SIMPLE AND HIGHLY SELECTIVE DIRECT STABILITY INDICATING ULTRAVIOLET AND INDIRECT VISIBLE SPECTROPHOTOMETRIC METHODS FOR DETERMINATION OF ENROFLOXACIN IN PHARMACEUTICALS

Three simple, economic, selective and accurate and precise spectrophotometric methods are developed for determination of enrofloxacin (EFX) in pharmaceuticals. Method A is based on the measurement of absorbance of EFX in 0.1M HOAc at 315 nm. The ketoxime formation reaction has been employed in method B, in which the absorbance measurement of EFX oxime product at 275 nm is described. The third method (Method C) is indirect one and is based on the oxidation of EFX by cerium(IV), reaction of unreacted cerium(IV) with p-toludine (p-TD) and measurement of coloured solution at 540 nm. The Beer’s law is obeyed in the concentration ranges of 1.2–24, 1–8, and 1–20 μg/mL EFX in methods A, B, and C, respectively, with the corresponding molar extinction coefficients of 1.52×104, 3.86×104, and 6.6×103 L/mol/cm. The regression coefficients of calibration lines are 0.9996, 0.9913, and –0.9965, in methods A, B, and C, respectively. The limits of detection (LOD) and quantification (LOQ) have also been reported for each method. The methods have been validated to check accuracy, precision, robustness and ruggedness. The application of the methods proposed to determine EFX in tablets has been described and the results have been compared with a standard method. The results of validation and application have been found to be with excellent agreement. The standard addition procedure has been adopted in recovery experiments to further ascertain the accuracy of the methods and the results of the experiments are well satisfied. The stability indicating ability of Method A has been studied by subjecting EFX to acid and alkaline hydrolysis, oxidative, thermal and UV degradation followed by measurement of absorbance of resultant EFX solutions at 315 nm. The results of degradation study indicated unsusceptible nature of EFX to any of the stress conditions.

Using photocaging for fast time-resolved structural biology studies

Careful selection of photocaging approaches is critical to achieve fast and well synchronized reaction initiation and perform successful time-resolved structural biology experiments. This review summarizes the best characterized and most relevant photocaging groups previously described in the literature. It also provides a walkthrough of the essential factors to consider in designing a suitable photocaged molecule to address specific biological questions, focusing on photocaging groups with well characterized spectroscopic properties. The relationships between decay rates (k in s−1), quantum yields (φ) and molar extinction coefficients (ɛmax in M −1 cm−1) are highlighted for different groups. The effects of the nature of the photocaged group on these properties is also discussed. Four main photocaging scaffolds are presented in detail, o-nitrobenzyls, p-hydroxyphenyls, coumarinyls and nitrodibenzofuranyls, along with three examples of the use of this technology. Furthermore, a subset of specialty photocages are highlighted: photoacids, molecular photoswitches and metal-containing photocages. These extend the range of photocaging approaches by, for example, controlling pH or generating conformationally locked molecules.

Determination of New IR and UV/VIS Spectroscopic Parameters of the C84-D2:22 Isomer for Its Quantitative Assessment, Identification and Possible Applications

The stable isomers of the higher fullerenes C76-D2 and C84-D2:22, as well as fullerenes C60 and C70 were isolated from carbon soot by the new and improved extraction and chromatographic methods and processes. Characterizations of the C84-D2:22 isomer in this study were performed by infrared and electronic absorption spectroscopy. All of the experimentally observed IR and UV/VIS bands were in excellent agreement with the semi-empirical, DFT and TB potential theoretical calculations for this molecule. The molar extinction coefficients and the integrated molar extinction coefficients of the observed larger number of completely separated infrared absorption maxima and shoulders of fullerene C84-D2:22, as well as of its main convoluted maxima, in different and new relevant entire integration ranges, including neighboring, and all surrounding absorption shoulders were determined and their relative intensities compared. In addition, the molar absorptivity of the electronic absorption bands of this carbon cluster was found. The new IR and UV/VIS spectroscopic parameters that are significant for the quantitative determination, identification and numerous possible applications of C84-D2:22 are obtained and their changes compared to C76-D2 observed. Isolated and characterized C84-D2:22, as well as other fullerenes from this research can be used in electronic, optical, chemical and biomedical devices, superconductors, semiconductors, batteries, catalysts, polymers, sensors, solar cells, nanophotonic lenses with better optical transmission, refraction and wettability, diagnostic and therapeutic pharmaceutical substances, such as those against diabetes, cancer, neurodegenerative disorders, free radical scavenging, radio nuclear, antibacterial and antiviral agents that can inhibit HIV 1, HSV, COVID-19, influenza, malaria and so forth.

Solid-Phase Synthesis of Asymmetric Cyanine Dyes

: Cyanine dyes (CD) are a functional class of organic molecules used in several applications ranging from photography to bioimaging. CDs most well-known features reside on high molar extinction coefficients up to 105 L mol-1cm-1 and on the absorption spectra, ranging from 500 to 1000 nm, which can be fine-tuned both by extending the length of the central methylene bridge or by modulating the terminal heterocycles. In the last decades, new synthetic methodologies, namely microwave-assisted and the solid-phase procedure, have been developed to overcome the limitation of the classical synthetic protocols. While the microwave approach usually reduces the exposure time of the reagents and products to thermal degradation, the solid-phase methodology allows easier synthetic protocols, which are translated into higher yields and simpler product purification. In the present review, a comprehensive analysis of the solid-phase methods for the synthesis of asymmetrical CDs is discussed, with a critical evaluation of the difference among the currently available solid-state approaches.

Smart Nanomaterials for Biomedical Applications—A Review

Recent advances in nanotechnology have forced the obtaining of new materials with multiple functionalities. Due to their reduced dimensions, nanomaterials exhibit outstanding physio-chemical functionalities: increased absorption and reactivity, higher surface area, molar extinction coefficients, tunable plasmonic properties, quantum effects, and magnetic and photo properties. However, in the biomedical field, it is still difficult to use tools made of nanomaterials for better therapeutics due to their limitations (including non-biocompatible, poor photostabilities, low targeting capacity, rapid renal clearance, side effects on other organs, insufficient cellular uptake, and small blood retention), so other types with controlled abilities must be developed, called “smart” nanomaterials. In this context, the modern scientific community developed a kind of nanomaterial which undergoes large reversible changes in its physical, chemical, or biological properties as a consequence of small environmental variations. This systematic mini-review is intended to provide an overview of the newest research on nanosized materials responding to various stimuli, including their up-to-date application in the biomedical field.

Determination of the main spectral characteristics and conditions for the extraction of the cationic dye pyronine G with higher carboxylic acids

The selection of the suitable cationic dye is one of the key steps in extraction-photometric methods for the quantitative determination of hydrophobic anions, in particular, higher carboxylic acids. No less important is the reasonable selection of the required polar phase pH for extraction systems. It is because higher carboxylic acids are well extracted by non-polar phase in molecular form. It was found that, in contrast to other cationic dyes, pyronine G, which is stable in high alkaline pH values, is well extracted in form of ionic associates with higher carboxylic acids. The optimal composition of organic phase (5% solution by volume of n-octanol-1 in heptane) was found for quantitative analysis of higher carboxylic acids in the form of associates with pyronine G, at which the blank sample has a rather low optical density. Molar extinction coefficient of dyes for quantitative photometric analysis is an equally important characteristic of their optical properties. These properties depend on not only the nature of the substance itself, but also on the solvent. The molar extinction coefficients for organic (5.3·104 l·mol-1·cm-1) and aqueous phases (3.6·104 l·mol-1·cm-1) were determined for the above-found optimal extraction system for pyronine G with palmitic acid (water – 5% solution by volume of n-octanol-1 in heptane). They are 1.5-2 times higher than the molar extinction coefficients of safranin T and other cationic dyes used in the photometric analysis of hydrophobic acids in high alkaline pH values. Thus, the cationic dye pyronine G use for quantitative extraction-photometric analysis of higher carboxylic acids seems to be very promising.

ZnSe Quantum Dots: Determination of Molar Extinction Coefficient for UV to Blue Emitters

<p>The focus on heavy metal-free visible emitters in optoelectronic devices has increased interest in ZnSe semiconductor quantum dots (QDs) over the past decade. Empirical fit equations correlating the lowest energy electron transition to their size and molar extinction coefficients (ε) are often used to determine the concentration of suspensions containing QDs. This is essential to the design and successful synthesis of complex semiconductor nanoparticles including core/shell and dot-in-rod heterostructures as well as consistent device fabrication. While these equations are known and heavily used for CdSe, CdTe, CdS, PbS, etc., they are not well established for ZnSe nanocrystals; the only two reports of ε in the literature differ by over an order of magnitude. In this study, a series of ZnSe QDs with diameters ranging from 2 to 6 nm were characterized with small angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and UV-Vis spectroscopy. SAXS-based size analysis enabled practical inclusion of small particles in the evaluation. Elemental analysis with microwave plasma atomic emission spectroscopy (MP-AES) yields a non-stoichiometric Zn:Se ratio consistent with zinc-terminated spherical ZnSe QDs. Using these combined results, molar extinction coefficients for each QD sample were calculated. Empirical fit equations correlating QD size with its lowest energy electron transition (i.e., 1S peak position) and molar extinction coefficients for both 1S peak and high energy wavelengths are reported. These results will enable the consistent and reliable use of ZnSe core particles in complex heterostructures and devices.</p>

ZnSe Quantum Dots: Determination of Molar Extinction Coefficient for UV to Blue Emitters

<p>The focus on heavy metal-free visible emitters in optoelectronic devices has increased interest in ZnSe semiconductor quantum dots (QDs) over the past decade. Empirical fit equations correlating the lowest energy electron transition to their size and molar extinction coefficients (ε) are often used to determine the concentration of suspensions containing QDs. This is essential to the design and successful synthesis of complex semiconductor nanoparticles including core/shell and dot-in-rod heterostructures as well as consistent device fabrication. While these equations are known and heavily used for CdSe, CdTe, CdS, PbS, etc., they are not well established for ZnSe nanocrystals; the only two reports of ε in the literature differ by over an order of magnitude. In this study, a series of ZnSe QDs with diameters ranging from 2 to 6 nm were characterized with small angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and UV-Vis spectroscopy. SAXS-based size analysis enabled practical inclusion of small particles in the evaluation. Elemental analysis with microwave plasma atomic emission spectroscopy (MP-AES) yields a non-stoichiometric Zn:Se ratio consistent with zinc-terminated spherical ZnSe QDs. Using these combined results, molar extinction coefficients for each QD sample were calculated. Empirical fit equations correlating QD size with its lowest energy electron transition (i.e., 1S peak position) and molar extinction coefficients for both 1S peak and high energy wavelengths are reported. These results will enable the consistent and reliable use of ZnSe core particles in complex heterostructures and devices.</p>