Hyaluronic Acid-Based Bioconjugate Systems, Scaffolds, and Their Therapeutic Potential.

In recent years, the development of hyaluronic acid or hyaluronan (HA) based scaffolds, medical devices, bioconjugate systems have expanded into a broad range of research and clinical applications. Research findings over the last two decades suggest that the abundance of HA in most mammalian tissues with distinctive biological roles and chemical simplicity for modifications have made it an attractive material with a rapidly growing global market. Besides its use as native forms, HA has received much interest on so-called "HA-bioconjugates" and "modified-HA systems". In this review, the importance of chemical modifications of HA, underlying rationale approaches, and various advancements of bioconjugate derivatives with their potential physicochemical, and pharmacological advantages are summarized. This review also highlights the current and emerging HA-based conjugates of small molecules, macromolecules, crosslinked systems, and surface coating strategies with their biological implications, including their potentials and key challenges discussed in detail.

Transition metal-free approach for late-stage benzylic C(sp3)-H etherifications and esterifications.

We report a transition metal-free approach for the regioselective functionalization of benzylic C(sp3)-H bonds using alcohols and carboxylic acids as the nucleophiles. This straightforward and general route has provided various benzylic ethers and esters, including twelve pharmaceutically relevant compounds.

Quercetin conjugated fluorescent nitrogen-doped carbon dots for targeted cancer therapy application.

In this work, we report the development of nitrogen-doped carbon dots (NDCDs) as a drug carrier using quercetin (QC) as a model drug for anti-cancer drug delivery application. NDCDs were prepared by a simple hydrothermal method using Luffa acutangula as a carbon source. The characterization of QC-NDCDs was done by UV-vis spectroscopy, fluorescence spectroscopy, zeta potential measurements, high-resolution transmission electron microscopy (HR-TEM), Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), and Raman spectroscopy. The as-synthesized NDCDs have a small particle size with hydroxyl and nitrogen-containing groups (pyridinic and amide groups), enhancing the fluorescence properties, and were obtained in a good quantum yield (14%). Furthermore, the in vitro alamarBlue® assay revealed that the NDCDs-QC conjugate was nontoxic to colon cancer cells. This NDCDs-QC conjugate is able to kill cancer cells in the NDCDs-QC form compared to free QC as confirmed by in vitro MTT assay results. Thus, the developed NDCDs conjugate can be used as a promising drug delivery and bio-imaging vehicle in cancer therapy.

Supramolecular self-assembly mediated aggregation-induced emission of fluorene-derived cyanostilbenes: multifunctional probes for live cell-imaging.

The first discovery of aggregation-induced emission (AIE), whereby luminogen aggregation plays a positive role in enhancing the light-emission efficiency, has piqued the interest of many researchers as it opens up a new avenue for the exploration of practically beneficial luminescent materials. Diverse AIE-active luminogens (or AIEgens) with tunable emission colours and very high quantum yields (up to unity) in the solid state have been extensively utilised in a broad range of fields including optoelectronics, energy and bioscience. In this article, we describe novel fluorene-based fluorogens that exhibit bright emission in the solid-state, mechanical stimuli-responsive optical properties and aggregation-induced emissive ability, and were able to modulate their donor and acceptor properties. The target compounds were synthesized by a Knoevenagel condensation followed by Suzuki cross-coupling reaction, which tends to result in good yields. The target cyanostilbenes (4a-4d) show different reversibly switched states with high contrast through morphology modulation and demonstrate solvatochromic, vapochromic, and AIE properties. These results strongly suggest that compound 4d has better properties than the other derivatives (4a-c) due to the presence of extended donor-acceptor ability. Moreover, density-functional theory (DFT) calculations strongly support the UV-Vis and fluorescence spectral studies. The formation of nano-flakes and cuboid-shaped nanocrystals was further confirmed by FE-SEM and AFM studies. The synthesized compound 4d displayed very bright emission in the solid state and in the aggregate state as compared with the other derivatives (4a-4c). These results might be due to the presence of high-color contrast, which is an advantage for elucidation and overcomes the challenges exhibited in live-cell imaging applications. Moreover, an MTT assay on live A549 cells incubated with the target compound (4d) showed very low cytotoxicity even at high concentrations.

A highly potential acyclic Schiff base fluorescent turn on sensor for Zn2+ ions and colorimetric chemosensor for Zn2+, Cu2+ and Co2+ ions and its applicability in live cell imaging.

Herein, we report two acyclic Schiff base receptors CS-1 and CS-2 capable of being selective fluorescent turn on for Zn2+ions and colorimetric chemosensor for Zn2+, Cu2+, and Co2+ ions by showing a colour change from colourless to yellow in 1:1 ratio of acetonitrile and HEPES buffer (1:1, v/v, pH 7.4) without the interference from other metal ions screened (Cd2+, Hg2+, Sn2+, Ni2+, Cr3+, Mn2+, Pb2+, Ba2+, Al3+, Ca2+, Mg2+, K+ and Na+). The fluorescence turn on enhancement towards Zn2+ ions is ascribed to PET blocking, suppression of -C=N- isomerisation, and the ESIPT process. The selectivity, competitivity and reversibility of the synthesised probes (CS-1 and CS-2) made them promising chemosensors for the detection of Zn2+, Cu2+, and Co2+ ions. The density functional theory (DFT) calculations have theoretically endorsed the colorimetric changes in the examined absorption spectra and binding mode of both CS-1/CS-2 with metals ions. In addition, 1H NMR titrations were also consistent with the recognition mechanism of Zn2+ ions with the CS-1/CS-2. Further, the Jobs plot analysis infers a 1:1 stoichiometric ratio for both evaluating receptors CS-1 and CS-2 with Zn2+, Cu2+ and Co2+ ions and was supported by DFT, NMR (only for Zn2+ ions), UV-Visible, and fluorescence spectroscopic studies. Moreover, the detection limits of CS-1 and CS-2 for Zn2+ ions were determined to be 7.69 and 5.35 nM, respectively, which is less compared to the detection limit of Cu2+, Co2+ ions as well as the limit approved by the United State Environmental Protection Agency (US EPA). The probes CS-1 and CS-2 found to show high fluorescence quantum yields at pH = 7 during the titration with Zn2+ as compared with other pHs (5-6 and 8-11). Gratifyingly, fluorescence microscopy imaging in HeLa cells revealed that the pair of receptors can be employed as an excellent fluorescent probe for the detection of Zn2+ions in living cells, indicating that this facile chemosensor has a huge potential in cellular imaging.

Novel Benzothiazole-Based Highly Selective Ratiometric Fluorescent Turn-On Sensors for Zn2+ and Colorimetric Chemosensors for Zn2+, Cu2+, and Ni2+ Ions.

Metal ions play a very important role in environmental as well as biological fields. The detection of specific metal ions at a minute level caught much attention, and hence, several probes are available in the literature. Even though benzothiazole-based molecules have a special place in the medicinal field, only very few chemosensors are reported based on this moiety. The current work describes the design and synthesis of the benzothiazole-based chemosensor for a highly selective and sensitive detection of biologically important metal ions such as Zn2+, Cu2+, and Ni2+. The sensing studies of compound-1 showed a ratiometric as well as colorimetric response toward Zn2+, Cu2+, and Ni2+ ions and color changes from colorless to yellow and is found to be insensitive toward various metal ions (Cd2+, Cr3+, Mn2+, Pb2+, Ba2+, Al3+, Ca2+, Fe2+, Fe3+, Mg2+, K+, and Na+). Further, compound-1 exhibited ratiometric as well as turn-on-enhanced fluorescence response toward Zn2+ ions and turn off response for Cu2+ and Ni2+ ions. The Job plots revealed that the binding stoichiometry of compound-1 and metal ions is 2:1. The detection limits were found to be 0.25 ppm for Zn2+, while it was 0.30 ppm and 0.34 ppm for Ni2+ and Cu2+, respectively. In addition, density functional theory results strongly support the colorimetric response of metals, and the reversibility studies suggested that compound-1 can be used as a powerful chemosensor for the detection of Zn2+, Cu2+, and Ni2+ ions. The bioimaging data illustrated that compound-1 is a very effective ratiometric sensor for Zn2+ ions in live cells.

A Tunable Palette of Molecular Rotors Allows Multicolor, Ratiometric Fluorescence Imaging and Direct Mapping of Mitochondrial Heterogeneity.

Environment-sensitive molecular probes offer the potential for a comprehensive mapping of the complex cellular milieu. We present here a radically new strategy of multiplexing highly sensitive, spectrally tuned fluorescent dyes for sensing cellular microenvironment. To achieve this multicolor, ratiometric cellular imaging, we first developed a series of highly sensitive, tunable molecular rotors for mitochondrial imaging, with emission wavelengths spanning the visible spectrum. These fluorogenic merocyanine dyes are all sensitive to solvent viscosity despite distinctive photophysical features. Our results show that merocyanine dyes can show a rotor-like behavior despite significant changes to the conventional donor-acceptor or push-pull scaffolds, thereby revealing conserved features of rotor dye chemistry. Developing closely related but spectrally separated dyes that have distinct response functions allows us to do ″two-color, two-dye″ imaging of the mitochondrial microenvironment. Our results with multidye, combinatorial imaging provide a direct visualization of the intrinsic heterogeneity of the mitochondrial microenvironment. The overall mitochondrial microenvironment (including contributions from local membrane order) as reported through two-color fluorescence ″ratio″ changes of multiplexed rotor dyes shows dynamic heterogeneity with distinct spatiotemporal signatures that evolve over time and respond to chemical perturbations. Our results offer a powerful illustration of how multiplexed dye imaging allows the quantitative imaging of mitochondrial membrane order and cellular microenvironment.

Turn-on Fluorescence Chemosensor for Zn2+ Ion Using Salicylate Based Azo Derivatives and their Application in Cell-Bioimaging.

The synthesis and optical studies of salicylate based azo derivatives (DPSAD and IPSAD) are reported. The receptors act as a versatile fluorogenic chemosensor for Zn2+ causing a selective enhancement of fluorescence over other competing cations. The complex formed between receptors and Zn2+ are identified on the basis of absorption and fluorescence titration and further confirmed by ESI-MS. DFT/TD-DFT calculations support the observed optical changes happens only upon complexation with Zn2+ ion. Moreover, receptors are further applied to intracellular sensing and imaging studies. Graphical Abstract Salicylate based azo derivatives (DPSAD and IPSAD) as fluorogenic chemosensor for the detection of Zn2+ ion.

Coumarin based hydrazone as an ICT-based fluorescence chemosensor for the detection of Cu2+ ions and the application in HeLa cells.

We have constructed a new coumarin based fluorescence probe BENZPYR with ICT character through condensation of N, N-diethylamino-3-acetyl coumarin with 2-hydrazinobenzothiazole. The absorbance and fluorescence spectral characteristics of BENZPYR revealed that the chemosensor can specifically detect for Cu2+ ions over other different metal ions and the lowest limit of detection was found in nano molar range. The turn off sensor of BENZPYR is related to chelation enhanced quenching (CHEQ) and intramolecular charge transfer (ICT) processes were serve as excellent fluorescent detection of Cu2+ ions in DMF medium. Fluorescence microscopy experiments revealed that probe BENZPYR may have application as a fluorophore to detect the Cu2+ in living cells. The simulated DFT analysis of electronic and structural properties and also UV-vis absorption spectra are in well accordance with the experimental UV-vis absorption spectra.

Bioresponsive drug delivery systems in intestinal inflammation: State-of-the-art and future perspectives.

Oral colon-specific delivery systems emerged as the main therapeutic cargos by making a significant impact in the field of modern medicine for local drug delivery in intestinal inflammation. The site-specific delivery of therapeutics (aminosalicylates, glucocorticoids, biologics) to the ulcerative mucus tissue can provide prominent advantages in mucosal healing (MH). Attaining gut mucosal healing and anti-fibrosis are main treatment outcomes in inflammatory bowel disease (IBD). The pharmaceutical strategies that are commonly used to achieve a colon-specific drug delivery system include time, pH-dependent polymer coating, prodrug, colonic microbiota-activated delivery systems and a combination of these approaches. Amongst the different approaches reported, the use of biodegradable polysaccharide coated systems holds great promise in delivering drugs to the ulcerative regions. The present review focuses on major physiological gastro-intestinal tract challenges involved in altering the pharmacokinetics of delivery systems, pathophysiology of MH and fibrosis, reported drug-polysaccharide cargos and focusing on conventional to advanced disease responsive delivery strategies, highlighting their limitations and future perspectives in intestinal inflammation therapy.

Anthracene-Based Highly Selective and Sensitive Fluorescent "Turn-on" Chemodosimeter for Hg2.

Three π-extended anthracene-bearing thioacetals (1-3) have been synthesized, and their fluorescence "turn-on" responses to Hg2+ ions are studied. The chemodosimetric fluorescence-sensing behavior and their resulting hydrolysis via a desulfurization reaction mechanism leads to the formation of highly fluorescent respective aldehyde substitutions. Furthermore, this mechanism was supported by increase in the quantum yields of their resulting aldehydes and is correlated to their molecular substitution. The chemosensors 1-3 have exhibited to be promising receptors toward Hg2+ ions in the presence of other competitive metal ions. Moreover, the detection limits of 1-3 have been found to be in the nanomolar range (94, 59, and 235, respectively). Fluorescence microscopic imaging studies show that 1-2 have been found to be effective for fluorescence imaging in live cells. Moreover, compounds 1-3 act as potential candidates for the detection of Hg2+ in environmental and biological systems as well as real samples.

Pineapple Peel-Derived Carbon Dots: Applications as Sensor, Molecular Keypad Lock, and Memory Device.

Herein, the fluorescent carbon dots (CDs) with blue emission were prepared by hydrothermal treatment using pineapple peel as a source of carbon. The as-prepared CDs exhibited turn-Off fluorescence behavior toward Hg2+ and subsequent turn-On behavior for l-cysteine along with enhanced biocompatibility and negligible cytotoxicity for cell imaging. The practical applicability of carbon dots was used for the quantification of Hg2+ in water. On the basis of the spectral characteristic changes, we have designed individual elementary logic operations such as NOT and IMP gates, by utilizing CD as probe and Hg2+ and l-Cys as chemical inputs. We have also demonstrated the utility of this system in electronic security devices and as memory element, with the idea of the switching.

Phenothiazine Based Donor-Acceptor Compounds with Solid-State Emission in the Yellow to NIR Region and Their Highly Selective and Sensitive Detection of Cyanide Ion in ppb Level.

Four new novel donor-acceptor (A-π-D-A, A-D-π-D-A) compounds (1 a, 1 b, 2 a and 2 b) based on ethylenedioxythiophene (EDOT) and phenothiazine (PTz) have been rationally designed and synthesized towards solid state emission ranging from yellow to near infrared (NIR). The compounds 1 b and 2 b, in thin film form, showed an emission maximum at 713 nm and 696 nm, respectively, with the corresponding absolute solid-state quantum yield of 3.3 % and 9.0 %. The fluorophores showed high emission in the doped state as well when dispersed in polystyrene (PS) matrix with emission maximum ranging from 536 nm to 648 nm with quantum yield in the range 12.4 %-64.4 %. The presence of dicyanovinyl (DCV) group in both the fluorophores was exploited towards cyanide sensing in DMSO leading to turn-on fluorescence emission with high selectivity and sensitivity for cyanide ion with a detection limit of as low as 0.32 µm (8 ppb) for 1 b and 0.57 µm (14 ppb) for 2 b. DFT and TTDFT calculations suggested that the addition of cyanide ion prevented the intramolecular charge transfer (ICT) from the donor (PTz or EDOT) to acceptor (DCV), thereby turning the fluorescence "On". Using fluorescent spectral and color switching, we have explored logic gates with single and two input signal amplification by applying chemical and light inputs in the form of CN- ion and UV.

Selective and sensitive fluorescent sensor for Pd2+ using coumarin 460 for real-time and biological applications.

The efficient fluorescent property of coumarin 460 (C460) is utilized to sense the Pd2+ selectively and sensitively. Fabrication of a sensor strip using commercial adhesive tape is achieved and the detection of Pd2+ is attempted using a handy UV torch. The naked eye detection in solution state using UV chamber is also attempted. The calculated high binding constant values support the strong stable complex formation of Pd2+ with C460. The detection limit up to 2.5 × 10-7 M is achieved using fluorescence spectrometer, which is considerably low from the WHO's recommendation. The response of coumarin 460 with various cations also studied. The quenching is further studied by the lifetime measurements. The binding mechanism is clearly explained by the 1H NMR titration. The sensing mechanism is established as ICT. C460 strip's Pd2+ quenching detection is further confirmed by solid-state PL study. The in-vitro response of Pd2+ in a living cell is also studied using fluorescent imaging studies by means of HeLa cell lines and this probe is very compatible with biological environments. It could be applicable to sense trace amounts of a Pd2+ ion from various industries. Compared with previous reports, this one is very cheap, sensitive, selective and suitable for biological systems.

A theranostic nanocomposite system based on iron oxide-drug nanocages for targeted magnetic field responsive chemotherapy.

In this work, a theranostic nanocage system was developed for the targeted delivery of the anti-cancer agents camptothecin (CPT) and luotonin A (LuA). The core of the nanocage system (Fe3O4@OA-AD-SP NCs) was formed by biogenically synthesized Fe3O4 nanoparticles (NPs) decorated with a model anti-cancer drug (AD) and biosurfactant saponin (SP). The Fe3O4@OA-AD-SP NCs showed a high lipophilic AD loading efficiency (>80%) and a controlled pH-responsive drug release in stimulated cancerous cells in pH 6.4 media buffer. In addition, Fe3O4@OA-AD-SP NCs exhibited better serum protein binding efficacy at physiological pH values (7.4), furthering the important role of SP surface decoration. Particularly, these NCs showed better chemotherapeutic efficacy when examined in MCF-7 and HeLa cancer cell lines with a specific targeting capacity. Therefore, this study provides a new nano platform based on magnetic targeting and pH responsive lipophilic anticancer drug delivery to the cancer site.

Rhodamine Diaminomaleonitrile Conjugate as a Novel Colorimetric Fluorescent Sensor for Recognition of Cd2+ Ion.

Rhodamine diaminomaleonitrile linked probe (RD-1) shows highly sensitive colorimetric and selective turn-on fluorescent response to Cd2+ over other metal ions. The fluorescence intensity and absorbance of the probe RD-1 showed a good linearity, with very low detection limits of 18.5 nm. The probe RD-1 was preliminarily applied to the determination of Cd2+ ion in water samples from river and tap water with satisfying results. The live cell image confocal microscopy, HeLa cell demonstrated that RD-1 had low cytotoxicity with good membrane permeable property is successfully applied to fluorescence microscopic imaging for the detection of Cd2+ ions.

Biomimetic Lipid-Based Nanosystems for Enhanced Dermal Delivery of Drugs and Bioactive Agents.

Clinical utility of conventional oral therapies is limited by their inability to deliver therapeutic molecules at the local or targeted site, causing a variety of side effects. Transdermal delivery has made a significant contribution in the management of skin diseases with enhanced therapeutic activities over the past two decades. In the modern era, various biomimetic and biocompatible polymer-lipid hybrid systems have been used to augment the transdermal delivery of therapeutics such as dermal patches, topical gels, iontophoresis, electroporation, sonophoresis, thermal ablation, microneedles, cavitational ultrasound, and nano or microlipid vesicular systems. Nevertheless, the stratum corneum still represents the main barrier to the delivery of vesicles into the skin. Lipid based formulations applied to the skin are at the center of attention and are anticipated to be increasingly functional as the skin offers many advantages for the direction of such systems. Accordingly, this review provides an overview of the development of conventional to advanced biomimetic lipid vesicles for skin delivery of a variety of therapeutics, with special emphasis on recent developments in this field including the development of transferosomes, niosomes, aquasomes, cubosomes, and other new generation lipoidal carriers.

Aminobenzohydrazide based colorimetric and 'turn-on' fluorescence chemosensor for selective recognition of fluoride.

Chemosensors based on aminobenzohydrazide Schiff bases bearing pyrene/anthracene as fluorophores have been designed and synthesized for F(-) ion recognition. The addition of fluoride ions to the receptors causes a dramatically observable colour change from pale yellow to brown/red. (1)H NMR studies confirm that the F(-) ion facilitates its recognition by forming hydrogen bond with hydrogens of amide and amine groups. Moreover these sensors have also been successfully applied to detection of fluoride ion in commercial tooth paste solution.

Aminoquinoline based highly sensitive fluorescent sensor for lead(II) and aluminum(III) and its application in live cell imaging.

We have synthesized a new probe 5-((anthracen-9-ylmethylene) amino)quinolin-10-ol (ANQ) based on anthracene platform. The probe was tested for its sensing behavior toward heavy metal ions Hg(2+), Pb(2+), light metal Al(3+) ion, alkali, alkaline earth, and transition metal ions by UV-visible and fluorescent techniques in ACN/H2O mixture buffered with HEPES (pH 7.4). It shows high selectivity toward sensing Pb(2+)/Al(3+) metal ions. Importantly, 10-fold and 5- fold fluorescence enhancement at 429 nm was observed for probe upon complexation with Pb(2+) and Al(3+) ions, respectively. This fluorescence enhancement is attributable to the prevention of photoinduced electron transfer. The photonic studies indicate that the probe can be adopted as a sensitive fluorescent chemosensor for Pb(2+) and Al(3+) ions.