Detection and classification of host–guest interactions using β-cyclodextrin-decorated carbon nanotube-based chemiresistors

Carbon nanotubes (CNTs) in a chemiresistor setup have been widely explored in bio/chemical sensing. Detection of certain molecules with environmental and health related importance such as 9-anthracenecarboxylic acid, diclofenac sodium, and curcumin using electrochemical methods/unfunctionalized CNTs suffer from lack of response, high limit of detection (LOD) and poor selectivity. The key to overcome these issues is to decorate CNTs with host (receptor) molecules like β-cyclodextrin (β-CD) that interact with guest (target) molecules by host–guest complex formation. To improve guest recognition, and consequently, the sensor performance, effective immobilization of β-CD on the CNT surface using a non-covalent bridging molecule such as 3, 4, 9, 10-perylene tetracarboxylic acid (PTCA) is required. Furthermore, the selectivity can be assessed using the conductance correlation patterns of different host–guest systems in conjunction with a pattern classification tool. Our results indicate that PTCA linked β-CD-decorated CNT chemiresistors showed a good linear detection range (∼100 pM–100 nM), sensitivity (∼3 × 10⁻³–9 × 10⁻² nM⁻¹) and LOD (∼62 pM–101 nM), compared to devices without PTCA, in the detection of the guest molecules. The distinction in correlation patterns of different host–guest systems was corroborated by pattern classification yielding a classification accuracy, sensitivity, and specificity of ∼91.83%, ∼90.13%, and ∼85.39%, respectively.     

Calculations of potential of mean force: application to ion-pairs and host–guest systems

ABSTRACT

We report the calculation of the potential of mean force (PMF) of different types of associations by various techniques: two no biased methods (thermodynamic integration and finite difference thermodynamic integration), a constraint biased technique (adaptive biasing force) and an umbrella biased method (umbrella sampling). We apply these methodologies to the association between two methane molecules in water, to the formation of an ion pair in water and to the formation of an insertion complex between a macrocycle and a cation. The different PMFs are compared to each other on the basis of the depth of the free energy minimum and on the location of different specific points.     

Tautomerization and solvent effects on the absorption and emission properties of the Schiff base N,N′-bis(salicylidene)-p-phenylenediamine – A TDDFT study

Time-dependent density functional theory combined with a polarized continuum model has been applied to study solvent effects on the geometrical and energetic properties, as well as the absorption and emission properties, of three tautomeric forms of N,N′-bis(salicylidene)-p-phenylenediamine (BSP). The calculated properties are in agreement with the available experimental data. It was observed that the solvent environment does not affect the vertical excitation energies significantly, whereas tautomerization strongly affects both the absorption and emission spectra of BSP.     

Spectral characteristics and fluorescence quenching of N,N′-bis(4-pyridyl)-3,4:9,10-perylenebis(dicarboximide) (BPPD)

The photophysical properties such as electronic absorption, molar absorptivity, emission spectra, fluorescence quantum yield and fluorescence lifetime of N,N′-bis(4-pyridyl)-3,4:9,10-perylene bis(dicarboximide) (BPPD) have been measured in different solvents. Both electronic absorption and fluorescence spectra are not sensitive to medium polarity, while the fluorescence quantum yield (?_f) is solvent dependent. The ground state geometry has been computed by using density functional theory (DFT), the transition from HOMO to LUMO from perylene core with maximum absorption at 512 nm and HOMO–LUMO energy difference equal 2.53 eV. BPPD dye undergoes molecular aggregation to dimmer or higher aggregates in dimethyl sulfoxide (DMSO). Crystalline solids of BPPD gives excimer-like emission at 676 nm. The fluorescence quenching of BPPD is also studied using hydrated ferric oxide nanoparticle (FeOOH), and the Stern–Volmer rate constants (K_sv) were calculated as 8×10⁶ and 9.2×10⁶ M^?1 in ethanol and ethylene glycol, respectively.     

UV–Vis and NMR spectroscopic investigations on effective and selective non-covalent interactions between fullerenes and calix[6]arene

Ground state non-covalent interactions between a macro cyclic calixarene receptor, namely, 4-tert-butylcalix[6]arene (1), and fullerenes (C₆₀ and C₇₀) were studied in toluene medium by absorption spectrophotometric method. Absorption band due to the charge transfer (CT) transition have been observed in the visible region between fullerenes and 1. Utilizing the CT absorption bands, various important physicochemical parameters like oscillator strength, resonance energy, transition dipole strength of the fullerene-1 complexes and ionization potential of 1 is determined in present investigations. From Jobs method of continuous variation, it is observed that both C₆₀ and C₇₀ form stable 1:1 complexes with 1. The most fascinating feature of the present study is that 1 binds selectively C₇₀ compared to C₆₀ as obtained from binding constant (K) data of C₆₀–1 (K_C60–1) and C₇₀–1 (K_C70–1) complexes, i.e., K_C60–1 = 32,400 dm³·mol^? 1 and K_C70–1 = 110,000 dm³.mol^? 1 and selectivity (K_C70–1/K_C60–1) = 3.4. ¹H NMR analysis provides very good support in favor of strong binding between C₇₀ and 1.     

Effect of oxidation state and coordination with Hg(II) on the electronic spectra of an anthraquinone–rhodamine sensor

ABSTRACT

In this study, a computational examination of the electronic transitions and through-space energy transfer processes lends insight into the experimental electronic spectra of a redox-sensitive rhodamine–anthraquinone dyad. Electronic transitions were calculated using density functional theory (DFT) and time-dependent DFT (TDDFT) based on models optimised from single-crystal X-ray diffraction (XRD) ion positions. DFT calculations were performed on gas-phase models using the Vienna Ab Initio Software Package (VASP) with the functional developed by Perdew, Burke, and Ernzerhof (PBE) on a basis set of plane waves. Using the DFT results, select transitions were evaluated based on a dipole–dipole coupling mechanism to find the Förster resonance energy transfer coupling, the square of which is approximately proportional to the rate of energy transfer between the donor and the acceptor. Electronic transitions during the relaxation of charge carriers are also investigated using nonadiabatic molecular dynamics. In order to investigate the transitions contributing to key peaks in the experimental absorbance spectra, TDDFT calculations were performed in Gaussian 09 with the B3LYP functional on the sensor in solution phase, which is simulated using a polarisable continuum model (PCM). The computed electron transfer process from the excited rhodamine to the quinone correlates better with the experimental data than does the computed Förster resonance energy transfer (FRET) process. This computed electron transfer process is faster than the radiative lifetime of the fluorescent state, which collectively suggests that the charge transfer process quenches fluorescence. These results support the observation that fluorescence is more prominent in the oxidised sensor than in the reduced sensor.     

1,4-bis[2-(4-pyridyl)ethenyl]-benzene衍生物热致变色研究

本文制备了三种在1,4-bis[2-(4-pyridyl)ethenyl]-benzene(bp-eb)上接枝不同烷基链长度的热致变色材料DC8、DC12、DC16. 在365 nm激发光下,随着温度升高,它们呈现出荧光颜色的改变,这种改变来自于晶体态与无定形态之间的转变. 此外,DC16也呈现出光致变色的性质. 通过差示扫描量热法测试得到的相转变温度高于实验过程中荧光颜色改变时的温度. 因此,这种变色行为来自于光与热共同作用的结果. 乙醇可以使粉末变回起始的晶体状态,从而使荧光颜色恢复,实现热致变色行为的可逆. 本研究对理解热致变色分子的结构-性质关系,指导热致变色分子设计具有重要意义.     

Fluorescent probe based on proton transfer in 4′-(diethylamino)-3-hydroxyflavone: Spectral and luminescent characteristics upon selective excitation

The spectral characteristics of acetonitrile solutions of 4′-(diethylamino)-3-hydroxyflavone dye with dual fluorescence are studied under selective excitation. This dye is a structural analog of 3-hydroxyflavone and exhibits excited-state proton transfer, which, in contrast to 3-hydroxyflavone, has a thermodynamic rather than a kinetic character. The fluorescence spectra at different excitation photon energies and the excitation spectra of different fluorescence bands are studied. It is found that the intensity ratio of the normal and tautomeric fluorescence bands lying near 507 and 570 nm, respectively, depends on the excitation wavelength, namely, this ratio is 1.45 and almost does not change in the region of the main absorption band (370–420 nm), while, in the region of the second singlet band (near 280 nm), it decreases to 1.15. This can be explained by an increase in the probability of proton transfer with formation of a tautomeric form in the case of excitation into the second band. Another interesting feature is the existence of a latent third emission band peaked at 535 nm, which was found and reliably recorded upon excitation at wavelengths of 470–500 nm. Addition of water quenches this emission, which indicates that it belongs to the anionic form of the dye.     

Specific solvent effects of hydroxylic solvents on the emission properties of ruthenium(ii)tris(2,2′-bipyridyl) chloride

The excited state of Ru(II)[bpy]₃ ²⁺ dissolved in hydroxylic solvents is subject to specific solvent effects, which were hitherto not understood on a quantitative basis. We determined the solvent effects of linear monovalent alcohols on the energy gap law of internal conversion with the help of lifetime and intensity measurements. An on-line method for measurement of the temperature dependence of quantum efficiencies was introduced. A modified Franck-Condon analysis of emission spectra by taking into account the shape of a Morse potential of the involved states was applied to compute excited-state energies.Abbreviations used Ru(II)[bpy]₃ ²⁺ ruthenium(II)tris(2,2-bipyridyl) chloride - MLCT metal-to-ligand charge transfer - PMT photomultiplier tube     

Ab initio investigations on lithium–superhalogen (Li–X) complexes (X = LiF2, BeF3, BF4 and PF6): competition between s-block and p-block anions

In this work, we investigate the formation of Li–X complexes by interaction of Li cation and superhalogen (X) anions belonging to s block (X = LiF₂, BeF₃) and p block (X = BF₄, PF₆). We discuss their structures and stabilities using the quantum chemical method at MP2/aug-cc-pVDZ level of theory. Considering polarisable continuum model, solvent effects are taken into account in a polar organic solvent, namely diethyl ether. Our findings establish that electronic and chemical properties of Li–LiF₂ and Li–BeF₃ closely resemble Li–BF₄ and Li–PF₆. However, Li–LiF₂ may dissociate preferably into LiF salt; Li–BeF₃ appears as a close analogue of Li–BF₄, which is significantly stabilised by the solvent. Thus, the superhalogen anions possess electronic integrity irrespective of the nature of central atom.     

The effects of polyethylene glycol and the coupling agent bis-(γ-triethoxysilylpropyl)-tetrasulfide (Si-69) on the interactions of silica-filled natural rubber

A Fourier Transform Infrared (FTIR) analysis using Fresnel Attenuated Total Reflectance (ATR) was performed on silica-filled cis-1,4-polyisoprene. Silica filler's detrimental effects on zinc-activated cure systems has been well documented. The silane coupling agent bis-(y-triethoxysilylpropyl)-tetrasulfide (Si-69) and polyethylene glycol (PEG) are industry standards used to offset the interactions caused by reaction between silica and the zinc-activated cure system. By adding PEG, it was found that the interaction peaks at 1040 and 1017 cm^-1 caused by the adsorption of natural rubber (NR) onto the surface of the silica were not formed. Also, by monitoring the zinc stearate peak at 1540 cm^-1, both Si-69 and PEG were found to reduce the soluble zinc ion reaction with the silica surface. Supporting evidence from the rheometer curves also shows that the additives reduce the cure retardation effects of the silica filler.     

Stabilities and interactions of CuRnX and XCuRn (X = F – I): ab initio calculations

Theoretical investigations on the CuRnX and XCuRn (X = F – I) series have been performed at the CCSD(T) theoretical level. Analyses on dissociation energy and frontier orbital show a decreased trend of stabilities down the periodic table. NBO analyses show the existence of σ_Cu-Rn and σ_Cu-X bonding orbital resulted from the overlap between Cu spd hybrid and Rn/X sp hybrid. The Cu–Rn, Cu–X and Rn–X interactions characterised by negative energy density values, positive Laplacian values and small electron densities at bond critical point (BCP) can be described as interactions of moderate strength with partial covalence. Analyses on electron localisation functions, electron density deformations, BCP properties (?G/V and G/ρ) and natural resonance theory demonstrate an increased covalence down the periodic table.     

Magnitude of O(α2) corrections and search for new effects in the electroweak interactions

A quick method of calculating certain combinations of the O(α²) corrections in the electroweak theory is presented. The results agree with earlier explicit calculations of the O(α²) corrections to the vector boson masses and in other cases provide an estimate of the lower limits for such corrections. Some non-standard effects like heavy fermion or supersymmetric contributions are also discussed. Detailed calculations show that even in the case of the strong supersymmetric contribution, the new one-loop corrections are comparable to the two-loop ones in the standard model.     

1,4-bis[2-(4-pyridyl)ethenyl]-benzene衍生物热致变色研究（英文）

本文制备了三种在1,4-bis [2-(4-pyridyl)ethenyl]-benzene(bpeb) 上接枝不同烷基链长度的热致变色材料 DC8、DC12、DC16.在365 nm激发光下,随着温度升高,它们呈现出荧光颜色的改变,这种改变来自于晶体态与无定形态之间的转变.此外,DC16也呈现出光致变色的性质.通过差示扫描量热法测试得到的相转变温度高于实验过程中荧光颜色改变时的温度.因此,这种变色行为来自于光与热共同作用的结果.乙醇可以使粉末变回起始的晶体状态,从而使荧光颜色恢复,实现热致变色行为的可逆.本研究对理解热致变色分子的结构-性质关系,指导热致变色分子设计具有重要意义.     

Scholte–Stoneley waves on an immersed solid dihedral: Generation,propagation and scattering effects

Scholte–Stoneley wave propagation on a dihedral and more precisely the diffraction effects occurring at the corners, has since long been of high importance for nondestructive testing of materials and structures. Experimental investigations have been reported in the past. Simulations based on radiation mode theory have been published before, explaining the only situation for which the model is applicable namely rectangular corners. The current report describes an investigation applying finite element simulations. Results are obtained not only for rectangular corners but for any possible corner angle. The outcome is in agreement with reported experiments. Moreover a critical corner angle is found below and beyond which different diffraction phenomena occur. The study is performed for different isotropic solids.     

High-transparency films for nonlinear integrated optics based on P(VDF-TrFE) and poly(α-methyl styrene) host materials

In search of waveguiding polymer films with both highly efficient NonLinear Optical (NLO) and optimum transmission properties the second harmonic generation of light is measured on poled films of P(VDF-TrFE) blended with 10% PMMA or covered by the polarizable guest-host system PMS, both pure and doped with 2% NLO dye The PMS films turn out to be stable electrets after annealing at about 50°C and poling at room temperature. They are thus particularly easily processable candidates for NLO and waveguiding applications.     

Spectral structure of barium–phosphate–silicate phosphor Ba10(PO4)4(SiO4)2:EuM+

The new apatite–silicate phosphor doped with Eu ions in Ba₁₀(PO₄)₄(SiO₄)₂ matrix was synthesized through solid-state reaction. It was found that the as-synthesized phosphor displayed apparent mixture of band and line emission peaks giving rise to pseudo white light. The narrow emission bands peaking at 410 nm can be assigned to the 4f⁶5d→4f⁷(⁸S_7/2) transition of Eu²⁺ ions, and the other band at 507 nm is ascribed to anomalous fluorescent emission. One group of line emission peaking at 595 nm and 613 m were due to the ⁵D₀→⁷F₁ and ⁵D₀→⁷F₂ transition of Eu³⁺ ions. The occurrence of photostimulated luminescence and discrete emission lines in violet (410 nm), green (507 nm) and red (595 nm and 613 nm) colors indicate that this material has potential application in fields of white-light-emitting.     

Relativistic effects on the structural and transport properties of III–V compounds: A first-principles study

We have performed ab initio self-consistent calculations based on the full potential linear augmented plane-wave method (FP-LAPW) with the local density approximation (LDA) and the Generalised Gradient Approximation (GGA) to investigate the relativistic effects, on the structural, and transport properties of III–V compounds. We found that the stabilisation (destabilisation) of s, p^∗(p,d) orbital energies (i) reduces the lattice parameters of III–V compounds, considerably reduces the band gaps of the III–V compounds, (ii) reduces the effective masse, and (iii) induces strong spin orbit splitting of heavier III–V compounds. Furthermore we circumvent the negative gap problem by combining non relativistic and Engel–Vosko approximations. These approaches open the gap of the most III–V compounds, and leads to a realistic band structure.     

Infrared and Mössbauer Spectral Studies on Some Tin(IV) Complexes: A Qualitative Correlitation with the Hard and Soft Acid-Base Theory

The principle of the hard and soft acid-base theory (HSAB) is that binding of hard acids with hard bases and soft acids with soft bases is preferred.¹ This implies that the maximum bond strength in a series of acid-base complexes should occur, all other factors being equal, where the degree of hardness or softness of the acid and base are most nearly matched. To test this hypothesis, we prepared a number of tin(IV) complexes of varying softness with the soft base 2,5-dithiahexane (CH₃SCH₂CH₂OCH₃, DTH) and the hard base 1,2-dimethoxyethane (CH₃OCH₂CH₂OCH₃, DME). The acids employed were SnCl₄, CH₃,SnCl₃, SnBr₄, and SnI₄. The complexes thus obtained were studied by infrared and Mcssbauer techniques in order to determine which, if any, of the complexes exhibited spectral details which could be correlated with HSAB.