Neutral Functional Groups Research Articles

Adsorption and desorption of aliphatic amines, amino acids and acetate by clay minerals and marine sediments

The adsorption and desorption behavior of three aliphatic amines, three amino acids, and acetate by organic-free clay minerals (kaolinite and montmorillonite) and by marine sediment was studied in laboratory experiments using 14C-labeled compounds. These compounds were chosen to represent basic, neutral, and acidic functional groups. Adsorption partition coefficients ranged from < 0.5 to 4.2 for acetate, < 1 to 15 for monomethyl-, dimethyl- and trimethyl amine, and < 1 to 128 for alanine, glutamic acid and lysine. Single desorption experiments were conducted using these compounds to calculate desorption partition coefficients. Repetitive desorption experiments and a consecutive desorption model were used to calculate partition coefficients for the reversible and resistant components of desorption. Adsorption of the three positively-charged amines and lysine was mostly reversible, but glutamic acid, alanine and acetate exhibited irreversible association. This is most likely related to the different adsorption mechanisms caused by the different functional groups on these compounds. Ion exchange and electrostatic interactions are more important for the positively-charged compounds while chemical interactions with surface organic functional groups may be more important for the neutral and negatively-charged compounds. Adsorption of amines, amino acids and acetate is greater in sediments with a higher organic content although the acidic and neutral compounds were affected more than the basic compounds. Oxidation state of the sediments may also be an important factor in adsorption behavior.

Germination and development of attachment structures by conidia of aquatic Hyphomycetes: light microscope studies

The time scales of conidial germination and production of postgermination attachment structures in species of the aquatic Hyphomycetes were investigated. The conidia of most species germinated within 2 h and formed appressoria within 6 h of settlement. Subsequent to settlement, appressoria were formed by all of the tetraradiate and branched conidia at the poles of the conidial arms. It is suggested that appressorium formation is an adaptation to aid fungal attachment to a substratum. Conidial germination was not influenced by the substratum; however, appressoria were both more numerous and more complex on a glass substratum. Mucilage was present on conidia, and mucilaginous sheaths were frequently observed to be associated with germ tubes and appressoria. The majority of species produced mucilages composed primarily of polysaccharide(s) with neutral or carboxyl functional groups. Key words: aquatic Hyphomycetes, germination, appressorium, attachment, settlement.

Fragmentations of gas-phase complexes between alkali metal ions and peptides: metal ion binding to carbonyl oxygens and other neutral functional groups

Fragmentations of gas-phase complexes between alkali metal ions and peptides: metal ion binding to carbonyl oxygens and other neutral functional groups

Fluorescent probes for asymmetric lipid bilayers: synthesis and properties in phosphatidyl choline liposomes and erythrocyte membranes.

We have synthesized three sets of fluorescent probes which we believe will be useful in studies of asymmetric membranes and have studied their interactions with model lipid bilayers and erythrocyte membranes. The probes were designed to partition preferentially into one face of a lipid bilayer with asymmetrically disposed phospholipids and to report lipid transitions in that monolayer. We synthesized more than twenty probes containing anthroyl-, dansyl-, or pyrene rings with acidic, basic, and neutral functional groups and alkyl "spacers" of various lengths. The interactions of these probes with liposomes of phosphatidyl choline and with erythrocyte membranes were characterized to determine whether probe insertion was asymmetric, how deeply the probe penetrated the bilayer, and whether the probe reflected thermotropic phase transitions in model membranes. The set of variously charged anthroyl esters, analogs of local anaesthetics, appears to be promising for studies of asymmetric membranes. Fluorescent probes have been used extensively to provide information on the lipid regions of biological membranes. Membrane fluidity, a composite of molecular packing and motion of acyl chains in lipid bilayers, has been assessed with a variety of fluorescent probes, the fluorescence of which undergoes some measurable change at the temperature of the membrane's thermotropic phase transition. A large number of fluorescent probes have been used for this purpose. Bashford, Morgan and Radda (Bashford, C.L., Morgan, C.G., Radda, G.K. 1976; Biochim. Biophys. Acta 426:157) and Thulborn and Sawyer (Thulborn, K.R., Sawyer, W. H. 1978; Biochim. Biophys. Acta 511:125) synthesized several fatty acid derivatives in which an anthracene group is attached (in ester linkage) along the acyl chain at various positions, and have shown that this set of probes may be useful in probing membrane fluidity at different depths within the bilayer. This report describes the synthesis and properties of several sets of amphipathic fluorescent probes, which may partition unequally into the two faces of an asymmetric lipid bilayer, and may therefore provide information about membranes complementary to that obtainable with existing probes.

Histidine uptake in mutant strains of Neurospora crassa via the general transport system for amino acids.

A transport double mutant of Neurospora crassa has been isolated that has only one of the three transport systems capable of l-histidine uptake. The substrate specificity of the remaining transport system, termed the general transport system, has been fully characterized with regard to the contributions to binding of the side chain, the alpha-amino group, and the carboxylate group. The positively charged alpha-amino group is necessary for binding; the negatively charged carboxylate group is of less importance, since its replacement by a neutral carbonyl functional group does not completely abolish binding. The greatest structural latitude for binding was found in the side chain; affinity for alpha-amino acids was uniformly high except for l-aspartic and l-glutamic acids, l-asparagine, and l-proline. Thus, this transport system is "general" with these restrictions.

Ion cyclotron resonance spectroscopy. Cyclotron double resonance provides a new technique for the study of ion-molecule reaction mechanisms.

Ion cyclotron resonance spectroscopy. Cyclotron double resonance provides a new technique for the study of ion-molecule reaction mechanisms.