Fenchyl substituted 1,2-dioxetanes as an alternative to adamantyl derivatives for bioanalytical applications

The synthesis and study of the chemiluminescence parameters and thermal stability of 1,2-dioxetanes containing a spirofenchyl substituent are reported. Three fenchyl-substituted 1,2-dioxetanes were synthesized by photooxygenation of the corresponding alkenes, obtained by Barton-Kellogg olefination of the readily available (-)-fenchone. The fenchyl-substituted 1,2-dioxetanes showed thermal stabilities similar to those of the corresponding spiroadamantyl-substituted derivatives, although being slightly more labile with respect to unimolecular decomposition than the latter derivatives, which are widely utilized as labels in a great variety of chemiluminescent immunoassays. Fluoride induced decomposition of one triggerable fenchyl 1,2-dioxetane derivative showed kinetic parameters similar to those of the corresponding adamantyl-substituted derivative. The chemiluminescence quantum yields in the one percent range are also similar to that of other widely utilized chemiluminescence systems as the luminol reaction. These results indicate that fenchyl-substituted 1,2-dioxetanes can potentially be utilized as a cheaper alternative to substitute the corresponding spiroadamantyl derivatives in bioanalytical applications. (C) 2010 Elsevier B.V. All rights reserved.

Stereoselective Nucleophilic Addition of Potassium Alkyltrifluoroborates to Cyclic N-Acyliminium Ions: a Simple and Mild Approach to Chiral 5-Alkyl-pyrrolidin-2-ones

The stereoselective nucleophilic addition of potassium alkyltrifluoroborates to cyclic N-acyliminium ions derived from N-benzyl-3,4,5-triacetoxy-pyrrolidin-2-one, which affords 5-substituted-pyrrolidin-2-ones, is described. The products are obtained in moderate to good yields and are produced predominantly as the anti diastereomer.

Experimental Evidence of the Occurrence of Intramolecular Electron Transfer in Catalyzed 1,2-Dioxetane Decomposition

The activation parameters for the thermal decomposition of 13 acridinium-substituted 1,2-dioxetanes, bearing an aromatic moiety, were determined and their chemiluminescence emission quantum yields estimated, utilizing in situ photosensitized 1,2-dioxetane generation and observation of its thermal decomposition kinetics, without isolation of these highly unstable cyclic peroxides. Decomposition rate constants show linear free-energy correlation for electron-withdrawing substituents, with a Hammett reaction constant of rho = 1.3 +/- 0.1, indicating the occurrence of an intramolecular electron transfer from the acridinium moiety to the 1,2-dioxetane ring, as postulated by the intramolecular chemically initiated electron exchange luminescence (CIEEL) mechanism. Emission quantum yield behavior can also be rationalized on the basis of the intramolecular CIEEL mechanism, additionally evidencing its occurrence in this transformation. Both relations constitute the first experimental evidence for the occurrence of the postulated intramolecular electron transfer in the catalyzed and induced decomposition of properly substituted 1,2-dioxetanes.

Isolation and characterization of four type 2 ribosome inactivating pulchellin isoforms from Abrus pulchellus seeds

Abrus pulchellus seeds contain at least seven closely related and highly toxic type 2 ribosome-inactivating pulchellins, each consisting of a toxic A-chain linked to a sugar binding B-chain. In the present study, four pulchellin isoforms (termed P I, P II, P III and P IV) were isolated by affinity, ion exchange and chromatofocusing chromatographies, and investigated with respect to toxicity and sugar binding specificity. Half maximal inhibitory concentration and median lethal dose values indicate that P I and P II have similar toxicities and that both are more toxic to cultured HeLa cells and mice than P III and P IV. Interestingly, the secondary structural characteristics and sugar binding properties of the respective pairs of isoforms correlate well with the two toxicity levels, in that P I/P II and P III/P IV form two specific subgroups. From the deduced amino acids sequences of the four isoforms, it is clear that the highest similarity within each subgroup is found to occur within domain 2 of the B-chains, suggesting that the disparity in toxicity levels might be attributed to subtle differences in B-chain-mediated cell surface interactions that precede and determine toxin uptake pathways.

Synthesis, characterization and biological analysis of the complex [VO(Hdhp)(2)] (H(2)dhp=2,3-dihydroxypyridine)

A new vanadium (IV) complex with the monoanion of 2,3-dihydroxypyridine (H(2)dhp), or 3-hydroxy-2(1H)-pyridone, was synthesized, characterized by physicochemical techniques and tested biologically. The EPR data for the [VO(Hdhp)(2)] complex in DMF are: g(x) = 1.9768, g(y) = 1.9768 and g(z) = 1.9390; A values (10(-4) cm(-1)): A(x), 59.4; A(y//), 59.4; A(z), 171.0. The vV=O band in the IR spectrum of the complex is at 986 cm(-1). The complex is paramagnetic, with mu(eff) = 1.65 BM (d(1), spin-only) at 25 degrees C. The irreversible oxidation process [V(V)/V(IV)] of the [VO(Hdhp)(2)] complex, as revealed in a cyclic voltammogram, occurs at 876 mV. The calculated molecular structure of [VO(Hdhp)(2)] shows the vanadium(IV) center in a distorted square pyramidal environment, with the oxo ligand in the apical position and the oxygen donor atoms of the Hdhp ligands in the basal positions. The ability of [VO(Hdhp)(2)] to mimic insulin, and its toxicity to hepato-biliary functions, were investigated in streptozotocin-induced diabetic rats and it was concluded that the length of treatment and the amount of [VO(Hdhp)(2)] administered were effective in reducing experimental diabetes.

Cationic and neutral phenylmercury(II) complexes with heterocyclic thione ligands. X-ray structures of [HgPh(dmpymtH)][BF(4)] center dot H(2)O and [{HgPh}(2)(mu-dtu)]

The neutral complex [HgPh(dmpymt)] 1 (dmpymtH = 4,6-dimethylpyrimidine-2(1H)-thione) reacts with HBF(4) to give the cationic complex [HgPh(dmpymtH)][BF(4)] 2. The X-ray molecular structure of the later revealed a [2+1] coordination sphere about the mercury(II) atom (C-Hg-S and Hg center dot center dot center dot N). In the dinuclear complex [(HgPh)(2)(mu-dtu)] 3 [dtuH(2) = 2,4(1H,3H)-pyrimidinedithione or dithiouracil] the coordination spheres are also [2+1] although dissimilar regarding the Hg center dot center dot center dot N secondary bonds. NMR spectroscopy ((1)H, (13)C and (199)Hg) studies were undertaken in solution and the results discussed in the light of the X-ray structures. (C) 2008 Elsevier B. V. All rights reserved.

Landscape perception by forest understory birds in the Atlantic Rainforest: black-and-white versus shades of grey

Even among forest specialists, species-specific responses to anthropogenic forest fragmentation may vary considerably. Some appear to be confined to forest interiors, and perceive a fragmented landscape as a mosaic of suitable fragments and hostile matrix. Others, however, are able to make use of matrix habitats and perceive the landscape in shades of grey rather than black-and-white. We analysed data of 42 Chiroxiphia caudata (Blue Manakin), 10 Pyriglena leucoptera (White-shouldered Fire-eye) and 19 Sclerurus scansor (Rufous-breasted Leaftosser) radio-tracked in the Atlantic Rainforest of Brazil between 2003 and 2005. We illustrate how habitat preferences may determine how species respond to or perceive the landscape structure. We compared available with used habitat to develop a species-specific preference index for each of six habitat classes. All three species preferred old forest, but relative use of other classes differed significantly. S. scansor perceived great contrast between old forest and matrix, whereas the other two species perceived greater habitat continuity. For conservation planning, our study offers three important messages: (1) some forest specialist species are able to persist in highly fragmented landscapes; (2) some forest species may be able to make use of different anthropogenic habitat types to various degrees; whereas (3) others are restricted to the remaining forest fragments. Our study suggests species most confined to forest interiors to be considered as potential umbrella species for landscape-scale conservation planning.

Langmuir and Langmuir-Blodgett (LB) films of tetrapyridyl metalloporphyrins

We report on the formation of Langmuir films of 5,10,15,20-tetra(4-pyridyl) 21H,23H-porphine,hereafter named tetrapyridyl porphyrins with distinct central ions (2H(+), Zn(2+), Cu(2+), Ni(2+)). The films were characterized with surface pressure and surface potential isotherms and in situ UV-vis absorbance. The measurements indicated strong aggregation of porphyrin monomers at the air-water interface, with a red shift of the Soret band in comparison with the spectrum obtained from CHCl(3) solutions. The shift was larger for the non-substituted H(2)TPyP, and depended on the metal ion. Significantly, aggregation occurred right after spreading of the Langmuir film, with on further shifts in the UV-vis spectra upon compression of the film, or even after transferring them onto solid substrates in the form of Langmuir-Blodgett (LB) films. The buildup of LB films from H(2)TPyP and ZnTPyP was monitored with UV-vis spectroscopy, indicating an equal amount of material deposited in each deposition step. Using FTIR in the transmission and reflection modes, we inferred that the H(2)TPyP molecules exhibit no preferential orientation in the LB films, while for ZnTPyP there is preferential orientation, with the porphyrin molecules anchored to the substrate by the lateral pyridyl groups. (C) 2008 Elsevier B.V. All rights reserved.

Tryptophan photooxidation promoted by new hybrid materials prepared by condensation of naphthalene imides with silicate by the sol-gel process

Three novel hybrid organic/inorganic materials were synthesized from 4-substituted (NO(2), Br, H) 1,8-naphthalene imide-N-propyltriethoxysilane by the sol-gel process. These materials were obtained as a xerogel and partially characterized. The ability to photosensitize the oxidation and degradation of tryptophan indole ring by these materials was studied through photophysical and photochemical techniques. Although the derivatives containing Br and NO(2) as substituent do not cause efficient tryptophan photodamage, the hybrid material obtained from 1,8-naphthalic anhydride is very efficient to promote tryptophan photooxidation. By using laser flash photolysis it was possible to verify the presence of naphthalene imide transient radical species. The presence of oxygen causes an increase of the yield of radical formation. These results suggest that the mechanism of photodegradation of tryptophan occurs by type I, i.e. the transient radical (TrpH(center dot+)) formed by the direct reaction of the triplet state of the naphthalene imide moiety with tryptophan. Thus a inorganic-organic hybrid material that can be used to promote the oxidation of biomolecules was obtained. (C) 2009 Elsevier B.V. All rights reserved.

Vibrational properties, crystal X-ray diffraction structure and quantum chemical calculations on a divalent sulfur substituted phthalimide: 1H-Isoindole-1,3(2H)-dione, 2-[(methoxycarbonyl)thio]

Structural and conformational properties of 1H-Isoindole-1,3(2H)-dione, 2-[(methoxycarbonyl)thio] (S-phthalimido O-methyl thiocarbonate) are analyzed using a combined approach including X-ray diffraction, vibrational spectra and theoretical calculation methods. The vibrational properties have been studied by infrared and Raman spectroscopies along with quantum chemical calculations (B3LYP and B3PW91 functional in connection with the 6-311++G** and aug-cc-pVDZ basis sets). The crystal structure was determined by X-ray diffraction methods. The substance crystallizes in the monoclinic P2(1)/c space group with a = 6.795(1), b = 5.109(1), c = 30.011(3) angstrom, beta = 90.310(3)degrees and Z = 4 molecules per unit cell. The conformation adopted by the N-S-C=O group is syn (C=O double bond in synperiplanar orientation with respect to the N-S single bond). The experimental molecular structure is well reproduced by the MP2/aug-cc-pVDZ method. (C) 2010 Elsevier B.V. All rights reserved.

Molecular conformation of the racemic indan derivative (+/-)-1-trans-3-(3,4-dichlorophenyl)-2,3-dihydro-1H-indene-1-carboxamide

This paper presents the structural characterization of the indan derivative (+/-)-1-trans-3-(3,4-dichlorophenyl)-2,3-dihydro-1H-indene-1-carboxamide, which was unambiguously determined by X-ray diffraction (XRD) to be a racemate (R/S: 50/50) crystallizing in an achiral crystal structure (P2(1)/c, a = 9.3180(1) , b = 7.9070(2) , c = 19.7550(4) , beta = 103.250(1)A degrees, V = 1416.75(5) (3) and Z = 4). The diastereomers are related by the inversion symmetry and linked by H bond forming a dimer. The crystal packing is stabilized by hydrogen bonds, including the classical one responsible for the formation of centrosymmetric dimers, and non-classical ones involving C-H center dot center dot center dot O and C-H center dot center dot center dot pi-aryl interactions. The intra and intermolecular geometry of the title compound is compared to the (+/-)-1-trans-3-(3,4-dichlorophenyl)-2,3-dihydro-1H-indene-1-carboxylic acid one, which also present an achiral crystal structure from racemates (R/S: 50/50). The two indan derivatives crystallize in a very similar unit cell.

Spectroscopic and theoretical studies of some N,N-diethyl-2-[(4 `-substituted)phenylsulfonyl]acetamides

The analysis of the IR carbonyl band of the N,N-diethyl-2-[(4`-substituted)phenylsulfonyl]acetamides Et(2)NC(O)CH(2)S(O)(2)-C(6)H(4)-Y (Y = OMe 1, Me 2,1-13, Cl 4, Br 5, NO(2) 6) supported by B3LYP/6-31G(d,p) calculations for 3, indicated the existence of three pairs (anti and syn) of cis (c) and gauche (g(1) and g(2)) conformers in the gas phase, being the gauche conformers significantly more stable than the cis ones. The anti geometry is more stable than the syn one, for each pair of cis and gauche conformers. The summing up of the orbital (NBO analysis) and electrostatic interactions justifies quite well the populations and the v(CO) frequencies of the anti and syn pairs of c, g(1) and g(2) conformers. The IR higher carbonyl frequency component whose population is ca. 10%, in CCl(4), may be ascribed to the least stable and most polar cis conformer pair (in the gas phase) and the lower frequency component whose population is ca. 90%, to the summing up of the populations of the two most stable and least polar gauche conformer pairs (g(1) and g(2)) (in the gas phase). The reversal of the cis(c)/gauche (g(1) + g(2)) population ratio observed in chloroform ca. 60% (cis)/40% (gauche) and the occurrence of the most polar cis(c) conformer only, in acetonitrile, strongly suggests the coalescence of the two gauche components in a unique carbonyl band in solution. A further support to this rationalization is given by the single point PCM solvation model performed by HF/6-31G(d,p) method, which showed a progressive increase of the c/(g(1) + g(2)) ratio going from gas to CCl(4), to CHCl(3) and to CH(3)CN. X-ray single crystal analysis of 4 indicates that this compound assumes, in the solid state, the syn-clinal (gauche) conformation with respect to the [O=C-CH(2)-S] moiety, and the most stable anti geometry relative to the [C(O)N(CH(2)CH(3))(2)] fragment. In order to obtain larger energy gain from the crystal packing the molecules of 4 are linked in centrosymmetric dimers through two C-H center dot center dot center dot O interactions (C-H([O-Ph])center dot center dot center dot O([SO2])) forming a step ladder. (C) 2011 Elsevier B.V. All rights reserved.

Conformational preferences for some 2-substituted N-methoxy-N-methylacetamides through spectroscopic and theoretical studies

The analysis of the IR carbonyl band of the 2-substituted N-methoxy-N-methylacetamides Y-CH(2)C(O)-N(OMe)Me (Y = F1, OMe 2, OPh 3, Cl 4), supported by B3LYP/6-311++G(3df, 3pd) calculations along with the NBO analysis for 1-4, indicated the existence of cis-gauche conformers i.e. (c) and (g) for 1 and 3, (c(1), c(2)) and (g(1), g(2)) for 2, and (c) and (g(1), g(2)) for 4. In the gas phase, the g conformer population prevails over the c one, for 1 and 3, the (c(1) + c(2)) population prevails over the (g(1) + g(2)) one for 2, and the (g(1) + g(2)) conformer population is more abundant than (c) one for 4. In n-hexane solution, the cis conformer is more abundant for 1-3. The occurrence of Fermi resonance in the nu(CO) region, in n-hexane, precludes the estimative of relative populations of the (c, g(1), g(2)) conformers for 4. The SCI-PCM calculations agree with the solvent effect on the nu(CO) band component relative intensities for 1-3. NBO analysis showed that the n(N) -> pi.(CO), orbital interaction is the main factor which stabilizes the gauche (g, g(1), g(2)) conformers for 1-4 into a larger extent relative to the cis (c, c(1), c(2)) ones. The n(y) -> pi(.)(Co,) sigma(C-Y) -> pi.(CO,) pi(CO) -> sigma(C-Y) and 7co orbital interactions still contribute, but into a minor extent for the stabilization of the gauche conformers relative to the cis ones. The existence of some pyramidalization at the nitrogen atom of the Weinreb amides 1-4 is responsible for the occurrence of Y(delta)-(4)center dot center dot center dot O(delta)-(9) and Y(delta)-(4)center dot center dot center dot N(delta)-(7) short contacts in the gauche (g, g(1), g(2)) conformers, which originates strong repulsive Coulombic interactions, acting in opposition to the large orbital stabilization of the gauche conformer with respect to the cis one. Therefore, a delicate balance of the Coulombic and orbital interactions seems to be responsible for the observed stabilization of the gauche (g, g(1), g(2)) and cis (c, c(1), c(2)) conformers, both in the gas phase and in the solution for 1-4. However, the cis conformer predominance, in non polar solvents, for the 2-substituted N-methoxy-N-methyl acetamides 1-3, bearing in a first raw (fluorine and oxygen) atoms, is in the opposite direction to the gauche conformer preference for the corresponding 2-substituted N,N-dialkyl-acetamides. (C) 2010 Elsevier B.V. All rights reserved.

2-(4,5,6,7-tetrafluorobenzimidazol-2-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl, a hydrogen-bonded organic quasi-1D ferromagnet

The title radical (F4BlmNN) is a stable nitronylnitroxide that forms hydrogen-bonded NH center dot center dot center dot ON chains in the solid state. The chains assemble the F4BlmNN molecules to form stacked contacts between the radical groups, in a geometry that is expected to exhibit ferromagnetic (FM) exchange based on spin polarization (SP) models. The experimental magnetic susceptibility of F4BlmNN confirms the expectation, showing 1-D Heisenberg chain FM exchange behavior over 1.8-300 K with an intrachain exchange constant Of J(chain)/k = +22 K. At lower temperatures, ac magnetic susceptibility and variable field heat capacity measurements show that F4BlmNN acts as a quasi-1-D ferromagnet. The dominant ferromagnetic exchange interaction is attributable to overlap between spin orbitals of molecules within the hydrogen-bonded chains, consistent with the SP model expectations. The chains appear to be antiferromagnetically exchange coupled, giving cusps in the ac susceptibility and zero field heat capacity at lower temperatures. The results indicate that the sample orders magnetically at about 0.7 K. The magnetic heat capacity ordering cusp shifts to lower temperatures as external magnetic field increases, consistent with forming a bulk antiferromagnetic phase below a Neel temperature of T-N(0) = 0.72 K, with a critical field of H-c approximate to 1800 Oe. The interchain exchange is estimated to be zJ/k congruent to (-)0.1 K.

Crystalline structure of mangiferin, a C-glycosyl-substituted 9H-xanthen-9-one isolated from the stem bark of Mangifera indica

The crystalline structure of mangiferin (= 2-beta-D-glucopyranosyl-1,3,6,7-tetrahydroxy-9H-xanthen-9-one; 1), a biologically active xanthenone C-glycoside, isolated from the stem bark of Mangifera indica (Anacardiaceae), was unambiguously determined by single-crystal X-ray diffraction (XRD). The crystal structure is summarized as follows: triclinic, P1, a = 7.6575(5), b = 11.2094(8), c = 11.8749(8) angstrom, alpha = 79.967(5), beta = 87.988(4), gamma = 72.164(4)degrees, V = 955.3(1) angstrom(3), and Z = 2. The structure also shows two molecules in the asymmetric unit cell and five crystallization H2O molecules. The packing is stabilized by several intermolecular H-bonds involving either the two symmetry-independent mangiferin molecules 1a and 1b, or the H2O ones.