The details of the electronic structure and bonding in ferrocenes and early transition metal bent metallocenes are probed by photoelectron spectroscopy. The fundamental electronic interaction of the methyl group substituted for a hydrogen on a metal-coordinated cyclopentadienyl ring is shown by a combined core and valence pe spectroscopic study of a series of methyl-substituted ferrocenes. Shifts of core and valence ionization energies upon methyl substitution are equivalent and additive for the iron atom. Knowledge of the core ionization energy shifts for both carbon and iron allow the relative changes in atomic charges upon methyl substitution to be found. In these molecules, the methyl group is found not to be an inductive electron donor as is commonly assumed. The primary electronic effect of methyl substitution is on the valence orbitals of the cyclopentadienyl ring. Methylation of the cyclopentadienyl rings of ferrocene causes a dramatic redistribution of valence electron density and greatly increases the covalent nature of metal-ring bonding. An understanding of the electronic effect of methylation of metal-coordinated cyclopentadienyl rings is used to establish the relative locations of ring π and Cl ionizations in the pe spectra of group IV and V early transition metal bent metallocene dichlorides with both unsubstituted cyclopentadienyl and pentamethylcyclopentadienyl ligands. The differences in chloride and methyl ligand bonding to an early transition metal center are reflected in the photoelectron data of the dichlorides and related dimethyls. The relative differences in metal-chlorine and metal-carbon bond strengths are also shown in the pe data. The relationship between bond strengths and ionization energies is detailed for early transition metal bent metallocenes of niobium and tantalum with a variety of ligands. The relative bond strength/ionization energy information for metal-hydrogen and metal-carbon bonds is shown to help in understanding the stability of niobocene and tantalocene ethylene-hydride complexes and their resistance to intramolecular olefin insertion. Evidence from the pe data concerning the electron distribution as well as the relative bond strengths in these ethylene-hydride complexes is found supporting the consideration of these complexes more properly as metallacyclopropane-hydrides.

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Understanding electron-transfer (ET) processes in proteins is of fundamental importance. In a series of photophysical studies of well-behaved peptide model systems, it has become evident that the ET through peptide spacers is greatly influenced by the separation between the acceptor (A) and the donor (D), the nature of the peptide backbone, the amino acid sequence, and the resulting flexibility of the peptide conjugates. In particular, it was suggested in the literature that the presence of H-bonding will increase the rate of ET, and there is experimental evidence, mostly in proteins, to suggest that H-bonding indeed increases the rate of ET.<p>My aim was to develop a potential-assisted deposition method for ferrocene peptide disulfides onto gold surfaces and investigate the electrochemical properties of these films. We made use of two classes of Fc-peptides: acylic ferrocenoyl (Fc)-peptide disulfides and cyclo-1,1-Fc-peptide disulfides, allowing the preparation of tightly packed films of cyclic and acylic Fc-peptides on gold surfaces within 30 minutes. This is a significant benefit compared to the conventional soaking method of self-assembly requiring several days for the assembly of well-packed films. Such films exhibited considerably improved stability. This electrodeposition method should find wide-spread applications for the formation of tightly-packed films from disulfides. Our studies allowed a direct comparison of the electron transfer kinetics of cyclic and acyclic Fc-peptide disulfide systems. Our results showed faster ET kinetics for films prepared from cyclic Fc-peptide conjugates compared to the acyclic systems, presumably as a result of the enhanced rigidity of the Fc-peptide conjugates on the surface and/or an increase of the number of conductive peptide wires to the surface. Following the idea of peptide dynamics as a major contributor to the observed electron transfer rate in peptides and peptide conjugates, variable temperature electrochemical studies of Fc-peptide films were performed. An estimation of the reorganization energy associated with ferrocene/ferrocenium (Fc/Fc+) redox process allowed us to probe the role of peptide dynamics. Three counter-ions were tested, exhibiting different strengths of association with the Fc+ group (BF4- < ClO4- < PF6-) and the reorganization energies were evaluated in each case. The highest reorganization energy was obtained for the weakly interacting anion BF4-. Weakly interacting anions also showed significant broadness in the redox peaks and emergence of the second oxidation peak which is attributed to phase separation of the ferrocene group. Ferrocene agglomeration was not observed for any of the cyclic Fc-peptide conjugates but occurred for some of the acyclic systems. In particular, for acyclic Val and Leu containing Fc-peptide conjugates agglomeration were observed and was presumably caused by lateral interactions between the hydrophobic side-groups of the peptides. Further experiments involving the interaction of Fc-peptide films with alkali metal ions gave additional evidence that electron transfer is influenced significantly by peptide dynamics.

Understanding electron-transfer (ET) processes in proteins is of fundamental importance. In a series of photophysical studies of well-behaved peptide model systems, it has become evident that the ET through peptide spacers is greatly influenced by the separation between the acceptor (A) and the donor (D), the nature of the peptide backbone, the amino acid sequence, and the resulting flexibility of the peptide conjugates. In particular, it was suggested in the literature that the presence of H-bonding will increase the rate of ET, and there is experimental evidence, mostly in proteins, to suggest that H-bonding indeed increases the rate of ET.<p>My aim was to develop a potential-assisted deposition method for ferrocene peptide disulfides onto gold surfaces and investigate the electrochemical properties of these films. We made use of two classes of Fc-peptides: acylic ferrocenoyl (Fc)-peptide disulfides and cyclo-1,1-Fc-peptide disulfides, allowing the preparation of tightly packed films of cyclic and acylic Fc-peptides on gold surfaces within 30 minutes. This is a significant benefit compared to the conventional soaking method of self-assembly requiring several days for the assembly of well-packed films. Such films exhibited considerably improved stability. This electrodeposition method should find wide-spread applications for the formation of tightly-packed films from disulfides. Our studies allowed a direct comparison of the electron transfer kinetics of cyclic and acyclic Fc-peptide disulfide systems. Our results showed faster ET kinetics for films prepared from cyclic Fc-peptide conjugates compared to the acyclic systems, presumably as a result of the enhanced rigidity of the Fc-peptide conjugates on the surface and/or an increase of the number of conductive peptide wires to the surface. Following the idea of peptide dynamics as a major contributor to the observed electron transfer rate in peptides and peptide conjugates, variable temperature electrochemical studies of Fc-peptide films were performed. An estimation of the reorganization energy associated with ferrocene/ferrocenium (Fc/Fc+) redox process allowed us to probe the role of peptide dynamics. Three counter-ions were tested, exhibiting different strengths of association with the Fc+ group (BF4- < ClO4- < PF6-) and the reorganization energies were evaluated in each case. The highest reorganization energy was obtained for the weakly interacting anion BF4-. Weakly interacting anions also showed significant broadness in the redox peaks and emergence of the second oxidation peak which is attributed to phase separation of the ferrocene group. Ferrocene agglomeration was not observed for any of the cyclic Fc-peptide conjugates but occurred for some of the acyclic systems. In particular, for acyclic Val and Leu containing Fc-peptide conjugates agglomeration were observed and was presumably caused by lateral interactions between the hydrophobic side-groups of the peptides. Further experiments involving the interaction of Fc-peptide films with alkali metal ions gave additional evidence that electron transfer is influenced significantly by peptide dynamics.

The preparations of multinuclear supramolecules assembled from ethynylferrocene(s) redox-active subunit end-capping with [(£b5-C5H5)(dppe)Ru] metal centers are described. Electrochemical measurements indicate that ferrocenyl-ethynyl spacers appear to be promising spacers which can ensure fast and quantitative transfer of information between two Ru2+ metal centers.

A series of ferrocenylimine [(£b5-C5H5)Fe(£b5-C5H4-C(Me)=N-R)]¡AR= nhexyl(1a)¡Acyclohexyl(1b)¡Aphenyl(1c)¡AN,N-dimethylethylamino(1d) ¡A4-methoxyphenyl(1e)¡A4-nitrophenyl(1f)¡Aand 2-methoxyethyl(1g)¡Ahave been synthesized by reaction of acetylferrocene and the corresponding amines through condensation reaction. Also 1,1¡¦-ferrocenyldiimines [Fe{(£b5-C5H4)-C(Me)=N-R}2]¡AR= nhexyl(2a)¡Acyclohexyl(2b)¡Aphenyl(2c)¡AN,N-dimethylethylamino(2d)¡A4-methoxyphenyl(2e)¡A4-nitrophenyl(2f)¡A3-nitrophenyl(2g)¡A2-methoxyethyl(2h) have been synthesized by reaction of 1,1¡¦-diacetylferoocene and the corresponding amines through condensation reaction. Solid state crystal X-ray structural analysis revealed the geometry of the ferrocene derivatives are various with the different substituents . In addition, these ferrocene derivatives might coordinate with CuBr to form a series of iminoferrcenyl copper(¢¹) complexes. Solid state crystal X-ray structural analysis revealed the iminoferrcenyl copper(¢¹) complexes 3a~3d showed monomeric or dimeric geometry and diiminoferrcenyl copper(¢¹) complexes 4a~4d exhibited polymeric or dimeric geometry. All synthesized ferrocenylimine and1,1¡¦-ferrocenyldiimines derivatives exhibited a reversible one ¡Velectron redox process in their cyclic voltammograms, and the values of their redox potentials relied on the R groups. The correlation between the redox potential and the Hammett substituent constant, £mp was quite well, with a correlation coefficient of 0.96 in CH2Cl2 and CH3CN. According to the cyclic voltammograms, iminoferrocenyl copper complexes showed that the substituents on the imino parts strongly affect the redox potentials of the iron centers in the ferrocenyl segments as well as the copper metal center. The Cu+/Cu2+ couple redox potentials are in the range of 0.269V and 0.719V dependent on solvent effect. The iminoferrocenyl copper complexes¡¦s UV-vis absorption seems to be red shift comparing with iminoferrocene. In the CH2Cl2, compound 3a¡B3b¡B4d shows emission at £fmax ~ 408 nm . In the CH3CN, compound 3a¡B3b¡B3c¡B3d¡B4a¡B4b and 4c show the blue shift emission band comparing with iminoferrocenyl copper complexes in CH2Cl2. In addition, complex 4d in CH2Cl2 and complex complex 3d in CH3CN showed higher quantum yield value. Moreover, compound 1a and 2a combined with CuBr exhibit good catalytic activity and controlling ability in the MMA ATRP process.

Structural determinations and electrochemical properties in the series of multinuclear ferrocenyl-ethynyl complexes with formula [(£b5-C5(CH3)5)(P2)MII-C¡ÝC-(fc)n-C¡ÝC-MII(P2)(£b5-C5(CH3)5)] (fc = ferrocenyl; M = Fe(II), Ru(II), Os(II); R = H, CH3; P2 = Ph2PCH2CH2PPh2 (dppe)) are reported. Complexes with more electron-rich ligand environment, were prepared with regard to the understanding of electronic coupling mechanism. These complexes undergo sequential reversible oxidation events from -0.2 V to 1.0 V referred to the Ag/AgCl electrode in anhydrous CH2Cl2 solution and the low-pontential waves have been assigned to the end-capped metallic centers. The magnitude of the electronic coupling between two terminal metallic centers in the series of complexes was estimated by electrochemical technique. Based on the correlation between the £GE1/2 values and the second redox potentials of the end-capping metallic centers in the series of complexes, a qualitative explanation for the different magnitude of the electronic coupling is given.

The planar-chiral C2-symmetrical dibromoferrocene derivatives, (S,S,Sp,Sp)-1,1'-dibromo-2,2'-di(2-butyl)ferrocene (88) and (S,S,Sp,Sp)-1,1'-dibromo-2,2'-bis{2-[1-(trimethylsilyl)propyl]} ferrocene (92), were synthesized using the well-established “Ugi’s amine” chemistry. The steric influences of the alkyl groups on ferrocenes 88 and 92 in salt-metathesis reactions were investigated. The reaction of 88 and 92 with iPr2NBCl2 yielded mixtures of bora[1]ferrocenophanes (bora[1]FCPs) 94 and 99 and 1,1'-bis(boryl)ferrocenes 95 and 100 respectively. Ferrocene 92 was expected to yield the highest product ratio of bora[1]FCPs to 1,1' bis(boryl)ferrocenes due to the significant amount of steric bulk on ferrocene from the alkyl groups; however, the product ratio was less than the product ratio obtained for the less bulky ferrocene 88. The product ratios for 88 and 92 were compared to the known product ratios for (Sp,Sp)-1,1'-dibromo-2,2'-di(isopropyl)ferrocene (78) and (Sp,Sp)-1,1'-dibromo-2,2'-di(3-pentyl)ferrocene (79) to determine the effects of the alkyl groups in salt-metathesis reactions. To gain more insight into the effects of the alkyl groups on ferrocenes 88 and 92, a series of conformational analyses of 78, 88, and 92 were performed using density functional theory (DFT) calculations. The DFT calculations aided in the explanation for the unexpectedly low product ratio obtained for ferrocene 92. In efforts to obtain new [1]ruthenocenophanes ([1]RCPs), the synthesis of the ruthenium analog of 78, (Sp,Sp)-1,1'-dibromo-2,2'-di(isopropyl)ruthenocene (105), was attempted. To accomplish this, (R,R)-1,1'-bis(α-N,N-dimethylaminoethyl)ruthenocene (109) was prepared using the same chemistry that was used to prepare its ferrocene analog. However, the synthesis of (R,R,Sp,Sp)-1,1'-dibromo-2,2'-bis(α-N,N-dimethylaminoethyl)ruthenocene (110) via the dilithiation of 109 was unsuccessful. The synthesis of dibromoferrocene derivatives using “Ugi’s amine” chemistry is a long and inflexible process. Therefore, a method to prepare dibromoferrocene derivatives through an alternative synthetic pathway was investigated. The synthesis of (Ss,Ss)-1,1'-bis(p-tolylsulfinyl) ferrocene (118) was accomplished by reacting dilithioferrocene•tmeda with (1R,2S,5R)-(-)-menthyl (SS)-p-tolylsulfinate (117). The diastereoselective dilithiation and subsequent silylation of 118 to obtain (Ss,Ss,Sp,Sp)-2,2'-bis(trimethylsilyl)-1,1'-bis(p-tolylsulfinyl)ferrocene (120) proved to be problematic.

Magister Scientiae - MSc / Glucose oxidase (GOx) and horseradish peroxidase (HRP) are important enzymes for the development of amperometric enzyme linked immunosensors. The selectivity of each enzyme towards its analyte deepens its importance in determining the sensitivity of the resultant immunosensor. In designing immunosensors that have customized transducer surfaces, the incorporation with FAD and iron based enzymes ensures that electron kinetics remains optimal for electrochemical measurement. Various different immobilization strategies are used to produce response signals directly proportional to the concentration of analyte with minimal interferences. The combination of self-assembled monolayers and supramolecular chemistry affords stability and simplicity in immunosensor design. In this work, two electrochemical strategies for the detection of human chorionic gonadotropin (hCG) is presented. This involves the modification of a gold surface with a thiolated β- cyclodextrin epichlorohydrin polymer (βCDPSH) to form a supramolecular inclusion complex with ferrocene (Fc)-functionalised carboxymethyl cellulose polymer (CMC). Cyclic voltammetry indicated that ferrocene is in close proximity to the electrode surface due to the supramolecular complex formed with βCDPSH. Furthermore, strategy (a) for the detection of hCG used α-antihCG labelled (HRP) as reporter conjugate. Strategy (b) maintained the CMC bifunctionalised with Fc and recognition antibody for hCG hormone. However, the system was functionalised with a HRP enzyme and detection is done by using GOx reporter conjugates for in situ production of hydrogen peroxide. The reduction of H2O2 was used for the amperometric detection of hCG by applying a potential of 200 mV. The sensitivity and limit of detection of both strategies were calculated from calibration plots. For strategy (a) the LOD was found to be 3.7283 ng/mL corresponding to 33.56 mIU/mL and a sensitivity of 0.0914 nA ng-1 mL-1. The corresponding values for strategy (b) are 700 pg/mL (6.3 mIU/mL) and 0.94 nA ng-1 mL-1.