Adsorption kinetics of surfactant mixtures from micellar solutions as studied by maximum bubble pressure technique

The adsorption kinetics of micellar solutions of anionic/cationic SDS/DATB mixtures with mixing ratios of 10/1 and 10/2, respectively, are studied experimentally by means of the maximum bubble pressure method. For long adsorption times the adsorption of the highly surface-active anionic/cationic complex leads to a decrease of dynamic surface tension in comparison to the single SDS system. However, the situation is the reverse for short adsorption times where the dynamic surface tension is increased by addition of the cationic surfactant, although the overall concentration is increased. This unexpected behavior is explained by partial solubilization of free SDS molecules into micelles formed by SDS/DTAB complexes. With increasing overall concentration, when eventually the CMC of SDS is reached, the anionic/cationic complex itself is solubilized by SDS micelles. Finally, no complex micelles, which for their part can solubilize an excess of SDS molecules, are present. Hence, the dynamic properties of the solution are no longer influenced by the depletion of SDS molecules and the mixture tends to behave like a pure SDS solution.     

Comparison of subcritical water and organic solvents for extracting kava lactones from kava root

Subcritical water extraction of lactones from a kava (Piper metlhysticum) root was compared to a Soxhlet extraction with water, to boiling in water, and to a sonication in acetone. For ground kava (250-500 microm), 2 h of subcritical water extraction were required for a complete extraction at 100 degrees C, while at 175 degrees C, 20 min were sufficient. For a complete extraction of the unground (shredded) kava, the time of extraction was extended to 40 min at 175 degrees C. Boiling for 2 h and extraction with Soxhlet apparatus for 6 h, both of which employed water at atmospheric pressure, produced yields 40-60% lower than those obtained with subcritical water. With unground kava, 40 min of subcritical water extraction yielded essentially the same recoveries of lactones as 18 h of sonication with acetone, methylene chloride, or methanol.     

FUROCOUMARIN-PHOTOSENSITIZEDHYDROXYLATION OF GUANOSINE IN RNA AND DNA

Abstract— Guanosine hydroxylation was used as a marker for assessing photooxidation of DNA and RNA sensitized by monofunctional and bifunctional furocoumarins. DNA or RNA, treated with sensitizer and UVA light, was enzymatically hydrolyzed, dephosphorylated and then analyzed by reversed-phase HPLC with electrochemical detection. Hydroxylated guanosine, i.e. 8-hydroxy-2'-deoxyguanosine (8-OHdG) or 8-hydroxyguanosine (8-OHG), was quantitated. 3-Carbethoxypsoralen (3-CP) was found to be an efficient photosensitizer for oxidation of guanosine in DNA, resulting in conversion of up to 0.4% of guanosine residues to 8-OHdG. In contrast, dramatically lower levels of guanosine hydroxylation were observed in 3-CP-photosensitized RNA. Psoralen was found to be a more efficient photosensitizer than angelicin in both DNA and RNA. Additional studies of oxidation of 3-CP-photosensitized DNA indicated that double-stranded DNA is 10 times more susceptible to photooxidation than single-stranded DNA, implicating 3-CP binding to DNA as an important mechanistic step in photooxidation of guanosine. The effects of D₂O and degassing with argon on photooxidation of guanosine in DNA sensitized by 3-CP were inconsistent with a mechanism involving ¹O₂. In addition, chelation of adventitious metal ions present in preparations of DNA photosensitized by 3-CP had no effect on hydroxylation of guanosine.     

Impact of deglycosylation methods on two-dimensional gel electrophoresis and matrix assisted laser desorption/ionization-time of flight-mass spectrometry for proteomic analysis

Glycosylation is a common post-translational modification that can add complexity to the proteome of many cell types. We used enzymatic and chemical methods of deglycosylation to treat a heavily glycosylated exoproteome sample from the filamentous fungus Trichoderma reesei. Deglycosylated samples were resolved on one-dimensional (1-D) and two-dimensional (2-D) gels in order to determine the effect of deglycosylation on the electrophoresis patterns and on the ability to identify proteins by peptide mass matching using matrix assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS) analysis of in-gel tryptic digests. We found that deglycosylation of the protein sample resulted in different protein patterns on 1-D and 2-D gels, reduced the complexity of gel patterns, and enhanced the protein identification of some proteins via MALDI-TOF-MS. Deglycosylation with trifluoromethanesulfonic acid (TFMS) was found to be more effective than enzymatic treatments. These deglycosylation techniques may be employed in whole proteome analysis to locate glycosylated proteins and assist in their identification by MS.     

Optimal choice of dividing surface for the computation of quantum reaction rates

We consider the calculation of quantum mechanical rate constants for chemical reactions via algorithms that utilize short-time values of the symmetrized flux-flux correlation function. We argue that the dividing surface that makes optimal use of the short-time quantum information is the surface that minimizes the value at the origin of the symmetrized flux-flux correlation function. We also demonstrate that, in the classical limit, this quantum variational criterion produces the same dividing surface as Wigner's variational principle. Finally, we argue that the quantum variational criterion behaves in a nearly optimal fashion with respect to the minimization of the extent of re-crossing flux.     

The NCI Drug Information System. 3. The DIS Chemistry Module

The Chemistry Module of the Drug Information System (DIS) handles a database of 400,000 structures. New or modified records are created in this database on a daily basis and are merged into the file promptly. The Chemistry database is searchable in a wide variety of ways and provides novel methods for both input and output of chemical structures.     

Alkaloids of Glycosmis arborea—II Structure of arborine

On the basis of a critical study of the ultra-violet and the infra-red absorption spectra of arborine, dihydroarborine, 1,2-dimethylquinazol-4-one, 2-ethyl-1-methylquinazol-4-one, 2,3-dihydro-1,2-dimethylquinazol-4-one and 2,3-dihydro-2-ethyl-1-methylquinazol-4-one, it has been shown that arborine is 2-benzyl-1-methylquinazol-4-one and not the tautomeric form, 2-benzylidene-1-methylquinazol-4-one. This has been confirmed on the basis of the nuclear magnetic resonance spectrum of arborine. Incidentally, it has been shown that 'glycosine' of Chatterjee and Ghosh Majumdar is not a new alkaloid and this name should be deleted from the literature.     

Temperature dependence of particle-particle adherence forces in ice and clathrate hydrates

Particle-particle pulloff adherence forces were measured as a function of temperature in the ice/n-decane/ice and tetrahydrofuran (THF) hydrate/n-decane/THF hydrate systems using a newly developed micromechanical testing technique. Experiments using approximately 200 microm radius particles were performed at atmospheric pressure over the temperature range 263-275 K. The ice and hydrate particles displayed very similar behavior. While the measured adherence forces had significant variation, the shapes of the cumulative force distribution curves were similar among the different sets of experiments. The measured adherence forces distributions shifted to lower force values as the temperature was decreased from the solid melting temperature. The observed forces and trends were explained by the capillary cohesion of rough surfaces, with the capillary bridging liquid being stabilized below its freezing point by the negative curvature of the bridging liquid/n-decane interface.     

Design of a fraction collector for capillary array electrophoresis

This paper describes a prototype instrument for high-throughput fraction collection with capillary array electrophoresis (CAE). The design of the system was based on a comprehensive collection approach, in which fractions from all capillaries were simultaneously collected in individual collection microwells in predefined time intervals. The location of the fractions in the microwells on the collection plate was determined by monitoring the individual zone velocities close to the end of each capillary. The collection microwell plate was fabricated from buffer-saturated agarose gel, which maintained permanent electrical contact with the separation capillaries during the collection process. Since the collection gel plate consisted of over 90% water, liquid evaporation from the collection wells was minimized. A 12-capillary array instrument was built with two-point detection using a side illumination scheme. The collection performance was demonstrated by reinjection of selected fractions of a double-stranded DNA (dsDNA) separation. The identity of collected DNA fragments was confirmed by PCR and sequencing.     

Mass spectra of geometrical isomers: The isomeric 3- and 7-cyclohexyl-2-norbornanols

The mass spectra of isomeric 3- and 7-cyclohexyl-2-norbornanols have been studied. The 3-substituted norbornanols give very similar mass spectra, whereas large differences were observed between the mass spectra of 7-syn and 7-anti isomers. While the mass spectra of these bicyclic alcohols show extensive rearrangements to give rise to many odd-electron ions, the Wagner-Meerwein rearrangement of the molecular ion prior to fragmentation or during the process of dehydration is not important. The origins and the mechanisms for the formation of some major ions are discussed in terms of low voltage spectra, defocused metastables and their relative abundances, and ionization or appearance potentials of the ions of interest.