A novel conformation of valinomycin in its barium complex

Knowledge of the molecular mechanisms involved in ionophore-mediated cation transport would be valuable for under-standing many essential functions of biological membranes1−3. Cations are transported in several stages, such as formation of the ionophore−cation complex, diffusion across the cell membrane and subsequent release of the cation. Several conformational rearrangements are involved in this process, and so a detailed understanding of all the conformational possibilities of the ionophore seems to be essential for elucidating the molecular mechanism of ion transport. We are carrying out spectroscopic and crystallographic studies to explore the possible conformational stages of ionophores by complexing them, in different solvents, with cations of various sizes and charges. We report here a novel conformation of the ionophore valinomycin in its barium complex. It can be described as an extended depsipeptide chain, without internal hydrogen bonds, wound in the form of an ellipse with the two barium ions located at the foci.

Synthesis and structure of some interesting oxides of bismuth

Synthesis and structures of several new oxides containing bismuth are described. Three types of structures are common among the multinary oxides containing trivalent bismuth. They are the sillenite structure of γ-Bi2O3, the layered perovskite structure of Aurivillius phases and the pyrochlore structure. The influence of Bi3+∶6s 2 lone pair electrons is seen in all the three structures. In transition metal oxides containing trivalent bismuth,d o cations (Ti4+, Nb5+, W6+) stabilize the layered perovskite structure, while cations containing partially-filledd orbitals (V4+, Cr3+, Fe3+) favour pyrochlore-related structures. Ferroelectric distortion ofMO6 octahedra of thed o cations seems to play an important role in stabilizing layered perovskite structures.

A note on mass transfer in turbulent wall jets

THE PROCESS of mass transfer from saturated porous surfaces virtual origin ; exposed to turbulent air streams finds many practical applitransverse coordinate; cations. In many cases, the air stream will be in the form of a height of nozzle above flat plate--radial wall jet; wall jet over the porous surface. The aerodynamics of both plane and radial wall jets have been investigated in detail and a vast amount of literature is available on the subject [l-3].

Structural and thermal properties of inorganic–organic montmorillonite: Implications for their potential environmental applications

Inorganic–organic clays (IOCs), clays intercalated with both organic cations such as cationic surfactants and inorganic cations such as metal hydroxy polycations have the properties of both organic and pillared clays, and thereby the ability to remove both inorganic and organic contaminants from water simultaneously. In this study, IOCs were synthesised using three different methods with different surfactant concentrations. Octadecyltrimethylammonium bromide (ODTMA) and hydroxy aluminium ([Al13O4 (OH)24(H2O)12]7+ or Al13) are used as the organic and inorganic modifiers (intercalation agents). According to the results, the interlayer distance, the surfactant loading amount and the Al/Si ratio of IOCs strictly depend on the intercalation method and the intercalation agent ratio. Interlayers of IOCs synthesised by intercalating ODTMA before Al13 and IOCs synthesised by simultaneous intercalation of ODTMA and Al13 were increased with increasing the ODTMA concentration used in the synthesis procedure and comparatively high loading amounts could be observed in them. In contrast, Al/Si decreased with increasing ODTMA concentration in these two types of IOCs. The results suggest that Al-pillars can be fixed within the interlayers by calcination and any increment in the amount of ODTMA used in the synthesis procedure did not affect the interlayer distance of the IOCs. Overall the study provides valuable insights into the structure and properties of the IOCs and their potential environmental applications.

Simultaneous adsorption of Cd(II) and phosphate on Al13 pillared montmorillonite

Al13 pillared montmorillonites (AlPMts) prepared with different Al/clay ratios were used to remove Cd(II) and phosphate from aqueous solution. The structure of AlPMts was characterized by X-ray diffraction (XRD), Thermogravimetric analysis (TG), and N2 adsorption–desorption. The basal spacing, intercalated amount of Al13 cations, and specific surface area of AlPMts increased with the increase of the Al/clay ratio. In the single adsorption system, with the increase of the Al/clay ratio, the adsorption of phosphate on AlPMts increased but that of Cd(II) decreased. Significantly enhanced adsorptions of Cd(II) and phosphate on AlPMts were observed in a simultaneous system. For both contaminants, the adsorption of one contaminant would increase with the increase of the initial concentration of the other one and increase in the Al/clay ratio. The enhancement of the adsorption of Cd(II) was much higher than that of phosphate on AlPMt. This suggests that the intercalated Al13 cations are the primary co-adsorption sites for phosphate and Cd(II). X-ray photoelectron spectroscopy (XPS) indicated comparable binding energy of P2p but a different binding energy of Cd3d in single and simultaneous systems. The adsorption and XPS results suggested that the formation of P-bridge ternary surface complexes was the possible adsorption mechanism for promoted uptake of Cd(II) and phosphate on AlPMt.

Fluorescent alamethicin fragments A study of membrane activity and aqueous phase aggregation

The linear polypeptide antibiotic alamethicin is known to form channels in artificial lipid membranes. Synthetic 13- and 17-residue alamethicin fragments, labelled with a fluorescent dansyl group at the N-terminus, have been shown to translocate divalent cations across phospholipid membranes and to uncouple oxidative phosphorylation in rat liver mitochondria, in a manner analogous to the parent peptides. From studies of the aqueous phase aggregation behavior of the peptides, as well as their interaction with rat liver mitochondria, it is concluded that the interaction of the peptides with membranes is a complex process, probably involving both aqueous and membrane phase aggregation.

Developments and Microbiological applications in African foods: Emphasis on Nigerian Wara cheese

African indigenous foods have received limited research. Most of these indigenous foods are fermented and they form part of the rich nutritional culture of many groups in African countries. The industrialization and commercialisation of these indigenous African fermented foods should be preceded by a thorough scientific knowledge of their processing which can be vital in the elimination of hunger and poverty. This study highlighted emerging developments and the microbiology of cereal-based and cassava-based food products that constitute a major part of the human diet in most African countries. In addition, investigations were also carried out on the coagulant of the Calotropis procera plant used in traditional production of Nigerian Wara cheese and on the effects of adding a nisin producing Lactococcus lactis strain originating from human milk to Nigerian Wara cheese. Fermented cereal-based food such as ogi utilize popular African and readily available grains maize, millet or sorghum as substrates and is popular as a weaning diet in infants. In this study, the bulkiness caused by starch gelatinization was solved by amylase treatments in the investigation on cooked and fermented oat bran porridge. A similar treatment could reduce the viscosity of any cereal porridge. The properties of the Sodom apple leaves (Calotropis procera) extract in cheesemaking were studied. C. procera was affected by monovalent (K+ and Na+) and divalent (Mg2+ and Ca2+) cations during coagulation. The rennet strength of this coagulant was found to be 7 % compared to animal rennet at 35 °C. Increasing the incubation temperature to 70 °C increased the rennet strength 28-fold. The molecular weight of the partially purified protease was determined by SDS-PAGE and was confirmed by Zymography to be approximately 60 kilodaltons. The high proteolytic activity at 70 °C supported the suitability of the protease enzyme as a coagulant in future commercial production of Nigerian Wara cheese. It was also possible to extend the shelf life of Wara cheese by a nisin producing lactic acid bacteria Lactococcus lactis LAC309. The levels of nisin in both whey and curd fractions of Wara were investigated, results showed a 3 log reduction of toxicogenic Bacillus licheniformis spiked on Wara after 3 days. These studies are the first in Finland to promote the advancement of scientific knowledge in African foods. Recognizing these indigenous food products and an efficient transfer of technology from the developed countries to industrialize them are necessary towards a successful realization of the United Nations Millenium Development Program.

Crystal and molecular structures of alkali- and alkaline-earth-metal complexes of N,N-dimethylformamide

Structures of lithium, sodium, magnesium, and calcium complexes of NJ-dimethylformamide (DMF) have been investigated by X-ray crystallography. Complexes with the formulas LiCl.DMF.1/2H20, NaC104.2DMF, CaC12.2DMF.2H20, and Mg(C104)2.6DMF crystallized in space groups P2]/c, P2/c, Pi, and Ella, respectively, with the following cell dimensions: Li complex, a = 13.022 (7) A, b = 5.978 (4) A, c = 17.028 (10) A, = 105.48 (4)O, Z = 8; Na complex, a = 9.297 (4)A, b = 10.203 (3) A, c = 13.510 (6) A, /3 = 110.08 (4)O, Z = 4; Ca complex, a = 6.293 (4) A, b = 6.944 (2) A, c = 8.853(5) A, a = 110.15 (3)O, /3 = 105.60 (6)", y = 95.34 (5)", Z = 1; Mg complex, a = 20.686 (11) A, b = 10.962 (18) A,c = 14.885 (9) A, /3 = 91.45 (5)O, Z = 4. Lithium is tetrahedrally coordinated while the other three cations are octahedrally coordinated; the observed metal-oxygen distances are within the ranges generally found in oxygen donor complexes of these metals. The lithium and sodium complexes are polymeric, with the amide and the anion forming bridging groups between neighboring cations. The carbonyl distances become longer in the complexes accompanied by a proportionate decrease in the length of the central C-N bond of the amide; the N-C bond of the dimethylamino group also shows some changes in the complexes. The cations do not deviate significantly from the lone-pair direction of the amide carbonyl and remain in the amide plane. Infrared spectra of the complexes reflect the observed changes in the amide bond distances.

Mechanisms of transmembrane cation transport studied by nuclear magnetic resonance spectroscopy

Several molecules like ionophores, vitamins, ion-binding cyclic peptides, acidic phospholipids, surfactants are known to expose the inner side of vesicles, to the externally added cations. Whereas ionophores and certain other systems bring about these changes by a selective transport (influx) of the cation by specialized mechanisms known as the carrier and channel mechanism, other systems cause lysis and vesicle fusion. These systems have been successfully studied using1H,31 P and13C nuclear magnetic resonance spectroscopy after the demonstration, fifteen years ago, of the ability of paramagnetic lanthanide ions to distinguish the inside of the vesicle from the outside. The results of these ’nuclear magnetic resonance kinetics’ experiments are reviewed.

Porphyrins with multiple crown ether voids: novel systems for cation complexation studies

Porphyrins appended with crown ether, benzo-15-crown-5, at the methine positions have been synthesized and characterized. The fully and partially substituted porphyrins and their metallo (Co, Cu, and Zn) derivatives describe one or more ether cavities in the periphery that are capable of recognizing spherical cations. The ability of these macrocycles to complex cations (Na+, K+, Mg2+, Ca2+, Ba2', and NH4+) is investigated by use of visible, 'H NMR, ESR, and emission spectral studies. The tetrasubstituted crown porphyrin (TCP) exhibits very high selectivity for K+. The cations (K', Ba2+, and NH4+) that require two crown ether cavities for complexation promote dimerization of the porphyrins. The ESR study of the cation-induced porphyrin dimers reveals axial symmetry with the porphyrin planes separated by -4.2 A. This distance increases from the fully substituted to partially substituted porphyrins. The cations (K', Ba2+, and NH4') quench efficiently the fluorescence of the free base porphyrins and their metallo derivatives. The quenching process is attributed to the steric geometry of the dimers.

Electrochemisorption - A Cluster Approach

A simple semiempirical quantum chemical approach (Extended Huckel Theory) is shown to give a reasonable description of the electronic structural aspects of chemisorption on the mercury model surface. Chemisorptive interaction of alkali metal atoms and cations, halogen atoms and anions, and water molecules with a charge-neutralized hexagonal close-packed cluster of seven Hg atoms is studied. Adsorption of H, C, N and O atoms on the same model cluster is studied for comparison with earlier work. Chemisorption energies, charge transfer, interaction distance and hydration effects are discussed and compared with experimental results where available.

Enzyme molecular choreography : studies on soluble inorganic pyrophosphatases

Inorganic pyrophosphatases (PPases, EC 3.6.1.1) hydrolyse pyrophosphate in a reaction that provides the thermodynamic 'push' for many reactions in the cell, including DNA and protein synthesis. Soluble PPases can be classified into two families that differ completely in both sequence and structure. While Family I PPases are found in all kingdoms, family II PPases occur only in certain prokaryotes. The enzyme from baker's yeast (Saccharomyces cerevisiae) is very well characterised both kinetically and structurally, but the exact mechanism has remained elusive. The enzyme uses divalent cations as cofactors; in vivo the metal is magnesium. Two metals are permanently bound to the enzyme, while two come with the substrate. The reaction cycle involves the activation of the nucleophilic oxygen and allows different pathways for product release. In this thesis I have solved the crystal structures of wild type yeast PPase and seven active site variants in the presence of the native cofactor magnesium. These structures explain the effects of the mutations and have allowed me to describe each intermediate along the catalytic pathway with a structure. Although establishing the ʻchoreographyʼ of the heavy atoms is an important step in understanding the mechanism, hydrogen atoms are crucial for the mechanism. The most unambiguous method to determine the positions of these hydrogen atoms is neutron crystallography. In order to determine the neutron structure of yeast PPase I perdeuterated the enzyme and grew large crystals of it. Since the crystals were not stable at ambient temperature, a cooling device was developed to allow neutron data collection. In order to investigate the structural changes during the reaction in real time by time-resolved crystallography a photolysable substrate precursor is needed. I synthesised a candidate molecule and characterised its photolysis kinetics, but unfortunately it is hydrolysed by both yeast and Thermotoga maritima PPases. The mechanism of Family II PPases is subtly different from Family I. The native metal cofactor is manganese instead of magnesium, but the metal activation is more complex because the metal ions that arrive with the substrate are magnesium different from those permanently bound to the enzyme. I determined the crystal structures of wild type Bacillus subtilis PPase with the inhibitor imidodiphosphate and an inactive H98Q variant with the substrate pyrophosphate. These structures revealed a new trimetal site that activates the nucleophile. I also determined that the metal ion sites were partially occupied by manganese and iron using anomalous X- ray scattering.

Studies on the Mechanism of Action of Miconazole: Effect of Miconazole on Respiration and Cell Permeability of Candida albicans

The antifungal drug, miconazole nitrate, inhibits the growth of several species of Candida. Candida albicans, one of the pathogenic species, was totally inhibited at a concentration of approximately 10 μg/ml. Endogenous respiration was unaffected by the drug at a concentration as high as 100 μg/ml, whereas exogenous respiration was markedly sensitive and inhibited to an extent of 85%. The permeability of the cell membrane was changed as evidenced by the leakage of 260-nm absorbing materials, amino acids, proteins, and inorganic cations. The results we present clearly show that the drug alters the cellular permeability, and thus the exogenous respiration becomes sensitive to the drug.

Stabilization of Phospholipid Coatings in Capillary Electrophoresis

The development of a simple method of coating a semi-permanent phospholipid layer onto a capillary for electrochromatography use was the focus of this study. The work involved finding good coating conditions, stabilizing the phospholipid coating, and examining the effect of adding divalent cations, cetyltrimethylammonium bromide, and polyethylene glycol (PEG)-lipids on the stability of the coating. Since a further purpose was to move toward more biological membrane coatings, the capillaries were also coated with cholesterol-containing liposomes and liposomes of red blood cell ghost lipids. Liposomes were prepared by extrusion, and large unilamellar vesicles with a diameter of about 100 nm were obtained. Zwitterionic phosphatidylcholine (PC) was used as a basic component, mainly 1-palmitoyl-2-oleyl-sn-glycero-3-phosphocholine (POPC) but also eggPC and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC). Different amounts of sphingomyelin, bovine brain phosphatidylserine, and cholesterol were added to the PC. The stability of the coating in 40 mM N-(2-hydroxyethyl)piperazine-N’-(2-ethanesulfonic acid) (HEPES) solution at pH 7.4 was studied by measuring the electroosmotic flow and by separating neutral steroids, basic proteins, and low-molar-mass drugs. The presence of PC in the coating solution was found to be essential to achieving a coating. The stability of the coating was improved by the addition of negative phosphatidylserine, cholesterol, divalent cations, or PEGylated lipids, and by working in the gel-state region of the phospholipid. Study of the effect on the PC coating of divalent metal ions calcium, magnesium, and zinc showed a molar ratio of 1:3 PC/Ca2+ or PC/Mg2+ to give increased rigidity to the membrane and the best coating stability. The PEGylated lipids used in the study were sterically stabilized commercial lipids with covalently attached PEG chains. The vesicle size generally decreased when PEGylated lipids of higher molar mass were present in the vesicle. The predominance of discoidal micelles over liposomes increased PEG chain length and the average size of the vesicles thus decreased. In the capillary electrophoresis (CE) measurements a highly stable electroosmotic flow was achieved with 20% PEGylated lipid in the POPC coating dispersion, the best results being obtained for disteroyl PEG (3000) conjugates. The results suggest that smaller particles (discoidal micelles) result in tighter packing and better shielding of silanol groups on the silica wall. The effect of temperature on the coating stability was investigated by using DPPC liposomes at temperatures above (45 C) and below (25 C) the main phase transition temperature. Better results were obtained with DPPC in the more rigid gel state than in the fluid state: the electroosmotic flow was heavily suppressed and the PC coating was stabilized. Also dispersions of DPPC with 0−30 mol% of cholesterol and sphingomyelin in different ratios, which more closely resemble natural membranes, resulted in stable coatings. Finally, the CE measurements revealed that a stable coating is formed when capillaries are coated with liposomes of red blood cell ghost lipids.

Intermolecular Interactions of Noble-Gas-Containing Species

The importance of intermolecular interactions to chemistry, physics, and biology is difficult to overestimate. Without intermolecular forces, condensed phase matter could not form. The simplest way to categorize different types of intermolecular interactions is to describe them using van der Waals and hydrogen bonded (H-bonded) interactions. In the H-bond, the intermolecular interaction appears between a positively charged hydrogen atom and electronegative fragments and it originates from strong electrostatic interactions. H-bonding is important when considering the properties of condensed phase water and in many biological systems including the structure of DNA and proteins. Vibrational spectroscopy is a useful tool for studying complexes and the solvation of molecules. Vibrational frequency shift has been used to characterize complex formation. In an H-bonded system A∙∙∙H-X (A and X are acceptor and donor species, respectively), the vibrational frequency of the H-X stretching vibration usually decreases from its value in free H-X (red-shift). This frequency shift has been used as evidence for H-bond formation and the magnitude of the shift has been used as an indicator of the H-bonding strength. In contrast to this normal behavior are the blue-shifting H-bonds, in which the H-X vibrational frequency increases upon complex formation. In the last decade, there has been active discussion regarding these blue-shifting H-bonds. Noble-gases have been considered inert due to their limited reactivity with other elements. In the early 1930 s, Pauling predicted the stable noble-gas compounds XeF6 and KrF6. It was not until three decades later Neil Bartlett synthesized the first noble-gas compound, XePtF6, in 1962. A renaissance of noble-gas chemistry began in 1995 with the discovery of noble-gas hydride molecules at the University of Helsinki. The first hydrides were HXeCl, HXeBr, HXeI, HKrCl, and HXeH. These molecules have the general formula of HNgY, where H is a hydrogen atom, Ng is a noble-gas atom (Ar, Kr, or Xe), and Y is an electronegative fragment. At present, this class of molecules comprises 23 members including both inorganic and organic compounds. The first and only argon-containing neutral chemical compound HArF was synthesized in 2000 and its properties have since been investigated in a number of studies. A helium-containing chemical compound, HHeF, was predicted computationally, but its lifetime has been predicted to be severely limited by hydrogen tunneling. Helium and neon are the only elements in the periodic table that do not form neutral, ground state molecules. A noble-gas matrix is a useful medium in which to study unstable and reactive species including ions. A solvated proton forms a centrosymmetric NgHNg+ (Ng = Ar, Kr, and Xe) structure in a noble-gas matrix and this is probably the simplest example of a solvated proton. Interestingly, the hypothetical NeHNe+ cation is isoelectronic with the water-solvated proton H5O2+ (Zundel-ion). In addition to the NgHNg+ cations, the isoelectronic YHY- (Y = halogen atom or pseudohalogen fragment) anions have been studied with the matrix-isolation technique. These species have been known to exist in alkali metal salts (YHY)-M+ (M = alkali metal e.g. K or Na) for more than 80 years. Hydrated HF forms the FHF- structure in aqueous solutions, and these ions participate in several important chemical processes. In this thesis, studies of the intermolecular interactions of HNgY molecules and centrosymmetric ions with various species are presented. The HNgY complexes show unusual spectral features, e.g. large blue-shifts of the H-Ng stretching vibration upon complexation. It is suggested that the blue-shift is a normal effect for these molecules, and that originates from the enhanced (HNg)+Y- ion-pair character upon complexation. It is also found that the HNgY molecules are energetically stabilized in the complexed form, and this effect is computationally demonstrated for the HHeF molecule. The NgHNg+ and YHY- ions also show blue-shifts in their asymmetric stretching vibration upon complexation with nitrogen. Additionally, the matrix site structure and hindered rotation (libration) of the HNgY molecules were studied. The librational motion is a much-discussed solid state phenomenon, and the HNgY molecules embedded in noble-gas matrices are good model systems to study this effect. The formation mechanisms of the HNgY molecules and the decay mechanism of NgHNg+ cations are discussed. A new electron tunneling model for the decay of NgHNg+ absorptions in noble-gas matrices is proposed. Studies of the NgHNg+∙∙∙N2 complexes support this electron tunneling mechanism.