Surface potential switching by metal ion complexation/decomplexation using bipyridinethiolate monolayers on gold

Surface potential switching on gold(111) surfaces is induced by complexation/decomplexation reactions of a bipyridine (BP) derivative and palladium(II) chloride, as observed by Kelvin probe force microscopy (KFM). On the basis of the theoretical predictions, a 4-(5-phenylethynyl-2,2'-bipyridine-5'-yl-ethynyl)benzenethiol (PhBP) derivative was synthesized and used as an active monolayer to catch transition metal ions. By using the microcontact printing (CP) technique, micron-size patterned PhBP monolayers, which act as effective hosts to coordinate palladium(II) chloride, were prepared on gold(111) surfaces. The KFM signal decreases by complexation of the Pd(II) chloride in PhBP monolayers and is recovered by removal of Pd ions using an ethylenediamine solution, as confirmed by X-ray photoelectron spectroscopy. This process is reversible, indicating that the surface potential switching is realized by complexation/decomplexation of Pd(II). A CP PhBP monolayer, when it detects the target palladium ion, shows sensitivity for the picomolar level detection judged from surface potential changes in KFM measurements. The dipole moment estimated by the surface potentials is much smaller than the calculated value, indicating that mechanisms for the reduction of the surface dipole moment exist in real monolayers prepared by the CP method.     

Metal ion interaction with phosphorylated tyrosine analogue monolayers on gold

Phosphorylated tyrosine analogue molecules (pTyr-PT) were assembled onto gold substrates, and the resulting monolayers were used for metal ion interaction studies. The monolayers were characterized by X-ray photoelectron spectroscopy (XPS), infrared reflection-absorption spectroscopy (IRAS), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS), both prior to and after exposure to metal ions. XPS verified the elemental composition of the molecular adsorbate and the presence of metal ions coordinated to the phosphate groups. Both the angle-dependent XPS and IRAS results were consistent with the change in the structural orientation of the pTyr-PT monolayer upon exposure to metal ions. The differential capacitance of the monolayers upon coordination of the metal ions was evaluated using EIS. These metal ions were found to significantly change the capacitance of the pTyr-PT monolayers in contrast to the nonphosphorylated tyrosine analogue (TPT). CV results showed reduced electrochemical blocking capabilities of the phosphorylated analogue monolayer when exposed to metal ions, supporting the change in the structure of the monolayer observed by XPS and IRAS. The largest change in the structure and interfacial capacitance was observed for aluminum ions, compared to calcium, magnesium, and chromium ions. This type of monolayer shows an excellent capability to coordinate metal ions and has a high potential for use as sensing layers in biochip applications to monitor the presence of metal ions.     

Acid-base-driven interconversion between a mononuclear complex and supramolecular coordination polymers in a terpyridine-functionalized dioxocyclam ligand

A polytopic cyclam-bis-terpyridine ligand has been used to accomplish an acid-base-triggered formation of either a mononuclear neutral complex or metallopolymers with Cu(2+) ions. A controlled interconversion between these two forms was achieved through the reversible displacement of a Cu(2+) cation from the macrocycle to the terpyridine units.     

Influence of the central metal ion on nonlinear optical and two-photon absorption properties of push-pull transition metal porphyrins

We present a quantum-chemical analysis of the central metal ion's effect on first hyperpolarizabilities and two-photon absorption (TPA) cross sections at the infrared region of a series of push-pull porphyrins whose synthesis and NLO properties have been reported earlier (J. Am. Chem. Soc. 2005, 127, 9710). The molecular geometries are obtained via the B3LYP/6-31G(d,p) level optimization including SCRF/PCM approach, and the NLO and TPA properties are calculated with the ZINDO/CV method including solvent effects. It is found that the CT transition between the metal ion's d orbital and the macrocycle pi orbitals plays an important role on NLO and TPA properties of metal porphyrins. Our data suggest a new approach to enhance TPA properties of porphyrin materials. We also present a quantum-chemical analysis on porphyrin dimers and trimers to understand the relationship between structural and collective NLO properties. It has been observed that beta values can be improved about an order of magnitude and TPA properties can be enhanced by 2 orders of magnitude by the formation of a trimer. The importance of our results with respect to the design of photonic and photodynamic therapy materials have been discussed.     

Porphyrin acidity and metal ion coordination revisited: electronic substitution effects

Macrocycle acidity and Zn²⁺ ion coordination are reported for three porphyrin derivatives which differ in both steric and electronic substitution effects on the macrocycle π-conjugated system. The role of the electronic substitution effects in the macrocycle deprotonation and metal ion chelating was found to be dominating whereas the macrocycle nonplanar distortions contribute to the acidity and metal chelation rate of the studied porphyrins in less extent. The contributions of both resonance and inductive electronic substitution effects have been distinguished based on the relationship between the weighted sum of resonance and inductive Hammett constants and the acidity and metal ion chelation rate.     

Folded metallodendrons: shell-selective metal coordination and conformational properties

The synthesis, structure, and conformational properties of folded metallodendrons are described. The enhanced coordination ability of oxazoline-functionalized pyridyl-2,6-dicarboxamides, compared with pyridyl-2.6-diarylamides, permits unique metals to be installed at the peripheral and focal shells of the dendron. Circular dichroism (CD) studies and X-ray crystallography indicate that the intrinsic helical preference of the parent dendron is not perturbed by coordination. However, the CD spectra become insensitive to temperature due to an increase in structural rigidity that occurs upon metal coordination. [structure: see text]     

Microscopic environment of metal ion controlled by the balance between preferential solvation and coordination

The preferential solvation and the coordination characterizing metal ions (Mg2+ and Zn2+) in solution, which control the microscopic environments around the metal ions, were directly observed through the mass spectrometric analysis of clusters isolated from liquid droplets.     

The density of surface ligands regulates the luminescence of thiolated gold nanoclusters and their metal ion response

The fascinating luminescence properties of gold nanoclusters(AuNCs) have drawn considerable research interests,and been widely harnessed for a wide range of applications.However,a fundamental understanding towards ligand density's role in the luminescence properties of these ultrasmall AuNCs remains unclear yet.In this communication,through systematic investigation of surface chemistries of glutathione-protected Au NCs(GSH-Au NCs) with diffe rent density of GSH as well as other thiolates,it is discovered that the density of surface ligands can significantly regulate the luminescence properties of AuNCs.Fluorescence lifetime spectroscopy and X-ray photoelectron spectroscopy showed that AuNCs with a higher density of electron-rich ligands facilitate their luminescence generation.Moreover,differences in the surface coverage of AuNCs can also affect their interactions with foreign species,as illustrated by significantly different fluorescence quenching capability of GSH-AuNCs with different ligand density towards Hg~(2+).This study provides new insight into the intriguing luminescence properties of metal NCs,which is hoped to stimulate further research on the design of metal NCs with strong luminescence and sensitive/specific responses for promising optoelectronic,sensing and imaging applications.     

Correlation between thermodynamic properties and coordination states of aqueous bivalent transition metal sulfates

The osmotic coefficients for CoSO₄, NiSO₄, CuSO₄, MnSO₄, and ZnSO₄ have been found to be approximately the same up to very highest concentrations, while they are significantly higher for MgSO₄. Negligible changes in the visible spectra of CoSO₄ and NiSO₄ induced by increasing concentration indicate little, if any, coordination of the sulfate anion, while the UV spectral effects indicate outer-sphere association. More distinct spectral effects are observed for CuSO₄. However, the free sulfate anion concentration is found to be the same in equimolal solutions of CoSO₄, NiSO₄, and ZnSO₄, and probably also in CuSO₄, while it is higher in the solutions of MgSO₄. The conclusion is drawn that the four isopiestic transition metal sulfates at any given molality are in corresponding coordination states. The general problem of correlation between thermodynamic properties of solutions and the coordination states of the dissolved salts is discussed.     

Selective detection of mercury (II) ion using nonlinear optical properties of gold nanoparticles

Contamination of the environment with heavy metal ions has been an important concern throughout the world for decades. Driven by the need to detect trace amounts of mercury in environmental samples, this article demonstrates for the first time that nonlinear optical (NLO) properties of MPA-HCys-PDCA-modified gold nanoparticles can be used for rapid, easy and reliable screening of Hg(II) ions in aqueous solution, with high sensitivity (5 ppb) and selectivity over competing analytes. The hyper Rayleigh scattering (HRS) intensity increases 10 times after the addition of 20 ppm Hg(2+) ions to modified gold nanoparticle solution. The mechanism for HRS intensity change has been discussed in detail using particle size-dependent NLO properties as well as a two-state model. Our results show that the HRS assay for monitoring Hg(II) ions using MPA-HCys-PDCA-modified gold nanoparticles has excellent selectivity over alkali, alkaline earth (Li(+), Na(+), K(+), Mg(2+), Ca(2+)), and transition heavy metal ions (Pb(2+), Pb(+), Mn(2+), Fe(2+), Cu(2+), Ni(2+), Zn(2+), Cd(2+)).     

Carboxymethylation of cage amines: control of alkylation by metal ion coordination

Reactions between chloroacetate and both "free" and coordinated forms of the cage amine diaminosarcophagine (1,8-diamino-3,6,10,13,16,19-hexaazabicyclo[6.6.6]icosane) result in the introduction of between one and four pendent carboxymethyl substituents on the nitrogen atoms of the cage. While at least the first two steps in the reaction of the free ligand have been found to involve only the secondary nitrogen centers, in both the Cu(II) and Co(III) complexes alkylation occurs only at the primary (1,8) centers, the greater ease of achieving a higher degree of alkylation of the Cu(II) complex being attributed to the lower charge of this species causing a lesser reduction of the nucleophilicity of the uncoordinated primary nitrogen atoms. All the new ligands have been characterized by X-ray structure determinations of their Cu(II) or Co(III) complexes. In some cases, this has shown that the methods used to isolate the crystalline complexes result in lactamization of the ligand.     

Electrochemical properties of mixed self-assembled monolayers on gold electrodes containing mercaptooctylhydroquinone and alkylthiols

Mixed self-assembled monolayers of 2-(mercaptooctyl)hydroquinone (QH2) and alkylthiols were formed on gold electrodes in EtOH and the redox process of the hydroquinone moiety of QH2 was characterized by cyclic voltammetry (CV) in 0.1 M H(2)SO(4). The monolayers were formed at a series of QH2:alkylthiol ratios and the QH2:alkylthiol ratio in solution was compared to the electrochemical response from QH2 in the obtained monolayer. Mixed monolayers of QH2 with hexylthiol, dodecylthiol, and octadecylthiol were studied. The length of the alkylthiol is crucial for the electrochemical response from QH2 in the monolayer. The total concentration of thiols during monolayer formation and incubation times were also studied and low concentrations of < 2.5 mM and long incubation times gave rise to lower peak separation, lower peak half widths in the CVs of the mixed monolayers, and lower background current. The stability of a pure QH2 monolayer and a 1:4 QH2:hexylthiol monolayer toward high potentials of up to 1.5 V versus Ag/AgCl was also studied and it was observed that the mixed monolayer is significantly more stable than the pure QH2 monolayer.     

Air microwave-induced plasma: Relation between ion density and atomic oxygen density

Electron temperature and ion density are measured in an air microwave-induced plasma (2450 MHz) by means of a floating double probe. A 'cinetic scheme for ion formation and decay is set up, and a relationship between atomic oxygen and ion densities is obtained. From this relationship an order-of-magnitude of atomic oxygen concentration in the discharge is derived and compared with results obtained by optical actinometry in another work.     

Structural properties of oligonucleotide monolayers on gold surfaces probed by fluorescence investigations

We present optical investigations on the conformation of oligonucleotide layers on Au surfaces. Our studies concentrate on the effect of varying surface coverage densities on the structural properties of layers of 12- and 24mer single-stranded DNA, tethered to the Au surface at one end while being labeled with a fluorescent marker at the opposing end. The distance-dependent energy transfer from the marker dye to the metal surface, which causes quenching of the observed fluorescence, is used to provide information on the orientation of the DNA strands relative to the surface. Variations in the oligonucleotide coverage density, as determined from electrochemical quantification, over 2 orders of magnitude are achieved by employing different preparation conditions. The observed enhancement in fluorescence intensity with increasing DNA coverage can be related to a model involving mutual steric interactions of oligonucleotides on the surface, as well as fluorescence quenching theory. Finally, the applicability of the presented concepts for investigations of heterogeneous monolayers is demonstrated by means of studying the coadsorption of mercaptohexanol onto DNA-modified Au surfaces.     

Effects of transition metal ion coordination on the collision-induced dissociation of polyalanines

Transition metal-polyalanine complexes were analyzed in a high-capacity quadrupole ion trap after electrospray ionization. Polyalanines have no polar amino acid side chains to coordinate metal ions, thus allowing the effects metal ion interaction with the peptide backbone to be explored. Positive mode mass spectra produced from peptides mixed with salts of the first row transition metals Cr(III), Fe(II), Fe(III), Co(II), Ni(II), Cu(I), and Cu(II) yield singly and doubly charged metallated ions. These precursor ions undergo collision-induced dissociation (CID) to give almost exclusively metallated N-terminal product ions whose types and relative abundances depend on the identity of the transition metal. For example, Cr(III)-cationized peptides yield CID spectra that are complex and have several neutral losses, whereas Fe(III)-cationized peptides dissociate to give intense non-metallated products. The addition of Cu(II) shows the most promise for sequencing. Spectra obtained from the CID of singly and doubly charged Cu-heptaalanine ions, [M + Cu - H](+) and [M + Cu](2+) , are complimentary and together provide cleavage at every residue and no neutral losses. (This contrasts with [M + H](+) of heptaalanine, where CID does not provide backbone ions to sequence the first three residues.) Transition metal cationization produces abundant metallated a-ions by CID, unlike protonated peptides that produce primarily b- and y-ions. The prominence of metallated a-ions is interesting because they do not always form from b-ions. Tandem mass spectrometry on metallated (Met = metal) a- and b-ions indicate that [b(n) + Met - H](2+) lose CO to form [a(n) + Met - H](2+), mimicking protonated structures. In contrast, [a(n) + Met - H](2+) eliminate an amino acid residue to form [a(n-1) + Met - H](2+), which may be useful in sequencing.     

Sulfur-containing terpyridine derivatives: synthesis, coordination properties, and adsorption on the gold surface

Approaches to the synthesis of organic aurophilic ligands, viz., sulfur-containing 2,2′:6′,2’-terpyridine derivatives, were developed. Complexation reactions of the terpyridine ligands having thiophenol, diaryl disulfide, and alkyl aryl sulfide fragments with Co ⁱⁱ , Ni ⁱⁱ , and Rh ⁱⁱⁱ salts were studied. The structures of the coordination compounds obtained were established based on the elemental analysis data, density functional calculations, and electron spectroscopy. The structure of the complex of 4′-(4-methylsulfanyl)-2,2′:6′,2"-terpyridine with Ni(BF₄)₂ was also established by X-ray diffraction analysis. A method was proposed for the preparation of gold nanoparticle dimeric aggregates via coordination interactions of the ligands adsorbed on the gold nanoparticle surface with transition metal ions. A degree of nanoparticle aggregation upon their reaction with solutions of complex compounds of aurophilic nitrogen-containing ligands was determined by the concentration of the solution of the complex used.     

Luminescent coordination polymer gels based on rigid terpyridyl phosphine and Ag(I)

Rigid bridging terpyridyl phosphine and AgOTf form nanofibres to induce gelation of organic solvents, and the gel emits blue luminescence by suppressing π-π interactions between ligands.     

A gold(I) mononuclear complex and its association into binuclear and cluster compounds by hydrogen bonding or metal ion coordination

The mononuclear Au(I) complex, Au(Spy)(PPh2py) (1), has been synthesized and characterized structurally. The complex possesses the expected linear coordination geometry with a S-Au-P bond angle of 176.03(6) degrees and no evidence of aurophilic interactions between nearest neighbor Au(I) ions in the solid state. Protonation of the pendant pyridyl groups of 1 leads to the formation of the H-bonded dimer [(Au(SpyH)(PPh2py))2](PF6)2 (2), which has also been structurally characterized. A linear coordination geometry at the Au(I) ions in 2 with a S-Au-P bond angle of 173.7(2) degrees is augmented by evidence of a strong aurophilic interaction with a Au...Au distance of 2.979(1) A. The pendant pyridyl groups of 1 have also been used to bind Cu(I) by reactions with [Cu(NCMe)4](PF6) and Cu(P(p-tolyl)3)2(NO3) leading to the formation of the heterobimetallic complexes [(AuCu(mu-Spy)(mu-PPh2py))2](PF6)2 (3) and [AuCu(P(p-tolyl)3)2(mu-Spy)(mu-PPh2py)](NO3) (4), respectively. A structure determination of 3 reveals a tetranuclear complex composed of two AuCu(mu-Spy)(mu-PPh2py)+ units held together by bridging thiolate ligands. A strong metal-metal interaction is noted between the two different d10 ions with nearest Au-Cu distances averaging 2.6395 A. The S-Au-P bond angles in 3 deviate slightly from linearity due to the Au...Cu interactions, while the coordination geometries at Cu(I) are distorted tetrahedral consisting of the two pyridyl nitrogen atoms, a bridging thiolate sulfur, and the interacting Au(I) ion. While mononuclear complex 1 is only weakly emissive in the solid state and in fluid solution, complexes 2-4 show stronger photoluminescence in the solid state and rigid media at 77 K, and in fluid solution. The emission maxima for 2-4 in ambient temperature fluid solution are 470, 635, and 510 nm, respectively. A tentative assignment of the emitting state as a S(p pi)-->Au LMCT transition is made on the basis of previous studies of Au(I) thiolate phosphine complexes. Shifts of lambda em result from the influence of H bonding or Cu(I) coordination on the filled thiolate orbital energy, or on the effect of metal-metal interaction on the Au(I) acceptor orbital energy. Crystal data for Au(Spy)(PPh2py) (1): triclinic, space group P1 (No. 2), with a = 8.3975(4) A, b = 11.0237(5) A, c = 12.4105(6) A, alpha = 98.6740(10) degrees, beta = 105.3540(10) degrees, gamma = 110.9620(10) degrees, V = 995.33(8) A3, Z = 2, R1 = 3.66% (I > 2 sigma(I)), wR2 = 9.04% (I > 2 sigma(I)) for 2617 unique reflections. Crystal data for [(Au(SpyH)(PPh2py))2](PF6)2 (2): triclinic, space group P1 (No. 2), with a = 14.0284(3) A, b = 14.1093(3) A, c = 15.7027(2) A, alpha = 97.1870(10) degrees, beta = 96.5310(10) degrees, gamma = 117.1420(10) degrees, V = 2692.21(9) A3, Z = 2, R1 = 7.72% (I > 2 sigma(I)), wR2 = 15.34% (I > 2 sigma(I)) for 5596 unique reflections. Crystal data for [(AuCu(mu-Spy)(mu-PPh2py))2](PF6)2 (3): monoclinic, space group P2(1)/c (No. 14), with a = 19.6388(6) A, b = 16.3788(4) A, c = 17.2294(5) A, beta = 91.48 degrees, V = 5540.2(3) A3, Z = 4, R1 = 3.99% (I > 2 sigma(I)), wR2 = 8.38% (I > 2 sigma(I)) for 10,597 unique reflections.     

四苯骈卟啉金属配合物轴向配位反应的热力学性质研究

金属卟啉在生命过程中起着重要的作用[1 - 4 ] 。CuTBP ,CoTBP与有机碱的反应,用光度法测定了轴配反应在不同温度下的速率常数和平衡常数,求得活化能及热力学参数,结果表明:它们与不同有机碱反应的活化能及平衡常数既与配体的碱性有关,也与空间位阻有关,同一温度下反应的平衡常数和速率常数的大小顺序均为:咪唑>吡啶>2 甲基吡啶>2 ,4 二甲基吡啶。1　实验部分1 .1　仪器与试剂日本产岛津UV 2 4 0G型分光光度计,上海分析仪器厂72 1型光度计(内装恒温套) ,重庆电机厂超级恒温槽。四苯骈卟啉金属配合物系自制[4] ,咪唑、吡啶、2 甲基吡…     

Effect of load on structural and frictional properties of alkanethiol self-assembled monolayers on gold: some odd-even effects

We have conducted molecular dynamics simulations to study the frictional properties of alkanethiols CH(3)(CH(2))(n-1)SH (Cn, 12 ≤ n ≤ 15) self-assembled monolayers (SAMs) on Au(111) surfaces, under various loading and shearing conditions. For the examined alkanethiols, we found some evidence of the friction coefficient being dependent on the number of carbon atoms in the molecule being odd or even. Alkanethiols with n = odd show consistently higher friction coefficients than those with n = even. Such odd-even effect seems to be independent of the sliding velocity. However, the effect is significant only at lower loads (<700 MPa). The structural origin of this odd-even effect has been discussed. The effect of loading on the structure is also studied. For dodecanethiol (n = 12) we find the film responds to increased loading initially by increasing the tilt and then by deformation of individual molecules. SAM-Au contacts under shear show periodic storage and release of energy and a clear stick-slip pattern in the shear stress, film thickness, and the tilt and tilt orientation angles.