Interpretation of temperature dependence of the in-plane electrical resistivity in YBa2Cu4O8: Electron–phonon approach

In this paper, we undertake a quantitative analysis of observed temperature-dependent in-plane normal state electrical resistivity of single crystal YBa₂Cu₄O₈. The analysis is within the framework of classical electron–phonon i.e., Bloch-Gruneisen model of resistivity. It is based on the inherent acoustic (low frequency) phonons (ω_ac) as well as high frequency optical phonons (ω_op), the contributions to the phonon resistivity were first estimated. The optical phonons of the oxygen breathing mode yields a relatively larger contribution to the resistivity compared to the contribution of acoustic phonons. Estimated contribution to in-plane electrical resistivity by considering both phonons i.e., ω_ac and ω_op, along with the zero-limited resistivity, when subtracted from single crystal data infers a quadratic temperature dependence over most of the temperature range [80 ? T ? 300]. Quadratic temperature dependence of ρ_diff. = [ρ_exp − {ρ₀ + ρ_e−ph (=ρ_ac + ρ_op)}] is understood in terms of electron–electron inelastic scattering. The relevant energy gap expressions within the Nambu-Eliashberg approach are solved imposing experimental constraints on their solution (critical temperature T_c). It is found that the indirect-exchange formalism provides a unique set of electronic parameters [electron–phonon (λ_ph), electron-charge fluctuations (λ_pl), electron–electron (μ) and Coulomb screening parameter (μ^*)] which, in particular, reproduce the reported value of T_c.     

Sulphonated poly(ether ether ketone): synthesis and characterisation

The paper describes the sulphonation of commercially available poly(ether ether ketone) PEEK (GATONE^TM, Gharda Chemicals Limited, India and VICTREX^®, ICI Limited, UK) by using concentrated sulphuric acid. The concentration of GATONE in conc. H₂SO₄ was varied from 4-10% (w/v) whereas in VICTREX^® the concentration was 4% (w/v). The temperature was varied from 35-55°C and the duration of reaction was 3-7 h. Structural characterisation of sulphonated polymers was done by elemental analysis, FT-IR and ¹H-NMR spectroscopy. On the basis of elemental analysis, the extent of sulphonation of GATONE was found to be 57-75%. The extent of sulphonation as determined by ¹H-NMR in case of GATONE was in the range of 53-80% and for VICTREX 58-87%. Thermal analysis, proton conductivity and water uptake of these samples were also studied. Proton conductivity of the films was comparable to the perflourinated polymer (Nafion).     

New cocrystals of heterocyclic drugs: structural,antileishmanial, larvicidal and urease inhibition studies

Many heterocycles have been developed as drugs due to their capacity to interact productively with biological systems. The present study aimed to synthesize cocrystals of the heterocyclic antitubercular agent pyrazinamide ( PYZ , 1 , BCS III) and the commercially available anticonvulsant drug carbamazepine ( CBZ , 2 , BCS class II) to study the effect of cocrystallization on the stability and biological activities of these drugs. Two new cocrystals, namely, pyrazinamide–homophthalic acid (1/1) ( PYZ:HMA , 3 ) and carbamazepine–5-chlorosalicylic acid (1/1) ( CBZ:5-SA , 4 ), were synthesized. The single-crystal X-ray diffraction-based structure of carbamazepine–trans-cinnamic acid (1/1) ( CBZ:TCA , 5 ) was also studied for the first time, along with the known cocrystal carbamazepine–nicotinamide (1/1) ( CBZ:NA , 6 ). From a combination drug perspective, these are interesting pharmaceutical cocrystals to overcome the known side effects of PYZ ( 1 ) therapy, and the poor biopharmaceutical properties of CBZ ( 2 ). The purity and homogeneity of all the synthesized cocrystals were confirmed by single-crystal X-ray diffraction, powder X-ray diffraction and FT–IR analysis, followed by thermal stability studies based on differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Detailed intermolecular interactions and the role of hydrogen bonding towards crystal stability were evaluated quantitatively via Hirshfeld surface analysis. The solubility of CBZ at pH 6.8 and 7.4 in 0.1 N HCl and H₂O were compared with the values of cocrystal CBZ:5-SA ( 4 ). The solubility of CBZ:5-SA was found to be significantly improved at pH 6.8 and 7.4 in H₂O. All the synthesized cocrystals 3 – 6 exhibited a potent urease inhibition (IC₅₀ values range from 17.32 ± 0.89 to 12.3 ± 0.8 µM), several times more potent than standard acetohydroxamic acid (IC₅₀ = 20.34 ± 0.43 µM). PYZ:HMA ( 3 ) also exhibited potent larvicidal activity against Aedes aegypti. Among the synthesized cocrystals, PYZ:HMA ( 3 ) and CBZ:TCA ( 5 ) were found to possess antileishmanial activity against the miltefosine-induced resistant strain of Leishmania major, with IC₅₀ values of 111.98 ± 0.99 and 111.90 ± 1.44 µM, respectively, in comparison with miltefosine (IC₅₀ = 169.55 ± 0.20 µM).     

Nanohybrid Comprising Gold Nanoparticles – MoS2 Nanosheets for Electrochemical Sensing of Folic Acid in Serum Samples

Folic acid (FA) deficiency is associated with several clinical conditions such as megaloblastic anemia, neuropsychiatric, and pregnancy-related syndromes, this makes FA an important metabolite to be monitored. We have fabricated an electrochemical biosensor based on gold nanoparticles decorated molybdenum disulfide nanosheets (AuNPs−MoS₂NSs) nanocomposite as a transducer matrix for specific and rapid electrochemical detection of FA. Differential pulse voltammetry (DPV) studies displayed a rapid analytical response of the fabricated AuNPs−MoS₂NSs/GCE sensor probe towards FA in a wide concentration range of 0.001–100 μM with a very low detection limit of 0.72±0.03 nM. The selectivity of the fabricated sensor probe has been examined in the presence of interferents such as dopamine, uric acid, ascorbic acid, glucose, and urea. The clinical potential of the fabricated biosensor was established by monitoring FA in human serum samples. The developed AuNPs−MoS₂NSs/GCE sensor probe showed high reproducibility and stability, indicating its promise for FA detection in clinical settings.