Biquinoline Research Articles

Enhanced antitumor effect of L-buthionine sulfoximine or ionizing radiation by copper complexes with 2,2´-biquinoline and sulfonamides on A549 2D and 3D lung cancer cell models.

Two ternary copper(II) complexes with 2,2'-biquinoline (BQ) and with sulfonamides: sulfamethazine (SMT) or sulfaquinoxaline (SDQ) whose formulae are Cu(SMT)(BQ)Cl and Cu(SDQ)(BQ)Cl·CH3OH, in what follows SMTCu and SDQCu, respectively, induced oxidative stress by increasing ROS level from 1.0μM and the reduction potential of the couple GSSG/GSH2. The co-treatment with L-buthionine sulfoximine (BSO), which inhibits the production of GSH, enhanced the effect of copper complexes on tumor cell viability and on oxidative damage. Both complexes generated DNA strand breaks given by-at least partially-the oxidation of pyrimidine bases, which caused the arrest of the cell cycle in the G2/M phase. These phenomena triggered processes of apoptosis proven by activation of caspase 3 and externalization of phosphatidylserine and loss of cell integrity from 1.0μM. The combination with BSO induced a marked increase in the apoptotic population. On the other hand, an improved cell proliferation effect was observed when combining SDQCu with a radiation dose of 2Gy from 1.0μM or with 6Gy from 1.5μM. Finally, studies in multicellular spheroids demonstrated that even though copper(II) complexes did not inhibit cell invasion in collagen gels up to 48h of treatment at the higher concentrations, multicellular resistance outperformed several drugs currently used in cancer treatment. Overall, our results reveal an antitumor effect of both complexes in monolayer and multicellular spheroids and an improvement with the addition of BSO. However, only SDQCu was the best adjuvant of ionizing radiation treatment.

Proton induced green emission from AIEE active 2,2′ biquinoline hydrosol and its selective fluorescence turn-on sensing property towards Zn2+ ion in water

A novel material showing aggregation induced enhanced emission (AIEE) is developed by reprecipitation method using 2,2′ biquinoline (BQN) in aqueous medium. Morphologies of the particles are characterized using optical and scanning electron microscopic (SEM) study. The selective fluorescence and absorbance response of aggregated BQN towards Zn2+ and H+ have been explained due to ground state complexation and protonation of BQN with Zn2+ and H+ respectively. Protonated BQN exhibits charge transfer character in transoid form with yellowish green emission but in BQN-Zn2+ complex, BQN changes to cis planer conformation and displays considerable intra ligand charge transfer (ILCT) character with sky blue color under UV excitation. A 2:1 BQN-Zn2+ complex have been confirmed using Job’s plot. Our study revealed that BQN hydrosol act as selective turn-on fluorescence sensor for Zn2+ ion both in acidic and alkaline medium. Further, the proton induced charge transfer character and the proposed binding modes of the receptor with Zn2+ have been supported by DFT based computational study.

A Candidate Anti-Prion Disease Agent, 2,2'-Biquinoline, Decreases Expression of Prion Protein and mRNA in Prion-Infected Cells

Transmissible spongiform encephalopathies (TSEs) are a family of invariably fatal neurodegenerative diseases. This group includes scrapie in sheep, bovine spongiform encephalopathy (BSE) in cattle, chronic wasting disease (CWD) in cervids, and Creutzfeldt-Jakob disease (CJD) in humans. These diseases are characterized by the accumulation of the abnormal isoform prion protein (PrPSc), which is a misfolded version of the cellular prion protein (PrPC) and is resistant to enzymatic degradation. Numerous compounds have been reported to inhibit prion replication and PrPSc accumulation in cell cultures. Among them, we selected 2,2'-biquinoline (BQ) and studied the mechanism of its anti-prion disease activity. Its effect on prion protein (PrP) expression was examined in mouse neuroblastoma (N2a) cells and in prion-infected N2a (ScN2a) cells, using proteinase K (PK) treatment to discriminate between PrPC and PrPSc. We found that BQ time dependently decreased the total amount of PrP and PrP mRNA expression in infected N2a cells, but not uninfected N2a cells. Our results indicate that the inhibition of PrPSc production by BQ was due to a decrease in the total amount of PrP.

The phosphorescent triplet states of aza-aromatics and their protonated cations in rigid solutions of ethanol and 1-butyl-3-methylimidazolium hexafluorophosphate

The lowest excited triplet (T 1) states of 2,2′-bipyridine (BPY), 6,6′-dimethyl-2,2′-bipyridine (DMBPY), 2,2′-biquinoline (BQ), 2-phenylpyridine (2-PPY), 3-phenylpyridine (3-PPY), 4-phenylpyridine (4-PPY), quinoline (QN) and isoquinoline (iso-QN) have been studied through measurements of the phosphorescence and EPR spectra in 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF 6]) and in ethanol. BPY, DMBPY and BQ have the trans conformation in the ground (G) and T 1 states in [BMIM][PF 6] and in ethanol. Although only neutral forms of BPY, DMBPY, BQ and 4-PPY were observed in ethanol, their singly protonated cations were observed in [BMIM][PF 6] in the G and T 1 states. In the T 1 states, the solvent effects of [BMIM][PF 6] on the electron spin distributions of the aza-aromatics studied and their singly protonated cations are small.

Spectroscopic characterizations of the mixed Langmuir–Blodgett (LB) films of 2,2′-biquinoline molecules: Evidence of dimer formation

This communication reports the π– A isotherms and spectroscopic characterizations of mixed Langmuir and Langmuir–Blodgett (LB) films of non-amphiphilic 2,2′-biquinoline (BQ) molecules, mixed with polymethyl methacrylate (PMMA) and stearic acid (SA). The π– A isotherms and mole fraction vs. area per molecule studies indicate complete immiscibility of sample (BQ) and matrix (PMMA or SA) molecules. This immiscibility may lead to the formation of microcrystalline aggregates of BQ molecules in the mixed LB films. The scanning electron micrograph gives the visual evidence of microcrystalline aggregates of BQ molecules in the mixed LB films. UV–vis absorption, fluorescence and excitation spectroscopic studies reveal the nature of these microcrystalline aggregates. LB films lifted at higher surface pressure indicate the formation of dimer or higher order n-mers.

Spectral and photophysical properties of mono and dinuclear Pt(II) and Pd(II) complexes: An unusual emission behaviour

Eight mononuclear complexes of the formula [M(N-N)(DHB)] and two binuclear complexes of the formula [M 2(BPY) 2(THB)] {where M = Pd(II) or Pt(II), N-N = 2,2′-bipyridine (BPY), 2,2′-biquinoline (BIQ), 4,7-diphenyl-1,10-phenanthroline (DPP), 1,10-phenanthroline (PHEN); DHB = dianion of 3,4-dihydroxybenzaldehyde and THB = tetraanion of 3,3′,4,4′-tetrahydroxy benzaldazine} were prepared and their electrochemical, spectral and photophysical properties were examined. These complexes were characterized by chemical analysis, IR and proton NMR spectroscopy. A detailed study on the absorption spectroscopy of these complexes was made. These complexes were found to show a low-energy solvatochromic ligand-to-ligand charge-transfer (LLCT) band. The electronic energies of these bands have been analyzed and compared with electrochemical data. Emission behaviour of the complexes of the series, [Pt(N-N)(DHB)], [Pt(N-N)(DHBA)] {where DHBA is the dianion of 3,4-dihydroxybenzoic acid} and [Pt 2(BPY) 2(THB)] was also investigated. These platinum complexes were found to emit from a low-energy state at low temperature and a high-energy state at room temperature. Photophysics of these complexes is also discussed.

Surface enhanced Raman scattering of 2,2′ biquinoline adsorbed on colloidal silver particles

Surface enhanced Raman scattering (SERS) in silver sol and normal Raman spectra in the bulk and in solution of 2,2′ biquinoline (BQ) molecule have been investigated. The observed Raman bands along with their corresponding FTIR bands have been assigned based on the established assignments of the vibrational bands of the parent napthalene and quinoline molecules. Existence of both the cis and trans form of the BQ molecule in solution and in the bulk are inferred from the normal Raman and FTIR spectra, whereas SERS study reveal that in the surface adsorbed state the molecule exists in the cis form. Definite evidence of the charge transfer interaction to the overall contribution in the SER enhancement have been reported. The excitation profile also supports the CT interaction. Estimated enhancement factor of the principal SERS bands indicate that the molecule is adsorbed on the silver surface through both the nitrogen atoms with the molecular plane almost perpendicular to the surface. This preferred orientation of the molecule is in conformity with its existence in the cis form in the surface adsorbed state.

Synthesis of a new chiral ligand, 6, 6'-dihydroxy-5, 5'-biquinoline (BIQOL) and its applications in the asymmetric addition of diethylzinc to aldehydes.

A new chiral ligand 6, 6'-dihydroxy-5, 5'-biquinoline (BIQOL, 2) was prepared via Cu2+ mediated coupling. The resolution was carried out by separating the corresponding ditrifluomethanesulfonate on chiral column. When applied to the enantioselective addition of diethylzinc to aromatic aldehydes, this ligand induced the reaction with enantioselectivity equivalent to that induced by BINOL. The effects of solvent and reaction temperature on enantioselectivity were also studied.

Spectral and photochemical behaviour of mononuclear and dinuclear α-diimine complexes of Pt(II) and Pd(II) with catechol derivatives

Mononuclear and dinuclear complexes with the formulae [M(DHB)NN)] (where MPd(II) or Pt(II); NN ≡ 2,2′-bipyridine (BPY), 2,2′-biquinoline (BIQ), 4,7-diphenyl-1,10-phenanthroline (DDP) or 1,10-phenanthroline (PHEN); DHB is the dianion of 3,4-dihydroxybenzaldehyde) and [{M(BPY)} 2(THB)] (where MPd(II) or Pt(II); BPY is 2,2′-bipyridine; THB is the tetraanion of 3,3,4,4-tetrahydroxybenzaldazine) photosensitize the oxidation of 2,2,6,6-tetramethyl-4-piperidinol (XH) in N, N-dimethyl-formamide (DMF) to give 4-hydroxy-2,2,6,6-tetramethyl-4-piperidinyloxy, a nitroxide free radical (XO). This photo-oxidation reaction involves singlet molecular oxygen ( 1O 2) as an intermediate and its presence is confirmed by quenching studies using bis(diethyldithiocarbamato)nickel(II) (Ni(DDTC) 2), a physical quencher of 1O 2. The ability of the mononuclear complexes to photosensitize the above photo-oxidation reaction follows the order: [Pt(DHB)(PHEN)] > [Pt(DHB)(DPP)] > [Pt(DHB)(BIQ)] > [Pt(DHB)(BPY)] > [Pd(DHB)(DPP)] ⩾ [Pd(DHB)(PHEN)] > [Pd(DHB)(BIQ)] ⩾ [Pd(DHB)(BPY)]. Moreover, the dinuclear complexes, in comparison with the analogous mononuclear complexes, follow the order: [{Pt(BPY)} 2(THB)] > [Pt(DHB)(BPY)] > [{Pd(BPY)}(DHB)] > [Pd(DHB)(BPY)]. These orders depend on the metal ion, the number of metal ions in the complex, the nature of the α-diimine ligand and the distortion from planar geometry of the metal complex.

Synthesis, spectral and electrochemical behaviour of α-diimine complexes of platinum(II) and palladium(II) with 3,4-dihydroxybenzoic acid

Eight complexes of the formula [M(NN)(DHBA)] {where M = Pd II or Pt II, NN = 2,2′-bipyridine (BPY), 2,2′-biquinoline (BIQ), 4,7-diphenyl-1,10-phenanthroline (DPP), 1,10-phenanthroline (PHEN) and DHBA is the dianion of 3,4-dihydroxybenzoic acid} were prepared and characterized by chemical analysis, IR and 1H NMR spectroscopy. These complexes were found to show a ligand-to-ligand charge-transfer (LLCT) band. The energies of these bands have been compared with the electrochemical data.

Transient resonance Raman and Raman spectroelectrochemical studies of copper(Cu I) complexes with polypyridyl ligands

Studies by laser flash photolysis, transient Raman spectroscopy, and Raman and UV-vis spectroelectrochemistry are described in which the techniques have been used in parallel to compare the lowest energy charge-transfer excited states of Cu(I) complexes ([Cu(L) 2 ] + and [(PPh 3 ) 2 Cu(L)] + [L= 2,2'-biquinoline (BIQ) or 6,7-dihydro5,8-dimethyldibenzo[b,j] [1,10]-phenanthroline (DMCH)) with the species produced by electrochemical reduction in the same group of complexes

Investigation of 1O 2 generation by water-soluble α-diimine complexes of platinum(II) and palladium(II) with 3,4-dihydroxybenzoic acid as photosensitizers

Eight complexes with the formula [M(NN)(DHBA)] (where MPd(II) or Pt(II), NN is 2,2′-bipyridine (BPY), 2,2′-biquinoline (BIQ), 1,10-phenanthroline (PHEN), 4,7-diphenyl-1,10-phenanthroline (DPP) and DHBA is 3,4-dihydroxybenzoic acid dianion) were found to photosensitize the oxidation of 2,2,6,6-tetramethyl-4-piperidinol (NH) in N, N-dimethylformamide (DMF) to the nitroxide radical. This photo-oxidation reaction involves singlet molecular oxygen ( 1O 2) as an intermediate and its presence was confirmed by quenching studies using bis(diethyldithiocarbamato)nickel(II), as well known 1O 2 quencher. The ability of these complexes to photosensitize the above photo-oxidation reaction follows the order, [Pt(PHEN)(DHBA)]·H 2O > [Pt(DPP)(DHBA)]·H 2O > [Pt(BIQ)(DHBA)] > [Pd(PHEN)(DHBA)] > [Pt(BPY)(DHBA)] > [Pd(DPP)(DHBA)] > [Pd(BPY)(DHBA)]·CH 3OH > [Pd(BIQ)(DHBA)]. This order depends on the metal ion, the nature of the α-diimine ligand and the geometry of the metal complex.

Effects of protonation and coordination to zinc(II) ion on the triplet state of 2,2′-biquinoline: A time-resolved ESR study

Time-resolved ESR spectra have been observed for the phosphorescent triplet states of 2,2′-biquinoline (BQ), 2,2′-biquinolinium (BQH +) and [Zn(bq)] 2+ in ethanol at 77 K. The analysis of the spectra showed that the sublevel initially populated by intersystem crossing is mainly T x in both BQ and BQH +, while it is mainly T y in [Zn(bq)] 2+ (the x axis is close to the long axis of the molecule and y is in the molecular plane).

Low-temperature luminescence spectrum of crystalline biquinoline: trap phosphorescence and delayed enlimer fluorescence

The sI~ectroscopy of the so-called double molecules, e.g. biphenyl [1 --5[, has attracted considerable attention as such compounds each represent, roughly speaking. two strongly interacting monomers [2] ; these systems have thus served as intriguing models with respect to exciton theory and other energy transfer phenomena [2]. Recent work in this laboratory has been concerned with the spectroscopy of 2,2'-biquinoline (BQ) [4,5]. While past efforts have been spent examining the low-temperature phosphorescence and optically detected magnetic resonance (ODMR) of BQ dispersed in Shpolskii matrices [4], some emission features of the neat crystalline phase have recently been observed and have proven to be of interest. It is our purpose here to report these results and to enumerate the various energy transport processes manifest in the spectra.

Water as a proton donor in excited state reactions of 6, 6′-biquinoline

6, 6′-biquinoline (BQ) in aqueous-alcoholic solutions exhibits doubleluminescence and two ESR signals in the triplet state. The structureless fluorescence band observed at room temperature was shown to be the result of the protonation of strongly basic 1 (BQ) * (pK * = 13). At low temperature the aggregation of the molecule has been observed. The low temperature absorption, luminescence, luminescence excitation spectra, and triplet ESR spectra of the aggregates have been measured and distinguished from the corresponding spectra of monomeric BQ.