Regulation of plant cell wall deposition and patterning is essential for the normal growth and development of plants. Small GTPases play pivotal roles in the modulation of primary cell wall formation ...by controlling cytoskeletal organization and membrane trafficking. However, the functions of small GTPases in secondary cell wall development are poorly understood. Recent studies on xylem cells revealed that the Rho of plants (ROP) group of small GTPases critically participates in the spatial patterning of secondary cell walls. In differentiating xylem cells, a specific GTPase-activating protein (GAP)/guanine nucleotide exchange factor (GEF) pair facilitates local activation of ROP11 to establish de novo plasma membrane domains. The activated ROP11 then recruits a microtubule-associated protein, MIDD1, to mediate the mutual inhibition between cortical microtubules and active ROP. Furthermore, recent works suggest that certain small GTPases, including ROP and Rab GTPases, regulate membrane trafficking to establish secondary cell wall deposition and patterning. Accordingly, this mini-review assesses and summarizes the current literature regarding the emerging functions of small GTPases in the development of secondary cell walls.
Single‐step process for production of porous scaffold based on poly(pentadecanolide) (PPDL) is reported. The scaffold is produced via in situ porosity generation during ring‐opening polymerization ...(ROP) of the lactone pentadecanolide (PDL) in high internal phase emulsion (HIPE) using a water soluble enzyme (Lipase TL) as catalyst. The enzyme present in dispersed aqueous phase of HIPE effectively carries out ROP of monomer present in continuous oil phase. The polymerization occurs at the interface of oil and water in HIPE and complete monomer conversion is achieved in 96 h at 40 °C. Porous scaffold having interconnected pores is obtained as the final product and formation of PPDL is confirmed by spectroscopic and thermal analysis. The process thus developed is a single‐step process to produce porous scaffolds via ROP of a lactone that can be extended to see its efficacy using monomer‐soluble organometallic catalysts and monomers other than PDL including lactones, lactides, and cyclic carbonates.
A single step solvent free process to create porous scaffold of an aliphatic polyester, poly(pentadecanolide) is devised. Scaffold is developed via in situ pore formation during ring‐opening polymerization (ROP) of high internal phase emulsion (HIPE) of pentadecanolide comprising continuous phase and catalyst, Lipase TL, present in dispersed aqueous phase. HIPE‐ROP may further be extended for fabrication of scaffolds based on other lactones and lactides.
Modern polymeric material design often involves precise tailoring of molecular/supramolecular structures which is also called macromolecular engineering. The available tools for molecular structure ...tailoring are controlled/living polymerization methods, click chemistry, supramolecular polymerization, self-assembly, among others. When polymeric materials with complex molecular architectures are targeted, it usually takes several steps of reactions to obtain the aimed product. Concurrent polymerization methods, i.e., two or more reaction mechanisms, steps, or procedures take place simultaneously instead of sequentially, can significantly reduce the complexity of the reaction procedure or provide special molecular architectures that would be otherwise very difficult to synthesize. Atom transfer radical polymerization, ATRP, has been widely applied in concurrent polymerization reactions and resulted in improved efficiency in macromolecular engineering. This perspective summarizes reported studies employing concurrent polymerization methods with ATRP as one of the reaction components and highlights future research directions in this area.
The current study investigates the wear life of button bits and rate of penetration (ROP) of rotary-percussive drilling machines by employing geotechnical rock properties. According to the research ...plan, three hydropower projects and six active mining quarries in Pakistan were included. The field work included recording of drill bit consumption (m/bit) and measurement of penetration rate (m/min) from the 11 selected rock units. A comprehensive laboratory testing plan on the collected rock units was carried out to include rock abrasivity assessment CERCHAR (CAI), LCPC (ABR) and abrasion value steel (AVS) tests, NTNU/SINTEF drillability parameters Sievers’ J-value (SJ), brittleness value (S
20
), Cutter Life Index™ (CLI) and Drilling Rate Index™ (DRI) and physico-mechanical properties uniaxial compressive strength (UCS), Brazilian tensile strength (BTS), porosity (n), density (ρ), p wave velocity (Vp), Schmidt rebound hardness (SRH) and brittleness index (B
3
). Moreover, XRD analyses were performed to compute equivalent quartz content (EQC %), rock abrasivity index (RAI) and Vickers hardness number of rock (VHNR). The least square regression technique was employed to predict bit life from geotechnical rock properties. Dependence of ROP on geotechnical rock parameters was also discussed. Finally, two multiple linear regression models were also proposed for the estimation of bit life based on the included geotechnical rock properties. The developed multi-variable models were validated using the F-test statistical method. The correlations so developed are particularly proposed for rock engineers involved in rock drilling projects.
Three series of polyesters based on monomer combinations of ε-caprolactone (ε-CL), ethylene brassylate (EB), and l-Lactide (LLA) with the alkyl substituted lactone ε-decalactone (ε-DL) were ...synthesized at different molar ratios. Copolymers were obtained via ring opening polymerization (ROP) employing TBD (1,5,7-triazabicyclo-4.4.0-dec-5-ene), an organic catalyst which can be handled under normal conditions, avoiding the use of glove box equipment. The molar monomer composition of resulting copolymers differed from theoretical values due to lower ε-DL reactivity; their Mn and Mw values were up to 14 kDa and 22.8 kDa, respectively, and distributions were (Ɖ) ≤ 2.57. The thermal stability of these materials suffered due to variations in their ε-DL molar content. Thermal transitions such as melting (Tm) and crystallization (Tc) showed a decreasing tendency as ε-DL molar content increased, while glass transition (Tg) exhibited minor changes. It is worth mentioning that changes in monomer composition in these polyesters have a strong impact on their thermal performance, as well as in their crystallization degree. Consequently, variations in their chemical structure may have an effect on hydrolyic degradation rates. It should be noted that, in future research, some of these copolymers will be exposed to hydrolytic degradation experiments, including characterizations of their mechanical properties, to determine their adequacy in potential use in the development of soft medical devices.
Five novel air- and moisture-stable polymetallic Ti and Zr amino acid-derived amine bis(phenolate) (ABP) complexes were synthesised and fully characterised, including X-ray crystallographic studies. ...The reaction of the ABP proligands with Ti or Zr alkoxides has resulted in the formation of polymetallic aggregates of different nuclearity. The steric bulk on the pendant arm of the ligand was found to play a critical role in establishing the nuclearity of the aggregated complex. Sterically, less-demanding groups, such as H or Me, facilitated the formation of tetrametallic Ti clusters, bridged by carboxylate groups, while increased steric bulk (tBu) led to the formation of binuclear μ-oxo-bridged species. The isolated complexes were employed as catalysts for the ring opening polymerisation (ROP) of rac-lactide. Overall, the Ti catalysts were all active with the smaller, bimetallic Ti aggregates exhibiting relatively faster rates. A monometallic, bis(ABP) Zr complex was found to exert remarkable ROP activity, albeit with limited control over the tacticity and molecular weight distribution of the polymer. A further oxo-bridged Zr cluster was shown to display a previously unprecedented trimetallic structure and achieved a moderate rate in the ROP of rac-lactide.
We have synthesized indium complexes containing a variety of metal bonding environments through use of polyfunctional dithiolate ligands and examined their reactivity as initiators for the ...ring-opening polymerization of l-lactide, rac-lactide, ε-caprolactone and β-butyrolactone. The facile reaction of Me3In with the corresponding polyfunctional dithiols in toluene, thf or diethyl ether resulted in the formation of MeIn(SOOS)2 (3), MeIn(SNNS) (4), MeIn(ONS2)3 (5), MeIn(NNS2) (6), MeIn(NNS2Pr) (7) and MeIn(pyrS)2 (8). The solid-state structures of 3 and 5 each show the corresponding ligand to be tridentate with an uncoordinated ligand O atom. Dimeric (3) and trimeric (5) structures result from short intermolecular In … S interactions. All structures show five coordinate indium centres in distorted trigonal bipyramidal bonding environments, but with various arrangements of donor atoms (eq/ax): SSC/OS (3,5), SNC/NS (4), SSN/NC (6), SSC/NS (7) and SSC/NN (8). DFT studies of model MeIn(SMe)2(NH3)2 systems show the bonding environments in 4 and 6 to be highly strained, while the axial In–Me bond of 6 shows the longest bond distance and lowest vibrational frequency. Compound 5 provided the best control of the polymerization of l-lactide and rac-lactide in THF at 70 °C, and a small heterotactic enrichment was observed for the latter. Compounds 3 and 4 provided the best control of the polymerization of β-BL in toluene at 70 °C in toluene, and compound 3 provided the best control of the polymerization of ε-CL in toluene at 70 °C. In all cases, polymerization rates were low. This work demonstrates a systematic approach to exploring the modification and reactivity of main group metal bonding motifs, which has resulted in identification of two novel “strained” bonding environments for indium.
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•Synthesis of six new methylindium dithiolate complexes incorporating a series of tetradentate dithiolate ligands.•Structural characterization of four and preliminary data for two compounds, revealing two new strained bonding environments for indium.•Computational studies to account for observed structures (i.e. monomer vs. dimer vs. trimer), and to quantify degrees of strain.•Exploration of reactivity through ROP studies of cyclic esters and analysis with respect to metal bonding environments.
This paper presents statistical analyses of rock engineering properties and the measured penetration rate of tunnel boring machine (TBM) based on the data of an actual project. The aim of this study ...is to analyze the influence of rock engineering properties including uniaxial compressive strength (UCS), Brazilian tensile strength (BTS), rock brittleness index (BI), the distance between planes of weakness (DPW), and the alpha angle (Alpha) between the tunnel axis and the planes of weakness on the TBM rate of penetration (ROP). Four
statistical regression models (two linear and two nonlinear) are built to predict the ROP of TBM. Finally a fuzzy logic model is developed as an alternative method and compared to the four statistical regression models. Results show that the fuzzy logic model provides better estimations and can be applied to predict the TBM performance. The R-squared value (R
) of the fuzzy logic model scores the highest value of 0.714 over the second runner-up of 0.667 from the multiple variables nonlinear regression model.
Purpose:
To assess long-term vascular density measured by optical coherence tomography angiography (OCT-A) in former preterm children with history of retinopathy of prematurity (ROP) with and without ...need of laser treatment.
Methods:
This observational study included former preterm children that developed ROP stage 2 or 3. Infants were divided in two groups according to previous need of laser treatment, and underwent a complete ophthalmologic evaluation, including assessment of macular morphologic and vascular parameters by OCT-A.
Results:
Fifteen eyes were included in group 1 (laser-requiring ROP) and 19 in group 2 (non-treated ROP). Group 1 had lower mean gestational age and birth weight values than group 2 (p < 0.001 and p < 0.001, respectively). Best corrected visual acuity (BCVA) was lower in group 1 (0.08 ± 0.04 logMAR vs 0.04 ± 0.07 logMAR, p = 0.03). Laser-requiring ROP had lower vascular parameters, especially of central and internal vascular density (9.15 ± 2.75 vs 10.52 ± 0.86 mm−1, p = 0.05; 13.74 ± 1.00 vs 15.86 ± 0.64 mm−1, p = 0.05; respectively), and lower avascular zone circularity (0.58 ± 0.06 vs 0.76 ± 0.02, p < 0.001). Mean macular thickness was higher in group 1 (300.50 ± 10.50 vs 281.11 ± 2.50 μm, p = 0.05). Best corrected visual acuity (BCVA) was correlated with superficial vascular density (p < 0.05).
Conclusion:
Laser-requiring ROP seems to result in a decrease of long-term BCVA, which is at least partially attributed to a decrease in superficial macular vascular density. However, prematurity degree was more pronounced in children that required treatment, which might have influenced our results.
Microwave-assisted ring opening polymerization (ROP) of ε-caprolactone was performed using three different carboxylic acids as initiators. In order to determine the effect of the acidity strength of ...the initiators on the molecular weight and terminal group functionality, the acids from strongest to weakest, i.e. trifluoro acetic acid, acetic acid, and benzoic acid, were used as initiators. The microwave power was kept at 600 W. The chemical structure and thermal properties of the synthesized low molecular weight PCLs were determined using Fourier Transform Infrared Spectroscopy (FTIR),
1
H Nuclear magnetic resonance (
1
H-NMR) spectroscopy, and differential scanning calorimetry (DSC). The molecular weight of the products was determined and compared using Light Scattering-Gel Permeation Chromatography (LS-GPC) and
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H-NMR spectroscopy. Their spectroscopic analyses showed that microwave-assisted polymerization is a useful technique in synthesizing the low molecular weight PCL without undesirable impurities. Melting points of the synthesized low molecular weight PCLs ranged from 52 °C to 63 °C, as determined by DSC. Their number-average molecular weights (Mn) and polydispersity index (PDI) were between 1.256—1.540 and 1.35—4.90 kDa, respectively. The Mn values obtained from the GPC were consistent with those calculated from
1
H-NMR and matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF) techniques. These findings highlighted the significance of the microwave technique in obtaining low molecular weight PCL for drug delivery formulations.
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