Conformations Of A Model Protein Revealed By An Aggregating Cuᴵᴵ Porphyrin: Sensing The Difference

Aggregated t-CuP binds to poly-L-glutamate through supramolecular interactions, revealing itself to be an extremely sensitive probe for the major conformations of the polymeric scaffold

Effect Of Zinc Cations On The Kinetics Of Supramolecular Assembly And The Chirality Of Porphyrin J-Aggregates

Dilute aqueous solutions of anionic meso-4-sulfonatophenyl-porphyrin (TPPS) extract zinc(ii) ions from glass or quartz surfaces at room temperature and efficiently form the corresponding metal complex (ZnTPPS). The partial or complete formation of ZnTPPS has been probed by UV/Vis spectroscopy and both static and time-resolved fluorescence. The source of zinc(ii) ions has been clearly identified through inductively coupled plasma optical emission spectrometry. The presence of increasing amounts of ZnTPPS slows down the rate of TPPS J-aggregate formation in acid solution. This influences the nucleation step and has a profound impact on the onset of chirality in these species. This evidence indicates the important role of this adventitious metal ion in the interpretation of various spectroscopic and kinetic data for the self-assembly of the TPPS porphyrin and provides some insights into controversial findings on their chirality. The use of this metal derivative as the starting compound for in situ formation of monomeric TPPS is suggested

Mechanism For Copper(II)-Mediated Disaggregation Of A Porphyrin J-Aggregate

J-aggregates of anionic meso-tetrakis(4-sulfonatophenyl)porphyrin form at intermediate pH (2.3–3.1) in the presence of NiSO₄ or ZnSO₄ (ionic strength, I.S. = 3.2 M). These aggregates convert to monomeric porphyrin units via metallation with copper(II) ions. The kinetics for the disassembly process, as monitored by UV/vis spectroscopy, exhibits zeroth-order behavior. The observed zeroth-order rate constants show a two-term dependence on copper(II) ion concentrations: linear and second order. Also observed is an inverse dependence on hydrogen ion concentration. Activation parameters have been determined for the disassembly process leading to ΔH^≠ = (+163 ± 15) kJ·mol⁻¹ and ΔS^≠ = (+136 ± 11) J·K⁻¹. A mechanism is proposed in which copper(II) cation is in pre-equilibrium with a reactive site at the rim of the J-aggregate. An intermediate copper species is thus formed that eventually leads to the final metallated porphyrin either through an assisted attack of a second metal ion or through a direct insertion of the metal cation into the macrocycle core

wetting ability modifications in biocompatible polymers induced by pulsed lasers

Wetting ability was measured in the surface of different biocompatible polymers, such as mylar, polyethylene, poly-methyl-methacrylate and teflon. Nanosecond pulse lasers at intensities of the order of 108 W/cm2 were employed at different doses to irradiate the polymeric surfaces and to induce wetting ability modifications due to the chemical and physical surface changes vs. irradiation time and laser wavelength. In particular, the contact angle as a function of the surface roughness was investigated, as will be presented and discussed

Chemical and physical modifications of polyethylene containing nanostructures

The polyethylene is an interesting polymer with a good mechanical strength, ductility, biocompatibility and chemical inertia. It founds several applications in many fields, such as chemistry, engineering, bio-medicine and micro-electronics. The polyethylene chemical and physical properties can be modified embedding different nanostructures in its bulk. Carbon nanotubes, metallic oxides, coloured pigments and other species can be inserted at different concentrations in the polymer material during the preparation phase of thin films and sheets. Mechanical, optical, thermal and chemical properties can be modified significantly depending on the filler concentration. The absorption coefficient at different radiations can be controlled by the amount of doping structure. In the visible region, for example, the high transparency of pure polyethylene can be strongly reduced by low concentrations of carbon nanotubes. The colour, the mechanical resistance, the wet ability of the polyethylene and other parameters can be changed by the doping species in order to prepare special devices useful for many applications

Influence of magnetic micelles on assembly and deposition of porphyrin J‐aggregates

Clusters of superparamagnetic iron oxide nanoparticles (SPIONs) have been incorporated into the hydrophobic core of polyethylene glycol (PEG)‐modified phospholipid micelles. Two different PEG‐phospholipids have been selected to guarantee water solubility and provide an external corona, bearing neutral (SPIONs@PEG‐micelles) or positively charged amino groups (SPIONs@NH2‐PEG‐micelles). Under acidic conditions and with specific mixing protocols (porphyrin first, PF, or porphyrin last, PL), the water‐soluble 5,10,15,20‐tetrakis‐(4‐ sulfonatophenyl)‐porphyrin (TPPS) forms chiral J‐aggregates, and in the presence of the two different types of magnetic micelles, an increase of the aggregation rates has been generally observed. In the case of the neutral SPIONs@PEG‐micelles, PL protocol affords a stable nanosystem, whereas PF protocol is effective with the charged SPIONs@NH2‐PEG‐micelles. In both cases, chiral J‐aggregates embedded into the magnetic micelles (TPPS@SPIONs@micelles) have been characterized in solution through UV/vis absorption and circular/linear dichroism. An external magnetic field allows depositing films of the TPPS@SPIONs@micelles that retain their chiroptical properties and exhibit a high degree of alignment, which is also confirmed by atomic force microscopy

Mass Quadrupole Spectrometry for Infrared Laser-Generated Plasmas Detection

A nanosecond pulsed Nd:YAG laser, operating at the fundamental wavelength of 1064 nm and at an intensity of about 10 10 W/cm 2 , was employed to irradiate the Cu 0.4 W 0.6 metallic alloy and the relative pure components (Cu and W) in vacuum to investigate about the ablation. Produced plasmas were characterized in terms of thermal and Coulomb interactions evaluating the equivalent temperatures and acceleration voltages developed in the non-equilibrium plasma core. The particles emission, produced along the normal to the target surface, was investigated by measuring, with the special electrostatic mass quadrupole spectrometer Hiden EQP 300, neutral and ion energy distributions and fitting experimental data with the "Coulomb-Boltzmann-shifted" function. Results indicated that the metal alloy stoichiometry, in a first approximation, is well transported to the ion and neutral stoichiometry of the plasma

Experimental Evidence For Self-Similar Structures In The Aggregation Of Porphyrins In Aqueous Solutions

We have studied the aggregation of the porphyrin t-H₂Pagg in aqueous solution by light scattering. The intensity profile of the elastically scattered light, studied in the exchanged wave-vector range 0.2 ≤ q ≤ 31.4 μ m⁻¹, indicates that the aggregation produces large monodisperse clusters having a fractal structure, and is driven by diffusion-limited aggregation kinetics. Additional measurements performed at different q values confirm such a picture giving a hydrodynamic radius R(H) consistent with the radius of gyration R(g) measured by elastic scattering. This is explained taking into account the q² dependence observed in the mean decay rate of the intensity-intensity correlation function and the effect on this latter dynamical quantity of anisotropies in the cluster structure

Modification induced by laser irradiation on physical features of plastics materials filled with nanoparticles

The Thermal Laser Welding (TLW) process involves localized heating at the interface of two pieces of plastic that will be joined. Polymeric materials of Ultra High Molecular Weight Polyethylene (UHMWPE), both pure and containing nanostructures at different concentrations (titanium and silver nanoparticles), were prepared as thin foils in order to produce an interface between a substrate transparent to the infrared laser wavelength and an highly absorbent substrate, in order to be welded by the laser irradiation. The used diode laser operates at 970 nm wavelength, in continuum, with a maximum energy of 100 mJ, for times of the order of 1 -60 s, with a spot of 300 μm of diameter. The properties of the polymers and of nanocomposite sheets, before and after the laser welding process, were measured in terms of optical characteristics, wetting ability, surface roughness and surface morphology