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Vivian Wing-Wah Yam

Publications and source records attributed to Vivian Wing-Wah Yam.

At least 19 recordsLinked to original sources
PubMed2007

Specific postcolumn detection method for HPLC assay of homocysteine based on aggregation of fluorosurfactant-capped gold nanoparticles.

Gold nanoparticles (GNPs) capped with nonionic fluorosurfactant molecules (Zonyl FSN) were synthesized, and with the colloidal solution as a probe reagent, a new postcolumn colorimetric detection method for HPLC assay of homocysteine (Hcy) has been developed. The FSN-capped GNPs exhibited excellent stability in aqueous solutions, even in the presence of high salt. The aggregation of the GNPs could be induced by either Hcy or cysteine, resulting in an absorption decrease of the colloidal solution at 525 nm and an absorption increase at longer wavelengths (600-700 nm); however, the GNPs did not respond to other amino acids and biomolecules such as glutathione, cysteinylglycine, and glucose. Under optimal conditions (i.e., high salt, neutral pH, and approximately 70 degrees C), the color change of the GNP solution could almost complete ( approximately 90%) within approximately 30 s upon the addition of Hcy. The high selectivity and very fast kinetics of the reaction make it a promising system for HPLC postcolumn detection. The new technique has been employed to determine total Hcy levels in human urine and plasma samples, and the results are satisfactory.

Amino Acids↗
PubMed2006

Single-stranded nucleic acid-induced helical self-assembly of alkynylplatinum(II) terpyridyl complexes.

Single-stranded nucleic acids, which carry multiple negative charges in an aqueous medium at near neutral pH, are found to induce the aggregation and self-assembly of the positively charged alkynylplatinum(II) terpyridyl complexes via electrostatic binding of the platinum complexes to the single-stranded nucleic acids, as revealed by the appearance of new UV-vis absorption and emission bands upon addition of single-stranded nucleic acids to a buffer solution of the complex. Changes in the intensity and pattern of circular dichroism (CD) spectroscopy are also observed, many of which are consistent with the assembly of the platinum complexes into helical structures, via metal...metal and pi...pi stacking interactions. The induced spectroscopic property changes are found to depend on the structural properties of the nucleic acids.

Nucleic Acid Conformation↗
PubMed2006

Computational studies on the photophysical properties and NMR fluxionality of the tetranuclear copper(I) complexes [Cu4(mu-dppm)4(mu4-E)]2+ (E = PPh and S).

Density functional theory (DFT) calculations at the hybrid Perdew, Burke, and Ernzerhof functional level were performed to study the electronic structures of the ground and excited states of the luminescent tetranuclear copper(I) complexes [Cu4(mu-dppm)4(mu4-E)]2+ [E = PPh (1) and S (2)] by using model complexes [Cu4(mu-H2PCH2PH2)4(mu4-E)]2+ [E = PPh (1a) and S (2a)]. The time-dependent DFT method at the same level associated with the conductor-like polarizable continuum model was used to study the nature of the low-energy transitions in their electronic absorption spectra. The results indicate that the lowest energy absorptions of both 1 and 2 are attributed to ligand-to-metal charge-transfer (LMCT) (E --> Cu4) with mixing of metal-cluster-centered (MCC) (3d --> 4s/3d --> 4p) singlet-singlet transitions. The geometry optimizations on the lowest energy triplet state reveal that the emissive states of both complexes involve a considerable structural distortion in which they are derived predominantly from an admixture of 3LMCT (E --> Cu4) and 3MCC (3d --> 4p) origin. In addition to the photophysical properties, the fluxional behavior of 2 observed from the NMR studies but not that of 1 was investigated. It is found that the fluxionality in 2 involves the shuttling of the sulfido ligand through the rectangular Cu4 core.

Journal Article↗
PubMed2006

Luminescent phosphine gold(I) thiolates: correlation between crystal structure and photoluminescent properties in [R3PAu{SC(OMe)=NC6H4NO2-4}] (R = Et, Cy, Ph) and [(Ph2P-R-PPh2){AuSC(OMe)=NC6H4NO2-4}2] (R = CH2, (CH2)2, (CH2)3, (CH2)4, Fc).

X-ray crystallography shows the gold atoms in [R3PAu{SC(OMe)=NC6H4NO2-4}] (R = Et, Cy, Ph; 1-3, respectively) and [(Ph2P-R-PPh2){AuSC(OMe)=NC6H4NO2-4}(2)] (R = CH2, (CH2)2, (CH2)3, (CH2)4, Fc; 4-8, respectively) are linearly coordinated by phosphorus and thiolate-sulfur; weak intramolecular Au...O interactions are featured in all structures. The smaller ethyl substituents in 1 allow for supramolecular association via Au...S and Au...Au interactions that are not found in 2 and 3, which contain larger phosphorus-bound Cy and Ph groups, respectively. Intramolecular Au...Au interactions are found in the dppm, dppe, dppp, and Fc structures but not in the dppp analogue, for which an anti conformation was found. The structures have been correlated with the results from photophysical study conducted in the solid state. Thus, photoexcitation of 1-7 with lambda > 350 in the solid state and in solution produces green and blue luminescence, respectively. The spectra in each medium are remarkably similar to each other, and so the emission energy and excitation maxima observed for 1-7 appear to be independent of the nature of the ancillary phosphines, as well as the presence or absence of Au...Au interactions, either intermolecularly or intramolecularly.

Journal Article↗
PubMed2006

Sensitive single-layered oxygen-sensing systems: polypyridyl ruthenium(II) complexes covalently attached or deposited as langmuir-blodgett monolayer on glass surfaces.

Oxygen-sensing elements containing single-layered structures of luminescent indicators of ruthenium(II) bipyridyl complexes on glass surfaces prepared by covalent attachment and LB deposition are described. They are capable of detecting gaseous oxygen concentration by luminescence quenching of the indicator with reproducible and large quenching efficiencies that are comparable to the best quenching efficiencies obtained by other ruthenium(II) polypyridine based complexes immobilized in matrixes. The large quenching efficiencies for both films imply that the probe complexes are effectively quenched by oxygen, which is probably due to the thin single-layered structures with large surface-to-area ratio and short distance between the probe complexes and oxygen.

Electrochemistry↗
PubMed2006

Triplet MLCT photosensitization of the ring-closing reaction of diarylethenes by design and synthesis of a photochromic rhenium(I) complex of a diarylethene-containing 1,10-phenanthroline ligand.

Synthesis of the diarylethene-containing ligand L1 based on Suzuki cross-coupling reaction between thienyl boronic acid and the dibromophenanthroline ligand is reported. On coordination to the rhenium(I) tricarbonyl complex system, the photochromism of L1 could be photosensitized and consequently extended from intraligand excitation at lambda< or =340 nm in the free ligand to metal-to-ligand charge-transfer (MLCT) excitation at lambda< or =480 nm in the complex. The photochromic reactions were studied by (1)H NMR, UV/Vis, and steady-state emission spectroscopy. Photosensitization was further probed by ultrafast transient absorption and time-resolved emission spectroscopy. The results provided direct evidence that the formation of the closed form by the MLCT-sensitized photochromic process was derived from the (3)MLCT excited state. This supports the photosensitization mechanism, which involves an intramolecular energy-transfer process from the (3)MLCT to the (3)IL(L1) state that initiated the ring-closure reaction. The photophysical and electrochemical properties of the complex were also investigated.

Journal Article↗
PubMed2006

Unprecedented formation of an acetamidate-bridged dinuclear platinum(II) terpyridyl complex-correlation of luminescence properties with the crystal forms and dimerization studies in solution.

An [corrected] acetamidate-bridged dinuclear platinum(ii) terpyridyl complex has been isolated in two crystal forms, a red form and a dark form, with different luminescence properties; electronic absorption, emission and (1)H NMR studies revealed the presence of a dimerization process in the solution state.

Amides↗
PubMed2006

Synthesis, characterization, spectroscopic, and electrochemiluminescence properties of a solvatochromic azacrown-containing cyanoruthenate(II): potential applications in separation and indirect photometric detection of cations and amino acids in HPLC.

A new anionic ruthenium(II) complex, (Et4N)[Ru(tpyA18C6)(CN)3] (tpyA18C6=N-[4'-(2,2':6',2''-terpyridyl)]-1,4,7,10,13-pentaoxa-16-azacyclohexadodecane), has been synthesized and characterized. The complex was found to show pronounced solvatochromic behavior and, when dissolved in solution, changed its color from purple to yellow when the solvent system was varied from pure acetonitrile to pure water. Its absorption and emission energies in various solvents showed a linear dependence of the Gutman's acceptor number. The characteristic photoluminescence and electrochemiluminescence (ECL) of the complex were also found to be progressively quenched as the proportion of water in a water/acetonitrile mixture increased. Large changes in the chemical shifts of the 1H NMR and 13C NMR signals of [Ru(tpyA18C6)(CN)3]- in different solvents were observed. The complex has also been demonstrated to serve as a mobile-phase additive in high-performance liquid chromatography for separation of metal cations and amino acids. Comparison studies with the crown-free analogue, (Et4N)[Ru(tpy)(CN)3] (tpy = 2,2':6',2''-terpyridine), showed that other than the ion-pair effect, the allosteric host-guest interaction provided by the presence of the pendant crown was essential to the separation performance of the complex. Indirect detection of nonabsorbing analytes has been achieved by monitoring the absorbance changes of the eluent at the metal-to-ligand charge-transfer (MLCT) absorption band maximum of the complex at 445 nm. The effects of pH, ionic strength, and polarity of the mobile phase as well as the complex concentration on the selectivity and resolution have also been studied.

Amino Acids↗
PubMed2006

Synthesis, luminescence and ion-binding properties of palladium(II) complexes with 1,2-bis[di(benzo-15-crown-5)phosphino]ethane (dbcpe).

A series of palladium(II) complexes with 1,2-bis[di(benzo-15-crown-5)phosphino]ethane ligand (dbcpe), [Pd(dbcpe)X2] (X = Cl 1, Br 2 and I 3), have been successfully synthesised and characterised. The X-ray crystal structure of dbcpe has also been determined. The cation-binding properties of the complexes have been studied and the stability constants with alkali metal cations determined. The crown-free analogue of dbcpe, 1,2-bis[bis(3,4-dimethoxyphenyl)phosphino]ethane (ddmppe), and the related complexes have also been prepared and comparison studies have been made.

Anisoles↗
PubMed2005

Luminescent platinum(II) terpyridyl complexes: effect of counter ions on solvent-induced aggregation and color changes.

A series of platinum(II) terpyridyl complexes [Pt(tpy)(C triple bond C-C triple bond CH)]X, 1-X (X=OTf-; PF6-; ClO4-; BF4-; BPh4-); [Pt(tpy)(C triple bond CC6H5)]X, 2-X (X=OTf-; PF6-; ClO4-; BF4-); [Pt(tpy)(C triple bond CC6H4OCH3-4)]OTf, 3-OTf, and [Pt(4'-CH3O-tpy)(C triple bond CC6H5)]OTf, 4-OTf (tpy=2,2':6',2''-terpyridine, OTf=trifluoromethanesulfonate) were synthesized and their photophysical properties determined. Electronic absorption and emission studies showed the formation of a new band upon increasing the diethyl ether content in an acetonitrile/diethyl ether mixture. This was ascribed to the formation of complex aggregates, the solution color of which is dependent on the nature of the anions. This indicates that counter ions play an important role in governing the degree of aggregation and the extent of interactions within these aggregates. Addition of various anions to solutions of 1-OTf and 1-PF6 produced anion-induced color changes upon solvent-induced aggregation, indicating that these complexes may serve as potential colorimetric anion probes.

Journal Article↗
PubMed2005

Hydrothermal-induced assembly of colloidal silver spheres into various nanoparticles on the basis of HTAB-modified silver mirror reaction.

Small colloidal silver spheres (diameter < 10 nm) were found to assemble into various silver nanoparticles including cubes, triangles, wires, and rods in water in the presence of HTAB (n-hexadecyltrimethylammonium bromide) at 120 degrees C, while the colloids were generated in situ on the basis of a HTAB-modified silver mirror reaction during the synthesis process. Adjustment of the synthesis parameters, in particular the concentrations of HTAB and [Ag(NH3)2]+, led to an obvious shape evolution of silver nanoparticles, thus resulting in the shape-selective formation of the silver nanoparticles. The monodisperse nanocubes with a well-defined crystallographical structure (a single crystal bounded by six {200} facets) have a strong tendency to assemble into two-dimensional arrays on substrates. The nanowires with uniform diameter usually existed in the form of two-dimensional alignments. The findings suggested that hydrothermal-induced assembly of small silver colloidal particles should be a convenient and effective approach to the preparation of various silver nanoparticles.

Journal Article↗
PubMed2005

Functionalized platinum(II) terpyridyl alkynyl complexes as colorimetric and luminescence pH sensors.

A series of platinum(II) terpyridyl alkynyl complexes that have been derivatized with basic amino functionalities, [Pt(tpy)(C[triple bond]C-C6H4-NR2-4]X (X = OTf-, R = CH3 1, R = CH2CH2OCH3 2, R = H 3; X = Cl-, R = CH3 4, R = CH2CH2OCH3 5, R = H 6) (tpy = 2,2':6',2' '-terpyridine), have been synthesized and characterized. Their photophysical responses at various acid concentrations were studied. The abilities of the complexes to function as colorimetric and luminescence pH sensors were demonstrated with dramatic color changes and luminescence enhancement upon introduction of acid.

Journal Article↗
PubMed2005

Room-temperature phosphorescence and energy transfer in luminescent multinuclear platinum(II) complexes of branched alkynyls.

A series of luminescent branched platinum(II) alkynyl complexes, [1,3,5-{RC[triple bond]C(PEt3)2PtC[triple bond]C-C6H4C[triple bond]C}3C6H3] (R=C6H5, C6H4OMe, C6H4Me, C6H4CF3, C5H4N, C6H4SAc, 1-napthyl (Np), 1-pyrenyl (Pyr), 1-anthryl-8-ethynyl (HC[triple bond]CAn)), [1,3-{PyrC[triple chemical bond]C(PEt3)2PtC[triple bond]CC6H4C[triple bond]C}2-5-{(iPr)3SiC[triple bond]C}C6H3], and [1,3-{PyrC[triple bond]C(PEt3)2PtC[triple bond]CC6H4C[triple bond]C}2-5-(HC[triple bond]C)C6H3], was successfully synthesized by using the precursors [1,3,5-{Cl(PEt3)2PtC[triple bond]CC6H4C[triple bond]C}3C6H3] or [1,3-{Cl(PEt3)2PtC[triple bond]CC6H4C[triple bond]C}2-5-{(iPr)3SiC[triple bond]C}C6H3]. The X-ray crystal structures of [1,3,5-{MeOC6H4C[triple bond]C(PEt3)2PtC[triple bond]CC6H4C[triple bond]C}3C6H3] and [1,8-{Cl(PEt3)2PtC[triple bond]C}2An] have been determined. These complexes were found to show long-lived emission in both solution and solid-state phases at room temperature. The emission origin of the branched complexes [1,3,5-{RC[triple bond]C(PEt3)2PtC[triple bond]CC6H4C[triple bond]C}3C6H3] with R=C6H5, C6H4OMe, C6H4Me, C6H4CF3, C5H4N, and C6H4SAc was tentatively assigned to be derived from triplet states of predominantly intraligand (IL) character with some mixing of metal-to-ligand charge-transfer (MLCT) (dpi(Pt)-->pi*(C[triple bond]CR)) character, while the emission origin of the branched complexes with polyaromatic alkynyl ligands, [1,3,5-{RC[triple bond]C(PEt3)2PtC[triple bond]CC6H4C[triple bond]C}3C6H3] with R=Np, Pyr, or HC[triple bond]CAn, [1,3-{PyrC[triple bond]C(PEt3)2PtC[triple bond]CC6H4C[triple bond]C}2-5-{(iPr)3SiC[triple bond]C}C6H3], [1,3-{PyrC[triple bond]C(PEt3)2PtC[triple bond]CC6H4C[triple bond]C}2-5-(HC[triple bond]C)C6H3], and [1,8-{Cl(PEt3)2PtC[triple bond]C}2An], was tentatively assigned to be derived from the predominantly 3IL states of the respective polyaromatic alkynyl ligands, mixed with some 3MLCT (d(pi)(Pt)-->pi*(C[triple bond]CR)) character. By incorporating different alkynyl ligands into the periphery of these branched complexes, one could readily tune the nature of the lowest energy emissive state and the direction of the excitation energy transfer.

Journal Article↗