Fernando Palacio

A luminescent molecular thermometer for long-term absolute temperature measurements at the nanoscale

Temperature is a fundamental thermodynamic variable, the measurement of which is crucial in countless scientific investigations and technological developments, accounting at present for 75%–80% of the sensor market throughout the world.[1] Traditional liquid-filled and bimetallic thermometers, thermocouples, pyrometers, and thermistors are generally not suitable for temperature measurements at scales below 10 μm. This intrinsic limitation has encouraged the development of new non-contact accurate thermometers with micrometric and nanometric precision, a challenging research topic increasingly hankered for [1–2].

Lanthanide-based luminescent molecular thermometers

Non-invasive accurate thermometers with high spatial resolution and operating at sub-micron scales, where the conventional methods are ineffective, are currently a very active field of research strongly stimulated in the last couple of years by the challenging demands of nanotechnology and biomedicine. This perspective offers a general overview of recent examples of accurate luminescent thermometers working at micrometric and nanometric scales, particularly those involving advanced Ln3+-based functional organic–inorganic hybrid materials.

MULTIFUNCTIONAL COORDINATION COMPOUNDS: DESIGN AND PROPERTIES

Abstract Cleverly designed molecular building blocks provide chemists with the tools of a powerful molecular-scale construction set. They enable them to engineer materials that possess a predictable order and useful solid-state properties. Hence, it is in the realm of supramolecular chemistry to follow a strategy for synthesizing materials which combine a selected set of properties, for instance from the areas of magnetism, photophysics and electronics. As a possible approach, host/guest solids which are based on extended anionic, homo- and bi-metallic oxalato-bridged transition-metal compounds with two- and three-dimensional connectivities are investigated. In particular, we report herein in detail about their structural properties and their multifunctional characteristics in the area of molecular magnetism and photophysics.

Production of magnetic nanoparticles in a polyvinylpyridine matrix

AbstractA commercial polyvinylpyridine polymer has been used for the in situ preparation of magnetic nanocomposites. Several procedures havebeen followed in the preparation of the nanoparticles based on the formation of polymer–metal complex gels. The use of mixtures of proticand aprotic solvents for the reaction of the polymer with the metal salts is discussed. Superparamagnetic nanoparticles of CoO and Fe 2 O 3 have been obtained with an average size of 50 and 10 nm, respectively. The utility of nitrogen base polymers for the fabrication of magneticnanocomposites is emphasized. q 2000 Elsevier Science Ltd. All rights reserved. Keywords: Polymer nanocomposites; Magnetic nanoparticles; Metal oxides 1. IntroductionMagnetic nanocomposites have many possible technolo-gical applications [1,2]. Several solid matrixes have beenused in this kind of material including gels, glasses, zeolites,metals, etc. Although, the most suitable matrix will alwaysdepend on the future application of the material, organicpolymers have been often a suitable choice because oftheir high processability and versatility. The in situ precipi-tation of the magnetic particles in a polymeric matrix is anexcellent method to control the mean size and size disper-sion of a nanoparticle population. Polymers employed forthis purpose in the past have been selected from variousconsiderations. Sulfonated polymers have often been useddue to the capability of the sulfonic groups to retain metalions [3–5]. Polymers with a tridimensional structure, suchas ion interchange resins, have rigid pores that set an upperlimit to the size of particles that grow inside [6]. Diblockcopolymers, composed of a part with charged radicals andanother part with hydrophobic groups, contain polar nanor-egions of a controllable size and shape [7] that serve asexcellent sites for the encapsulation of inorganic particles[8]. Cross-linking iron ions in polysaccharide complex gelsare known to act as nucleation centers for iron oxide nano-particles [9]. Polypirrole polymers have been chosen aselectrical conductive matrixes [10]. Phenolic polymerspermit the fabrication of submicron spherical composites[11]. In general, polymers used as a matrix for the precipita-tion of magnetic nanoparticles are polyelectrolytes becauseof their capability to absorb metal ions. However, neutralpolymers might be more advantageous concerning proces-sability and versatility. Recently, we have successfullygrown several kind of magnetic nanoparticles in N-basedpolymeric matrixes[12]. In this work, a commercial poly(4-vinylpyridine) (PVP) polymer has been used to producenanocomposites of iron and cobalt oxides. As a precedent,Mo¨ssbauer spectroscopy studies had already revealed ananomalous magnetic behavior in polyvinylpyridine–iron-chloride compounds [13]. Later, magnetic nanoparticleswere grown in a PVP matrix by a laborious method invol-ving precipitation, reduction to metallic iron and furtheroxidation to magnetite [14]. Some of the advantages ofPVP as a matrix for magnetic nanocomposites are thefollowing: easily available; soluble in slightly acidicaqueous media and in polar organic solvents; resistant todegradation by acids, alkalis, reductors and oxidants; itmelts congruently; and it is thermally stable. In this work,complexes of PVP with several metal ions have beenprepared by various procedures.2. ExperimentalHigh purity reagents were purchased from Aldrich andFluka. Solvents were dried following the standard procedureand deoxygenated under an argon flow. PVP, of averagemolecular weight of 50,000 Da was supplied by Sigma.Polymer–metal coordination compounds were obtained

Magnetic Properties of Thiazyl Radicals

A series of thiazyl radicals related to the trithiadiazolylium radical cation, S3N 2 +• are described. In many instances the compounds exist as spin-paired singlets which are consequently diamagnetic. However, when the dimerisation process can be inhibited, these open shell molecules exhibit very strong exchange interactions, characterised by Weiss constants, θ, up to 102 K. Magneto-structural correlations show that, in the majority of instances, the magnetic exchange interactions are propagated via close intermolecular S···N and S···S contacts (typically in the region 3.1–3.7 A). Examples of thiazyl radicals exhibiting magnetic ordering temperatures in excess of 50 K are described. In addition, the phenomenon of bistability (in which both open-shell monomeric and closed-shell dimeric forms are stable over the same temperature range) is discussed and examples of thiazyl radicals exhibiting bistability up to room temperature described.

Joining Time-Resolved Thermometry and Magnetic-Induced Heating in a Single Nanoparticle Unveils Intriguing Thermal Properties

Whereas efficient and sensitive nanoheaters and nanothermometers are demanding tools in modern bio- and nanomedicine, joining both features in a single nanoparticle still remains a real challenge, despite the recent progress achieved, most of it within the last year. Here we demonstrate a successful realization of this challenge. The heating is magnetically induced, the temperature readout is optical, and the ratiometric thermometric probes are dual-emissive Eu(3+)/Tb(3+) lanthanide complexes. The low thermometer heat capacitance (0.021·K(-1)) and heater/thermometer resistance (1 K·W(-1)), the high temperature sensitivity (5.8%·K(-1) at 296 K) and uncertainty (0.5 K), the physiological working temperature range (295-315 K), the readout reproducibility (>99.5%), and the fast time response (0.250 s) make the heater/thermometer nanoplatform proposed here unique. Cells were incubated with the nanoparticles, and fluorescence microscopy permits the mapping of the intracellular local temperature using the pixel-by-pixel ratio of the Eu(3+)/Tb(3+) intensities. Time-resolved thermometry under an ac magnetic field evidences the failure of using macroscopic thermal parameters to describe heat diffusion at the nanoscale.

Magnetic behaviour of a hybrid polymer obtained from ethyl acrylate and the magnetic cluster Mn12O12(acrylate)16

The magnetic properties of polymers prepared by polymerization of the magnetic cluster Mn12O12(acrylate)16 with various portions of ethyl acrylate as co-monomer are reported. According to SAXS studies, the clusters are homogeneously distributed in the polymer. Ac susceptibility measurements show superparamagnet-like behaviour of the cluster-crosslinked polymers with relaxation following an Arrhenius law with τ0 = 4–8 × 10−8 s and an energy barrier in the range 45–65 K.

Molecular electronics: A dual-action material

In the drive for smaller electronic components, chemists are thinking on a molecular scale. By combining two simple molecules, a hybrid has been produced that is both magnetic and an electrical conductor.

Weak ferromagnetism in the linear chain RbMnF4⋯H2O

Abstract Single crystal ac magnetic susceptibility and magnetization measurements of the linear chain RbMnF 4 ⋯H 2 O are reported. A broad maximum around 42 K in the susceptibility fits to a Heisenberg S = 2 linear chain with | J |/ k = 6.2 K and g = 2.03. At 7.3 K a sharp peak in X ′ d (alternating field parallel to the chains) accompanied by large X ″ d signals indicates weak ferromagnetic behaviour. Magnetization measurements leads to a canting angle of ∼ 1.5°.

Temperature dependence of antiferromagnetic susceptibility in ferritin

Departamento de F´isica and CICECO, Universidade de Aveiro, 3810-193 Aveiro, Portugal(Dated: February 6, 2009)We show that antiferromagnetic susceptibility in ferritin increases with temperature between 4.2K and 180 K (i. e. below the N´eel temperature) when taken as the derivative of the magnetization athigh fields (30×10