Abstract: Here we report the fibrillation of egg white ovalbumin (OVA) induced by the biomineralization of two alkali halides (KCl, NaCl) in the Langmuir-Blodgett (LB) film of OVA. The pressure-area isotherm of OVA shows the salt-induced increment of apparent area/monomer of OVA. Fibrillation of OVA in the LB film is monitored by FE-SEM imaging. Formation of fibrillar aggregates is concomitant with an increase of salt concentration. HR-TEM and EDX measurements allowed us to identify nanostructured crystals of salt, which are associated with this fibrillar structure. FTIR spectroscopic study of the amide band in LB films as well as CD spectroscopy in solution qualitatively indicates the increase in β-sheet to α-helix ratio in the presence of salt, indicating unfolding of protein. We suggest that the ion attachment to the peptide chain leads to unfolding and that subsequent recrystallization in the transferred monolayer leads to fibrillation of protein as well as biomineralization of alkali halide salts. This finding demonstrates that the fibrillation of OVA is induced by the biomineralization of alkali halides.
Abstract: Here, we report the glycosylation of human adult hemoglobin (Hb) studied in aqueous solution and at the air-water interface by the Langmuir-Blodgett (LB) technique. Pressure-area (π-A) and pressure-time (π-t) measurements show that the concentration of glucose (GLC) and interaction time have an effect on Hb molecular area as well as on surface activity. Solution studies by UV-vis absorption and emission spectroscopy show that the GLC can alter the local conformation of Hb to some extent at the tryptophan and heme residues. CD spectroscopic studies in solution indicate that the α-helix content increases in the presence of GLC at the secondary structure level, which may be the cause of an increased adsorption rate of Hb. Also, secondary structure calculation using FTIR technique in the LB film follows the decrease in α-helix and increase in β-sheet structure as well as the formation of intermolecular aggregates. AFM images of Hb in the LB film indicate the transition from globular to an ellipsoid-like structure of Hb in the presence of GLC. FTIR studies of the LB film support the AFM imaging and the analysis of π-t kinetics. The molecular docking study revealed that Val 1 and Lys 132 are the most favorable docked sites along with some other sites such as Hem 147, Trp 37, Asp 94, Tyr 145, Leu 91, His 143, Glu 43 etc. The overall study may predict the processes of interactions with the increased concentration of GLC on Hb as well as on other long lived proteins.
Abstract: Nanoscience is now an expanding field of research and finds potential application in biomedical area, but it is limited due to lack of comprehensive knowledge of the interactions operating in nano-bio system. Here, we report the studies on the interaction and formation of nano-bio complex between silver nanoparticle (AgNP) and human blood protein hemoglobin (Hb). We have employed several spectroscopic (absorption, emission, Raman, FTIR, CD, etc.) and electron diffraction techniques (FE-SEM and HR-TEM) to characterize the Hb-AgNP complex system. Our results show the Hb-AgNP interaction is concentration and time dependent. The AgNP particle can attach/come closer to heme, tryptophan, and amide as well aromatic amine residues. As a result, the Hb undergoes conformational change and becomes unfolded through the increment of β-sheet structure. The AgNP-Hb can form charge-transfers (CT) complex where the Hb-heme along with the AgNP involved in the electron transfer mechanism and form Hb-AgNP assembled structure. The electron transfer mechanism has been found to be dependent on the size of silver particle. The overall study is important in understanding the nano-bio system and in predicting the avenues to design and synthesis of novel nano-biocomposite materials in material science and biomedical area.
Abstract: Herein, we report the aggregation behavior of catanionic mixtures of the anionic surfactant sodium dodecyl sulfate (SDS) and the cationic surfactant cetyltrimethylammonium bromide (CTAB) in solution and at the air/water interface obtained by the Langmuir-Blodgett (LB) technique. We employed Fourier transform infrared spectroscopy, in situ phase-contrast inverted microscopy, scanning electron microscopy, and atomic force microscopy to characterize the systems in solution, at the air/water interface, and in LB films. We found spherical vesicles at the SDS/CTAB ratio of 35/65 in aqueous solution and an ordered aggregated morphology called surface micelles at SDS/CTAB ratios of 35/65 to 65/35 at the air/water interface. Other mixtures (SDS/CTAB = 90/10, 10/90) were found to contain mostly disordered aggregated microstructures. An in situ time-dependent study of surface micelle formation at the air/water interface showed micelle ripening through the fusion of smaller micelles. These micelles were successfully immobilized on a glass substrate by the LB technique. Overall, the study might find application in the fundamental science of the physical chemistry of surfactant systems, as well as in the preparation of drug delivery system.
Abstract: We report here the influence of KCl on the interfacial surface activity and conformation of human adult hemoglobin (Hb) using Langmuir and Langmuir-Blodgett (LB) techniques. The studies were done in absence and in presence of KCl salt in the subphase. We have studied the surface pressure-area (π-A) isotherm and surface pressure-time (π-t) kinetics of Hb with the variation of KCl concentrations (C(KCl)). The π-t study shows that the surface activity as well as the magnitude of diffusion and rearrangement of Hb at air/water interface is a function of C(KCl). Conformational study was done by CD spectroscopy and by the FTIR technique. Both the studies show an increasing trend of the α-helix form of Hb in the presence of KCl which may be responsible for the increased surface activity of Hb. The free energy calculations show that the compression of the Hb monolayer is involved in the small free energy change (∼5-25 kcal mol(-1)) of Hb. The changes in area per molecule and free energy, as well as other results, indicate that the influence of KCl on the Hb monolayer is in line with modified DLVO theory of ion-protein interaction. FE-SEM study shows that the LB films in absence of KCl comprise higher aggregates, whereas in the presence of KCl (0.5 M) it comprises lower aggregates, indicating the structural change of Hb. KCl salt here enhances the α-helix from of Hb, promoting the folded conformation by perturbing the water structure. The overall results show that the intermolecular forces and the surface activity as well as the population of the α-helix of Hb can be tuned by KCl salt.
Abstract: In this report, we have studied the formation of iron-oxide nanoparticle at biologically relevant phospholipids, DPPC Langmuir monolayer at air/water interface. Water subphase contains FeCl(3). Adsorption and agglomeration of Fe(3+) ions at DPPC head group have being monitored by Langmuir and Langmuir Blodgett (LB) technique. Adsorption kinetics (pi-t) as well as the surface pressure area (pi-A) isotherms measurement demonstrate the incorporation of Fe(3+) ion at DPPC monolayer. The amount of incorporation of Fe(3+) to the DPPC monolayer is FeCl(3) concentration and time dependent. This reaction kinetics is well fitted by single exponential association equation. The composite monolayers transferred to different substrates are characterized by UV-vis absorption spectroscopy and electron microscopy (FE-SEM and HR-TEM). Study shows the formation of monodisperse Fe(3)O(4) nanoparticle having size approximately 20 nm coated with DPPC mono or multilayer. The overall study indicates that the formation as well as assembly of iron-oxide nanoparticle in two dimensions is possible using lipid monolayer as a template.
Abstract: The incorporation/entrapment of water-soluble surface-active enzyme, pepsin (PEP) within an insoluble cationic octadecylamine (ODA) monolayer is studied by Langmuir-Blodgett technique. The observation suggests that the incorporation of PEP is less preferable at compressed region (~30mN/m). The electrostatic interaction plays a significant role for the greater incorporation of PEP in cationic ODA monolayer. The surface pressure-area isotherms along with FE-SEM analysis indicates the squeezing out of PEP from the monolayer at higher surface pressure. This will assist to select the optimum surface pressure to obtain a good quality and well-ordered Langmuir monolayer. FTIR study of amide bands together with FE-SEM imaging of ODA-PEP mixed film indicates that ODA perturbs the PEP by the increment of beta-structure resulting into larger unfolding, intra, and intermolecular aggregates.
Abstract: In this article, we report the results of the extent of interaction as well as the formation of a bioconjugate of human hemoglobin (Hb) with silver (Ag). The complexation process and conformational changes are characterized using different spectroscopic and microscopic techniques. The UV-vis study demonstrates the perturbation of the soret/heme band and generates conformational heterogeneity within the heme group in the presence of silver. A fluorescence study suggests that the Tryptophan (Trp) residues of Hb are in a more polar environment after conjugation. Initial fluorescence enhancement with addition of silver is due to metal-enhanced fluorescence. Moreover, the fluorescence quenching after the formation of the Hb-Ag bioconjugate follows the modified Stern-Volmer (S-V) plot. The S-V plot along with the time-resolved fluorescence study indicates the presence of both static and dynamic types of quenching. In addition, the reduction potential values of the entities (Hb-heme, Ag(+), and Trp) indicate the possible electron transfer. The secondary structure calculation from CD and FTIR spectra indicate alpha-helix to beta-sheet conversion, and unfolding of Hb is also responsible for the bioconjugate formation. In addition, FE-SEM, phase contrast inverted microscopy (PCIM) images demonstrate the formation of the silver-protein bioconjugate. The overall data show that there is a change in the secondary as well as the tertiary structure of Hb after conjugation with silver.
Abstract: Tailor made synthesis of the isomeric azoaromatics, HL(1)-HL(4) [HL = (arylamino)phenylazopyridine] containing a single hydrophobic tail (C(n) = C(10) and C(12)) is described. The coordination induced C-N bond fusion synthetic protocol has been successfully used for the synthesis of the compounds, which are subsequently characterized using various spectroscopic techniques. The single crystal X-ray structure of compound HL(4) has revealed that the hydrophobic chain in it orients itself with all-trans conformation of alkyl groups. Studies of their surface properties clearly demonstrate that these behave as surfactants. Amphiphilic properties of the compounds are followed by the studies of compression isotherms and their surface morphologies are studied with the use of high resolution field emission scanning electron microscopy (FE-SEM) as well as atomic force microscopy (AFM). Distinct differences in surface properties in the two HL isomers are observed and disposition of the hydrophobic tail with respect to the head group is shown to play a significant role in the organization process of the molecules at the air-water interface. Transferred monolayers of the above two isomeric compounds show agglomerated nano-domain structures. This phenomenon has been explained considering hydrophobic tail-tail repulsive interaction within the adjacent molecules. Surface properties of the double tail complex, [Co(L(1))(2)]ClO(4) (1) along with that of the single tail complex, [Co(L(1))(L(5))]ClO(4) (3) are also reported. Amphiphilic behavior of the above azoaromatics are distinctly different than those in their metal free state. Notably, the double tail complex (1) favors bi-layer formation even at low surface pressure region (approximately 10 mN m(-1)). The single tail cobalt complex (3), on the other hand, forms a monolayer at high surface pressure region leading finally to the collapse at a very high pressure approximately 60 mN m(-1).
Abstract: The incorporation/entrapment of water-soluble surface-active enzyme, pepsin (PEP) within an insoluble cationic octadecylamine (ODA) monolayer is studied by Langmuir-Blodgett technique. The observation suggests that the incorporation of PEP is less preferable at compressed region (similar to 30 mN/m). The electrostatic interaction plays a significant role for the greater incorporation of PEP in cationic ODA monolayer. The surface pressure-area isotherms along with FE-SEM analysis indicates the squeezing out of PEP from the monolayer at higher surface pressure. This will assist to select the optimum surface pressure to obtain a good quality and well-ordered Langmuir monolayer. FTIR study of amide bands together with FE-SEM imaging of ODA-PEP mixed film indicates that ODA perturbs the PEP by the increment of beta-structure resulting into larger unfolding, intra, and intermolecular aggregates. (C) 2009 Elsevier B.V. All rights reserved.
Abstract: In this Article, we report the surface activity of the human globular blood protein, hemoglobin (Hb), at the air/water interface. The Langmuir-Blodgett technique is used for monolayer characterization. The adsorption growth-kinetics study shows that the adsorption process at the air/water interface is involved with two mechanisms: one diffusion with adsorption and the other rearrangement with unfolding. The kinetics is found to be dependent on pH and protein concentration in the subphase. The CD and FTIR studies suggest larger intermolecular aggregate and beta-sheet formation in the film lifted from the air/acidic water subphase. In alkaline pH and in isoelectric pH (6.8), not much variation is observed. The FE-SEM images support this observation. The acidic pH induced such conformational changes, and aggregation is explained with the argument of alpha-helix to beta-sheet conversion as well as the competition between protonation and deprotonation of the aromatic-amino acid residues at the air/water interface.
Abstract: The present work demonstrates the immobilization of phospholipids and phospholipids-protein vesicles on solid substrate by simple drop-cast technique. We have also studied the structural and conformational transition of protein (OVA) molecules when they are loaded in immobilized vesicles of DPPC. High-resolution FE-SEM imaging is used to study the structural aspects of the immobilized vesicles of DPPC and OVA loaded DPPC. FTIR analyses of amide bands are being used to inspect the extent of the conformational transitions of beta-sheet to a-helix of OVA in immobilized DPPC vesicles. Immobilized OVA-DPPC vesicles provide the structure of individual OVA molecule attached with DPPC, without aggregation amongst them. (C) 2008 Elsevier B.V. All rights reserved.
Abstract: We report here the effect of salt (KCl) on the interfacial surface activity of yeast alcohol dehydogenease (ADH) at air/water interface using the Langmuir-Blodgett technique. Effect of salt content in the water subphase on ADH structure has been studied. The change of area/molecule, compressibility, rigidity, and unfolding of ADH are insignificant up to 10 mM KCl concentration. The significant changes are observed above 0.1 M KCl concentrations. Observations are explained in the context of DLVO theory. FTIR study of amide band together with AFM imaging of ADH monolayer indicate that KCl perturbs the ADH monolayer by the increment of beta-structure resulting into larger unfolding and intermolecular aggregates at high salt concentration.
Abstract: This paper describes a new approach for the preparation of Ovalbumin (OVA)-phospholipids (DPPC) thin film, where we minimize the aggregation among protein molecules. A comparative study on the films fabricated by self-assembly (SA) of protein-lipid mixed vesicle on hydrophilic glass substrate and SA of protein alone on prefabricated Langmuir-Blodgett (LB) film of DPPC is being carried out. Far UV circular dichroism spectroscopy, FTIR analysis of amide bands and surface morphology study by FE-SEM imaging is being used to examine the extent of conformational change as well as aggregation of protein. Protein-lipid thin film prepared by the former method provides the secondary structure of individual OVA molecules with increment of alpha-helical segments. In this process, OVA molecules do not show larger aggregation among themselves. However, in the second method, we find unfolded larger aggregated structure of OVA with increment of beta-structure of OVA.
Abstract: We report herein the formation of pepsin monomolecular layer by the Langmuir-Blodgett film deposition technique. An effort was made to find an optimal subphase by adjusting the concentration of salt (KCl) and pH by monitoring the growth kinetics of pepsin for the formation of Langmuir monolayer by using as little as possible pepsin molecules to build up ultra thin film and to measure the extent of denaturation. Significant changes of area/molecule, compressibility, rigidity and unfolding of pepsin are observed at optimized subphase than pure water subphase. Observations at optimal subphase are explained in context of the modified DLVO theory and the site dissociation model. FTIR analysis of amide band together with the observed surface morphology of pepsin film in FE-SEM images indicate that at optimal subphase the pepsin molecules modify their structures by incrementing the beta-structure, resulting into larger unfolding and inter-molecular aggregates.
Abstract: Langmuir-Blodgett (LB) films of 4-methyl 3-phenyl coumarin (MPC), a non-amphiphilic derivative of coumarin mixed with stearic acid (SA) are studied. The surface pressure-area (pi-A) isotherm study at air-water interface reveals a repulsive type of interaction between the MPC and SA molecules resulting in the formation of aggregates of MPC molecules. Absorption, fluorescence and phosphorescence studies indicate the formation of J-type aggregate in LB film. Low temperature (77 K) phosphorescence lifetime is found to be decreased due to aggregate formation. Micro structured aggregates are observed after examining the surface morphology of LB film by scanning electron microscopy (SEM). (c) 2007 Elsevier B.V. All rights reserved.
Abstract: In this communication we demonstrated the incorporation of water-soluble surface-active protein OVA within an insoluble cationic ODA monolayer and compared with zwitterionic (DPPC) and anionic (SA) monolayer. The incorporation of OVA is found to be more in ODA as compared to that of DPPC and SA. The kinetics of protein adsorption in lipid monolayer gives the idea that unfolding of OVA is less in case of DPPC than SA and ODA. The pi-A isotherm and compressibility study gives the information about the different states of the protein-lipid mixed monolayer. At higher pressure, OVA tend to squeeze out from the lipids monolayer. High-resolution field emission scanning electron microscope (FE-SEM) images confirm this observation. The surface morphology of DPPC-OVA LB film is far better than ODA-OVA and SA-OVA LB film. OVA forms large irregular aggregates on SA and ODA monolayer. Fluorescence study reveals that protein structure is perturbed more in SA and ODA system compared to that of DPPC. The overall results indicate that DPPC monolayer is better to get protein lipid mixed film than SA and ODA monolayer.
Abstract: In this communication, the surface activity of the ovalbumin (OVA) at the air/water interface was studied to establish the nature of the interaction with the stearic acid (SA) monolayer, based on Langmuir-Blodgett (LB) technique. The interaction was monitored by studying the time (t) variation of surface pressure (pi) at constant area (A). The growth of pi with time indicates a positive association between the SA and the OVA molecules. The surface compressibility analysis has been performed to specify the phase transition of OVA-SA mixed monolayer. Incorporation/association of OVA within the SA monolayer led to noteworthy changes in surface compressibility and was surface pressure as well as protein concentration dependent. Both the hydrophobic and the Vander wall type interactions are found to be responsible for the association. The quenching of tyrosine band in tryptophan excitation spectrum is observed in steady-state fluorescence spectroscopy. This suggests that the tyrosine is the probable binding site with SA. Due to incorporation of SA, the energy transfer from tyrosine to tryptophan is hindered. At higher pressure, OVA tend to squeeze out from the SA monolayer. The high-resolution field emission scanning electron microscope (FE-SEM) image confirms this observation. Aggregated protein structure observed at high pressure indicates unfolding of protein.
Abstract: Interaction of native ovalbumin (OVA) with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) Langmuir-Blodgett monolayer has been studied at the air-water interface. A compressibility study shows the positive association with DPPC. Adsorption kinetics shows that the protein adsorption is a one-step process and the amount of protein adsorbed depends on the concentration of protein at the water subphase. Incorporation of protein into the DPPC layer is surface-pressure dependent. The compressibility study indicates that the DPPC-OVA interaction is hydrophobic in nature and structural reorganization is eminent to adjust the hydrophobic mismatch between DPPC acyl chains and OVA hydrophobic moieties. At higher pressure, OVA tends to squeeze out from the DPPC monolayer. A nanometer scale FE-SEM image confirms this observation. Globular aggregates of protein of dimension 60-80 nm were observed in DPPC-OVA supported film. Steady-state fluorescence spectroscopy suggests that the tryptophan residues of OVA are main emitting species. The blue shift of tryptophan fluorescence in supported film may be due to the tryptophan molecule of protein exposed to the hydrophobic air phase.
Abstract: The adsorption of biologically important Rhodamine 123 molecule on silver colloids has been investigated by Surface enhanced resonance Raman scattering (SERRS) spectroscopy. The SERRS spectra are compared with its FTIR spectrum and normal Raman spectrum (NRS) in solution. The optimized structural parameters and computed vibrational wavenumbers have been estimated from ab initio (Hatree-Fock) and density functional theory (DFT) calculations. Some vibrational modes have been reassigned. From frontier orbital theory, the direction of charge transfer (CT) mechanism is concluded. (C) 2006 Elsevier B.V All rights reserved.
Abstract: A new technique has been developed to make Langmuir-Blodgett films (LB) on solid substrate containing silver nano-particle clusters. It is based on electrostatic attraction between negatively charged acid groups of stearic acid and positively charged silver nano-particles in silver sol. TEM picture shows that the cluster growth is fractal in nature of dimensions ranging from 1.4 to 1.8 depending on the growth time. After sufficient time of immersion in silver sol, the fractal structure is transformed to lumpy structures. Possible reasons for the formation of silver nano-cluster in LB film are discussed. (C) 2004 Elsevier B.V. All rights reserved.
Abstract: A Monte Carlo method has been employed to simulate electroluminescence (EL) from organic light-emitting devices (LEDs) under an alternating applied field. EL responses under forward and reverse bias modes have been simulated with different experimental parameters. Dependences of EL on the frequency of an applied field, electrode work function, band gap and film thickness of the active organic material, etc., have been studied. The origin of EL under alternating current (ac) mode has been explained in terms of radiative recombination of excitons formed via injected holes and electrons present from the previous cycle of ac voltage. The time response of EL intensity and its profile during forward and reverse bias half-cycles has been found to depend on carrier injection and also on their temporal and spatial distribution along the thickness of the emitting material. Efforts have been made to match a simulated EL response with representative experimental results. The Monte Carlo simulation results presented here provides a way to select certain parameters to fabricate efficient ac LEDs. (C) 2003 American Institute of Physics.
Abstract: Surface-enhanced Raman spectra (SERS) of 5,10,15,20-tetrakis(1-decylpyridium-4-yl)-21H,23H-porphintetrabromide or Por 10 (H(2)Tdpyp) adsorbed on silver hydrosols are compared with the FTIR and resonance Raman spectrum (RRS) in the bulk and in solution. Comparative analysis of the RR and the FTIR spectra indicate that the molecule, in its free state, has D(2h) symmetry rather than C(2v). The SERS spectra, obtained on adsorption of this molecule on borohydride-reduced silver sol, indicate the formation of silver porphyrin. With the change in the adsorbate concentration, the SERS shows that the molecule changes its orientation on the colloidal silver surface. The appearance of longer wavelength band in the electronic absorption spectra of the sol has been attributed to the coagulation of colloidal silver particles in the sol. The long wavelength band is found to be red-shifted with the decrease in adsorbate concentration. The excitation profile study indicates that the resonance of the Raman excitation radiation with the original sol band is more important than that with the new aggregation band for the SERS activity. This indicates a large contribution of electromagnetic effect to surface enhancement.
Abstract: Surface-enhanced Raman scattering(SERS) of the Rhodamine 123 (Rh 123) molecule on ion-induced silver colloids has been studied. A time-dependent study of the SER spectra at a particular pH confirms charge transfer interaction between the probe molecule and the metal. The SER spectra of Rh 123 in Ag sol is compared with that of the molecules organized in a monolayer on silver island films by the Langmuir-Blodgett (LB) technique. The origin of high SERS activity of Rh 123 molecules in a monolayer on a silver island film is shown to be due to physisorption whereas in the ion-induced colloidal SERS both physisorption and chemisorption machanisms are involved. From these results, the contribution of charge transfer interaction to SERS in Ag sol has been estimated. In monolayer SERS, all the in-plane and out-of-plane (of xanthene ring) modes are more or less equally enhanced. This indicates that the xanthene plane of Rh 123 molecule organized in a LB film is oriented neither flat nor perpendicular to the silver island surface but is tilted. Copyright 2001 Academic Press.
Abstract: We have fabricated light-emitting devices based on alizarin violet. Transient responses of such devices have been studied by applying a sequence of two square-wave voltage pulses. Concentration of the active material in the emitting layer, and the amplitude of the voltage pulse have been varied to study the affects of space-charges in device operation. The devices have been operated under CW and pulsed modes. Current-voltage and luminance-current characteristics under two such modes have been compared. The rise in device temperature under CW mode has been estimated from the ratio of current densities in the two modes. Higher temperature under CW mode has resulted in lower luminance as compared to pulsed mode. (C) 2001 Kluwer Academic Publishers. %> internal-pdf://(2001)_J.Mat.Sci.Mat.inElectronics _12_37-40-0019917824/(2001)_J.Mat.Sci.Mat.inElectronics _12_37-40.pdf
Abstract: Poly o-methoxyaniline (POMA) has been successfully organized in LB films. UV-Vis absorption spectroscopy shows that as-prepared LB film is partially protonated and can be easily deprotonated and reprotonated by alkali and acid treatment respectively. Normal Raman spectrum (NRS), surface enhanced Raman spectrum (SERS) of POMA in LB film on silver islands and tentative assignment of the relevant Raman bands for POMA characterisation are reported. Three orders of magnitude enhancement in Raman intensity has been observed in SERS compared to that in NRS. Layer effect study showed maximum enhancement in a two-layered LB film suggesting the presence of voids in the monolayer film. Surface plasmon resonance is found to be the dominant factor for enhancement. SERS study reveals that in the LB film the organisation of POMA is such that the quinoid ring is out of the plane and the benzoid ring is in the plane of the film surface.
Abstract: Light-emitting diodes based on the molecularly thin him of a porphyrin derivative have been fabricated. Langmuir-Blodgett (LB) films at two different surface pressures have been used as active materials of the device and their characteristics have been studied and compared. Devices with LB films deposited at a higher pressure show rectifying behaviour and electroluminescence (EL) was observed only in the forward bias. The other type of devices with LB films deposited at a lower pressure, yields EL in both bias directions. The effect of thickness of the active layers has been investigated. The turn-on currents for both the cases have also been compared. (C) 1998 Elsevier Science Ltd. All rights reserved. %> internal-pdf://(1998)_SSC_10_7725-7729-1901778689/(1998)_SSC_10_7725-7729.pdf
Abstract: The spectroscopic and photophysical characterization of rhodamine 123 (dye 1), 4,5-dibromorhodamine methyl ester (dye 2) and 4,5-dibromorhodamine n-butyl ester (dye 3) are reported in homogeneous media like water and some alcohols and also in microheterogeneous media; anionic sodium dodecylsulfate (SDS), cationic cetyltrimethylammonium bromide (CTAB) and neutral triton X-100 (TX) micelles. The selective biodistribution of these ionic drugs in tissues and membranes strongly influence their photosensitizing properties which have been part of our earlier studies, Results suggest that the hydrogen bonding capability of the amino end group lone pair of these dyes dominates in water. All these dyes interact with anionic SDS micelles, The interaction is mainly electrostatic in nature. At low SDS concentrations (below c.m.c,), dye-SDS aggregate formation takes place, But above c.m.c, only the monomeric dye form is observed. The penetration of dye 3 in SDS is a little less compared to dyes 1 and 2, Dyes 2 and 3 show a finite interaction with CTAB micelle unlike dye 1, With neutral TX micelles all the dyes form strong complexes. The fluorescence quantum yield (Phi(F)) of these three dyes in TX is lower. In time-resolved fluorescence experiments, two lifetimes are observed. The effects of the TX concentration on the fluorescence decay are measured. The decay associated spectra of dye 2 in TX are obtained by global compartmental analysis, The dye-surfactant interaction mechanisms are also discussed.
Abstract: The synthesis of some bromine-substituted rhodamine derivatives viz., 4,5-dibromorhodamine methyl ester (dye 2) and 4,5-dibromorhodamine n-butyl ester (dye 3) are reported. These dyes were synthesized to promote a more efficient cancer cell photosensitizer for potential use in in vitro bone marrow purging in preparation for autologous bone marrow transplantation. Spectroscopic and photophysical characterization of these dyes together with rhodamine 123 (dye 1) are reported in water, methanol, ethanol and also in a microheterogeneous system, sodium dodecyl sulfate. The possible mechanism of photosensitization is characterized in terms of singlet oxygen efficiency of these dyes. Singlet oxygen quantum yields for bromine-substituted dyes are in the range of 0.3-0.5 depending on the solvent. For dye 1 no singlet oxygen production is found. The photodynamic actions of these dyes in different cell lines are tested. It was found that dye 2 and dye 3 are efficient photosensitizers and mediate eradication of K562, EM2, myeloid cell lines (CML) and the SMF-AI rhabdomyosarcoma line.
Abstract: Steady state and time-resolved fluorescence spectroscopy were employed to study the fluorescence from non-metastatic, metastatic and non-tumorigenic cell lines from different species. Excitations at 310 nm and 350 nm were used to monitor tryptophan and reduced nicotinamide adenine dinucleotide (NADH) fluorescence respectively. Subtle and consistent differences were observed between different categories of cell lines. It was found that the tryptophan to NADH fluorescence intensity ratio is higher in metastatic cell lines than in non-metastatic and normal cell lines. The fluorescence decay of the tryptophan residue in different cell lines was best described by triple exponential kinetics, whereas the NADH fluorescence decay was best described by mainly double and, in some cases, triple exponential kinetics. The average fluorescence lifetimes for tryptophan were in the range 2.5-3.7 ns. The average lifetime of NADH was lower (by a factor of approximately three) in metastatic cells than in non-metastatic cells and this finding is consistent for cell lines from different origins (rat or human). Correcting the fluorescence intensity for the average fluorescence lifetime of each species and for the volume of each cell line, it was shown that the concentrations of tryptophan and NADH are consistently higher in malignant metastatic cancer cells than in non-metastatic cells.
Abstract: Photo- and dark conduction in alpha-sexithienyl (alpha-6T) is studied as a function of applied voltage and temperature. The results suggest that a single discrete trapping level is involved in the conduction process. From this study some transport parameters are evaluated. The dependence of photocurrent on light intensity indicates that the carrier generation process is a one photon process and is trap limited. With increase of excitation light intensity, the recombination process changes from bimolecular to monomolecular. The dependence of the photocurrent on wavelength indicates that the carrier generation process is extrinsic in nature and that surface recombination is high for holes.
Abstract: Dark and photoconductive properties of alpha-omega-di-2-naphthyl polyenes were studied at different applied voltages and temperatures. These studies indicate that a single dominant trapping level is involved in both conduction processes. From this study some transport parameters are evaluated. Dependence of photocurrent on excitation light intensity indicates that the carrier generation process is a one-photon process and is trap-limited. The photocurrent decay study indicates that most of the photocarriers decay exponentially with time. Trap depths are calculated from the temperature dependence of decay constant and is found to be the same as that obtained from thermally stimulated current. The dependence of photocurrent on wavelength indicates two mechanisms of photocarrier generation process: one is excitonic and the other is intrinsic electron-hole pair production.
Abstract: The miscibility of crocetindialdehyde (CDA) and stearic acid (SA) in air-water subphase has been studied from the surface pressure-area isotherms by using the surface phase rule and excess area criterion. Positive deviation from the additivity rule and positive values of Gibb's free energy indicate strong repulsive interaction between CDA and SA molecules. This repulsive interaction may facilitate aggregate formation of CDA in air-water subphase. CDA has been incorporated into Langmuir-Blodgett (LB) films when mixed with SA. Absorption and emission spectra of CDA have been studied in solution, in LB films, and in an ethanol-water mixture. The resemblence between the absorption spectrum of CDA in a ethanol-water mixture and in LB film supports aggregate formation of CDA. Dual fluorescence of CDA has been observed in solution and in LB films and for the first time in an organized molecular layer of a carotenoid. A comparison of emission and absorption spectra of CDA in solution and in LB films confirms formation of aggregates in LB films. The aggregate formation of carotenoids has been discussed in the framework of possible self-organization in biological membranes.
Abstract: The absorption, emission and excitation spectra of crocetin dialdehyde (CDA) were obtained in solution and in Langmuir-Blodgett (LB) films. Dual fluorescence was observed in both cases and, for the first time, in an organized molecular layer of a carotenoid. Comparison of the emission and absorption spectra in solution and LB films suggests the formation of aggregates in LB films. The observation of dual emission and the shift in the excited states in carotenoid LB films are discussed with particular relevance to the possible self-organization in photosynthetic light-harvesting antennae.
Abstract: A stable monolayer of alcohol dehydrogenase (ADH) enzyme has been prepared by spreading an aqueous solution of ADH on a water subphase containing stearic acid monolayer. This ADH-stearic acid monolayer has been successfully transferred onto a conducting polypyrrole-coated glass electrode by the Langmuir-Blodgett (LB) technique. ADH catalyses the reaction between the coenzyme beta-NAD + (beta form of oxidized nicotinamide adenine dinucleotide) and ethanol to produce NADH and acetaldehyde. Conducting polypyrrole acts as a mediator for transferring electrons produced on NADH oxidation. This LB-immobilized polypyrrole-mediated enzyme electrode can be used as an ethanol sensor. It shows better sensitivity than sensors consisting of ADH immobilized by chemical cross-linking with glutaraldehyde. This LB sensor can be used for low ethanol concentration (in the micro-molar range).
Abstract: The conjugated polyenes beta-carotene, lutein, retinoic acid and beta-apo-8'-carotenal are shown to form charge-transfer (CT) complexes with the electron acceptor iodine. The conductivity increases by several orders of magnitude and the activation energy decreases on CT complex formation. Using these complexes as cathodic material, batteries with the configuration Mg/(polyene iodine CT complex)/graphite are developed. Different battery parameters are evaluated. The effects of ambient temperature and humidity on battery performance are also studied. Results show that a beta-apo-8'-carotenal-I2 based battery has the maximum power density and longest self-life and is suitable for use as a micro-electronic gadget energizer.
Abstract: Spectroscopic evidence has been provided to confirm that zeaxanthin, lutein and fucoxanthin form molecular charge-transfer (CT) complexes with iodine in the solid state. The semiconductive and photoconductive properties of CT complexes have been investigated in polycrystals in a sandwich cell configuration. Both dark and photoconductivity increases by several orders of magnitude on complex formation. The identical values of thermal activation energies for dark and photoconduction have been obtained for the complexes and this has been attributed to spontaneous carrier generation by CT interaction and their migration by trapping and detrapping mechanisms. Photoconduction action spectra in pure polyene and in polyene-iodine complex suggest that photoinjection from the electrode and direct electron hole pair production are the two photocarrier generation mechanisms operative in these crystals. The second mechanism predominates in pure materials whereas the first one becomes important in the complexes.
Abstract: Photoconductive properties of polyenes have been studied. The results suggest that a single descrete trapping level is involved in carrier generation. SCLC theory has been used to evaluate various transport parameters. Polyenes behave as a non-extrinsic material for dark conduction but for photoconduction these become extrinsic. The light intensity dependence suggests that carrier generation is one-photon process and is trap limited. The photoconduction action spectrum suggests two distinct mechanisms of photocarrier generation, one through photoinjection from the illuminated electrode and the other through direct electron-hole pair production.
Abstract: Both the dark- and photo-current-voltage characteristics of zeaxanthin and lutein is ohmic in the lower field regime followed by non-ohmic behaviour in the higher voltage regime, which has been satisfactorily explained by the anomalous Poole-Frenkel effect. A single dominant donor level is the major contributor to the dark-current while a single dominant trap level is the major contributor to the photo-current, both levels have been identified from Arrhenius type plots. Photo-action spectra suggest that the predominant mechanism of charge carrier generation is the same both in dark and illuminated conditions.
Abstract: The photoconductivity decay in a number of polyene crystals has been studied. Two photocarrier decay mechanisms have been observed. A fast decay has been observed in a short time domain whereas in a longer time domain, a slow decay is manifested. Most of the photocurrent decays in the shorter time domain. The decay in the shorter time domain is dominant shallow trap limited, and the trap depth has been obtained from the activation energy of mean decay time, tau-0. Field and temperature dependence studies in the longer time domain reveal the existence of additional traps distributed exponentially in some polyenes. T(c), the exponential trap distribution parameter, changes with applied field, but there is no appreciable change with sample temperature. Field effect on T(c) has been attributed to the field effect on its trapping rate.
Abstract: The presence of various adsorbed gases increases the semiconduction current of carotenoids. Among different carotenoids crocetin is the most sensitive sensor for ethanol vapour. A thin film surface cell shows faster response and recovery. A very high photoconductive response is obtained for crocetinal-dehyde and can be used for optical switching devices. Carotenoids are capable of forming a charge-transfer complex with iodine. About seven order of current enhancement is observed for lycopene-iodine CT complex. A Mg/lycopene-iodine CT complex/C solid state battery is developed. Battery parameters indicate its applicability for a microgadget energizer.
Abstract: The energy distribution of gap states in methylbixin crystallites has been investigated by photoconductivity decay measurements. The results show that the shallow states decrease exponentially with characteristic temperature T//c approximately 900 K at an applied field of 1. 77 multiplied by 10**3 V/cm. T//c is independent of sample temperature but depends inversely on applied field. It is suggested that field effect on T//c may arise from the field effect on trapping rate.
Notes: Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap.
Abstract: An apparatus for irradiating a biological substance with a substantially uniform quantity of radiation energy comprises a radiation-generating device for producing radiation energy, a support structure for receiving the biological substance, and a ...
Notes: Patent record available from the US Patent Office
