The DEMON/ANGEL suite of computer programs has been developed to carry out density modification by non‐crystallographic symmetry‐averaging, solvent‐flattening and histogram‐mapping techniques. This suite consists of programs that allow molecular envelopes to be defined and modified, non‐crystallographic symmetry operators to be refined either within one crystal form or between several crystal forms, and iterative density modification to be carried out, including non‐crystallographic symmetry averaging of electron densities within or between crystal forms.
Application of different engineered nanomaterials is fast‐growing, leading to increased chances of environmental release. Consequently, a robust preliminary detection method for nanomaterials in major ecological environments is beneficial. We report a facile strategy using intensity and number metric of dynamic light scattering to detect presence of nanomaterials in river water. Samples from eight locations of the Tennessee River within Chattanooga were analyzed using our dynamic light scattering technique as a representative assessment of an urban region of Southeastern United States. The average particle sizes (108–294 nm) indicated a possibility of nanomaterials in this region. The results were complemented via scanning electron microscopy. We found that a criteria of identifying peaks at the smallest size distribution for the intensity metric was useful in detecting presence of nanomaterials in environmental samples. The novelty of our approach is the ability to rapidly assess environmental water in solution form with minimum sample preparation artifacts.
The use of diverse metal nanoparticles (MNPs) in a wide range of commercial products has led to their co-existence in the aqueous environment. The current study explores the dispersion and aggregation fate of five prominent MNPs (silver, copper, iron, nickel, and titanium), in both their individual and co-existing forms. We address a knowledge gap regarding their environmental fate under turbulent condition akin to flowing rivers. We present tandem analytical techniques based on dynamic light scattering, ultraviolet-visible spectroscopy, and inductively coupled plasma atomic emission spectroscopy for discerning their dispersion behavior under residence times of turbulence, ranging from 0.25 to 4 h. The MNPs displayed a multimodal trend for dispersion and aggregation behavior with suspension time in aqueous samples. The extent of dispersion was variable and depended upon intrinsic properties of MNPs. However, the co-existing MNPs displayed a dominant hetero-aggregation effect, independent of the residence times. Further research with use of real-world environmental samples can provide additional insights on the effects of sample chemistry on MNPs fate.
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