Lenize Fernandes Maia

Recent technological advances have produced miniaturized, portable Raman spectrometers, enabling direct field analysis, even under challenging conditions or on samples that cannot be removed from the original site, such as confined artifacts or monuments. This study comparatively analyzed portable and high-resolution Raman spectrometers for organic matter (OM) and mineralogical characterization of bulk outcrop rock and thin-section samples from the Tamengo and Bocaina Formations of the Corumbá group in Mato Grosso do Sul, Brazil. The results demonstrate that, despite differences in spectral sensitivity and spatial resolution, the portable Raman spectrometer provides representative average spectra of heterogeneous rock surfaces that are consistent with the average of a spectral map obtained from high-resolution micro-Raman mapping over equivalent areas. Nevertheless, weak or very weak bands are not detectable using a portable instrument. These findings confirm the feasibility of a portable Raman instrument for rapid in situ geological investigations, especially for the preliminary characterization of OM and minerals; however, they underscore the necessity of high-resolution micro-Raman spectrometers for detailed characterization of those samples.

Raman spectroscopy is a powerful tool for assessing the thermal maturity of kerogen; however, its application to carbonate-rich source rocks is hampered by methodological challenges, particularly spectral interference from fluorescent mineral matrices and sample heterogeneity. This study systematically evaluates three preparation protocols: fresh (raw), macerated (ground), and decarbonated, on samples from the Formação Coqueiros (Campos Basin-RJ, Brazil) to identify the most reliable workflow, using Rock-Eval pyrolysis as a geochemical benchmark. Direct analysis of fresh samples proved unreliable, yielding inconsistent data in which the combined effects of heterogeneity and mineral fluorescence masked the true kerogen signal. While mechanical maceration successfully addressed physical heterogeneity, allowing for a basic qualitative distinction between maturity levels, it was insufficient, as the fundamental problem of spectral interference remained unresolved. The decarbonated protocol, however, yielded the optimal result. This two-step procedure, involving mechanical grinding followed by targeted chemical removal of carbonates, successfully mitigated both issues, producing stable, precise, and geologically coherent maturity data that correlates with the Rock-Eval temperature of maximum hydrocarbon generation (Tmax) benchmark. This work validates the targeted procedure as a robust, accessible workflow that avoids aggressive chemical treatments that risk altering the kerogen structure, offering a more efficient and potentially more accurate path for analysis in these common lithologies.

Silicification in carbonate deposits refers to a diagenetic process in which silica replaces carbonate minerals, which are typically associated with hydrothermal fluids. During silica deposition under hydrothermal conditions, quartz crystallites often form on the surfaces of microorganisms, acting as nucleation sites. This silica replacement involves the simultaneous chemical transformation of the original skeletal materials, followed by precipitation. Organic matter-filled silica sphere-like structures were identified in the thin sections from the Barra Velha Formation chert (Santos Basin, Brazil), by the use of the Raman spectroscopy mapping technique and Scanning Electron Microscopy (SEM). The remaining organic matter showed two typical bands in the first-order Raman spectrum, i.e., the D-band located at approximately 1350 cm^–1 and the G-band at about 1600 cm^–1. The analysis of Raman parameters such as G-FWHM­(Full Width at Half-Maximum of the G-band) and RBS (Raman Band Separation) led to inference of the thermal maturity of samples by calibration against vitrinite standards. Differences in the spectral profile of organic matter obtained with 532 and 632.8 nm excitation radiations revealed the richness of chemical signatures preserved as sphere-like from the pre-salt deep-water Tupi/Lula Field. The SEM analysis revealed silica microsphere morphologies as indicative of the presence of microfossils in this rock. The chemical composition of silica sphere-like structures in BVF may be interpreted as biosignatures preserved in the chert.

In this work, Raman spectroscopy was employed to identify compounds present in different ripening stages of various exocarp varieties of peppers from the Solanaceae family, pink peppercorns (Anacardiceae), and black and white peppercorns (Piperaceae). In situ analysis of Solanaceae peppers revealed the characteristic bands of phenolic compounds, carotenoids, fatty acids, and alkaloids such as capsaicin. In the malagueta peppers, habanero, “biquinho”, and red karneval, a shift of the ν(C=C) stretching bands of carotenoids to lower wavenumbers and an increase in the band intensity were observed during ripening. In pink peppercorns, analyses of the peel and seeds at different ripening stages did not show significant changes. However, bands attributed to anthocyanins, such as pelargonidin, were observed, suggesting that these flavonoids are responsible for the color of the peel. Analyses of black and white peppercorns revealed characteristic bands mainly attributed to piperine. The assignment of Raman bands was proposed through comparison with literature data and spectra obtained by the Density Functional Theory (DFT) method. The sum of the theoretical spectra was used to simulate the spectral profile and the contribution of each substance in the experimentalspectra.

In this work, Raman spectroscopy and DFT calculations have been used to identify pigments biosynthesized during the ripening of tomatoes. In situ analysis of the exocarp from tomatoes at six stages of maturation showed Raman bands attributed mainly to carotenes and flavonoids. The Raman spectra of the exocarp in earlier stages (green and breaker) are rich in carotenoids with nine conjugated double bonds, while later stages (light‐red and red) are dominated by ones with 11 conjugated unsaturation. The Raman structural characterization of carotenoids biosynthesized from the phytoene, phytofluene, to β‐carotene is reported for the first time. Changes in carotenoid composition were observed along with the maturation; however, flavonoids/polyphenols that are concomitantly biosynthesized since the green stage presented the same spectral pattern along the process. Here, we present some clues based on Raman spectroscopy of the chemical synergism between carotenoids and flavonoids in coloring tomatoes.

Sponges (phylum Porifera) are colorful filter feeding animals that harbor a large number of microorganisms in their tissue‐like structures in a symbiotic relationship. The colors exhibited by sponges implied in physiological and ecological process can be biosynthetically derived or acquired from the symbiont. In this work, the coloration pattern of nine species of sponges collected in the littoral of Rio de Janeiro State, Brazil, was identified by vibrational spectroscopy. An unprecedented study combining Raman and infrared spectroscopies revealed that carotenoids are responsible for the color of red‐orange, green, and blue species, while melanin was addressed to the black species. The analysis of the spectral features of Raman bands presented in both in situ and crude extracts samples showed that carotenoids may occur as a mixture of isomers or alternatively, be bonded to proteins (carotenoproteins). It is noteworthy that the carotenoid‐based pigmentation in sponges is provided by the symbionts, which may be implied to the evolutionary and ecological success of this most ancient animal. The application of vibrational spectroscopy mainly in the in situ mode can be a valuable tool in the identification of structural differentiation of carotenoids in the microbiome of sponges collected in different environments.