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.     

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.     

Syntheses and structures of anomeric quaternary ammonium β-glucosides and comments on the anomeric C-N bond lengths

We report convenient syntheses of anomeric quaternary ammonium β-glucosides in both protected and deprotected forms, together with X-ray structural investigations of two of the products. Both the quaternisation of a protected anomeric N,N-(dimethylamino)glucose, derived in two high-yielding steps from the anomeric azide, and the direct reaction of glucose or 6-O-trityl glucose with a secondary amine, followed by protection and quaternisation, are viable routes. We also discuss the significance, in terms of stereoelectronic effects, of the observed C-N bond lengths and the stabilities of the products.     

“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.     

Substituent-dependent negative hyperconjugation in 2-aryl-1,3-N,N-heterocycles. fine-tuned anomeric effect?

The epimerization reactions of conformationally inflexible 2-aryl-1,3-N,N-heterocycles were used as model systems to study the role of the nitrogen lone pair-C2 associated antibonding orbital hyperconjugative interactions in the experimentally observed substituent-dependent generalized anomeric effect. The measured reaction free enthalpies were found to correlate well with the sum of the hyperconjugative stabilization energies of all the vicinal donor-acceptor orbital overlaps around C2, obtained from ab initio NBO analysis, and both quantities correlated linearly with the Hammett-Brown substituent constant. The individual stereoelectronic interactions (n(N)-sigma(C2)(-)(N), n(N)-sigma(C2)(-)(Ar), n(N)-sigma(C2)(-)(H)) were also observed to exhibit a substituent dependence, despite their distance from the 2-aryl substituent and their nonperiplanar arrangement. The higher the electron-withdrawing effect of the 2-aryl substituent, the larger was the stabilization for n(N)-sigma(C2)(-)(Ar), while the overlaps n(N)-sigma(C2)(-)(N) and n(N)-sigma(C2)(-)(H) changed in the opposite sense. The different polarization of the acceptor sigma orbitals, caused by the 2-aryl substituent, accounted for the observed propagation of the substituent effect. These results promote a detailed explanation of the useful tautomeric behavior of the 2-aryl-1,3-X,N-heterocycles, and reveal the nature of the connection between the anomeric effect and the Hammett-type linear free energy relationship.     

Sensing or no sensing: can the anomeric effect be probed by a sensing molecule?

The anomeric effect plays a central role in carbohydrate chemistry, but its origin is controversial, and both the hyperconjugation model and the electrostatic model have been proposed to explain this phenomenon. Recently, Cocinero et al. designed a peptide sensor, which can bind to a sugar molecule methyl D-galactose, and claimed that the anomeric effect can be sensed by the spectral changes from the β- to the α-complex, which are ultimately attributed to the lone pair electron density change on the endocyclic oxygen atom [Nature 2011, 469, 76; J. Am. Chem. Soc. 2011, 133, 4548]. Here, we provide strong computational evidence showing that the observed spectral changes simply come from the conformational differences between the α- and β-anomers, as the replacement of the endocyclic oxygen atom with a methylene group, which disables both the endo- and the exo-anomeric effects in methyl D-galactose, leads to similar spectral shifts. In other words, the "sensor" cannot probe the anomeric effect as claimed. We further conducted detailed energetic and structural analyses to support our arguments.     

“Climate change” and the “butterfly effect” in an eighteenth century monograph

Long before the phrases “climate change” and “butterfly effect” were incorporated into the mainstream literature, these phrases appeared in an appropriate context almost verbatim in the first Chapter of a book entitled “The Emigrant” published in the mid-nineteenth century (in 1846) by Sir Francis Bond Head (1793–1875). Head was Upper Canada’s sixth Lieutenant Governor under King George IV and Queen Victoria. Head claimed that forest wildfires were “changing the climate” of North America as manifested in a warming effect “on the thermometer”. In that author’s account, these fires were provoked by First Nations to create fly-free zones meant to attract game that they could then hunt more readily. Head used language such as “swarms of little flies, strange as it may sound, are, and for many years have been, most materially altering the climate…” which is remarkably reminiscent of E. N. Lorenz’s (1917–2008) “butterfly effect” of the theory of chaotic dynamical systems. The historical context and the rationales that may have led Head to use this contemporary environmental language in a proper context are briefly discussed.     

Evaluation of solvents’ effect on solubility,intermolecular interaction energies and habit of ascorbic acid crystals

Solubility of active pharmaceutical ingredient (API) in solvents is very important for drug development and manufacturing. Solubility data may provide further information such as thermochemical properties and intermolecular interactions that may lead to a better understanding of the formation of API crystals. In this study, solubility of ascorbic acid was determined by gravimetric method in four different commonly used polar protic solvents: water, methanol, ethanol and 2-propanol. The solubility of ascorbic acid crystal was also predicted using Conductor-like Screening Model – Realistic Solvent (COSMO-RS) approach. In this computational analysis, the generated ΔG values are based on the solubilities that were experimentally obtained to simulate the intermolecular forces. The intermolecular interaction data from COSMO-RS provide an insight into the relationship between the intermolecular interactions and its crystal habit across four different polar protic solvents. The habit of the crystals was then determined using light microscopy and scanning electron microscopy techniques, while the polymorphic form of the crystals was identified by X-ray powder diffraction and single X-ray diffraction techniques. The solubility and characterization data showed that the solvents with high polarity increased the solubility of ascorbic acid. The data also showed that different solvent polarity influenced the crystal habit, but did not change the crystal structure to form a new polymorph.     

“In situ” EPR studies of interaction between benzene and ZSM-5 zeolites

The effect of the state of adsorbed layers on the formation of monomeric and dimeric benzene cation-radicals (CR) on ZSM-5 zeolites has been studied. Removal of benzene is shown to be accompanied by disappearance of CR, which is reversible and takes place with preservation of the sites for their stabilization.

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- (KP) ZSM-5. , KP, .

     

Tailoring of multifunctional cellulose fibres with “lotus effect” and flame retardant properties

This research aimed to create multifunctional cellulose fibres with water- and oil-repellent, self-cleaning, and flame retardant properties. A sol mixture of fluoroalkyl-functional siloxane, organophosphonate and methylol melamine resin was applied to cotton fabric by the pad-dry-cure method. Successful coating was verified by atomic force microscopy and Fourier transform infrared spectroscopy. The functional properties of the coated fibres were investigated using the static contact angles of water and n-hexadecane, the water sliding angles, the vertical test of flammability, the limiting oxygen index, and simultaneous thermal analysis. The results reveal that a homogeneous composite inorganic–organic polymer film formed on the cotton fabric surface exhibited the following properties: static contact angle of water of 150° and of n-hexadecane of 128°, water sliding angle of 10°, limiting oxygen index of 34 %, and high thermal stability. These results demonstrate the synergistic activity of the compounds in the coating, which resulted in the creation of a “lotus effect” on the fabric surface as well as excellent flame retardancy and thermal stability.     

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     

DFT study of the conductance of molecular wire:The effect of coupling geometry and intermolecular interaction on the transport properties

The density functional theory (DFT) combining with the non-equilibrium Green functions (NEGF) method is applied to the study of the electronic transport properties for a Di-thiol-benzene (DTB) molecule coupled to two Au(111) surfaces. The dependence of the transport properties on the bias, the coupling geometry of the molecule-electrode interface, and the intermolecular interaction are examined in detail. The results show that the existence of the hydrogen atom at the end of the DTB molecule would significantly decrease the transmission coefficients, and then the differential conductance (dI/dV). By changing the position of the DTB molecule located between two electrodes a maximum value of calculated current is observed. It is also found that the intermolecular interaction will strongly influence the transport properties of the system studied.     

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:

     

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.     

Fragmentation of benzylpyridinium “thermometer” ions and its effect on the accuracy of internal energy calibration

Electrospray ionization mass spectrometry (ESI-MS) is a powerful analytical method to study biomolecules and noncovalent complexes. The prerequisite for their intact observation is soft ionization. In ESI, the internal energy of ions is primarily influenced by collisional activation in the source. The survival yield method is frequently used to probe the energy deposition in ions during the electrospray process. In the present work, we investigate the fragmentation pathways of para-substituted benzylpyridinium ions, the most widely used “thermometer ions” in the survival yield method. In addition to the C-N bond cleavage, alternative fragmentation channels were found for the compounds studied. We consider these pathways to result from intramolecular rearrangements. The effect of these additional fragments on the accuracy of the internal energy calibration is estimated for both collision-cell and in-source collision-induced dissociation (CID). Altogether, results presented suggest that a correction of the energy scale is necessary for the method based on benzylpyridinium ions to precisely quantify ion internal energies.     

Photochromic fulgides and spirooxazines: mechanism and substituent effect on photoreactions

Molecular design, synthesis and photochromic properties of spirooxazines and fulgides are described. In the case of fulgides, the change of the substituents may lead to different photochromic properties and different photoreactions of the kind of compounds. In photochromic process of pyrryl-substituted fulgides, the excited singlet state is the mam species, but the excited triplet state is also involved. However, no excited triplet state has been observed in cyclization of aryl-substituted fulgides. In the case of spirooxazines, the substituents at 2'-position have great effect on the formation of photoproduct and on the mechanism of photoreaction. The increase of steric hindrance of the 2'-position substituent gives rise to the decrease of the quantum yield for the formation of photochromic merocyanine (PMC) and the increase of the relative quantum yield for the charge separated twist intermediate (CT).     

Experimental and theoretical determination of the accurate CH/π interaction energies in benzene-alkane clusters: correlation between interaction energy and polarizability

The CH/π interaction energies in benzene-alkane model clusters were precisely determined by laser spectroscopy and theoretical calculations. Two-color resonant two-photon ionization spectroscopy was employed to experimentally determine the interaction energies with isomer selectivity. High precision ab initio calculations were also performed to evaluate the CCSD(T) level interaction energies of various isomers at the basis set limit. Binary clusters of benzene with ethane, propane, n-butane, iso-butane, and cyclohexane were studied. The experimental interaction energies were well reproduced by the theoretical evaluations. The magnitude of the interaction energy clearly correlates with the average polarizability of the alkane moiety, demonstrating that the CH/π interaction energy is dominated by the dispersion interaction. On the other hand, the number of C-H groups in contact with the phenyl ring has no relation to the magnitude of the interaction energy, and it indicates that the role of the hydrogen atom in the CH/π interaction is essentially different from that in hydrogen bonds.     

Is there a generalized reverse anomeric Effect? substituent and solvent effects on the configurational equilibria of neutral and protonated N-arylglucopyranosylamines and N-aryl-5-thioglucopyranosylamines

The effects of substitution and solvent on the configurational equilibria of neutral and protonated N-(4-Y-substituted-phenyl) peracetylated 5-thioglucopyranosylamines (Y = OMe, H, CF(3), NO(2)) 1-4 and N-(4-Y-substituted-phenyl) peracetylated glucopyranosylamines (Y = OMe, H, NO(2)) 9-11 are described. The configurational equilibria were determined by direct integration of the resonances of the individual isomers in the (1)H NMR spectra after equilibration of both alpha- and beta-isomers. The equilibrations of the neutral compounds 1-4 in CD(3)OD, CD(3)NO(2), and (CD(3))(2)CO were achieved by HgCl(2) catalysis and those of the neutral compounds 9-11 in CD(2)Cl(2) and CD(3)OD by triflic acid catalysis. The equilibrations of the protonated compounds in both the sulfur series (solvents, CD(3)OD, CD(3)NO(2), (CD(3))(2)CO, CDCl(3), and CD(2)Cl(2)) and oxygen series (solvents, CD(2)Cl(2) and CD(3)OD) were achieved with triflic acid. The substituent and solvent effects on the equilibria are discussed in terms of steric and electrostatic effects and orbital interactions associated with the endo-anomeric effect. A generalized reverse anomeric effect does not exist in neutral or protonated N-aryl-5-thioglucopyranosylamines and N-arylglucopyranosylamines. The anomeric effect ranges from 0.85 kcal mol(-)(1) in 2 to 1.54 kcal mol(-)(1) in 10. The compounds 1-4 and 9-11 show an enhanced endo-anomeric effect upon protonation, ranging from 1.73 kcal mol(-)(1) in 2 to 2.57 kcal mol(-)(1) in 10. We estimate the increase in the anomeric effect upon protonation of 10 to be approximately 1.0 kcal mol(-)(1). However, this effect is offset by steric effects due to the associated counterion which we estimate to be approximately 1.2 kcal mol(-)(1). The values of K(eq)(axial-equatorial) in protonated 1-4 increase in the order OMe < H < CF(3) < NO(2), in agreement with the dominance of steric effects (due to the counterion) over the endo-anomeric effect. The values of K(eq)(axial-equatorial) in protonated 9-11 show the trend OMe > H < NO(2) that is explained by the balance of the endo-anomeric effect and steric effects in the individual compounds. The trends in the values of the C(1)-H(1) coupling constants for 1-4 and the corresponding deacetylated compounds 5-8 as a function of substituent and alpha- or beta-configuration are discussed in terms of the Perlin effect and the interplay of the endo- and exo-anomeric effects.