Synthesis and Conformational Switching of Partially and Differentially Bridged Resorcin[4]arenes Bearing Fluorescent Dye Labels. Preliminary Communication

We report the synthesis of modified Cram‐type cavitands bearing one or two fluorescent labels for single‐molecule spectroscopic studies of vase? kite conformational switching (Scheme 3). Syntheses were performed by stepwise bridging of the four couples of neighboring H‐bonded OH groups of resorcin[4]arene bowls (Schemes 2 and 3). The new substitution patterns enable the construction of a large variety of future functional architectures. ¹H‐NMR Investigations showed that the new partially and differentially bridged cavitands feature temperature‐ and pH‐triggered vase? kite conformational isomerism similar to symmetrical cavitands with four identical quinoxaline bridges (Table). It was discovered that vase? kite switching of cavitands is strongly solvent‐dependent.     

Thick-target PIGE analysis of plant materials preconcentrated by dry ashing

An analytical methodology has been developed for the UV-spectrophotometric determination of carbaryl in waters after its preconcentration onto a polyether type polyurethane foam followed by on-line elution. The aforementioned strategy offers an easy way for in-field sampling and to improve the analytical sensitivity. Several chemical and flow variables (mass of sorbent, sample flow rate, sample volume and carrier flow rate) were studied to ensure the best performance of the system. Recovery studies, carried out on natural water samples spiked with known amounts of carbaryl at concentration levels between 250 and 500 mug l(-1), provided recovery percentages between 94 and 105%. A detection limit of 12 mug l(-1) was achieved and a variation coefficient of 3.4% was obtained at 0.50 mug ml(-1).     

Molecular dynamics simulations of biotin carboxylase

Biotin carboxylase catalyzes the ATP-dependent carboxylation of biotin and is one component of the multienzyme complex acetyl-CoA carboxylase that catalyzes the first committed step in fatty acid synthesis in all organisms. Biotin carboxylase from Escherichia coli, whose crystal structures with and without ATP bound have been determined, has served as a model system for this component of the acetyl-CoA carboxylase complex. The two crystal structures revealed a large conformational change of one domain relative to the other domains when ATP is bound. Unfortunately, the crystal structure with ATP bound was obtained with an inactive site-directed mutant of the enzyme. As a consequence the structure with ATP bound lacked key structural information such as for the Mg2+ ions and contained altered conformations of key active-site residues. Therefore, nanosecond molecular dynamics studies of the wild-type biotin carboxylase were undertaken to supplant and amend the results of the crystal structures. Specifically, the protein-metal interactions of the two catalytically critical Mg2+ ions bound in the active site are presented along with a reevaluation of the conformations of active-site residues bound to ATP. In addition, the regions of the polypeptide chain that serve as hinges for the large conformational change were identified. The results of the hinge analysis complemented a covariance analysis that identified the individual structural elements of biotin carboxylase that change their conformation in response to ATP binding.     

Rapid optical sampling of relaxation-phenomena employing two time-correlated picosecond pulsetrains

Two flashlamp-pumped, mode-locked and optically coupled dye lasers produce trains of picosecond pulses with definite, but variable time correlation. One pulsetrain is used to bleach the sample, while the other probes the decay of its transient transmission. Relaxation times between 15 ps and 1 ns can be monitored by one simultaneous activation of the two lasers.     

In-line application of electric field in capillary separation systems: Joule heating, pH and conductivity

This study concerns the technique electric field-assisted capillary liquid chromatography. In this technique, an electric field is applied over the separation capillary in order to provide an additional selectivity. In this technique, the electric field is applied in-line in the separation capillary and here the electric current is the factor limiting the magnitude of applied electric field. The influence of Joule heating and other factors on the current in such systems has been investigated. The temperature in the capillary was first measured within a standard CE set-up, as function of effect per unit of length. Then the same cooling system was applied to an in-line set-up, to replicate the conditions between the two systems, and thus the temperature. Thus Joule heating effects could then be calculated within the in-line system. It was found that for systems applying an electric field in line, the direct influence from Joule heating was only relatively small. The pH in the capillary was measured in the in-line set-up using cresol red/TRIS solutions as pH probe. Significant changes in pH were observed and the results suggested that electrolysis of water is the dominant electrode reaction in the in-line system. In summary, the observed conductivity change in in-line systems was found to be mainly due to the pH change by hydrolysis of water, but primarily not due the temperature change in the capillary column.     

Trends in UV irradiance of tanning devices in Norway: 1983-2005

Abstract Indoor tanning increases skin cancer risk, but the importance of different parts of the UV spectrum is unclear. We assessed irradiance of tanning devices in Norway for the period 1983-2005. Since 1983, all tanning models needed approval before being sold or used. UV Type 3 limits were valid from late 1992 (<0.15 W m(-2) for CIE-weighted, i.e. erythemally weighted, short and long wave irradiances). We analyzed data from 90% of the approved tanning models (n = 446 models) and two large inspection surveys in 1998/1999 and 2003 (n = 1341 tanning devices). Mean CIE-weighted short wave irradiance of approved models increased from 0.050 W m(-2) (95% confidence interval [CI] 0.045-0.055) in 1983-1992 to 0.101 W m(-2) (95% CI 0.098-0.105) in 1993-2005, and mean long wave from 0.091 W m(-2) (95% CI 0.088-0.095) to 0.112 W m(-2) (95% CI 0.109-0.115), respectively. Inspection surveys revealed short wave irradiances much higher than that approved. In 1998-1999, only 28% (293/1034) of the devices were equipped with correct sunlamps and only 1 out of 130 inspected establishments fulfilled all requirements. In 2003, corresponding numbers were 59% (180/307) of devices and 2 out of 52 establishments. Mean short and long wave irradiances of the inspected tanning devices in 2003 were 1.5 and 3.5 times, respectively, higher than the irradiance of natural summer sun in Oslo. In conclusion, the short wave irradiance has increased in indoor tanning devices in Norway over the last 20 years. Due to the high long wave irradiance throughout this period, the percentage of short wave irradiance was much lower than for natural sun.