Aligned cellulose nanocrystals and directed nanoscale deposition of colloidal spheres

Cellulose nanocrystals are aligned in wrinkled polydimethylsiloxane templates and transferred to polyethyleneimine-coated silica surfaces in a printing process similar to microcontact printing. The highly aligned nanorods were deposited onto the surfaces with a line-to-line distance of 225–600 nm without loss of alignment. It was also possible to repeat the transfer process on the same surface at a 90-degree angle to create a network structure. This demonstrates the versatility of the technique and creates more options for advanced multilayering of materials. To demonstrate that the surface properties of the anionic cellulose nanorods were unaffected by the transfer process and to prove the concept of functionalizing transferred particles, cationic latex particles were electrostatically self-assembled onto the cellulose nanorods. The directed deposition of these particles resulted in excellent site specificity and the highest resolution to date for controlled deposition of colloids on an electrostatically patterned surface.     

Counterion influence on the N–I–N halogen bond

A detailed investigation of the influence of counterions on the [N–I–N]⁺ halogen bond in solution, in the solid state and in silico is presented. Translational diffusion coefficients indicate close attachment of counterions to the cationic, three-center halogen bond in dichloromethane solution. Isotopic perturbation of equilibrium NMR studies performed on isotopologue mixtures of regioselectively deuterated and nondeuterated analogues of the model system showed that the counterion is incapable of altering the symmetry of the [N–I–N]⁺ halogen bond. This symmetry remains even in the presence of an unfavorable geometric restraint. A high preference for the symmetric geometry was found also in the solid state by single crystal X-ray crystallography. Molecular systems encompassing weakly coordinating counterions behave similarly to the corresponding silver(i) centered coordination complexes. In contrast, systems possessing moderately or strongly coordinating anions show a distinctly different behavior. Such silver(i) complexes are converted into multi-coordinate geometries with strong Ag–O bonds, whereas the iodine centered systems remain linear and lack direct charge transfer interaction with the counterion, as verified by ¹⁵N NMR and DFT computation. This suggests that the [N–I–N]⁺ halogen bond may not be satisfactorily described in terms of a pure coordination bond typical of transition metal complexes, but as a secondary bond with a substantial charge-transfer character.     

Latex diffusion at high volume fractions studied by fluorescence microscopy

The behavior of fluorescent latex probes (radii 0.05, 0.1, and 0.5 mum) in latex host particle suspensions was investigated by fluorescence microscopy with image analysis. The volume fraction of the host latex was varied between 0 and 0.50. A careful statistical analysis was performed to examine the accuracy of the fluorescence microscopy method, from which the direct observation of the Brownian motion gives the diffusion coefficient. The method was found to meet all statistical requirements. From rheological measurements, the maximum volume fraction and the intrinsic viscosity can be obtained. The Krieger-Dougherty equation can be used for the prediction of sample viscosities. The predicted viscosities were used to obtain the theoretical diffusion coefficients with the Stoke-Einstein equation. When comparing the theoretical diffusion coefficients with the experimental ones, it turned out that all models tested yielded acceptable predictions of the diffusion coefficients.     

Global calculations of ground-state axial shape asymmetry of nuclei

Important insight into the symmetry properties of the nuclear ground-state (gs) shape is obtained from the characteristics of low-lying collective energy-level spectra. In the 1950s, experimental and theoretical studies showed that in the gs many nuclei are spheroidal in shape rather than spherical. Later, a hexadecapole component of the gs shape was identified. In the 1970-1995 time frame, a consensus that reflection symmetry of the gs shape was broken for some nuclei emerged. Here we present the first calculation across the nuclear chart of axial symmetry breaking in the nuclear gs. We show that we fulfill a necessary condition: Where we calculate axial symmetry breaking, characteristic gamma bands are observed experimentally. Moreover, we find that, for those nuclei where axial asymmetry is found, a systematic deviation between calculated and measured masses is removed.     

Polyolefin photo-stabilisation mechanisms. Reactions of tetramethylpiperidine derivatives in model systems

The relative rate of cyclohexyl radical scavenging by oxygen or 4-oxo-2,2,6,6-tetramethylpiperidino-N-oxyl has been measured at 25°C, together with the relative rates of cyclohexyl peroxy radical attack on cyclohexane or substituted hydroxylamines derived from 2,2,6,6-tetramethylpiperidine. These competitive processes are important in the stabilisation of polymers against photo-oxidative destruction by piperidine derivatives. Peroxy radical scavenging by the substituted hydroxylamine appears to be considerably more important than alkyl radical scavenging by the nitroxide, although both processes are essential for prolonged ultra violet (uv) stabilisation of a polymer. However, a comparison of experimental photo-protection with that predicted by the measured rate constant ratios shows that other processes are needed to account entirely for the observed stabilisation. Other factors which may be involved in piperidine photo-protection of polymers include thermal decomposition of the substituted hydroxylamine to reform nitroxide in polar(oxidised) zones and especially the association of nitroxides with hydroperoxide groups (the dominant photo-initiator in degrading polyolefins).     

Determination of 2-mercaptopropionylglycine in plasma and urine by high-performance liquid chromatography

Methods for quantitative analysis of total and non-protein-bound 2-mercaptopropionylglycine (2-MPG) in plasma, and total 2-MPG in urine, have been developed. By reduction of urine, plasma or deproteinized plasma samples with tributylphosphine, 2-MPG is liberated from its disulphides, and after clean-up of the sample, 2-MPG is derivatized with N-(7-dimethylamino-4-methyl-3-coumarinyl)maleimide (DACM). The 2-MPG-DACM derivative is then quantified by high-performance liquid chromatography (HPLC) with fluorimetric detection. Both ion-suppression and ion-pair HPLC gave satisfactory chromatograms. The precision of the methods was satisfactory (coefficient of variation 3.1-5.8%), analytical recovery was quantitative (85-99%) and the two HPLC techniques were well correlated (r = 0.99). Five healthy subjects receiving 500 mg of 2-MPG showed maximal total plasma concentration of 13.8-26.9 mumol/l at 3-5 h after intake, and their non-protein-bound 2-MPG was, at the same time, 62-77% of the total 2-MPG. The urinary excretion was 27.8 +/- 3.8% (mean +/- S.D.) of the given dose, most of it excreted within 12 h after intake.     

Ligand design by targeting a binding site water

Solvent reorganization is a major driving force of protein–ligand association, but the contribution of binding site waters to ligand affinity is poorly understood. We investigated how altered interactions with a water network can influence ligand binding to a receptor. A series of ligands of the A_2A adenosine receptor, which either interacted with or displaced an ordered binding site water, were studied experimentally and by molecular dynamics simulations. An analog of the endogenous ligand that was unable to hydrogen bond to the ordered water lost affinity and this activity cliff was captured by molecular dynamics simulations. Two compounds designed to displace the ordered water from the binding site were then synthesized and evaluated experimentally, leading to the discovery of an A_2A agonist with nanomolar activity. Calculation of the thermodynamic profiles resulting from introducing substituents that interacted with or displaced the ordered water showed that the gain of binding affinity was enthalpy driven. Detailed analysis of the energetics and binding site hydration networks revealed that the enthalpy change was governed by contributions that are commonly neglected in structure-based drug optimization. In particular, simulations suggested that displacement of water from a binding site to the bulk solvent can lead to large energy contributions. Our findings provide insights into the molecular driving forces of protein–ligand binding and strategies for rational drug design.

Solvent reorganization is a major driving force of protein–ligand association, but the contribution of binding site waters to ligand affinity is poorly understood.     

Rapid ion-exchange chromatography for preparative separation of proteins. Application to porcine and bovine carbonic anhydrases

A method of rapid ion-exchange chromatography of DEAE-cellulose for preparative purposes is described. Basically, the flow-rate is increased by applying an air pressure on the column. By this technique it is possible to purify gram quantities of protein in 2-4 h with acceptable resolution. In preparations of bovine and porcine carbonic anhydrases the elution times were reduced by a factor of about ten compared to those of conventional methods. The enzymes purified in this way showed a high degree of homogeneity. The method should be generally applicable in protein purification, and especially advantageous in purification of unstable proteins where time-consuming separations often give rise to low yields of active material.     

Natural radiative lifetimes in the2 S 1/2 and2 D 3/2, 5/2 sequences of neutral copper

Natural radiative lifetimes have been measured of the 3d ¹⁰ ns ² S _1/2 (n=6?10) and of the 3d ¹⁰ nd ² D _{3/2, 5/2} (n=5?9) sequences by using two step excitation of copper atoms in an atomic beam. The states investigated were populated by the light from two pulsed dye lasers pumped by the same Nd:YAG laser. The lifetimes of the² D sequence increase regularly with increasing principal quantum number. This is not the case for the² S series, because of configuration interaction in the² P series. In addition the lifetime of the 3d ¹⁰5p ² P _3/2 state has been measured together with its branching ratio.