Are there reliable DFT approaches for 13C NMR chemical shift predictions of fullerene C60 derivatives?

The relationships between experimental and theoretical ¹³C NMR chemical shifts of a pristine fullerene C₆₀, monoadducts from [2 + n] cycloaddition (n = 1–3), and one [2 + 1] bis‐adduct are systematically analyzed for the first time by using diverse quantum‐chemical levels of theory. These levels involved B3LYP, B3PW91, B97‐2, mPW1PW91, PBE1PBE, and X3LYP hybrid functionals combined with 3‐21G, 6‐31G, 6‐31G(d), 6‐31G(d,p), 6‐31G(d,2p), LanL2DZ, and SDDAll basis sets. X3LYP/6‐31G approach is determined to have the lowest deviations from the ¹³C NMR experimental data compared to the other methods for all the fullerene compounds (mean absolute error value is 0.856 ppm and root mean squared error value is 1.197 ppm). The highest deviations are characteristic for α (sp² C2/C5/C8/C10) and β (sp² C6/C7/C11/C12) carbon atoms relative to a functionalization site and for those (sp³ C1/C9) directly attached with a side fragment in the [2 + n] monoadducts (n = 1–3). A probable reason of such deviation is that the approaches do not take into account a contribution of paramagnetic ring currents to ¹³C NMR chemical shifts. The results will be useful in design of novel fullerene derivatives and in performing unambiguous ¹³C NMR chemical shift assignments with modern quantum chemistry calculations.     

Effect of Laser-Induced Optical Breakdown on the Structure of Bsa Molecules in Aqueous Solutions: An Optical Study

The influence of laser radiation of a typical surgical laser on the physicochemical properties of the Bovine Serum Albumin (BSA) protein was studied. It was established that the physicochemical characteristics of optical breakdown weakly depend on the concentration of protein molecules. At the same time, the patterns observed for an aqueous solution of BSA irradiated with a laser for different time periods were extremely similar to the classical ones. It was established that after exposure to laser radiation, the optical density of protein solutions increases. At the same time, the intensity of BSA fluorescence due to aromatic amino acid residues decreases insignificantly after exposure to laser radiation. In this case, the position of the excitation and emission maximum does not change, and the shape of the fluorescence spot on 3D maps also does not change significantly. On the Raman spectrum after exposure to laser radiation, a significant decrease in 1570 cm⁻¹ was observed, which indicates the degradation of α-helices and, as a result, partial denaturation of BSA molecules. Partial denaturation did not significantly change the total area of protein molecules, since the refractive index of solutions did not change significantly. However, in BSA solutions, after exposure to laser radiation, the viscosity increased, and the pseudoplasticity of aqueous solutions decreased. In this case, there was no massive damage to the polypeptide chain; on the contrary, when exposed to optical breakdown, intense aggregation was observed, while aggregates with a size of 400 nm or more appeared in the solution. Thus, under the action of optical breakdown induced by laser radiation in a BSA solution, the processes of partial denaturation and aggregation prevail, aromatic amino acid residues are damaged to a lesser extent, and fragmentation of protein molecules is not observed.     

Adsorbed liposome deformation studied with quartz crystal microbalance

Deformation of surface-adsorbed liposomes is an important parameter that governs the kinetics of their transformations, but one that is very difficult to measure in the case of nm-size liposomes. We investigate the deformation of dimyristoyl phosphatidyl choline liposomes by quartz crystal microbalance (QCM) as a function of temperature and show that it follows the dependence of this lipid's bending modulus on temperature, as expected from theoretical considerations. To corroborate our approach, we model QCM response from adsorbed liposomes by explicitly considering their shape and mechanical properties.     

Amine-Reactive BODIPY Dye: Spectral Properties and Application for Protein Labeling

A boron-dipyrromethene (BODIPY) derivative reactive towards amino groups of proteins (NHS-Ph-BODIPY) was synthesized. Spectroscopic and photophysical properties of amine-reactive NHS-Ph-BODIPY and its non-reactive precursor (COOH-Ph-BODIPY) in a number of organic solvents were investigated. Both fluorescent dyes were characterized by green absorption (521–532 nm) and fluorescence (538–552 nm) and medium molar absorption coefficients (46,500–118,500 M⁻¹·cm⁻¹) and fluorescence quantum yields (0.32 – 0.73). Solvent polarizability and dipolarity were found to play a crucial role in solvent effects on COOH-Ph-BODIPY and NHS-Ph-BODIPY absorption and emission bands maxima. Quantum-chemical calculations were used to show why solvent polarizability and dipolarity are important as well as to understand how the nature of the substituent affects spectroscopic properties of the fluorescent dyes. NHS-Ph-BODIPY was used for fluorescent labeling of a number of proteins. Conjugation of NHS-Ph-BODIPY with bovine serum albumin (BSA) resulted in bathochromic shifts of absorption and emission bands and noticeable fluorescence quenching (about 1.5 times). It was demonstrated that the sensitivity of BSA detection with NHS-Ph-BODIPY was up to eight times higher than with Coomassie brilliant blue while the sensitivity of PII-like protein PotN (PotN) detection with NHS-Ph-BODIPY and Coomassie brilliant blue was almost the same. On the basis of the molecular docking results, the most probable binding sites of NHS-Ph-BODIPY in BSA and PotN and the corresponding binding free energies were estimated.     

Dissipative plasmon‐solitons in multilayer graphene

Nonlinear properties of a multi‐layer stack of graphene sheets are studied. It is predicted that such a structure may support dissipative plasmon‐solitons generated and supported by an external laser radiation. Novel nonlinear equations describing spatial dynamics of the nonlinear plasmons driven by a plane wave in the Otto configuration are derived and the existence of single and multi‐hump dissipative solitons in the graphene structure is predicted.     

Reflections on spontaneous asymmetric synthesis by amplifying autocatalysis

Spontaneous generation of chirality was observed in the course of studying the mechanism of asymmetric autocatalysis by NMR in ZnR2 alkylation of pyrimidin-5-aldehydes. A systematic study was carried out in order to discover its origins. Even in clean fresh non-glass reaction vessels spontaneous ee was clearly observed, and was not dependent on any single reaction parameter. For comparison it was demonstrated that enantiomerically pure Zn alkoxide catalyst could control the configuration of the reaction product even when present at below micromolar concentrations. The high propensity of the Soai reaction system to produce an enantiomerically enriched product without initial bias is suggested to result from stochastic effects. These are especially important in autocatalysis because all the final products can be derived by breeding from a small number of initial events. The statistical excess of one enantiomer in that set is sufficient to generate a measurable ee in the product. The process is aided by the requirement for dimerisation before the product is an active catalyst. An enumeration that rationalises these observations is provided.     

Solvent extraction and self-assembly of nanosized aggregates of p-tert-butyl thiacalix[4]arenes tetrasubstituted at the lower rim by tertiary amide groups and monocharged metal cations in the organic phase

New p-tert-butyl thiacalix[4]arenes functionalized with morpholide and pyrrolidide groups at the lower rim in cone, partial cone, and 1,3-alternate conformations were synthesized, and their receptor properties for monocharged cations (alkali metal and silver ions) were studied using the picrate extraction method and dynamic light scattering (DLS). To evaluate the ability of the p-tert-butyl thiacalix[4]arene derivatives to recognize metal ions, liquid-liquid extraction of their picrate salts has been carried out in a mutually saturated water-dichloromethane system. The degrees of extraction and the extraction constants for monocharged metal cations (Li⁺, Na⁺, K⁺, Cs⁺) have been determined. The ability of the systems, consisting of host and guest molecules, to self-assembly was proved by DLS using a Zetasizer Nano ZS particle size analyzer. It was shown that all the investigated thiacalix[4]arenes are able to form nanoscale particles with silver cations under the experimental conditions. The pyrrolidide derivative in the cone conformation showed both self-association and aggregation processes with lithium cations. The degree of extraction for all the investigated systems that formed nanoscale aggregates in the organic phase was more than 67% and the extraction constants, log K_ex determined by the picrate extraction method, more than 6.     

Development of High-Power Long-Pulse Submillimeter-Wave Free-Electron Lasers on the Basis of the Linear Induction Accelerator Complex

Radiophysics and Quantum Electronics - The high-power long-pulse submillimeter-wave free-electron laser (FEL) is developed jointly by the Institute of Nuclear Physics and the Institute of Applied...