Silver Nanoparticles Using Eucalyptus or Willow Extracts (AgNPs) as Contact Lens Hydrogel Components to Reduce the Risk of Microbial Infection.

Eucalyptus leaves (ELE) and willow bark (WBE) extracts were utilized towards the formation of silver nanoparticles (AgNPs(ELE), AgNPs(WBE)). AgNPs(ELE) and AgNPs(WBE) were dispersed in polymer hydrogels to create pHEMA@AgNPs(ELE)_2 and pHEMA@AgNPs(WBE)_2 using hydroxyethyl-methacrylate (HEMA). The materials were characterized in a solid state by X-ray fluorescence (XRF) spectroscopy, X-ray powder diffraction analysis (XRPD), thermogravimetric differential thermal analysis (TG-DTA), differential scanning calorimetry (DTG/DSC) and attenuated total reflection spectroscopy (ATR-FTIR) and ultraviolet visible (UV-vis) spectroscopy in solution. The antimicrobial potential of the materials was investigated against the Gram-negative bacterial strain Pseudomonas aeruginosa (P. aeruginosa) and the Gram-positive bacterial strain of the genus Staphylococcus epidermidis (S. epidermidis) and Staphylococcus aureus (S. aureus), which are involved in microbial keratitis. The percentage of bacterial viability of P. aeruginosa and S. epidermidis upon their incubation over the pHEMA@AgNPs(ELE)_2 discs is interestingly low (28.3 and 6.8% respectively), while the inhibition zones (IZ) formed are 12.3 ± 1.7 and 13.2 ± 1.2 mm, respectively. No in vitro toxicity of this material towards human corneal epithelial cells (HCEC) was detected. Despite its low performance against S. aureus, pHEMA@AgNPs(ELE)_2 could be an efficient candidate towards the development of contact lenses that reduces microbial infection risk.

Ultrafast ring-opening and solvent-dependent product relaxation of photochromic spironaphthopyran.

The ultrafast dynamics of unsubstituted spironaphthopyran (SNP) were investigated using femtosecond transient UV and visible absorption spectroscopy in three different solvents and by semi-classical nuclear dynamics simulations. The primary ring-opening of the pyran unit was found to occur in 300 fs yielding a non-planar intermediate in the first singlet excited state (S1). Subsequent planarisation and relaxation to the product ground state proceed through barrier crossing on the S1 potential energy surface (PES) and take place within 1.1 ps after excitation. Simulations show that more than 90% of the trajectories involving C-O bond elongation lead to the planar, open-ring product, while relaxation back to the S0 of the closed-ring form is accompanied by C-N elongation. All ensuing spectral dynamics are ascribed to vibrational relaxation and thermalisation of the product with a time constant of 13 ps. The latter shows dependency on characteristics of the solvent with solvent relaxation kinetics playing a role.

Photochromism of Amphiphilic Dithienylethenes as Langmuir-Schaefer Films.

Surface pressure-area isotherms were recorded under different irradiation conditions for single-component Langmuir films of three photochromic amphiphilic dithienylethenes. Nonirradiated films of these photochromic amphiphiles were mechanically stable. In addition, a shift of the isotherms to larger mean molecular areas was observed for films prepared from UV-light-irradiated dithienylethenes. Unexpectedly, a significant expansion was observed for a film prepared from visible-light-irradiated dithienylethene incorporating large branched alkyl chains. Upon further study, atomic force microscopy and transmission electron microscopy images of Langmuir-Schaefer films revealed that this pronged dialkyl derivative undergoes a photoinduced change in morphology, as circular aggregates coalesce into larger continuous aggregated structures. Nevertheless, its photoisomerization was completely reversible as single-component multilayer thin films upon direct UV or visible light irradiation.

Synthesis of Bidimensional Prussian Blue Analogue Using an Inverted Langmuir-Schaefer Method.

One of the aspects of modern materials science that has been captivating scientific interest for the past decade is low-dimensional systems. This stems from the fact that the physical, chemical, and biological properties of such systems are often vastly different from their bulk counterparts. Additionally, low-dimensionality structures frequently serve as a convenient platform for device applications. However, such materials are typically constructed from building blocks that are inherently three-dimensional, and so, from a morphological point of view, these can still be categorized as bulk powders or crystals. To push the boundaries of reduced dimensionality, we synthesized truly two-dimensional films of Prussian blue analogues (mixed valence tetracyanides) by combining an air-water interface reaction and a novel inverted Langmuir-Schaefer technique. The methodology introduced in this study offers control and tailoring over the Prussian blue analogues' film characteristics, which is an important step toward their incorporation into tangible applications. Standard isotherms were collected as a function of the initial reactant volume, and a number of characterization techniques such as X-ray photoelectron spectroscopy (XPS), UV-visible spectroscopy (UV-vis), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and atomic force microscopy (AFM) were performed on films transferred on various substrates. The results indicated a collection of single-crystalline and polycrystalline flakes possessing different thicknesses and having a structural coherence length of 11 ± 3 nm.