Ring-opening reactions of oxetanes: A review of methodology development and synthetic applications

Ring-opening reactions of oxetanes yield important functionalized products depending upon the nature of nucleophiles as well as substitution pattern on the oxetane ring. Ring opening of oxetanes can be carried out under a variety of reaction conditions. In this review article, an up-to-date overview of major synthetic methodologies involved in the ring opening of oxetanes as well as their synthetic applications has been presented.     

A New and Pragmatic Approach to the GIX/Geo/c/N Queues Using Roots

A simple and complete solution to determine the distributions of queue lengths at different observation epochs for the model GI^X/Geo/c/N is presented. In the past, various discrete-time queueing models, particularly the multi-server bulk-arrival queues with finite-buffer have been solved using complicated methods that lead to results in a non-explicit form. The purpose of this paper is to present a simple derivation for the model GI^X/Geo/c/N that leads to a complete solution in an explicit form. The same method can also be used to solve the GI^X/Geo/c/N queues with heavy-tailed inter-batch-arrival time distributions. The roots of the underlying characteristic equation form the basis for all distributions of queue lengths at different time epochs. All queue-length distributions are in the form of sums of geometric terms.

     

Effect of Sodium Alkanoates on Micellization of Dodecylbenzyldimethylammonium Chloride in Aqueous Medium

The present study deals with the interaction of sodium alkanoates viz. sodium acetate, sodium propionate, sodium butanoate, sodium hexanoate and sodium benzoate on the micellization of dodecylbenzyldimethylammonium chloride using conductometeric and flourscence quenching experiments carried out at 25°C. The analysis has been made through study of variation of critical micelle concentration (cmc), degree of counterion binding (β), aggregation number (N), and micropolarity with the concentration of these hydrophobic salts. The differentiation between the effects of hydrophobic and inorganic salts was made by comparing the above results with the influence of NaCl on cmc, β, and N.     

Modification of Lysine Residues of Horseradish Peroxidase and Its Effect on Stability and Structure of the Enzyme

Biotechnology is consistently seeking improved enzyme stability. Enzymes have great properties, although their marginal stability limits their applications. Among the strategies for improving stability of the enzymes, chemical modification is a simple and effective technique. In the present study, chemical modification of horseradish peroxidase (HRP) was carried out with 2,3-dichloromaleic anhydride and 2,3-dimethylmaleic anhydride. HRP is an important heme-containing enzyme. It is widely applied in pharmacological, chemical, and medical industries. Here, thermal stability of HRP was investigated at different temperatures. In addition, the enzyme stability was evaluated in urea, DMSO, alkaline pH, and hydrogen peroxide solutions by spectroscopic techniques. Structural investigation indicated that the both anhydrides slightly decrease compactness of the enzyme structure. The results also indicated that 2,3-dichloromaleic anhydride increases thermal stability of the enzyme and its stability in urea and DMSO solutions, but 2,3-dimethylmaleic anhydride only stabilizes HRP in urea solution. Furthermore, the experiments implied that none of the modifiers are effective on the stability of HRP in extreme pH and oxidative condition. Catalytic efficiency and activation energy did not change remarkably following reaction of the enzyme with the both carboxylic anhydrides. Consequently, improvement in the stability of HRP depends on not only the type of modifier but also denaturing condition.     

Rheological response and small-angle neutron-scattering study of diester-bonded cationic biodegradable gemini surfactants in presence of different additives

Morphological changes and internal packing arrangements of planar dicationic-ester-bonded biodegradable gemini surfactants ethane-1, 2-diyl-bis(N,N-dimethyl-N-alkylammonium acetoxy) dichlorides (m-E2-m) have been explored by exploiting small-angle neutron-scattering (SANS) measurements. The data have been analyzed on the basis of Hayter and Penfold model for macroion solutions to obtain information about the aggregation behavior at the molecular level. The extent of micellar growth and structural changes of the micelles formed by these surfactants have been found to depend on the number of methylene units in their tail length. The growth and variation of micellar shape are more pronounced for the surfactant with longer tail length (m?=?16), whereas the surfactants with shorter tail length showed less variation of these properties in aqueous solution. Semi-major axes of the micelles show flexibility while varying the concentration and temperature of the systems; however, semi-minor axes remain rigid. Changes in the structural parameters of the micelles with addition of different salts were also inferred from SANS measurements. The intensity of scattered neutrons at the low Q region was found to increase while varying the nature of salt from monovalent to trivalent. On the basis of rheological responses, the rich aggregation behavior resulting from the addition of sodium salicylate (NaSal) is attributed to the special molecular structure of the gemini surfactant and the appropriate interaction between the surfactant and NaSal. This is inferred on the basis of behavior observed by varying the chain length (m) of the gemini surfactant that resulted in the formation of different types of microstructures.     

Atomic-scale characterization of graphene grown on copper (100) single crystals

Growth of graphene on copper (100) single crystals by chemical vapor deposition has been accomplished. The atomic structure of the graphene overlayer was studied using scanning tunneling microscopy. A detailed analysis of moire? superstructures present in the graphene topography reveals that growth occurs in a variety of orientations over the square atomic lattice of the copper surface. Transmission electron microscopy was used to elucidate the crystallinity of the grown graphene. Pristine, defect-free graphene was observed over copper steps, corners, and screw dislocations. Distinct protrusions, known as "flower" structures, were observed on flat terraces, which are attributed to carbon structures that depart from the characteristic honeycomb lattice. Continuous graphene growth also occurs over copper adatoms and atomic vacancies present at the single-crystal surface. The copper atom mobility within vacancy islands covered with suspended graphene sheets reveals a weak graphene-substrate interaction. The observed continuity and room-temperature vacancy motion indicates that copper mobility likely plays a significant role in the mechanism of sheet extension on copper substrates. Lastly, these results suggest that the quality of graphene grown on copper substrates is ultimately limited by nucleation at the surface of the metal catalyst.     

Identification of novel inhibitory candidates against two major Flavivirus pathogens via CADD protocols: in silico analysis of phytochemical binding,reactivity, and pharmacokinetics against NS5 from ZIKV and DENV

Structural Chemistry - Zika and dengue virus are flaviviruses which with the passage of time have become a serious challenge affecting millions of people around the world. To lessen the impact of...     

Electrical behaviour of fine particle, co-precipitation prepared Ni-Zn ferrites

Co-precipitation technique using chlorides of constituents was used to prepare fine particles Ni-Zn ferrites. The particle size was estimated from X-ray diffraction data using Sherrer's formula. The dc electrical resistivity and thermo-power was measured in the temperature range 300-450 K and it was found that all the samples are degenerate type semi-conductors. The results of dc resistivity and thermo-electric power confirm that the conduction mechanism in these ferrites is due to small polaron hopping.