摘要:

Mendeleev Communications Electronic Version, Issue 4, 2001 (pp. 125.164) An unusual Bamford.Stevens reaction of 17-toluenesulfonylhydrazono- 3¥â-acetoxy-14¥á-hydroxyandrost-5-ene Vladimir A. Khripach,*a Vladimir N. Zhabinskii,a Anna I. Kotyatkina,a Galina P. Fando,a Alexander S. Lyakhov,a Alla A. Govorova,a Jaap van der Louw,b Marinus B. Groenb and Aede de Grootc a Institute of Bioorganic Chemistry, National Academy of Sciences of Belarus, 220141 Minsk, Belarus. Fax: +375 17 264 8647; e-mail: vz@ns.iboch.ac.by b Department of Medicinal Chemistry, N.V. Organon, P.O. Box 20, 5340 BH Oss, The Netherlands c Laboratory of Organic Chemistry and Research Centre, Wageningen University, 6703 HB Wageningen, The Netherlands 10.1070/MC2001v011n04ABEH001448 The Bamford.Stevens reaction of 17-toluenesulfonylhydrazono-3¥â-acetoxy-14¥á-hydroxyandrost-5-ene was found to proceed with migration of the 18-methyl group and formation of a 13,14-epoxide. The cleavage of aliphatic tosyl hydrazones under basic conditions (Bamford.Stevens reaction1) is widely used in organic chemistry for the generation of diazoalkanes and their transformation products.Many attempts have been done to study this reaction in steroids,2,3 including the reaction of 17-tosyl hydrazones, 4 which was shown to give cyclopropane derivatives or a mixture of olefins.We present here a detailed study of the Bamford.Stevens reaction of tosyl hydrazone 1¢Ó containing a hydroxy group at C14.5 It is known that the introduction of a functional group in the close vicinity of the reaction centre may result in formation of new products because of involvement of this group in the process.The heating of tosyl hydrazone 1 in diethylene glycol in the presence of KOH for 1.5 h at 110.120 ¡ÆC followed by usual work-up and column chromatography gave epoxide 2 (Scheme 1).¢Ô Its structure was assigned on the basis of the NMR data and confirmed by X-ray analysis.¡× An ORTEP6 view of epoxide 2 with an atom-numbering scheme is shown in Figure 1.The bond distances and angles in 2 are consistent with those observed previously for analogous compounds.7 A study of the molecular packing revealed that they are linked by O.H¡�¡�¡�O hydrogen bonds forming chains parallel with the x axis of the unit cell. The proposed reaction mechanism is outlined in Scheme 2.The treatment of tosyl hydrazone 1 with a base gave anion 3, which, on elimination of the tosyl group, was converted into the diazoalkane 4. Under the reaction conditions, it was protonated to give cation 5. The elimination of nitrogen led to cation 6, which was subjected to a Wagner.Meerwein rearrangement8 to give 7. Epoxide ring closure in 7 followed by deprotonation gave epoxide 2.Apart from 2, the formation of diol 8¢Ò was also observed as a result of epoxide ring opening under the reaction conditions (Scheme 3). It should be noted that the reductive opening of ¢Ó 17-Toluenesulfonylhydrazono-3 ¥â-acetoxy-14 ¥á-hydroxyandrost-5-ene 1 was prepared from 3¥â-acetoxy-14¥á-hydroxyandrost-5-ene (Organon N.V.) in 95% yield, mp 264.266 ¡ÆC (EtOH). 1H NMR, d: 1.06 (s, 3H, 18-Me), 1.14 (s, 3H, 19-Me), 2.04 (s, 3H, OAc), 2.20 (s, 3H, Ts), 4.60 (m, 1H, C3.H), 5.44 (br. s, 1H, C6.H), 7.10 (s, 1H, Ts), 7.36 (s, 1H, Ts), 7.82 (s, 1H, Ts). IR, n/cm.1: 1730, 1710, 1480, 1300, 1190, 1070. ¢Ô 13 ¥á,14 ¥á-Epoxy-3 ¥â-hydroxy-19-nor-17 ¥â-methylandrost-5-ene 2. Yield 69%, mp 141.144 ¡ÆC (hexane.EtOAc) (lit.,5 mp 139.142 ¡ÆC). 1HNMR, d: 0.92 (s, 3H, 19-Me), 0.94 (d, 3H, C17.Me, J 7 Hz), 3.54 (m, 1H, C3.H), 5.44 (t, 1H, C6.H, J 3 Hz). 13C NMR, d: 16.7, 18.5, 23.2, 23.6, 27.6, 28.0, 28.4, 31.4, 34.3, 36.2, 36.3, 37.2, 42.1, 43.6, 70.4, 71.7, 71.9, 121.5, 140.5. IR, n/cm.1: 1460, 1440, 1380, 1330, 1315, 1230, 1060, 970, 910. ¡× Crystal data for 2: C19H28O2, M = 288.41, orthorhombic, space group P212121, a = 8.433(2) A, b = 9.045(2) A, c = 21.119(4) A, V = 1610.9 A3, Z = = 4, dcalc = 1.189 g cm.3, m(MoK¥á) = 0.75 cm.1.Data collection (1.93¡Ìq¡Ì ¡Ì 30.06¡Æ) was performed on a Nicolet R3m diffractometer (MoK¥á, graphite monochromator, w/2q scan) at 293 K. The structure was solved using direct methods (SIR97)9 and refined by full-matrix least-squares (SHELXL-97),10 giving R1 = 0.0460 for 194 parameters and 2125 reflections with I > 2s(I) and wR2 = 0.1505 for all 2796 unique reflections (GOOF = 1.026).The positional parameters of all the H atoms were calculated geometrically and refined using a riding model with U(H) = = 1.2Ueq of attached atom [for methyl groups U(H) = 1.5Ueq]. Atomic coordinates, bond lengths, bond angles and thermal parameters have been deposited at the Cambridge Crystallographic Data Centre (CCDC).For details, see ¡®Notice to Authors¡�, Mendeleev Commun., Issue 1, 2001. Any request to the CCDC for data should quote the full literature citation and the reference number 1135/93. AcO H H OH NNHTs HO H H O H DEG KOH 1 2 Scheme 1 N N Ts H OH . Ts N H OH N + H+ N H OH H N . N2 H OH H 3 4 5 6 H H OH 7 H H 2 O . H+ Scheme 2 O(1) C(3) C(2) C(4) C(5) C(1) C(6) C(19) C(10) C(9) C(11) C(12) C(13) C(7) C(8) C(14) O(2) C(15) C(16) C(17) C(18) Figure 1 ORTEP drawing of the molecular structure of 2.Displacement ellipsoids are shown at the 50% probability level; hydrogen atoms are represented by spheres of arbitrary radii.Mendeleev Communications Electronic Version, Issue 4, 2001 (pp. 125.164) epoxide 2 af-forded 14¥á-alcohol 9,¢Ó¢Ó i.e., the ultimate result of this reaction sequence is a 1,2-shift of the 18-methyl group.References 1 W. R. Bamford and T. S. Stevens, J. Org. Chem., 1952, 4735. 2 R. Hirshmann, C. S. Snoddy, Jr., C. F. Hiskey and N. L. Wendler, J. Am. Chem. Soc., 1954, 76, 4013. 3 H. Mitsuhashi, Y. Shimizu and N. Kawahara, Tetrahedron, 1968, 24, 2789. 4 L. Cagliotti, P. Grasselli and A.Selva, Gazz. Chim. Ital., 1964, 94, 537. 5 M. Tanabe and D. F. Crowe, J. Org. Chem., 1963, 28, 3197. 6 L. J. Farrugia, J. Appl. Crystallogr., 1997, 30, 565. 7 F. H. Allen and O. Kennard, Chemical Design Automation News, 1993, 8, 31. 8 W. F. Johns, J. Org. Chem., 1961, 26, 4583. 9 A. Altomare, M. C. Burla, M. Camalli, G. Cascarano, C. Giacovazzo, A. Guagliardi, A. G. G.Moliterni, G. Polidori and R. Spagna, J. Appl. Crystallogr., 1999, 32, 115. 10 G. M. Sheldrick, Program for Crystal Structure Refinement, University of Gottingen, 1997. ¢Ò 3 ¥â,13 ¥â,14 ¥á-Trihydroxy-19-nor-17 ¥â-methylandrost-5-ene 8: yield 9.3%, mp 187.190 ¡Æ (hexane.EtOAc). 1HNMR, d: 0.94 (d, 1H, C17.Me, J 7 Hz), 1.00 (s, 3H, 19-Me), 3.50 (m, 1H, C3.H), 5.40 (m, 1H, C6.H). 13C NMR (600 MHz) d: 12.8, 19.8, 20.0, 25.5, 28.3, 29.0, 32.0, 34.0, 35.1, 37.0, 37.8, 39.0, 42.6, 43.4, 72.1, 81.4, 83.8, 122.0, 140.5. ¢Ó¢Ó 3 ¥â,14 ¥á-Dihydroxy-19-nor-17 ¥â-methylandrost-5-ene 9: yield 63%, mp 186.188 ¡ÆC (hexane.EtOAc). 1H NMR, d: 0.96 (s, 3H, 19-Me), 0.99 (d, 3H, 18-Me, J 6 Hz), 3.43.3.60 (m, 1H, C3.H), 5.35.5.42 (m, 1H, C6.H). 13C NMR, d: 19.0, 19.5, 23.0, 25.4, 25.5, 30.5, 31.7, 35.3, 36.2, 36.5, 41.3, 42.2, 44.0, 56.0, 71.6, 81.4, 121.6, 139.9. O H H HO H H H OH HO 2 DEG KOH H H OH H 8 9 LiAlH4 Scheme 3 Received: 12th March 2001; Com.

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年代:2001

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Mendeleev Communications Electronic Version, Issue 4, 2001 (pp. 125–164) Ozonolysis of N-acetyl-2-(cyclopent-2-enyl)aniline Akhat G. Mustafin,*a Denis I. D’yachenko,b Tat’yana V. Khakimova,a Leonid V. Spirikhin,a Gumer Yu. Ishmuratov,a Il’dus B. Abdrakhmanova and Genrikh A. Tolstikova a Institute of Organic Chemistry, Ufa Research Centre of the Russian Academy of Sciences, 450054 Ufa, Russian Federation.Fax: +7 3472 356 066; e-mail: chemorg@anrb.ru b Bashkir State Agrarian University, 450001 Ufa, Russian Federation 10.1070/MC2001v011n04ABEH001444 Double cyclization of N-acetyl-2-(cyclopent-2-enyl)aniline initiated by ozonolysis resulted in 9-acetyl-2-hydroxy-2,3,4,4a,9,9ahexahydropyrano[ 2,3-b]indole. Alkaloids containing oxygen cyclic fragments {alkaloids Daphniphyllum [(+)-codaphniphylline1], ipecac alkaloids [deacetylisoipecoside2], Strychnos indole alkaloids3–5} are of considerable interest.The cyclization of ortho-alkenylarylamines is an effective method for the synthesis of heterocyclic structures.6,7 To prepare natural compounds and their analogues8,9 using alkenylarylamines, we studied the ozonolysis of N-acetyl-2-(cyclopent- 2-enyl)aniline 1 in methanol at 0 °C.Previously, it was found that the ozonolysis of 2-alkenylanilines or their N-trifluoroacetyl derivatives with the subsequent treatment with dimethyl sulfide resulted in indole compounds and derivatives with the aldehyde function.10,11 Indole derivatives were formed during the ozonolysis of 2-alkenylanilines via the interaction between the carbonyl group and the amino group, whereas in case of N-trifluoroacetyl derivatives, aldehydes, which undergo cyclization during the removal of the protecting trifluoroacetyl group, were formed.An interesting fact of the double cyclization of 1 was found: the interaction of the amide group and the carbonyl group derived from the ozonolysis of compound 1 results in 2-hydroxy derivative of indoline 3, which was cyclised into 9-acetyl-2-hydroxy- 2,3,4,4a,9,9a-hexahydropyrano[2,3-b]indole 4 in 85% yield (Scheme 1).† Compounds 3a and 3b were identified in a mixture with product 4 by the 13C NMR spectra recorded in the J-modulation mode without the known signals of compounds 4a and 4b.These equilibrium diastereomers were recrystallised from ethanol. The signals of compounds 3a and 3b are of different intensities (1:4); therefore, the signals of a higher intensity were assigned to one diastereomer and those of a lower intensity to the other.The compound with the upfield shifts of signals due to the carbon atoms C(2) and C(3) was identified as a cis-isomer.12 The structure of compound 4 was assigned by 1H and 13C NMR spectroscopy. The 13C NMR spectrum of 4 showed a doubled number of signals for practically all carbon atoms, the intensity ratio was approximately 1:5.These signals were assigned to two diastereomers 4a and 4b. The doubling of some proton signals at C(2), C(9a) and C(4a) was observed in the 1H NMR spectrum. The cis-coupling for the ring junction protons was determined from the values of 5.9 and 5.3 Hz for spin–spin coupling constants (SSCC) between protons at C(9a) and C(4a) for both of the diastereomers.In the 1H NMR spectrum of a diastereomer with a higher intensity of signals (4a), the triplet proton signal at the carbon atom coupled with a hydroxyl group was observed. In this case, an anomeric effect is observed, i.e., the hydroxyl group is axial13 and syn positioned to the C(9a)–N bond of the indole ring.For minor diastereomer 4b, the same proton appeared as a double doublet (J 2.3, 9.2 Hz). A higher SSCC value testified the axial–axial interaction between two protons. Thus, the minor diastereomer is shifted conformationally with the prevail of conformers with the equatorial hydroxyl group. In the 13C NMR spectrum, the signals of carbon atoms C(2) and C(9a) for diastereomer 4a were upfield positioned (91.02 and 83.13 ppm, respectively) in comparison with those of the minor isomer (92.93 and 87.81 ppm, respectively).The signals of C(2) and C(9a) for the major diastereomer were observed to appear NH Ac NH Ac O O N Ac OH O 1' 3' 3 2 N Ac O OH 1 2 3 4 4a 5 6 7 8 9 9a 1 2 3a,b 4a, b i, O3 ii, Me2S Scheme 1 † A solution of N-acetyl-2-(cyclopent-2-enyl)aniline 1 (0.5 g, 2.5 mmol) in methanol (15 ml) was ozonised with an equimolar quantity of ozone at 0 °C and stirred until the starting product was disappeared (TLC control).Then, the reaction mixture was treated with dimethyl sulfide (1.6 ml), the solvent was evaporated on a rotary evaporator, the residue was washed with water (3×10 ml), the crystals were filtered off and dried in a vacuum.Recrystallisation from ethanol gave compound 4 in 85% yield (0.49 g); mp 136–137 °C. 1H and 13C NMR spectra were obtained using a Bruker AM-300 spectrometer at 300 and 75.5 MHz, respectively; solvent CDCl3; TMS as an internal standard. 1-Acetyl-cis-2-hydroxy-3-(3'-oxopropyl)indoline 3a: 13C NMR (CDCl3) d: 18.32 [t, C(1')], 23.11 [q, C(9)], 40.16 [d, C(3)], 42.05 [t, C(2')], 91.57 [d, C(2)], 116.97 [d, C(7)], 123.00 [d, C(5)], 124.09 [d, C(4)], 127.96 [d, C(6)], 128.37 [s, C(3a)], 142.46 [s, C(7a)], 169.92 [s, C(8)], 200.86 [d, C(3')]. 1-Acetyl-trans-2-hydroxy-3-(3'-oxopropyl)indoline 3b: 13CNMR (CDCl3) d: 20.95 [t, C(1')], 23.26 [q, C(9)], 40.56 [d, C(3)], 42.1 [t, C(2')], 93.25 [d, C(2)], 116.96 [d, C(7)], 122.82 [d, C(5)], 124.01 [d, C(4)], 128.05 [d, C(6)], 128.38 [s, C(3a)], 142.64 [s, C(7a)], 170.36 [s, C(8)], 201.02 [d, C(3')]. 9-Acetyl-syn-2-hydroxy-2,3,4,4a,9,9a-hexahydropyrano[2,3-b]indole 4a: 1H NMR (CDCl3) d: 1.52–1.67 [m, 1H, C(3)Ha], 1.75–1.90 [m, 1H, C(3)Hb], 1.80–1.98 [m, 1H, C(4)Ha], 2.31 [s, 3H, C(11)H3], 2.30–2.48 [m, 1H, C(4)Hb], 3.41 [dd, 1H, C(4a)H, J 7.05, 5.9 Hz], 4.99 [br. s, 1H, C(2)OH], 5.20 [t, 1H, C(2)H, J 4.8, 4.9 Hz], 5.89 [d, 1H, C(9a)H, J 5.9 Hz], 7.05–7.24 [m, 3H, C(5)H, C(6)H, C(7)H], 8.12 [d, 1H, C(8)H, J 7.95 Hz]. 13C NMR (CDCl3) d: 18.09 [t, C(4)], 22.83 [q, C(2')], 26.70 [t, C(3)], 39.84 [d, C(4a)], 83.13 [d, C(9a)], 91.02 [d, C(2)], 116.56 [d, C(8)], 122.88 [d, C(5)], 123.86 [d, C(6)], 127.51 [d, C(7)], 132.47 [s, C(4b)], 141.91 [s, C(8a)], 170.05 [s, C(10)]. N-Acetyl-anti-2-hydroxy-2,3,4,4a,9,9a-hexahydropyrano[2,3-b]indole 4b: 1H NMR (CDCl3) d: 1.52–1.67 [m, 1H, C(3)Ha], 1.75–1.90 [m, 1H, C(3)Hb], 1.80–1.98 [m, 1H, C(4)Ha], 2.39 [s, 3H, C(11)H3], 2.30–2.48 [m, 1H, C(4)Hb], 3.18–3.35 [m, 1H, C(4a)H], 4.88 [dd, 1H, C(2)H, J 2.3, 9.2 Hz], 5.00 [br.s, 1H, C(2)OH], 5.70 [d, 1H, C(9a)H, J 5.3 Hz], 7.05– 7.24 [m, 3H, C(5)H, C(6)H, C(7)H], 8.09 [d, 1H, C(8)H, J 7.8 Hz]. 13C NMR (CDCl3) d: 20.60 [t, C(4)], 22.85 [q, C(2')], 27.61 [t, C(3)], 38.45 [d, C(4a)], 87.81 [d, C(9a)], 92.93 [d, C(2)], 116.56 [d, C(8)], 122.51 [d, C(5)], 123.75 [d, C(6)], 127.51 [d, C(7)], 132.47 [s, C(4b)], 141.91 [s, C(8a)], 170.05 [s, C(10)]. For 4a and 4b found (%): C, 67.09; H, 6.25; N, 5.73. Calc. for C13H15NO3 (%): C, 66.95; H, 6.44; N, 6.01.Mendeleev Communications Electronic Version, Issue 4, 2001 (pp. 125–164) in the higher field due to the effect of the 1,3-syn-interaction between the hydroxyl group and the C(9a)–N bond.12 Thus, the indole fragment and the hydroxyl group are positioned syn in diastereomer 4a, and anti in diastereomer 4b. References 1 C. H. Heathcock, J. C. Kath and R. B. Ruggeri, J. Org. Chem., 1995, 60, 1120. 2 A. Itoh, T. Tanahashi and N. Nagakura, Chem. Pharm. Bull., 1994, 42, 2208. 3 M. E. Kuehne and F. Xu, J. Org. Chem., 1993, 58, 7490. 4 M. E. Kuehne, F. Xu and C. S. Brook, J. Org. Chem., 1994, 59, 7803. 5 J. Bonjoch, D. Sole and J. Bosch, J. Am. Chem. Soc., 1995, 117, 11017. 6 I. B. Abdrakhmanov, V. M. Sharafutdinov and G. A. Tolstikov, Izv. Akad. Nauk SSSR, Ser. Khim., 1982, 2160 (Bull.Acad. Sci. USSR, Div. Chem. Sci., 1982, 31, 1910). 7 Ch. Duschek, W. Hobold, R. Naick, H. Schmidt and N. T. Yen, J. Prakt. Chem., 1975, 317, 491. 8 A. G. Mustafin, I. N. Khalilov, V. M. Sharafutdinov, D. I. D’yachenko, I. B. Abdrakhmanov and G. A. Tolstikov, Izv. Akad. Nauk, Ser. Khim., 1997, 630 (Russ. Chem. Bull., 1997, 46, 608). 9 D. I. D’yachenko, A. G. Mustafin, V. V. Shereshovets, N. N. Kabal’nova, V. P. Kazakov, I. B. Abdrakhmanov and G. A. Tolstikov, Izv. Akad. Nauk, Ser. Khim., 1998, 1654 (Russ. Chem. Bull., 1998, 47, 1611). 10 S. J. Danishefsky and G. B. Phillips, Tetrahedron Lett., 1984, 25, 3159. 11 W. B. Lutz, C. R. McNamara, M. R. Olinger, D. F. Schmidt, D. E. Doster and M. D. Fiedler, J. Heterocycl. Chem., 1984, 21, 1183. 12 J. B. Stothers, Carbon-13 NMR Spectroscopy, Academic Press, New York, 1972, p. 56. 13 N. S. Zefirov and N. M. Shekhtman, Usp. Khim., 1971, 40, 593 (Russ. Chem. Rev., 1971, 40, 315). Received: 23rd February 2001; Com. 01/1770

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出版商:RSC    

年代:2001

数据来源: RSC

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Silver nanoparticles stabilised with heteropoly anions in an aqueous solution optical properties and electronic polarisation 2W17O61 10�C Boris G. Ershov* and Andrei V. Gordeev Institute of Physical Chemistry Russian Academy of Sciences 117915 Moscow. Fax +7 095 335 1778; e-mail ershov@ipc.rssi.ru The optical absorption spectra and electronic polarisation of silver nanoparticles prepared by the radiation-chemical reduction of silver ions in an aqueous solution in the presence of the heteropoly anions PW11O39 7�C and P2W17O61 10�C were studied. Nanosized metal particles exhibit lyophobic properties and various organic compounds (such as polymers polyelectrolytes and surfactants) are primarily used to stabilise them in water (see for example ref. 1 and references therein).Here we report on the possibility of using the nanosized heteropoly anions PW11O39 7�C and P2W17O61 10�C for this purpose by the example of the preparation of silver sols. The heteropoly anions have been used earlier to stabilize Rh and Ir nanoparticles.2 The distinctive property of these anions is that they can add electrons (undergo reduction) to form so-called blues with the retention of their structures.3 Therefore it would be expected that the application of heteropoly compounds to stabilise metal nanoparticles will make it possible to affect purposefully their electronic characteristics. Thus the reduction of the stabilising layer of a heteropoly compound in nanosized aggregates can induce its electronic polarization that is affect the charge of a metal nucleus.Previously,4 electrons were pumped into silver sols by the discharge of alcohol radicals generated by a microsecond pulse of accelerated electrons in an alcohol-containing solution. A process of this kind was more clearly demonstrated by the direct charging of silver sols at a cathode.5 In both of the above cases the electronic polarisation of silver particles was accompanied by a shift of the absorption band due to surface plasmons towards the UV region (blue shift). Chemically pure (NH4)7PW11O39 and K10P2W17O61 as well as AgClO4 from Aldrich were used. Solutions were prepared using triply distilled water and deaerated by pumping to a high vacuum before irradiation. Samples in special glass vessels equipped with quartz cells for optical measurements were ¦Ã-irradiated using a 60Co source.The absorbed dose rate was 25 Gy s�C1 as measured with the ferrous sulfate dosimeter. The absorption spectra were recorded on Specord UV-VIS or Shimadzu UV-3100 instruments at ambient temperature. Samples for electron-microscopic studies were prepared by applying a drop of the test solution to a carbon �Ccopper grid followed by drying in an argon atmosphere. A Phillips EM-30 electron microscope was used. Figure 1 shows the optical absorption spectra of an evacuated aqueous 10�C4 M AgClO4 solution containing isopropanol (0.1 mol dm�C3) and a P2W17O62 10�C additive before (curve 1) and after ¦Ã-irradiation (curve 2). The action of ¦Ã-radiation on isopropanol-containing solutions results in the formation of hydrated electrons which are powerful reducing agents (reduction potential of �C2.7 V) and Me2C¡�OH radicals (�C1.5 V).6 The latter species appear in the reactions of H atoms and OH radicals (water radiolysis products) with isopropanol.It can be seen that irradiation resulted in the appearance of optical absorption with a maximum at 392 nm which is typical of silver sols and a band with a maximum at 650 nm which is due to the reduction product of P2W17O62 10�C (blue).3,7 The subsequent ¦Ã-irradiation of the solution caused no detectable changes in the spectra. Therefore the radiation dose in use (0.75 kGy) was sufficient for the radiation-chemical reduction of all of the silver ions and P heteropoly anions.Note that the molar absorption coefficient of silver clusters is high namely e = 1.9¡Á104 dm3 mol�C1 cm�C1. Electron-microscopic data (Figure 2) demonstrated that the resulting silver particles are spherical in shape and the particle size is 10�C20 nm. The admission of air (Figure 1 curve 3) resulted in the oxidation of the blue and in the disappearance of the rele- Mendeleev Communications Electronic Version Issue 4 2001 (pp. 125�C164) 200 l/nm Figure 1 Absorption spectra of a deaerated solution containing AgClO4 (1¡Á10�C4 mol dm�C3) Me2CHOH (0.1 mol dm�C3) and P2W17O61 10�C (2¡Á10�C4 mol dm�C3) (1) before irradiation (2) after ¦Ã-irradiation for 30 min (3) after the admission of air and (4) after repeated irradiation for 30 min.Absorbed dose rate 1.5 kGy h�C1. Approximately 6.6¡Á10�C6 mol dm�C3 of hydrated electrons and 8.4¡Á10�C6 mol dm�C3 of Me2COH radicals per minute of irradiation were formed. 11O39 7�C vant absorption band at 650 nm. In this case the intensity of the band due to silver nanoparticles dramatically decreased and this band was shifted to the long-wavelength region (lmax = 410 nm). The repeated ¦Ã-irradiation of the solution under a vacuum restored the initial absorption spectrum (Figure 1 curve 4). The above oxidation�Creduction procedure can be repeated several times with the same optical effects. Silver nanoparticles stabilised with the heteropoly compound or its reduction product (blue) in an aqueous solution were found to be stable for a very long time (in a matter of months).A similar behaviour towards optical changes in silver sols was observed with the use of the PW heteropoly anion (10�C5�C10�C4 M) as a stabilising agent. The observed reversible changes in the absorption of silver nanoparticles are due to reversible changes in their electronic states in the cyclic reduction�Coxidation of the heteropoly anion. The electronic polarisation of silver nanoparticles is attained by discharging powerful reducing species (hydrated electrons and Me2COH alcohol radicals) on these particles. The reduction of the heteropoly compound which forms a stabilising layer of nanoparticles is also responsible for an increase in the electron density on a metal nucleus. This resulted in an increase in the absorption band intensity and in a blue shift relative to the case of clusters with oxidized heteropoly compounds (410 nm).According to the Mie�CDrude theory,8,9 the position of the absorption band maximum of the surface plasmon in the metal is determined by the equation l2 max = (2¦�c)2m(e0 + 2n)/4¦�Nee2 (1) where c is the velocity of light m is the effective electron mass e is the electron charge e0 is the permittivity of silver n is the refractive index of the medium and Ne is the density of free electrons in the metal. It can be seen that an increase in Ne results in a shift of the plasmon absorption band of the metal towards the UV region and a decrease in Ne results in a shift Optical density 10.1070/MC2001v011n04ABEH001462 2.0 1.5 1.0 2 0.5 4 1 3 0.0 800 400 600 silver sol when the absorption band was shifted from 404 to 392 nm.This shift corresponds to a change in the sol charge by 6.2%.5 The standard reduction potential of the pair HPCn�C/HPC (HPC is a heteropoly compound) is approximately equal to �C0.3 V.3 We found that the position of an absorption band due to surface plasmons in silver at 392 nm corresponds to an equilibrium charge of silver sols at the above potential. Note that it is most likely that the relationship between the charge of metal nanoparticles and the properties of the medium found for silver will also manifest itself in reactions catalysed by other transition metal nanoparticles. This work was supported in part by the Russian Foundation for Basic Research (grant no.00-03-32107). 100 nm References 1 A. D. Pomogailo Usp. Khim. 1997 66 750 (Russ. Chem. Rev. 1997 66 679). 2 J. D. Aiken and R. G. Finke J. Am. Chem. Soc. 1998 120 9545. Figure 2 Electron micrograph of silver particles prepared by ¦&Atild) Me2CHOH (0.1 mol dm�C3) and P2W17O61 10�C (2¡Á10�C5 mol dm�C3). The irradiation conditions are specified in Figure 1. towards the visible region. It also follows from equation (1) that the positions of the absorption bands are related to the relative concentrations of electrons on the metal nuclei by the expression (2) f 2/ l2 = Nf /Ni 3 M. T. Pope Heteropoly and Isopoly Oxometalates Springer-Verlag New York 1983.4 A. Henglein P. Mulvaney and T. Linnert Faraday Discuss. Chem. Soc. 1991 92 31. 5 T. Ung M. Giersig D. Dunstan and P. Mulvaney Langmuir 1997 13 1773. 6 B. G. Ershov Usp. Khim. 1997 66 103 (Russ. Chem. Rev. 1997 66 93). 7 A. V. Gordeev and B. G. Ershov Khim. Vys. Energ. 1999 33 258 [High Energy Chem. (Engl. Transl.) 1999 33 218]. 8 W. T. Doyle Phys. Rev. 1958 111 1067. 9 R. H. Doremus J. Chem. Phys. 1965 42 414. Received 19th April 2001; Com. 01/1788 li where the subscripts ¡®i¡� and ¡®f¡� refer to the initial and final states respectively. As well as Henglein et al.4 and Mulvaney et al.,5 we cannot establish a direct correlation of the position of the absorption band of silver nanoparticles with the charge of particles. The charge cannot be calculated from the positions of li and lf with a required accuracy because of the uncertainty of the values of e0 and n which results in particular from the uncertain composition of the nearest environment of nanoparticles. However we found using equation (2) that the reduction of the heteropoly compound and the formation of the blue increase the electron density on silver sols by 9.4%. This value is somewhat higher than that attained in the electrochemical charging of a Mendeleev Communications Electronic Version Issue 4 2001 (p

ISSN:0959-9436     

出版商:RSC    

年代:2001

数据来源: RSC