Saturated molecular species

Fractionation or winterization is a process in which the more saturated molecular species in the oil are solidified during low temperature treatment and subsequently removed cold storage stability is thereby increased. When partially hydrogenated soybean oil is fractionated, the more saturated molecular species are removed to produce a clear oil that meets the requirements of a salad oil and a high-stability liquid oil. 

Inoue and Nojima (1968) used a similar method for the synthesis of racemic diphosphatidylglycerol. These workers used a benzyl protecting group instead of the tert-hutyl group and, therefore, had to use catalytic hydrogenolysis for its removal. Consequently, their method can be used only for saturated molecular species. 

A decisive step in the understanding of the lipid contribution to chilling-sensitivity of plants was later realized by Murata (10) when this author showed (by fluorescence polarization measurements) that the phosphatidylglycerols from chilling-sensitive plants, but no other lipids, contained large proportions of "saturated" molecular species which undergo phase transition at room temperature or above. Since a major part of... 

Prior to 1980 it was widely believed that oleate (18 1) and 16 0 were desaturated in plants as their CoA esters. It was acknowledged however, that plant glycerolipids seemed to be first assembled from radioactive precursors as relatively saturated molecular species and only approached a degree of unsaturation matching that revealed by chemical analysis after a considerable... 

AT2") for palmitoyl-ACP. Given that chloroplast AT2 always incorporates palmitate at the sn-2 position of PA, then the first 50% of the 16 0 observed in PG, and in other lipid classes, in these experiments is probably esterified at the sn-2 position. When 16 0 is present at less than 50% we have supplemented the other fatty acids gt sn-2, first with 14 0, then 18 0 and lastly with 18 1 to make up the difference. Any remaining 16 0 must be esterified at the sn-1 position. By this reasoning, the percentage of di-saturated molecular species of PG can be estimated from the data in Table 2. These manipulations produce numbers for molecular species of PG which compare favorably with data taken from the... 

Pea. These chloroplasts also possess a mechanism for producing unsaturated molecular species of PA, but do so to the exclusion of di-saturated species. However, ATI from pea, while selecting 18 1-ACPfrom a mixture in favor of 16 0 ACP, does not display nearly the selectivity of the spinach and tobacco enzymes (Figure 1). These facts hint that AT2 may possibly select for 18 1-LPA in the synthesis of PA. From the molecular species composition of DG and PG (Table 3), it is obvious that a small amount of di-saturated species of PA must exist in these chloroplasts. There is a marked enrichment for di-saturated molecular species at the level of the headgroup enzymes in these chloroplasts. 

The phosphatidylglycerols (PC), but no other lipid classes, from the chilling-sensitive plants, contain a large proportion of saturated molecular species, 1,2-dipalmitoyl-PG and sn-1-palmitoyl-2-(trans-3)hexadecenoy1-PG, which undergo a thermotrophic phase transition at the room temperature range or above (Murata et al. 1982 Murata 1983 Murata and Yamaya 1984). 

After the heat shock, we noted first, the apparition of more saturated molecular species like 16 0/18 1, 18 0/18 3,18 1/18 2 PC and 16 0/18 3 MGDG. Secondly the eukaryotic molecular species 16 0/18 3 increased markely in the three lipid classes. Finally the ratio of totd Cii/C 6 to C18/C18 molecular species in MGEKj was reduced from 6.6 to 2.6 in stressed plants. 

This technique is the most widely used and the most useful for the characterization of molecular species in solution. Nowadays, it is also one of the most powerful techniques for solids characterizations. Solid state NMR techniques have been used for the characterization of platinum particles and CO coordination to palladium. Bradley extended it to solution C NMR studies on nanoparticles covered with C-enriched carbon monoxide [47]. In the case of ruthenium (a metal giving rise to a very small Knight shift) and for very small particles, the presence of terminal and bridging CO could be ascertained [47]. In the case of platinum and palladium colloids, indirect evidence for CO coordination was obtained by spin saturation transfer experiments [47]. 

The fluorescent components are denoted by I (intensity) followed by a capitalized subscript (D, A or s, for respectively Donors, Acceptors, or Donor/ Acceptor FRET pairs) to indicate the particular population of molecules responsible for emission of/and a lower-case superscript (d or, s) that indicates the detection channel (or filter cube). For example, / denotes the intensity of the donors as detected in the donor channel and reads as Intensity of donors in the donor channel, etc. Similarly, properties of molecules (number of molecules, N quantum yield, Q) are specified with capitalized subscript and properties of channels (laser intensity, gain, g) are specified with lowercase superscript. Factors that depend on both molecular species and on detection channel (excitation efficiency, s fraction of the emission spectrum detected in a channel, F) are indexed with both. Note that for all factorized symbols it is assumed that we work in the linear (excitation-fluorescence) regime with negligible donor or acceptor saturation or triplet states. In case such conditions are not met, the FRET estimation will not be correct. See Chap. 12 (FRET calculator) for more details. 

Already in the early twentieth century it was realized that definitions such as (D1) do not adequately cover all units of interest in chemistry. Thus, by 1902 Werner had demonstrated (Section 4.5.1) that numerous covalently saturated ligand (L) species (L = CO, NH3, H20, etc.) could exist both as free molecular species and in coordinated form as components of transition-metal complexes ML with open-shell metals M,... 

One characteristic difference between organic and aqueous solution, therefore, lies in the cation-anion relationship. In aqueous solution the ions are dissociated from each other, the cation s coordination shell is saturated with water, and the anion and cation interact primarily electrostatically. In organic solution they are covalently associated to give a neutral molecular species. 

One hundred and eighty-one molecular species of TGs have been identified 79 of them were saturated, 44 monounsaturated, and 58 polyunsaturated. The majority of the unsaturated TGs (61) contained only one unsaturated fatty acid, 41 contained two, and 5 had all three fatty acids unsaturated. Furthermore, ten TGs that contained linear or branched odd-carbon-number fatty acids have been identified. In Table 6, identified species are mentioned with retention times and peak numbers corresponding to the chromatogram in Fig. 43. 

There is no difficulty in focusing a laser beam to a diameter of 0.1 mm. A one-watt laser could then provide an irradiance of about lCPw/cin and a one-kilowatt laser an irradiance of about 10 MW/cm2. Since one watt and one kilowatt are powers typical of CW and pulsed dye lasers respectively, it may be seen that if saturation is a goal, then CW laser sources are not appropriate for studying molecular species. 

Use of Saturation. Because of the potential for simplification of the population balance equations, much recent work has concentrated on studying saturation phenomena. First proposed by Piepmeier (9), and elaborated on by Daily (10), saturation in atomic species can lead to complete elimination of the need to know any collisional rates, and in molecular species may provide substantial simplification of the balance equation analysis. 

Saturation in molecular species is more difficult due to syphoning of population to other levels. Thus higher laser powers are required. Baronavski and McDonald (15) have studied the approach to saturation of C2 and suggested means to use the saturation curve to extract collisional rate information. 

Currently it appears that there are no difficulties in saturating atomic species, while molecular species may be saturated with sufficient laser power. There are some difficulties associated with saturation. Because of chemistry, the quasi-equilibrium population of a species may change substantially when excited. See, for example, Daily and Chan (7), and Muller, et al. (17). 

One of the main problems met in Laser Induced Fluorescence measurements is the excited population dependence on the quenching due to collisional deexcitation. The saturation mode proposed to avoid this dependence is very difficult to achieve U ) (2 ) particularly with molecular species and moreover the very strong laser pulses required may cancel the non-perturbing characteristic of the method. Therefore precise knowledge of the quenching is necessary in some experimental circumstances. 

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