Effects of Refractive Index and Viscosity on Fluorescence and Anisotropy Decays of Enhanced Cyan and Yellow Fluorescent Proteins

The fluorescence lifetime strongly depends on the immediate environment of the fluorophore. Time-resolved fluorescence measurements of the enhanced forms of ECFP and EYFP in water–glycerol mixtures were performed to quantify the effects of the refractive index and viscosity on the fluorescence lifetimes of these proteins. The experimental data show for ECFP and EYFP two fluorescence lifetime components: one short lifetime of about 1 ns and a longer lifetime of about 3.7 ns of ECFP and for EYFP 3.4. The fluorescence of ECFP is very heterogeneous, which can be explained by the presence of two populations: a conformation (67% present) where the fluorophore is less quenched than in the other conformation (33% present). The fluorescence decay of EYFP is much more homogeneous and the amplitude of the short fluorescence lifetime is about 5%. The fluorescence anisotropy decays show that the rotational correlation time of both proteins scales with increasing viscosity of the solvent similarly as shown earlier for GFP. The rotational correlation times are identical for ECFP and EYFP, which can be expected since both proteins have the same shape and size. The only difference observed is the slightly lower initial anisotropy for ECFP as compared to the one of EYFP.     

Formation of poly(ethylene phosphates) in polycondensation of H3PO4 with ethylene glycol. Kinetic and mechanistic study

Conditions of synthesis of poly(ethylene phosphates) in reaction of H₃PO₄ with HOCH₂CH₂OH (EG), the actual path of polycondensation, and structure of the obtained polymers (mostly oligomers) and kinetics of reaction are described. Preliminary kinetic information, based on the comparison of the MALDI‐TOF‐ms and ³¹P{¹H} NMR spectra as a function of conversion is given as well. Because of the dealkylation process fragments derived from di‐ and triethylene glycols are also present in the repeating units. Structures of the end groups (? CH₂CH₂OH or ? OP(O)(OH)₂) depend on the starting ratio of [EG]₀/[H₃PO₄]₀, although even at the excess of EG the acidic end groups prevail because of the dealkylation process. In MALDI‐TOF‐ms products with P_n equal up to 21 have been observed. The average polymerization degrees (P_n) are lower and have been calculated from the proportion of the end groups. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 830–843, 2008     

On a conjecture of grant walker for the first occurrence of irreducible modular representations of general linear groups

Let GL _n = GL(n,F _p ) be the group of all n×ninvertible matrices over the field F _p of p elements, p a prime number. As well known, a complete set of irreducible GL _n -modules as submodules of the polynomial algebra was constructed by Stephen Doty and Grant Walker, Ton That Tri (see [1], [4]). Grant Walker has a conjecture that the occurence of these modules is the first occurence of these modules as submodules in the polynomial algebra. The aim of this paper is to give a proof of the above conjecture for p= 2.     

Prediction of yield and long‐term failure of oriented polypropylene: Kinetics and anisotropy

The time‐dependent yield and failure behavior of off‐axis loaded uniaxially oriented polypropylene tape is investigated. The yield and failure behavior is described with an anisotropic viscoplastic model. A viscoplastic flow rule is used with an equivalent stress, based on Hill's anisotropic yield criterion, and the Eyring flow theory combined with a critical equivalent strain definition. This model is based on factorization of the rate and draw ratio dependence and is capable of quantitatively predicting the rate, angle and draw ratio dependence of the yield stress as well as time‐to‐failure in various off‐axis tensile loading conditions characterized solely from the transverse direction. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2026–2035, 2009     

Large-deformation properties of wheat dough in uni- and biaxial extension. Part II. Gluten dough

Glutens were isolated from flour of three European wheat cultivars which perform differently in cereal products. The rheological and fracture properties of gluten-water doughs were determined in uniaxial and biaxial extension at large deformations and small angle sinusoidal oscillation tests and compared with the mechanical properties of the parental flour doughs. At 25 °C the linear region was in the same range as that of flour dough, while at a higher temperature (45 °C) the linear region was more than an order of magnitude higher. At 45 °C the storage modulus and tan were lower than at 25 °C. Variation in moduli between cultivars was much more pronounced for gluten than for flour doughs.Similarly to flour dough in both uniaxial and biaxial extension the stress () increased more than proportionally with the strain, a phenomenon called strain hardening. The stress at a set strain and strain hardening depended much more strongly on the type of deformation for gluten than for flour dough: was higher in biaxial extension for gluten than for flour dough, but was much higher in uniaxial extension. This indicates that orientational effects in elongational flow are of even larger importance for the mechanical properties of gluten than of flour dough. It is likely that it is the glutenin fraction that, because of its large size, confers these direction dependent properties to gluten and flour doughs. Fracture stresses were much higher for gluten than for flour dough, while fracture strains were in the same range or higher. For gluten dough fracture strains increased less strongly with increasing strain rate than for flour dough. Glutens exhibiting a higher stress at a certain strain had a smaller fracture strain.Our findings confirm the conviction that the large deformation properties of flour dough are mainly governed by the gluten fraction. However, there are also differences. Compared to flour dough gluten dough exhibits (i) a stronger strain hardening, (ii) a larger difference in between uniaxial and biaxial extension and (iii) a smaller strain rate dependency of the fracture strain.     

Iron(II)-catalyzed amidation of aldehydes with iminoiodinanes at room temperature and under microwave-assisted conditions

A method for the amidation of aldehydes with PhI=NTs/PhI=NNs as the nitrogen source and an inexpensive iron(II) chloride + pyridine as the in situ formed precatalyst under mild conditions at room temperature or microwave assisted conditions is described. The reaction was operationally straightforward and accomplished in moderate to excellent product yields (20-99%) and with complete chemoselectivity with the new C-N bond forming only at the formylic C-H bond in substrates containing other reactive functional groups. By utilizing microwave irradiation, comparable product yields and short reaction times of 1 h could be accomplished. The mechanism is suggested to involve insertion of a putative iron-nitrene/imido group to the formylic C-H bond of the substrate via a H-atom abstraction/radical rebound pathway mediated by the precatalyst [Fe(py)(4)Cl(2)] generated in situ from reaction of FeCl(2) with pyridine.