Regularities of homo- and heteroassociation of the pinacyanol cation in aqueous solution

The ability of the cation of the cyanine dye (pinacyanol) to association in an aqueous solution was studied. The most probable structures of the pinacyanol cation, its dimer, and heteroassociates with anionic forms of several dyes were proposed on the basis of an analysis of the spectral and calculated data. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1379–1389, July, 2008.     

4-(1-Alkylbenzimidazol-2-ylazo)-2-pyrazolin-5-ones: specific features of prototropic tautomerism

Quantum chemical calculations, ¹H and ¹³C NMR, and X-ray studies showed that, in contrast to 4-arylazo-2-pyrazolin-5-ones, 4-(1-alkylbenzimidazol-2-ylazo)-2-pyrazoline-5-ones mainly exist in the condensed phase as unusual ketoazine tautomers of high polarity, while the ketohydrazone tautomer stabilized by intramolecular hydrogen bond apparently predominates in the gas phase. According to calculations, various types of tautomerism are possible for 4-(benzimidazol-2-ylazo)-2-pyrazolin-5-ones, including mono- and bimolecular 1,3-, 1,5-, and 1,7-prototropic migrations proceeding by the single- and double-proton transfer mechanism with low activation energies (ΔE ^≠ ≈ 2–14 kcal mol⁻¹). Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1467–1478, July, 2008.     

Photo-induced energy and charge transfer dynamics in Y6 dimers

Y6 (BTP-4F) is one of the novel non-fullerene acceptors and its photo-physics significantly affects the efficiency of organic solar cells. Here, the photo-induced energy and charge transfer (CT) dynamics in four typical dimers (Y, C, S1, and S2)-TYPE from Y6 films are revealed by combining electronic structure theory calculations, rate theories, and quantum dynamics simulations. The rate theories show that in ground-state CT processes the Y-TYPE is bipolar with the largest rate among all dimers, and in excitation energy transfer the triplet rates are about 10⁵ smaller than the singlet ones, however, the singlet rates can reach 10¹³s⁻¹, which may lead to the rate theories invalid. The stochastic Schrödinger equation based on the diabatic Hamiltonian is thus adopted to reveal excited-state dynamics. The results show that three of the four dimers are H-aggregate except for S1-TYPE with J-aggregate property. However, these J/H-aggregate properties are excited-state dependent, for instance, the Y-TYPE becomes J-aggregate in the second excited-state. Furthermore, CT states are strongly mixed with the first two excited states, which can dramatically impact the energy transfer. Indeed, the dynamic simulations clarify that the excited-state energy relaxation mediated by CT states can be performed in the first 20 fs, and the CT-state population is even non-negligible in the quasi-stationary distribution.     

Tetrel-Centered Exchange Cascades to Decouple Inhibition and Induction of Thiol-Mediated Uptake: Introducing Cell-Penetrating Thiolactones,Focus on Reversible Michael Acceptor Dimers

This study adds thiolactones to the collection of cascade exchangers (CAXs) and reports with dynamic covalent Michael acceptor dimers the first CAXs that rather inhibit than enable thiol-mediated uptake. The superior performance of dimers compared to monomeric Michael acceptors as inhibitors might suggest that top inhibitors move along thiol/ate arrays without losing covalent contact, while cell penetrators exchange along disulfide arrays. This decoupling of inhibition and induction of thiol-mediated uptake is important because the latter is promising for drug delivery, while the former possibly helps to reveal targets associated with antiviral, antithrombotic and antitumor activity, leading to drug discovery. These results are consistent with the working model of thiol-mediated uptake as a general complex network in charge of bringing matter into cells, and thus support its validity.     

Synthesis,characterization of new carboxylic acid derivatives bearing 1,3,4-thiadiazole moiety and study their liquid crystalline behaviors

Thirteen carboxylic acid derivatives containing 1,3,4-thiadiazole ring in their core and swinging alkoxy terminal were synthesized. They were characterized by ¹H, ¹³C NMR spectroscopy, FTIR, and mass spectrometry. Their liquid crystalline behaviors have been studied by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The 1,3,4-thiadiazole compounds in this study were 2,5 di-substituted asymmetrical, alkoxy, and carboxy linkages. The compounds with alkoxy of long carbon chains (n > 7) displayed Smectic C phase. The liquid crystal properties were found to be affected by the length of alkoxy chain attached to the phenyl moiety and the two types of the dimeric form were resulted from the hydrogen bonding interaction between carboxylic acid molecules.     

Magnetic and redox properties in hydroxo‐ and alkoxo‐bridged Fe(III) binuclear complexes: A density functional study

DFT calculations were carried out in order to deduce the dependence of magnetic coupling on the structure of doubly hydroxide/alkoxide‐bridged diiron(III) dimers. The broken‐symmetry formalism was employed to calculate the magnetic exchange parameter J. The potential surfaces of the ground state display a geometrical minimum at an Fe O(H) Fe angle of 105° and FeFe distance of 3.2 Å, in good agreement with experimental values. The calculated correlation between the magnetic coupling with the geometrical structure agrees well with the experimental literature data, although always overestimated. Electrochemical measurements show that a one‐electron reduction is likely to cause dissociation into pseudooctahedral, monomeric subunits, and, consequently, no calculations were made for the reduced dimeric species. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 72: 61–71, 1999     

Molecular Recognition Studies on Modified Cyclodextrins

This account describes our research progress in recent years in the areas of the molecular recognition studies on modified cyclodextrins, including positively charged cyclodextrins, cyclodextrin derivatives with hydrophobic substituent, and dimeric cyclodextrins. Calorimetric titration and various spectrometric techniques were employed to determine the complex stability constants, as well as the thermodynamic parameters, for their inclusion complexation with diverse guest molecules. The results obtained have been discussed from the viewpoint of size/shape‐matching, induced‐fit, geometric compensation, and multiple recognition. Thermodynamically, the compensatory relationship between ΔH and TΔS was found to be exhibited in the inclusion complexation of modified cyclodextrin.     

Synthesis and mesomorphic behavior of symmetrical chiral liquid crystal dimers incorporating ester linked biphenyl- naphthyl cores and terminal vinyl group

A series of symmetrical chiral, liquid crystal dimeric molecules possessing ester- linked, biphenyl-naphthyl cores with varied spacer lengths and terminal vinyl groups have been synthesized using Naproxen as the synthetic precursor. The synthesized symmetrical chiral dimers were characterized by 1H NMR spectroscopy, and their liquid crystalline behavior was confirmed by DSC and HOPM studies. Structural effects on the mesomorphic and physicochemical properties were investigated in terms of variation of chiral chain length. The synthesized dimeric compounds exhibited SmX^*, SmC^*, SmA^*, N^*, BPI^*, and BPII^* mesophase sequences. An odd-even effect was observed in the dimers and the duration of the mesophase decreased with increasing spacer length. The synthesized vinyl substituted liquid crystalline dimers are particularly useful in understanding liquid crystal polymorphism and act as model compounds for liquid crystal polymers.     

ARelativisticDensityFunctionalStudyofEarlyTransitionMetalGroupⅢB－VBDimers￣＊

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A Non-Covalent Dimer Formation of Quaternary Ammonium Cation with Unusual Charge Neutralization in Electrospray-Ionization Mass Spectrometry

Specific and nonspecific non-covalent molecular association of biomolecules is characteristic for electrospray-ionization mass spectrometry analysis of biomolecules. Understanding the interaction between two associated molecules is of significance not only from the biological point of view but also gas phase analysis by mass spectrometry. Here we reported a formation of non-covalent dimer of quaternary ammonium denatonium cation with +1 charge detected in the positive ion mode electrospray ionization mass spectrometry analysis of denatonium benzoate. Hydrogen deuterium exchange of amide and carbon-bonded hydrogens revealed that charge neutralization of one denatonium cation is the consequence of amide hydrogen dissociation. DFT (Density Functional Theory) calculations proved high thermodynamic stable of formed dimer stabilized by the short and strong N..H-N hydrogen bond. The signal intensity of the peak characterizing non-covalent dimer is low intensity and does not depend on the sample concentration. Additionally, dimer observation was found to be instrument-dependent. The current investigation is the first experimental and theoretical study on the quaternary ammonium ions dimer. Thus the present study has great significance for understanding the structures of the biomolecules as well as materials.