OH Stretch Research Articles

Catalytic torrefaction effect on waste wood boards for sustainable biochar production and environmental remediation

Wood boards used in construction are generally treated with toxic chemicals, making them unsuitable for further use and causing environmental pollution. This study evaluates the possibility of using catalytic torrefaction as a pretreatment to improve wood pyrolysis and combustion for greener biochar production. Waste beech boards were impregnated with different K2CO3 solutions (0–0.012 M), then torrefied between 5 and 60 min at 275 °C. The ICP-AES showed that the board's surface held more potassium than the core. Torrefaction coupled with potassium decreased the C–O and –OH stretches. Thermogravimetric analysis of torrefied wood showed that the board's internal heating degraded the core more than the surface. The exothermic reactions made potassium's catalytic action more efficient in the core. Interactions between the potassium content and torrefaction duration decreased the pyrolysis' maximum devolatilization temperature. During combustion, potassium decreased the ignition temperature by up to 9% and 3% at the surface and core, respectively, while the torrefaction increased it. The catalytic torrefaction significantly decreased the devolatilization peak during combustion, thus making the wood's combustion similar to that of coal, having only the char oxidation step. These findings highlight the advantages and challenges of waste wood's catalytic-torrefaction for biochar production to reduce environmental pollution.

Wound healing and antidiabetic properties of green synthesized silver nanoparticles in 3T3-L1 mouse embryo fibroblast cells through 2-NBDG expression

The antibacterial and antifungal properties of silver and silver-based compounds have been recognized for quite some time. This study employed an extracellular method to produce silver nanoparticles (AgNPs) using the leaves of Barringtonia racemosa (B. racemosa). B. racemosa's aqueous leaf extract underwent a color change from grey to dark brown, which revealed the formation of AgNPs. UV spectrophotometry analysis confirmed the presence of silver with the maximum absorbance of 427 nm. FTIR analysis supported the existence of alcohols with the OH stretch and alkenes with the CC stretch. The existence of AgNPs with an average hydrodynamic diameter of 36.58 nm was confirmed using dynamic light scattering (DLS). Energy dispersive X-ray spectroscopy (EDX) confirmed the presence of silver. Additionally, the AgNPs showed spherical structure particles with the size distribution ranging from 10 to 17 nm with polydispersity, under transmission electron microscopy (TEM). Thermogravimetric analysis (TGA) findings revealed that AgNPs maintain good thermal stability even at high temperatures. A variety of bacterial and fungal pathogens were successfully inhibited by the AgNPs, with S. epidermidis (27 mm) showing the strongest antibacterial activity and a 20 mm inhibitory zone was against Candida albicans for its antifungal activity. Furthermore, AgNPs also showed a positive synergistic impact with the tested antibiotic and antifungal agents. In addition, the AgNPs demonstrated strong antioxidant activity. The considerable inhibition of alpha amylase and alpha glucosidase by the AgNPs were noted by their respective IC50 values of 16.65 μg/ml and 18.97 μg/ml. Flow cytometry analysis revealed a significant increase in glucose uptake by 3T3-L1 cells after exposure to AgNPs, as indicated by the upregulation of 2-(N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl) amino)-2-deoxyglucose (2-NBDG) expression. In 3T3/L cells, the AgNPs also demonstrated remarkable potential in accelerating wound healing achieving 92% closure of wounds after 48 h of incubation. As a result, it can be concluded that the AgNPs exhibit positive antidiabetic properties, suggesting their potential applications in the pharmaceutical industry including in the management of diabetic foot ulcers.

Isolation and Identification of Acetobacter tropicalis From Selected Malaysian Local Fruits for Potential BC Production

Acetobacter spp. that are commonly found on fruits, can perform oxidation processes, resulting in acetic acid production in vinegar. Besides that, Acetobacter spp. able to produce bacterial cellulose (BC), which is an essential by-product. This present study was carried out to isolate Acetobacter spp. from selected local fruits. Species verification of the bacterial isolates was performed using molecular and bioinformatic approaches. A total of six local fruits (starfruit, jackfruit, watermelon, pineapple, honeydew & banana) were subjected to seven days of fermentation in a brown sugar solution. Acetobacter spp. were isolated from the fermented medium using bromocresol green ethanol agar as the selective medium. Thirteen bacterial isolates were obtained and subjected to molecular works, including DNA extraction and PCR amplification using universal primers, targeting the 16S rRNA genes. PCR-amplified products were selected for single-pass sequencing. BLASTn analysis of the sequencing results showed three isolates (23.1%) belonging to Acetobacter tropicalis and one isolate (7.7%) representing Gluconobacter oxydans might have potential in BC production. However, the remaining nine isolates (69.2%) hit the Lactobacillus genus. Morphological observation using FESEM showed that the BC produced by all the positive bacterial isolates is similar to dried nata de coco and BC produced by Acetobacter xylinum. In addition, four similar regions of -OH stretch (3400 - 3300 cm-1), -CH stretch (2970 to 2800 cm-1), -OH bending (1620 cm-1), and -COC stretch (1100 to 1073 cm-1) are identified in the BC samples. In the future, the isolated Acetobacter and Gluconobacter strains could be further utilized for large-scale BC production in a suitable fermentation medium.

Investigating Intramolecular H Atom Transfer Dynamics in β-Diketones with Ultrafast Infrared Spectroscopies and Theoretical Modeling.

The vibrational signatures and ultrafast dynamics of the intramolecular H-bond in a series of β-diketones are investigated with 2D IR spectroscopy and computational modeling. The chosen β-diketones exhibit a range of H atom donor-acceptor distances and asymmetry along the H atom transfer coordinate that tunes the intramolecular H-bond strength. The species with the strongest H-bonds are calculated to have very soft H atom potentials, resulting in highly red-shifted OH stretch fundamental frequencies and dislocation of the H atom upon vibrational excitation. These soft potentials lead to significant coupling to the other normal mode coordinates and give rise to the very broad vibrational signatures observed experimentally. The 2D IR spectra in both the OH and OD stretch regions of the light and deuterated isotopologues reveal broadened and long-lived ground-state bleach signatures of the vibrationally hot molecules. Polarization-sensitive transient absorption measurements in the OH and OD stretch regions reveal notable isotopic differences in orientational dynamics. Orientational relaxation was measured to occur on ∼600 fs and ∼2 ps time scales for the light and deuterated isotopologues, respectively. The orientational dynamics are interpreted in terms of activated H/D atom transfer events driven by collective intramolecular structural rearrangements.

Soy protein isolate-guar gum-goose liver oil O/W Pickering emulsions that remain stable under accelerated oxidation at high temperatures.

Goose liver oil (GLO) is a solid-liquid mixture, rich in polyunsaturated fatty acids and high in nutritional value, but poor in fluidity and easily oxidized. Therefore, oil-in-water (O/W) Pickering emulsions of three polysaccharides and soy protein isolate (SPI) with GLO were prepared to improve the stability of it. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), Fourier-transform infrared spectroscopy, and zeta potential revealed that the SPI and complexes with konjac glucomannan, pectin, and guar gum (GG) ranged from 17 to 75 kDa, with the site of action being the -OH stretch and the amide group, and bound by hydrogen bonding. Adding konjac glucomannan and GG significantly increased the water contact angle of the SPI to 74.1° and 59.0°, respectively. Therefore, the protein-polysaccharide complexes could enhance the emulsion stability. In addition, the O/W Pickering emulsions with GLO had near-Newtonian fluid rheological properties with a significant increase in apparent viscosity and viscoelasticity, forming a dual network structure consisting of a ductile and flexible protein network and a rigid and brittle polysaccharide network. The microstructure observation indicated that the O/W emulsions were spherical and homogeneous. The highest emulsification activity was observed for the SPI-GG-GLO emulsions, without significant delamination or flocculation and high oxidative stability after 7 days in storage. These results demonstrate that the construction of SPI-GG-GLO O/W Pickering emulsions can stabilize GLO even at high temperatures that promote oxidation. © 2023 Society of Chemical Industry.

FOURIER-TRANSFORM INFRARED SPECTROSCOPY ANALYSIS OF MAULI BANANA (MUSA ACUMINATA) EXTRACT AS A POTENTIAL PULP WOUND HEALING

Background: Pulp wound healing is a critical aspect of endodontics, aiming to preserve the vitality and function of dental pulp tissues. Natural compounds have gained attention for their potential therapeutic applications in dentistry. Mauli banana (Musa acuminata) is a tropical fruit in South Kalimantan as one of the natural plants that have the ability as antibacterial, antifungal, anti-inflammatory, antioxidant, and immunomodulatory effects contains various bioactive molecules with potential pulp wound healing properties. Purpose: to identify and evaluate the functional groups present in mauli banana stem extracts. Methods: This study is true experimental research, the samples were mauli banana stem that were extracted with maceration technique and were subjected to Fourier-Transform Infrared Spectroscopy test. Results: Identification of functional groups of organic compounds from mauli banana are as follows: a) Peak 3638.95 cm-1 show O-H (nonbonded hydroxy group, OH stretch primary) component alcohol, b) Peak 3265.82 cm-1is C-H (alkane), c) Peak 2928.09 cm-1 refer to OH (carboxylic acid hydrogen bonds) and aldehydes groups, d) peak 1571.35 cm-1 refers to amide, C=O - asymetric stretching, e) peak 1400.82 cm-1, refers to CO2- symetric stretching and carboxylate (carboxylic acid salt) CH2 scissoring, f) peak 1030.17 cm-1 refers to C=C (alkanes), aliphatic phosphate, g) Peak 520.53 cm-1 refers to inorganic phosphates. Conclusion: FTIR spectra analysis of mauli banana stem extract show the presence of O-H hydroxy groups, aldehydes groups, carbonyl groups, aliphatic groups, carbonyl groups, amides groups and C-O stretching vibrations suggests that the extract contains various bioactive molecules with potential pulp wound healing properties.

(Invited) In-Situ Optical Diagnostics of Plasma Electrochemical Reactors

Many methods for synthesizing nanomaterials are complex and can require high temperature, acids, bases, or reducing agents. The plasma electrochemical reactor (PEC), composed of an atmospheric-pressure low-temperature plasma in contact with an aqueous electrode, may provide unique physico-chemical conditions that sidestep these disadvantages because non-equilibrium electrochemistry and nucleation are initiated in solution without additional heating or strong/toxic reagents. Indeed, PECs have successfully synthesized graphene quantum dots (GQD) [1,2].The precise mechanism of GQD growth is likely to be complex, involving non-equilibrium plasma chemistry and interactions near the plasma-liquid interface. Up to now, investigations of the liquid-phase chemistry have relied principally on ex situ measurements with little or no spatially-resolved information. In addition, conventional experimental techniques can suffer from a lack of selectivity and/or degradation of dyes, chemical probes, or spin traps introduced into the liquid.To extend the scope of diagnostics, we employ an in situ approach using multiple diagnostic techniques to study a wide range of physical and chemical properties at the plasma-water interface. The centrepiece of this platform is in situ spontaneous Raman microspectroscopy, which is advantageous because of its non-intrusiveness, selectivity, versatility, and straightforward calibration. Shaping the laser beam into a light sheet enables probing of the interfacial region with micron-scale spatial resolution. To observe the effect of the plasma on the solvent, we tracked the Raman spectrum of water. Analysis of the –OH stretch band reveals that the plasma weakens the hydrogen bonding network of water. This effect becomes especially pronounced near the interface, at a depth of a few tens of microns. Likewise, at a similar depth, the concentrations of aqueous H2O2 and NO3 - both exceed those of the bulk liquid [3]. Similar interfacial layers have been modeled in past studies for radical species such as OH but not for long-lived species such as NO3 -.Concerning GQDs, we tracked their production via in situ photoluminescence (PL) and UV-VIS absorption spectroscopies. Both the PL and absorption intensities reached a maximum not at the interface but rather at a depth of a few millimeters. This observation corroborates with liquid flow field measurements by particle image velocimetry, which revealed a low-velocity zone at this depth. Under certain conditions, we could observe the consumption of the carbon precursor over the course of plasma treatment using in situ Raman spectroscopy. Finally, we characterized plasma properties near the interface, such as the electron number density, using optical emission spectroscopy. Together, these results provide the fullest description to date of the reaction environment during GQD synthesis. Acknowledgments Financial support: ANR grants ANR-15-CE06-0007-01 and ANR-11-LABX-0017-01, PHC Orchid 40938YL, CNRS-IEA “GRAFMET”, Fédération Plas@Par, EUR PLASMAScience, Poitou-Charentes region (CPER program) References [1] Orrière, T., Kurniawan, D., Chang, Y. C., Pai, D. Z., & Chiang, W. H. (2020). Nanotechnology 31 (485001).[2] Yang, J. S., Pai, D. Z., & Chiang, W. H. (2019). Carbon 153, 315-319.[3] Pai, D. Z. (2021) J. Phys. D. : Appl. Phys. 54, 355201

Unified view of the hydrogen-bond structure of water in the hydration shell of metal ions (Li+, Mg2+, La3+, Dy3+) as observed in the entire 100–3800 cm−1 regions

Hydrogen-bond (H-bond) structure of water in the hydration shell of an anion is fairly well understood, but the corresponding knowledge for cation hydration shell is sparse, mainly because of the overwhelming effect of anion on water that easily masks the subtle effect of cation. Moreover, most of the hydration shell investigations are confined to the OH stretch band of water. Using Raman difference spectroscopy with simultaneous curve fitting (Raman-DS-SCF), we have retrieved the spectrum of water pertaining to the hydration shell of different metal ions (Li+, Mg2+, La3+, Dy3+) in the entire spectral region of 100–3800 cm−1, encompassing the intermolecular H-bond stretch (HOH---OH2; 200 cm−1), librational (300–1000 cm−1), HOH bend (1640 cm−1), bend-librational combination (2120 cm−1) and intramolecular O–H stretch (3000–3700 cm−1) of water. The hydration shell spectra and their polarization dependence (Polarized Raman) are compared for different metal ions and with the hydration shell of Cl− anion and also the high temperature water component (80 °C; extracted by Raman-DS-SCF). These results reveal that the hydration shells of high charge density metal ions have “enhanced” as well as “reduced” H-bond structure. The intermolecular H-bonds become stiffer and the librational freedom of the water gets restricted in the hydration shell. The bend-librational combination band blue-shifts to a large extent and appears toward the tail of the OH stretch, which is expected to facilitate the ultrafast energy dissipation of higher vibrational modes of water.

Effects of thermal and chemical modification on the physical properties of Ugandan Mutaka Kaolin

This study investigates the impact of thermal treatment at temperatures ranging from 600 ​°C to 1050 ​°C and chemical treatment using (COOH)2·2H2O and Al2(MoO4)3 ​at concentrations of 0.01 ​M, 0.05 ​M, and 0.1 ​M. The modified kaolin samples’ pH, oil adsorption capacity, refractive index, specific gravity, and viscosity were examined. Comprehensive analyses were performed to characterize the modified kaolin samples. The spectrum results revealed dealumination, with a corresponding increase in silicon content due to chemical treatment, while the aluminum content decreased compared to thermal treatment results. As observed with the calcined kaolin sample, a significant portion of the OH stretch groups vanished with disappearance stretches along the bands at 1229.6 and 1009.2 ​cm−1, corresponding to Si–O stretching vibrations. The specific gravity of calcined kaolin was observed to be relatively lower than TiO2. Furthermore, the obtained pH of 4.0 or lower, or a pH of 9.0 or higher, is classified as corrosive. The ideal temperature range for achieving optimal oil absorption lies within the 800 ​°C–900 ​°C range, where metakaolin properties favor effective oil uptake. The chemical concentration had a notable impact on the dispersion of kaolin powders, in contrast to calcined kaolin. At 800 ​°C, calcined kaolin attained an almost ideal refractive index for water-based paints, closely aligning with the refractive index of water.

Anharmonic Assignment of the Water Octamer Spectrum in the OH Stretch Region.

We interface the quasi-classical trajectory approach with an ab initio potential energy surface for water to assign the vibrational spectroscopical features of the OH stretch region of the water octamer cluster, which is considered to be a precursor of ice. An attempt by Li et al. to assign their recent reference experiment involved lower-level calculations based on an ad hoc scaled harmonic approach. Differently from the conclusions of this previous assignment, which invoked the contribution of 5 conformers and a solvated form of the water heptamer in the spectrum, we find out that the spectroscopic features can be related to the 4 conformers of the octamer lying lower in energy.

Endosymbiotic bacteria from donkeys milk in the inhibition of human pathogens

Donkey milk is known for its beneficial aspects such as low fat and cholesterol, total protein and casein content, high lactose, whey protein, calcium, selenium and vitamin D3 content. It also has nutraceutical and utilitarian properties that can boost invulnerability, regulate digestion and conveniently change gut microbiota. The current study was focused on the effect of probiotic bacterial metabolites from donkey milk against human bacterial pathogens. The effective isolate VITRAAJ14 was found to be non-hemolytic and was tolerant to acid, NaCl and bile salt. Antibacterial activity by cross streak method showed maximum zone of inhibition. Well diffusion method also exhibited effective inhibition against Escherichia coli (MTCC No. 9721), Staphylococcus aureus (MTCC No. 3160) and Salmonella enterica (MTCC No. 8587) with fractions obtained from chloroform: ethyl acetate. The metabolites capable of inhibiting pathogens were identified as oleyl alcohol by Gas chromatography- mass spectrometry (GCMS). Lead compounds detected in GCMS was studied for its functional group by Fourier transform infrared spectroscopy (FTIR), which revealed the presence of alcoholic stretch, carboxylic acid OH stretch, alkene and amide bond. The isolate VITRAAJ14 was identified to be the closest neighbour of Bacillus species (MH100985) by 16S rRNA gene sequencing. To our knowledge, current study is the first-time report on the presence of Bacillus sp. from donkey milk showing antibacterial activity due to its ability to produce oleyl alcohol. Scanning electron microscopic images revealed the presence of rod-shaped morphology of the effective bacterium VITRAAJ14.

Effect of hydrogen bonding on the mixing behaviour of ternary aqueous mixtures

This study correlates the solution behaviour of an aqueous mixture to hydrogen bonding between its three components (water, liquid Pluronic L31 and either tetrahydrofuran, THF or dimethyl-sulfoxide, DMSO). Pluronic L31 is miscible in either THF, DMSO or water, but separates from ternary mixtures, at specific solvent to water ratios. Water species can either donate a single (SD) or two hydrogens (DD), and accept a single (SA) or two (DA) hydrogens, depending on the other components in the mixture. This is reflected in the OH stretch band, as probed using attenuated total reflectance-Fourier transform infrared spectroscopy. Pluronic L31 and THF both compete for hydrogen bonding with DD-DA, with up to 30% THF (v/v, relative to water), where separation occurs. Above 30% THF, Pluronic L31 and THF do not compete for the same water species and mix freely. Pluronic L31 separates from DMSO-water mixtures with 10–80% DMSO. Competition for similar water species explains separation up to 50% DMSO. Above 50% DMSO, we must also consider two-way interactions between all components. At low DMSO concentrations, DMSO mainly interacts with water trough the SO group, while methyl groups from DMSO can interact with Pluronic L31. At higher DMSO contents, the methyl groups of DMSO interact more markedly with water. The second derivative of the νasCH3 peak displays a split with ≤ 50% DMSO, which disappears at higher DMSO percentages. The four peaks in the second derivative of the of the νasCH3 peak correlate to the interactions between DMSO and the four water species.

Elucidation of the pH-Dependent Electric Double Layer Structure at the Silica/Water Interface Using Heterodyne-Detected Vibrational Sum Frequency Generation Spectroscopy

The silica/water interface is one of the most abundant charged interfaces in natural environments, and the elucidation of the water structure at the silica/water interface is essential. In the present study, we measured the interface-selective vibrational (χ(2)) spectra in the OH stretch region of the silica/water interface in a wide pH range of pH 2.0-12.0 while changing the salt concentration by heterodyne-detected vibrational sum-frequency generation spectroscopy. With the help of singular value decomposition analysis, it is shown that the imaginary part of the χ(2) (Imχ(2)) spectra can be decomposed into the spectra of the diffuse Gouy-Chapman layer (DL) and the compact Stern layer (SL), which enables us to quantitatively analyze the spectra of DL and SL separately. The salt-concentration dependence of the DL spectra at different pH values is analyzed using the modified Gouy-Chapman theory, and the pH-dependent surface charge density and the pKa value (4.8 ± 0.2) of the silica/water interface are evaluated. Furthermore, it is found that the pH-dependent change of the SL spectra is quantitatively explained by three spectral components that represent the three characteristic water species appearing in different pH regions in SL. The quantitative understanding obtained from the analysis of each spectral component in the Imχ(2) spectra provides a clear molecular-level picture of the electric double layer at the silica/water interface.

Unraveling the Vibrational Spectral Signatures of a Dislocated H Atom in Model Proton-Coupled Electron Transfer Dyad Systems.

Phenol-benzimidazole and phenol-pyridine proton-coupled electron transfer (PCET) dyad systems are computationally investigated to resolve the origins of the asymmetrically broadened H-bonded OH stretch transitions that have been previously reported using cryogenic ion vibrational spectroscopy in the ground electronic state. Two-dimensional (2D) potentials describing the strongly shared H atom are predicted to be very shallow along the H atom transfer coordinate, enabling dislocation of the H atom between the donor and acceptor groups upon excitation of the OH vibrational modes. These soft H atom potentials result in strong coupling between the OH modes, which exhibit significant bend-stretch mixing, and a large number of normal mode coordinates. Vibrational spectra are calculated using a Hamiltonian that linearly and quadratically couples the H atom potentials to over two dozen of the most strongly coupled normal modes treated at the harmonic level. The calculated vibrational spectra qualitatively reproduce the asymmetric shape and breadth of the experimentally observed bands in the 2300-3000 cm-1 range. Interestingly, these transitions fall well above the predicted OH stretch fundamentals, which are computed to be surprisingly red-shifted (<2000 cm-1). Time-dependent calculations predict rapid (<100 fs) relaxation of the excited OH modes and instant response from the lower-frequency normal modes, corroborating the strong coupling predicted by the model Hamiltonian. The results highlight a unique broadening mechanism and complicated anharmonic effects present within these biologically relevant PCET model systems.

Is Unified Understanding of Vibrational Coupling of Water Possible? Hyper-Raman Measurement and Machine Learning Spectra

The impact of the vibrational coupling of the OH stretch mode on the spectra differs significantly between IR and Raman spectra of water. Unified understanding of the vibrational couplings is not yet achieved. By using a different class of vibrational spectroscopy, hyper-Raman (HR) spectroscopy, together with machine-learning-assisted HR spectra calculation, we examine the impact of the vibrational couplings of water through the comparison of isotopically diluted H2O and pure H2O. We found that the isotopic dilution reduces the HR bandwidths, but the impact of the vibrational coupling is smaller than in the IR and parallel-polarized Raman. Machine learning HR spectra indicate that the intermolecular coupling plays a major role in broadening the bandwidth, while the intramolecular coupling is negligibly small, which is consistent with the IR and Raman spectra. Our result clearly demonstrates a limited impact of the intramolecular vibration, independent of the selection rules of vibrational spectroscopies.

High electrochemical response of TiO2@C-dots nanocomposites as electrode modifiers for Pb (II) detection

The synthesis of new modifiers based on nanomaterials as Pb (II) sensing electrode composites has attracted much attention in recent years. Modifiers are believed to produce stable electrodes with good sensitivity. In this study, we synthesized TiO2-incorporated carbon dots (TiO2@C-dots) and tested their performance as modifiers in the detection of Pb (II) using a carbon paste electrode (CPE). The fabrication of TiO2@C-dots-decorated CPE (CPE/TiO2@C-dots) has been carried out using several methods including electrochemical, hydrothermal impregnation, and mechanical homogenization at low temperatures. Based on the results of SEM, XRD, and FTIR characterization, the morphology of the nanocomposites is known to consist of uniform solid particles. Also, there are voids on the nanocomposite surface. The nanocomposite has an average particle size of 22.61 nm and a specific 2θ angle of 26.33°. The nanocomposites actively absorb IR at specific wavenumbers of 3600 cm−1 (-OH stretch) and 1759 cm−1 (CO stretch). Performance test results for Pb (II) detection showed that decorative modifiers (TiO2@C-dots) and CPE affected the peak redox current of Pb (II). This effect correlates with the mass of TiO2@C-dots, with a mass of 10.0 mg being the best mass for TiO2@C-dots. During the detection process, Pb (II) underwent redox reactions with oxidation (Epa) and reduction (Epc) potential values of −0.38 V and −0.50 V, respectively. During application, it is controlled by the interaction diffusivity with the Pb (II) molecule, yielding an accuracy of 0.36%.

Design of an Electrostatic Frequency Map for the NH Stretch of the Protein Backbone and Application to Chiral Sum Frequency Generation Spectroscopy.

We develop an electrostatic map for the vibrational NH stretch (amide A) of the protein backbone with a focus on vibrational chiral sum frequency generation spectroscopy (chiral SFG). Chiral SFG has been used to characterize protein secondary structure at interfaces using the NH stretch and to investigate chiral water superstructures around proteins using the OH stretch. Interpretation of spectra has been complicated because the NH stretch and OH stretch overlap spectrally. Although an electrostatic map for water OH developed by Skinner and co-workers was used previously to calculate the chiral SFG response of water structures around proteins, a map for protein NH that is directly responsive to biological complexity has yet to be developed. Here, we develop such a map, linking the local electric field to vibrational frequencies and transition dipoles. We apply the map to two protein systems and achieve much better agreement with experiment than was possible in our previous studies. We show that couplings between NH and OH vibrations are crucial to the line shape, which informs the interpretation of chiral SFG spectra, and that the chiral NH stretch response is sensitive to small differences in structure. This work increases the utility of the NH stretch in biomolecular spectroscopy.

Microhydration of the Pyrrole Cation (Py+) Revealed by IR Spectroscopy: Ionization-Induced Rearrangement of the Hydrogen-Bonded Network of Py+(H2O)2

Microhydration of heterocyclic aromatic molecules can be an appropriate fundamental model to shed light on intermolecular interactions and functions of macromolecules and biomolecules. We characterize herein the microhydration process of the pyrrole cation (Py+) by infrared photodissociation (IRPD) spectroscopy and dispersion-corrected density functional theory calculations (B3LYP-D3/aug-cc-pVTZ). Analysis of IRPD spectra of mass-selected Py+(H2O)2 and its cold Ar-tagged cluster in the NH and OH stretch range combined with geometric parameters of intermolecular structures, binding energies, and natural atomic charge distribution provides a clear picture of the growth of the hydration shell and cooperativity effects. Py+(H2O)2 is formed by stepwise hydration of the acidic NH group of Py+ by a hydrogen-bonded (H2O)2 chain with NH···OH···OH configuration. In this linear H-bonded hydration chain, strong cooperativity, mainly arising from the positive charge, strengthens both the NH···O and OH···O H-bonds with respect to those of Py+H2O and (H2O)2, respectively. The linear chain structure of the Py+(H2O)2 cation is discussed in terms of the ionization-induced rearrangement of the hydration shell of the neutral Py(H2O)2 global minimum characterized by the so-called "σ-π bridge structure" featuring a cyclic NH···OH···OH···π H-bonded network. Emission of the π electron from Py by ionization generates a repulsive interaction between the positive π site of Py+ and the π-bonded OH hydrogen of (H2O)2, thereby breaking this OH···π hydrogen bond and driving the hydration structure toward the linear chain motif of the global minimum on the cation potential.

Computing excited OH stretch states of water dimer in 12D using contracted intermolecular and intramolecular basis functions.

Due to the ubiquity and importance of water, water dimer has been intensively studied. Computing the (ro-)vibrational spectrum of water dimer is challenging. The potential has eight wells separated by low barriers, which makes harmonic approximations of limited utility. A variational approach is imperative, but difficult because there are 12 coupled vibrational coordinates. In this paper, we use a product contracted basis whose functions are products of intramolecular and intermolecular functions computed using an iterative eigensolver. An intermediate matrix F facilitates calculating matrix elements. Using F, it is possible to do calculations on a general potential without storing the potential on the full quadrature grid. We find that surprisingly many intermolecular functions are required. This is due to the importance of coupling between inter- and intra-molecular coordinates. The full G16 symmetry of water dimer is exploited. We calculate, for the first time, monomer excited stretch states and compare P(1) transition frequencies with their experimental counterparts. We also compare with experimental vibrational shifts and tunneling splittings. Surprisingly, we find that the largest tunneling splitting, which does not involve the interchange of the two monomers, is smaller in the asymmetric stretch excited state than in the ground state. Differences between levels we compute and those obtained with a [6+6]D adiabatic approximation [Leforestier et al. J. Chem. Phys. 137 014305 (2012)] are ∼0.6 cm-1 for states without monomer excitation, ∼4 cm-1 for monomer excited bend states, and as large as ∼10 cm-1 for monomer excited stretch states.

The Role of Water Hydrogen Bonds in the Formation of Associates and Condensates in Dispersions of Serum Albumin with Shungite Carbon and Quartz Nanoparticles

The role of the network of water hydrogen bonds in the regulation of the intermolecular interaction’s responsible for colloidal stability of dispersions has been studied in order to search for general patterns of interaction between water, nanoparticles, and bio-macromolecules. Raman spectroscopy for mixed dispersions of bovine serum albumin (SA), shungite carbon nanoparticles (ShC NPs), and quartz nanoparticles (quartz NPs) was performed within the wave number range 3200–3600 cm−1. The main spectral lines in this range are caused by the OH stretch vibrations of water molecules. We analyzed the state of the water hydrogen bonding network for dispersions of varied ratios of both fatty acid-containing and fatty acid-free SA macromolecules, ShC NPs, and silica NPs in the range 0.01–10 mg/mL.We used dynamic light scattering to control the sizes of the protein associates and protein associates with ShC NPs and quartz NPs. The strength of the hydrogen bonds in water depends essentially non-linearly, but in a qualitatively similar way, on the concentrations of the dispersion components. The initial strengthening of the bonds is followed by their loosening with a further increase in the concentration of the components. This is accompanied by the association of the dispersion components. We estimate the thickness of the protein corona layer as 20–25 nm for ShC NPs and 28–33 nm for quartz NPs, depending on the SA concentration. Colloidal stability of the aqueous dispersion is determined almost completely by an association of the protein with NPs. In contrast, colloidal stability of a pure protein solution is regulated by the formation of protein clusters of two main types and sizes. The association effects of SA with ShC NPs are evident in microscopic images of condensate films. The structures differ significantly for native and fatty acid-free SA in shape and size.