Overestimation in angular path integration precedes Alzheimer's dementia

Path integration (PI) is impaired early in Alzheimer's disease (AD) but reflects multiple sub-processes that may be differentially sensitive to AD. To characterize these sub-processes, we developed a novel generative linear-angular model of PI (GLAMPI) to fit the inbound paths of healthy elderly participants performing triangle completion, a popular PI task, in immersive virtual reality with real movement. The model fits seven parameters reflecting the encoding, calculation, and production errors associated with inaccuracies in PI. We compared these parameters across younger and older participants and patients with mild cognitive impairment (MCI), including those with (MCI+) and without (MCI-) cerebrospinal fluid biomarkers of AD neuropathology. MCI patients showed overestimation of the angular turn in the outbound path and more variable inbound distances and directions compared with healthy elderly. MCI+ were best distinguished from MCI- patients by overestimation of outbound turns and more variable inbound directions. Our results suggest that overestimation of turning underlies the PI errors seen in patients with early AD, indicating specific neural pathways and diagnostic behaviors for further research.

How do (perceptual) distracters distract?

When a target stimulus occurs in the presence of distracters, decisions are less accurate. But how exactly do distracters affect choices? Here, we explored this question using measurement of human behaviour, psychophysical reverse correlation and computational modelling. We contrasted two models: one in which targets and distracters had independent influence on choices (independent model) and one in which distracters modulated choices in a way that depended on their similarity to the target (interaction model). Across three experiments, participants were asked to make fine orientation judgments about the tilt of a target grating presented adjacent to an irrelevant distracter. We found strong evidence for the interaction model, in that decisions were more sensitive when target and distracter were consistent relative to when they were inconsistent. This consistency bias occurred in the frame of reference of the decision, that is, it operated on decision values rather than on sensory signals, and surprisingly, it was independent of spatial attention. A normalization framework, where target features are normalized by the expectation and variability of the local context, successfully captures the observed pattern of results.

In the real world, visual scenes usually contain many objects. As a consequence, we often have to make perceptual judgments about a specific ‘target’ stimulus in the presence of irrelevant ‘distracter’ stimuli. For instance, when hanging a picture frame, we want to discern whether it is hanging straight, ignoring the surrounding, potentially tilted frames. Laboratory experiments have shown that the presence of distracter stimuli (i.e. other picture frames) makes this type of perceptual judgment less accurate. However, the specific effect distracters have on judgments is controversial. Here, we conducted a series of experiments to compare two alternative theories of distracter influence: one in which distracters compete with targets to determine choices (independent model) and one in which distracters wield a more indirect influence on choices (interaction model). We found evidence for the latter account. Our results suggest distracters affect perceptual decisions by adjusting how sensitive decisions are to the target stimulus.

Iron/Magnetite Nanoparticles as Magnetic Delivery Systems for Antitumor Drugs

In this study we investigate on the possible use of a new kind of magnetic nanostructures as drug delivery systems for anticancer drugs. The starting particles are formed by an inner core of iron, coated by magnetite as a stabilizing, magnetic layer. These units are further coated by a poly(ethylenglycol) (PEG) layer to make them less prone to the attack by macrophages and to favour longer stays in the blood stream. The resulting particles consist of several magnetic cores encapsulated by a polymer layer around 5 nm thick. The crystal structure of the designed nanostructures, as determined by X-ray powder diffraction, is compatible with a crystalline magnetite component, whereas the magnetization hysteresis data indicate a superparamagnetic behavior. Both the initial susceptibility and the saturation magnetization are lower than for the bare magnetic cores, but still significant. Drug adsorption and release tests were performed on two anticancer drugs, namely 5-fluorouracil and doxorubicin. Both are found to adsorb on the particles, but only the latter appears to be released at a reasonable rate, which is found to be very slow for 5-fluorouracil.

Preparation of multi-functionalized Fe3O4/Au nanoparticles for medical purposes

In this work, we investigate a route towards the synthesis of multi-functionalized nanoparticles for medical purposes. The aim is to produce magnetite/gold (Fe3O4/Au) nanoparticles combining several complementary properties, specifically, being able to carry simultaneously an antitumor drug and a selected antibody chosen so as to improve specificity of the drug vehicle. The procedure included, firstly, the preparation of Fe3O4 cores coated with Au nanoparticles: this was achieved by using initially the layer-by-layer technique in order to coat the magnetite particles with a three polyelectrolyte (cationic-anionic-cationic) layer. With this, the particles became a good substrate for the growth of the gold layer in a well-defined core-shell structure. The resulting nanoparticles benefit from the magnetic properties of the magnetite and the robust chemistry and the biostability of gold surfaces. Subsequently, the Fe3O4/Au nanoparticles were functionalized with a humanized monoclonal antibody, bevacizumab, and a chemotherapy drug, doxorubicin. Taken together, bevacizumab enhances the therapeutic effect of chemotherapy agents on some kinds of tumors. In this work we first discuss the morphology of the particles and the electrical characteristics of their surface in the successive synthesis stages. Special attention is paid to the chemical stability of the final coating, and the physical stability of the suspensions of the nanoparticles in aqueous solutions and phosphate buffer. We describe how optical absorbance and electrokinetic data provide a follow up of the progress of the nanostructure formation. Additionally, the same techniques are employed to demonstrate that the composite nanoparticles are capable of loading/releasing doxorubicin and/or bevacizumab.

Coordination of peroxide to the Cu(M) center of peptidylglycine α-hydroxylating monooxygenase (PHM): structural and computational study

Many bioactive peptides, such as hormones and neuropeptides, require amidation at the C terminus for their full biological activity. Peptidylglycine α-hydroxylating monooxygenase (PHM) performs the first step of the amidation reaction-the hydroxylation of peptidylglycine substrates at the Cα position of the terminal glycine. The hydroxylation reaction is copper- and O(2)-dependent and requires 2 equiv of exogenous reductant. The proposed mechanism suggests that O(2) is reduced by two electrons, each provided by one of two nonequivalent copper sites in PHM (Cu(H) and Cu(M)). The characteristics of the reduced oxygen species in the PHM reaction and the identity of the reactive intermediate remain uncertain. To further investigate the nature of the key intermediates in the PHM cycle, we determined the structure of the oxidized form of PHM complexed with hydrogen peroxide. In this 1.98-Å-resolution structure (hydro)peroxide binds solely to Cu(M) in a slightly asymmetric side-on mode. The O-O interatomic distance of the copper-bound ligand is 1.5 Å, characteristic of peroxide/hydroperoxide species, and the Cu-O distances are 2.0 and 2.1 Å. Density functional theory calculations using the first coordination sphere of the Cu(M) active site as a model system show that the computed energies of the side-on L(3)Cu(M)(II)-O(2) (2-) species and its isomeric, end-on structure L(3)Cu(M)(I)-O(2) (·-) are similar, suggesting that both these intermediates are significantly populated within the protein environment. This observation has important mechanistic implications. The geometry of the observed side-on coordinated peroxide ligand in L(3)Cu(M)(II)O(2) (2-) is in good agreement with the results of a hybrid quantum mechanical-molecular mechanical optimization of this species.

Functionalized magnetic nanoparticles as vehicles for the delivery of the antitumor drug gemcitabine to tumor cells. Physicochemical in vitro evaluation

Gemcitabine is a chemotherapy drug used in different carcinomas, although because it displays a short biological half-life, its plasmatic levels can quickly drop below the effective threshold. Nanoparticle-based drug delivery systems can provide an alternative approach for regulating the bioavailability of this and most other anticancer drugs. In this work we describe a new model of composite nanoparticles consisting of a core of magnetite nanoparticles, coated with successive layers of high molecular weight poly(acrylic acid) and chitosan, and a final layer of folic acid. The possibility of using these self-assembled nanostructures for gemcitabine vehiculization is explored. First, the surface charge of the composite particles is studied by means of electrophoretic mobility measurements as a function of pH for poly(acrylic acid) (carbopol) of different molecular weights. The adsorption of folic acid, aimed at increasing the chances of the particles to pass the cell membrane, is followed up by optical absorbance measurements, which were also employed for drug adsorption determinations. As a main result, it is shown that gemcitabine adsorbs onto the surface of chitosan/carbopol-coated magnetite nanoparticles. In vitro experiments show that the functionalized magnetic nanoparticles are able to deliver the drug to the nuclei of liver, colon and breast tumor cells.

Electrophoretic characterization of insulin growth factor (IGF-1) functionalized magnetic nanoparticles

The synthesis of composite nanoparticles consisting of a magnetite core coated with a layer of the hormone insulin growth factor 1 (IGF-1) is described. The adsorption of the hormone in the different formulations is first studied by electrophoretic mobility measurements as a function of pH, ionic strength, and time. Because of the permeable character expected for both citrate and IGF-1 coatings surrounding the magnetite cores, an appropriate analysis of their electrophoretic mobility must be addressed. Recent developments of electrokinetic theories for particles covered by soft surface layers have rendered possible the evaluation of the softness degree from raw electrophoretic mobility data. In the present contribution, the data are quantitatively analyzed based on the theoretical model of the electrokinetics of soft particles. As a result, information is obtained on both the thickness and the charge density of the surrounding layer. It is shown that IGF-1 adsorbs onto the surface of citrate-coated magnetite nanoparticles, and adsorption is confirmed by dot-blot analysis. In addition, it is also demonstrated that the external layer of IGF-1 exerts a shielding effect on the surface charge of citrate-magnetite particles, as suggested by the mobility reduction upon contacting the particles with the hormone. Aging effects are demonstrated, providing an electrokinetic fingerprint of changes in adsorbed protein configuration with time.

Surface modification of glass plates and silica particles by phospholipid adsorption

The effect of phospholipid adsorption on the hydrophobicity of glass plates and on the surface charge of silica particles using contact angle and electrophoretic mobility measurements, respectively, was investigated. Deposition of successive statistical monolayers of dipalmitoylphosphatidylcholine (DPPC) on the glass surface showed zig-zag changes of water contact angle, especially on the first few monolayers. This behavior is qualitatively coherent with the oscillations observed in zeta potential values for increasing DPPC concentration. The results indicate that the phospholipid is adsorbed vertically on the plates, exposing alternately its polar head and non-polar hydrocarbon chains in successive layers. On the other hand, experiments conducted on glass plates prior hydrophobized by contact with n-tetradecane suggest that DPPC molecules may to some extent dissolve in the relatively thick n-alkane film and then expose their polar heads over the film surface thus producing polar electron-donor interactions. The effect of both DPPC and dioleoylphosphatidylcholine (DOPC) on the electrokinetic potential of silica spheres confirms adsorption of the phospholipids, leading to a decrease in the (originally negative) zeta potential of silica and even reversal of its sign to positive at acidic pH. Hydrophobic interactions between phospholipid molecules in the medium and those already adsorbed may explain the overcharging. The adsorption of neutral phospholipids may reduce the zeta potential as a consequence of the shift of the electrokinetic or slip plane. The effect is more evident in the case of DOPC, suggesting a less efficient packing of this phospholipid because of the presence of double bonds in its molecule, which in fact is well known.

A trinuclear nickel(II) enediolate complex: synthesis, characterization, and O2 reactivity

Using a new N(4)-donor chelate ligand having a mixture of hydrophobic phenyl and hydrogen-bond-donor appendages, a trinuclear nickel(II) complex of the doubly deprotonated form of 2-hydroxy-1,3-diphenylpropane-1,3-dione was isolated, characterized (X-ray crystallography, elemental analysis, UV-vis, (1)H NMR, FTIR, and magnetic moment measurement), and evaluated for O(2) reactivity. This complex, [(6-NA-6-Ph(2)TPANi)(2)(mu-PhC(O)C(O)C(O)Ph)(2)Ni](ClO(4))(2) (4), has two terminal pseudooctahedral Ni(II) centers supported by the tetradentate chelate ligand and a central square-planar Ni(II) ion ligated by oxygen atoms of two bridging enediolate ligands. In CH(3)CN, 4 exhibits a deep orange/brown color and lambda(max) = 463 nm (epsilon = 16 000 M(-1)cm(-1)). The room temperature magnetic moment of 4, determined by Evans method, is mu(eff) = 5.3(2) mu(B). This is consistent with the presence of two noninteracting high-spin Ni(II) centers, a diamagnetic central Ni(II) ion, and an overall quintet ground state. Exposure of a CH(3)CN solution of 4 to O(2) results in the rapid loss of the orange/brown color to give a green solution. The products identified from this reaction are [(kappa(3)-6-NA-6-Ph(2)TPA)Ni(O(2)Ph)(H(2)O)]ClO(4) (5), benzil [PhC(O)C(O)Ph], and CO. Identification of 5 was achieved via its independent synthesis and a comparison of its (1)H NMR and mass spectral features with those of the 6-NA-6-Ph(2)TPA-containing product generated upon reaction of 4 with O(2). The independently prepared sample of 5 was characterized by X-ray crystallography, elemental analysis, UV-vis, mass spectrometry, and FTIR. The O(2) reactivity of 4 has relevance to the active-site chemistry of Ni(II)-containing acireductone dioxygenase (Ni(II)ARD).

Glyoxalase I-type hemithioacetal isomerization reactivity of a mononuclear Ni(II) deprotonated amide complex

The synthesis, characterization, and hemithioacetal isomerization reactivity of a mononuclear Ni(II) deprotonated amide complex, [(bppppa-)Ni]ClO4.CH3OH (1, bppppa- = monoanion of N,N-bis-[(6-phenyl-2-pyridyl)methyl]-N-[(6-pivaloylamido-2-pyridyl)methyl]amine), are reported. Complex 1 was characterized by X-ray crystallography, 1H NMR, UV-vis, FTIR, and elemental analysis. Treatment of 1 with an equimolar amount of the hemithioacetal PhC(O)CH(OH)SCD3 in dry acetonitrile results in the production of the thioester PhCH(OH)C(O)SCD3 in approximately 60% yield. This reaction is conveniently monitored via 2H NMR spectroscopy. A protonated analogue of 1, [(bppppa)Ni](ClO4)2 (2), is unreactive with the hemithioacetal, thus indicating the requirement of the anionic chelate ligand in 1 for hemithioacetal isomerization reactivity. Complex 1 is unreactive with the thioester product, PhCH(OH)C(O)SCD3, which indicates that the pKa value for the PhCH(OH)C(O)SCD3 proton of the thioester must be significantly higher than the pKa value of the C-H proton of the hemithioacetal (PhC(O)CH(OH)SCD3). Complex 1 is the first well-characterized Ni(II) coordination complex to exhibit reactivity relevant to Ni(II)-containing E. coli glyoxalase I. Treatment of NiBr2.2H2O with PhC(O)CH(OH)SCD3 in the presence of 1-methylpyrrolidine also yields thioester product, albeit the reaction is slower and involves the formation of multiple -SCD3 labeled species, as detected by 2H NMR spectroscopy. The results of this study provide the first insight into hemithioacetal isomerization promoted by a synthetic Ni(II) coordination complex versus a simple Ni(II) ion.

Acireductone Dioxygenase- (ARD-) Type Reactivity of a Nickel(II) Complex Having Monoanionic Coordination of a Model Substrate: Product Identification and Comparisons to Unreactive Analogues

A mononuclear Ni(II) complex ([(6-Ph2TPA)Ni(PhC(O)C(OH)C(O)Ph)]ClO4 (1)), supported by the 6-Ph2TPA chelate ligand (6-Ph2TPA = N,N-bis((6-phenyl-2-pyridyl)methyl)-N-((2-pyridyl)methyl)amine) and containing a cis-beta-keto-enolate ligand having a C2 hydroxyl substituent, undergoes reaction with O2 to produce a Ni(II) monobenzoate complex ([(6-Ph2TPA)Ni(O2CPh)]ClO4 (3)), CO, benzil (PhC(O)C(O)Ph), benzoic acid, and other minor unidentified phenyl-containing products. Complex 3 has been identified through independent synthesis and was characterized by X-ray crystallography, 1H NMR, FAB-MS, FTIR, and elemental analysis. A series of cis-beta-keto-enolate Ni(II) complexes supported by the 6-Ph2TPA ligand ([(6-Ph2TPA)Ni(PhC(O)CHC(O)Ph)]ClO4 (4), [(6-Ph2TPA)Ni(CH3C(O)CHC(O)CH3)]ClO4 (5), and [(6-Ph2TPA)Ni(PhC(O)CHC(O)C(O)Ph) (6)) have been prepared and characterized. While these complexes exhibit structural and/or spectroscopic similarity to 1, all are unreactive with O2. The results of this study are discussed in terms of relevance to Ni(II)-containing acireductone dioxygenase enzymes, as well as in the context of recently reported cofactor-free, quercetin, and beta-diketone dioxygenases.

A cadmium hydroxide complex of a N3S-donor ligand containing two hydrogen bond donors: synthesis, characterization, and CO2 reactivity

Treatment of the ebnpa (N-2-(ethylthio)ethyl-N,N-bis((6-neopentylamino-2-pyridyl)methyl)amine) ligand with a molar equivalent amount of Cd(ClO(4))(2).5H(2)O in CH(3)CN followed by the addition of [Me(4)N]OH.5H(2)O yielded the cadmium hydroxide complex [(ebnpaCd)(2)(mu-OH)(2)](ClO(4))(2) (1). Complex 1 has a binuclear cation in the solid-state with secondary hydrogen-bonding and CH/pi interactions involving the ebnpa ligand. In acetonitrile, 1 forms a binuclear/mononuclear equilibrium mixture. The formation of a mononuclear species has been confirmed by conductance measurements of 1 at low concentrations. Variable temperature studies of the binuclear/mononuclear equilibrium provided the standard enthalpy and entropy associated with the formation of the monomer as DeltaH degrees = +31(2) kJ mol(-1) and DeltaS degrees = +108(8) J mol(-1) K(-1), respectively. Enhanced secondary hydrogen-bonding interactions involving the terminal Cd-OH moiety may help to stabilize the mononuclear complex. Treatment of 1 with CO(2) in acetonitrile results in the formation of a binuclear cadmium carbonate complex, [(ebnpaCd)(2)(mu-CO(3))](ClO(4))(2) (2).

Chemistry of a Ni(II) Acetohydroxamic Acid Complex: Formation, Reactivity with Water, and Attempted Preparation of Zinc and Cobalt Analogues

Mononuclear Ni(II), Co(II), and Zn(II) complexes of the bppppa (N,N-bis[(6-phenyl-2-pyridyl)methyl]-N-[(6-pivaloylamido-2-pyridyl)methyl]amine) ligand have been synthesized and characterized by X-ray crystallography, 1H NMR, UV-vis (Ni(II) and Co(II)) and infrared spectroscopy, and elemental analysis. Each complex has the empirical formula [(bppppa)M](ClO4)2 (M = Ni(II), 2; Zn(II), 3; Co(II), 4) and in the solid state exhibits a metal center having a coordination number of five; albeit, the cation of 2 also has a sixth weak interaction involving a perchlorate anion. Treatment of [(bppppa)Ni](ClO4)2 (2) with 1 equiv of acetohydroxamic acid results in the formation of [(bppppa)Ni(HONHC(O)CH3)](ClO4)2 (1), a novel Ni(II) complex having a coordinated neutral acetohydroxamic acid ligand. In 1, one phenyl-appended pyridyl donor of the bppppa chelate ligand is dissociated from the metal center and acts as a hydrogen bond acceptor for the hydroxyl group of the bound acetohydroxamic acid ligand. Treatment of 1 with excess water results in the formation of 2 and free acetohydroxamic acid. We hypothesize that this reaction occurs due to disruption of the intramolecular hydrogen bonding interaction involving the bound acid. In this series of reactions, the bppppa ligand exhibits behavior reminiscent of a type III hemilabile ligand in terms of one phenylpyridyl donor. Treatment of 3 or 4 with acetohydroxamic acid results in no reaction, indicating that the bppppa-ligated Ni(II) derivative 2 exhibits unique coordination chemistry with respect to reaction with acetohydroxamic acid within this series of complexes. We attribute this reactivity to the ability of the bppppa-ligated Ni(II) center to adopt a pseudo-octahedral geometry, whereas the Zn(II) and Co(II) complexes retain five coordinate metal centers.

Neutral acetohydroxamic acid coordination to a mononuclear Ni(ii) center stabilized by an intramolecular hydrogen-bonding interaction

Treatment of a new chelate ligand having both amide- and phenyl-appended pyridyl moieties with Ni(ClO4).6H2O and acetohydroxamic acid in methanol solution results in the production of a novel pseudo-octahedral Ni(II) complex having a neutral acetohydroxamic acid ligand stabilized by a hydrogen-bonding interaction.