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Sugars (saccharides) are sweet-tasting carbohydrates that are abundant in foods and play very important roles in living organisms, particularly as sources and stores of energy, and as structural elements in cellular membranes. They are desirable therapeutic targets, as they participate in multiple metabolic processes as fundamental elements. However, the physicochemical characterization of sugars is a challenging task, mostly due to the structural similarity shared by the large diversity of compounds of this family. The need for fast, accurate enough, and cost-effective analytical methods for these substances is of extreme relevance, in particular because of the recently increasing importance of carbohydrates in Medicine and food industry. With this in view, this work focused on the development of chemometric models for semi-quantitative analysis of samples of different types of sugars (glucose, galactose, mannitol, sorbose and fructose) using infrared spectra as data, as an example of application of a novel approach, where the Principal Component Analysis (PCA) score plots are used to estimate the composition (weight-%) of the mixtures of the sugars. In these plots, polygonal geometric shapes emerge in the vectorial space of the most significant principal components, that allow grouping different types of samples on the vertices, edges, faces and interior of the polygons according to the composition of the samples. This approach was applied successfully to mixtures of up to 5 sugars and shown to appropriately extract the compositional information from the hyper-redundant complex spectral data. Thought the method has been applied here to a specific problem, it shall be considered as a general procedure for the semi-quantitative analysis of other types of mixtures and applicable to other types of data reflecting their composition. In fact, the methodology appears as an efficient tool to solve three main general problems: (i) use hyper-redundant (in variables) data, as spectral information, directly and with minimum pre-treatment, to evaluate semi-quantitatively the composition of mixtures; (ii) do this for systems which produce data that can be considered rather similar; and (iii) do it for a number of substances present in the mixtures that might be greater than that usually considered in chemistry, which in general is limited to 3 components. In addition, this work also demonstrates that, similarly to the developed analysis based on the PCA score plots, the Multivariate Curve Resolution with Alternating Least Squares (MCR-ALS) chemometric method can also be used successfully for the qualitative (when used without any previous knowledge of the components present in the samples) or semi-quantitative (when the pure components spectral profiles are provided as references) analyses of mixtures of (at least) up to 5 distinct sugars., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: ANNA LUIZA BIZERRA DE BRITO, RUI FAUSTO MARTINS RIBEIRO DA SILVA LOURENCO, LUIS PEDRO DA FRANCA E SILVA CALEIRAS VIEGAS has patent Chemometrics Protocol for Semi-Quantitative Analysis of Mixtures Using Spectral Data or Other Composition Dependent Hyper-Redundant Data pending to 119690. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier B.V. All rights reserved.)

Intermolecular hydrogen bonds between carboxyl (COO - ) and amino groups are a common weak interaction in proteins. Infrared (IR) spectral assignment of such an intermolecular hydrogen bond provides a fingerprint for studying protein-protein interactions as its absorption frequency is affected by the molecular electrostatic environment. Temperature-dependent FTIR and temperature-jump time-resolved IR absorbance difference spectra of several typical amino acids and those of wild type and single-site mutated αB-crystallin were performed. It was found that the antisymmetric vibrational frequency of the COO - groups in amino acids decreases from approximately 1626 to 1610 cm -1 upon the formation of intermolecular hydrogen bonds, which was further supported by DFT calculations, while the IR frequency of the intermolecular hydrogen bonds on the formation of intermolecular hydrogen bonds, which was further supported by DFT calculations, while the IR frequency of the intermolecular hydrogen bonded COO - groups at the αB-crystallin dimeric interface was also observed around 1610 cm -1 . With this spectral label, the active site of αB-crystallin, a heat shock molecular chaperone against the UV-light-damaged γD-crystallin was investigated. The active site was found to be localized at an arch loop structure connecting the two β-strands locked by intermolecular hydrogen bonds at the dimeric interface. It is the liberated arch loop after breaking of the intermolecular hydrogen bond locks that binds the damaged γD-crystallin, leading to the observed chaperone-like activity of αB-crystallin.

Isomerization is a key process in many (bio)chemical systems. In microbial rhodopsins, the photoinduced isomerization of the all-trans retinal to the 13-cis isomer initiates a cascade of structural changes of the protein. The interplay between these changes and the thermal relaxation of the isomerized retinal is one of the crucial determinants for rhodopsin functionality. It is therefore important to probe this dynamic interplay with chromophore specific markers that combine gapless temporal observation with spectral sensitivity. Here we utilize the near-UV and mid-IR fingerprint region in the framework of a systematic (time-resolved) spectroscopic study on H + - (HsBR, (G)PR), Na + - (KR2, ErNaR) and Cl - -(NmHR) pumps. We demonstrate that the near-UV region is an excellent probe for retinal configuration and-being sensitive to the electrostatic environment of retinal-even transient ion binding, which allows us to pinpoint protein specific mechanistic nuances and chromophore-charge interactions. The combination of the near-UV and mid-IR fingerprint region hence provides a spectroscopic analysis tool that allows a detailed, precise and temporally fully resolved description of retinal configurations during all stages of the photocycle., (© 2024 The Author(s). Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Molybdenum nitrogenase plays a crucial role in the biological nitrogen cycle by catalyzing the reduction of dinitrogen (N 2 ) to ammonia (NH 3 ) under ambient conditions. However, the underlying mechanisms of nitrogenase catalysis, including electron and proton transfer dynamics, remain only partially understood. In this study, we covalently attached molybdenum nitrogenase (MoFe) to gold electrodes and utilized surface-enhanced infrared absorption spectroscopy (SEIRA) coupled with electrochemistry techniques to investigate its catalytic mechanism. Our biohybrid system enabled electron transfer via a mild mediator, likely mimicking the natural electron flow through the P-cluster to FeMoco, the enzyme's active site. For the first time, we experimentally observed both terminal and bridging S-H stretching frequencies, resulting from the protonation of bridging sulfides in FeMoco during turnover conditions providing direct evidence of their role in catalysis. These experimental observations are further supported by QM/MM calculations. Additionally, we investigated CO inhibition, demonstrating both CO binding and unbinding dynamics under electrochemical conditions. These insights not only advance our understanding of the mechanistic cycle of molybdenum nitrogenase but also establish a foundation for studying alternative nitrogenases, including vanadium and iron nitrogenases.

Patterns of disease and therapeutic responses vary widely among patients with autoimmune glomerulonephritis. This study introduces groundbreaking personalized infrared (IR)-based diagnostics for real-time monitoring of disease status and treatment responses in lupus nephritis (LN). We have established a relative absorption difference (RAD) equation to assess characteristic spectral indices based on the temporal peak heights (PHs) of two characteristic serum absorption bands: ν 1 as the target signal and ν 2 as the PH reference for the ν 1 absorption band, measured at each dehydration time (t) during dehydration. The RAD gap (Ψ), defined as the difference in the RAD values between the initial and final stages of serum dehydration, enables the measurement of serum levels of IgG glycosylation (ν 1 (1030 cm -1 ), ν 2 (1171 cm -1 )), serum lactate (ν 1 (1021 cm -1 ), ν 2 (1171 cm -1 )), serum hydrophobicity (ν 1 (2930 cm -1 ), ν 2 (2960 cm -1 )), serum hydrophilicity (ν 1 (1550 cm -1 ), ν 2 (1650 cm -1 )), and albumin (ν 1 (1400 cm -1 ), ν 2 (1450 cm -1 )). Furthermore, this IR-based assay incorporates an innovative algorithm and our proprietary iPath software (ver. 1.0), which calculates the prognosis prediction function (PPF, Φ) from the RAD gaps of five spectral markers and correlates these with conventional clinical renal biomarkers. We propose that this algorithm-assisted, IR-based approach can augment the patient-centric care of LN patients, particularly by focusing on changes in serum IgG glycosylation.