Halide coordination to zinc porphyrin sensitizers anchored to nanocrystalline TiO2

The coordination of halide ions to 5-(3,5-dicarboxyphenyl)-10,15,20-tri- p-tolylporphinatozinc(II) anchored to mesoporous nanocrystalline (anatase) TiO 2 thin films (TiO 2/ZnP) immersed in propylene carbonate was quantified. The addition of tetrabutylammonium halide salts to the external propylene carbonate electrolyte resulted in a red shift in the absorption spectrum with the maintenance of five isosbestic points. The absorption spectra were within experimental error the same for ZnP and ZnP-X (-) compared to TiO 2/ZnP and TiO 2/ZnP-X (-): A SoretZnP = 427 nm (epsilon = 574 000 M (-1) cm (-1)), A SoretZnP-Cl (-) = 435 nm (epsilon = 905 000 +/- 12 000 M (-1) cm (-1)), A SoretZnP-Br (-) = 436 nm (epsilon = 776 000 +/- 30 000 M (-1) cm (-1)), and A SoretZnP-I (-) = 437 nm (epsilon = 620 000 +/- 56 000 M (-1) cm (-1)). Titration studies with the halides revealed sharp isosbestic points consistent with formation of a 1:1 halide/porphyrin adduct. Equilibrium constants for ZnP were found to be 1670 M (-1) for Cl (-), 96 M (-1) for Br (-), and 5.5 M (-1) for I (-), and the corresponding values for TiO 2/ZnP were significantly smaller, 780 M (-1), 70 M (-1) and 3.4 M (-1). A quasi-reversible wave was observed by cyclic voltammetry of TiO 2/ZnP, E 1/2(ZnP (+/0)) = +790 mV vs Ag/AgCl, that was shifted 160 mV after addition of excess chloride, E 1/2(ZnP-Cl (0/-)) = +630 mV. In regenerative solar cells with quinone/hydroquinone redox mediators, TiO 2/ZnP and TiO 2/ZnP-X (-), where X is Cl, Br, or I, were found to convert light into electrical power. The photocurrent action spectrum demonstrated that energy conversion was initiated by light absorption of ZnP and/or the halide adduct.     

Nonconcerted cycloaddition of 2H-azirines to acylketenes: a route to N-bridgehead heterocycles

Reactions of acylketenes, generated from diazo diketones, with 2-unsubstituted and 2-monosubstituted 3-aryl-2H-azirines lead to 1:1 or 2:1 adducts, which are derivatives of 5-oxa-1-azabicyclo[4.1.0]hept-3-ene or 5,7-dioxa-1-azabicyclo[4.4.1]undeca-3,8-diene. According to DFT B3LYP/6-31G(d) computations, the formation of (4+2)-monoadducts proceeds via a stepwise non-pericyclic mechanism. Reaction with methanol transforms quantitatively both 1:1 and 2:1 adducts into 1,4-oxazepine derivatives.     

From BN-Naphthalenes to Benzoborole Dianions

The synthesis of benzoborole dianions by alkali metal reduction of BN-naphthalene derivatives via a ring-contraction strategy has been developed. Reduction of 1-alkynyl 2,1-benzazaborine 1 a in Et₂O led to the elimination of alkynyllithium with the formation of 1-amino-1-benzoborole trilithium salt 2 a , whereas reduction of 1-phenyl 2,1-benzazaborine 1 c in THF yielded 1-phenyl-1-benzoborole dilithium salt 2 c with the elimination of ArNHLi. The trilithium and dilithium salts 2 a and 2 c have been fully characterized. Treatment of trilithium salt 2 a with Et₃NHCl led to the selective protonation of the amino lithium to afford the dilithium salt 2 aH , which could be cleanly oxidized to 1-amino-1-benzoborole 3 in an excellent yield. Reaction of 1-phenyl-1-benzoborole dilithium salt 2 c with MeI yielded the lithium borate 4 c , which is luminescent both in solution and in the solid state.     

电化学发光分析法测定糖尿病相关二肽

将纳米金粒子负载于氧化铟锡导电玻璃(ITO)表面作为电化学发光(ECL)工作电极,建立了简单、快速测定二肽的方法.采用透射电镜、扫描电镜、电化学和光谱等技术方法表征材料和所制备电极的性能.在最优条件下,组氨酸-丙氨酸二肽分子(His-Ala)对鲁米诺在此电极上的ECL有显著的猝灭作用,从而可以对二肽进行检测.在2.44×10-11~1.22×10-7 mol/L浓度范围内,ECL响应和二肽浓度有良好的线性关系,检出限为2.42×10-12 mol/L(S/N=3).人体内胰高血糖素样肽-1(GLP-1)在二肽基肽酶IV(PDD-IV)作用下失去活性并释放出同量的His-Ala二肽,因此,本方法可通过测定血液中二肽浓度间接测定GLP-1,以及评估PDD-IV和其抑制剂的活性.上述DPP-IV抑制剂可调节2型糖尿病人血液GLP-1在正常水平,是糖尿病研究和治疗中具有潜在价值的药物设计靶点.     

Synthetic routes to cyclopropylidenecarbinols and to cyclopropylidienes

Functionalized alkylidine cyclopropanes have beeen prepared from 1-seleno 1-vinyl cyclopropanes using [2,3] sigmatropic rearrangement of their corresponding selenonium ylides. A comparison with sulphur analogues is presented.     

A high-throughput microfluidic assay to study neurite response to growth factor gradients

Studying neurite guidance by diffusible or substrate bound gradients is challenging with current techniques. In this study, we present the design, fabrication and utility of a microfluidic device to study neurite guidance under chemogradients. Experimental and computational studies demonstrated the establishment of a steep gradient of guidance cue within 30 min and stable for up to 48 h. The gradient was found to be insensitive to external perturbations such as media change and movement of device. The effects of netrin-1 (0.1-10 μg mL(-1)) and brain pulp (0.1 μL mL(-1)) were evaluated for their chemoattractive potential on neurite turning, while slit-2 (62.5 or 250 ng mL(-1)) was studied for its chemorepellant properties. Hippocampal or dorsal root ganglion (DRG) neurons were seeded into a micro-channel and packed onto the surface of a 3D collagen gel. Neurites grew into the matrix in three dimensions, and a gradient of guidance cue was created orthogonal to the direction of neurite growth to impact guidance. The average turning angle of each neurite was measured and averaged across multiple devices cultured under similar conditions to quantify the effect of guidance cue gradient. Significant positive turning towards gradient was measured in the presence of brain pulp and netrin-1 (1 μg mL(-1)), relative to control cultures which received no external guidance cue (p < 0.001). Netrin-1 released from transfected fibroblasts had the most positive turning effect of all the chemoattractive cues tested (p < 0.001). Slit-2 exhibited strong chemorepellant characteristics on both hippocampal and DRG neurite guidance at 250 ng mL(-1) concentration. Slit-2 also showed similar behavior on DRG neuron invasion into 3D collagen gel (p < 0.01 relative to control cultures). Taken together, the results suggest the utility of this microfluidic device to generate stable chemogradients for studying neurobiology, cell migration and proliferation, matrix remodeling and co-cultures with other cell lines, with potential applications in cancer biology, tissue engineering and regenerative medicine.     

Addition of polyfluoropolyhaloethanes to alkenes

In the presence of CrCl3/Fe redox system, polyfluoropolyhaloethanes readily added to electron-deficient or electron-rich alkenes, giving the corresponding 1:1 hydropolyfluoroalkyla-tion product or 1:1 adduct in high yields. This reaction provided a simple and convenient method to synthesize building blocks containing a CF3 or CF2 moiety.     

Photoaddition of N-ethylmaleimide to cumene

The photoaddition of N-ethylmaleimide (NEMI) to cumene is compared with that of benzene. The equilibrium constants of the CT-complexes were determined by means of ¹H-N.M.R. spectroscopy (K_benzene-NEMI = 0.035 kg mole^?1, K_cumene-NEMI = 0.049 kg mole). By irradiation with light of wavelength 254 nm the 2:1 adduct cumene-NEMI is formed. The structure was determined by ¹ H-N.M.R. and mass spectrometry. These data indicate that only one of the possible isomers is formed and that the free rotation of the isopropyl group is hindered in the adduct. Furthermore two isomeric 1 : 1 adducts could be detected and assigned to the 1 : 1 cycloaddition product and to cumyl-N-ethyl-succinimide.     

Modulation of base excision repair alters cellular sensitivity to UVA1 but not to UVB1

Oxidative DNA damage has been implicated in some of the biological properties of UVA but so far not in the acute photosensitivity or cellular sensitivity. In contrast to pyrimidine dimers, oxidative DNA damage is predominantly processed by base excision repair (BER). In order to further clarify the role of oxidative DNA damage and its repair in the acute cellular response to UV light, we studied UVA1 and UVB sensitivities in three different cell model systems with modified BER. 8-Oxoguanine-DNA-glycosylase 1-/- (OGG1-/-) mouse embryonal fibroblasts and human fibroblasts in which BER was inhibited by incubation with methoxyamine were hypersensitive to UVA1, in particular to low doses. This hypersensitivity could be partially corrected by reexpression of OGG1 in OGG1-/- cells. The Chinese hamster ovary (CHO) cells with upregulated AP-endonuclease 1 exhibited reduced UVA1 sensitivity. UVB sensitivity was not altered in any of the cell models. These results indicate that DNA damage, in particular oxidative DNA damage, contributes to cellular UVA1 sensitivity and underline a pivotal role of its repair in the cellular responses to UVA1.     

Dichlorocarbene Addition to

In contrast to the terminal phosphinidene complex PhPW(CO)(5) (2), which adds to [5]metacyclophane (1) in a 1,4-fashion, dichlorocarbene preferentially adds in a 1,2-fashion to the formal "anti-Bredt" type double bond of the aromatic ring of 1 to afford the norcaradiene 11b, which immediately rearranges to the bridged cycloheptatriene 12b and further by a [1,5] sigmatropic chlorine migration to the isomeric 13b as the first observable product. More slowly, the latter isomerizes via a dissociative mechanism to give 15b. A computational study supports the notion that the [1,5] chlorine migration in the rearrangement 12b --> 13b, for which an activation barrier of 70.2 kJ mol(-)(1) was calculated, is essentially concerted with minor charge separation. In contrast, the analogous [1,5] chlorine migration in the flat model compound 7,7-dichlorocycloheptatriene (12a) displays features of a dissociative pathway.     

Selective oxoammonium salt oxidations of alcohols to aldehydes and aldehydes to carboxylic acids

The oxidation of alcohols to aldehydes using stoichiometric 4-acetamido-2,2,6,6-tetramethylpiperidine-1-oxoammonium tetrafluoroborate (1) in CH(2)Cl(2) at room temperature is a highly selective process favoring reaction at the carbinol center best able to accommodate a positive charge. The oxidation of aldehydes to carboxylic acids by 1 in wet acetonitrile is also selective; the rate of the process correlates with the concentration of aldehyde hydrate. A convenient and high yield method for oxidation of alcohols directly to carboxylic acids has been developed.     

Arsenic binding to human metallothionein

The number of reported cases of chronic arsenic poisoning is on the rise throughout the world, making the study of the long-term effects of arsenic critical. As(3+) binds readily to biological thiols, including mammalian metallothionein (MT), which is an ubiquitous sulfur-rich metalloprotein known to coordinate a wide range of metals. The two-domain mammalian protein binds divalent metals (M) into two metal-thiolate clusters with stoichiometries of M(3)S(cys9) (beta) and M(4)S(cys11) (alpha). We report that As(3+) binds with stoichiometries of As(3)S(cys9) (beta) and As(3)S(cys11) (alpha) to the recombinant human metallothionein (rhMT) isoform 1a protein. Further, we report the complete kinetic analysis of the saturation reactions of the separate alpha and beta domains of rhMT with As(3+). Speciation in the metalation reactions was determined using time- and temperature-resolved electrospray ionization mass spectrometry. The binding reaction of As(3+) to the alpha and beta MT domains is shown to be noncooperative and involves three sequential, bimolecular metalation steps. The analyses allow for the first time the complete simulation of the experimental data for the stepwise metalation reaction of MT showing the relative concentrations of the metal-free, apo MT and each of the As-MT intermediate species as a function of time and temperature. At room temperature (298 K) and pH 3.5, the individual rate constants for the first, second, and third As(3+) binding to apo-alphaMT are 5.5, 6.3, and 3.9 M(-)(1) s(-)(1) and for apo-betaMT the constants are 3.6, 2.0, and 0.6 M(-)(1) s(-)(1). The activation energy for formation of As(1)-H(6)-betaMT is 32 kJ mol(-)(1), for As(2)-H(3)-betaMT it is 35 kJ mol(-)(1), for As(3)-betaMT it is 29 kJ mol(-)(1), for As(1)-H(8)-alphaMT it is 33 kJ mol(-)(1), for As(2)-H(5)-alphaMT it is 29 kJ mol(-)(1), and for As(3)-H(2)-alphaMT it is 23 kJ mol(-)(1).     

Mercaptan addition to allylglucosides

Addition of ethyl-, n-propyl-, and butylmercaptans to 1-O-allyl-2,3,4,6-tetra-O-acetyl-β-D-glucopyranose in the presence of two catalysts, benzoyl peroxide and cobalt octacarbonyl, to produce the corresponding 1-O-(3-ethylthiopropyl)-2,3,4,6-tetra-O-acetyl-β-D-glucopyranose, 1-O-(3-propylthiopropyl)-2,3,4,6-tetra-O-acetyl-β-D-glucopyranose, and 1-O-(3-butylthiopropyl)-2,3,4,6-tetra-O-acetyl-β-D-glucopyranose was studied for the first time. It was found that these reactions occurred mainly according to the Farmer rule.     

Addition of thiophenols to N-vinylpyrroles

Thiophenols add to 1-vinyl-4,5,6,7-tetrahydroindole and 1-vinyl-2-phenylpyrrole in the presence of azobisisobutyronitrile to form 1-(2-arylthioethyl)pyrroles. The major products in the absence of initiator are the isomeric 1-(1-arylthioethyl)pyrrole -adducts. NH-Pyrroles inhibit the radical process and form selectively the -adducts.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 750–752, June, 1990.     

Cyclopentadienylrhodium coordination to alkenylarenes

Photochemical reaction of [Rh(eta-C(5)H(5))(C(2)H(4))(2)] (5) with alkenyl benzene derivatives PhC(R(1))=CHR(2) results in the formation of four types of cyclopentadienylrhodium complexes: the mononuclear ethylene eta(2)-alkenylbenzene complexes [Rh(eta-C(5)H(5))(eta-C(2)H(4))(eta(2)-PhC(R(1))=CHR(2))] 9 a (R(1)=H, R(2)=Ph), 9 b (R(1)=Ph, R(2)=H), 9 c (R(1)=CH(3), R(2)=H), the mononuclear eta(4)-alkenylbenzene complex [Rh(eta-C(5)H(5))[beta,alpha,1,2-eta-C(6)H(5)C(Ph)=CH(2)]] (10), the dinuclear mu-eta(4):eta(4)-alkenylbenzene complex [anti-[Rh(eta-C(5)H(5))](2)[mu-beta,alpha,1,2-eta:3,4,5,6-eta-C(6)H(5)C(Ph)C=CH(2)]] (11), and the dinuclear rhodaindenyl complexes [Rh(eta-C(5)H(5))[1-3,8,9-eta-[1-(eta-C(5)H(5))]-3-R(1)-1-rhodaindenyl]] 12 a (R(1)=Ph), 12 b (R(1)=CH(3)). Reaction of 5 with triisopropenylbenzene gives the dinuclear complex [[Rh(eta-C(5)H(5))](2)(mu-beta,alpha,1,2-eta:beta',alpha',4,3-eta-C(6)H(3)[C(CH(3))=CH(2)](3))] (13). In the complexes 9, only the olefinic side chain of the alkenylbenzene binds to the metal. In the complexes 10, 11, 12, and 13, an arene nucleus coordinates to rhodium as a 1,3-diene moiety (or part thereof). The rhodaindenyl complexes 12 result from C-H activation of the alkenylbenzene at the beta and ortho positions. The crystal and molecular structures of 9 a, 9 b, 10, 11, and 12 a, b were determined. The role of 9-11 and 13 as models for intermediates during alkenylbenzene-assisted self-assembly of tricobalt clusters is discussed.     

RNA binding to antioxidant flavonoids

Flavonoids are an interesting group of natural polyphenolic compounds that exhibit extensive bioactivities such as scavenging free radical, antitumor and antiproliferative effects. The anticancer and antiviral effects of these natural products are attributed to their potential biomedical applications. While flavonoids complexation with DNA is known, their bindings to RNA are not fully investigated. This study was designed to examine the interactions of three flavonoids; morin (Mor), apigenin (Api) and naringin (Nar) with yeast RNA in aqueous solution at physiological conditions, using constant RNA concentration (6.25 mM) and various pigment/RNA (phosphate) ratios of 1/120 to 1/1. FTIR, UV-visible spectroscopic methods were used to determine the ligand binding modes, the binding constant and the stability of RNA in flavonoid-RNA complexes in aqueous solution. Spectroscopic evidence showed major binding of flavonoids to RNA with overall binding constants of K(morin) = 9.150 x 10(3) M(-1), K(apigenin)=4.967 x 10(4) M(-1), and K(naringin)=1.144 x 10(4) M(-1). The affinity of flavonoid-RNA binding is in the order of apigenin>naringin>morin. No biopolymer secondary structural changes were observed upon flavonoid interaction and RNA remains in the A-family structure in these pigment complexes.     

Novel approaches to dialkylhetarylphosphonates

Abstract

Dialkyl-1-oxoalky1-, 1-oxo-2-alkenyl-, and 3-oxo-1-alkenylphosphonates are very useful substrates for the synthesis of a series of Dialkylphosphonates with a heterocyclic substituent.     

Kinetics of competitive addition of methyldichlorosilane to 1-hexene and to acetone

The competitive addition of methyldichlorosilane (MDChS) to 1-hexene and acetone^** has been studied. The estimated relative constant is effective and depends on acetone concentration and does not obey the Arrhenius temperature equation. A possible explanation is the complexation of methlydichlorosilyl radicals by acetone molecules.

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Initiated by -irradiation of⁶⁰Co.     

Free-radical addition of 1-thiosugars to alkenes a new general approach to the synthesis of 1-thioglycosides

Addition of peracetylated 1-thiosugars to alkenes in the presence of azobis(isobutyronitrile) (AIBN) as initiator constitutes an efficient route to alkyl 1-thioglycosides as well as to 1-thioglycosides bearing a reactive group on the aglycon.     

Base-Catalyzed cyclization of N-propargylamides to oxazoles

The base-catalyzed cyclization of some N-propargylamides to oxazoles has been studied in the presence of sodium hydride and potassium carbonate. The α-arylsubstituted propargylamides 1c-d (Ar = p-OMeC₆H₄ ( 1c ), C₆H₅ ( 1d ), and p-O₂NC₆H₄ ( 1e )) cyclized with markedly higher rates ( 1e > 1d > 1c ) than the unsubstituted and α-methyl substituted propargylamides 1a and 1b . A ¹H nmr spectroscopic experiment demonstrated the presence of an allenic intermediate in the potassium carbonate-catalyzed ring closure of 1e . The observed rank order of reactivities correlates well with the acidities of the respective propargylic hydrogens of the amides and with the ability of the ring closed intermediates to stabilize an oxazole anion. The results demonstrate that the base-catalyzed formation of oxazoles from propargylamides may proceed via an allenic intermediate.