Ion C. Baianu

The role of chloride in O2 evolution by thylakoids from salt-tolerant higher plants

(1) Thylakoids isolated from leaves of two salt-tolerant higher plant species were found to require high (greater than 250 mM) concentrations of Cl− for maximal rates of photosynthetic O2 evolution and maximum variable chlorophyll a fluorescence yield. These activities were also tolerant to extremely high (2–3 M) salt concentrations. Their pH dependence was markedly different in the absence and presence of sufficient salt levels. (2) When Cl− was provided as CaCl2, as opposed to MgCl2, KCl or NaCl, higher rates of O2 evolution were obtained, suggesting that Ca2+ has an important role in Photosystem II reactions. (3) The site of Cl− action was located on the electron donor side of Photosystem II. (4) O2 evolution in the presence of optimal Cl− concentrations showed a pH dependence closely matched by that of 35Cl-NMR line broadening, which is indicative of Cl− binding. This pH-dependent 35Cl-NMR line-width broadening was not altered significantly by treatment of the thylakoids with EDTA; it was, however, abolished by heat treatment. (5) Only anions with similar ionic radii (Br−, NO−3) were effective in replacing Cl−. Small anions such as F− and OH− were inhibitory; larger ions had no effect. The inhibition by F− is due, at least in part, to displacement of Cl−. The selectivity is attributed to a combination of steric and ionic field effects. (6) It is proposed that Cl− facilitates Photosystem II electron transport by reversible ionic binding to the O2-evolving complex itself or to the thylakoid membrane in close proximity to it.

Novel liposome microencapsulation techniques for food applications

Abstract Microencapsulation technology presents exciting opportunities for the food technologist in areas such as flavor retention and release, and the enhanced stability and shelf life of sensitive ingredients. Liposome microencapsulation of food ingredients is a novel approach to microencapsulation that has the advantage of using inexpensive, ‘generally recognized as safe’ materials. Several techniques for the manufacture and characterization of liposome microcapsules are reviewed.

COMMENTS ON THE POSSIBLE ROLES OF BICARBONATE AND CHLORIDE IONS IN PHOTOSYSTEM II

Publisher Summary This chapter presents the comments on the possible roles of bicarbonate and chloride ions in photosystem II (PSII). It reviews the role of two anions, HCO3– and Cl–, in photosystem II. HCO3– appears to function on the electron acceptor side, whereas Cl– functions on the electron donor side of PSII. A nuclear magnetic resonanace technique has been used for the first time to learn more about the Cl binding to the thylakoid membrane and its relationship to the molecular mechanism of O2 evolution. The major function of HCO3 is to change the conformation of the QB or a nearby protein to allow the efficient exchange of with a plastoquinone molecule. On the other hand, the major function of Cl is to stabilize the positive charges on the electron donor water side of PSII, possibly via a reversible binding to the Mn-containing oxygen evolving enzyme.

Polymerization of N, N-Dimethylaminopropyl-Acrylamide Through Hydrogen Transfer Induced by the Propagation of the Polyacrolein Anion

Abstract The anionic polymerization of acrolein (AL) with N, N-dimethylamino-propylacrylamide (DMAPA) in the presence of water was investigated in tetrahydrofuran, benzene, and ethanol at 0°C in a nitrogen atmosphere. The resulting polymers were found to be essentially vinyl polymers with one DMAPA attached and an aldehyde side chain. From observations of the polymerization process by 1H NMR, we find that polymerization was initiated by the hydroxyl anion formed in the thermodynamic equilibrium between the amine of DMAPA and water. The hydrogen transfer reaction of DMAPA was caused by the propagating poly-AL anion. On the other hand, the monomer reactivity ratios and the Q2-e2values of DMAPA were determined by the free-radical copolymerization of styrene (St, M1) with DMAPA and AIBN as initiator.

Molecular Dynamics of Water in Foods and Related Model Systems: Multinuclear Spin Relaxation Studies and Comparison with Theoretical Calculations

A review of recent studies of molecular dynamics of water in foods and model systems is presented, and the theoretical results are compared with experimental data obtained by several techniques. Both theoretical and experimental approaches are discussed for electrolytes, carbohydrates, and food proteins in solution. Theoretical results from Monte Carlo simulations are compared with experimental NMR relaxation data for quadrupolar nuclei such as those of deuterium and oxygen-17. Hydration studies of wheat, soybean, corn, and myofibrillar proteins by multinuclear spin relaxation techniques are discussed, and several new approaches to the analysis of the experimental data are considered. Correlation times of water motions in hydrated food systems are determined from NMR and dielectric relaxation data. The values of the correlation times for dilute solutions of electrolytes and carbohydrates estimated by NMR are in good agreement with those calculated from dielectric relaxation data, but seem to differ significantly from those proposed from Monte Carlo simulations. Several new and important results concerning the hydration of potato and cereal starches are presented, showing the very different hydration behaviors of these two major groups of starches. The combination of molecular dynamics computations with NMR relaxation techniques will hopefully stimulate novel technological developments in food engineering based on such fundamental studies.

Multinuclear Spin Relaxation and High-Resolution Nuclear Magnetic Resonance Studies of Food Proteins, Agriculturally Important Materials and Related Systems

An overview of the applications of Nuclear Magnetic Resonance (NMR) techniques in Agriculture and Food Chemistry, covering high-resolution, solid-state, pulsed gradient and two-dimensional techniques is presented. The systems investigated by such techniques range from purified proteins to mixtures, starch granules and wheat grains. Both hydration and structural/composition approaches that employ NMR techniques are discussed from the point of view of applications rather than technique development. Hydration models derived from multinuclear studies are discussed for food proteins and enzymes. The role of protein-protein interactions in the analysis of the NMR results on hydration is also discussed. Amongst the food proteins considered are: wheat gliadins, glutenins, corn zeins, soy glycinins and conglycinins, as well as muscle proteins. Several new applications and new directions of development of NMR in Agriculture and Food Chemistry are suggested, and potential practical applications are pointed out.

Kinetics of the Copolymerization of Methyl Vinyl Ketone and Acrylamide Initiated by the Adduct of Methyl Vinyl Ketone and Imidazole

Abstract N-(Butyl-3-one)imidazole acts as an initiating adduct which is formed in the anionic polymerization of methyl vinyl ketone (MVK) induced by imidazole (Im) and is directly formed from Im and the MVK monomer. The kinetics of the anionic homopolymerization of MVK and acrylamide (AAm) under argon in the presence of the adduct were investigated in tetrahydrofuran (THF). The rate of polymerization for the MVK system is expressed as Rp = k[Adduct] [MVK], where k = 3.1 × 10−6 L/(mol·s)in THF at 30°C. The overall activation energy, Ea , was found to be 5.34 kcal/mol. The Rp for the AAm system is expressed as Rp = k[Adduct] [AAm], where k = 6.8 × 10−6 L/(mol·s) in THF at 30°C, with Ea 7.78 kcal/mol. The mechanism of the polymerization induced by the initiator adduct is discussed on the basis of these results.

Polymerization of Methyl Methacrylate in the Presence of Imidazole Derivatives. Additive Effect of the Initiator Adduct and Copolymerization with Acrylamide

Abstract In the anionic polymerization of methyl methacrylate (MMA) induced by imidazole (Im), an Im‐MMA adduct forms as an initiator adduct in methanol at 30°C in an argon atmosphere by the equimolar reaction of Im with the MMA monomer. The additive effect of the adduct on the homopolymerization of MMA in tetrahydrofuran at 30°C was investigated by dilatometry. The existence of the adduct increased the duration of the propagation step without shortening the formation step of the initiator adduct. The H‐D exchange reaction of the adduct was observed in D2O by 1H NMR. Proton transfer of the MMA unit in the adduct was not observable until 45 h after initiation. The copolymerizability of MMA with acrylamide (AAm) induced by the Im catalyst in THF at 30°C was also investigated. It was found that the homo‐and copolymerizations proceeded at the same time. On the other hand, in the MMA homopolymerization system, the addition of AAm monomer during the initial propagation step yielded copolymer of MMA and AAm for ...