A pioneer of acrylic painting: new insights into Carmen Herrera’s studio practice

Carmen Herrera, born on May 30th, 1915, is a Cuban American abstract minimalist artist, whose first solo show was held at the Whitney Museum of American Art, New York, in 2016–2017. On this occasion, a scientific study of five paintings from the artist’s time in Paris (1948–1953) revealed her pioneering use of solvent-based acrylic paints in post-war Europe. This article presents a second phase of research into Herrera’s work aiming to shed light on her studio practice and ascertain the possible presence of other early acrylic paints in her pre-1963 artistic production. A selection of four paintings, namely Iberia #25 (1948), Iberic (1949), Flights of Colors #16 (1949), and Early Dynasty (1953), was subjected to an analytical campaign that relied on both non-invasive and micro-invasive techniques. Results confirmed the use of both oil and solvent-based acrylic paints, supporting our primary research and uncovering the first-known occurrence of acrylic binders in Herrera’s Iberia #25. In all cases, the ground layer consists of a mixture of titanium white in its tetragonal form of rutile, anhydrite, and talc, while the color palette was found to be based on both traditional and modern pigments. In most areas, several paint layers appeared to be overlaid on top of one another, revealing a creative process that developed through subsequent compositions. Remnants of earlier paint layers, which appeared to have been scraped off before new ones were applied, were observed directly above the ground in some of the samples examined. In addition, Iberia #25 and Iberic, with analogous geometric and chromatic schemes, underwent technical imaging, which exposed pencil lines and notes underneath the paint layers likely indicative of the intended design and polychromy. Besides corroborating a major alteration in the current scholarship on the availability and use of acrylic-based artists’ paints in post-war Europe, this research provides new insights into Herrera’s materials, techniques, and studio practice. In addition, the results of this scientific study assisted the development of a suitable treatment plan for Iberic in preparation for its display in The Metropolitan Museum of Art’s galleries as part of the museum’s 150th anniversary exhibition Making The Met, 1870–2020.

The II–I Phase Transition Behavior of Butene-1 Copolymers with Hydroxyl Groups

The crystallization and II–I phase transition of functionalized polybutene-1 with hydroxyl groups were investigated by differential scanning calorimetry. The results show that the incorporated hydroxyl groups increase the nucleation density but decrease the growth rate in melt crystallization. Interestingly, for the generated tetragonal form II, the presence of polar hydroxyl groups can effectively accelerate the phase transition into the thermodynamically stable modification of trigonal form I, especially with stepwise annealing and high incorporation. Using stepwise annealing, II–I phase transition was enhanced by an additional nucleation step performed at a relatively low temperature, and the optimal nucleation temperature to obtain the maximum transition degree was ‒10 °C, which is independent from the content of hydroxyl groups. Furthermore, the accelerating effect of hydroxyl groups on the II–I transition kinetics can be increased by reducing the crystallization temperature when preparing form II crystallites. These results provide a potential molecular design approach for developing polybutene-1 materials.

Nanostructured kesterite (Cu2ZnSnS4) for applications in thermoelectric devices

Kesterite (Cu2ZnSnS4, CZTS) powders were produced by reactive high-energy milling, starting from stoichiometric mixtures of the elemental components. CZTS forms fine crystals with a cubic structure, which evolves to the stable tetragonal form after thermal treatment. Tablets were produced by cold pressing of the ball milled powder, and sintered up to 660 °C. Seebeck coefficient, electrical resistivity, and thermal diffusivity were measured on the sintered tablets, pointing out the positive effect of CZTS nanostructure and of the rather large fraction of porosity: thermal conductivity is rather low (from ~0.8 W/(m K) at 20 °C to ~0.42 W/(m K) at 500 °C), while electrical conduction is not seriously hindered (electrical resistivity from ~8500 µΩ m at 40 °C to ~2000 µΩ m at 400 °C). Preliminary results of thermoelectric behavior are promising.

Synthesis and Characterization of Low Density Bi-2223 Superconductors via Co-Precipitation Method

High temperature Bi1.6Pb0.4Sr2Ca2Cu3Oδ of low density has been synthesized via co-precipitation method and its electrical and structural properties have been studied. The optimum porosity of the samples was obtained using variety amount of sucrose C12H22O11 which is used as supplementary filler. The electrical properties of superconductor such as critical temperature, Tc and critical current density, Jc were determined using the four-probe method. X-ray diffraction (XRD) was used to analyze the structural properties of the samples. The density of samples was measured using densitometer. The obtained results have revealed a significant influence of the pore presence in superconducting samples on the electrical properties. The Tc for low density Bi-2223 with 0.1g sugar sucrose is much higher compared to 0.05g, 0.15g and standard sample which is Tc zero is 98 K. The Jc for low density Bi-2223 with 0.1g sugar sucrose is 6 A/cm2 at 60 K which is higher than high density samples. The crystallographic structure remains in the tetragonal form where a=b≠c for all samples.

Monoclinic HEWL derivative structure at 0.75 Å resolution

Tris-dipicolinate lanthanide complex, Na3.[Ln(DPA)3], where DPA stands for pyridine-2,6 dicarboxylate, has been proven to be especially interesting to produce derivative crystals with high phasing power [1]. The lanthanide complex can act as a cross-linking agent, which binds at the interface between protein molecules, leading to a supramolecular interaction at the crystal scale [2]. In the case of hen egg-white lysozyme (HEWL), derivative crystals obtained by co-crystallization with Yb(DPA)33-belong to the space group C2, in similar crystallization conditions that normally lead to the tetragonal form P43212. Data were collected on a derivative crystal up to a resolution of 0.75 Å at the EMBL beamline P13 at PETRA III at DESY (Hamburg, Germany). Taking advantage of the high the resolution and the strong anomalous signal of the Yb3+(f″ = 5.2 e-at 17 keV), the structure was solved by both SAD and ab initio methods. Data collection, experimentally phased electron density maps and the structure, especially with respect to the vicinity of the lanthanide binding sites, will be discussed.

Biomolecular systems under pressure

Biological systems are often regarded as the ultimate goal of all knowledge in this respect that they can provide the clue for understanding the origin of life and the means for improving the life conditions and healthcare. Hence the interest in high-pressure behavior of organic and biomolecular systems. Such simple organic systems were among the first structural studies at high pressure at all. They included chloroform by Roger Fourme in 1968 [1] and benzene by Piermarini et al. in 1969, still with the use of photographic technique. The efficient studies on bio-macromolecular crystals had to wait for several decades till synchrotron radiation became more accessible and Roger Fourme again stood in the avant-garde of these studies [2]. At the turn of centuries his innovations in the laboratory equipment and experimental setup let him exploring high-pressure conformations of proteins, viral capsids and the double-helix molecular architecture in nucleic acids. These directions of high-pressure studies are continued for simple and macromolecular systems of biological importance. Recently new surprising facts were revealed about the compression of urea, sucrose, and other organic compounds, as well as of macromolecular crystals. Sugars are the main energy carriers for animals as well as building blocks in the living tissue, they are also ideal models for studying pressure-induced changes of OH···O and CH···O interactions. Different types of transformations occur in compressed urea, the first organic compound synthesized in laboratory. Hen egg-white lysozyme was investigated at moderate pressure in a beryllium vessel and the compression of both tetragonal and orthorhombic modifications were measured to 1.0 GPa in a DAC; the high-pressure structure of the tetragonal form was determined and refined at still higher pressure by Fourme et al. [3] Can high pressure provide information about the remarkable polymorphism of lysozyme?

An orthorhombic polymorph of a cyclization product of perindopril

Low-temperature X-ray diffraction experiments were employed to investigate the crystal structures of an orthorhombic polymorph of the intramolecular cyclization product of perindopril, a popular angiotensive-converting enzyme (ACE) inhibitor, namely ethyl (2S)-2-[(3S,5aS,9aS,10aS)-3-methyl-1,4-dioxo-5a,6,7,8,9,9a,10,10a-octahydro-3H-pyrazino[1,2-a]indol-2-yl]pentanoate, C19H30N2O4, (Io), and its tetragonal equivalent, (It), which was previously reported at ambient temperature [Bojarskaet al.(2013).J. Chil. Chem. Soc.58, 1415–1417]. Polymorph (Io) crystallizes in the orthorhombic space groupP212121with two molecules in the asymmetric unit, while tetragonal form (It) crystallizes in the space groupP41212 with one molecule in the asymmetric unit. The geometric parameters of (Io) are very similar to those of (It). The six-membered rings in both polymorphs adopt a slightly deformed chair conformation and the piperazinedione rings are in a boat conformation. However, the proline rings adopt an envelope conformation in (Io), while in (It) the ring exists in a slightly deformed half-chair conformation. The most significant difference between the two structures is the orientation of the ethyl pentanoate chain. Molecules associate in pairs in a head-to-tail manner forming infinite columns. In (Io), molecules are related by a twofold screw axis forming identical columns, while in (It), molecules in successive neighbouring columns are related by alternating twofold screw axes and fourfold screw axes. In both cases, the crystal packing is stabilized by weak intermolecular C—H...O interactions only.