Model Behavior: Characterization of Hydroxyacetone at the Air-Water Interface Using Experimental and Computational Vibrational Sum Frequency Spectroscopy.

Small atmospheric aldehydes and ketones are known to play a significant role in the formation of secondary organic aerosols (SOA). However, many of them are difficult to experimentally isolate, as they tend to form hydration and oligomer species. Hydroxyacetone (HA) is unusual in this class as it contributes to SOA while existing predominantly in its unhydrated monomeric form.

Interfacial Insights into a Carbon Capture System: CO Uptake to an Aqueous Monoethanolamine Surface.

Monoethanolamine (MEA) is a benchmark scrubber for CO gas emissions reductions. Preliminary studies have indicated surface monoethanolamine could influence the greater chemistry of CO uptake. MEA is known to be surface active and orients at aqueous surfaces such that its nitrogen lone pair electrons are pointing toward the gas phase.

Correction: In solution SERS sensing using mesoporous silica-coated gold nanorods.

Correction for 'In solution SERS sensing using mesoporous silica-coated gold nanorods' by Zhe Gao, et al., Analyst, 2016, 141, 5088-5095.

In solution SERS sensing using mesoporous silica-coated gold nanorods.

Mesoporous silica-coated gold nanorods (AuNR@MS) act as a colloidally stable Raman sensing platform with a built-in analyte size cutoff. Herein, these core-shell plasmonic nanostructures were presented with a range of thiolated Raman-active molecules to probe the limits of this platform for SERS sensing. The experimental results show generally, that the transport of molecules through the mesopores is highly dependent on the size of the molecule and specifically, that AuNR@MS with pores of ∼4 nm diameter are able to sense analytes with molecular dimensions smaller than 1.

Solvation station: microsolvation for modeling vibrational sum-frequency spectra of acids at aqueous interfaces.

Vibrational sum-frequency spectra of a pair of poly(methacrylic acid) isomers at an oil/water interface and glutaric acid at an air/water interface were calculated in the carbonyl stretching region. Orientational, conformational, and solvation information was determined using classical molecular dynamics (MD), while second-order susceptibility vibrational response tensors were determined for a set of density functional theory (DFT) structures. The DFT structures were microsolvated with water molecules corresponding to the major solvation states present in the MD calculations.

A means to an interface: investigating monoethanolamine behavior at an aqueous surface.

The use of amine scrubbers to trap carbon dioxide from flue gas streams is one of the most promising avenues for atmospheric carbon dioxide reduction. However, modifications are necessary to efficiently scale these scrubbers for use in fossil fuel plants. Current advances in tailoring amines for CO2 capture involve improvements of bulk kinetic and thermodynamic parameters, with little consideration to surface chemistry and behavior.

Hydration, Orientation, and Conformation of Methylglyoxal at the Air-Water Interface.

Aqueous-phase processing of methylglyoxal (MG) has been suggested to constitute an important source of secondary organic aerosol (SOA). The uptake of MG to aqueous particles is higher than expected because its carbonyl moieties can hydrate to form geminal diols, as well as because MG and its hydration products can undergo aldol condensation reactions to form larger oligomers in solution. MG is known to be surface active, but an improved description of its surface behavior is crucial to understanding MG-SOA formation.

Twist and turn: effect of stereoconfiguration on the interfacial assembly of polyelectrolytes.

Understanding the conditions that promote the adsorption, assembly, and accumulation of charged macromolecules at the interface between aqueous and hydrophobic liquids is important to a multitude of biological, environmental, and industrial processes. Here, the oil-water interfacial behavior of stereoisomers of polymethacrylic acid (PMA), a model system for both naturally occurring and synthetic polyelectrolytes, is investigated with a combination of vibrational sum-frequency (VSF) spectroscopy, surface tension, and computations. Syndiotactic and isotactic isomers both show rapid adsorption to the oil-water interface with a net orientation indicative of a high degree of ordering.

Doubling down: delving into the details of diacid adsorption at aqueous surfaces.

The behavior of complex interfacial systems is central to an ever-increasing number of applications. Vibrational sum frequency (VSF) spectroscopy is a powerful technique for obtaining surface specific structural information. The coherent nature of VSF that provides surface specificity, however, also creates difficulty in spectral interpretation especially as the system complexity increases.

Ion-induced reorientation and distribution of pentanone in the air-water boundary layer.

Organic material at the surface of atmospheric aerosols is ubiquitous and plays an important role in Earth's atmosphere. Small ketones, such as 3-pentanone, are found in aerosols and as surface-active species on aerosols. This study uses 3-pentanone as a model ketone to understand how such molecules adsorb at the vapor-water interface on aqueous solutions containing sulfate, carbonate, or chloride ions.

Brightening of carbon nanotube photoluminescence through the incorporation of sp3 defects.

Semiconducting carbon nanotubes promise a broad range of potential applications in optoelectronics and imaging, but their photon-conversion efficiency is relatively low. Quantum theory suggests that nanotube photoluminescence is intrinsically inefficient because of low-lying 'dark' exciton states. Here we demonstrate the significant brightening of nanotube photoluminescence (up to 28-fold) through the creation of an optically allowed defect state that resides below the predicted energy level of the dark excitons.

Sink or surf: atmospheric implications for succinic acid at aqueous surfaces.

Small organic compounds are increasingly being invoked as important players in atmospheric processes that occur on aerosol surfaces. The diacid succinic acid is one such constituent that is prevalent in the troposphere, surface active, and also water-soluble. This article presents a thorough examination of the surface characteristics of succinic acid at the vapor/water interface using a combination of theoretical simulation and experiments using vibrational sum frequency spectroscopy and surface tension.

Staying hydrated: the molecular journey of gaseous sulfur dioxide to a water surface.

A water surface is a dynamic and constantly evolving terrain producing a vast array of unique molecular properties and interactions with chemical species in the environment. The complex dynamics of water surfaces permit life on earth to continue, but also complicate the development of a complete microscopic picture of the specific behaviors that take place within interfacial aqueous environments. This computational study examines a piece of the water puzzle by elucidating the bonding, dynamic interactions, and hydrate structures of sulfur dioxide gas adsorbing to a water cluster.

Propagative Sidewall Alkylcarboxylation that Induces Red-Shifted Near-IR Photoluminescence in Single-Walled Carbon Nanotubes.

Semiconducting single-walled carbon nanotubes (SWCNTs) are direct band gap materials in which exciton photoluminescence (PL) occurs at the same wavelength as excitation. Here, we show that propagative sidewall alkylation can induce a new PL peak in (6,5) SWCNTs red-shifted from the E11 near-infrared exciton excitation and emission by ∼140 meV. The magnitude of the red-shift is weakly dependent on the terminal functional group.

Structure enhancement factor relationships in single gold nanoantennas by surface-enhanced Raman excitation spectroscopy.

Determining the existence of any direct spectral relationship between the far-field scattering properties and the near-field Raman-enhancing properties of surface-enhanced Raman spectroscopy (SERS) substrates has been a challenging task with only a few significant results to date. Here, we prove that hot spot dominated systems show little dependence on the far-field scattering properties because of differences between near- and far-field localized surface plasmon resonance (LSPR) effects as well as excitation of new plasmon modes via a localized emitter. We directly probe the relationship between the near- and far-field light interactions using a correlated LSPR-transmission electron microscopy (TEM) surface-enhanced Raman excitation spectroscopy (SERES) technique.

Near-infrared surface-enhanced Raman spectroscopy (NIR-SERS) for the identification of eosin Y: theoretical calculations and evaluation of two different nanoplasmonic substrates.

This work demonstrates the development of near-infrared surface-enhanced Raman spectroscopy (NIR-SERS) for the identification of eosin Y, an important historical dye. NIR-SERS benefits from the absence of some common sources of SERS signal loss including photobleaching and plasmonic heating, as well as an advantageous reduction in fluorescence, which is beneficial for art applications. This work also represents the first rigorous comparison of the enhancement factors and the relative merits of two plasmonic substrates utilized in art applications; namely, citrate-reduced silver colloids and metal film over nanosphere (FON) substrates.

A semiconducting organic radical cationic host-guest complex.

The self-assembly and solid-state semiconducting properties of single crystals of a trisradical tricationic complex composed of the diradical dicationic cyclobis(paraquat-p-phenylene) (CBPQT(2(•+))) ring and methyl viologen radical cation (MV(•+)) are reported. An organic field effect transistor incorporating single crystals of the CBPQT(2(•+))⊂MV(•+) complex was constructed using lithographic techniques on a silicon substrate and shown to exhibit p-type semiconductivity with a mobility of 0.05 cm(2) V(-1) s(-1).

Combined quantum mechanics (TDDFT) and classical electrodynamics (Mie theory) methods for calculating surface enhanced Raman and hyper-Raman spectra.

Multiscale models that combine quantum mechanics and classical electrodynamics are presented, which allow for the evaluation of surface-enhanced Raman (SERS) and hyper-Raman scattering spectra (SEHRS) for both chemical (CHEM) and electrodynamic (EM) enhancement mechanisms. In these models, time-dependent density functional theory (TDDFT) for a system consisting of the adsorbed molecule and a metal cluster fragment of the metal particle is coupled to Mie theory for the metal particle, with the surface of the cluster being overlaid with the surface of the metal particle. In model A, the electromagnetic enhancement from plasmon-excitation of the metal particle is combined with the chemical enhancement associated with a static treatment of the molecule-metal structure to determine overall spectra.

Single-molecule surface-enhanced Raman spectroscopy of crystal violet isotopologues: theory and experiment.

Single-molecule surface-enhanced Raman spectroscopy (SMSERS) of crystal violet (CV) has been reported since 1997, yet others have offered alternative explanations that do not necessarily imply SMSERS. Recently, the isotopologue approach, a statistically significant method to establish SMSERS, has been implemented for members of the rhodamine dye family. We provide the first demonstration of SMSERS of a triphenylmethane dye using the isotopologue approach.

Theoretical studies of surface enhanced hyper-Raman spectroscopy: the chemical enhancement mechanism.

Hyper-Raman spectra for pyridine and pyridine on the surface of a tetrahedral 20 silver atom cluster are calculated using static hyperpolarizability derivatives obtained from time dependent density functional theory. The stability of the results with respect to choice of exchange-correlation functional and basis set is verified by comparison with experiment and with Raman spectra calculated for the same systems using the same methods. Calculated Raman spectra were found to match well with experiment and previous theoretical calculations.

Structure-activity relationships in gold nanoparticle dimers and trimers for surface-enhanced Raman spectroscopy.

Understanding the detailed relationship between nanoparticle structure and activity remains a significant challenge for the field of surface-enhanced Raman spectroscopy. To this end, the structural and optical properties of individual plasmonic nanoantennas comprised of Au nanoparticle assemblies that are coated with organic reporter molecules and encapsulated by a SiO(2) shell have been determined using correlated transmission electron microscopy (TEM), dark-field Rayleigh scattering microscopy, surface-enhanced Raman scattering (SERS) microscopy, and finite element method (FEM) calculations. The distribution of SERS enhancement factors (EFs) for a structurally and optically diverse set of nanoantennas is remarkably narrow.

Methyl substituent effects in radical cation Diels-Alder reactions.

The effect of methyl substitution on the Diels-Alder radical cation reaction was studied using B3LYP with a 6-31G* basis set. Five separate pathways, one concerted and four stepwise, were examined for each possible position of a methyl substituent. None of the concerted transition structures could be located without symmetry constraints, and all but one of the structures obtained under these conditions were destabilized by a second-order Jahn-Teller distortion.