The third order nonlinear optical properties of gold nanoparticles in glasses, part II

The optical properties of gold nanoparticles have been known for a number of years and recent advances in laser power have now allowed the non-linear optical properties to be studied. In this short review paper, the various theories that have been used to describe the optical properties of gold nanoparticles are presented. Methods of preparing gold nanoparticles in glasses are explained briefly, as well as characterization techniques. The optical properties of gold nanoparticles are reviewed, as well as the effects of particle size, shape, concentration and c.     

Nanomaterial Transformations in the Environment: Effects of Changing Exposure Forms on Bioaccumulation and Toxicity

In the environment, nanomaterials (NMs) are subject to chemical transformations, such as redox reactions, dissolution, coating degradation, and organic matter, protein, and macromolecule binding, and physical transformations including homo or heteroagglomeration. The combination of these reactions can result in NMs with differing characteristics progressing through a functional fate pathway that leads to the formation of transformed NM functional fate groups with shared properties. To establish the nature of such effects of transformation on NMs, four main types of studies are conducted: 1) chemical aging for transformation of pristine NMs; 2) manipulation of test media to change NM surface properties; 3) aging of pristine NMs water, sediment, or soil; 4) NM aging in waste streams and natural environments. From these studies a paradigm of aging effects on NM uptake and toxicity can be developed. Transformation, especially speciation changes, largely results in reduced potency. Further reactions at the surface resulting in processes, such as ecocorona formation and heteroagglomeration may additionally reduce NM potency. When NMs of differing potency transform and enter environments, common transformation reaction occurring in receiving system may act to reduce the variation in hazard between different initial NMs leading to similar actual hazard under realistic exposure conditions.     

Characterization of sorption sites on Pilayella littoralis and metal binding assessment using 113Cd and 27Al nuclear magnetic resonance

Metal interactions with the cellular structures of the marine alga Pilayella littoralis have been investigated to better understand how biomaterials sorb dissolved metals. Algae metal binding capacity at pH 5.0 was 2000, 850, 430, and 560 micromol g(-1) of dried material for Al(III), Cu(II), Cd(II), and Co(II), respectively. Binding site characterization was assessed by 1H and 13C nuclear magnetic resonance spectroscopy. Also, Fourier Transform Infrared spectroscopy (FTIR) provided some information about the types of functional groups that appear to be present in the algal material. The results suggested the presence of carboxylate, ether, amino, and hydroxyl groups. Investigation of metal competition for the alga binding sites was performed using 27Al and 113Cd NMR spectroscopy, which proved to be a valuable technique for Al and Cd sorption assessment. Aluminum and Cu were efficiently sorbed by the alga sites, and the binding affinity order of these metals was Al(III) > Cu(II) > Cd(II) > Co(II).     

The Photodynamic Antibacterial Effects of Silicon Phthalocyanine (Pc) 4

The emergence of antibiotic-resistant strains in facultative anaerobic Gram-positive coccal bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA), is a global health issue. Typically, MRSA strains are found associated with institutions like hospitals but recent data suggest that they are becoming more prevalent in community-acquired infections. It is thought that the incidence and prevalence of bacterial infections will continue to increase as (a) more frequent use of broad-spectrum antibiotics and immunosuppressive medications; (b) increased number of invasive medical procedures; and (c) higher incidence of neutropenia and HIV infections. Therefore, more optimal treatments, such as photodynamic therapy (PDT), are warranted. PDT requires the interaction of light, a photosensitizing agent, and molecular oxygen to induce cytotoxic effects. In this study, we investigated the efficacy and characterized the mechanism of cytotoxicity induced by photodynamic therapy sensitized by silicon phthalocyanine (Pc) 4 on (a) methicillin-sensitive Staphylococcus aureus (MSSA) (ATCC 25923); (b) community acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) (ATCC 43300); and (c) hospital acquired methicillin-resistant Staphylococcus aureus (HA-MRSA) (PFGE type 300). Our data include confocal image analysis, which confirmed that Pc 4 is taken up by all S. aureus strains, and viable cell recovery assay, which showed that concentrations as low as 1.0 μM Pc 4 incubated for 3 h at 37 °C followed by light at 2.0 J/cm² can reduce cell survival by 2–5 logs. These results are encouraging, but before PDT can be utilized as an alternative treatment for eradicating resistant strains, we must first characterize the mechanism of cell death that Pc 4-based PDT employs in eliminating these pathogens.     

Aromatic Zipper Topology Dictates Water-Responsive Actuation in Phenylalanine-Based Crystals

Water-responsive (WR) materials that reversibly deform in response to relative humidity (RH) changes are gaining increasing interest for their potential in energy harvesting and soft robotics applications. Despite progress, there are significant gaps in the understanding of how supramolecular structure underpins the reconfiguration and performance of WR materials. Here, three crystals are compared based on the amino acid phenylalanine (F) that contain water channels and F packing domains that are either layered (F), continuously connected (phenylalanyl-phenylalanine, FF), or isolated (histidyl-tyrosyl-phenylalanine, HYF). Hydration-induced reconfiguration is analyzed through changes in hydrogen-bond interactions and aromatic zipper topology. F crystals show the greatest WR deformation (WR energy density of 19.8 MJ m⁻³) followed by HYF (6.5 MJ m⁻³), while FF exhibits no observable response. The difference in water-responsiveness strongly correlates to the deformability of aromatic regions, with FF crystals being too stiff to deform, whereas HYF is too soft to efficiently transfer water tension to external loads.  These  findings reveal aromatic topology design rules for WR crystals and provide insight into general mechanisms of high-performance WR actuation. Moreover, the best-performing crystal, F emerges as an efficient WR material for applications at scale and low cost.