Tuning Reactivity of Platinum(II) Complexes

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constants of CH3PhisoqPtCl decrease by a factor of about three or lower depending on the nucleophiles. The expectation would be an increase in the rate of substitution due to the extended π-conjugation, which should enhance π-backbonding effect. 16,17 In the case of pyPhenPtCl and PtCl the expected trend is observed with pyPhenPtCl being more reactive than PtCl. To provide an explanation to this trend it is important that the properties of the coordinated ligand to the platinum metal is understood. Looking at the structures of the Pt(II) complexes which are shown in Scheme 3.1, one notes that they are all characterised by the presence of a delocalised π-system that allows for facile electron transfer from the metal to the ligand. This giving rise to metal-to-ligand-charge transfer (MLCT) absorption spectra that are usually found in the wavelength range 350-450 nm, 33-35 and is also seen in Figure 3.5 Since the π-acceptor property of the complex can be viewed as transfer of electron density from the HOMO orbital of the complex into the LUMO, any difference in energies of the d-orbital HOMOs of the complex and the π*- LUMOs localised on the ligands, would determine the HOMO-LUMO energy gap and hence the energy of the MLCT absorption, and hence the reactivity. Absorbance 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 CH3PhPtCl CH3PhisoqPtCl 200 250 300 350 400 450 500 21 393 nm Wavelength (nm) 399 nm Figure 3.5: Absorption spectra of CH3PhPtCl and CH3PhisoqPtCl in acetonitrile
The electronic absorption spectra of CH3PhPtCl, CH3PhisoqPtCl, PtCl and pyPhenPtCl have been reported in literature. 20,21 These results reveal that the order of decreasing MLCT absorption energies follow the trend: CH3PhisoqPtCl > CH3PhPtCl > PtCl > pyPhenPtCl. This observation is consistent with the understanding that pyphen ligand is the strongest π-acceptor and 4’–(2’’’–CH3–phenyl)–6–(3’’–isoquinoyl)–2,2’– bipyridine the weakest. The results also represent the electronegativiy of the ligands as well as the extent of π-delocalisation. 36 These results are in agreement with the DFT- calculations which illustrate the π-acceptor properties of the tridentate ligands and quantify the HOMO-LUMO energy gap of the frontier orbitals. Given the typically associative character of the d 8 square-planar Pt(II) complexes, the transition state is stabilised by the transfer of the electron density to the tridentate N- donor ligands, making the metal centre more positively charged, thus enhancing the substitution reactions. This is in contrast to the increase of electron density around the Pt(II) centre which tends to stabilise the ground state while destabilising the 18-electron five-coordinate transition state with a net effect of slowing substitution reactions. Therefore, the difference in reactivity of investigated complexes can be accounted for in terms of the strength of the π-backbonding of the coordinating ligand. The higher reactivity of CH3PhPtCl compared to CH3PhisoqPtCl is due to the fact that the three coplanar pyridine rings of terpy ligand are better at delocalising the negative charge from the Pt(II) centre through π-backbonding. The “unusual” decrease in reactivity of CH3PhisoqPtCl is due to the relative poor π-acceptor property of the isoquinoline ligand. This means that the electrophilicity of the metal centre is decreased, resulting in the retardation of the incoming nucleophiles. Similar results have been reported by our group 14 and other workers, 9, 22 but these have been due to the increase in the cis σ- effect and not the decrease in the delocalisation of the π-electron density being reported here. The results show that isoquinoline ligand is a net σ-donor. The difference in reactivity between PtCl and pyPhenPtCl is because of the fused-ring system in the latter that gives rise to a favourable overlap of the dπ orbitals of the metal 22
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Tuning Reactivity of Platinum(II) C
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Declaration This thesis report is b
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Abstract Systematic kinetic and the
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Table of contents Acknowledgements
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2.5.5 Effect of Non-participating G
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5.2.1 Chemical and Solutions ......
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7.2 Experimental Section ..........
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procurements, Messers P. Forder and
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Figure 2.2 Potential energy profile
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Figure 4.6 Concentration dependence
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Figure 6.1 Spectrophotometric titra
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List of Tables Table 2.1 A selectio
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Table 6.4 Summary of rate constants
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TU thiourea DMTU 1,3-dimethyl-2-thi
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Table of Contents-1 Chapter 1 .....
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1.0 Introduction 1.1 Cancer Disease
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toxic potential. The most well-know
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1.3.2.2 Cellular Uptake Cisplatin i
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H 3N OH 2 Pt H 3N OH 2 Active Pt(II
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transformational pathways that comp
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the hydrolysis of the complex, wher
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1.3.4 Terpyridine Platinum(II) Comp
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H 3 N Cl Pt NH 3 H 3 N NH 2 (CH 2 )
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1.4 Kinetic Interest The platinum-b
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3. The effect of varying the positi
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17 R. A. Henderson, The Mechanism o
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Altona J. H. van Boom, G. A. van de
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76 (a)J. Kašpárková, J. Zehnulov
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Table of Contents-2 Chapter Two ...
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List of Tables Table 2.1: A selecti
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The mononuclear Pt(II) complexes 1-
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Potential Energy R + X RX 1 transit
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For the associative mechanism (A),
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the concentration of one of the rea
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k obs , s -1 0.00030 0.00025 0.0002
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k = Ae -Ea/RT 2.14 lnk = lnA - E a
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= 23.76 + R Hence, a plot of ln ⎛
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Page 78 and 79: conventional methods are classical
Page 80 and 81: Figure 2.6: Schematic diagram of a
Page 82 and 83: The light transmitted from the samp
Page 84 and 85: c. Oxidizability: Ligands that are
Page 86 and 87: Table 2.1: A selection of n o pt va
Page 88 and 89: eaction with different nucleophiles
Page 90 and 91: eaction site from direct attack by
Page 92 and 93: PEt 3 PEt 3 R PEt 3 Pt Pt Y Y Cl R
Page 94 and 95: direct displacement of the leaving
Page 96 and 97: therefore, weaken the bond of the l
Page 98 and 99: σ-Donation According to classical
Page 100 and 101: References 1 (a) J. Reedijk, Chem.
Page 102 and 103: 34 R. B. Jordan, Reaction Mechanism
Page 104 and 105: Table of Contents-3 Chapter 3.The
Page 106 and 107: Chapter 3 The π-Acceptor Effect in
Page 108 and 109: In order to extend our understandin
Page 110 and 111: after which water was added to quen
Page 112 and 113: O CH 3 + I + N O oH - N O O 7 CH 3
Page 114 and 115: 84% (34.7 mg, 0.0618 mmol). 1 H NMR
Page 116 and 117: PhCN PhCN Pt Cl Cl + N N CH 3 N CH
Page 118 and 119: Complex Structure HOMO LUMO PtCl CH
Page 120 and 121: The geometry-optimised structures i
Page 122 and 123: against the concentration of the in
Page 124 and 125: Table 3.2: Summary of the second-or
Page 128 and 129: with π*-orbitals of the ligand. Th
Page 130 and 131: 3.6 References 1 D. Rosenberg, L. V
Page 132 and 133: 30 Microcal TM Origin TM Version 5.
Page 134 and 135: Figure S3.1: Kinetic trace at 448 n
Page 136 and 137: ln(k 2 /T) -6.0 -7.5 -9.0 -10.5 -12
Page 138 and 139: Table S3.3b: Average observed rate
Page 140 and 141: Table S3.5b: Temperature dependence
Page 142 and 143: Table S3.8: DFT calculated electros
Page 144 and 145: List of Figures Figure 4.1: Structu
Page 146 and 147: Table 4.2: Summary of pKa values fo
Page 148 and 149: 4.1 Introduction Platinum compounds
Page 150 and 151: cis geometry, leading to dramatic c
Page 152 and 153: ligand was added to the [{cis-PtCl(
Page 154 and 155: spectra were measured in and refere
Page 156 and 157: 4.3.1 DFT calculated Optimized Stru
Page 158 and 159: Table 4.1: A summary of the DFT cal
Page 160 and 161: H2O-Pt-L-Pt-OH2 H2O-Pt-L-Pt-OH2 H2O
Page 162 and 163: electrophilicity and acidity of the
Page 164 and 165: (A) 18 Absorbance 0.08 0.07 0.06 0.
Page 166 and 167: k obs(3 rd ) , s -1 -5 6.00x10 TMTU
Page 168 and 169: 4.3.4 Kinetics with NMR The substit
Page 170 and 171: ln([ML] t ) 4.0 3.5 3.0 2.5 2.0 1.5
Page 172 and 173: ln(k 2(1 st ) /T) -3.5 -4.0 -4.5 -5
Page 174 and 175: Comple x Table 4.4: Summary of Acti
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The decrease in reactivity of 2,6pz
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Table 4.5: DFT calculated (NBO) cha
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eaction proceeds via bimolecular pa
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References 1 T. Storr, K. H.Thomson
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36 D. Jaganyi, D. Reddy, J.A. Gerte
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Appendix 4 THE INFLUENCE OF THE PYR
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Absorbance at 368. 0 nm 0. 0 8 0. 0
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Table S4.3: Average observed rate c
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k nd obs(2 ) , s-1 0.003 TU DMTU TM
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k obs2 , s -1 2.40x10 -4 2.20x10 -4
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Table S4.13: Average observed rate
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k obs(1 st ) , s -1 0.06 0.04 0.02
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ln(k 2(3 rd ) /T) -10.0 -10.5 -11.0
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SpinWorks 2.5: 2,6 pznClO4 in D2O N
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Table of Contents-5 Chapter 5 .....
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List of Tables Table 5.1: A summary
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5.1 Introduction Multinuclear plati
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onding. For this reason, pKa titrat
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400-300 cm -1): 3308, 3117, 3071 (N
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5.2.6 Spectrophotometric pKa Titrat
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Table 5.1: A summary of DFT-calcula
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However, because the highest occupi
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Table 5.2: Acid dissociation consta
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Table 5.3: A summary of DFT calcula
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H3N 6 eq TU 0 eq TU Ha NH3 Ha Cl TU
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third step due to the trans-effect
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[H 2 O-Pt-(NN)-Pt-OH 2 ] +4 [NU-Pt-
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k obs(1st) / s -1 0.20 TU DMTU TMTU
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thiourea nucleophile is large enoug
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ln(k st 2(1 ) /T) -3 -4 -5 -6 -7 -8
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is the same as the electron-withdra
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associative mode of substitution me
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16 H. Ertürk, J. Maigut, R. Puchta
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43 (a) D. Jaganyi, A. Hofmann and R
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276 nm Absorbance 0 . 6 5 0 . 6 4 0
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k obs(1 st ) , s -1 0.4 0.3 0.2 0.1
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ln(k 2(2 nd ) /T) -8.0 TU -8.5 -9.0
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pzn PPM -1750.0 -1850.0 -1950.0 -20
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Figure S5.13: UV/Visible spectra fo
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k obs(1 st ) in s -1 0.030 0.025 0.
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ln(k 2(2 nd ) /T) -10 -11 -12 -13 -
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9.61 ppm Ha PPM 9.8 9.6 9.4 9.2 9.0
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k obs(3rd) / s -1 -5 8 .00 x 10 T U
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ln(k st 2(1 ) /T) -1.5 TU DMTU TMTU
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ln(k rd 2(3 ) /T) -8.5 -9.0 -9.5 -1
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SpinWorks 2.5: znPt(II)-OP4 in D2O
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Figure S5.31: Mass spectrum for com
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ln(k st 2(1 ) /T) -4 -5 -6 -7 -8 -9
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SpinWorks 2.5: phtPt(II)-OP2 in D2O
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Figure S5.41: Mass spectrum for com
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List of Figures Figure 6.1: Spectro
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Chapter 6 Tuning Reactivity of Plat
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Against this background, several re
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6.2.2 Instruments Microanalyses wer
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Metal Complex Pt3 Yield: 52.5 mg (0
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6.3 Results 6.3.1 Synthesis and Cha
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The pKa values obtained are summari
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Table 6.2: DFT-calculated parameter
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that of dinuclear Pt(II) complexes
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It can be concluded that substituti
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ate constants, kobs(1 st /2 nd ), w
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Table 6.3: Summary of rate constant
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6.3.6 Activation Parameters The act
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pKa1 values become smaller. In addi
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of steric influence is felt by the
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6.5 Conclusion The present study ha
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17 O. F. Wendt and L. I. Elding, 19
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51 Y. Iwadata, K. Kawamura, K. Igar
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Table S6.4(b): Average observed rat
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ln(k 2(2 nd ) /T) -4 -6 -8 -10 -12
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45.0 40 35 30 25 20 %T 15 10 5 0 -5
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k st obs(1 ) in s-1 0.30 Br TU 0.25
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-2304.16 ppm H 3N PPM -2200.0 -2220
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Absorbance 1.6 1.4 1.2 1.0 0.8 0.6
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SH N SH + Mechanism Br N + CO 3 2-
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Figure 7.5: 195Pt NMR spectra of mi
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linker remained coordinated to the
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complexes, have a lower charge and
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ange 326-400 cm -1 (weak) for Pt-Cl
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ButPt, HexPt, OctPt and DecPt, were
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7.3 Results 7.3.1 DFT Calculations
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Structure HOMO LUMO EnPt (C2h) Prop
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Absorbance Table 7.2: Summary of pK
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coordination to the soft Pt(II) cen
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observed at -2962.4 and -3024.1 ppm
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H 3N NH 3 Pt NH 2 OH 2 n NH 3 NH 2
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k obs2 , in s -1 -3 TU 1.2x10 DMTU
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7.3.4 Activation Parameters The tem
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density is located on the metal cen
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acetylmethionine, which reported th
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References 1 (a) B. Rosenberg, L. V
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32 N. Summa, J. Maigut, R. Puchta a
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Appendix 7 Table S7.1: Summary of s
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k obs(2 nd ) , in s -1 0.00020 0.00
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ln(k 2(2 nd ) /T) -8.5 -9.0 -9.5 -1
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k obs(1 st ) , in s -1 0.06 TU DMTU
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ln(k 2(1 st ) /T) -3.2 TU DMTU TMTU
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Table S7.11: Summary of kobs(2 nd )
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%T 22.0 20 18 16 14 12 10 8 6 4 2 0
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k st obs(1 ) , in s-1 0.10 0.08 0.0
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ln(k st 2(1 ) /T) -4.0 TU DMTU TMTU
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Figure S7.23: Mass spectra for HexP
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Table S21: Average observed rate co
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Table S7.23: Summary of kobs(2 nd )
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90.0 80 70 60 50 40 30 20 %T 10 0 -
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Figure S7.37: Mass spectrum for Hex
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Chapter 8 Tuning Reactivity of plat
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dinuclear Pt(II) complexes to relea
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finally Pt2. The order of reactivit
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• prolonged survival in the cell
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