Silver clusters were produced by two different synthesis procedures, related with
different reduction species. PVA (polyvinyl alcohol) was successfully utilized as a
source to reduce silver (Ag) metal ions without using any additional reducing
agents to obtain Ag clusters. Silver clusters with atoms numbering 5-29 are
registered through mass spectrometry using MALDI TOF and MALDI TOF/TOF
techniques. Analysis showed that clusters with magic numbers are the largest,
while those with an odd number of atoms are larger than clusters with an even
number of atoms. Stability of these molecules, magic number actually, is in
relation with their electronic configuration

Cindrić, Mario

Cvetićanin, Jelena M.

Kačarević-Popović, Zorica M.

Krklješ, Aleksandra N.

Nešković, Olivera M.

Trpkov, Đorđe

Repository of the Vinča Nuclear Institute (VinaR)

       PHYSICAL CHEMISTRY 2010  10th International Conference on Fundamental and Applied Aspects of Physical Chemistry  Proceedings      The Conference is dedicated to the 100th Anniversary of the academician Pavle Savić birthday and 20th Anniversary of the Society of Physical Chemists of Serbia         21-24 September 2010 B E L G R A D E                            ISBN 978-86-82475-17-0 Title: Physical Chemistry 2010. (Proceedings) Editors: S. Anić and Ž. Čupić Published by: Society of Physical Chemists of Serbia, Studentski trg 12-16 P.O.Box 47, 11158 Beograd, 218, Srbija Publisher: Society of Physical Chemists of Serbia For Publisher: S. Anić, President of Society of Physical Chemists of Serbia Printed by: “Jovan” Printing and Publishing Company; 200 Copies; Number of pages 16 + 388, Format: B5; Printing finished in September 2010.  Text and Layout: “Jovan”  200 - Copy printing    II   The Society of Physical Chemists of Serbia  in co-operation with   Institute of Catalysis, Bulgarian Academy of Sciences  Boreskov Institute of Catalysis, Siberian Branch of  the Russian Academy of Sciences  Faculty of Physical Chemistry, University of Belgrade, Serbia  Institute of Chemistry Technology and Metallurgy, University of Belgrade, Serbia  Vinča Institute, University of Belgrade, Serbia   Institute of General and Physical Chemistry, Serbia                         IV  International Organizing Committee  Chairman:             S. Anić (Serbia) Vice-chairman:     N. Stepanov (Russia)                                B. Adnađević (Serbia)  Members: M. Gabrovska (Bulgaria), N. Cvijetićanin (Serbia), T. Grozdić (Serbia),  D. Jovanović (Serbia), M. Lalić (BiH), D. Marković (Serbia), B. Milosavljević (USA), N. Miljević (Serbia), M. Mojović (Serbia), N. Ostrovski (Serbia), C. Pona (Italy), B. Simonović (Serbia), D. Stanisavljev (Serbia), A. G. Stepanov (Russia), V. Vasić (Serbia), N. Vukelić (Serbia), V. Vukojević (Sweden)   International Scientific Committee  Chairman:              Ž. Čupić (Serbia) Vice-chairmans:     V. N. Parmon (Russia)                                 M. Franko (Slovenia)  V. Vasić (Serbia)  Members: A. Antić-Jovanović (Serbia), G. Bačic (Serbia), R. Cervellati (Italy), R. Compton (United Kingdom), V. Gaspar (Hungary),  M. Jeremić (Serbia), A. L. Kawczyñski (Poland), Lj. Kolar-Anić (Serbia), S. Kuchanov (Russia), R. Leblanc (USA),  S. Mentus (Serbia), S. Milonjić (Serbia), Lj. Morozova-Roche (Sweden),  D. Moscone (Italy), J. Nedeljković (Serbia), Z. Noszticzius (Hungary), M. Perić (Serbia), V. Petruševski (Macedonia), M. Plavšić (Serbia), G. Smulevich (Italy),  G. Schmitz (Belgium), I. Schreiber (Czech), P. Ševčik (Slovakia), N. Stepanov (Russia), M. Trtica (Serbia), D. Veselinović (Serbia)  Local Executive Committee  Chairman:              B. Adnadjević Vice-chairmans:    S. Blagojević                                 A. Ivanović  Members: A. Abu Rabi-Stanković, P. Banković, N. Begović, S. N. Blagojević,  N. Cvjetičanin, M. Daković, A. Đerić, A. Ignjatović, Lj. Ignjatović, A. Jović,  J. Krstić, S. Kuprešak, D. Lončarević, J. Maksimović, V. Marković, M. Milenković, M. Milojević, Z. Mojović, B. Nedić, I. Pašti, N. Pejić, A. Popović-Bjelić, M. Petković, N. Potkonjak, D. Ranković, R. Ranković, M. Stević,  I. Stojković, B. Šljukić, M. Vujković    VMASS SPECTROMETRIC INVESTIGATION OF SILVER CLUSTERS  J. Cvetićanin1,xx, A. Krklješ1, Z. Kačarević-Popović1, Đ. Trpkov1, M. Cindrić2 and O. Nešković1,x  1 Vinca Institute of Nuclear Sciences, Belgrade, Serbia; 2„Pliva“, Zagreb, Croatia. x oliveran@vinca.rs;     x xcvetic@vinca.rs  Abstract Silver clusters were produced by two different synthesis procedures, related with different reduction species. PVA (polyvinyl alcohol) was successfully utilized as a source to reduce silver (Ag) metal ions without using any additional reducing agents to obtain Ag clusters. Silver clusters with atoms numbering 5-29 are registered through mass spectrometry using MALDI TOF and MALDI TOF/TOF techniques. Analysis showed that clusters with magic numbers are the largest, while those with an odd number of atoms are larger than clusters with an even number of atoms. Stability of these molecules, magic number actually, is in relation with their electronic configuration.   Introduction For the first time some ten years ago, absorption spectra of silver clusters produced by different techniques in the 2.5–6.2 eV energy range were measured on clusters embedded in gas matrices or by gamma irradiation [1–3]. The spectra of small clusters (n < 12) are made of several narrow or broad peaks in the 3.0–4.5 eV range, while those of larger clusters are characterized by the emergence of a dominant and relatively broad peak between 3.2 and 3.8 eV. The position of this later was interpreted by the authors using a model based on the Mie theory in which the peak was described as the excitation of s-type electrons without direct contributions from d-type electrons. Nevertheless, the nature of the excitations needed to be confirmed by calculations in which the effect of d electrons would be taken explicitly into account. Hence, several theoretical ab initio studies have been investigated in order to reproduce the experimental spectra and to elucidate the real role played by the interband transitions associated to d-electrons. There are few experimental results, as we lack information about the stability and amplitude of different clusters as well as on ionisation energy. The experimental mass spectrometry spectra of neutral, small and intermediate-size Agn (n=5-29) silver clusters produced by gamma irradiation, have been measured.  Materials and Methods Silver clusters are created using radiolysis of the aqueous solution of AgNO3 system, carbon nanotubes and PVA. Silver clusters and silver cluster decorated carbon nanotubes were created and have been further examined using mass 60spectrometry methods. Reduction of silver ions was performed in the current of Ar or N2O. The experiment showed that larger clusters were created and are more stable when radiolysis takes place in the current of N2O. The irradiation was performed at a dose rate of 10 kGy/h up to the absorbed dose of 55 kGy. MALDI TOF and MALDI TOF/TOF techniques were used to analyze produced silver clusters. An aliquot of each sample solutions containing an internal standard was combined 1:1, with the CHCA matrix and mixed thoroughly. Aliquots (0.50 μL) of the mixtures were spotted onto a 100-spot sample plate (Applied Biosystems) and air-dried. Mass analysis was performed in the positive ion reflector mode using a 200 Hz frequency pulsed N2 laser operating at 337 nm. Five spectra at each of 10 randomly selected positions were accumulated per spot between 170 and 500 g/mol using the MS positive ion reflector mode acquisition method. Calibration of the instrument was realized using Calibration mixture 2 as the external standard. To generate spectra with high mass accuracy, an internal calibration was performed. For the analysis of silver clusters, 1.0 mg/mL solutions in 0.10 % trifluoracetic acid were prepared. Positive-ion MALDI-TOF and MALDI-TOF/TOF mass spectra were performed using the 4700 Proteomics Analyzer (Applied Biosystems).  Results and Discussion  496.0 1073.6 1651.2 2228.8 2806.4 3384.0Mass (m/z)01.3E+40102030405060708090100% IntensityVoyager Spec #1[BP = 359.9, 58594]5 791113 1517 19 21 23 25 27 29970.2236974.2052575.7501 754.4372966.2509583.7502758.4299517.3524579.75241401.8032978.2040 1619.5553 2051.1242571.7535 2266.90341186.0295 1835.34631397.8189859.3452 3132.6342529.3752 2699.1074 2916.81382258.98192043.1329 2487.59781611.59731148.3901  Fig.1. MALDI TOF spectrum of silver clusters. Numbers above the mass values (5 to 29) show the number of silver atoms in the clusters.  Silver clusters with the number of atoms from 5 to 21 showed satisfactory stability. Only clusters with 11 atoms of silver appeared to be unstable, and decomposed in the time of flight reflectronic way. Fragments which were produced during this process, were cationized with Na positive single ions. The ancestry of these ions is unknown, and it may be speculated that these have appeared out of a cluster forming system. MALDI TOF spectrum of the obtained positive cluster ions is shown on Figure 1.   Conclusion Our novel method of silver cluster formation from silver salts is reproductive and very simple. Clusters with the number of atoms from 5 to 29 were registered by 61mass spectrometry, where silver clusters with the number of atoms from 5 to 21 showed satisfactory stability.  The literature predicted the matching magic numbers which are in relation with the electronic configuration of the cluster. Evidently, the most stable clusters are those with closed electron shells. The results obtained from MS/MS analysis of the different clusters clearly demonstrate that MALDI-TOF/TOF can be used to discriminate unstable silver clusters with good reproducibility.  Acknowledgement This work was financially supported by the Ministry of Science and Technological Development, Republic of Serbia, under Project No. 142001.  References [1]  S. Fedrigo, W. Harbish, J. Buttet, Phys. Rev. B, 1993, 47, 10706. [2]  A. Krklješ, M. Marinović-Cincović, Z. Kačarević-Popović, J. Nedeljković, Thermochim. Acta, 2007, 460, 28-34. [3]  J. Cvetićanin, A. Krklješ, Z. Kačarević-Popović, M. Mitrić, Z. Rakočević, Đ. Trpkov, O. Nešković, Appl. Surf. Sci., in press, DOI 10.1016-j.apsusc.2010.05.023. 62

Mass spectrometric investigation of silver clusters

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Mass spectrometric investigation of silver clusters

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