A Study of the Relative Importance of Lipophilic, π–π and Dipole–Dipole Interactions on Cyanopropyl, Phenyl and Alkyl LC Phases Bonded onto the Same Base Silica

Cyano (CN), butyl (C₄), phenyl and octadecyl (C₁₈) phases prepared from the same base silica gel were chromatographically characterized in order to assess the relative importance of lipophilic, π–π and dipole–dipole interactions in governing retention on these differing phases. Dipole interactions of analytes (possessing dipole moments and low lipophilicity) with CN phases were primarily responsible for the elution order. However, as the analytes’ lipophilicity increased, the lipophilic interaction predominated over the dipole interaction. In comparison, retention on the phenyl phase appeared to be complex, being controlled by a mixture of lipophilic, π–π and dipole–dipole interactions. Retention on the C₄ and C₁₈ phases was dictated by the analyte’s lipophilicity and its accessibility into the phase.     

The use of 2-hydroxymethyl benzoic acid as an effective water surrogate in the Passerini reaction: A straightforward access to α-hydroxyamides

Dozens of strategies have been described for the synthesis of α-hydroxyamides over the years, but they share common drawbacks in terms of generality and tolerability, especially to acid labile functionalities. Here we report a truncated Passerini reaction suitable for the easy and mild preparation of functionalized α-hydroxyamides. In particular, this procedure is tolerant to acid sensitive protecting groups, which remain intact during the multicomponent reaction.     

Asymmetric synthesis of N-protected amino acids by the addition of organolithium carboxyl synthons to ROPHy/SOPHy-derived aldoximes and ketoximes

A new asymmetric synthesis of alpha-amino acids is described in which the key step is the highly diastereoselective addition of organolithium carboxyl synthons (2-furyllithium, phenyllithium, vinyllithium) to (R)- and (S)-O-(1-phenylbutyl) oximes to give hydroxylamines, with vinyllithium being the most satisfactory nucleophilic reagent. Subsequent reductive cleavage of the N-O bond in hydroxylamines, followed by N-protection, and oxidative cleavage of the carboxyl precursor gave a range of N-protected amino acids and esters. The method was exemplified by the synthesis of a range of derivatives of non-proteinogenic amino acids such as 4-bromophenylalanine, tert-leucine, norvaline, cyclohexyl- and aryl-glycines, 2-amino-8-oxodecanoic acid (Aoda) and alpha-methylvaline.     

STRUCTURAL RELATIONSHIPS OF THE PHOTOSYSTEM I AND PHOTOSYSTEM II CHLOROPHYLL a/b AND a/c LIGHT-HARVESTING APOPROTEINS OF PLANTS AND ALGAE

Polyclonal antibodies against four different apoproteins of either the chlorophyll (Chl) a/b light-harvesting antenna of photosystem I or II, or a chlorophyll-protein complex homologous to CP26 from Chlamydomonas reinhardtii, crossreact with11–13 thylakoid proteins of Chlamydomonas, Euglena gracilis and higher plants. The number of antigenically-related proteins correlates with the quantity of light-harvesting chlorophyll-protein complex (LHC) gene types that have been sequenced in higher plants. The antibodies also react specifically with Chi a/c-binding proteins of three diatoms and Coccolithophora sp. as determined by immunoblot and Ouchterlony assays. Four to six crossreacting proteins are observed in each chromophyte species and a functional role for some can be deduced by antibody reactivity. It appears that despite major differences in the structures of their pigment ligands, at least some domains of Chl-binding LHC apoproteins have been conserved during their evolution, possibly functioning in protein: protein, as opposed to pigment: protein, interactions in photosynthetic membranes.     

Influence of co-matrix proton affinity on oligonucleotide ion stability in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

In this article we investigated the role organic base co-matrices play in reducing oligonucleotide fragmentation during analysis using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). The organic base co-matrix plays an important role in influencing the gas-phase behavior of desorbed oligonucleotides. No correlation was found between the solution pH values and the molecular ion stability of two model oligonucleotides. Instead, a direct correlation between the co-matrix proton affinity and the oligonucleotide molecular ion stability is seen. A co-matrix whose proton affinity is close to or greater than the proton affinity of the nucleobases can serve as a “proton sink. ” We propose that upon laser desorption/ionization, the co-matrix competes with the nucleobases of the oligonucleotide for additional protons from the matrix. When a co-matrix such as triethylamine is added, the co-matrix, rather than the oligonucleotide nucleobases, is the preferred site of proton transfer from the matrix. Titration of standard oligonucleotide matrices with several co-matrices of differing proton affinity demonstrates that the co-matrix mole fraction is an important factor in oligonucleotide molecular ion stability. When the mole fraction of the co-matrix approaches that of the matrix, nearly complete elimination of oligonucleotide fragmentation is seen. Control experiments utilizing pyridine, a co-matrix whose proton affinity is less than that of thymine or the phosphodiester backbone, demonstrate that the co-matrix plays an active role in oligonucleotide stabilization. Information on matrix:co-matrix interactions with these analytes should facilitate improvements in MALDI-MS of oligonucleotides.     

Highly stereoselective Saucy-Marbet rearrangement using chiral ynamides. Synthesis of highly substituted chiral homoallenyl alcohols

[reaction: see text] A highly stereoselective Saucy-Marbet rearrangement using chiral ynamides and propargyl alcohols is described here. This rearrangement can be catalyzed by para-nitrobenzenesulfonic acid leading to high diastereoselectivities for a range of different chiral propargyl alcohols and ynamides in a stereochemically intriguing matched, mismatched, or indifferent manner. This provides an excellent entry to highly substituted chiral homoallenyl alcohols.     

Reaction of silicate minerals to form tetramethoxysilane

Several silicon dioxide sources were used as reagents in the base-mediated reaction with dimethyl carbonate (DMC) to make tetramethoxysilane (Q'). Several commercially available diatomaceous earth materials were investigated. High throughput screening was employed to explore over 200 silicate rocks and minerals as alternative silicon dioxide sources for formation of Q' from DMC and base. Amorphous silicon dioxide materials are effective reagents for the Q' forming reaction. Effective silicon dioxide sources in addition to the diatomaceous earth materials include opal and various synthetic silicates (Li, Co, and Ca).     

Bulk and dispersed aqueous phase behavior of phytantriol: effect of vitamin E acetate and F127 polymer on liquid crystal nanostructure

Phytantriol (3,7,11,15-tetramethylhexadecane-1,2,3-triol, PHYT) is a cosmetic ingredient that exhibits similar lyotropic phase behavior to monoolein (GMO), forming bicontinuous cubic liquid crystalline structures (Q(II)) at low temperatures and reversed hexagonal phase (H(II)) at higher temperatures in excess water. Despite these similarities, phytantriol has received little attention in the scientific community. In this study, the thermal phase behavior of the binary PHYT-water and ternary PHYT-vitamin E acetate (VitEA)-water systems have been studied and compared with the behavior of the dispersed cubosomes and hexosomes formed with the aid of a stabilizer (Pluronic F127). The phase behavior and nanostructure were studied using crossed polarized light microscopy (CPLM), differential scanning calorimetry (DSC), and small-angle X-ray scattering (SAXS) techniques. The presence of lipophilic VitEA in the PHYT-water system suppressed the temperature of the Q(II)-to-H(II)-to-L2 transitions, indicating that lipophilic compounds, in relatively small amounts, may have a significant impact on the phase behavior. Increasing the F127 concentration in the phytantriol-based cubosome system did not induce the Q(II)(Pn3m) to Q(II)(Im3m) transition known for the GMO-water system. This indicates a different mode of interaction between F127 and the lipid domains of phytantriol-water systems. Taken together, these results indicate that phytantriol may not only provide an alternative lipid for preparation of liquid crystalline systems in excess water but may also provide access to properties not available when using GMO.     

Raman spectroscopy of short-lived terthiophene radical cations generated by photochemical and chemical oxidation.

The Raman spectra of various terthiophene radical cations are investigated; namely those of unsubstituted terthiophene and two styryl-substituted terthiophenes. Transient pump-probe resonance Raman spectroscopy is used to measure the short-lived radical cation spectra of non-end-capped 2,2':5',2'-terthiophene (3T) and 3'-[(E)-2-(4-nitrophenyl)ethenyl]-2,2':5',2'-terthiophene (NO2-pe3T). For these two compounds, the radical cations are generated via either direct photogeneration or photochemically using the electron acceptor tetracyanoethylene. The radical cation of 5,5'-dimethyl-3'-[(E)-2-phenylethenyl]-2,2':5',2'-terthiophene (DM-pe3T) is stable for up to five minutes as a result of the two alpha end caps and continuous-wave resonance Raman spectroscopy and chemical oxidation is used to obtain the spectrum of this radical cation. The resonance Raman spectra of all three terthiophene radical cations are dominated by a group of very intense bands in the low-frequency region. These bands have been assigned, by density functional theory methods, to C-S stretching modes coupled to thiophene ring deformations. These modes are significantly less intense in the sigma-dimer of NO2-pe3T [i.e. the corresponding styryl sexithiophene (NO2-pe3T)2]. This observation is attributed to a smaller change in the C--S bond order in the sexithiophene compared to the analogous terthiophene. This bond order difference may be rationalised by consideration of the singly occupied molecular orbital and lowest unoccupied molecular orbital, which are involved in the electronic transition probed by the laser excitation wavelength.