A theoretical investigation of intermolecular interaction of a phthalimide based “on–off” sensor with different halide ions: tuning its efficiency and electro-optical properties

The interaction between chemosensor, N-(2-methyl-1,3-dioxo-indan-5-yl)-benzamide (1) and different halide ions (F ^? , Cl^? and Br^?) has been investigated using density functional theory (DFT). A clear insight of the sensor anion binding process has been presented. Our calculations revealed that the observed colorimetric and fluorescent signals are induced due to the ground state deprotonation of the sensor molecule caused by F^? which has two times higher binding affinity than other halide ions (Cl^? and Br^?). Derivatives of system 1 have been made to find a better sensor with higher binding affinity and longer wavelength of absorption. All the derivatives are better sensors than the parent 1 except 4-methyl-N-(2-methyl-1,3-dioxo-indan-5-yl)-benzamide (2). Among these derivatives, trimethyl-[4-(2-methyl-1,3-dioxo-indan-5-ylcarbamoyl)-phenyl]-ammonium (8) and (5-benzoylamino-1,3-dioxo-indan-2-yl)-trimethyl-ammonium (9) showed a change to higher binding energies of about 58 Kcal/mol and longer absorption wavelengths of 53 nm after deprotonation process than the parent system 1 which is highly demanded in selective chemical sensing. Systems 8, 9 and their deprotonated zwitterionic forms (8z and 9z) have also been studied for their nonlinear optical responses. Systems 8, 9 showed significantly good first hyperpolarizability (β) of 84 × 10^?30 and 40 × 10^?30 esu, respectively. These β values increase in zwitterionic states up to 216 × 10^?30 and 109 × 10^?30 esu, respectively after deprotonation with F^?, representing a new signal of deprotonation.     

Spectrofluorimetric determination of formaldehyde by a flow-injection method based on its catalytic effect on the acridine yellow–bromate reaction

A flow-injection configuration for the determination of formaldehyde is proposed. The method is based on the enhancing effect of formaldehyde on the oxidation of acridine yellow by bromate in acidic medium. The proposed procedure is simple, inexpensive, sensitive and suitable for concentrations of formaldehyde between 1 and 56 microg mL(-1). A sampling-rate of 60 samples h(-1) was achieved. The effect of several organic and inorganic species was studied. The method was applied to the determination of formaldehyde in pharmaceuticals, milk and air in work environments. The accuracy of the method was confirmed by comparing the results with those obtained using the standard acetylacetone method.     

An experimental investigation on the heat transfer characteristics of closed-loop pulsating heat pipe with graphene–water nanofluid

Journal of Thermal Analysis and Calorimetry - The heat transfer performance of a closed-loop pulsating heat pipe (CLPHP) having 2.2 mm inner diameter is experimentally studied at different...     

Biophysical and biochemical investigation on the binding of a manganese–cyanonitrosyl complex with DNA

The interaction of a cyanonitrosyl–manganate complex with DNA has been studied by u.v.–vis spectroscopy, circular dichroism, fluorescence and gel electrophoresis techniques. As the DNA 260 nm band remained insensitive to interaction, the interaction ratio was determined by monitoring the CN⁻→ Mn LMCT band observed at 222 nm, and the interaction ratio was found to be in the complex (D): DNA (P)=1:0.30 from the spectrophotometric titration. The above-mentioned physical measurements indicate that the binding mode is not intercalative and the cyanonitrosyl system is a groove binder.     

LC–ELISA as a contribution to the assessment of matrix effects with environmental water samples in an immunoassay for estrone (E1)

Accreditation and Quality Assurance - Estrone (E1), a metabolite of the estrogenic hormones 17β-estradiol (β-E2) and 17α-estradiol (α-E2), is itself a potent estrogen which can...     

Dispersion interactions of carbohydrates with condensate aromatic moieties: theoretical study on the CH-π interaction additive properties

In this article we present the first systematic study of the additive properties (i.e. degree of additivity) of the carbohydrate-aromatic moiety CH-π dispersion interaction. The additive properties were studied on the β-D-glucopyranose, β-D-mannopyranose and α-L-fucopyranose complexes with the naphthalene molecule by comparing the monodentate (single CH-π) and bidentate (two CH-π) complexes. All model complexes were optimized using the DFT-D approach, at the BP/def2-TZVPP level of theory. The interaction energies were refined using single point calculations at highly correlated ab initio methods at the CCSD(T)/CBS level, calculated as E + (E(CCSD(T))-E(MP2))(Small Basis). Bidentate complexes show very strong interactions in the range from -10.79 up to -7.15 and -8.20 up to -6.14 kcal mol(-1) for the DFT-D and CCSD(T)/CBS level, respectively. These values were compared with the sum of interaction energies of the appropriate monodentate carbohydrate-naphthalene complexes. The comparison reveals that the bidentate complex interaction energy is higher (interaction is weaker) than the sum of monodentate complex interaction energies. Bidentate complex interaction energy corresponds to 2/3 of the sum of the appropriate monodentate complex interaction energies (averaging over all modeled carbohydrate complexes). The observed interaction energies were also compared with the sum of interaction energies of the corresponding previously published carbohydrate-benzene complexes. Also in this case the interaction energy of the bidentate complex was higher (i.e. weaker interaction) than the sum of interaction energies of the corresponding benzene complexes. However, the obtained difference is lower than before, while the bidentate complex interaction energy corresponds to 4/5 of the sum of interaction energy of the benzene complexes, averaged over all structures. The mentioned comparison might aid protein engineering efforts where amino acid residues phenylalanine or tyrosine are to be replaced by a tryptophan and can help to predict the changes in the interactions. The observed results also show that DFT-D correctly describes the CH-π interaction energy and their additive properties in comparison to CCSD(T)/CBS calculated interaction energies. Thus, the DFT-D approach might be used for calculation of larger complexes of biological interest, where dispersion interaction plays an important role.     

Synthesis of “bioinspired” copolymers: experimental and theoretical investigation on poly(vinyl benzyl thymine-co-triethyl ammonium chloride)

Abstract

“Bioinspired” copolymers based on vinylbenzyl thymine (VBT) and an ionically-charged monomer, such as vinylbenzyl triethylammonium chloride (VBA), were synthesized and theoretically investigated. These water-soluble copolymers are polystyrene- (PS) based, and their structure mimics DNA. In the presence of short-wavelength UV light, the thymine groups dimerize into non-toxic, environmentally benign, and biodegradable photo-resistant materials. Copolymerizations with different comonomer ratios were carried out at 65°C. Samples were taken along the reactions to determine monomer conversion, chemical composition, and molecular weight distribution. While average molecular weights fall along the reaction, the average composition remains almost constant and coincident with the initial comonomer ratios, thus indicating a similar reactivity of all the comonomer radicals. A mathematical model was developed that simulates the synthesis of the base biopolymer, in the sense of predicting the evolution of the global reaction variables and molecular structure of the polymer. The termination and propagation kinetic constants were adjusted to the experimental data. The resulting values are quite different to those of a normal styrene homopolymerization, thus suggesting a noticeable effect of the solvent and the comonomer pending groups.     

Spectroscopic investigation of the solvatochromic behavior of a new synthesized non symmetric viologen dye: Study of the solvent–solute interactions

This work deals with the design, synthesis, and characterization of a new solvatochromic dye. The intense solvatochromic behavior of this new synthesized non symmetric viologen was investigated using UV–Vis spectrophotometry. A further purpose was the study of the interactions between the solvent and solute molecules responsible for the solvatochromism. Several protic and aprotic solvents were used, and the resulting absorption maxima wavenumbers obtained via UV–Vis spectrophotometry, were correlated with the solvent polarity parameters, E _T (30) (Dimroth–Reichardt solvent polarity parameter) and the Gutmann’s donor number (DN) using the biparametric model introduced by Krygowski and Fawcett. The analysis of the relative contribution of each parameter has clearly shown that the dominating interaction responsible for the solvatochromic behavior observed is the proton donation by the solute molecules to the solvent molecules, the latter acting as a Lewis bases. This is an interaction which can be described by DN. Additionally, the good correlation with the Kamlet–Taft parameter β is in good agreement.     

The development of a rapid method for the isolation of four azaspiracids for use as reference materials for quantitative LC–MS–MS methods

The azaspiracids are a family of lipophilic polyether marine biotoxins that have caused a number of human intoxication incidents in Europe since 1995 after consumption of contaminated shellfish (Mytilus edulis). Levels of azaspiracids in shellfish for human consumption are monitored in accordance with EU guidelines: only shellfish with less than 160 μg kg⁻¹ are deemed safe. The limited availability of commercially available standards for azaspiracids is a serious problem, because validated LC–MS methods are required for routine analysis of these toxins in shellfish tissues. The procedure described herein has been used for the separation and the isolation of four azaspiracid (AZA) toxins from shellfish, for use as LC–MS–MS reference materials. Five separation steps have been used to isolate azaspiracids 1, 2, 3, and 6. The purity of the toxins obtained has been confirmed by multiple mass spectrometric methods using authentic azaspiracid standards. The same techniques have been used for quantification of the toxins extracted. The isolation procedure involves several chromatographic purification techniques: solid-phase extraction (diol sorbent, 90% mass reduction, and 95 ± 1% toxin recovery); Sephadex size-exclusion chromatography (87% mass reduction and up to 95 ± 2% toxin recovery), Toyopearl HW size-exclusion chromatography (90% mass reduction and up to 92.5 ± 2.5% toxin recovery), and semi-preparative LC (78 ± 3% toxin recovery). The procedure effectively separates the toxins from the sample matrix and furnishes azaspiracid toxins (AZA1, AZA2, AZA3 and AZA6) of sufficient purity with an average yield of 65% (n = 5). Triple-quadrupole mass spectrometry was used for qualitative and quantitative monitoring of the isolation efficiency after each stage of the process. High-resolution mass spectrometric evaluation of the toxic isolated material in both positive and negative modes suggests high purity.     

Platinum electrode coated with a bentonite–carbon composite as an environmental sensor for detection of lead

A Pt wire coated with a bentonite–carbon composite in a poly(vinyl chloride) membrane was used for detection of lead. The sensor has a Nernstian slope of 29.42±0.50 mV per decade over a wide range of concentration, 1.0×10⁻⁷ to 1.0×10⁻³ mol L⁻¹ Pb(NO₃)₂. The detection limit is 5.0×10⁻⁸ mol L⁻¹ Pb(NO₃)₂ and the electrode is applicable in the pH range 3.0–6.7. It has a response time of approximately 10 s and can be used at least for three months. The electrode has good selectivity relative to nineteen other metal ions. The practical analytical utility of the electrode is demonstrated by measurement of Pb(II) in industrial waste and river water samples.     

Experimental and theoretical study of the dissociation enthalpy of the N–O bond on 2-hydroxypyridine N-oxide: theoretical analysis of the energetics of the N–O bond for hydroxypyrydine N-oxide isomers

The standard (p^∘=0.1 MPa) molar enthalpy of formation of crystalline 2-hydroxypyridine N-oxide was measured, at T=298.15 K, by static bomb calorimetry and the standard molar enthalpy of sublimation, at T=298.15 K, was obtained using Calvet microcalorimetry. These values were used to derive the standard molar enthalpy of formation of 2-hydroxypyridine N-oxide in gaseous phase, and to evaluate the dissociation enthalpy of the N–O bond. Additionally, high-level density functional theory calculations using the B3LYP hybrid exchange-correlation energy functional have been performed for the three isomers of hydroxypyridine N-oxide in order to confirm the experimental trend for the dissociation enthalpy of the (N–O) bond.     

Evidence for side-chain π-delocalization in a planar substituted benzene: an experimental and theoretical charge density study on 2,5-dimethoxybenzaldehyde thiosemicarbazone

The charge density in 2,5-dimethoxybenzaldehyde thiosemicarbazone (1) has been studied experimentally using Mo-K(α) X-ray diffraction at 100 K, and by theory using DFT calculations at the B3LYP/6-311++G(2d,2p) level. The quantum theory of atoms in molecules (QTAIM) was used to investigate the extent of π-delocalization in the thioamide side-chain, which is virtually coplanar with the benzene ring. The experimental and theoretical ellipticity profiles along the bond paths were in excellent agreement, and showed that some of the formal single bonds in the side-chain have significant π-bond character. This view was supported by the magnitudes of the topological bond orders and by the delocalization indices δ(Ω(A), Ω(B)). An orbital decomposition of δ(Ω(A), Ω(B)) demonstrated that there was significant π-character in all the interchain non-H chemical bonds. On the other hand, the source function referenced at the interchain bond critical points could not provide any evidence for π-delocalization, showing instead only limited σ-delocalization between nearest neighbors. Overall, the topological evidence and the atomic graphs of the oxygen atoms did not provide convincing evidence for π-delocalization involving the methoxy substituents.     

Theoretical and experimental investigation on the near-infrared and UV–vis spectral regions of a newly synthesized triarylamine electrochromic system

A new triarylamine derivative, N,N′-Bis(4-heptanoylamidophenyl)-N,N′-di(4-methoxyphenyl)-1,4-phenylenediamine, with stable electrochromism in near-infrared and visible light regions, has been synthesized and characterized at theoretical and experimental level. The detected and simulated spectra, with and without the presence of an external potential at different values, clearly show that this mixed-valence system undergoes ionization at a low value of the applied potential, and the formed radical cation absorbs in the near-infrared region with an intense peak located at 1,040 nm. Density functional computations give the geometrical structure and absorption properties in very good agreement with experiment, allowing assigning the electronic transition and contributing to an understanding of the electron-transfer process between the two redox centers.     

Theoretical studies on the electron capture properties of the H2SO4...HOO˙ complex and its implications as an alternative source of HOOH

To better understand the potential role of sulfuric acid aerosols in the atmosphere, the electron capture properties of the H(2)SO(4)...HOO˙ complex have been systematically investigated by employing the MP2 and B3LYP methods in combination with the atoms in molecules (AIM) theory, energy decomposition analysis (EDA), and ab initio molecular dynamics. It was found that the electron capture process is a favorable reaction thermodynamically and kinetically. The excess electron can be captured by the HOO˙ fragment initially, and then the proton of the H(2)SO(4) fragment associated with the intermolecular H-bonds is transferred to the HOO˙ fragment without any activation barriers, resulting in the formation of the HOOH species directly. Therefore, the electron capture process of the H(2)SO(4)...HOO˙ complex provides an alternative source of HOOH in the atmosphere. The nature of the coupling interactions in the electron capture products are clarified, and the most stable anionic complex is also determined. Additionally, the influences of the adjacent water molecules on the electron capture properties are investigated, as well as the distinct IR features of the most stable electron capture product.     

Can weak interactions modify the binding properties of a strong nitrogen donor? Unusual N-coordination of a phosphoranylidene-substituted pyrazolone unit towards palladium(II) centres: an experimental and theoretical study

Selective N(2)-binding of 3-methyl-1-phenyl-4-(triphenylphosphoranylidene)-2-pyrazolin-5-one (L) has been found in two palladium(II) complexes, [PdCl(2)L(2)](2) and [Pd(o-C(6)H(4)CH(2)NMe(2))Cl](3). X-Ray diffraction studies show that the pyrazole rings lie almost perpendicular to the coordination plane. In both complexes the metal atom is located out of the plane defined by the pyrazole ring(s)(dihedral angle between the plane and the Pd-N vector approximately 30 degrees). To investigate the origin of this distortion, a theoretical study was carried out on a simplified model of complex , where a single pyrazolone ligand was replaced by NH(3). From this study it could be inferred that the out-of-plane distortion mainly involves weak, electrostatic interactions between a chlorine atom and an ortho-aromatic H atom of the N(1)-linked phenyl group, as well as between the other chlorine atom and an ortho-aromatic H atom of the PPh(3) group.     

New model for a theoretical density functional theory investigation of the mechanism of the carbonic anhydrase: how does the internal bicarbonate rearrangement occur?

A theoretical density functional theory (DFT, B3LYP) investigation has been carried out on the catalytic cycle of the carbonic anhydrase. A model system including the Glu106 and Thr199 residues and the "deep" water molecule has been used. It has been found that the nucleophilic attack of the zinc-bound OH on the CO(2) molecule has a negligible barrier (only 1.2 kcal mol(-1)). This small value is due to a hydrogen-bond network involving Glu106, Thr199, and the deep water molecule. The two usually proposed mechanisms for the internal bicarbonate rearrangement have been carefully examined. In the presence of the two Glu106 and Thr199 residues, the direct proton transfer (Lipscomb mechanism) is a two-step process, which proceeds via a proton relay network characterized by two activation barriers of 4.4 and 9.0 kcal mol(-1). This pathway can effectively compete with a rotational mechanism (Lindskog mechanism), which has a barrier of 13.2 kcal mol(-1). The fast proton transfer found here is basically due to the effect of the Glu106 residue, which stabilizes an intermediate situation where the Glu106 fragment is protonated. In the absence of Glu106, the barrier for the proton transfer is much larger (32.3 kcal mol(-1)) and the Lindskog mechanism becomes favored.