Colorless Form Research Articles

Effect of cyclodextrins on the thermodynamic and kinetic properties of cyanidin-3-O-glucoside

In this study, the effect of α and β-cyclodextrin on cyanidin-3-O-glucoside color was investigated by UV–visible absorption techniques. The equilibrium and kinetic constants of the network of chemical reactions taking place in cyanidin-3-O-glucoside were also studied in water at 25°C by UV–visible absorption techniques. The results showed that the addition of β-cyclodextrin resulted in the fading of anthocyanin solution, and this fading effect was greater at higher pH. This anti-copigmentation effect is caused by the selective inclusion and stabilization of the anthocyanin colorless forms into the β-cyclodextrin cavity. Oppositely, no changes were observed in the cyanidin-3-O-glucoside absorption spectra with the addition of α-cyclodextrin.Direct pH jump, from thermally equilibrated solutions at pH=1.0 (flavylium cation, AH+), shows three kinetic processes: formation of the base A, hydration reaction to form the hemiketal B and the chalcone cis–trans isomerization (Cc–Ct). The results obtained clearly indicated that the equilibrium and kinetic constants of the network of chemical reactions taking place in cyanidin-3-O-glucoside were affected by the presence of β-cyclodextrin. Molecular inclusion in the β-cyclodextrin cavity resulted in the increase of the isomerization observed rate constant (kobs) at pH5.3 and in the increase of the hydration equilibrium constant Kh which is in agreement with the fading of the anthocyanin solution. For the macrocycle α-cyclodextrin, no significant changes were observed on the equilibrium and kinetic constants, which suggests that the inclusion of cyanidin-3-glucoside in the α-cyclodextrin's cavity is not favored.

Force-induced cleavage of C–O bond in photochromic naphthopyrans

Force-induced cleavage of C–O bond in photochromic naphthopyrans in the pure microcrystalline solid state is described. The ring-closed isomers (colorless form) of naphthopyrans undergo cleavage of C–O bond under stress and are converted to ring-open isomers (colored form) in solid state. It is found that the threshold stress required to produce cleavage of C–O bond in naphthopyran derivatives in pure microcrystalline solid state is more than 2 MPa. Besides, the cleavage of C–O bond in photochromic naphthopyrans in the pure microcrystalline solid state can also be achieved by grinding.

Crystallization and Interconversions of Vapor-Sensitive, Luminescent Polymorphs of [(C6H11NC)2AuI](AsF6) and [(C6H11NC)2AuI](PF6)

The remarkable, vapor-induced transformation of the yellow polymorphs of [(C(6)H(11)NC)(2)Au(I)](AsF(6)) and [(C(6)H(11)NC)(2)Au(I)](PF(6)) into the colorless forms are reported along with related studies of the crystallization of these polymorphs. Although the interconversion of these polymorphs is produced by vapor exposure, molecules of the vapor are not incorporated into the crystals. Thus, our observations may have broad implications regarding the formation and persistence of other crystal polymorphs where issues of stability and reproducibility of formation exist. Crystallographic studies show that the colorless polymorphs, which display blue luminescence, are isostructural and consist of linear chains of gold(I) cations that self-associate through aurophilic interactions. Significantly, the yellow polymorph of [(C(6)H(11)NC)(2)Au(I)](AsF(6)) is not isostructural with the yellow polymorph of [(C(6)H(11)NC)(2)Au(I)](PF(6)). Both yellow polymorphs exhibit green emission and have the gold cations arranged into somewhat bent chains with significantly closer Au···Au separations than are seen in the colorless counterparts. Luminescence differences in these polymorphs clearly enhance the ability to detect and monitor their phase stability.

Synthesis of a Novel Photochromic Fluorescence Switching Diarylethene for Optical Recording Storage

A new unsymmetrical photochromic diarylethene bearing a benzothiophene aryl unit, 1-[2-methyl-5-(1,3-dithiolpentane)-3-thienyl]-2-[2-methyl-3-benzothiophenyl]perfluoroyclopentene has been synthesized, and its photochromic, fluorescence and optical recording strorage properties were investigated. The compound exhibited pronounced photochromic and clear fluorescence switching properties upon alternating irradiation with UV and visible light; the colorless open form with fluorescence character could be regenerated by irradiation with visible light. In terms of potential use for optical storage and readout, this compound displays fluorescence discrimination between its open and closed form. This fluorescence switching could be the basis of a remote control nondestructive readout method.

Sensitive detection of histamine using fluorescently labeled oxido-reductases

A detection scheme is described by which the histamine contents of biological samples can be established. The scheme is based on the use of methylamine dehydrogenase (MADH) which converts primary amines into the corresponding aldehydes and ammonia. The generated reducing equivalents are subsequently transferred to the physiological partner of MADH, amicyanin, which thereby is converted from the oxidized blue-colored form into the reduced colorless form. The change in absorption is detected by monitoring the fluorescence of a covalently attached Cy5 dye label whose fluorescence is (partly) quenched by Förster resonance energy transfer (FRET) to the Cu-site of the amicyanin. The quenching efficiency and, thereby, the label fluorescence, depends on the oxidation state of the amicyanin. When adding histamine to the assay mixture the proportionality between the substrate concentration and the observed rate of the fluorescence increase has enabled this assay as a sensor method with high sensitivity. The MADH and amicyanin composition can be tuned so that the sensor can be adapted over a broad range of histamine concentrations (13nM–225μM). The lowest concentration detected so far is 13nM of histamine. The sensor retained its linearity up to 225μM with a coefficient of variation of 11% for 10 measurements of 100nM histamine in a 100μL sample volume. The use of a label fluorescing around 660nm helps circumventing the interference from background fluorescence in biological samples. The sensor has been tested to detect histamine in biological fluids such as fish extracts and blood serum.

Synthesis, Optoelectronic Properties of a New Photochromic Diarylethene Bearing Benzothienyl and Malononitrile Group

An unsymmetrical diarylethene derivative bearing both benzothienyl and thienyl moieties, in which a malononitrile group was substituted at the 5-position of the thienyl ring, was synthesized. This compound undergo a reversible electrocyclic rearrangement, generating strongly colored closed-ring isomer upon irradiation with UV-light which show nonfluorescence, while exposure to light in the visible range triggers the cycloreversion to the colorless open-ring form that exhibits strong fluorescence properties. This properties of molecular photochromism were developed that showed both photo switches and fluorescence switches. The erasable and rewritable photo-images on this photochromic diarylethene were successfully demonstrated. This developments are crucial for fundamental research and eventual technical application for high-density optical data storage.

スピロオキサジンの光キレート化反応制御

Spirooxazines (SOs) exhibit the well-known photochromic reaction of photoinduced interconversion between the original colorless form and the colored merocyanine (MC) form. The MC easily coordinates to specific metal ions (e.g., Zn2+) in solvents and forms a fluorescent chelate complex. It is difficult to dissociate the complex in solvents because it is stable to heat and visible light. The control of the interaction between the SO molecule and metal ion is required for the reversible photochromic reaction. For example, MC forms a reversible complex with metal bonding to oxide networks such as silica gel and it is dissociated by visible irradiation because the MC is weakly coordinated to the metal ion. Such photochromic reaction can be control in the sol-gel matrix by organic modification of the silicon due to increasing the pore volume changing the polarity. The elucidation of the formation and dissociation of such metal chelates leads to create novel photofunctional materials.

Photodegradation of malachite green and malachite green carbinol under irradiation with different wavelength ranges

The dye malachite green (MG) is used worldwide as a fungicide in aquaculture. It is a toxic substance which in aqueous solutions is partly converted into its non-ionic colorless form (leucocarbinol). The equilibrium between these two forms is pH-dependent (pK = 6.9). To assess the photodegradation of MG under sunlight conditions, both species were irradiated separately in aqueous solutions with different pH values (4.0 and 12.0) using various ultraviolet and visible wavelength ranges (UV/VIS). A 700 W high-pressure mercury lamp with special filters was used. No artificial photooxidizers such as H 2O 2 or TiO 2 were added. MG leucocarbinol proved to be much more sensitive to irradiation than the dye form. Quantum yields Φ were calculated for some wavelength ranges as follows: MG carbinol: Φ (280–312nm) is 4.3 × 10 −3, Φ (313–410nm) is 5.8 × 10 −3, and MG dye: Φ (280–312nm) is 4.8 × 10 −5, Φ (313–365nm) is 1.1 × 10 −5, and Φ (>365nm) is 0, respectively. Therefore, the solar photolysis of MG is an important sink and primarily depends on the photodegradation of the colorless leucocarbinol. During the irradiation of MG leucocarbinol with wavelengths >365 nm, an intermediate was formed which has photocatalytical properties.

Synthesis, characterisation and in situ colorimetry of electrochromic Ruthenium purple thin films

Ruthenium purple (RP) films on transmissive tin-doped indium oxide (ITO)/glass substrates have been synthesised by an electrochemical coagulation technique using an aqueous RP colloidal suspension prepared from separate very dilute aqueous solutions of iron(III) chloride and potassium hexacyanoruthenate(II), with dilute potassium chloride as supporting electrolyte solution. To aid stability of the RP films, ruthenium(III) chloride was added to the RP colloidal suspension. Using the CIE (Commission Internationale de l’Eclairage) system of colorimetry, the colour stimulus of the electrochromic RP films and the changes that take place on reversibly switching to the colourless form have been calculated from in situ visible spectra recorded under electrochemical control. On electrochemical reduction, the intensely absorbing bright purple mixed-valence iron(III) hexacyanoruthenate(II) chromophore is reduced to the colourless iron(II) hexacyanoruthenate(II) form. Sharp and reversible changes in the hue and saturation occur, as shown by the track of the CIE 1931 xy chromaticity coordinates. Concurrently, as the purple chromophore is bleached, a large increase in the relative luminance of the electrochromic film is observed. For the purple state, the CIELAB 1976 colour space coordinates were L* = 64, a* = 27 and b* = −36, with a complementary wavelength ( λ c) calculated as 555 nm, in excellent agreement with the absorption maximum ( λ max) of 550 nm for the intervalence charge-transfer (IVCT) band.

ChemInform Abstract: Characterization of Electrochromic Nickel Oxide Thin Films Prepared by Anodic Deposition.

Nickel oxide (NiOx) thin films have been prepared on transparent conducting indium tin oxide (ITO) substrates by anodic deposition from a nickel ammine complex solution. Electrochromic (EC) behaviour of these films was observed in a borate buffer solution at pH 10 in the potential range 0–1 V vs. Ag/AgCl; an as-prepared film (PF) was cathodically reduced to a colourless form (RF) and oxidized to a brown form (OF) by anodic polarization. Characterization of these films by low-angle incident X-ray diffraction and X-ray photoelectron spectroscopy with argon-ion (Ar+) etching revealed that the EC properties are based on the electrolytic transformation of the NiOx structure between β-NiOOH and β-Ni(OH)2, i.e. involving the redox reaction Ni3++ e ⇄ Ni2+.

Mercury ion induced activation of the C–O bond in a photo-responsive spiropyran

The conversion of 7-hydroxy-BIPS in solution from colourless form to colored form can be induced using both light and the addition of Hg 2+ ion. No significant color change is observed when other ions (Ca 2+, Mg 2+, Zn 2+, Cd 2+, Co 2+, Cu 2+, Mn 2+, Fe 2+, Ni 2+, Pb 2+, K +, Na +, Li +, and Ag +) were used.

A-βcyclodextrin/siloxane hybrid polymer: synthesis, characterization and inclusion complexes

A hybrid polymer derived from siloxane and β-cyclodextrin (β-CD) was obtained by reaction of β-CD with g-isocyanatopropyltriethoxysilane (IPTS), followed by hydrolysis/condensation reactions, generating a β-CD-modified polysilsesquioxane resin (PSS-β-CD). PSS-β-CD hybrid was characterized by infrared spectroscopy and 13C and 29Si nuclear magnetic resonance. This hybrid was typically amorphous and thermally stable up to 180 ºC. PSS-β-CD was able to form films and its morphology was evaluated by scanning electron microscopy. The capability of β-CD grafted in the hybrid polymer to form inclusion complex was evaluated by the formation of a β-CD-phenolphthalein complex using UV-Vis spectroscopy. Even without changes in pH, the red form of phenolphthalein converts to the colorless one when PSS-β-CD is immersed in the solution. Theoretical calculations (AM1 and DFT methods) show that the complex is formed through the inclusion of the phenolate ring into β-CD cavity, favoring the colorless form of phenolphthalein by more than 15 kcal mol-1.

Photo-induced carbonation of lime-TiO2 mortars

In this work, titanium dioxide (TiO2) has been used as an additive in lime binder (Ca(OH)2), in order to benefit from its photocatalytic properties and study both the photocatalytic properties of the produced mixtures and the effect of photocatalytically produced carbon dioxide on the carbonation process of lime. TiO2 was added in three different portions (3, 6 and 10% w/w) in lime mixtures and their physicochemical and photocatalytic properties were studied and compared to those of a reference, made exclusively of lime. The photocatalytic properties of the mixtures were studied through the photo-oxidation of an organic model pollutant solution (methyl orange) to a colorless form, as well as by studying the microstructure and carbonation depth in different groups of mixtures subjected to photocatalysis cycles in the laboratory and exposed for a 2 month period in the open air (urban environment).Laboratory results confirmed that lime-TiO2 composite mixtures exhibit photocatalytic properties in both UV radiation conditions and direct exposure to sunlight. Moreover, analytical results indicated an enhanced carbonation of lime-TiO2 composites. TiO2 can be added to lime successfully and can have applications in lime-based mortars used in the conservation of architectural heritage, enhancing their performance against soiling and amenity loss.

Colour development during storage of sulphited syrup in pan supply tanks

The Syrup from multiple effect evaporators was bleached with sulphur dioxide gas to reduce coloured ferric compounds to colourless ferrous form and stored temporarily before crystallization in the double sulphitation process of sugar manufacture followed in India. The syrup was exposed to atmospheric air and the iron surface stored in mild steel tanks which were open to atmospheric air. The sulphited syrup develops dark colour when exposed to air because of oxidation. Further, there is increase of syrup colour due to reaction of iron with polyphenols present in sugarcane. Due to this phenomenon there was an increase of colour of the syrup just before the crystallization.

1-(4-Bromophenyl)-1-(4-nitrobenzoyl)thiourea

The title compound, C14H10BrN3O3S, crystallizes as two concomitant polymorphs that differ in colour (one yellow and one colourless). Only the structure of the colourless form could be determined. The mol­ecule exists in the thio­amide form with an intra­molecular N—H⋯O=C hydrogen bond across the thio­urea system. Mol­ecules are linked into layers parallel to (120) by Br⋯Onitro contacts [3.103 (1) Å], classical hydrogen bonds from the other NH function to the S atom and Nnitro⋯O=C contacts. The layers are linked by weak C—H⋯Onitro hydrogen bonds to produce the observed three-dimensional network.

Innovative Combination of Three Alternating Current Relaxation Techniques: Electrical Charge, Mass, and Color Impedance Spectroscopy. Part II: Prussian Blue ⇆ Everitt’s Salt Process

The simultaneous recording of three impedance functions (electrochemical impedance, color, and mass impedance) allows the role of different species to be distinguished easily during electrochemical processes in conducting and electrochromic films. Herein, this technique has been applied to the study of the Prussian blue films at several potentials between the blue form (Prussian blue) and the colorless form (Everitt’s salt). At these potentials, these electrochemical reactions take place by means of exchange of different ions. Thus, the exchange of potassium cations is related to the changes of absorbance at 690 nm, whereas the exchange of protons does not introduce color changes at this wavelength. There is also another site for potassium insertion that does not produce any color change at this wavelength. The analysis of experimental results obtained from this technique has allowed these contributions to be distinguished. Besides, the fitting of the different impedance signals has allowed independent in...

Self-Assembly Multi-Layer of 1,3-Bisdicyanovinylindane and Its Spectral Sensing Properties

The multi-layer dye film as an acid-alkali reversible sensing material has been fabricated using poly(diallyldimethylammonium chloride) (PDDAC) and 1,3-bisdicyanovinylindane dye compound by electrostatic forces and layer-by-layer self-assembly attractions. These dye layers show reversible color switchable properties. The dye shows blue colored characteristic in alkaline condition. However, when strong acidic atmospheres are subjected to colored dye structure, it converts to the colorless form of the dye structure within the multi film layers. These results were characterized using absorbance measurement and Atomic Force Microscopy (AFM). UV-vis absorption spectra of the multi-layer films increased linearly at 583 nm, which indicated that fabrication of the dye layer as a sensing moiety proceeded regularly. The dye fabrication films also clearly showed the hydrochloric gas sensing properties with reversible color changes.

Weak acid triggers the ring opening of an otherwise long-lived triangle terthiazole closed isomer

The stability of the colored cyclized form of a compound from the new class of photochromic triangle terthiazoles was found to be strongly decreased by the presence of trifluoroacetic acid (TFA) in acetonitrile at room temperature. The apparent first-order process rate constant of the observed bleaching is of the same order of magnitude as if the acid-free sample was heated to about 100 °C. Association constants with TFA were determined from the kinetics analysis and by NMR titration and were found to be moderate for the colored form and very weak for the colorless form. These results were interpreted considering the basicity of the molecules and the solvent effect on the acid strength. The structural consequences of the protonation on the ring-closed compound and on the entire ring-opening process were examined by DFT calculations. Protonated closed and open forms were found to be geometrically “closer” than their non-protonated parents and the altered bond-length alternation may explain the diminution of the activation barrier. The puzzling instability of the protonated terthiazole was compared to a related thermally stable imidazolium homologue. From structural DFT considerations, it was concluded that this different behavior may be explained in term of charge stabilization, the sulfur being less efficient than the nitrogen.

Synthesis and Photochromic Properties of Poly(4-vinylpyridine-co-styrene) with Pendant Spiroxazine Moieties

An ionic polymer with pendant photochromic moieties was prepared by the reaction of poly(4-vinylpyridine-co-styrene) and 1,3,3-trimethyl-6'-bromohexyloxyspiro[2H]-indol-2,3'-[3H]-naphth[2,1-b][1,4]oxazine. The photochromic reaction in question is caused by the reversible heterolytic cleavage of the C(spiro)-O bond under UV irradiation, yielding the colored form that can return to the colorless form by ring closure under visible light irradiation or in dark. The visible range absorption of the corresponding polymer increased gradually by UV irradiation which is ascribed to the generation of the open merocyanine form from the closed spiro form. The ionic conductivity of polymer increased upon UV irradiation, which brought about the generation of zwitterions form, and subsequently decreased in dark, which brought about the generation of closed spiro form. Sufficient reversibility was found in this polymer and this response was completely synchronized with that in the absorbance changes.

PRINTING WITHOUT INK

POINT, SHOOT , and print. Soon, photographers in even the most remote corners of the globe will be able to do just that and get instant prints of their digital photos. The secret to getting these snapshots in a snap lies in some clever chemistry developed at Zink Imaging, a company based in Waltham, Mass. Scientists at Zink—which is short for zero ink—have come up with a photo printing process that requires no ink. The key to photos on the go lies within Zink's thermally activated photo paper. Direct thermal printing, the basis for the new photo printer, has been around for about 50 years. It was originally developed—and is still used—to print cash-register receipts. The cash register uses a special paper that's loaded with an indicator dye in its colorless form and small particles of a solid acid, usually a phenol. The cash register's print head is made up of ...