Publications by authors named "Jianmin Shi"

26 Publications

  • Page 1 of 1

Foliar nutrient-allocation patterns in Banksia attenuata and Banksia sessilis differing in growth rate and adaptation to low-phosphorus habitats.

Ann Bot 2021 Feb 3. Epub 2021 Feb 3.

School of Biological Sciences, and Institute of Agriculture, The University of Western Australia, Perth, WA, Australia.

Background And Aims: Phosphorus (P) and nitrogen (N) are essential nutrients that frequently limit primary productivity in terrestrial ecosystems. Efficient use of these nutrients is important for plants growing in nutrient-poor environments. Plants generally reduce foliar P concentration in response to low soil P availability. We aimed to assess ecophysiological mechanisms and adaptive strategies for efficient use of P in Banksia attenuata (Proteaceae), naturally occurring on deep sand, and B. sessilis, occurring on shallow sand over laterite or limestone, by comparing allocation of P among foliar P fractions.

Methods: We carried out pot experiments with slow-growing B. attenuata, which resprouts after fire, and faster-growing opportunistic B. sessilis, which is killed by fire, on substrates with different P availability using a randomised complete block design. We measured leaf P and N concentrations, photosynthesis, leaf mass per area, relative growth rate, and P allocated to major biochemical fractions in B. attenuata and B. sessilis.

Key Results: The two species had similarly low foliar total P concentrations, but distinct patterns of P allocation to P-containing fractions. The foliar total N concentration of B. sessilis was greater than that of B. attenuata on all substrates. The foliar total P and N concentrations in both species decreased with decreasing P availability. The relative growth rate of both species was positively correlated with concentrations of both foliar nucleic acid P and total N, but there was no correlation with other P fractions. Faster-growing B. sessilis allocated more P to nucleic acids than B. attenuata did, but other fractions were similar.

Conclusions: The nutrient-allocation patterns in faster-growing opportunistic B. sessilis and slower-growing B. attenuata revealed different strategies in response to soil P availability which matched their contrasting growth strategy.
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http://dx.doi.org/10.1093/aob/mcab013DOI Listing
February 2021

Plasma Membrane Blebbing Dynamics Involved in the Reversibly Perforated Cell by Ultrasound-Driven Microbubbles.

Ultrasound Med Biol 2021 Mar 24;47(3):733-750. Epub 2020 Dec 24.

Department of Instrument Science and Engineering, Shanghai Jiao Tong University, Shanghai, China. Electronic address:

The perforation of plasma membrane by ultrasound-driven microbubbles (i.e., sonoporation) provides a temporary window for transporting macromolecules into the cytoplasm that is promising with respect to drug delivery and gene therapy. To improve the efficacy of delivery while ensuring biosafety, membrane resealing and cell recovery are required to help sonoporated cells defy membrane injury and regain their normal function. Blebs are found to accompany the recovery of sonoporated cells. However, the spatiotemporal characteristics of blebs and the underlying mechanisms remain unclear. With a customized platform for ultrasound exposure and 2-D/3-D live single-cell imaging, localized membrane perforation was induced with ultrasound-driven microbubbles, and the cellular responses were monitored using multiple fluorescent probes. The results indicated that localized blebs undergoing four phases (nucleation, expansion, pausing and retraction) on a time scale of tens of seconds to minutes were specifically involved in the reversibly sonoporated cells. The blebs spatially correlated with the membrane perforation site and temporally lagged (about tens of seconds to minutes) the resealing of perforated membrane. Their diameter (about several microns) and lifetime (about tens of seconds to minutes) positively correlated with the degree of sonoporation. Further studies revealed that intracellular calcium transients might be an upstream signal for triggering blebbing nucleation; exocytotic lysosomes not only contributed to resealing of the perforated membrane, but also to the increasing bleb volume during expansion; and actin components accumulation facilitated bleb retraction. These results provide new insight into the short-term strategies that the sonoporated cell employs to recover on membrane perforation and to remodel membrane structure and a biophysical foundation for sonoporation-based therapy.
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http://dx.doi.org/10.1016/j.ultrasmedbio.2020.11.029DOI Listing
March 2021

Fast photothermal poly(NIPAM-co-β-cyclodextrin) supramolecular hydrogel with self-healing through host-guest interaction for intelligent light-controlled switches.

Soft Matter 2020 Dec 20;16(46):10558-10566. Epub 2020 Oct 20.

State Key Laboratory of Chemical Engineering, College of Chemical and Biological Engineering, Zhejiang University, Hangzhou 310027, China.

A graphene oxide/poly(N-isopropylacrylamide-co-β-cyclodextrin) (GO/poly(NIPAM-co-β-CD)) hydrogel has been synthesized through host-guest interaction between β-cyclodextrin (β-CD) and the isopropyl group of N-isopropylacrylamide (NIPAM). The product exhibits rapid responses to the stimuli of temperature and near-infrared (NIR) irradiation, self-healing properties, and excellent mechanical properties. The host-guest interaction serves as the main physical cross-linker, while a hydrogen bond between the hydroxyl group of β-CD, GO sheets and amide group of NIPAM acts as a secondary cross-linker. The volume phase transition temperature and NIR response rate of such a hydrogel are controlled by its contents of β-CD and GO. The obtained hydrogels showing excellent properties might be applied in remote contactless control devices in advanced smart technologies. Based on the excellent characteristics of the hydrogels, remote light-controlled switches have been designed, and more applications will be explored, such as intelligent light-controlled drivers and soft robots.
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http://dx.doi.org/10.1039/d0sm01501fDOI Listing
December 2020

Do cluster roots of red alder play a role in nutrient acquisition from bedrock?

Proc Natl Acad Sci U S A 2019 06 4;116(24):11575-11576. Epub 2019 Jun 4.

College of Forestry, Jiangxi Agricultural University, Nanchang 330045, People's Republic of China.

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http://dx.doi.org/10.1073/pnas.1905336116DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6575300PMC
June 2019

Manipulating triplet states: tuning energies, absorption, lifetimes, and annihilation rates in anthanthrene derivatives.

Phys Chem Chem Phys 2018 Nov;20(45):28412-28418

Air Force Research Laboratory, Materials and Manufacturing Directorate, Functional Materials Division, Wright-Patterson AFB, Ohio 45433-7750, USA.

The photophysical properties of anthanthrene, four anthanthrene derivatives containing varying phenyl and p-tBu-phenyl substituents, and two anthanthrones with phenyl and p-tBu-phenyl substituents are examined. In general, as the anthanthrenes and anthanthrones become more substituted, red-shifts are observed in the peak maxima of the ground- and excited-state absorption and fluorescence spectra. The anthanthrones have large (>0.8) intersystem crossing (ISC) quantum yields (ΦT) likely caused by nπ* character in the ground or excited states. A bromo-substituted anthanthrene has a unity ISC yield due to an ISC rate constant of 2.5 × 1010 s-1 caused by heavy-atom induced, spin-orbit coupling. This leads to low fluorescence quantum yields (ΦF) in these three derivatives. The parent anthanthrene and remaining derivatives behave much differently. All have ΦF values from 0.58-0.84 with lower ΦT values as radiative decay outcompetes ISC. The anthanthrones have remarkable excited-state absorption with strong, broad transitions across the visible region with weaker transitions extending to nearly two μm. The anthanthrenes have very similar-shaped, broad transitions in the visible which can be shifted ∼60 nm by controlling the substituents. The triplet lifetimes range from 31-1200 μs and increase as the ISC yields decrease; the bromo-substituted anthanthrene is the shortest, followed by the anthanthrones then the other anthanthrenes. The rate of triplet-triplet annihilation is also affected by the presence of substituents; as the amount of steric bulk is increased, the rate of annihilation decreases.
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http://dx.doi.org/10.1039/c8cp06048gDOI Listing
November 2018

Unusual expansion of CD3+CD56+ natural killer T-like cells in peripheral blood after anticytokine treatment for graft-versus-host disease: A case report.

Medicine (Baltimore) 2018 Sep;97(38):e12429

Bone Marrow Transplantation Center, The First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou Department of Hematology, Ningbo First Hospital, Ningbo, Zhejiang Province, China.

Rationale: Basiliximab and etanercept have achieved promising responses in steroid-refractory graft versus host disease (SR-GVHD). However, the in vivo immune changes following the treatment have not been elucidated.

Patient Concerns: A 14-year-old boy presented with skin rash and diarrhea 20 days after haploidentical hemotopoietic stem cell transplantation.

Diagnoses: We made the diagnose of grade 3 acute GVHD with skin and gastrointestinal involvement.

Interventions: After the failure of the first-line treatment with methylprednisolone, combined anti-cytokine therapies with basiliximab and etanercept were prescibed.

Outcomes: He achieved complete remission by basiliximab and etanercept. Furthermore, we detected that donor CD3CD56 Natural killer T(NKT)-like cells expanded gradually after the period of lymphocytopenia caused by GVHD and anti-cytokine therapy. The expansion of NKT-like cells was in association with high serum IFN-γ. NKT-like cells showed preferred proliferation in response to IFN-γ and potent cytotoxicity against leukemia cells. The expansion persisted > 2 years and the patient had a leukemia-free survival of 66 months.

Lessons: Our case indicated that combined anti-cytokine treatment may reset the immune system and cause NKT-like cells to exhibit a predilection for expansion.
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http://dx.doi.org/10.1097/MD.0000000000012429DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6160206PMC
September 2018

Atomic Layer Deposition of Nickel Carbide from a Nickel Amidinate Precursor and Hydrogen Plasma.

ACS Appl Mater Interfaces 2018 Mar 23;10(9):8384-8390. Epub 2018 Feb 23.

School of Advanced Materials, Shenzhen Graduate School , Peking University , Shenzhen 518055 , China.

A new atomic layer deposition (ALD) process for depositing nickel carbide (NiC ) thin films is reported, using bis( N, N'-di- tert-butylacetamidinato)nickel(II) and H plasma. The process shows a good layer-by-layer film growth behavior with a saturated film growth rate of 0.039 nm/cycle for a fairly wide process temperature window from 75 to 250 °C. Comprehensive material characterizations are performed on the NiC films deposited at 95 °C with various H plasma pulse lengths from 5 to 12 s, and no appreciable difference is found with the change of the plasma pulse length. The deposited NiC films are fairly pure, smooth, and conductive, and the x in the nominal formula of NiC is approximately 0.7. The ALD NiC films are polycrystalline with a rhombohedral NiC crystal structure, and the films are free of nanocrystalline graphite or amorphous carbon. Last, we demonstrate that, by using this ALD process, highly uniform NiC films can be conformally deposited into deep narrow trenches with an aspect ratio as high as 20:1, which thereby highlights the broad and promising applicability of this process for conformal NiC film coatings on complex high-aspect-ratio 3D architectures in general.
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http://dx.doi.org/10.1021/acsami.8b00388DOI Listing
March 2018

The response of nucleus pulposus cell senescence to static and dynamic compressions in a disc organ culture.

Biosci Rep 2018 04 9;38(2). Epub 2018 Mar 9.

Department of Orthopaedics, Yantai Yeda Hospital, Yantai 264006, Shandong, China

Mechanical stimuli obviously affect disc nucleus pulposus (NP) biology. Previous studies have indicated that static compression exhibits detrimental effects on disc biology compared with dynamic compression. To study disc NP cell senescence under static compression and dynamic compression in a disc organ culture, porcine discs were cultured and subjected to compression (static compression: 0.4 MPa for 4 h once per day; dynamic compression: 0.4 MPa at a frequency of 1.0 Hz for 4 h once per day) for 7 days using a self-developed mechanically active bioreactor. The non-compressed discs were used as controls. Compared with the dynamic compression, static compression significantly promoted disc NP cell senescence, reflected by the increased senescence-associated β-galactosidase (SA-β-Gal) activity, senescence-associated heterochromatic foci (SAHF) formation and senescence markers expression, and the decreased telomerase (TE) activity and NP matrix biosynthesis. Static compression accelerates disc NP cell senescence compared with the dynamic compression in a disc organ culture. The present study provides that acceleration of NP cell senescence may be involved in previously reported static compression-mediated disc NP degenerative changes.
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http://dx.doi.org/10.1042/BSR20180064DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5843747PMC
April 2018

Static compression down-regulates N-cadherin expression and facilitates loss of cell phenotype of nucleus pulposus cells in a disc perfusion culture.

Biosci Rep 2018 02 8;38(1). Epub 2018 Feb 8.

Department of Orthopedic Surgery, No. 89 Hospital of PLA, Weifang, Shandong 261026, China

Mechanical compression often induces degenerative changes of disc nucleus pulposus (NP) tissue. It has been indicated that N-cadherin (N-CDH)-mediated signaling helps to preserve the NP cell phenotype. However, N-CDH expression and the resulting NP-specific phenotype alteration under the static compression and dynamic compression remain unclear. To study the effects of static compression and dynamic compression on N-CDH expression and NP-specific phenotype in an disc organ culture. Porcine discs were organ cultured in a self-developed mechanically active bioreactor for 7 days and subjected to static or dynamic compression (0.4 MPa for 2 h once per day). The noncompressed discs were used as controls. Compared with the dynamic compression, static compression significantly down-regulated the expression of N-CDH and NP-specific markers (laminin, brachyury, and keratin 19); decreased the Alcian Blue staining intensity, glycosaminoglycan and hydroxyproline contents; and declined the matrix macromolecule (aggrecan and collagen II) expression. Compared with the dynamic compression, static compression causes N-CDH down-regulation, loss of NP-specific phenotype, and the resulting decrease in NP matrix synthesis.
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http://dx.doi.org/10.1042/BSR20171551DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5803491PMC
February 2018

Divergent regeneration-competent cells adopt a common mechanism for callus initiation in angiosperms.

Regeneration (Oxf) 2017 06 27;4(3):132-139. Epub 2017 Aug 27.

National Key Laboratory of Plant Molecular Genetics CAS Center for Excellence in Molecular Plant Sciences Institute of Plant Physiology and Ecology Shanghai Institutes for Biological Sciences Chinese Academy of Sciences 300 Fenglin Road Shanghai 200032 China.

In tissue culture, the formation of callus from detached explants is a key step in plant regeneration; however, the regenerative abilities in different species are variable. While nearly all parts of organs of the dicot are ready for callus formation, mature regions of organs in monocot rice () and other cereals are extremely unresponsive to tissue culture. Whether there is a common molecular mechanism beyond these different regenerative phenomena is unclear. Here we show that the and rice use different regeneration-competent cells to initiate callus, whereas the cells all adopt () and during cell fate transition. Different from which maintains regeneration-competent cells in mature organs, rice exhausts those cells during organ maturation, resulting in regenerative inability in mature organs. Our study not only explains this old perplexity in agricultural biotechnology, but also provides common molecular markers for tissue culture of different angiosperm species.
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http://dx.doi.org/10.1002/reg2.82DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5617900PMC
June 2017

Model for the role of auxin polar transport in patterning of the leaf adaxial-abaxial axis.

Plant J 2017 Nov 26;92(3):469-480. Epub 2017 Sep 26.

National Laboratory of Plant Molecular Genetics, Shanghai Institute of Plant Physiology and Ecology, Chinese Academy of Sciences, 300 Fenglin Road, Shanghai, 200032, China.

Leaf adaxial-abaxial polarity refers to the two leaf faces, which have different types of cells performing distinct biological functions. In 1951, Ian Sussex reported that when an incipient leaf primordium was surgically isolated by an incision across the vegetative shoot apical meristem (SAM), a radialized structure without an adaxial domain would form. This led to the proposal that a signal, now called the Sussex signal, is transported from the SAM to emerging primordia to direct leaf adaxial-abaxial patterning. It was recently proposed that instead of the Sussex signal, polar transport of the plant hormone auxin is critical in leaf polarity formation. However, how auxin polar transport functions in the process is unknown. Through live imaging, we established a profile of auxin polar transport in and around young leaf primordia. Here we show that auxin polar transport in lateral regions of an incipient primordium forms auxin convergence points. We demonstrated that blocking auxin polar transport in the lateral regions of the incipient primordium by incisions abolished the auxin convergence points and caused abaxialized leaves to form. The lateral incisions also blocked the formation of leaf middle domain and margins and disrupted expression of the middle domain/margin-associated marker gene WUSCHEL-RELATED HOMEOBOX 1 (SlWOX1). Based on these results we propose that the auxin convergence points are required for the formation of leaf middle domain and margins, and the functional middle domain and margins ensure leaf adaxial-abaxial polarity. How middle domain and margins function in the process is discussed.
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http://dx.doi.org/10.1111/tpj.13670DOI Listing
November 2017

Photodriven Oxygen Removal via Chromophore-Mediated Singlet Oxygen Sensitization and Chemical Capture.

Inorg Chem 2017 Aug 11;56(15):9273-9280. Epub 2017 Jul 11.

U.S. Army Research Laboratory , 2800 Powder Mill Road, Adelphi, Maryland 20783-1138, United States.

We report a general, photochemical method for the rapid deoxygenation of organic solvents and aqueous solutions via visible light excitation of transition metal chromophores (TMCs) in the presence of singlet oxygen scavenging substrates. Either 2,5-dimethylfuran or an amino acid (histidine or tryptophan methyl ester) was used as the substrate in conjunction with an iridium or ruthenium TMC in toluene, acetonitrile, or water. This behavior is described for solutions with chromophore concentrations that are pertinent for both luminescence and transient absorption spectroscopies. These results consistently produce TMC lifetimes comparable to those measured using traditional inert gas sparging and freeze-pump-thaw techniques. This method has the added benefits of providing long-term stability (days to months); economical preparation due to use of inexpensive, commercially available oxygen scrubbing substrates; and negligible size and weight footprints compared to traditional methods. Furthermore, attainment of dissolved [O] < 50 μM makes this method relevant to any solution application requiring low dissolved oxygen concentration in solution, provided that the oxygenated substrate does not interfere with the intended chemical process.
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http://dx.doi.org/10.1021/acs.inorgchem.7b01226DOI Listing
August 2017

Exogenous melatonin reduces somatic cell count of milk in Holstein cows.

Sci Rep 2017 02 27;7:43280. Epub 2017 Feb 27.

National Engineering Laboratory for Animal Breeding, Key Laboratory of Animal Genetics and Breeding of the Ministry of Agriculture, Beijing Key Laboratory for Animal Genetic Improvement, College of Animal Science and Technology, China Agricultural University, Beijing, China.

High somatic cell counts in milk caused by mastitis significantly influence the quality of milk and result in substantial annual economic loss. This study evaluated the beneficial effects of melatonin (MT) on milk somatic cell count (SCC) in cows. To examine the effects of melatonin on SCC, one hundred twenty cows were divided into four groups based on milk SCC. In each group, half of the cows were treated with melatonin (S.C.). Melatonin treatment significantly reduced milk SCC. To explore the potential mechanism, 20 cows with relatively high SCC were selected to evaluate the biochemical and immunological profiles of their blood after melatonin treatment. Treatment with MT significantly reduced SCC in milk, lowered serum cortisol concentrations and increased the levels of albumin, alanine transaminase and lactate dehydrogenase. Following treatment with MT, the concentration of IgG and IgM rose transiently then decreased significantly, similar to changes observed for white blood cells and lymphocytes. In conclusion, MT treatment improved the quality of milk by reducing SCC. This may be due to melatonin improving immune activity in cows.
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http://dx.doi.org/10.1038/srep43280DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5327427PMC
February 2017

Nonlinear optical characterization of multinuclear iridium compounds containing tricycloquinazoline.

Appl Opt 2017 Jan;56(3):B179-B183

Nonlinear optical properties were characterized for a series of multinuclear iridium compounds of the form TCQ[IrIII(ppz)2]n, where n=1, 2, or 3, TCQ is tricycloquinazoline, and ppz is 1-phenylpyrazole. Transient absorption (TA) spectroscopy indicated that the triplet metal-to-ligand charge transfer excited state was formed on a subpicosecond time scale and decayed back to the ground state on a microsecond time scale, consistent with precedents in the literature. TA bands were observed for all three compounds from 475 to 900 nm, implying the potential for reverse-saturable absorption (RSA) at those wavelengths. Z-scan measurements using picosecond and nanosecond pulses were obtained at 532 nm and confirmed the presence of RSA behavior for all three compounds. The triplet excited state cross sections and the RSA figure of merit were found to decrease with increasing n:1>2∼3.
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http://dx.doi.org/10.1364/AO.56.00B179DOI Listing
January 2017

Melatonin and its receptor MT1 are involved in the downstream reaction to luteinizing hormone and participate in the regulation of luteinization in different species.

J Pineal Res 2016 Oct 1;61(3):279-90. Epub 2016 Jul 1.

National Engineering Laboratory for Animal Breeding, Key Laboratory of Animal Genetics and Breeding of the Ministry of Agriculture, Beijing Key Laboratory for Animal Genetic Improvement, College of Animal Science and Technology, China Agricultural University, Beijing, China.

The functions of melatonin in preovulatory fluid remain elusive. In the current study, we observed that the extremely high level of expression of MT1 in mice granulosa cells was rapidly induced by hCG (equivalent LH) within 2 hours and this was referred as MT1 surge. In cumulus cells, serotonin N-acetyltransferase (SNAT) was also upregulated by hCG and led to elevated melatonin levels in ovarian follicle fluid. Melatonin application before MT1 surge significantly promoted embryo implantation, and this was probably attributed to a rise in progesterone levels in the serum. The mechanistic studies indicated that melatonin/MT1 (MLT/MT1) signaling remarkably improved the expression of corpus luteum marker genes, that is, Akr1c18 and Cyp11a1. High-throughput sequencing results suggested that extracellular matrix (ECM) receptor interaction, focal adhesion, and activation of PI3K/Akt pathway which are involved in granulosa cell luteinization might mediate the actions of MLT/MT1 signal. In addition, this effect on luteinization was compared in different species. It was verified that high melatonin levels exist in serum at estrum of cows and help to improve the first estrus fecundation rate. These results suggested that both melatonin and MT1 are involved in the downstream reaction of hCG (LH) and they play important roles in luteinization. These findings provide the novel information on the physiology of melatonin in animal reproduction.
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http://dx.doi.org/10.1111/jpi.12345DOI Listing
October 2016

Germostatin resistance locus 1 encodes a PHD finger protein involved in auxin-mediated seed dormancy and germination.

Plant J 2016 Jan;85(1):3-15

Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 300 Fenglin Road, 200032, Shanghai, China.

Seed dormancy and germination are important physiological processes during the life cycle of a seed plant. Recently, auxin has been characterized as a positive regulator that functions during seed dormancy and as a negative regulator during germination. Through chemical genetic screenings, we have identified a small molecule, germostatin (GS), which effectively inhibits seed germination in Arabidopsis. GSR1 (germostatin resistance locus 1) encodes a tandem plant homeodomain (PHD) finger protein, identified by screening GS-resistant mutants. Certain PHD fingers of GSR1 are capable of binding unmethylated H3K4, which has been reported as an epigenetic mark of gene transcriptional repression. Biochemical studies show that GSR1 physically interacts with the transcriptional repressor ARF16 and attenuates the intensity of interaction of IAA17/ARF16 by directly interacting with IAA17 to release ARF16. Further results show that axr3-1, arf10 arf16 are hyposensitive to GS, and gsr1 not only resists auxin-mediated inhibition of seed germination but also displays decreased dormancy. We therefore propose that GSR1 may form a co-repressor with ARF16 to regulate seed germination. Besides promoting auxin biosynthesis via upregulating expression of YUCCA1, GS also enhances auxin responses by inducing degradation of DΙΙ-VENUS and upregulating expression of DR5-GFP. In summary, we identified GSR1 as a member of the auxin-mediated seed germination genetic network, and GS, a small non-auxin molecule that specifically acts on auxin-mediated seed germination.
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http://dx.doi.org/10.1111/tpj.13086DOI Listing
January 2016

Oxidation kinetics of nitrogen doped TiO(2-δ) thin films.

Phys Chem Chem Phys 2012 Oct;14(37):12930-7

Institut für Physikalische und Theoretische Chemie, Technische Universität Braunschweig, Hans-Sommer-Str. 10, D-38106 Braunschweig, Germany.

The oxidation kinetics of nitrogen doped, oxygen deficient titanium dioxide thin films has been studied in atmospheres of pure oxygen or nitrogen at 500 °C, 550 °C, and 600 °C, respectively, by means of in situ optical spectroscopy. The thin films show high electronic absorbance in the visible and NIR region, accompanied by a red shift of the absorption edge of about 0.4 eV, e.g., from about 2.9 to 2.5 eV at 600 °C. The time dependent decrease of absorbance due to oxidation is found to follow a parabolic rate law. An activation energy of about 1.96 eV can be obtained from the temperature dependence of the parabolic oxidation rate constant. In the framework of a microscopic oxidation model, this energy barrier is attributed to the diffusion of titanium interstitials in the re-oxidized part of the thin films as a rate-determining process. In addition, an attempt is made to evaluate the kinetics of nitrogen release from the time dependent blue shift of the absorption edge during re-oxidation.
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http://dx.doi.org/10.1039/c2cp42559aDOI Listing
October 2012

Defect chemistry, redox kinetics, and chemical diffusion of lithium deficient lithium niobate.

Phys Chem Chem Phys 2011 Apr 23;13(15):6925-30. Epub 2011 Feb 23.

Institute of Physical and Theoretical Chemistry, Technische Universität Braunschweig, Hans-Sommer-Str. 10, 38106 Braunschweig, Germany.

High-temperature optical in situ spectroscopy was used to investigate the defect absorption, redox kinetics, and chemical diffusion of a lithium deficient (48.4 mol% Li(2)O) congruent melting lithium niobate single crystal (c-LN). Under reducing atmospheres of various oxygen activities, a(O(2)), UV-Vis-NIR spectra measured at 1000 °C are dominated by an absorption band due to free small polarons centered at about 0.93 eV. The polaron band intensity was found to follow a power law of the form a(O(2))(m) with m = -1/4. A chemical reduction model involving electrons localized on niobium ions on regular lattice sites can explain the observed defect absorption and its dependence on oxygen activity. The kinetics of reduction and oxidation processes upon oxygen activity jumps and the associated chemical diffusion coefficients are found in close agreement over a range from -0.70 to -14.70 in log a(O(2)), indicating a reversible redox process. Assuming coupled fluxes of lithium vacancies and free small polarons for the attainment of stoichiometry, the diffusion coefficients of lithium vacancies as well as of lithium ions in the lithium deficient c-LN have been determined at 1000 °C.
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http://dx.doi.org/10.1039/c0cp02703kDOI Listing
April 2011

Kinetics of cation distribution in cobalt-containing olivine, (Co0.6Mg0.4)2)SiO4.

Phys Chem Chem Phys 2008 Jul 21;10(26):3895-902. Epub 2008 May 21.

Institut für Physikalische und Theoretische Chemie, Technische Universität Braunschweig, Hans-Sommer-Str. 10, D-38106 Braunschweig, Germany.

In olivines, (A,B)(2)SiO(4), the A and B cations are distributed over two non-equivalent sites of octahedral coordination, M1 and M2. In the case of temperature dependent cation distributions, the kinetics of cation redistribution between these two sublattices can be studied by means of temperature-jump experiments. In situ experiments of this type are reported for a cobalt-containing olivine single crystal, (Co(0.6)Mg(0.4))(2)SiO(4). The relaxation experiments were performed by means of optical spectroscopy under in situ conditions in the temperature range between 480 and 690 degrees C yielding an activation energy of about 2.0 eV. The results are discussed in the framework of microscopic models of cation sublattice exchange. Implications for quench experiments are addressed.
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http://dx.doi.org/10.1039/b718182eDOI Listing
July 2008

Blue phosphorescence from mixed cyano-isocyanide cyclometalated iridium(III) complexes.

Inorg Chem 2007 Mar;46(5):1603-11

Army Research Laboratory, 2800 Powder Mill Road, Adelphi, Maryland 20783, USA.

The synthesis, structure, and photophysical and electrochemical properties of cyclometalated iridium complexes with ancillary cyano and isocyanide ligands are described. In the first synthetic step, cleavage of dichloro-bridged dimers [Ir(N=C)2(mu-Cl)]2 (N=C = 2-phenylpyridine, 2-(2-fluorophenyl)pyridine, and 2-(2,4-difluorophenyl)pyridine) by isocyanide ligands gave monomeric species of the types Ir(N=C)2(RNC)(Cl) (RNC = t-butyl isocyanide, 1,1,3,3-tetramethylbutyl isocyanide, 2-morpholinoethyl isocyanide, and 2,6-dimethylphenyl isocyanide). In turn, the chloride was replaced by cyanide giving Ir(N=C)2(RNC)(CN). The X-ray structures for two of the complexes show that the trans-pyridyl/cis-phenyl geometry of the parent dimer is preserved, with the ancillary ligands positioned trans to the cyclometalated phenyls. The cyano complexes all display strong blue photoluminescence in ambient, deoxygenated solutions with the first lambdamax ranging from 441 to 458 nm, quantum yields spanning 0.60 to 0.75, and luminescent lifetimes of 12.0-21.4 mus. A lack of solvatochromism and highly structured emission indicate that the lowest energy excited state is triplet ligand centered with some admixture of singlet metal-to-ligand charge-transfer character.
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http://dx.doi.org/10.1021/ic061513vDOI Listing
March 2007

Photophysical properties of anthanthrene-based tunable blue emitters.

J Phys Chem A 2005 Sep;109(34):7677-81

Center for Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio 43403, USA.

Anthanthrene (1) derivatives substituted at the 4,10 and 6,12 positions (2-6) were synthesized as promising candidates for organic light emitting diodes (OLEDs). The emission of these compounds can be manipulated in the blue region (lambda(max) = 437-467 nm) through structural modifications. Photophysical and electrochemical properties (phi(F) = 0.20-0.47; tau(F) = 2.97-6.06 ns; HOMO-LUMO energy gap = 2.25-2.56 eV) as well as geometry optimized structures of 1-6 are reported.
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http://dx.doi.org/10.1021/jp052337zDOI Listing
September 2005

Photophysical and electrochemical properties of heteroleptic tris-cyclometalated iridium(III) complexes.

Inorg Chem 2005 Jun;44(13):4445-7

Army Research Laboratory, 2800 Powder Mill Road, Adelphi, Maryland 20783, USA.

Mixed (difluoro)phenylpyridine/(difluoro)phenylpyrazole tris-cyclometalated iridium complexes were prepared in order to study the effect of fluorination and the pyridine/pyrazole ratio on the emission and electrochemical properties. Increasing fluorination and replacement of pyridine by pyrazole both leads to a widening of the HOMO-LUMO gap and generally leads to a blue shift in emission.
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http://dx.doi.org/10.1021/ic050324uDOI Listing
June 2005

Effect of time on bond strength in indirect bonding.

Angle Orthod 2004 Apr;74(2):245-50

Department of Orthodontics, College of Denistry, University of Hamburg, Germany.

The purpose of this in vitro investigation was to determine the influence of a reduced time interval before debonding on shear bond strength of stainless steel brackets bonded with a custom base indirect technique. A total of 135 bovine permanent mandibular incisors was randomly divided into nine groups of 15 specimens each. Three base composite-sealant combinations were investigated: (1) Phase II base composite, Custom I.Q. sealant, (2) Phase II base composite, Maximum Cure sealant, and (3) Transbond XT base composite, Sondhi Rapid Set sealant. Shear bond strength was measured for three different debonding time intervals: (1) time of transfer tray removal as recommended by the manufacturer, (2) 30 minutes after bonding of the sealant, and (3) 24 hours after bonding of the sealant. For groups bonded with Maximum Cure or Sondhi Rapid Set sealants, no influence of debonding time on shear bond strength was found. The Custom I.Q. sealant groups showed significantly lower bond strength measurements when debonded at the recommended tray removal time, and the Weibull analysis indicated a higher risk of bond failure at clinically relevant levels of stress. All base composite-sealant combinations showed acceptable bond strength at 30 minutes and 24 hours after bonding of the sealant.
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http://dx.doi.org/10.1043/0003-3219(2004)074<0245:EOTOBS>2.0.CO;2DOI Listing
April 2004

In vitro evaluation of a moisture-active adhesive for indirect bonding.

Angle Orthod 2003 Dec;73(6):697-701

Department of Orthodontics, College of Dentistry, University of Hamburg, Hamburg, Germany.

The aim of this in vitro investigation was to evaluate bond strength for a cyanoacrylate adhesive in combination with an indirect bonding technique. Eighty bovine permanent mandibular incisors were randomly divided into four groups of 20 teeth each. The influence of two factors on shear bond strength was investigated: (1) type of adhesive (Smartbond cyanoacrylate, Sondhi Rapid Set composite sealant) and (2) time of debonding (30 minutes and 24 hours after bonding). Stainless steel mesh-based brackets were used. Although, bond strength was not significantly different for the two debonding time periods, significantly lower bond strength measurements were found for the cyanoacrylate adhesive (P < .001). The mean bond strength for the cyanoacrylate adhesive group was 5.44 +/- 1.65 MPa for debonding 30 minutes and 6.92 +/- 1.48 MPa for debonding 24 hours after the bonding procedure vs 16.16 +/- 5.25 MPa and 14.98 +/- 2.85 MPa for the composite adhesive groups debonded at 30 minutes and 24 hours, respectively. The Weibull analysis indicated that there was an increased risk of bond failure at clinically relevant levels of stress for indirect bonding with the cyanoacrylate adhesive.
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http://dx.doi.org/10.1043/0003-3219(2003)073<0697:IVEOAM>2.0.CO;2DOI Listing
December 2003

In vitro investigation of indirect bonding with a hydrophilic primer.

Angle Orthod 2003 Aug;73(4):445-50

Department of Orthodontics, College of Dentistry, University of Hamburg, Germany.

The aim of this in vitro investigation was to evaluate bond strength for a custom base indirect bonding technique using a hydrophilic primer on moisture-contaminated tooth surfaces. Stainless steel brackets were bonded to 100 permanent bovine incisors using a light-cured custom base composite adhesive, a chemically cured sealant, and the hydrophilic primer Transbond MIP (3M-Unitek, Monrovia, Calif). Five groups (A-E) of 20 teeth each were formed according to the time of contamination (before or after application of the primer) and the type of contaminant (distilled water or saliva): A, control group with no contamination; B, contamination with saliva before application of the primer; C, contamination with water before application of the primer; D, contamination with saliva before and after application of the primer; and E, contamination with water before and after application of the primer. Mean bond strength for the group without contamination (A) was 15.07 +/- 4.14 MPa and was not significantly different from bond strengths for groups B (14.91 +/- 3.99 MPa) and C (16.12 +/- 3.67 MPa), in which contamination occurred before application of the hydrophilic primer. Average bond strength in group D was 11.92 +/- 4.76 MPa. The lowest mean bond strength was measured for group E (9.85 +/- 3.77 MPa) and was significantly lower than for groups A, B, and C. Contamination after primer application resulted in an increased risk of bond failure at clinically relevant levels of stress.
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http://dx.doi.org/10.1043/0003-3219(2003)073<0445:IVIOIB>2.0.CO;2DOI Listing
August 2003

Bond strength with custom base indirect bonding techniques.

Angle Orthod 2003 Apr;73(2):176-80

Department of Orthodontics, College of Dentistry, University of Hamburg, Hamburg, Germany.

Different types of adhesives for indirect bonding techniques have been introduced recently. But there is limited information regarding bond strength with these new materials. In this in vitro investigation, stainless steel brackets were bonded to 100 permanent bovine incisors using the Thomas technique, the modified Thomas technique, and light-cured direct bonding for a control group. The following five groups of 20 teeth each were formed: (1) modified Thomas technique with thermally cured base composite (Therma Cure) and chemically cured sealant (Maximum Cure), (2) Thomas technique with thermally cured base composite (Therma Cure) and chemically cured sealant (Custom I Q), (3) Thomas technique with light-cured base composite (Transbond XT) and chemically cured sealant (Sondhi Rapid Set), (4) modified Thomas technique with chemically cured base adhesive (Phase II) and chemically cured sealant (Maximum Cure), and (5) control group directly bonded with light-cured adhesive (Transbond XT). Mean bond strengths in groups 3, 4, and 5 were 14.99 +/- 2.85, 15.41 +/- 3.21, and 13.88 +/- 2.33 MPa, respectively, and these groups were not significantly different from each other. Groups 1 (mean bond strength 7.28 +/- 4.88 MPa) and 2 (mean bond strength 7.07 +/- 4.11 MPa) showed significantly lower bond strengths than groups 3, 4, and 5 and a higher probability of bond failure. Both the original (group 2) and the modified (group 1) Thomas technique were able to achieve bond strengths comparable to the light-cured direct bonded control group.
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http://dx.doi.org/10.1043/0003-3219(2003)73<176:BSWCBI>2.0.CO;2DOI Listing
April 2003