We study the properties of water molecules adjacent to a hydrophobic molecular layer with vibrational sum-frequency generation spectroscopy. We find that the water molecules at D2O/hexane, ...D2O/heptane, and D2O/polydimethylsiloxane interfaces show an enhanced ordering and stronger hydrogen-bond interactions than the water molecules at a D2O/air interface. With increasing temperature (up to 80 °C) the water structure becomes significantly less ordered and the hydrogen bonds become weaker.
The unprecedented emergence of perovskite‐based solar cells (PSCs) has been accompanied by an intensive search of suitable materials for charge‐selective contacts. For the first time a ...hole‐transporting self‐assembled monolayer (SAM) as the dopant‐free hole‐selective contact in p–i–n PSCs is used and a power conversion efficiency of up to 17.8% with average fill factor close to 80% and undetectable parasitic absorption is demonstrated. SAM formation is achieved by simply immersing the substrate into a solution of a novel molecule V1036 that binds to the indium tin oxide surface due to its phosphonic anchoring group. The SAM and its modifications are further characterized by Fourier‐transform infrared and vibrational sum‐frequency generation spectroscopy. In addition, photoelectron spectroscopy in air is used for measuring the ionization potential of the studied SAMs. This novel approach is also suitable for achieving a conformal coverage of large‐area and/or textured substrates with minimal material consumption and can potentially be extended to serve as a model system for substrate‐based perovskite nucleation and passivation control. Further gains in efficiency can be expected upon SAM optimization by means of molecular and compositional engineering.
A novel concept for the formation of the hole selective layer in efficient perovskite solar cells is presented. Carbazole‐based material is synthesized and used for the formation of a self‐assembled monolayer on top of the indium tin oxide transparent conductive substrate. Power conversion efficiency as high as 17.8% is achieved.
We study the properties of water at the surface of an antifreeze protein with femtosecond surface sum frequency generation spectroscopy. We find clear evidence for the presence of ice-like water ...layers at the ice-binding site of the protein in aqueous solution at temperatures above the freezing point. Decreasing the temperature to the biological working temperature of the protein (0 °C to −2 °C) increases the amount of ice-like water, while a single point mutation in the ice-binding site is observed to completely disrupt the ice-like character and to eliminate antifreeze activity. Our observations indicate that not the protein itself but ordered ice-like water layers are responsible for the recognition and binding to ice.
Significance Antifreeze proteins (AFPs) enable the survival of various organisms in freezing or subfreezing habitats by preventing the macroscopic growth of ice crystals. Understanding how AFPs recognize and bind ice crystals is the most important step to unravel their working mechanism. Using surface-specific sum frequency generation spectroscopy, we were able to directly probe the ice-binding site of the protein and discovered that, already at room temperature and in an aqueous solution, the antifreeze proteins arrange water molecules into an ice-like array, which they then use to bind to ice crystals.
We study the orientation of water and urea molecules and protein amide vibrations at aqueous α-lactalbumin and α-lactalbumin/urea interfaces using heterodyne-detected vibrational sum frequency ...generation. We vary the net charge of the protein by changing the pH. We find that the orientation of the water and urea molecules closely follows the net charge of the protein at the surface of the solution. In contrast, the net orientation of the amide groups of the backbone of the protein is independent of pH. We discuss the implications of these results for the mechanism by which urea denatures proteins.
Several neurodegenerative diseases, like Alzheimer's and Parkinson's are linked with protein aggregation into amyloid fibrils. Conformational changes of native protein into the β-sheet structure are ...associated with a significant change in the vibrational spectrum. This is especially true for amide bands which are inherently sensitive to the secondary structure of a protein. Raman amide bands are greatly intensified under resonance conditions, in the UV spectral range, allowing for the selective probing of the peptide backbone. In this work, we examine parallel β-sheet forming GGVVIA, the C-terminus segment of amyloid-β peptide, using UV-Vis, FTIR, and multiwavelength Raman spectroscopy. We find that amide bands are enhanced far from the expected UV range, i.e., at 442 nm. A reasonable two-fold relative intensity increase is observed for amide II mode (normalized according to the δCH
/δCH
vibration) while comparing 442 and 633 nm excitations; an increase in relative intensity of other amide bands was also visible. The observed relative intensification of amide II, amide S, and amide III modes in the Raman spectrum recorded at 442 nm comparing with longer wavelength (633/785/830 nm) excited spectra allows unambiguous identification of amide bands in the complex Raman spectra of peptides and proteins containing the β-sheet structure.
We used vibrational sum-frequency generation (VSFG) spectroscopy to elucidate the possible effect of various levels of isotopic substitution (H/D) on the properties of the DPPC monolayer by probing ...DPPC/D2O interface. We found that deuteration of the choline group has a great impact on monolayer properties, while monolayers with deuterated alkyl chains do not exhibit any differences under our experimental conditions. In addition, deuteration of the choline group strongly affected the hydration of the phosphate group. We showed by probing symmetric stretching vibration of phosphate group that denser packing only slightly reduced the hydration of DPPC-d13 and DPPC-d75 monolayers. Moreover, addition of calcium ions, which generally cause a marked dehydration of the lipid monolayer, had no effect on lipid monolayers with deuterated choline group. We proposed that one way to explain this experimental finding could be deuteration induced changes in the structure of lipid’s choline group, resulting in a well-hydrated but Ca2+ ion blocking structure. These results have important implications for various spectroscopic techniques, which commonly use deuteration of phospholipids to circumvent overlapping between vibrational bands.
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•VSFG revealed that deuteration of DPPC affects its monolayer properties.•Choline group deuteration strongly affects the hydration of lipids headgroup.•Protiated choline group lipids showed expected dehydration.•Deuterated choline group lipids maintained a well-hydrated headgroup.
We use surface-specific intensity vibrational sum-frequency generation and attenuated total reflection spectroscopy to probe the ionization state of the amino-acids l-alanine and l-proline at the ...air/water surface and in the bulk. The ionization state is determined by probing the vibrational signatures of the carboxylic acid group, representing the nondissociated acid form, and the carboxylate anion group, representing the dissociated form, over a wide range of pH values. We find that the carboxylic acid group deprotonates at a significantly higher pH at the surface than in the bulk.
Theoretical calculations of structures, stability and vibrational spectra of 1-butene secondary ozonide (SOZ) conformers were performed using DFT method B3LYP with a 6-311++G(3df, 3pd) basis set. The ...calculations predict six staggered structures of 1-butene SOZ. The FTIR spectra of 1-butene SOZ isolated in Ar, N
2
and Xe matrices were recorded. It was found that nitrogen is the best suited for the matrix isolation of 1-butene SOZ. The bandwidth of the spectral bands of the ozonide isolated in nitrogen was as narrow as 2 cm
−1
. For the first time the existence of five conformers of 1-butene SOZ were confirmed experimentally by means of matrix isolation infrared absorption spectroscopy. The
equatorial gauche
(∠OCCC=−66.1°) conformer was proved theoretically and experimentally to be the most stable. It was found that due to high potential barriers of the conformational transitions annealing of the matrix is useless for the assignment of spectral bands to various conformers of 1-butene SOZ. Using the hot nozzle technique the van’t Hoff experimental plots were made for three additional conformers of 1-butene SOZ and experimental Δ
H
values for these additional conformers were established. The crystallization problems of 1-butene SOZ are discussed which accounts for the rich conformational diversity of the ozonide as well as high conformational barriers for
axial-equatorial
transitions.
We study the orientation of water and urea molecules and protein amide vibrations at aqueous α-lactalbumin and α-lactalbumin/urea interfaces using heterodyne-detected vibrational sum frequency ...generation. We vary the net charge of the protein by changing the pH. We find that the orientation of the water and urea molecules closely follows the net charge of the protein at the surface of the solution. In contrast, the net orientation of the amide groups of the backbone of the protein is independent of pH. We discuss the implications of these results for the mechanism by which urea denatures proteins.
We study the orientation of water and urea molecules and protein amide vibrations at aqueous α-lactalbumin and α-lactalbumin/urea interfaces using heterodyne-detected vibrational sum frequency generation.
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