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101.
We demonstrate a novel technique for the generation of mode-locked pulses from a continuous-wave (cw) optical parametric oscillator (OPO). The technique is based on the deployment of a phase modulator in combination with an antiresonant ring interferometer internal to a cw OPO, simultaneously providing spectral broadening and phase-to-amplitude feedback modulation. The scheme is implemented in a doubly-resonant cw OPO based on MgO:sPPLT, configured in a standing-wave cavity and pumped at 532 nm. With the phase modulator activated and the cavity length synchronized, a stable train of 800 ps pulses is generated at a repetition rate of 160 MHz. Using single-pass second harmonic generation (SHG) of the OPO output, we observe a four times enhancement in SHG compared with cw operation, confirming the real achievement of energy concentration as a result of mode-locked operation. 相似文献
102.
Vivek Goel Tirtha Chatterjee Lindsay Bombalski Koray Yurekli Krzysztof Matyjaszewski Ramanan Krishnamoorti 《Journal of Polymer Science.Polymer Physics》2006,44(14):2014-2023
The melt state viscoelastic properties of styrene–acrylonitrile random copolymers grafted to silica nanoparticles and prepared by in situ atom transfer radical polymerization are examined. Linear dynamic oscillatory viscoelastic measurements indicate that nanocomposites with silica contents as low as 1.2 vol % exhibit solid‐like response. Steady shear results in considerable alteration to the mesoscale structure and results in the failure of the Cox‐Merz rule. Flow reversal studies confirm the elastic nature of the mesoscale structure and demonstrate that the relaxation of the flow altered structure is slow, non‐Brownian, and possibly cooperative. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2014–2023, 2006 相似文献
103.
Dr. Kavita Kumar Dr. Laetitia Dubau Dr. Michel Mermoux Dr. Jingkun Li Dr. Andrea Zitolo Dr. Jaysen Nelayah Dr. Frédéric Jaouen Dr. Frédéric Maillard 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(8):3261-3269
Fe-N-C catalysts containing atomic FeNx sites are promising candidates as precious-metal-free catalysts for oxygen reduction reaction (ORR) in proton exchange membrane fuel cells. The durability of Fe-N-C catalysts in fuel cells has been extensively studied using accelerated stress tests (AST). Herein we reveal stronger degradation of the Fe-N-C structure and four-times higher ORR activity loss when performing load cycling AST in O2- vs. Ar-saturated pH 1 electrolyte. Raman spectroscopy results show carbon corrosion after AST in O2, even when cycling at low potentials, while no corrosion occurred after any load cycling AST in Ar. The load-cycling AST in O2 leads to loss of a significant fraction of FeNx sites, as shown by energy dispersive X-ray spectroscopy analyses, and to the formation of Fe oxides. The results support that the unexpected carbon corrosion occurring at such low potential in the presence of O2 is due to reactive oxygen species produced between H2O2 and Fe sites via Fenton reactions. 相似文献
104.
A new series of synthesis of 2-tert-butylimino-3-hepta-O-benzoyl-β-D-lactosylimino-4-S-benzyl-6-arylimino-2,3-dihydro-1,3,5-thiadiazines (hydrochloride) were synthesized by the interaction of 1-aryl-5-hepta-O-benzoyl-β-D-lactosyl-2-S-benzyl-2,4-isodithiobiurets with tert-butyl isocyanodichloride. The identities of these newly synthesized N-lactosides have been established on the basis of usual chemical transformations and infrared, 1H NMR, and mass spectral analysis.
[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.] 相似文献
105.
Investigating structural aspects to understand the putative/claimed non‐toxicity of the Hg‐based Ayurvedic drug Rasasindura using XAFS 下载免费PDF全文
Nitya Ramanan Debdutta Lahiri Parasmani Rajput Ramesh Chandra Varma A. Arun T. S. Muraleedharan K. K. Pandey Nandita Maiti S. N. Jha Surinder M. Sharma 《Journal of synchrotron radiation》2015,22(5):1233-1241
XANES‐ and EXAFS‐based analysis of the Ayurvedic Hg‐based nano‐drug Rasasindura has been performed to seek evidence of its non‐toxicity. Rasasindura is determined to be composed of single‐phase α‐HgS nanoparticles (size ~24 nm), free of Hg0 or organic molecules; its structure is determined to be robust (<3% defects). The non‐existence of Hg0 implies the absence of Hg‐based toxicity and establishes that chemical form, rather than content of heavy metals, is the correct parameter for evaluating the toxicity in these drugs. The stable α‐HgS form (strong Hg—S covalent bond and robust particle character) ensures the integrity of the drug during delivery and prevention of its reduction to Hg0 within the human body. Further, these comparative studies establish that structural parameters (size dispersion, coordination configuration) are better controlled in Rasasindura. This places the Ayurvedic synthesis method on par with contemporary techniques of nanoparticle synthesis. 相似文献
106.
Aromatic carboxylic acids bound to Amberlyst A-26 react with α-acetobromoglucose to form 2,3,4,6-tetra-O-acetyl-1-0-aroyl-β-D-glucopy ranose derivatives in good yield. Glucosylation occurs satisfactorily with carboxylic acids and nitrophenols (pKa 7–4), but not with phenols whose pKa values are higher (pka ~ 10). Selective glucosylation at the carboxylic group is easily achieved in the case of phenolic acids. 相似文献
107.
Synthesis of an amino acid analog. N-α-Fmoc-N-ε-tetrabutyl ester EDTA-L-Lysine, suitable for incorporating a strong metal binding site at any internal sequence position in a peptide is described. To overcome the solubility and purification problems during the synthesis, we prepared esters of N-α-Fmoc-N-ε-Boc-L-Lysine. Since the t- butyl group on the amino acid is acid labile and Fmoc group at α-amino group is base sensitive, protection of N-α-Fmoc-N-ε-Boc-L-Lysine requires an ester that can be prepared and removed under neutral conditions. A scheme for selective protection and deprotection of lysine is reported. 相似文献
108.
Kattesh V. Katti Raghuraman Kannan Kavita K. Katti Nagavarakishore Pillarsetty Charles L. Barnes 《Phosphorus, sulfur, and silicon and the related elements》2013,188(6-7):1587-1589
Unnatural or modified amino acids have become important biochemical vectors because of their potential utility in diagnostic or therapeutic medicine. Our ongoing research in hydroxymethyl phosphine chemistry has provided unique reaction pathways to produce unnatural aminoacid. The reaction of tris(hydroxymethyl)phosphine (THP) with chiral aminoacid L-alanine produced trimeric alanine in excellent yields. The X-ray crystal structure of 1 shows an unusual layered structure with water molecules sandwiched between the layers. Implications of this new chemistry in such emerging areas as chiral technology and drug discovery will be presented. 相似文献
109.
Thijs Stuyver Rajeev Ramanan Dibyendu Mallick Sason Shaik 《Angewandte Chemie (International ed. in English)》2020,59(20):7915-7920
This contribution follows the recent remarkable catalysis observed by Groves et al. in hydrogen‐abstraction reactions by a) an oxoferryl porphyrin radical‐cation complex [Por?+FeIV(O)Lax] and b) a hydroxoiron porphyrazine ferric complex [PyPzFeIII(OH)Lax], both of which involve positively charged substituents on the outer circumference of the respective macrocyclic ligands. These charge‐coronated complexes are analogues of the biologically important Compound I (Cpd I) and synthetic hydroxoferric species, respectively. We demonstrate that the observed enhancement of the H‐abstraction catalysis for these systems is a purely electrostatic effect, elicited by the local charges embedded on the peripheries of the respective macrocyclic ligands. Our findings provide new insights into how electrostatics can be employed to tune the catalytic activity of metalloenzymes and can thus contribute to the future design of new and highly efficient hydrogen‐abstraction catalysts. 相似文献
110.
Kavita Poonia Sunita Maanju Pratibha Chaudhary R. V. Singh 《Transition Metal Chemistry》2007,32(2):204-208
Synthesis and characterization of titanium(IV) and zirconium(IV) complexes of the types Cp2M(Cl)(HPO), Cp2M(HPO)2, Cp2M(O∩N∩O) and Cp2M(O∩N∩S) (where M represents titanium or zirconium and HPO, O∩N∩O and O∩N∩S represent the donor sets of the ligands) have been reported. These new derivatives have been prepared by the reactions of
titanocene dichloride or zirconocene dichloride with 2-hydroxy-N-phenyl benzamide(HPOH), 1-[(2-hydroxyphenyl)-1-N-phenylamino]hydrazine-carboxamide
(HO∩N∩OH) and 2-hydroxy-N-phenyl benzamide benzothiazoline (HO∩N∩SH) in different molar ratios. The ligands and their complexes have been characterized by the elemental analyses, conductance
measurement, molecular weight determinations and spectral studies. On the basis of electronic, I.r., 1H.-n.m.r. and 13C.-n.m.r. spectral studies, trigonal bipyramidal and octahedral geometries have been proposed for the resulting complexes.
All the ligands and their complexes have been screened for their biological activity on several pathogenic fungi and bacteria
and were found positive in this respect. 相似文献