Polyamine Colloids Cross-Linked with Phosphate Ions: Towards Understanding the Solution Phase Behavior

Ionically crosslinked poly(allylamine)/phosphate (PAH/Pi) colloids consist of self-assembled nanostructures stabilized by supramolecular interactions. Under physiological conditions, these interactions should be present at high ionic strength and only in a narrow pH window to be effective as drug delivery agents. In this work we study the effect of the pH and ionic strength in the chemical behaviour of inorganic phosphate (Pi), poly(allylamine hydrochloride) (PAH) and their mixture in aqueous solution (PAH−Pi). By combination of experimental measurements and a theoretical model, we demonstrate that the driving force that leads to the formation of colloids is the electrostatic pairing between the positively charged amino groups in PAH and negatively charged HPO₄²⁻ ions. Increasing the ionic strength of the system by addition of KCl weakens the PAH−Pi interactions and narrows the pH stability window from 4 to 1.8 pH units. In addition, a fully reversible system was obtained in which the colloids assemble and disassemble by changing the pH between 6.8 and 7.1 at high ionic strength, making them suitable for use as pH-responsive nanocarriers.     

Can super-resolution microscopy become a standard characterization technique for materials chemistry?

The characterization of newly synthesized materials is a cornerstone of all chemistry and nanotechnology laboratories. For this purpose, a wide array of analytical techniques have been standardized and are used routinely by laboratories across the globe. With these methods we can understand the structure, dynamics and function of novel molecular architectures and their relations with the desired performance, guiding the development of the next generation of materials. Moreover, one of the challenges in materials chemistry is the lack of reproducibility due to improper publishing of the sample preparation protocol. In this context, the recent adoption of the reporting standard MIRIBEL (Minimum Information Reporting in Bio–Nano Experimental Literature) for material characterization and details of experimental protocols aims to provide complete, reproducible and reliable sample preparation for the scientific community. Thus, MIRIBEL should be immediately adopted in publications by scientific journals to overcome this challenge. Besides current standard spectroscopy and microscopy techniques, there is a constant development of novel technologies that aim to help chemists unveil the structure of complex materials. Among them super-resolution microscopy (SRM), an optical technique that bypasses the diffraction limit of light, has facilitated the study of synthetic materials with multicolor ability and minimal invasiveness at nanometric resolution. Although still in its infancy, the potential of SRM to unveil the structure, dynamics and function of complex synthetic architectures has been highlighted in pioneering reports during the last few years. Currently, SRM is a sophisticated technique with many challenges in sample preparation, data analysis, environmental control and automation, and moreover the instrumentation is still expensive. Therefore, SRM is currently limited to expert users and is not implemented in characterization routines. This perspective discusses the potential of SRM to transition from a niche technique to a standard routine method for material characterization. We propose a roadmap for the necessary developments required for this purpose based on a collaborative effort from scientists and engineers across disciplines.

SRM, an advanced nanoscopy technique demands a transition from being a niche sophisticated technique to standard routine method for material characterization. The roadmap of necessary developments through multidisciplinary collaboration is discussed.     

A Koszul complex over skew polynomial rings

We construct a Koszul complex in the category of left skew polynomial rings associated with a flat endomorphism that provides a finite free resolution of an ideal generated by a Koszul regular sequence.     

Indefinite Abstract Splines with a Quadratic Constraint

We study an extension to Krein spaces of the abstract interpolating spline problem in Hilbert spaces, introduced by M. Atteia. This is a quadratically constrained quadratic programming problem, where the objective function is not convex, while the equality constraint is sign indefinite. We characterize the existence of solutions and, if there are any, we describe the set of solutions as the union of a family of affine manifolds parallel to a fixed subspace, which depend on the original data.

     

Co-sensitized cells from Antarctic resources using Ag nanoparticles

In the present work, we explore in photoanodes of dye-sensitized solar cell (DSSC) the co-sensitization of the red protein phycoerythrin extracted from Antarctic algae with spherical silver nanoparticles between 10 and 200 nm and triangular nanoparticles of ~100 nm. We found that the order of addition of the sensitizers matters. Best results achieved for a sequential approach was phycoerythrin used as a dipping solution at the first step and nanoparticles at the second. We found that cell efficiency depends on the protein concentration, although no main differences detected with the nanoparticle shape or size. Our results show an average increase of 25% in the conversion efficiency values in the presence of nanoparticles.     

The Trigonal Prism in Coordination Chemistry

Herein we analyze the accessibility of the trigonal‐prismatic geometry to metal complexes with different electron configurations, as well as the ability of several hexadentate ligands to favor that coordination polyhedron. Our study combines i) a structural database analysis of the occurrence of the prismatic geometry throughout the transition‐metal series, ii) a qualitative molecular orbital analysis of the distortions expected for a trigonal‐prismatic geometry, and iii) a computational study of complexes of several transition‐metal ions with different hexadentate ligands. Also the tendency of specific electron configurations to present a cis bond‐stretch Jahn–Teller distortion is analyzed.     

Ratiometric fluorescence sensing of phenylalanine derivatives by synthetic macrocyclic receptors

The supramolecular analytical behavior of eight pseudopeptidic fluorescent receptors (1a–c, 2a–c, 3, 4) has been studied. The receptors are either macrocyclic or open chain derivatives based on the naphthalene chromophore. The ability of 1–4 for the molecular recognition of amino acids (as Z-protected derivatives) has been evaluated in dichloromethane. The signal observed corresponds to a fluorescence emission of turn-on type. The preferential binding of all the receptors for phenylalanine (Phe) over aliphatic amino acids (Ala, Val) by a factor of 3–4 has been found. Among the family of studied fluorescent molecules, two macrocyclic receptors (1a and 1b) display high exciplex emissions and great fluorescence changes both at long (fluorescence quenching at 390 nm) and short wavelengths (fluorescence enhancement at 340 nm). This feature makes the macrocycles 1a and 1b potentially practical as fluorescent ratiometric sensors for Phe. As a proof of concept, 1a and 1b have been assayed as analytical tools for the identification of model samples enriched with Phe, mimicking the concentrations found in the pathology phenylketonuria (PKU). This result opens the door to the development of new Phe-sensing sensors based on the exciplex signaling mechanism as a new strategy for the analysis of aminoacidemias.