Mechanical behaviour of a hydrogel film with embedded voids under the tensile load

The behaviour of alginate gel film in response to the tensile load is analysed in this paper. The bubbles of 0.5?mm diameter were embedded in the film by the fluidic method prior to gelation, thus providing uniform voidage over the entire film. Further, the intrinsic porosity of the gel matrix around the voids was varied by removing water through either evaporation under vacuum, or employing lyophilisation. The Poisson’s ratio and the modulus of elasticity were estimated from direct measurements. The viscoelasticity of the gel matrix was characterized from stress-relaxation measurement. The transient response to tensile loading and the evolution of stress contours were studied through numerical simulation in ANSYS. The ultimate strength was studied for the gel films with embedded voids of different sizes. The numerical simulations were validated by experimental measurements.

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Photooxidation of a Twisted Isoquinolinone

Understanding the oxidation mechanism and positions of twistacenes and twistheteroacenes under ambient conditions is very important because such knowledge can guide us to design and synthesize novel, larger stable analogues. Herein, we demonstrated for the first time that a twisted isoquinolinone can decompose under oxygen and light at room temperature. The as‐decomposed product 1 was fully characterized through conventional methods as well as single‐crystal structure analysis. Moreover, the physical properties of the as‐obtained product were carefully investigated and the possible formation mechanism was proposed.     

Improved micellar hydration and gelation characteristics of PEO-PPO-PEO triblock copolymer solutions in the presence of LiCl

LiCl-induced changes in the micellar hydration and gelation characteristics of aqueous solutions of the two triblock copolymers F127 (EO(100)PO(70)EO(100)) and P123 (EO(20)PO(70)EO(20)) (where EO represents the ethylene oxide block and PO represents the propylene oxide block) have been studied by small-angle neutron scattering (SANS) and viscometry. The effect of LiCl was found to be significantly different from those observed for other alkali metal chloride salts such as NaCl and KCl. This can be explained on the basis of the complexation of hydrated Li(+) ions with the PEO chains in the micellar corona region. The interaction between the chains and the ions is more significant in the case F127 because of its larger PEO block size, and therefore, micelles of this copolymer show an enhanced degree of hydration in the presence of LiCl. The presence of the hydrated Li(+) ions in the micellar corona increases the amount of mechanically trapped water there and compensates more than the water molecules lost through the dehydration of the PEO chains in the presence of the Cl(-) ions. The enhancement in micellar hydration leads to a decrease in the minimum concentration required for the F127 solution to form a room-temperature cubic gel phase from 18% to 14%. Moreover, for both copolymers, the temperature range of stability of the cubic gel phase also increases with increasing LiCl concentration, presumably because of the ability of the Li(+) ions to reduce micellar dehydration with increasing temperature. Viscosity studies on a poly(ethylene glycol) (PEG) homopolymer with a size equivalent to that of the PEO block in F127 (4000 g/mol) also suggest that the dehydrating effect of the Cl(-) ion on the PEG chain is compensated by its interaction with the hydrated Li(+) ions.     

Photoinduced electron transfer dynamics in porphyrin donor dyads

Intramolecular photoinduced electron transfer (PET) processes occurring in dyads with a free base porphyrin-tetraazaanthracene donor (P) and either a tetracyanonaphthoquinidodimethane (TCQ) or benzoquinone (BQ) acceptor linked by a rigid six σ-bond polynorbornane bridge ([6]) have been investigated. For P[6]BQ, PET in the polar solvent benzonitrile (_s = 25.9) occurs with a rate constant (k_PET) of 1.6 × 10⁸ s⁻¹ but is not evident in solvents less polar than tetrahydrofuran (_s = 7.52). For P[6]TCQ, highly efficient forward PET occurs in both polar and non-polar solvents (k_PET > 2 × 10¹⁰ s⁻¹). For P[6]TCQ the lifetime of the resulting charge-separated state decreases markedly with increasing solvent polarity. The results are discussed in the context of the likely mechanisms for electronic coupling and current theories for PET processes in such linked molecular systems.     

Posaconazole (Noxafil, SCH 56592), a new azole antifungal drug, was a discovery based on the isolation and mass spectral characterization of a circulating metabolite of an earlier lead (SCH 51048)

Posaconazole (SCH 56592) is a novel triazole antifungal drug that is marketed in Europe and the United States under the trade name 'Noxafil' for prophylaxis against invasive fungal infections. SCH 56592 was discovered as a possible active metabolite of SCH 51048, an earlier lead. Initial studies have shown that serum concentrations determined by a microbiological assay were higher than those determined by HPLC from animals dosed with SCH 51048. Subsequently, several animals species were dosed with (3)H-SCH 51048 and the serum was analyzed for total radioactivity, SCH 51048 concentration and antifungal activity. The antifungal activity was higher than that expected based on SCH 51048 serum concentrations, confirming the presence of active metabolite(s). Metabolite profiling of serum samples at selected time intervals pinpointed the peak that was suspected to be the active metabolite. Consequently, (3)H-SCH 51048 was administered to a large group of mice, the serum was harvested and the metabolite was isolated by extraction and semipreparative HPLC. LC-MS/MS analysis suggested that the active metabolite is a secondary alcohol with the hydroxyl group in the aliphatic side chain of SCH 51048. All corresponding monohydroxylated diastereomeric mixtures were synthesized and characterized. The HPLC retention time and LC-MS/MS spectra of the diastereomeric secondary alcohols of SCH 51048 were similar to those of the isolated active metabolite. Finally, all corresponding individual monohydroxylated diasteriomers were synthesized and evaluated for in vitro and in vivo antifungal potencies, as well as pharmacokinetics. SCH 56592 emerged as the candidate with the best overall profile.     

Synthesis and DFT calculations of oxido and phenylimido-rhenium(V) complexes incorporating the N,O donor ligand 2-[(2-hydroxyethylimino)methyl]phenol

The reactions of equimolar amounts of trans-[ReOC1₃(PPh₃)₂] or trans-[Re(NPh)(PPh₃)₂Cl₃] with a Schiff base formed by condensation of 2-hydroxy-4-methoxybenzaldehyde and ethanolamine (H₂L) result in the formation of cis-[ReO(HL)PPh₃Cl₂] (1a) and trans-[Re(NPh)(HL)(PPh₃)Cl₂] (2b), respectively, in good yields. 1a and 2b have been characterized by a range of spectroscopic and analytical techniques. The X-ray crystal structures of 1a and 2b reveal that 1a is an octahedral cis-Cl,Cl oxorhenium(V) complex, while 2b is a trans-Cl,Cl phenylimidorhenium(V) complex. The complexes are weakly emissive at room temperature with quantum yields of 10^?4. Density functional theory calculations of the electronic properties of the complexes were performed and are in agreement with the experimental results. The complexes display quasi-reversible Re(V)/Re(VI) redox couples in acetonitrile. There is reasonable agreement between the experimental and calculated redox potentials of 1a and 2b.     

A Colorimetric and Fluorimetric Chemodosimeter for Copper Ion Based on the Conversion of Dihydropyrazine to Pyrazine

In this research, we successfully synthesized and fully characterized the new compound 5,8,13,16,21,24‐hex‐(triisopropylsilyl)ethynyl)‐6,23‐dihydro‐6,7,14,15,22,23‐hexaza‐trianthrylene ( HHATA , brown color in a mixed solvent of CH₂Cl₂/CH₃CN 1:1, v/v, weakly blue fluorescent), which can be easily oxidized to 5,8,13,16,21,24‐hex‐(triisopropylsilyl)ethynyl)‐6,7,14,15,22,23‐hexazatrianthrylene ( HATA ) (yellow color in CH₂Cl₂/CH₃CN 1:1, v/v), red fluorescent) by Cu²⁺ ions. This reaction only proceeds efficiently in the presence of Cu²⁺ ions when compared with other common metal ions such as Fe³⁺, Co²⁺, Mn²⁺, Hg²⁺, Ni²⁺, Pb²⁺, Ag⁺, Mg²⁺, Ca²⁺, K⁺, Na⁺, and Li⁺. Our result suggests that this reaction can be developed as an effective method for the detection of Cu²⁺ ions.     

Urea-based ruthenium(II)-polypyridyl complex as an optical sensor for anions: synthesis, characterization, and binding studies

A new ruthenium(II) complex [Ru(bpy)2(1-(6-nitro-[1,10]phenanthrolin-5-yl)-3-(4-nitrophenyl)-urea)] (bpy=2,2'-bipyridyl) was synthesized and characterized using standard analytical and spectroscopic techniques. Detailed absorption, emission, and 1H NMR spectral studies revealed that this receptor molecule acts as a sensor for F-, CH3COO-, and H2PO4- in acetonitrile solution. Binding of these anions caused an appreciable change in the color of the acetonitrile solution, which could be detected with the naked eye. At relatively lower concentration of anions, 1:1 H-bonded adduct was formed; however, at higher concentration, classical Br?nsted acid-base-type reaction prevailed. The relative binding affinity of different anions toward this receptor was evaluated and was rationalized with quantum chemical calculations. Narrowing of the gap between the highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels on deprotonation of the receptor molecule caused a faster decay of the luminescence lifetime for the Rudpi-->Lpi*/bpypi*-based triplet excited state.     

An experimental and computational analysis on the differential role of the positional isomers of symmetric bis-2-(pyridyl)-1H-benzimidazoles as DNA binding agents

Three symmetrical positional isomers of bis-2-(n-pyridyl)-1H-benzimidazoles (n=2, 3, 4) were synthesized and DNA binding studies were performed with these isomeric derivatives. Like bisbenzimidazole compound Hoechst 33258, these molecules also demonstrate AT-specific DNA binding. The binding affinities of 3-pyridine (m-pyben) and 4-pyridine (p-pyben) derivatized bisbenzimidazoles to double-stranded DNA were significantly higher compared to 2-pyridine derivatized benzimidazole o-pyben. This has been established by combined experimental results of isothermal fluorescence titration, circular dichroism, and thermal denaturation of DNA. To rationalize the origin of their differential binding characteristics with double-stranded DNA, computational structural analyses of the uncomplexed ligands were performed using ab initio/Density Functional Theory. The molecular conformations of the symmetric head-to-head bisbenzimidazoles have been computed. The existence of intramolecular hydrogen bonding was established in o-pyben, which confers a conformational rigidity to the molecule about the bond connecting the pyridine and benzimidazole units. This might cause reduction in its binding affinity to double-stranded DNA compared to its para and meta counterparts. Additionally, the predicted stable conformations for p-, m-, and o-pyben at the B3LYP/6-31G* and RHF/6-31G* levels were further supported by experimental pKa determination. The results provide important information on the molecular recognition process of such symmetric head to head bisbenzimidazoles toward duplex DNA.     

Synthesis of a novel cage-functionalized chiral binaphthol host: a potential new agent for enantioselective recognition of chiral ammonium salts

Optically active, cage-functionalized crown ether (R)-3 which contains a 1,1′-bi-2-naphthol moiety has been prepared. Subsequently, the ability of (R)-3 to selectively recognize the enantiomers of guest ammonium salts, i.e., 4 and 5 in transport experiments was studied. Host (R)-3 displays significantly enhanced enantiomeric selectivity toward complex formation with 4 vis-à-vis complex formation with 5. The relative energetics of various relevant host–guest complexes have been investigated computationally.