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In aqueous solution, 2-(4-fluorophenylamino)-5-(2,4-dihydroxybenzeno)-1,3,4-thiadiazole (FABT) was found to emit dual emission and the longer wavelength emission was assigned to the combination of aggregation and conformational change. In a number of molecules that possess an intramolecular hydrogen bond between the proton donor and the acceptor, the longer wavelength emission is often observed due to the emission from the tautomer formed by excited state intramolecular proton transfer (ESIPT). Therefore, an analogue of FABT, 2-phenylamino-5-(2-hydroxybenzono)-1,3,4-thiadiazole (PHBT), was synthesized to determine the origin of the longer wavelength emission. The luminescence of PHBT and its methoxy derivatives was studied and compared with that of FABT. Theoretical calculations were also performed on both FABT and PHBT. Based on the experimental and theoretical investigations, the nonexistence of the keto tautomer in the ground state and the origin of the longer wavelength emission are divulged.

In this study, the aggregation induced emission enhancement (AIEE) of 2-(2'-hydroxyphenyl)benzimidazole (HPBI) is reported. To investigate the AIEE process of HPBI, absorption/fluorescence spectroscopy, fluorescence imaging and field emission scanning electron microscopy were employed. A comparative study with 2-phenylbenzimidazole (PBI) divulges the significance of the hydroxyl group in the AIEE process. Further, molecular dynamics simulations have been carried out with explicit solvent molecules to follow the aggregation process of HPBI with time. The obtained molecular dynamics simulation results not only predicted the formation of aggregates but also provided detailed insight and information on the molecular interactions. The cellular studies showed aggregates yield higher fluorescence in the visible region inside HeLa cells in comparison to monomeric compounds which failed to exhibit any visible fluorescence inside the cell. The obtained aggregates were further found to be biocompatible and therefore can be used for bio-imaging applications.

The mechanism for the dual emission of 2-(4'-N,N-dimethylaminophenyl)imidazo[4,5-c]pyridine (DMAPIP-c) in protic solvents was investigated by synthesizing and studying its analogues. Theoretical calculations were carried out to corroborate the experimental findings. The deprotonation studies suggest that the enhancement in the TICT emission of anionic forms of DMAPIP-c is limited to a protic environment. The spectral characteristics of DMAPIP-c were also studied in a methanol-acetonitrile binary solvent mixture. Unlike DMAPIP-c, the methyl derivatives do not emit dual fluorescence in protic solvents. The relative intensity of the TICT emission (with respect to that of normal emission) rises with the methanol amount in the acetonitrile-methanol binary solvent mixture. The studies also show that a 1:3 hydrogen bonded complex is formed between DMAPIP-c and methanol and it is responsible for the TICT emission. Based on the results a relay proton transfer tiggered TICT emission is proposed. TDDFT calculations were performed to predict the emission energies.

The spectral characteristics of trans-2-[4'-(N,N-dimethylamino)styryl]imidazo[4,5-b]pyridine (t-DMASIP-b) have been investigated using absorption and fluorescence techniques, and compared with 2-(4'-N,N-dimethylamino)imidazo[4,5-b]pyridine (DMAPIP-b). The study reveals that introduction of a C[double bond, length as m-dash]C double bond strongly perturbs the photophysics of the system. Unlike DMAPIP-b, t-DMASIP-b emits a single emission in aprotic and protic solvents. The emission occurs from the locally excited state in nonpolar solvents and from a planar intramolecular charge transfer (PICT) state in polar solvents. Multiple linear regression analysis suggests that among the different solvent parameters, the dipolar interaction contributes more to the stabilization of the system in both the ground and excited states. Theoretical calculations suggest that, unlike in DMAPIP-b, proton coupled twisted intramolecular charge transfer (TICT) emission does not occur in t-DMASIP-b. The higher quantum yield obtained in the viscous solvent glycerol is attributed to the restriction of the twisting of the olefinic bond. The photoirradiation of t-DMASIP-b shows that isomerization takes place in all solvents, including viscous glycerol. The theoretically simulated potential energy surface shows that isomerization occurs via a phantom state, which is a nonradiative process. The rise in temperature favors the photoisomerization, thus, the fluorescence quantum yield decreases. The prototropic study indicates that, unlike in DMAPIP-b, the protonation takes place at different places to form the monocations.

Click chemistry approaches are tailored to generate molecular building blocks quickly and reliably by joining small units together selectively and covalently, stably and irreversibly. The vegetable tannins such as hydrolyzable and condensed tannins are capable to produce rather stable radicals or inhibit the progress of radicals and are prone to oxidations such as photo and auto-oxidation, and their anti-oxidant nature is well known. A lot remains to be done to understand the extent of the variation of leather stability, color variation (lightening and darkening reaction of leather), and poor resistance to water uptake for prolonged periods. In the present study, we have reported click chemistry approaches to accelerated vegetable tanning processes based on periodates catalyzed formation of oxidized hydrolysable and condensed tannins for high exhaustion with improved properties. The distribution of oxidized vegetable tannin, the thermal stability such as shrinkage temperature (T s) and denaturation temperature (T d), resistance to collagenolytic activities, and organoleptic properties of tanned leather as well as the evaluations of eco-friendly characteristics were investigated. Scanning electron microscopic analysis indicates the cross section of tightness of the leather. Differential scanning calorimetric analysis shows that the T d of leather is more than that of vegetable tanned or equal to aldehyde tanned one. The leathers exhibited fullness, softness, good color, and general appearance when compared to non-oxidized vegetable tannin. The developed process benefits from significant reduction in total solids and better biodegradability in the effluent, compared to non-oxidized vegetable tannins.

The interaction of 2-(2'-hydroxyphenyl)benzimidazole (HPBI) and its nitrogen substituted analogues 2-(2'-hydroxyphenyl)-3H-imidazo[4,5-b]pyridine (HPIP-b) and 2-(2'-hydroxyphenyl)-1H-imidazo-[4,5-c]pyridine (HPIP-c) with BSA was explored. Upon interaction with BSA both normal and tautomer emissions are significantly enhanced. However, the fluorescence ratios of the normal band to the tautomer band of HPBI and HPIP-b decrease, but that of HPIP-c increases. From the tautomer emission, the stoichiometry and association constants were determined. HPBI exists as cis- and trans-enolic and zwitterionic forms, whereas HPIP-b and HPIP-c are present as monoanions in addition to cis- and trans-enols. The study shows that different conformers of all three molecules bind at different binding sites of BSA.

The aim of the study was to evaluate the androgen (AR) and estrogen receptors' (ER) expression in epididymis of polychlorinated biphenyls (PCBs)-exposed rats. The rats were assigned to groups. Group I controls were treated with corn oil 80 µL/d intraperitoneally (ip), group II were treated with 2 mg/kg/d of A1254 ip; and group III were treated with 2 mg/kg/d of A1254 ip along with simultaneous oral supplementation of 4 mg/kg/d lycopene . The treatment was given daily for 30 days. After 24 hours of treatment, the rats were killed, and the epididymal regions (caput, corpus, and cauda) were dissected out, weighed, and prepared to estimate the levels of sialic acid, glyceryl phosphoryl choline (GPC), hydrogen peroxide (H2O2), and lipid peroxidation (LPO). The messenger RNA (mRNA) expressions of AR, ERα, and ERβ were analyzed by reverse transcriptase-polymerase chain reaction, and ERα and ERβ protein expressions were analyzed by immunoblotting. The toxicity of PCBs was also confirmed by histology. There was a marked decrease in epididymal weight, sialic acid, and GPC levels, while oxidative stress markers H2O2 and LPO were increased in PCBs-treated rats. The mRNA and protein expression of AR, ERα, and ERβ were decreased in PCBs-treated groups, and the histology confirms the cytoplasmic damage in the regions of caput, corpus, and cauda in PCBs-treated rats. Simultaneous supplementation of lycopene to PCBs-exposed rats resulted in significant decrease in the oxidative stress markers as that of control, while the AR, ERα, and ERβ gene expressions were near to control. The results suggest that lycopene has ameliorative effect against PCBs-induced toxicity in epididymis.

The spectral characteristics of 2-(4'-N,N-dimethylaminophenyl)oxazolo[4,5-b]pyridine (DMAPOP) have been investigated in solvents of different polarity and hydrogen bonding capacity. Unlike its imidazole analogue, DMAPOP emits single emission in both aprotic and protic solvents and the hydrogen-bond induced TICT emission is not observed in any protic solvents. The solvent effect on both absorption and the emission spectral data are analyzed by multiple parametric regression analysis. The prototropic studies reveal that two kinds of monocations are formed by protonation of pyridine nitrogen (MC1) and the dimethylamino nitrogen (MC3) in both ground and excited states. However three kinds of dications are formed by protonation of pyridine and oxazole nitrogens (DC1), pyridine and dimethylamino nitrogens (DC2), and dimethylamino and oxazole nitrogens (DC3).

Polychlorinated biphenyls (PCBs) exposure produces profound damage to the developing as well as adult central nervous system. Locomotor activities which are closely linked to dopaminergic neurotransmission are often impaired in PCBs toxicity. Targeting PCBs-induced oxidative stress using natural antioxidants is an attractive approach. Quercetin, a flavonoid is a safe and potent neuroprotective antioxidant. In this study, we sought to examine the protective role of quercetin against PCBs-induced neurodegeneration and dysfunction of dopaminergic receptors in the cerebellar region of adult male rats. They were divided into four groups. Group I received only vehicle (corn oil) intraperitoneally (i.p); Group II received Aroclor 1254 at a dose of 2 mg/kg bwt/day (i.p); Group III received Aroclor 1254 (i.p) and simultaneously quercetin (50 mg/kg bwt/day) through gavage; Group IV received quercetin alone (gavage). After 30 days treatment, rats were euthanized. The cerebellum was dissected from each rat brain, the levels of hydrogen peroxide, lipid peroxidation, protein carbonyl content, and activities of creatine kinase, acetylcholine esterase, membrane-bound ATPases were evaluated. Expressions of dopaminergic receptors and tyrosine hydroxylase in cerebellum were studied by semi-quantitative RT-PCR and western blot analysis, respectively. The PCBs-induced neurodegeneration was assessed by histological studies. Results proclaim that PCBs disturb dopaminergic receptors and also causes neurodegeneration in cerebellum via production of ROS. Simultaneous quercetin treatment had scavenged the free radicals induced by PCBs and protected dopaminergic receptors dysfunction in rat cerebellum.

The N-alkylated products of 2-(4'-N,N-dimethylaminophenyl)imidazo[4,5-b]pyridine (DMAPIP-b) were synthesized to study the effect of long alkyl chains on the photophysics of the fluorophore. Two different compounds were synthesized: in molecule 1, the alkyl chain was attached to the pyridine nitrogen of DMAPIP-b and in molecule 2 the alkyl chain was substituted on the imidazole nitrogen of DMAPIP-b. Absorption, steady state and time-resolved fluorescence techniques were employed to investigate the spectral properties in different solvents. Density functional theory (DFT) and restricted configuration by singles (CIS) combined with time-dependent DFT (TDDFT) calculations were performed on the ground state and the excited state respectively to calculate the geometrical and the electronic properties of the molecules. Unlike DMAPIP-b, where dual emission was observed in protic solvents, which originates from both a locally excited state and an intramolecular charge transfer (ICT) state, the pyridine nitrogen alkylated product (1) emits a single emission from the ICT state and the imizadole nitrogen alkylated molecule (2) emits dual emission only in methanol and water.

The effect of beta-cyclodextrin (beta-CD) inclusion complex formation on the hydrogen bond-induced intramolecular charge transfer (ICT) of 2-(4'-N,N-dimethylamino)phenylimidazo[4,5-b]pyridine (DMAPIP-b) has been examined by fluorescence excitation, emission and time-resolved fluorescence techniques. The study reveals that DMAPIP-b forms 1 : 1 inclusion complex with beta-CD. The host-guest complex is formed by partial inclusion of DMAPIP-b, i.e. only the dimethylaminophenyl ring is encapsulated inside the core of the beta-CD nanocavity. The imidazopyridine ring of the guest molecule resides outside CD cavity and forms H-bonds with the water molecules that are present near the rim and in the bulk phase. (1)H NMR studies are used to confirm the inclusion complex. The H-bond of water with the pyridine nitrogen ensures the formation of the ICT state and both normal and ICT emissions are enhanced inside the beta-CD cavity. Fluorescence lifetime measurements suggest that the formation of the ICT state from the locally excited state is irreversible. Dual emission is observed in the presence of beta-CD at pH approximately 3.5, due to emission from monocations formed by the protonation of pyridine nitrogen (MC1) and imidazole nitrogen (MC2).

Prostate cancer is a leading cause of death among the aging men. Surgical or radiotherapy is effective when the cancer is confined to the prostate gland but once the cancer spreads beyond the pelvis even chemotherapy and hormonal ablation therapy fails in curing this disease. Our previous studies have shown that diallyl disulfide (DADS) induces cell cycle arrest and also induces apoptosis in PC-3 cells. And now the present study is focused to see whether there is an activation of caspase cascade pathway. Hence, in the present study the apoptotic effect of DADS is studied by Western blot analysis of caspase-3, -9, -10 and Bcl-2, Bad, and Bax protein. The Apoptotic cells were assessed by Hoechst 33342 staining with 25 and 40 microM concentrations of DADS for 24 h. The results have shown that DADS at 25 and 40 microM concentrations has induced the activation of caspases. There is a significant increase in the expression of caspases (3, 9, and 10). The proapoptotic protein Bax has significantly increased at 40 microM of DADS treatment and there is significant increase of Bad protein at both the concentration. Bcl-2 protein has significantly decreased in DADS treated cells. Therefore, the present investigation serves as evidence that DADS may be a therapeutic drug in the treatment of prostate cancer.

The [2Fe-2S] ferredoxin from the extreme haloarchaeon Halobacterium salinarum is stable in high (>1.5 M) salt concentration. At low salt concentration the protein exhibits partial unfolding. The kinetics of unfolding was studied in low salt and in presence of urea in order to investigate the role of salt ions on the stability of the protein. The urea dependent unfolding, monitored by fluorescence of the tryptophan residues and circular dichroism, suggests that the native protein is stable at neutral pH, is destabilized in both acidic and alkaline environment, and involves the formation of kinetic intermediate(s). In contrast, the unfolding kinetics in low salt exhibits enhanced rate of unfolding with increase in pH value and is a two state process without the formation of intermediate. The unfolding at neutral pH is salt concentration dependent and occurs in two stages. The first stage, involves an initial fast phase (indicative of the formation of a hydrophobic collapsed state) followed by a relatively slow phase, and is dependent on the type of cation and anion. The second stage is considerably slower, proceeds with an increase in fluorescence intensity and is largely independent of the nature of salt. Our results thus show that the native form of the haloarchaeal ferredoxin (in high salt concentration) unfolds in low salt concentration through an apparently hydrophobic collapsed form, which leads to a kinetic intermediate. This intermediate then unfolds further to the low salt form of the protein.

Background: Cancer metastasis, involving multiple processes and various cytophysiological changes, is a primary cause of cancer death and may complicate the clinical management, even lead to death. Quercetin is a flavonoid and widely used as an antioxidant and recent studies have revealed its pleiotropic anticancer and antiproliferative capabilities. Gelatinases A and B (matrixmetalloproteinases 2 and 9) are enzymes known to involve in tumor invasion and metastases. In this study, we observed the precise involvement of quercetin role on these proteinases expression and activity., Design and Methods: PC-3 cells were treated with quercetin at various concentrations (50 and 100 microM), for 24 h period and then subjected to western blot analysis to investigate the impact of quercetin on matrix metalloproteinase-2 (MMP-2) and 9 (MMP-9) expressions. Conditioned medium and cell lysate of quercetin-treated PC-3 cells were subjected to western blot analysis for proteins expression of MMP-2 and MMP-9. Gelatin zymography was also performed in quercetin treated PC-3 cells., Results: The results showed that quercetin treatment decreased the expressions of MMP-2 and MMP-9 in dose-dependent manner. The level of pro-MMP-9 was found to be high in the 100 microM quercetin-treated cell lysate of PC-3 cells, suggesting inhibitory role of quercetin on pro-MMP-9 activation. Gelatin zymography study also showed the decreased activities of MMP-2 and MMP-9 in quercetin treated cells., Conclusion: Hence, we speculated that inhibition of metastasis-specific MMPs in cancer cells may be one of the targets for anticancer function of quercetin, and thus provides the molecular basis for the development of quercetin as a novel chemopreventive agent for metastatic prostate cancer.

The photoreactions of 1,4-diphenyl-1,3-butadienes (DPB) fused with a bicyclo[2.2.1]heptano ring under direct irradiation were examined in solution at room temperature and in organic glass at liquid nitrogen temperature. Photocyclization yielding a phenylnaphthalene compound was shown to be preceded by facile E,E to E,Z photoisomerization. The reverse E,Z to E,E isomerization took place with equal ease in low temperature organic glass and in solution at room temperature. The pattern of reaction at low temperature is consistent with the involvement of the Hula-twist mechanism. However, complexity in conformational population, suggested by ab initio calculated data, made the experimental evidence less clear-cut than in previously reported examples of HT.

A matrix of trans-1-(2-naphthyl)-1-phenylethene (t-NPE) fluorescence spectra obtained from benzene solutions at 20 degrees C by varying the excitation wavelength (lambdaexc) and the oxygen concentration is resolved into pure conformer fluorescence spectra by use of principal component analysis with self-modeling based on optimum global Stern Volmer constant criteria. The resulting fractional contributions of the two components to the fluorescence spectra are combined with observed fluorescence quantum yields as a function of lambdaexc to obtain the conformer-specific quantum yields. These quantum yields and fluorescence lifetimes are used to determine conformer-specific radiative and radiationless rate constants. Comparison with results from an analogous study in methylcyclohexane reveals pronounced, diferential enhancements of all these rate constants in benzene (Bz). Preliminary measurements of emission from a cis-1-(2-naphthyl)-1-phenylethene (c-NPE) solution in Bz at 20 degrees C, under static cell conditions, are dominated by sequential two-photon-induced t-NPE fluorescence due to excitation of t-NPE formed photochemically from the cis isomer. The spectra also reveal a weak structureless broad emission, which is assigned to 1c-NPE* by comparison with the published low temperature fluorescence spectrum of c-NPE in a hydrocarbon glass. The conformational origin of this emission is addressed.