Stereochemical effects during [M-H]- dissociations of epimeric 11-OH-17beta-estradiols and distant electronic effects of substituents at C(11) position on gas phase acidity

The affinity of estradiol derivatives for the estrogen receptor (ER) depends strongly on nature and stereochemistry of substituents in C(11) position of the 17beta-estradiol (I). In this work, the stereochemistry effects of the 11alpha-OH-17beta-estradiol (III(alpha)) and 11beta-OH-17beta-estradiol (III(beta)) were investigated using CID experiments and gas-phase acidity (DeltaH degrees (acid)) determination. The CID experiments showed that the steroids decompose via different pathways involving competitive dissociations with rate constants depending upon the alpha/beta C(11) stereochemistry. It was shown that the fragmentations of both deprotonated [III(alpha)-H]- and [III(beta)-H]- epimers were initiated by the deprotonation of the most acidic site, i.e. the phenolic hydroxyl at C(3). This view was confirmed by H/D exchange and double resonance experiments. Furthermore, the DeltaH degrees (acid) of both epimers (III(alpha) and III(beta)), 17beta-estradiol (I), and 17-desoxyestradiol (II) was determined using the extended Cooks' kinetic method. The resulting values allowed us to classify steroids as a function of their gas-phase acidity as follows: (III(beta)) >> (II) > (I) > (III(alpha)). Interestingly, the alpha/beta C(11) stereochemistry appeared to influence strongly the gas-phase acidity. This phenomenon could be explained through stereospecific proton interaction with pi-orbital cloud of A ring, which was confirmed by theoretical calculation.

Straightforward synthesis of new polyoxometalate-based hybrids exemplified by the covalent bonding of a polypyridyl ligand

A new polyoxometalate-based organic-inorganic platform has been designed for further facile derivatization and covalent attachment of organic linkers; this is exemplified by the grafting of a polypyridyl ligand.

Can cluster structure affect kinetic method measurements? The curious case of glutamic acid's gas-phase acidity

The gas-phase acidities of aspartic, glutamic, and 2-aminoadipic acid have been determined by the kinetic method in a triple-quadrupole instrument. Although aspartic acid behaves in the conventional way and gives a DeltaH(acid) value of 1340 kJ mol(-1), glutamic and 2-aminoadipic acids give kinetic method plots with two distinct slopes. This leads to DeltaH(acid) values of 1350 and 1366 kJ mol(-1) for glutamic acid, and 1355 and 1369 kJ mol(-1) for 2-aminoadipic acid. The value for aspartic acid and the low collision energy value for glutamic acid are consistent with recent measurements by Poutsma and co-workers in a quadrupole ion trap. The experiments are supported by calculations at the G3(MP2) and OLYP/aug-cc-pVTZ levels. Computational studies of model clusters of the amino acids with trifluoroacetate suggest there are distinct preferences. Glutamic and 2-aminoadipic acid prefer clusters where the amino acid adopts a zwitterion-like structure whereas aspartic acid prefers to adopt a conventional (canonic) structure in its clusters. This result along with the computed stabilities of zwitterion-like conformations of the deprotonated amino acids leads to the following explanation for the presence of two slopes in the kinetic method plots. At low collision energies, the deprotonated amino acid dissociates from the cluster, with rearrangement if necessary, to give its preferred conformation, but at high collision energies, the deprotonated amino acid directly dissociates in the conformation preferred in the cluster. For glutamic and 2-aminoadipic acids, this is a zwitterion-like structure that is about 20 kJ mol(-1) less stable than the global minimum.

Investigation of double-stranded DNA/drug interaction by ESI/FT ICR: orientation of dissociations relates to stabilizing salt bridges

Noncovalent complexes of DNA and Hoechst 33258 were investigated by ESI-FT/ICR MS in various activation modes (collision-induced dissociation (CID), sustained off-resonance irradiation collision-induced dissociation (SORI-CID), infrared multiphoton dissociation (IRMPD) and electron detachment dissociation (EDD)). The binding selectivity of Hoechst 33258 was confirmed by the comparative study of its noncovalent association with different DNA sequences. The CID spectra of [ds + HO - 5H](5-) obtained with a linear hexapole ion trap resulted in unzipping of the strands. This outcome is a clue to the drug-binding mode, shading light on the localization of the binding sites of Hoechst 33258 to the DNA sequence. The IRMPD and SORI-CID experiments mainly gave DNA backbone cleavages and internal fragment ions. From this result, information on the localization of the binding sites of Hoechst 33258 in the DNA sequence was obtained. No sodium cationization was observed on the DNA sequence ions although they were present on fragmentation of the duplex, indicating that the backbone cleavages were generated from the single strand associated with the Hoechst 33258 where the number of alkali cation is restricted. Under electron detachment (ED) conditions, multiple EDs were achieved for the [ds + HO - 5H](5-) ion without any significant dissociation. The presence of drug appears to enhance the stability of the multiply charged system. It was proposed that the studied noncovalent complex involved the formation of zwitterions and consequently strong salt-bridge interactions between DNA and drug.

Investigation by mass spectrometry of metal complexes of new molecular hosts: cyclic oligomer of sugar amino acid and sugar-aza-crown ethers

The affinity of cyclic oligomers of sugar amino acid and sugar-aza-crown ether compounds towards various transition metal cations (Cu(II), Ni(II), Co(II), Fe(II) and Zn(II)) was investigated with positive-ion electrospray mass spectrometry. The binding between the receptors (M) and the different metals (Met) is evidenced mainly by the presence of the [M + Met(II)Cl](+) ion. The experimental results showed that all studied receptors present specificity to Cu(II). An attempt has been made with CuI but no complexation was obtained. The formation of these complexes can be rationalized by considering the presence of two oxygens and two nitrogens on the receptor rim. The lone electron pair can serve as the electron donor to Cu(II). Theoretical calculations were carried out in order to show the structure of the complex and, in particular, to determine if Cu(2+) is situated either on the outer surface, on the rim of the receptor or inside the cavity. Comparison of complex formation was carried out by mixing the four receptors with various amounts of Cu(II) (one equivalent and five equivalents). It appears that the best complexation was obtained with the sugar-aza-crown ethers (amine linker) for both benzylated and methylated compounds. In addition, the stereochemical effects have been investigated.

Replaying the tape: recurring biogeographical patterns in Cape Verde Conus after 12 million years

Isolated oceanic islands are excellent natural laboratories to test the relative role of historical contingency and determinism in evolutionary diversification. Endemics of the marine venomous snail Conus in the Cape Verde archipelago were originated from at least two independent colonizations of 'small' and 'large' shelled species separated by 12 million years. In this study, we have reconstructed phylogenetic relationships within large-shelled Conus (C. ateralbus, C. pseudonivifer, C. trochulus, and C. venulatus) based on mitochondrial cox1 and nad4 haplotype sequences. The reconstructed molecular phylogeny revealed three well-supported and relatively divergent clades (A, B, and C) that do not correspond to current species classification based on shell colour and banding patterns. Clade A grouped specimens assigned either to C. pseudonivifer or C. trochulus, clade B is composed of specimens assigned to C. venulatus, and clade C comprises specimens assigned either to C. venulatus or C. ateralbus. Geometric morphometric analyses found significant differences between the radular teeth shape of C. pseudonivifer/C. trochulus and C. venulatus/C. ateralbus. In clades A and B, northwestern Boavista and Maio specimens cluster together to the exclusion of eastern Boavista samples. In Sal, populations form a monophyletic island assemblage (clade C). The large-shelled Conus have remarkably replicated biogeographical patterns of diversification of small-shelled Conus. Similar selective forces (i.e. nonplanktonic lecithotrophy with limited larval dispersal and allopatric diversification) together with repeated instances of low sea level stands during glacial maxima that allowed connection between islands, have overcome the effect of historical contingency, and explain the observed recurring biogeographical patterns.

Synthetic sulfogalactosylceramide (sulfatide) and its use for the mass spectrometric quantitative urinary determination in metachromatic leukodystrophies

3-O-Sulfogalactosylceramides (sulfatides) accumulate in the genetic disease metachromatic leukodystrophy which is due to a defect in the catabolic enzyme, arylsulfatase A. Clinical diagnosis is usually confirmed by in vitro enzymatic deficiency of arylsulfatase A activity. The diagnosis may be complicated because of arylsulfatase A pseudo-deficiencies and another cause of MLD, sphingolipid activator B deficiency. As large quantities of sulfatides can be found in the urine in this disease, sulfatiduria appears as an extremely useful test. As recently enzyme replacement is underway, the quantitative determination, using an internal standard, appears particularly useful as a follow-up. Thus a non-physiological sulfatide was synthesized for this purpose, i.e. 3-O-sulfo-beta-D-C17 galactosylceramide (3-O-Sulfo-D: -Galactosyl-beta1'-->1-N-Heptadecanoyl-D-erythro-Sphingosine). It has been prepared through condensation of an azidosphingosine derivative with a protected D-galactopyranosyltrichloroacetimidate. Reduction of the azide was followed by acylation of a C-17 fatty acid. The key step was achieved by selective sulfation of the desired hydroxyl group on the sugar residue of the galactosylceramide using the stannylene methodology to give a 3'-sulfated beta-galactosyl C-17 ceramide.

Increased Lewis Acidity in Hafnium-Substituted Polyoxotungstates

Monolacunary polyoxotungstates [alpha(1)-P(2)W(17)O(61)](10-) and [alpha-PW(11)O(39)](7-) react with HfCl(4) to yield [alpha(1)-HfP(2)W(17)O(61)](6-) and [alpha-Hf(OH)PW(11)O(39)](4-), isolated as organo-soluble tetrabutylammonium (TBA) salts. Subsequent analyses, including mass spectrometry, show that they are stronger Lewis acids than (TBA)(5)H(2)[alpha(1)-YbP(2)W(17)O(61)]. The new polyoxotungstates catalyze Lewis acid mediated organic reactions, such as Mukaiyama aldol and Mannich-type additions. In particular, reactions with aldehydes, which were impossible with lanthanide polyoxotungstates, are made possible. Thus these modifications of the polyoxometalate composition allowed fine tuning of the Lewis acidity. The catalysts could be easily recovered and reused.

Non-covalent complexes between bis-β-carbolines and double-stranded DNA: A study by electrospray ionization FT-ICR mass spectrometry (I)

The non-covalent complexes of five bis-beta-carbolines alkaloids with three different double-stranded oligodeoxynucleotides d(GCGCGATCGCGC)(2), d(GCGCAATTGCGC)(2), and d(GCGAAATTTCGC)(2) were investigated by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. These five antitumor compounds all showed DNA-binding abilities. Binding affinities in the order of 2>3, 4>5, and 1 with double-stranded DNA were obtained, which mean that the length of the linkage chain between two beta-carbolines has a remarkable effect on the formation of the non-covalent complexes. Additionally, the preliminary results indicated that bis-beta-carbolines had no notable sequence selectivities.

Negative-charge driven fragmentations for evidencing zwitterionic forms from doubly charged coppered peptides

In aqueous solution, amino acids (AA) and peptides are known to exist as zwitterions over a large pH range. However, in the gas phase, i.e. in electrospray (ESI), the zwitterionic form becomes unfavorable owing to the absence of stabilizing effects from intermolecular solvation. Nevertheless, during mass spectrometry experiments, the presence of a metallic cation can reinforce the zwitterionic character of the molecule and thus influence its fragmentation under low energy collision-induced dissociation (CID) conditions. The [M + Cu(II)](2+) complexes of six pentapeptides (YGGFL, YGGFL(NH(2)), YGGFK, YGGFQ, KYGGF and QYGGF) were analyzed by collision to highlight the presence of zwitterions. The experiments were performed on a 3D-ion trap equipped with an orthogonal ESI source. For each peptides studied, negative-charge driven fragmentations on globally positively charged ions were observed. These fragmentation mechanisms, generally observed in the negative mode, suggest the competitive deprotonation of the C-terminal carboxylic acid or of the tyrosine side-chain residue for each peptide studied and thus a zwitterionic form to preserve the charge balance. Moreover, the specific loss of (CH(3)--C(6)H(4)--O)(*) characterizes YGGFK compared to YGGFQ and the specific loss of styrene characterizes KYGGF compared to QYGGF. These results allow the differentiation of the two couples of isobaric pentapeptides. An unusual loss of NH(4) (+), which occurred from the N-terminus, was also observed for YGGFL, YGGFL(NH(2)), YGGFK and YGGFQ. Finally, the reduction of Cu(II) to Cu(I), concomitant with the (CH(3)--C(6)H(4)--O)(*) release, was pointed out for YGGFK.

Charge dependent behavior of PNA/DNA/PNA triplexes in the gas phase

Intact noncovalent complexes were studied in the gas phase using negative ion nano-ESI mass spectrometry. Among various noncovalent systems studied in the gas phase, the interaction of DNA strands with peptide nucleic acids (PNAs) presents a strong interest as biologically relevant systems. PNAs originally described by Nielsen are used as DNA mimics as possible medical agents by imprisoning DNA single strands into stable noncovalent complexes. Two types of PNAs were investigated in the PNA/DNA multiplex: the original Nielsen's PNA and a modified backbone PNA by the introduction of syn- and anti-(aminoethyl)thiazolidine rings. We first investigated the stoichiometry of PNA/DNA multiplexes formed in solution and observed them in the gas phase via qualitative kinetics of complementary strand associations. It resulted in observing PNA2/DNA triplexes (ts) as the multiply deprotonated species, most stable in both the solution and gas phase. Second, charge-dependant decompositions of these species were undertaken under low-energy collision conditions. It appears that covalent bond cleavages (base releasing or skeleton cleavage) occur from lower ts charge states rather than ts unzipping, which takes place from higher charge states. This behavior can be explained by considering the presence of zwitterions depending on the charge state. They result in strong salt-bridge interactions between the positively charged PNA side chain and the negatively charged DNA backbone. We propose a general model to clearly display the involved patterns in the noncovalent triplex decompositions. Third, the relative stability of three PNA2/DNA complexes was scrutinized in the gas phase by acquiring the breakdown curves of their ts(6-) form, corresponding to the ts unzipping. The chemical structures of the studied PNAs were chosen in order to evidence the possible influence of backbone stereochemistry on the rigidity of PNA2/DNA complexes. It provided significantly different stabilities via V(m) measurements. The relative gas-phase stability order obtained was compared to that found in solution by Chassaing et al., and shows qualitative agreement.

Functionally different pools of Shiga toxin receptor, globotriaosyl ceramide, in HeLa cells

Many studies have investigated the intracellular trafficking of Shiga toxin, but very little is known about the underlying dynamics of its cellular receptor, the glycosphingolipid globotriaosyl ceramide. In this study, we show that globotriaosyl ceramide is required not only for Shiga toxin binding to cells, but also for its intracellular trafficking. Shiga toxin induces globotriaosyl ceramide recruitment to detergent-resistant membranes, and subsequent internalization of the lipid. The globotriaosyl ceramide pool at the plasma membrane is then replenished from internal stores. Whereas endocytosis is not affected in the recovery condition, retrograde transport of Shiga toxin to the Golgi apparatus and the endoplasmic reticulum is strongly inhibited. This effect is specific, as cholera toxin trafficking on GM(1) and protein biosynthesis are not impaired. The differential behavior of both toxins is also paralleled by the selective loss of Shiga toxin association with detergent-resistant membranes in the recovery condition, and comparison of the molecular species composition of plasma membrane globotriaosyl ceramide indicates subtle changes in favor of unsaturated fatty acids. In conclusion, this study demonstrates the dynamic behavior of globotriaosyl ceramide at the plasma membrane and suggests that globotriaosyl ceramide-specific determinants, possibly its molecular species composition, are selectively required for efficient retrograde sorting on endosomes, but not for endocytosis.

Diastereomeric differentiation of peptides with CuII and FeII complexation in an ion trap mass spectrometer

Complexation by transition metal ions (CuII and FeII) was successfully used to differentiate the diastereomeric YAGFL, YDAGFL and Y(D)AGF(D)L pentapeptides by electrospray ionization-ion trap mass spectrometry in the positive ion mode using low-energy collision conditions. This distinction was allowed by the stereochemical effects due to the (D)Leu/(L)Leu and the (D)Ala/(L)Ala residues yielding various steric interactions which direct relative dissociation rate constants of the binary [(M - H) + MeII]+ complexes (Me = Cu or Fe) subjected to low-energy, collision-induced dissociation processes. The interpretation of the collision-induced dissociation spectra obtained from the diastereomeric cationized peptides allowed the location of the deprotonated site(s), leading to the postulation of ion structures and fragmentation pathways for both the [(M - H) + CuII]+ and [(M - H) + FeII]+ complexes, which differed significantly. With CuII, consecutive fragmentations, initiated by the decarboxylation at C-terminus, were favored relative to sequence product ions. On the other hand, with FeII, competitive fragmentations resulting in abundant sequence product ions and significant internal losses were preferred. This could be explained by different localizations of the negative charge, which directs the orientation of both the [(M - H) + CuII]+ and [(M - H) + FeII]+ binary complexes fragmentations. Indeed, the free negative charge of the [(M - H) + CuII]+ ions was mainly located at one oxygen atom: either at the C-terminal carboxylic group or, to a minor extent, at the Tyr phenol group (i.e. zwitterionic forms). On the other hand, the negative charge of the [(M - H) + FeII]+ ions was mainly located at one of the nitrogen atoms of the peptide backbone and coordinated to FeII (i.e. salt non-zwitterionic form).Moreover, this study reveals the particular behavior of CuII reduced to CuI, which promotes radical losses not observed from the peptide-FeII complexes. Finally, this study shows the analytical potentialities of the complexation of transition metal ions with peptides providing structural information complementary to that obtained from low-energy, collision-induced dissociation processes of protonated or deprotonated peptides.

Key role played by RhoA in the balance between planar and apico-basal cell divisions in the chick neuroepithelium

The cell division axis determines the position of daughter cells and is therefore critical for cell fate. During vertebrate neurogenesis, most cell divisions take place within the plane of the neuroepithelium (Das, T., Payer, B., Cayouette, M., and Harris, W.A. (2003). In vivo time-lapse imaging of cell divisions during neurogenesis in the developing zebrafish retina. Neuron 37, 597-609. Haydar, T.F., Ang, E., Jr., and Rakic, P. (2003). Mitotic spindle rotation and mode of cell division in the developing telencephalon. Proc Natl Acad Sci U S A 100, 2890-5. Kosodo, Y., Roper, K., Haubensak, W., Marzesco, A. M., Corbeil, D., and Huttner, W. B. (2004). Asymmetric distribution of the apical plasma membrane during neurogenic divisions of mammalian neuroepithelial cells. EMBO J. 23, 2314-24). The cellular constraints responsible for this preferential orientation are poorly understood. Combining electroporation and time-lapse confocal imaging of chick neural progenitors, the events responsible for positioning the mitotic spindle and their dependence on RhoA were investigated. The results indicate that the spindle forms with a random orientation. However, the final orientation of cell divisions is dependent on two main factors: (i) an early rotation of the spindle that aligns it within the plane of the neuroepithelium, and (ii) a specific limitation of spindle oscillations, despite free rotation around the apico-basal axis. Expressing a dominant-negative RhoA leads to apico-basal cell divisions after a correct initial rotation of the spindle. Our data reveal a specific role for RhoA in the maintenance of spindle orientation, prior to anaphase. Thus, RhoA could be a key player potentially regulated by the neurogenic program or by the neural stem cell environment to control the balance between planar and apico-basal divisions, during normal or pathological development.

Psoralen analogues: synthesis, inhibitory activity of growth of human tumor cell lines and computational studies

Eight psoralens have been evaluated for their ability to inhibit the in vitro growth of three human tumor cell lines representing different tumor types, MCF-7 (breast cancer), NCI-H460 (non-small cell lung cancer) and SF-268 (CNS cancer). The synthesis of four new psoralens (benzofurocoumarins) is presented as well as the results of the ab initio calculations to find the parameters that relate the structure with the antitumor activity. This work provides supplementary information that could allow the development of new psoralen analogues with this type of biological activity.

Production and Reactions of Organic-Soluble Lanthanide Complexes of the Monolacunary Dawson [α1-P2W17O61]10- Polyoxotungstate

The incorporation of lanthanides into polyoxometalates provides entry to new classes of potentially useful materials that combine the intrinsic properties of both constituents. To utilize the [alpha1-Ln(H2O)4P2W17O61]7- species in applications of catalysis and development of luminescent materials, the chemistry of this family of lanthanide polyoxometalates in organic solvents has been developed. Organic-soluble polyoxometalate-lanthanide complexes TBA5H2[alpha1-Ln(H2O)4P2W17O61] (Ln = La(III), Sm(III), Eu(III), Yb(III)) were prepared and characterized by elemental analysis, acid-base titration, IR, 31P NMR, and mass spectrometry. The synthetic procedure involves a cation metathesis reaction in aqueous solution under strict pH control. A solid-liquid-phase transfer protocol yielded a unique species (TBA)8K3[Yb(alpha1-YbP2W17O61)2] with three ytterbium ions and two [alpha1-P2W17O61]10- polyoxotungstates. A centrosymmetric dimeric complex [{alpha1-La(H2O)4P2W17O61}2]14- was crystallized from aqueous solution and characterized by X-ray diffraction. ESI mass spectral analysis of the complexes TBA5H2[alpha1-Ln(H2O)4P2W17O61] shows that similar dimers exist in organic solution, in particular for the early lanthanides. Fragmentation in the mass spectrometer of the complexes from dry acetonitrile solution involves double protonation of an oxo ligand and loss of one water molecule. Low mass tungstate fragments combine into [(WO3)n]2- (n = 1-5) ions and their condensation products with phosphate. Reaction of TBA5H2[alpha1-Eu(H2O)4P2W17O61] with 1,10-phenanthroline or 2,2'-bipyridine showed an increase of the europium luminescence. This result is explained by the formation of a ternary complex of [alpha1-Eu(H2O)4P2W17O61]7- and two sensitizing ligands.

Lipopolysaccharide mediated regulation of neuroendocrine associated proprotein convertases and neuropeptide precursor processing in the rat spleen

Within the secretory pathway, the family of proprotein convertases cleave inactive precursors at paired basic residues to generate a myriad of biologically active peptides. Within the PC family, PC1/3 and PC2 are well known for their preferential expression within neuroendocrine cells. However, various data now indicate their potential expression in immune cells. The aim of our study was two fold: (1) survey PC expression in immune tissues, with emphasis on PC1/3 and PC2 and (2) examine PC expression under conditions that mimic an infectious state using lipopolysaccharide, known to activate immune cells via toll-like receptors. Spatial and temporal analyses of tissues from control and lipopolysaccharide treated rats were carried out using in situ hybridization histochemistry, Northern blot, mass spectrometry and antibacterial assays. Our tissue survey showed the basal expression of all PCs in the lymph nodes, thymus and spleen including PC1/3 and PC2. Focusing on the spleen, basal expression of PC1/3 was seen in the red pulp/marginal zone areas, suggesting expression within macrophages. Lipopolysaccharide treatment produced significant changes in PC1/3 expression and notably an induction in B lymphocytes within germinal centers. Similarly, PC2, which was undetectable in control spleens, was induced in germinal centers following lipopolysaccharide treatment. The PC1/3 and PC2 substrate proenkephalin was also induced following lipopolysaccharide treatment in the marginal zone, where PC1/3 expression was also found. Mass spectrometry analysis of spleen extracts demonstrated the presence of the antibacterial peptide enkelytin. Our studies confirmed that PC1/3 and PC2 expression was not restricted to neurons and endocrine cells, but was also found under basal conditions in both macrophage and lymphocytes. Additionally, plasticity of PC expression in immune cells was observed under conditions that mimic pathogen-like infections, suggesting a mechanistic link through Toll-like receptors. Collectively, these data clearly implicate PCs in immune responses, both innate and acquired.