Surface modification of polyamide 12 angioplasty balloons by photochemical reaction with an aromatic azide

Polyamide 12 (PA12) is used in a variety of applications when low moisture absorption, good dimensional stability, and toughness are required. Polyamide 12 is one of the polymers most frequently employed to fabricate angioplasty balloon catheters; however, its high hydrophobicity and chemical inertness require the application of coatings to make its surface more hydrophilic and biocompatible. In this work, an alternative method, based on the photochemical reaction of PA12 with a hydrophilic aromatic azide, was developed. Static and dynamic contact angle measurements evidenced that the surface modification process was able to improve PA12 wettability and that the effects were retained even after 12 months from surface treatment. Polyamide 12 modification resulted in an increase of its surface free energy, as evaluated by the van Oss, Good, and Chaudhury method. X‐ray photoelectron spectroscopy confirmed the presence of the aromatic azide on PA12 surface. Finally, compliance tests showed that the modification process did not reduce the mechanical performance of balloons.     

Low-pressure pyrolysis of tBu2SO: synthesis and IR spectroscopic detection of HSOH

Sulfenic acid (HSOH, 1 ) has been synthesized in the gas‐phase by low‐pressure high‐temperature (1150 °C) pyrolysis of di‐tert‐butyl sulfoxide (tBu₂SO, 2 ) and characterized by means of matrix isolation and gas‐phase IR spectroscopy. High‐level coupled‐cluster (CC) calculations (CCSD(T)/cc‐pVTZ and CCSD(T)/cc‐pVQZ) support the first identification of the gas‐phase IR spectrum of 1 and enable its spectral characterization. Five of the six vibrational fundamentals of matrix‐isolated 1 have been assigned, and its rotational‐resolved gas‐phase IR spectrum provides additional information on the O–H and S–H stretching fundamentals. Investigations of the pyrolysis reaction by mass spectrometry, matrix isolation, and gas‐phase FT‐IR spectroscopy reveal that, up to 500 °C, 2 decomposes selectively into tert‐butylsulfenic acid, (tBuSOH, 3 ), and 2‐methylpropene. The formation of the isomeric sulfoxide (tBu(H)SO, 3 a ) has been excluded. Transient 3 has been characterized by a comprehensive matrix and gas‐phase vibrational IR study guided by the predicted vibrational spectrum calculated at the density functional theory (DFT) level (B3LYP/6‐311+G(2d,p)). At higher temperatures, the intramolecular decomposition of 3 , monitored by matrix IR spectroscopy, yields short‐lived 1 along with 2‐methylpropene, but also H₂O, and most probably sulfur atoms. In addition, HSSOH ( 6 ), H₂, and S₂O are found among the final pyrolysis products observed at 1150 °C in the gas phase owing to competing intra‐ and intermolecular decomposition routes of 3 . The decomposition routes of the starting compound 2 and of the primary intermediate 3 are discussed on the basis of experimental results and a computational study performed at the B3LYP/6‐311G* and second‐order Møller–Plesset (MP2/6‐311G* and RI‐MP2/QZVPP) levels of theory.     

Structure and bonding in monomeric iron(III) complexes with terminal oxo and hydroxo ligands

We report on the structure and bonding in the title iron(III) complexes, containing the tris[(N'-tert-butylureayl)-N-ethyl]amine ligand, with density functional theory techniques. In agreement with the experimental data, a high-spin electronic state is favored for all of the systems we considered. H bonds between the terminal oxo and hydroxo ligands and NH groups present in the organic ligand coordinated to the metal have a remarkable effect on the overall coordination geometry. In fact, the structure of model complexes without H bonds shows shorter Fe-O bond lengths. This is a consequence of the ability of the H bonds to stabilize a remarkable amount of electron density localized on the terminal oxo and hydroxo ligands. Energy analysis indicates that each H bond stabilizes the nonheme complexes by roughly 35 kJ/mol. Molecular orbital analysis indicates a reduction of two Fe-O bonding electrons on going from a complex with a terminal oxo ligand to a complex with a terminal hydroxo ligand. This reduction in the number of bonding electrons is also supported by frequency analysis.     

Solid-State Dynamics and High-Pressure Studies of a Supramolecular Spiral Gear

The structures and solid-state dynamics of the supramolecular salts of the general formula [(12-crown-4)₂ ⋅ DABCOH₂](X)₂ (where DABCO=1,4-diazabicyclo[2.2.2]octane, X=BF₄, ClO₄) have been investigated as a function of temperature (from 100 to 360 K) and pressure (up to 3.4 GPa), through the combination of variable-temperature and variable-pressure XRD techniques and variable-temperature solid-state NMR spectroscopy. The two salts are isomorphous and crystallize in the enantiomeric space groups P3₂2₁ and P3₁2₁. All building blocks composing the supramolecular complex display dynamic processes at ambient temperature and pressure. It has been demonstrated that the motion of the crown ethers is maintained on lowering the temperature (down to 100 K) or on increasing the pressure (up to 1.5 GPa) thanks to the correlation between neighboring molecules, which mesh and rotate in a concerted manner similar to spiral gears. Above 1.55 GPa, a collapse-type transition to a lower-symmetry ordered structure, not attainable at a temperature of 100 K, takes place, proving, thus, that the pressure acts as the means to couple and decouple the gears. The relationship between temperature and pressure effects on molecular motion in the solid state has also been discussed.     

Temperature accelerated Monte Carlo (TAMC): a method for sampling the free energy surface of non-analytical collective variables

We introduce a new method to simulate the physics of rare events. The method, an extension of the Temperature Accelerated Molecular Dynamics, comes in use when the collective variables introduced to characterize the rare events are either non-analytical or so complex that computing their derivative is not practical. We illustrate the functioning of the method by studying the homogeneous crystallization in a sample of Lennard-Jones particles. The process is studied by introducing a new collective variable that we call Effective Nucleus Size N. We have computed the free energy barriers and the size of critical nucleus, which result in agreement with data available in the literature. We have also performed simulations in the liquid domain of the phase diagram. We found a free energy curve monotonically growing with the nucleus size, consistent with the liquid domain.     

The complex of a bivalent derivative of galanthamine with torpedo acetylcholinesterase displays drastic deformation of the active-site gorge: implications for structure-based drug design

Bifunctional derivatives of the alkaloid galanthamine, designed to interact with both the active site of the enzyme acetylcholinesterase (AChE) and its peripheral cation binding site, have been assayed with Torpedo californica AChE (TcAChE), and the three-dimensional structures of their complexes with the enzyme have been solved by X-ray crystallography. Differences were noted between the IC(50) values obtained for TcAChE and those for Electrophorus electricus AChE. These differences are ascribed to sequence differences in one or two residues lining the active-site gorge of the enzyme. The binding of one of the inhibitors disrupts the native conformation of one wall of the gorge, formed by the loop Trp279-Phe290. It is proposed that flexibility of this loop may permit the binding of inhibitors such as galanthamine, which are too bulky to penetrate the narrow neck of the gorge formed by Tyr121 and Phe330 as seen in the crystal structure.     

Regioselective synthesis of isochromenones by iron(III)/PhSeSePh-mediated cyclization of 2-alkynylaryl esters

A series of 4-Se-(Te, S)-isochromenones and 3-substituted isochromenones were synthesized in good yields via FeCl(3)-mediated cyclization of alkynylaryl esters with different diorganyl dichalcogenides. This methodology was carried out at room temperature, using inexpensive and environmentally friendly iron salts as metallic source and under air atmosphere. The reaction showed to be tolerant to a range of substituents bonded into the aromatic ring of the diorganyl dichalcogenides as well as to alkyl groups directly bonded to the chalcogen atom. Alternatively, the cyclization reaction of 2-alkynylaryl esters with FeCl(3), in the absence of diorganyl dichalcogenide, gave the isochromenones without the chalcogen moiety in the structure. This approach proved to be highly regioselective, providing only six-membered ring products, once the possible five-membered products were not observed in any experiments.     

Amphiphilic folded dendrimer discs and their thermosensitive self-assembly in water

Folded dendrimers with peripheral ether side chains show a thermally induced hierarchical aggregation process, in which the transition temperature and the dimensions of the aggregates can readily be tuned via the generation number (see figure).