Effect of POSS-Modified Montmorillonite on Thermal, Mechanical, and Electrical Properties of Unsaturated Polyester Nanocomposites.

Montmorillonite (MMT) displays excellent cohesion with an unsaturated polyester (UP) matrix to generate a material which exhibits an extensive range of commercial applications. The organic modification of MMT using polyhedral oligomeric silsesquioxanes (POSS) and the effect of POSS-MMT on the thermal, mechanical, and electrical properties of UP are reported here. Transmission electron microscopy (TEM) images were used to characterize the modification of MMT using POSS. Modified MMT (POSS-MMT) was incorporated, at different wt.% (0.5, 1, 3, 5), into UP via in-situ polymerization. The presence of POSS-MMT enhanced the characteristic properties of UP as a consequence of good dispersion in the polymer matrix. Scanning electron microscopy (SEM) images support effective POSS-MMT dispersion leading to tensile strength enhancement of a UP/POSS-MMT nanocomposite (3 wt.% POSS-MMT) by 54.7% as compared to that for unmodified UP. TGA displays a 35 °C improvement of thermal stability (10% mass loss) at 5% POSS-MMT incorporation, while the electrical conductivity is improved by 108 S/m (3 wt.% POSS-MMT) in comparison to that for unmodified UP. The conventional obstacle of UP associated with shrinkage weight loss during curing seems to be moderated with POSS-MMT incorporation (3%) resulting in a 27.8% reduction in shrinkage weight loss. These fabricated nanocomposites expand the versatility of UP as a high-performance material owing to enhancements of properties.

Novel Unsaturated Polyester Nanocomposites via Hybrid 3D POSS-Modified Graphene Oxide Reinforcement: Electro-Technical Application Perspective.

The latest trends in technologies has shifted the focus to developing innovative methods for comprehensive property enhancement of the polymer composites with facile and undemanding experimental techniques. This work reports an elementary technique to fabricate high-performance unsaturated polyester-based nanocomposites. It focuses on the interactive effect of polyhedral oligomeric silsesquioxanes (POSS)-functionalized graphene oxide (GO) within the unsaturated polymermatrix. The hybrid framework of POSS-functionalized graphene oxide has been configured via peptide bonding between the aminopropyl isobutyl POSS and graphene oxide. The synergistic effect of POSS and graphene oxide paved the way for a mechanism to inculcate a hybrid framework within the unsaturated polyester (UP) via in situ polymerization to develop UP/GO-POSS nanocomposites. The surface-appended POSS within the graphene oxide boosted its dispersion in the UP matrix, furnishing an enhancement in tensile strength of the UP/GO-POSS composites by 61.9%, thermal decomposition temperature (10% mass loss) by 69.8 °C and electrical conductivity by 108 S/m, in contrast to pure UP. In particular, the homogenous influence of the POSS-modified GO could be vindicated in the surging of the limiting oxygen index (%) in the as-prepared nanocomposites. The inclusive property amelioration vindicates the use of fabricated nanocomposites as high-performance nanomaterials in electrotechnical applications.

A Novel Approach to Enhance Mechanical and Thermal Properties of SLA 3D Printed Structure by Incorporation of Metal-Metal Oxide Nanoparticles.

Silver (Ag) ornamented TiO2 semiconducting nanoparticles were synthesized through the sol-gel process to be utilized as nanofillers with photo resin to enhance the mechanical and thermal properties of stereolithography 3D printed objects. The as-prepared Ag-TiO2 nanoparticles (Ag-TNP) were typified and qualified by XRD, XPS, Raman, and FESEM; TEM analysis dissected the morphologies. The enhancement in the tensile and flexural strengths of SLR/Ag-TNP nanocomposites was noted as 60.8% and 71.8%, respectively, at the loading content of 1.0% w/w Ag-TNP within the SLR (stereolithography resin) matrix. Similarly, the thermal conductivity and thermal stability were observed as higher for SLR/Ag-TNP nanocomposites, equated to neat SLR. The nanoindentation investigation shows an excerpt hike in reduced modulus and hardness by the inclusion of Ag-TNP. The resulted thermal analysis discloses that the introduction of Ag-TNP can appreciably augment the glass transition temperature (Tg), and residual char yield of SLR nanocomposites remarkably. Hence, the significant incorporation of as-prepared Ag-TNP can act as effective nanofillers to enhance the thermal and mechanical properties of photo resin.

Enhanced Mechanical and Thermal Properties of Stereolithography 3D Printed Structures by the Effects of Incorporated Controllably Annealed Anatase TiO2 Nanoparticles.

Fabrication of low-cost, durable and efficient metal oxide nanocomposites were successfully synthesized and reinforced with photo-resin via 3-dimensional printing. Here, we put forward a novel approach to enhance the mechanical and thermal behaviors of stereolithography (SLA) 3D printed architecture by adding TiO2 nanoparticles (TNPs) in different crystalline phases (anatase and rutile), which were obtained at different annealing temperatures from 400 °C to 1000°C. The heat-treated anatase TNPs were scrutinized by X-ray diffraction(XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, diffusive reflectance spectroscopy (DRS), and transmission electron microscopy (TEM) analysis. Among all the samples, at 800 °C, annealed anatase TNPs exposed a highly crystalline anatase phase, having a low energy bandgap and a comparably high tensile strength (47.43 MPa) and high elastic modulus (2.261 GPa) for the 3D printed samples, showing improvement by 103% and 32%, respectively, compared with the printed pristine stereolithography resin (SLR) sample. Moreover, enhanced storage modulus and tan δ values were achieved via the better interfacial interactions between the incorporated nanofillers and the SLR matrix. In addition to this, enhanced thermal conductivity and thermal stability of the SLR matrix were also noted. The low energy bandgap and nanoscale size of the fillers helped to achieve good dispersion and allowed the UV light to penetrate at a maximum depth through the photo resin.

Alkylidene Oxapenem ß-Lactamase Inhibitors Revisited: Potent Broad Spectrum Activity but New Stability Challenges.

We present a comprehensive study of C6-alkylidene containing oxapenems. We show that this class of ß-lactamase inhibitors possesses an unprecedented spectrum with activity against class A, C, and D enzymes. Surprisingly, this class of compounds displayed significant photolytic instability in addition to the known hydrolytic instability. Quantum mechanical calculations were used to develop models to predict the stability of new analogues.

Design and synthesis of triazolopyrimidine acylsulfonamides as novel anti-mycobacterial leads acting through inhibition of acetohydroxyacid synthase.

Novel triazolopyrimidine acylsulfonamides class of antimycobacterial agents, which are mycobacterial acetohydroxyacid synthase (AHAS) inhibitors were designed by hybridization of known AHAS inhibitors such as sulfonyl urea and triazolopyrimidine sulfonamides. This Letter describes the synthesis and SAR studies of this class of molecules by variation of two parts of the molecule, the phenyl and triazolopyrimidine rings. SAR study describes optimisation of enzyme potency, whole cell potency and evidence of mechanism of action.

Assessment of Mycobacterium tuberculosis pantothenate kinase vulnerability through target knockdown and mechanistically diverse inhibitors.

Pantothenate kinase (PanK) catalyzes the phosphorylation of pantothenate, the first committed and rate-limiting step toward coenzyme A (CoA) biosynthesis. In our earlier reports, we had established that the type I isoform encoded by the coaA gene is an essential pantothenate kinase in Mycobacterium tuberculosis, and this vital information was then exploited to screen large libraries for identification of mechanistically different classes of PanK inhibitors. The present report summarizes the synthesis and expansion efforts to understand the structure-activity relationships leading to the optimization of enzyme inhibition along with antimycobacterial activity. Additionally, we report the progression of two distinct classes of inhibitors, the triazoles, which are ATP competitors, and the biaryl acetic acids, with a mixed mode of inhibition. Cocrystallization studies provided evidence of these inhibitors binding to the enzyme. This was further substantiated with the biaryl acids having MIC against the wild-type M. tuberculosis strain and the subsequent establishment of a target link with an upshift in MIC in a strain overexpressing PanK. On the other hand, the ATP competitors had cellular activity only in a M. tuberculosis knockdown strain with reduced PanK expression levels. Additionally, in vitro and in vivo survival kinetic studies performed with a M. tuberculosis PanK (MtPanK) knockdown strain indicated that the target levels have to be significantly reduced to bring in growth inhibition. The dual approaches employed here thus established the poor vulnerability of PanK in M. tuberculosis.

Thiazolopyridone ureas as DNA gyrase B inhibitors: optimization of antitubercular activity and efficacy.

Scaffold hopping from the thiazolopyridine ureas led to thiazolopyridone ureas with potent antitubercular activity acting through inhibition of DNA GyrB ATPase activity. Structural diversity was introduced, by extension of substituents from the thiazolopyridone N-4 position, to access hydrophobic interactions in the ribose pocket of the ATP binding region of GyrB. Further optimization of hydrogen bond interactions with arginines in site-2 of GyrB active site pocket led to potent inhibition of the enzyme (IC50 2 nM) along with potent cellular activity (MIC=0.1 µM) against Mycobacterium tuberculosis (Mtb). Efficacy was demonstrated in an acute mouse model of tuberculosis on oral administration.

Thiazolopyridine ureas as novel antitubercular agents acting through inhibition of DNA Gyrase B.

A pharmacophore-based search led to the identification of thiazolopyridine ureas as a novel scaffold with antitubercular activity acting through inhibition of DNA Gyrase B (GyrB) ATPase. Evaluation of the binding mode of thiazolopyridines in a Mycobacterium tuberculosis (Mtb) GyrB homology model prompted exploration of the side chains at the thiazolopyridine ring C-5 position to access the ribose/solvent pocket. Potent compounds with GyrB IC50 ≤ 1 nM and Mtb MIC ≤ 0.1 µM were obtained with certain combinations of side chains at the C-5 position and heterocycles at the C-6 position of the thiazolopyridine core. Substitutions at C-5 also enabled optimization of the physicochemical properties. Representative compounds were cocrystallized with Streptococcus pneumoniae (Spn) ParE; these confirmed the binding modes predicted by the homology model. The target link to GyrB was confirmed by genetic mapping of the mutations conferring resistance to thiazolopyridine ureas. The compounds are bactericidal in vitro and efficacious in vivo in an acute murine model of tuberculosis.