Short-chain Components Research Articles

Transition Highly Aggregated ComplexesSoluble Complexes via Polyelectrolyte Exchange Reactions: Kinetics, Structural Changes, and Mechanism

The dissolution of highly aggregated polyelectrolyte complex particles formed in water after addition of salt was studied. The dissolution of aggregates proceeded to soluble complexes on the molecular level of the long-chain component. The driving force of the process is the polyelectrolyte exchange reaction between the aggregates and the free long chains in excess. The kinetics of the process was studied by different light scattering techniques. The rate of dissolution showed a strong dependence on the salt concentration in the solution and on the concentration of the species. The dependence on concentration of the species in solution weakened with increasing salt concentration. Investigations of the structural changes during the dissolution process revealed the presence of only two generations of particles in solution: aggregates and soluble complexes. While the scattering intensity decreased strongly, the dimensions of the aggregates changed only slightly during dissolution, indicating a spontaneous disaggregation of the particles. A mechanism of the dissolution process was proposed, which is in agreement with the experimental findings and previous results in the literature. The process represents a two-step reaction: The first step consists of the release of the short-chain component from the aggregates by an exchange reaction via the free long-chain component in solution (second-order reaction). The second step is the destruction of the aggregates by increasing osmotic pressure in the particle (first-order reaction). The dissolution process may be understood as a model process for the release of DNA from polyelectrolyte complexes in gene therapy.

Molecular orientation relaxation in binary blends of poly(methyl methacrylate) by rheo-optical Fourier-transform infrared spectroscopy

Rheo-optical Fourier-transform infrared spectroscopy, a technique combining simultaneous mechanical measurements and infrared dichroism spectroscopy, has been employed in order to investigate the molecular chain orientation and orientation relaxation behaviour in uniaxially stretched films of binary blends of long perdeuterated and short undeuterated chains of linear poly(methyl methacrylate) (PMMA). The solution cast film samples have been stretched at constant strain rate up to 100% elongation and subsequently allowed to relax at constant strain at various temperatures above the glass transition temperature. The results reported here show that for the short-chain component a threshold value of molecular weight exists below which a drastic decrease of the long- and short-chain orientation and a change in the relaxation behaviour of the short chains are observed.

Simulated degradation of glyceryl ethers by hydrous and flash pyrolysis

Hydrous and flash pyrolysis were carried out on phytanyl ethers isolated from a methanogen ( Methanosarcina barkeri), a haloalkaphile ( Haloalkaphile sp.) and a thermoacidophile ( Sulfolobus sulfotaricus). No thermal alteration products of the intact ether lipids were observed below 150°C. From 150–300°C, slight pyrolysis of the intact glyceryl ethers was observed, although recovery of the parent compounds averaged >95%. As pyrolysis temperature increased, the alcohol and aldehyde were the first products formed following direct cleavage of the ether bond. At 600°C, the corresponding alkene also became a dominant flash pyrolysis product. With increases in pyrolysis temperature to 900°C, increasing amounts of volatile alkenes were produced. Based on the observed fragmentation patterns, we suggest that phytanol is first cleaved from the intact glyceryl ethers, followed by degradation of the phytanol to the corresponding alkanes or shorter chain components. In addition, as shown by other investigators, the alteration products may also be directly incorporated into higher molecular weight fractions.

Polysiloxane interpenetrating network materials as electronic device encapsulants: Synthesis and properties

Thermally curable interpenetrating networks employing short and long chain components were successfully prepared via the sol-gel route. Their mechanical properties were assessed and correlated to their composition and structure. The role of the organic cross-links was found to be a larger determinant of the mechanical properties than the inorganic network. Their low frequency dielectric properties were investigated and found to be comparable to those of conventional encapsulation materials. Observed mass losses at 523 K ranged between 3–5% after 1000 minutes, the suspected mechanism being the development of organic cross-links.

Silicone rubber staining of terracotta surfaces

Abstract Silicone rubbers have been widely used in the molding of museum and cultural artifacts. Conservators have noted that the RTV 2 (room temperature vulcanizing) class of silicone rubbers leaves an oil-like stain on the surface being molded. The staining medium was found to be composed of ‘silicone oil’, or the short-chain silicone component of RTV 2 silicone rubber compounds. Color measurement using the CIELAB coordinate system was employed to quantify the degree of staining left by different molding compounds on a standard terracotta substrate. The total color shift as recorded in this coordinate system was found to relate to the viscosity and set time of the silicone rubber used, and all of the silicone rubbers tested were found to stain to some extent. Options for further study are proposed.

Atomistic Monte Carlo Simulations of Liquids of Chain Molecules Confined by Solid Surfaces: Methods and Recent Results

Abstract The molecular arrangements of liquid tridecane near solid surfaces and in narrow slits have been studied by atomistic Monte Carlo computer simulations. A single surface perturbs the liquid over a distance of 1.5 nm, inducing the formation of progressively less dense and ordered layers of thickness 0.4 nm. Chains with atoms in the first layer tend to run parallel to the surface. The tendency to form layer structures is maintained or destroyed in narrow slits, depending on the slit thickness. For instance, it is slighly increased in slits of thickness 1.2 nm, while it is practically destroyed when the slit thickness is reduced to 1.0 nm. When added in small amounts, shorter-chain components are preferentially adsorbed at the solid surface, making the first layer of liquid in contact with these surfaces much less ordered.

Herbivorous or omnivorous? On the significance of lipid compositions as trophic markers in Antarctic copepods

Three dominant Antarctic copepods, Calanoides acutus, Rhincalanus gigas and Metridia gerlachei (copepodite stages V and females), were collected during summer (January/ February) in the southern Weddell Sea south of 70°S. Detailed analyses of their lipid and fatty acid/ alcohol compositions were carried out. The trophic positions of these copepods were elucidated by means of the lipid compositions (“marker lipids”). High amounts of wax esters were found in C. acutus (92% of total lipids) and in R. gigas (84–86%). The level of wax esters in M. gerlachei was relatively low (27–42%), while the accumulation of triacylglycerols tended to be higher (19–22%). Characteristic lipid components of C. acutus were the long-chain monounsaturated fatty acids and fatty alcohols 20:1 (n-9) and 22:1 (n-11). These components together with elevated amounts of the 18:4 (n-3) and, to a lesser degree, of the 16:! (n-7) fatty acids, typical of phytoplankton lipids, indicate herbivorous feeding for C. acutus. Other abundant fatty acids were 20:5 (n-3) and 22:6 (n-3). The fatty acid composition of M. gerlachei was characterized by very high amounts of these 22:6 and 20:5 acids. Other important fatty acids were 18:1 (n-9) and 16:0, but only small amounts of 16:1 (n-7) and 18:4 (n-3) occurred. In contrast to C. acutus the fatty alcohols of M. gerlachei consisted almost exclusively of the short-chain components 14:0 and 16:0 M. gerlachei is known as an omnivorous species, which was clearly reflected by its lipid and fatty acid/alcohol pattern. Few data are available on the feeding of R. gigas, but it is usuaally described as an herbivorous small-particle feeder. R. gigas showed fatty acid/alcohol characteristics typical of either C. acutus or M. gerlachei. Higher amounts of the 16:1 (n-7) and 18:4 (n-3) fatty acids suggest herbivorous feeding, whereas the dominance of short-chain alcohols (14:0 and 16:0) resembled the lipid pattern found in the omnivorous M. gerlachei. Hence, the lipid composition of R. gigas showed an intermediate pattern, which implies a tendency towards an opportunistic feeding mode, positioned somewhere between the other two species.

Structure of the amylopectin fraction of amylomaize

The amylopectin fraction (Ap-fraction) from three amylomaize starches (amylose content, 36, 41, and 59%) was fractionated into three amylopectin components (having different molecular size) and a short-chain component by gel-permeation chromatography. The content of the largest amylopectin component was relatively low in a high-amylose maize starch and it had an iodine affinity (i.a., g/100 g) of 1.94–2.50 and average chain length (c̄l̄) of 29–30. Both values incrased with decrease of molecular size (i.a. < 7.23, c̄l̄ <41). The proportion of long side chains [weight-average dp (d̄p̄ w) 99-110] increased with decrease of molecular size, whereas that of short side chains (d̄p̄ w 17-22) decreased. This is the reason why a smaller component had a larger i.a. and c̄l̄. Very long (d̄p̄ w 400–690) and medium-size (d̄p̄ w 45–48) side chains were present in similar proportions, regardless of molecular size. The short-chain component was slightly branched (number of chains, 1.9–2.1 on average) and had an i.a. of 8.20–9.57, d̄p̄ w of 120, and number-avearge dp of 92–95. A large amount of the short-chain component (27% of the Ap-fraction, by weight) was found in teh high-amylose (59%) maize starch.

米とトウモロコシなどの澱粉に関する研究

Structures of amyloses and amylopectins of rice (japonica and indica), maize (normal, sugary-2, amylomaize) and other nine origins have been examined by the methods involving newly devised procedures, and were found to be of characteristic in the origins. Ultra-centrifugation of crude amyloses from exhaustively defatted starches was effective for purification. Purified amyloses having iodine affinities (i. a., g/100 g) of 19.4-21.7 were confirmed to be free of amylopectin by gel-permeation chromatography. Amyloses had various sizes [number-average d. p. (d. p.n) 690-5090], numbers (1.9-12.4) of chains and average chain-length (c.1. 200-525), and were composed of linear and slightly branched (4.9-19.3 chains on average) molecules in various ratios (branched molecule; 11-70% by mole). Branched molecules appeared to be larger than linear molecules. Several varieties of rice and maize had generally a small amylose (d. p.n, rice 920-1110, maize 690-960) and branched molecule with a small number (d. p.n, rice 5.7-9.7, maize 4.9-6.1) of chains compared with the other plants. Branched molecules of rice (Nihonbare) and maize (normal, unknown sp.) had side-chains with wide d. p. distribution (about 6-4000) with a peak d. p. of about 20, and the rice branched molecule was 1.6 times as large as the linear molecule. Rice and maize amylopectins had i. a. of 0.39-2.57 and 0.8-4.63, respectively, and c. 1. of 19-21 and 20-32, respectively, while amylopectins from the other origins had i. a. of 0-0.51 and c.1. of 21-24. Amylopectins with a high i. a. were found to be composed of a large amount of very long chains (d. p. >100) and a small amount of short (weight-average d. p. about 20) or long (d. p.n about 45) chains. The very long chains appeared to be poorly branched. Amylomaize starches were comprised of amylopectin components with various sizes and an unusual, short chain component having d. p.n, of about 90 and about 2 chains on average. The amylose content of starch has to be calculated by considering amylopectin i. a, since its i. a. differed in the origins. Indica rice starches had the same amylose content (about 18%) as japonica rice starches.

Molecular model for the mechanical properties of elastomers. 4. Interpenetrating networks

Simultaneous and sequential interpenetrating networks (IPNs) are studied theoretically. Results for bimodal networks made through interpenetration of long by very short PDMS chains show no synergism in mechanical properties. Tensile strength and toughness values for IPNs are usually lower than those for the corresponding interconnected networks. Based on our model results, a new type of IPN is proposed in which the long chains form macrocycles which are threaded by the short-chain component. Those novel IPNs show very high toughness values which are comparable to those of the interconnected bimodal networks

Phase separation in short-chain lecithin/gel-state long chain lecithin aggregates

Small bilayer particles form spontaneously from gel-state long-chain phospholipids such as dipalmitoylphosphatidylcholine and 0.2 mol fraction short-chain lecithins (e.g., diheptanoyl-phosphatidylcholine). When the particles are incubated at temperatures greater than the Tm of the long-chain phosphatidylcholine (PC), the particles rapidly fuse (from 90-A to greater than or equal to 5000-A radius); this transition is reversible. A possible explanation for this behavior involves patching or phase separation of the short-chain component within the gel-state particle and randomization of both lipid species above Tm. Differential scanning calorimetry, 1H T1 values of proteodiheptanoyl-PC in diheptanoyl-PC-d26/dipalmitoyl-PC-d62 matrices of varying deuterium content, solid-state 2H NMR spectroscopy as a function of temperature, and fluorescence pyrene excimer-to-monomer ratios as a function of mole fraction diheptanoyl-PC provide evidence that such phase separation must occur. These results are used to construct a phase diagram for the diheptanoyl-PC/dipalmitoyl-PC system, to propose detailed geometric models for the different lipid particles involved, and to understand phospholipase kinetics toward the different aggregates.

Hydroxy acids in Antarctic lake sediments and their geochemical significance

Hydroxy acids in sediments of Lakes Bonney, Fryxell, Joyce and Vanda, and unnamed ponds (B2, NF1, NF2 and L4) as well as in cyanobacterial mats from the McMurdo Sound region of southern Victoria Land in Antarctica have been studied to clarify their features and elucidate their source organisms. Normal and branched ( iso and anteiso) 2-hydroxy acids were found in all the samples studied with the predominance of even- and odd-carbon numbers, respectively. The most dominant 2-hydroxy acids in the sediments were mainly short-chain components (<C 20). Normal and branched 3-hydroxy acids were detectewith the predominance of even- and odd-carbon numbers, respectively, in total concentrations between 0.48 and 53 μg/g of dry sediment. (ω-1)-Hydroxy acids were all long-chains (C 22, C 24, C 26, C 28 and C 30). 9,10-Dihydroxyhexadecanoic and/or 9,10-dihydroxyoctadecanoic acids were identified in all the sediments and a cyanobacterial mat. The composition of hydroxy acids differ considerably among the lakes and ponds, suggesting the difference of source organisms. These 2-, 3- and (ω-1)-hydroxy, and 9,10-dihydroxy acids may be derived from cyanobacteria and microalgae, in addition to non-photosynthetic microorganisms. Cyanobacteria and microalgae which are widely distributed in the world, may be important sources of hydroxy acids in the natural environments.

Effect of heparin on synthesis of short chain collagen by chondrocytes and smooth muscle cells.

The treatment of embryonic chick chondrocyte cultures with heparin results in a decrease in collagen synthesis. One of the collagens synthesized by hypertrophic chondrocytes, specifically type X collagen, may play an important role in cartilage mineralization and endochondral ossification. Recently a new short chain collagenous component was found in cultures of rat vascular smooth muscle cells (Majack, R. A., and P. Bornstein, 1985, J. Cell Biol., 100: 613-619). The present study was initiated to investigate heparin's effect on type X collagen in embryonic chick chondrocytes and to further evaluate the nature of the short chain component synthesized by rat vascular smooth muscle cells. Different tissues may respond differently to the administration of heparin. In chondrocyte cultures heparin decreased both total collagen synthesis as well as the synthesis of type X collagen. There was an accumulation of collagen precursors, found principally in the cell layer compartment, which appeared to be the result of heparin's inhibition of the NH2-terminal protease. In cultures of rat vascular smooth muscle cells heparin was found to increase the synthesis of a short chain collagenous component as previously reported. However, comparison with a type X collagen standard showed this to be different from type X. In all cases, the effect of heparin on collagen chain precursors, chondrocyte type X synthesis, and synthesis of a vascular smooth muscle short chain collagen was shown to be reversible. Similar effects were obtained by adding chondroitin sulfate to chondrocytes, suggesting a role for extracellular matrix components in the modulation of collagen synthesis. These findings are consistent with the concept of a group of short chain collagens with type X collagen being unique to hypertrophic chondrocytes.

Short-chain lecithin/long-chain phospholipid unilamellar vesicles: asymmetry, dynamics, and enzymatic hydrolysis of the short-chain component.

Asymmetric unilamellar vesicles are produced when short-chain phospholipids (fatty acyl chain lengths of 6-8 carbons) are mixed with long-chain phospholipids (fatty acyl chain lengths of 14 carbons or longer) in ratios of 1:4 short-chain/long-chain component. Short-chain lecithins are preferentially distributed on the outer monolayer, while a short-chain phosphatidylethanolamine derivative appears to localize on the inner monolayer of these spontaneously forming vesicles. Lanthanide NMR shift experiments clearly show a difference in head-group/ion interactions between the short-chain and long-chain species. Two-dimensional 1H NMR studies reveal efficient spin diffusion networks for the short-chain species embedded in the long-chain bilayer matrix. The short-chain lecithin is considerably more mobile than the long-chain component but has hindered motion compared to short-chain lecithin micelles. This differentiation in physical characteristics of the two phospholipid components is critical to understanding the activity of phospholipases toward these binary systems.

Studies on methanolysis of triglycerides on thin layer chromatoplate

AbstractMethanolysis of triglycerides on thin layer chro‐matography plate, for the preparation of correspond‐ing fatty acid methyl esters suitable for gas liquid chromatography analysis, has been studied with synthetic mixtures of pure tricaprylin, trilaurin, tri‐palmitin, and triolein. The long chain saturated glyc‐eride, tripalmitin, has been found to be least suscep‐tible to methanolysis. Plate temperature of 65 C and KOMe‐methanol reagent concentration of 1.0 N have been found to be optimal for samples containing large amount of trisaturated glyceride like tripalmitin without appreciable loss in short chain components by evaporation. For fats containing lower proportions of trisaturated glyceride like vegetable oils, a lower concentration, i.e., 0.5 N of the reagent can be used at the above temperature. Addition of lipid solvent like benzene in the reagent has little effect on the conversion. Long chain triglycerides containing one or more double bonds in the molecule respond more to this reaction than do trisaturated glycerides of the same carbon number. Fatty acid compositions of cottonseed and peanut oil triglycerides obtained by the GLC analysis of the methyl esters prepared by the present method and that of Luddy et al. [JAOCS 45:549 (1968)] have been found to agree well.

Sicklepod Leaflet, Petiole, Stem, and Seed Total Hydrocarbon Content

Hydrocarbon content of sicklepod (Cassia obtusifolia L.) leaflets, petioles, stems, and seed were measured by gas-liquid chromatography. The content of n-alkane was not uniform. Short carbon chain components (Cn ≤ 25) comprised the majority of the hydrocarbons present, but composition varied between organs. Major long-chain constituents were n-hentriacontane (C31), n-dotriacontane (C32), n-tritriacontane (C33), and n-tetratriacontane (C34) in leaflets; C32 and C33 in petioles; C33 in stems; and n-nonadocosane (C29) in seeds. Odd-numbered n-alkanes were not the major constituents in leaflets and petioles. Therefore, selection of morphologically uniform samples for chemotaxonomic comparisons of n-alkane contents is essential.

Relation of fatty acid structure to release and esterification of free fatty acids.

After incubation of rat adipose tissue with corticotrophin in buffer-albumin, the composition of the free fatty acids (FFA) in the tissue and in the medium was determined; the medium contained proportionately more myristic, palmitoleic, linoleic, and linolenic acids. The ratio of the amount of each free acid in the medium to that in the tissue increased with decreasing chain length and increasing unsaturation. Free acids produced in adipose tissue by corticotrophin stimulation were esterified by subsequent exposure of the tissue to glucose and insulin. Among the saturated and monoenoic acids the shorter chain components were esterified to a greater extent, while at a given chain length the more unsaturated acids were more readily esterified. Thus the more polar FFA were more readily released from and esterified in adipose tissue. These results could have been produced by a variety of processes including differences between the acids in aqueous solubility or the presence of tissue-binding sites with varying affinities for the different acids.