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Peptides are able to self-organize in structural elements including cross-β structures. Taking advantage of this tendency, in the last decades, peptides have been scrutinized as molecular elements for the development of multivalent supramolecular architectures. In this context, different classes of peptides, also with completely aromatic sequences, were proposed. Our previous studies highlighted that the (FY)3 peptide, which alternates hydrophobic phenylalanine and more hydrophilic tyrosine residues, is able to self-assemble, thanks to the formation of both polar and apolar interfaces. It was observed that the replacement of Phe and Tyr residues with other noncoded aromatic amino acids like 2-naphthylalanine (Nal) and Dopa affects the interactions among peptides with consequences on the supramolecular organization. Herein, we have investigated the self-assembling behavior of two novel (FY)3 analogues with Trp and Dopa residues in place of the Phe and Tyr ones, respectively. Additionally, PEGylation of the N-terminus was analyzed too. The supramolecular organization, morphology, and capability to gel were evaluated using complementary techniques, including fluorescence, Fourier transform infrared spectroscopy, and scanning electron microscopy. Structural periodicities along and perpendicular to the fiber axis were detected by grazing incidence wide-angle X-ray scattering. Finally, molecular dynamics studies provided interesting insights into the atomic structure of the cross-β that constitutes the basic motif of the assemblies formed by these novel peptide systems.

Carbon dots are carbon-based nanoparticles renowned for their intense light-emitting capabilities covering the whole visible light range. Achieving carbon dots emitting in the red region with high efficiency is extremely relevant due to their huge potential in biological applications and in optoelectronics. Currently, photoluminescence in such an energy interval is often associated with polyheterocyclic molecular domains forming during the synthesis that, however, present low emission efficiency and issues in controlling the optical features. Here, we overcome these problems by solvothermally synthesizing carbon dots starting from Neutral Red, a common red-emitting dye, as a molecular precursor. As a result of the synthesis, such molecular fluorophore is incorporated into a carbonaceous core while retaining its original optical properties. The obtained nanoparticles are highly luminescent in the red region, with a quantum yield comparable to that of the starting dye. Most importantly, the nanoparticle carbogenic matrix protects the Neutral Red molecules from photobleaching under ultraviolet excitation while preventing aggregation-induced quenching, thus allowing solid-state emission. These advantages have been exploited to develop a fluorescence-based color conversion layer by fabricating polymer-based highly concentrated solid-state carbon dot nanocomposites. Finally, the dye-based carbon dots demonstrate both stable Fabry-Perot lasing and efficient random lasing emission in the red region.

Bombyx mori silk fibroin (SF) has been reported as a convenient natural material for regenerative medicine, optoelectronics, and many other technological applications. SF owes its unique features to the hierarchical organization of the fibers. Many efforts have been made to set up protocols for dissolution since many applications of SF are based on regenerated solutions and fibers, but chaotropic conditions required to disassemble the packing of the polymer afford solutions with poor crystalline behavior. Our previous research has disclosed a dissolution and regeneration process of highly crystalline fibers involving lanthanide ions as chaotropic agents, demonstrating that each lanthanide has its own unique interaction with SF. Herein, we report elucidation of the structure of Ln-SF fibers by the combined use of Raman spectroscopy, wide-angle X-ray scattering (WAXS), and solid-state NMR techniques. Raman spectra confirmed the coordination of metal ions to SF, WAXS results highlighted the crystalline content of fibers, and solid-state NMR enabled the assessment of different ratios of secondary structures in the protein., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

One major concern toward the performance and stability of halide perovskite-based optoelectronic devices is the formation of metallic lead that promotes nonradiative recombination of charge carriers. The origin of metallic lead formation is being disputed whether it occurs during the perovskite synthesis or only after light, electron, or X-ray beam irradiation or thermal annealing. Here, we show that the quantity of metallic lead detected in perovskite crystals depends on the concentration and composition of the precursor solution. Through a controlled crystallization process, we grew black-colored mixed dimethylammonium (DMA)/methylammonium (MA) lead tribromide crystals. The black color is suggested to be due to the presence of small lead clusters. Despite the unexpected black coloring, the crystals show higher crystallinity and less defect density with respect to the standard yellow-colored DMA/MAPbBr 3 crystals, as indicated by X-ray rocking curve and dark current measurements, respectively. While the formation of metallic lead could still be induced by external factors, the precursor solution composition and concentration can facilitate the formation of metallic lead during the crystallization process. Our results indicate that additional research is required to fully understand the perovskite precursor solution chemistry.

ConspectusFor almost a decade now, lead halide perovskite nanocrystals have been the subject of a steadily growing number of publications, most of them regarding CsPbBr 3 nanocubes. Many of these works report X-ray diffraction patterns where the first Bragg peak has an unusual shape, as if it was composed of two or more overlapping peaks. However, these peaks are too narrow to stem from a nanoparticle, and the perovskite crystal structure does not account for their formation. What is the origin of such an unusual profile, and why has it been overlooked so far? Our attempts to answer these questions led us to revisit an intriguing collective diffraction phenomenon, known for multilayer epitaxial thin films but not reported for colloidal nanocrystals before. By analogy, we call it the multilayer diffraction effect.Multilayer diffraction can be observed when a diffraction experiment is performed on nanocrystals packed with a periodic arrangement. Owing to the periodicity of the packing, the X-rays scattered by each particle interfere with those diffracted by its neighbors, creating fringes of constructive interference. Since the interfering radiation comes from nanoparticles, fringes are visible only where the particles themselves produce a signal in their diffraction pattern: for nanocrystals, this means at their Bragg peaks. Being a collective interference phenomenon, multilayer diffraction is strongly affected by the degree of order in the nanocrystal aggregate. For it to be observed, the majority of nanocrystals within the sample must abide to the stacking periodicity with minimal misplacements, a condition that is typically satisfied in self-assembled nanocrystal superlattices or stacks of colloidal nanoplatelets.A qualitative understanding of multilayer diffraction might explain why the first Bragg peak of CsPbBr 3 nanocubes sometimes appears split, but leaves many other questions unanswered. For example, why is the split observed only at the first Bragg peak but not at the second? Why is it observed routinely in a variety of CsPbBr 3 nanocrystals samples and not just in highly ordered superlattices? How does the morphology of particles (i.e., nanocrystals vs nanoplatelets) affect the appearance of multilayer diffraction effects? Finally, why is multilayer diffraction not observed in other popular nanocrystals such as Au and CdSe, despite the extensive investigations of their superlattices?Answering these questions requires a deeper understanding of multilayer diffraction. In what follows, we summarize our progress in rationalizing the origin of this phenomenon, at first through empirical observation and then by adapting the diffraction theory developed in the past for multilayer thin films, until we achieved a quantitative fitting of experimental diffraction patterns over extended angular ranges. By introducing the reader to the key advancements in our research, we provide answers to the questions above, we discuss what information can be extracted from patterns exhibiting collective interference effects, and we show how multilayer diffraction can provide insights into colloidal nanomaterials where other techniques struggle. Finally, with the help of literature patterns showing multilayer diffraction and simulations performed by us, we demonstrate that this collective diffraction effect is within reach for many appealing nanomaterials other than halide perovskites.

CsPbBr 3 nanoclusters have been synthesized by several groups and mostly employed as single-source precursors for the synthesis of anisotropic perovskite nanostructures or perovskite-based heterostructures. Yet, a detailed characterization of such clusters is still lacking due to their high instability. In this work, we were able to stabilize CsPbBr 3 nanoclusters by carefully selecting ad hoc ligands (benzoic acid together with oleylamine) to passivate their surface. The clusters have a narrow absorption peak at 400 nm, a band-edge emission peaked at 410 nm at room temperature, and their composition is identified as CsPbBr 2.3 . Synchrotron X-ray pair distribution function measurements indicate that the clusters exhibit a disk-like shape with a thickness smaller than 2 nm and a diameter of 13 nm, and their crystal structure is a highly distorted orthorhombic CsPbBr 3 . Based on small- and wide-angle X-ray scattering analyses, the clusters tend to form a two-dimensional (2D) hexagonal packing with a short-range order and a lamellar packing with a long-range order.

The research on two-dimensional colloidal semiconductors has received a boost from the emergence of ultrathin lead halide perovskite nanoplatelets. While the optical properties of these materials have been widely investigated, their accurate structural and compositional characterization is still challenging. Here, we exploited the natural tendency of the platelets to stack into highly ordered films, which can be treated as single crystals made of alternating layers of organic ligands and inorganic nanoplatelets, to investigate their structure by multilayer diffraction. Using X-ray diffraction alone, this method allowed us to reveal the structure of ∼12 Å thick Cs-Pb-Br perovskite and ∼25 Å thick Cs-Pb-I-Cl Ruddlesden-Popper nanoplatelets by precisely measuring their thickness, stoichiometry, surface passivation type and coverage, as well as deviations from the crystal structures of the corresponding bulk materials. It is noteworthy that a single, readily available experimental technique, coupled with proper modeling, provides access to such detailed structural and compositional information.

Colloidal superlattices are fascinating materials made of ordered nanocrystals, yet they are rarely called "atomically precise". That is unsurprising, given how challenging it is to quantify the degree of structural order in these materials. However, once that order crosses a certain threshold, the constructive interference of X-rays diffracted by the nanocrystals dominates the diffraction pattern, offering a wealth of structural information. By treating nanocrystals as scattering sources forming a self-probing interferometer, we developed a multilayer diffraction method that enabled the accurate determination of the nanocrystal size, interparticle spacing, and their fluctuations for samples of self-assembled CsPbBr 3 and PbS nanomaterials. The multilayer diffraction method requires only a laboratory-grade diffractometer and an open-source fitting algorithm for data analysis. The average nanocrystal displacement of 0.33 to 1.43 Å in the studied superlattices provides a figure of merit for their structural perfection and approaches the atomic displacement parameters found in traditional crystals.

We report the colloidal synthesis of a series of surfactant-stabilized lead chalcohalide nanocrystals. Our work is mainly focused on Pb 4 S 3 Br 2 , a chalcohalide phase unknown to date that does not belong to the ambient-pressure PbS-PbBr 2 phase diagram. The Pb 4 S 3 Br 2 nanocrystals herein feature a remarkably narrow size distribution (with a size dispersion as low as 5%), a good size tunability (from 7 to ∼30 nm), an indirect bandgap, photoconductivity (responsivity = 4 ± 1 mA/W), and stability for months in air. A crystal structure is proposed for this new material by combining the information from 3D electron diffraction and electron tomography of a single nanocrystal, X-ray powder diffraction, and density functional theory calculations. Such a structure is closely related to that of the recently discovered high-pressure chalcohalide Pb 4 S 3 I 2 phase, and indeed we were able to extend our synthesis scheme to Pb 4 S 3 I 2 colloidal nanocrystals, whose structure matches the one that has been published for the bulk. Finally, we could also prepare nanocrystals of Pb 3 S 2 Cl 2 , which proved to be a structural analogue of the recently reported bulk Pb 3 Se 2 Br 2 phase. It is remarkable that one high-pressure structure (for Pb 4 S 3 I 2 ) and two metastable structures that had not yet been reported (for Pb 4 S 3 Br 2 and Pb 3 S 2 Cl 2 ) can be prepared on the nanoscale by wet-chemical approaches. This highlights the important role of colloidal chemistry in the discovery of new materials and motivates further exploration into metal chalcohalide nanocrystals.

There is huge research activity in the development of flexible and biocompatible piezoelectric materials for next-generation compliant micro electro-mechanical systems (MEMS) transducers to be exploited in wearable devices and implants. This work reports for the first time on the development of flexible Sc x Al (1- x ) N films deposited by sputtering technique onto polyimide substrates, assessing their piezoelectricity and biocompatibility. Flexible Sc x Al (1- x ) N films have been analyzed in terms of morphological, structural, and piezoelectric properties. Sc x Al (1- x ) N layer exhibits a good surface roughness of 4.40 nm and moderate piezoelectricity with an extracted effective piezoelectric coefficient ( d 33 eff ) value of 1.87 ± 0.06 pm/V, in good agreement with the diffraction pattern analysis results. Cell viability assay, performed to study the interaction of the Sc x Al (1- x ) N films with human cell lines, shows that this material does not have significant effects on tested cells. Furthermore, the Sc x Al (1- x ) N layer, integrated onto a flexible device and analyzed by bending/unbending measurements, shows a peak-to-peak open-circuit voltage ( V OC ) of 0.32 V and a short-circuit current ( I SC ) of 0.27 μA, with a generated power of 19.28 nW under optimal resistive load, thus demonstrating the potential of flexible Sc x Al (1- x ) N films as active layers for next-generation wearable/implantable piezoelectrics.

The photoluminescence (PL), color purity, and stability of lead halide perovskite nanocrystals depend critically on surface passivation. We present a study on the temperature-dependent PL and PL decay dynamics of lead bromide perovskite nanocrystals characterized by different types of A cations, surface ligands, and nanocrystal sizes. Throughout, we observe a single emission peak from cryogenic to ambient temperature. The PL decay dynamics are dominated by surface passivation, and a postsynthesis ligand exchange with a quaternary ammonium bromide (QAB) results in more stable passivation over a larger temperature range. The PL intensity is highest from 50 to 250 K, which indicates that ligand binding competes with the thermal energy at ambient temperature. Despite the favorable PL dynamics of nanocrystals passivated with QAB ligands (monoexponential PL decay over a large temperature range, increased PL intensity and stability), surface passivation still needs to be improved to achieve maximum emission intensity in nanocrystal films.

Sources of single photons are a fundamental brick in the development of quantum information technologies. Great efforts have been made so far in the realization of reliable, highly efficient, and on demand quantum sources that could show an easy integration with quantum devices. This has recently culminated in the use of solid state quantum dots as promising candidates for future sources of quantum technologies. However, some challenges, like their complex fabrication, random distribution, and difficult integrability with silicon technology, could hinder their broad application, making necessary the study of alternative systems. In this work, we clearly demonstrate single photon emission from quantum dots formed in nonstoichiometric bulk perovskites. Their simple growing procedures, exceptional stability under constant illumination, easy control of their optical properties, as well as ease of integrability make these materials very interesting candidates for the development of quantum light sources in the near-infrared.

Films made of colloidal CsPbBr 3 nanocrystals packed in isolated or densely-packed superlattices display a remarkably high degree of structural coherence. The structural coherence is revealed by the presence of satellite peaks accompanying Bragg reflections in wide-angle X-ray diffraction experiments in parallel-beam reflection geometry. The satellite peaks, also called "superlattice reflections", arise from the interference of X-rays diffracted by the atomic planes of the orthorhombic perovskite lattice. The interference is due to the precise spatial periodicity of the nanocrystals separated by organic ligands in the superlattice. The presence of satellite peaks is a fingerprint of the high crystallinity and long-range order of nanocrystals, comparable to those of multilayer superlattices prepared by physical methods. The angular separation between satellite peaks is highly sensitive to changes in the superlattice periodicity. These characteristics of the satellite peaks are exploited to track the superlattice compression under vacuum, as well as to observe the superlattice growth in situ from colloidal solutions by slow solvent evaporation., Competing Interests: The authors declare no competing financial interest., (Copyright © 2019 American Chemical Society.)

Biofilm formation is one of the main obstacles that occur during in vivo implantation, which compromises the implant functionality and patients' health. This is the inspiration for the development of novel implant materials that contain broad-spectrum antimicrobial activity, including antibacterial and antifungal, and enable the local release of antimicrobial agents. Here, multifunctional calcium phosphate-ionic liquid (IL) materials, possessing antimicrobial and repair/regeneration features plus injectability, are proposed as implants in minimally invasive surgery. This approach was based on the loading of 1-alkyl-3-alkylimidazolium chloride ionic liquids (ILs) (C n MImCl ( n = 4, 10, 16) and (C 10 ) 2 MImCl) during the in situ sol-gel synthesis of calcium phosphates (CaP) and study of their effects on CaP crystallization and biological properties. Physical, morphological, and biological investigations were performed to evaluate the bionanocomposites' properties. The IL N-alkyl chain length influenced the crystallization of CaP and, consequently, the biological properties, which afforded bionanocomposites (when loaded with C 16 MImCl or (C 10 ) 2 MImCl) that, (i) inhibit both in vitro bacterial and fungal growth; (ii) reduce the in vitro inflammatory response; (iii) induce osteogenic differentiation in the basal medium of human mesenchymal stem cells; and (iv) are injectable. This will enable the design of multifunctional injectable implants with antimicrobial, anti-inflammatory, and regenerative properties to be used in minimally invasive surgery of bone and maxillofacial defects.

The development of green and scalable syntheses for the preparation of size- and shape-controlled metal nanocrystals is of high interest in many areas, including catalysis, electrocatalysis, nanomedicine, and electronics. In this work, a new synthetic approach based on the synergistic action of physical parameters and reagents produces size-tunable octahedral Pt nanocrystals, without the use of catalyst-poisoning reagents and/or difficult-to-remove coatings. The synthesis requires sodium citrate, ascorbic acid, and fine control of the reduction rate in aqueous environment. Pt octahedral nanocrystals with particle size as low as 7 nm and highly developed {111} facets have been achieved, as demonstrated by transmission electron microscopy, X-ray diffraction, and electrochemical methods. The absence of sticky molecules together with the high quality of the surface makes these nanocrystals ideal candidates in electrocatalysis. Notably, 7 nm bismuth-decorated octahedral nanocrystals exhibit superior performance for the electrooxidation of formic acid in terms of both specific and mass activities.

The preparation of heteronanoparticles (NPs) with doxorubicin (DOXO) and cyclopamine (CYP) conjugates is presented. Biological evaluation on A431 cell lines confirms the maintenance of the activity of the parental drugs. The in vivo study shows that self-assembled NPs reduce tumor growth and toxicity of chemotherapy.

Solid-state luminescent materials with long lifetimes are the subject of ever-growing interest from both a scientific and a technological point of view. However, when dealing with organic compounds, the achievement of highly efficient materials is limited by aggregation-caused quenching (ACQ) phenomena on one side and by ultrafast deactivation of the excited states on the other. Here, we report on a simple organic molecule, namely, cyclic triimidazole (C 9 H 6 N 6 ), 1, showing crystallization-induced emissive (CIE) behavior and, in particular, ultralong phosphorescence due to strong coupling in H-aggregated molecules. Our experimental data reveal that luminescence lifetimes up to 1 s, which are several orders of magnitude longer than those of conventional organic fluorophores, can be realized under ambient conditions, thus expanding the class of organic materials for phosphorescence applications.

We report a low-temperature colloidal synthesis of single-layer, five-atom-thick, β-In 2 Se 3 nanosheets with lateral sizes tunable from ∼300 to ∼900 nm, using short aminonitriles (dicyandiamide or cyanamide) as shape controlling agents. The phase and the monolayer nature of the nanosheets were ascertained by analyzing the intensity ratio between two diffraction peaks from two-dimensional slabs of the various phases, determined by diffraction simulations. These findings were further backed-up by comparing and fitting the experimental X-ray diffraction pattern with Debye formula simulated patterns and with side-view high-resolution transmission electron microscopy imaging and simulation. The β-In 2 Se 3 nanosheets were found to be indirect band gap semiconductors (E g = 1.55 eV), and single nanosheet photodetectors demonstrated high photoresponsivity and fast response times.

Conjugated polymers are complex multichromophore systems, with emission properties strongly dependent on the electronic energy transfer through active subunits. Although the packing of the conjugated chains in the solid state is known to be a key factor to tailor the electronic energy transfer and the resulting optical properties, most of the current solution-based processing methods do not allow for effectively controlling the molecular order, thus making the full unveiling of energy transfer mechanisms very complex. Here we report on conjugated polymer fibers with tailored internal molecular order, leading to a significant enhancement of the emission quantum yield. Steady state and femtosecond time-resolved polarized spectroscopies evidence that excitation is directed toward those chromophores oriented along the fiber axis, on a typical time scale of picoseconds. These aligned and more extended chromophores, resulting from the high stretching rate and electric field applied during the fiber spinning process, lead to improved emission properties. Conjugated polymer fibers are relevant to develop optoelectronic plastic devices with enhanced and anisotropic properties.

This study is aimed at investigating the structure of a scaffold made of bovine gelatin and hydroxyapatite for bone tissue engineering purposes. In particular, the detailed characterization of such a material has a great relevance because of its application in the healing process of the osteochondral defect that consists of a damage of cartilage and injury of the adjacent subchondral bone, significantly compromising millions of patient's quality of life. Two different techniques exploiting X-ray radiation, with table-top setups, are used: microtomography (micro-CT) and microdiffraction. Micro-CT characterizes the microstructure in the three dimensions at the micrometer scale spatial resolution, whereas microdiffraction provides combined structural/morphological information at the atomic and nanoscale, in two dimensional microscopy images with a hundred micrometer spatial resolution. The combination of these two techniques allowed an appropriate structural characterization for the purpose of validating the engineering approach used for the realization of the hydroxyapatite gradient across the scaffold, with properties close to the natural model.

A new method for achieving high efficiency planar CH3NH3I3-xClx perovskite photovoltaics, based on a low pressure, reduced temperature vapor annealing is demonstrated. Heterojunction devices based on this hybrid halide perovskite exhibit a top PCE of 16.8%, reduced J-V hysteresis, and highly repeatable performance without need for a mesoporous or nanocrystalline metal oxide layer. Our findings demonstrate that large hysteresis is not an inherent feature of planar heterojunctions, and that efficient charge extraction can be achieved with uniform halide perovskite materials with desired composition. X-ray diffraction, valence band spectroscopy, and transient absorption measurements of these thin films reveal that structural modifications induced by chlorine clearly dominate over chemical and electronic doping effects, without affecting the Fermi level or photocarrier lifetime in the material.

We investigate the relationship between structural and optical properties of organo-lead mixed halide perovskite films as a function of the crystallization mechanism. For methylammonium lead tri-iodide, the organic cations rearrange within the inorganic cage, moving from crystals grown in a mesoporous scaffold to larger, oriented crystals grown on a flat substrate. This reduces the strain felt by the bonds forming the cage and affects the motion of the organic cation in it, influencing the electronic transition at the onset of the optical absorption spectrum of the semiconductor. Moreover, we demonstrate that in mixed-halide perovskite, though Cl(-) ions are not present in a detectable concentration in the unit cell, they drive the crystallization dynamics. This induces a preferential order during crystallization, from a molecular, i.e., organic-inorganic moieties arrangement, to a nano-mesoscopic level, i.e., larger crystals with anisotropic shape. Finally, we show that while Cl is mainly expelled from flat films made of large crystals, in the presence of an oxide mesoporous scaffold they are partially retained in the composite.

The peculiar architecture of a novel class of anisotropic TiO2(B) nanocrystals, which were synthesized by an surfactant-assisted nonaqueous sol-gel route, was profitably exploited to fabricate highly efficient mesoporous electrodes for Li storage. These electrodes are composed of a continuous spongy network of interconnected nanoscale units with a rod-shaped profile that terminates into one or two bulgelike or branch-shaped apexes spanning areas of about 5 × 10 nm(2). This architecture transcribes into a superior cycling performance (a charge capacitance of 222 mAh g(-1) was achieved by a carbon-free TiO2(B)-nanorods-based electrode vs 110 mAh g(-1) exhibited by a comparable TiO2-anatase electrode) and good chemical stability (more than 90% of the initial capacity remains after 100 charging/discharging cycles). Their outstanding lithiation/delithiation capabilities were also exploited to fabricate electrochromic devices that revealed an excellent coloration efficiency (130 cm(2) C(-1) at 800 nm) upon the application of 1.5 V as well as an extremely fast electrochromic switching (coloration time ∼5 s).

In the realm of semiconductor nanomaterials, a crystal lattice heavily doped with cation/anion vacancies or ionized atomic impurities is considered to be a general prerequisite to accommodating excess free carriers that can support localized surface plasmon resonance (LSPR). Here, we demonstrate a surfactant-assisted nonaqueous route to anisotropic copper sulfide nanocrystals, selectively trapped in the covellite phase, which can exhibit intense, size-tunable LSPR at near-infrared wavelengths despite their stoichiometric, undoped structure. Experimental extinction spectra are satisfactorily reproduced by theoretical calculations performed by the discrete dipole approximation method within the framework of the Drude-Sommerfeld model. The LSPR response of the nanocrystals and its geometry dependence are interpreted as arising from the inherent metallic-like character of covellite, allowed by a significant density of lattice-constitutional valence-band free holes. As a consequence of the unique electronic properties of the nanocrystals and of their monodispersity, coherent excitation of symmetric radial breathing modes is observed for the first time in transient absorption experiments at LSPR wavelengths.

A colloidal crystal-splitting growth regime has been accessed, in which TiO(2) nanocrystals, selectively trapped in the metastable anatase phase, can evolve to anisotropic shapes with tunable hyperbranched topologies over a broad size interval. The synthetic strategy relies on a nonaqueous sol-gel route involving programmed activation of aminolysis and pyrolysis of titanium carboxylate complexes in hot surfactant media via a simple multi-injection reactant delivery technique. Detailed investigations indicate that the branched objects initially formed upon the aminolysis reaction possess a strained monocrystalline skeleton, while their corresponding larger derivatives grown in the subsequent pyrolysis stage accommodate additional arms crystallographically decoupled from the lattice underneath. The complex evolution of the nanoarchitectures is rationalized within the frame of complementary mechanistic arguments. Thermodynamic pathways, determined by the shape-directing effect of the anatase structure and free-energy changes accompanying branching and anisotropic development, are considered to interplay with kinetic processes, related to diffusion-limited, spatially inhomogeneous monomer fluxes, lattice symmetry breaking at transient Ti(5)O(5) domains, and surfactant-induced stabilization. Finally, as a proof of functionality, the fabrication of dye-sensitized solar cells based on thin-film photoelectrodes that incorporate networked branched nanocrystals with intact crystal structure and geometric features is demonstrated. An energy conversion efficiency of 6.2% has been achieved with standard device configuration, which significantly overcomes the best performance ever approached with previously documented prototypes of split TiO(2) nanostructures. Analysis of the relevant photovoltaic parameters reveals that the utilized branched building blocks indeed offer light-harvesting and charge-collecting properties that can overwhelm detrimental electron losses due to recombination and trapping events.

We demonstrate that it is possible to convert CdSe nanocrystals of a given size, shape (either spherical or rod shaped), and crystal structure (either hexagonal wurtzite, i.e., hexagonal close packed (hcp), or cubic sphalerite, i.e., face-centered cubic (fcc)), into ZnSe nanocrystals that preserve all these characteristics of the starting particles (i.e., size, shape, and crystal structure), via a sequence of two cation exchange reactions, namely, Cd(2+) ⇒Cu(+) ⇒Zn(2+). When starting from hexagonal wurtzite CdSe nanocrystals, the exchange of Cd(2+) with Cu(+) yields Cu(2)Se nanocrystals in a metastable hexagonal phase, of which we could follow the transformation to the more stable fcc phase for a single nanorod, under the electron microscope. Remarkably, these metastable hcp Cu(2)Se nanocrystals can be converted in solution into ZnSe nanocrystals, which yields ZnSe nanocrystals in a pure hcp phase.

We report a phosphine-free synthesis of p-type copper(I) selenide nanocrystals by a colloidal approach in a mixture of oleylamine and 1-octadecene. The nanocrystals had a cuboctahedral shape and cubic berzelianite phase. Films of these nonstoichiometric copper-deficient Cu(2-x)Se nanocrystals were highly conductive and showed high absorption coefficient in the near-infrared region. These nanocrystals could be used as hole-injection layers in optoelectronic devices.

A colloidal nonaqueous approach to semiconductor-magnetic hybrid nanocrystals (HNCs) with selectable heterodimer topologies and tunable geometric parameters is demonstrated. Brookite TiO(2) nanorods, distinguished by a curved shape-tapered profile with richly faceted terminations, are exploited as substrate seeds onto which a single spherical domain of inverse spinel iron oxide can be epitaxially grown at either one apex or any location along their longitudinal sidewalls in a hot surfactant environment. The topologically controlled arrangement of the component material lattices, the crystallographic relationships holding between them, and strain distribution across individual heterostructures have been studied by combining X-ray diffraction and absorption techniques with high-resolution transmission electron microscopy investigations. Supported by such structural knowledge, the synthetic achievements are interpreted within the frame of various mechanistic models offering complementary views of HNC formation. The different HNC architectures are concluded to be almost equivalent in terms of surface-interface energy balance associated with their formation. HNC topology selection is rationalized on the basis of a diffusion-limited mechanism allowing iron oxide heterogeneous nucleation and growth on the TiO(2) nanorods to switch from a thermodynamically controlled to a kinetically overdriven deposition regime, in which the anisotropic reactivity offered by the uniquely structured seeds is accentuated under high spatially inhomogeneous monomer fluxes. Finally, the multifunctional capabilities of the heterostructures are highlighted through illustration of their magnetic and photocatalytic properties, which have been found to diverge from those otherwise exhibited by their individual material components and physical mixture counterparts.

Arranging anisotropic nanoparticles into ordered assemblies remains a challenging quest requiring innovative and ingenuous approaches. The variety of interactions present in colloidal solutions of nonspherical inorganic nanocrystals can be exploited for this purpose. By tuning depletion attraction forces between hydrophobic colloidal nanorods of semiconductors, dispersed in an organic solvent, these could be assembled into 2D monolayers of close-packed hexagonally ordered arrays directly in solution. Once formed, these layers could be fished onto a substrate, and sheets of vertically standing rods were fabricated, with no additional external bias applied. Alternatively, the assemblies could be isolated and redispersed in polar solvents, yielding suspensions of micrometer-sized sheets which could be chemically treated directly in solution. Depletion attraction forces were also effective in the shape-selective separation of nanorods from binary mixtures of rods and spheres. The reported procedures have the potential to enable powerful and cost-effective fabrication approaches to materials and devices based on self-organized anisotropic nanoparticles.

A colloidal two-step seeded-growth approach has been devised to selectively synthesize three-component magnetic/semiconductor hybrid nanocrystals (HNCs) with a matchstick-like profile and tunable geometric parameters. The newly developed heterostructures individually comprise a single metallic Co head connected to either apexes of one rod-shaped section made of a CdSe core eccentrically embedded in a CdS shell. The specific topological arrangement realized arises from the peculiar anisotropic reactivity of the noncentrosymmetric CdSe@CdS core@shell nanorods that have been used as substrates to seed heterogeneous nucleation of Co in a surfactant-free environment from an organometallic precursor. The HNCs retain appreciable fluorescent emission in spite of photoexcited charge transfer from the semiconductor to the metal domain and exhibit unusual ferromagnetic-like behavior at room temperature.

We report the synthesis, the structural and optical characterization of CdSe/CdS/ZnS "double shell" nanorods and their exploitation in cell labeling experiments. To synthesize such nanorods, first "dot-in-a-rod" CdSe(dot)/CdS(rod) core/shell nanocrystals were prepared. Then a ZnS shell was grown epitaxially over these CdSe/CdS nanorods, which led to a fluorescence quantum yield of the final core-shell-shell nanorods that could be as high as 75%. The quantum efficiency was correlated with the aspect ratio of the nanorods and with the thickness of the ZnS shell around the starting CdSe/CdS rods, which varied from 1 to 4 monolayers (as supported by a combination of X-ray diffraction, elemental analysis with inductively coupled plasma atomic emission spectroscopy and high resolution transmission electron microscopy analysis). Pump-probe and time-resolved photoluminescence measurements confirmed the reduction of trapping at CdS surface due to the presence of the ZnS shell, which resulted in more efficient photoluminescence. These double shell nanorods have potential applications as fluorescent biological labels, as we found that they are brighter in cell imaging as compared to the starting CdSe/CdS nanorods and to the CdSe/ZnS quantum dots, therefore a lower amount of material is required to label the cells. Concerning their cytotoxicity, according to the MTT assay, the double shell nanorods were less toxic than the starting core/shell nanorods and than the CdSe/ZnS quantum dots, although the latter still exhibited a lower intracellular toxicity than both nanorod samples.

We report a general synthetic approach to tetrapod-shaped colloidal nanocrystals made of various combinations of II-VI semiconductors. Uniform tetrapods were prepared using preformed seeds in the sphalerite structure, onto which arms were grown by coinjection of the seeds and chemical precursors into a hot mixture of surfactants. By this approach, a wide variety of core materials could be chosen (in practice, most of the II-VI semiconductors that could be prepared in the sphalerite phase, namely, CdSe, ZnTe, CdTe); in contrast, the best materials for arm growth were CdS and CdTe. The samples were extensively characterized with the aid of several techniques.

A colloidal seeded-growth strategy, relying on time-programmed delivery of selected stabilizing surfactants, has been developed to synthesize bimagnetic hybrid nanocrystals (HNCs) that consist of a single-crystal tetrapod-shaped skeleton of ferrimagnetic (FiM) iron oxide functionalized with multiple polycrystalline spherical domains of ferromagnetic (FM) Co. Due to the direct bonding interfaces formed between the two materials at the relevant junction regions, the HNCs exhibit FiM-FM exchange coupling, which transcribes into a rich scenario of significantly modified properties (not otherwise achievable with any of the single components or with their physical mixtures), including higher saturation magnetization and coercitivity values, exchange biasing, and enhanced thermal stability due to induced extra anisotropy. The availability of these new types of HNCs suggests that development of appropriate synthetic tools for arranging distinct material domains in predetermined spatial arrangements could lead to a more rational design of nanoheterostructures potentially exploitable as active elements in future generations of magnetic recording devices.

A surfactant-assisted nonaqueous strategy, relying on high-temperature aminolysis of titanium carboxylate complexes, has been developed to access anisotropically shaped TiO2 nanocrystals selectively trapped in the metastable brookite phase. Judicious temporal manipulation of precursor supply to the reaction mixture enables systematic tuning of the nanostructure geometric features over an exceptionally wide dimensional range (30-200 nm). Such degree of control is rationalized within the frame of a self-regulated phase-changing seed-catalyzed mechanism, in which homogeneous nucleation, on one side, and heterogeneous nucleation/growth processes, on the other side, are properly balanced while switching from the anatase to the brookite structures, respectively, in a continuous unidirectional crystal development regime. The time variation of the chemical potential for the monomer species in the solution, the size dependence of thermodynamic structural stability of the involved titania polymorphs, and the reduced activation barrier for brookite nucleation onto initially formed anatase seeds play decisive roles in the crystal-phase- and shape-tailored growth of titania nanostructures by the present approach.

A one-pot, two-step colloidal strategy to prepare bimagnetic hybrid nanocrystals (HNCs), comprising size-tuned fcc FePt and inverse spinel cubic iron oxide domains epitaxially arranged in a heterodimer configuration, is described. The HNCs have been synthesized in a unique surfactant environment by temperature-driven sequential reactions, involving the homogeneous nucleation of FePt seeds and the subsequent heterogeneous growth of iron oxide. This self-regulated mechanism offers high versatility in the control of the geometric features of the resulting heterostructures, circumventing the use of more elaborate seeded growth techniques. It has been found that, as a consequence of the exchange coupling between the two materials, the HNCs exhibit tunable single-phase-like magnetic behavior, distinct from that of their individual components. In addition, the potential of the heterodimers as effective contrast agents for magnetic resonance imaging techniques has been examined.

Colloidal semiconductor-magnetic hybrid nanocrystals with topologically controlled composition are fabricated by heterogeneous nucleation of spherical epsilon-Co domains onto anatase TiO2 nanorods. The latter can be selectively decorated at either their tips or at multiple locations along their longitudinal sidewalls, forming lattice-matched heterointerfaces regardless of the metal deposition sites. The possibility of switching between either heterostructure growth modes arises from the facet-dependent chemical reactivity of the oxide seeds, which is governed mainly by selective adhesion of the surfactants rather than by small differences in misfit-induced interfacial strain at the relevant junction points.

Asymmetric binary nanocrystals (BNCs), comprising one c-axis elongated anatase TiO2 section and one gamma-Fe2O3 spherical domain attached together, are synthesized by heterogeneous nucleation of iron oxide onto the longitudinal facets of TiO2 nanorods in a ternary surfactant mixture. The topologically controlled composition of the BNCs is ascertained by a combination of powder X-ray diffraction, Raman and Mössbauer spectroscopy, high-angle annular dark-field imaging, and high-resolution transmission electron microscopy lattice fringe mapping, while their size-dependent magnetic behavior is demonstrated by ac susceptibility measurements. The heteroepitaxial growth proceeds through a mechanism never observed before for colloidal nanoheterostructures: the two domains share a restricted and locally curved junction region, which accommodates efficiently the interfacial strain and retards the formation of misfit dislocations. It is believed that these BNCs, which combine the properties of two technologically relevant oxide materials, can pave the way to reinforced applications in several fields of nanoscience, such as in photocatalysis, in malignant cell treatments, and in nanocrystal assembly.

Tetrapod-shaped maghemite nanocrystals are synthesized by manipulating the decomposition of iron pentacarbonyl in a ternary surfactant mixture under mild thermal conditions. Adjustment of the reaction parameters allows for the systematic tuning of both the width and the length of the tetrapod arms, which grow preferentially along the 111 easy axis direction. Such degree of control leads to modulation of the magnetic behavior of the nanocrystals, which evolves systematically as their surface magnetization phase and shape anisotropy are progressively increased.

We describe an approach to synthesize colloidal nanocrystal heterodimers composed of CoPt(3) and Au. The growth is based on the nucleation of gold domains on preformed CoPt(3) nanocrystals. It is a highly versatile methodology which allows us to tune independently the size of the two domains in each dimer by varying several reaction parameters. The statistical analysis of the distribution of the domain sizes in the dimers and the compositional mapping achieved by dark field imaging and energy dispersive spectroscopy confirm that the two domains in each dimer are indeed made of CoPt(3) and Au, respectively. Structural characterization by high-resolution transmission electron microscopy shows that the two domains, both having cubic fcc Bravais lattice, can share a common {111}, {100}, or {110} facet, depending on the size of the initial CoPt(3) seeds. The magnetization measurements evidence a ferromagnetic CoPt(3) phase with a relatively low anisotropy as a consequence of their disordered crystalline structure, regardless of the presence of a Au tip. We believe that this prototype of nanocrystal dimer, which can be manipulated under air, can find several applications in nanoscience, as the Au section can be exploited as the preferential anchor point for various molecules, while the CoPt(3) domain can be used for magnetic detection.

Branching in semiconductor nanocrystals, which leads to tetrapods and to more complex architectures, is the subject of intensive investigation. Here we support the model according to which branching in CdTe nanocrystals is driven by the formation of multiple wurtzite twins. This is in contrast to previous models for this material. We found that twinning, as well as anisotropic growth, can be triggered by the presence of suitable molecules, such as for instance methylphosphonic acid. In the case of CdTe nanocrystals, we designed a robust growth scheme in which the variation of a single parameter (the concentration of methylphosphonic acid in solution) leads to the controlled formation of nanocrystals with shapes ranging from spheres to anisotropic structures with varying level of branching, as both twinning and anisotropic growth are progressively favored. We believe that these concepts can be extended to other nanocrystal systems.

Two new metabolites, named halipeptins A and B, have been isolated from the marine sponge Haliclona sp. Their structures were determined by extensive use of one- and two-dimensional NMR experiments, mass spectrometry, and UV and IR spectroscopy. Halipeptin A is a novel 17-membered cyclic depsipeptide, consisting of five residues including two alanines (with L stereochemistry) and three new residues that appear to be previously undescribed from natural sources: 1,2-oxazetidine-4-methyl-4-carboxylic acid, 3-hydroxy-2,2,4-trimethyl-7-methoxydecanoic acid (HTMMD), and N-methyl-delta-hydroxyisoleucine. The HTMMD residue is substituted with 3-hydroxy-2,2,4-trimethyl-7-hydroxydecanoic acid in halipeptin B. Halipeptin A was found to possess very potent anti-inflammatory activity in vivo, causing about 60% inhibition of edema in mice at the dose of 300 microg/kg (i.p.).

A new nonsymmetric dimeric steroid, crellastatin A (1), was isolated from the Vanuatu Island marine sponge Crella sp. Structural assignment was accomplished through extensive 2D NMR spectroscopy. The stereochemistry of 1 was established from an analysis of ROESY experiments and from molecular mechanics and dynamics calculations. Crellastatin A (1), which possesses an unprecedented connection through the side chains, exhibits in vitro cytotoxic activity against NSCLC-N6 cells (IC(50) of 1.5 &mgr;g/mL).