Dark and Photochemical Interactions of Dimethyltetrahydrobenzoangelicin with DNA

A study of dark interaction and photoreaction between 4,6-dimethyltetrahydrobenzoangelicin (THBA) and DNA is described. 4,6-Dimethyltetrahydrobenzoangelicin is a furocoumarin derivative in which 4'and 5'carbons are linked by a four-methylene bridge. In spite of the bulky aliphatic ring, THBA forms a complex with DNA in the dark and, on UVA irradiation, reacts with pyrimidine bases of DNA yielding monoadducts only involving its furan side double bond. Two main photoproducts form: they derive from a C₄-cycloaddition to thymine and cytosine, respectively, and account for 56% and 39% of the total photoreaction yield. Both show cis-syn configuration. Two other isomers, one with thymine and one with cytosine, formed with so much lower yield ( ca 3 and 1%, respectively) that their structure could not be assigned. Furthermore, in spite of its angular structure, THBA induces a small number of crosslinks in DNA.     

A chelating resin containing trihydroxybenzoic acid as the functional group: synthesis and adsorption behavior for Th(IV) and U(VI) ions

A novel glycidyl methacrylate chelating resin has been synthesized through copolymerization of glycidyl methacrylate (GMA) in the presence of divinylbenzene (DVB), the resulting resin was immobilized with 3,4,5-trihydroxybenzoic acid (THBA) to give GMA/DVB/THBA chelating resin. The adsorption of Th(IV) and U(VI) on GMA/DVB/THBA adsorbent was studied as a function of initial concentration, pH, shaking time and temperature. The novel chelating resin shows a high capacity for Th(IV) and U(VI), maximum adsorption of Th(IV) and U(VI) were 56 and 83.6 mg/g, respectively. Kinetic studies showed that the adsorption follows the pseudo second order model referring to the influence of the textural properties of the resin on the rate of adsorption. Thermodynamic parameters such as ?H° and ?S° were studied and indicated an endothermic process.     

1-(2,3,4-Trihydroxybenzylideneamino)-8-hydroxynaphthalene-3,6-disulfonic acid as reagent for spectrophotometric determination of boron in plants

A highly sensitive and selective method has been developed for spectrophotometric determination of boron in plants, the method based on the color reaction of new reagent 1-(2,3,4-trihydroxybenzylideneamino)-8-hydroxynaphthalene-3,6-disulfonic acid (THBA) with boron (III). In an ammonium acetate solution of pH 8.0, boron(III) reacts with THBA to form a 1:2 yellow complex which has a maximum absorption peak at 430 nm. The reaction can complete within 90 min and the absorbance of the complex remains maximum and almost constant at least for 24 h under a temperature range from 0 to 35 °C. The apparent molar absorptivity and Sandell's sensitivity are 2.95 × 10⁴ l mol⁻¹ cm⁻¹ and 0.00036 ng cm⁻², respectively. The limit of quantification, limit of detection and relative standard deviations were found to be 5.1, 1.5 ng ml⁻¹ and 1.12%, respectively. Under the optimum conditions, the absorbency of the complex (λ_max = 430 nm) increases linearly with concentration up to 0.8 μg ml⁻¹ of boron(III). The influences of foreign ions on the determination of boron were investigated in detail. Most of foreign ions can be tolerated in considerable amounts. Experiments have indicated that THBA as chromogenic reagent for spectrophotometric determination of boron has excellent analytical characteristics. Its sensitivity is more than 4.2-fold that of azomethine-H, and stability is advantage over other derivatives of azomehine-H remarkably. Moreover, the synthesis of THBA and its physicochemical properties of THBA were also investigated in detail. Proposed method has been applied to the determination of boron in plants with satisfactory results.     

Catalytic spectrophotometric determination of vanadium in seawaters based on the bromate oxidative coupling reaction of metol and 2,3,4-trihydroxybenzoic acid.

A new, simple, sensitive and selective catalytic method is developed for the determination of vanadium in natural and sea waters. The method is based on the catalytic effect of V(V) and/or V(IV) on the bromate oxidative-coupling reaction of metol with 2,3,4-trihydroxybenzoic acid (THBA). The reaction is followed spectrophotometrically by tracing the oxidation product at 380 and/or 570 nm after 5 min of mixing the reagents. The optimum reaction conditions are 6.4 x 10(-3) mol l-1 of metol, 2.0 x 10(-3) mol l-1 of THBA and 0.16 mol l-1 of bromate at 35 degrees C and in the presence of an activator-buffer solution of 1 x 10(-2) mol l-1 of tartrate (pH = 3.10). Following the recommended procedure, V(V) and/or V(IV) can be determined with linear calibration graphs up to 0.75 ng ml-1 and detection limits, based on the 3Sb criterion, of 0.008 and 0.018 ng ml-1 at 380 and 570 nm, respectively. The developed method was successfully applied, without any separation or preconcentration processes, to the determination of vanadium in natural and seawaters following the direct calibration and standard addition techniques, respectively.     

Two –COOH Decorated Anionic Metal‐organic Frameworks with Open Cu2+ Sites Afforded Highly C2H2/CO2 and C2H2/CH4 Separation and Removal of Organic Dyes

An anionic multifunctional porous metal organic framework (MOF), [Cu₂THBA(H₂O)₂] · (C₃H₇NO)₁₂ · (H₂O)₁₀ ( 1 ) (H₄THBA = p‐terphenyl‐3,2′′,3′′,5,5′′,5′′′‐ hexcarboxylic acid) with NbO‐type topology was synthesized and characterized. Due to multiple functional sites and suitable pore size, the desolvated compound 1a exhibits high separation selectivity for C₂H₂/CO₂ of 30 and C₂H₂/CH₄ of 131 at 1 kPa at room temperature. Compound 1 can also efficiently and completely separate methylene blue (MB⁺) molecules of low concentrations from aqueous solution in 12 h.     

2.4 A crystal structure of an oxaliplatin 1,2-d(GpG) intrastrand cross-link in a DNA dodecamer duplex

(1R,2R-Diaminocyclohexane)oxalatoplatinum(II) (oxaliplatin) is a third-generation platinum anticancer compound that produces the same type of inter- and intrastrand DNA cross-links as cisplatin. In combination with 5-fluorouracil, oxaliplatin has been recently approved in Europe, Asia, and Latin America for the treatment of metastatic colorectal cancer. We present here the crystal structure of an oxaliplatin adduct of a DNA dodecanucleotide duplex having the same sequence as that previously reported for cisplatin (Takahara, P. M.; Rosenzweig, A. C.; Frederick, C. A.; Lippard, S. J. Nature 1995, 377, 649-652). Pt-MAD data were used to solve this first X-ray structure of a platinated DNA duplex derived from an active platinum anticancer drug other than cisplatin. The overall geometry and crystal packing of the complex, refined to 2.4 A resolution, are similar to those of the cisplatin structure, despite the fact that the two molecules crystallize in different space groups. The platinum atom of the [Pt(R,R-DACH)](2+) moiety forms a 1,2-intrastrand cross-link between two adjacent guanosine residues in the sequence 5'-d(CCTCTGGTCTCC), bending the double helix by approximately 30 degrees toward the major groove. Both end-to-end and end-to-groove packing interactions occur in the crystal lattice. The latter is positioned in the minor groove opposite the platinum cross-link. A novel feature of the present structure is the presence of a hydrogen bond between the pseudoequatorial NH hydrogen atom of the (R,R)-DACH ligand and the O6 atom of the 3'-G of the platinated d(GpG) lesion. This finding provides structural evidence for the importance of chirality in mediating the interaction between oxaliplatin and duplex DNA, calibrating previously published models used to explain the reactivity of enantiomerically pure vicinal diamine platinum complexes with DNA in solution. It also provides a new kind of chiral recognition between an enantiomerically pure metal complex and the DNA double helix.     

Samarium versus aluminium Lewis acidity in a mixed alkyl carboxylate complex related to alkylaluminium activation in diene polymerization catalysis

[(C5Me5)2Sm(mu-O2CPh)]2 reacts with iBu3Al to form a mixed bridge samarium aluminium complex [(C5Me5)2Sm(mu-O2CPh)(mu-iBu)Al(iBu)2], that displays two different carboxylate orientations toward the metals in a single crystal.     

Binding of serotonin to the human serotonin transporter. Molecular modeling and experimental validation

Molecular modeling and structure-activity relationship studies were performed to propose a model for binding of the neurotransmitter serotonin (5-HT) to the human serotonin transporter (hSERT). Homology models were constructed using the crystal structure of a bacterial homologue, the leucine transporter from Aquifex aeolicus, as the template and three slightly different sequence alignments. Induced fit docking of 5-HT into hSERT homology models resulted in two different binding modes. Both show a salt bridge between Asp98 and the charged primary amine of 5-HT, and both have the 5-HT C6 position of the indole ring pointing toward Ala173. The difference between the two orientations of 5-HT is an enantiofacial discrimination of the indole ring, resulting in the 5-hydroxyl group of 5-HT being vicinal to either Ser438/Thr439 or Ala169/Ile172/Ala173. To assess the binding experimentally, binding affinities for 5-HT and 17 analogues toward wild type and 13 single point mutants of hSERT were measured using an approach termed paired mutant-ligand analogue complementation (PaMLAC). The proposed ligand-protein interaction was systematically examined by disrupting it through site-directed mutagenesis and re-establishing another interaction via a ligand analogue matching the mutated residue, thereby minimizing the risk of identifying indirect effects. The interactions between Asp98 and the primary amine of 5-HT and the interaction between the C6-position of 5-HT and hSERT position 173 was confirmed using PaMLAC. The measured binding affinities of various mutants and 5-HT analogues allowed for a distinction between the two proposed binding modes of 5-HT and biochemically support the model for 5-HT binding in hSERT where the 5-hydroxyl group is in close proximity to Thr439.     

One-dimensional metallic conducting pathway of cyclohexyl-substituted spiro-biphenalenyl neutral radical molecular crystal

The unprecedented metallic character of the cyclohexyl-substituted spiro-biphenalenyl neutral radical molecular crystal (5) suggested by its Pauli paramagnetism [Science 2005, 309, 281] is contradicted by the thermally activated conduction measured along the needle axis of crystal 5 and by an optical gap of Eg = 0.34 eV. Herein we provide the first high quality ab initio electronic structure calculations using density functional theory to reconcile these properties. The calculations point toward 5 being a quasi one-dimensional (1-D) material, with a 1-D conducting pathway along the [101] pi-chain direction. Along any directions other than the pi-chain, conduction is impeded by the small interchain overlap. 5 has a quarter-filled band structure with a density of states of N(Ef) = 7.5 states eV-1 at the Fermi level, leading to a metallic character along the pi-chain.     

Correspondence between molecular functionality and crystal structures. Supramolecular chemistry of a family of homologated aminophenols

The crystal structures and packing features of a family of 13 aminophenols, or supraminols, are analyzed and correlated. These compounds are divided into three groups: (a) compounds 1-5 with methylene spacers of the general type HO-C6H4-(CH2)n-C6H4-NH2 (n = 1 to 5) and both OH and NH2 in a para position; (b) compounds 1a, 2a, 2b, 2c, and 3a in which one or more of the methylene linkers in 1 to 3 are exchanged with an S-atom; and (c) compounds 2d, 1b, and 6a prepared with considerations of crystal engineering and where the crystal structures may be anticipated on the basis of structures 1-5,1a, 2a, 2b, 2c, and 3a. These 13 aminols can be described in terms of three major supramolecular synthons based on hydrogen bonding between OH and NH2 groups: the tetrameric loop or square motif, the infinite N(H)O chain, and the beta-As sheet. These three synthons are not completely independent of each other but interrelate, with the structures tending toward the more stable beta-As sheet in some cases. Compounds 1-5 show an alternation in melting points, and compounds with n = even exhibit systematically higher melting points compared to those with n = odd. The alternating melting points are reflected in, and explained by, the alternation in the crystal structures. The n = odd structures tend toward the beta-As sheet as n increases and can be considered as a variable series whereas for n = even, the beta-As sheet is invariably formed constituting a fixed series. Substitution of a methylene group by an isosteric S-atom may causes a change in the crystal structure. These observations are rationalized in terms of geometrical and chemical effects of the functional groups. This study shows that even for compounds with complex crystal structures the packing may be reasonably anticipated provided a sufficient number of examples are available.     

Pillar[n]MaxQ: A New High Affinity Host Family for Sequestration in Water

We report the synthesis, X‐ray crystal structure, and molecular recognition properties of pillar[n]arene derivative P[6]AS , which we refer to as Pillar[6]MaxQ along with analogues P[5]AS and P[7]AS toward guests 1 – 18 . The ultratight binding affinity of P[5]AS and P[6]AS toward quaternary (di)ammonium ions renders them prime candidates for in vitro and in vivo non‐covalent bioconjugation, for imaging and delivery applications, and as in vivo sequestration agents.     

Reinforced HNA backbone hydration in the crystal structure of a decameric HNA/RNA hybrid

The crystal structure of a decameric HNA/RNA (HNA = 2',3'-dideoxy-1',5'-anhydro-d-arabinohexitol nucleic acid) hybrid with the RNA sequence 5'-GGCAUUACGG-3' is the first crystal structure of a hybrid duplex between a naturally occurring nucleic acid and a strand, which is fully modified to contain a six-membered ring instead of ribose. The presence of four duplex helices in the asymmetric unit allows for a detailed discussion of hydration, which revealed a tighter spinelike backbone hydration for the HNA- than for the RNA-strands. The reinforced backbone hydration is suggested to contribute significantly to the exceptional stability of HNA-containing duplexes and might be one of the causes for the evolutionary preference for ribose-derived nucleic acids.     

Fibronectin conformation switch induced by coadsorption with human serum albumin

The dynamic adsorption of human serum albumin (HSA) and plasma fibronectin (Fn) onto hydrophobic poly(hydroxymethylsiloxane) (PHMS) and the structures of adsorbed protein layers from single and binary protein solutions were studied. Spectroscopic ellipsometry (SE) and quartz crystal microbalance with dissipation monitoring (QCM-D) together with atomic force microscopy (AFM) were used to measure the effective mass, thickness, viscoelastic properties, and morphology of the adsorbed protein films. Adsorbed HSA formed a rigid, tightly bound monolayer of deformed protein, and Fn adsorption yielded a thick, very viscoelastic layer that was firmly bound to the substrate. The mixed protein layers obtained from the coadsorption of binary equimolecular HSA-Fn solutions were found to be almost exclusively dominated by Fn molecules. Further sequential adsorption experiments showed little evidence of HSA adsorbed onto the predeposited Fn layer (denoted as Fn ? HSA), and Fn was not adsorbed onto predeposited HSA (HSA ? Fn). The conformational arrangement of the adsorbed Fn was analyzed in terms of the relative availability of two Fn domains. In particular, (4)F(1)·(5)F(1) binding domains in the Hep I fragment, close to the amino terminal of Fn, were targeted using a polyclonal antifibronectin antibody (anti-Fn), and the RGD sequence in the 10th segment, in the central region of the molecule, was tested by cell culture experiments. The results suggested that coadsorption with HSA induced the Fn switch from an open conformation, with the amino terminal subunit oriented toward the solution, to a close conformation, with the Fn central region oriented toward the solution.     

Preparation of L-Alanine Crystals Containing Gold Nanoparticles

Amino acids provide useful foods, medicines, health foods, and nutritional supplements. We studied the morphology control of alanine, an amino acid. We also studied the effects of amino acid addition on the dispersion stability of gold nanoparticles. We then studied hybridization between alanine crystals and arginine-capped gold nanoparticles. Alanine crystal growth in a supersaturated alanine solution was found to increase linearly over time, and alanine crystal growth stopped as supersaturation decreased. Alanine crystals with arginine grew toward the c-axis because arginine was adsorbed onto the face (120) of alanine crystals. Absorption wavelengths of colloidal solutions changed for gold nanoparticles with arginine, suggesting that arginine was adsorbed onto gold nanoparticles. The change in alanine crystal morphology was the same for alanine crystals with arginine-capped gold nanoparticles in that it grew toward the c-axis. Alanine crystals contained arginine-capped gold nanoparticles toward the c-axis.     

Morphological phase behaviour under pressure of polycatenar mesogens with a perfluorinated moiety

Two polycatenar materials composed of a four-aromatic-ring core with a perfluorinated moiety attached in one terminal position through either butylene- or pentylene spacer groups, and three tetradecyloxy chains at the other end (abbreviated as 14PC₄F and 14PC₅F), were investigated to study the effect of pressure on the phase transition behaviour. A polarizing optical microscope equipped with a high pressure optical hot stage, was used for the purpose. The T vs. P phase diagrams of 14PC₄F and 14PC₅F were constructed in the pressure region up to 100 MPa. 14PC₄F showed the stable crystal (Cr₁)-columnar tetragonal (Col_tet)-smectic A (SmA)-columnar hexagonal (Col_h)-isoropic liquid (I) phase transition sequence under all pressures. 14PC₅F exhibited the phase sequence metastable crystal (Cr₂)-cubic (Cub)-Col_tet-SmA-I in a melt-cooled sample on heating under pressure. But when the melt-cooled Cr₂ sample was annealed at 52-54°C for 2-3 h, the stable crystal (Cr₁) was formed slowly, giving a stable Cr₁-Cub-Col_tet-SmA-I phase sequence. The temperature region of the stable cubic phase broadened with increasing pressure. Furthermore a new mesophase of 14PC₅F was pressure-induced between the I and SmA phases on cooling at pressures above about 16 MPa. Since the monotropic mesophase exhibited a texture very similar to that of the high temperature Col_h phase of 14PC₄F with planar orientation, the new phase was assigned at a high temperature columnar hexagonal phase of 14PC₅F.     

A Self-Assembled Rhombohedral DNA Crystal Scaffold with Tunable Cavity Sizes and High-Resolution Structural Detail

DNA is an ideal molecule for the construction of 3D crystals with tunable properties owing to its high programmability based on canonical Watson–Crick base pairing, with crystal assembly in all three dimensions facilitated by immobile Holliday junctions and sticky end cohesion. Despite the promise of these systems, only a handful of unique crystal scaffolds have been reported. Herein, we describe a new crystal system with a repeating sequence that mediates the assembly of a 3D scaffold via a series of Holliday junctions linked together with complementary sticky ends. By using an optimized junction sequence, we could determine a high-resolution (2.7 Å) structure containing R3 crystal symmetry, with a slight subsequent improvement (2.6 Å) using a modified sticky-end sequence. The immobile Holliday junction sequence allowed us to produce crystals that provided unprecedented atomic detail. In addition, we expanded the crystal cavities by 50 % by adding an additional helical turn between junctions, and we solved the structure to 4.5 Å resolution by molecular replacement.     

First total synthesis of louisianin A

The first total synthesis of louisianin A, 4-allyl-6,7-dihydro-1-hydroxycyclopenta[c]pyridin-5-one, is achieved from 2-chloro-4-cyanopyridine 5 via seven steps in an overall 24% yield. The key step is a cyclization-decarboxylation sequence toward the formation of a cyclopentenone ring.     

Synthesis, complexation properties and crystal structure of 4'''',5''''-dibromo-oxylyl-17-crown-5 ether

4',5'-Dibromo-o-xylyl-17-crown-5 ether (2BrB17C5) was synthesized,starting from 1,2-dibromo-4,5-bis(bromomethyl)-benzene and tetraethylene glycol,and was characterized by 1H NMR,MS and elemental analysis.Pale yellow prismatic single crystal obtained from anhydrous ethanol was investigated by X-ray structural analysis.The complexation properties toward alkali metal ions were examined using the solvent extraction method and UV absorption spectroscopy.The crown ether was found to be conformationally deformed and oblate-like and is highly selective for lithium ion.     

多相光催化分解H2S中阴离子表面活性剂对半导体催化剂CdS表面的影响

研究了在H₂S碱性溶液中,CdS粉末催化剂存在时,光催化分解H₂S释氢和生成硫反应。考察了阴离子表面活性剂——十二烷基硫酸钠(SDS)对催化剂的表面性质和催化活性的影响。通过模拟该反应体系,用电化学方法测定了单晶CdS电极在上述反应体系中加入SDS(浓度低于临界胶团浓度CMC值)后的平带电位的变化。结果表明:单晶CdS电极的平带电位,由于该体系加入SDS而正移,与n型多晶半导体CdS在加入SDS的H₂S碱性溶液中,光催化分解H₂S的释氢量减少相一致。并探讨了在该体系中,由于表面活性剂的阴离子与S^2-在单晶CdS电极表面上的竞争吸附,而引起单晶CdS电极的平带电位正移。     

KInSe~2的中温固相合成及结构表征

采用反应性熔盐法,以n(K~2Se~3):n(In):n(Se)=1:1:5的摩尔比,在500℃下反应5d,生成淡黄色柱状晶体KInSe~2。该晶体属于单斜晶系,空间群为C2/c,晶胞参数,a=1.414(2)nm,b=1.1410(2)nm,c=1.5586(3)nm,β=100.60(3)°,Z=16,R=0.0656。KInSe~2晶体具有层状结构,每层由具有二维网状结构的[InSe~2]^-负离子和K^+组成,层与层之间按ABAB方式堆积。