Sensing by molecules is an intriguing phenomenon that can lead to next-generation intelligent materials. Stimuli-responsive organic molecules or molecular complexes, although less reported, can open up new avenues and opportunities in the area of artificial intelligence and memory. Extending the scope of organo-sulfonated Anils as stimuli-responsive materials, we report hydrated sulfonated Anil 1 and its nonstoichiometric bipyridyl complex 1.BPY. The formation of new materials is well supported and further substantiated through the solid-state structural elucidation of 1. Thermal and crystallographic studies validate the presence of two lattice water molecules each in 1 and 1.BPY. Structural studies also indicate that 1 undergoes intramolecular proton transfer between sulfonate and imine groups and exists in the zwitterionic form. Both 1 and 1.BPY respond to external stimuli: temperature, solvent polarity, and ammonia vapor. The thermochromism in both forms is reversible and interestingly triggered by the breathing of lattice water, a rare phenomenon in organic materials, supported by Fourier-transform infrared (FT-IR), thermal, and diffraction studies. Compared with the transition temperature of 130 °C for 1, 1.BPY undergoes a color change at 65 °C, and their heated forms, 1-Heat and 1.BPY-Heat, in turn, can be used as humidity sensors. Both solid forms exhibit solvatochromism and show emission turn-on in nonprotic polar solvents, dimethyl sulfoxide (DMSO) and dimethylformamide (DMF). The incipience of emission of 1.BPY in highly polar solvents DMSO (φ = 12%) and DMF (φ = 46%), and its absence in the solvents of relatively lower polarity such as H2O and MeOH as well as in solid forms, may be attributed to aggregation-induced quenching, which is supported by the solubility and DLS studies of 1 and 1.BPY in the solvents. Very interestingly and to the best of our knowledge, molecular solids 1 and 1.BPY represent the first examples of organic materials that exhibit emission turn-on on exposure to fumes of a base. When exposed to the fumes of ammonia, 1 and 1.BPY undergo a color change from maroon and orange to yellow, respectively, and the 1.NH 3 and 1.BPY-NH 3 forms show a striking green emission, which may be attributed to proton transfer within the molecular systems most likely involving the excited-state intermolecular proton-transfer (ESIPT) pathway. The overall analyses of the results indicate that the molecular complex 1.BPY is a better material vis-à-vis its response time (thermochromism), intensity (solvatochromic), and fatigue (vapochromism) and substantiate the scope of the crystal-engineering principles in designing next-generation smart materials.
A simple and straightforward approach for the synthesis of dihydropyrimidones via sequential Kornblum oxidation/Biginelli reaction has been developed. The protocol involves an in situ oxidation of benzyl halides which serve as a carbonyl equivalents followed by cyclocondensation with (thio) urea and ethylacetoacetate to furnish dihydropyrimidones under catalyst and base free conditions in a one-pot tandem manner under microwave irradiation. Further, the product purification using aqueous recrystallization avoids large quantities of volatile and a toxic organic solvent usually required for work-up and very less time required for this process makes the method environmental-and nature-friendly.
Crystal engineering is one green alternative to organic synthesis that can be used to manipulate molecular behavior promptly and economically. We report the preparation and characterization of the pharmaceutical organic salt (FLC-C) of fluconazole (FLC) and organosulfonate (NDSA-2H), based on the sulfonate-pyridinium supramolecular synthon. Structural studies validate the crystallization of the two-component stoichiometric crystal with two molecules of water in the triclinic P1̅ space group. The anticipated proton transfer between the crystal forms leads to ionic interactions, augmenting the organic salt’s thermal stability. Hirshfeld studies of FLC-C help to understand the role and significance of different types of intermolecular interactions responsible for crystal packing. The structural and theoretical studies indicate the absence of π–π interactions in FLC-C, which account for the incipience of solid-state emission in the product. The solubility studies establish augmented aqueous solubility of FLC-C over pristine FLC at physiological pH values of 2 and 7. Interestingly, in in vitro studies, FLC-C appears to serve as a potential alternative to FLC, displaying a wide spectrum of antifungal activity. FLC-C is active against several human pathogenic yeast strains, including the leading and emerging Candida strains (Candida albicans and Candida auris, respectively), at comparable and/or lower drug concentrations without showing any enhanced host cell toxicity. Interestingly, the pharmaceutical co-crystal also displays fluorescence properties inside the Candida cells.
Nanotechnology offers multiple benefits. Nanomedicine and nanodelivery systems are relatively new areas in nanotechnology. There are number of outstanding applications of the nanomedicine in diagnosing diseases, delivering drugs to its target location, and thus treating human diseases. Here materials in the nanoscale range are employed to serve as means of diagnostic tools and also to deliver precise medicines to specific targeted sites in a controlled manner. Also, metal nanoparticles offer great interest in modern chemistry and materials research because of their applications in diverse fields such as photochemistry, nanoelectronics, optics, and catalysis. Chemistry provides various nanostructured materials either synthetic or isolated from natural sources offers opportunities and challenges in drug delivery and their applications including biomedical imaging, biosensing, diagnostic, and therapy. Thymoquinone, a bioactive compound in Nigella sativa, after encapsulation in lipid nanocarrier, has been found to show six-fold increase in bioavailability in comparison to free thymoquinone. In addition to this, organic nanomaterials have recently become of great interest for photovoltaic applications also.
Nanotechnology as an emerging scientific field has enabled humanity to manipulate the environment at molecular and atomic level and has touched and even revolutionized all scientific fields due to its characteristic features. Medicine is one of the important fields that witnessed a nanotechnological revolution that guided medical scientists to device new approaches to study pathologies and explore genuine therapeutic tricks by exploring nanotechnology to operate on more specific molecular targets and to reduce the adverse risks and side effects imposed by the conventional approaches. By manipulating drugs and other materials, the fundamental properties and bioactivity of the materials can be altered at the nano scale. These tools can led to the different characteristics of drugs or agents such as a) modulation in solubility and blood pool retention time, b) controlled release over short or long durations, c) environmentally triggered controlled release or highly specific site-targeted deliver.
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