Spectroscopic Study of Solvent Polarity on the Optical and Photo-Physical Properties of Novel 9,10-bis(coumarinyl)anthracene

Novel 7,7′-((anthracene-9,10-diylbis(methylene))bis(oxy))bis(4-methyl-2H-chromen-2-one) (BisCA) was prepared as fluorescent probe. The chemical structure of the novel BisCA was confirmed by spectroscopic data as well as elemental analyses. The solvatochromic characteristics of the new proble and its precursors were investigated in different solvents including, ethanol, DMF and toluene as protic polar, aprotic polar and non-polar solvents, respectively. Photo-physical parameters of probes, such as fluorescence quantum yields, fluorescence lifetime of excited state, radiative and non-radiative decay, were assessed in different media. The intermolecular H-bond effect on absorption and excitation spectra of the novel probe was reported in different solvents. Also, Onsager cavity radius and dipole moment of ground state and excited state of the probe were calculated as described by Bakhshiev and Reichardt methods.     

Rapid and efficient routes to phosphatidylinositol 3,4,5-trisphosphates via myo-inositol orthobenzoate

Efficient routes to two phosphatidylinositol 3,4,5-trisphosphate [PtdIns(3,4,5)P₃] analogues with different acyl chains have been developed by using cheaply available myo-inositol as the starting material. The high yield of the orthobenzoate derivative, preferential formation of the required protected inositol diastereomer in its desymmetrization and ease of separation make the synthesis expedient, economical and high yielding. Due to the inherent problem of racemization of diacylglycerol (DAG), the synthesis of phosphatidylinositol phosphates [PIPns] with unambiguous stereochemical purity has always been difficult. Our methodology excludes the possibility of racemization in the DAG unit and thus provides access to PtdIns(3,4,5)P₃ of high optical purity. Since the acyl functionalities are introduced last, the methodology reported is amenable to the synthesis of PtdIns(3,4,5)P₃ with any acyl chain (or even a library of analogues).     

Enthalpic changes on mixing two couples of S- and R-enantiomers of heptane-2-ol, octane-2-ol, nonane-2-ol, 3-chloro-propane-1,2-diol, 2-methyl-1,4-butanediol at 298.15 K

Enthalpies of mixing of (R)- and (S)-enantiomers of liquid chiral compounds such as heptane-2-ol, octane-2-ol, nonane-2-ol, 3-chloro-propane-1,2-diol and 2-methyl-1,4-butanediol have been measured over a range of mole fractions at 298.15 K, albeit very small values. Mixing of heterochiral liquids of heptane-2-ol, octane-2-ol, nonane-2-ol, 3-chloro-propane-1,2-diol, realized enthalpic destabilization over the whole range of mole fractions, whereas that of 2-methyl-1,4-butanediol realized enthalpic stabilization over entire compositions. The maximum values of enthalpies of mixing and the intermolecular interaction of cohesive energy density and entropy of vaporization showed a linear correlation except for the compounds having two chiral centers and others.     

A Molecular‐Level Study of Metamorphosis and Strengthening of Gels by Spontaneous Polymorphic Transitions

Many weak gels often undergo spontaneous transformation to form a stronger gel upon aging. Herein, the molecular‐level changes that occur during the transformation of a weak gel into a strong gel are shown by using various time‐dependent techniques. Diol 1 forms a metastable transparent gel (TG) in a mixture of CH₂Cl₂/hexane and undergoes a fast transition to an opaque gel (OG) accompanied by gradual strengthening of the gel, as evidenced from time‐dependent T_gel and rheology studies. Differential scanning calorimetry and thermogravimetric analyses suggest that these two gels correspond to two different polymorphs. By using FTIR spectroscopy and powder XRD experiments, it is shown that the TG‐containing kinetic polymorph, with weakly hydrogen‐bonded self‐assembly, spontaneously changes into the OG containing a strongly hydrogen‐bonded stable polymorph and this leads to strengthening of the gel and metamorphosis. Time‐dependent IR studies prove the gradual change in hydrogen‐bonding pattern. This is the first molecular‐level study of polymorphic transitions in gels.     

Conformation and molecular dynamics of single polystyrene chain confined in coordination nanospace

Molecules confined in nanospaces will have distinctly different properties to those in the bulk state because of the formation of specific molecular assemblies and conformations. We studied the chain conformation and dynamics of single polystyrene (PSt) chains confined in highly regular one-dimensional nanochannels of a porous coordination polymer [Zn 2(bdc) 2ted] n ( 1; bdc = 1,4-benzenedicarboxylate, ted = triethylenediamine). Characterization by two-dimensional (2D) heteronuclear (1)H- (13)C NMR gave a direct demonstration of the nanocomposite formation and the intimacy between the PSt and the pore surfaces of 1. Calorimetric analysis of the composite did not reveal any glass transition of PSt, which illustrates the different nature of the PSt encapsulated in the nanochannels compared with that of bulk PSt. From N 2 adsorption measurements, the apparent density of PSt in the nanochannel was estimated to be 0.55 g cm (-3), which is much lower than that of bulk PSt. Results of a solid-state (2)H NMR study of the composite showed the homogeneous mobility of phenyl flipping with significantly low activation energy, as a result of the encapsulation of single PSt chains in one-dimensional regular crystalline nanochannels. This is also supported by molecular dynamics (MD) simulations.     

<Emphasis Type="Italic">Rhizopus stolonifer</Emphasis> LAU 07: a novel source of fructosyltransferase

Increasing awareness of the importance of fructooligosaccharides (FOS) as ingredients of functional foods has led to intensive search of new sources of fructosyltransferases (FTase), enzymes responsible for the conversion of sucrose to fructooligosaccharides. A local strain of Rhizopus stolonifer isolated from spoilt orange fruit with high fructosyltransferase activity (U _t) of 12.31–45.70 U mL⁻¹ during a fermentation period of 24–120 h is herein reported. It showed low hydrolytic activity (U _h) in the range of 0.86–1.78 U mL⁻¹ during the same period. FOS yield of 34 % (1-kestose, GF₂, nystose, GF₃) was produced by FTase obtained from a 72 h-old culture using 60 g of sucrose per 100 mL of the substrate. When the isolate was grown in a defined submerged medium, its pH dropped sharply from the intial value of 5.5 to 1.0 within 24 h, and this value was maintained throughout the fermentation. The biomass content ranged from 8.8 g L⁻¹ at 24 h of fermentation to reach the maximum of 10 g L⁻¹ at 72 h. It was reduced to 5.6 g L⁻¹ at the end of 120 h of fermentation. This report represents the first reference to a strain of Rhizopus as a source of FTase for the production of FOS. The high U _t/U _h ratio shown by this isolate indicates that it may be a good strain for the industrial and commercial production of FOS. However, there is a need of further optimization of the bioprocess to increase the conversion efficiency of sucrose to FOS by the enzyme.     

Oxidative dehydrogenation of dihydropyrimidinones and dihydropyrimidines

[reaction: see text] A mild, practical procedure for oxidative dehydrogenation with catalytic amounts of a Cu salt, K2CO3, and tert-butylhydroperoxide (TBHP) as a terminal oxidant has been developed. This oxidation procedure is generally applicable to dihydropyrimidinones and most dihydropyrimidines.     

Azide–Alkyne Interactions: A Crucial Attractive Force for Their Preorganization for Topochemical Cycloaddition Reaction

A new class of attractive intermolecular interaction between azide and ethynyl structural entities in a wide range of molecular crystals is reported. This interaction was systematically evaluated by using 11 geometrically different structural motifs that are preorganized to direct a solid-state topochemical azide–alkyne cycloaddition (TAAC) reaction. The supramolecular features of the azide–alkyne interaction were mapped by various crystallographic and quantum chemical approaches. Topological analysis shows the noticeable participation of electron density in the azide⋅⋅⋅alkyne interactions. Interestingly, reorientation of the atomic polarizabilities in vicinal azide and alkyne groups upon interaction in crystals favors soft orbital-guided TAAC reactions. Moreover, various solid-state and gas-phase energy decomposition methods of individual azide⋅⋅⋅alkyne interactions summarize that the strength (varies from −5.7 to −30.1 kJ mol⁻¹) is primarily guided by the dispersion forces with a influencing contribution from the electrostatics.     

Spectroscopic Behavior and Photophysical Parameters of 2-(Acetoxymethyl)-6-(1,2,4-triazinylaminodihydroquinazolinyl)tetrahydropyran Derivative in Different Solid Hosts

Journal of Fluorescence - Optical and photophysical properties of 6-substituted-1,2,4-Triazine fluorescent derivative dye doped in silicate based sol–gel, homopolymer of methyl methacrylate...     

Magnetic Circularly Polarized Luminescence from PtIIOEP and F2-ppyPtII(acac) under North-up and South-up Faraday Geometries

The magnetic circularly polarized luminescence (MCPL) and photoluminescence (PL) spectra of achiral (2,3,7,8,12,13,17,18-octaethylporphyrinato)platinum(II), PtOEP , and [2-(4′,6′-difluorophenyl)pyridinato-N,C^2′]platinum(II) acetylacetonate-O,O, F₂-ppyPt(acac) , in toluene and dichloromethane solutions were recorded under an external magnetic field of 1.6 T with N-up and S-up Faraday geometries. The MCPL signs of PtOEP and F₂-ppyPt(acac) were controlled solely by changing the N-up and S-up geometries. The MCPL/PL wavelengths of F₂-ppyPt(acac) in solutions were varied by the ratio of the monomeric and excimeric species.