Synthesis,biocompatibility and luminescence properties of quantum dots conjugated with amino acid-functionalized β-cyclodextrin

A series of CdSe and CdSe/CdS quantum dots (QDs) labeled with amino acid-modified β-cyclodextrin (β-CD) was prepared by a simple ultrasonic method. These amino acid-modified β-CD-coated QDs are very soluble and stable in biological buffer. They also have high colloidal stability and strong optical emission properties that are similar to those of untreated tri-n-octylphosphine oxide (TOPO)-coated QDs. The quantum yields (QYs) of these amino acid-modified β-CD-coated CdSe and CdSe/CdS QDs in biological buffer were found to be very high. In particular, the QYs of the positively charged l-His-β-CD-coated CdSe/CdS QDs were as high as 33.5±1.8%. In addition, the fluorescence lifetime of these QDs was also very long in PBS solutions as determined by frequency domain spectroscopy. For example, the lifetime of l-His-β-CD-coated CdSe/CdS QDs was 8.6 ns. The in vitro cytotoxicity of these QDs in ECV-304, SH-SY5Y and HeLa cells was found to be lower. l-His-β-CD-coated CdSe/CdS QDs were the least cytotoxic (IC₅₀ 95.6±3.2 mg mL^?1 in ECV-304 cells after 48 h). The flow cytometry results show that the positively charged amino acid led to a considerable increase in biocompatibility of QDs. This may be attributed to the presence of an amino acid-modified β-CD outer layer, which enhanced the biocompatibility.     

Anthranilamides with quinoline and β-carboline scaffolds: design,synthesis, and biological activity

Molecular Diversity - In the present study, we report the design and synthesis of novel amide-type hybrid molecules based on anthranilic acid and quinoline or β-carboline heterocyclic...     

Ti-assisted β-SiC nanowhiskers by pyrolysis of PTFE: synthesis and mechanical properties

Large quantities of Ti-catalyzed β-SiC nanowhiskers were efficiently prepared via a SHS process by pyrolysis of poly (tetrafluoroethylene) (PTFE). The as-synthesized β-SiC whiskers appear to be structurally uniform with width from 50?nm to 2?μm and length of up to several hundred microns, and they are single crystalline in nature. Results demonstrated that Ti particles could significantly accelerate the absorption and dissolving of Si- and C-related fragments. A Ti–Si–C alloy droplet was detected at the end of an individual β-SiC whisker, which indicated that β-SiC whiskers were grown via the vapor–liquid–solid (VLS) growth mechanism. The elastic bending modulus of individual whiskers was measured by an in-situ transmission electron microscopy (TEM) process; the average value of the elastic bending modulus of individual as-synthesized whiskers was 554?GPa.     

First-principles calculation of the electronic structure,chemical bonding,and thermodynamic properties of β-US_2

The electronic structure, magnetic states, chemical bonding, and thermodynamic properties of β-US2 are investigated by using first-principles calculation through the density functional theory(DFT) +U approach. The obtained band structure exhibits a direct band gap semiconductor at Γ point with a band gap of 0.9 e V for β-US2, which is in good agreement with the recent experimental data. The charge-density differences, the Bader charge analysis, and the Born effective charges suggest that the U–S bonds of the β-US2 have a mixture of covalent and ionic characters, but the ionic character is stronger than covalent character. The Raman-active, infrared-active, and silent modes at the Γ point are further assigned and discussed. The obtained optical-mode frequencies indicate that the three apparent LO–TO(longitudinal optical–transverse optical) splittings occur in B1 u, B2 u, and B3 umodes, respectively. Furthermore, the Helmholtz free energy ?F, the specific heat ?E, vibrational entropy S, and constant volume CVare studied over a range from 0 K~100 K. We expect that our work can provide some valuable information for further experimental investigation of the dielectric properties and the infrared reflectivity spectrum of uranium chalcogenide.     

Atomic-scale simulation of nano-grains:structure and diffusion properties

Nanograins are characterized by a typical grain size from lto 100 nm.Mclecular dynamics aimubations have been carried out for the nanograin sphere with the diameters from 1.45 to 10.12 nm.We study the influence of grain size on structure and diffusion properties of the nanograins.The results reveal that as the grain size is reduced,the fraction of grain surface increases significantly,and the surface width is approximately constant；the diffusicn coefficlent is increased sharply,and the relation of the diffusion coefficient and the grain size is close to exponential relation below 10nm.     

Optical and mechanical properties of hollow-core fibers with cobweb cladding structure

This paper explores the possibility of realizing a hollow-core optical fiber, whose cladding is composed of cylindrical alternating layers of air and high-index material with supporting structure. The optical properties and the design criteria of the proposed fiber are evaluated by the compact two-dimensional (2D) finite-difference time-domain (FDTD) method. In particular, the influence of the number and width of supporting strips on the leakage loss of the fiber is investigated. Furthermore, the mechanical performances of the fiber are estimated by finite-element method, confirming that hollow-core fibers with a reasonable size and number of supporting strips are reliable.     

Dielectric behaviour of α-cyclodextrin,heptakis (2,3,6-tri-Omethyl)-β-cyclodextrin,randomly methylated β-cyclodextrin and low frequency Raman spectra of α- and β-cyclodextrins

The frequency and temperature dependence of the real (?′) and imaginary (?″)parts of the dielectric constant of α-cyclodrextrin (form 1; α-CD. 5.9H₂O) and α-cyclodextrin (form III; α-CD.7.6H₂O) and of the corresponding dried forms (α-CD.1.1H₂O, α-CD.2.9H₂O, respectively) has been investigated over the frequency range 0–100 k Hz and temperature range 130–350 K. In addition the dielectric behaviour has been investigated of heptakis-(2,3,6-tri-O-methyl)-β-cyclodextrin (β-CD.TRIME. 0.3H₂O) and randomly methylated β-cyclodextrin (β-CD.RAME.0.8H₂O). The dielectric behaviour is described well by Debyetype relaxation (α-disperson). All α-CD systems exhibit an additional ω-dispersion at low frequencies, which is attributed to proton transport. The fact that the ?′ values of α-CD form III are larger than those of α-CD form I is attributed to the different numbers and different strengths of the intramolecular hydrogen bonds. Form III has a stable conformation which is shown by the constant values of ?′ in the temperature range 125–250 K. By contrast, in form I the ?′ values increased linearly with temperature, indicating that the system passed through succesive conformations. The temperature dependence of ?″ and phase shift ∞ in all the specimens of α-CD (forms I, III) and fully methylated β-CD do not reveal any orderdisorder transition, because the developed hydrogen bonds ae not of the flip-flop type according to their crystal structures. The partially methylated β-CD reveals the characteristics of the order-disorder transition, which was observed before in the systems dried β-CD.2H₂O and non-dried β-CD.9.8H₂O. There is a direct relation between the hydroxyl groups of β-CD and the order-disorder transition. The order-disorder transition could also be shown in dried β-CD.2.4H₂O and non-dried β-CD.9.8H₂O samples but not in dried α-CD.1.1H₂O and non-dried a-CD.5.9H₂O samples, by low frequency Raman spectroscopy (< 180 cm^?1). The step-like temperature dependence of the band at 33.7cm^?1 reveals a transition at about 223K for both β-CD samples. In the case of α-CD samples the almost linear temperature dependence of the band at 49.1 cm^?1 does not reveal any transition.     

A study of fluorescence properties of citrinin in β-cyclodextrin aqueous solution and different solvents

Citrinin (CIT) is a nephrotoxic mycotoxin initially isolated from filamentous fungus Penicilliu citrinum. It was later isolated from several other species, such as Aspergillus and Monascus. It has a conjugated, planar structure that gives it a natural fluorescence ability, which can be used to develop sensitive methods for detecting CIT in food. In this paper, we used the spectro?uorescence technique to study the effects of pH value, β-cyclodextrin (β-CD) and organic solvents on the CIT fluorescence intensity. The results show that lower pH value, aceitc acid, β-CD and acetonitrile can induce a higher fluorescence intensity of CIT, but methanol or H₂O has a decreasing effect on the fluorescence intensity of CIT. Findings in this study provide a theoretical basis for development of a high sensitivity fluorescence-based trace analysis for CIT detection.     

Encapsulation of Labetalol, Pseudoephedrine in β-cyclodextrin Cavity: Spectral and Molecular Modeling Studies

The absorption and fluorescence spectra of labetalol and pseudoephedrine have been studied in different polarities of solvents and β-cyclodextrin (β-CD). The inclusion complexation with β-CD is investigated by UV-visible, steady state and time resolved fluorescence spectra and PM3 method. In protic solvents, the normal emission originates from a locally excited state and the longer wavelength emission is due to intramolecular charge transfer (TICT). Labetalol forms a 1:2 complex and pseudoephedrine forms 1:1 complex with β-CD. Nanosecond time-resolved studies indicated that both molecules show triexponential decay. Thermodynamic parameters (ΔG, ΔH, ΔS) and HOMO, LUMO orbital investigations confirm the stability of the inclusion complex. The geometry of the most stable complex shows that the aromatic ring is deeply self included inside the β-CD cavity and intermolecular hydrogen bonds were established between host and guest molecules. This suggests that hydrophobic effect and hydrogen bond play an important role in the inclusion process.     

Azo-hydrazo Tautomerism and Inclusion Complexation of 1-phenylazo-2-naphthols with Various Solvents and β-cyclodextrin

Spectral characteristics of sudan I (SDI), sudan II (SDII) and mordant violet-5 (MV5) have been studied in various solvents and β-cyclodextrin (β-CD). The inclusion complex of the above molecules with β-CD was analyzed by UV-visible, fluorometry, and DFT methods. The solvent study shows that azo-hydrazo tautomer is present in these molecules. The increase in the fluorescence intensity and a large bathochromic shift in the S₁ state indicate these molecules forms 1:1 inclusion complex with β-CD.     

Transport properties of aqueous solutions of calcium lactate in the absence and presence of β-cyclodextrin

Mutual diffusion coefficients and electrical conductivity of a well-known food additive and supplement, or excipient in pharmaceutical formulations, calcium lactate, have been measured in the absence and presence of β-cyclodextrin in aqueous solutions, at 298.15 K. The dependence of conductivity on concentration has been analysed using the Fuoss-Edelson method. The values of the Nernst diffusion coefficients, for binary solutions, derived from conductance and from diffusion experiments are in good agreement. The presence of β-cyclodextrin leads to a non-expected effect on the transport properties of the aqueous solutions of calcium lactate. These data have been justified with help of ¹H NMR spectroscopy. The effect on the water structure, reducing the hydration shell of lactate, is argued. This leads to an increase of the effective concentration of calcium lactate in solution contributing to an increase in the diffusion coefficients and a decrease in the dependence of the electrical conductance on the concentration.     

One-pot hydrothermal synthesis of β-MnO2 crystals and their magnetic properties

β-MnO₂ nanorods and flower-like structures were synthesized via a one-pot hydrothermal route at 160 °C without using any template and surfactant. It is demonstrated that H⁺ in the solution has a significant effect on the morphology and resultant magnetic property of β-MnO₂ crystals. Magnetic measurements indicate that the Néel temperature of the β-MnO₂ flower-like structures is 98 K, which is about 2 K higher than that of the nanorods counterpart.     

Luminescent properties and structure of multicomponent naphthalene-β-cyclodextrin complexes. 1. Effect of adding third parties, o-carborane or/and adamantane

Luminescence spectra of water solution of β-cyclodextrin (β-CD) inclusion complexes with naphthalene have been studied in the presence of carcass compounds (CC), adamantane and ocarborane, added in solution as the third parties. It was observed that the CC structure completely determines luminescence type displayed by the three-component complex. Adding adamantane to the solution leads to the disappearance of the spontaneous excimer fluorescence observed usually along with a monomer fluorescence of naphthalene and the appearance of the long lived phosphorescence at room temperature. At the same time, introducing o-carborane in solution of β-CD inclusion complexes with naphthalene results in the dramatic growth of intensity of the excimer band at the expense of lowering intensity of monomer fluorescence. These phenomena were explained using results of the quantum-chemical calculation of the structure and complexation energies at the semi-empirical PM3 and DFT levels of theory.     

Studies on the Interaction of Tricyclazole with β-cyclodextrin and human Serum Albumin by Spectroscopy

The interaction of tricyclazole (TCZ) with β-cyclodextrin (β-CD) and human serum albumin (HSA) were studied by fluorescence spectrum, UV-visible spectrum and second-order scattering technology. It was shown that TCZ has quite a strong ability to quench the fluorescence launching from HSA by reacting with it and forming a certain kind of new compound. The quenching and the energy transfer mechanisms were discussed, respectively. The binding constants and thermodynamic parameters at four different temperatures, the binding locality, and the binding power were obtained. The conformation of HSA was discussed by synchronous and three-dimensional fluorescence techniques. The inclusion reaction between β-CD and TCZ was explored by scattering method, the inclusion constants and the thermodynamic parameters at 297 K and 311 K were figured out, respectively. The mechanism of inclusion reaction was speculated and linkage among the toxicity of TCZ, the exterior environment and its concentration was attempted to explain on molecule level.     

Dual fluorescence of dothiepin, doxepin drugs—effect of solvents and β-cyclodextrin

The absorption and fluorescence spectra of dothiepin and doxepin have been recorded in solvents of different polarities and β-cyclodextrin (β-CD). The inclusion complex of both drugs with β-CD is investigated by UV-visible, fluorimetry, DFT, FT-IR and scanning electron microscopy (SEM). In all solvents, the absorption and emission maxima of dothiepin are red shifted than doxepin. β-CD studies reveal that both drugs form a mixture inclusion complex with β-CD. The structured longer wavelength emission in β-CD aqueous solution suggests that viscosity plays major role in the β-CD. This study also confirms van der Waals forces and hydrophobic interactions are the driving forces for the inclusion complexes.     

Auto-combustion synthesis,Mössbauer study and catalytic properties of copper-manganese ferrites

Spinel ferrites with nominal composition Cu _0.5Mn _0.5Fe ₂ O ₄ and different distribution of the ions are obtained by auto-combustion method. Mössbauer spectroscopy, X-ray Diffraction, Thermogravimetry-Differential Scanning Calorimetry, Scanning Electron Microscopy and catalytic test in the reaction of methanol decomposition is used for characterization of synthesized materials. The spectral results evidence that the phase composition, microstructure of the synthesized materials and the cation distribution depend on the preparation conditions. Varying the pH of the initial solution microstructure, ferrite crystallite size, cation oxidation state and distribution of ions in the in the spinel structure could be controlled. The catalytic behaviour of ferrites in the reaction of methanol decomposition also depends on the pH of the initial solution. Reduction transformations of mixed ferrites accompanied with the formation of Hägg carbide χ-Fe ₅ C ₂ were observed by the influence of the reaction medium.     

Synthesis and properties of β-modifiedmesotetra(aryl, heteryl)porphyrins

A series of chemical conversions of formyl derivatives of tetraphenylporphyrin is implemented, including the dimerization under the action of low-valence titanium, formation of a vinyl derivative by Wittig's reaction, and also the intramolecular cyclization with formation of isomeric verdins. By means of radical nitration, nitro derivatives of heterylporphyrins are obtained, which are exposed to a reaction of vicarious nucleophilic substitution of hydrogen with formation of 2,3-disubstituted derivatives. The previously unknown derivatives of the above-named porphyrins are obtained, and means for synthesis of well-known compounds are considerably improved. Reported at the VIIIth International Conference on Spectroscopy of Porphyrins and Their Analogs, Minsk, September 22–26, 1998. I. I. Mechnikov Odessa State University, 2, Dvoryanskaya Str., Odessa, 270026, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 4, pp. 512–515, July–August, 1999.     

Synthesis and characterization of β-cyclodextrin/fraxinellone inclusion complex and its influence on interaction with human serum albumin

Aqueous solubility is one of the key determinants in developing new chemical entities as drugs. In this study, to improve the solubility of fraxinellone, a novel β-cyclodextrin/fraxinellone inclusion complex was prepared and characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray diffraction, and elemental analysis. Moreover, the influence of inclusion of small molecule by cyclodextrins on its binding with transporter in human body is essential for drug development. For the first time, we report the interaction of fraxinellone and its inclusion complex with human serum albumin. Fluorescence quenching of albumin by fraxinellone and its inclusion complex is a static process through complex formation. The results indicated that β-cyclodextrin did not affect the binding force and site of fraxinellone to the protein. Furthermore, circular dichroism showed that both fraxinellone and its inclusion complex induced a significant change in the secondary structure of human serum albumin.