SERS and DFT investigation of 1-(2-pyridylazo)-2-naphthol and its metal complexes with Al(III), Mn(II), Fe(III), Cu(II), Zn(II) and Pb(II)

A simple, fast and inexpensive approach to quantify low concentrations of iron in biodiesel by voltammetry after extraction induced by microemulsion breaking

An alternative approach to assay iron (Fe) in biodiesel by differential pulse adsorptive cathodic stripping voltammetry (DPAdCSV) is presented herein. The sample treatment involved a simple, rapid, but effective extraction of Fe from biodiesel into an aqueous phase after microemulsion (ME) breaking. Then, Fe was determined as the complex Fe(III)-PAN (1-(2-pyridylazo)-2-naphthol) on a glassy carbon electrode (GCE) in the presence of bismuth (Bi(III)). The extraction induced by microemulsion breaking (EIMB) was achieved by adding 0.80 mL of ultrapure water into a water-in-oil ME containing 7.00 mL biodiesel, 2.70 mL n-propanol and 0.30 mL of 0.25 mol L-1 HNO3 solution. No deliberate addition of surfactant was necessary to form and maintain the ME. The EIMB resulted in a 1.30 mL lower aqueous phase extract (APhEx) and an upper oily phase. DP voltammograms were recorded with a portable potentiostat, showing the potentiality of carrying out the determination out of a central laboratory. Another feature was the non-necessity of deaerating the solution to eliminate the dissolved O2. The limits of detection (LOD) and quantification (LOQ) were 1.7 μg L-1 (140 mg kg-1) and 5.5 μg L-1 (455 mg kg-1), respectively. The accuracy of the method was evaluated by recovery assays of spiked samples, by analyzing a standard reference material and by comparisons with high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GF AAS).

Electrode surface embedded manganese(iii)–pincer complexes: efficient electrocatalysts for the oxygen evolution reaction

Highly stable and robust gold electrode surface anchored Mn(iii)–pincer complex exhibits an excellent electrocatalytic activity towards the oxygen evolution reaction at a low overpotential with a medium Tafel slope under neutral pH condition.

Optimization of a doped sol–gel glass with a nanoporous structure as a chemical sensor for the determination of cobalt(ii): analysis of food, pharmaceutical and biological samples

A PAN incorporated sol–gel glass with a nanoporous structure as an optical sensor for the detection of Co(ii).

Yeast cell wall - Silver nanoparticles interaction: A synergistic approach between surface-enhanced Raman scattering and computational spectroscopy tools

Candida species are becoming one of the pathogens developing antifungal resistance due to inappropriate treatment and overuse of antimycotic drugs in building construction and agriculture. Further, fungal infections are often difficult to detect, also due to slow in vitro growth of the organisms from clinical specimens. Thus, fast detection and discrimination of yeast cells in direct patient materials is essential for an adequate treatment and success rate. In this work, we investigated Candida species isolated from patients, by using surface-enhanced Raman scattering (SERS) combined with computational spectroscopy tools, aiming to detect and discriminate between the three considered species, Candida albicans, Candida glabrata, and Candida parapsilosis. Density functional theory (DFT) was used to calculate Raman spectra of yeasts' main cell wall components for elucidating the origin of the observed bands. Accurate assignments of normal modes helped for a better understanding of the interaction between silver nanoparticles with yeasts' cell wall. Further, SERS spectra were used as samples in a database on which we performed multivariate analyses. By Principal component analysis (PCA), we obtained a maximum variation of 79% between the three samples. Linear discriminant analysis (LDA) was successfully used to discriminate between the three species.

Application of Mn-Cu Helical Star-Shaped (Pine-Tree-Like) Sculpted Thin Films with Different Symmetries Using Surface-Enhanced Raman Spectroscopy (SERS)

In this work, the surface engineering method is used to produce Mn helical star-shaped (pine-tree-like) nanosculptured thin films with three-, four-, and fivefold symmetries on Cu substrates using an oblique angle deposition technique together with rotation of the sample holder at certain angles. Nano structure and morphologies of the produced samples were obtained by means of atomic force microscope and field emission scanning electron microscope. Raman spectroscopy of the Mn/Cu samples impregnated by 4,4'-bipyridine (C₁₀H₈N₂) solution with different concentrations, zidovudine (C₁₀H₁₃N₅O₄), and L-histidine (C₆H₉N₃O₂) was performed using 532 nm laser wavelength. A high degree of enhancement is achieved on Raman spectroscopy of all of these specimens. Comparison of the surface-enhanced Raman spectroscopy (SERS) results for 4,4' bipyridine (bipy) obtained in this work with the published literature using Ag and Au substrates in different shapes showed a significant enhancement improvement by using Mn sculptured structures. Reduction of the bipy concentration changed the enhancement factor. Enhancement factors of 10⁷ and 10⁵ were obtained for threefold symmetry sample using 2.885 × 10^-2 and 10^-3mol L^-1 bipy concentrations, respectively. Surface-enhanced Raman spectroscopy results of this work show that Mn nanostructures designed and engineered in this work can not only replace Ag and Au materials, but also provide a much higher enhancement factor.

A green and general strategy for the synthesis of hollow Ag/CdS nanocomposites for superior SERS performance

In this study, we developed a convenient, environmentally friendly approach for the fabrication of hollow Ag/CdS composites, which presented superior SERS performance.

Computational insights into the molecular interaction and ion-pair structures of a novel zinc-functionalized ionic liquid, [Emim][Zn(TFSI)₃]

The ion pair structures of a novel CO2 capture material in the form of a metal chelate anion-containing room temperature ionic liquid (IL), 1-ethyl-3-methylimidazolium tri[bis(trifluoromethylsulfonyl)imide]zincate(II), [Emim][Zn(TFSI)3], were elucidated by correlating the infrared spectra generated using density functional theory (DFT) calculations with the experimental spectrum derived from a room temperature infrared spectroscopic measurement. A free volume energy minimization algorithm revealed stable structures where the zinc ion forms an octahedral, homoleptic complex with the ligand bis(trifluoromethylsulfonyl)imide through coordination with the oxygen of the sulfone group, with 1-ethyl-3-methylimidazolium acting as the counterion. The method of analysis was built around 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [Emim][TFSI], involving direct comparison with published data, and extended to the more complex [Emim][Zn(TFSI)3] system. The DFT calculations reproduced the vibrational spectra of [Emim][Zn(TFSI)3] and [Emim][TFSI] using their optimized geometries, with correlation slopes of 0.9996 and 1.0022, respectively. Comparison of the vibrational modes of [Emim][TFSI] and [Emim][Zn(TFSI)3] provided insights into the ion pair structure of, and molecular interactions in the ILs analyzed.

Highly uniform indicator-mediated SERS sensor platform for the detection of Zn2+

An indicator-mediated surface-enhanced Raman scattering (SERS) sensor platform with highly uniform SERS sensitivity was fabricated by modifying 4-mercaptopyridine (4-MPY) molecules as an indicator onto the surface of Ag nanoparticles that were anchored onto a silicon wafer.

Adsorption and trace detection of pharmacologically significant 5-methylthio-1, 3, 4-thiadiazole-2-thiol molecule adsorbed on silver nanocolloids and understanding the role of Albrecht's "A" and Herzberg-Teller contributions in the SERS spectra

The surface enhanced Raman scattering (SERS) spectra of biologically and industrially significant 5-methylthio-1, 3, 4-thiadiazole 2-thiol molecule have been investigated. The SERS spectra at various concentrations of the adsorbate are compared with the Fourier transform Infrared (FTIR) and normal Raman spectra (NRS) of the probe molecule recorded in different environmental conditions. The optimized molecular structures of the most probable thione and the thiol forms of the molecule have been estimated from the density functional theory (DFT) calculations. The vibrational signatures of the molecule have been assigned from the potential energy distributions (PEDs). The detail vibrational analyses reveal that ∼54% of the thione form of the molecule is prevalent in the solid state and its population increases to ∼65% in ACN solvent medium. Concentration dependent SERS, together with the 2-dimensional correlation spectra (2D-COS), corroborate the presence of both the thione and the thiol forms of the molecule even in the surface adsorbed state. The orientations of the thione and the thiol forms of the molecule on the nanocolloidal silver surface have been predicted from the surface selection rule. The selective enhancement of Raman bands in the SERS spectra have been explored from the view of the Albrecht's "A" and Herzberg-Teller (HT) charge transfer (CT) contribution.

Insight into luminescent bisazoaromatic CNN pincer palladacycle: synthesis, structure, electrochemistry and some catalytic applications in C–C coupling

The 2-(phenylazo)azobenzene furnished novel palladacycles in excellent yield, which showed luminescence at rt and catalytic activity. The optoelectronic and electrochemical responses were substantiated with DFT and TDDFT.

Determination of metal ion concentrations by SERS using 2,2′-bipyridyl complexes

SERS of bipyridyl complexes for the discrimination of six different metal ions.

Conformation of azo-bridge in 3,3'-dinitro-2,2'-azobipyridine and its 4,4'(or 5,5' or 6,6')-dimethyl-derivatives: vibrational studies and DFT quantum chemical calculations

Syntheses of 3,3'-dinitro-2,2'-azobipyridine and 4,4' (or 5,5' or 6,6')-dimethyl-3,3'-dinitro-2,2'-azobipyridine have been described. Molecular structures of these compounds have been determined and compared, to the basic compound, azobipyridine, reported by us earlier. The conformation of the azo-bond and other structural data are discussed in terms of substitution place of methyl chromophore. Fourier transform IR and Raman spectra of these compounds have been measured and analysed. The 6-311G (2d,2p) basis set with the B3LYP functional have been used to discuss the space conformation and dynamics of the studied compounds.

Molecular and electronic structure of nonradical homoleptic pyridyl-azo-oxime complexes of cobalt(iii) and the azo-oxime anion radical congener: an experimental and theoretical investigation

Synthesis and optoelectronic study of Co(iii)–pyridyl-azo-oxime complexes and isolation of Co(iii)-bound azo-oxime anion radical.