Study on the resonance Rayleigh scattering and resonance non‐linear scattering spectra of ion‐association complexes of [PdI4]2−‐protein systems and their analytical applications

In an acid medium solution, proteins such as bovine serum albumin, human serum albumin, ovalbumin, hemoglobin, lysozyme, γ‐globulin, α‐chymotrypsin and papain could react with [PdI₄]^2? by virtue of electrostatic attraction and hydrophobic force to form ion‐association complexes. As a result, the resonance Rayleigh scattering (RRS) and resonance nonlinear scattering such as second‐order scattering (SOS) and frequency doubling scattering (FDS) intensities were enhanced greatly and new scattering spectra appeared. The maximum scattering peaks of RRS, SOS and FDS were at 367, 720 and 370 nm, respectively. The enhanced RRS, SOS and FDS intensities were directly proportional to the concentrations of proteins. The detection limits for the different proteins were 2.4–11.8 ng/mL for RRS method, 9.5–47.9 ng/mL for SOS method and 4.6–18.5 ng/mL for FDS method. In this work, the influences of the interaction of [PdI₄]^2? with proteins on spectral characteristics of RRS, SOS and FDS were investigated and the optimum conditions were tested. Meanwhile, the effects of coexisting substances were tested and the results showed that the method exhibited a good selectivity. Based on the above research, a highly sensitive, simple and rapid method for the determination of trace amounts of proteins by resonance light scattering technique has been developed. It can be applied to the determination of proteins in tablet, human serum and urine samples. Copyright © 2009 John Wiley & Sons, Ltd.     

Study on the interaction between ligustrazine and 12‐tungstophosphoric acid using resonance Rayleigh scattering and resonance nonlinear scattering spectra,and its analytical applications

In an HCl medium (pH 1.5), ligustrazine (2,3,5,6‐tetramethylpyrazine, TMP) reacted with 12‐tungstophosphoric acid (TP) to form a 3 : 1 ion‐association complex. As a result, the intensities of resonance Rayleigh scattering (RRS), second‐order scattering (SOS) and frequency doubling scattering (FDS) were greatly enhanced and new scattering spectra appeared. The maximum RRS, SOS and FDS wavelengths of the ion‐association complexes were located at 379, 738 and 395 nm, respectively. The scattering intensity increments (ΔI_RRS, ΔI_SOS and ΔI_FDS) were directly proportional to the concentration of ligustrazine within certain ranges. The detection limits (3σ) of RRS, SOS and FDS were 1.6, 3.2 and 2.8 ng/mL. Optimal conditions for the RRS method and factors influencing the method were discussed, and the structure of the ion‐association complex and the reaction mechanism were investigated. Transmission electron microscopy (TEM) was used to characterize the structures of the ion‐association complex. Based on the ion‐association reaction and its spectral response, a rapid, simple and sensitive RRS method for the determination of TMP was developed. It was applied to the determination of TMP in tablet and urine samples with satisfactory results. Copyright © 2014 John Wiley & Sons, Ltd.     

Study on the ternary system of MoO42‐–enzyme–PdCl2 by resonance Rayleigh scattering,second‐order scattering and frequency‐doubling scattering spectra and its analytical application

In pH 4.0 Britton–Robinson buffer medium, PdCl₂ was able to react with enzymes (EZ) such as lysozyme (LYSO) and papain (PAP) to form a coordination complex (EZ–PdCl₂), which further reacted with MoO₄^2‐ to form a ternary complex (MoO₄^2‐–EZ–PdCl₂). As a result, the absorption and fluorescence spectra changed; new spectra of resonance Rayleigh scattering (RRS), second‐order scattering (SOS) and frequency‐doubling scattering (FDS) appeared and their intensities were enhanced greatly. The maximum RRS, SOS and FDS wavelengths of two ternary complexes were located at 310, 560 and 350 nm, respectively. The increments of scattering intensity were directly proportional to the concentrations of EZ within certain ranges. The detection limits (3σ) of LYSO and PAP were 4.5 and 14.0 ng/mL (RRS method), 9.6 and 57.8 ng/mL (SOS method), and 5.2 and 106.0 ng/mL (FDS method). Taking the MoO₄^2‐–LYSO–PdCl₂ system, which was more sensitive, as an example, the effects of coexisting substances were evaluated. The methods showed excellent selectivity. Accordingly, new rapid, convenient, sensitive and selective scattering methods for the determination of LYSO and PAP were proposed and applied to determine LYSO in egg white with satisfactory results. The reaction mechanism and basis of the enhancement of scattering were discussed. Copyright © 2012 John Wiley & Sons, Ltd.     

Determination of doxepin hydrochloride in spiked human plasma and capsule after derivatization with eosin Y using resonance Rayleigh scattering,second-order scattering and frequency doubling scattering methods

Doxepin hydrochloride (DOX) is a tricyclic antidepressant drug. Three sensitive spectrofluorimetric methods, namely resonance Rayleigh scattering (RRS), frequency doubling scattering (FDS) and second-order scattering (SOS), were developed and validated for their estimation of doxepin in spiked human plasma and formulation using liquid–liquid extraction method through the formation of an ion pair complex with eosin Y at a pH of 4.5. Various factors affecting fluorescence intensity were optimized, and the reaction kinetics was determined using the Arrhenius equation method. Different scattering methods such as RRS, FDS and SOS were developed at maximum scattering wavelengths λ_ex/λ_em = 567/567 nm for RRS, 720/360 nm for SOS and 260/520 nm for FDS, respectively. The methods exhibited high sensitivities, and the detection limits for DOX were found to be 0.82, 1.20 and 1.03 ng/ml for RRS, FDS and SOS methods, respectively. The FDS method exhibited the highest sensitivity. The methods were validated using the International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use guidelines and applied to determine DOX in capsule and spiked human plasma samples.     

Effects of the interaction between Na2Wo4‐6‐benzylaminopurine anionic chelate and rhodamine 6G on the resonance Rayleigh scattering and fluorescence spectra and their analytical applications

In pH 4.99‐6.06 Britton‐Robinson (BR) buffer medium, 6‐benzylaminopurine (6‐BA) reacted with Na₂WO₄ to form 1:1 anionic chelate (6‐BA·WO₄)^2‐, which further reacted with rhodamine 6G to form ternary ion complexes at room temperature. This resulted in a significant enhancement of resonance Rayleigh scattering (RRS) with a maximum RRS wavelength of 316 nm. Meanwhile, the fluorescence of the solution was quenched and excitation (λ_ex) and emission (λ_em) wavelengths of the fluorescence were 290 and 559 nm, respectively. Intensities of RRS enhancing (ΔI_RRS) and fluorescence quenching (ΔI_F) were directly proportional to concentrations of 6‐BA. As a result, RRS and fluorescence quenching for determination of trace amounts of 6‐BA were developed. Under optimal conditions, linear ranges and detection limits of the two methods were 0.05‐15.00 µg/mL and 8.2 ng/mL (RRS), 0.50‐15.00 µg/mL and 17.0 ng/mL, respectively. It was found that the RRS method was superior to fluorescence quenching. The influence of these methods were investigated and results showed that RRS had good selectivity. RRS was applied to determine 6‐BA in vegetable samples with satisfactory results. Furthermore, the reaction mechanisms of the ternary ion‐association system are discussed. In addition, the polarization experiment revealed that the resonance light scattering (RLS) peak of Na₂WO₄‐6‐BA‐R6G consisted mainly of depolarized resonance fluorescence and resonance scattering. It was speculated that light emission fluorescence energy (E_L) transformed into resonance light scattering energy (E_RLS), which was a key reason for enhancement of RRS. Copyright © 2012 John Wiley & Sons, Ltd.     

Oxidation of copper(II)-coordinated diethylenetriamine by hexacyanoferrate(III) ion. A kinetic investigation

The stoichiometry and kinetics of the reaction between [Cu(dien)(OH)]⁺ and [Fe(CN)₆]³⁻ in aqueous alkaline medium are described. The rate equation − (d[Fe(III)]/dt = {k₁[OH⁻]²[[Cu(dien)(OH)]⁺] + k₂[OH⁻] × [[Cu(dien)(OH)]⁺]²}([Fe(III)]/[Fe(II)]) (Fe(III) = [Fe(CN)₆]³⁻; Fe(II) = [Fe(CN)₆]⁴⁻, the 4:4:1 OH⁻/Fe(III)/[Cu(dien)(OH)]⁺ stoichiometric ratio and the nature of the ultimate products identified in the reaction solution suggest the fast formation of a doubly deprotonated Cu(III)-diamido complex which slowly undergoes an internal redox process where the ligand is oxidised to the Schiff base H₂NCH₂CH₂NCHCHNH.The [[Cu(dien)(OH)]⁺]² term in the rate equation is explained with the formation of a transient μ-hydroxo mixed-valence Cu dimer. A two-electron internal reduction of the Cu(III) complex yielding a Cu(I) intermediate is suggested to account for the presence of monovalent copper in a precipitate which forms at relatively high reactant concentrations and in the absence of dioxygen.     

Antibacterial,antifungal and in vitro antileukaemia activity of metal complexes with thiosemicarbazones

1‐phenyl‐3‐methyl‐4‐benzoyl‐5‐pyrazolone 4‐ethyl‐thiosemicarbazone (HL) and its copper(II), vanadium(V) and nickel(II) complexes: [Cu(L)(Cl)]·C₂H₅OH·( 1 ), [Cu(L)₂]·H₂O ( 2 ), [Cu(L)(Br)]·H₂O·CH₃OH ( 3 ), [Cu(L)(NO₃)]·2C₂H₅OH ( 4 ), [VO₂(L)]·2H₂O ( 5 ), [Ni(L)₂]·H₂O ( 6 ), were synthesized and characterized. The ligand has been characterized by elemental analyses, IR, ¹H NMR and ¹³C NMR spectroscopy. The tridentate nature of the ligand is evident from the IR spectra. The copper(II), vanadium(V) and nickel(II) complexes have been characterized by different physico‐chemical techniques such as molar conductivity, magnetic susceptibility measurements and electronic, infrared and electron paramagnetic resonance spectral studies. The structures of the ligand and its copper(II) ( 2 , 4 ), and vanadium(V) ( 5 ) complexes have been determined by single‐crystal X‐ray diffraction. The composition of the coordination polyhedron of the central atom in 2 , 4 and 5 is different. The tetrahedral coordination geometry of Cu was found in complex 2 while in complex 4 , it is square planar, in complex 5 the coordination polyhedron of the central ion is distorted square pyramid. The in vitro antibacterial activity of the complexes against Escherichia coli, Salmonella abony, Staphylococcus aureus, Bacillus cereus and the antifungal activity against Candida albicans strains was higher for the metal complexes than for free ligand. The effect of the free ligand and its metal complexes on the proliferation of HL‐60 cells was tested.     

Chemistry of the binary mixture of 1,10-phenanthroline and zinc perchlorate hexahydrate in methanol and gas phase. Monohydroxo species and tricoordination of zinc and water clusters

ESIMS reveals that methanol solutions of 1:1, 1:2 and 1:3 mixtures of Zn(ClO₄)₂ · 6H₂O and 1,10-phenanthroline (phen) generate [Zn(phen)(OH)]⁺, [Zn(phen)(H₂O)₄(OH)]⁺, [Zn(phen)₂(H₂O)(OH)]⁺and [Zn(phen)₂(H₂O)₄(OH)]⁺ ions in the gas phase. DFT calculations at the B3LYP/LanL2DZ level show that zinc is planar tricoordinate in [Zn(phen)(OH)]⁺ and the cis configuration is more stable than the trans one for the hexacoordinate ion [Zn(phen)₂(H₂O)(OH)]⁺. DFT calculations also show that the [Zn(phen)(H₂O)₄(OH)]⁺ and [Zn(phen)₂(H₂O)₄(OH)]⁺ ions are actually [Zn(phen)(H₂O)(OH)]⁺ · 3H₂O and [Zn(phen)₂(H₂O)(OH)]⁺ · 3H₂O containing extended motifs of H-bonded water clusters. The aqua species corresponding to the monohydroxo ions are acidic. Their acid dissociations are modeled collectively by equilibrium (see below) where other ligands around Zn are not specified. An attempt is then made to estimate K_a

     

Direct determination of polymyxin B sulfate using resonance Rayleigh scattering and resonance non‐linear scattering methods with hexatungstate

At pH 1.3–1.6, tungstate WO₄^2–, can be converted to hexatungstate W₆O₁₉^2–, which can react with positively charged polymyxin B sulfate (PMB) to result in enhancement of resonance Rayleigh scattering (RRS) and resonance non‐linear scattering, including second order scattering and frequency doubling scattering. Linear relationships can be established between enhanced scattering intensity and PMB concentration. The detection limits (3σ) were 5.5 ng/mL (RRS), 10.1 ng/mL (second order scattering) and 34.6 ng/mL (frequency doubling scattering). The optimum reaction conditions, influencing factors and related analytical properties were tested. The interaction mechanism was investigated via absorption spectrum, circular dichroism spectra and atomic force microscopy imaging. The basis of scattering enhancement is discussed. PMB in eardrops, human serum and urine, were quantified satisfactorily by RRS. Copyright © 2013 John Wiley & Sons, Ltd.     

Resonance Rayleigh-scattering method for the determination of proteins with gold nanoparticle probe

Gold nanoparticles with a 12-nm diameter were used as probes for the determination of proteins by resonance Rayleigh-scattering techniques. In weak acidic solution, large amounts of citrate anions will self-assemble on the surface of positively charged gold nanoparticles to form supermolecular compounds with negative charges. Below the isoelectric point, proteins with positive charges such as human serum albumin (HSA), bovine serum albumin (BSA), and ovalbumin (Ova) can bind gold nanoparticles to form larger volume products (the diameter of the binding product of gold nanoparticles with HSA is 23 nm.) through electrostatic force, hydrogen bonds, and hydrophobic effects, which can result in a red shift of the maximum absorption wavelength, the remarkable enhancement of the resonance Rayleigh-scattering intensity (RRS), and the appearance of the RRS spectra. At the same time, the second-order-scattering (SOS) and frequency-doubling-scattering (FDS) intensities are also enhanced. The binding products of gold nanoparticles with different proteins have similar spectral characteristics and the maximum wavelengths are located near 303 nm for RRS, 540 nm for SOS, and 390 for FDS, respectively. The scattering enhancement (DeltaI) is directly proportional to the concentration of proteins. Among them, the RRS method has the highest sensitivity and the detection limits are 0.38 ng/ml for HSA, 0.45 ng/ml for BSA, and 0.56 ng/ml for Ova, separately. The methods have good selectivity. A new RRS method for the determination of trace proteins using a gold nanoparticle probe has been developed. Because gold nanoparticle probes do not need to be modified chemically in advance, the method is very simple and fast.     

Preparation, characterization and pH-metric measurements of 4-hydroxysalicylidenechitosan Schiff-base complexes of Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Ru(III), Rh(III), Pd(II) and Au(III)

The 4-hydroxysalicylidenechitosan Schiff-base (2CS-Hdhba) was prepared by the condensation of 2,4-dihydroxybenzaldehyde with chitosan, and its metal complexes, [M(2CS-dhba)Cl₂(H₂O)₂] (M(III) = Fe, Ru, Rh), [M′(2CS-dhba)(AcO)(H₂O)₂] (M′(II) = Co, Ni, Cu, Zn), [Pd(2CS-dhba)Cl(H₂O)] and [Au(2CS-dhba)Cl₂], are reported. These complexes were characterized by elemental analysis, by spectral data (FTIR, solid-phase ¹³C NMR, UV–vis and ESR spectroscopy), by morphological observations (SEM and XRD), and by magnetic and thermal measurements. The Schiff base (2CS-Hdhba) behaves as a bidentate chelate with a single negative charge. The azomethine nitrogen and the deprotonated 2-hydroxy centres with the pendant glucosamine hydroxy functionality play no role in coordination. The dissociation constants of 2CS-Hdhba and the stability constants of some of its metal complexes have been determined pH-metrically.     

Synthetic, structural and solution speciation studies on binary Al(III)–(carboxy)phosphonate systems. Relevance to the neurotoxic potential of Al(III)

Efforts to delineate the interactions of neurotoxic Al(III) with low molecular mass substrates relevant to neurodegenerative processes, led to the investigation of the pH-specific synthetic chemistry of the binary Al(III)-[N-(phosphonomethyl) iminodiacetic acid] (Al-NTAP), Al(III)-[nitrilo-tris(methylene-phosphonic acid)] (Al-NTA3P), and Al(III)-[1-hydroxy ethylidene-1,1-diphosphonic acid] (Al-HEDP) systems, in correlation with solution speciation studies. Reaction of Al(NO₃)₃·9H₂O with NTAP at pH 7.0 and 4.0 afforded the new species (CH₆N₃)₄[Al₂(C₅H₆NPO₇)₂(OH)₂]·8H₂O (1) and (NH₄)₂[Al₂(C₅H₆NPO₇)₂(H₂O)₂]·4H₂O (2), while reaction of Al(NO₃)₃·9H₂O with NTA3P led to K₈[Al₂(C₃H₆NP₃O₉)₂(OH)₂]·20H₂O (3). Complexes 1–3 were characterized by elemental analysis, FT-IR, ¹³C, ³¹P, ¹H NMR (for 1–2 solid state and solution NMR where feasible), and X-ray crystallography. The structures of 1–3 reveal the presence of uniquely defined dinuclear complexes of octahedral Al(III) bound to fully deprotonated phosphonate ligands, water and hydroxo moieties. The aqueous solution speciation studies on the aforementioned binary systems project a clear picture of the binary Al(III)–(carboxy)phosphonate interactions and species under variable pH-conditions and specific Al(III):ligand stoichiometry. The concurrent solid state and solution work (a) exemplifies essential structural and chemical attributes of soluble aqueous species, reflecting well-defined interactions of Al(III) with phosphosubstrates and (b) strengthens the potential linkage of neurotoxic Al(III) chemical reactivity toward O,N-containing (carboxy)phosphate-rich cellular targets.     

Preparation, structures and properties of dinuclear and trinuclear copper(II) complexes bridged by one oximato and one hydroxo ligands

The dinuclear and trinuclear copper(II) complexes [Cu₂(L)(OH)(ClO₄)(phen)(H₂O)]ClO₄ · [Cu₂(L)(OH)(ClO₄)₂(phen)(CH₃OH)] (1) and [Cu₃(L)₂(OH)₂(H₂O)₂](NO₃)₂ (2) (HL=2-[2-(α-pyridyl)ethyl]imino-3-butanone oxime and phen=1,10-phenanthroline) were prepared and their crystal structures have been determined by X-ray crystallography. Complex 1 is composed of [Cu₂(L)(OH)(ClO₄)(phen)(H₂O)]ClO₄ (1a) and [Cu₂(L)(OH)(ClO₄)₂(phen)(CH₃OH)] (1b). In 1a and 1b, one oximato of L and one hydroxo group bridge two copper(II) ions. The linear trinuclear cation [Cu₃(L)₂(OH)₂(H₂O)₂]²⁺ in 2 is centrosymmetric, and one oximato and one hydroxo group bridge the central and terminal copper(II) ions. The strong antiferromagnetic interactions within the dinuclear and trinuclear complexes 1 and 2 have been observed (2J=∼−900 cm⁻¹ for 1 and 2, respectively, H=−2JS₁·S₂).     

Aminocarboxylate complexes of vanadium(III): Electronic structure investigation by high-frequency and -field electron paramagnetic resonance spectroscopy

Aminocarboxylate complexes of vanadium(III) are of interest as models for biologically and medicinally relevant forms of this interesting and somewhat neglected ion. The V(III) ion is paramagnetic, but not readily suited to conventional EPR, due to its integer-spin ground state (S = 1) and associated large zero-field splitting (zfs). High-frequency and -field EPR (HFEPR), however, has the ability to study such systems effectively. Three complexes, all previously structurally characterized: Na[V(trdta)] · 3H₂O, Na[V(edta)(H₂O)] · 3H₂O, and [V(nta)(H₂O)₃] · 4H₂O (where trdta stands for trimethylenediamine-N,N,N′,N′-tetraacetate and nta stands for nitrilotriacetate) were studied by HFEPR. All the investigated complexes produced HFEPR responses both in the solid state, and in aqueous solution, but those of [V(nta)(H₂O)₃] · 4H₂O were poorly interpretable. Analysis of multi-frequency HFEPR spectra yielded a set of spin Hamiltonian parameters (including axial and rhombic zfs parameters: D and E, respectively) for these first two complexes as solids: Na[V(trdta)] · 3H₂O: D = 5.60 cm⁻¹, E = 0.85 cm⁻¹, g = 1.95; Na[V(edta)(H₂O)] · 3H₂O: D = 1.4 cm⁻¹, E = 0.14 cm⁻¹, g = 1.97. Spectra in frozen solution yielded similar parameters and showed multiple species in the case of the trdta complex, which are the consequence of the flexibility of this ligand. The EPR spectra obtained in frozen aqueous solution are the first, to our knowledge, of V(III) in solution in general and show the applicability of HFEPR to these systems. In combination with very insightful previous studies of the electronic absorption of these complexes which provided ligand-field parameters, it has been possible to describe the electronic structure of V(III) in [V(trdta)]⁻ and [V(edta)(H₂O)]⁻; the quality of data for [V(nta)(H₂O)₃] does not permit analysis. Qualitatively, six-coordinate V(III) complexes with O,N donor atoms show no electronic absorption band in the NIR region, and exhibit relatively large magnitude zfs (D ? 5 cm⁻¹), while analogous seven-coordinate complexes do have a NIR absorption band and show relatively small magnitude zfs (D < 2 cm⁻¹).     

Synthesis and physicochemical characterization of a novel precursor for covalently bound macromolecular MRI contrast agents

 The ligand DOTASA was designed and synthesized in the aim of obtaining a kinetically and thermodynamically stable Gd(III) chelate which, through its uncoordinated carboxylate function, will provide an efficient pathway to couple the complex to bio- or macromolecules without affecting the coordination pattern of DOTA. Furthermore, it allows us to study the influence of an extra carboxylate arm on the parameters determining proton relaxivity in comparison to the commercial agent [Gd(DOTA)(H₂O)]^–. A combined variable-temperature ¹⁷O NMR, EPR and nuclear magnetic relaxation dispersion study on the Gd(III) chelate resulted in k ²⁹⁸ _ex=(6.3±0.2)×10⁶ s^–1 for the water exchange rate and τ²⁹⁸ _R=125±2 ps for the rotational correlation time. The slight increase in both k ²⁹⁸ _ex and τ²⁹⁸ _R, as compared to those for [Gd(DOTA)(H₂O)]^–, is attributed to the presence of the extra negative charge. The longer rotational correlation time results in a proton relaxivity of 5.03 mM^–1 s^–1 for [Gd(DOTASA)(H₂O)]^2–, which is approximately 30% higher than that for [Gd(DOTA)(H₂O)]^–. The increased water exchange rate of [Gd(DOTASA)(H₂O)]^2– has no consequence for proton relaxivity since this latter is exclusively limited by fast rotation for both complexes. However, for slowly rotating macromolecular agents, which contain a covalently coupled DOTASA unit instead of a coupled DOTA, this increased exchange rate will have a significant positive effect. Received: 31 December 1998 / Accepted: 4 March 1999     

Preparation of planar chiral ferrocenes containing a fluorous alcohol function

Ferrocene reacts with hexafluoroacetone trihydrate in refluxing octane to afford >80% yields of [CpFe(η⁵-C₅H₄C(CF₃)₂OH)] (X-ray), carrying out the reactions at 180 °C gives an additional 5% yield of [Fe(η⁵-C₅H₄C(CF₃)₂OH)₂] (X-ray).The mono alcohol is lithiated with Bu^tOK/BuⁿLi/TMEDA affording partial conversion to mixtures of [CpFe(1,2-η⁵-C₅H₃C(CF₃)₂OH)(X)] and [Fe(η⁵-C₅H₄X)(1,2-η⁵-C₅H₃C(CF₃)₂OH)(X)] (X = SMe, CPh₂OH) upon reaction with Me₂S₂ or OCPh₂.For X = CPh₂OH both structures are crystallographically characterised.Enantiopure [CpFe(1,2-η⁵-C₅H₃C(CF₃)₂OH)(SMe)] can be prepared from (R)-[CpFe(η⁵-C₅H₄S(O)C₆H₄Me)] via [CpFe(1,2-η⁵-C₅H₃S(O)C₆H₄Me)(C(CF₃)₂OH)] (X-ray) or [CpFe(1,2-η⁵-C₅H₃S(O)C₆H₄Me)(SMe)].Related procedures allow the preparation of [CpFe(1,2-η⁵-C₅H₃CPh₂OH)(Y)] (Y = SMe, CHO (X-ray), C(CF₃)₂OH) and[CpFe(1,2-η⁵-C₅H₃C(CF₃)₂OH)(CHO)].     

Infrared and Raman studies of [UO2(salen)(L)] (L=H2O and CH3OH)

The infrared and Raman spectra of [UO₂(salen)(H₂O)] and [UO₂(salen)(CH₃OH)] (salen=N,N′-ethylenebis(salicylideneimine) have been recorded. Assignments for the fundamental vibrations are proposed on the basis of C_2v symmetry for the former species and C_s for the latter. The calculated values of the stretching force constant of the uranyl group, F_UO, are 6.87 and 6.63 mdyn Å⁻¹ for [UO₂(salen)(H₂O)] and [UO₂(salen)(CH₃OH)], respectively. The corresponding values of the UO bond lengths calculated as 1.738 and 1.745 Å.     

Chiral Recognition of Tyrosine Enantiomers Based on Decreased Resonance Scattering Signals With Silver Nanoparticles as Optical Sensor

A novel chiral sensing platform, employing silver nanoparticles capped with N‐acetyl‐L‐cysteine (NALC‐Ag NPs), was utilized for the discrimination of L‐tyrosine and D‐tyrosine. This nanosensor, which could be used as an optical sensing unit and chiral probe, was characterized by transmission electron microscopy (TEM) and resonance Rayleigh scattering (RRS) spectroscopy. After the proposed sensing platform interacted with L‐tyrosine and D‐tyrosine, a decreased resonance scattering signal was only obtained from L‐tyrosine. This phenomenon offered a useful assay for the selectivity and determination of L‐tyrosine with the RRS method. The linear range and detection limit of L‐tyrosine were 0.2838–20.0 µg⋅mL^‐1 and 0.0860 µg⋅mL^‐1, respectively. In addition, experimental factors such as acidity, interaction time, and the concentration of enantiomers were investigated with regard to the effect on enantioselective interaction. Chirality 27:194–198, 2015. © 2014 Wiley Periodicals, Inc.     

Theoretical Studies on α-Helix—DNA Interactions

Abstract

The ¹H NMR relaxation effects produced by paramagnetic Cr(III) complexes on nucleoside 5′-mono- and -triphosphates in D₂O solution at Ph′=3 were measured. The paramagnetic probes were [Cr(III)(H₂O) ₆]³⁺, [Cr(III)(H₂O)₃ (HATP)], [Cr(III)(H₂O)₃(HCTP)] and [Cr(III) (H₂O)₃(UTP)^?, while the matrix nucleotides (0.1 M) were H₂AMP, HIMP^?, and H₂ATP^2-. For the aromatic base protons, the ratios of the transverse to longitudinal paramagnetic relaxation rates (R_2p/R_1p) for the [Cr(III)(H₂O)₆]³⁺/H₂ATP^2-, [Cr(III)(H₂O)₃(HATP)]/H₂ATP^2-, [Cr(III)(H₂O)₃(HCTP)]/H₂ATP² and [Cr(III)(H₂O)₃(UTP)]^?/H₂ATP² systems were below 2.33 so the dipolar term predominates. For a given nucleotide, R_1p for the purine H(8) signal was larger than for the H(2) signal with the [Cr(III)(H₂O)₆]³⁺ probe, while R_1p for the H(2) signal was larger with all the other Cr(III) probes. Molecular mechanics computations on the [Cr(III)(H₂O)₄(HPP)(α,β)], [Cr(III)(NH₃)₄(HPP)(α,β)], [Co(III)(NH₃)₃(H₂PPP)(α,βγ)] and [Co(III)(NH₃)₄(HPP)(α,β)] complexes gave calculated energy-minimized geometries in good agreement with those reported in crystal structures. The molecular mechanics force constants found were then used to calculate the geometry of the inner sphere [Cr(III)(H₂O)₆]³⁺ and [Cr(III)(H₂O)₃(HATP)(α,βγ)] complexes as well as the structures of the outer sphere [Cr(III) (H₂O)₆]³⁺-(H₂AMP) and [Cr(III)(H₂O)₆]-(HIMP)^? species. The gas-phase structure of the [Cr(III)(H₂O)₃(HATP)(α,βγ)] complex shows the existence of a hydrogen bond interaction between a water ligand and the adenine N(7) (O…N = 2.82 Å). The structure is also stabilized by intramolecular hydrogen bonds involving the -O(2′)H group and the adenine N(3) (O…N = 2.80 Å) as well as phosphate oxygen atoms and a water molecule (O…O = 2.47 Å). The metal center has an almost regular octahedral coordination geometry.

The structures of the two outer-sphere species reveal that the phosphate group interacts strongly with the hexa-aquochromium probe. In both complexes, the nucleotides have a similar “anti” conformation around the N(9)-C(l′) glycosidic bond. However, a very important difference characterizes the two structures. For the (HIMP)^? complex, strong hydrogen bond interactions exist between one and two water ligands and the inosine N(7) and O(6) atoms, respectively (O…O = 2.63 Å O…N = 2.72, 2.70 Å). For the H₂AMP complex, the [Cr(III) (H₂O)c]³⁺ cation does not interact with N(7) since it is far from the purine system. Hydrogen bonds occur between water ligands and phosphate oxygens. The Cr-H(8) and Cr-H(2) distances revealed by the energy-minimized geometries for the two outer sphere species were used to calculate the R_1p values for the H(8) and H(2) signals for comparison with the observed R_1p values: 0.92(c), 1.04(ob) (H(8)) and 0.06(c), 0.35(ob) (H(2)) for H₂AMP; and 3.76(c), 4.53(ob) (H(8)) and 0.16(c), 0.77(ob) s^?1 (H(2)) for HIMP^?. These results suggest that the dynamic relaxation effects can be only partially understood with molecular mechanics computations, although the success of the geometry calculations suggests that future efforts in the development of computational methods are justified.     

Computer simulation for effect of Pr(III) on Ca(II) speciation in human interstitial fluid

A mutiphase model of metal ion speciation in human interstitial fluid was constructed and the effect of Pr(III) on Ca(II) speciation was studied. Results show that Ca(II) mainly distributes in free Ca²⁺, [Ca(HCO₃)], and [Ca(Lac)]. Because of the competition of Pr(III) for ligands with Ca(II), with the total concentration of Pr(III) rising, the percentages of free Ca²⁺, [Ca(Lac)] and [Ca(His)(Thr)H₃], gradually increase and the percentages of CaHPO₄(aq) and [Ca(Cit)(His)H₂] gradually decrease. However, the percentages of [Ca(HCO₃)] and CaCO₃(aq) first increase, and then begin to decrease when the total concentration of Pr(III) exceeds 6.070×10⁻⁴ M.