Tuning Reactivity of Platinum(II) Complexes

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density is located on the metal centre, which makes the Pt(II) centre less electrophilic and less acidic. This is supported by the shortening of the Pt–Ndiamine bond lengths and the reduction in the NBO charges on the Pt(II) centres as the chain length of the linker increases across the series (Table 7.1). Compared to the mononuclear analogues: cis-[Pt(NH3)3H2O] 2+ (pKa = 6.37) 51 the pKa values (5.31-6.22) for most of the investigated dinuclear complexes are slightly lower. As already explained, the inductive effect of the linker and a higher overall charge of +4 on the Pt atom are the reasons for the lower pKa values of the dinuclear complexes compared with the +2 charged mononuclear analogues. By increasing the chain length of the system, the individual metal centre environment approaches that of the mononuclear analogue. These findings are in agreement with reports by Farrell and co- workers 43 and van Eldik and his group. 30 Changing the position of the water ligand from trans- to cis- has little or no effect, if at all, on the value of the pKa of Pt-metal complex, shown in Table 7.2 where the values of cis and trans- counterparts 26 are compared. 7.4.2 Substitution Process Comparing the general reactivity, using the TU nucleophile as a reference, the second- order rate constants for the first step lie in the range 5.0 ± 0.1 ≥ k2,1 st ≥ 2.6 ± 0.02 M -1 s -1, progressively decreasing marginally from EnPt to DecPt. The difference in reactivity can be attributed to the decrease in the overall effect of charge additions experienced by the metal centre and σ–donicity of the coordinated alkanediamine linker in these complexes. 26, 29,52 The retardation of the rate of substitution in the first step, on increasing the alkanediamine chain length from EnPt up to DecPt, is attributed to the strong σ-donor ability of the (CH2)n moiety, which causes accumulation of the electron density at the metal centre. 52,53 This decelerates the substitution process by making the Pt(II) centre more electronegative or less electrophilic. The σ-inductive effect does not only prevent the approach of the nucleophile, but also through the accumulation of electron density at the metal centre suppresses the stabilization of the transition state, which slows down the substitution reaction. Consistent with this view is that the pKa and HOMO-LUMO energy gap values of the ground state of the dinuclear Pt(II) complexes increase on 26
introduction of a greater number of (CH2)n from n = 2 up to 10. A further factor is the decrease in-space electrostatic charge additions at the metal centre due to the increase in the linker chain. 13,29,30 This leads to a decrease in electrophilicity at the Pt(II) centre thereby making the metal centre less reactive. It has been demonstrated that the 1,1/c,c geometry results in slower substitution reactions because of the steric hindrance of the bridge around the Pt(II) centre. 14 The steric factor is mainly due to the flexibility of the (CH2)n units of the alkanediamine ligand. 26 In this study the overall steric effect was found to have been non-existent or had no significant influence on the first substitution step of the aqua ligands. It can therefore be concluded that electronic effect is the main factor that controls the first substitution step. A general look at the results in Table 7.3 shows that the rate constants, k2,2 nd , for the second substitution step are about 1-2 orders of magnitude smaller than those obtained for the simultaneous substitution of the aqua ligands in the first step in all the six complexes. The second substitution reaction is slower than the first step due to a number of reasons. Firstly, a facilitated attack (due to the strong trans-effect of the first coordinated TU) by a second thiourea molecule on the trans-positioned ammine nitrogen is slowed down as a result of steric constraints around the Pt(II) centre from the first substitution. Secondly, is the increase in electron donation to the Pt metal due to the coordinated TU from the first substitution reactions. The third reason is the fact that the leaving group in the first substitution is different to that in the second substitution. The Pt–OH2 bond is stronger than that of Pt–NH3. 54 Finally, the trans-effect of the two substitution process is also different, as such influencing the overall reactivity In this study, the proton ( 1 H) and 195 Pt NMR data have demonstrated that for 1,1/c,c dinuclear Pt(II) complexes, a second step which involved release of ammine ligand following the coordination of a further thiourea to the Pt(II) centre is observed. In contrast, the first data reported in literature on di-platinum metal complexes for the trans analogues (1,1/t,t) 26 gave only a single reaction step, which is most likely a combination of the two steps. The results of the trans analogues (1,1/t.t) also contradicts NMR studies by Farrell et al. 31(a) for the reaction of 1,1/t,t (n =6) with N- 27
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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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iii. # Δ V ≈ 10 cm3 mol-1 featur
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conventional methods are classical
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Figure 2.6: Schematic diagram of a
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The light transmitted from the samp
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c. Oxidizability: Ligands that are
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Table 2.1: A selection of n o pt va
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eaction with different nucleophiles
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eaction site from direct attack by
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PEt 3 PEt 3 R PEt 3 Pt Pt Y Y Cl R
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direct displacement of the leaving
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therefore, weaken the bond of the l
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σ-Donation According to classical
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References 1 (a) J. Reedijk, Chem.
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34 R. B. Jordan, Reaction Mechanism
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Table of Contents-3 Chapter 3.The
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Chapter 3 The π-Acceptor Effect in
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In order to extend our understandin
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after which water was added to quen
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O CH 3 + I + N O oH - N O O 7 CH 3
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84% (34.7 mg, 0.0618 mmol). 1 H NMR
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PhCN PhCN Pt Cl Cl + N N CH 3 N CH
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Complex Structure HOMO LUMO PtCl CH
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The geometry-optimised structures i
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against the concentration of the in
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Table 3.2: Summary of the second-or
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constants of CH3PhisoqPtCl decrease
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with π*-orbitals of the ligand. Th
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3.6 References 1 D. Rosenberg, L. V
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30 Microcal TM Origin TM Version 5.
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Figure S3.1: Kinetic trace at 448 n
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ln(k 2 /T) -6.0 -7.5 -9.0 -10.5 -12
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Table S3.3b: Average observed rate
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Table S3.5b: Temperature dependence
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Table S3.8: DFT calculated electros
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List of Figures Figure 4.1: Structu
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Table 4.2: Summary of pKa values fo
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4.1 Introduction Platinum compounds
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cis geometry, leading to dramatic c
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ligand was added to the [{cis-PtCl(
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spectra were measured in and refere
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4.3.1 DFT calculated Optimized Stru
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Table 4.1: A summary of the DFT cal
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H2O-Pt-L-Pt-OH2 H2O-Pt-L-Pt-OH2 H2O
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electrophilicity and acidity of the
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(A) 18 Absorbance 0.08 0.07 0.06 0.
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k obs(3 rd ) , s -1 -5 6.00x10 TMTU
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4.3.4 Kinetics with NMR The substit
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ln([ML] t ) 4.0 3.5 3.0 2.5 2.0 1.5
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ln(k 2(1 st ) /T) -3.5 -4.0 -4.5 -5
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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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Page 334 and 335: Table S6.3: Average observed rate c
Page 336 and 337: Table S6.4(b): Average observed rat
Page 338 and 339: ln(k 2(2 nd ) /T) -4 -6 -8 -10 -12
Page 340 and 341: 45.0 40 35 30 25 20 %T 15 10 5 0 -5
Page 342 and 343: k st obs(1 ) in s-1 0.30 Br TU 0.25
Page 344 and 345: Table S6.9: Average observed rate c
Page 346 and 347: -2304.16 ppm H 3N PPM -2200.0 -2220
Page 348 and 349: Table S6.10: Average observed rate
Page 352 and 353: Absorbance 1.6 1.4 1.2 1.0 0.8 0.6
Page 354 and 355: SH N SH + Mechanism Br N + CO 3 2-
Page 356 and 357: Figure 7.5: 195Pt NMR spectra of mi
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Page 360 and 361: complexes, have a lower charge and
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Page 364 and 365: ButPt, HexPt, OctPt and DecPt, were
Page 366 and 367: 7.3 Results 7.3.1 DFT Calculations
Page 368 and 369: Structure HOMO LUMO EnPt (C2h) Prop
Page 370 and 371: Absorbance Table 7.2: Summary of pK
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Page 374 and 375: observed at -2962.4 and -3024.1 ppm
Page 376 and 377: H 3N NH 3 Pt NH 2 OH 2 n NH 3 NH 2
Page 378 and 379: k obs2 , in s -1 -3 TU 1.2x10 DMTU
Page 380 and 381: 7.3.4 Activation Parameters The tem
Page 384 and 385: acetylmethionine, which reported th
Page 386 and 387: References 1 (a) B. Rosenberg, L. V
Page 388 and 389: 32 N. Summa, J. Maigut, R. Puchta a
Page 390 and 391: Appendix 7 Table S7.1: Summary of s
Page 392 and 393: k obs(2 nd ) , in s -1 0.00020 0.00
Page 394 and 395: ln(k 2(2 nd ) /T) -8.5 -9.0 -9.5 -1
Page 396 and 397: k obs(1 st ) , in s -1 0.06 TU DMTU
Page 398 and 399: ln(k 2(1 st ) /T) -3.2 TU DMTU TMTU
Page 400 and 401: Table S7.11: Summary of kobs(2 nd )
Page 404 and 405: %T 22.0 20 18 16 14 12 10 8 6 4 2 0
Page 406 and 407: k st obs(1 ) , in s-1 0.10 0.08 0.0
Page 408 and 409: ln(k st 2(1 ) /T) -4.0 TU DMTU TMTU
Page 410 and 411: Figure S7.23: Mass spectra for HexP
Page 412 and 413: Table S21: Average observed rate co
Page 414 and 415: Table S7.23: Summary of kobs(2 nd )
Page 418 and 419: 90.0 80 70 60 50 40 30 20 %T 10 0 -
Page 420 and 421: Figure S7.37: Mass spectrum for Hex
Page 422 and 423: Chapter 8 Tuning Reactivity of plat
Page 424 and 425: dinuclear Pt(II) complexes to relea
Page 426 and 427: finally Pt2. The order of reactivit
Page 428: • prolonged survival in the cell
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