AIBN Special Seminar: A/Prof Tadaharu Ueda, Assistant Prof Shingo Hadano, Assistant Prof. Kenji Matsumoto

Presenter: 1.30 – 2.00 pm:

A/Prof Tadaharu Ueda, Synthesis and Characterization of novel Polyoxometalates

2.00 – 2.30 pm:

Assistant Prof Shingo Hadano,

Synthesis, nanostructures, and thermal properties of ABA-type amphiphilic triblock copolymers consisting of side-chain liquid crystalline polymethacrylate as a hydrophobic A-block and poly(ethylene oxide) as a hydrophilic B-block

2.30 – 3.00 pm:

Assistant Prof. Kenji Matsumoto,

Functional metal complexes utilized non-covalent interactions–siderophores, catalysts, luminescent complexes


26 September 2013

1:30pm – 3:00pm

Level 4 Seminar Room, AIBN Building (75) Corner College and Cooper Road, St Lucia

Abstract:Polyoxometalates (POMs) have been attractive compounds since many of them exhibit

interesting chemical properties, such as redox, catalysis, and chromism. In fact, there have been

a large number of reports on the synthesis, characterization and application of POMs. Recently,

various supermolecular has been prepared using POMs as building units. However, the

formation mechanism and electrochemical redox mechanism of POMs are still ambiguous

since they are very complicated. My group has focused on the elucidation of formation and

redox mechanism of POM as well as the synthesis of novel POMs. In this seminar, I will report

the recent achievements of our research. Recently, novel POMs, such as organophosphate-centered POMs with inverted-Keggin structure and vanadium-substituted tungstosulphates with Wells-Dawson structure could be isolated as a tetra-butyl ammonium salt and characterized with IR, Raman, UV-Vis, NMR, EPR and voltammetry. An electrochemical study of Keggin-type vanadium-substituted polyoxometalates , [X(VxM12-x)O40](3+x)- (x=0,1; X=S,P,As,V; M=Mo,W) has been performed with cyclic voltammetry in acetonitrile. For all of [X(VM11)O40]4-, the reversible potential for the vanadium

(V/IV) couple occurs at a more positive value than for molybdenum or tungsten processes. In

particular, the influence of acid on the voltammetry of this couple was extensively investigated

and interpreted with the assistance of NMR and EPR spectra obtained before and after

controlled potential bulk electrolysis, respectively. A comparison of the experimental behavior

with simulated voltammetric responses was used to establish the details of the reduction

mechanism in the presence and absence of acid.

PEOn-b-PMA(Az)m, an amphiphilic diblock copolymer consisting of poly(ethylene oxide) and poly(methacrylate) bearing azobenzene moiety on the side chain, thin film forms cylindrical

microphase-separation structure in which PEO cylinder oriented perpendicular and arranged hexagonally with decananometer periodicity by just thermal annealing and the films have been

applied for fabrication of various metal nanoarrays.1,2 I’m interested in “multi”block copolymers consisting of PEO and PMA(Az) block from viewpoint of their microphase separation

structure and domain size. In this study, we synthesized ABA-type triblock copolymers, PMA(Az)m-b-PEOn-b-PMA(Az)m (Fig. 1), and investigated their microphase-separation structure

and thermal properties in nanodomains. Six PMA(Az)m-b-PEOn-b-PMA(Az)ms, (n = 90, m = 15, 27, 35,

and 78), (n = 250, m = 14 and 39), were synthesized by atom transfer radical polymerization and the polydispersity of all triblock copolymers were smaller than 1.25. All triblock copolymers formed cylindrical microphase separation structure as same as diblock copolymer. The cylinder periodicity and

cylinder diameter of PMA(Az)m-b-PEOn-b-PMA(Az)m was similar to that of PEO1/2-b-PMA(Az)m diblock copolymer, which suggests a possibility to form smaller microphase separation structure with keeping film forming ability. In addition, melting point of PEO nanodomains (Tm,PEO) in

PMA(Az)m-b-PEO90-b-PMA(Az)m was below to 0 ºC which was much lower than that of homopolymer or PEO domains in diblock copolymers having similar molecular weight.

Non-covalent interactions such as hydrogen bonds and π-π stacking interactions are weaker in

comparison with covalent bonds but are very important for the development of activity, selectivity

and specificity for various reactions and high functionalities. For example, enzymes in body are able

to perform the various reactions which are difficult in laboratory using them under natural condition.

We focus on the efficacy and importance of non-covalent interactions and study on functional

metal complexes utilized non-covalent interactions. There are three main type of them;

iron-transporting agents, asymmetric catalysts, and luminescent materials. Firstly, the

iron-transporting agents produced by microorganisms to take up iron in their body are called as

siderophore(s). Siderophores are the multidentate ligands which have hydroxamates and phenolates

as iron(III) binding sites and form very stable iron(III) complexes. As a result of the investigation

with various hydroxamate-type artificial siderophores, we have found that multiple intramolecular

hydrogen bonds are the important factor in the formation of iron(III)-siderophore complexes. 1)

Secondly, in order to achieve high selectivity and efficiency in asymmetrical catalytic reactions, the

catalysts have to possess highly recognizing and activating abilities of substrates. We synthesized

novel bis(oxazoline) ligands with amide groups as the interaction site for substrates. The copper(II)

complexes showed high asymmetrical catalytic activity for a Diels-Alder reaction.2) On the other

hand, the copper(II) complexes of bis(oxazoline) ligands without amide groups did not. Thirdly,

N-heterocyclic carbenes (NHCs), which resemble the coordination properties of phosphine, form

stable metal complexes with low valent metals. Although many luminescent metal–phosphine

complexes have been reported, there are only a few papers reported about the luminescence of metal complexes with NHCs. We have investigated the photoluminescence of the copper(I) complex with the bis(NHC) ligand in which two NHCs are bridged by one methylene group and have found

interesting photophysical properties of the Cu(I)–bis(NHC) complex caused by non-covalent

interactions. 3)




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