The
growing production of biodiesel as a promising alternative
and renewable fuel led as the main problem the dramatic increase of
its by-product: glycerol. Different strategies for glycerol derivatization
have been reported so far, some more efficient or sustainable than
others. Herein, we report a very promising and eco-friendly transformation
of glycerol in nontoxic solvents and chemicals (i.e., solketal, ketals),
proposing three new families of Fe(III) compounds capable of catalysing
glycerol acetalization with unpublished turn over frequencies (TOFs),
and adhering most of the principles of green chemistry. The comparison
between the activity of complexes of formula [FeCl
3
(
1-R
)] (
1-R
= substituted pyridinimine), [FeCl(
2-R
,
R′
)] (
2-R
,
R′
= substituted
O
,
O
′-deprotonated
salens) and their corresponding simple salts reveals that the former
are extremely convenient because they are able to promote solketal
formation with excellent TOFs, up to 10
5
h
–1
. Satisfactory performances were shown with respect to the entire
range of substrates, with results being competitive to those reported
in the literature so far. Moreover, the experimental activity was
supported by an accurate and complete ab initio study, which disclosed
the fundamental role of iron(III) as Lewis acid in promoting the catalytic
activity. The unprecedented high activity and the low loading of the
catalyst, combined with the great availability and the good eco-toxicological
profile of iron, foster future applications of this catalytic process
for the sustainable transformation of an abundant by-product in a
variety of chemicals.
Shewanella sp. HM13 is a cold-adapted Gram-negative bacterium isolated from the intestine of a horse mackerel. It produces a large amount of outer membrane vesicles (OMVs), which are particles released in the medium where the bacterium is cultured. This strain biosynthesizes a single major cargo protein in the OMVs, a fact that makes Shewanella sp. HM13 a good candidate for the production of extracellular recombinant proteins. Therefore, the structural characterization of the components of the vesicles, such as lipopolysaccharides, takes on a fundamental role for understanding the mechanism of biogenesis of the OMVs and their applications. The aim of this study was to investigate the structure of the oligosaccharide (OS) isolated from Shewanella sp. HM13 cells as the first step for a comparison with that from the vesicles. The lipooligosaccharide (LOS) was isolated from dry cells, purified, and hydrolyzed by alkaline treatment. The obtained OS was analyzed completely, and the composition of fatty acids was obtained by chemical methods. In particular, the OS was investigated in detail by 1H and 13C NMR spectroscopy and MALDI-TOF mass spectrometry. The oligosaccharide was characterized by the presence of a residue of 8-amino-3,8-dideoxy-manno-oct-2-ulosonic acid (Kdo8N) and of a d,d-heptose, with both residues being identified in other oligosaccharides from Shewanella species.
Lipopolysaccharides (LPS) are surface glycoconjugates embedded in the external leaflet of the outer membrane (OM) of the Gram-negative bacteria. They consist of three regions: lipid A, core oligosaccharide (OS), and O-specific polysaccharide or O-antigen. Lipid A is the glycolipid endotoxin domain that anchors the LPS molecule to the OM, and therefore, its chemical structure is crucial in the maintenance of membrane integrity in the Gram-negative bacteria. In this paper, we reported the characterization of the lipid A and OS structures from Pseudoalteromonas nigrifaciens Sq02-Rifr, which is a psychrotrophic Gram-negative bacterium isolated from the intestine of Seriola quinqueradiata. The immunomodulatory activity of both LPS and lipid A was also examined.
Bacterial extracellular membrane vesicles (EMVs) are membrane-bound particles released during cell growth by a variety of microorganisms, among which are cold-adapted bacteria. Shewanella vesiculosa HM13, a cold-adapted Gram-negative bacterium isolated from the intestine of a horse mackerel, is able to produce a large amount of EMVs. S. vesiculosa HM13 has been found to include a cargo protein, P49, in the EMVs, but the entire mechanism in which P49 is preferentially included in the vesicles has still not been completely deciphered. Given these premises, and since the structural study of the components of the EMVs is crucial for deciphering the P49 transport mechanism, in this study the complete characterization of the lipooligosaccharide (LOS) isolated from the cells and from the EMVs of S. vesiculosa HM13 grown at 18 °C is reported. Both lipid A and core oligosaccharide have been characterized by chemical and spectroscopic methods.
Aeromonas species are found in the aquatic environment, drinking water, bottled mineral water, and different types of foods, such as meat, fish, seafood, or vegetables. Some of these species are primary or opportunistic pathogens for invertebrates and vertebrates, including humans. Among the pathogenic factors associated with these species, there are the lipopolysaccharides (LPSs). LPSs are the major components of the external leaflet of Gram-negative bacterial outer membrane. LPS is a glycoconjugate, generally composed of three portions: lipid A, core oligosaccharide, and O-specific polysaccharide or O-antigen. The latter, which may be present (smooth LPS) or not (rough LPS), is the most exposed part of the LPS and is involved in the pathogenicity by protecting infecting bacteria from serum complement killing and phagocytosis. The O-antigen is a polymer of repeating oligosaccharide units with high structural variability, particularly the terminal sugar, that confers the immunological specificity to the O-antigen. In this study, we established the structure of the O-chain repeating unit of the LPS from Aeromonas bivalvium strain 868 ET (=CECT 7113T = LMG 23376T), a mesophilic bacterium isolated from cockles (Cardium sp.) and obtained from a retail market in Barcelona (Spain), whose biosynthesis core LPS cluster does not contain the waaE gene as most of Aeromonas species. After mild acid hydrolysis, the lipid A was removed by centrifugation and the obtained polysaccharide was fully characterized by chemical analysis and NMR spectroscopy. The polymer consists of a heptasaccharide repeating unit containing D-GalNAc, L-Rha, D-GlcNAc, and D-FucNAc residues.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.