Preparation of liposomes: A novel application of microengineered membranes–From laboratory scale to large scale

This article was accepted for publication in the journal, Colloids and Surfaces B: Biointerfaces [© Elsevier B.V.] and the definitive version is available at: http://dx.doi.org/10.1016/j.colsurfb.2013.07.066A novel ethanol injection method using microengineered nickel membrane was employed to produce POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) and Lipoid® E80 liposomes at different production scales. A stirred cell device was used to produce 73 ml of the liposomal suspension and the product volume was then increased by a factor of 8 at the same transmembrane flux (140 l m−2 h−1), volume ratio of the aqueous to organic phase (4.5) and peak shear stress on the membrane surface (2.7 Pa). Two different strategies for shear control on the membrane surface have been used in the scaled-up versions of the process: a cross flow recirculation of the aqueous phase across the membrane surface and low frequency oscillation of the membrane surface (∼40 Hz) in a direction normal to the flow of the injected organic phase. Using the same membrane with a pore size of 5 μm and pore spacing of 200 μm in all devices, the size of the POPC liposomes produced in all three membrane systems was highly consistent (80–86 nm) and the coefficient of variation ranged between 26 and 36%. The smallest and most uniform liposomal nanoparticles were produced in a novel oscillating membrane system. The mean vesicle size increased with increasing the pore size of the membrane and the injection time. An increase in the vesicle size over time was caused by deposition of newly formed phospholipid fragments onto the surface of the vesicles already formed in the suspension and this increase was most pronounced for the cross flow system, due to long recirculation time. The final vesicle size in all membrane systems was suitable for their use as drug carriers in pharmaceutical formulations

Systematic design for trait introgression projects

We demonstrate an innovative approach for designing Trait Introgression (TI) projects based on optimization principles from Operations Research. If the designs of TI projects are based on clear and measurable objectives, they can be translated into mathematical models with decision variables and constraints that can be translated into Pareto optimality plots associated with any arbitrary selection strategy. The Pareto plots can be used to make rational decisions concerning the trade-offs between maximizing the probability of success while minimizing costs and time. The systematic rigor associated with a cost, time and probability of success (CTP) framework is well suited to designing TI projects that require dynamic decision making. The CTP framework also revealed that previously identified ‘best’ strategies can be improved to be at least twice as effective without increasing time or expenses

Empirical Comparison of Simple Sequence Repeats and Single Nucleotide Polymorphisms in Assessment of Maize Diversity and Relatedness

While Simple Sequence Repeats (SSRs) are extremely useful genetic markers, recent advances in technology have produced a shift toward use of single nucleotide polymorphisms (SNPs). The different mutational properties of these two classes of markers result in differences in heterozygosities and allele frequencies that may have implications for their use in assessing relatedness and evaluation of genetic diversity. We compared analyses based on 89 SSRs (primarily dinucleotide repeats) to analyses based on 847 SNPs in individuals from the same 259 inbred maize lines, which had been chosen to represent the diversity available among current and historic lines used in breeding. The SSRs performed better at clustering germplasm into populations than did a set of 847 SNPs or 554 SNP haplotypes, and SSRs provided more resolution in measuring genetic distance based on allele-sharing. Except for closely related pairs of individuals, measures of distance based on SSRs were only weakly correlated with measures of distance based on SNPs. Our results suggest that 1) large numbers of SNP loci will be required to replace highly polymorphic SSRs in studies of diversity and relatedness and 2) relatedness among highly-diverged maize lines is difficult to measure accurately regardless of the marker system

Heterosis as Investigated in Terms of Polyploidy and Genetic Diversity Using Designed Brassica juncea Amphiploid and Its Progenitor Diploid Species

Fixed heterosis resulting from favorable interactions between the genes on their homoeologous genomes in an allopolyploid is considered analogous to classical heterosis accruing from interactions between homologous chromosomes in heterozygous plants of a diploid species. It has been hypothesized that fixed heterosis may be one of the causes of low classical heterosis in allopolyploids. We used Indian mustard (Brassica juncea, 2n = 36; AABB) as a model system to analyze this hypothesis due to ease of its resynthesis from its diploid progenitors, B. rapa (2n = 20; AA) and B. nigra (2n = 16; BB). Both forms of heterosis were investigated in terms of ploidy level, gene action and genetic diversity. To facilitate this, eleven B. juncea genotypes were resynthesized by hybridizing ten near inbred lines of B. rapa and nine of B. nigra. Three half diallel combinations involving resynthesized B. juncea (11×11) and the corresponding progenitor genotypes of B. rapa (10×10) and B. nigra (9×9) were evaluated. Genetic diversity was estimated based on DNA polymorphism generated by SSR primers. Heterosis and genetic diversity in parental diploid species appeared not to predict heterosis and genetic diversity at alloploid level. There was also no association between combining ability, genetic diversity and heterosis across ploidy. Though a large proportion (0.47) of combinations showed positive values, the average fixed heterosis was low for seed yield but high for biomass yield. The genetic diversity was a significant contributor to fixed heterosis for biomass yield, due possibly to adaptive advantage it may confer on de novo alloploids during evolution. Good general/specific combiners at diploid level did not necessarily produce good general/specific combiners at amphiploid level. It was also concluded that polyploidy impacts classical heterosis indirectly due to the negative association between fixed heterosis and classical heterosis

Evolution des catalyseurs métalliques déposés sur support

On traite, au moyen d'exemples, les problèmes relatifs à l'évolution des cataly-seurs pendant leur activation et durant leur utilisation dans les réactions de conversion des hydrocarbures. L'activation comprend une étape de réduction du composé de l'élément actif à l'état métallique. Les conséquences d'une réduc-tion incomplète sont décrites ainsi que les effets promoteurs ou inhibiteurs de la réduction. L'Influence des conditions de réduction sur la dispersion de la phase métallique est indiquée. L'importance des phénomènes de réduction du support et des impuretés qu'Il contient est soulignée. L'évolution des catalyseurs pendant la réaction amène à considérer l'influence des dépôts carbonés sur les activités et sélectivités catalytiques et aussi sur l'état de la phase métallique et du support. Le dernier point abordé est celui du frittage du métal et des moyens d'inhiber ce phénomène

Etat actuel des recherches fondamentales sur les catalyseurs bimétalliques à base de platine, sur support alumine, comparables à ceux utilisés dans l'industrie pétrolière.

L'article concerne essentiellement les couples (Pt, Re), (Pt, Ir), (Pt, Ru) traités dans l'ordre - préparation des catalyseurs (imprégnation du support, réduction par l'hy-drogène); -- caractérisation des catalyseurs réduits ; - activités catalytiques ; - essais d'extrapolation aux catalyseurs industriels , - conclusions. On met l'accent en particulier sur I) la difficulté d'obtenir des informations sur le degré de réduction qui soient significafives de l'état du catalyseur dans des conditions normales de travail, d'où la nécessité d'associer plusieurs techniques parmi : l'analyse thermique différentielle (ATD), l'analyse thermogravimétrique (ATG), la volumétrie, la catharométrie, la spectroscopie électronique (ESCA), la spectroscopie infrarouge, la thermodésorption de H2, les mesures des activités catalytiques ; 2) la différence entre diagrammes de phase des systèmes divisés et massiques ; 3) l'application des titrages par H2 de l'oxygène adsorbé, pour mettre en évi-dence la présence de petites particules de Mell pur dans un catalyseur (Pt, Mell)/ AI203 , 4) la dépendance de l'état final du catalyseur du mode d'activation. Le couple (Pt, Re) peut être stabilisé à l'état de particules d'alliage de compositions superfi-cielle et moyenne voisines ou à l'état de mélange de particules de (Pt, Re) de teneur en Re inférieure à la composition nominale et de Re pur très bien dispersé. Les couples (Pt, Ir) et surtout (Pt, Ru) se caractérisent par la difficulté d'obtenir l'état alliage avec une composition constante d'une particule métallique à l'autre 5) les variations d'activité catalytique, dues à l'addition de Mell à Pt, reflétant un ou plusieurs des effets a) augmentation de dispersion du Pt sans (ou avec) modification de ses pro-priétés intrinsèques, par les ions de faible valence de W, Mo, Cr... b) formation de Mell à l'état métallique donnant éventuellement un alliage avec Pt; c) rôle des dépôts carbonés promoteurs diminuant l'hydrogénolyse ou (et) inhibiteurs par encrassement ; 6) le fait que dans les 158 références de l'article la moitié date de 1976 et après, souligne l'intérêt croissant porté aux recherches fondamentales dans ce domaine