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Non-invasive blood glucose sensing can be achieved using mid-infrared spectroscopy, although no practical device based on this method has yet been developed. Here, we propose mid-infrared passive spectroscopic imaging for glucose measurements from a distance. Spectroscopic imaging of thermal radiation from the human body enabled, for the first time in the world, the detection of glucose-induced luminescence from a distance. In addition, glucose emission spectra of the wrist acquired at regular intervals up to 60 min showed that there was a strong correlation between the glucose emission intensity and blood glucose level measured using an invasive sensor. Thus, the new technology proposed here is expected to be applied to real-time monitoring of diabetic patients to detect hypoglycemic attacks during sleep and to detect hyperglycemia in a population. Moreover, this technology could lead to innovations that would make it possible to remotely measure a variety of substances.

The absolute coverage of CO has been a missing piece in the mechanistic puzzle of the CO reduction reaction (CORR) on Cu. For the first time, we revealed the upper bound of the CO coverage under electrocatalytic conditions to be 0.05 monolayer at atmospheric pressure and the saturation CO coverage to be ∼0.25 monolayer by conducting surface enhanced infrared spectroscopy at CO pressures up to 60 barg in a custom-designed spectroelectrochemical cell. CORR activities on Cu were also determined in the same pressure range. Calculated reaction orders of C

Hydrogen bonding (HB) has been receiving attention from both experimental and theoretical researchers since its discovery in the 1920s due to its impact on many chemical and biological processes. However, despite the large number of investigations conducted on this topic, the nature of the HBs and, in particular, the estimation of intramolecular HB energies are still very active subjects of research. In this context, here we report a matrix isolation infrared spectroscopy study of 2,3-dihydroxybenzaldehyde (2,3-DHBA) and 2,4-dihydroxybenzaldehyde (2,4-DHBA), which contain two [one resonance-assisted HB (RAHB) and one conventional HB] and one (RAHB) intramolecular hydrogen bonds, respectively, in their most stable conformer. After isolation of the compounds in cryogenic (15 K) krypton matrices, ultraviolet irradiation led to the formation of higher-energy conformers (by a 180° rotation of the hydroxyl and aldehyde groups), which implies breaking of the intramolecular HBs initially existing in the isolated species and, in the case of 2,3-DHBA, to the formation of a new intramolecular HB. In this way, we were able to manipulate the structure of the molecules, allowing to characterize a diversity of intramolecular HBs in which the OH groups participate (from strong intramolecular RAHBs to weaker conventional HBs, and also no intramolecular HBs) through the corresponding vibrational signatures. The spectroscopic studies were complemented by natural bond orbital analysis and the molecular tailoring approach method, in order to estimate the relative intramolecular HB energies and explore the substitution effects on HB strength.

Nearfield spectroscopic imaging techniques can be a powerful tool to map both cellular ultrastructure and molecular composition simultaneously but are currently limited in measurement capability. Resonance enhanced (RE) atomic force microscopy infrared (AFM-IR) spectroscopic imaging offers high-sensitivity measurements, for example, but probe-sample mechanical coupling, nonmolecular optical gradient forces, and noise overwhelm recorded chemical signals. Here, we analyze the key factors limiting AFM-IR measurements and propose an instrument design that enables high-sensitivity nanoscale IR imaging by combining null-deflection measurements with RE sensitivity. Our developed null-deflection scanning probe IR (NDIR) spectroscopic imaging provides ∼24× improvement in signal-to-noise ratio (SNR) compared with the state of the art, enables optimal signal recording by combining cantilever resonance with maximum laser power, and reduces background nonmolecular signals for improved analytical accuracy. We demonstrate the use of these properties for high-sensitivity, hyperspectral imaging of chemical domains in 100-nm-thick sections of cellular acini of a prototypical cancer model cell line, MCF-10A. NDIR chemical imaging enables facile recording of label-free, chemically accurate, high-SNR vibrational spectroscopic data from nanoscale domains, paving the path for routine studies of biomedical, forensic, and materials samples.

Uronic acids are carbohydrates carrying a terminal carboxylic acid and have a unique reactivity in stereoselective glycosylation reactions. Herein, the competing intramolecular stabilization of uronic acid cations by the C-5 carboxylic acid or the C-4 acetyl group was studied with infrared ion spectroscopy (IRIS). IRIS reveals that a mixture of bridged ions is formed, in which the mixture is driven towards the C-1,C-5 dioxolanium ion when the C-5,C-2-relationship is cis, and towards the formation of the C-1,C-4 dioxepanium ion when this relation is trans. Isomer-population analysis and interconversion barrier computations show that the two bridged structures are not in dynamic equilibrium and that their ratio parallels the density functional theory computed stability of the structures. These studies reveal how the intrinsic interplay of the different functional groups influences the formation of the different regioisomeric products.

In conventional two-dimensional infrared (2D-IR) spectroscopy, the inherently short vibrational lifetimes limit the time window to observe molecular dynamics typically to tens of picoseconds. The rather complex dynamics of organized molecular systems (e.g., glass formers, polymers, membranes, proteins), however, span a wide range of timescales from femto- to microseconds and beyond. Vibrationally Promoted Electronic Resonance (VIPER) 2D-IR negates the limitations of 2D-IR spectroscopy, for its signal decays with the electronic lifetime. Here, we present 2-Isopropylthioxanthone as the first VIPER 2D-IR probe to exploit intersystem crossing, thereby covering even the microsecond timescale. We achieved the required signal-to-noise ratio and resolution by introducing the Fourier-transform approach to the VIPER 2D-IR pulse sequence. Now, we are in a position to monitor dynamics via spectral diffusion several orders of magnitude beyond the vibrational lifetime of 2D-IR labels.

Spontaneous aggregation of amyloid beta (Aβ) proteins leading to the formation of oligomers and eventually into fibrils has been identified as a key pathological signature of Alzheimer's disease. The structure of late-stage aggregates have been studied in depth by conventional structural biology techniques, including nuclear magnetic resonance, X-ray crystallography, and infrared spectroscopy; however, the structure of early-stage aggregates is less known due to their transient nature. As a result, the structural evolution of amyloid aggregates from early oligomers to mature fibrils is still not fully understood. Here, we have applied atomic force microscopy-infrared nanospectroscopy to investigate the aggregation of Aβ 16-22, which spans the amyloidogenic core of the Aβ peptide. Our results demonstrate that Aβ 16-22 involves a structural transition from oligomers with parallel β-sheets to antiparallel fibrils through disordered and possibly helical intermediate fibril structures, contrary to the known aggregation pathway of full-length Aβ.

We report fingerprint infrared multiple-photon dissociation (IRMPD) spectra of the isolated gaseous hexa-coordinated complex of the macrocycle hexa-aza-18-crown-6 (hexacyclen, 1,4,7,10,13,16-hexaazacyclooctadecane, 18-azacrown-6) with Ni

In the light of the current food security crisis, food adulteration has resurfaced on the international scene, inflicting potential safety issues and leading more and more consumers into deception. This situation led food control actors to remobilise their potential to face this problem, particularly in terms of analytical chemistry competencies. Similar to honey, grape molasses may be considered very likely to be adulterated leading to quality and authenticity issues, especially in the Eastern Mediterranean, where it is widely consumed as a traditional sweetener. This work reports the use of attenuated total reflectance-mid-infrared spectroscopy (ATR-MIR) coupled to chemometrics, as an alternative to complex, expensive and time-consuming analytical techniques, in the aim of detecting fraudulent glucose, fructose, sucrose and apple molasses additions to pure grape molasses. After collecting a widespread unadulterated grape molasses database, spiked samples with increasing concentrations (w/w) of the selected adulterants were prepared. In order to establish a qualitative model, whose potential is to detect adulteration and discriminate between the different adulterants, samples underwent ATR-MIR analyses without any prior preparation, and the collected spectral data were subjected to independent components analysis (ICA), where Random_ICA was used to retrieve the optimal number of independent components (ICs). Thereupon, the extraction of seven ICs allowed the establishment of a qualitative model with a clear discrimination between molasses adulterated with fructose, sucrose and glucose syrup, relying on MIR specific signals and incorporated ratios of the different adulterants. However, it failed in detecting apple molasses adulteration, calling for the development of a different analytical approach. The developed model underwent a verification step using a control set recorded on a different spectrometer, proving its potential to provide reproducible discrimination and classification rates.

The spectral range of femtosecond time-resolved infrared spectroscopy is limited by the bandwidth of mid-IR pulses (100~400 cm−1) generated from the combination of Ti:Sapphire amplifier, Optical Parametric Amplifier (OPA), and Difference Frequency Generation (DFG). To overcome this limitation, we implement a compact continuum mid-IR source producing ultrafast pulses that span the frequency range from 1000 to 4200 cm−1 (from 10 to 2.4 μm), which utilize the mixing of fundamental, second-harmonic, and third-harmonic of 800 nm pulse in the air. After building an IR spectrometer with continuum IR and a monochromator, we found that the distortion of the measured IR spectrum originated from the contamination of higher-order diffraction. We used bandpass filters to eliminate the higher-order contributions and correct the measured IR spectrum. We further characterized the spectral properties of fundamental, second-harmonic, and third-harmonic fields after the plasmonic filamentation process, which helps to improve the efficiency of the continuum IR generation. Using the generated continuum IR pulses, we measured the IR absorption spectrum of a water–benzonitrile mixture, which was found to be consistent with the spectrum obtained with a commercial FT-IR spectrometer. The present work will be useful for the efficient generation of continuum IR pulses for IR pump-probe and two-dimensional IR spectroscopy experiments in the future.

Organic molecules, including α-hydroxyacids, are ubiquitous in the natural environment. Often found at water-air interfaces, organic molecules can alter the structure of the interface or participate in interfacial chemistry. Despite their prevalence in the environment, the structure and ordering of α-hydroxyacids have not been widely investigated at water-air interfaces, and the impact of the hydrophobic tail length on structure has not been explored. Here, for the first time, we use infrared reflection-absorption spectroscopy to assess the vibrational structure of α-hydroxyacids at a water surface as a function of surface partitioning and surface coverage. We study lactic acid, 2-hydroxyoctanoic acid, and 2-hydroxystearic acid, which have 1 carbon, 6 carbon, and 16 carbon tails, respectively. Vibrational features compared across the set of α-hydroxyacids studied here are used to determine the interaction of the polar headgroup with the water subphase and the ordering of the hydrophobic tail. We find that the carbonyl and α-hydroxyl groups participate in a complex hydrogen-bonding motif at the water-air interface that can be affected by the hydrophobic tail length and places the polar headgroup in or below the water-air interface. Furthermore, molecular ordering increases with the tail length or the surface coverage. The presence of the α-hydroxyl group causes the α-hydroxyacids to maintain a tilted orientation with respect to the surface normal even at high surface coverages. A combination of polar headgroup and hydrophobic tail effects dictates the overall orientation of α-hydroxyacids and can thus affect their ability to participate in chemistry and alter organic coatings on water surfaces.

Given the continuous improvement in the capabilities of road vehicles to detect obstacles, the road friction coefficient is closely related to vehicular braking control, thus the detection of road surface conditions (RSC), and the level is crucial for driving safety. Non-contact technology for RSC sensing is becoming the main technological and research hotspot for RSC detection because of its fast, non-destructive, efficient, and portable characteristics and attributes. This study started with mapping the relationship between friction coefficients and RSC based on the requirement for autonomous driving. We then compared and analysed the main methods and research application status of non-contact detection schemes. In particular, the use of infrared spectroscopy is expected to be the most approachable technology path to practicality in the field of autonomous driving RSC detection owing to its high accuracy and environmental adaptability properties. We systematically analysed the technical challenges in the practical application of infrared spectroscopy road surface detection, studied the causes, and discussed feasible solutions. Finally, the application prospects and development trends of RSC detection in the fields of automatic driving and exploration robotics are presented and discussed.

Experimental and theoretical studies have highlighted protonated water clusters (PWCs) as important models of the excess proton in aqueous systems. A significant focus has been characterizing the spectral signatures associated with different excess proton solvation motifs. Accurate vibrational frequency calculations are crucial for connecting the measured spectra to the structure of PWCs. In this paper, we extend and characterize a coupled local mode (CLM) approach for calculating the infrared spectra of PWCs using the [Formula: see text] cluster as a benchmark system. The CLM method is relatively low cost and incorporates the anharmonicity and coupling of OH vibrations. Here, we demonstrate the accuracy of the technique compared to experiments. We also illustrate the dependence of calculated spectral features on the underlying electronic structure theory and basis sets used in the local mode frequency and coupling calculations.

Dielectric metasurfaces governed by bound states in the continuum (BIC) are actively investigated for achieving high-quality factors and strong electromagnetic field enhancements. Traditional approaches reported for tuning the performance of quasi-BIC metasurfaces include tuning the resonator size, period, and structure symmetry. Here we propose and experimentally demonstrate an alternative approach through engineering slots within a zigzag array of elliptical silicon resonators. Through analytical theory, three-dimensional electromagnetic modeling, and infrared spectroscopy, we systematically investigate the spectral responses and field distributions of the slotted metasurface in the mid-IR. Our results show that by introducing slots, the electric field intensity enhancement near the apex and the quality factor of the quasi-BIC resonance are increased by a factor of 2.1 and 3.3, respectively, in comparison to the metasurface without slots. Furthermore, the slotted metasurface also provides extra regions of electromagnetic enhancement and confinement, which holds enormous potential in particle trapping, sensing, and emission enhancement.

Cysteine S–H bonds have a spectroscopically convenient stretching frequency of ∼2550 cm−1. However, their cross section is low, and the band can be strongly broadened in heterogeneous environments, making detection very challenging. With two-dimensional infrared (2D-IR) setups achieving ever higher sensitivities in recent years, systematic use of the weak cysteine sulfhydryls (Cys–SHs) absorption band is now within reach, even at low millimolar protein concentrations. Here, we demonstrate the capabilities of Cys–SH as an intrinsic 2D-IR label in pyruvate oxidase from E. coli, an enzyme with ten cysteines in its native sequence. 1D-IR measurements on the wild-type and individual cysteine knock-out variants show that two such residues have especially narrow SH signatures, caused by their intrahelical hydrogen bonding. 2D-IR analysis of these bands reveals an extraordinarily high anharmonicity (∼110 cm−1) and a long vibrational lifetime (∼4 ps). This allows monitoring spectral diffusion via center line slope analysis for up to 10 ps—separately for both the ground and excited states. The unique spectroscopic features and its ease of introduction make Cys–SH a useful IR spectroscopic label.

The ability to detect and characterize multiple secondary structures or polymorphs within peptide and protein aggregates is crucial to treatment and prevention of amyloidogenic diseases, production of novel biomaterials, and many other applications. Here we report a label-free method to distinguish multiple β-sheet configurations within a single peptide aggregate using two-dimensional infrared spectroscopy. By calculating the transition dipole strength (TDS) spectrum from the ratio of linear and two-dimensional signals, we can extract maximum TDS values which provide higher sensitivity to vibrational coupling, and thus specifics of protein structure, than vibrational frequency alone. TDS spectra of AcKFE8 aggregates reveal two distinct β-sheet structures within fibers that appear homogeneous by other techniques. Furthermore, TDS spectra taken during early stages of aggregation show additional peaks that may indicate the presence of more weakly coupled β-sheet structures. These results demonstrate a unique and powerful spectroscopic method capable of distinguishing multiple oligomeric and polymorphic motifs throughout the aggregation using only native vibrational modes.

This study aims to collect information about soil investigation by FTIR. As we know, the FTIR technique is most often used in organic and bioorganic chemistry, while in geochemistry FTIR spectroscopy is not used very often. Therefore, there is a problem with the identification and interpretation of the IR spectra of minerals contained in sediments and soils. The reason for this is a deficiency of data about characteristic wavenumbers for minerals. Therefore, this study reviews and sums up, in one place, published articles that are connected to an investigation of minerals from 2002 to 2021 (based on the Scopus database). Additionally, the present review highlights various analytical techniques (ATR-FTIR, DRIFT, 2D-IR, and SR-FTIR) and discusses some of them for geochemical study. Additionally, the study describes helpful tools in the data pre-processing of IR spectra (normalization, baseline correction, and spectral derivatives).

Ultrafast two-dimensional infrared (2D-IR) spectroscopy of

Photothermal induced resonance (PTIR), also known as AFM-IR, enables nanoscale infrared (IR) imaging and spectroscopy by using the tip of an atomic force microscope to transduce the local photothermal expansion and contraction of a sample. The signal transduction efficiency and spatial resolution of PTIR depend on a multitude of sample, cantilever, and illumination source parameters in ways that are not yet well understood. Here, we elucidate and separate the effects of laser pulse length, pulse shape, sample thermalization time (τ), interfacial thermal conductance, and cantilever detection frequency by devising analytical and numerical models that link a sample's photothermal excitations to the cantilever dynamics over a broad bandwidth (10 MHz). The models indicate that shorter laser pulses excite probe oscillations over broader bandwidths and should be preferred for measuring samples with shorter thermalization times. Furthermore, we show that the spatial resolution critically depends on the interfacial thermal conductance between dissimilar materials and improves monotonically, but not linearly, with increasing cantilever detection frequencies. The resolution can be enhanced for samples that do not fully thermalize between pulses (i.e., laser repetition rates ≳ 1/3τ) as the probed depth becomes smaller than the film thickness. We believe that the insights presented here will accelerate the adoption and impact of PTIR analyses across a wide range of applications by informing experimental designs and measurement strategies as well as by guiding future technical advances.

Repackaging and tampering with labels of foods to extend their shelf life is an illegal practice, increasingly common in some Brazilian coffee retail markets. Fast, easy-to-use, and low-cost analytical techniques for the large-scale screening of aging time have been demanded lately to fight the growth of these frauds in retail coffee markets. In this work

A novel method based on GC-MS, near-infrared (NIR) and mid-infrared (MIR) spectroscopy combined with chemometrics was established to simultaneously analyze differential volatile components (DVCs) of herb samples. Herein, Florists Chrysanthemum was adopted as the representative sample. Through the introduction of Automatic data analysis workflow (AntDAS) and one-class partial least squares discriminant analysis (O-PLSDA) model, five kinds of terpenes and five kinds of alcohols were efficiently screened as DVCs. By using the selected NIR-MIR spectra sections combined with O-PLSDA, it could achieve the accurate identification of Florists Chrysanthemum from Chrysanthemum morifolium Ramat. What's more, since the selected spectra sections were closely related to the structural and content of DVCs, they could be further used for simultaneous quantitative analysis of DVCs combined with optimized variable-weighted least-squares support vector machine based on particle swarm optimization (PSO-VWLS-SVM). This method only adopted the same NIR-MIR sections for multiple component accurate quantification, highlighting its convenience.

In a recent study [J. Phys. Chem. B 126, 4584–4598 (2022)], we have used infrared spectroscopy to investigate the solvation and dynamics of solitary water in ionic liquids and dipolar solvents. Complex shapes observed for water OH-stretching bands, common to all high-polarity solvents, were assigned to water in several solvation states. In the present study, classical molecular dynamics simulations of a single water molecule in four ionic liquids and three dipolar solvents were used to test and refine this interpretation. Consistent with past assignments, simulations show solitary water usually donates two hydrogen bonds to distinct solvent molecules. Such symmetrically solvated water produces the primary pair of peaks identified in the OH spectra of water in nearly all solvents. We had further proposed that additional features flanking this main peak are due to asymmetric solvation states, states in which only one OH group makes a hydrogen bond to solvent. Such states were found in significant concentrations in all of the systems simulated. Simulations of the OH stretching spectra using a semiclassical description and the vibrational map developed by Auer and Skinner [J. Chem. Phys. 128, 224511–224512 (2008)] provided semi-quantitative agreement with experiment. Analysis of species-specific spectra confirmed assignment of the additional features in the experimental spectra to asymmetrically solvated water. The simulations also showed that rapid water motions cause a marked motional narrowing compared with the inhomogeneous limit. This narrowing is largely responsible for making the additional features due to minority solvation states manifest in the spectra.

Funder: Wellcome Trust, The brains of patients suffering from traumatic brain-injury (TBI) undergo dynamic chemical changes in the days following the initial trauma. Accurate and timely monitoring of these changes is of paramount importance for improved patient outcome. Conventional brain-chemistry monitoring is performed off-line by collecting and manually transferring microdialysis samples to an enzymatic colorimetric bedside analyzer every hour, which detects and quantifies the molecules of interest. However, off-line, hourly monitoring means that any subhourly neurochemical changes, which may be detrimental to patients, go unseen and thus untreated. Mid-infrared (mid-IR) spectroscopy allows rapid, reagent-free, molecular fingerprinting of liquid samples, and can be easily integrated with microfluidics. We used mid-IR transmission spectroscopy to analyze glucose, lactate, and pyruvate, three relevant brain metabolites, in the extracellular brain fluid of two TBI patients, sampled via microdialysis. Detection limits of 0.5, 0.2, and 0.1 mM were achieved for pure glucose, lactate, and pyruvate, respectively, in perfusion fluid using an external cavity-quantum cascade laser (EC-QCL) system with an integrated transmission flow-cell. Microdialysates were collected hourly, then pooled (3-4 h), and measured consecutively using the standard ISCUSflex analyzer and the EC-QCL system. There was a strong correlation between the compound concentrations obtained using the conventional bedside analyzer and the acquired mid-IR absorbance spectra, where a partial-least-squares regression model was implemented to compute concentrations. This study demonstrates the potential utility of mid-IR spectroscopy for continuous, automated, reagent-free, and online monitoring of the dynamic chemical changes in TBI patients, allowing a more timely response to adverse brain metabolism and consequently improving patient outcomes.

Atomic force microscopy integrated with infrared spectroscopy (AFM‐IR) has been used to topographically and chemically examine the medulla of human hair fibres with nanometre scale lateral resolution. The mapping of cross‐sections of the medulla showed two distinct structural components which were subsequently characterised spectroscopically. One of these components was shown to be closely similar to cortical cell species, consistent with the fibrillar structures found in previous electron microscope (EM) investigations. The other component showed large chemical differences from cortical cells and was assigned to globular vacuole species, also confirming EM observations. Further characterisation of the two components was achieved through spectral deconvolution of the protein Amide‐I and ‐II bands. This showed that the vacuoles have a greater proportion of the most thermodynamically stable conformation, namely the antiparallel β‐sheet structures. This chimes with the observed lower cysteine concentration, indicating a lower proportion of restrictive disulphide cross‐link bonding. Furthermore, the large α‐helix presence within the vacuoles points to a loss of matrix‐like material as well as significant intermolecular stabilisation of the protein structures. By analysing the carbonyl stretching region, it was established that the fibrillar, cortical cell‐like components showed considerable stabilisation from H‐bonding interactions, similar to the cortex, involving amino acid side chains whereas, in contrast, the vacuoles were found to only be stabilised significantly by structural lipids.

This study aimed to evaluate the applicability and efficiency of Near-Infrared Spectroscopy (NIR) by using dispersive NIR and Fourier Transform NIR to analyse 267 samples of Brazilian wheat flour contaminated with deoxynivalenol (DON). For this, Partial Least-squares Discriminant Analysis (PLS-DA) and Principal Component Analysis-Linear Discriminant Analysis (PC-LDA) were used as discriminatory methods. Next, the samples were classified according to the maximum tolerated limits (MTL) for DON in Brazil, 750 μg kg

Sodiated complexes of the aliphatic amino acids, Gly, Ala, Val, Leu, and Ile, were examined with infrared multiple-photon dissociation action spectroscopy utilizing light from a free-electron laser. To identify structures, the experimental spectra were compared to linear spectra calculated at the B3LYP/6-311+G(d,p) level of theory. Relative energetics of all complexes were calculated at B3LYP, B3P86, MP2(full), B3LYP-GD3BJ, and M06-2X levels using a 6-311+G(2d,2p) basis set. Spectral comparison for all complexes indicates that the dominant conformation, [N, CO], binds to the amino nitrogen and carbonyl oxygen. For all complexes except Gly, contributions are observed from [CO2-] structures, where the sodium cation binds to both oxygens of the carboxylate group in the zwitterionic form of the amino acid. The semiquantitative distribution between these two structures appears to be best-predicted by the B3LYP and MP2(full) levels of theory, with predictions from the other three levels inconsistent with the experiment.

Proteins function as ensembles of interconverting structures. The motions span from picosecond bond rotations to millisecond and longer subunit displacements. Characterization of functional dynamics on all spatial and temporal scales remains challenging experimentally. Two-dimensional infrared spectroscopy (2D IR) is maturing as a powerful approach for investigating proteins and their dynamics. We outline the advantages of IR spectroscopy, describe 2D IR and the information it provides, and introduce vibrational groups for protein analysis. We highlight example studies that illustrate the power and versatility of 2D IR for characterizing protein dynamics and conclude with a brief discussion of the outlook for biomolecular 2D IR.

An efficient anharmonic vibrational method is developed exploiting the locality of molecular vibration. Vibrational coordinates localized to a group of atoms are employed to divide the potential energy surface (PES) of a system into intra- and inter-group contributions. Then, the vibrational Schrodinger equation is solved based on a PES, in which the inter-group coupling is truncated at the harmonic level while accounting for the intra-group anharmonicity. The method is applied to a pentagonal hydrogen bond network (HBN) composed of internal water molecules and charged residues in a membrane protein, bacteriorhodopsin. The PES is calculated by the quantum mechanics/molecular mechanics (QM/MM) calculation at the level of B3LYP-D3/aug-cc-pVDZ. The infrared (IR) spectrum is computed using a set of coordinates localized to each water molecule and amino acid residue by second-order vibrational quasi-degenerate perturbation theory (VQDPT2). Benchmark calculations show that the proposed method yields the N-D/O-D stretching frequencies with an error of 7 cm-1 at the cost reduced by more than five times. In contrast, the harmonic approximation results in a severe error of 150 cm-1. Furthermore, the size of QM regions is carefully assessed to find that the QM regions should include not only the pentagonal HBN itself but also its HB partners. VQDPT2 calculations starting from transient structures obtained by molecular dynamics simulations have shown that the structural sampling has a significant impact on the calculated IR spectrum. The incorporation of anharmonicity, sufficiently large QM regions, and structural samplings are of essential importance to reproduce the experimental IR spectrum. The computational spectrum paves the way for decoding the IR signal of strong HBNs and helps elucidate their functional roles in biomolecules.

International audience; A near-infrared fluorescent (NIRF) substrate-based probe (SBP) was conceived to monitor secreted human proteinase 3 (hPR3) activity. This probe, called pro3-SBP, is shaped by a fused peptide hairpin loop structure, which associates a hPR3 recognition domain (Val-Ala-Asp-Nva-Ala-Asp-Tyr-Gln, where Nva is norvaline) and an electrostatic zipper (consisting of complementary polyanionic (d-Glu)5 and polycationic (d-Arg)5 sequences) in close vicinity of the N- and C-terminal FRET couple (fluorescent donor, sulfoCy5.5; dark quencher, QSY21). Besides its subsequent stability, no intermolecular fluorescence quenching was detected following its complete hydrolysis by hPR3, advocating that pro3-SBP could further afford unbiased imaging. Pro3-SBP was specifically hydrolyzed by hPR3 (kcat/Km= 440 000 ± 5500 M-1·s-1) and displayed a sensitive detection threshold for hPR3 (subnanomolar concentration range), while neutrophil elastase showed a weaker potency. Conversely, pro3-SBP was not cleaved by cathepsin G. Pro3-SBP was successfully hydrolyzed by conditioned media of activated human neutrophils but not by quiescent neutrophils. Moreover, unlike unstimulated neutrophils, a strong NIRF signal was specifically detected by confocal microscopy following neutrophil ionomycin-induced degranulation. Fluorescence release was abolished in the presence of a selective hPR3 inhibitor, indicating that pro3-SBP is selectively cleaved by extracellular hPR3. Taken together, the present data support that pro3-SBP could be a convenient tool, allowing straightforward monitoring of human neutrophil activation.

Mid-infrared photothermal microscopy is a new chemical imaging technology in which a visible beam senses the photothermal effect induced by a pulsed infrared laser. This technology provides infrared spectroscopic information at submicrometer spatial resolution and enables infrared spectroscopy and imaging of living cells and organisms. Yet, current mid-infrared photothermal imaging sensitivity suffers from a weak dependence of scattering on the temperature, and the image quality is vulnerable to the speckles caused by scattering. Here, we present a novel version of mid-infrared photothermal microscopy in which thermosensitive fluorescent probes are harnessed to sense the mid-infrared photothermal effect. The fluorescence intensity can be modulated at the level of 1% per Kelvin, which is 100 times larger than the modulation of scattering intensity. In addition, fluorescence emission is free of interference, thus much improving the image quality. Moreover, fluorophores can target specific organelles or biomolecules, thus augmenting the specificity of photothermal imaging. Spectral fidelity is confirmed through fingerprinting a single bacterium. Finally, the photobleaching issue is successfully addressed through the development of a wide-field fluorescence-detected mid-infrared photothermal microscope which allows video rate bond-selective imaging of biological specimens.

Microplastics are a widespread contaminant found not only in various natural habitats but also in drinking waters. With spectroscopic methods, the polymer type, number, size, and size distribution as well as the shape of microplastic particles in waters can be determined, which is of great relevance to toxicological studies. Methods used in studies so far show a huge diversity regarding experimental setups and often a lack of certain quality assurance aspects. To overcome these problems, this critical review and consensus paper of 12 European analytical laboratories and institutions, dealing with microplastic particle identification and quantification with spectroscopic methods, gives guidance toward harmonized microplastic particle analysis in clean waters. The aims of this paper are to (i) improve the reliability of microplastic analysis, (ii) facilitate and improve the planning of sample preparation and microplastic detection, and (iii) provide a better understanding regarding the evaluation of already existing studies. With these aims, we hope to make an important step toward harmonization of microplastic particle analysis in clean water samples and, thus, allow the comparability of results obtained in different studies by using similar or harmonized methods. Clean water samples, for the purpose of this paper, are considered to comprise all water samples with low matrix content, in particular drinking, tap, and bottled water, but also other water types such as clean freshwater., B. E. Oßmann thanks the Bavarian State Ministry of the Environment and Consumer Protection for funding the projects “Detection of microplastics in selected foods” and “Expansion of the analytics of microplastics in food.” S. Lacorte acknowledges funding from the Ministry of Science and Innovation of Spain (project PID2019-105732GB-C21). J. Weisser, K. Glas, T. Hofmann, N. P. Ivleva, and E. von der Esch receive funding from the Bavarian Research Foundation (Bayerische Forschungsstiftung (BFS), AZ-1258-16 (“MiPAq”). N. P. Ivleva thanks the Federal Ministry of Education and Research (Bundesministerium für Bildung und Forschung (BMBF), projects 02WPL1443A “SubμTrack” and 03F0851B “HOTMIC”) for financial support. D. Fischer and F. Fischer acknowledge funding from the projects MicroCatch_Balt, PLASTRAT, PLAWES by the BMBF in the call “Plastics in the environment,” as well as from the BONUS BLUE BALTIC project MICROPOLL, which has received funding from BONUS (Art 185), funded jointly by the EU and the BMBF. N. Zumbülte and C. S. Witzig acknowledge funding by the BMBF of the project “MicBin.”

We demonstrate a method to address the problem of spectral overlap in multidimensional vibrational spectroscopy and use it to investigate supercooled aqueous sorbitol solutions. The absence of crystallization in these solutions has been attributed to “soft” confinement of water in subnanometer voids in the sorbitol matrix, but the details of the hydrogen-bond structure are still largely unknown. 2D-IR spectroscopy of the OH-stretch mode is an excellent tool to investigate hydrogen bonding, but in this case it seems difficult because of the overlapping water and sorbitol contributions to the 2D-IR spectrum. Using the difference in OH-stretch lifetimes of water and sorbitol we can cleanly separate these contributions. Surprisingly, the separated 2D-IR spectra show that the hydrogen-bond disorder of soft-confined water is independent of temperature and decoupled from its orientational order. We believe the approach we use to separate overlapping 2D-IR spectra will enhance the applicability of 2D-IR spectroscopy to study multicomponent systems.

A durable and reversible acid-induced discoloration azobenzene UV-curable lignin-based waterborne polyurethane polymeric dye (EDA-ULPD) is prepared from lignin, azobenzene and pentaerythritol triacrylate(PETA) by chemical modification of waterborne polyurethane. Lignin and PETA are chemically bonded to the polyurethane chain to improve thermal stability, UV resistance and color fastness, while also endow the polymeric dye with UV curing performance, which is a green and environmentally friendly fixing way. The acid-induced discoloration property of EDA-ULPD with azobenzene chromophore side chain is comparable to those of 4-ethyl-4-2,2'-dihydroxy diethylamine azobenzene (EDA). As the pH value decreases from 7 to 1, the maximum absorption peak of EDA-ULPD from 420 nm to 530 nm, and the color change from yellow to pink due to the transformation of EDA molecular structure from diazo to hydrazone. Interestingly, when EDA-ULPD is fixed to the fabric in the way of UV curing, its printed fabric exhibits the performance of high concentration acid-induced discoloration (1 mol·L-1 HCl) due to the cross-linked structure formed by EDA-ULPD. The acid-induced discoloration property of EDA-ULPD printed fabrics also presents outstanding repetitious stability. The stimulus response printed fabric with reversible high concentration acid discoloration possesses a broad application prospect in smart textiles.

New exogenous probes are needed for both imaging diagnostics and therapeutics. Here, we introduce a novel nanocomposite near-infrared (NIR) fluorescent imaging probe and test its potency as a photosensitizing agent for photodynamic therapy (PDT) against triple-negative breast cancer cells. The active component in the nanocomposite is a small molecule, pyropheophorbide a-phosphatidylethanolamine-QSY21 (Pyro-PtdEtn-QSY), which is imbedded into lipid nanoparticles for transport in the body. The probe targets abnormal choline metabolism in cancer cells; specifically, the overexpression of phosphatidylcholine-specific phospholipase C (PC-PLC) in breast, prostate, and ovarian cancers. Pyro-PtdEtn-QSY consists of a NIR fluorophore and a quencher, attached to a PtdEtn moiety. It is selectively activated by PC-PLC resulting in enhanced fluorescence in cancer cells compared to normal cells. In our in vitro investigation, four breast cancer cell lines showed higher probe activation levels than noncancerous control cells, immortalized human mammary gland cells, and normal human T cells. Moreover, the ability of this nanocomposite to function as a sensitizer in PDT experiments on MDA-MB-231 cells suggests that the probe is promising as a theranostic agent.

The article describes the application of the alanine-scanning technique used in combination with Raman, surface-enhanced Raman, attenuated total reflection Fourier transform infrared, and surface-enhanced infrared absorption (SEIRA) spectroscopies, which allowed defining the role of individual amino acid residues in the C-terminal 6–14 fragment of the bombesin chain (BN6–14) on the path of its adsorption on the surface of Ag (AgNPs) and Au nanoparticles (AuNPs). A reliable analysis of the SEIRA spectra of these peptides was possible, thanks to a curve fitting of these spectra. By combining alanine-scanning with biological activity studies using cell lines overexpressing bombesin receptors and the intracellular inositol monophosphate assay, it was possible to determine which peptide side chains play a significant role in binding a peptide to membrane-bound G protein-coupled receptors (GPCRs). Based on the analysis of spectral profiles and bioactivity results, conclusions for the specific peptide–metal and peptide–GPCR interactions were drawn and compared.

Plant cryptochromes are central blue light receptors in land plants and algae. Photoreduction of the flavin bound to the photolyase homology region (PHR) causes a dissociation of the C-terminal extension (CCT) as effector via an unclear pathway. We applied the recently developed in-cell infrared difference (ICIRD) spectroscopy to study the response of the full-length pCRY from Chlamydomonas reinhardtii in living bacterial cells, because the receptor degraded upon isolation. We demonstrate a stabilization of the flavin neutral radical as photoproduct and of the resulting β-sheet reorganization by binding of cellular ATP. Comparison between light-induced structural responses of full-length pCRY and PHR reveals a downshift in frequency of the β-sheet signal, implying an association of the CCT close to the only β-sheet of the PHR in the dark. We provide a missing link in activation of plant cryptochromes after flavin photoreduction by indicating that β-sheet reorganization causes the CCT release and restructuring.

Funding Information: The financial support of the Austrian Federal Ministry of Digital and Economic Affairs and the National Foundation for Research, Technology and Development , Austria, is gratefully acknowledged. We also thank the industrial partners Mondi, Canon Production Printing, Kelheim Fibres, and SIG Combibloc for their support. Publisher Copyright: © 2021 Copyright: Copyright 2021 Elsevier B.V., All rights reserved. Hydrophobization of cellulosic materials and particularly paper products is a commonly used procedure to render papers more resistant to water and moisture. Here, we explore the hydrophobization of unsized paper sheets via the gas phase. We employed three different compounds, namely palmitoyl chloride (PCl), trifluoroacetic anhydride/acetic anhydride (TFAA/Ac2O)) and hexamethyldisilazane (HMDS) which were vaporized and allowed to react with the paper sheets via the gas phase. All routes yielded hydrophobic papers with static water contact angles far above 90° and indicated the formation of covalent bonds. The PCl and TFAA approach negatively impacted the mechanical and optical properties of the paper leading to a decrease in tensile strength and yellowing of the sheets. The HMDS modified papers did not exhibit any differences regarding relevant paper technological parameters (mechanical properties, optical properties, porosity) compared to the non-modified sheets. XPS studies revealed that the HMDS modified samples have a rather low silicon content, pointing at the formation of submonolayers of trimethylsilyl groups on the fiber surfaces in the paper network. This was further investigated by penetration dynamic analysis using ultrasonication, which revealed that the whole fiber network has been homogeneously modified with the silyl groups and not only the very outer surface as for the PCl and the TFAA modified papers. This procedure yields a possibility to study the influence of hydrophobicity on paper sheets and their network properties without changing structural and mechanical paper parameters.

Microplastics are ubiquitous in the environment, including in food and drinking water. Consequently, there is growing concern about the human health risks associated with microplastic exposure through diet. However, the occurrence of microplastics in the human body, particularly in mothers and fetuses, is incompletely understood because of the limited amount of data on their presence in the body and the human placenta. This study evaluated the presence and characteristics of microplastics in 17 placentas using laser direct infrared (LD-IR) spectroscopy. Microplastics were detected in all placenta samples, with an average abundance of 2.70 ± 2.65 particles/g and a range of 0.28 to 9.55 particles/g. Among these microplastics, 11 polymer types were identified. The microplastics were mainly composed of polyvinyl chloride (PVC, 43.27 %), polypropylene (PP, 14.55 %), and polybutylene succinate (PBS, 10.90 %). The sizes of these microplastics ranged from 20.34 to 307.29 μm, and most (80.29 %) were smaller than 100 μm. Most of the smaller microplastics were fragments, but fibers dominated the larger microplastics (200-307.29 μm). Interestingly, the majority of PVC and PP were smaller than 200 μm. This study provides a clearer understanding of the shape, size, and nature of microplastics in the human placenta. Importantly, these data also provide crucial information for performing risk assessments of the exposure of fetuses to microplastics in the future.

The fundamental transitions that contribute to the diffuse OH stretching spectrum of water are known to increase in width and intensity with increasing red shift from the free OH frequency. In contrast, the profile of the higher-energy combination band involving the OH stretching and the intramolecular HOH bending modes displays a qualitatively different spectral shape with a much faster falloff on the lower-energy side. We elucidate the molecular origin of this difference by analyzing the shapes of the combination bands in the IR spectra of cryogenically cooled H

Ethanol is a molecule of fundamental interest in combustion, astrochemistry, and condensed phase as a solvent. It is characterized by two methyl rotors and

We used two-dimensional infrared spectroscopy to disentangle the broad infrared band in the amide II vibrational regions of Bombyx mori native silk films, identifying the single amide II modes and correlating them to specific secondary structure. Amide I and amide II modes have a strong vibrational coupling, which manifests as cross-peaks in 2D infrared spectra with frequencies determined by both the amide I and amide II frequencies of the same secondary structure. By cross referencing with well-known amide I assignments, we determined that the amide II (N-H) absorbs at around 1552 and at 1530 cm–1 for helical and β-sheet structures, respectively. We also observed a peak at 1517 cm−1 that could not be easily assigned to an amide II mode, and instead we tentatively assigned it to a Tyrosine sidechain. These results stand in contrast with previous findings from linear infrared spectroscopy, highlighting the ability of multidimensional spectroscopy for untangling convoluted spectra, and suggesting the need for caution when assigning silk amide II spectra.

Atomic force microscopy has been used for decades to study the topography of proteins during aggregation but with a lack of information on the secondary structure. On the contrary, infrared spectroscopy was able to study structural changes during the aggregation, but this analysis is complicated due to the presence of different species in mixtures and the poor spatial (~μm) resolution of the FTIR microscopy. Recently, Professor Alexandre Dazzi combined those techniques in the so-called AFM-IR. This method allows acquiring IR spectra at the nanometric scale and becomes a new standard method for the characterization of amyloid fibrils and, more generally, for the aggregation of proteins.

Determining the secondary and tertiary structures of proteins at aqueous interfaces is crucial for understanding their function, but measuring these structures selectively at the interface is challenging. Here we demonstrate that two-dimensional infrared (2D-IR) spectroscopy of protein stabilized emulsions offers a new route to measuring interfacial protein structure with high levels of detail. We prepared hexadecane/water oil-in-water emulsions stabilized by model LK peptides that are known to fold into either alpha-helix or beta-sheet conformations at hydrophobic interfaces and measured 2D-IR spectra in a transmission geometry. We saw clear spectral signatures of the peptides folding at the interface, with no detectable residue from remaining bulk peptides. Using 2D spectroscopy gives us access to correlation and dynamics data, which enables structural assignment in cases where linear spectroscopy fails. Using the emulsions allows one to study interfacial spectra with standard transmission geometry spectrometers, bringing the richness of 2D-IR to the interface with no additional optical complexity.

The nanoscale structure and dynamics of proteins on surfaces has been extensively studied using various imaging techniques, such as transmission electron microscopy and atomic force microscopy (AFM) in liquid environments. These powerful imaging techniques, however, can potentially damage or perturb delicate biological material and do not provide chemical information, which prevents a fundamental understanding of the dynamic processes underlying their evolution under physiological conditions. Here, we use a platform developed in our laboratory that enables acquisition of infrared (IR) spectroscopy and AFM images of biological material in physiological liquids with nanometer resolution in a cell closed by atomically thin graphene membranes transparent to IR photons. In this work, we studied the self-assembly process of S-layer proteins at the graphene-aqueous solution interface. The graphene acts also as the membrane separating the solution containing the proteins and Ca 2+ ions from the AFM tip, thus eliminating sample damage and contamination effects. The formation of S-layer protein lattices and their structural evolution was monitored by AFM and by recording the amide I and II IR absorption bands, which reveal the noncovalent interaction between proteins and their response to the environment, including ionic strength and solvation. Our measurement platform opens unique opportunities to study biological material and soft materials in general.

Fourier Transform Infrared (FTIR) microspectroscopy is well known for its effectiveness in spectral and biochemical analyses of various materials. It enables to determine the sample biochemical composition by assigning detected frequencies, characteristic for functional groups of main biological macromolecules. In analysis of tissue sections one of two measurement modes, namely transmission and transflection, is usually applied. The first one has relatively straightforward geometry, hence it is considered to be more precise and accurate. However, IR-transparent media are very fragile and expensive. Transflection does not require expensive substrates, but is more prone to disruptive influence of Mie scattering as well as electric field standing wave effect. The excessive comparison of spectra' characteristics, obtained via both measurement modes, was performed in this paper. By the means of Mann-Whitney non-parametrical U test and PCA, the comparison of results obtained with both modes and assessment of usefulness of IR spectra obtained with transmission and transflection modes to differentiate between healthy and GBM-affected tissue, were performed. The main objective of the presented research is to compare the results of FTIR analysis of unfixed biological samples performed with transflection and transmission mode. In frame of the study we demonstrated the discrepancies between results of biochemical analysis performed based on data obtained with transmission and transflection. Such observation suggests that caution should be taken in drawing conclusions from the results obtained with transflection geometry, as its more prone to disruptive effects. Despite that, IR spectra developed with both modes allowed to distinguish GBM area from healthy tissue, which proves their diagnostic potential. Especially, application of the ME-EMSC correction of spectra before PCA enhances the performance of both methods to distinguish the analysed tissue areas.

This work is aimed at the study at studying the influence of the interaction of solvate shells on the profiles of the IR spectra of sodium chloride solutions in the 2750-4000 cm