Exploring the Concept of Aromaticity on Complexes of a Fourfold Benzannulated Cyclopentadienyl Ligand

The ligand dibenzo[c,g]fluorenide (Dbf^?), combines a cyclopentadienide ligand and 1,1′‐binaphthyl fragment in one molecule. Preliminary investigations confirmed the special electronic situation in this 6π‐electron donor by way of a series of novel transition‐metal complexes. Herein, the electron delocalization was investigated in detail by means of DFT calculations in combination with calculations on the nucleus‐independent chemical shifts (NICS). These results clearly prove that the Dbf^? ion gains the largest aromatic stabilization among all benzannulated fluorenides, and there are two almost olefinic C?C bonds in this structure. These bonds undergo cyclopropanation when treated with ZnEt₂ and ClCH₂I in a modified Simmons–Smith reaction.     

Weakly Bound Environment of Molecular Oxygen as a Catalyst of Photooxidation

In the review, the spectral and photochemical manifestations of the catalytic effect of a weakly bound environment on photoprocesses involving oxygen in a gas, solutions, and on the surface are examined in historical sequence. The progress in an experimental study of the nature of supramolecular photochemistry of weakly bound oxygen complexes associated with the use of X–O2 van der Waals complexes generated in molecular beams as a model system is considered. A review of the results of studying supramolecular photochemistry in X–O2 complexes using the velocity map imaging of photofragments is given. The nature of the “dramatic” enhancement of UV absorption in weakly bound oxygen complexes and the mechanism of photochemical processes provided by the “enhanced” absorption are discussed. Available experimental data and conclusions on the nature of absorption bands appearing in weakly bound X–O2 complexes, which give rise to the formation of singlet oxygen and other photooxidation intermediates, are considered.     

The Inner Phase of Molecular Container Compounds as a Novel Reaction Environment

The conceptual idea of molecular container compoundsand their synthesis has opened an entirely new andvery interesting research field: the chemistry of andwithin molecular container compounds and theircomplexes. Molecular containers have inner phases justlarge enough to accommodate a single guest molecule.Beginning with Donald J. Cram's first synthesis of acarcerand, which permanently entrapped a single guestmolecule, many other containers such ashemicarcerands, molecular lantern, self-assembledcapsules and fullerenes have been synthesized andstudied. Not only is the design and development of newcontainer compounds an ongoing challenge for organicchemists, but also the systematic investigation ofchemical reactions within their inner phases. Theresults of a large variety of inner phase reactionsspanning acid-base, reduction, oxidation, nucleophilicsubstitution, addition, thermal, photochemical andpericyclic reactions have provided us with moreinsight into the relationship between bulk phase andinner phase reactants and the mechanism of thetransfer of electrons and photons through theinsulating shell of a container molecule. They havealso led to very spectacular applications of molecularcontainer compounds such as the stabilization ofreactive intermediates by incarceration. Thesehighlights of inner phase chemistry and the currentefforts and successes towards using molecularcontainers as catalytic reaction vessels are presentedand discussed.     

Molecular imprinted Nylon-6 as a recognition material of amino acids

Nylon-6 was functionalized by phase inversion molecular imprinting technique to introduce l-glutamine recognition property. For imprinting l-glutamine in the polymer, 20 wt.% of Nylon-6-formic acid solution with 8 wt.% of l-glutamine template was used for the phase inversion process in water. The resulted polymer including the template molecule was washed with acetic acid solution to extract the template from the polymer. The substrate binding experiments of the l-glutamine imprinted polymer were examined in aqueous l-glutamine, d-glutamine, l-glutamic acid, and d-glutamic acid solution. The binding of l-glutamine increased with the increase of the amino acid concentration from 5 to 20 μM. The value of equilibrium binding constant for l-glutamine, K_E=4.9×10⁵ M⁻¹, was larger than that for d-glutamine, K_E=1.5×10⁵ M⁻¹. The recognition experiments were extended to membrane filtration and quartz-crystal microbalance response by using the imprinted Nylon-6. Evidence was also presented by FT-IR analysis that the amide-hydrogen-bonding interaction between the imprinted Nylon-6 and template was originated for the amino acid recognition.     

Using Molecular Quantum Similarity Measures as Descriptors in Quantitative Structure-Toxicity Relationships

Abstract

In this paper molecular quantum similarity measures (MQSM) are used to describe molecular toxicity and to construct Quantitative Structure-Toxicity Relationships (QSTR) models. This study continues the recently described relationships between MQSM and log P values, which permits to use the theoretical MQSM as an alternative to the empirical hydrophobic parameter in QSPR studies. In addition a new type of MQSM is presented in this work: it is based on the expectation value of electron–electron repulsion energy. The molecular properties studied here, as application examples are aquatic toxicity, toxicology on Bacteria and inhibition of a macromolecule employing four different molecular sets.     

Colorectal Adenocarcinoma Cell Culture in a Microfluidically Controlled Environment with a Static Molecular Gradient of Polyphenol

To study the simultaneous effect of the molecular gradient of polyphenols (curcumin, trans-resveratrol, and wogonin) and biological factors released from tumor cells on apoptosis of adjacent cells, a novel microfluidic system was designed and manufactured. The small height/volume of microfluidic culture chambers and static conditions allowed for establishing the local microenvironment and maintaining undisturbed concentration profiles of naturally secreted from cells biochemical factors. In all trials, we observe that these conditions significantly affect cell viability by stimulating cell apoptosis at lower concentrations of polyphenols than in traditional multiwell cultures. The observed difference varied between 20.4–87.8% for curcumin, 11.0–37.5% for resveratrol, and 21.7–62.2% for wogonin. At low concentrations of polyphenols, the proapoptotic substances released from adjacent cells, like protein degradation products, significantly influence cell viability. The mean increase in cell mortality was 38.3% for microfluidic cultures. Our research has also confirmed that the gradient microsystem is useful in routine laboratory tests in the same way as a multiwell plate and may be treated as its replacement in the future. We elaborated the new repetitive procedures for cell culture and tests in static gradient conditions, which may become a gold standard of new drug investigations in the future.     

Molecular rotation as a tool for exploring specific solute-solvent interactions.

Solute-solvent interactions play an important role in determining the physicochemical properties of liquids and solutions. As a consequence, understanding these interactions has been one of the long-standing problems in physical chemistry. This Minireview describes our approach towards attaining this goal, which is to investigate rotational relaxation of a pair of closely related, medium-sized nondipolar solutes in a set of appropriately chosen solvents. Our studies indicate that solute-solvent hydrogen bonding significantly hinders solute rotation. We have also examined the role of solvent size both in the absence and presence of specific interactions and it has been observed that the size of the solvent has a bearing on solute rotation especially in the absence of specific interactions. Our results point to the fact that only strong solute-solvent hydrogen bonds have the ability to impede the rotation of the solute molecule because, in such a scenario, hydrogen-bonding dynamics and rotational dynamics transpire on comparable time scales. This aspect has been substantiated by measuring the reorientation times of the chosen solutes in solvents such as ethanol and trifluoroethanol, which have distinct hydrogen-bond donating and accepting abilities, and correlating them with solute-solvent interaction strengths. As an alternative treatment, it has been shown that specific interactions between the solute and the solvent can be modeled as dielectric friction with the extended charge distribution model. This approach is not unrealistic considering the fact that specific as well as non-specific interactions are electrostatic by nature and the differences between them are subtle.     

无机化学中空间效应的定量研究 Ⅳ.剩余空间容纳新配体的可能性

以含有三个π键环戊二烯的金属有机物分子片(MCp_3)为例,说明了剩余空间与新配体的匹配是弱轨道作用条件下分子片与新配体结合的必要条件。     

Chelate Complexes with the P=O Double Bond – a New Concept for Molecular Recognition

Compounds capable of forming chelate complexes with their P=O double bond systems represent excellent host molecules for most of the biologically important classes of organic cations in polar media. Additional cooperative hydrogen bonds render even simple bisphosphonates highly selective: mono- and disaccharides, 1,2- and 1,3-amino alcohols, arginine derivatives in peptidic environment and aromatic guanidines can now be recognized with high efficiency and high selectivity. The Review Article presents this relatively new concept for molecular recognition which imitates in many cases the recognition motifs found in nature itself     

Aromaticity strongly affected by substituents in fulvene and heptafulvene as a new method of estimating the resonance effect

Very good dependences of the variation in π-electron delocalisation expressed by the aromatic character of the ring, defined by the geometry-based HOMA model and NICS index in mono 6-substituted fulvene and 8-substituted heptafulvene derivatives on the nature of substituent allows us for defining the substituent through resonance effect (by means of σ_p⁺ and σ_p⁻ scale of the substituent effect). The analysis is based on 35 optimised systems at DFT B3LYP/6-311+G^** level of theory.     

[32]π Fused Core‐Modified Heptaphyrin with Möbius Aromaticity

A new fused core‐modified 32π heptaphyrin with Möbius aromatic character is reported. The ¹H NMR data indicated a weak Möbius aromaticity at 298 K; however, at 213–183 K, the molecule predominates [4n]π Möbius conformation with strong diatropic ring current, which was further confirmed by X‐ray analysis. The protonation experiment led to preservation of the Möbius aromaticity at 298 K. Nevertheless, the experimental results were further supported by theoretical studies. Overall, this study represents the first example of Möbius aromatic fused core‐modified expanded porphyrin.     

Molecular Umbrella as a Nanocarrier for Antifungals

A molecular umbrella composed of two O-sulfated cholic acid residues was applied for the construction of conjugates with cispentacin, containing a “trimethyl lock” (TML) or o-dithiobenzylcarbamoyl moiety as a cleavable linker. Three out of five conjugates demonstrated antifungal in vitro activity against C. albicans and C. glabrata but not against C. krusei, with MIC₉₀ values in the 0.22–0.99 mM range and were not hemolytic. Antifungal activity of the most active conjugate 24c, containing the TML–pimelate linker, was comparable to that of intact cispentacin. A structural analogue of 24c, containing the Nap-NH₂ fluorescent probe, was accumulated in Candida cells, and TML-containing conjugates were cleaved in cell-free extract of C. albicans cells. These results suggest that a molecular umbrella can be successfully applied as a nanocarrier for the construction of cleavable antifungal conjugates.