Facile Tailoring of Structures for Controlled Release of Paracetamol from Sustainable Lignin Derived Platforms

Nowadays, sustainable materials are receiving significant attention due to the fact that they will be crucial for the development of the next generation of products and devices. In the present work, hydrogels have been successfully synthesized using lignin which is non-valorized biopolymer from the paper industry. Hydrogels were prepared via crosslinking with Poly(ethylene) glycol diglycidyl ether (PEGDGE). Different crosslinker ratios were used to determine their influence on the structural and chemical properties of the resulting hydrogels. It has been found that pore size was reduced by increasing crosslinker amount. The greater crosslinking density increased the swelling capacity of the hydrogels due to the presence of more hydrophilic groups in the hydrogel network. Paracetamol release test showed higher drug diffusion for hydrogels produced with a ratio lignin:PEGDGE 1:1. The obtained results demonstrate that the proposed approach is a promising route to utilize lignocellulose waste for producing porous materials for advanced biomedical applications in the pharmacy industry.     

Contributions of quantum chemistry to the development of ring opening polymerizations and chemical recycling

Quantum chemistry has increasingly become an integral component for the development of homogeneous catalytic processes to form polymers and to break them down. This review examines how quantum chemistry has been utilized to gain insights on mechanisms and selectivities in polymerization and depolymerization reactions by homogeneous catalysts, from some of the earliest uses of theory to the most recent efforts. Key aspects of catalysis by transition-metal catalysts, organocatalytic bases and organic acids will be highlighted.     

Electrocatalytic Hydrogen Evolution Using A Molecular Antimony Complex under Aqueous Conditions: An Experimental and Computational Study on Main-Group Element Catalysis

Electrocatalytic hydrogen gas production is considered a potential pathway towards carbon-neutral energy sources. However, the development of this technology is hindered by the lack of efficient, cost-effective, and environmentally benign catalysts. In this study, a main-group-element-based electrocatalyst, SbSalen , is reported to catalyze the hydrogen evolution reaction (HER) in an aqueous medium. The heterogenized molecular system achieved a Faradaic efficiency of 100 % at −1.4 V vs. NHE with a maximum current density of −30.7 mA/cm². X-ray photoelectron spectroscopy of the catalyst-bound working electrode before and after electrolysis confirmed the molecular stability during catalysis. The turnover frequency was calculated as 43.4 s⁻¹ using redox-peak integration. The kinetic and mechanistic aspects of the electrocatalytic reaction were further examined by computational methods. This study provides mechanistic insights into main-group-element electrocatalysts for heterogeneous small-molecule conversion.     

Dynamic kinetic resolution of 2-methyl-2-nitrocyclohexanol: Combining the intramolecular nitroaldol (Henry) reaction & lipase-catalysed resolution

Efforts to combine the intramolecular nitroaldol reaction with lipase-catalysed resolution of the resulting nitroaldol adduct in a one-pot dynamic kinetic resolution (DKR) are described. Significant challenges were encountered in the combination of the two systems. trans-2-Methyl-2-nitrocyclohexyl acetate (±)-3b was isolated in excellent enantiopurity (>98% ee) via a sequential DKR sequence where the lipase-mediated resolution and base-mediated interconversion of 2-methyl-2-nitrocyclohexanol 2 were effected alternately, demonstrating the feasibility of this approach initially. Further work showed, for the first time, evidence that a DKR-type system is possible for 2. Reaction engineering allowed the design of a sequential one-pot reaction system which furnished the products with excellent enantioselectivity, and good diastereoselectivity.     

On a monotonic trigonometric sum

By establishing a cosine analogue of a result of Askey and Steinig on a monotonic sine sum, this paper sharpens and unifies several results associated with Young's inequality for the partial sums of k ^–1 cosk.     

Synthesis of 2-aryl-6-methyl-5-nitroquinoline derivatives as potential prodrug systems for reductive activation

A range of novel 2-aryl-5-nitroquinolines have been synthesised as potential prodrug systems for bioreductive activation. Thus 5-nitroquinoline underwent vicarious nucleophilic substitution at C-6 with bromoform anion to give, after hydrolysis and reduction, the quinoline-6-methanol. Introduction of chlorine at C-2 was followed by palladium-catalysed Suzuki coupling to install the 2-aryl substituent. A fluorescent model ‘drug’, 7-hydroxy-4-methylcoumarin was coupled to the 6-hydroxymethyl group, and its fragmentation upon reduction of the nitro group was investigated.     

Predictions of substituent effects in thermal azide 1,3-dipolar cycloadditions: implications for dynamic combinatorial (reversible) and click (irreversible) chemistry

Substituent effects in 1,3-dipolar cycloadditions of azides with alkenes and alkynes were investigated with the high-accuracy CBS-QB3 method. The possibilities for noncatalytic activation and the reversibility or irreversibility of these reactions was explored; the possibilities for uses in dynamic combinatorial chemistry (DCC) or click chemistry were explored. The activation enthalpies for reactions of ethylene and acetylene with hydrazoic acid, formyl, phenyl-, methyl-, and methanesulfonylazides exhibit modest variation, with Delta H++ ranging from 17 to 20 kcal/mol. A detailed study of formylazide cycloadditions with various alkenes and alkynes reveals a narrow range of activation enthalpies (17-21 kcal/mol). The activation enthalpies for the reactions of azides with alkenes and alkynes are similar. FMO theory and distortion/interaction energy control have been used to rationalize the rates and regiochemistries of cycloadditions involving alkene dipolarophiles. Significantly, triazoles, formed from alkynes, are 30-40 kcal/mol more stable than tetrazolines formed from alkenes. On the basis of initial reactant concentrations, kinetic and thermodynamic values are suggested for the identification of reversible reactions that approach equilibrium over 24 h, as well as for fast irreversible reactions. Although azide cycloadditions are suitable for irreversible chemistry and are typically unsuitable for reversible applications, theoretical procedures established by these studies have provided guidelines for the prediction of useful reversible libraries.     

Self Organising Maps for distinguishing polymer groups using thermal response curves obtained by dynamic mechanical analysis

Self Organising Maps are described including the U-Matrix, component planes, hit histograms, quality indicators as mean quantisation error and topological error. Software was written in Matlab and several new approaches for visualising multiclass maps are employed. The method is applied to a dataset consisting of the Dynamic Mechanical Analysis of 293 polymers, involving heating the polymers over a temperature range of -51 degrees C to 270 degrees C. These can be characterised in three different ways (a) amorphous or semi-crystalline (b) as 9 groups (c) as 30 grades.     

Linkage isomerism in the binding of pentapeptide Ac-His(Ala)3His-NH2 to (ethylenediamine)palladium(II): effect of the binding mode on peptide conformation

The reaction of the pentapeptide Ac-His1-Ala2-Ala3-Ala4-His5-NH2 (AcHAAAHNH2) (1) with [Pd(en)(ONO2)2] (en = NH2CH2CH2NH2) in either DMF-d(7) or H2O:D2O (90%:10%) gave three linkage isomers of [Pd(en)(AcHAAAHNH2)](2+) (2), 2a, 2b, and 2c, which differ only in which pair of imidazole nitrogen atoms bind to Pd. In the most abundant isomer, 2a, Pd is bound by N1 from each of the two imidazole rings. In the minor isomers 2b and 2c, Pd is bound by N1(His1) and N3(His5) and by N3(His1) and N1(His5), respectively. The reactions of [Pd(en)(ONO2)2] with the N-methylated peptides Ac-(N3-MeHis)-Ala-Ala-Ala-(N3-MeHis)-NH2 (AcH*AAAH*NH2) (3), Ac-(N3-MeHis)-Ala-Ala-Ala-(N1-MeHis)-NH2 (AcH(*)AAAH(#)NH2) (4), and Ac-(N1-MeHis)-Ala-Ala-Ala-(N3-Me-His)-NH2 (AcH(#)AAAH(*)NH2) (5) each gave a single species [Pd(en)(peptide)](2+) in N,N-dimethylformamide (DMF) or aqueous solution, 7, 8, and 9, respectively, with Pd bound by the two nonmethylated imidazole nitrogen atoms in each case. These complexes were analogous to 2a, 2b, and 2c, respectively. Ac-(N1-MeHis)-Ala-Ala-Ala-(N1-MeHis)-NH2 (AcH(#)AAAH(#)NH2) (6) with [Pd(en)(ONO2)2] in DMF slowly gave a single product, [Pd(en)(AcH(#)AAAH(#)NH2)](2+) (10), in which Pd was bound by the N3 of each imidazole ring. The corresponding linkage isomer of 2 was not observed. Complex 10 was also the major product in aqueous solution, but other species were also present. All compounds were exhaustively characterized in solution by multinuclear 1D ((1)H , (13)C, and, with (15)N-labeled ethylenediamine, (15)N) and 2D (correlation spectroscopy, total correlation spectroscopy, transverse rotating-frame Overhauser effect spectroscopy (T-ROESY), heteronuclear multiple-bond correlation, and heteronuclear single quantum coherence) NMR spectra, circular dichroism (CD) spectra, electrospray mass spectroscopy, and reversed-phase high-performance liquid chromatography. ROESY spectra were used to calculate the structure of 2a, which contained a single turn of a peptide alpha helix in both DMF and water, the helix being better defined in DMF. The Pd(en)(2+) moiety was not used in structure calculations, but its location and coordination by one imidazole N1 from each histidine to form a 22-membered metallocycle were unambiguously established. Convergence of the structures was greatest when calculated with two hydrogen-bond constraints (Ala4 peptide NH...OC acetyl and His5 peptide NH...OC-His1) that were indicated by the low temperature dependence of these NH chemical shifts. Vicinal HN-CHalpha coupling constants and chemical shifts of alpha-H atoms were also consistent with a helical conformation. Similar long-range ROE correlations were observed for [Pd(en)(AcH(*)AAAH(*)NH2)](2+) (7), which displayed a CD spectrum in aqueous solution that suggested the presence of some helicity. Long-range ROE correlations were not observed for 8, 9, or 10, but a combination of NMR data and CD spectroscopy was interpreted in terms of the conformational behavior of the coordinated pentapeptide. Only for the linkage isomer [Pd(en)(AcH(*)AAAH(#)NH2)](2+) (8) was there evidence of a contribution from a helical conformation. The data for 8 were interpreted as interconversion between the helix and random coil conformations. Zn(2+) with peptides gave broad NMR peaks attributed to lability of this metal ion, while reactions of cis-[Pt(NH3)2(ONO2)2] were slow, giving a complex mixture of products rather than the macrochelate ring observed with Pd(en)(2+). In summary, these studies indicate that Pd(en)(2+) coordinates to histidine with similar preference for each of the two imidazole nitrogens, enabling the formation of up to four linkage isomers in its complexes with pentapeptides His-xxx-His. Only the N1-N1 linkage isomer that forms a 22-membered macrochelate ring is able to induce an alpha-helical peptide conformation, whereas the 20- and 21-membered rings of linkage isomers do not. This suggests that linkage isomeric mixtures may compromise histidine coordination to metal ions and reduce alpha-helicity.