Efficient, Stable, and Reusable Silicoaluminophosphate for the One-Pot Production of Furfural from Hemicellulose

Development of stable, reusable, and water-tolerant solid acid catalysts in the conversion of polysaccharides to give value-added chemicals is vital because catalysts are prone to undergo morphological changes during the reactions. With the anticipation that silicoaluminophosphate (SAPO) catalysts will have higher hydrothermal stability, those were synthesized, characterized, and employed in a one-pot conversion of hemicellulose. SAPO-44 catalyst at 170 °C within 8 h could give 63% furfural yield with 88% mass balance and showed similar activity up to at least 8 catalytic cycles. The morphological studies revealed that SAPO catalysts having hydrophilic characteristics are stable under reaction conditions

<i>Toxoplasma gondii</i> aspartic protease 5: structural basis of substrate binding and inhibition mechanism

Toxoplasma gondii, a worldwide prevalent parasite is responsible for causing toxoplasmosis in almost all warm-blooded animals, including humans. Golgi-resident T. gondii aspartic protease 5 (TgASP5) plays an essential role in the maturation and export of the effector proteins those modulate the host immune system to establish a successful infection. Hence, inhibiting this enzyme can be a possible therapeutic strategy against toxoplasmosis. This is the first report of the detailed structural investigations of the TgASP5 mature enzyme using molecular modeling and an all-atom simulation approach which provide in-depth knowledge of the active site architecture of TgASP5. The analysis of the binding mode of the TEXEL (Toxoplasma EXport Element) substrate to TgASP5 highlighted the importance of the active site residues. Ser505, Ala776 and Tyr689 in the S2 binding pocket are responsible for the specificity towards Arg at the P2 position of TEXEL substrate. The molecular basis of inhibition by the only known inhibitor RRLStatine has been identified, and our results show that it blocks the active site by forming a hydrogen bond with a catalytic aspartate. Besides that, known aspartic protease inhibitors were screened against TgASP5 using docking, MD simulations and MM-PBSA binding energy calculations. The top-ranked inhibitors (SC6, ZY1, QBH) showed higher binding energy than RRLStatine. Understanding the structural basis of substrate recognition and the binding mode of these inhibitors will help to develop potent mechanistic inhibitors against TgASP5. This study will also provide insights into the structural features of pepsin-like aspartic proteases from other apicomplexan parasites for developing antiparasitic agents. Communicated by Ramaswamy H. Sarma</p

Chemical Transformation for 5‑Hydroxymethylfurfural Production from Saccharides Using Molten Salt System

Herein, we have demonstrated using a eutectic ternary LiNO₃–NaNO₃–KNO₃ (LSP) molten salt melt under mild conditions for chemical transformation of 5-hydroxymethylfurfural (HMF) production directly from biomass-derived saccharides, such as fructose, glucose, cellobiose, starch, and cellulose. In addition, 2-<i>sec</i>-butylphenol (SBP) was used for enhancing HMF production through efficient extraction from LSP salt melts. Notably, LSP salt can be recovered and reused without compromising activity, which could make this chemical transformation sustainable. Moreover, a simple vacuum distillation system can be employed for easy separation of HMF while processing. The aforementioned chemical transformation through LSP molten salt melts could be attributed to the intrinsic unique acid–base pair and saccharide molecule perturbation by small cations present in molten salt melts

The Enolization Chemistry of a Thioester-Dependent Racemase: The 1.4 Å Crystal Structure of a Reaction Intermediate Complex Characterized by Detailed QM/MM Calculations

In the active site of the bacterial α-methylacyl-CoA racemase of Mycobacterium tuberculosis (MCR), the chirality of the 2-methyl branched C2-atom is interconverted between (<i>S</i>) and (<i>R</i>) isomers. Protein crystallographic data and quantum mechanics/molecular mechanics (QM/MM) computational approaches show that this interconversion is achieved via a planar enolate intermediate. The crystal structure, at 1.4 Å, visualizes the mode of binding of a reaction intermediate analogue, 2-methylacetoacetyl-CoA, in a well-defined planar enolate form. The computational studies confirm that in the conversion from (<i>S</i>) to (<i>R</i>), first a proton is abstracted by Nδ1 (His126), and subsequently the planar enolate form is reprotonated by Oδ2 (Asp156). The calculations also show that the negatively charged thioester oxygen of the enolate intermediate is stabilized by an oxyanion hole formed by N (Asp127), as well as by the side chain atoms of the catalytic residues, Asp156 and His126, both being protonated simultaneously, at the intermediate stage of the catalytic cycle. The computational analysis also reveals that the conversion of the (<i>S</i>)- to (<i>R</i>)- chirality is achieved by a movement of 1.7 Å of the chiral C2-carbon, with smaller shifts (approximately 1 Å) of the carbon atom of the 2-methyl group, the C3-atom of the fatty acid tail, and the C1-carbon and O1-oxygen atoms of the thioester moiety