Investigation on non-radioactive behavior of an acylhydrazone-based fluorescent probe: Coexistence of PET and TICT mechanisms.

A fluorescent probe (E)-((2,4-dihydroxybenzyl)diazenyl)(pyridin-2-yl)methanone (HL) to effectively and selectively detect Al3+ was designed and synthesized in the experiment. Herein, we explained the excited state dynamics mechanism of HL by using density functional theory (DFT) and time-dependent density functional theory (TD-DFT). The potential energy surfaces (PESs) proved that the excited-state intramolecular proton transfer (ESIPT) process hardly occurs due to the high reaction barriers, so the fluorescence quenching behavior of HL was not based on ESIPT. The frontier molecular orbitals (FMOs) and spectral properties were analyzed to better understand the origination of fluorescence quenching. It was found that an electron on C = N in HL could be transferred to the fluorophore during excitation in the absence of Al3+, accompanied by the PET process. The excited state could undergo a twisted intramolecular charge transfer (TICT) process, releasing non-radiative decay. After binding to Al3+, the photo-induced electron transfer (PET) process has no longer occurred, and the TICT process is eliminated, resulting in a significant fluorescence enhancement. Therefore, the calculation results well explain the quenching and enhancement behaviors of fluorescence before and after the reaction with Al3+.

Solvent effect on the excited-state intramolecular double proton transfer of 1,3-bis(2-pyridylimino)-4,7-dihydroxyisoindole.

Density functional theory (DFT) and time-dependent density functional theory (TDDFT) are used to study the solvatochromic effect and the excited-state intramolecular double proton transfer (ESIDPT) of 1,3-Bis(2-pyridylimino)-4,7-dihydroxyisoindole (BPI-OH) in different kinds of solvents. The hydrogen bonding parameters and IR spectra reveal that in the excited state, the strength of excited hydrogen bond increase with the decrease of solvent polarity. Furthermore, the reduction density gradient (RDG) analysis confirms the corresponding conclusion. Frontier molecular orbitals (FMOs) are analyzed, illuminating that the smaller the polarity of solvent, the smaller the energy gap between the HOMO and LUMO. The structures of BPI-OH (N) (normal), BPI-OH (T1) (single), and BPI-OH (T2) (double) were optimized. Previous reports found the double protons in BPI-OH molecule are transferred step-by-step process BPI-OH(N)→BPI-OH(T1)→BPI-OH(T2) in the ground state (S0) and the first excited singlet state (S1). Here, the potential energy curves of O1-H2 and O4-H5 in the S0 and S1 states were scanned in four kinds of solvents, respectively. It was found that in S1 state, BPI-OH(N)→BPI-OH(T1) was more prone to proton transfer than BPI-OH(T1)→BPI-OH(T2). In addition, by comparing the reaction energy barriers of the four kinds of solvents, it can be found that ESIPT is difficult to occur with the increase of solvent polarity. Meanwhile, it was also studied that MeOH as an explicit solvent was more likely to promote the ESIPT process than other implicit solvents.

Production of a single cyclic type of fructooligosaccharide structure by inulin-degrading Paenibacillus sp. LX16 newly isolated from Jerusalem artichoke root.

A novel inulin-degrading bacterium was isolated from a soil sample collected on Jerusalem artichoke roots. It is a Gram-positive, aerobic, motile and central endospore-forming straight rod, and exhibits phenotypic properties being consistent with its classification in the genus Paenibacillus. The predominant cellular fatty acids were anteiso-C15:0, C16:0 and anteiso-C17:0. This strain represents a novel species of the genus Paenibacillus on the basis of phenotypic data together with phylogenetic analysis, and it is here designated as LX16 and deposited in China centre for type collection, China (= CCTCC 2015256). Strain LX16 could produce a cyclofructooligosaccharide fructanotransferase catalysing the formation of one type of fructooligosaccharide (FOS) from inulin. The FOS was identified as a cyclofructooligosaccharide with a degree of polymerization of 6. Such homology in inulin degradation products may be beneficial for the functional FOS production.

Complete genome sequence of a xanthan-degrading Microbacterium sp. strain XT11 with the potential for xantho-oligosaccharides production.

Here, we reported a high-quality complete genome sequence of a xanthan-degrading bacterium Microbacterium sp. XT11, newly isolated from garden soil, China. Several genes probably involved in xanthan degradation pathway were detected as a gene cluster in the genome. The genome information of strain XT11 will be valuable for clarifying the molecular mechanism for xanthan degradation and producing xantho-oligosaccharides.

Isolation and properties of an endo-ß-mannanase-producing Bacillus sp. LX114 capable of degrading guar gum.

Endo-ß-mannanase, catalyzing the random hydrolysis of ß-1,4-mannosidic linkage in the backbone of (hetero) mannan, can increase feed conversion efficiency of animal feed or form functional mannanooligosaccharides. In this study, a gram-positive, straight-rod, facultative anaeorobic bacterium producing endo-ß-mannanase was isolated from soil sample. The isolate only fermented glucose, galactose, sorbose, and raffinose to acid. The test in hydrogen sulfide production was positive. Combining the data acquired from phenotypic analysis and phylogenetic analysis based on 16S rRNA gene sequences, this strain presumably represented a novel species of the genus Bacillus and was designated as LX114. The strain LX114 could break down guar gum molecules, leading to a rapid decrease of the viscosity of guar gum solutions. Endo-ß-mannanase activity was also detected in the culture supernatant. The isolate LX114 would be useful for potential application in degrading plant cell walls for increasing feed conversion efficiency and formation of functional oligosaccharides.

Characterization of volatile aroma compounds in different brewing barley cultivars.

BACKGROUND: Beer is a popular alcoholic malt beverage resulting from fermentation of the aqueous extract of malted barley with hops. The aroma of brewing barley impacts the flavor of beer indirectly, because some flavor compounds or their precursors in beer come from the barley. The objectives of this research were to study volatile profiles and to characterize odor-active compounds of brewing barley in order to determine the variability of the aroma composition among different brewing barley cultivars. RESULTS: Forty-one volatiles comprising aldehydes, ketones, alcohols, organic acids, aromatic compounds and furans were identified using solid phase microextraction combined with gas chromatography/mass spectrometry, among which aldehydes, alcohols and ketones were quantitatively in greatest abundance. Quantitative measurements performed by means of solvent extraction and calculation of odor activity values revealed that acetaldehyde, 2-methylpropanal, 3-methylbutanal, 2-methylbutanal, hexanal, heptanal, octanal, nonanal, 3-methyl-1-butanol, cyclopentanol, 2,3-butanedione, 2,3-pentanedione, 2-heptanone, acetic acid, ethyl acetate, 2-pentylfuran and benzeneacetaldehyde, whose concentrations exceeded their odor thresholds, could be considered as odor-active compounds of brewing barley. CONCLUSION: Principal component analysis was employed to evaluate the differences among cultivars. The results demonstrated that the volatile profile based on the concentrations of aroma compounds enabled good differentiation of most barley cultivars.

Dielectric barrier discharge plasma as a novel approach for improving 1,3-propanediol production in Klebsiella pneumoniae.

Dielectric barrier discharge plasma was used to generate a stable strain of Klebsiella pneumoniae (designated to as Kp-M2) with improved 1,3-propanediol production. The specific activities of glycerol dehydrogenase, glycerol dehydratase and 1,3-propanediol oxidoreductase in the crude cell extract increased from 0.11, 9.2 and 0.15 U mg(-1), respectively, for wild type to 0.67, 14.4 and 1.6 U mg(-1) for Kp-M2. The glycerol flux of Kp-M2 was redistributed with the flux to the reductive pathway being increased by 20% in batch fermentation. The final 1,3-propanediol concentrations achieved by Kp-M2 in batch and fed-batch fermentations were 19.9 and 76.7 g l(-1), respectively, which were higher than those of wild type (16.2 and 49.2 g l(-1)). The results suggested that dielectric barrier discharge plasma could be used as an effective approach to improve 1,3-propanediol production in K. pneumoniae.