Anomalous diffusion in living yeast cells

The viscoelastic properties of the cytoplasm of living yeast cells were investigated by studying the motion of lipid granules naturally occurring in the cytoplasm. A large frequency range of observation was obtained by a combination of video-based and laser-based tracking methods. At time scales from 10(-4) to 10(2) s, the granules typically perform subdiffusive motion with characteristics different from previous measurements in living cells. This subdiffusive behavior is thought to be due to the presence of polymer networks and membranous structures in the cytoplasm. Consistent with this hypothesis, we observe that the motion becomes less subdiffusive upon actin disruption.     

Field Theory on Kappa-spacetime

A general formalism is developed, that allows the construction of field theory on quantum spaces which are deformations of ordinary spacetime. The symmetry group of spacetime is replaced by a quantum group. This formalism is demonstrated for the -deformed Poincaré algebra and its quantum space. The algebraic setting is mapped to the algebra of functions of commuting variables with a suitable -product. Fields are elements of this function algebra. As an example, the Klein-Gordon equation is defined and derived from an action.     

Hydrolysis and retro‐aldol cleavage of ethyl threo‐2‐(1‐adamantyl)‐3‐hydroxybutyrate: competing reactions

The hydrolysis of ethyl threo‐2‐(1‐adamantyl)‐3‐hydroxybutyrate ( 1 ) and the parent ester ethyl 3‐hydroxybutyrate ( 4 ) has been studied experimentally and computationally. In the hydrolysis of threo‐ester 1 with 2 M NaOH, predominantly retro‐aldol product was observed, whereas the hydrolyzed product was present in a minor amount. When the reaction is carried out under the same conditions with the parent ester ethyl 3‐hydroxybutyrate ( 4 ), hydrolyzed product is exclusively observed. The competitive pathways, namely hydrolysis and the retro‐aldol reaction for 1 and 4 were investigated using DFT calculations in the both gas and solvent phase. The calculated results in the solvent phase at B3LYP/6–31 + G* level revealed that the formation of retro‐aldol products is kinetically preferred over the hydrolysis of threo‐ester 1 in the presence of a base. However, the parent ester 4 showed that the retro‐aldol process is less favored than the hydrolysis process under similar conditions. The steric effect imposed by the bulky adamantyl group to enhance the activation barriers for the hydrolysis of the ethyl threo‐2‐(1‐adamantyl)‐3‐hydroxybutyrate ( 1 ) was further supported by the calculations performed with tert‐butyl group at the α‐carbon atom of ethyl 3‐hydroxybutyrate ( 7 ). Copyright © 2010 John Wiley & Sons, Ltd.     

Cavity effects in coiled coil IR reference source

We performed a high resolution imaging of a coiled coil filament used in tungsten lamps, a standard reference source in spectroscopy. The radiometric results using two-wavelength thermometry indicate that its configuration also introduces cavity effects and non-uniformity of filament temperature distribution, with the average temperature calculated to be 2869 K. Considering the tungsten source as an extended body, significant temperature variations of up to +19 K are found above its nominal 2850 K value.     

A novel and efficient 4-oxothiazolidine-1,2-dithiole rearrangement induced by Lawesson's reagent

Functionalized 1,2-dithioles have been synthesized by a ring opening-closing process of 5-substituted- and 5-unsubstituted-2-alkylidene-4-oxothiazolidines with Lawesson's reagent. The ¹³C NMR data confirmed the meso-ionic structure of these aromatic-type 1,2-dithioles.     

The influence of non-easily ionized elements on emission intensities in a d.c. arc plasma

Higher concentrations of non-easily ionized elements (NEIE) increase the spectral line intensity of trace elements in the arc plasma. It was found that these additives do not greatly affect the evaporation processes of the trace elements. Changes in temperature, electron density and transport velocities together can optimize the excitation for particular atomic species. The importance of the investigations is to underline the possible application of NEIE in spectrochemical practice.     

New epoxyisoindolines by intramolecular diels-alder reactions of some methyl-substituted allylaryl-2-furfurylamines

N-Alkenyl-N-(5-substituted-2-furfuryl)-N-p-toluidines 1–10 have been selected to study the intramolecular Diels-Alder reaction of furans. New epoxyisoindolines 11–20 were prepared and fully characterised.     

Computational exploration of rearrangements related to the vitamin B12-dependent ethanolamine ammonia lyase catalyzed transformation

DFT (B3LYP/6-31G) and ab initio molecular orbital theory (QCISD/cc-pVDZ) are used to investigate several possible mechanisms involving free radical intermediates as well as their protonated forms for processes related to the coenzyme B(12)-dependent rearrangement catalyzed by ethanolamine ammonia lyase. Two major types of rearrangements are discussed in detail, intramolecular migration and dissociation of the amine/ammonia groups, for both of which several scenarios are considered. According to the calculations, the complete dissociation of the migrating group and its subsequent association constitute an unlikely route for both the protonated and the unprotonated reactant because of the high-energy barriers (more than 23 kcal/mol) involved in these steps. Direct migration of the protonated amine group is far more favorable (10.4 kcal/mol) and therefore presents the most likely candidate for the actual enzymatic reaction. The calculations further imply that the direct loss of an ammonium cation (10.6 kcal/mol) represents a feasible pathway as well. Comparing the rearrangements for the aminoethanol radical and its protonated counterpart, in line with previous findings reported by Golding, Radom, and co-workers, we find that the migration of a protonated group is in general associated with lower energy barriers, suggesting that the actual enzyme substrate quite likely corresponds to (partially) protonated aminoethanol. As the extent of the substrate protonation/deprotonation by the active site of the enzyme may vary, the actual energy barriers are expected to range between the values calculated for the two extreme cases of a substrate, that is, the aminoethanol radical 2 and its fully protonated form 6.     

Osmotic and Activity Coefficients of {yKCl+(1−y)MgCl2}(aq) at T=298.15 K

Isopiestic vapor-pressure measurements were made at the temperature 298.15 K for aqueous KCl + MgCl₂ solutions using KCl(aq) as the reference standard. The measurements for these ternary solutions were made at KCl ionic strength fractions of y=0.0, 0.1989, 0.3996, 0.5993, 0.7925 and 1.0 (with two additional sets at y=0.0, 0.2021, 0.3998, 0.6125, 0.8209 and 1.0) for the ionic strength range from 0.4014 to 6.2790 mol?kg^?1. Our results, and those from two previous isopiestic studies, were combined and used with previously determined parameters for KCl(aq) and those determined here for MgCl₂(aq) to evaluate mixing parameters for the Clegg-Pitzer-Brimblecombe model. These combined data were also used to determine the mixing parameters of the Scatchard model. Both sets of model parameters are valid for ionic strengths of I≤12.8 mol?kg^?1, where higher-order electrostatic effects have been included in the Clegg-Pitzer-Brimblecombe mixture model. The activity coefficients for KCl and MgCl₂ were calculated from these models and the results for KCl were compared to experimental data from Emf measurements. The Scatchard model interaction parameters were used for calculation of the excess Gibbs energy as a function of the ionic strength and ionic strength fraction of KCl. The Zdanovskii-Robinson-Stokes rule of linearity for mixing of isopiestic solutions was tested.     

Structural rationalization of a large difference in RNA affinity despite a small difference in chemistry between two 2'-O-modified nucleic acid analogues

Chemical modification of nucleic acids at the 2'-position of ribose has generated antisense oligonucleotides (AONs) with a range of desirable properties. Electron-withdrawing substituents such as 2'-O-[2-(methoxy)ethyl] (MOE) confer enhanced RNA affinity relative to that of DNA by conformationally preorganizing an AON for pairing with the RNA target and by improving backbone hydration. 2'-Substitution of the ribose has also been shown to increase nuclease resistance and cellular uptake via changes in lipophilicity. Interestingly, incorporation of either 2'-O-[2-(methylamino)-2-oxoethyl]- (NMA) or 2'-O-(N-methylcarbamate)-modified (NMC) residues into AONs has divergent effects on RNA affinity. Incorporation of 2'-O-NMA-T considerably improves RNA affinity while incorporation of 2'-O-NMC-T drastically reduces RNA affinity. Crystal structures at high resolution of A-form DNA duplexes containing either 2'-O-NMA-T or 2'-O-NMC-T shed light on the structural origins of the surprisingly large difference in stability given the relatively minor difference in chemistry between NMA and NMC. NMA substituents adopt an extended conformation and use either their carbonyl oxygen or amino nitrogen to trap water molecules between phosphate group and sugar. The conformational properties of NMA and the observed hydration patterns are reminiscent of those found in the structures of 2'-O-MOE-modified RNA. Conversely, the carbonyl oxygen of NMC and O2 of T are in close contact, providing evidence that an unfavorable electrostatic interaction and the absence of a stable water structure are the main reasons for the loss in thermodynamic stability as a result of incorporation of 2'-O-NMC-modified residues.