Calculation of UV/VIS absorption spectra of liquid crystals and dye molecules An INDO MO approach

Abstract

The electronic transitions in the UV/VIS range of liquid crystals and stilbene dyes, which are of commercial and applicational interest, have been studied theoretically by a semi-empirical INDO (intermediate neglect of differential overlap) CI (configuration interaction) approach. Experimentally obtained polarized UV/VIS spectra of the systems investigated can be reproduced with reliable accuracy by the theoretical model. Measured and calculated π-π? transitions differ frequently by less than 30 nm. The main absorption bands are strongly polarized parallel to the principal molecular axis.     

Identification of Natural and Early Synthetic Textile Dyes with HPLC and UV/Vis-Spectroscopy by Diode Array Detection

Abstract

The separation and identification of complex mixtures of natural and synthetic textile dyes was investigated using HPLC with diode array detection. Separation was carried out on a reversed phase column with acetonitrile-phosphoric acid gradient elution. The results show that the anthraquinones from madder root and the insect dye cocheneal present in ancient red dyes can easily be distinguished from azo-dyes present in later textile fibres. They further show that for an analysis of the numerous flavones and flavonoles, constituting most of the yellow natural dyestuffs, the combination of HPLC with on-line optical spectroscopy is particularly useful. Even when retention times are identical - as for instance for quercetin and luteolin - the ratio of a mixture can still be estimated by evaluating the ratio-chromatogram.     

Synthesis and Characterization of Novel Monoazo Naphthalimide Disperse Dyes Containing Carboxylic Acid Group with High Heat Fastness Properties

A group of novel monoazo disperse dyes containing carboxylic acid‐1,8‐naphthalimide group has been synthesized. All intermediates and dyes were purified by recrystalization and the column chromatography method. The purified products were characterized by ¹H NMR, ¹³C NMR, FTIR, DSC, UV‐VIS and Elemental Analysis. Spectrophotometric investigations of the synthesized dyes in different solvents were carried out in order to obtain their absorption maxima, molar extinction coefficients and solvatochromic effects. The absorption maxima of the synthesized dyes in acetone varied (513‐549 nm) and the molar extinction coefficient was (17405‐38939 l/mol cm). By changing the media from chloroform to DMF, the solvatochromism effect for all dyes increased. Dispersion of the synthesized dyes was prepared in water containing dispersing agent and applied to polyester fabrics. The dyed fabrics showed that all of the synthesized dyes were suitable for coloring polyester fibers, producing deep red to bluish red with very good fastness properties.     

A Reverse Phase HPLC Method to Determine Six Food Dyes Using Buffered Mobile Phase.

Abstract

A reverse phase high performance liquid chromatographic (HPLC) method to determine six food dyes (Sunset Yellow (E-110), Carminic acid (E-120) Carmoisine (E-122), Amaranth (E-123), Ponceau 4R (E-124) and Erythrosine (E-127) is developed in this paper. The separation was made on a Nova-Pack C18 column using methanol -NaH₂PO₄/Na₂HPO₄ pH=7 buffer solution 0.1M as mobile phase with an elution gradient system. The detection was made with a variable UV-Vis. detector fixed at 520 nm.

The effect of mobile phase composition such as the percentage of methanol or acetonitrile, pH value and ionic strength on retention times of the dyes was investigated. In the chromatographic conditions selected, the dyes were eluted in four minutes. Two calibration graphs for each dye were established by measuring the peak area and the peak height in the chromatograms. Determination limits ranging from 0.8 to 9.2 ng were obtained when the peak area was measured.

Several commercial products containing some of these dyes were analyzed.     

Fabrication of flexible graphene oxide paper-like adsorbent doped with magnetite nanoparticles for removal of dyes

Organic dyes are used in many industries, e.g., textile, cosmetics and food. Hence, contamination of organic dyes to water sources is a critical issue. To reduce water pollution by organic dyes, we propose a paper-like adsorbent with a practical and economical production procedure. Subsequently, a flexible adsorbent was produced using a one-step approach by vacuum filtration of graphene oxide (GO) and iron oxide nanoparticles (Fe₃O₄-NPs) containing dispersion through a membrane and quoted as GO/Fe₃O₄ paper. For comparison, GO paper was also prepared using the same procedure. Both papers were characterized using UV–VIS absorption spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, electron diffraction X-ray analysis, X-ray photoelectron spectroscopy, and powder X-ray diffraction techniques. At the steady-state conditions, GO/Fe₃O₄ and GO papers were performed as adsorbent for cationic dyes of methylene blue, neutral red, and anionic dyes of methyl orange and fluorescein. In general, the removal efficiency of GO/Fe₃O₄ paper was higher than that of GO paper for adsorption of all dyes and this adsorbent revealed satisfactory adsorption properties for cationic dyes when compared to anionic dyes.

     

Synthesis and spectral characterization of some new azo dyes and their metal complexes

A series of azo-metal chelate dyes have been synthesized by coupling substituted o-nitroaniline and p-t-/s-butylphenol. The spectral characterization of the azo dyes containing o-hydroxy group and azo-metal(II) chelate [metal(II): Cu, Ni, Co] dyes by IR spectra, UV–VIS spectra, NMR spectra, elemental analysis and magnetic susceptibility techniques are reported. The stoichiometry of the azo-metal chelates was determined by the spectroscopic titration method to be 1:2 (ML₂).     

Synthesis and characterization of some <Emphasis Type="Italic">o</Emphasis>,<Emphasis Type="Italic">o</Emphasis>′-dihydroxyazo dyes and their metal complexes

The synthesis and characterization of azo dyes containing o,o′-dihydroxy groups and their azo-metal(II) [Cu, Co, Ni, Zn] chelates by ¹H N.M.R., IR, AAS, UV–VIS, magnetic susceptibility and thin-layer chromatography techniques are reported. The stochiometry of the azo-metal chelates was determined by the spectroscopic titration method to be 1:2 (ML₂). The synthesized azo dyes and azo-metal chelate dyes were applied on wool fabric. Fastness to light and washing were measured.     

Hplc Method for Kinetic Study of Mutarotation of Sugars

Abstract

A high-performance liquid chromatographic (HPLC) method was established for kinetic studies of the interconversion (mutarotation) between pyranose sugar anomers in solution. At very low temperature, HPLC chromatograms of each sugar indicated the concentrations of each anomer in the state prior to the HPLC analysis. Thus, when one of the pyranose anomers obtained by recrystallization was dissolved into water and was analyzed by HPLC repeatedly, gradual changes in the chromatogrphic patterns were observed. The equilibrium concentrations of each sugar anomer in different solvents were found to vary, which was also investigated by HPLC.     

Detection of Mycoplasma Contamination in Lymphoblastoid Cultures by a Simple,HPLC Method

Abstract

A simple method for detecting mycoplasma contamination of lymphoid cell cultures is discussed. This method is based on high pressure liquid chromatographic (HPLC) detection of citrulline by reversed-phase separation of its ortho-phthaldialdehyde (OPA) derivative. Formation of citrulline via conversion of arginine using the enzyme arginine deiminase present in most of the commonly encountered strains of mycoplasma is measured by this sensitive technique. The use of HPLC techniques offers an extremely sensitive indication of mycoplasma contamination in cells having large nuclei which make detection by staining with Hoechst dyes difficult to interpret.     

Two Novel Push?Pull Series of Benzothiazole‐Based Dyes: Synthesis and Characterization

New dichromophoric cyanine dyes based on benzothiazol‐2‐amines as push? pull systems were synthesized in two series of disperse and cationic forms (see 4 in Scheme 1 and 5 in Scheme 2, resp.). Their thermal stabilities, UV/VIS, fluorescence, and solvatochromic behavior, which are important parameters in push? pull systems, were also studied.     

Photochemistry of 6‐Formylpterin in Alkaline Medium

6‐formylpterin solutions at pH 11 were photolyzed at 350 nm at room temperature. The photochemical reactions were followed by UV/VIS spectrophotometry, thin layer chromatography (TLC), and high‐performance liquid chromatography (HPLC). In the presence of oxygen, 6‐carboxypterin is the only photoproduct detected by the analytical techniques mentioned. In the absence of oxygen, a new compound showing an absorbance maximum at 480 nm is observed. The latter compound is thermally oxidized very fast in the presence of oxygen to 6‐carboxypterin. The quantum yields of substrate disappearance and of photoproduct formation are reported     

Crown-containing butadienyl dyes 8. Structures and complexation of chromogenic dithia-15(18)-crown-5(6) ethers

The structures of new butadienyl dyes of the benzothiazole series containing the dithia-15-crown-5 (2a) or dithia-18-crown-6 (2b) fragments were established by X-ray diffraction. Complexation of dyes 2a,b with Hg²⁺, Pb²⁺, Cd²⁺, Ag⁺, Zn²⁺, and alkaline-earth cations in aqueous-acetonitrile solutions was studied by spectrophotometry. At a high percentage of water in solutions (P _w ≈ 50%), these dyes have a very low ability to bind Pb²⁺ cations (logK < 2) and virtually do not bind Cd²⁺, Zn²⁺, and alkaline-earth cations. At the same time, these dyes form stable 1: 1 complexes with Hg²⁺ and Ag⁺ cations at all P _w. The stability constants of complexes with the Ag⁺ cation increase with increasing P _w because the free energy of hydration of this cation is much lower than the free energy of solvation in acetonitrile. In the P _w range from 0 to 75%, the stability constants of the complexes of dyes 2a,b with the Hg²⁺ cation are larger than those of the corresponding complexes with the Ag⁺ cation by more than four orders of magnitude. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 90–96, January, 2006.     

Synthesis and characterization of guest-host azo dyes with broad absorption bands

Abstract

Three groups of dyes were synthesized and characterized in order to examine their solubility, absorption spectrum, and order parameter in liquid crystal hosts. Our synthesis method allowed the formation of the diazonium salts and the diazo coupling in ethyl acetate instead of an aqueous medium, permitting the formation of long and neutral azo dyes. In the liquid crystal BDH-E7, they showed order parameters in the range of 0.52 to 0.76. The two dyes with the longest molecular lengths were particularly interesting due to their very broad absorption spectra in the visible region. Each of these two compounds behave as single component black dye guest/host systems, which generally require a mixture of two or three dyes in the liquid crystal host. These dyes were also evaluated for use in polymer dispersed liquid crystal films.     

Azidinium-Salze. 25. Mitteilung. Symmetrische Azopyridinon-Farbsalze: Synthese,spektrophotometrische und acidobasische Eigenschaften,Metallkomplex-Bildung und kinetische Untersuchung der Azo-Kupplung

Symmetrical Azopyridinone Dyes: Synthesis, Spectrophotometrical and Acidobasic Properties, Metal-Complex Formation and Kinetical Investigation of the Azo-Dye Formation The 13 substituted symmetrical azopyridinone dyes 2a–n were synthesized and their VIS spectra measured. The pK*_a values of some dyes and of pyridinone coupling components were determined in MeOH/H₂O 64:36. The metal-complex formation of the dyes with Cd²⁺, Zn²⁺, Co²⁺, Ni²⁺, and Cu²⁺ was investigated, and complex-formation constants of the 1:1 complexes were determined in H₂O for 2k (Table 2) and in dimethylformamide/H₂O 1:1 for some other azopyridinone dyes (Table 3). The mechanism of the azo-dye formation was investigated and found to be much more complicated than expected. A mechanism of the coupling reaction was developed (see Scheme 4) and fitted by least-squares calculations.     

检测钠离子的荧光探针：含稠合外环的硼-二吡咯亚甲基染料的合成与光物理性质研究

本文报道了两种中位为苯并冠醚亚单元取代的含稠合外环的硼-二吡咯亚甲基染料的合成、光谱和电化学性质。研究结果表明：在荧光团中引入吸电子的酯基使化合物2成为一种高灵敏性的检测钠离子的荧光探针。     

Study of the Lipophilic Character of Xanthine and Adenosine Derivatives: II. Relationships Between Log K', RM and Log P Values

Abstract

The log k' values of a series of xanthine and adenosine derivatives were measured by means of a reversed-phase HPLC. The HPLC data were shown to be well correlated with previously reported R_M and R_MC18 values. The equations describing the relationships log k'/R_M and log k'/R_MC18 allowed the calculation of the log k' values of some compounds, which were not tested in the HPLC system. Since the relationship log k'/log P is very close to the previously described relationships R_M/log P and R_MC18/log P one can conclude that reversed-phase TLC and HPLC are very similar in describing the lipophilicity of the compounds.     

Metachromatic behavior of methylorange in the presence of ionenes

The addition of different ionenes, polycations with defined structure and charge distances, to methylorange1 in very dilute solutions of water resulted in an observable shift of the absorption maxima from 464 nm to shorter wavelengths. The extent of this so-called metachromasy effect was found to be dependent on the nature of the hydrophobic unit of the polymer backbone. The comparison of UV/VIS spectra's of these solutions with the absorption of a film of a model substance — a dication with methylorange as counteranion — lead to the conclusion that ionenes undergo an exchange of the counteranions when added to a dilute solution of methylorange. Precipitation is slowed down, but the absorption is equivalent with solid product. The new absorption spectra of methylorange can be explained by the interaction of the quaternary nitrogen with the dye anion.     

Synthesis,Structure, Spectroscopic Studies,and Complexation of Novel Crown Ether Butadienyl Dyes

Butadienyl dyes of the benzothiazole series with various fragments of benzocrown ethers 1a – c were synthesized for the first time. The structures and spectral properties of crown‐containing butadienyl dyes and their complexes with alkali and alkaline‐earth metal cations were studied by X‐ray diffraction analysis and ¹H‐NMR, UV/VIS, and resonance Raman spectroscopy. To interpret the experimental results, quantum‐chemical calculations were performed. In the case of Sr²⁺ and Ba²⁺ ions, the formation of strong sandwich complexes [M( 1b )₂]²⁺ of an unusual structure involving stacking interactions was established; the dye molecules are arranged one above another in the complex according to the ‘head‐to‐head' pattern.     

Colloidal Gold Nanoparticles Protected by Cationic Polyelectrolytes

Abstract

Several stable gold colloids were prepared by the in-situ reduction of hydrogen tetrachloroaurate (HAuCl₄) in the presence of various cationic polyelectrolytes. Several types of such polyelectrolytes were investigated for their ability to stabilize gold colloids, and UV – VIS spectroscopy was used to follow the in-situ reductions and to further characterize the colloids. The particle sizes and size distributions were determined by transmission electron microscopy (TEM). TEM micrographs and UV-VIS spectra were also used to characterize the stability of the colloids after storage for nine months in air at room temperature. Colloids protected by the cationic polyelectrolytes with ammonium side-groups along a hydrophobic polymer backbone frequently exhibited very good stability.     

New Near-Infrared Cyanine Dyes for Labelling of Proteins

Isothiocyanato-functionalized cyanine dyes 7 and 11 for labelling of proteins at amino groups have been synthesized. The dyes and their adducts with amines show strong absorbance and fluorescence in the near-infrared region of 750-850 nm.