Carbonyl Vibrations Research Articles

Resonating with Cellular Pathways: Transcriptome Insights into Nonthermal Bioeffects of Middle Infrared Light Stimulation and Vibrational Strong Coupling on Cell Proliferation and Migration.

Middle infrared stimulation (MIRS) and vibrational strong coupling (VSC) have been separately applied to physically regulate biological systems but scarcely compared with each other, especially at identical vibrational frequencies, though they both involve resonant mechanism. Taking cell proliferation and migration as typical cell-level models, herein, we comparatively studied the nonthermal bioeffects of MIRS and VSC with selecting the identical frequency (53.5 THz) of the carbonyl vibration. We found that both MIRS and VSC can notably increase the proliferation rate and migration capacity of fibroblasts. Transcriptome sequencing results reflected the differential expression of genes related to the corresponding cellular pathways. This work not only sheds light on the synergistic nonthermal bioeffects from the molecular level to the cell level but also provides new evidence and insights for modifying bioreactions, further applying MIRS and VSC to the future medicine of frequencies.

5,8-Quinolinedione Attached to Quinone Derivatives: XRD Diffraction, Fourier Transform Infrared Spectra and Computational Analysis

Quinoline and isoquinoline moieties occur in many natural and synthetic compounds exhibiting high biological activity. The purpose of this study was to analyze the chemical structures of 5,8-quinolinedione and 5,8-isoquinoline derivatives using FT-IR spectroscopy supplemented with theoretical DFT calculations. Spectroscopic measurements were conducted using the attenuated total reflection (ATR) mode in the frequency range of 4000–400 cm−1. An analysis of FT-IR spectra was carried out, assigning the characteristic vibration frequencies of various functional groups to individual peaks. It was found that the experimental and calculated FT-IR spectra showed a good correlation for all the compounds under study. The most significant difference in the spectra occurred in the region of carbonyl bands. For compounds with the 5,8-quinolinedione moiety, two separated C=O vibration peaks were observed, while for compounds with the 5,8-isoquinolinedione moiety, the carbonyl vibrations created only one peak. This difference makes it possible to distinguish between the 5,8-quinolinedione and 5,8-isoquinolinedione derivatives.

Synthesis of L-Ornithine- and L-Glutamine-Linked PLGAs as Biodegradable Polymers.

L-ornithine and L-glutamine are amino acids used for ammonia and nitrogen transport in the human body. Novel biodegradable synthetic poly(lactic-co-glycolic acid) derivatives were synthesized via conjugation with L-ornithine or L-glutamine, which were selected due to their biological importance. L-ornithine or L-glutamine was integrated into a PLGA polymer with EDC coupling reactions as a structure developer after the synthesis of PLGA via the polycondensation and ring-opening polymerization of lactide and glycolide. The chemical, thermal, and degradation property-structure relationships of PLGA, PLGA-L-ornithine, and PLGA-L-glutamine were identified. The conjugation between PLGA and the amino acid was confirmed through observation of an increase in the number of carbonyl carbons in the range of 170-160 ppm in the 13C NMR spectrum and the signal of the amide carbonyl vibration at about 1698 cm-1 in the FTIR spectrum. The developed PLGA-L-ornithine and PLGA-L-glutamine derivatives were thermally stable and energetic materials. In addition, PLGA-L-ornithine and PLGA-L-glutamine, with their unique hydrophilic properties, had faster degradation times than PLGA in terms of surface-type erosion, which covers their requirements. L-ornithine- and L-glutamine-linked PLGAs are potential candidates for development into biodegradable PLGA-derived biopolymers that can be used as raw materials for biomaterials.

Reinvestigating the concurring reactions in early-stage cellulose pyrolysis by solution state NMR spectroscopy

Low temperature pre-treatments increase the char yield during cellulose carbonization. Although this effect is mostly understood on a kinetic basis, the formed chemical structures leave room for scrutiny. In ongoing ambitions to enhance the char yield of bioderived precursors, the thereby occurring chemistry was reinvestigated. A set of isothermal heating protocols ranging from 150° to 250°C was applied to man-made Ioncell® cellulose fibers and to Avicel® PH-101 microcrystalline cellulose. The prepared cellulosic samples were examined by solution state NMR using a tetra-n-butyl phosphonium acetate ([P4444][OAc]): DMSO-d6 (1:4 wt%) electrolyte as dissolving medium. Complementary, IR spectroscopy, size-exclusion chromatography (SEC) and thermogravimetric analysis coupled with mass spectroscopy (TGA-MS) measurements were performed. The NMR spectra evidenced the formation of levoglucosan end capped moieties as being the first and major occurring reaction during low temperature pre-treatments. In contrast to other mechanistic proposals, no signs for carbonyl or alkene functionalities were discernible in the cellulosic material soluble in the NMR electrolyte, even after treatment at 250 °C for several hours. Thermal cross-linking was observed in SEC already at temperatures not known to significantly influence the overall char yield. In the solution state analytics only partial solubility was observed, owing to the formation of a reluctant fraction previously described as “thermostable condensed phase”. This resulted in analytical blind spots and led to discrepancies between NMR results and FTIR spectra in which carbonyl and alkene vibrations were clearly discernible. Those discrepancies might also imply the co-existence of different fractions in the early stages of cellulose pyrolysis.

Cellulose-g-poly (acrylic acid) interpenetrated by fulvic acid for potential Cu (II) removal from wastewater

The cellulose-g-poly (acrylic acid) copolymer preparation in the presence of fulvic acid as an interpenetrating agent (C-g-PAA/FA) has been successfully conducted using gamma radiation. The acrylic acid was utilized as a functional monomer and N, N’-methylene bisacrylamide was used as a crosslinking agent. The fulvic acid addition to C-g-PAA was intended to enhance the number of functional groups responsible for the chelating agent. The infrared spectra of the obtained copolymer verified the incorporation of fulvic acid and acrylic acid in the cellulose network structure by the appearance of phenyl vibration and changes in the carbonyl vibration at 1560 and 1725 cm−1, respectively. Moreover, the thermogravimetric analysis showed that the C-g-PAA/FA increased the thermal resistance of the cellulose structure, which could be explained by the formation of robust and more chemical bonds that contributed to the network structure. Scanning electron microscope images revealed that the C-g-PAA/FA possesses a more compact and stronger network structure compared to pristine cellulose. Energy-dispersive X-ray analysis confirmed the presence of copper ions on the surface of C-g-PAA/FA after Cu (II) removal. In addition, the C-g-PAA/FA has effectively been used as Cu (II) removal in the aqueous solution, with a removal percentage of up to 56 %.

A new technique for recovering aged mineral oil to promote lifetime and sustainability

Using mineral oil (MO) derived from petroleum, e.g., transformer insulation, raises environmental risk and affects sustainability. Due to its affordability and easy availability, MO will ineluctably be preferred over other biodegradable oils. Therefore, tools must be developed to recover aged MO, extend the life cycle, and increase its sustainability. The work presented here is aimed at the investigation of the electrical insulation properties of thermally-aged recovered-aged mineral oil (RAMO), as well as of aged cellulose pressboard impregnated by fresh mineral oil (FMO), aged mineral oil (AMO), and RAMO. The AMO is recovered using the combined adsorbents, A* and B*, which are Chitosan-activated Bentonite (CTN-aB) and Polyaniline coated Kapok Fibre (PANI-c-KPF) mix. According to FTIR, the recovered oil, RAMO, displays less C=C double bonds and carbonyl vibrations at 140°C, indicating lower oil ageing compared to AMO. The distribution of the crystalline and amorphous peaks is uniform for aged oil-impregnated pressboard (PB) with FMO and RAMO. Overall, it has been discovered that PB is impregnated with RAMO, resulting in an extended lifetime for the solid insulation. As a result, the increase in emissions slows down, and global sustainability targets are met.

Antenna-coupled infrared nanospectroscopy of intramolecular vibrational interaction

Many photonic and electronic molecular properties, as well as chemical and biochemical reactivities are controlled by fast intramolecular vibrational energy redistribution (IVR). This fundamental ultrafast process limits coherence time in applications from photochemistry to single quantum level control. While time-resolved multidimensional IR-spectroscopy can resolve the underlying vibrational interaction dynamics, as a nonlinear optical technique it has been challenging to extend its sensitivity to probe small molecular ensembles, achieve nanoscale spatial resolution, and control intramolecular dynamics. Here, we demonstrate a concept how mode-selective coupling of vibrational resonances to IR nanoantennas can reveal intramolecular vibrational energy transfer. In time-resolved infrared vibrational nanospectroscopy, we measure the Purcell-enhanced decrease of vibrational lifetimes of molecular vibrations while tuning the IR nanoantenna across coupled vibrations. At the example of a Re-carbonyl complex monolayer, we derive an IVR rate of (25±8) cm-1 corresponding to (450±150) fs, as is typical for the fast initial equilibration between symmetric and antisymmetric carbonyl vibrations. We model the enhancement of the cross-vibrational relaxation based on intrinsic intramolecular coupling and extrinsic antenna-enhanced vibrational energy relaxation. The model further suggests an anti-Purcell effect based on antenna and laser-field-driven vibrational mode interference which can counteract IVR-induced relaxation. Nanooptical spectroscopy of antenna-coupled vibrational dynamics thus provides for an approach to probe intramolecular vibrational dynamics with a perspective for vibrational coherent control of small molecular ensembles.

In situ monitoring of galactolipid digestion by infrared spectroscopy in both model micelles and spinach chloroplasts

Galactolipids are the main lipids from plant photosynthetic membranes and they can be digested by pancreatic lipase related protein 2 (PLRP2), an enzyme found in the pancreatic secretion in many animal species. Here, we used transmission Fourier-transform infrared spectroscopy (FTIR) to monitor continuously the hydrolysis of galactolipids by PLRP2, in situ and in real time. The method was first developed with a model substrate, a synthetic monogalactosyl diacylglycerol with 8-carbon acyl chains (C8-MGDG), in the form of mixed micelles with a bile salt, sodium taurodeoxycholate (NaTDC). The concentrations of the residual substrate and reaction products (monogalactosylmonoglyceride, MGMG; monogalactosylglycerol, MGG; octanoic acid) were estimated from the carbonyl and carboxylate vibration bands after calibration with reference standards. The results were confirmed by thin layer chromatography analysis (TLC) and specific staining of galactosylated compounds with thymol and sulfuric acid. The method was then applied to the lipolysis of more complex substrates, a natural extract of MGDG with long acyl chains, micellized with NaTDC, and intact chloroplasts isolated from spinach leaves. After a calibration performed with α-linolenic acid, the main fatty acid (FA) found in plant galactolipids, FTIR allowed quantitative measurement of chloroplast lipolysis by PLRP2. A full release of FA from membrane galactolipids was observed, that was not dependent on the presence of bile salts. Nevertheless, the evolution of amide vibration band in FTIR spectra suggested the interaction of membrane proteins with NaTDC and lipolysis products.

Synthesis and Characterization of Poly(lactic-co-glycolic acid) Derived with LGlutamic Acid and L-Aspartic Acid

Poly(lactic-co-glycolic acid) (PLGA) is a biocompatible, biodegradable polymer approved by the FDA and EMA, which is the most widely used in the field of health. In this study, PLGA was synthesized primarily from lactide and glycolide by polycondensation and ring-opening polymerization. Then, amino acid derivatives of PLGA were synthesized by the reaction of PLGA and amino acids in the presence of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC). The polymers synthesized were PLGA, PLGA-L-glutamic acid (PLGA-G), and PLGA-L-aspartic acid (PLGA-A). The chemical structure of these polymers was confirmed by 1H and 13C Nuclear Magnetic Resonance (1H NMR and 13C NMR), Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), and Gel Permeation Chromatography (GPC). When the 13C NMR analyses of PLGA-amino acid derivatives were observed, an increase in the number of carbonyl carbons around 170 ppm was found and the structure accuracy was supported. In addition, when the FTIR analyses of PLGA-amino acid derivatives were examined, the structure was confirmed by observing the signal of the amide bond carbonyl vibration at 1700 cm-1. While the typical endothermic thermogram of the PLGA-amino acid derivative structures was observed by DSC analysis, it was shown that the structures were low molecular weight polymers [~5000-6000 Da] by GPC analysis.

THz-PCR Based on Resonant Coupling between Middle Infrared and DNA Carbonyl Vibrations

The carbonyl groups of deoxyribonucleotide can resonantly couple with 53 THz middle infrared, which can highly transmit water without ionization-based damage to DNA molecules. Herein, we predict that vibrational coupling with THz irradiation could lower down the hybridization landscape of nucleic acids and thus affect DNA replication. Using polymerase chain reaction (PCR) as a measure, we found that THz shining can reduce the denature temperature of DNA duplexes by about 3 °C, which allows one to conduct PCR at lower temperature, facilitating long-time amplification reaction without losing enzymatic fidelity, i.e., normal PCR should be carried out at denaturing temperature ∼4 °C higher than the melting temperature (Tm), but THz-PCR only requires temperature ∼1 °C higher than Tm due to the nonthermal effect of THz shining. Moreover, the melting time can also be shortened to 1/5 due to the enhanced vibration coupling with 53 THz irradiation. We proposed THz-PCR as an innovated DNA amplification technique with ultrahigh specificity and sensitivity and also successfully demonstrated its advantages in forensic detections.

Synchrotron-Radiation-Based Fourier Transform Infrared Microspectroscopy as a Tool for the Differentiation between Staphylococcal Small Colony Variants.

Small colony variants (SCVs) are clinically significant and linked to persistent infections. In this study, synchrotron-radiation-based Fourier transform infrared (SR-FTIR) is used to investigate the microspectroscopic differences between the SCVs of Staphylococcus aureus (S. aureus) and diabetic foot Staphylococcus epidermidis (S. epidermidis) in two main IR spectral regions: (3050-2800 cm-1), corresponding to the distribution of lipids, and (1855-1500 cm-1), corresponding to the distribution of protein amide I and amide II and carbonyl vibrations. SR-FTIR successfully discriminated between the two staphylococcal species and between the SCV and the non-SCV strains within the two IR spectral regions. Combined S. aureus SCVs (SCVhMu) showed a higher protein content relative to the non-SCV wild type. Complemented S. aureus SCV showed distinguishable differences from the SCVhMu and the wild type, including a higher content of unsaturated fatty acids. An increase in the CH2/CH3 ratio was detected in S. epidermidis SCV samples compared to the standard control. Protein secondary structure in standard S. epidermidis and SCVs consisted mainly of an α-helix; however, a new shoulder at 1635 cm-1, assigned to β-sheets, was evident in the SCV. In conclusion, SR-FTIR is a powerful method that can discriminate between staphylococci species and to differentiate between SCVs and their corresponding natural strains.

Coupling Pulse Radiolysis with Nanosecond Time-Resolved Step-Scan Fourier Transform Infrared Spectroscopy: Broadband Mid-Infrared Detection of Radiolytically Generated Transients.

We describe the first implementation of broadband, nanosecond time-resolved step-scan Fourier transform infrared (S2-FT-IR) spectroscopy at a pulse radiolysis facility. This new technique allows the rapid acquisition of nano- to microsecond time-resolved infrared (TRIR) spectra of transient species generated by pulse radiolysis of liquid samples at a pulsed electron accelerator. Wide regions of the mid-infrared can be probed in a single experiment, which often takes < 20-30 min to complete. It is therefore a powerful method for rapidly locating the IR absorptions of short-lived, radiation-induced species in solution, and for directly monitoring their subsequent reactions. Time-resolved step-scan FT-IR detection for pulse radiolysis thus complements our existing narrowband quantum cascade laser-based pulse radiolysis-TRIR detection system, which is more suitable for acquiring single-shot kinetics and narrowband TRIR spectra on small-volume samples and in strongly absorbing solvents, such as water. We have demonstrated the application of time-resolved step-scan FT-IR spectroscopy to pulse radiolysis by probing the metal carbonyl and organic carbonyl vibrations of the one-electron-reduced forms of two Re-based CO2 reduction catalysts in acetonitrile solution. Transient IR absorption bands with amplitudes on the order of 1 × 10-3 are easily detected on the sub-microsecond timescale using electron pulses as short as 250 ns.

Dynamic effect of polymers at the surfactant-water interface: an ultrafast study.

Interfaces play a role in controlling the rates and outcomes of chemical processes. Characterizing the interactions at heterogeneous interfaces is critical to developing a comprehensive model of the role of interfaces and confinement in modulating chemical reactions. Reverse micelles are an ideal model system for exploring the effect of encapsulated species on interfacial environments. Here, we use a combination of ultrafast two-dimensional infrared (2D IR) spectroscopy and molecular dynamics (MD) simulations to characterize the picosecond interfacial dynamics in reverse micelles (RMs) containing acrylamide monomers and polyacrylamide polymers within the aqueous phase. The ester carbonyl vibrations of the sorbitan monostearate surfactants are examined to extract interfacial hydrogen-bonding populations and dynamics. Hydrogen bond populations at the ester carbonyl positions remain unchanged with the inclusion of either polymer or monomer species. Hydrogen-bond dynamics are not altered with the addition of monomer but are slowed down twofold in the presence of encapsulated polyacrylamide polymer species as a result of polymer chains partially localizing to the interface. These findings imply that kinetics of reactions that occur at interfaces or in confined environments could be modulated by interfacial localization of the different components.

Design and synthesis of piezochromic materials exploring intermolecular charge transfer: chalconoids bound to the p-sulfonatocalix[6]arene macrocycle.

Solid-state systems composed of chalconoid encapsulated within p-sulfonatocalix[6]arene (SCX6) scaffolds that exhibit mechanochromism and thermochromism have been developed. An introduction of a supramolecular host promises a variety of applications in diverse areas, which makes them fascinating. Largely hydrogen bonding as well as π···π interactions are responsible for the host-guest complexation. The complex shows partial encapsulation of the guest with one of the phenyl rings of chalcone (guest) is held inside the SCX6 cavity, whilst other phenyl rings that exclude the cavity are hydrogen-bonded to sulfonate portals of the host. The hydrogen bonding conducing such complexation triggers proton transfer engendering a mechanochromic switch. The complexes are further characterized by a variety of experiments such as cyclic voltammetry (CV), steady-state fluorescence, vibrational spectroscopy, and 1H or 2D NMR (NOESY) spectroscopy experiments. Detailed structure furnished through the NMR shows deshielding of the Ha-e (guest) protons whereas, the hydroxyl protons from the host experience shielding as evidenced from the 1H NMR spectra. These inferences have further been corroborated through the density functional theory. Electrochemical investigations suggested an irreversible one-electron transfer in the host-guest binding. The characteristic 'frequency shift' for the intense carbonyl vibration in the infrared spectra, which can be correlated to the kinetic energy density parameter, G(r), in the quantum theory of atoms in molecules (QTAIM).

Bulk Response of Carboxylic Acid Solutions Observed with Surface Sum-Frequency Generation Spectroscopy.

We study the molecular properties of aqueous acetic acid and formic acid solutions with heterodyne-detected vibrational sum-frequency generation spectroscopy (HD-VSFG). For acid concentrations up to ∼5 M, we observe a strong increase of the responses of the acid hydroxyl and carbonyl stretch vibrations with increasing acid concentration due to an increase of the surface coverage by the acid molecules. At acid concentrations >5 M we observe first a saturation of these responses and then a decrease. For pure carboxylic acids we even observe a change of sign of the Im[χ(2)] response of the carbonyl vibration. The decrease of the response of the hydroxyl vibration and the decrease and sign change of the response of the carbonyl vibration indicate the formation of cyclic dimers, which only show a quadrupolar bulk response in the HD-VSFG spectrum because of their antiparallel conformation. We also find evidence for the presence of a quadrupolar response of the CH vibrations of the acid molecules.

Deterioration of Kaihua handmade paper: Evolution of molecular, supermolecular and macroscopic structures

Valued for its toughness and durability, Kaihua paper has been famous in China since the Qing Dynasty. It attracts great attention on the extension of paper life. Understanding of the complex degradation behavior of handmade paper under various aging conditions is an essential precondition for preparing long-life handmade paper. However, it is still difficult to explain the reactions sequence of cellulose microstructure and its relationship with the macroscopic deterioration of handmade paper. Herein, different types of Kaihua handmade papers, produced by various raw materials and crafts, were artificially aged. The evolution of their multi-scale structures in dry-heat (DH) and wet-heat (WH) conditions was explored systematically. Two-dimensional correlation spectroscopy (2D-COS) distinguished possible carbonyl vibrations involving hydrolysis and oxidation of cellulose and gave sequential changes of various carbonyl groups, illustrating different evolutionary behaviors of molecular structure of papers in DH and WH aging process. The energy and distance of hydrogen bond, crystal size and microfiber accessibility were quantitatively calculated during the degradation of cellulose. In addition, correlations between microstructural evolution and macroscopic deterioration of handmade papers involving reduced mechanical properties and yellowing were revealed. The current results will help to establish a platform for the multi-scale detection of handmade paper and improve the understanding of the degradation mechanism of handmade paper under different reaction paths. It also provides useful foundation on the preparation of long-life paper and the conservation of paper-based culture relics.

Preparation and Characterization of Dextran Coated Iron Oxide Nanoparticles Thin Layers.

In the present study, we report the synthesis of a dextran coated iron oxide nanoparticles (DIO-NPs) thin layer on glass substrate by an adapted method. The surface morphology of the obtained samples was analyzed by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), optical, and metallographic microscopies. In addition, the distribution of the chemical elements into the DIO-NPs thin layer was analyzed by Glow Discharge Optical Emission Spectrometry (GDOES). Furthermore, the chemical bonds formed between the dextran and iron oxide nanoparticles was investigated by Fourier Transform Infrared Spectroscopy (FTIR). Additionally, the HepG2 viability incubated with the DIO-NPs layers was evaluated at different time intervals using MTT (3-(4, 5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. The goal of this study was to obtain a DIO-NPs thin layer which could be used as a coating for medical devices such as microfluidic channel, microchips, and catheter. The results of the surface morphology investigations conducted on DIO-NPs thin layer suggests the presence of a continuous and homogeneous layer. In addition, the GDOES results indicate the presence of C, H, Fe, and O signal intensities characteristic to the DIO-NPs layers. The presence in the IR spectra of the Fe-CO metal carbonyl vibration bonds prove that the linkage between iron oxide nanoparticles and dextran take place through carbon–oxygen bonds. The cytotoxicity assays highlighted that HepG2 cells morphology did not show any noticeable modifications after being incubated with DIO-NPs layers. In addition, the MTT assay suggested that the DIO-NPs layers did not present any toxic effects towards HEpG2 cells.

Effects of temperature and pH on the structure of a protease from Lactobacillus brevis R4 isolated from Harbin dry sausage and molecular docking of the protease to the meat proteins

Spectroscopy and molecular dynamics were utilized to evaluate the influence of pH and temperature on the structural characteristics of Lacobacillus brevis R4 protease isolated from Harbin dry sausage. The protease has a stable spatial structure at pH 7 and 40 °C, and the extended secondary structure of the protease was identified. The structure of the protease can be changed or denatured at pH 8 and 70 °C, the changes at which predominantly manifested as changes in the secondary structure, such as α-helices, β-sheets, β-turns and random coils. In addition, carbonyl vibration, –NH vibration, C–H stretching vibration and disulfide bonds were present in the L. brevis R4 protease at various pH and temperatures. Molecular docking showed that the protease can interact with the myosin light chain, myosin heavy chain and troponin, which demonstrates the protease may accelerate the degradation of meat proteins, promote meat tenderness and then improve the flavor and quality of Harbin dry sausages.

Study on enhanced mechanical, barrier and optical properties of chemically modified mango kernel starch films

The main aim of this study was to chemically modify mango kernel starch (MKS) and assess its impact on packaging film properties. MKS exhibited limited application due to low solubility, retrogradation, higher gelatinization temperature and hydrophilicity. These limitations could be effectually overcome by integrating modifications to native starch. Chemical modifications of MKS were performed by oxidation and benzylation with a low degree of substitution. X‐ray diffractogram presented A‐type pattern of crystal structure which was in accordance to endosperm starch. Fourier‐transform infrared (FTIR) spectra of the native and modified starch samples exhibited strong bands in the regions corresponding to OH and CH stretching. Additionally, absorption bands were found in the regions for carbonyl and aromatic phenyl vibrations signifying the substitution of functional groups within native starch. Modified starch films presented increased lightness L* representing that the films were lighter in colour than native film. Tensile strength (TS) of modified films was found to increase more than twice that of native starch film. Starch recrystallization was interrupted by oxidation thereby preventing retrogradation. Benzylation lowered the water vapour permeability by 58% and improved UV absorption by 80% when compared with native film.

Effect of the Hydration Shell on the Carbonyl Vibration in the Ala-Leu-Ala-Leu Peptide.

The vibrational spectrum of the Ala-Leu-Ala-Leu peptide in solution, computed from first-principles simulations, shows a prominent band in the amide I region that is assigned to stretching of carbonyl groups. Close inspection reveals combined but slightly different contributions by the three carbonyl groups of the peptide. The shift in their exact vibrational signature is in agreement with the different probabilities of these groups to form hydrogen bonds with the solvent. The central carbonyl group has a hydrogen bond probability intermediate to the other two groups due to interchanges between different hydrogen-bonded states. Analysis of the interaction energies of individual water molecules with that group shows that shifts in its frequency are directly related to the interactions with the water molecules in the first hydration shell. The interaction strength is well correlated with the hydrogen bond distance and hydrogen bond angle, though there is no perfect match, allowing geometrical criteria for hydrogen bonds to be used as long as the sampling is sufficient to consider averages. The hydrogen bond state of a carbonyl group can therefore serve as an indicator of the solvent’s effect on the vibrational frequency.