PGx01 series

High Energy Broadly Tunable Picosecond OPA
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  • High energy picosecond OPA
  • Ultra-broad tuning from 193 to 16 000 nm
  • Up to 1 mJ in VIS
  • 50 Hz repetition rate
  • High energy picosecond OPA
  • Ultra-broad tuning from 193 to 16 000 nm
  • Up to 1 mJ in VIS
  • 50 Hz repetition rate

Features & Applications

Features

  • Ultra-wide spectral range from 193 to 16000 nm
  • High peak power (>50 MW) ideal for non-linear spectroscopy applications
  • Narrow linewidth <6 cm⁻¹ (for UV < 9 cm-1)
  • Motorized hands-free tuning in 193 – 2 300 nm or 2 300 – 16 000 nm range
  • PC control via USB port (RS232 is optional) and LabVIEW™ drivers
  • Remote control via keypad

Applications

  • Nonlinear spectroscopy: vibrational-SFG, surface-SH, CARS, Z-scan
  • Pump-probe experiments
  • Laser-induced fluorescence (LIF)
  • Other laser spectroscopy applications

Description

Travelling Wave Optical Parametric Generators (TWOPG) are an excellent choice for researchers who need an ultra‑fast tunable coherent light source from UV to mid IR.

Design

The units can be divided into several functional modules:

  • optical parametric generator (OPG);
  • diffraction grating based linewidth narrowing system (LNS);
  • optical parametric amplifier (OPA);
  • electronic control unit.

The purpose of the OPG module is to generate parametric superfluores-cence (PS). Spectral properties of the PS are determined by the properties of a nonlinear crystal and usually vary with the generated wavelength.

In order to produce narrowband radiation, the output from OPG is narrowed by LNS down to 6 cm⁻¹ and then used to seed OPA.

Output wavelength tuning is achieved by changing the angle of the nonlinear crystal(s) and grating. To ensure exceptional wavelength reproducibility, computerized control unit driven precise stepper motors rotate the nonlinear crystals and diffraction grating. Nonlinear crystal temperature stabilization ensures long‑term stability of the output radiation wavelength.

In order to protect nonlinear crystals from damage, the pump pulse energy is monitored by built-in photodetectors, and the control unit produces an alert signal when pump pulse energy exceeds the preset value.

For customer convenience the laser can be operated from master device or personal computer through USB (VCP, ASCII commands), RS232 (ASCII commands) or LAN (REST API) interfaces or from remote control pad with backlit display that is easy to read even while wearing laser safety glasses.

Available Models

ModelFeatures
PG401Model has a tuning range from 420 to 2300 nm and is optimized for providing highest pulse energy in the visible part of the spectrum. The wide tuning range makes PG401 units suitable for many spectroscopy application.
PG501-DFGModel has a tuning range from 2300 to 16000 nm. The PG501-DFG1 model is the optimal choice for vibrational-SFG spectroscopy setups.

Specifications

Model PG401 PG401-SHPG401-DUV PG501-DFG1PG501-DFG2
OPA 1)
Tuning range
    DUV193 – 209.95 nm
    SH210 – 340, 370 – 419 nm
    Signal 420 – 680 nm
    Idler 740 – 2300 nm
    DFG2300 – 10000 nm2300 – 16000 nm
Output pulse energy 2)> 1000 µJ at 450 nm> 100 µJ at 300 nm> 50 µJ at 200 nm> 250 µJ at 3700 nm
> 50 µJ at 10000 nm
> 250 µJ at 3700 nm
> 80 µJ at 10000 nm
Linewidth< 6 cm-1< 9 cm-1< 6 cm-1
Max pulse repetition rate 50 Hz
Scanning step
    Signal 0.1 nm
    Idler 1 nm
Typical beam size 3) ~4 mm ~3 mm ~9 mm
Beam divergence 4)< 2 mrad
Beam polarizationvertical horizontal
    Signal horizontal
    Idler horizontal
Typical pulse duration~15 ps~12 ps~20 ps
PUMP LASER REQUIREMENTS
Pump energy
   at 355 nm10 mJ
   at 532 nm10 mJ
   at 1064 nm2 mJ6 mJ15 mJ
Recommended pump source 5)PL2231-50-TH,
PL2251A-TH
PL2231-50-TH,
PL2251A-TH
PL2231A-50-SH,
PL2251B-SH
Beam divergence< 0.5 mrad
Beam profilehomogeneous, without hot spots, Gaussian fit >90 %
Pulse duration 6)30 ± 5 ps
PHYSICAL CHARACTERISTICS
Size (W x L x H) 456 × 633 × 244 mm 456 × 1031 × 249 ± 3 mm
OPERATING REQUIREMENTS
Room temperature 15 – 30 °C
Power requirements 100 – 240 V AC single phase, 47 – 63 Hz
Power consumption< 100 W
  1. Due to continuous improvement, all specifications are subject to change without notice. Parameters marked typical are not specifications. They are indications of typical performance and will vary with each unit we manufacture. Unless stated otherwise, all specifications are measured at 450 nm for PG401 units, 3000 nm for PG501 units and 300 nm for PG401SH units and for basic system without options.
  2. See tuning curves for typical pulse energies at other wavelengths. Higher energies are available, please contact Ekspla for more details.
  3. Beam diameter is measured at the 1/e² level.
  4. Full angle measured at the FWHM point.
  5. If a pump laser other than PL2250 or PL2230 is used, measured beam profile data should be presented when ordering.
  6. Should be specified if non-EKSPLA pump laser is used.

Note: Laser must be connected to the mains electricity all the time. If there will be no mains electricity for longer that 1 hour then laser (system) needs warm up for a few hours before switching on.

Customized for Specific Requirements

Please note that these products are custom solutions tailored for specific applications or specific requirements.

PG401-DFG1 provides:

  • The broadest hands-free tuning range – from 420 to 10000 nm
  • It can be further extended up to 16000 nm with -DFG2 option. It should be noted, that for the 8000 – 16000 nm range a different nonlinear crystal is used, and exchange of the crystals needs to be done manually

PG402 features:

  • Gap-free tuning range 410 – 709, 710 – 2300 nm
  • Linewidth < 18 cm-1

Tuning Curves

Optical Layouts & Drawings

Publications

Found total :
15 articles, 15 selected
Application selected :
All Applications
All Applications
Laser Spectroscopy
SFG – sum frequency generation vibrational spectroscopy
Photoluminescence Spectroscopy
Fluorescence Spectroscopy
Time-resolved Spectroscopy

Structure Determination of Hen Egg-White Lysozyme Aggregates Adsorbed to Lipid/Water and Air/Water Interfaces

Related applications:  SFG Laser Spectroscopy

Authors:  S. Strazdaite, E. Navakauskas, J. Kirschner, T. Sneideris, G. Niaura

We use vibrational sum-frequency generation (VSFG) spectroscopy to study the structure of hen egg-white lysozyme (HEWL) aggregates adsorbed to DOPG/D2O and air/D2O interfaces. We find that aggregates with a parallel and antiparallel β-sheet structure together with smaller unordered aggregates and a denaturated protein are adsorbed to both interfaces. We demonstrate that to retrieve this information, fitting of the VSFG spectra is essential. The number of bands contributing to the VSFG spectrum might be misinterpreted, due to interference between peaks with opposite orientation and a nonresonant background. Our study identified hydrophobicity as the main driving force for adsorption to the air/D2O interface. Adsorption to the DOPG/D2O interface is also influenced by hydrophobic interaction; however, electrostatic interaction between the charged protein’s groups and the lipid’s headgroups has the most significant effect on the adsorption. We find that the intensity of the VSFG spectrum at the DOPG/D2O interface is strongly enhanced by varying the pH of the solution. We show that this change is not due to a change of lysozyme’s and its aggregates’ charge but due to dipole reorientation at the DOPG/D2O interface. This finding suggests that extra care must be taken when interpreting the VSFG spectrum of proteins adsorbed at the lipid/water interface.

Published: 2020.   Source: Langmuir 2020, 36, 17, 4766-4775

Heavy Anionic Complex Creates a Unique Water Structure at a Soft Charged Interface

Related applications:  SFG Laser Spectroscopy

Authors:  W. Rock, B. Qiao, T. Zhou, A. E. Clark, A. Uysal

Ion hydration and interfacial water play crucial roles in numerous phenomena ranging from biological to industrial systems. Although biologically relevant (and mostly smaller) ions have been studied extensively in this context, very little experimental data exist about molecular-scale behavior of heavy ions and their complexes at interfaces, especially under technologically significant conditions. It has recently been shown that PtCl6 2− complexes adsorb at positively charged interfaces in a two-step process that cannot fit into well-known empirical trends, such as Hofmeister series. Here, a combined vibrational sum frequency generation and molecular dynamics study reveals that a unique interfacial water structure is connected to this peculiar adsorption behavior. A novel subensemble analysis of molecular dynamics simulation results shows that after adsorption PtCl6 2− complexes partially retain their first and second hydration spheres and that it is possible to identify three different types of water molecules around them on the basis of their orientational structures and hydrogen-bonding strengths. These results have important implications for relating interfacial water structure and hydration enthalpy to the general understanding of specific ion effects.

This in turn influences interpretation of heavy metal ion distribution across, and reactivity within, liquid interfaces.

Published: 2018.   Source: J. Phys. Chem. C 2018, 122, 29228−29236

Vibrational fingerprint of localized excitons in a two-dimensional metal-organic crystal

Related applications:  SFG Laser Spectroscopy

Authors:  M. Corva, A. Ferrari, M. Rinaldi, Z. Feng, M. Roiaz, C. Rameshan, G. Rupprechter, R. Costantini, M. Dell’Angela, G. Pastore, G. Comelli, N. Seriani, E. Vesselli

Long-lived excitons formed upon visible light absorption play an essential role in photovoltaics, photocatalysis, and even in high-density information storage. Here, we describe a self-assembled two-dimensional metal-organic crystal, composed of graphene-supported macrocycles, each hosting a single FeN4 center, where a single carbon monoxide molecule can adsorb. In this heme-like biomimetic model system, excitons are generated by visible laser light upon a spin transition associated with the layer 2D crystallinity, and are simultaneously detected via the carbon monoxide ligand stretching mode at room temperature and near-ambient pressure. The proposed mechanism is supported by the results of infrared and time-resolved pump-probe spectroscopies, and by ab initio theoretical methods, opening a path towards the handling of exciton dynamics on 2D biomimetic crystals.

Published: 2018.   Source: Nature Communications, vol. 9, art. 4703 (2018)

How nature covers its bases

Related applications:  Laser Spectroscopy Photoluminescence Spectroscopy

Authors:  S. Boldissar, M. S. de Vries

The response of DNA and RNA bases to ultraviolet (UV) radiation has been receiving increasing attention for a number of important reasons: (i) the selection of the building blocks of life on an early earth may have been mediated by UV photochemistry, (ii) radiative damage of DNA depends critically on its photochemical properties, and (iii) the processes involved are quite general and play a role in more biomolecules as well as in other compounds. A growing number of groups worldwide have been studying the photochemistry of nucleobases and their derivatives. Here we focus on gas phase studies, which (i) reveal intrinsic properties distinct from effects from the molecular environment, (ii) allow for the most detailed comparison with the highest levels of computational theory, and (iii) provide isomeric selectivity. From the work so far a picture is emerging of rapid decay pathways following UV excitation. The main understanding, which is now well established, is that canonical nucleobases, when absorbing UV radiation, tend to eliminate the resulting electronic excitation by internal conversion (IC) to the electronic ground state in picoseconds or less. The availability of this rapid “safe” de-excitation pathway turns out to depend exquisitely on molecular structure. The canonical DNA and RNA bases are generally short-lived in the excited state, and thus UV protected. Many closely related compounds are longer lived, and thus more prone to other, potentially harmful, photochemical processes. It is this structure dependence that suggests a mechanism for the chemical selection of the building blocks of life on an early earth. However, the picture is far from complete and many new questions now arise.

Published: 2018.   Source: Phys. Chem. Chem. Phys., 2018,20, 9701-9716

Excited-State Dynamics of Isocytosine: A Hybrid Case of Canonical Nucleobase Photodynamics

Related applications:  Laser Spectroscopy

Authors:  J. A. Berenbeim, S. Boldissar, F. M. Siouri, G. Gate, M. R. Haggmark, B. Aboulache, T. Cohen, M. S. de Vries

We present resonant two-photon ionization (R2PI) spectra of isocytosine (isoC) and pump–probe results on two of its tautomers. IsoC is one of a handful of alternative bases that have been proposed in scenarios of prebiotic chemistry. It is structurally similar to both cytosine (C) and guanine (G). We compare the excited-state dynamics with the Watson–Crick (WC) C and G tautomeric forms. These results suggest that the excited-state dynamics of WC form of G may primarily depend on the heterocyclic substructure of the pyrimidine moiety, which is chemically identical to isoC. For WC isoC we find a single excited-state decay with a rate of ∼1010 s–1, while the enol form has multiple decay rates, the fastest of which is 7 times slower than for WC isoC. The excited-state dynamics of isoC exhibits striking similarities with that of G, more so than with the photodynamics of C.

Published: 2017.   Source: J. Phys. Chem. Lett.20178205184-5189

Excited State Dynamics of 6‑Thioguanine

Related applications:  Laser Spectroscopy Photoluminescence Spectroscopy

Authors:  F. M. Siouri, S. Boldissar, J. A. Berenbeim, M. S. de Vries

Here we present the excited state dynamics of jet-cooled 6-thioguanine (6-TG), using resonance-enhanced multiphoton ionization (REMPI), IR–UV double resonance spectroscopy, and pump–probe spectroscopy in the nanosecond and picosecond time domains. We report data on two thiol tautomers, which appear to have different excited state dynamics. These decay to a dark state, possibly a triplet state, with rates depending on tautomer form and on excitation wavelength, with the fastest rate on the order of 1010 s–1. We also compare 6-TG with 9-enolguanine, for which we observed decay to a dark state with a 2 orders of magnitude smaller rate. At increased excitation energy (∼+500 cm–1) an additional pathway appears for the predominant thiol tautomer. Moreover, the excited state dynamics for 6-TG thiols is different from that recently predicted for thiones.

Published: 2017.   Source: J. Phys. Chem. A 2017, 121, 28, 5257-5266

Structure of the Fundamental Lipopeptide Surfactin at the Air/Water Interface Investigated by Sum Frequency Generation Spectroscopy

Related applications:  SFG Laser Spectroscopy

Authors:  S. A. Goussous, M. T. L. Casford, A. C. Murphy, G. P. C. Salmond, F. J. Leeper and P. B. Davies

The lipopeptide surfactin produced by certain strains of Bacillus subtilis is a powerful bio-surfactant possessing potentially useful antimicrobial properties. In order to better understand its surface behaviour, we have used surface sensitive Sum Frequency Generation (SFG) vibrational spectroscopy in the C-H and C=O stretching regions to determine its structure at the air/water interface. Using surfactin with the leucine groups of the peptide ring perdeuterated we have shown that the majority of the SFG signals arise from the 4 leucine residues. We find that surfactin forms a robust film, and that its structure is not affected by the number density at the interface or by pH variation of the sub-phase. The spectra show that the ring of the molecule lies in the plane of the surface rather than perpendicular to it, with the tail lying above this, also in the plane of the interface.

Published: 2017.   Source: J. Phys. Chem. B 2017, 121, 19, 5072-5077

A structural and temporal study of the surfactants behenyltrimethylammonium methosulfate and behenyltrimethylammonium chloride adsorbed at air/water and air/glass interfaces using sum frequency generation spectroscopy

Related applications:  SFG Laser Spectroscopy

Authors:  S. A. Goussous, M. T.L. Casford, S. A. Johnson, P. B. Davies

Molecular scale information about the structure of surfactants at interfaces underlies their application in consumer products. In this study the non-linear optical technique of Sum Frequency Generation (SFG) vibrational spectroscopy has been used to investigate the structure and temporal behaviour of two cationic surfactants used frequently in hair conditioners. SFG spectra of films of behenyltrimethylammonium methosulfate (BTMS) and behenyltrimethylammonium chloride (BTAC) were recorded at the air/water interface and on glass slides following Langmuir Blodgett (LB) deposition. The assignment of the BTMS and BTAC spectral features (resonances) to the C--H stretching modes of the surfactants was consolidated by comparison with the SFG spectrum of deuterated cetyltrimethylammonium bromide (d-CTAB) and by recording spectra on D2O as well as on water. The C--H resonances arise from the methylene and methyl groups of the tail and head-groups of the surfactants. A slow collapse mechanism was observed following film compression of both BTAC and BTMS. The change in molecular structure of the films undergoing this slow collapse was followed by recording sequential SFG spectra in the C--H region, and by monitoring the SFG intensity at specific wavenumbers over time. Additionally, LB deposition onto glass was used to capture the state of the film during the slow collapse, and these SFG spectra showed close similarity to the corresponding spectra on water. Complementary Atomic Force Microscopy (AFM) was used to elucidate the layering of the compressed and relaxed films deposited onto mica by LB deposition.

Published: 2017.   Source: Journal of Colloid and Interface Science 488 (2017) 365–372

2D and 3D imaging of the gas phase close to an operating model catalyst by planar laser induced fluorescence

Related applications:  Laser Spectroscopy Fluorescence Spectroscopy

Authors:  S. Blomberg, J. Zhou, J. Gustafson, J. Zetterberg, E. Lundgren

In recent years, efforts have been made in catalysis related surface science studies to explore the possibilities to perform experiments at conditions closer to those of a technical catalyst, in particular at increased pressures. Techniques such as high pressure scanning tunneling/atomic force microscopy (HPSTM/AFM), near ambient pressure x-ray photoemission spectroscopy (NAPXPS), surface x-ray diffraction (SXRD) and polarization-modulation infrared reflection absorption spectroscopy (PM-IRAS) at semi-realistic conditions have been used to study the surface structure of model catalysts under reaction conditions, combined with simultaneous mass spectrometry (MS). These studies have provided an increased understanding of the surface dynamics and the structure of the active phase of surfaces and nano particles as a reaction occurs, providing novel information on the structure/activity relationship. However, the surface structure detected during the reaction is sensitive to the composition of the gas phase close to the catalyst surface. Therefore, the catalytic activity of the sample itself will act as a gas-source or gas-sink, and will affect the surface structure, which in turn may complicate the assignment of the active phase. For this reason, we have applied planar laser induced fluorescence (PLIF) to the gas phase in the vicinity of an active model catalysts. Our measurements demonstrate that the gas composition differs significantly close to the catalyst and at the position of the MS, which indeed should have a profound effect on the surface structure. However, PLIF applied to catalytic reactions presents several beneficial properties in addition to investigate the effect of the catalyst on the effective gas composition close to the model catalyst. The high spatial and temporal resolution of PLIF provides a unique tool to visualize the on-set of catalytic reactions and to compare different model catalysts in the same reactive environment. The technique can be applied to a large number of molecules thanks to the technical development of lasers and detectors over the last decades, and is a complementary and visual alternative to traditional MS to be used in environments difficult to asses with MS. In this article we will review general considerations when performing PLIF experiments, our experimental set-up for PLIF and discuss relevant examples of PLIF applied to catalysis.

Published: 2016.   Source: J. Phys.: Condens. Matter 28 453002

Quantitative picosecond laser-induced fluorescence measurements of nitric oxide in flames

Related applications:  Laser Spectroscopy Fluorescence Spectroscopy Time-resolved Spectroscopy

Authors:  Christian Brackmann, Joakim Bood, Jenny D. Nauclér, Alexander A. Konnov, Marcus Aldén

Quantitative concentrations measurements using time-resolved laser-induced fluorescence have been demonstrated for nitric oxide (NO) in flame. Fluorescence lifetimes measured using a picosecond Nd:YAG laser and optical parametric amplifier system have been used to directly compensate the measured signal for collisional quenching and evaluate NO concentration. The full evaluation also includes the spectral overlap between the ∼15 cm−1 broad laser pulse and multiple NO absorption lines as well as the populations of the probed energy levels. Effective fluorescence lifetimes of 1.2 and 1.5 ns were measured in prepared NO/N2/O2 mixtures at ambient pressure and temperature and in a premixed NH3-seeded CH4/N2/O2 flame, respectively. Concentrations evaluated from measurements in NO/N2/O2 mixtures with NO concentrations of 100–600 ppm were in agreement with set values within 3% at higher concentrations. An accuracy of 13% was estimated by analysis of experimental uncertainties. An NO profile measured in the flame showed concentrations of ∼1000 ppm in the post-flame region and is in good agreement with NO concentrations predicted by a chemical mechanism for NH3 combustion. An accuracy of 16% was estimated for the flame measurements. The direct concentration evaluation from time-resolved fluorescence allows for quantitative measurements in flames where the composition of major species and their collisional quenching on the probed species is unknown. In particular, this is valid for non-stationary turbulent combustion and implementation of the presented approach for measurements under such conditions is discussed.

Published: 2016.   Source: Proceedings of the Combustion Institute, vol. 36:3, pp. 4533-4540 (2017)

Retrieval of complex χ(2) parts for quantitative analysis of sum-frequency generation intensity spectra

Related applications:  SFG Laser Spectroscopy

Authors:  M. J. Hofmann, P. Koelsch

Vibrational sum-frequency generation (SFG) spectroscopy has become an established technique for in situ surface analysis. While spectral recording procedures and hardware have been optimized, unique data analysis routines have yet to be established. The SFG intensity is related to probing geometries and properties of the system under investigation such as the absolute square of the second-order susceptibility |χ(2)|2 . A conventional SFG intensity measurement does not grant access to the complex parts of χ(2) unless further assumptions have been made. It is therefore difficult, sometimes impossible, to establish a unique fitting solution for SFG intensity spectra. Recently, interferometric phase-sensitive SFG or heterodyne detection methods have been introduced to measure real and imaginary parts of χ(2) experimentally. Here, we demonstrate that iterative phase-matching between complex spectra retrieved from maximum entropy method analysis and fitting of intensity SFG spectra (iMEMfit) leads to a unique solution for the complex parts of χ(2) and enables quantitative analysis of SFG intensity spectra. A comparison between complex parts retrieved by iMEMfit applied to intensity spectra and phase sensitive experimental data shows excellent agreement between the two methods.

Published: 2015.   Source: J Chem Phys. 2015 Oct 7; 143(13): 134112.

Quantitative Sum-Frequency Generation Vibrational Spectroscopy of Molecular Surfaces and Interfaces: Lineshape, Polarization, and Orientation

Related applications:  SFG Laser Spectroscopy

Authors:  H. Wang, L. Velarde, W. Gan, L. Fu

Sum-frequency generation vibrational spectroscopy (SFG-VS) can provide detailed information and understanding of the molecular composition, interactions, and orientational and conformational structure of surfaces and interfaces through quantitative measurement and analysis. In this review, we present the current status of and discuss important recent developments in the measurement of intrinsic SFG spectral lineshapes and formulations for polarization measurements and orientational analysis of SFG-VS spectra. The focus of this review is to present a coherent description of SFG-VS and discuss the main concepts and issues that can help advance this technique as a quantitative analytical research tool for revealing the chemistry and physics of complex molecular surfaces and interfaces.

Published: 2015.   Source: Annu. Rev. Phys. Chem. 2015. 66:189–216

Unified treatment and measurement of the spectral resolution and temporal effects in frequency-resolved sum-frequency generation vibrational spectroscopy (SFG-VS)

Related applications:  SFG Laser Spectroscopy

Authors:  L. Velarde, H. F. Wang

The lack of understanding of the temporal effects and the restricted ability to control experimental conditions in order to obtain intrinsic spectral lineshapes in surface sum-frequency generation vibrational spectroscopy (SFG-VS) have limited its applications in surface and interfacial studies. The emergence of high-resolution broadband sum-frequency generation vibrational spectroscopy (HR-BB-SFG-VS) with sub-wavenumber resolution [Velarde et al., J. Chem. Phys., 2011, 135, 241102] offers new opportunities for obtaining and understanding the spectral lineshapes and temporal effects in SFG-VS. Particularly, the high accuracy of the HR-BB-SFG-VS experimental lineshape provides detailed information on the complex coherent vibrational dynamics through direct spectral measurements. Here we present a unified formalism for the theoretical and experimental routes for obtaining an accurate lineshape of the SFG response. Then, we present a detailed analysis of a cholesterol monolayer at the air/water interface with higher and lower resolution SFG spectra along with their temporal response. With higher spectral resolution and accurate vibrational spectral lineshapes, it is shown that the parameters of the experimental SFG spectra can be used both to understand and to quantitatively reproduce the temporal effects in lower resolution SFG measurements. This perspective provides not only a unified picture but also a novel experimental approach to measuring and understanding the frequency-domain and time-domain SFG response of a complex molecular interface.

Published: 2013.   Source: Phys. Chem. Chem. Phys., 2013, 15, 19970-19984

Investigating buried polymer interfaces using sum frequency generation vibrational spectroscopy

Related applications:  SFG Laser Spectroscopy

Authors:  Z. Chen

This paper reviews recent progress in the studies of buried polymer interfaces using sum frequency generation (SFG) vibrational spectroscopy. Both buried solid/liquid and solid/solid interfaces involving polymeric materials are discussed. SFG studies of polymer/water interfaces show that different polymers exhibit varied surface restructuring behavior in water, indicating the importance of probing polymer/water interfaces in situ. SFG has also been applied to the investigation of interfaces between polymers and other liquids. It has been found that molecular interactions at such polymer/liquid interfaces dictate interfacial polymer structures. The molecular structures of silane molecules, which are widely used as adhesion promoters, have been investigated using SFG at buried polymer/silane and polymer/polymer interfaces, providing molecularlevel understanding of polymer adhesion promotion. The molecular structures of polymer/solid interfaces have been examined using SFG with several different experimental geometries. These results have provided molecularlevel information about polymer friction, adhesion, interfacial chemical reactions, interfacial electronic properties, and the structure of layerbylayer deposited polymers. Such research has demonstrated that SFG is a powerful tool to probe buried interfaces involving polymeric materials, which are difficult to study by conventional surface sensitive analytical techniques.

Published: 2010.   Source: Prog Polym Sci. 2010 Nov 1; 35(11): 1376–1402.

Probing the Orientation and Conformation of α-Helix and β-Strand Model Peptides on Self-Assembled Monolayers Using Sum Frequency Generation and NEXAFS Spectroscopy

Related applications:  SFG Laser Spectroscopy

Authors:  Tobias Weidner, Julia S. Apte, Lara J. Gamble, David G. Castner

The structure and orientation of amphiphilic α-helix and β-strand model peptide films on self-assembled monolayers (SAMs) have been studied with sum frequency generation (SFG) vibrational spectroscopy and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The α-helix peptide is a 14-mer, and the β-strand is a 15-mer of hydrophilic lysine and hydrophobic leucine residues with hydrophobic periodicities of 3.5 and 2, respectively. These periodicities result in the leucine side chains located on one side of the peptides and the lysine side chains on the other side. The SAMs were prepared from the assembly of either carboxylic acid- or methyl-terminated alkyl thiols onto gold surfaces. For SFG studies, the deuterated analog of the methyl SAM was used. SFG vibrational spectra in the C-H region of air-dried peptides films on both SAMs exhibit strong peaks near 2965, 2940, and 2875 cm-1 related to ordered leucine side chains. The orientation of the leucine side chains was determined from the phase of these features relative to the nonresonant gold background. The relative phase for both the R-helix and β-strand peptides showed that the leucine side chains were oriented away from the carboxylic acid SAM surface and oriented toward the methyl SAM surface. Amide I peaks observed near 1656 cm-1 for the R-helix peptide confirm that the secondary structure is preserved on both SAMs. Strong linear dichroism related to the amide π* orbital at 400.8 eV was observed in the nitrogen K-edge NEXAFS spectra for the adsorbed β-strand peptides, suggesting that the peptide backbones are oriented parallel to the SAM surface with the side chains pointing toward or away from the interface. For the α-helix the dichroism of the amide π* is significantly weaker, probably because of the broad distribution of amide bond orientations in the α-helix secondary structure.

Published: 2009.   Source: Langmuir 2010, 26(5), 3433–3440

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