Graphs whose acyclic graphoidal covering number is one less than its maximum degree

An acyclic graphoidal cover of a graph G is a collection ψ of paths in G such that every path in ψ has at least two vertices, every vertex of G is an internal vertex of at most one path in ψ and every edge of G is in exactly one path in ψ. The minimum cardinality of an acyclic graphoidal cover of G is called the acyclic graphoidal covering number of G and is denoted by η_a. In this paper we characterize the class of graphs G for which η_a=Δ−1 where Δ is the maximum degree of a vertex in G.     

Optical fiber communication—An overview

This paper deals with the historical development of optical communication systems and their failures initially. Then the different generations in optical fiber communication along with their features are discussed. Some aspects of total internal reflection, different types of fibers along with their size and refractive index profile, dispersion and loss mechanisms are also mentioned. Finally the general system of optical fiber communication is briefly mentioned along with its advantages and limitations. Future soliton based optical fiber communication is also highlighted.     

Solid-State Isolation of Cyclic Alkyl(Amino) Carbene (cAAC)-Supported Structurally Diverse Alkali Metal-Phosphinidenides

Cyclic alkyl(amino) carbene (cAAC)-supported, structurally diverse alkali metal-phosphinidenides 2 – 5 of general formula ((cAAC)P-M)_n(THF)_x [ 2 : M=K, n=2, x=4; 3 : M=K, n=6, x=2; 4 : M=K, n=4, x=4; 5 : M=Na, n=3, x=1] have been synthesized by the reduction of cAAC-stabilized chloro-phosphinidene cAAC=P-Cl ( 1 ) utilizing metallic K or KC₈ and Na-naphthalenide as reducing agents. Complexes 2 – 5 have been structurally characterized in solid state by NMR studies and single crystal X-ray diffraction. The proposed mechanism for the electron transfer process has been well-supported by cyclic voltammetry (CV) studies and Density Functional Theory (DFT) calculations. The solid state oligomerization process has been observed to be largely dependent on the ionic radii of alkali metal ions, steric bulk of cAAC ligands and solvation/de-solvation/recombination of the dimeric unit [(cAAC)P-M(THF)_x]₂.     

Enantioselective synthesis of HIV protease inhibitor amprenavir via Co-catalyzed HKR of 2-(1-azido-2-phenylethyl)oxirane

A short and efficient enantioselective synthesis of the HIV protease inhibitor amprenavir 1 (99% ee) as well as a formal synthesis of saquinavir 3 have been achieved in high enantiomeric purity starting from commercially available materials. Our strategy mainly comprises a Co-catalyzed two-stereocentred hydrolytic kinetic resolution (HKR) of racemic 2-(1-azido-2-phenylethyl)oxirane as the chirality inducing step. Also presented is a concise synthesis of (S)-3-hydroxytetrahydrofuran 4, the key structural feature, in high enantiomeric purity (98% ee).     

Antimagic labeling of generalized pyramid graphs

An antimagic labeling of a graph withq edges is a bijection from the set of edges to the set of positive integers{1,2,...,q}such that all vertex weights are pairwise distinct,where the vertex weight of a vertex is the sum of the labels of all edges incident with that vertex.A graph is antimagic if it has an antimagic labeling.In this paper,we provide antimagic labelings for a family of generalized pyramid graphs.     

Ultrasound-promoted regioselective and stereoselective synthesis of novel spiroindanedionepyrrolizidines by multicomponent 1,3-dipolar cycloaddition of azomethine ylides

A series of novel spiroindanedionepyrrolizidines have been synthesized by multicomponent 1,3-dipolar cycloaddition of a variety of (E)-3-aryl-1-(thiophen-2-yl)prop-2-en-1-ones with unstabilized azomethine ylides generated from ninhydrin and l-proline. The reactions were highly regioselective and stereoselective and were conducted with both conventional heating and ultrasonic irradiation conditions. In general, milder conditions, and moderate improvement in rates, reaction times, and yields were observed when the reactions were performed under ultrasonic conditions. The regioselective and stereoselective nature of the products was established by use of single-crystal X-ray structure and spectroscopic techniques.     

Regioselective synthesis of 3,4,6,7-tetrahydro-3,3-dimethyl-9-phenyl-2H-xanthene-1,8(5H,9H)-diones through ascorbic acid catalyzed three-component domino reaction

An efficient, three-component domino reaction of dimedone 1, aromatic aldehydes (2a–o), and 1,3-cyclohexanedione 1a in the regio-selective synthesis of 3,3-dimethyl-9-phenyl-2H-xanthene-1,8(5H,9H)-diones (3a–o) is reported. The desired product, 3 is efficiently promoted by ascorbic acid as an organo catalyst.     

Highly fluorescent mono‐substituted poly(arylacetylene)s containing tolane chromophores

A new class of highly fluorescent mono‐substituted polyarylacetylenes ( P1–P3 ) has been successfully prepared with good yields and high molecular weights from a series of phenylethynylene‐substituted arylacetylenes ( M1–M3 ), using W‐based catalyst. These polymers are readily soluble in common organic solvents (e.g., THF, toluene, and chloroform) and thermally stable up to ～350 °C. Both ¹H NMR and IR studies confirmed that all the monomers were selectively polymerized at the terminal triple bond. The ¹H NMR results showed that both P1 and P2 have essentially trans‐polyene backbone structures, while P3 contains significant amounts of both cis‐ and trans‐structures. Coincidently, the photoluminescence (PL) intensity of P3 is also much lower than both P1 and P2 . Nevertheless, the PL intensity of P1–P3 are all much higher than that of PPA , suggesting that the introduction of phenylethynylene group to the phenyl rings of PPA s have made the in general nonemissive PPA s to become highly photoluminescent. Most interestingly, although P1 did not contain any substituent group on its tolane pendant group, it is already highly soluble in common organic solvent and emitting blue fluorescence (416 nm) with a reasonably good quantum yield (0.36). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5483–5498, 2008     

A rapid and highly sensitive method for the determination of glimepiride in human plasma by liquid chromatography-electrospray ionization tandem mass spectrometry: application to a pre-clinical pharmacokinetic study

A sensitive and specific liquid chromatography-positive electrospray ionization-tandem mass spectrometry method has been developed and validated for the determination of glimepiride (GPD) in human plasma. GPD and the internal standard (IS, glibenclamide) were extracted from a small aliquot of human plasma (200 microL) by a simple liquid-liquid extraction technique using ethyl acetate as extraction solvent. The compounds were separated on a YMC Propack, C18, 4.6x50 mm column using a mixture of ammonium acetate buffer, acetonitrile and methanol (30:60:10, v/v) as mobile phase at 0.5 mL/min on an API 4000 Sciex mass spectrometer connected to an Agilent HPLC system. Method validation and pre-clinical sample analysis was performed as per FDA guidelines and the results met the acceptance criteria. GPD and IS were detected without any interference from human plasma matrix. The method was proved to be accurate and precise at linearity range of 0.02-100.00 ng/mL with a correlation coefficient of 0.999. The method was robust with a lower limit of quantitation of 0.02 ng/mL. Intra- and inter-day accuracies for GPD were 88.60-113.50 and 96.82-103.93%, respectively. The inter-day precision was better than 12.21%. This method enabled faster and reliable determination of GPD in a pre-clinical study.     

Metal-Free,Photoredox-Catalyzed Synthesis of Quinazolin-4(3H)-ones and Benzo[4,5]imidazo[1,2-c]quinazolines Using Trialkylamines as Alkyl Synthon

Highly functionalized quinazolin-4(3H)-ones were synthesized from reactions of N-aryl-2-aminobenzamides with trialkylamines under photocatalytic conditions by using eosin Y (EY) as a catalyst. The reaction proceeds under mild conditions in aqueous acetonitrile and has a broad substrate scope. Mechanistic studies disclosed the electron-donor nature of the intermediate 2,3-dihydroquinazolin-4(1H)-one ( 3’ ) in the photocatalytic cycle to afford the 2,3-disubstituted-quinazolin-4(3H)-ones ( 3 ). This methodology has been extended to synthesize benzo [4,5] imidazole[1,2-c] quinazolines and 3 aa on a large scale. Furthermore, the synthesis of potent central nervous system depressant (CNS) drug molecules such as methaqualone ( 3 la ) and mecloqualone ( 3 pa ) was also achieved successfully.