Navegando por Assunto "Infrared spectroscopy"

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    Application of mid-infrared vibrational spectroscopy with Fourier transform (FTIR) in quality evaluation in commercial coffees
    (CDRR Editors) Fontes, Vitória; Pereira, Douglas Cubas; Lyra, Lucas Ferreira; Sakane, Kumiko Koibuchi
    Currently, Brazil is the largest exporter and producer of coffee in the world, and it is the second most consumed beverage in the world, only behind water. In the years 2019 and 2020 it is estimated that the world consumption of coffee was 168.84 million bags of 60 kg, Brazil consumed 20 million bags of coffee, the second-largest consumer in the world, only behind the United States with 25 million bags. The techniques such as infrared spectroscopy has been applied in the food industry, as it is a fast, easy technique, without the need for reagents, free from polluting processes, and capable of analyzing the simultaneous composition of the constituents. The present study aims to analyze the changes in the chemical constituents of Brazilian commercial coffees as a function of shelf life through Fourier transformed infrared spectroscopy (FT-IR) associated with chemometric methods. The experiments were carried out within the expiration date, 6 months, and a year after the expiration date. Spectra were obtained in the range from 4000 to 500 cm-1. The studies of Principal Component Analysis (PCA) and Hierarchical Cluster Analysis (HCA) were made as discrimination methods. The areas in the region from 2970 to 2830 cm-1 and 1765 to 1720 cm-1 were calculated to analyze the alteration as a function over time. The results suggest that these bands in coffee are sensitive over time and to the storage conditions, promoting changes in aroma and flavor.
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    Can Implicit Solvation Methods Capture Temperature Effects on the Infrared Features of Astrophysical Ices?
    (MDPI) Bonfim, Victor de Souza A.; Oliveira, Daniel Augusto Barra de; Fantuzzi, Felipe; Pilling, Sergio
    Astrophysical ices play a crucial role in the chemistry of cold interstellar environments. However, their diverse compositions, temperatures, and grain morphologies pose significant challenges for molecular identification and quantification through infrared observations. We investigate the ability of implicit solvation approaches to capture temperature-dependent infrared spectral features of CO2 molecules embedded in astrophysical ice analogues, comparing their performance to that of explicit ice models and experimental data. Using DFT calculations and vibrational frequency scaling, we model CO2 trapped in both amorphous (cold) and crystalline (warm) H2O ice clusters. The implicit model qualitatively identifies certain trends but fails to reliably capture the magnitude of frequency shifts and band strengths. Explicit models correctly reproduce the gas-to-solid redshifts for both the asymmetric stretch and bending modes; however, neither approach successfully replicates the experimentally observed temperature-dependent trend in the bending mode. While continuum-like methods may be useful as first-order approximations, explicit modelling of the molecular environment is essential for accurately simulating the infrared spectral behaviour of CO2 in astrophysical ices and for interpreting observational data on ice composition and evolution.