Intramolecular hydrogen bonding in a monoglyceride lipid studied by Fourier transform infrared spectroscopy

Effect of monoglycerides and fatty acids on a ceramide bilayer

Monoglycerides and unsaturated fatty acids, naturally present in trace amounts in the stratum corneum (top layer of skin) lipid matrix, are commonly used in pharmaceutical, cosmetic and health care formulations. However, a detailed molecular understanding of how the oil additives get incorporated into the skin lipids from topical application and, once incorporated, how they affect the properties and integrity of the lipid matrix remains unexplored. Using ceramide 2 bilayers as skin lipid surrogates, we use a series of molecular dynamics simulations with six different natural oil ingredients at multiple concentrations to investigate the effect of the oils on the properties and stability of the bilayers. The six oils: monoolein, monostearin, monoelaidin, oleic acid, stearic acid and linoleic acid - all having the same length of the alkyl chain, C18, but a varying degree of saturation, allow us to systematically address the effect of unsaturation in the additives. Our results show that at low oil concentration (∼5%) the mixed bilayers containing any of the oils and ceramide 2 (CER2) become more rigid than pure CER2 bilayers due to more efficient lipid packing. Better packing also results in the formation of larger numbers of hydrogen bonds between the lipids, which occurs at the expense of the hydrogen bonds between lipids and water. The mixed bilayers with saturated or trans-unsaturated oils remain stable over the whole range of oil concentration. In contrast, the presence of the oils with at least one cis-double bond leads to bilayer instability and complete loss of bilayer structure at the oil content of about 50-65%. Two cis-double bonds in the lipid tail induce bilayer disruption at even lower concentration (∼30%). The mixed bilayers remain in the gel phase (without melting to a fluid phase) until the phase transition to a non-bilayer phase occurs. We also demonstrate that the stability of the bilayer strongly correlates with the order parameter of the lipid tails.

On the interaction of water-soluble binders and nano silicon particles: alternative binder towards increased cycling stability at elevated temperatures

Silicon based composites are among the most promising negative electrodes for lithium ion battery applications due to their high theoretical capacities. One major drawback of silicon based anodes are their large volume changes during lithiation and delithiation. Although many efforts have been made in view of new binder materials and improved electrolytes, the resulting battery cell suffers from severe capacity fading at ambient or elevated temperatures, respectively. The strong reactivity with the electrolyte is considered to be responsible for the reduced cycle life at elevated temperatures. In this work we introduce silicon composite anodes with a novel composition based on a gellan gum binder material that show an improved cycling performance at ambient temperature and at 60 °C. To elucidate the influence of the binder material, we investigated the structure of the silicon based composite anodes in order to understand the nature of the interaction of the gellan gum based binder polymers with the silicon particles in comparison with a common CMC binder. Also the influence of the choice of binder on the interactions at the interface between electrode surface and electrolyte were studied. A combination of powerful techniques including solid state NMR, TEM and EELS, XPS as well as FTIR were applied.

Nucleotide recognition and phosphate linkage hydrolysis at a lipid cubic interface

Mononucleotides, when entrapped within a mono-olein-based cubic Ia3d liquid crystalline phase, have been found to undergo hydrolysis at the sugar-phosphate ester bond in spite of their natural inertness toward hydrolysis. Here, kinetics of the hydrolysis reaction and interactions between the lipid matrix and the mononucleotide adenosine 5'-monophosphate disodium salt (AMP) and its 2'-deoxy derivative (dAMP) are thoroughly investigated in order to shed some light on the mechanism of the nucleotide recognition and phosphate ester hydrolysis. Experiments evidenced that molecular recognition occurs essentially through the sn-2 and the sn-3 alcoholic OH groups of mono-olein. As deduced from the apparent activation energies, the mechanism underlying the hydrolysis reaction is the same for AMP and dAMP. Nevertheless, the reaction proceeds slower for the latter, highlighting a substantial difference in the chemical behavior of the two nucleotides. A model that explains the hydrolysis reaction is presented. Remarkably, the hydrolysis mechanism appears to be highly specific for the Ia3d phase.

Oxygen Uptake upon Photolysis of 1,4-Benzoquinones and 1,4-Naphthoquinones in Air-Saturated Aqueous Solution in the Presence of Formate, Amines, Ascorbic Acid, and Alcohols

The effects of oxygen in the photoreduction of 1,4-benzoquinone (BQ), 1,4-naphthoquinone (NQ), and a series of derivatives were studied in aqueous solution in the presence of acetonitrile and formate, aliphatic amines, e.g., EDTA or triethylamine, ascorbic acid, and alcohols, e.g., methanol or 2-propanol. The quinone triplet state is quenched, whereby the semiquinone and donor radicals are formed which react subsequently with oxygen. The overall reaction is oxidation of the donors and conversion of oxygen via the hydroperoxyl/superoxide radical into hydrogen peroxide. The quantum yield (Phi-O2) of this oxygen uptake changes in 2-propanol-water (1:10) from <0.01 for BQ to Phi-O2 = 0.5-0.8 for NQ. Generally Phi-O2 increases with increasing donor concentration. The specific properties of quinone structure, the radical equilibria and reactivity, and the concentration dependences are discussed.

Encapsulation of hemoglobin in a bicontinuous cubic phase lipid

The effects of encapsulating bovine hemoglobin (BHb) in the bicontinuous cubic phase formed by monooleoylglycerol and water was investigated with Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction. Cubic phase was formed in the presence of 1-10 wt% BHb. Studies using X-ray diffraction reveal that at 0.5-2.5 wt% BHb, the cubic phase structure is characterized by the double diamond lattice (Pn3m). At 2.5-5 wt% BHb, coexistence of two cubic phase structures, Pn3m and the gyroid lattice (Ia3d), was observed while at BHb, concentrations higher than 5 wt% the gyroid structure persists. FTIR shows there is an increase in intensity of the free nu C = O (1745 cm-1) and a corresponding decrease in the intensity of the hydrogen bonded nu C = O (1720 cm-1) as the BHb concentration is increased. The nu C-O-CO peak shifts from 1183 cm-1 to 1181 cm-1 as the concentration of BHb raised from 2.5 to 10 wt% indicating BHb may induce subtle changes in the interfacial region of cubic phase monoolein. The bandwidth of the nu asCH2 stretch (2926 cm-1) increased in the presence of 5 wt% BHb compared to samples with 2.5 or 10 wt% BHb. The increase in frequency of the nu sCH2 stretch (2854 cm-1) induced by increasing temperature 20 to 60 degrees C was dampened when BHb was present compared to samples heated in isotonic buffer. Analysis of the amide I band at 1650 cm-1 showed that the secondary structure of BHb is not affected by encapsulation in monoolein. In vitro release studies showed that 45% of the entrapped BHb was released after 144 h at 37 degrees C. The porous nature of bulk cubic phase was further demonstrated by diffusion of K2Fe(CN)6 and conversion of 73% of the oxyhemoglobin to methemoglobin after 1 h. These results suggest that the cubic phase may be useful for encapsulation of Hb as a red cell substitute and for the encapsulation and delivery of other bioactive agents.

Models and molecular orbital semiempirical calculations in the study of the spectroscopic properties of bovine serum amine oxidase quinone cofactor

The electronic properties of 2,4,5-trihydroxyphenylalanine quinone (TPQ), the cofactor of bovine serum amine oxidase [Janes, S. M., Mu, D., Wemmer, D., Smith, A. J., Kaur, S., Maltby, D., Burlingame, A. L., & Klinman, J. P. (1990) Science 248, 981-987], and some adducts with hydrazines were investigated by means of low-molecular-weight models and semiempirical molecular orbital calculation methods. The enzyme visible band was assigned to the first pi-->pi* transition of the cofactor in p-quinonic form, with the C-4 hydroxyl ionized and hydrogen bonded either to a water molecule or to a basic protein residue. The spectra of the protein adducts with some substituted hydrazines were well accounted for by assuming the inhibitor bound to the C-5 carbonyl, usually in azo form. The adduct with the unsubstituted hydrazine was instead assigned an o-quinone hydrazone form, stabilized by an internal hydrogen bond between the amino group and the ortho carbonyl oxygen, a larger electron delocalization, and formation of a hydrogen bond at the C-6 ionized hydroxyl. On the basis of these assignments, the reaction of the protein with benzylhydrazine [Morpurgo, L., Agostinelli, E., Muccigrosso, J., Martini, F., Mondovi, B., & Avigliano, L. (1989) Biochem. J. 260, 19-25] was rewritten. All examined electronic transitions, though highly sensitive to cofactor ionization and hydrogen bonding, could be accounted for without introducing perturbations due to copper. This confirms that copper is not within bonding distance of the oxidized cofactor.

FTIR study of lamellar and reversed micellar phases in the mono-oleoylglycerol/water system

The lamellar liquid crystalline (L alpha) and the reversed micellar (L2) phases of mono-oleoylglycerol (MO) in water were investigated by Fourier transform infrared (FTIR) spectroscopy. From polarized infrared spectra of aligned bilayers of MO/water, order parameters (S) were determined for vibrational modes in the hydrocarbon chain region (symmetric CH2 stretch and olefinic CH=CH stretch) and the aggregate surface region (C=O stretch and asymmetric CO-O-C stretch). The phase transition between L alpha and L2 (10 wt% water) occurs in the temperature range 43-46 degrees C. Already at about 32 degrees C the LD value for the C-OH stretching vibration has decreased to 50% of its value at 25 degrees C. A similar relative decrease in LD is obtained for the C=O stretch and the asymmetric CO-O-C stretch at about 38 degrees C and for the CH=CH stretch at about 43 degrees C. It is concluded that the molecular ordering in the region of the aggregate surface starts to decrease at a lower temperature than for the acyl chain region. Infrared spectra show a significant decrease in the conformational order of the hydrocarbon chains at the L alpha/L2 phase transition.