Photoswitchable Phosphonate–Fullerene Hybrids with Cholinesterase Activity

Modern progress in photopharmocology calls for new generation of compounds joining bioactivity, photoswitchable properties and high selectivity of response to light wavelength. Introduced here, phosphonate–fullerene hybrids are the first representatives of such compounds. Phosphonate–fullerene hybrids were synthesized on a base of fullerene C₆₀ and organophosphates with the function of photoswitchable cholinesterase activity—phosphorylated thiazolotriazole and aminomalonate compounds and studied with FTIR, UV–VIS spectroscopy and IPC-micro neurotoxin amperometric analysis. As a result of spectroscopic and bioactivity characterization, it was not only demonstrated butyrylcholinesterase (BuChE) inhibition increase in phosphonate–fullerene hybrids compared with pure phosphonates but also pronounced response of inhibition degree to laser irradiation of hybrids. It was found opposite behavior of hybrids as a result of laser irradiation—BuChE inhibition drop-off for thiazolotriazole–fullerene and pronounced growth for aminomalonate–fullerene. The other remarkable peculiarity of presented phosphonate–fullerene hybrids is high selectivity of inhibition change degree to laser wavelength (266 or 325 nm).     

Ion trap collision-induced dissociation of multiply deprotonated RNA: c/y-ions versus (a-B)/w-ions

The dissociation of model RNA anions has been studied as a function of anion charge state and excitation amplitude using ion trap collisional activation. Similar to DNA anions, the precursor ion charge state of an RNA anion plays an important role in directing the preferred dissociation channels. Generally, the complementary c/y-ions from 5′ P-O bond cleavage dominate at low to intermediate charge states, while other backbone cleavages appear to a limited extent but increase in number and relative abundance at higher excitation energies. The competition between base loss, either as a neutral or as an anion, as well as the preference for the identity of the lost base are also observed to be charge-state dependent. To gain further insight into the partitioning of the dissociation products among the various possible channels, model dinucleotide anions have been subjected to a systematic study. In comparison to DNA, the 2′-OH group on RNA significantly facilitates the dissociation of the 5′ P-O bond. However, the degree of excitation required for a 5′ base loss and the subsequent 3′ C-O bond cleavage are similar for the analogous RNA and DNA dinucleotides. Data collected for protonated dinucleotides, however, suggest that the 2′-OH group in RNA can stabilize the glycosidic bond of a protonated base. Therefore, base loss from low charge state oligonucleotide anions, in which protonation of one or more bases via intramolecular proton transfer can occur, may also be stabilized in RNA anions relative to corresponding DNA anions.     

Effect of linker and spacer on the design of a fibronectin-mimetic peptide evaluated via cell studies and AFM adhesion forces

The design of a fibronectin-mimetic peptide that specifically binds to the alpha 5beta 1 integrin has been widely studied because of this integrin's participation in many physiological and pathological processes. A promising design for such a peptide includes both the primary binding site RGD and the synergy site PHSRN connected by a linker and extended off of a surface by a spacer. Our original hypothesis was that the degree of hydrophobicity/hydrophilicity between the two sequences (RGD and PHSRN) in fibronectin is an important parameter in designing a fibronectin-mimetic peptide (Mardilovich, A.; Kokkoli, E. Biomacromolecules 2004, 5, 950-957). A peptide-amphiphile, PR_b, that was previously designed in our laboratory employed a hydrophobic tail connected to the N terminus of a peptide headgroup that was composed of a spacer, the synergy site sequence, a linker mimicking both the distance and hydrophobicity/hydrophilicity present in the native protein fibronectin (thus presenting an overall "neutral" linker), and finally the primary binding sequence. Even though our previous work (Mardilovich, A.; Craig, J. A.; McCammon, M. Q.; Garg, A.; Kokkoli, E. Langmuir 2006, 22, 3259-3264) demonstrated that PR_b is a promising sequence compared to fibronectin, this is the first study that tests our hypothesis by comparing PR_b to other peptides with hydrophobic or hydrophilic linkers. Furthermore, different peptide-amphiphiles were designed that could be used to study the effect of building blocks systematically, such as the peptide headgroup linker length and hydrophobicity/hydrophilicity as well as the headgroup spacer length on integrin adhesion. Circular dichroism spectroscopy was first employed, and the collected spectra demonstrated that only one peptide-amphiphile exhibited a secondary structure. Their surface topography was evaluated by taking atomic force microscopy (AFM) images of Langmuir-Blodgett peptide-amphiphile membranes supported on mica. Their adhesion was first evaluated with AFM force measurements between the different sequences and an AFM tip functionalized with purified integrins. The amphiphiles were further characterized via 1-12 h cell studies that examined human umbilical vein endothelial cell adhesion and extracellular matrix fibronectin production. The AFM studies were in good agreement with the cell studies. Overall, the adhesion studies validated our hypothesis and demonstrated for the first time that a "neutral" linker, which more closely mimics the cell adhesion domain of fibronectin, supports higher levels of adhesion compared to other peptide designs with a hydrophobic or hydrophilic linker or even fibronectin. Neutral linker lengths that were within the distance found between PHSRN and RGD in fibronectin performed equally well. However, the 10 amino acid neutral linker gave slightly better cell adhesion than did the control fibronectin at all times. Also, a short spacer was shown to give higher adhesion than other sequences with no spacer or a longer spacer, suggesting that a short spacer is necessary to extend the sequence further away from the interface. In conclusion, this work outlines a logical approach that can be applied for the rational design of any protein-mimetic peptide with two binding sites.     

Mono- and diprotonation of the superbasic bisguanidine 1,2-Bis(N,N,N',N'-tetramethylguanidino)benzene (btmgb) and Pt II and Pt IV complexes of chelating bisguanidines and guanidinates

New Pt complexes of chelating bisguanidines and guanidinate ligands were synthesized and characterized. 1,2-Bis(N,N,N',N'-tetramethylguanidino)benzene (btmgb) was used as a neutral chelating bisguanidine ligand, and 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidinate (hpp(-)) as a guanidinate ligand. The salts [btmgbH](+)[HOB(C(6)F(5))(3)](-) and [btmgbH(2)]Cl(2) and the complexes [(btmgb)PtCl(2)], [(btmgb)PtCl(dmso)](+)[PtCl(3)(dmso)](-), and [(btmgb)PtCl(dmso)](+)[Cl(-)] were synthesized and characterized. In the [btmgbH](+) cation the proton is bound to only one N atom. In the other complexes, both imine N atoms are coordinated to the Pt(II), thus adopting a eta(2)-coordinational mode. The hpp(-) anion, which usually prefers a bridging binding mode in dinuclear complexes, is eta(2)-coordinated in the Pt(IV) complex [(eta(2)-hpp)(hppH)PtCl(2){N(H)C(O)CH(3)}], which is formed (in low yield) by reaction between cis-[(hppH)(2)PtCl(2)] and H(2)O(2) in CH(3)CN.     

Water solubility, antioxidant activity and cytochrome C binding of four families of exohedral adducts of C60 and C70

Over the past decade, surface-modified, water soluble fullerenes have been shown by many different investigators to exhibit strong antioxidant activity against reactive oxygen species (ROS) in vitro and to protect cells and tissues from oxidative injury and cell death in vivo. Nevertheless, progress in developing fullerenes as bona fide drug candidates has been hampered by three development issues: 1) lack of methods for scalable synthesis; 2) inability to produce highly purified, single-species regioisomers compatible with pharmaceutical applications; and 3) inadequate understanding of structure-function relationships with respect to various surface modifications (e.g., anionic versus cationic versus charge-neutral polarity). To address these challenges, we have designed and synthesized more than a dozen novel water soluble fullerenes that can be purified as single isomers and which we believe can be manufactured to scale at reasonable cost. These compounds differ in addition pattern, lipophilicity and number and type of charge and were examined for their water solubility, antioxidant activity against superoxide anions and binding of cytochrome C. Our results indicate that dendritic water soluble fullerene[60] monoadducts exhibit the highest degree of antioxidant activity against superoxide anions in vitro as compared with trismalonate-derived anionic fullerenes as well as cationic fullerenes of similar overall structure. Among the higher adducts, anionic derivatives have a higher antioxidant activity than comparable cationic compounds. To achieve sufficient water solubility without the aid of a surfactant or co-solvent at least three charges on the addends are required. Significantly, anionic in contrast to cationic fullerene adducts bind with high affinity to cytochrome C.     

Gas-phase spectroscopy of protonated 3-OH kynurenine and argpyrimidine. comparison of experimental results to theoretical modeling

The aging process of the human lens is associated with accumulation of chromophores and fluorophores that impair visual function. In the present study, we examined the photodissociation of 3-OH-kynurenine and argpyrimidine. Furthermore, absorption spectra obtained in gas phase using an electrostatic ion storage ring were studied as gas phase absorption have been shown to be more similar to the in vivo condition than absorption spectra obtained in the liquid phase. Experimental results were compared to theoretical modeling using the multistate, multireference perturbation theory approach combined with advanced molecular modeling tools to account for the solvent effects and to provide direct support for band assignments. Absorption maxima were determined both experimentally and theoretically and significant differences between the two chromophores were found. In particular, 3-OH-kynurenine demonstrated a blue-shift of more than 130 nm in the aqueous phase compared to the gas-phase due to the existence of different 3-OH-kynurenine conformers, which are stable under different conditions and originate from the interplay between intra- and intermolecular interactions. Photodissociation of argpyrimidine and 3-OH-kynurenine was observed in vacuum thus confirming the results previously obtained in liquid phase demonstrating that the photodestruction takes place in both media.     

Iodochlorination of silyl- and germylphenylacetylenes

Reactions of Si- and Ge-substituted alkynes with KICl₂ were investigated. (1-Germatranyl)-phenylacetylenes and (triphenylsilyl)phenylacetylene gave Z-iodochloroalkenes with chlorine and phenyl groups attached to the same carbon atom. Adduct structures were confirmed by X-ray diffraction studies. © 2004 Wiley Periodicals, Inc. Heteroatom Chem 15:169–174, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20001     

Monodisperse Particles Based on Copolymers of Methyl methacrylate or Styrene with N-Vinylformamide

Sammary: Various techniques of one-step batch emulsion copolymerization of methyl methacrylate (MMA) or styrene (St) with N-vinylformamide (NVF) initiated by 2,2′-azobis(2-methylpropanamidine) (AIBA) or 2,2′-azobis[4,5-dihydroimidazol-2-yl] (AIP) dihydrochlorides in the presence of dextran, cetyltrimethylammonium bromide (CTAB) or without any stabilizers were examined to obtain monodisperse submicron and nano- particles, having both positive surface charge and hydrophilic surface. After hydrolysis in acidic media, the particle surface contained amino groups originating from NVF units along with carboxylic groups from hydrolyzed initiator residues. The obtained particles were tested as building blocks of hierarchic structures. Owing to their amphiphilic surface, the particles were capable of self-assembling from their dispersions into three-dimentional (3D) ordered arrays.     

Nucleophilic difluoromethylenation of aldehydes and ketones using diethyl difluoro(trimethylsilyl)methylphosphonate

A new nucleophilic difluoromethylenation of aldehydes and ketones using diethyl difluoro(trimethylsilyl)methylphosphonate (1) has been achieved. The reactive carbanion species were generated under mild reaction conditions with a catalytic amount of initiator. This methodology was compatible with non-enolizable and in some cases with enolizable aldehydes and ketones and provided a straightforward access to phosphates of syn and anti 2,2-difluoro-1,3-diols.     

Rational Design of an Organometallic Glutathione Transferase Inhibitor

Double trouble : A hybrid organic–inorganic (organometallic) inhibitor was designed to target glutathione transferases. The metal center is used to direct protein binding, while the organic moiety acts as the active‐site inhibitor (see picture). The mechanism of inhibition was studied using a range of biophysical and biochemical methods.