Synthesis,Structure, and Characterization of [FeIIILCl3] (L = 1, 4, 8‐Triazacycloundecane, 1, 4, 7‐Triazacyclononane)

The structures of [Fe^III(tacud)Cl₃] ( 1 ) and [Fe^III(tacn)Cl₃] ( 2 ) (tacud = 1, 4, 8‐triazacycloundecane, tacn = 1, 4, 7‐triazacyclononane) are reported. Both compounds crystallize in the orthorhombic space group Pnma with a = 12.5570(9), b = 12.0028(9), c = 8.2577(6) Å, V = 1244.59(16) ų, and Z = 4 for 1 and a = 12.095(4), b = 11.125(4), c = 7.963(3) Å, V = 1071.5(6) ų, and Z = 4 for 2 . The structures of 1 and 2 feature iron(III) in distorted octahedral arrangement with three facially coordinated nitrogen ligands and three chlorides. Bidirectional intermolecular hydrogen bonding between N–H groups and coordinated chlorides is seen for 1 and 2 . Compound 1 is the first example of iron(III) bonded to tacud and compound 2 is only the second structure reported of a 1:1 complex between iron and tacn. The Fe^3+/2+ redox couple for 1 is observed at E_1/2 = 0.25 V (ΔE_p = 99 mV), and for 2 at E_1/2 = 0.09 V (ΔE_p = 108 mV) versus NHE in DMF at 298 K. Comparison of structural, magnetic, and electrochemical properties for 1 and 2 reveal subtle differences consistent with the stronger coordinating properties of tacn relative to tacud.     

Surface‐enhanced Raman spectra of melamine and other chemicals using a 1550 nm (retina‐safe) laser

Many trace chemical analyses are being transitioned from the lab to the field, among which is surface‐enhanced Raman spectroscopy. Although initial portable Raman analyzers primarily employ 785 nm laser excitation, recent studies suggest longer wavelengths, with an appropriate surface‐enhanced Raman‐active substrate, may provide equal sensitivity. Furthermore, 1550 nm excitation may provide added safety for the user, in that permanent retina damage does not occur. Here, we show that a reasonable enhancement factor can be obtained for melamine using 1550 nm laser excitation that is nearly equivalent to those obtained using 785 and 1064 nm laser excitation. We also demonstrate that a number of other chemicals of interest can be measured by 1550 nm surface‐enhanced Raman scattering, albeit only modest sensitivity is achieved because of instrument limitations, not enhancement factors. Copyright © 2011 John Wiley & Sons, Ltd.     

An alternate mode of binding of the polyphenol quercetin with serum albumins when complexed with Cu(II)

Polyphenols find wide use as antioxidants, cancer chemopreventive agents and metal chelators. The latter activity has proved interesting in many aspects. We have probed the binding characteristics of the polyphenol quercetin–Cu(II) complex with human serum albumin (HSA) and bovine serum albumin (BSA). Fluorescence studies reveal that the quercetin–Cu(II) complex can quench the fluorescence of the serum albumins. The binding constant (K_b) values are of the order of 10⁵ M^?1 which increased with rise in temperature in case of HSA and BSA interacting with the quercetin–Cu(II) complex. Displacement studies reveal that both the ligands bind to site 1 (subdomain IIA) of the serum albumins. However, thermodynamic parameters calculated from temperature dependent studies indicated that the mode of interaction of the complexes with the proteins differs. Both ΔH° and ΔS° were positive for the interaction of the quercetin–Cu(II) complex with both proteins but the value of ΔH° was negative in case of the interaction of quercetin with the proteins. This implies that after chelation with metal ions, the polyphenol alters its mode of interaction which could have varying implications on its other physicochemical activities.     

1-(d-Glucopyranosyl-2′-deoxy-2′-iminomethyl)-2-hydroxynaphthalene as chemo-sensor for Fe in aqueous HEPES buffer based on colour changes observable with the naked eye

A new glucose-based C2-derivatized colorimetric chemo-sensor (L₁) has been synthesized by a one-step condensation of glucosamine and 2-hydroxy-1-naphthaldehyde for the recognition of transition metal ions. Among the eleven metal ions studied, viz., Mg²⁺, Ca²⁺, Mn²⁺, Fe²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺ and Hg²⁺, L₁ results in visual colour change only in the presence of Fe²⁺, Fe³⁺and Cu²⁺ in methanol. However, in an aqueous HEPES buffer (pH 7.2) it is only the Fe³⁺ that gives a distinct visual colour change even in the presence of other metal ions, up to a concentration of 280 ppb. The changes have been explained based on the complex formed, and the composition has been determined to be 2:1 between L₁ and Fe³⁺ based on Job’s plot as well as ESI MS. The structure of the proposed complex has been derived based on HF/6-31G calculations.     

Binuclear cobalt(II/II) and cobalt(II/III) chelates with O<Subscript>2</Subscript>N<Subscript>2</Subscript> ligands: synthesis,structure and magnetic studies

Abstract  The title complexes and have been synthesized in excellent yields by reacting Co(OAc)₂·4H₂O with H₂L¹ and H₂L², respectively, in acetonitrile solution. Here, [L¹]²⁻ and [L²]²⁻ are the deprotonated forms of N,N-bis(2-hydroxybenzyl)-N′,N′-dimethylethylenediamine and N,N-bis(2-hydroxybenzyl)-2-picolylamine, respectively. The crystal structures of and were determined by x-ray crystallography. In , each cobalt atom has distorted trigonal bipyramid geometry, while in , each cobalt atom has distorted octahedral geometry. Variable temperature magnetic moment measurements show weak antiferromagnetic interaction in . The magnetic characterization for is in agreement with the presence of Co(II) and Co(III) centers. Graphical Abstract  The title complexes and have been synthesized in excellent yields by reacting Co(OAc)₂·4H₂O with dianionic N₂O₂ coordinating ligands. In complex 1, each cobalt atom has distorted trigonal bipyramid geometry, while in complex 2, each cobalt atom has distorted octahedral geometry. Variable temperature magnetic moment measurements show weak antiferromagnetic interaction in complex 1. The magnetic characterization for complex 2 is in agreement with the presence of Co(II) and Co(III) centers. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Heterometallic 3d–4f Complexes as Single‐Molecule Magnets

Heterometallic 3d‐4f complexes are being investigated, for some time, as being useful in molecular magnetism, particularly as single‐molecule magnets (SMMs). This interest is primarily because of the possibility of an increased ligand‐mediated super‐exchange phenomenon between the 3d and 4f metal ions. Such an interaction, apart from bestowing a favorable ground‐state spin to the complex, also assists in reducing quantum tunneling of magnetization that is widely prevalent in SMMs making them to lose magnetization. However, assembling both 3d as well as 4f ions using same ligand system is challenging and involves the design of multi‐site coordination ligands with specific coordination compartments for the 3d and the 4f metal ions while at the same time allowing these disparate metal ions to be linked to each other through a bridging ligating atom. This review presents a summary of the 3d‐4f complexes primarily derived from the author's work while alluding to important examples from the literature. We also provide an outlook for the future design of such complexes.     

Causality in Discrete Time Physics Derived from Maupertuis Reduced Action Principle

Causality describes the process and consequences from an action: a cause has an effect. Causality is preserved in classical physics as well as in special and general theories of relativity. Surprisingly, causality as a relationship between the cause and its effect is in neither of these theories considered a law or a principle. Its existence in physics has even been challenged by prominent opponents in part due to the time symmetric nature of the physical laws. With the use of the reduced action and the least action principle of Maupertuis along with a discrete dynamical time physics yielding an arrow of time, causality is defined as the partial spatial derivative of the reduced action and as such is position- and momentum-dependent and requests the presence of space. With this definition the system evolves from one step to the next without the need of time, while (discrete) time can be reconstructed.     

Acid-base properties of solid polyelectrolytes: Dissociation of cellulosic polyanions

The potentiometric titration behavior of nitrogen dioxide and periodate-chlorite oxycellulose has been studied both in the presence and absence of sodium chloride. The apparent pK values in general increase with increasing degree of dissociation, but the reverse is true for periodate-chlorite oxycellulose in the absence of added salt. This behavior is interpreted in terms of electrostatic and hydrogen bonding interaction of carboxyl groups. The Gibbs–Donnan theory of polyaid dissociation was applied to calculate the intrinsic dissociation constant pK′₀. Assuming a model having a uniform potential distributin throughout the fiber, good agreement with the expected value of 3.24 was found (compared to pK′₀ = 3.25 calculated for periodate-chlorite oxycellulose).