Characterization of the copper(II) complexes formed with the tetraoctarepeat peptide at low and high metal-to-ligand ratios and in a large pH range, would provide a breakthrough in the interpretation of biological relevance of the different metal complexes of copper(II)-tetraoctarepeat system. In the present work, the potentiometric, UV/Vis, circular dichroism (CD), and electron paramagnetic resonance (EPR) studies were carried out on copper(II) complexes with a PEG-ylated derivative of the tetraoctarepeats peptide sequence (Ac-PEG27 -(PHGGGWGQ)4 -NH2 ) and the peptide Ac-(PHGGGWGQ)2 -NH2 . Conjugation of tetraoctarepeat peptide sequence with polyethyleneglycol improved the solubility of the copper(II) complexes. The results enable a straightforward explanation of the conflicting results originated from the underestimation of all metal-ligand equilibria and the ensuing speciation. A complete and reliable speciation is therefore obtained with the released affinity and binding details of the main complexes species formed in aqueous solution. The results contribute to clarify the discrepancies of several studies in which the authors ascribe the redox activity of copper(II)-tetraoctarepeat system considering only the average effects of several coexisting species with very different stoichiometries and binding modes.

Fluorine is known to strongly influence the dopant diffusion and electrical activation in Si. Similar effects might be exploited in Ge for optimizing its application in microelectronics. The role of F on the electrical activation of As in Ge after thermal treatments is elucidated. We have found that F, enriching the Ge matrix with vacancies strongly affects the electrical response of As-doped junctions. We also demonstrated that the F-interstitials clusters, formed next to the end-of-range region, have an acceptor-like behavior. These phenomena are characterized by chemical and electrical profiling analyses and by positron annihilation lifetime spectrometry. (C) 2012 The Electrochemical Society. All rights reserved.

The peptide sequence PHSRN is the second cell binding site of the human fibronectin protein, a glycoprotein which plays a critical adhesive role during development, tissue repair and angiogenesis. The copper(II) complexes with the peptide fragment PHSRN were characterized by potentiometric and UV–visible, CD, EPR spectroscopic methods. Thermodynamic and spectroscopic evidences indicate that at physiological pH, only one copper(II) complex species, [CuLH−2], is present and the metal ion is bound to one imidazole and two amide nitrogen atoms (NIm, 2N−) in a tetrahedral distorted square planar coordination. Two new β-cyclodextrin–ethylendiamino derivatives with the PHSRN covalently attached were synthesized as multitargeting molecules, able to have a site-specific recognition sequence, to interact with copper(II) ions and to be a potential carrier of hydrophobic drugs. Copper(II) complexes with these β-cyclodextrin derivatives were characterized by means of potentiometric and spectroscopic techniques. The comparison of the experimental parameters determined at different pH values with those obtained for the parent peptide complex species, shows that at physiological pH the ethylendiamino-β-CD moiety does not influence the peptide interaction with copper ions and the β-CD hydrophobic cavity is not blocked, being available to host hydrophobic drugs such as naproxen.

The Pro-His-Ser-Arg-Asn (PHSRN) sequence in fibronectin is a second cell-binding site that synergistically affects Arg-Gly-Asp (RGD). The PHSRN peptide also induces cell invasion and accelerates wound healing. We report on the surface immobilization of PHSRN by spontaneous adsorption on polysiloxane thin films which have different surface free energy characteristics. Low-surface energy (hydrophobic) polysiloxane and the corresponding high-surface energy (hydrophilic) surfaces obtained by UV-ozone treatments were used as adsorbing substrates. The peptide adsorption process was investigated by quartz crystal microbalance with dissipation monitoring and atomic force microscopy. Both adsorption kinetics and peptide rearrangement dynamics at the solid interface were significantly different on the surface-modified films compared to the untreated ones. Fibroblast cells cultures at short times and in a simplified environment, i.e., a medium-free solution, were prepared to distinguish interaction events at the interface between cell membrane and surface-immobilized peptide for the two cases. It turned out that the cell-adhesive effect of immobilized PHSRN was different for hydrophobic compared to hydrophilic ones. Early signatures of cell spreading were only observed on the hydrophilic substrates. These effects are explained in terms of different spatial arrangements of PHSRN molecules immobilized on the two types of surfaces. (C) 2009 Elsevier Inc. All rights reserved.

Aggregation of the amyloid beta-peptide (Abeta) into insoluble fibrils is a key pathological event in Alzheimer's Disease (AD). There is now compelling evidence that metal binding to Abeta is involved in AD pathogenesis. The amino acid region 1-16 is widely considered as the metal binding domain of Abeta. In this work, we used a combined potentiometric, NMR, and electrospray ionization mass spectrometry (ESI-MS) approach to study the zinc(II) binding to a new polyethylene glycol (PEG)-conjugated peptide fragment encompassing the 1-16 amino acid sequence of Abeta (Abeta(1-16)PEG). Our results demonstrate for the first time that the Abeta(1-16) is able to coordinate up to three zinc ions, all the histidyl residues acting as independent anchor sites. The study was complemented by systematically investigating the zinc(II) complexes of a series of shorter peptide fragments related to the Abeta(1-16) sequence, namely, Abeta(1-4), Abeta(1-6), AcAbeta(1-6), AcAbeta(8-16)Y10A. The comparison of the whole results allowed the identification of the zinc(II) preferred binding sites within the longer Abeta(1-16) amino acid sequence. Unlike copper(II) that prefers the N-terminal amino group as the main binding site, the zinc(II) is preferentially placed in the 8-16 amino acidic region of Abeta(1-16).

Alzheimer's disease (AD) is becoming a rapidly growing health problem, as it is one of the main causes of dementia in the elderly. Interestingly, copper(II) (together with zinc and iron) ions are accumulated in amyloid deposits, suggesting that metal binding to A beta could be involved in AD pathogenesis. In A beta, the metal binding is believed to occur within the N-terminal region encompassing the amino acid residues 1-16. In this work, potentiometric, spectroscopic (UV-vis, circular dichroism, and electron paramagnetic resonance), and electrospray ionization mass spectrometry (ESI-MS) approaches were used to investigate the copper(II) coordination features of a new polyethylene glycol (PEG)-conjugated A beta peptide fragment encompassing the 1-16 amino acid residues of the N-terminal region (A beta(1 - 16)PEG). The high water solubility of the resulting metal complexes allowed us to obtain a complete complex speciation at different metal-to-ligand ratios ranging from 1:1 to 4:1. Potentiometric and ESI-MS data indicate that A beta(1-16)PEG is able to bind up to four copper(II) ions. Furthermore, in order to establish the coordination environment at each metal binding site, a series of shorter peptide fragments of A beta, namely, A beta(1-4), A beta(1-6), AcA beta(1-6), and AcA beta(8-16)Y10A, were synthesized, each encompassing a potential copper(II) binding site. The complexation properties of these shorter peptides were also comparatively investigated by using the same experimental approach.

6-Deoxy-6-{4-[N-(2-aminoethyl)propaneamide]imidazolyl}cyclohepta amylose (CDcarc) and 6-{3-amine-N-[2-(imidazol-4-yl)ethyl]propaneamide}-6-deoxycyclohepta amylose (CDcrac) were synthesized with the aim to obtain copper(II) complexes able to scavenge superoxide radical. The copper(II) complexes were studied by means of UV–Vis, ESR, CD, ESI-MS spectroscopies to gain information about the species present in solution as function of the pH. The antioxidant activity was assayed against superoxide enzymatically generated and compared with that obtained from copper(II) complex with underivatized carcinine. The hydroxyl radical scavenging ability of these new ligands was also tested.

Interest in the 37-residue human islet amyloid polypeptide (hIAPP) is related to its ability to form amyloid deposits in patients affected by type II diabetes. Attempts to unravel the molecular features of this disease have indicated several regions of this polypeptide to be responsible for either the ability to form insoluble fibrils or the abnormal interaction with membranes. To extend these studies to peptides that enclose His18, whose ionization state is believed to play a key role in the aggregation of hIAPP, we report on the synthesis of two peptides, hIAPP17-29 and rIAPP17-29, encompassing the 17-29 sequences of human and rat IAPP, respectively, as well as on their conformational features in water and in several membrane-mimicking environments as revealed by circular dichroism (CD) and 2D-NMR studies. hIAPP17-29 adopts a beta-sheet structure in water and its solubility increases at low pH. Anionic sodium dodecyl sulfate (SDS) micelles promoted the formation of an alpha-helical structure in the peptide chain, which was poorly influenced by pH variations. rIAPP17-29 was soluble and unstructured in all the environments investigated, with a negligible effect of pH. The membrane interactions of hIAPP17-29 and rIAPP17-29 were assessed by recording differential scanning calorimetry (DSC) measurements aimed at elucidating the peptide-induced changes in the thermotropic behaviour of zwitterionic (DPPC) and negatively charged (DPPC/DPPS 3:1) model membranes (DPPC=1,2-dipalmitoyl-sn-glycero-3-phosphocholine, DPPS=1,2-dipalmitoyl-sn-glycero-3-phosphoserine). Results of DSC experiments demonstrated the high potential of hIAPP17-29 to interact with DPPC membranes. hIAPP17-29 exhibited a negligible affinity for negatively charged DPPC/DPPS model membranes at neutral pH. On the other hand, rIAPP17-29 did not interact with neutral or negatively charged membranes. The role played by His18 in the modulation of the biophysical properties of this hIAPP region was assessed by synthesising and studying the R18HrIAPP17-29 peptide; the replacement of a single Arg with a His residue is not sufficient to induce either amyloidogenic propensity or membrane interaction in this region. The results show that the 17-29 domain of hIAPP has many properties of the full-length protein "in vitro" and this opens up new perspectives for both research and eventually therapy.

Copper(II) complexes of the neurotoxic peptide fragments of human and chicken prion proteins were studied by potentiometric, UV-vis, CD, and EPR spectroscopic and ESI-MS methods. The peptides included the terminally blocked native and scrambled sequences of HuPrP106-126 (HuPrPAc106-126NH2 and ScrHuPrPAc106-126NH2) and also the nona- and tetrapeptide fragments of both the human and chicken prion proteins (HuPrPAc106-114NH2, ChPrPAc119-127NH2, HuPrPAc109-112NH2, and ChPrPAc122-125NH2). The histidyl imidazole-N donor atoms were found to be the major copper(II) binding sites of all peptides; 3N and 4N complexes containing additional 2 and 3 deprotonated amide-N donors, respectively, are the major species in the physiological pH range. The complex formation processes for nona- and tetrapeptides are very similar, supporting the fact that successive deprotonation and metal ion coordination of amide functions go toward the N-termini in the form of joined six- and five-membered chelates. As a consequence, the peptide sequences investigated here, related to the neurotoxic region of the human PrP106-126 sequence, show a higher metal-binding affinity than the octarepeat fragments. In the case of the HuPrP peptide sequences, a weak pH-dependent binding of the Met109 residue was also detected in the 3N-coordinated complexes.

We addressed issues related to quantitative carrier profiling by scanning capacitance microscopy (SCM) on doped layers with different dimensions, starting from thick (∼5 μm) uniformly doped Si layers down to Si/Si1−xGex/Si quantum wells with nanometre width. We preliminarily discuss the influence of the SCM hardware on the quantification, by comparing the analyses performed on Si calibration standards with two different atomic force microscopes, i.e. DI3100 by Veeco and XE-100 by PSIA, equipped with different SCM sensors. Furthermore, concentration sensitivity and spatial resolution are deeply discussed considering measurements on special designed samples containing quantum wells of Si0.75Ge0.25 layers strained between Si films. Measurements were taken on sample cross-sections and on bevelled samples. A nanometre SCM spatial resolution was demonstrated not only in terms of signal sensitivity, but also in terms of quantitative majority carrier profiling.

The prion protein (PrPc) is a copper-binding glycoprotein that can misfold into a β-sheet-rich and pathogenic isoform (PrPsc) leading to prion diseases. The first non-mammalian PrPc was identified in chicken and it was found to keep many structural motifs present in mammalian PrPc, 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.

The condensation reaction of 6-deoxy-6-amino(2-aminoethyl)-cyclomaltoheptaose (β-CyDen) and racemic [(R, S)-2-(6-methoxy-2-naphthyl) propanoic acid] (R,S-naproxen) affords two new diastereoisomeric naproxen-appended β-cyclodextrin derivatives. The structural analysis of these two β-CyD derivatives, undertaken by combined use of circular dichroism (CD) and 1D or 2D NMR techniques, shows that the naphthalene ring of the naproxen is included in the CyD cavity in both derivatives. The CD spectra are consistent with an axial complexation model, moreover, the self-inclusion mode is further corroborated by 1H NMR ROESY spectra which also suggest the orientation of the naphthyl moiety in the cavity of both the diastereoisomers.

An abnormal interaction between copper and the prion protein is believed to play a pivotal role in the pathogenesis of prion diseases. Copper binding has been mainly attributed to the N-terminal domain of the prion protein, but this hypothesis has recently been challenged in some papers which suggest that the C-terminal domain might also compete for metal anchoring. In particular, the segment corresponding to the helix II region of the prion protein, namely PrP180-193, has been shown both to bind copper and to exhibit a copper-enhanced cytotoxicity, as well as to interact with artificial membranes. The present work is aimed at extending these results by choosing the most representative model of this domain and by determining its copper affinity. With this aim, the different role played by the electrostatic properties of the C- and N-termini of PrP180-193 (VNITIKQHTVTTTT) in determining its conformational behaviour, copper coordination and ability to perturb model membranes was investigated. Owing to the low solubility of PrP180-193, its copper affinity was evaluated by using the shorter PrPAc184-188NH2 (IKQHT) analogue as a model. ESI-MS, ESR, UV/Vis, and CD measurements were carried out on the copper(II)/PrPAc184-188NH2 and copper(II)/PrP180-193NH2 systems, and showed that PrPAc184-188NH2 is a reliable model for the metal interaction with the helix II domain. The affinity of copper(II) for the helix II fragment is higher than that for the octarepeat and PrP106-126 peptides. Finally, the different ability of PrP180-193 analogues to perturb the DPPC model membrane was assessed by DSC measurements. The possible biological consequences of these findings are also discussed briefly.