Shift Of Λmax Research Articles

Ultrasound‐assisted adsorption of reactive blue 21 dye on TiO2 in the presence of some rare earths (La, Ce, Pr & Gd)

AbstractAdsorption of reactive blue (RB) 21 dye in the aqueous solution has been carried out on TiO2 alone and in combination with rare earth ions [La3+, Ce4+, Pr3+ and Gd3+] in the presence and absence of ultrasound. The formation of adsorbent (TiO2) from tetra n‐butyl orthotitanate and its characterisation has been done through X‐ray diffraction (XRD), scanning electron microscopy (SEM), diffuse reflectance spectroscopy (DRS), Raman spectroscopy and N2 adsorption techniques. Complete decolourisation was achieved in 5 min in the presence of US + TiO2 + Ce. The effects of initial concentration of dye, adsorbent dose and contact time on the decolourisation of dye have been examined under different experimental conditions. The removal of dye in the presence of ultrasound was (88–99%) compared to conventional stirring (62–69%). Adsorption behaviour has been analysed using Langmuir, Freundlich, Dubinin–Radushkevich and Temkin isotherm models. RE–TiO2 combination had higher adsorption equilibrium constant (Kc) and better adsorption capacity (qmax) than TiO2 alone, both in the absence and presence of ultrasound, indicating the formation of Dye‐RE complex before sorption. This is confirmed from the shift in λmax from 626 to 616 cm−1. The kinetic data fit well with the pseudo‐second order kinetic model, and the adsorption process was spontaneous in the presence of rare earths. The mechanism of adsorption has been explained with the help of Weber–Morris intraparticle diffusion and Boyd kinetic models. A batch adsorber has been proposed for different TiO2 dose to effluent volume ratios using the Langmuir equation.

Thiazole-Containing Conjugated Polymer as a Visual and Fluorometric Sensor for Iodide and Mercury

A neutral conjugated polymer poly-p-phenylene (PPP) derivative, poly(1,4-bis-(8-(4-phenylthiazole-2-thiol)-octyloxy)-benzene) (PPT), was prepared using a simple and economical method of oxidative polymerization reaction. This newly synthesized polymer PPT was characterized by means of Fourier transform infrared spectroscopy (FT-IR), (1)H nuclear magnetic resonance ((1)H NMR), ultraviolet-visible (UV-Vis), and fluorescence spectroscopy. PPT displays fluorescence "turn-off/turn-on" characteristics and colorimetric responses to I(-) and Hg(2+). The UV-Vis and fluorescence spectra of the PPT showed a significant shift in λmax via the addition of iodides and mercury. A colorless PPT solution turns to deep yellow in the presence of iodide salts, which subsequently becomes colorless again on addition of Hg(2+) salts that could be easily detected visually by the naked eye. The Stern-Volmer constant (Ksv) value obtained for the detection of iodide is 0.13 × 10(5) M(-1), confirming very high sensitivity of this polymer for iodide salts. The detection limit of Hg(2+) salt using the PPT polymer was found to be 2.1 nM in water. The detection of both iodide and mercury was also possible in solid state by using a membrane film prepared by mixing 1% PPT in polystyrene. This membrane changes color in the presence of iodide as well as mercury salts. These results confirm that the PPT polymer can be applied for the colorimetric as well as fluorometric sensing of I(-) and Hg(2+) ions in a competent environment in solution, as well as in the solid state, using a membrane film rapidly.

Spectral, electrochemical and docking studies of 5-indanol:β-CD inclusion complex

Inclusion complex of 5-indanol with β-cyclodextrin (β-CD) has been investigated by ultraviolet (UV) spectroscopy and cyclic voltammetry (CV) techniques. The red shift in λmax and enhanced absorption in β-CD medium confirm the cyclopentene ring present in the interior part of β-CD and –OH group containing benzene ring in the upper part of the β-CD cavity. The formation of complex has been confirmed by Benesi–Hildebrand plot obtained from the results of UV and CV studies. The pK a values of prototropic species, stability constant K1:1 and the thermodynamic parameters (ΔG, ΔH and ΔS) of inclusion process were determined. The results indicated that the inclusion process was an exergonic and spontaneous process. The solid 5-indanol:β-CD complex was investigated by fourier transform infrared spectroscopy, nuclear magnetic resonance, X-ray diffraction and scanning electron microscope methods. The 5-indanol:β-CD inclusion complex obtained by docking studies was in good correlation with the results obtained through experimental methods.

Potential of capillary electrophoresis with wavelength-resolved fluorescence detection for protein unfolding studies using β-lactoglobulin B as a test compound

Capillary electrophoresis (CE) with wavelength-resolved fluorescence detection (wrFlu) was evaluated for the study of protein unfolding using non-reduced and reduced β-lactoglobulin B (β-LGB) as model compounds. Protein unfolding was achieved by incubation in sodium phosphate (pH 3.0) containing increasing concentrations of urea (0-7.1 M). CE-wrFlu was performed using the incubation media as background electrolytes (BGEs). At low urea concentrations (0-3.1 M), CE-wrFlu analysis of non-reduced β-LGB showed a single peak with a maximum emission wavelength (λmax) of 333 nm, indicating the protein was in its folded state. When β-LGB was exposed to 3.6 and 4.1 M urea, CE-wrFlu revealed an additional peak with a λmax of 353 nm and a reduced migration time, suggesting the formation of fully unfolded species. Upon further raising the urea concentration up to 6.5 M, the peak intensity of the unfolded protein increased. At the same time, the later-migrating peak became wider and lower, showing a decrease of migration time and a shift of λmax (333-353 nm), indicating gradual unfolding. Construction of a λmax-based transition curve for the later-migrating β-LGB species provided a denaturant-concentration midpoint of unfolding (cm) of 5.39 M, which was similar to the cm determined by plotting the corrected effective electrophoretic mobility (μeff,c) vs. urea concentration. Stand-alone fluorescence spectroscopy of the same β-LGB solutions revealed a lower cm (4.97 M), most probably because the respective β-LGB species were not separated, yielding ensemble average data. For reduced β-LGB, at all tested urea concentrations one protein peak was observed, whereas λmax and μeff,c indicated protein unfolding at much lower urea concentrations (cm of 1.2 M). We conclude that CE-wrFlu can distinguish protein conformational states and thus may provide useful additional information on unfolding pathways.

Optoelectronic and structural properties of a family of thiophene functionalized 1,5-dithia-2,4,6,8-tetrazocines

The dithiatetrazocine (DTTA) ring has been functionalized with thiophene (5a), 5-hexylthiophene (5b) and 5-bromothiophene (5c), and the optoelectronic and structural properties have been probed. All three derivatives possess low-lying LUMO levels near −3.5 eV and exhibit irreversible reduction and oxidation processes. Inspection of their absorption profiles reveals a small bathochromic shift in λmax with substitution of the thiophene ring. The HOMO–LUMO band gaps, determined from electrochemical, optical and computational studies, decrease across the series in the following manner: 5a > 5c > 5b. DFT calculated frontier molecular orbitals for 5a–c (R = Me for 5b) indicate delocalized electron density over the entire tricyclic framework for the HOMO, whereas the electron density for the LUMO is localized on the DTTA ring. Single crystal X-ray diffraction on 5b,c show structures consisting of molecules with planar molecular frameworks arranged in slipped π-stack arrays. Although both compounds exhibit close intermolecular interactions, the contacts observed in 5c are between π-stacks, while they are exclusively within the π-stacks for 5b.

Dynamics of the l -fucose/H + symporter revealed by fluorescence spectroscopy

FucP of Escherichia coli catalyzes L-fucose/H(+) symport, and a crystal structure in an outward-facing conformation has been reported. However, nothing is known about FucP conformational dynamics. Here, we show that addition of L-fucose to purified FucP in detergent induces ∼20% quenching of Trp fluorescence in a concentration-dependent manner without a shift in λ(max). Quenching is essentially abolished when both Trp38 and Trp278, which are positioned on opposing faces of the outward-facing cavity walls, are replaced with Tyr or Phe, and reduced quenching is observed when either Trp is mutated. Therefore, both Trp residues are involved in the phenomenon. Furthermore, replacement of either Trp38 or Trp278, predominantly Trp38, causes decreased quenching, decreased apparent affinity for L-fucose, and significant inhibition of active L-fucose transport, indicating that the two residues are likely involved directly in sugar binding. It is proposed that sugar binding induces a conformational change in which the outward-facing cavity in FucP closes, thereby bringing Trp38 and Trp278 into close proximity around the bound sugar to form an "occluded" intermediate. The location of these two Trp residues provides a unique method for analyzing structural dynamics in FucP.

Synthesis, spectral properties and dyeing on polyester of monoazo dyes from indol‐2‐one derivatives

Three series of phenylazo disperse dyes were prepared by coupling diazotised 4-aniline dyes with 5-indol-2-one dyes. The structures of these dyes were determined by proton nuclear magnetic resonance, Fourier Transform–infrared and elemental analysis. The effects of solvent on the ultraviolet–visible absorption spectra of these dyes were studied. The dyes displayed a λmax shift of between 399 and 438 nm. The dyes were finally applied in the dyeing of polyester fibres in order to investigate their colour range and dyeing properties. Most of the dyes displayed high rubbing fastness and good washing and sublimation fastnesses on polyester fibres.

Preparation and Application of PEG/PVP Copolymers

In this study, we produced a series of environmentally friendly multifunctional additives by polymerization of biodegradable polyethylene glycol (PEG) and N-Vinyl-2-pyrrolidone in different proportions. The copolymer molecular structure was confirmed by Fourier transform infrared spectroscopy, and the impact of the copolymers on dye absorption and dye interaction was investigated. The results showed that the series of copolymers produced displayed enhanced dye decolorization with increasing copolymer dose and time. Additionally, the PEG/polyvinylpyrrolidone (PVP) copolymers and dye molecules interacted; addition of copolymer enabled shifts of the dye λmax toward shorter wavelengths and decreased the UV absorbance. The addition of copolymers reduced the overall Zeta potential of the dye and increased the particle sizes, facilitating dye decolorization. In particular, the dye decolorization effect was the best when the PEG/PVP molar ratio was 8:1.

Interaction of Short Chain Phenylalkanoic Acids Within Cationic and Anionic Surfactants

Short chain phenylalkanoic acids have been investigated by UV spectroscopy to ascertain their solubilization into cationic surfactant, cetyltrimethylammonium bromide (CTAB), and anionic surfactant, sodium dodecyl sulfate (SDS). The increasing surfactant concentrations caused bathochromic shift in the spectra of additive acids. CTAB exhibited greater λmax shift, whereas λmax values are slightly altered in SDS solution. Moreover, the critical micelle concentration (CMC) of CTAB with and without phenylalkanoic acids was determined by conductivity measurements. The λmax and CMC data were used to calculate the electronic transition energy (ΔET) and Gibbs free energy change of micellization \({({\Delta G_{\rm mic}^{\circ}})}\) of CTAB in presence of additive acids.

Spectroscopic studies on interactions between cholesterol-end capped polyethylene glycol and liposome

In order to confirm that the cholesterol end groups of cholesterol-end capped polyethylene glycol really insert into the liposome bilayer and investigate how the incorporation affects the microenvironment of liposome bilayer, two kinds of molecular probes, namely Nile Red and pinacyanol chloride, were used. Their UV–visible and fluorescence spectrum were recorded before and after the addition of the polymer. Shifts of the maximum absorbance (λmax) of Nile Red show that the bilayer microenvironment around Nile Red is becoming more polar with increasing polymer concentration while shifts of λmax of pinacyanol chloride indicate that the surrounding environment of pinacyanol chloride is becoming more apolar with addition of polymer. Effect of composition of liposome was also studied. With high ratio of dimethyldioctadecylammonium bromide (DODAB) fraction in liposome, λmax of Nile Red is more easily affected by the addition of Chol-PEG-Chol while liposome with cholesterol shows relatively high stability to the addition of Chol-PEG-Chol.

α‐Propargyl amino acid‐derived optically active novel substituted polyacetylenes: Synthesis, secondary structures, and responsiveness to ions

AbstractNovel optically active substituted acetylenes HC CCH2CR1(CO2CH3)NHR2 [(S)‐/(R)‐1: R1 = H, R2 = Boc, (S)‐2: R1 = CH3, R2 = Boc, (S)‐3: R1 = H, R2 = Fmoc, (S)‐4: R1 = CH3, R2 = Fmoc (Boc = tert‐butoxycarbonyl, Fmoc = 9‐fluorenylmethoxycarbonyl)] were synthesized from α‐propargylglycine and α‐propargylalanine, and polymerized with a rhodium catalyst to provide the polymers with number‐average molecular weights of 2400–38,900 in good yields. Polarimetric, circular dichroism (CD), and UV–vis spectroscopic analyses indicated that poly[(S)‐1], poly[(R)‐1], and poly[(S)‐4] formed predominantly one‐handed helical structures both in polar and nonpolar solvents. Poly[(S)‐1a] carrying unprotected carboxy groups was obtained by alkaline hydrolysis of poly[(S)‐1], and poly[(S)‐4b] carrying unprotected amino groups was obtained by removal of Fmoc groups of poly[(S)‐4] using piperidine. Poly[(S)‐1a] and poly[(S)‐4b] also exhibited clear CD signals, which were different from those of the precursors, poly[(S)‐1] and poly[(S)‐4]. The solution‐state IR measurement revealed the presence of intramolecular hydrogen bonding between the carbamate groups of poly[(S)‐1] and poly[(S)‐1a]. The plus CD signal of poly[(S)‐1a] turned into minus one on addition of alkali hydroxides and tetrabutylammonium fluoride, accompanying the red‐shift of λmax. The degree of λmax shift became large as the size of cation of the additive. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Effects of UV Radiation on Helical Twisting in Cholesteric Systems Containing Photosensitive Azoxy Nematics

For cholesteric liquid crystal systems containing photosensitive nematic ZhK-440 and a mixture of cholesterol derivatives, the changes in helical twisting induced by UV radiation are studied. The UV-induced shift of the selective reflection maximum λmax is shown to depend on the concentration of the nematic component. For low concentrations of ZhK-440, λmax increases, which correlates with the corresponding temperature-induced changes. For higher azoxy nematic concentrations, λmax decreases, regardless of the temperature behavior of the system. To explain the experimental data, a theoretical description is proposed on the basis of the development of molecular models of helical twisting. Good agreement was obtained between calculated and measured values of the UV-induced shift as a function of the azoxy nematic concentration, with two extrema and an inversion point. The extra twisting arises from the cholesteric mesophase-induced orientation of short molecular axes of cis-isomers formed as a result of irradiation.

Rational aspect ratio and suitable antibody coverage of gold nanorod for ultra-sensitive detection of a cancer biomarker

We report a simple, ultra-sensitive, and straightforward method for non-labeling detection of a cancer biomarker, using Rayleigh light scattering spectroscopy of the individual nanosensor based on antibody-antigen recognition and localized surface plasmon resonance (LSPR) λ(max) shifts. By experimentally measuring the refractive index sensitivity of Au nanorods, the Au nanorod with an aspect ratio of ~3.5 was proven optimal for the LSPR sensing. To reduce the steric hindrance effect as well as to immobilize a large amount of ligand on the nanoparticle surface, various mixtures containing different molar ratios of HS(CH(2))(11)(OCH(2)CH(2))(6)OCH(2)COOH and HS(CH(2))(11)(OCH(2)CH(2))(3)OH were applied to form different self-assembled monolayer surfaces. The results showed that the best molar ratio for antibody conjugation was 1 : 10. When using individual Au nanorod sensors for the detection of prostate specific antigen (PSA), the lowest concentration recorded was ~1 aM (~6 × 10(5) molecules), corresponding to LSPR λ(max) shifts of ~4.2 nm. These results indicate that sensor miniaturization down to the nanoscale level, the reduction of steric hindrance, and optimization of size, shape, and aspect ratio of nanorods have led to a significant improvement in the detection limit of sensors.

An Effector of Hemoglobin Structure: The Guanosine 3', 5'-Triphosphate

The effect of guanosine 3', 5'-triphosphate (GTP) on the hemoglobin structure was studied by UV-visible, fluorescence and circular dichroism (CD) spectroscopies, and cyclic voltammetry. UV-visible absorption spectra showed an increase in absorbance in the regions of 420 nm and 280 nm. Fluorescence spectra showed that the Trp fluorescence intensity increased upon excitation at 280 nm, when guanosine 3', 5'-triphosphate concentration was increased in hemoglobin solution. Along with the increased fluorescence intensity, a slightly shift of λmax was also observed toward the higher wavelengths. CD spectral analysis demonstrated a significant decrease in negative ellipsity in the region of 205–235 nm. After adding guanosine 3', 5'-triphosphate to the hemoglobin solution α-helix structure decreases by 20 % while β-sheet conformation increases by 9 %. The effects of GTP on hemoglobin resulted in a 61 mV shift in the cathodic and 40 mV for anodic peak of hemoglobin in the CD. Our data showed the change of secondary and tertiary structure of hemoglobin in the presence of guanosine 3', 5'-triphosphate. (doi: 10.5562/cca1955)

Characterisation of sugar beet pectin fractions providing enhanced stability of anthocyanin-based natural blue food colourants

The bathochromic effect resulting from the addition of sugar beet pectin (SBP) to black currant juice, purified anthocyanins (ACN-E) and purified polyphenol extracts comprising both anthocyanins and non-anthocyanin phenolics (PP-E), respectively, were monitored by VIS spectroscopy at varying pH relevant to food formulations (pH 3.6–5.0). Furthermore, a low molecular pectic polysaccharide fraction (PPF) was isolated from SBP using 70% aqueous 2-propanol and further characterised with respect to its chemical composition and mineral content. The marked bathochromic effect was found to be due to the formation of anthocyanin–metal chelate complexes. Only at pH 5.0 SBP entailed a moderate bathochromic shift of 12nm in model solutions containing ACN-E. This effect was enhanced in PPF model solutions resulting in a λmax shift up to 50nm, bringing about an intense blue colour. The bathochromic shift was boosted with increasing pH and upon purification of the anthocyanins. In contrast, after SBP and PPF addition to black currant juice, the bathochromic effect was almost annihilated. Model solutions were stored at 20°C in the dark for 12days, and optimum stability of the blue colour was observed at pH 5.0.

Comparative shelf life and efficacy of LDPE and PVC degrading bacterial consortia under bioformulation

The present study elucidates the development of the talc-based formulation for long-term sustenance / storage of bacterial consortia, pertains to degrade polymer (LDPE and PVC). Four potential bacterial consortia were employed which consisted of Microbacterium sp., Pseudomonas putida, P. aeruginosa, P. otitidis, Bacterium Te68R, Bacillus aerius, B. cereus and Acanthopleurobacter pedis. The viability of consortia was ascertained by measuring the colony forming units per mL besides assuring the polymer biodegradation potential after formulation in talc by carrying out in vitro assays. The analysis was done by determination of λ-max shifts and scanning electron microscopy for changes in polymer composition and surface dissolution, respectively. It reveals that using the described formulations, all the consortia were able to successfully retain their characteristic biodegradation property even after 70 days of storage at ambient conditions. Furthermore, the SEM micrographs documented significant disruption of surface texture of polymer (LDPE and PVC) film by respective consortia recovered after storage. Thus, the talc-based formulation may be useful for the storage and handling of polymer-degrading consortia for large-scale applications to minimize the solid waste disposal. Keywords: biodegradation, bioformulation, talc, consortia, shelf life, LDPE, PVC, SEM

Non-Exponential Decay: Understanding the Correlation of Wavelength and Lifetime caused by Heterogeneity

We report work that leads naturally to the missing underlying universal physical principle accounting for the strong correlation between tryptophan (Trp) decay associated (DAS) fluorescence wavelength (λmax) and lifetime (τf), in the absence of solvent relaxation. The familiar broad fluorescence spectrum of a solvent-exposed chromophore is actually an ensemble average of single molecular λmax values, fluctuating on a femtosecond time scale typically over 4000 cm−1 or 40 nm. In this dynamic picture, those conformers having shorter wavelength emission spectra, i.e., higher average energy, have an increased probability for transient fast electron transfer (ET) during large fluctuations in environment that bring a high energy, non-fluorescent charge transfer (CT) state and the fluorescing state (S1) into resonance. For Trp, the CT state lies well above the S1 state, and the wavelength is quite sensitive to local electric field. In these cases, heterogeneity and relaxation both can lead to time dependent red shifting fluorescence, making heterogeneity difficult to prove. Studies using non-natural amino acids expose the reality of heterogeneity by contrasting behavior. The fluorescence decays of 5-fluoroTrp incorporated in proteins are much more nearly monoexponential. This probe is not as easily quenched by ET as Trp because of its higher ionization potential, but it retains full wavelength sensitivity. Abbyad et al.(2007), find that time resolved fluorescence spectra of Aladan behave oppositely. When incorporated at several sites in the protein GB1, λmax shifts to shorter wavelength on the nanosecond time scale-- unequivocally revealing ground-state heterogeneity, because relaxation always requires a red shift in time; this is consistent with the observation that τf for this probe decreases with increasing solvent polarity by an internal mechanism.

Product-assisted Catalysis as the Basis of the Reaction Specificity of Threonine Synthase

Threonine synthase (TS), which is a pyridoxal 5'-phosphate (PLP)-dependent enzyme, catalyzes the elimination of the γ-phosphate group from O-phospho-L-homoserine (OPHS) and the subsequent addition of water at Cβ to form L-threonine. The catalytic course of TS is the most complex among the PLP enzymes, and it is an intriguing problem how the elementary steps are controlled in TS to carry out selective reactions. When L-vinylglycine was added to Thermus thermophilus HB8 TS in the presence of phosphate, L-threonine was formed with k(cat) and reaction specificity comparable with those when OPHS was used as the substrate. However, in the absence of phosphate or when sulfate was used in place of phosphate, only the side reaction product, α-ketobutyrate, was formed. Global analysis of the spectral changes in the reaction of TS with L-threonine showed that compared with the more acidic sulfate ion, the phosphate ion decreased the energy levels of the transition states of the addition of water at the Cβ of the PLP-α-aminocrotonate aldimine (AC) and the transaldimination to form L-threonine. The x-ray crystallographic analysis of TS complexed with an analog for AC gave a distinct electron density assigned to the phosphate ion derived from the solvent near the Cβ of the analog. These results indicated that the phosphate ion released from OPHS by γ-elimination acts as the base catalyst for the addition of water at Cβ of AC, thereby providing the basis of the reaction specificity. The phosphate ion is also considered to accelerate the protonation/deprotonation at Cγ.

A new method for non-labeling attomolar detection of diseases based on an individual gold nanorod immunosensor

Herein, we present the use of a single gold nanorod sensor for detection of diseases on an antibody-functionalized surface, based on antibody-antigen interaction and the localized surface plasmon resonance (LSPR) λ(max) shifts of the resonant Rayleigh light scattering spectra. By replacing the cetyltrimethylammonium bromide (CTAB), a tightly packed self-assembled monolayer of HS(CH(2))(11)(OCH(2)CH(2))(6)OCH(2)COOH(OEG(6)) has been successfully formed on the gold nanorod surface prior to the LSPR sensing, leading to the successful fabrication of individual gold nanorod immunosensors. Using prostate specific antigen (PSA) as a protein biomarker, the lowest concentration experimentally detected was as low as 111 aM, corresponding to a 2.79 nm LSPR λ(max) shift. These results indicate that the detection platform is very sensitive and outperforms detection limits of commercial tests for PSA so far. Correlatively, its detection limit can be equally compared to the assays based on DNA biobarcodes. This study shows that a gold nanorod has been used as a single nanobiosensor to detect antigens for the first time; and the detection method based on the resonant Rayleigh scattering spectrum of individual gold nanorods enables a simple, label-free detection with ultrahigh sensitivity.

Theoretical and Experimental Studies of the Optical Properties of Conjoined Gold−Palladium Nanospheres

We identify and report on UV−vis spectral features of AucorePdshell nanoparticles. Chains of conjoined nanospheres are formed with clear core/shell segregation and identified via experimental spectral red shifts of λmax and scanning transmission electron microscopy (STEM) imaging. Theoretical calculations performed using the discrete dipole approximation (DDA) validate our findings. The DDA simulation method is then used to delve further into possible spectroscopic implications of geometric and environmental changes. Structural configurations including extended chains of nanospheres, differing levels of nanosphere conjoinment, and increased Pd shell thickness are investigated, as well as variations of the surrounding dielectric medium.