal dyshomeostasis and abnormal protein degradative pathways in the upstream events, triggering neurodegeneration.

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 Ba(2+) 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.

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.

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.

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.

Copper(II) complexes with chicken prion repeats: influence of proline and tyrosine residues on the coordination features.

The prion protein (PrP(c)) is a copper-binding glycoprotein that can misfold into a beta-sheet-rich and pathogenic isoform (PrP(sc)) leading to prion diseases. The first non-mammalian PrP(c) was identified in chicken and it was found to keep many structural motifs present in mammalian PrP(c), despite the low sequence identity (approximately 40%) between the two primary structures. The present paper describes the synthesis and the coordination properties of some hexapeptide fragments (namely, PHNPGY , HNPGYP and NPGYPH) as well as a bishexapeptide (PHNPGYPHNPGY), which encompasses two hexarepeats. The copper(II) complexes were characterized by means of potentiometric, UV-vis, circular dichroism and electron paramagnetic resonance techniques. We also report the synthesis of three hexapeptides (PHNPGF, HNPGFP and NPGFPH), in which one tyrosine was replaced by phenylalanine as well as two bishexapeptides in which either one (PHNPGFPHNPGY and PHNPGYPHNPGF), or two tyrosines were replaced by phenylalanine, in order to check whether tyrosine was involved in copper(II) binding. Overall, the results indicate that the major copper(II) species formed by the chicken PrP dodecapeptides are stabler than the analogous species reported for the peptide fragments containing two octarepeat peptides from the mammalian prion protein. It is concluded that the presence of four prolyl residues, that are break points in copper coordination, induces the metal-assisted formation of macrochelates as well as the formation of binuclear species. Furthermore, it has been shown that the phenolic group is directly involved in the formation of copper binuclear species.