Mechanistic Study on Gold(I)-Catalyzed Unsaturated Spiroketalization Reaction

The mechanism of metal-catalyzed spiroketalization of propargyl acetonide is explored by employing DFT with the B3LYP/6-31+G(d) method. Acetonide is used as a regioselective regulator in the formation of monounsaturated spiroketal. The energies of transition states, intermediates, reactants and products are calculated to provide new insight into the mechanism of the reaction. The energetic features, validation of the observed trends in regioselectivity are conferred in terms of electronic indices via FMO analysis. The presence of acetonide facilitates a stepwise spiroketalization as it masks the competing nucleophile, and thus hydroxyl group present, exclusively acts as a nucleophile. The vinyl gold intermediate 3 is formed from 2 via activation barrier TS1. This is the first ring formation, which is 6-exo-dig cyclization. The intermediate 3 is converted into allenyl ether 4, which isomerizes to the intermediate oxocarbenium ion 5 via activation barrier TS2. The intermediate 5 cyclizes to 6 via TS3. This is the second ring formation. The intermediate 6 on protodeauration turns into 6,6-monounsaturated spiroketal 7. It is concluded that acetonide as a protecting group serves the purpose, and thus a wide range of spiroketals can be prepared, regioselectivity.

Cambial Activity of Moringa peregrina (Forssk.) Fiori in Arid Environments

Moringa peregrina (Forssk.) Fiori, one of 13 species of the Moringaceae family widely distributed throughout the dry tropics, has the potential to become one of the most economically important medicinal plants in Egypt. However, despite its tolerance for drought and heat, it is also threatened by increasing temperatures and decreasing precipitation. Although the phenophase of this species is well documented, almost nothing is known about its period of cambial activity in desert regions. Ring formation and the general environmental adaptability of trees are affected by the timing of cambial activation. In our study site, we observe a distinct coupling of the development of new green leaves at the onset of vegetative growth in October and the phase of cambial activity (November–January). The onset of cambial activity seems to be related to a drop in temperature in October and the onset of torrential rains in the region. There might even be a short phase between the end of cambial activity and the onset of bud formation without xylem formation, but with photosynthetic activity. If so, we assume that all assimilates are stored as non-structural carbohydrates (NSC) in the parenchyma of the new ring. This potential gap opens new questions regarding the correlation between NSC storage capacity and the timing of remobilization for subsequent ring formation.

Synthesis of enantiomerically pure oxa[9]helicene derivatives via a nucleophilic cyclodehydration reaction of helical 1,1'-bibenzo[c]phenanthrenylidene-2,2'-dione

Enantiomerically pure 9-Substituted-11-oxa[9]helicene derivatives have been synthesized through furan-ring formation via a nucleophilic cyclodehydration reaction of enantiomerically pure helical polycondensed-2,2'-diphenoquinone derivatives (1,1'-bibenzo[c]phenanthrenylidene-2,2'-dione). (P)-2,2'-diphenoquinone derivatives afforded (P)-oxa[9]helicenes, while (M)-2,2'-diphenoquinone derivatives afforded their corresponding (M)-oxa[9]helicenes. Thus, the ring-closing reaction afforded the corresponding enantiomerically pure products without decreasing the enantiomeric excess and proceeded stereospecifically while retention the configuration. The thermal stability of oxa[9]helicene was studied by determining the decrease in the enantiomeric excess at various temperatures, and its racemization barrier was found to be 165.6 kJmol-1.

Serial Combination Optimization Method of Packet Transport Network

Packet transport network (PTN) has problems such as waste of resources and low network stability due to the excessive complexity of the existing network or improper network architecture design. The optimization of the transport networks can not only make the network structure more reasonable but also reduce all kinds of unexpected scenarios in the network operation, improving the network efficiency and reducing the failure rate. This research will be optimized from three aspects. (1) In order to solve the problem of the same active and standby routing in the existing network, an optimization algorithm for the same active and standby routing of LSP is proposed. The essence of the optimization algorithm is to search the existing routing using the K -shortest path (KSP) between two network nodes as protection routing for LSP protection. (2) Aiming at the link with a high CIR bandwidth occupancy rate, a method is completed without adding optical fibers and other physical resources; an optimization method for the committed information rate bandwidth occupancy rate based on the KSP algorithm is proposed. (3) When the PTN ring formation rate is low, the security of the PTN is seriously reduced. In order to solve the problem of low ring formation rate in the network, this paper proposes a ring formation rate optimization scheme for PTN access layer equipment based on network elements accounting income. Through the experimental verification on the mobile PTN in one city, Hubei Province, the combination optimization method can improve the network LSP protection rate by 24%, the CIR bandwidth occupancy rate is reduced by 13.82%, and the nonring forming rate was reduced by 17.9%. This method improved network stability, reducing the risk of failure in service transportation effectively.

Chromosomes Behavior at Meiosis in Chlorophytum stenopetalum Bak at Pachytene, Diakinesis and Diplotene

Meiotic prophase is classically subdivided into five stages: leptotene, zygotene, pachytene, diplotene, and diakinesis. The objective of this paper is to evaluate the behaviours of Chromosomes in Chlorophytum stenopetalum Bak.at pachytene /diakinesis and metaphase. The flower buds at right age were harvested, fixed in Cornoy’s solution (3 part of absolute alcohol and 1 part of acetic alcohol) and preserved in a refrigerator at -4°𝐶 for at least thirty minutes. The flower buds were then hydrolyzed in 10% HCl for 3-5 minutes. Prepared slides were viewed using an Armscope microscope equipped with digital automatic camera. At diakinesis seven bivalents (7 II) were predominantly observed (74.2%). Chromosomal stickiness is quite evidence. In addition, cross configuration and its resultant, ring formation at metaphase indicate the presence of translocation heterozgosity in the chromosomes of the species investigated. These abnormalities are likely to affect microsporogenesis and pollen viability.