SOLUBILIZATION OF PHOTOSYNTHETIC PIGMENT-PROTEIN COMPLEXES

Studies utilizing fractionation of photosynthetic pigment-protein complexes from the chloroplast thylakoid membrane often employ dodecylsulfate at a concentration of 10 mg mL^?1 to disrupt membrane structure prior to electrophoretic fractionation of the complexes. We investigated the effect of varying dodecylsulfate concentration on the solution/air interfacial surface tension in the absence and presence of the same concentrations of thylakoid membranes used by four different fractionation systems that have been commonly employed to fractionate photosynthetic pigment-protein complexes. Concentrations of dodecylsulfate in the range5–10 mg mL^?1, normally utilized to treat thylakoids prior to fractionation, were effective in reducing the interfacial surface tension to levels equivalent to control solutions without added thylakoid membranes. However, thylakoid membranes treated with these concentrations of dodecylsulfate are not resolved into discrete pigment-protein complexes when subjected to electrophoresis on an agarose gel, and do not produce significant amounts of pigment-containing complexes with a molecular size < 100 000 as measured by filtration with size-exclusion membranes. We conclude that many surfactant systems empirically developed to fractionate photosynthetic pigment-protein complexes may not fully solubilize the complexes prior to the electrophoretic step.     

On the C-16 configuration of sitsirikine

The indole alkaloid sitsirikine has been synthesised by a biomimetic conversion of strictosidine and its C-16 configuration established as R by cyclisation to a 16,17-dihydroheteroyohimbine.     

Initiation of polymerization of alkyl 2-cyanoacrylates in aqueous solutions of glycine and its derivatives

The polymerization of methyl 2-cyanoacrylate and heptyl 2-cyanoacrylate was carried out with the use of aqueous solutions of ¹⁴C-tagged glycine, methyl glycine, and acetyl glycine as initiators. When glycine and methyl glycine were used, radioactive polymers were formed. When acetyl glycine was used, the polymer formed was not radioactive. The data seem to indicate that free NH₂ groups appear to be necessary for the incorporation of the glycine initiator in the polymer. A possible mechanism for the polymerization is presented.     

The indole side chain of tryptophan as a versatile pi-donor

Single-armed, 15- and 18-membered lariat ether receptor systems having indolylethyl side arms bind Na+ and K+ in the ring. The indole residue serves as a pi-donor to the ring-bound cation. Whether the five- or six-membered ring interacts most directly with Na+ or K+ depends on whether the sidearm is attached to indole's 3- or 5-position. This suggests that structural as well as electronic factors are important in pi-complexation of alkali metal cations.     

Electron conduction across electrode-immobilized neutravidin bound with biotin-labeled ruthenium pentaamine

Voltammetry is reported here of a self-assembled redox-protein conjugate consisting of neutravidin conjugated with a biotin derivative redox probe, Ru(NH3)5(N-[(N-[(4-pyridyl)methyl]biotinamide], immobilized on gold electrodes modified by self-assembled monolayers of mercaptoundecanoic acid. This voltammetry indicates that self-assembly of the conjugate/electrode electronic interface, driven by electrostatic binding between the monolayer and a single redox probe, favors orientation of the conjugate, resulting in electronic accessibility of the remaining three redox probes.     

Polyamine-based anion receptors: Extraction and structural studies

In the discussion that follows some of the more recent progress in the area of anion binding by synthetic polyamine receptors is presented, with emphasis given to work undertaken by the authors’ groups. A continuing theme in these studies has been the relationship between receptor structure and its anion extraction properties.Systematic solvent extraction and structural studies for halide and perrhenate complexes with polyamines of tripodal, macrocyclic and macrobicyclic architecture that contain both aromatic moieties and four to eight amine functions have been performed in order to derive relevant structure-binding/extractability relationships. The results demonstrate that the binding and extraction behaviour of the polyamines towards halides and perrhenate is a complex function of their structural features, degree of protonation and lipophilic properties. The extraction is characterized by the preferred formation of mono- and diprotonated amine species in the organic phase. X-ray structure studies of iodide and perrhenate complexes with open-chain tetraamino derivatives and octaamino cryptands in different protonation states lead to the conclusion that in the first case only limited chelation of the anion occurs and in the second only highly protonated species are able to encapsulate the anion. The structural patterns observed are strongly influenced by the presence of water molecules in the crystals.     

Aggregation of iron colloids in estuaries: a heterogeneous kinetics study using continuous mixing of river and sea waters

The kinetics of iron colloid aggregation in estuaries have been simulated with a model estuary in which seawater is continuously pumped into a reservoir initially containing river water. Profiles of colloidal Fe concentration versus salinity produced in this apparatus closely resembled field data for actual estuaries. Synthetic Fe colloids prepared by peptising Fe(OH)₃ with humic acid and phosphate showed very similar kinetic behaviour. Aggregation rate was found to be almost independent of velocity shear rate, implying that most aggregations are induced by brownian interparticle collisions. A heterogeneous kinetic model is proposed to explain the kinetic behaviour of Fe colloids during seawater-induced aggregation. This model describes kinetic behaviour in terms of a log-normal distribution of rate constants characterised by a mean value k and a standard deviation γ. Experiments showed that k is linearly related to the rate constant for salinity increase during mixing. This coupling of salinity changes and aggregation rate leads to Fe-salinity profiles that are nearly independent of the rate of salinity change, but which are dependent on γ.     

New guaianolides from Berlandiera Pumila and B. Texana,and the X-ray crystal structure of pumilin

The isolation and structure determination of two new guaianolides, pumilin and its 2,3-epoxide, from Berlandiera pumila and B. texana are reported. The structure of pumilin was determined from nmr and mass spectral data, and from an X-ray single crystal study; the structure of the epoxide was found by comparison of nmr spectra. Pumilin is shown to be a Δ¹⁽¹⁰⁾-cis-guaianolide with a cyclopentenone ring attached to C1 and C5, and an α-methylene-γ-lactone ring trans-fused to C6 and C7. The absolute configuration was inferred from spectral considerations and knowledge of previous structural determinations. The cd spectrum of pumilin exhibits a negative Cotton effect, and the lactone chromophore has left-handed chirality. The cyclo-heptene ring is in the chair configuration, with the lactone a half-chair and the cyclopentenone essentially planar. Crystals are orthorhombic, a = 7.065, b = 13.652, c = 19.586 Å, space group P2₁2₁2₁, Z = 4, and the final R value is 3.9%. The crystal structure is strengthened by an O···O hydrogen bond linking the molecules into infinite chains.     

Solid state radioluminescent lighting

We have demonstrated novel types of tritium-powered, solid-phase radioluminescent (RL) light sources. These lights include: (1) all-organic formulations comprised of polystyrene and fluorescent organic dyes; (2) polydimethylsiloxane-based systems incorporating inorganic phosphors; and (3) inorganic aerogel-based systems doped with phosphors. Three principal design consideration for these new RL lights are described. These include: (1) incorporation of tritium into the solid matrix; (2) molecular engineering to maximize light-output efficiency; and (3) strategies for increasing longevity. The advanced RL lights, which are of interest due to potential advantages in efficiency, brightness and safety, are being developed for emergency lighting uses and for battery and lighting applications in remote locations.     

NMR spectra of salicylohydroxamic acid in DMSO-d6 solution: a DFT study

The ¹H, ¹³C and ¹H, ¹³C COSY NMR spectra of salicylohydroxamic acid (sha) were measured in DMSO-d₆ solution. The B3LYP GIAO method with the 6-311++G(d,p) basis set was chosen to reproduce the experimental spectra. All possible zusammen and entgegen conformers of monomeric sha were computed. After geometry optimisation (B3LYP/6-311++G(d,p)) only nine independent models of the molecule were shown to be stable. Additionally, the NMR chemical shifts of the Onsager model of the most stable monomer were calculated. The computed chemical shifts for the labile protons for all aforementioned geometries meaningfully underestimated experimental results suggesting the existence of the H-bonded structure of sha in DMSO solution. The most probable two dimeric structures along with two solvent-bounded aggregates were subsequently calculated at the same level of theory. The best agreement was obtained for sha H-bonded with two DMSO molecules (confirmed by the absence of concentration effect). The relative error not exceeding 10 and 4% for chemical shifts in ¹H and ¹³C NMR spectra of sha–(DMSO)₂, respectively, showed that the applied method with the B3LYP/6-311++G(d,p) basis set was efficient to predict the NMR shifts of a compound with strong H-bonds. Thus, this allows to assign properly NMR resonances to specific structure formed in DMSO solution.