Role of Nonresonant Sum-Frequency Generation in the Investigation of Model Liquid Chromatography Systems

Quast, Arthur D.; Curtis, Alexander D.; Horn, Brent A.; Goates, Steven R.; Patterson, James E.

doi:10.1021/ac2032035

Cited by 24 publications

(20 citation statements)

References 39 publications

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“…In this temporal order, IR and Vis beams are not simultaneously present at the surface to generate electronic transitions at the SF, effectively suppressing non-resonant signals from the metal substrate. 56–59 Background suppressed spectra were used to identify peak positions (ω k ), which were then given as parameters for the fit of the spectra with non-resonant background to determine the phases ϕ k using Eq. (2).…”

Section: Methodsmentioning

confidence: 99%

Interkingdom Signaling: Integration, Conformation, and Orientation of N-Acyl-l-homoserine Lactones in Supported Lipid Bilayers

Barth

Jakubczyk²,

Kubas³

et al. 2012

Langmuir

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N-Acyl-l-homoserine lactones (AHLs) are small cell-to-cell signaling molecules involved in the regulation of population density and local gene expression in microbial communities. Recent evidence shows that contact of this signaling system, usually referred to as quorum sensing, to living eukaryotes results in interactions of AHL with host cells in a process termed "inter-kingdom signaling". So far details of this process and the binding site of the AHLs remain unknown; both an intracellular and a membrane-bound receptor seem possible, the first of which requires passage through the cell membrane. Here, we used sum-frequency-generation (SFG) spectroscopy to investigate the integration, conformation, orientation, and translocation of deuterated N-Acyl-L-homoserine lactones (AHL-dn) with varying chain length (8, 12, and 14 C atoms) in lipid bilayers consisting of a 1:1 mixture of POPC:POPG supported on SiO2 substrates (prepared by vesicle fusion). We found that all AHL-dn derivatives are well-ordered within the supported lipid bilayer (SLB) in a preferentially all-trans conformation of the deuterated alkyl chain and integrated into the upper leaflet of the SLB with the methyl terminal groups pointing downwards. For the bilayer system described above, no flip-flop of AHL-dn from the upper leaflet to the lower one could be observed. Spectral assignments and interpretations were further supported by Fourier transform infrared and Raman spectroscopy.

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Section: Methodsmentioning

confidence: 99%

Interkingdom Signaling: Integration, Conformation, and Orientation of N-Acyl-l-homoserine Lactones in Supported Lipid Bilayers

Barth

Jakubczyk²,

Kubas³

et al. 2012

Langmuir

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“…It is a challenge to measure orientation heterogeneity. For decades, surface-specific vibrational sum frequency generation spectroscopy (referred to as 1D VSFG hereafter) − has been used to determine the mean tilt angle, under the assumption of a narrow orientational distribution. However, in this case, the knowledge of orientational distribution is lost, and the measured mean tilt angle can deviate from the real mean tilt angle when the orientational distribution is large, which is the well-known “magic angle” challenge.…”

Section: Introductionmentioning

confidence: 99%

Solving the “Magic Angle” Challenge in Determining Molecular Orientation Heterogeneity at Interfaces

Xiong

2016

J. Phys. Chem. C

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It is critical to determine conformations of molecular monolayers in order to understand and control their functions and properties, such as efficiencies of self-assembly-based biosensors and turnover frequency of surface-bound electrocatalysts. However, surface molecules of the monolayers can adopt conformations with many different orientations. Thus, it is necessary to describe the orientations of surface molecular monolayers using both mean tilt angle and orientational distribution, which together we refer as orientation heterogeneity. Orientation heterogeneity is difficult to measure. In most cases, in order to calculate the mean tilt angle, it is assumed that the orientational distribution is narrow. This assumption causes ambiguities in determining the mean tilt angle, and loss of orientational distribution information, which is known as the "magic angle" challenge. Using heterodyne two-dimensional vibrational sum frequency generation (HD 2D VSFG) spectroscopy, we report a novel method to solve the "magic angle" challenge, by simultaneously measuring mean tilt angle and orientational distribution of molecular monolayers. We applied this new method to a CO2 reduction catalyst/gold interface and found that the catalysts formed a monolayer with a mean tilt angle between its quasi-C3 symmetric axis and the surface normal of 53°, with 5° orientational distribution. The narrow orientational distribution indicates that the surface molecules are rigid, which sample only limited configurations for facilitating a reaction, because of the short anchoring groups. Although applied to a specific system, this method is a general way to determine the orientation heterogeneity of an ensemble-averaged molecular interface.3

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“…First a new 1 L Erlenmeyer flask was washed with piranha solution in order to remove organic contaminants from the surface of the glass. The inside glass surface was then silanized using a solution of ∼5 mM octadecyltrichlorosilane in acetonitrile for 24 h to render it hydrophobic 56 which greatly reduced material loss due to AuNP adsorption onto an otherwise hydrophilic surface. 800 mL of acetonitrile and 200 mL of toluene were then added and mixed.…”

Section: Methodsmentioning

confidence: 99%

Gold Core Nanoparticle Mimics for Asphaltene Behaviors in Solution and at Interfaces

et al. 2016

Self Cite

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Asphaltenes are a poorly defined class of self-assembling and surface active molecules present in crude oils. The nature and structure of the nanoaggregates they form remain subjects of debate and speculation. In this exploratory work, the surface properties of asphaltene nanoaggregates are probed using electrically neutral 5 nm diameter gold-core nanoparticles with alkyl, aromatic, and alkanol functionalities on their surfaces. These custom synthesized nanoparticles are characterized, and their enthalpies of solution at near infinite dilution and the interfacial tensions of solutions containing these nanoparticles are compared with the corresponding values for Athabasca pentane asphaltenes. The enthalpies of solution of these asphaltenes in toluene, heptane, pyridine, ethanol, and water are consistent with the behavior of gold-alkyl nanoparticles. The interfacial tension values of these asphaltenes at toluene–water and (toluene + heptane)–water interfaces are consistent with the behavior of gold-biphenyl nanoparticles as are the tendencies for these asphaltenes and gold-biphenyl nanoparticles to “precipitate” in toluene + heptane mixtures. Gold-alkyl nanoparticles are minimally surface active at toluene–water and (toluene + heptane)–water interfaces and remain dispersed in all toluene + heptane mixtures. The behavior of these asphaltenes in solution and at interfaces is inconsistent with the behavior of gold-n-alkanol nanoparticles. The outcomes of this formative work indicate potential roles for aromatic submolecular motifs on aggregate surfaces as a basis for interpreting asphaltene nanoparticle flocculation and interfacial properties, while alkyl submolecular motifs on aggregate surfaces appear to provide a basis for interpreting other aspects of asphaltene solution behavior. A number of lines of inquiry for future work are suggested.

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Role of Nonresonant Sum-Frequency Generation in the Investigation of Model Liquid Chromatography Systems

Cited by 24 publications

References 39 publications

Interkingdom Signaling: Integration, Conformation, and Orientation of N-Acyl-l-homoserine Lactones in Supported Lipid Bilayers

Interkingdom Signaling: Integration, Conformation, and Orientation of N-Acyl-l-homoserine Lactones in Supported Lipid Bilayers

Solving the “Magic Angle” Challenge in Determining Molecular Orientation Heterogeneity at Interfaces

Gold Core Nanoparticle Mimics for Asphaltene Behaviors in Solution and at Interfaces

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