The Surfaces of the Ceratonia siliqua L. (Carob) Leaflet: Insights from Physics and Chemistry

The production of superhydrophobic coatings inspired by the surface of plant leaves is a challenging goal. Such coatings hold a bright technological future in niche markets of the aeronautical, space, naval, building, automobile, and biomedical sectors. This work is focused on the adaxial (top) and abaxial (bottom) surfaces of the leaflet of the Ceratonia silique L. (carob), a high-commercial-value Mediterranean tree cultivated in many regions of the world. The adaxial and abaxial surfaces feature hydrophobic and superhydrophobic behaviors, respectively. Their chemical composition is very simple: monopalmitin ester and palmitic acid are protuberant in the epicuticular and intracuticular wax layers of the adaxial surface, respectively, whereas 1-octacosanol dominates in the abaxial wax layers. In both surfaces, epicuticular wax is organized along a randomly oriented and intricate network of nanometer-thick and micrometer-long plates, whose density and degree of interconnection are significantly higher in the abaxial surface. The measured tilting angles for the abaxial surface (12-70°) reveal unusual variable density and water adhesion of the nanostructured plate-based texture. Optical measurements demonstrate that light reflectance/absorbance of the glaucous abaxial surface is significantly higher/lower than that of the nonglaucous adaxial surface. In both surfaces, diffuse reflectance is dominant, and the absorbance is weakly dependent on the light incidence angle. We show that the highly dense nanostructured platelike texture of the epicuticular abaxial layer of the C. siliqua leaflet works as a sophisticated light and water management system: it reflects solar radiation diffusely to lower the surface temperature, and it has superhydrophobic character to keep the surface dry. Such attributes enable efficient gas exchange (photosynthesis and respiration), transpiration, and evaporation. To mimic for the first time the abaxial surface, a templation approach was adopted using poly(dimethylsiloxane) (PDMS)/poly(methylphenylsiloxane) (PMPS) positive/negative replicas and a soft polymer/siloxane negative replica produced by the sol-gel process. Because high topographical variations of the biotemplate and wax adhesion to the biohybrid film affected the replication quality, the reproduction of the wax texture via the synthesis of 1-octacosanol-grafted siloxane-based hybrid materials is proposed as a suitable route to duplicate the abaxial surface with high fidelity. The natural chemical/physical strategy adopted by the C. siliqua leaflet to face the harsh Mediterranean climate is a powerful source of bioinspiration for the development of diffuse reflecting and superhydrophobic material systems with foreseen applications as dual-functional antiglare and water-repelling coatings.

Facile and scalable synthesis of sub-micrometer electrolyte particles for solid acid fuel cells

Nanostructuring fuel cell electrodes is a viable pathway to reach high performance with low catalyst loadings. Thus, in solid acid fuel cells, small CsH₂PO₄ electrolyte particles are needed for the composite powder electrodes as well as for thin electrolyte membranes. Previous efforts have resulted in significant improvements in performance when using sub-micrometer CsH₂PO₄ particles, but laborious methods with low throughput were employed for their synthesis. In this work, we present a simple, robust, and scalable method to synthesize CsH₂PO₄ particles with diameters down to below 200 nm. The method involves precipitating CsH₂PO₄ by mixing precursor solutions in alcohol in the presence of a dispersing additive. The influence of the concentrations, the batch size, the solvent, and the mixing process is investigated. The particle size decreases down to 119 nm with increasing amount of dispersing additive. Mixing in a microreactor leads to a narrower particle size distribution. The particle shape can be tuned by varying the solvent. The ionic conductivity under solid acid fuel cell conditions is 2.0 × 10^-2 S cm^-1 and thus close to that of CsH₂PO₄ without dispersing additive.

Synthesis, Characterization, and Bromine Substitution by 4,4‘-Di(5-nonyl)-2,2‘-bipyridine in CuII(4,4‘-di(5-nonyl)-2,2‘-bipyridine)Br2

The crystal structure of a novel compound Cu(II)(dNbpy)Br(2) (dNbpy = 4,4'-di(5-nonyl)-2,2'-bipyridine), which is used in the reverse atom transfer radical polymerization, is reported. Cu(II)(dNbpy)Br(2) crystallizes in the triclinic P1 space group with a = 12.5283(11) A, b = 15.0256(14) A, c = 17.7900(16) A, alpha = 90.350(2) degrees, beta = 99.360(2) degrees, gamma = 107.937(2) degrees, and Z = 2. The Cu(II) center in the complex has a distorted square planar geometry and is coordinated by two nitrogen atoms of a single dNbpy ligand (Cu-N = 2.011(7) and 2.022(7) A) and two bromine atoms (Cu-Br = 2.3621(14) and 2.3567(13) A). The similarity of the absorption spectra in the solid state and in solution suggested that the geometry of the complex remained unchanged upon dissolution. In the presence of dNbpy, Cu(II)(dNbpy)Br(2) undergoes Br substitution to form ionic [Cu(II)(dNbpy)(2)Br](+)[Br](-). DeltaH degrees and DeltaS degrees values for this equilibrium were negative and dependent on the polarity of the medium. It was found that, under the typical polymerization conditions (T > or =90 degrees C and the total copper concentration in the range 1.0 x 10(-2)-1.0 x 10(-1) M), Cu(II)Br(2) and 2 equiv of dNbpy will predominantly form the neutral Cu(II)(dNbpy)Br(2) complex. In a polar medium under the same conditions, [Cu(II)(dNbpy)(2)Br](+)[Br](-) is preferred.

Selective imidazolidine ring opening during complex formation of iron(III), copper(II), and zinc(II) with a multidentate ligand obtained from 2-pyridinecarboxaldehyde N-oxide and triethylenetetramine

The condensation of 2-pyridinecarboxaldehyde N-oxide and triethylenetetramine yields a product with two imidazolidine rings, as proven by a solid-state X-ray structure analysis as well as by NMR solution spectra. This ligand, L1, undergoes a ring-opening reaction on complex formation with Cu(II), yielding [CuL2]2+ where L2 functions as a pentadentate ligand, containing only one imidazolidine ring. On complexation with Zn(II) and Fe(III), both rings are opened and the complexes [ZnL3]2+ and [FeL3]3+ with a hexadentate L3 ligand are formed. The recrystallization of [ZnL3]2+ from DMSO solution results in the complex [ZnL1(DMSO)2]2+ in which L1 behaves as a tetradentate ligand. Thus L1, L2, and L3 are structural isomers with two, one, or no imidazolidine rings, as confirmed by X-ray structure analyses. The intramolecular ring formation is the result of the nucleophilic addition of the N(amino) group to the electrophilic sp2-hybridized -HC delta+=N site. Owing to the absence of the chelate effect on the sp3-hybridized carbon atom belonging to the imidazolidine ring, the ring opening is facilitated and readily observed upon complex formation with Cu(II), Zn(II), and Fe(III).