Crystal Structure and Quantum Chemical Ab Initio Calculations of Ibotenic Acid,an Excitatory Amino Acid Receptor Agonist

Ibotenic acid, a constituent of Amanita muscaria, is a potent NMDA receptor agonist. The structure of the ibotenic acid zwitterion monohydrate in the crystalline state has been determined by X-ray crystallography. The crystal structure has two ibotenic acid monohydrate formula units in the asymmetric unit and features an extensive hydrogen bond network. The ibotenic acid zwitter-ions in the crystalline state are compared to the in vacuo structure calculated by quantum chemical ab initio calculations at the HF/6-31+G* level and the effects of the hydrogen bond network on the structures in the solid state are discussed. The calculated potential energy curve with respect to side-chain orientation displays a single energy minimum. The conformations corresponding to the solid-state conformations are calculated to be ca. 2 kcal/mol higher in energy than the minimum-energy conformation in vacuo.     

Cyclization of the Reaction Products of p-Phenylenediamine with Maleic Acid

Treatment of p-phenylenediamine with maleic acid and its diethyl ester gave di- and tetracarboxylic amino acids and their esters. A benzene derivative having an -alanine and an aspartic acid residue has been prepared. The cyclization of aminocarboxylic acids to imidazole and pyrimidine derivatives has been carried out.     

Discovery of Potential,Dual-Active Histamine H3 Receptor Ligands with Combined Antioxidant Properties

In an attempt to find new dual acting histamine H₃ receptor (H₃R) ligands, we designed a series of compounds, structurally based on previously described in our group, a highly active and selective human histamine H₃ receptor (hH₃R) ligand KSK63. As a result, 15 obtained compounds show moderate hH₃R affinity, the best being the compound 17 (hH₃R K_i = 518 nM). Docking to the histamine H₃R homology model revealed two possible binding modes, with key interactions retained in both cases. In an attempt to find possible dual acting ligands, selected compounds were tested for antioxidant properties. Compound 16 (hH₃R K_i = 592 nM) showed the strongest antioxidant properties at the concentration of 10⁻⁴ mol/L. It significantly reduced the amount of free radicals presenting 50–60% of ascorbic acid activity in the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay, as well as showed antioxidative properties in the ferric reducing antioxidant power (FRAP) assay. Despite the yet unknown antioxidation mechanism and moderate hH₃R affinity, 16 (QD13) constitutes a starting point for the search of potential dual acting H₃R ligands-promising tools for the treatment of neurological disorders associated with increased neuronal oxidative stress.     

TheT g displacement measurements: A way to foresee the physical behaviour and the use of glassy polymers

The effect of ageing temperature (belowT _g) on physical ageing of glassy PET has been investigated by differential scanning calorimetry. The position of the glass transition endotherm was found to be strongly dependent on the annealing conditions (time, annealing temperature). A single relaxation time model is proposed for the analysis of physical ageing.The variations of the equilibrium relaxation time _iso with annealing temperature allow the determination of the parameters of the model. Finally, using these constants, one can determine the thermal past and foresee the thermal future of unknown samples which are of prime importance in processes using temperatures around the glass transition temperature.

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Zusammenfassung Mittels DSC wurde der Einfluß der Alterungstemperatur (unterhalbT _g) auf das physikalische Altern von glasartigen PET untersucht. Die Lage der Glasumwandlungsendothermen hängt stark von den Temperungsbedingungen (Dauer, Temperungstemperatur) ab. Es wird ein Relaxationszeitmodell für die Analyse physikalischen Alterns vorgeschlagen.Die Parameter dieses Modelles knnen aus der Änderung der Gleichgewichtsrelaxationszeit _iso mit der Temperungstemperatur ermittelt werden. Unter Benutzung dieser Konstanten kann die thermische Vergangenheit unbekannter Proben bestimmt und die thermische Zukunft derselben vorhergesagt werden, was für Vorgänge bei Temperaturen um den Glasumwandlungspunkt von primärer Wichtigkeit ist.

     

Fabrication and Characterization of an Electro-Compacted Collagen/Elastin/Hyaluronic Acid Sheet as a Potential Skin Scaffold

The development of biomimetic structures with integrated extracellular matrix (ECM) components represents a promising approach to biomaterial fabrication. Here, an artificial ECM, comprising the structural protein collagen I and elastin (ELN), as well as the glycosaminoglycan hyaluronan (HA), is reported. Specifically, collagen and ELN are electrochemically aligned to mimic the compositional characteristics of the dermal matrix. HA is incorporated into the electro-compacted collagen-ELN matrices via adsorption and chemical immobilization, to give a final composition of collagen/ELN/HA of 7:2:1. This produces a final collagen/ELN/hyaluronic acid scaffold (CEH) that recapitulates the compositional feature of the native skin ECM. This study analyzes the effect of CEH composition on the cultivation of human dermal fibroblast cells (HDFs) and immortalized human keratinocytes (HaCaTs). It is shown that the CEH scaffold supports dermal regeneration by promoting HDFs proliferation, ECM deposition, and differentiation into myofibroblasts. The CEH scaffolds are also shown to support epidermis growth by supporting HaCaTs proliferation, differentiation, and stratification. A double-layered epidermal-dermal structure is constructed on the CEH scaffold, further demonstrating its ability in supporting skin cell function and skin regeneration.     

A group theoretical study of f n systems in an environment of approximately icosahedral symmetry

Group theoretical methods are developed to determine in a generalised format for an f ⁿ ion in a crystal field environment of icosahedral symmetry, the effect on the energy level scheme when a crystal field distortion is considered parallel to any direction. As an illustration, the effect on the g-tensor components are examined as a function of the magnitude and the direction of the crystal field distortion. All appropriate reduced matrix elements in group theoretical terminology are evaluated for the f ⁿ -ion ground states. Specific results are given for the f ³-ion case and compared with electron paramagnetic resonance, optical, and magnetic susceptibility data.     

Dithiobiuretes in reactions with electrophilic acetylenes. New derivatives of 1,3,5-dithiazines,-thiadiazines and-triazines as the products of competing reactions of nucleophilic cycloaddition

The nucleophilic addition of 2,4-dithiobiurete, 1- and 1,4-substituted 2,4-dithiobiuretes (2 a-e) with benzoylacetylene (1) has been studied. 2-(Benzoylmethyl)-4-(R¹-imino)-6-(R²-imino)dihydro-4H-1,3,5-dithiazinium perchlorates (3 a-e) are obtained in glacial acetic acid (AcOH) in the presence of equimolar quantities of HClO₄. The reaction of benzoylacetylene with 1,5-diphenyl-2,4-dithiobiurete in either of MeOH, C₆H₆, or MeCN solvents proceeds non-selectively to give a mixture of products such as 2-(benzoylmethyl)-4,6-di(phenylimino)dihydro-4H-1,3,5-dithiazine (5), 2-(benzoylmethyl)-4-(β-benzoylvinyl)thio-3-phenyl-6-(phenylimino)-3,6-dihydro-2H-1,3,5-thiadiazine (8), 2-(benzoylmethyl)-1,3-diphenylhexahydro-1,3,5-triazine-4,6-dithione (7) and N-(β-benzoylvinyl)-N-phenylthioureas (6).     

The group-theoretical structure of the atomic g shell: connection with the alternating group <Emphasis Type="Italic">A</Emphasis><Subscript>6</Subscript> as <Emphasis Type="Italic">L</Emphasis><Subscript>2</Subscript>(9)

The special projective linear groups PSL(2ℓ + 1) or L ₂(2ℓ + 1) of order 2ℓ(2ℓ + 1)(ℓ + 1) can be used to study atomic shells of electrons with angular momentum quantum number ℓ corresponding to the atomic p, d, f, and g shells for ℓ = 1, 2, 3, 4, respectively. For the atomic g shell the group L ₂(9) is isomorphic with the alternating group A ₆ on six objects of order 360 or the symmetry group of the 5-dimensional simplex, a 5-dimensional analogue of the tetrahedron with 6 vertices and 15 edges. This leads to the subgroup chain SO(9) ⊃ SO(5) ⊃ L ₂(9) for the atomic g shell analogous to the subgroup chain SO(7) ⊃ G ₂ ⊃ L ₂(7) ≈⁷ O for the atomic f shell. In the L ₂(9) group only the representations of spherical harmonics or sums thereof, Γ(Y_ℓ), with dimensions dim Γ(Y_ℓ) or dim Γ(Y_ℓ) ± 1 divisible by 9 are found to be individually reducible to irreducible representations (irreps) or sums of irreps of L ₂(9). This leads to term groupings such as S, PD, G, PF, DH, L, PK, DI, FH, M, FI, PO, DN, HK, R, etc., of increasing total dimension for the irreps of SO(9) for various g ⁿ configurations in the atomic g shell.     

Electron-excited dioxygen generated by the tri-tert-butoxyaluminum—tert-butyl hydroperoxide system as an efficient oxidant of aniline and some N-substituted anilines

The tri-tert-butoxyaluminum—tert-butyl hydroperoxide system generates molecular oxygen in the electron-excited singlet state (¹O₂), which oxidizes diphenylamine, N-ethylaniline, aniline, and 2,6-diisopropylaniline to form nitroxyl radicals. The latters were identified by ESR at 240—293 K. Oxidation proceeds via the intermediate formation of nitrogen-containing N-peroxide compounds.     

Synthesis and properties of new chelating resin with a spacer containing alpha-nitroso-beta-naphthol as the functional group

A new chelating ion-exchange resin with a spacer CH₂-NH-C₆H₄- based on a microreticular chloromethylated styrene-divinylbenzene copolymer containing α-nitroso-β-naphthol as a functional group has been synthesized. The sorption characteristics for manganese(II), iron(III), cobalt(II), nickel(II), copper(II), and zinc(II) have been investigated over the pH range 1.0–7.0. The resin is highly stable in acidic and alkaline medium. Iron(III) and cobalt(II); copper(II) and iron(III) are separated very effectively in a column operation by stepwise elution.     

NOTE: Synthesis and Characterization of a Poly(acrylamide) with Pendant 1,4-piperazine-2,5-dione Moieties via Post-polymerization Cyclization

A poly(acrylamide) was synthesized from N ^α -Boc-N ^? -acrolyl-l-lysylglycine methyl ester via radical polymerization. This polymer typically had Mn ～ 100,000 g/mol, Mw ～ 300,000 g/mol, and a T_g of 93°C. Removal of Boc with TFA and cyclization with DABCO? in DMSO at 65°C afforded a soluble piperazinedione-containing polymer that had a T_g of 157°C and thermal stability up to 300°C. These results demonstrate a viable and efficient synthetic route to piperazinedione-containing polyacrylamides of high molecular weight. Related polymers that incorporate substituted indane moieties could be useful high T_g materials for fabrication of LC and NLO devices.     

The ring opening and oligomerisation reactions of an epoxide and an episulfide on aluminosilicates in the liquid phase

The ring opening reactions of propylene oxide (methyloxirane) or ethylene sulfide )thiirane) were studied in the liquid phase over HZSM-5, HY-FAU or AlMCM-41 at 363 K or 423 K and under 1 or 20 bar pressure in a batch reactor. The proportion of these routes were identified: (i) single C−O scission providing non-cyclic products, (ii) double C−O cleavage leading to the loss of the heteroatom, (iii) oligomerisation resulting in cyclic dimers and the trimer of thiirane and a non-cyclic dimer of methyloxirane. The reaction pathway depended on the conditions and the solid acids used. Findings are compared to those in the gas phase over the same solid acids. Transformation mechanisms are also suggested.     

Solid-phase Extraction and High Performance Liquid Chromatographic Determination of Folic Acid in Fortified Foodstuffs: a Recommended Process Utilizing a New Strong Anion Exchange Sorbent

Journal of Analytical Chemistry - A highly efficient solid-phase extraction (SPE) column filled with a silica-based strong anion exchange sorbent was reported in the current study. The fabricated...     

New Azido Coumarins as Potential Agents for Fluorescent Labeling and Their “Click” Chemistry Reactions for the Conjugation with closo-Dodecaborate Anion

Novel fluorescent 7-methoxy- and 7-(diethylamino)-coumarins modified with azido-group on the side chain have been synthesized. Their photophysical properties and single crystals structure characteristics have been studied. In order to demonstrate the possibilities of fluorescent labeling, obtained coumarins have been tested with closo-dodecaborate derivative bearing terminal alkynyl group. Cu^I catalyzed Huisgen 1,3-dipolar cycloaddition reaction has led to fluorescent conjugates formation. The absorption–emission spectra of the formed conjugates have been presented. The antiproliferative activity and uptake of compounds against several human cell lines were evaluated.     

Molecular Structure of tert-Butylazide: A Gas-Phase Electron Diffraction and Quantum Chemical Study

The molecular structure of tert-butylazide has been determined by gas-phase electron diffraction and quantum chemical calculations. The HF/6-31G* and B3LYP/6-31G** calculations yielded near C _s symmetry for the tert-butyl group, anti conformation of the (C)N—N bond with respect to one of the bonds, and an essentially free rotation around the bond with a 0.34 kcal/mol energy difference between syn and anti conformations of the CNNN moiety, the anti being the more stable form. The electron diffraction analysis was carried out by modeling a mixture of conformational isomers, generated by rotating the terminal nitrogen of the azide group, using a computed rotational potential. The data are consistent with C _s symmetry for the tert-butyl group. The bond, however, was found to be rotated out of the anti position, with respect to one of the bonds, by 12.5(12)°. The electron diffraction analysis yielded the following bond lengths (r _g), bond angles, and torsional angles: , .     

Enamines of the 1,2,3,4-tetrahydroiso-quinoline series in the Chichibabin synthesis of pyrrolo[2,1-a]isoquinolines and in reaction with oxalyl chloride

It has been shown that the Chichibabin reaction of enamines of the 1,2,3,4-tetrahydroisoquinoline series and 1,2,3,4-tetrahydrobenzo[f]isoquinoline series with p-bromophenacyl bromide leads to pyrrolo[2,1-a]isoquinoline derivatives. The same heterocyclic system is obtained on interaction of 1-alkyl-3,4-dihydroisoquinolines or their benzo[f]-analogs with oxalyl chloride. The obtained dioxopyrrolines form derivatives of benzo[g]quinoxalino[2,3-b]indolizine on condensation with o-phenylenediamine. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 1068–1074, July, 2007.     

Structure and Internal Rotation of Molecules in Chlorodifluoroacetic Acid

The potential energy profile of an isolated CF₂ClCOOH molecule with a CF₂Cl group rotating around the C–C bond was determined by the Hartree–Fock method using the 6-31G(d) basis set. Barriers to internal rotation were estimated for this molecule; its geometrical parameters were found for the equilibrium and transition states that are due to the torsion potential with unequal wells. Crystal effect on CF₂Cl reorientations in solid chlorodifluoroacetic acid has been evaluated.     

Modification of the Peripheral Substituents in Chlorophylls a and b and Their Derivatives (Review)

The extensive published data on methods for the modification of peripheral substituents in chlorophylls a and b and their various semisynthetic derivatives are classified and analyzed. Special attention is paid to specific transformations arising from the presence of the unique macrocyclic tetrapyrrole fragment. Data on certain main pathways to modification of the exocyclic fragment of chlorophylls are also presented.     

Highly Efficient Synthesis of Substituted Benzenes in the Presence of B(HSO4)3 as a New and Reusable Catalyst Under Solvent-Free Conditions

A highly efficient and simple procedure for the synthesis of substituted benzenes is described. A broad range of ketones (alkyl–aryl ketones and cyclic ketones) were condensed via a cyclotrimerization reaction in the presence of catalytic amounts of boron sulfonic acid [B(HSO₄)₃], a new, highly efficient, and reusable catalyst, under solvent-free conditions. All reactions completed in short times without formation of any by-products. The catalyst was recovered and reused successfully for 15 cycles of the reaction.

Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file.     

微量热法研究丹皮酚及其两种同分异构体与γ-环糊精在水溶液中的相互作用

在298.15 K下利用纳瓦级等温滴定微量热法研究了γ-环糊精与丹皮酚(Pae)及其两种同分异构体(2'-羟基-5'-甲氧基苯乙酮, Hma; 4'-羟基-3'-甲氧基苯乙酮, Ace)在水溶液中的相互作用, 并结合核磁共振对其相互作用的微观结构进行了表征. 试验表明, γ-环糊精与三种药物分子都是1∶1结合, 其中 Pae, Hma与γ-环糊精相互作用过程是焓驱动, 而Ace与γ-环糊精相互作用却是焓-熵共驱动; ¹H NMR 谱表明 Pae, Ace 与γ-环糊精形成典型的包结物, 其中 Pae 分子从 g-环糊精空穴的小口端进入, Ace分子从 g-环糊精空穴的大口端进入, 而 Hma 与γ-环糊精之间只是以弱相互作用结合而非包结作用. 结果显示γ-环糊精对三种同分异构体具有明显的分子识别功能.