Lower Stability (lower + stability)

Distribution by Scientific Domains

Selected Abstracts

Mechanism of Selective and Unselective Enclathration by a Host Compound Possessing Open, Flexible Host Frameworks

Kazunori Nakano
Abstract Molecular recognition of o -, m -, and p -xylenes (oX, mX, and pX) through enclathration of cholic acid (CA) is described. All of the xylenes give lattice inclusion crystals with CA, and crystallographic studies reveal that they are included in different open host frameworks. In particular, oX has two polymorphs, depending on the recrystallization temperatures. Competitive recrystallization from mixtures of xylenes resulted in selective enclathrations and the formation of racemic mixed crystals. In the presence of an equimolar amount of oX, CA selectively includes mX or pX in the host frameworks, which are identical to those obtained from the pure mX or pX, respectively. The low affinity of oX is explained in terms of a lower stability of CA·oX than of the other two complexes, as judged from the low PCcavity, the volume ratio of the guest compound to the host cavity. Meanwhile, mixtures of mX and pX yield inclusion crystals that accommodate both of the guests. These have the same open host framework as obtained from pure mX, and the guest components are disordered statically in the host cavity. The ratios of the xylene mixtures in the single crystals are similar to those in the original recrystallization mixtures, and also in the bulk crystals, indicating that CA forms mixed crystals of mX and pX. This non-selectivity is attributed to the similar stabilities of CA·mX and CA·pX, according to the moderate PCcavity. The inclusion behavior of CA from mixtures of xylenes is quite similar to chiral recognition by diastereomer-salt methods. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]

Complete primary structure of rainbow trout type I collagen consisting of ,1(I),2(I),3(I) heterotrimers

FEBS JOURNAL, Issue 10 2001
Masataka Saito
The subunit compositions of skin and muscle type I collagens from rainbow trout were found to be ,1(I),2(I),3(I) and [,1(I)]2,2(I), respectively. The occurrence of ,3(I) has been observed only for bonyfish. The skin collagen exhibited more susceptibility to both heat denaturation and MMP-13 digestion than the muscle counterpart; the former had a lower denaturation temperature by about 0.5 °C than the latter. The lower stability of skin collagen, however, is not due to the low levels of imino acids because the contents of Pro and Hyp were almost constant in both collagens. On the other hand, some cDNAs coding for the N-terminal and/or a part of triple-helical domains of pro,(I) chains were cloned from the cDNA library of rainbow trout fibroblasts. These cDNAs together with the previously cloned collagen cDNAs gave information about the complete primary structure of type I procollagen. The main triple-helical domain of each pro,(I) chain had 338 uninterrupted Gly-X-Y triplets consisting of 1014 amino acids and was unique in its high content of Gly-Gly doublets. In particular, the bonyfish-specific ,(I) chain, pro,3(I) was characterized by the small number of Gly-Pro-Pro triplets, 19, and the large number of Gly-Gly doublets, 38, in the triple-helical domain, compared to 23 and 22, respectively, for pro,1(I). The small number of Gly-Pro-Pro and the large number of Gly-Gly in pro,3(I) was assumed to partially loosen the triple-helical structure of skin collagen, leading to the lower stability of skin collagen mentioned above. Finally, phylogenetic analyses revealed that pro,3(I) had diverged from pro,1(I). This study is the first report of the complete primary structure of fish type I procollagen. [source]

Relative energies of conformations and sulfinyl oxygen-induced pentacoordination at silicon in 4-bromo- and 4,4-dibromo-4-silathiacyclohexane 1-oxide: A computational study

Fillmore Freeman
Abstract The equilibrium geometries and relative energies of the chair, twist, and boat conformations of cis - and trans -4-bromo-4-silathiacyclohexane 1-oxide and 4,4-dibromo-4-silathiacyclohexane 1-oxide have been calculated at the B3LYP/6-311G(d,p) and MP2/6-311+G(d,p) theoretical levels. The axial (SO) chair conformers of the sulfoxides are of lower energy than the chair conformers of the corresponding equatorial (SO) sulfoxides. The chair conformer of the axial (SO) trans -4-bromo-4-silathiacyclohexane 1-oxide is only 0.10 kcal/mol more stable than the corresponding 1,4-boat conformer which is stabilized by a transannular coordination of the sulfinyl oxygen with silicon that results in trigonal bipyramidal geometry at silicon. The 1,4-boat structure of equatorial (SO) trans -4-bromo-4-silathiacyclohexane 1-oxide is a transition state and is 5.77 kcal/mol higher in energy than the respective chair conformer. The 1,4-boat conformer of axial (SO) 4,4-dibromo-4-silathiacyclohexane 1-oxide is also stabilized by transannular coordination of the sulfinyl oxygen and silicon, but it is 4.31 kcal/mol higher in energy than the corresponding chair conformer. The relatively lower stability of the 1,4-boat conformer of 4,4-dibromo-4-silathiacyclohexane 1-oxide may be due to repulsive interactions of the axial halogen and sulfinyl oxygen atom. The relative energies of the conformers and transition states are discussed in terms of hyperconjugative interactions, orbital interactions, nonbonded interactions, and transannular sulfinyl oxygen-silicon coordination. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [source]

Microencapsulation of Fish Oil by Spray Granulation and Fluid Bed Film Coating

Sri Haryani Anwar
Abstract:, The stability of microencapsulated fish oil prepared with 2 production processes, spray granulation (SG) and SG followed by film coating (SG-FC) using a fluid bed equipment, was investigated. In the 1st process, 3 types of fish oil used were based on the ratios of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) (10/50, 33/22, and 18/12). Each type was emulsified with soluble soybean polysaccharide (SSPS) and maltodextrin to produce 25% oil powders. In the 2nd process, 15% film coating of hydroxypropyl betacyclodextrin (HPBCD) was applied to the granules from the 1st process. The powder stability against oxidation was examined by measurement of peroxide values (PV) and headspace propanal after storage at room temperature and at 3 to 4 °C for 6 wk. Uncoated powder containing the lowest concentration of PUFA (18/12) was found to be stable during storage at room temperature with maximum PV of 3.98 ± 0.001 meq/kg oil. The PV increased sharply for uncoated powder with higher concentration of omega-3 (in 33/22 and 10/50 fish oils) after 3 wk storage. The PVs were in agreement with the concentration of propanal, and these 2 parameters remained constant for most of the uncoated powders stored at low temperature. Unexpectedly, the outcomes showed that the coated powders had lower stability than uncoated powders as indicated by higher initial PVs; more hydroperoxides were detected as well as increasing propanal concentration. The investigation suggests that the film-coating by HPBCD ineffectively protected fish oil as the coating process might have induced further oxidation; however, SG is a good method for producing fish oil powder and to protect it from oxidation because of the "onion skin" structure of granules produced in this process. [source]

Comparison of bovine and porcine ,-lactoglobulin: a mass spectrometric analysis

Gaetano Invernizzi
Abstract Nano-electrospray-ionization mass spectrometry (nano-ESI-MS) is applied to comparison of bovine and porcine ,-lactoglobulin (BLG and PLG). The conformational and oligomeric properties of the two proteins under different solvent and experimental conditions are analyzed. The pH-dependence of dimerization is described for the pH range 2,11. The results indicate maximal dimer accumulation at pH 6 for BLG and pH 4 for PLG, as well as a lower stability of the PLG dimer at pH 4 compared to BLG at pH 6. Conformational stability appears to be higher for BLG at acidic pH, but higher for PLG at basic pH. The higher stability of BLG at low pH is revealed by means of either chemical or thermal denaturation. Equilibrium folding intermediates of both proteins are detected. Finally, conditions are found that promote dissociation of the BLG dimer at pH 6 into folded monomers. Copyright © 2006 John Wiley & Sons, Ltd. [source]

2-Bromo-6-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)pyridine, a new unexpected bifunctional building block for combinatorial chemistry

Jana Sopková-de Oliveira Santos
The first reported structure of a pyridin-2-ylboron derivative, viz. the title compound, C11H15BBrNO2, (I), is compared with its regioisomer 2-bromo-5-(4,4,5,5-tetra­methyl-1,3,2-dioxa­borolan-2-yl)­pyridine, (II) [Sopková-de Oliveira Santos, Lancelot, Bouillon & Rault (2003). Acta Cryst. C59, o111o113]. Structural differences are observed, firstly in the orientation of the dioxaborolane ring with respect to the pyridine ring and secondly in the bond angles of the BO2 group. These differences do not explain the experimentally observed differences in chemical reactivity between (I) and (II) but do confirm the relatively lower stability of (I). However, ab initio calculations of the HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital), based on the known crystal structures of the two compounds, show different distributions, which correspond to the differences observed during chemical reactions. [source]

Impact of water-dispersible beadlets as a vehicle for the delivery of carotenoids to cultured cells

BIOFACTORS, Issue 3-4 2002
Siranoush Shahrzad
Abstract Water-dispersible beadlets of carotenoids were used as supplements for human umbilical vein endothelial cells (HUVECs), human peripheral blood mononuclear cells (PBMCs) and human monocytes. Stability, cellular association and cytotoxicity of the carotenoid beadlets were compared with carotenoids delivered with tetrahydrofuran (THF). Incubations with lycopene, ,-carotene, lutein and astaxanthin dissolved in THF resulted in a lower stability in the medium, lower cellular association, and a higher standard deviation. Beadlets provided 60, 4, 6, and 2 times greater accumulation of lycopene, ,-carotene, lutein and astaxanthin, respectively, by PBMCs than THF. The cellular association of carotenoids delivered by THF seems to be more carotenoid-specific than when carotenoids are delivered by beadlets. After 48,h of incubation under cell culture conditions all of the four carotenoids (1 ,M) delivered by beadlets to the medium showed a reduction less than 30%. In addition, no cytotoxic effect of the carotenoid beadlets or the vehicle alone was detected in a concentration range of 0.5-5 ,M. The results show that beadlets are a non-toxic vehicle for supplementing and stabilizing carotenoids in culture media offering a reasonable compromise in term of cell accumulation efficiency. [source]

A Feasible Enzymatic Process for d -Tagatose Production by an Immobilized Thermostable l -Arabinose Isomerase in a Packed-Bed Bioreactor

Hye-Jung Kim
To develop a feasible enzymatic process for d -tagatose production, a thermostable l -arabinose isomerase, Gali152, was immobilized in alginate, and the galactose isomerization reaction conditions were optimized. The pH and temperature for the maximal galactose isomerization reaction were pH 8.0 and 65 °C in the immobilized enzyme system and pH 7.5 and 60 °C in the free enzyme system. The presence of manganese ion enhanced galactose isomerization to tagatose in both the free and immobilized enzyme systems. The immobilized enzyme was more stable than the free enzyme at the same pH and temperature. Under stable conditions of pH 8.0 and 60 °C, the immobilized enzyme produced 58 g/L of tagatose from 100 g/L galactose in 90 h by batch reaction, whereas the free enzyme produced 37 g/L tagatose due to its lower stability. A packed-bed bioreactor with immobilized Gali152 in alginate beads produced 50 g/L tagatose from 100 g/L galactose in 168 h, with a productivity of 13.3 (g of tagatose)/(L-reactor·h) in continuous mode. The bioreactor produced 230 g/L tagatose from 500 g/L galactose in continuous recycling mode, with a productivity of 9.6 g/(L·h) and a conversion yield of 46%. [source]

Molecular modeling of chiral-modified zeolite HY employed in enantioselective separation

CHIRALITY, Issue 6 2007
Siricharn S. Jirapongphan
Abstract Insight into enantioselective separation utilizing chiral-modified zeolite HY could be useful in designing a chiral stationary phase for resolving pharmaceutical compounds. A model was employed to better understand the enantioseparation of valinol in zeolite HY that contains (+)-(1R;2R)-hydrobenzoin as a chiral modifier. This model incorporates the zeolite support and accounts for the flexible change. Results from grand canonical Monte Carlo and molecular dynamics simulations indicate that the associated diastereomeric complex consists of a single (+)-(1R;2R)-hydrobenzoin and a single valinol molecules located in the zeolite HY supercage. Supercage-based docking simulation predicted an enantioselectivity of 2.6 compared with that of 1.4 measured experimentally. Also, the supercage-based docking simulation demonstrated a single binding motif in the S complex, and two binding motifs in the R complex. The multiple binding modes in the R complex resulted in its lower stability. This is hypothesized to be the origin of the weaker binding between (,)-(R)-valinol and the chiral modifier, and explains why (+)-(R)-valinol is retained more in the chiral-modified zeolite system studied. Chirality, 2007. © 2007 Wiley-Liss, Inc. [source]