The interplay of chirality and restricted rotation: stabilisation of chiral, frustrated mesophases over a wide thermal range.

Introducing restricted rotation in a molecule, often achieved through the incorporation of double or triple bonds, constitutes a crucial approach to induce a frustrated mesophase. Furthermore, the inclusion of a chiral moiety, such as cholesterol, serves to enhance the stabilization of chiral frustrated mesophases. This study presents the synthesis and characterization of novel optically active dimers incorporating cholesterol and phenyl 3-phenylpropiolate segments interconnected by an ω-oxyalkanoyloxy spacer with varying lengths and parity. Comprehensive characterization using POM, DSC, and X-ray diffraction techniques reveals that these mesogens exhibit enantiotropic liquid crystal (LC) phases. Due to the restricted rotation caused by the triple bonded system, these dimers stabilized the frustrated chiral mesophase TGBC* over a wide temperature range. The identified phases include BP-I/II, N*, and SmA, with odd-membered dimers commonly displaying N* and SmA phases and one member additionally exhibiting BP-I/II. Even-membered dimers exhibit N* and TGBC* phases, with the latter spanning an impressive thermal range of 37 °C to 84 °C. Notably, the thermal range of the TGBC* phase widens with an increase in the terminal tail length. Across the series, clearing temperatures generally decrease with the elongation of the terminal tail, and even-membered dimers consistently exhibit higher clearing temperatures than their odd-membered counterparts, illustrating the spacer's parity-dependent odd-even effect on the dimers' phase transition behavior.

A Situational Analysis of the Impact of the COVID-19 Pandemic on Digital Health Research Initiatives in South Asia.

The objective of this paper was to evaluate and compare the quantity and sustainability of digital health initiatives in the South Asia region before and during the COVID-19 pandemic. The study used a two-step methodology of (a) descriptive analysis of digital health research articles published from 2016 to 2021 from South Asia in terms of stratification of research articles based on diseases and conditions they were developed, geography, and tasks wherein the initiative was applied and (b) a simple and replicable tool developed by authors to assess the sustainability of digital health initiatives using experimental or observational study designs. The results of the descriptive analysis highlight the following: (a) there was a 40% increase in the number of studies reported in 2020 when compared to 2019; (b) the three most common areas wherein substantive digital health research has been focused are health systems strengthening, ophthalmic disorders, and COVID-19; and (c) remote consultation, health information delivery, and clinical decision support systems are the top three commonly developed tools. We developed and estimated the inter-rater operability of the sustainability assessment tool ascertained with a Kappa value of 0.806 (±0.088). We conclude that the COVID-19 pandemic has had a positive impact on digital health research with an improvement in the number of digital health initiatives and an improvement in the sustainability score of studies published during the COVID-19 pandemic.

Assessment of the effect of frequency of low-level laser therapy exposure at different intervals on orthodontic tooth movement - A systematic review and meta-analysis.

OBJECTIVE: To assess the optimal intervals of exposure of low-level LASER therapy (LLLT) that would optimally accelerate orthodontic tooth movement. Second objective was to quantitatively analyze the difference in the time taken for alignment of anterior teeth with and without the application of LASER. MATERIALS AND METHODS: PROSPERO database registry was done (CRD42020196472) and review was conducted based on PRISMA guidelines. A search was systematically conducted in five major electronic databases without restrictions up to June 2020 along with a hand search of selected journals. The quality of evidence was assessed using the Grading of Recommended Assessment, Development, and Evaluation tool, risk of bias using Cochrane risk of bias tool, and meta-analysis was carried out using RevMan 5.4 software. RESULTS: Ten randomized controlled trials which met the inclusion criteria were evaluated and tabulated. A random-effects meta-analysis demonstrated that there is a statistically significant increase in the orthodontic tooth movement when patients were exposed to minimum of four intervals of LLLT in the first month, at P =0.03 by a standard mean difference of 0.46 mm with an overall heterogeneity of I2 = 0% at 95% confidence interval. There was a statistically highly significant reduction in the number of days taken for alignment of anterior teeth with the application of LASER (P <.00001). CONCLUSION: Application of LLLT for minimum of four irradiations in the first month has yielded better results in accelerating orthodontic tooth movement than application of LLLT once a month.

Phase behaviour and adsorption of deoxyribonucleic acid onto an azobenzene liquid crystalline ligand at the interfaces.

Azobenzene liquid crystalline (ALC) ligand contains a cholesteryl group linked to an azobenzene moiety through a carbonyl dioxy spacer (C7) and terminated with an amine group as a polar head. The phase behaviour of the C7 ALC ligand at the air-water (A-W) interface is investigated employing surface manometry. The surface pressure-area per molecule isotherm shows that C7 ALC ligand exhibit two different phases following the phase sequence viz., liquid expanded (LE1 and LE2) and then collapse to three-dimensional crystallites. Further, our investigations under different pH conditions and in the presence of DNA reveal the following. Compared to the bulk, the acid dissociation constant (pKa) of an individual amine reduces to 5 at the interfaces. For pH (3.5) < pKa, the protonation of amine groups of C7 ALC ligand facilitates the condensation of the film and enhances the stability. For pH values > pKa, the phase behaviour of the ligand remains the same due to the partial dissociation of the amine groups. The presence of DNA in the sub-phase result in the expansion of isotherm to the higher area per molecule and the compressional modulus extracted reveals the phase sequence; liquid expanded, liquid condensed, followed by a collapse. Further, the kinetics of adsorption of DNA to the amine groups of the ligand is investigated, suggesting the interactions are influenced by surface pressure corresponding to different phases and pH of the sub-phase. Brewster angle microscope studies are carried out at different surface densities of the ligand as well as in the presence of DNA also supports this inference. Atomic force microscope is employed to acquire the surface topography and height profile of C7 ALC ligand (1 layer) after transferring on onto a silicon substrate using Langmuir Blodgett deposition. The difference in the surface topography and thickness of the film indicates the adsorption of DNA onto the amine groups of the ligand. The characteristic UV-visible absorption bands of the ligand films (10 layers) at the air-solid interface are tracked and the hypsochromic shift of these bands is also attributed to these DNA interactions.

A highly selective electron affinity facilitated H2S sensor: the marriage of tris(keto-hydrazone) and an organic field-effect transistor.

Conjugated polymers (CPs) are emerging as part of a promising future for gas-sensing applications. However, some of their limitations, such as poor specificity, humidity sensitivity and poor ambient stability, remain persistent. Herein, a novel combination of a polymer-monomer heterostructure, derived from a CP (PDVT-10) and a newly reported monomer [tris(keto-hydrazone)] has been integrated in an organic field-effect transistor (OFET) platform to sense H2S selectively. The hybrid heterostructure shows an unprecedented sensitivity (525% ppm-1) and high selectivity toward H2S gas. In addition, we demonstrated that the PDVT-10/tris(keto-hydrazone) OFET sensor has the lowest limit of detection (1 ppb), excellent ambient stability (∼5% current degradation after 150 days), good response-recovery behavior, and exceptional electrical behavior and gas response reproducibility. This work can help pave the way to incorporate futuristic gas sensors in a multitude of applications.

Thiolated polymer nanocarrier reinforced with glycyrrhetinic acid for targeted delivery of 5-fluorouracil in hepatocellular carcinoma.

The present work investigates the targeting efficacy of a novel thiolated polymer-based nanocomposite reinforced with glycyrrhetinic acid (GA) and loaded with 5-fluorouracil in hepatocellular carcinoma (HCC). The thiolated polymers were synthesized by EDAC-mediated conjugation reactions and lyophilization. The nanoparticles were prepared by solvent diffusion and high-pressure homogenization method. The prepared nanocomposite was characterized by Fourier transform infrared (FTIR) radiation, x-ray diffraction (XRD), dynamic light scattering (DLS), scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. Pharmacological evaluation of the formulation was carried out on a rat model of diethylnitrosamine (DEN), and carbon tetrachloride (CCl4)-induced HCC and MTT assay was carried out with HEP-G2 cell line. In silico studies were conducted to investigate the probable mechanistic pathway of the nanocomposite. FTIR and XRD analysis indicated the successful thiolation of the polymers and confirmed the formation of the nanocomposite without any incompatibilities. DLS, SEM/EDX and AFM characterization confirmed that the nanoparticles were within the nano-size range. MTT assay implied the cytotoxic nature of the nanocomposite against hepatic carcinoma cells. The in vivo study revealed that serum SGOT, SGPT, ALP, GGT and total bilirubin levels were significantly reduced, in comparison with disease control and the result was confirmed by histopathology studies. The results of the HPLC analysis of liver homogenate confirmed the liver targeting ability of the nanocomposite. In silico studies exhibited significant binding affinity of GA and thiolated Eudragit towards liver homolog receptor-1 (LRH-1) suggesting that the developed nanocomposite could be a potential material for the treatment of HCC.

Chiral plasmonic liquid crystal gold nanoparticles: self-assembly into a circular dichroism responsive helical lamellar superstructure.

Owing to their proven and promising potential in various technological endeavors ranging from catalysis and sensing to invisibility cloaks made from metamaterials, chiral plasmonic superstructures resulting from the directed self-assembly of optically active metal nanoparticles (MNPs) have been pursued intensively in recent years. Several strategic efforts have emerged especially to accomplish advanced nanomaterials assembling into liquid crystalline (LC) helical structures, where MNPs are regularly packed in fluid/frozen arrays/layers or wires (columns). While the helical fluid columnar arrays (molecular wires) showing circular dichroism (CD) have been realized, the discovery of fluid chiral lamellar ordering, where the dielectric and conducting regimes are arranged alternatively, has hitherto remained highly elusive. Herein we report the first examples of monodisperse LC-gold NPs (LC-GNPs) self-assembling into a fluid/frozen lamellar structure exhibiting CD activity. Notably, these new, exceptional LC-GNPs have been realized by simple, hassle-free protocols that involve the room temperature addition of LC dimer-like arylamines to Au(iii), where the amines not only reduce Au(iii) to Au(0) but also bind strongly to the central GNP scaffold. Their molecular structure, mesomorphism, and ability to interact with circularly polarized light have been evidenced unambiguously and could play an important role in realizing metamaterials in the visible region.

Photo-tunable epsilon-near-zero behavior in a self-assembled liquid crystal - nanoparticle hybrid material.

Dynamic tuning of electromagnetic response is an important parameter to realize exotic applications of optical metamaterials. Self-assembly achieved via the incorporation of soft materials is an attractive approach to achieve tunable optical properties. Among the soft materials, liquid crystals are highly sought after due to the inherent soft-stimuli responsiveness. This article reports experimental evidence of tunable epsilon-near-zero (ENZ) behavior brought about by an optical field in a self-assembled liquid crystal - nanoparticle system. The material consists of Au nanoparticles capped with a photo-active chiral liquid crystal ligand. In the liquid crystalline state, the system self-assembles into a helical lamellar superstructure, confirmed by polarizing optical microscopy, HRTEM, XRD, and circular dichroism studies. Upon irradiation with UV light, the localized surface plasmon resonance peak of Au red-shifts by ∼10 nm and gets restored with white light illumination. The effective permittivity of the system obtained from ellipsometry indicates ENZ behavior in the visible spectrum with a bandwidth of ∼45 nm which gets enhanced by a factor of 1.6 on UV illumination. Theoretical calculations, carried out using the effective medium approach, support the experimental findings, making the system an efficient ENZ metamaterial in the optical regime.

Green and low-cost synthesis of zinc oxide nanoparticles and their application in transistor-based carbon monoxide sensing.

There has been steady progress in developing reliable and cost-effective strategies for the clean production of zinc oxide (ZnO) nanoparticles (NPs) owing to their unique structural and wide functional characteristics. While the green synthesis of such NPs from plant extracts has emerged as a sustainable and eco-friendly protocol, it is greatly restricted owing to the scarcity of potential natural precursors necessitating comprehensive investigations in this direction. Herein, we report a facile, low-cost green synthesis and characterization of ZnO NPs along with the demonstration of their usage as an active media in organic field-effect transistor (OFET) devices for sensing carbon monoxide (CO) gas. The ZnO NPs obtained from Nelumbo nucifera (lotus) leaf extract-mediated solution combustion synthesis at a much lower initiation temperature, the first of its kind, were characterized by various techniques such as UV-vis spectroscopy, XRD, EDX analysis, TEM and FESEM. The data derived from these experiments clearly evidence the formation of very pure and crystalline ZnO NPs possessing nearly spherical-shape with a size of 3-4 nm. The p-type organic field-effect transistor (OFET) device, fabricated using poly(3-hexylthiophene-2,5-diyl) (P3HT) and ZnO NPs, showed a field-effect mobility of 10-2 cm2 V-1 sec-1 with a slightly enhanced response of detecting CO gas at room temperature (RT). The phenomenon was further confirmed by the variation in electrical parameters of the OFET such as field-effect mobility (µ), on-current (I on), and off-current (I off). The selectivity and sensitivity of the fabricated device in CO gas detection was found to be more prominent than the other reducing gases (hydrogen sulphide, H2S and ammonia, NH3) and methanol vapours tested.

Light-Emitting Chiral Nematic Dimers with Anomalous Odd-Even Effect.

In this report, based on the results derived from the extensive study into the thermal and photophysical properties, an anomalous mesomorphic behavior of photoluminescent, chiral nematic (N*) liquid crystalline dimers, belonging to two different series has been revealed. They comprise cholesterol and fluorescent three-ring Schiff base or salicylaldimine core interlinked via an ω-oxyalkanoyloxy spacer of varying length and parity. The effect of molecular structure on the liquid crystal (LC) behavior and photophysical properties of both the series has been probed by varying the length of the terminal n-alkoxy tails for a fixed (odd or even) parity of the spacer. The detailed investigations using complementary techniques not only evidenced the existence of the N* phase in all the dimers synthesized but also the occurrence of an intriguing odd-even effect; blue phases (BPs) exist in all the dimers comprising even-membered spacer, which surprisingly remains totally absent in their odd-membered counterparts. While the results reported hitherto are exactly opposite to the aforesaid findings, this atypical behavior has been interpreted in terms of the over-all shape of the dimers rendered by the orientation of terminal tails. Photophysical studies carried out clearly revealed the intrinsic light emitting feature of the dimers not only in their dilute solutions but also in their three condensed states viz., solid, N* phase, and isotropic liquid state; the emission intensities of the N* phase varies with the change in temperature, as expected. CD spectra of the N* phase recorded as a function of temperature show bisignate CD band characteristically, signifying large chiral correlations in the molecular self-assembly, while the origin of bands from positive to negative region suggests a right-handed twist of the N* helix.