Intermolecular interaction between squarylium cyanine and porphyrin

In this paper, the interaction between squarylium cyanine and porphyrin in chloroform is investigated by absorption and fluorescence spectroscopy. Emphasis has been put on the mechanism of intermolecular energy transfer. The overlap integral J between the absorption spectrum of squarylium cyanine and the fluorescence spectrum of porphyrin was calculated, which reveals that the singlet-singlet energy transfer may occur from porphyrin to squarylium cyanine in solution. In comparison of the observed rate constant [kqII=6.1 ×1013 (mol/L)-1·s-1] for fluorescence quenching of porphyrin by squarylium cyanine with the diffusion rate constant in chloroform [kdif=1.1×1010 (mol/L)-1·s-1] and the rate of energy transfer [ket≤6.7×104 (mol/L)-1·s-1 in the experimentally dilute solutions] estimated from Forster formula, the possibility of energy transfer by electron exchange or/and coulombic mechanism could be excluded. So it has been definitely convinced that the intermolecuiar energy transfer between them is     

Geminal interaction and “anomeric effect”

Quantum-chemical calculations by the methods of RHF/6-31G(d) and MP2/6-31+G(d) show equal ratio of the lengths of axial and equatorial bonds and electron density on the atoms forming them in cyclohexane and its mono derivatives and in six-membered heterocyclic molecules as well. This feature is due to the interaction of atoms in the chair form of these molecules regardless of the presence in them of a heteroatom. Introducing heteroatom to a cyclohexane ring leads only to increase in the difference between axial and equatorial bonds. This equation excludes the possibility to ascribe the elongation of axial bonds and increase in the electron density on atoms forming them in the heterocyclic molecules to the p,σ*-conjugation of the lone electron pair of the ring heteroatom with the antibonding orbital of the axial bond. Features of molecular geometry defined by the mutual influence of atoms in them, including inductive and non-inductive interaction of geminal atoms in triatomic groups Y-Z-M, result in energetic preference of gauche conformations of these molecules and “anomeric effect” in them.     

Fluorescence enhancement effect and the interaction between donor and acceptor

A new theoretical equation for fluorescence enhancement effect between donor and acceptor has been introduced.By using it we determined the binding constants and numbers of binding sites of five medicines,including chlorogenic acid,forsythiaside norfloxacin,Ciprofloxacin and fluorenone,to γ-globulin.     

Vibronic interaction between nπ and ππ states and phosphorescence of Norharmane

Solvent effects on phosphorescence and excitation spectra and its polarization characteristics indicate that the two major spin-orbit coupling mechanisms through which the ³ππ^* state of Norharmane acquires dipole-allowed character via nπ^* states are:

     

Geminal interaction and effect of “positive charge”

Quantum-chemical calculations of the molecules containing Cl-C-M group (M=C, N, O, F) were carried out using RHF/6-31G(d) and MP2/6-31+G(d) methods. The calculations are aimed at verifying concept on “positive charge” effect of the central atom of the group suggested as understanding of non-inductive effect of heteroatom M on the Cl (Y) atom in Y-Z-M moieties (geminal interaction). It is shown that C atom in such systems bears negative or small positive charge, and hence “positive charge” effect is excluded. The non-inductive effect originates from the polarization of Cl-C (Y-Z) bonds due to the influence of the charge on any M atom directly through space on any Y and Z.     

Mechanism of membrane interaction and disruption by α-synuclein

Parkinson's disease is a common progressive neurodegenerative condition, characterized by the deposition of amyloid fibrils as Lewy bodies in the substantia nigra of affected individuals. These insoluble aggregates predominantly consist of the protein α-synuclein. There is increasing evidence suggesting that the aggregation of α-synuclein is influenced by lipid membranes and, vice versa, the membrane integrity is severely affected by the presence of bound aggregates. Here, using the surface-sensitive imaging technique supercritical angle fluorescence microscopy and F?rster resonance energy transfer, we report the direct observation of α-synuclein aggregation on supported lipid bilayers. Both the wild-type and the two mutant forms of α-synuclein studied, namely, the familiar variant A53T and the designed highly toxic variant E57K, were found to follow the same mechanism of polymerization and membrane damage. This mechanism involved the extraction of lipids from the bilayer and their clustering around growing α-synuclein aggregates. Despite all three isoforms following the same pathway, the extent of aggregation and their effect on the bilayers was seen to be variant and concentration dependent. Both A53T and E57K formed cross-β-sheet aggregates and damaged the membrane at submicromolar concentrations. The wild-type also formed aggregates in this range; however, the extent of membrane disruption was greatly reduced. The process of membrane damage could resemble part of the yet poorly understood cellular toxicity phenomenon in vivo.     

“Up-hill” diffusion and hydrogen-hydrogen interaction in palladium-platinum alloys

The reported anomalous “up-hill” diffusion of hydrogen in PdPt and PdAg alloys is explained in terms of attractive, long-range, non-local, elastic interactions between dissolved hydrogen atoms. A statistical model based on the continuum elasticity theory is presented, and model calculations for the Pd₈₁Pt₁₉ system are shown to give results that are in semi-quantitative agreement with experimental data.     

Carbocation-π interaction: the 1,1-dimethylallyl cation and benzene

Computational studies of the interaction of 1,1-dimethylallyl cation with benzene reveal that its potential energy surface has a rich complexity. The lowest energy π-complex, which involves binding of both ends of the cation to the benzene ring, is calculated to be 4.5 kcal mol⁻¹ lower in energy than its related σ-complex. The results provide further support for the idea that π complexation of carbocations is stronger over the periphery of aromatic systems, and offer insight into why biological reactions involving this type of carbocation do not lead via σ-complex formation to electrophilic substitution of the aromatic rings in proteins.     

Correlation effects and interaction energy of π-electron shells in cumulene and acetylene molecules

By means of Hartree—Fock energy variance calculations it has been shown that the specific electroncorrelation energy in extended cumulene molecules is approximately 0.3 eV/electron and the specific energy of interaction between -electron shells is 0.1 eV/electron.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 29, No. 6, pp. 514–517, November–December, 1993.     

Synergistic interaction between anti-allergic drug and cationic/anionic surfactants–Experimental and theoretical analysis

To search a new drug delivery excipient, this effort deals with the effects of cationic (hexadecyltrimethylammonium bromide, CTAB) and anionic (sodium dodecylbenzene sulfonate, SDBS) surfactants on the physicochemical properties of the anti-allergic drug (diphenhydramine hydrochloride, DPH). The tensiometric study has been done to find the nature of the interaction between drug and ionic surfactants. Numerous micellar, surface and conforming energetic parameters have been intended from this technique. Several physical models (Clint, Rubingh, Rosen, and Motomura) based on pseudo-phase approximation and regular solution theory, have been applied to compute these meaningful physical parameters. The DPH is a positively charged amphiphilic drug, while CTAB and SDBS are positively and negatively charged surfactants. It is experienced stronger attractive interaction of DPH with SDBS as compared to CTAB.     

Mechanism of simultaneously refolding and purification of proteins by hydrophobic interaction chromatographic unit and applications

The hydrophobic amino acid residues of a denatured protein molecule tend to react with the particles of the stationary phase of hydrophobic interaction chromatography (STHIC). These hydrophobic interactions prevent the denatured protein molecules from aggregating with each other. The STHIC can provide high enough energy to a denatured protein molecule to make it dehydration and to refold it into its native or various intermediate states. The outcome not only depends on the specific interactions between amino acids, the structure of STHIC, but also depends on the association between the STHIC and mobile phase. The mechanism of protein refolding and the principle of its quality control by HPHIC were also presented. By appropriate selection of the chromatographic condition, several denatured proteins can be refolded and separated simultaneously in a single chromatographic run. A specially designed unit, with diameter much larger than its length, was designed and employed for both laboratory and preparative     

Transient free-exciton luminescence and exciton—lattice interaction in pyrene crystals

Time-resolved spectra and luminescence decay time in pyrene crystals have been studied by a time-correlated photon-counting technique over the temperature range 295−136 K (above the phase-transition point). Transient free-exciton luminescence is observed as well as thermally activated free-exciton luminescence. The rate of decay of transient free-exciton luminescence σ is proportional to exp(− E_B/kT, where k is the Boltzmann constant and T the temperature. The ST barrier height E_B is found to be 260 cm⁻¹. The ratio of the ST barrier height against the exciton bandwidth is found to be 0.1. The lower bound of the time required for excitons to tunnel through the ST barrier is estimated to be 36 ps.     

Electrochemical studies of (−)-epigallocatechin gallate and its interaction with DNA

In this paper, an electrochemical investigation of (−)-epigallocatechin gallate (EGCG) and its interaction with DNA is presented. Via an electrochemical approach assisted by ultraviolet–visible (UV–Vis) spectroscopy, we propose that EGCG can intercalate into DNA strands forming a nonelectroactive complex, which results in the decrease of the anodic peak current of EGCG. Meanwhile, an electrochemical study with the DNA–Cu(II)–EGCG system shows that damage to DNA can be recognized electrochemically via the increase in the anodic peak current resulting from the oxidation of guanine and adenine bases. The damage can also be recognized spectrophotometrically via an increase in the 260 nm absorption band. In addition, it was found that EGCG is able to discriminate dsDNA from ssDNA, making a potential electrochemical indicator for the detection of DNA hybridization events. A rapid and convenient method of detecting EGCG was also developed in this work. Figure Interaction of EGCG with DNA and damage to DNA in the presence of Cu(II) Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

Crystallographic and theoretical studies of 1-(1-naphthyl)-2-thiourea with intermolecular N-H...S heteroatom interaction and N-H...π interaction

A single crystal X-ray diffraction study of 1-(1-naphthyl)-2-thiourea (1) C₁₁H₁₀N₂S indicates crystallization in the monoclinic space group C2/c, Z = 8, with unit cell parameters a = 15.3864(14) Å, b = 7.6090(7) Å, c = 17.0836(16) Å, β = 91.7420(30)°. In the crystal structure, two components of 1 are connected via intermolecular NH...S hydrogen bonds (the N...S distance of 3.371 Å). In 1 there is an NH...π interaction (with the N...π distance of 3.804 Å and a possible N-H...π distance of 3.196 Å). The calculations of 1 at the B3LYP/cc-pVTZ, RHF/cc-pVTZ, RIMP2/cc-pVDZ, and RIMP2/cc-pVTZ levels of theory can almost reproduce the X-ray geometry. In addition, the binding energies of a dimer of 1 calculated by RIMP2 using the cc-pVDZ and cc-pVTZ corrected BSSE basis sets are ?36.1 kJ/mol and ?41.7 kJ/mol. The results suggest that complex 1 is significantly important for the attractive intermolecular interaction in 1.     

Complete configuration interaction and π-shell structure in 10-center conjugated systems

An exact -electron calculation is presented for the ground singlet and lowest triplet states in naphthalene, azulene, and linear and cyclic decapentaene.Kharkov University. Translated from Teoreticheskaya i Éksperimental'naya, Vola 27, No. 4, pp. 452–455, July–August 1991. Original article submitted January 14, 1991.     

The interaction between silica flat substrate and functional group–modified nanoparticles

Inspired by nature, the research of functionalized nanoparticles and nanodevices has been in-depth developed in recent years. In this paper, we theoretically studied the interaction between functional polyelectrolyte brush layer–modified nanoparticles and a silica flat substrate. Based on the Poisson–Nernst–Planck equations, the mathematical model is established. The changes of the volume charge density and electric field energy density when the nanoparticle interacts with the silica flat substrate under multi-ions regulation were investigated. The results show that when there is a strong interaction between the silica flat substrate and nanoparticles, such as the distances between the nanoparticle and silica flat substrate, which are 2 or 5 nm, the isoelectric point shift under the influence of silica flat substrate and the total charge density in the brush layer is jointly controlled by the cations in the solution and the volume charge density of the brush layer. With the increase of the distances between the nanoparticle and silica flat substrate, the regulation of the volume charge density of the brush layer dominates. These results will provide guidance for the movement mechanism of functionalized nanoparticles in silica nanochannels.     

Effect of cationic and anionic surfactants on the addition–elimination-type interaction between o-toluidine and d-glucose

The kinetics of the o-toluidine–d-glucose reaction has been studied as a function of [o-toluidine], [d-glucose], [acetic acid], and temperature by UV–visible spectrophotometry at 630 nm in the absence and presence of cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS). The reaction follows second-order kinetics, being unity in each of the reactants in both media. The effect of added surfactants has also been investigated. The model of micellar catalysis, such as the Menger–Portony model modified by Bunton, is applied to explain the catalytic role of CTAB and SDS micelles. The association/incorporation constants (K _s and K _n), the rate constant in micellar media (k _m), and the activation parameters of this system have been calculated and discussed. The value of the rate constant is found to be higher in SDS than in CTAB. Hydrophobic and electrostatic interactions are responsible for higher reaction rates in SDS. From all observed facts, a reaction mechanism involving a nucleophilic addition–elimination path has been suggested.     

Copper(II) interaction with amyloid-β: Affinity and speciation

Numerous conflicting values have been proposed regarding the affinity of Cu²⁺ for amyloid-β (Aβ) peptide, the causative agent of Alzheimer's disease. In the present review, we critically compare the two approaches employed so far (the K_d and the stability constant approach) to express the affinity of copper(II) for the amyloid-β (Aβ) peptide and highlight the limits and the advantages of the two approaches. We also analyze the conditions employed for some experiments, which we have taken as examples, highlighting some of the points that may have generated the deriving divergent propositions. Through the analysis of the species distribution, we show the implications that a correct speciation may have on data interpretation as well as on experiment planning. By doing so, this review aims at shifting the perspective on the binding issue from the classic K_d approach, based on low and high affinity binding sites – often referred to as component I and II, or form I and II – to stoichiometry determination and, as a consequence, to the speciation of Cu–Aβ complexes. Additionally, this review has the purpose of demonstrating that a quantitative assessment of the coordination sphere is complicated by the variety of equilibria often occurring over a relatively narrow pH range.