Self-Assembly of PEGylated Diphenylalanines into Photoluminescent Fibrillary Aggregates

Diphenylalanine (FF) represents one of the most studied self-assembling peptides. As a consequence of non-covalent interactions (aromatic stacking and hydrogen bonds), FF is able to generate different nanoarchitectures, proposed in the last years as innovative tools for several applications. The identification of the relationship between the chemical building block composition and the supramolecular structure of final material is the objective of intense research. Different FF analogues were synthetized and studied. At the state of art, in the high number of FF derivatives, PEGylation has not been studied yet, notwithstanding its role has been demonstrated for longer poly-phenylalanine peptides. Herein, we describe the synthesis and the supramolecular behavior of two PEGylated-FF derivatives, PEG2-FF and PEG6-FF, in which the zwitterionic FF has been derivatized at the N-terminus with two or six ethoxylic moieties, respectively. Spectroscopic methodologies (fluorescence, circular dichroism, Fourier transform infrared) allowed the identification of their secondary structure and the calculation of the critical aggregation concentration. PEGylation of the dipeptide induces a modification of the conformational organization from nanotubes with hexagonal symmetry to β-sheet rich fibrils. This structural organization confers photoluminescence features to the supramolecular structures.     

Charge‐Induced Shifts in Chiral Surface Plasmon Modes in Gold Nanorod Assemblies

A detailed investigation of the effect of electron injection on the chiral plasmon modes of helical nanorod assemblies is presented. An increased surface plasmon frequency of the electron gas due to the addition of electrons leads to a blue‐shift in the corresponding chiral surface plasmon modes. The mechanism behind the shift in plasmonic chirality due to nanorod charging is investigated using theoretical simulations. Charging of the nanorods alters the surface electron density, thereby modifying the plasma frequency and causing a change in the dielectric function. The nature of the plasmon shift and the intensity of chiral surface plasmons are found to be largely dependent on the extent of electron addition. At extended periods of time, the blue shifted band slowly shifts back toward the red, due to transfer of electrons back to the medium, leading to discharging of the nanorods.     

Lock‐In Thermography to Analyze Plasmonic Nanoparticle Dispersions

The physicochemical properties of nanoparticles (NPs) strongly rely on their colloidal stability, and any given dispersion can display remarkably different features, depending on whether it contains single particles or clusters. Thus, developing efficient experimental methods that are able to provide accurate and reproducible measures of the NP properties is a considerable challenge for both research and industrial development. By analyzing different NPs, through size and concentration, it is demonstrated that lock‐in thermography, based on light absorption and heat generation, is able to detect and differentiate the distinct aggregation and re‐dispersion behavior of plasmonic NPs, e.g., gold and silver. Most importantly, the approach is nonintrusive and potentially highly cost‐effective compared to standard analytical techniques.     

Luminescent Molecular Octopuses with a Polyhedral Oligomeric Silsesquioxane (POSS) Core and Iridium(III) Polypyridine Arms: Synthesis,Aggregation Induced Emission,Cellular Uptake,and Bioimaging Studies

A new class of luminescent molecular hybrids in which eight cyclometalated iridium(III) polypyridine complexes are grafted onto a polyhedral oligomeric silsesquioxane (POSS) unit [POSS-{Ir(N^C)₂(py-im)}₈](PF₆)₈ [py-im=pyridine imine; HN^C=N-phenylpyrazole (Hppz) ( 1 a ), 2-phenylpyridine (Hppy) ( 2 a ), 2-phenylquinoline (Hpq) ( 3 a )] were synthesized and characterized. On photoexcitation, the complexes showed intense and long-lived orange-red to red emission in fluid solutions at room temperature and in low-temperature glasses. The photophysical properties including aggregation-induced emission and biological properties of these complexes were studied and compared with those of their POSS-free counterparts [Ir(N^C)₂(py-im)](PF₆) [HN^C=Hppz ( 1 b ), Hppy ( 2 b ), Hpq ( 3 b )]. The (photo)cytotoxicity of the complexes was examined by the MTT assay, and their cellular uptake and intracellular localization were investigated by inductively coupled plasma-mass spectrometry and laser-scanning confocal microscopy.     

Unstable Supramolecular Structure of [Bmim][BF4] in Aqueous Solution

To unravel the exact composition and structure of aggregates in an aqueous solution of 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF₄]), we performed static and dynamic light-scattering measurements, as well as transmission electron microscopy (TEM). Results from this work show that the aggregates are vesicles and unstable; herein, we discuss the driving force behind the self-assembly. Apart from the van der Waals forces and repulsive electrostatic interactions between adjacent cation clusters, the hydrogen-bonding forces as well as counterion effects might also contribute to this driving force. The information obtained here is useful for a better understanding of the vital role that aggregation behavior plays in the field of ionic liquid recovery, and its potential use in controlled release, drug delivery, and petroleum recovery.     

Adjusting Aggregation Modes and Photophysical and Photovoltaic Properties of Diketopyrrolopyrrole-Based Small Molecules by Introducing B←N Bonds

The packing mode of small-molecular semiconductors in thin films is an important factor that controls the performance of their optoelectronic devices. Designing and changing the packing mode by molecular engineering is challenging. Three structurally related diketopyrrolopyrrole (DPP)-based compounds were synthesized to study the effect of replacing C−C bonds by isoelectronic dipolar B←N bonds. By replacing one of the bridging C−C bonds on the peripheral fluorene units of the DPP molecules by a coordinative B←N bond and changing the B←N bond orientation, the optical absorption, fluorescence, and excited-state lifetime of the compounds can be tuned. The substitution alters the preferential aggregation of the molecules in the solid state from H-type (for C−C) to J-type (for B←N). Introducing B←N bonds thus provides a subtle way of controlling the packing mode. The photovoltaic properties of the compounds were evaluated in bulk heterojunctions with a fullerene acceptor and showed moderate performance as a consequence of suboptimal morphologies, bimolecular recombination, and triplet-state formation.     

Matrix Coordination Induced Emission in a Three-Dimensional Silver Cluster-Assembled Material

Developing highly luminescent and extensively stable silver cluster-assembled materials (SCAMs) from the inferior luminogens and unstable silver cluster is an important and challenging issue. Herein, a new luminescent three-dimensional SCAM ( Ag₁₂CPPP , [Ag₁₂(StBu)₆(CF₃COO)₆(CPPP)₂(DMAc)₁₂]_n; CPPP=2,5-bis(4-cyanophenyl)-1,4-bis(4-(pyridine-4-yl)-phenyl)-1,4-dihydropyrrolo[3,2-b]pyrrole, DMAc=dimethylacetamide) was designed and synthesized with a quadridentate rigid emission ligand ( CPPP ) and a silver–chalcogenolate cluster (SCC) containing 12 Ag^I atoms. The luminescence study indicates that CPPP is an aggregation-caused quenching (ACQ) molecule with twisted intramolecular charge transfer (TICT) character. Benefiting from the strong immobilization effect in the robust framework, the quantum yield of CPPP is greatly enhanced in Ag₁₂CPPP compared with that of CPPP in solution or in the solid state. As a result, Ag₁₂CPPP exhibits typical matrix coordination induced emission (MCIE) effect. Such efficient rigidifying methodology provides a promising approach for enhancing luminescence of ACQ molecules in an aggregated state and strengthening the silver cluster in an unstable state.     

A novel fluorescent sensor for Sn4+ detection: Dark resonance energy transfer from silole to rhodamine

A novel dark resonance energy transfer (DRET) off–on cassette SR1 was constructed by coupling a silole donor with a rhodamine acceptor. Due to the intramolecular rotations of the phenyl rings, the silole fluorophore served as a dark donor in solution state and fluorescence leakage from the donor emission could be avoided. Binding with Sn⁴⁺ ion induced the ring‐opening of the rhodamine acceptor, thus increase the overlapping between the emission spectra of the donor and absorption spectra of the acceptor. DRET was turned on and energy was transferred from the silole donor to the rhodamine acceptor. Emission from the rhodamine acceptor was achieved with a large Stokes shift up to 198 nm. The sensor showed good sensitivity and selectivity towards Sn⁴⁺ to other metal ions in methanol aqueous solution through the formation of a 1:1 complex between SR1 and Sn⁴⁺. This research provides a new approach for the development of rhodamine‐based sensors towards metal ions with large Stokes shifts.     

Molecular dynamics simulation study on the inhibitory effects of choline-O-sulfate on hIAPP protofibrilation

Type 2 diabetes mellitus (T2Dm) is a neurodegenerative disease, which occurs due to the self-association of human islet amyloid polypeptide (hIAPP), also known as human amylin. It was reported experimentally that choline-O-sulfate (COS), a small organic molecule having a tertiary amino group and sulfate group, can prevent the aggregation of human amylin without providing the mechanism of the action of COS in the inhibition process. In this work, we investigate the influence of COS on the full-length hIAPP peptide by performing 500 ns classical molecular dynamics simulations. From pure water simulation (without COS), we have identified the residues 11–20 and 23–36 that mainly participate in the fibril formation, but in the presence of 1.07 M COS these residues become totally free of β-sheet conformation. Our results also show that the sulfate oxygen of COS directly interacts with the peptide backbone, which leads to the local disruption of peptide–peptide interaction. Moreover, the presence of favorable peptide-COS vdW interaction energy and high coordination number of COS molecules in the first solvation shell of the peptide indicates the hydrophobic solvation of the peptide residues by COS molecules, which also play a crucial role in the prevention of β-sheet formation. Finally, from the potential of mean force (PMFs) calculations, we observe that the free energy between two peptides is more negative in the absence of COS and with increasing concentration of COS, it becomes unfavorable significantly indicating that the peptide dimer formation is most stable in pure water, which becomes less favorable in the presence of COS. © 2019 Wiley Periodicals, Inc.     

Simulated and experimental analysis of electrodeposited β' Brass composition with DLA morphology

Electrodeposition of two ions like Copper and Zinc in the alloy of β^' Brass is done in thin gap 2D geometry. The growth follows a Diffusion Limited Aggregation (DLA) like morphology. It is observed that the ratio of the two ions deposited remains almost constant with the distances from cathode. This ratio also depends on the composition of the cathodes. This has been shown experimentally and using a unique two-ion simulation model developed by us. The compositional analysis by EDX of the electrodeposited layers at different separations of 0.5?cm, 1.0?cm and 1.5?cm from the negative electrode shows a uniform ratio of 2.3087 for the two ions of copper and zinc. A two-ion simulation model made by us with different masses for the ions and for the same composition of cathode shows a uniform ratio of 2.3133 for the two ions systems and therefore, support the experimental observation to a high degree of accuracy. The results obtained have been explained theoretically.