RESUMO
Odd-electron bonds, i.e., the two-center, three-electron (2c/3e), or one-electron (2c/1e) bonds, have attracted tremendous interest owing to their novel bonding nature and radical properties. Herein, complex [K(THF)6][LSn:···Sn:L] (1), featuring the first and unsupported 2c/1e Sn···Sn σ-bond with a long distance (3.2155(9) Å), was synthesized by reduction of stannylene [LSn:] (L = N,N-dpp-o-phenylene diamide) with KC8. The one-electron Sn-Sn bond in 1 was confirmed by the crystal structure, DFT calculations, EPR spectroscopy, and reactivity studies. This compound can be viewed as a stabilized radical by delocalizing to two metal centers and can readily mediate radical reactions such as C-C coupling of benzaldehyde.
RESUMO
Self-assembly of sophisticated polyhedral cages has drawn much attention because of their elaborate structures and potential applications. Herein, we report the anion-coordination-driven assembly of the first A8L12 (A = anion, L = ligand) octanuclear cubic structures from phosphate anion and p-xylylene-spaced bis-bis(urea) ligands via peripheral templating of countercations (TEA+ or TPA+). By attaching terminal aryl rings (phenyl or naphthyl) to the ligand through a flexible (methylene) linker, these aryls actively participate in the formation of plenty of "aromatic pockets" for guest cation binding. As a result, multiple peripheral guests (up to 22) of suitable size are bound on the faces and vertices of the cube, forming a network of cation-π interactions to stabilize the cube structure. More interestingly, when chiral ligands were used, either diastereomers of mixed Λ- and Δ-configurations (with TEA+ countercation) for the phosphate coordination centers or enantiopure cubes (with TPA+) were formed. Thus, the assembly and chirality of the cube can be modulated by remote terminal groups and peripheral templating tetraalkylammonium cations.
RESUMO
The α-diimine-ligated Zn-Zn-bonded compound [K(THF)2]2[LZn-ZnL] (1, L = [(2,6-iPr2C6H3)NC(Me)]22-) displays diverse reactivities toward a variety of ketones. In the reaction of 1 with benzophenone or 4,4'-di-tert-butylbenzophenone, a multielectron transfer process was observed to give bimetallic (Zn/K) complexes with both ketyl radical fragments and C-C coupled pinacolate moieties (products 2 and 3). In contrast, treating 1 with 9-fluorenone only afforded pinacolate complex 5. Moreover, the reactions of 1 with N- or O-heterocycle-functionalized ketones, i.e., di(2-pyridyl)ketone, 2,2-pyrrolidinone, 9-xanthenone, or 10-methyl-9(10H)-acridone, were also carried out. Besides different transformations of the ketone moiety, the heteroatoms (nitrogen or oxygen) are also involved in coordination with zinc or potassium ions, yielding discrete aggregates or polymeric structures of products 6-9.
RESUMO
BACKGROUND: The impact of exercise dosages based on American College of Sports Medicine(ACSM) recommendations on lipid metabolism in patients after PCI remains unclear. This study conducted a meta-analysis of reported exercise dosages from the literature to address this knowledge gap. METHODS: A comprehensive search of databases was conducted to identify eligible randomized controlled studies of exercise interventions in patients after PCI, following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. Based on the recommended exercise dosages from ACSM for patients with coronary heart disease, exercise doses in the literature that met the inclusion criteria were categorized into groups that were highly compliant with ACSM recommendations and those with low or uncertain ACSM recommendations. The topic was the effect of exercise dose on lipid metabolism in post-PCI patients. This was assessed using standardized mean difference (SMD) and 95% confidence intervals (95% CI) for changes in triglycerides, total cholesterol, LDL, and HDL. RESULTS: This systematic review included 10 randomized controlled studies. The subgroup analysis revealed statistically significant differences in the high compliance with ACSM recommendations group for triglycerides [SMD=-0.33 (95% CI -0.62, -0.05)], total cholesterol [SMD=-0.55 (95% CI -0.97, -0.13)], low-density lipoprotein [SMD=-0.31 (95% CI -0.49, -0.13)], high-density lipoprotein [SMD = 0.23 (95% CI 0.01, 0.46)], and body mass index [SMD=-0.52 (95% CI -0.87, -0.17)]. Compared to the low or uncertain compliance with ACSM recommendations group, the high compliance group exhibited significant differences in improving TC levels (-0.55(H) vs. -0.46(L)), HDL levels (0.23(H) vs. 0.22(L)), and BMI (-0.52(H) vs. -0.34(L)). CONCLUSIONS: This study supports that high compliance with ACSM-recommended exercise dosages has significant impacts on improving TC levels, HDL levels, and BMI. However, no advantage was observed for TG or LDL levels.
Assuntos
Exercício Físico , Metabolismo dos Lipídeos , Intervenção Coronária Percutânea , Ensaios Clínicos Controlados Aleatórios como Assunto , Triglicerídeos , Humanos , Exercício Físico/fisiologia , Triglicerídeos/sangue , Medicina Esportiva , HDL-Colesterol/sangue , Colesterol/sangue , Masculino , LDL-Colesterol/sangue , Terapia por ExercícioRESUMO
Functional thin films, being fabricated by incorporating discrete supramolecular architectures, have potential applications in research areas such as sensing, energy storage, catalysis, and optoelectronics. Here, we have determined that an anion-coordinated triple helicate can be solution-processed into a functional thin film by incorporation into a polymethyl methacrylate (PMMA) matrix. The thin films fabricated by the incorporation of the anion-coordinated triple helicate show multiple optical properties, such as fluorescence, CD, and CPL. In addition, the film has the ability to recognize choline and choline derivatives in a water system. The successful recognition of Ch+ by the film represents the first example of utilizing 'aniono'-supramolecular architectures for biomolecule detection in aqueous solution and opens up a new route for designing biocompatible functional materials.
RESUMO
Control of phosphate capture and release is vital in environmental, biological, and pharmaceutical contexts. However, the binding of trivalent phosphate (PO4 3-) in water is exceptionally difficult due to its high hydration energy. Based on the anion coordination chemistry of phosphate, in this study, four charge-neutral tripodal hexaurea receptors (L1-L4), which were equipped with morpholine and polyethylene glycol terminal groups to enhance their solubility in water, were synthesized to enable the pH-triggered phosphate binding and release in aqueous solutions. Encouragingly, the receptors were found to bind PO4 3- anion in a 1 : 1 ratio via hydrogen bonds in 100 % water solutions, with L1 exhibiting the highest binding constant (1.2×103â M-1). These represent the first neutral anion ligands to bind phosphate in 100 % water and demonstrate the potential for phosphate capture and release in water through pH-triggered mechanisms, mimicking native phosphate binding proteins. Furthermore, L1 can also bind multiple bioavailable phosphate species, which may serve as model systems for probing and modulating phosphate homeostasis in biological and biomedical researches.
Assuntos
Ânions , Fosfatos , Água , Fosfatos/química , Água/química , Ânions/química , Concentração de Íons de Hidrogênio , Materiais Biomiméticos/química , Materiais Biomiméticos/metabolismo , Ligação de Hidrogênio , Estrutura Molecular , Sítios de LigaçãoRESUMO
The assembly of discrete architectures has been an important subject in supramolecular chemistry because of their elegant structures and fascinating properties. During the last several decades, supramolecular chemists have developed manifold strategies for hierarchical assembly, which are normally classified by two main types of driving force: covalent and noncovalent interactions. Typical noncovalent interactions include metal coordination, hydrogen bonding, and other weak forces. These approaches have achieved great progress in the construction of various supramolecular structures, such as macrocycles, cages, polyhedra, and interlocked systems. Among these methods, metal-coordination-driven assembly is attractive due to the well-defined coordination properties of metal ions. Indeed, in terms of supramolecular chemistry, the concept of "coordination" has been expanded beyond transition metals. In particular, anion coordination chemistry, which was first proposed by Lehn in 1978 [ Acc. Chem. Res. 1978, 11, 49] and then elucidated in detail by Bowman-James two decades later [ Acc. Chem. Res. 2005, 38, 671], has grown up to a subfield of supramolecular chemistry. It is noticeable that anions also show "dual valencies" like transition metals, wherein the "primary valence" is the charge balance for anions by countercations while the "secondary valence", i.e., the coordination, refers to hydrogen bonding interactions where the electron flow is from the electron-rich anion (the coordination center) to hydrogen bonding donors (the ligands). Thus, anions also display certain coordination numbers and specific coordination geometries. Although such features are far less regular than those of transition metals, they are sufficient to allow anion coordination to serve as the driving force for assembling discrete supramolecular architectures. In this Account, the anion-coordination-driven assembly (ACDA), a new assembling strategy established by us during the past decade, will be presented. We summarize our work in the construction of a series of "aniono" supramolecular structures, especially triple helicates and tetrahedral cages, based on the coordination between oligourea ligands and anions (mostly phosphate). In particular, we will detail the considerations in the design of ligands, the assembling process including structural transformation, and functionalization of the systems toward guest inclusion, supramolecular catalysis, photoswitches, and molecular devices. These results demonstrate the great potential of ACDA in fabricating novel anion-based systems. Although the design concept was originally loaned from traditional coordination chemistry of transition metals, and structures of anion complexes bear some resemblance to metal complexes, there are significant differences of the aniono supramolecular assemblies from the metallo analogues. For example, these metal-free systems are held together by multiple hydrogen bonds (dozens to nearly 100), thus facilitating assembly/disassembly under mild conditions and relatively flexible structures for adaptive guest inclusion. To this end, intriguing applications (supramolecular chirality, catalysis, energy storage, etc.) may be expected for aniono systems. We hope the current Account will attract more attention from researchers in supramolecular assembly and inspire more efforts in this fascinating area.
Assuntos
Complexos de Coordenação , Elementos de Transição , Ânions/química , Ligantes , Complexos de Coordenação/química , Ligação de Hidrogênio , Metais/químicaRESUMO
The α-diimine-ligated dimagnesium(I) compound [K(thf)3 ]2 [LMg-MgL] (1, L=[(2,6-iPr2 C6 H3 )NC(Me)]2 2- ) displays diverse reactivities toward carbodiimides (RN=C=NR) with different R substituents. In the reaction of 1 with Me3 SiNCNSiMe3 , one of the easily leaving trimethylsilyl groups is lost to yield the Me3 SiNCN- moiety that either bridges two MgII centers (2) or terminally coordinated (3). In contrast, with the similarly bulky tBuNCNtBu, the carbodiimide inserts into Mg-Mg bond with accompanying C-H activation of a ligand or solvent (products 4 and 5). In the case of dicyclohexyl or diisopropyl carbodiimide, reductive C-C coupling of two RNCNR molecules occurs to form the [C2 (NR)4 ]2- diamido moiety, which bridges two Mg centers, giving complexes [{K(dme)2 }2 LMg(µ-{C2 (NR)4 })MgL] (6, R=Cy; 7, R=iPr) and [Lâ - Mg(µ-{C2 (NR)4 })MgLâ - ] (8). Most interestingly, upon treating 1 with Me3 SiC≡CSiMe3 , the acetylide complex [K(dme)][LMg(C≡CSiMe3 )(dme)] (9) was prepared, which undergoes a rare "double insertion" with CyNCNCy to afford [K(solv)][K(dme)2 LMg(NCy)2 C-C≡C-C(NCy)2 MgL] (10) containing an acetylenediide-coupled bis(amidinate) ligand that bridges two Mg atoms.
RESUMO
The reactivity of two α-diimine-ligated digallanes, [L2-Ga-GaL2-] (La = [(2,6-iPr2C6H3)NC(CH3)]2, dpp-dad, 1; Lb = 1,2-[(2,6-iPr2C6H3)NC]2C10H6, dpp-bian, 2), and a gallylene, [(La)2-GaNa(THF)3] (3), toward organic azides was studied. Reaction of digallane 1 or 2 with trimethylsilyl azide (Me3SiN3), 2-azido-benzonitrile (2-CNC6H4N3), or tosylazide (TosN3) results in imido-bridged complexes, [(La)·-Ga(µ-NSiMe3)2Ga(La)·-] (4) [(Lb)·-Ga(µ-NSiMe3)2Ga(Lb)·-] (5), [(Lb)·-Ga(µ-2-CNC6H4N)2Ga(Lb)·-] (6), and [(Lb)·-Ga(µ-NTos)2Ga(Lb)·-] (7), with elimination of dinitrogen. Treatment of 1 or 2 with 1-adamantyl azide (1-AdN3), on the other hand, affords the unsymmetrical dinuclear complexes [(La)·-Ga(NAd)(N3Ad)Ga(La)·-] (8) and [(Lb)·-Ga(NAd)(N3Ad)Ga(Lb)·-] (9), which contain both imido and triazene bridges. Different from the Ga(II) complexes 1 and 2, the reactions of Ga(I) species 3 with benzylazide or trimethylsilyl azide result in the tetrazene complex {Na(THF)}2[(La)2-Ga(benzyl-N4-benzyl)]2 (10) and amide complex {Na(THF)4}[(La)2-Ga(NHSiMe3)(benzyl)] (11). It is likely that these latter transformations proceed via the transient formation of the corresponding GaâN imide complex, which undergoes either cycloaddition with a second azide (to form 10) or activation of the C-H bond of methyl in one solvent toluene molecule (to yield 11).
RESUMO
Anion-coordination-driven assembly (ACDA) has proven to be a very effective strategy for the construction of polyhedral structures. Here we demonstrate that variation of the "angle" of the backbone of C3 -symmetric tris-bis(urea) ligands, from triphenylamine to triphenylphosphine oxide, results in the change of the final construct from an A4 L4 tetrahedron to a higher-nuclearity, A6 L6 trigonal antiprism (A=anion, herein PO4 3- ; L=ligand). Most interestingly, this assembly features a huge hollow internal space that is divided into three compartments: one central cavity and two large outer pockets. This multi-cavity character enables the binding of different guests, namely monosaccharides or polyethylene glycol molecules (PEG600, PEG1000 and PEG2000), respectively. The results prove that anion coordination by multiple hydrogen bonds may provide both sufficient strength and flexibility, thus making possible the formation of complicated structures with adaptive guest binding ability.
RESUMO
The phosphate-coordination triple helicates A2 L3 (A=anion) with azobenzene-spaced bis-bis(urea) ligands (L) have proven to undergo a rare in situ photoisomerization (without disassembly of the structure) rather than the typically known, stepwise "disassembly-isomerization-reassembly" process. This is enabled by the structural self-adaptability of the "aniono" assembly arising from multiple relatively weak and flexible hydrogen bonds between the phosphate anion and bis(urea) units. Notably, the ZâE thermal relaxation rate of the isomerized azobenzene unit is significantly decreased (up to 20-fold) for the triple helicates compared to the free ligands. Moreover, the binding of chiral guest cations inside the cavity of the Z-isomerized triple helicate can induce optically pure diastereomers, thus demonstrating a new strategy for making light-activated chiroptical materials.
RESUMO
Supramolecular cages have been constructed by anion-coordination-driven assembly (ACDA) in recent years and have shown unique host-guest interactions. However, most of the reported cages are made of the phosphate ion (PO4 3- ); other anions have rarely been explored. Here we show for the first time that the sulfate ion (SO4 2- ) is also able to form the A4 L4 tetrahedral motif with tris-bis(urea) ligands, but this is dependent on the stoichiometry of the sulfate ion (in solution). Notably, the sulfate cages display enhanced resistance for both Brønsted (pH as low as 4.3 in acetone containing 15 % water) and Lewis acids (metal complexes) compared to the corresponding phosphate cages, and thus could find applications where an acidic (proton or metals) environment is required.
Assuntos
Complexos de Coordenação , Sulfatos , Ânions , Ligantes , UreiaRESUMO
Two bis-bis(urea) ligands (L1 and L2) incorporating the photoactive 9,10-diphenylanthracene fragment were designed for the construction of anion-coordination-driven assemblies and subsequent oxygenation of anthracene moieties for singlet oxygen storage. The corresponding A2L2-type sulfate complexes [TEA]4[(SO4)2(L1)2] (1) and [TEA]4[(SO4)2(L2)2] (2), where TEA = tetraethylammonium, were achieved by coordinating the ligands L1 or L2 with sulfate anions. Both 1 and 2 were able to undergo [4 + 2] photooxygenation to form endoperoxide photoproducts 1-EPO and 2-EPO, which can be partially converted back to the original anthracene compounds after heating. The structures of 1-EPO and 2-EPO were unambiguously confirmed by X-ray crystallography, NMR and UV-vis spectroscopy, and high-resolution electrospray ionization mass spectrometry.
RESUMO
Reactivity of transition metal complexes containing the redox-active gallylene (dpp-bian)Ga ligand (dpp-bian = 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene) toward isocyanide, isocyanate, isothiocyanate, and ketene substrates is described. The reaction of [(dpp-bian)GaCr(CO)5] (1) with tBuNC results in a dative complex [(dpp-bian)Ga(CNtBu)Cr(CO)5] (2), while compound [(dpp-bian)GaCr(CO)5]2[Na(THF)2]2 (3) reacts with tBuNC to give the coordination polymer [(dpp-bian)GaCr(CO)5][Na(CNtBu)(THF)]n (5). Treatment of [(dpp-bian)GaCr(CO)5]2[Na(THF)2]2 with an excess of PhNCO results in trimerization of the latter and formation of complex [(dpp-bian)GaCr(CO)5][Na(PhNCO)3(Et2O) (DME)] (4). [(dpp-bian)GaFeCp(CO)2] (7) treated with Ph2CCO or PhNCS results in cycloaddition products [(dpp-bian)(Ph2CCO)GaFeCp(CO)2] (8) and [(dpp-bian)(PhNCS)GaFeCp(CO)2] (9). The formation of 2 and 9 was found to be reversible, which offers a means for facile regulation of transition metal center reactivity and cooperative substrate activation. New compounds were characterized by EPR (2), NMR (4, 8, and 9), and IR spectroscopy (2, 4, 5, 8, and 9). The molecular structures of 2, 4, 5, 8, and 9 were established by single-crystal X-ray diffraction analysis. Electronic structures of the compounds have been examined by DFT calculations.
RESUMO
AIM: The role of lipids in periodontitis has not been well studied. Thus, this study aimed to explore periodontitis-associated lipid profile changes and identify differentially expressed lipid metabolites in gingival tissues. MATERIALS AND METHODS: Gingival tissues from 38 patients with periodontitis (periodontitis group) and 38 periodontally healthy individuals (control group) were collected. A ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry-based non-targeted metabolomics platform was used to identify and compare the lipid profiles of the two groups. The distribution and expression of related proteins were subsequently analysed via immunohistochemistry to further validate the identified lipids. RESULTS: Lipid profiles significantly differed between the two groups, and 20 differentially expressed lipid species were identified. Lysophosphatidylcholines (lysoPCs), diacylglycerols (DGs), and phosphatidylethanolamines (PEs) were significantly up-regulated, while triacylglycerols (TGs) were downregulated in the periodontitis group. Moreover, the staining intensity of ABHD5/CGI-58, secretory phospholipase A2 (sPLA2), and sPLA2-IIA was significantly stronger in the gingival tissues of patients with periodontitis than in those of healthy controls. CONCLUSIONS: LysoPCs, DGs, and PEs were significantly up-regulated, whereas TGs were down-regulated in gingival tissues of patients with periodontitis. Correspondingly, the immunohistochemical staining of ABHD5/CGI-58, sPLA2, and sPLA2-IIA in gingival tissues was consistent with the downstream production of lipid classes (lysoPCs, TGs, and DGs).
Assuntos
Periodontite , Fosfolipases A2 Secretórias , 1-Acilglicerol-3-Fosfato O-Aciltransferase , Diglicerídeos , Humanos , Lipidômica , Lisofosfatidilcolinas , Fosfatidiletanolaminas , TriglicerídeosRESUMO
Anion-coordination-driven assembly (ACDA) is showing increasing power in the construction of anionic supramolecular architectures. Herein, by expanding the anion centers from oxoanion (phosphate or sulfate) to organic tris-carboxylates, an Archimedean solid (truncated tetrahedron) and a highly entangled, double-walled tetrahedron featuring a ravel topology have been assembled with tris-bis(urea) ligands. The results demonstrate the promising ability of tris-carboxylates as new anion coordination centers in constructing novel topologies with increasing complexity and diversity compared to phosphate or sulfate ions on account of the modifiable size and easy functionalization character of these organic anions.
RESUMO
An azobenzene-functionalized bis-bis(urea) ligand (Lazo ) and phosphate anion assemble to give the first photoactive "aniono" constructs, tetrahedron (A4 L6 ) and helicate (A2 L3 ), which readily undergo interconversion through cis-trans isomerization of the azo group under irradiation/heating. Most strikingly, the tetrahedral cage can accommodate an [18]crown-6 molecule, which can capture two tetramethylammonium (TMA+ ) ions with an unusually high affinity, even capable of replacing K+ in [K([18]crown-6)]+ to form a {(TMA)2â ([18]crown-6)} â cage "Russian doll" structure. Thus, the current work may provide a model for the light-driven binding and exchange of the biologically important K+ and TMA+ ions.
Assuntos
Compostos de Amônio Quaternário , Ureia , Ânions , PotássioRESUMO
The fabrication of anion-coordinated assemblies into functional soft materials remains a major challenge. To this end, four C2 -symmetric anion-binding ligands equipped with ortho-phenylene-bridged bis(urea) and amine or amide ends were designed, which generated A2 L3 triple helical architectures upon self-assembly with phosphate ions. Hierarchical intermolecular hydrogen bonds among the terminal amine/amide groups and urea moieties resulted in the formation of functional gels. The obtained gels were further applied for conductive adhesion between different surfaces, displaying excellent flexibility and selective wettability. The viscoelastic gels constructed from anion-coordinated assemblies described in this work represent the first example of a new class of anion-coordination-driven smart materials.
Assuntos
Adesivos , Amidas , Amidas/química , Aminas , Ânions/química , Géis/química , Modelos Moleculares , Ureia/químicaRESUMO
The dialanes [(dpp-Bian)Al-Al(dpp-Bian)] (1) and [(dpp-dad)Al(THF)-(THF)Al(dpp-dad)] (2) (dpp-Bian = 1,2-[(2,6-iPr2C6H3)NC]2C12H6, dpp-dad = [(2,6-iPr2C6H3)NC(CH3)]2) react with some isothiocyanates, isocyanates, and diphenylketene via [2 + 4] cycloaddition of the CâO or CâS bond across the CâC-N-Al fragment to afford complexes [L(XâC-Y)Al-Al(XâC-Y)L] with an intact Al-Al single bond (3, L = dpp-Bian, X = PhN, Y = O; 4, L = dpp-Bian, X = Ph2C, Y = O; 6, L = dpp-dad, X = BnN, Y = S; 7, L = dpp-dad, X = tBuN, Y = O; 8, L = dpp-dad, X = iPrN, Y = S; and 9, L = dpp-dad, X = CyN, Y = S). A mixed CâN and CâO mode cycloadduct, [(dpp-Bian)(TosNâC-O)Al-Al(TosN-CâO)(dpp-Bian)] 5, was obtained in the reaction of 1 with tosylisocyanate. Heating the solution of 3 resulted in a thermal transformation and a change of the cycloaddition mode from CâO to CâN to give the product [(dpp-Bian)(PhN-CâO)Al(O)Al(PhN-CâO)(dpp-Bian)] 10. The reduction of 7 and 8 with Na yielded the products [Na(THF)n]2[(dpp-dad-H)(XâC-Y)Al]2 (12, X = iPrN, Y = S, n = 2 and 13, X = tBuN, Y = O, n = 3) in which one of the methyl groups of the backbone of the initial dpp-dad ligand was dehydrogenated. When 2 was reacted with the bulky adamantyl isocyanate AdNCO, the C-C coupling of two substrates occurred to form 14 [(dpp-dad)Al(OâC-NAd)2Al(dpp-dad)] in which the coupled dianionic oxamide ligand bridged two Al atoms in a µ,η4-N,O/N,O mode. Moreover, in the presence of 2.0 equiv of Na metal, precursor 2 reacts with tBuNCS, p-TolylNCS, or Me3SiNCO, possibly through the reduced AlI intermediate, to yield the sulfur- or oxygen-bridged dimer [Na(solv)n]2[(dpp-dad)Al(µ-E)]2 (15, E = S, solv = THF, n = 3 and 16, E = O, solv = DME, n = 2) upon CâS or CâO bond cleavage. Dialane 1 reacts with dimethylsulfone to give a Lewis adduct [(dpp-Bian)(Me2SO2)Al]2 (17), which releases dimethylsulfone upon heating. The diamagnetic compounds 3-10 and 12-17 were characterized by NMR and IR spectroscopy. The molecular structures of 3-17 were established by single-crystal X-ray diffraction analysis. Electronic structures of the compounds and possible isomers have been examined by DFT calculations.
RESUMO
ε-Poly-L-lysine (ε-PL) is a naturally-occurring L-lysine homopolymer having a broad-spectrum antimicrobial activity and used widely as a food preservative. In the present study, the combined use of immobilization and in situ product removal (ISPR) was evaluated for the production of ε-PL by Streptomyces ahygroscopicus GIM8. Results showed that ε-PL production in the flask cultures decreased from 0.84 to 0.38-0.56 g/L upon immobilization on loofah sponge with different amounts (0.5-3 g in 50 mL medium in a flask). By applying continuous ISPR to the immobilized flask cultures, ε-PL production as high as 3.51 g/L was obtained compared to 0.51 g/L of the control. A satisfactory titer of 1.84 g/L ε-PL could also be achieved with intermittent ISRP (three cycles of ISPR operation during cultivation). Further investigation showed that low levels of ε-PL retained in the broth appeared to favor its biosynthesis. In the repeated-batch fermentation in a 5 L immobilized bioreactor, with continuous ISPR, the final average ε-PL concentration and productivity were 3.35 g/L and 0.797 g/L/day, respectively, and 3.18 g/L and 0.756 g/L/day for the alternative (intermittent ISPR), in comparison to 1.16 g/L and 0.277 g/L/day with no ISPR usage. In the fed-batch fermentation with immobilized cells, the combined use of intermittent ISPR and extra nutrient feeding increased ε-PL concentration and productivity up to 24.57 g/L and 9.34 g/L/day. The fermentation processes developed could serve as an effective approach for ε-PL production and, moreover, the combination could greatly simplify downstream processing for ε-PL separation and purification.