Modelling intra- and intermolecular vibrations under the harmonic oscillator approximation: from symmetry-adapted to coarse-grained coordinate approaches

Motions of some four-body spring–mass systems are analyzed as models of normal-mode vibrations of bimolecular systems interacting via intermolecular forces. The formulation is first introduced with Cartesian coordinates, and the basis is subsequently transformed to symmetry-adapted coordinates; this transformation easily leads to coarse graining of atomic displacement vectors. We derived an analytical form for the eigenfrequencies of homodimeric coupled oscillators, and an approximated form for heterodimeric coupled oscillator. Compared to the primitive pseudodiatomic approximation, this approach provides a more realistic view of intermolecular stretching motions.     

Theoretical studies on the intra- and intermolecular C-H activation by T-shaped pincer complexes

Three coordinated, T-shaped (PNP)M^I (M = Co, Ru, Rh, Os and Ir) and [(PCP)Pt⁰]⁻, as well as their reactivities for intra- and intermolecular C-H activation have been studied by DFT methods. The experimental observed reactivities were well reproduced. The calculation also generated structural and energetic information which the experimental values were not yet available. We found that the intramolecular C-H activation is in general possible for the low spin (PNP)M^I. Intermolecular C-H activation is not preferred either thermodynamically or kinetically, but could be in competition if the intramolecular activation is reversible. Using model compounds, we found that the intramolecular C-H activation reactivity is not sensitive to steric effects of the bulky ligands. However, the strain of the four-membered ring in the product significantly reduces the reactivity, and the driving force increases by 4.51-12.95 kcal/mol if the strain was largely removed by changing from a four-membered ring to a five-membered ring. The C-H activation step is quite difficult for metals with a d¹⁰ configuration. Part of the reason is that one phosphine ligand dissociates during the reaction because the product has a d⁸ configuration and prefers a square planar structure.     

Continuous intra- and intermolecular energy transfer in light-harvesting gels from natural amino acids-based dendrons

The gels and co-gels from glycine (Gly) and glutamic acid (Glu)-based dendrons with either tyrosine (Tyr) or tryptophan (Trp), two of the luminescent amino acid residues in natural proteins, at the focal point were prepared (Tyr-AB₄ and Trp-AB₄). It was found that such gels, especially the co-gels from Tyr-AB₄/Trp-AB₄, showed a high efficient energy transfer (ET) and light-harvesting behaviors. Moreover, luminescent gels with tunable emission ranging from blue to green were also observed owing to the cascade intra- and intermolecular ET from dendritic gelators to the guest molecules (PDNS) in the host-guest gel sample (co-gel with PDNS as the guest molecule), which mimicked the natural light-harvesting systems.     

Rates of intra- and intermolecular electron transfers in hydrogenase deduced from steady-state activity measurements

Electrons are transferred over long distances along chains of FeS clusters in hydrogenases, mitochondrial complexes, and many other respiratory enzymes. It is usually presumed that electron transfer is fast in these systems, despite the fact that there has been no direct measurement of rates of FeS-to-FeS electron transfer in any respiratory enzyme. In this context, we propose and apply to NiFe hydrogenase an original strategy that consists of quantitatively interpreting the variations of steady-state activity that result from changing the nature of the FeS clusters which connect the active site to the redox partner, and/or the nature of the redox partner. Rates of intra- and intermolecular electron transfer are deduced from such large data sets. The mutation-induced variations of electron transfer rates cannot be explained by changes in intercenter distances and reduction potentials. This establishes that FeS-to-FeS rate constants are extremely sensitive to the nature and coordination of the centers.     

Gold-catalyzed formation of oxonium ions from enynes and their intra- and intermolecular trapping with allylsilanes

Gold-catalyzed ring closure of 1,5-enyne containing a silyl ether at the allylic position induces a skeletal rearrangement to form an oxonium intermediate, which then undergoes a smooth allylation in both an intra- and intermolecular manner. In the intramolecular allyl transfer, the additive alcohol becomes positioned on the silicon of the silyl ether by forming a new Si-OR bond, whereas, in the intermolecular allylation, the alcohol is incorporated in the homoallylic carbon by forming a C-OR bond.     

One-pot synthesis of tetrahydroindolizines by catalytic intra- and intermolecular alkylation of 1,2-disubstituted pyrroles

Russian Journal of Organic Chemistry -     

Organocatalytic functionalization of carboxylic acids: isothiourea-catalyzed asymmetric intra- and intermolecular Michael addition--lactonizations

Tetramisole promotes the catalytic asymmetric intramolecular Michael addition-lactonization of a variety of enone acids, giving carbo- and heterocyclic products with high diastereo- and enantiocontrol (up to 99:1 dr, up to 99% ee) that are readily derivatized to afford functionalized indene and dihydrobenzofuran carboxylates. Chiral isothioureas also promote the catalytic asymmetric intermolecular Michael addition-lactonization of arylacetic acids and α-keto-β,γ-unsaturated esters, giving anti-dihydropyranones with high diastereo- and enantiocontrol (up to 98:2 dr, up to 99% ee).     

Preparation of nanoscale cellulose materials with different morphologies by mechanical treatments and their characterization

Rod-like cellulose nanowhiskers and spherical cellulose nanoparticles were prepared from wood-pulp-derived cellulose powder by mechanical refining processes such as high-pressure homogenization (HPH) and ball-milling (BM). The nanowhiskers obtained by the HPH method were found to be 200–500 nm long and 11–16 nm wide. The diameters of the nanoparticles were in the range 40–200 nm, depending on the BM time, and were reduced to 25–50 nm after extra HPH. By adjusting the BM time, cellulose nanoparticles having different polymorphs with similar morphologies were prepared. The X-ray diffraction patterns revealed the recrystallization of cellulose I (1 h of BM time) or cellulose II (4–8 h of BM time) in ball-milled nanoparticles after water washing and solvent exchange treatments. The nanowhisker widths derived from the specific surface areas (SSA) by adsorption methods such as Congo red dye, nitrogen, and water vapor, sorptions were in agreement with those obtained from transmission electron microscopy and atomic force microscopy images. Similar SSA values were obtained for micro- and nano-scale cellulose materials using water vapor adsorption methods, and the SSAs of nanoparticles obtained by different adsorption methods are also discussed.     

Palladium-catalyzed aerobic oxidative amination of alkenes: development of intra- and intermolecular aza-Wacker reactions

Palladium-catalyzed methods for the aerobic oxidative coupling of alkenes and oxygen nucleophiles (e.g., water and carboxylic acids) have been known for nearly 50 years. The present account summarizes our development of analogous aerobic oxidative amination reactions, including the first intermolecular aza-Wacker reactions compatible with the use of unactivated alkenes. The reactions are initiated by intra- or intermolecular aminopalladation of the alkene. The resulting alkylpalladium(II) intermediate generally undergoes beta-hydride elimination to produce enamides or allylic amide products, but in certain cases, the Pd-C bond can be trapped to achieve 1,2-difunctionalization of the alkene, including carboamination and aminoacetoxylation. Mechanistic studies have provided a variety of fundamental insights into the reactions, including the effect of ancillary ligands on palladium catalysts, the origin of the Br?nsted-base-induced switch in regioselectivity in the oxidative amination of styrene, and evidence that both cis- and trans-aminopalladations of alkenes are possible. Overall, these reactions highlight the potential utility of an "organometallic oxidase" strategy for the selective aerobic oxidation of organic molecules.     

Inter- and intra-molecular H-bonds induced different nanostructures from a multi-H-bonding (MHB) amphiphile: nanofibers and nanodisks

An MHB amphiphile, N-stearoyl-l-glutamic acid (C(18)-Glu), forms disk- and fiber-like nanostructures respectively in hydrophilic and hydrophobic environments due to the inter- and intra-molecular H-bonds.     

Thiourea-catalyzed asymmetric michael addition of activated methylene compounds to alpha,beta-unsaturated imides: dual activation of imide by intra- and intermolecular hydrogen bonding

A thiourea-catalyzed asymmetric Michael addition of activated methylene compounds to alpha,beta-unsaturated imides derived from 2-pyrrolidinone and 2-methoxybenzamide has been developed. In the case of 2-pyrrolidinone derivatives, the reaction with malononitrile proceeded in toluene with high enantioselectivity, providing the Michael adducts in good yields. However, the nucleophiles that could be used for this reaction were limited to malononitrile due to poor reactivity of the substrate. Further examination revealed that N-alkenoyl-2-methoxybenzamide was the best substrate among the corresponding benzamide derivatives bearing different substituents on the aromatic ring. Indeed, several activated methylene compounds such as malononitrile, methyl alpha-cyanoacetate, and nitromethane could be employed as a nucleophile to give the Michael adducts in good to excellent yields with up to 93% ee. The results of spectroscopic experiments clarified that this enhanced reactivity can be attributed to the intramolecular hydrogen-bonding interaction between the N-H of the imide and the methoxy group of the benzamide moiety. Thus, the key to the success of the catalytic enantioselective Michael addition is dual activation of the substrate by both intramolecular hydrogen bonding in the imide and intermolecular hydrogen bonding with thiourea 1a, as well as the activation of a nucleophile by the tertiary amine of the bifunctional thiourea.     

Synthesis and self-association properties of flexible guanidiniocarbonylpyrrole-carboxylate zwitterions in DMSO: intra- versus intermolecular ion pairing

We have synthesized a new class of flexible zwitterions 6a-e, in which a carboxylate is linked via an alkyl chain with variable length (one to five methylene groups) to a guanidiniocarbonylpyrrole cation. The self-association properties of these zwitterions were determined by NMR dilution studies in DMSO and by ESI-MS experiments. The stability and hence also the size of the aggregates formed via self-assembly is critically dependent on the length and therefore flexibility of the spacer. Whereas the smallest zwitterion 6a forms large aggregates already at low concentrations, the more flexible zwitterions only form small oligomers (6b) or dimers (6c-e) at much larger concentrations. The differences between the five zwitterions can be explained based on the different extent of intramolecular ion pairing within the monomers. Any intramolecular ion pairing, which becomes possible with increasing linker length, stabilizes the monomer and therefore destabilizes any oligomer.     

Strong fluorescence emission induced by supramolecular assembly and gelation: luminescent organogel from nonemissive oxadiazole-based benzene-1,3,5-tricarboxamide gelator

Supramolecular aggregation of a novel nonfluorescent gelator yields highly luminescent organogels in aprotic organic solvents through intermolecular hydrogen bonding, which is a key motif for both self-assembly and photophysical process control.     

Ion current rectification: from nanoscale to microscale

Ion current rectification(ICR) is an electrodynamic phenomenon in electrolyte solution which is defined as the asymmetric potential-dependent ion flux through a confined environment, giving rise to asymmetric electrical current-voltage characteristics induced by the influence of an asymmetric electrical double layer structure. Since the discovery of the ICR phenomenon, the observation and application of ICR at nanoscale and microscale have been widely investigated experimentally and theoretically.Here, the recent progress of ICR from nanoscale to microscale is systematically reviewed. Nano/micropore structures of different materials, shapes and pore sizes are first discussed. Then, the factors influencing ICRs by thermodynamically or kinetically regulating the electrical double layer structure are introduced. Moreover, theoretical models are presented to explain the mechanism of ICRs. Based on the understanding of this phenomenon, the applications, especially in biosensors, are discussed.Finally, future developments of this area are briefly presented. This review covers the representative related literature published since 2010 and is intended to give a systematic introduction to this area.     

The preparation and intra- and intermolecular addition reactions of acyclic N-acylimines: application to the synthesis of (+/-)-sertraline

Intramolecular endo-cyclization reactions of N-acyliminium ions have seen wide application for the synthesis of heterocyclic compounds. The corresponding exocyclic variant, which would provide 1-aminotetralin derivatives, for example, has little precedent. We have discovered that acyclic N-acylcarbamates can be readily reduced to the corresponding N-acylhemiaminal derivatives in high yield using DIBAL as the reducing agent. These intermediates are remarkably stable and, if desired, can be purified and stored. The acyclic N-acylhemiaminals undergo both intra- and intermolecular nucleophilic addition reactions mediated by strong Lewis acids, such as TiCl(4). Diastereoselectivity, induced either by a substituent on the newly formed ring, or by utilizing a chiral ester on the carbamic acid, was disappointingly low. This methodology was successfully applied to the synthesis of the racemic form of the marketed antidepressant sertraline.     

Alkynes as synthetic equivalents to stabilized Wittig reagents: intra- and intermolecular carbonyl olefinations catalyzed by Ag(I), BF3, and HBF4

[reaction: see text] The first use of cationic silver (AgSbF4) as a catalyst for intra- and intermolecular alkyne-carbonyl coupling to form conjugated enones is described, and a comparison to corresponding Br?nsted acid (HBF4) and Lewis acid (BF3) catalyst systems is made. Notably, intermolecular coupling proceeds stereoselectively to afford the corresponding trisubstituted enones as single geometrical isomers. This transformation represents a completely atom economical alternative to the use of stabilized Wittig reagents in carbonyl olefination and may be viewed as a formal alkyne-carbonyl metathesis.     

Liquid crystal engineering--new complex mesophase structures and their relations to polymer morphologies, nanoscale patterning and crystal engineering

This critical review focuses on recent progress in the field of T-shaped ternary amphiphiles. These molecules can self-assemble into a series of new liquid crystalline (LC) phases with polygonal cylinder structures, new lamellar phases and LC phases combining columns and layers. These structures are analyzed on the basis of symmetry, net topology and tiling pattern (Laves and Archimedean tilings) and discussed in relation to morphologies of multiblock copolymers, self organized DNA super-lattices, metal-organic frameworks, crystal-engineering and self-assembled periodic superstructures on surfaces (210 references).     

fac-Acetato-bis(pyrazole) complexes: A systematic study on intra- and intermolecular hydrogen bonds

Acetato-bis(pyrazole) complexes [Mo(η³-methallyl)(O₂CMe)(CO)₂(pz^∗H)₂], (methallyl = CH₂C(CH₃)CH₂) and fac-[M(O₂CMe)(CO)₃(pz^∗H)₂], (pz^∗H = pyrazole or 3,5-dimethylpyrazole, dmpzH; M = Mn, Re) are obtained from [Mo(η³-methallyl)Cl(CO)₂(NCMe)₂] or fac-[MBr(CO)₃(NCMe)₂] [M = Mn (synthesized in situ), Re], 2 equiv. of pyrazole, and 1 equiv. of sodium acetate for Mo complexes, or silver acetate for Mn or Re complexes. The chlorido-complexes [Mo(η³-methallyl)Cl(CO)₂L₂] (L = pzH, dmpzH), obtained from the same starting material by substitution of MeCN by pzH or dmpzH, are also described. The crystal structures of the fac-acetato-bis(dimethylpyrazole) complexes present the same pattern of intramolecular hydrogen bonds between the acetate and the dimetylpyrazole ligands, whereas the crystal structures of the fac-acetato-bis(pyrazole) complexes show different hydrogen bonds patterns, with intermolecular interactions. NMR data indicate that these interactions are not maintained in solution.     

Crystal structure of cyclic sulfin- and sulfonamides of the thiazine series: Conformation,intra- and intermolecular interactions

An X-ray crystallographic study of a new compound is performed and the structure of five sulfin- and sulfonamides of the thiazine series is discussed. The conformation of the thiazine ring in all structures (a distorted boat) is stabilized by the intramolecular interaction of the C-H…N type. The nitrogen atom of the thiazine ring has a pyramidal configuration. The geometry of isolated molecules is calculated at density functional theory level (PBE1PBE, 6-31G(d,p)) and compared to that observed in the crystals. In the crystal structures different packing motifs are implemented with the formation of supramolecular associates of different types due to classical hydrogen bonds such as N-H…O.