Antonio Doménech

Maya Blue as a nanostructured polyfunctional hybrid organic―inorganic material: the need to change paradigms

Maya Blue, an ancient nanostructured organic–inorganic hybrid material resulting from the attachment of indigo, a natural dye, to a phyllosilicate clay, palygorskite, has received considerable attention of late. Despite intensive research, several aspects remain unsolved, in particular the nature of the indigo–palygorskite association. Recent results suggest that the Maya Blue pigment is a complex system in which different topological isomers of various indigoid molecules attached to the palygorskite matrix coexist.

From Maya Blue to “Maya Yellow”: A Connection between Ancient Nanostructured Materials from the Voltammetry of Microparticles

Financial support is gratefully acknowledged from the Generalitat Valenciana GV04B/441 I + D + I Project and the MEC Projects CTQ2004-06754-C03-01 and 02, CTQ2006-15672-C05-05/BQU, and CTQ2008-06727-C03-01 and 02/BQU, which are also supported with ERDEF funds. The authors would like to thank to Dr. Jose Luis Moya Lopez and Manuel Planes Insausti (Microscopy Service of the Universitat Politecncia de Valencia) for their technical support.

Selective recognition of carboxylate anions by polyammonium receptors in aqueous solution. Criteria for selectivity in molecular recognition

The interaction in aqueous solution of the polyammonium receptor 1,4,7,10,13,16,19-heptaazacyclohenicosane (8, [21]aneN7) with the carboxylic species, 1,2-benzenedicarboxylic (1), 1,3-benzenedicarboxylic (2), 1,2,3-benzenetricarboxylic (3), 1,3,5-benzenetricarboxylic (4), cis,cis-1,3,5-trimethyl-1,3,5-cyclohexanetricarboxylic (5), cis,trans-1,3,5-trimethyl-1,3,5-cyclohexanetricarboxylic (6), and citric (7) acids has been followed by potentiometry and cyclic voltammetry at 298.1 K in 0.15 mol dm–3 NaClO4, as well as by NMR spectroscopy. The analysis of the potentiometric and electrochemical data show the formation of 1:1 adducts. A novel method based on both potentiometry and cyclic voltammetry to establish selectivity patterns in systems presenting different protonation possibilities is introduced. Preorganization of the substrates in a shape complementary to the receptor yields interesting features such as the selective recognition of 5 over its epimer 6 and recognition of the dicarboxylic species 1 and 2 over the tricarboxylic ones 6 and 7.

Model compounds for the active sites of oxo-transfer molybdoenzymes. Synthesis, structural characterization, and electrochemical properties of [NH4]2[MoO2{O2CC(S)Ph2}2]

[NH4]2[MoO2{O2CC(S)Ph2}2]middot;2H2O has been prepared and its crystal structure solved, providing the first example of a co-ordinatively saturated molybdenum complex which reacts readily and reversibly with organophosphines at room temperature in water or methanol; its variable-temperature 13C{1H} NMR spectra and electrochemical properties are presented.

Layer-by-layer identification of copper alteration products in metallic works of art using the voltammetry of microparticles.

An in situ technique for layer-by-layer electrochemical analysis of solid surfaces using the voltammetry of microparticles is presented. The method is based on the determination of several shape-dependent parameters for voltammetric curves recorded at a graphite pencil working electrode in contact with the sample, all immersed into aqueous electrolytes. Repetitive square wave voltammetry and sequential application of constant potential reductive steps and voltammetric scans yield discernible responses for the corrosion products distributed in stratified layers on metal-based surfaces. This methodology is applied to identify alteration products of copper and copper alloys distributed in different layers in copper coupons submitted to different corrosive treatments and a contemporary brass sculpture.

Quantitation from Tafel Analysis in Solid-State Voltammetry. Application to the Study of Cobalt and Copper Pigments in Severely Damaged Frescoes

A novel method, using Tafel plots, for quantifying electroactive species in solid materials when their voltammetric signals are strongly overlapped is described. This is applied to the analysis of submicrosamples from the highly damaged frescoes painted by Palomino (1707) in the ceiling vault of the Sant Joan del Mercat church in Valencia, Spain. These paintings, which were fired in 1936, contained cobalt smalt plus azurite mixtures, this last being altered to tenorite (CuO). The reported method provides a quantitation of the cobalt smalt/azurite, tenorite/(azurite + smalt) relationships in samples, thus providing direct information on pigment dosage (smalt/azurite ratio) in pristine paintings, extent of alteration, and temperature experienced by the frescoes during the gunfire episode. Distinction between Palomino paintings and other painters was clearly obtained due to the presence of malachite in these last.

Electrochemical characterization of iron sites in ex-framework FeZSM-5

Abstract The electrochemical response of FeZSM-5 prepared by an ex -framework method has been studied using Paraloid B72 polymer film electrodes immersed in aqueous media using H 2 SO 4 , HCl, Na 2 EDTA and NaCl electrolytes. The ex -framework method comprises the hydrothermal synthesis of isomorphously substituted FeZSM-5, followed by calcination at 823 K and subsequent steam treatment (300 mbar H 2 O in N 2 ) at 873 K. During this process iron is extracted to extra-framework positions. Also partial dealumination of the zeolite framework takes place. Characteristic voltammetric responses in the +1.0 to −0.6 V versus SCE potential range have been recorded and were used to characterize the iron species present in the materials during the different preparation stages. Different species were identified, including tetrahedral framework iron, octahedral extra-framework iron ions, dimeric or oligomeric iron oxo-complexes, and iron oxide nano-aggregates. Iron oxide nano-aggregates displayed reductive or oxidative dissolution processes, while framework iron species displayed one electron transfer processes involving Fe(III) and Fe(II) species confined to boundary sites of the zeolite matrix.

Study of behaviour on simulated daylight ageing of artists’ acrylic and poly(vinyl acetate) paint films

AbstractThis work proposes a multi-method approach that combines advanced microscopy (SEM/EDX, AFM) and spectroscopy (UV-vis and FTIR) techniques. This approach not only characterises the behaviour of the additives of two commercial poly(vinyl acetate) (PVAc) and acrylic emulsion paints but also simultaneously characterises the changes in chemical composition and morphology observed in the paint films as a result of ageing due to the paints being exposed to an intense source of simulated daylight. In parallel, a series of mechanical tests were performed that correlate the chemical changes in composition and the changes observed in the films’ mechanical properties. This work was a comparative study between both types of acrylic and PVAc paints. The results obtained are of great interest for the modern paint conservation field as they provide valuable information on the mid- and long-term behaviours of these synthetic paints. FigureTensile test of phthalocianyne blue Liquitex® paint film

Tracing, authenticating and dating archaeological metal using the voltammetry of microparticles

Electrochemical techniques provide information of archaeometric interest. An overview on the application and future developments of the voltammetry of microparticles to the study of archaeological metals and their alteration products is presented. A report on the state of the art and future developments of this technique with regard to identification and origin studies of materials, authentication, chronology and dating of archaeological metal is provided.

Mn(II) complexes of scorpiand-like ligands. A model for the MnSOD active centre with high in vitro and in vivo activity.

Manganese complexes of polyamines consisting of an aza-pyridinophane macrocyclic core functionalised with side chains containing quinoline or pyridine units have been characterised by a variety of solution techniques and single crystal x-ray diffraction. Some of these compounds have proved to display interesting antioxidant capabilities in vitro and in vivo in prokaryotic (bacteria) and eukaryotic (yeast and fish embryo) organisms. In particular, the Mn complex of the ligand containing a 4-quinoline group in its side arm which, as it happens in the MnSOD enzymes, has a water molecule coordinated to the metal ion that shows the lowest toxicity and highest functional efficiency both in vitro and in vivo.