Kinetic Study of the Al-Schiff's Base Initiated Polymerization of ε-caprolactone and Synthesis of Graft Poly(methylmethacrylate-g-caprolactone)

Graft copolymers of polycaprolactone (PCL) on polymethacrylate (PMMA) backbone have been successfully synthesized and characterized by SEC, ¹H and ¹³C NMR spectroscopy. The strategy used consisted of polymerizing ε-CL, followed by end-functionalization of the resulting PCL using methacryloyl chloride. Free radical polymerization of the methacryl double bond lead to the C-C polymer backbone and an overall graft copolymer. The polymerization of ε-caprolactone was achieved using Al-Schiff's base isopropoxide (HAPENAlOⁱPr) in DCM at ambient temperature. SEC and MALDI analysis of the polymers confirmed that mostly linear chains were obtained with the Al initiator, up until high monomer conversion. The low molar mass PCL was then end-capped with a methacryloyl group, in a quantitative manner, as evidenced by ¹H NMR. The macromonomer thus obtained was copolymerized in small proportions with methyl methacrylate by conventional free radical polymerization and atom transfer radical polymerization (ATRP). Analysis of the products by NMR and SEC showed the presence of true graft copolymers and the absence of homopolymers.     

Polymerization of ε-Caprolactone and its Copolymerization with γ-Butyrolactone using Metal Complexes

Solution polymerization of ε-caprolactone (ε-CL) was performed using four different initiators namely: tin(II) octanoate (Sn(Oct)₂)/ethanolamine, aluminium Schiff's base complex-HAPENAlOⁱPr, lithium diisopropyl amide (LDA) and aluminium isopropoxide. The reaction conditions varied with the initiator used. LDA gave rise to the most rapid polymerization with the highest amount of cyclic species as detected by ¹³C NMR. However, no cyclic species were detected when HAPENAlOⁱPr was used as initiator. The tin(II) octanoate/ethanolamine system lead to an α,ω-dihydroxy-polycaprolactone (PCL). The copolymerization of ε-CL was then performed with the hard to oligomerize γ-butyrolactone using the four initiators. GPC (Gel Permeation Chromatography) analyses showed the formation of copolymers. The highest incorporation of polybutyrolactone (PBL) in the copolymer was obtained using HAPENAlOⁱPr as evidenced by ¹H NMR. ¹³C NMR indicated the presence of pseudoperiodic random copolymers with short blocks of PCL whose block length varied with initiator used. The longest and shortest block length were obtained using Sn(Oct)₂ and HAPENAlOⁱPr respectively as calculated from ¹³C NMR. The reactivity ratios were determined using the Finemann-Ross method at low conversion with HAPENAlOⁱPr as initiator. The values obtained, r_CL = 19.4 and r_BL = 0.11, confirmed the presence of long blocks of CL units in the copolymer.     

Synthesis of polylactides by new aluminium Schoff's base complexes

The kinetics of DL‐lactide polymerization was studied in CH₂Cl₂ and dioxane at 25°C and in toluene at 70°C with different aluminium Schiff's base initiators namely HAPENAlOMe, HAPENAlOⁱPr, 5‐ClSALENAlOⁱPr and 5‐ClSALOPHENAlOⁱPr. It was observed that HAPEN‐type complexes derived from 2‐hydroxyacetophenone lead to much faster polymerization as compared to SALEN‐ or 5‐ClSALEN‐type initiators derived from salicylaldehyde. Moreover, substitution of the methoxide group coordinated to the central aluminium by an isopropoxide group brings about an increase in the polymerization rate but leads to transesterification reactions at much lower percentage conversion. On the other hand, replacement of the flexible ethylene diamino group by the more rigid phenylenediamino substituent slows down considerably the polymerization reaction. Analysis of the microstructure of all poly(DL‐lactides) obtained revealed the presence of isotactic sequences in agreement with a first order Markovian statistics.     

Oxygen atom transfer promoted nitrate to nitric oxide transformation: a step-wise reduction of nitrate → nitrite → nitric oxide

Nitrate reductases (NRs) are molybdoenzymes that reduce nitrate (NO₃⁻) to nitrite (NO₂⁻) in both mammals and plants. In mammals, the salival microbes take part in the generation of the NO₂⁻ from NO₃⁻, which further produces nitric oxide (NO) either in acid-induced NO₂⁻ reduction or in the presence of nitrite reductases (NiRs). Here, we report a new approach of VCl₃ (V³⁺ ion source) induced step-wise reduction of NO₃⁻ in a Co^II-nitrato complex, [(12-TMC)Co^II(NO₃⁻)]⁺ (2,{Co^II–NO₃⁻}), to a Co^III–nitrosyl complex, [(12-TMC)Co^III(NO)]²⁺ (4,{CoNO}⁸), bearing an N-tetramethylated cyclam (TMC) ligand. The VCl₃ inspired reduction of NO₃⁻ to NO is believed to occur in two consecutive oxygen atom transfer (OAT) reactions, i.e., OAT-1 = NO₃⁻ → NO₂⁻ (r₁) and OAT-2 = NO₂⁻ → NO (r₂). In these OAT reactions, VCl₃ functions as an O-atom abstracting species, and the reaction of 2 with VCl₃ produces a Co^III-nitrosyl ({CoNO}⁸) with V^V-Oxo ({V^V O}³⁺) species, via a proposed Co^II-nitrito (3, {Co^II–NO₂⁻}) intermediate species. Further, in a separate experiment, we explored the reaction of isolated complex 3 with VCl₃, which showed the generation of 4 with V^V-Oxo, validating our proposed reaction sequences of OAT reactions. We ensured and characterized 3 using VCl₃ as a limiting reagent, as the second-order rate constant of OAT-2 (k₂^/) is found to be ∼1420 times faster than that of the OAT-1 (k₂) reaction. Binding constant (K_b) calculations also support our proposition of NO₃⁻ to NO transformation in two successive OAT reactions, as K_{b(Co^II–NO2⁻)} is higher than K_{b(Co^II–NO3⁻)}, hence the reaction moves in the forward direction (OAT-1). However, K_{b(Co^II–NO2⁻)} is comparable to K_b{CoNO}⁸, and therefore sequenced the second OAT reaction (OAT-2). Mechanistic investigations of these reactions using ¹⁵N-labeled-¹⁵NO₃⁻ and ¹⁵NO₂⁻ revealed that the N-atom in the {CoNO}⁸ is derived from NO₃⁻ ligand. This work highlights the first-ever report of VCl₃ induced step-wise NO₃⁻ reduction (NRs activity) followed by the OAT induced NO₂⁻ reduction and then the generation of Co-nitrosyl species {CoNO}⁸.

Single metal-induced reduction of NO₃⁻ → {NO₂⁻} → NO via oxygen atom transfer reaction.     

Determination of Antioxidants by DPPH Radical Scavenging Activity and Quantitative Phytochemical Analysis of Ficus religiosa

The use of F. religiosa might be beneficial in inflammatory illnesses and can be used for a variety of health conditions. In this article, we studied the identification of antioxidants using (DPPH) 2,2-Diphenyl-1-picrylhydrazylradical scavenging activity in Ficus religiosa, as F. religiosa is an important herbal plant, and every part of it has various medicinal properties such as antibacterial properties that can be used by the researchers in the development and design of various new drugs. The 2,2-Diphenyl-1-picrylhydrazyl (DPPH) is a popular, quick, easy, and affordable approach for the measurement of antioxidant properties that includes the use of the free radicals used for assessing the potential of substances to serve as hydrogen providers or free-radical scavengers (FRS). The technique of DPPH testing is associated with the elimination of DPPH, which would be a stabilized free radical. The free-radical DPPH interacts with an odd electron to yield a strong absorbance at 517 nm, i.e., a purple hue. An FRS antioxidant, for example, reacts to DPPH to form DPPHH, which has a lower absorbance than DPPH because of the lower amount of hydrogen. It is radical in comparison to the DPPH-H form, because it causes decolorization, or a yellow hue, as the number of electrons absorbed increases. Decolorization affects the lowering capacity significantly. As soon as the DPPH solutions are combined with the hydrogen atom source, the lower state of diphenylpicrylhydrazine is formed, shedding its violet color. To explain the processes behind the DPPH tests, as well as their applicability to Ficus religiosa (F. religiosa) in the manufacture of metal oxide nanoparticles, in particular MgO, and their influence on antioxidants, a specimen from the test was chosen for further study. According to our findings, F. religiosa has antioxidant qualities and may be useful in the treatment of disorders caused by free radicals.     

Laser-Patterned Carbon-Supported Graphitic Carbon Nitride Quantum Dots for Flexible Nanozyme-Based Fluoride Sensor

Graphitic carbon nitride quantum dots (g-CNQDs)-based colorimetric sensors are typically solution-based and hence incompatible with wearable electronics. Today's competitive technology demands safe and reliable, high-performance sensors suitable for integration with sophisticated electronics—all at a low cost. Herein, a flexible and reusable solid-state fluoride ion sensor manufactured by combining the intriguing surface properties of laser-patterned carbon (LP-C) with the sensitivity of g-CNQDs is reported. LP-C is obtained by direct IR-laser writing onto polyimide films, and g-CNQDs are synthesized via a solvent-free and zero-waste green process. The hybrid of LP-C and g-CNQDs (g-CNQDs/LP-C), mimics the natural enzyme horseradish peroxidase and oxidizes the chromogenic substrate 3,3’,5,5’-tetramethylbenzidine in the presence of H₂O₂ in acidic media. The highly selective and user-friendly nanozyme sensors feature a lower limit of detection of 0.568 ± 0.006  × 10⁻⁶ m (23.8 ± 1.5 µg L⁻¹) with linearity in the range of 0.5 × 10⁻⁶ to 100  × 10⁻⁶ m . A sensing mechanism based on the electronic transitions of g-CNQDs and LP-C, the two variants of nitrogen-containing carbon used in this work, is established. Finally, the device is tested for fluoride ion sensing in natural water samples collected from the Uhl river in Mandi, India.     

Effect of Boundaries on Pattern Formation in a Monolayer of Interacting Dipoles

Self-organization can be defined as a process of arrangement of entities that start out in an irregular arrangement and evolve into a stable, regular pattern without the aid of an external agent. A system of magnetic particles that are constrained to move only in a plane is reported. The individual components in the system have dipole moments in an orientation perpendicular to the plane of motion and the interaction between components is purely repulsive. For such a system, it is attempted to understand the influence of the boundary of the monolayer on the patterns that emerge. A system with a small number of magnets is found where the range of the magnetic interactions is of the size of the boundary; the symmetry of the boundary imposed on the monolayer plays a crucial role in determining the pattern types, the number of different pattern types, and the frequency of appearance of a particular pattern type. The effect of scaling up the size of the system while maintaining the characteristics of individual components as well as the component areal density is also discussed.     

Facile synthesis of Mn-Ni bimetal organic framework decorated with amine as an electrode for a high-performance supercapacitor

Journal of Solid State Electrochemistry - In the recent years, the whole world is looking for better energy storage devices. Supercapacitors are among the most promising high-capacity...