Colorimetric Chemosensor and Turn on Fluorescence Probe for pH Monitoring Based on Xanthene Dye Derivatives and its Bioimaging of Living Escherichia coli Bacteria

Facile and highly precise pH-value estimation using common pH paper based on machine learning techniques and supported mobile devices

Numerous scientific, health care, and industrial applications are showing increasing interest in developing optical pH sensors with low-cost, high precision that cover a wide pH range. Although serious efforts, the development of high accuracy and cost-effectiveness, remains challenging. In this perspective, we present the implementation of the machine learning technique on the common pH paper for precise pH-value estimation. Further, we develop a simple, flexible, and free precise mobile application based on a machine learning algorithm to predict the accurate pH value of a solution using an available commercial pH paper. The common light conditions were studied under different light intensities of 350, 200, and 20 Lux. The models were trained using 2689 experimental values without a special instrument control. The pH range of 1: 14 is covered by an interval of ~ 0.1 pH value. The results show a significant relationship between pH values and both the red color and green color, in contrast to the poor correlation by the blue color. The K Neighbors Regressor model improves linearity and shows a significant coefficient of determination of 0.995 combined with the lowest errors. The free, publicly accessible online and mobile application was developed and enables the highly precise estimation of the pH value as a function of the RGB color code of typical pH paper. Our findings could replace higher expensive pH instruments using handheld pH detection, and an intelligent smartphone system for everyone, even the chef in the kitchen, without the need for additional costly and time-consuming experimental work.

Recent Advancements in Colorimetric and Fluorescent pH Chemosensors: From Design Principles to Applications

Due to the immense biological significance of pH in diverse living systems, the design, synthesis, and development of pH chemosensors for pH monitoring has been a very active research field in recent times. In this review, we summarize the designing strategies, sensing mechanisms, biological and environmental applications of fluorogenic and chromogenic pH chemosensors of the last three years (2018-2020). We categorized these pH probes into seven types based on their applications, including 1) Cancer cell discriminating pH probes; 2) Lysosome targetable pH probes; 3) Mitochondria targetable pH probes; 4) Golgi body targetable pH probes; 5) Endoplasmic reticulum targetable pH probes; 6) pH probes used in nonspecific cell imaging; and 7) pH probes without cell imaging. All these different categories exhibit diverse applications of pH probes in biological and environmental fields.

Evolution of Acridines and Xanthenes as a Core Structure for the Development of Antileishmanial Agents

Nowadays, leishmaniasis constitutes a public health issue in more than 88 countries, affecting mainly people from the tropics, subtropics, and the Mediterranean area. Every year, the prevalence of this infectious disease increases, with the appearance of 1.5–2 million new cases of cutaneous leishmaniasis and 500,000 cases of visceral leishmaniasis, endangering approximately 350 million people worldwide. Therefore, the absence of a vaccine or effective treatment makes the discovery and development of new antileishmanial therapies one of the focuses for the scientific community that, in association with WHO, hopes to eradicate this disease shortly. This paper is intended to highlight the relevance of nitrogen- and oxygen-containing tricyclic heterocycles, particularly acridine and xanthene derivatives, for the development of treatments against leishmaniasis. Thus, in this review, a thorough compilation of the most promising antileishmanial acridine and xanthene derivatives is performed from both natural and synthetic origins. Additionally, some structure–activity relationship studies are also depicted and discussed to provide insight into the optimal structural features responsible for these compounds’ antileishmanial activity.

Comparison of two diphenyl polyenes as acid-sensitive additives during the biodegradation of a thermoset polyester polyurethane coating

AIMS

Biochemical hydrolysis and chemical catalysis are involved in the successful biodegradation of polymers. In order to evaluate the potential separation between biochemical and chemical catalysis during the biodegradation process, we report the use of two diphenylpolyenes (DPPs), all trans-1,4-diphenylbutadiene (DPB) and all trans-1,6-diphenylhexatriene (DPH), as potential acid-sensitive indicators in polymers.

METHODS AND RESULTS

1,4-Diphenylbutadiene and DPH (0.1% w/w) were melt-cast successfully with poly(ethylene succinate) hexamethylene (PES-HM) polyurethane (thermoset polyester polyurethane) coatings above 80℃. When these two DPP/PES-HM coatings were exposed to a concentrated supernatant with significant esterase activity resulting from the growth of a recently isolated and identified strain of Tremellomycetes yeast (Naganishia albida 5307AI), the DPB coatings exhibited a measurable and reproducible localized decrease in the blue fluorescence emission in regions below where hydrolytic biodegradation was initiated in contrast with DPH blended coatings. The fluorescence changes observed in the biodegraded DPB coating were similar to exposing them to concentrated acids and not bases.

CONCLUSIONS

Our experiments resulted in (1) a method to blend DPP additives into thermoset coatings, (2) the first report of the biodegradation of polyester polyurethane coating by N. albida, and (3) demonstration that hydrolytic supernatants from this strain generate acidic region within degrading polyester coatings using DPB as the indicator.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our experiments confirm that N. albida is an active polyester degrader and that DPB is a promising acid sensitive polymer coating additive.

Xanthene-based Fluorescence Turn-on Probe for Highly Acidic pH Range in Aqueous Solution

A xanthene-based probe, Xanth-NPr, is developed as a molecular system that exhibits sensitivity for the highly acidic environments with fluorescence turn-on behavior. Xanth-NPr is designed on the principle of photoinduced electron transfer (PET), which controls the fluorescence profile of the probe. The structure of Xanth-NPr contains the dipropylaniline group as a PET promoting unit. Xanth-NPr exhibited quenched fluorescence as long as it is present in neutral or moderately acidic conditions. However, in the highly acidic pH range, it displayed a strong red-colored fluorescence at 592 nm as the protonation of dipropylaniline moiety inhibits the PET process. A model probe Xanth-M without any PET promoting unit was also synthesized. The model probe along with theoretical calculations was employed to explain the role of the PET process in regulating the fluorescence behavior of Xanth-NPr. Xanth-NPr showed linear fluorescence response as a function of pH in the range of 1 to 4.1 with the pKa value of 2.72. Likewise, its fluorescence profile is not altered by the presence of biologically relevant cations.