Structures and nuclear quadrupole coupling tensors of a series of chlorine-containing hydrocarbons

Rotational spectra for {\em gauche}-1,2-dichloroethane (12DCE), {\em gauche}-1-chloro-2-fluoroethane (1C2FE) and both {\em anti}- and {\em gauche}-2,3-dichloropropene (23DCP) have been observed using chirped-pulse Fourier-transform microwave (FTMW) spectroscopy in the 6-18 GHz region. Although the {\em anti} conformers for all three species are predicted to be more stable than the {\em gauche} forms, they are nonpolar (12DCE) or nearly nonpolar (predicted dipole components for {\em anti}-1C2FE: $\mu_a = 0.11$ D, $\mu_b = 0.02$ D and for {\em anti}-23DCP: $\mu_a = 0.25$ D, $\mu_b = 0.02$ D)nevertheless, it was also possible to observe and assign the spectrum of {\em anti}-23DCP. Assignments of parent spectra and $^{37}$Cl and $^{13}$C substituted isotopologues utilized predictions at the MP2/6-311++G(2d,2p) level and Pickett's SPCAT/SPFIT programs. For the weak {\em anti}-23DCP spectra, additional measurements also utilized a resonant-cavity FTMW spectrometer. Full chlorine nuclear quadrupole coupling tensors for {\em gauche}-12DCE and both {\em anti}- and {\em gauche}-23DCP have been diagonalized to allow comparison of coupling constants. Kraitchman's equations were used to determine $r_s$ coordinates of isotopically substituted atoms and $r_0$ structures were also deduced for {\em gauche} conformers of 12DCE and 1C2FE. Structural details and chlorine nuclear quadrupole coupling constants of all three molecules will be compared, and effects of differing halogen substitution and carbon chain length on molecular properties will be evaluated

Growth Dynamics of Colloidal Silver-Gold Core-Shell Nanoparticles Studied by Second Harmonic Generation and Extinction Spectroscopy

The growth dynamics of colloidal silver-gold core-shell (Ag@Au CS) nanoparticles (NPs) in water are monitored in a stepwise synthesis approach using time-dependent second harmonic generation (SHG) and extinction spectroscopy. Three sequential additions of chloroauric acid, sodium citrate, and hydroquinone are added to the silver nanoparticle solution to grow a gold shell around a silver core. The first addition produces a stable urchin-like surface morphology, while the second and third additions continue to grow the gold shell thickness as the surface becomes more smooth and uniform, as determined using transmission electron microscopy. The extinction spectra after each addition are compared to finite-difference time-domain (FDTD) calculations, showing large deviations for the first and second additions due to the bumpy surface morphology and plasmonic hotspots while showing general agreement after the third addition reaches equilibrium. The SHG signal is dominated by the NP surface, providing complementary information on the growth time scales due to changes to the surface morphology. This combined approach of synthesis and characterization of Ag@Au CS nanoparticles with SHG spectroscopy, extinction spectroscopy, and FDTD calculations provides a detailed foundation for investigating complex colloidal nanoparticle growth mechanisms and dynamics in developing enhanced plasmonic nanomaterial technologies

Influence of Acetaminophen on Molecular Adsorption and Transport Properties at Colloidal Liposome Surfaces Studied by Second Harmonic Generation Spectroscopy

Time-resolved second harmonic generation (SHG) spectroscopy is used to investigate acetaminophen (APAP)-induced changes in the adsorption and transport properties of malachite green isothiocyanate (MGITC) dye to the surface of unilamellar 1,2-dioleoyl--glycero-3-phosphocholine (DOPC) liposomes in an aqueous colloidal suspension. The adsorption of MGITC to DOPC liposome nanoparticles in water is driven by electrostatic and dipole-dipole interactions between the positively charged MGITC molecules and the zwitterionic phospholipid membranes. The SHG intensity increases as the added MGITC dye concentration is increased, reaching a maximum as the MGITC adsorbate at the DOPC bilayer interface approaches a saturation value. The experimental adsorption isotherms are fit using the modified Langmuir model to obtain the adsorption free energies, adsorption equilibrium constants, and the adsorbate site densities to the DOPC liposomes both with and without APAP. The addition of APAP is shown to increase MGITC adsorption to the liposome interface, resulting in a larger adsorption equilibrium constant and a higher adsorption site density. The MGITC transport times are also measured, showing that APAP decreases the transport rate across the DOPC liposome bilayer, especially at higher MGITC concentrations. Studying molecular interactions at the colloidal liposome interface using SHG spectroscopy provides a detailed foundation for developing potential liposome-based drug-delivery systems

Monitoring the growth dynamics of colloidal gold-silver core-shell nanoparticles using in situ

© 2019 Author(s). The growth dynamics of gold-silver core-shell (Au@Ag) nanoparticles are studied using in situ time-dependent second harmonic generation (SHG) and extinction spectroscopy to investigate the nanoparticle shell formation. The silver shell is grown by reduction of silver cations onto a 14 nm gold core using ascorbic acid in colloidal aqueous solution under varying reaction concentrations producing Au@Ag nanoparticles of final sizes ranging from 51 to 78 nm in diameter. The in situ extinction spectra show a rapid increase in intensity on the timescale of 5-6 s with blue shifting and narrowing of the plasmonic peak during the silver shell formation. The in situ SHG signals show an abrupt rise at early times of the reaction, followed by a time-dependent biexponential decrease, where the faster SHG lifetime corresponds to the timescale of the shell growth, and where the slower SHG lifetime is attributed to changes in the nanoparticle surface charge density. A large enhancement in the SHG signal at early stages of the reaction is caused by plasmonic hot spots due to the nanoparticle surface morphology, which becomes smoother as the reaction proceeds. The final extinction spectra are compared to finite-difference time-domain (FDTD) calculations, showing general agreement with experiment, where the plasmon peak red shifts and increases in spectral width as the silver shell thickness increases. These in situ SHG and extinction spectroscopy results, combined with FDTD calculations, help characterize the complicated processes involved in colloidal nanoparticle shell formation in real time for developing potential plasmon-enhanced nanomaterial applications

Combinatorial Delivery of miRNA‐Nanoparticle Conjugates in Human Adipose Stem Cells for Amplified Osteogenesis

© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim It is becoming more apparent in tissue engineering applications that fine temporal control of multiple therapeutics is desirable to modulate progenitor cell fate and function. Herein, the independent temporal control of the co-delivery of miR-148b and miR-21 mimic plasmonic nanoparticle conjugates to induce osteogenic differentiation of human adipose stem cells (hASCs), in a de novo fashion, is described. By applying a thermally labile retro-Diels–Alder caging and linkage chemistry, these miRNAs can be triggered to de-cage serially with discrete control of activation times. The method relies on illumination of the nanoparticles at their resonant wavelengths to generate sufficient local heating and trigger the untethering of the Diels–Alder cycloadduct. Characterization of the photothermal release using fluorophore-tagged miRNA mimics in vitro is carried out with fluorescence measurements, second harmonic generation, and confocal imaging. Osteogenesis of hASCs from the sequential co-delivery of miR-21 and miR-148b mimics is assessed using xylenol orange and alizarin red staining of deposited minerals, and quantitative polymerase chain reaction for gene expression of osteogenic markers. The results demonstrate that sequential miRNA mimic activation results in upregulation of osteogenic markers and mineralization relative to miR-148b alone, and co-activation of miR-148b and miR-21 at the same time

Monitoring the Seed-Mediated Growth of Gold Nanoparticles Using in Situ Second Harmonic Generation and Extinction Spectroscopy

© 2018 American Chemical Society. In situ second harmonic generation (SHG) coupled with extinction spectroscopy is used for real-time monitoring of seed-mediated growth dynamics of colloidal citrate-stabilized gold nanoparticles in water. The time-dependent in situ SHG results capture an early stage of the growth process where a large enhancement in the SHG signal is observed, which is attributed to the formation of plasmonic hot spots from a rough and uneven nanoparticle surface. The temporal peak in the SHG signal is followed by a decay that is fit to an exponential function to characterize the size-dependent nanoparticle growth lifetime, which varies from 0.45 to 1.7 min for final nanoparticle sizes of 66 and 94 nm, respectively. This early growth stage also corresponds to a broadening of the plasmon spectra, as monitored using time-dependent in situ extinction spectroscopy. Over the course of the seed-mediated growth reaction, the nanoparticle becomes more thermodynamically stable through surface reconstruction resulting in a smoother, more uniform surface, corresponding to lower, stable SHG signals and narrower plasmon spectra. With real-time monitoring of nanoparticle formation, in situ SHG spectroscopy combined with in situ extinction spectroscopy provides an important insight for controlling nanoparticle synthesis and surface morphology for potential nanoscale engineering of different colloidal nanomaterials