Structural studies of Schiff-base [2 + 2] macrocycles derived from 2,2′-oxydianiline and the ROP capability of their organoaluminium complexes

The molecular structures of a number of solvates of the [2 + 2] Schiff-base macrocycles {[2-(OH)-5-(R)-C6H2-1,3-(CH)2][O(2-C6H4N)2]}2 (R = Me L1H2, tBu L2H2, Cl L3H2), formed by reacting 2,6-dicarboxy-4-R-phenol with 2,2′-oxydianiline (2-aminophenylether), (2-NH2C6H4)2O, have been determined. Reaction of LnH2 with two equivalents of AlR′3 (R′ = Me, Et) afforded dinuclear alkylaluminium complexes [(AlR′2)2L1–3] (R = R′ = Me (1), R = tBu, R′ = Me (2), R = Cl, R′ = Me (3), R = Me, R′ = Et (4), R = tBu, R′ = Et (5), R = Cl, R′ = Et (6)). For comparative studies, reactions of two equivalents of AlR′3 (R′ = Me, Et) with the macrocycle derived from 2,2′-ethylenedianiline and 2,6-dicarboxy-R-phenols (R = Me L4H2, tBu L5H2) were conducted; the complexes [(AlMe)(AlMe2)L5]·2¼MeCN (7·2¼MeCN) and [(AlEt2)2L4] (8) were isolated. Use of limited AlEt3 with L3H2 or L5H2 afforded mononuclear bis(macrocyclic) complexes [Al(L3)(L3H)]·4toluene (9·4toluene) and [Al(L5)(L5H)]·5MeCN (10·5MeCN), respectively. Use of four equivalents of AlR′3 led to transfer of alkyl groups and isolation of the complexes [(AlR′2)4L1′–3′] (R = L2′, R′ = Me (11); L3′, R′ = Me (12); L1′, R′ = Et (13); L2′, R′ = Et (14); L3′, R′ = Et (15)), where L1′–3′ is the macrocycle resulting from double alkyl transfer to imine, namely {[2-(O)-5-(R)C6H2-1-(CH)-3-C(R′)H][(O)(2-(N)-2′-C6H4N)2]}2. Molecular structures of complexes 7·2¼MeCN, 8, 9·4toluene, 10·5MeCN and 11·1¾toluene·1¼hexane are reported. These complexes act as catalysts for the ring opening polymerisation (ROP) of ε-caprolactone and rac-lactide; high conversions were achieved over 30 min at 80 °C for ε-caprolactone, and 110 °C over 12 h for rac-lactide

Modeling and experimental analysis of polypropylene honeycomb multi-layer sandwich composites under four-point bending

The behavior of a simple and innovative multi-layer sandwich panels having a polypropylene honeycomb core has been investigated carefully, theoretically and experimentally. A four-point bending test was performed to detect the mechanical characteristics of the multi-layer core. The experimental results emphasize a better rigidity of the multi-layer structure compared to the weakness displayed by the single-layer configuration. In fact, a small increase in the final weight of the component leads to a significant increase of the mechanical properties. In the second part of this study, analytical and numerical homogenization approaches were developed to compute the effective properties of the single polypropylene honeycomb core. The numerical model complies with the experimental protocol, and the simulation conducted is aiming to reproduce a typical four-point bending test on a polypropylene honeycomb multi-layer sandwich panel. Both numerical and experimental results are presented in details and a good correlation between them is highlighted

Coordination chemistry of [2+2] Schiff-base macrocycles derived from the dianilines [(2-NH2C6H4)2X] (X = CH2CH2,O): structural studies and ROP capability towards cyclic esters

Reaction of the [2 + 2] Schiff-base macrocycles {[2-(OH)-5-(R)-C 6H 2-1,3-(CH) 2][CH 2CH 2(2-C 6H 4N) 2]} 2(R = Me, L 1H 2;tBu, L 2H 2) with FeBr 2afforded the complexes [FeBr(L 1H 2)] 2[(FeBr 3) 2O]·2MeCN (1·2MeCN), [FeBr(L 2H 2)][X] (X = 0.5(FeBr 3) 2O,2·0.5MeCN, X = Br,3·5.5MeCN), respectively. Reaction of L 2H 2with [KFe(OtBu) 3(THF)] (formedin situfrom FeBr 2and KOtBu), following work-up, led to the isolation of the complex [Fe(L 2)(L 2H)]·3MeCN (4·3MeCN), whilst with [CuBr 2] afforded [CuBr(L 2H 2)][CuBr 2]·2MeCN (5·2MeCN). Attempts to form mixed Co/Ti species by reaction of [CoBrL 2][CoBr 3(NCMe)] with TiCl 4resulted in [L 2H 4][CoBr 4]·2MeCN (6·2MeCN). Use of the related oxy-bridged Schiff-base macrocycles {[2-(OH)-5-(R)-C 6H 2-1,3-(CH) 2][O(2-C 6H 4N) 2]} 2(R = Me, L 3H 2;tBu, L 4H 2) with CoBr 2led to the isolation of the complexes [(CoBr) 2(L 3)]·2C 3H 6O (7·2C 3H 6O), [Co(NCMe) 2(L 4H 2)][CoBr 4]·5MeCN (8·5MeCN), [Co(NCMe) 6][CoBr 3(MeCN)] 2·2MeCN (9·2MeCN). For comparative structural/polymerisation studies, the complexes {CoBr(NCMe)L 5} 2·2MeCN (10·2MeCN) and [Co(NCMe) 2L 5] 2[CoBr 3(NCMe)] 2(11), [FeBr(NCMe)L 5] 2·2MeCN (12·2MeCN) where L 5H = 2,6-(CHO) 2-4-tBu-C 6H 2OH, as well as the chelate-free salt [Fe(NCMe) 6][FeBr 3OFeBr 3] (13) have been isolated and structurally characterized. The ability of these complexes to act as catalysts for the ring opening polymerisation (ROP) of ε-caprolactone (ε-CL) and δ-valerolactone (δ-VL) was investigated, as well as co-polymerisation of ε-CL withrac-lactide (r-LA) andvice versa

Deep-level Transient Spectroscopy of GaAs/AlGaAs Multi-Quantum Wells Grown on (100) and (311)B GaAs Substrates

Si-doped GaAs/AlGaAs multi-quantum wells structures grown by molecular beam epitaxy on (100) and (311)B GaAs substrates have been studied by using conventional deep-level transient spectroscopy (DLTS) and high-resolution Laplace DLTS techniques. One dominant electron-emitting level is observed in the quantum wells structure grown on (100) plane whose activation energy varies from 0.47 to 1.3 eV as junction electric field varies from zero field (edge of the depletion region) to 4.7 × 106 V/m. Two defect states with activation energies of 0.24 and 0.80 eV are detected in the structures grown on (311)B plane. The Ec-0.24 eV trap shows that its capture cross-section is strongly temperature dependent, whilst the other two traps show no such dependence. The value of the capture barrier energy of the trap at Ec-0.24 eV is 0.39 eV

Interface intermixing and magnetoresistance in Co/Cu spin valves with uncoupled Co layers

The interpretation of experiments on the effect of interface intermixing on the giant magnetoresistance (GMR) effect in antiferromagnetic-coupled multilayers can be complicated by the fact that interface intermixing also changes the coupling strength; therefore, we have grown an artificially intermixed region in Co/Cu spin valves with uncoupled Co layers. The structure we used was a newly engineered spin valve composed of 100 Å Co+6 Å Ru+25 Å Co+40 Å Cu+100 Å Co. Here the Ru layer provides an antiparallel alignment of the Co layers and the Cu layer decouples the upper two Co layers. An intermixed CoCu region has been grown at the Cu/Co interface and in some cases also at the Co/Cu interface by alternately sputtering 1 Å Co and 1 Å Cu. X-ray measurements confirm the existence of an intermixed region, although no reduction of magnetic moment is observed as is reported for homogeneous sputtered Co0.5Cu0.5 alloys. This indicates the existence of Co clusters in the intermixed regions. There is no difference in GMR between an intermixed layer of thickness t at one Co/Cu interface or two intermixed layers of thickness t/2 at both Co/Cu interfaces. Thus, it seems that the total thickness of the intermixed regions is decisive for the magnitude of the GMR. Because G, ¿G, and ¿G/Gap all show a gradual decrease when the nominal thickness of the intermixed region increases from 0 to 36 Å, this indicates that there is no strong spin-dependent scattering in this region. This is in agreement with calculations on a model bilayer Co/Cu/Co with the Camley–Barnas model

Genomics-assisted breeding in four major pulse crops of developing countries: present status and prospects

The global population is continuously increasing and is expected to reach nine billion by 2050. This huge population pressure will lead to severe shortage of food, natural resources and arable land. Such an alarming situation is most likely to arise in developing countries due to increase in the proportion of people suffering from protein and micronutrient malnutrition. Pulses being a primary and affordable source of proteins and minerals play a key role in alleviating the protein calorie malnutrition, micronutrient deficiencies and other undernourishment-related issues. Additionally, pulses are a vital source of livelihood generation for millions of resource-poor farmers practising agriculture in the semi-arid and sub-tropical regions. Limited success achieved through conventional breeding so far in most of the pulse crops will not be enough to feed the ever increasing population. In this context, genomics-assisted breeding (GAB) holds promise in enhancing the genetic gains. Though pulses have long been considered as orphan crops, recent advances in the area of pulse genomics are noteworthy, e.g. discovery of genome-wide genetic markers, high-throughput genotyping and sequencing platforms, high-density genetic linkage/QTL maps and, more importantly, the availability of whole-genome sequence. With genome sequence in hand, there is a great scope to apply genome-wide methods for trait mapping using association studies and to choose desirable genotypes via genomic selection. It is anticipated that GAB will speed up the progress of genetic improvement of pulses, leading to the rapid development of cultivars with higher yield, enhanced stress tolerance and wider adaptability

Transient charge density wave dynamics in pure, non-stoichiometric and V-doped blue bronzes A0.30MoO3 (A= K, Rb)

We report the observation of the transient voltage response to current pulses in pure, non-stoichiometric and V-doped blue bronzes A0.30MoO3 (A= K, Rb) near threshold for depinning of the charge density wave. The transient response waveforms involve overshoot and sluggish behaviors at the leading edge of the pulse in pure samples, weak sluggish response in non-stoichiometric samples and strong sluggish behavior in V-doped blue bronzes. The time decays of the transient responses obey stretched exponential laws. The characteristic time for the overshoot obeys a power law as a function of the electric field and is divergent as threshold is approached from above, suggesting that depinning can be viewed as a dynamical critical phenomenon. The transient response has also been studied under inhomogeneous conditions when a current pulse is injected in a segment of the sample while a dc current is flowing in a neighboring segment. The different regimes found in the transient response are analyzed in analogy with strain transient and plastic yielding of a crystal and in terms of combined motion of edge and screw charge density wave phase dislocations interacting with impurities

Experimental/numerical investigation of mechanical behaviour of internally pressurized cylindrical shells with external longitudinal and circumferential semi-elliptical defects

This paper presents an experimental-numerical investigation on the mechanical behaviour of pressurized cylindrical shells with external longitudinal and circumferential cracks of semi-elliptical shape. The research is motivated by the need to develop advanced design methodologies for shell structures. For that purpose, strain gauges are utilized to monitor strain concentrations near the cracks, and finite element simulations are carried out to predict the corresponding stress intensity factor distributions. A good agreement between numerical simulations and experimental data is found. This confirms that virtual simulations/calculations provide a reliable approach to evaluating mechanical behaviour of pressurized cylindrical shells with crack defects