Publications by authors named "Sheng Geng"

20 Publications

  • Page 1 of 1

Fabrication of food-grade Pickering high internal phase emulsions stabilized by the mixture of β-cyclodextrin and sugar beet pectin.

Int J Biol Macromol 2021 Apr 7. Epub 2021 Apr 7.

School of Food Science, Henan Institute of Science and Technology, Xinxiang 453003, China. Electronic address:

Food-grade Pickering high internal phase emulsions (HIPEs) stabilized by a mixture of β-cyclodextrin (β-CD) and sugar beet pectin (SBP) were fabricated for the first time. The factors affecting the microstructures, mechanical properties, and stabilities of the Pickering HIPEs were systematically investigated. The corresponding hybrid particles were also separated and characterized to reveal the formation mechanism. The results indicated that the mixture could induce the formation of HIPEs with an oil phase volume fraction (φ) of 75% using a one-step high-speed shearing process at room temperature. The composition (the mass ratio of β-CD to SBP, R) and concentration (W) of the mixture had significant effects on the formation and properties of HIPEs. When W ≥ 1.0% and R = 2:2 or 3:1, HIPEs had smaller oil droplets, higher gel strengths, better centrifugation stabilities and lutein protection effects. The spectral analysis suggested that SBP could adhere to the surface of β-CD particles to form hybrid particles during the homogenization. Compared with native β-CD particles, these hybrid particles had higher ζ-potential absolute values, and the SBP could also increase the viscosity of the aqueous phase, which contributed to the formation and properties of these HIPEs.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.ijbiomac.2021.04.002DOI Listing
April 2021

Multi-scale stabilization mechanism of pickering emulsion gels based on dihydromyricetin/high-amylose corn starch composite particles.

Food Chem 2021 Mar 23;355:129660. Epub 2021 Mar 23.

Key Laboratory of Biorheological Science and Technology, Ministry of Education, Bioengineering College, Chongqing University, Chongqing 400044, China. Electronic address:

For Pickering emulsifying effect, starch must be subjected to the pretreatments of acid hydrolysis, esterification, which are complicated and eco-unfriendly. In this study, a practical and green strategyto fabricate Pickering emulsion gels with dihydromyricetin (DMY)/high-amylose corn starch (HCS) composite particles was introduced for the first time. The DMY content in composite particles and the amount of addition of composite particles had obvious synergistic effect on the formation and properties of emulsion gels. The obtained emulsion gels were not sensitive to ionic strength, which could be attributed to emulsifying capacity and viscosity effect of composite particles. The spectral analysis confirmed the presence of DMY/amylose host-guest supramolecules. The molecular simulation of the supramolecular complexes in the oil-water system indicated that these complexes could spontaneously aggregate and anchor to the oil-water interface, reducing the interfacial tension. Based on experimental and theoretical results, the multi-scale relationship of "molecular interaction-particle characteristics-gel properties" was established.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.foodchem.2021.129660DOI Listing
March 2021

Fabrication and characterization of novel edible Pickering emulsion gels stabilized by dihydromyricetin.

Food Chem 2021 May 28;343:128486. Epub 2020 Oct 28.

Key Laboratory of Biorheological Science and Technology, Ministry of Education, Bioengineering College, Chongqing University, Chongqing 400044, China. Electronic address:

The edible Pickering emulsion gels stabilized by dihydromyricetin were fabricated for the first time. To clarify the formation mechanism, dihydromyricetin particles were first characterized. Then, the factors influencingthe gel formation, microstructure and mechanical properties were investigated. Finally, the molecular dynamics simulation was performed to clarify the microscopic behavior of dihydromyricetin in an oil-water system. The results indicated that dihydromyricetin particles occurred as regular rod-shaped crystals with amphiphilicity. They formed a 3D steric network by overlapping with each other, separating oil droplets and stabilizing O/W emulsion gels. The dihydromyricetin concentration and oil-phase weight fraction had a significant influence on the formation and mechanical properties of gels. The alkali and low ionic strength conditions benefited the gel stability. The molecular dynamics showed that dihydromyricetin could spontaneously and quickly transfer to the oil-water interface, reduce the interfacialtension and enhance the interface thickness, which agreed with the experimental results.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.foodchem.2020.128486DOI Listing
May 2021

Three common caffeoylquinic acids as potential hypoglycemic nutraceuticals: Evaluation of α-glucosidase inhibitory activity and glucose consumption in HepG2 cells.

J Food Biochem 2020 09 6;44(9):e13361. Epub 2020 Jul 6.

School of Food Science, Henan Institute of Science and Technology, Xinxiang, China.

The demand for plant-derived antidiabetic nutraceuticals is increasing. In this study, the effects of three common caffeoylquinic acids (CQAs) (chlorogenic acid, isochlorogenic acid A, and cynarin) on α-glucosidase activity and glucose consumption in HepG2 cells were systematically compared. Their α-glucosidase inhibitory activities followed the order of isochlorogenic acid A > chlorogenic acid > cynarin. The fluorescence analysis indicated that they exerted the inhibitory role by forming the complex with α-glucosidase at the molar ratio of 1:1. Isochlorogenic acid A possessed the highest binding capacity, followed by chlorogenic acid and cynarin. The effect of caffeoyl group distribution on the α-glucosidase inhibitory activity was clarified by the molecular docking results. In the HepG2 cells, isochlorogenic acid A also showed the best glucose consumption with negligible cytotoxicity, which might be related to its reactive oxygen species scavenging capacity in cells. Our results confirm its potential application as the antidiabetic nutraceutical. PRACTICAL APPLICATIONS: The hypoglycemic activities of three common CQAs (chlorogenic acid, isochlorogenic acid A, and cynarin) were systemically evaluated in this study. Isochlorogenic acid A exhibited the strongest α-glucosidase inhibitory activity and highest glucose consumption in HepG2 cells with low cytotoxicity. The results suggest that isochlorogenic acid A can be used as the potential hypoglycemic nutraceutical in functional foods.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/jfbc.13361DOI Listing
September 2020

Structuring of sunflower oil by stearic acid derivatives: Experimental and molecular modelling studies.

Food Chem 2020 Sep 13;324:126801. Epub 2020 Apr 13.

School of Food Science, Henan Institute of Science and Technology, Xinxiang 453003, China. Electronic address:

Structuring of vegetable oils has potential application in food, pharmaceutical and cosmetic products. In this study, structuring effects of stearic acid derivatives on sunflower seed oil were systematically investigated by experimental and molecular simulation methods. Stearic acid (SA), 12-hydroxy stearic acid (HSA) and 2-hydroxyethyl stearate (HES) were able to structure sunflower seed oil, among which the structuring ability of HES was reported for the first time. The oleogel formed with HSA exhibited good mechanical properties (such as hardness, fracturability, adhesiveness, chewiness and storage modulus), which coincided with its highest solid fat content and degree of crystallinity. Oleogels containing SA and HES showed similar mechanical properties. Both the molecular dynamics (MD) simulation and independent gradient model (IGM) confirmed that the HSA dimer possessed the strongest interaction during the self-assembly process while the dimers of HES and SA had similar interactions, which could explain their structuring performance.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.foodchem.2020.126801DOI Listing
September 2020

Interaction mechanism of flavonoids and bovine β-lactoglobulin: Experimental and molecular modelling studies.

Food Chem 2020 May 23;312:126066. Epub 2019 Dec 23.

Key Laboratory of Biorheological Science and Technology, Ministry of Education, Bioengineering College, Chongqing University, Chongqing 400044, China. Electronic address:

In this study, the quantitative structure-affinity relationship of 28 flavonoids with bovine β-lactoglobulin (β-lg) was investigated based on experimental and theoretical methods. The binding constants (K) of these flavonoids with β-lg were systematically compared by spectrofluorimetry, and a multivariate linear model (R = 0.8769, Q = 0.7963) was established that could explain the effect of the structure parameters of flavonoids on their affinity (lgK) for β-lg. Then, the underlying interaction mechanism was further clarified with myricetin and baicalin as representative flavonoids. Thermodynamic analysis showed that hydrogen bonds and van der Waals force played the main roles in maintaining the complexes, which was consistent with the independent gradient model (IGM) and the MM/PBSA binding free energy results. The redshift of the maximum emission peak of tryptophan residues in the synchronous fluorescence was attributed to the interaction of myricetin or baicalin with Trp19 of β-lg, according to the root mean square fluctuation (RMSF) results.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.foodchem.2019.126066DOI Listing
May 2020

Interaction Mechanism of Flavonoids and α-Glucosidase: Experimental and Molecular Modelling Studies.

Foods 2019 Aug 21;8(9). Epub 2019 Aug 21.

School of Food Science, Henan Institute of Science and Technology, Xinxiang 453003, China.

Flavonoids are known to play a role in hypoglycemia by inhibiting α-glucosidase. However, their interaction mechanism with α-glucosidase still needs to be elaborated. In this study, the α-glucosidase inhibitory activities of 15 flavonoids were investigated. Their molecular volume had a negative effect on inhibitory activity, while the number of phenolic hydroxyl groups on the B ring was positively correlated with inhibitory activity. To explain the significant differences in activity, the interaction behaviors of myricetin and dihydromyricetin, which have similar structures, were compared by spectrofluorimetry, molecular docking, and the independent gradient model (IGM). In the fluorescence analysis, myricetin exhibited a higher binding capacity. Based on molecular docking and IGM analysis, their non-covalent interactions with α-glucosidase could be visualized and quantified. It was found that they had different binding modes with the enzymes and that myricetin possessed stronger hydrogen bonding and van der Waals force interactions, which explained the thermodynamic results.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3390/foods8090355DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6770089PMC
August 2019

Preparation and characterization of lutein ester-loaded oleogels developed by monostearin and sunflower oil.

J Food Biochem 2019 11 1;43(11):e12992. Epub 2019 Aug 1.

Henan Institute of Science and Technology, Xinxiang, China.

The marigold (Tagetes erecta L.) flower is rich in lutein ester with many health-promoting activities. In this study, the effects of vegetable oil type and extracting the temperature on the extraction efficiency of lutein ester in the marigold flower were evaluated. Then, the structuring of the lutein ester-loaded sunflower oil with the addition of different amounts of monostearin and cooling temperatures (4 and 20°C) was investigated. The XRD analysis suggested that these oleogels were stabilized by the network formed by monostearin crystals in the sunflower oil. The textural properties (firmness, cohesiveness, and hardness) of oleogels were positively related to the monostearin dosage, but negatively related to the cooling temperature. According to the rheological results, the oleogels belonged to the pseudoplastic gel and their gelation temperature (T ) was only related to the concentration of monostearin. The light stability of lutein ester in the oleogels was also significantly improved in a monostearin dosage-dependent manner. PRACTICAL APPLICATIONS: The edible lutein ester-loaded oleogel for foods developed by structuring the sunflower oil with monostearin is introduced in this study. Its texture and rheological properties can be adjusted to cater to different requirements in the food industry by changing the monostearin dosage and cooling temperature. This study provides a reference for the development of other liposoluble nutraceuticals.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/jfbc.12992DOI Listing
November 2019

Hypervelocity cluster ion impacts on free standing graphene: Experiment, theory, and applications.

J Chem Phys 2019 Apr;150(16):160901

Department of Chemistry, Texas A&M University, College Station, Texas 77843-3144, USA.

We present results from experiments and molecular dynamics (MD) simulations obtained with C and Au impacting on free-standing graphene, graphene oxide (GO), and graphene-supported molecular layers. The experiments were run on custom-built ToF reflectron mass spectrometers with C and Au-LMIS sources with acceleration potentials generating 50 keV C and 440-540 keV Au. Bombardment-detection was in the same mode as MD simulation, i.e., a sequence of individual projectile impacts with separate collection/identification of the ejecta from each impact in either the forward (transmission) or backward (reflection) direction. For C impacts on single layer graphene, the secondary ion (SI) yields for C and C emitted in transmission are ∼0.1 (10%). Similar yields were observed for analyte-specific ions from submonolayer deposits of phenylalanine. MD simulations show that graphene acts as a trampoline, i.e., they can be ejected without destruction. Another topic investigated dealt with the chemical composition of free-standing GO. The elemental composition was found to be approximately COH. We have also studied the impact of Au clusters on graphene. Again SI yields were high (e.g., 1.25 C/impact). 90-100 Au atoms evaporate off the exiting projectile which experiences an energy loss of ∼72 keV. The latter is a summation of energy spent on rupturing the graphene, ejecting carbon atoms and clusters and a dipole projectile/hole interaction. The charge distribution of the exiting projectiles is ∼50% neutrals and ∼25% either negatively or positively charged. We infer that free-standing graphene enables detection of attomole to zeptomole deposits of analyte via cluster-SI mass spectrometry.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1063/1.5080606DOI Listing
April 2019

The interaction mechanism of oligopeptides containing aromatic rings with β-cyclodextrin and its derivatives.

Food Chem 2019 Jul 14;286:441-448. Epub 2019 Feb 14.

Key Laboratory of Biorheological Science and Technology, Ministry of Education, Bioengineering College, Chongqing University, Chongqing 400044, PR China; Chongqing Engineering Research Center of High-Resolution and Three-Dimensional Dynamic Imaging Detection Technology, Chongqing 400714, PR China; School of Food Science, Henan Institute of Science and Technology, Xinxiang 453003, PR China. Electronic address:

We investigate the formation mechanism of supramolecular complexes of four antioxidant oligopeptides (YW, WY, WYS, and WYSL) with β-cyclodextrin (β-CD), hydroxypropyl-β-cyclodextrin (HP-β-CD) and 6-O-α-maltosyl-β-cyclodextrin (M-β-CD) by combined computational and experimental methods. The formation of complexes is determined by UV, IR and DSC, and the rank-ordered acquired stability of the complexes is as follows: WYSL/HP-β-CD > WYS/HP-β-CD > WY/HP-β-CD > YW/M-β-CD > YW/HP-β-CD > YW/β-CD. The H NMR analysis and molecular docking results reveal that the aromatic rings of these oligopeptides are embedded into the cavities of the studied β-CD and its derivatives, indicating that hydrophobic interaction is a major driving force for the formation of the complexes. We also demonstrate that H-bonds play a key role in maintaining the supramolecular complexes. In addition, the results of the antioxidant assay indicate that the radical scavenging capacity of the oligopeptides is enhanced by the CD-based inclusion.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.foodchem.2019.02.021DOI Listing
July 2019

Lipase-catalyzed synthesis mechanism of tri-acetylated phloridzin and its antiproliferative activity against HepG2 cancer cells.

Food Chem 2019 Mar 23;277:186-194. Epub 2018 Oct 23.

Key Laboratory of Biorheological Science and Technology, Ministry of Education, Bioengineering College, Chongqing University, Chongqing 400044, China. Electronic address:

Herein, we perform the regioselective acetylation of phloridzin catalyzed by immobilized Candida antarctica lipase B (CALB). We show that the enzyme amount and reaction time can significantly influence the composition of mono-, di- and tri-acetylated phloridzin in the product. The last acetylated derivative of phloridzin is isolated and identified as 4, 3″, 6″-3-O-acetyl-phloridzin by HPLC, UV, IR, MS and NMR. Molecular docking suggests that the first acetylation of phloridzin catalyzed by CALB occurs in 6″-OH, followed by 3″-OH, then 4-OH. During this process, hydrogen bond and hydrophobic forces play an important role in maintaining the binding interaction of CALB with phloridzin or its acetylated derivatives. Although, tri-acetylated phloridzin has moderate to minimal adverse-effects on LO-2, its anti-proliferative activity against human HepG2 cancer cells is superior to that of phloridzin, which attributes to its high capacity of inducing cell apoptosis, retarding cell cycle, lowering mitochondrial membrane potential and scavenging intracellular ROS.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.foodchem.2018.10.111DOI Listing
March 2019

Interaction mechanism of flavonoids and zein in ethanol-water solution based on 3D-QSAR and spectrofluorimetry.

Food Chem 2019 Mar 17;276:776-781. Epub 2018 Oct 17.

School of Food Science, Henan Institute of Science and Technology, Xinxiang 453003, China. Electronic address:

Zein has the potential application of establishing the delivery systems for flavonoids. But there are few reports about the effect of the molecular structures of flavonoids on their interaction with zein. In this study, the binding behaviour of 21 flavonoids and zein was investigated by spectrofluorimetry. The corresponding 3D-QSAR model was also established by Topomer CoMFA method, whose steric and electrostatic field analysis could explain the binding performance of the tested flavonoids with zein. The fluorescence analysis suggested that the flavonoids could interact with zein by forming the complex at the molar ratio of 1. The flavonoids with glucosyl groups at ring A exhibited the outstanding binding capacity with zein, and their binding process with zein was driven by hydrophobic force. The synchronous and 3D fluorescence spectra showed that there was no apparent change in the microenvironment surrounding the tyrosine residues of zein during the interaction.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.foodchem.2018.10.083DOI Listing
March 2019

Self-assembled mechanism of hydrophobic amino acids and β-cyclodextrin based on experimental and computational methods.

Food Res Int 2018 10 7;112:136-142. Epub 2018 Jun 7.

key Laboratory of Biorheological Science and Technology, Ministry of Education, Bioengineering College, Chongqing University, Chongqing 400044, People's Republic of China; School of Food Science, Henan Institute of Science and Technology, Xinxiang 453003, People's Republic of China; Chongqing Engineering Research Center of High-Resolution and Three-Dimensional Dynamic Imaging Detection Technology, Chongqing 400714, People's Republic of China. Electronic address:

The β-cyclodextrin (β-CD) can be used to remove bitter taste of protein hydrolysates, which is attributed to its interaction with hydrophobic amino acids included within peptides. But the corresponding mechanism has not been fully clarified. Herein, we systematically investigate the interaction between β-CD and three hydrophobic amino acids involving tryptophan (Trp), tyrosine (Tyr), and phenylalanine (Phe). We prove the formation of amino acid/β-CD supermolecular complexes determined by FS, UV, IR, DSC and NMR, manifesting that no new chemical bond is formed in these complexes. The theoretical interaction conformations are given by molecule docking and further supported by ONIOM (our Own N-layer Integrated Orbital molecular Mechanics) calculations, with the consideration of structural assignments, binding orientations, solvent effects, interaction energies and main forces to form these complexes. Molecular docking results suggest that the hydrophobic amino acids prefer to interact with β-CD by their aromatic ring, meaning hydrophobic interactions are main forces for them entering into the cavity of β-CD. ONIOM-based calculations provide a number of quantum-chemical parameters to confirm our experimental results; meanwhile, to demonstrate that H-bonds play an important role in maintaining the stability of three amino acid/β-CD complexes. This work is help for demonstrating the interaction mechanism of amino acid/β-CD supermolecular system, and guiding how to remove bitterness or undesirable taste of bioactive peptides, even other interested molecules.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.foodres.2018.06.017DOI Listing
October 2018

"Trampoline" ejection of organic molecules from graphene and graphite via keV cluster ions impacts.

J Chem Phys 2018 Apr;148(14):144309

Department of Chemistry, Texas A&M University, College Station, Texas 77843-3144, USA.

We present the data on ejection of molecules and emission of molecular ions caused by single impacts of 50 keV C on a molecular layer of deuterated phenylalanine (D8Phe) deposited on free standing, 2-layer graphene. The projectile impacts on the graphene side stimulate the abundant ejection of intact molecules and the emission of molecular ions in the transmission direction. To gain insight into the mechanism of ejection, Molecular Dynamic simulations were performed. It was found that the projectile penetrates the thin layer of graphene, partially depositing the projectile's kinetic energy, and molecules are ejected from the hot area around the hole that is made by the projectile. The yield, Y, of negative ions of deprotonated phenylalanine, (D8Phe-H), emitted in the transmission direction is 0.1 ions per projectile impact. To characterize the ejection and ionization of molecules, we have performed the experiments on emission of (D8Phe-H) from the surface of bulk D8Phe (Y = 0.13) and from the single molecular layer of D8Phe deposited on bulk pyrolytic graphite (Y = 0.15). We show that, despite the similar yields of molecular ions, the scenario of the energy deposition and ejection of molecules is different for the case of graphene due to the confined volume of projectile-analyte interaction. The projectile impact on the graphene-D8Phe sample stimulates the collective radial movement of analyte atoms, which compresses the D8Phe layer radially from the hole. At the same time, this compression bends and stretches the graphene membrane around the hole thus accumulating potential energy. The accumulated potential energy is transformed into the kinetic energy of correlated movement upward for membrane atoms, thus the membrane acts as a trampoline for the molecules. The ejected molecules are effectively ionized; the ionization probability is ∼30× higher compared to that obtained for the bulk D8Phe target. The proposed mechanism of ionization involves tunneling of electrons from the vibrationally excited area around the hole to the molecules. Another proposed mechanism is a direct proton transfer exchange, which is suitable for a bulk target: ions of molecular fragments (i.e., CN) generated in the impact area interact with intact molecules from the rim of this area. There is a direct proton exchange process for the system D8Phe molecule + CN.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1063/1.5021352DOI Listing
April 2018

Interaction of phenolic acids with trypsin: Experimental and molecular modeling studies.

Food Chem 2017 Aug 28;228:1-6. Epub 2017 Jan 28.

Key Laboratory of Biorheological Science and Technology, Ministry of Education, School of Bioengineering, Chongqing University, Chongqing 400044, PR China. Electronic address:

Trypsin is a kind of protease for digestion and food processing, whose activity can be inhibited by phenolic acids in plant foods. However, most reports explained the inhibitory difference of phenolic acids based on the number and position of substituent groups, which failed to reveal the comprehensive inhibitory mechanism. In this work, the inhibitory effects of 11 common phenolic acids on trypsin were investigated. Amongst the tested cinnamic and benzoic acid derivatives, caffeic acid and gallic acid showed the strongest anti-trypsin activity with a noncompetitive inhibition pattern, respectively. The fluorescence analysis displayed that both the quenching rate constant (K) and binding constant (K) of caffeic acid were higher than those of gallic acid. Molecular docking illustrated their different binding modes with trypsin. The ONIOM calculations revealed that the binding capacity of caffeic acid was higher than that of gallic acid, which could explain their difference in their inhibitory behaviors.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.foodchem.2017.01.126DOI Listing
August 2017

Ejection-ionization of molecules from free standing graphene.

J Chem Phys 2017 Feb;146(8):084308

Department of Chemistry, Texas A&M University, College Station, Texas 77843-3144, USA.

We present the first data on emission of C60- stimulated by single impacts of 50 keV C602+ on the self-assembled molecular layer of C deposited on free standing 2 layer graphene. The yield, Y, of C60- emitted in the transmission direction is 1.7%. To characterize the ejection and ionization of molecules, we have measured the emission of C60- from the surface of bulk C (Y = 3.7%) and from a single layer of C deposited on bulk pyrolytic graphite (Y = 3.3%). To gain insight into the mechanism(s) of ejection, molecular dynamic simulations were performed. The scenario of the energy deposition and ejection of molecules is different for the case of graphene due to the confined volume of projectile-analyte interaction. In the case of 50 keV C602+ impacts on graphene plus C, the C atoms of the projectile collide with those of the target. The knocked-on atoms take on a part of the kinetic energy of the projectile atoms. Another part of the kinetic energy is deposited into the rim around the impact site. The ejection of molecules from the rim is a result of collective movement of the molecules and graphene membrane, where the membrane movement provides the impulse for ejection. The efficient emission of the intact molecular ions implies an effective ionization probability of intact C. The proposed mechanism of ionization involves the tunneling of electrons from the vibrationally exited area around the hole to the ejecta.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1063/1.4976832DOI Listing
February 2017

The collision of a hypervelocity massive projectile with free-standing graphene: Investigation of secondary ion emission and projectile fragmentation.

J Chem Phys 2017 Feb;146(5):054305

Department of Chemistry, Texas A&M University, College Station, Texas 77843-3144, USA.

We present here the study of the individual hypervelocity massive projectiles (440-540 keV, 33-36 km/s Au cluster) impact on 1-layer free-standing graphene. The secondary ions were detected and recorded separately from each individual impact in the transmission direction using a time-of-flight mass spectrometer. We observed C ions emitted from graphene, the projectiles which penetrated the graphene, and the Au fragment ions in mass spectra. During the projectile-graphene interaction, the projectile loses ∼15% of its initial kinetic energy (∼0.18 keV/atom, 72 keV/projectile). The Au projectiles are neutralized when approaching the graphene and then partially ionized again via electron tunneling from the hot rims of the holes on graphene, obtaining positive and negative charges. The projectile reaches an internal energy of ∼450-500 eV (∼4400-4900 K) after the impact and then undergoes a ∼90-100 step fragmentation with the ejection of Au atoms in the experimental time range of ∼0.1 μs.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1063/1.4975171DOI Listing
February 2017

Antioxidant Activity and α-Glucosidase Inhibitory Activities of the Polycondensate of Catechin with Glyoxylic Acid.

PLoS One 2016 9;11(3):e0150412. Epub 2016 Mar 9.

School of Food Science, Henan Institute of Science and Technology, Xinxiang, 453003, China.

In order to investigate polymeric flavonoids, the polycondensate of catechin with glyoxylic acid (PCG) was prepared and its chemically antioxidant, cellular antioxidant (CAA) and α-glucosidase inhibitory activities were evaluated. The DPPH and ABTS radical scavenging activities and antiproliferative effect of PCG were lower than those of catechin, while PCG had higher CAA activity than catechin. In addition, PCG had very high α-glucosidase inhibitory activities (IC50 value, 2.59 μg/mL) in comparison to catechin (IC50 value, 239.27 μg/mL). Inhibition kinetics suggested that both PCG and catechin demonstrated a mixture of noncompetitive and anticompetitive inhibition. The enhanced CAA and α-glucosidase inhibitor activities of PCG could be due to catechin polymerization enhancing the binding capacity to the cellular membrane and enzymes.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0150412PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4784921PMC
August 2016

SIMS of transfer ribonucleic acid molecules encapsulated between free-standing graphene sheets.

Biointerphases 2016 Jun 1;11(2):02A324. Epub 2016 Jun 1.

Department of Chemistry, Texas A&M University, College Station, Texas 77843-3144.

In this study, the authors used cluster-secondary ion mass spectrometry method to investigate the preserved transfer ribonucleic acid (tRNA) encapsulated between two free-standing graphene sheets. Single impacts of 50 keV C60 (2+) projectiles generated the emission of tRNA fragment ions in the transmission direction for mass selection and detection in a time-of-flight mass spectrometer. Ribonucleic acid (RNA) is extremely unstable and prone to rapid enzymatic degradation by ribonucleases. Employing graphene to isolate RNA from the environment, the authors prevent the aforementioned process. Encapsulation was achieved by drop casting a solution of tRNA, prepared using deuterated water, onto one graphene sheet and covering it with another. The event-by-event bombardment/detection mode allowed us to use colocalization analysis method to characterize the tRNA and its immediate environment. The authors found that upon drying, tRNA agglomerated into nanostructures ∼60 nm in diameter via formation and subsequent drying of aqua cells. The tRNA nanoagglomerates had a density of ∼42 structures per μm(2) with coverage of ∼12% of the surface area. In addition, trace amounts of water remained mostly around the tRNA nanoagglomerates, probably in the form of hydration.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1116/1.4942879DOI Listing
June 2016

Single impacts of keV fullerene ions on free standing graphene: Emission of ions and electrons from confined volume.

J Chem Phys 2015 Oct;143(16):164302

Department of Chemistry, Texas A&M University, College Station, Texas 77843-3144, USA.

We present the first data from individual C60 impacting one to four layer graphene at 25 and 50 keV. Negative secondary ions and electrons emitted in transmission were recorded separately from each impact. The yields for C(n)(-) clusters are above 10% for n ≤ 4, they oscillate with electron affinities and decrease exponentially with n. The result can be explained with the aid of MD simulation as a post-collision process where sufficient vibrational energy is accumulated around the rim of the impact hole for sputtering of carbon clusters. The ionization probability can be estimated by comparing experimental yields of C(n)(-) with those of C(n)(0) from MD simulation, where it increases exponentially with n. The ionization probability can be approximated with ejecta from a thermally excited (3700 K) rim damped by cluster fragmentation and electron detachment. The experimental electron probability distributions are Poisson-like. On average, three electrons of thermal energies are emitted per impact. The thermal excitation model invoked for C(n)(-) emission can also explain the emission of electrons. The interaction of C60 with graphene is fundamentally different from impacts on 3D targets. A key characteristic is the high degree of ionization of the ejecta.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1063/1.4933310DOI Listing
October 2015