Copolymeric (lR-trans)-N,N'-1,2-cyclohexylene-bisbenzamide oligodimethylsiloxane chiral stationary phase for gas chromatography

A copolymeric stationary phase, consisting of a chiral selective part, i.e. (1R-trans)-N,N'-1,2-cyclohexylenebisbenzamide, and an efficient siloxane oligomeric part, was successfully applied to open tubular column GC analysis. The efficiency and the chiral selectivity of this stationary phase were studied in detail, and high capacity and efficiency at elevated GC temperatures were especially noted. Several drugs and other enantiomeric pairs were separated. The shown examples demonstrate a broad application range for this type of chiral stationary phase in GC analysis.     

Proton uptake of rhodobacter capsulatus reaction center mutants modified in the primary quinone environment

Flash-induced absorbance spectroscopy was used to analyze the proton uptake and electron transfer properties of photosynthetic reaction centers (RC) of Rhodobacter capsulatus that have been genetically modified near the primary quinone electron acceptor (Q(A)). M246Ala and M247Ala, which are symmetry-related to the positions of two acidic groups, L212Glu and L213Asp, in the secondary quinone electron acceptor (QB) protein environment, have been mutated to Glu and Asp, respectively. The pH dependence of the stoichiometry of proton uptake upon formation of the P+Q(A)- (H+/P+Q(A)-) and PQ(A) (H+/Q(A)-) (P is the primary electron donor, a noncovalently linked bacteriochlorophyll dimer) states have been measured in the M246Ala --> Glu and the M247Ala --> Asp mutant RC, in the M246Ala-M247Ala --> Glu-Asp double mutant and in the wild type (WT). Our results show that the introduction of an acidic group (Glu or Asp) in the QA protein region induces notable additional proton uptake over a large pH region (approximately 6-9), which reflects a delocalized response of the protein to the formation of Q(A)-. This may indicate the existence of a widely spread proton reservoir in the cytoplasmic region of the protein. Interestingly, the pH titration curves of the proton release caused by the formation of P+ (H+/P+: difference between H+/P+Q(A)- and H+/PQ(A)- curves) are nearly superimposable in the WT and the M246Ala --> Glu mutant RC, but substantial additional proton release is detected between pH 7 and 9 in the M247Ala --> Asp mutant RC. This effect can be accounted for by an increased proton release by the P+ environment in the M247Ala --> Asp mutant. The M247Ala --> Asp mutation reveals the existence of an energetic and conformational coupling between donor and acceptor sides of the RC at a distance of nearly 30A.     

Analysis of CL-20 in environmental matrices: water and soil

Analytical techniques for the detection of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazatetracyclo(5.5.0.05,9.03,11)dodecane (CL-20) in water and soil are developed by adapting methods traditionally used for the analysis of nitroaromatics. CL-20 (a new explosives compound) is thermally labile, exhibits high polarity, and has low solubility in water. These constraints make the use of specialized sample handling, preparation, extraction, and analysis necessary. The ability to determine the concentrations of this new explosive compound in environmental matrices is helpful in understanding the environmental fate and effects of CL-20; understanding the physical, chemical, and biological fate of CL-20; and can be used in developing remediation technologies and determining their efficiency. The toxicity and mobility of new explosives in soil and groundwater are also of interest, and analytical techniques for quantitating CL-20 and its degradation products in soil and natural waters make these investigations possible.     

Re-casting traditional organic experiments into green guided-inquiry based experiments: student perceptions

ABSTRACT

Green Chemistry principles can be used to re-cast traditional Organic chemistry experiments into more guided-inquiry based experiments. Inquiry questions related to green chemistry principles and metrics have been incorporated into our laboratory for the development of more guided-inquiry based experiments. Re-casting traditional experiments provides time for guided-inquiry by allowing students to evaluate reaction conditions and wastefulness of reactions. This includes evaluating solvent choices, heating methods, use of renewal materials, and contemplating reactants and products impacts on human health and environment. Students examine the changes as it pertains to green chemistry, the success of the reaction and the potential impacts on the mechanism. Involving students in these discoveries rooted in a guiding question made the Organic experiments guided-inquiry. Students were surveyed about their exposure to green chemistry and guided-inquiry based labs. Examples of some of the re-casted experiments, excerpts from student reports, and student impressions of the theme are presented.     

Expedient Diels-Alder assembly of 4-aryl-4-phenylsulfonyl cyclohexanones

The efficient preparation of 4-aryl-4-phenylsulfonyl cyclohexanones, containing a quaternary sulfone-bearing carbon centre, is described. Their synthesis proceeds in 38-78% overall yield by way of three steps: (i) sulfinate alkylation; (ii) methylenation; and (iii) regioselective Diels-Alder condensation with 2-trimethylsiloxybutadiene. The scope and limitations of the one-pot Mannich-type methylenation described were examined.     

Remediation of <Superscript>137</Superscript>Cs radionuclide in nuclear waste effluents by polymer composite: adsorption kinetics,isotherms and gamma irradiation studies

Polypyrrole is incorporated with activated carbon in large size dopant solution and investigated for ¹³⁷Cs removal studies. Adsorption experiments showed optimum conditions within 240 min contact time, pH 6, 0.2 g adsorbent and?≤?100 mg/l adsorbate dose, respectively, while the kinetic data followed pseudo-first-order model. Isotherm data were reproducible by the Langmuir isotherm yielding 23 mg/g maximum sorption capacity. Regeneration of adsorbent was attempted and indicated promising results within three cycles. The surface behavior has also been examined and revealed a well-ordered structure under gamma irradiation. This is a cheap adsorbent to consider and has also proven to possess higher sorption capacity than most highly-cost inorganic materials in use.     

L-Proline Functionalized Polymers Prepared by RAFT Polymerization and Their Assemblies as Supported Organocatalysts

We have prepared a range of well-defined copolymers of styrene and L-proline functionalized styrene (5-11 kDa) using reversible addition-fragmentation chain transfer (RAFT) polymerization techniques and explored their use in supported catalysis. Upon deprotection of the L-proline functionalities, the solution self-assembly of these copolymers was investigated in mixed solvent systems. The resulting assemblies were characterized by dynamic light scattering, transmission electron microscopy (on graphene oxide substrates, along with cryo-TEM and tomography), and scanning electron microscopy. The application of these functional assemblies as supported catalysts for the aldol condensation reaction was explored using cyclohexanone and 4-nitrobenzaldehyde. The rate and selectivity of solution catalysis in our self-assembled system were comparable to those of L-proline, and a significant advantage of our system was that the polymer support could be utilized at lower catalyst loadings with comparable activity and also could be recycled a number of times while maintaining activity and selectivity.     

Average orientation of a molecular rotor embedded in a Langmuir-Blodgett monolayer

A molecular rotor in which a naphthalene rotator is attached through a silicon atom to three fatty acid chains has been synthesized, and Langmuir-Blodgett techniques were used to deposit on silica surfaces monolayers of its calcium salt, both neat and diluted with stearic acid salts. The monolayer films have been characterized by ellipsometry and Fourier transform infrared (FT-IR) grazing-incidence attenuated total internal reflection (GATR) spectroscopy on Si-SiO(2) and by UV-vis absorption spectroscopy on SiO(2). The measurements were combined with calculations of the electronic (INDO/S) and vibrational (DFT) transition moment directions to deduce the average orientation of the rotor molecules, including the naphthalene ring, relative to the surface. In both neat and mixed films, the naphthalene ring is found to preferentially tilt toward the surface, enough that its rotation is most likely hindered. A comparable picture was obtained from molecular mechanics calculations on a mixed film of the naphthalene rotor and stearic acid.     

Modeling the interface between islet amyloid polypeptide and insulin-based aggregation inhibitors: correlation to aggregation kinetics and membrane damage

Human islet amyloid polypeptide (hIAPP) forms cytotoxic fibrils in type-2 diabetes and insulin is known to inhibit formation of these aggregates. In this study, a series of insulin-based inhibitors were synthesized and assessed for their ability to slow aggregation and impact hIAPP-induced membrane damage. Computational studies were employed to examine the underlying mechanism of inhibition. Overall, all compounds were able to slow aggregation at sufficiently high concentrations (10× molar excess); however, only two peptides showed any inhibitory capability at the 1:1 molar ratio (EALYLV and VEALYLV). The results of density functional calculations suggest this is due to the strength of a salt bridge formed with the Arg11 side chain of hIAPP and the inhibitors' ability to span from the Arg11 to past the Phe15 residue of hIAPP, blocking one of the principal amyloidogenic regions of the molecule. Unexpectedly, slowing fibrillogenesis actually increased damage to lipid membranes, suggesting that the aggregation process itself, rather than the fibrilized peptide, may be the cause of cytotoxicity in vivo.