Articles

The Influence of Auxiliary Ligands on the Photophysical Characteristics of a Series of Ruthenium (II) Polypyridyl Complexes

Luke O'Neill et al. — Mon, 15 Oct 2012 07:00:26 PDT

A series of ruthenium polypyridyl complexes were studied using UV/Vis absorption and luminescence spectroscopy as well as luminescence lifetime determination by time correlated single photon counting (TCSPC). The complexes were characterised with regard to the variation in the electronic band-gap as a result of the sequential variation of the auxiliary ligand 2,2’-bipyridine (bpy), 1,10-phenanthroline (phen) and 2,2’-biquinoline (biq) ligands while the main ligand remained constant for three different main ligand types. Luminescence yields were calculated and correlated with structural and electronic variation. It was found that both the absorption and emission characteristics could be tailored through the systematic variation of the electron affinity of the individual auxiliary ligand. This was shown to be the case regardless of the functional group at the end of the main ligand. Stokes shift and Raman spectroscopy was employed as a means to gauge the effect of ligand change on the conjugation and vibrational characteristics of the complexes. Luminescence yield and lifetimes were also shown to be well-defined with regards to systematic structure variations. The well-defined trends established elucidate the effect which variation of auxiliary ligands has on the electronic characteristics of the ruthenium polypyridyl systems. These well-defined relationships can potentially be extended to optimise luminescence yield and lifetimes and therefore suitability of such compounds for the application in for example photodynamic therapy.

A Study Examining the Effects of Tissue Processing on Human Tissue Sections using Vibrational Spectroscopy

Eoghan O'Faolain et al. — Thu, 21 Jul 2011 02:12:38 PDT

The use of vibrational spectroscopy in the detection of cancer is a newly emerging diagnostic field, which has shown great potential to date. Many investigations have been carried out on frozen tissue samples, which by their very nature are hard to obtain. However, histology departments have archives of thousands of tissue samples, preserved and mounted in wax blocks. If this archival material can be shown to yield good Raman and IR spectra capable of differentiating between normal and cancerous tissue, it would improve the diagnostic capabilities of spectroscopy even further. Results from these formalin-fixed paraffin processed (FFPP) tissue sections, will give a better understanding of the effects of processing and could unlock the potential diagnostic capabilities of FFPP sections. This study investigated the effect of freezing, formalin fixation, wax embedding and de-waxing. Spectra were recorded from parallel tissue sections of placenta to examine biochemical changes before, during and after processing with both Raman and IR spectroscopy. FFPP sections were shown to provide good quality Raman and IR spectra but new peaks due to freezing and formalin fixation as well as shifts in the amide bands resulting from changes in protein conformation and possible cross-links were found. Residual wax peaks were observed clearly in the Raman spectra. In the FT-IR spectra a single wax contribution was seen which may contaminate the characteristic CH3 deformation band in biological tissue. This study has therefore confirmed that FFPP sections have diagnostic potential provided that researchers are aware of the biochemical changes due to tissue processing highlighted by this study.

Water-soluble CuII and MnII bis-phenanthroline octanedioate complexes with unprecedented nano and picomolar in vitro cytotoxicity as promising leads for chemotherapeutic drug development

Andrew Kellett et al. — Tue, 19 Jul 2011 03:42:30 PDT

Dinuclear Cu^II and Mn^II bis-phenanthroline octanedioate complexes exhibit rapid, unprecedented nano and picomolar in vitro cytotoxicity against colorectal cancer lines and are less toxic than cisplatin when examined in vivo. The complexes are potent generators of cellular reactive oxygen species, avid DNA binders and induce O₂ dependent cleavage of DNA. The Cu(II) complex was found to have self-cleaving nuclease activity.

Enantioselective Complexation of Amino Acids by 6A-Deoxy-6A-hydroxyethylamino- β -Cyclodextrin and its Metallo-Derivatives in Aqueous Solution

Nicole Van Hoof et al. — Mon, 18 Jul 2011 07:05:11 PDT

Enantioselectivity towards several amino acids by metallo-6A-deoxy-6A-hydroxyethylamino-β-cyclodextrins (metallo- β CDea’s) was investigated by potentiometric titration of the various amino acid/metallo- β CDea systems with NaOH solution. It was shown that the cyclodextrin derivative is capable of distinguishing between enantiomers of amino acid species in the presence of certain metal ions (Co, Ni, Cu and Zn). Ni- β CDea complexes show the most enantioselectivity,whereas for Cu and Co2C-_CDea complexes less selectivity is observed. As expected, Zn- β CDea complexes exhibit no enantioselectivity. Stability and selectivity, however, do not go hand in hand, since the most stable complexes are formed with Cu2C. Several factors play a role in determining stability and selectivity in binary and ternary complexes and further study is required to gain a more comprehensive understanding of these.

Characterization of the Interaction of Gamma Cyclodextrin with Single-Walled Carbon Nanotubes

Gordon Chambers et al. — Mon, 18 Jul 2011 06:57:56 PDT

In this study a number of composite-like samples of ç-cyclodextrin and HiPco carbon nanotubes were prepared. The first sample was prepared by a simple grinding procedure, which has been reported to cut HiPco carbon nanotubes. The other samples were obtained via a refluxing procedure analogous to similar studies on other fullerenes and ç-cyclodextrin. The samples were analyzed using absorption and Raman spectroscopy, and differential scanning calorimetry. The results presented show clear evidence of an intermolecular interaction between ç-cyclodextrin and single-walled carbon nanotubes.

Correlation of Vibrational Intensity with Fluorescence Lifetimes in π Conjugated Polymers

Luke O'Neill et al. — Mon, 24 Jan 2011 11:52:47 PST

A series of novel pi (p) conjugated polymers, originating from the archetypical Polyphenylene vinylene, in which the phenyl units are successively replaced by the larger naphthyl and anthryl acene units, were previously found to have a well-defined relationship between their relative fluorescence yields and their vibrational characteristics, as determined by Raman spectroscopy. In this study the Strickler–Berg equation is used to probe the influence of continual substitution of higher order acene units into the conjugated backbone in terms of the variation of the radiative and non-radiative rates. The deconvolution of the radiative and non-radiative rates enables the correlation of the reduction of the Raman intensity and concomitant increase in the fluorescence yield with the reduction of the non-radiative rate. This confirms that the reduction of the non-radiative rate is the dominant process introduced by the vibrational confinement originating from systematic substitution of higher order acene units into the polymer backbone.

A Systematic Study of the Effects of Naphthalene and Anthracene Substitution on the Properties of PPV Derivative Conjugated Systems

Patrick Lynch et al. — Mon, 24 Jan 2011 11:52:46 PST

The systematic synthesis of poly(phenylvinylene) (PPV) derivatives by the Wittig-Horner reaction is reported. The phenyl units of the PPV structure are methodically substituted by naphthyl and anthryl units to form a homologous series of structures. The 2,6 attachment of the vinylene linkage on the anthryl ring provides novel structures that have not been reported before due to their synthetic inaccessibility. The introduction of naphthyl units results in a hypsochromatic shift in the absorption and emission spectra, while the introduction of anthryl units leads to a bathochromatic shift relative to the naphthalene structures. The observed structural variation of the spectroscopic properties is explained in terms of a combination of the increased conjugation of the substituent acene units and the decreased electronic contribution across the vinyl linkage.

Vibrational Characterisation and Fluorescence Optimisation of Polycyclic Polymers

Luke O'Neill et al. — Mon, 24 Jan 2011 11:52:45 PST

A systematic series of polycyclic novel polymers was studied by Raman spectroscopy. The effect of the sequential introduction of polycyclic aromatic ring substituents into the delocalized backbone was examined in relation to the variation of the relative ring breathing and stretching as well as the vinyl stretch frequencies. Replacement of the phenyl units by higher order acene moieties such as naphthyl and anthryl results in a shift of the characteristic stretching frequencies, and analysis of the vinyl stretch leads to the confirmation that higher order acene substitution into the delocalized backbone substantially weakens the vinyl bond. Semiquantitative integrated Raman analysis shows a well-defined variation of the vibrational characteristics with structure. The structural variation of the integrated Raman intensity elucidates the effect of the electronic and vibrational decoupling introduced by the continual systematic acene substitution and points toward the ability to tailor the vibrational characteristic of the polymeric systems much the same as the electronic characteristics are manipulated. Relative fluorescence yields calculated for absorption and fluorescence spectroscopy can be seen to be well-correlated with integrated Raman intensities, implying that the reduction of the vibrational intensity limits the avenues of nonradiation, hence optimizing the fluorescence yield.

Spectroscopic Characterisation of Novel Polycyclic Aromatic Polymers

Luke O'Neill et al. — Mon, 24 Jan 2011 11:52:43 PST

A series of novel polyphenylenevinylene (PPV) derivative polymers were studied by absorption and photoluminescence spectroscopies. The effect of the sequential introduction of polycyclic aromatic ring substituents into the delocalized backbone was examined with relation to hypsochromatic and bathochromatic shifting. While the replacement of the phenyl units by naphthyl units results in a substantial hypsochromic shift of both the absorption and emission spectra, their subsequent substitution by anthryl units results in a bathochromic shift. The system is modeled according to, and is found to be consistent with, a previous study of donor-acceptor polyenes of varying length. The electronic structure of the backbone is found to be a balance between that of the high electron affinity polycyclic ring system and the contribution to conjugation across the linking vinyl unit. The model is adapted based on electron affinities of the constituent units, and a clear structure-property relationship for the absorption and emission properties of the system is elucidated. The Stokes shift is examined and is seen to be well-correlated with the vinyl contribution to the electron affinity total (EAtotal). The trends observed in the optical properties of the polymeric system are supported by Raman spectroscopy, whereby the spectral signature of the connecting vinyl bond is seen to soften in a fashion which is correlated with the modeled electron affinity parameters.

Chirality Studies on Metallo-Cyclodextrins for the Separation of L/D-DOPA

Ciaran Potter et al. — Mon, 24 Jan 2011 11:45:02 PST

The derivatives 6-Deoxy-6-[1-(2-amino)ethylamino]-b-Cyclodextrin (CDEn), 6-Deoxy-6-[1-(3-amino)propylamino]- b-Cyclodextrin (CDPn) and 6-Deoxy-6-[1-(4-amino)butylamino]-b-Cyclodextrin (CDBn) were assessed with a view to demonstrating that increasing the chain length of the diaminoalkane moiety can affect the chiral selectivity of the metallo-complexes of these materials. It was shown that IR and Raman spectroscopies can be used to characterise these compounds. The results obtained from the electronic absorption spectra suggested the formation of CuCDAm binary complexes and that the derivatives CDEn and CDPn act as bidentate ligands while CDBn acts as a monodentate ligand due to its longer alkane chain. This study also showed that in the ternary complexes with DOPA there is further coordination of the metal ion to the amino nitrogen atom and the hydroxyl oxygen atom of the drug. On the basis of the results of the circular dichroic spectroscopic studies it was suggested that CuCDEn is the better enantioselective material for DOPA and it acts in a multi-site recognition manner, utilising the inclusion properties of the CD cavity in cooperation with the coordination properties of the metal ion.

Temperature Dependent Spectroscopic Studies of HiPco SWNT Composites

Sinead Keogh et al. — Mon, 24 Jan 2011 11:45:00 PST

Electrochemical Characterisation of Poly Arylene Vinylenes

Jonathan Moghal et al. — Fri, 14 Jan 2011 05:05:41 PST

The electrochemical properties of a newly synthesised set of PPV derivatives were measured by cyclic voltammetry. A new octyloxy substituted PPV derivative was first synthesised (POPV). The structure of the POPV is varied systematically by the replacement of the phenyl units by naphthyl and anthryl units and the effect of these variations on the electrochemical properties is explored. The HOMO–LOMO levels of the polymers were determined from the onset potentials for the p-doping and n-doping scans. From this the electrochemical bandgap for each of the polymers was calculated. The systematic change in the structure of the POPV results in a systematic increase in the LOMO level of the polymer series whereas a concomitant increase in HOMO level results in an overall increase in the bandgap of the polymers series. The variation in the electrochemical, optical properties and vibrational properties observed within the polymer series were all found to correlate with the structural changes made, pointing towards structure property relationships and a guide to future synthetic strategies.

Synthesis and Characterization of a Colloidal Novel Folic Acid–β-cyclodextrin Conjugate for Targeted Drug Delivery

Antonio Clementi et al. — Fri, 14 Jan 2011 04:50:49 PST

A novel folic acid–b-cyclodextrin (b-CD) conjugate was synthesized and preliminarily characterized by 1H NMR, ESI-MS, and MALDI-MS. 1H NMR shows the presence of a- and c-conjugates which are generated by b-CD linkage in turn with both carboxylic functions of folic acid. Moreover ROESY evidences supramolecular interactions between the benzene ring of the folic acid and the b-CD cavity. DOSY suggests that ethylenediamine derived b-CD–folic acid forms a colloidal dispersion difficult to purify from free folic acid. An analysis of self-diffusion coefficient (Ds) of the three species (a-, c-conjugates, and free folic acid) and relaxation times (T1 and T2) is reported to tentatively explain the colloidal behaviour of the new species in an aqueous solution.

Hexakis(prop-2-enamide)copper(II) bis(perchlorate) and hexakis(prop-2- enamide)manganese(II) bis(perchlorate)

Mary McNamara et al. — Fri, 14 Jan 2011 04:50:47 PST

The structures of [Cu(AA)6](ClO4)2, (I), and [Mn(AA)6](ClO4)2, (II) (AA is acrylamide, also known as prop-2-enamide; C3H5NO), display both intra- and intermolecular N-H...O hydrogen bonding. A three-dimensional network is propagated via the perchlorate counter-ions. There are two crystallographically independent molecules in the copper complex, with the most significant difference between them being the conformation of one symmetry-related pair of AA ligands which are in the unusual syn conformation. The copper complex exhibits syn/anti disorder of the =CH2 group in one pair of symmetry-related AA ligands. The CuII and MnII centres are both situated on centres of inversion. The copper complex cation has octahedral coordination geometry with typical Jahn-Teller distortions.