Binding properties of alginic acid and chitin

The binding properties of granular alginic acid(H-alg.) and chitin to iodine, bromine, cadmium ion, calcium ion and cholesterol were investigated. Chitin-iodine and chitin-bromine compounds closely resemble those of H-alg. The amount of iodine included by these polysaccharides increased with a decrease in the concentration of potassium iodide (KI). The number of sugar residues bound to one iodine molecule extrapolated to 0 g of KI was around 6.0 for H-alg. and 6.4 for chitin. These saccharides, which do not form a gel in water, were found to also absorb KI and radioactive iodide or iodine in aqueous solution. H-alg. did not show as much affinity to cadmium ion and calcium ion and cholesterol in iso-propyl alcohol as metalalginates.Presented at the Fourth International Symposium on Inclusion Phenomena and the Third International Symposium on Cyclodextrins, Lancaster, U.K., 20–25 July 1986.     

Protonation enthalpies in fluorosulfonic acid using ab initio self-consistent reaction field theory

Electrostatic solvation free energies were computed for several small neutral bases and their conjugate acids using a continuum solvation model called the self-consistent isodensity polarizable continuum model (SCIPCM). The solvation energies were computed at the restricted Hartree–Fock (RHF) and second-order Møller–Plesset (MP2) levels of theory, as well as with the Becke3–Lee–Yang–Parr (B3LYP) density functional theory, using the standard 6–31G** Gaussian basis set. The RHF solvation energies are similar to those computed at the correlated MP2 and B3LYP theoretical levels. A model for computing protonation enthalpies for neutral bases in fluorosulfonic acid solvent leads to the equation ΔH(B)=−PA(B)+ΔE_t(BH⁺)−ΔE_t(B)+β, where PA(B) is the gas phase proton affinity for base B, ΔE_t(BH⁺) is the SCIPCM solvation energy for the conjugate acid, and ΔE_t(B) is the solvation energy for the base. A fit to experimental values of ΔH(B) for 10 neutral bases (H₂O, MeOH, Me₂O, H₂S, MeSH, Me₂S, NH₃, MeNH₂, Me₂NH, and PH₃) gives β=238.4±2.9 kcal/mol when ΔΔE_t is computed using the 0.0004 e⋅bohr⁻³ isodensity surface for defining the solute cavity at the RHF/6–31G** level. The model predicts that for carbon monoxide ΔH(CO)=10 kcal/mol. Thus, protonation of CO is endothermic, and the conjugate acid HCO⁺ (formyl cation) behaves as a strong acid in fluorosulfonic acid. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 250–257, 1998     

Synthesis and characterization of copolymers from 4-halo(chloro, bromo) salicylic acid

Copolymers have been prepared by condensing a mixture of either 4-chloro or 4-bromosalicylic acid and any one of the comonomer like salicylic acid,p-hydroxybenzoic acid,p-aminosalicylic acid,p-aminobenzoic acid,p-cresol andp-halo(chloro, bromo)phenol with formaldehyde in the presence of 5M H₂SO₄. Copolymer composition of each of the copolymer has been estimated on the basis of halogen content and/or on the basis of results of non-aqueous titrations of the copolymer against standard sodium methoxide and/or tetra-n-butylammonium hydroxide. The IR spectral characteristics of copolymers have been noted. The viscometric and thermal studies of copolymers have also been carried out.     

Coulometric redox titrations of some biologically active thiols with iodine in methanol and bromine in acetic acid

The possibility of coulometric titrations of cysteine, 2-thio-uracil, 6-mercaptopurine, and 6-thioguanine with iodine and bromine in methanol and with bromine in acetic acid has been investigated. Conditions have been found for the direct titration of the test substances with iodine in methanol based on their 1-electron oxidation to the corresponding disulphides and for their direct and indirect determination with bromine in acetic acid based on their 6-electron oxidation to the corresponding sulphonic acids.On leave from Department of Analytical Chemistry, Charles University, Prague, Czechoslovakia     

卤代-2-(3-甲基-5-取代-4H-1,2,4-三唑-4-基)-苯甲酸的合成

邻氮基苯甲酸;缩合反应;卤代-2-(3-甲基-5-取代-4H-1;2;4-三唑-4-基)-苯甲酸的合成     

溴与其他卤族元素及卤水溴、氯含量与矿化度的相关关系

研究了地下卤水、土壤、食品和人体组织中Br与其他卤族元素,以及卤水Br、Cl含量与矿化度的相关关系.结果表明,Br与Cl及Br与Ⅰ呈显著正相关关系,其他卤族元素间无显著相关性;Br与矿化度及Cl与矿化度高度相关.利用建立的各类卤水的回归模型,评估了“浓缩均衡矿物滴”(CMD)的盐卤属性.     

Molecular assembly of dithiaparacyclophanes mediated by non-covalent X…X,X…Y and C–H…X (X,Y=Br,S, N) interactions

Regioselectivity for the 5,8,15,18-substituted isomer over the 5,8,14,17-isomer was observed in a series of mercaptan–bromide coupling reactions leading to the formation of 2,11-dithia[3.3]paracyclophanes. Their molecular assembly was established by X-ray crystallographic studies. In the crystal packing of these paracyclophanes, several types of non-covalent interactions including halogen–halogen interaction, halogen-bonding interaction, weak hydrogen-bonding interaction, etc. are observed in crystals 3a, 3b and 3c. There is evidence to indicate that weak non-covalent Br…Br, Br…S, Br…N, C–H…S, S…S and C–H…N interactions play an important role in governing their molecular assembly assumed in the solid state. The attractive interactions of Br…Br, Br…S and Br…N are also rationalised and supported in terms of the density functional theory calculations.

     

氟磺酸改性磺酸型聚合物催化剂在甲醛羰基化中的性能研究

采用水热合成、原位磺化法制备了固体磺酸型聚合物PDS-1.0催化剂,以三氟甲烷磺酸对其进行接枝改性得到PDS-1.0-F催化剂;采用N_2吸附-脱附、TG、FT-IR、~(31)P M AS NMR和XPS等技术对催化剂的物理和化学性质进行了表征,以甲醛羰基化制乙醇酸为探针反应对其催化性能进行了评价研究。结果表明,与PDS-1.0催化剂相比,氟磺酸改性后的PDS-1.0-F催化剂的比表面积、孔容积和酸量均降低,但是酸强度和热稳定性显著增加,由此对甲醛羰基化反应具有较好的催化性能,乙醇酸收率达到91.2%。     

Chiral smectogens with four-phenyl-ring molecular core,laterally substituted by iodine atom

Two series of lactic acid derivatives, based on four-ring molecular core laterally substituted by iodine atom, have been synthesised and their liquid crystalline properties studied. The non-chiral chain length has been varied and its influence on mesomorphic properties studied. All new compounds reveal the SmA*-SmC* phase sequence in an extremely broad temperature interval. The experimental techniques, namely the polarising optical microscopy, DSC, X-ray diffraction and helical pitch measurements, have been applied to establish the physical properties. New materials denoted JFRm/6 and JFRm/MB (with varying m as a number of carbon atoms in the non-chiral chain) are compared with the previously synthesised analogues (non-substituted and laterally substituted by a different halogen atom, namely bromine and chlorine).     

Application of a New Dehydroascorbic Acid Reducing Agent in the Analysis of Vitamin C Content in Food

The analysis of total vitamin C content in food is most frequently performed by reducing dehydroascorbic acid to ascorbic acid, which is then assayed with the technique of high-performance liquid chromatography combined with spectrophotometric detection. Tris(2-carboxyethyl)phosphine is currently the only agent in use that efficiently reduces dehydroascorbic acid at pH < 2. Therefore, there is a continued need to search for new reducing agents that will display a high reactivity and stability in acidic solutions. The objective of the study was to verify the applicability of unithiol and tris(hydroxypropyl)phosphine for a reducing dehydroascorbic acid in an extraction medium with pH < 2. The conducted validation of the newly developed method of determining the total content of vitamin C using tris(hydroxypropyl)phosphine indicates its applicability for food analysis. The method allows obtaining equivalent results compared to the method based on the use of tris(2-carboxyethyl)phosphine. The low efficiency of dehydroascorbic acid reduction with the use of unithiol does not allow its application as a new reducing agent in vitamin C analysis.     

Halogenation of the N-Terminus Tyrosine 10 Promotes Supramolecular Stabilization of the Amyloid-β Sequence 7–12

Here, we demonstrate that introduction of halogen atoms at the tyrosine 10 phenol ring of the DSGYEV sequence derived from the flexible amyloid-β N-terminus, promotes its self-assembly in the solid state. In particular, we report the crystal structures of two halogen-modified sequences, which we found to be stabilized in the solid state by halogen-mediated interactions. The structural study is corroborated by Non-Covalent Interaction (NCI) analysis. Our results prove that selective halogenation of an amino acid enhances the supramolecular organization of otherwise unstructured biologically-relevant sequences. This method may develop as a general strategy for stabilizing highly polymorphic peptide regions.     

Halogenation of the Hexaphosphabenzene Complex [(Cp*Mo)2(μ,η6:η6-P6)]: Snapshots on the Reaction Progress

The oxidation of [(Cp*Mo)₂(μ,η⁶:η⁶-P₆)] ( 1 ) with halogens or halogen sources was investigated. The iodination afforded the ionic complexes [(Cp*Mo)₂(μ,η³:η³-P₃)(μ,η¹:η¹:η¹:η¹-P₃I₃)][X] (X=I₃⁻, I⁻) ( 2 ) and [(Cp*Mo)₂(μ,η⁴:η⁴-P₄)(μ-PI₂)][I₃] ( 3 ), while the reaction with PBr₅ led to the complexes [(Cp*Mo)₂(μ,η³:η³-P₃)(μ-Br)₂][Cp*MoBr₄] ( 4 ) [(Cp*MoBr)₂(μ,η³:η³-P₃)(μ,η¹-P₂Br₃)] ( 5 ) and [(Cp*Mo)₂(μ-PBr₂)(μ-PHBr)(μ-Br)₂] ( 6 ). The reaction of 1 with the far stronger oxidizing agent PCl₅ was followed via time- and temperature-dependent ³¹P{¹H} NMR spectroscopy. One of the first intermediates detected at 193 K was [(Cp*Mo)₂(μ,η³:η³-P₃)(μ-PCl₂)₂][PCl₆] ( 8 ) which rearranges upon warming to [(Cp*Mo)₂(μ-PCl₂)₂(μ-Cl)₂] ( 9 ), [(Cp*MoCl)₂(μ,η³:η³-P₃)(μ-PCl₂)] ( 10 ) and [(Cp*Mo)₂(μ,η⁴:η⁴-P₄)(μ-PCl₂)][Cp*MoCl₄] ( 11 ), which could be isolated at room temperature. All complexes were characterized by single-crystal X-ray diffraction, NMR spectroscopy and their electronic structures were elucidated by DFT calculations.     

Isomerization of Maleic Acid to Fumaric Acid Catalyzed by Bromate Ion and Bromine

In the presence of a relatively small amount of bromate, maleic acid in aqueous sulfuric acid isomerizes catalytically to fumaric acid in the dark at room temperature. The concomitant presence of a suitable amount of bromine in CCI, phase raises the rate and yield significantly. The yield and rate of isomerization depend on the relative amounts of maleic acid, bromate, bromine, and sulfuric acid. For a favorable condition, nearly 90% yield can be obtained. Raising the temperature accelerates the production of fumaric acid while decreases the final yield. The isomerization reaction competes favorably with the redox reaction at room temperature while the latter dominates at high temperature. For the heterogeneous case, the agitation of the reaction mixture delays the isomerization. The presence of cumene or benzene inhibits the isomerization. Hypobromous acid is proposed to play a major role in catalyzing the isomerization. A mechanism is proposed to rationalize the experimental results.     

Halogen Bonding of N-Halosuccinimides with Amines and Effects of Brønsted Acids in Quinuclidine-Catalyzed Halocyclizations

An arguable expectation in halogen chemistry is that an amine will react oxidatively with an N-halosuccinimide (NXS) to form an N-halogenated species bearing a covalent N−X bond. While likely for NCS under most conditions, we find this expectation simply not true for NIS and largely inaccurate for NBS. Herein, we disclose evidence through systematic NMR and X-ray studies that non-covalent halogen bonded amine complexes of NIS predominate over covalent N-halogenated species, even with primary and secondary amines. For example, during the catalytic electrophilic halocyclization of gem-disubstituted alkenes by cinchona-like amines, the quinuclidine complexes of NIS and NBS display lower reactivity than their parent N-halosuccinamides and require the presence of an appropriate Brønsted acid. Specifically, a Brønsted acid and quinuclidine jointly catalyze the halo-cycloetherification of γ-alkenyl alcohols with NIS or NBS, while only quinuclidine acts as a catalyst in the halolactonization of γ-alkenoic acids. Although our evidence confirms a transient N-halogenated quaternary ammonium salt as the halonium species, it is important to note that NIS predominantly forms ‘off-cycle’ halogen bonded amine complexes in solution.     

一种硝基三氮杂蔻化合物的合成及性质研究

通过往蒄中引入氮原子,以氟磺酸为催化剂,通过成环反应合成出目标化合物,并对产物进行了结构表征,对该化合物的性质做了测试,表明该化合物可以作为发光器件分子用于制备电致发光材料。     

笼形聚偕氨肟树脂吸附溴和碘

用酸、碱处理的笼形聚偕氨肟树脂（ACAO、BCAO）吸附溴和碘,发现它们的吸附能力无显著差别。吸附客量与溴和碘浓度关系符合Freundlich方程．从扫描电子显微镜观察到碘在树脂表面形成微晶．联系到溴和碘的超当量吸附现象,初步认为,它们是通过物理吸附在树脂表面富集。     

Synthesis and Structure of Trimethylplatinum(IV) Iodide Complex of 4'-(4-Methoxyphenyl)-2,2':6',2'-terpyridine Ligand and its Halogen Bonding Property

The synthesis and structural characterization of a new trimethylplatinum(IV) iodide complex of 4'-(4-methoxyphenyl)-2,2':6',2''-terpyridine ligand L, {PtMe₃IL} ( 1 ) is reported. The X-ray crystal structure shows that the terpyridine ligand L binds the platinum(IV) metal center in bidentate fashion, which is well supported by the ¹H NMR spectrum of 1 . The complex 1 upon crystallization with 1,4-diiodotetrafluorobenzene (DITFB) forms the halogen bonded complex 1a ( 1· DITFB). The structural investigation shows that 1a exhibits the halogen bonding interaction in which the non-coordinated pyridyl nitrogen acts as halogen bond acceptors by forming I ··· N interaction with iodine atom of DITFB. In addition iodine atom of complex 1 also acts as weak halogen bond acceptor.     

Determination Coulometrique de L'acide β Amino-Naphtylamido Thioglycolique (Thionalide)

Abstract

Mercury and silver were determined by precipitation from aqueous solution with β amino-naphthylamido thioglycolic acid (thionalid). The metallic thionalidate phases were separated, dissolved in ethanol and analyzed by coulometric titration of the thionalid with electrogenerated iodine.     

Refinement of the Superstructure of C-Type Gallium Tris(metaphosphate), Ga(PO3)3

Single crystals of Ga(PO₃)₃ were grown in polyphosphoric acid melts by heating a mixture of Ga₂O₃ and H₃PO₄ (350 °C, 7 d). The compound belongs to the series of metaphosphates M^III(PO₃)₃ forming the C-type structure (monclinic, Cc, Z = 12, a = 13.0058(21), b = 18.915(3), c = 9.3105(15) Å, β = 126.900(11), 5348 independent reflections (I > 0); 354 variables; 39 atoms in asymetric unit; R1 = 0.048, wR2 = 0.1034). The structure is characterized by a superstructure with tripled monoclinic b-axis. Three crystallographically independent Ga^IIIO₆ octahedra (d¯(Ga–O) = 1.950 Å) are linked by ¹_∞(PO₃)^– chains.     

B(C6F5)3 catalyzed synthesis of dihydropyrano[3,2-b]chromenediones under solvent-free conditions

Abstract

A simple, efficient, solventless, and one step, B(C₆F₅)₃ catalyzed, synthesis of dihydropyrano[3,2-b]chromenediones from dimedone, aldehyde and kojic acid is described. This protocol proceeds smoothly, accommodates aromatic as well as heteroaromatic aldehydes and gives dihydropyrano[3,2-b]chromenediones in excellent yield.