Rodrigo De Paula

Limited access to analytical instrumentation motivates the development of affordable alternatives. This study describes the construction and evaluation of two ESP32-based optical prototypes: an RGB colorimeter using a TCS34725 sensor and an ultraviolet radiometer using an AS7331 sensor. The RGB device combined a darkened chamber with a mirror-assisted optical path and was evaluated using colored papers and solutions of potassium permanganate, methylene blue, rhodamine B, zinc phthalocyanine, and free-base tetraphenylporphyrin. Paper measurements distinguished colors but differed from nominal RGB codes due to factors as print configuration and paper type. Comparisons with a benchtop spectrophotometer revealed analyte- and channel-dependent linear ranges, with R² values of 0.950-0.999 for selected RGB fits. In a test using an unfocused UV flashlight, the recorded signal decreased with increasing source-sensor distance, exhibiting behavior close to that predicted by the inverse-square law. Solar monitoring yielded temporal profiles qualitatively similar to commercial records obtained at a different location and date. Dedicated applications supported data acquisition, visualization, and storage. Artificial intelligence assisted development under human supervision. The results indicate potential for accessible instrumentation, experimental teaching, and connected monitoring, while emphasizing application-specific calibration and the limitations of the evaluated configurations.

THE PROPAGATION OF THE ERROR IN THE pKa OF WATER IN ORGANIC CHEMISTRY TEXTBOOKS. In organic chemistry, the pKa is a property used to compare the acidity behavior for many substances, and to locate the position of equilibria in acid-base reactions and to provide information about structure and reactivity. Evidence in the literature shows that the values of pKa for water and hydronium ion, commonly cited in organic chemistry textbooks, are incorrect. The values of 15.74 for H2O and −1.74 for H3O+ are due to a propagated misconception in the equilibrium calculations while the correct values are 14.0 for H2O and 0.0 for H3O+. This subtle difference of 1.74 units on the pKa scale between both values reflects an error greater than 55 times in the level of acidity for these chemical species. An immediate correction of these values is necessary for the adequate teaching of organic chemistry. A literature search was conducted on the most used organic chemistry books in graduate and undergraduate courses in Brazil, revealing that almost all values cited were inadequate. The textbook Chemistry of Organic Compounds, 3rd edition (1965), by Carl Robert Noller is suggested as possible source of this misinformation in organic chemistry textbooks.

An imidazolium tetrasubstituted cationic porphyrin derivative (the free base and its Zn(II) complex) with five-membered heterocyclic groups in the meso-positions were synthesized using microwave irradiation, and the compounds obtained characterized by ¹H-NMR and mass spectrometry. We observed that under microwave irradiation the yield is similar to when the synthesis is performed under conventional heating, however, the time required to prepare the porphyrins decreases enormously. In order to investigate the electronic state of these compounds, we employed UV-Vis and fluorescence spectroscopy combined with quantum chemical calculations. The results reveal the presence, in both compounds, of a large number of electronic states involving the association between the Soret and a blue-shifted band. The Soret band in both compounds also shows a considerable solvent dependence. As for emission, these compounds present low quantum yield at room temperature and no solvent influence on the fluorescence spectra was observed.