Molecular spectroscopic study on the interaction of tetracyclines with serum albumins

A molecular spectroscopic investigation of the interaction between tetracyclines antibiotics and human serum albumin or bovine serum albumin was reported. The influences of some metal ions on the interaction were also studied. When tetracyclines drugs were added into the solution containing serum albumins, the fluorescence intensity of serum albumins decreased with the increasing of the drugs concentrations, which is due to the formation of new non-fluorescence complexes of drug-serum albumin. The tetracyclines acted as quenchers and quenched the fluorescence of the serum albumins. The binding constants and the number of the binding sites of the reaction of tetracyclines and serum albumins were obtained. The main sorts of acting force between the drugs and serum albumins were found and the action distances and the energy transfer efficiencies between donor-acceptor were calculated based on the Foster energy transference.     

Polymeric complexes of bivalent transition metal ions with 2-hydroxy-1-naphthaldehyde oxaldihydrazone and 2-hydroxy-1-naphthaldehyde malondihydrazone

Summary Polymeric complexes prepared by solid-solution reactions, from 2-hydroxy-1-naphthaldehyde oxaldihydrazone (HNODH) and 2-hydroxy-1-naphthaldehyde malondihydrazone (HNMDH), had the empirical composition M(L-2H)·nH₂O where M=Fe^II, Mn^II, Co^II, Ni^II, Cu^II, Zn^II, Cd^II and Hg^II; L=HNODH, HNMDH andn=0,1, 2. The complexes, which are intensely coloured and insoluble in common organic solvents, were characterized by elemental analysis, magnetic susceptibility, electronic and i.r. spectral data. The absence of anions indicates that the ligands which bind the metal ions from the hydroxyl and the imino groups have been deprotonated.     

Interaction of cinnamic acid derivatives with serum albumins: a fluorescence spectroscopic study

Cinnamic acid (CA) derivatives are known to possess broad therapeutic applications including anti-tumor activity. The present study was designed to determine the underlying mechanism and thermodynamic parameters for the binding of two CA based intramolecular charge transfer (ICT) fluorescent probes, namely, 4-(dimethylamino) cinnamic acid (DMACA) and trans-ethyl p-(dimethylamino) cinnamate (EDAC), with albumins by fluorescence spectroscopy. Stern-Volmer analysis of the tryptophan fluorescence quenching data in presence of the added ligand reveals fluorescence quenching constant (κ(q)), Stern-Volmer constant (K(SV)) and also the ligand-protein association constant (K(a)). The thermodynamic parameters like enthalpy (ΔH) and entropy (ΔS) change corresponding to the ligand binding process were also estimated. The results show that the ligands bind into the sub-domain IIA of the proteins in 1:1 stoichiometry with an apparent binding constant value in the range of 10(4) dm(3) mol(-1). In both the cases, the spontaneous ligand binding to the proteins occur through entropy driven mechanism, although the interaction of DMACA is relatively stronger in comparison with EDAC. The temperature dependence of the binding constant indicates the induced change in protein secondary structure.     

Investigating the interaction of juglone (5-hydroxy-1, 4-naphthoquinone) with serum albumins using spectroscopic and in silico methods

The interaction between juglone at the concentration range of 10–110 µM and bovine serum albumin (BSA) or human serum albumin (HSA) at the constant concentration of 11 µM was investigated by fluorescence and UV absorption spectroscopy under physiological-like condition. Performing the experiments at different temperatures showed that the fluorescence intensity of BSA/HSA was decreased in the presence of juglone by a static quenching mechanism due to the formation of the juglone–protein complex. The binding constant for the interaction was in the order of 10³ M^?1, and the number of binding sites for juglone on serum albumins was determined to be equal to one. The thermodynamic parameters including enthalpy (ΔH), entropy (ΔS) and Gibb’s free energy (ΔG) changes were obtained by using the van’t Hoff equation. These results indicated that van der Waals force and hydrogen bonding were the main intermolecular forces stabilizing the complex in a spontaneous association reaction. Moreover, the interaction of BSA/HSA with juglone was verified by UV absorption spectra and molecular docking. The results of synchronous fluorescence, UV–visible and CD spectra demonstrated that the binding of juglone with BSA/HSA induces minimum conformational changes in the structure of albumins. The increased binding affinity of juglone to albumin observed in the presence of site markers (digoxin and ibuprofen) excludes IIA and IIIA sites as the binding site of juglone. This is partially in agreement with the results of molecular docking studies which suggests sub-domain IA of albumin as the binding site.     

Energy transfer photophysics from serum albumins to sequestered 3-hydroxy-2-naphthoic acid, an excited state intramolecular proton-transfer probe

The steady-state and time-resolved studies of the sensitized emission of the excited-state proton transfer (ESIPT) probe 3-hydroxy-2-naphthoic acid (3HNA) when bound to bovine serum albumin (BSA) and human serum albumin (HSA) indicate that the nonradiative dipole-dipole F?rster type energy transfer from Trp singlet state of proteins to the ESIPT singlet state of 3HNA is greater in the case of HSA. This is supported by the distance and the orientation of the donor-acceptor pair obtained from the protein-ligand docking studies. The docking studies of the complex of BSA-3HNA also indicate that Trp 134 rather than Trp 213 is involved in the energy transfer process. The local environment of Trp 134 in BSA rather than that of Trp 213 is perturbed because of interaction with 3HNA as revealed by the optical resolution of Trp 134 phosphorescence in the complex at 77 K. Docking studies support the larger rotational correlation time, thetac (approximately 50 ns), observed for Trp residue/residues in the complexes of HSA and BSA compared with that in the free proteins.     

Tautomerism in Schiff bases. The cases of 2-hydroxy-1-naphthaldehyde and 1-hydroxy-2-naphthaldehyde investigated in solution and the solid state

Schiff bases derived from hydroxyl naphthaldehydes and o-substituted anilines have been prepared and their tautomerism assessed by spectroscopic, crystallographic, and computational methods. Tautomeric equilibria have also been studied and reveal in most cases a slight preference of imine tautomers in solution; a fact supported by DFT calculations in the gas phase as well as incorporating solvent effects through the SMD model. To simulate the effect exerted by the crystal lattice on tautomer stability, we have developed a computational protocol in the case of 1-tert-butyl-2-(2-hydroxy-1-naphthylmethylene)aminobenzene whose data have been obtained experimentally at 120 K. Although a rapid imine-enamine interconversion may be occurring in the solid state, the imine tautomer becomes the most stable form and the energy difference should be related to the difference in the packing of the molecules.     

Study of the noncovalent interaction of squarylium dyes with serum albumins

The noncovalent interaction of zwitterionic indolium squarylium dyes (hydrophilic and hydrophobic) and a structurally analogous ionic indodicarbocyanine (hydrophilic) dye with serum albumins was studied by spectral and fluorescent methods. It has been found that the hydrophilic squarylium dye with sulfonate groups most efficiently interacts with albumins, which is probably due to the double negative charge of the dye molecule at the expense of the sulfonate groups and the possibility to form hydrogen bonds with albumin. The hydrophobic squarylium dye, as well as the hydrophilic indodicarbocyanine dye without the squarylium fragment in its structure, bind with albumins much weaker than the structurally relevant hydro- philic squarylium dye. The properties of the latter dye permit us to recommend it for using as a spectral and fluorescent probe for serum albumins in extracellular media of living organisms.     

Gravimetric determination of uranyl ion with 2-hydroxy-1-naphthaldehyde /2H-1N/

The precipitation of uranyl ion with 2-hydroxy-1-naphthaldehyde /2H–1N=HL/ was studied. The solid complex /orange crystals/ was characterized by IR, UV-Vis spectra. Uranium was determined as U₃O₈ after calcination of the complex at 850°C /37.78% U experimental, 36.64% U calculated for C₂₂H₁₄O₆U, UO₂L₂/. Using a statistical experimental design, the best conditions for quantitative precipitation were obtained. A gravimetric method for the determination of UO ₂ ²⁺ is proposed by weighing the complex after drying at 110°C.On leave from Instituto de Química, U.N.A.M.     

Fluorescence excitation and excited state intramolecular proton transfer of jet-cooled naphthol derivatives: Part 1. 1-Hydroxy-2-naphthaldehyde

The S(0) → S(1) fluorescence excitation spectrum of jet-cooled 1H2N with origin at 25484 cm(-1) has been measured. Twelve totally symmetric modes and five non-totally symmetric modes have been assigned in the excitation spectrum. Theoretical calculations at DFT B3LYP/6-31G** and CIS/6-31G** levels indicate that the 1H2N molecular geometry is more planar in the S(1) state than in the ground state. The geometry of the naphthalene ring changes upon excitation and promotes a number of totally symmetric ring stretching modes, in the excitation spectrum. As a result of the geometry change upon excitation a number of non-totally symmetric modes gain intensity. Based on a rotational envelope fitting procedure the average excited rotational state lifetime was estimated to be between 7 and 16 ps for 0 ≤E≤ hc × 800 cm(-1) (E is excess energy above the S(1) origin). The decay rate coefficients, k, of the rotational S(1) states, are not constant over this range of excess energies. By applying a Golden Rule model, it was determined that internal conversion to S(0) is unlikely to be the sole non-radiative process contributing to the decay of the excited states. It was concluded that excited state intramolecular proton transfer (ESIPT) plays a role in the observed behaviour of the rate co-efficient with excess energy. The observation of (i) a sharp increase in rate coefficient, k, above an excess energy of ～550 cm(-1), and (ii) a significant number of high intensity fluorescence excitation spectrum features above an excess energy of ～700 cm(-1), may indicate the presence of an energy barrier of ～550 cm(-1), between the enol and keto geometries in the S(1) state. This result supports the conclusions of S. De, S. Ash, S. Dalai and A. Misra, J. Mol. Struc. Theochem, 2007, 807, 33-41, who estimated a barrier to ESIPT of ～750 cm(-1). It was concluded that ESIPT occurs in 1H2N, across an energy barrier with a rate constant, k(pt)≤ 10(11) s(-1). Hence, at low excess energies (≤ 550 cm(-1)), the observed emission band originates predominantly from the keto tautomer. Above an excess energy of ～1600 cm(-1), 1H2N decays predominantly via a non-radiative mechanism.     

Fluorescence excitation and excited state intramolecular proton transfer of jet-cooled naphthol derivatives: part 2. 2-Hydroxy-1-naphthaldehyde

The S(1)← S(0) fluorescence excitation spectrum of jet-cooled 2-hydroxy-1-naphthaldehyde (2H1N) with origin at 26,668 cm(-1) has been measured. Nine totally symmetric modes and three non-totally symmetric modes have been assigned in the excitation spectrum. Ab initio calculations indicate that 2H1N undergoes a planarity change upon excitation, which may account for the unusual intensity of non totally symmetric vibrational modes in the excitation spectrum. A number of low intensity features were observed on the low energy side of the origin which have been assigned to the 2H1N dimer rather than different ground state confomers of 2H1N. The origin of the S(1)← S(0) electronic transition of the dimer lies at ~26,401 cm(-1); combinations of two low frequency intermolecular modes of the dimer (59 cm(-1) and 17 cm(-1)) were also observed. The occurrence of excited state intramolecular proton transfer (ESIPT) in 2H1N cannot be proven on the basis of this work. A comparison of the (photo)physical properties of 2H1N with 1-hydroxy-2-naphthaldehyde (1H2N) [A. McCarthy and A.A. Ruth, PCCP, 2011, 13, 7485-7499 (Part 1)], however, indicate the plausibility of an ESIPT process in 2H1N. The strength of the intramolecular hydrogen bond (IMHB) in 2H1N was computed as ~10.6 kcal/mol, a value comparable to the IMHB strength of 1H2N. The establishment of a lower limit on the state lifetimes of 2H1N, of ~1.8 ps, indicates that any proposed ESIPT reaction in 2H1N may not proceed barrierlessly. Above an excess energy of ~1000 cm(-1), the intensity of the fluorescence excitation spectrum reduces significantly, indicating the onset of a non-radiative decay mechanism.     

Fluorimetric kinetic studies and sub-muM determination of aluminium with 2-hydroxy-1-naphthaldehyde p-methoxybenzoylhydrazone

A fluorimetric study has been made of the kinetics of the reaction of 2-hydroxy-1-naphthaldehyde p-methoxybenzoylhydrazone with aluminium, and a rate equation and a possible kinetic scheme are proposed. Experimental conditions are defined under which 0.020-10.0muM aluminium can be determined with an average error of 3.7% and a coefficient of variation of about 4.6%.     

Studies on the energy transfer system of terbium-norfloxacin chelate and its interaction with serum albumins

The energy absorbed by norfloxacin could be transferred to terbium(Ⅲ) through chela-tion of norfloxacin with terbium(Ⅲ),then the characteristic fluorescence emission could be observed.The interaction of serum albumins with norfloxacin have been investigated in this paper.The results showed that HSA could inhibit the energy transfer between norfloxacin and terbium(Ⅲ).But,BSA could not.It was shown that the binding properties of norfloxacin to HSA and BSA were totally different.     

Spectral and fluorescent study of the noncovalent interaction of a meso-substituted cyanine dye with serum albumins

A comparative study of the noncovalent interaction of the cyanine dye probe 3,3′-di-(γ-sulfopropyl)-4,5,4′,5′-dibenzo-9-ethylthiacarbocyanine betaine with serum albumins of different vertebrates: rat, rabbit, bovine, and human serum albumins (RSA, TSA, BSA, and HSA, respectively) has been performed by spectral and fluorescent methods. It has been shown that, the dye forms only one product, the trans-monomer bound to HSA, by interacting with HSA, whereas other binding products are also formed with other albumins. This is probably explained by a higher interaction energy of the dye with HSA than with other serum albumins.     

Reaction of N,N-Bis(2-hydroxy-1-naphthaldehyde)-ethylenediimine with ethylene chlorophosphite

Russian Journal of General Chemistry -     

Spectral and fluorescent study of the interaction of anionic cyanine dyes with serum albumins

The noncovalent interaction of two anionic cyanine dyes with human and bovine serum albumins was studied by spectral and fluorescent methods. Upon the interaction with albumins, a growth of fluorescence and, in most cases, a long-wavelength shift of the dye absorption band are observed. For the meso-substituted cyanine dye 3,3′-di-(γ-sulfopropyl)-9-methylthiacarbocyanine betaine (K1), a mobile cis-trans equilibrium is observed: the dye in the free state occurs mainly as the cis-isomer, whereas in the complex with albumins the equilibrium is shifted toward the trans-isomer (this shift is greater for human albumin). Dye K1 is recommended as a spectral and fluorescent probe for serum albumins.     

Spectral study of coumarin-3-carboxylic acid interaction with human and bovine serum albumins

Fluorescence spectroscopy and circular dichroism (CD) spectroscopy were used to investigate the interaction of coumarin-3-carboxylic acid with human serum albumin (HSA) and bovine serum albumin (BSA) under physiological conditions in a buffer solution of pH 7.4.      

Destructive and protective action of sodium dodecyl sulphate micelles on the native conformation of Bovine Serum Albumin: A study by extrinsic fluorescence probe 1-hydroxy-2-naphthaldehyde

The interaction of the anionic surfactant sodium dodecyl sulphate (SDS) with water soluble protein Bovine Serum Albumin (BSA) has been investigated spectroscopically using fluorescence probe 1-hydroxy-2-naphthaldehyde (HN12). The characteristic intramolecular proton transfer fluorescence band of HN12 has been used as an efficient reporter for the study of binding of SDS with BSA. The changes of spectral properties of HN12 demonstrate that SDS plays two opposite roles in the stability of protein BSA. It acts as a stabilizer at low concentration and destabilizer at high concentration to urea-denatured BSA.     

Synthesis of homobimetallic molybdenum(VI) complex of bis(2-hydroxy-1-naphthaldehyde)malonoyldihydrazone and its reaction with electron and proton bases

The diamagnetic dioxomolybdenum(VI) complex [(MoO₂)₂(CH₂L)(H₂O)₂]H₂O (1) has been isolated in solid state from reaction of MoO₂(acac)₂ with bis(2-hydroxy-1-naphthaldehyde)malonoyldihydrazone (CH₂LH₄) in 3:1 molar ratio in ethanol at higher temperature. The reaction of the complex (1) with electron donor bases gives diamagnetic molybdenum(VI) complexes having composition [Mo₂O₅(CH₂LH₂)]·2A·2H₂O (where A = pyridine (py, 2), 2-picoline (2-pic, 3), 3-picoline (3-pic, 4), 4-picoline (4-pic, 5)). Further, when the complex (1) is allowed to react with protonic bases such as isonicotinoylhydrazine (inhH₃) and salicyloylhydrazine (slhH₃), reduction of molybdenum(VI) centre occurs leading to isolation of homobimetallic molybdenum(V) complexes [Mo₂(CH₂L)(inh)₂(H₂O)₂] (6) and [Mo₂(CH₂L)(slh)₂] (7), respectively. The composition of the complexes has been established by analytical, thermo-analytical and molecular weight data. The structure of the molybdenum(VI) complexes (1)–(5) has been established by electronic, IR, ¹H NMR and ¹³C NMR spectral studies while those of the complexes (6) and (7) by magnetic moment, electronic, IR and EPR spectral studies. The dihydrazone is coordinated to the metal centres in staggered configuration in complex (1) while in anti-cis configuration in complexes (2)–(7). The complexes (6) and (7) possess magnetic moment of 2.95 and 3.06 BM, respectively, indicating presence of two magnetic centre in the complexes per molecule each with one unpaired electron on each metal centre without any metal–metal interaction. The electronic spectra of the complexes are dominated by strong charge transfer bands. All of the complexes involve six coordinated molybdenum centre with octahedral arrangement of donor atoms except in the complex (6), in which the molybdenum centre has rhombic arrangement of ligand donor atoms. The probable mechanism for generation of oxo-group in the complexes (2)–(5) involving coordinated water molecule has been proposed.     

Electronic and quantum dynamical insight into the ultrafast proton transfer of 1-hydroxy-2-acetonaphthone

The ultrafast proton-transfer dynamics of 1-hydroxy-2-acetonaphthone has been theoretically analyzed in the ground and first singlet excited electronic states by density functional theory calculations and quantum dynamics. The potential energies obtained in the ground electronic state reveal that the proton-transfer process does not lead to a stable keto tautomer unless the transfer of the hydrogen from the enol form is accompanied by an internal rotation of the newly formed O-H bond. Calculations in the first singlet excited electronic state point to a very low barrier for the formation of the keto tautomer. The analysis of the calculated frequencies of the two tautomers in the excited state unveils a coupling of the skeletal motions (low frequency modes) with the proton-transfer process, as it has been stated from time-resolved experiments. The electronic energies obtained by the time-dependent density functional theory formalism have been fitted to a monodimensional potential energy surface in order to perform an exact quantum dynamics study of the process. Our results show that the proton-transfer process is completed within 25.5 fs, in remarkable good agreement with experiments.