Fluorescent Formazans and Tetrazolium Salts - Towards Fluorescent Cytotoxicity Assays.

Formazan-based colorimetric cytotoxicity assays, such as the MTT assay, are typically used to assess cell viability with only metabolically active cells reducing tetrazolium salts into the formazans, which is then quantified by absorbance. Fluorescence offers several advantages compared to colorimetric assays and would enable techniques such as flow cytometry and confocal microscopy to be used for analysis. Here, fluorescent formazans 10, 11 and 12, and their corresponding tetrazolium salts 13, 16 and 24, respectively, were synthesised by incorporation of a known fluorophore backbone (coumarin, fluorescein and rhodol) with disruption of the conjugated system preventing or reducing fluorescence of the tetrazolium salts. These tetrazolium salts were successfully reduced to the fluorescent formazans with cells and offer a step forward in the development of fluorescent cytotoxicity assays.

Click chemistry generated model DNA-peptide heteroconjugates as tools for mass spectrometry.

UV cross-linking of nucleic acids to proteins in combination with mass spectrometry is a powerful technique to identify proteins, peptides, and the amino acids involved in intermolecular interactions within nucleic acid-protein complexes. However, the mass spectrometric identification of cross-linked nucleic acid-protein heteroconjugates in complex mixtures and MS/MS characterization of the specific sites of cross-linking is extremely challenging. As a tool for the optimization of sample preparation, ionization, fragmentation, and detection by mass spectrometry, novel synthetic DNA-peptide heteroconjugates were generated to act as mimics of UV cross-linked heteroconjugates. Click chemistry was employed to cross-link peptides to DNA oligonucleotides. These heteroconjugates were fully characterized by high resolution FTICR mass spectrometry and by collision-induced dissociation (CID) following nuclease P1 digestion of the DNA moiety to a single nucleotide monophosphate. This allowed the exact site of the cross-linking within the peptide to be unambiguously assigned. These synthetic DNA-peptide heteroconjugates have the potential to be of use for a variety of applications that involve DNA-peptide heteroconjugates.

Photoluminescent carbon dots from 1,4-addition polymers.

Photoluminescent carbon dots were synthesised directly by thermopyrolysis of 1,4-addition polymers, allowing precise control of their properties. The effect of polymer composition on the properties of the carbon dots was investigated by TEM, IR, XPS, elemental analysis and fluorescence analysis, with carbon dots synthesised from nitrogen-containing polymers showing the highest fluorescence. The carbon dots with high nitrogen content were observed to have strong fluorescence in the visible region, and culture with cells showed that the carbon dots were non-cytotoxic and readily taken up by three different cell lines.

Peptides for cell-selective drug delivery.

The ability to target specific cell types to achieve optimal distribution of therapeutic entities into diseased tissues, while limiting possible adverse off-target effects, has long been a goal of many research groups and pharmaceutical organizations. This review focuses on peptidic tissue-specific biomarkers that allow peptides to act as homing devices for specific tissue types or organs, with a focus on homing peptides (HPs) and cell-penetrating homing peptides (CPHPs). These HPs, in addition to promoting cellular uptake, can deliver a variety of cargos (drugs, oligonucleotides and nanoparticles) into cells. Two such peptides that have entered clinical trials are the tumor-homing peptide asparagine-glycine-arginine (NGR) (fused to human tumor necrosis factor), which selectively binds CD13, an aminopeptidase that is overexpressed on tumor blood vessels, and cyclo[Arg-Gly-Asp-D-Phe-(NMeVal)] (cRGD, cilengitide), an anti-angiogenic agent that targets the α(v)ß(3) and α(v)ß(5) integrins.

Synthesis and evaluation of indatraline-based inhibitors for trypanothione reductase.

The search for novel compounds of relevance to the treatment of diseases caused by trypanosomatid protozoan parasites continues. Screening of a large library of known bioactive compounds has led to several drug-like starting points for further optimisation. In this study, novel analogues of the monoamine uptake inhibitor indatraline were prepared and assessed both as inhibitors of trypanothione reductase (TryR) and against the parasite Trypanosoma brucei. Although it proved difficult to significantly increase the potency of the original compound as an inhibitor of TryR, some insight into the preferred substituent on the amine group and in the two aromatic rings of the parent indatraline was deduced. In addition, detailed mode of action studies indicated that two of the inhibitors exhibit a mixed mode of inhibition.

IDENTIFICATION OF CONOIDIN A AS A COVALENT INHIBITOR OF PEROXIREDOXIN II.

Conoidin A (1) is an inhibitor of host cell invasion by the protozoan parasite Toxoplasma gondii. In the course of studies aimed at identifying potential targets of this compound, we determined that it binds to the T. gondii enzyme peroxiredoxin II (TgPrxII). Peroxiredoxins are a widely conserved family of enzymes that function in antioxidant defense and signal transduction, and changes in PrxII expression are associated with a variety of human diseases, including cancer. Disruption of the TgPrxII gene by homologous recombination had no effect on the sensitivity of the parasites to 1, suggesting that TgPrxII is not the invasion-relevant target of 1. However, we showed that 1 binds covalently to the peroxidatic cysteine of TgPrxII, inhibiting its enzymatic activity in vitro. Studies with human epithelial cells showed that 1 also inhibits hyperoxidation of human PrxII. These data identify Conoidin A as a novel inhibitor of this important class of antioxidant and redox signaling enzymes.

Liquid-crystal properties of octyl 6'-O-alkylmelibiosides.

6-O-alpha-D-Galactopyranosyl-D-glucopyranose (melibiose) derivatives with alkyl groups at the terminal 1-O and 6'-O positions have been synthesized. They show thermotropic and lyotropic liquid-crystal properties. The d-spacings of the strong inner X-ray diffraction rings correspond to approximately 0.9 times the extended length of the molecule. The molecules are therefore either extended in monomolecular layers or U-shaped in bimolecular layers.

The tetrasaccharide nystose trihydrate: crystal structure analysis and hydrogen bonding.

The crystal structure of nystose trihydrate, O-beta-D-fructofuranosyl-(2-->1)-O-beta-D-fructofuranosyl-(2-->1)-beta-D -fructofuranosyl alpha-D-glucopyranoside trihydrate, C24H42O21.3H2O, has been determined using Cu K alpha X-ray data at 121 K. The space group is P2(1)2(1)2(1), with 4 molecules in a unit cell of dimensions a = 10.155(1), b = 13.506(1), and c = 23.278(2) A. The structure was refined to R = 0.052 and RW = 0.048 for 2734 observed structure amplitudes. The alpha-D-glucopyranose unit of the molecule has the normal 4C1 chair conformation and the three fructofuranose units have twist conformations lying between E3 and 4T5. One of the three water molecules is distributed over two sites: W-3 with occupancy 0.80 and W-3' with occupancy 0.20. All the hydrogen atoms were located on the difference synthesis with the exception of those attached to the low-occupancy water site. All hydroxyls, two of the three linkage oxygen atoms, and the water molecules are involved in a complex three-dimensional network which can be decomposed into a series of infinite chains intersecting at the water molecules to form homo- and hetero-dromic cycles.

Crystal structure and n.m.r. analysis of lactulose trihydrate.

The 13C CPMAS n.m.r. spectrum of 4-O-beta-D-galactopyranosyl-D-fructose (lactulose) trihydrate, C12H22O11.3 H2O, identifies the isomer in the crystals as the beta-furanose. This is confirmed by a crystal structure analysis, using CuK alpha X-ray data at room temperature. The space group is P212121, with Z = 4 and cell dimensions a = 9.6251(3), b = 12.8096(3), c = 17.7563(4) A. The structure was refined to R = 0.031 and Rw 0.025 for 1929 observed structure amplitudes. All the hydrogen atoms were unambigously located on difference syntheses. The conformation of the pyranose ring is the normal 4C1 chair and that of the furanose ring is 4T3. The 1----4 linkage torsion angles are O-5'-C-1'-O-1'-C-4 = 79.9(2) degrees and C-1'-O-1'-C-4-C-5 = -170.3(2) degrees. All hydroxyls, ring and glycosidic oxygens, and water molecules are involved in the hydrogen bonding, which consists of infinite chains linked together by water molecules to form a three-dimensional network. There is a three-centered intramolecular, interresidue hydrogen bond from O-3-H to O-5' and O-6'. The n.m.r. spectrum of the amorphous, dehydrated trihydrate suggests the occurrence of a solid-state reaction forming the same isomeric mixture as was observed in crystalline anhydrous lactulose, although the mutarotation of the trihydrate when dissolved in Me2SO is very slow.

The crystal structure of D-threitol at 119 K and 198 K.

A sample of DL-threitol, C4H10O4 (Sigma Chemical Co.), on recrystallization provided crystals of D- and L-threitol. The crystal structure was determined at 119 K and 298 K. The space group of D-threitol is P3(1)21, with three molecules in a unit cell at 119 K [298 K] of a = 10.0995(5) [10.1405(8)], c = 4.8407(4) [4.8767(4)] A. The final agreement R-factor was 0.050 for 302 intensities [0.069 for 244 intensities]. The molecules have the straight carbon-chain conformation with twofold axial symmetry. The hydroxyl groups are hydrogen bonded in infinite chains extending in the direction of the threefold screw axis. One of the hydroxyl hydrogens is twofold disordered, so that alternate chains have reversed donor-acceptor directions.

Hydrogen bonding in the crystal structure of alpha,beta-panose.

The crystal structure of panose, O-alpha-D-glucopyranosyl-(1----6)-O-alpha-D-glucopyranosyl-(1----4)-D-gl ucose, C18H32O16, has been refined using low-temperature, 123 K, CuK alpha X-ray data. Difference syntheses and least-squares refinement showed a 16% substitution of alpha-panose by the beta anomer. All the hydrogen atoms were located on difference synthesis with the exception of one attached to the low occupancy (beta) O-1". The final R-factor was 0.036 for 2135 observed structure amplitudes. The molecular conformation is stabilized by two interresidue intramolecular hydrogen bonds. All the hydroxyls and glycosidic oxygen atoms are involved in the hydrogen bonding, which is a two-dimensional network formed from finite and infinite chains.

Hydrogen bonding in the crystal structure of the tetrasaccharide stachyose hydrate: a 1:1 complex of two conformers.

The crystal structure of stachyose hydrate, O-alpha-D-galactopyranosyl-(1----6)-O-alpha-D-galactopyrano- syl-(1----6)-alpha-D-glucopyranosyl beta-D-fructofuranoside tetrahydrate, has been refined using X-ray data at 119 K. The crystal structure is a 1:1 complex of conformers which differ in the fructofuranosyl and glucopyranosyl residues. Each conformer has an associated hydrogen-bond structure which includes different sites for the water molecules. When superimposed in the crystal, this gives rise to two sites of 0.5 occupancy for one carbon and one oxygen atom of the fructofuranose component, and for three oxygen atoms of the glucopyranose component. The corresponding three carbon atoms of the glucopyranose component have anomalous thermal motion parameters. The four water molecules are distributed over nine sites, six with occupancy 0.5, two with occupancy 0.4, and one with occupancy 0.2. Four of the water sites are associated with one conformer, and four with the other. The hydrogen bonding includes infinite chains which are linked to form irregular ribbons, extending in the direction of the alpha axis. All hydroxyl, ring, and linkage oxygen atoms are involved in the hydrogen bonding, which includes two-centered, three-centered, and four-centered hydrogen bonds.

The hydrogen bonding in the crystal structure of raffinose pentahydrate.

The crystal structure of raffinose pentahydrate, O-alpha-D-galactopyranosyl-(1----6)-O-alpha-D-glucopyranosyl-(1----2)- beta-D- fructofuranose pentahydrate, C18H32O16.5H2O, has been redetermined using low-temperature, 119 K, CuK alpha X-ray data. All hydrogen atoms were unambiguously located on difference syntheses. The final R-factor is 0.036 for 2423 observed structure amplitudes. The hydrogen bonding is composed of infinite chains, which are linked through the water molecules to form a three-dimensional network containing a chain of five linked water molecules. Three of the infinite chains extend in the directions of the crystallographic axis of the space group P2(1)2(1)2(1). Four of the water molecules accept two hydrogen bonds and one accepts one. All the hydroxyls and the ring and glycosidic oxygen atoms are involved in the hydrogen bonding. With one exception, the ring and glycosidic oxygens are hydrogen-bonded by means of the minor components of unsymmetrical three-center bonds.

The crystal structure and thermotropic liquid-crystal properties of N-n-undecyl-D-gluconamide.

N-n-Undecyl-D-gluconamide, C17H35O6, crystallizes in space group P1, with one molecule in a unit cell a = 5.2267(6), b = 19.628(9), c = 4.7810(4) A, alpha = 93.23(2), beta = 95.60(1), gamma = 89.58(2) degrees, V = 487.35 A3, Dx = 1.19 g.cm-3. The crystal lattice is isostructural with N-n-heptyl-D-gluconamide having monolayer head-to-tail molecular packing. The molecules have a V-shaped conformation. The hydrogen bonding of the gluconamide moieties includes a four-link homodromic cycle. The transition to a smectic A liquid-crystal phase at 156.7 degrees is preceded by two crystal-to-crystal phase transitions at 77.2 degrees and 99.4 degrees. The long d-spacing of the intermediate crystal phase of 39 A, and the d-spacing of the liquid-crystal phase of 32 A, are consistent with a transition to a bilayer head-to-head molecular packing.

Structure of 3,4,5-trihydroxybenzoic acid octyl ester (octyl gallate) dihydrate at 123 K. A non-mesogenic amphiphilic molecule.

The crystal structure of 3,4,5-trihydroxybenzoic acid octyl ester (octyl gallate) dihydrate, C15H22O5.2H2O, is triclinic, P1, with a = 6.617 (1) [6.648 (1)], b = 9.956 (2) [9.995 (3)], c = 14.088 (4) [14.327 (7)] A, alpha = 79.08 (2) [79.78 (3)], beta = 85.58 (3) [86.59 (4)], gamma = 70.80 (2) [70.99 (3)] degrees, V = 860.5 A3, Z = 2, Dx = 1.229 1.229 [1.183] g cm-3, lambda(Mo K alpha) = 0.7093 A, mu = 0.58 cm-1, F(000) = 344 at 123 K [290 K]. The structure was solved by direct methods and refined to R(F2) = 0.059 for 302 parameters and 3655 observations. The alkyl chain of the molecule is in the fully extended conformation. The molecular packing is head-to-head bilayer with interdigitizing alkyl chains. The gallate head groups are hydrogen bonded with the water molecules to form a strong system of intra- and intermolecular hydrogen bonds consisting of finite and infinite chains. The crystals undergo crystal-to-crystal phase transitions at 365 K on heating and at 333 K on cooling, but despite the molecular packing which is analogous to that of the mesogenic alkyl glycosides, there is no thermotropic liquid crystal phase prior to the formation of the isotropic liquid phases at 376 K. Similary, no lyotropic liquid crystal phases are observed at room temperature in contact with a mixture of water and propanediol in which the crystals are soluble.

The stereochemistry of the water molecules in the hydrates of small biological molecules.

An examination of the stereochemistry of the water molecules in the hydrates of amino acids and peptides, carbohydrates, purines and pyrimidines, and nucleosides and nucleotides, reveals a variety of hydrogen-bonded configurations within a radius of 3.0 A from the water oxygen atom. Water molecules which accept one hydrogen bond are more common than those that accept two, by a factor of 1.4. There are nine examples where the water is not a hydrogen-bond acceptor, but only one where it does not donate two hydrogen bonds. Of the 621 OWH...A bonds examined, 15% were three centered and 2% were four centered or three-center bifurcated. The amino-acid and peptide hydrates displayed the greatest variety with 15 different hydrogen-bond configurations. The coordination of the donor and acceptor atoms within 3.0 A of the water oxygen atom ranged from two to seven.

Crystallographic studies of carbohydrates.

The monosaccharides which constitute the monomer units of many important industrial and biological macromolecules are well represented among the 2000 crystal structures of the carbohydrate class 45 of the Cambridge Structural Database. There are few examples of crystal structure analyses of the corresponding acids, but many of their calcium salts and calcium salt complexes. With the exception of the disaccharides and cyclodextrins, the oligosaccharides are not well represented, with less than ten trisaccharides, one tetrasaccharide and one hexasaccharide-iodide complex. Two important conformational factors are the Hassel-Ottar effect and the anomeric effect, both of which have been studied using crystallographic data. Hydrogen bonding is ubiquitous in carbohydrate crystals and generally involves all the hydroxyls as both donors and acceptors, and some of the ring and glycosidic oxygens as acceptors. These hydrogen bonds tend to form finite or infinite chains. In hydrates, these chains are linked through the water molecules to form networks. Cyclic hydrogen-bond systems are observed in the cyclodextrins. Long-chain alkylated carbohydrates provide a large class of thermotropic and lyotropic liquid crystals, and some non-ionic surfactants which have been shown to be useful for membrane-protein solubilization and crystallization.

The lyotropic liquid crystal properties of n-octyl 1-O-beta-D-glucopyranoside and related n-alkyl pyranosides.

X-ray diffraction patterns have been obtained for the lyotropic phases of n-octyl 1-O-beta-D-glucopyranoside and the related n-heptyl, n-nonyl and n-decyl compounds with water. The octyl compound exhibits all three liquid crystal phases and forms a micellar solution with increasing solvation, when the crystal come into contact with water at room temperature. The X-ray diffraction patterns show a one-dimensional lamellar phase with [dx] = 28.4 A, a three-dimensional face-centered cubic phase with [a] = 51.2 A, and a two-dimensional hexagonal phase with [a] = [b] = 36.7 A. The micellar solution has a distribution pattern with a maximum at [dx] = 33.8 A. Crystals of the heptyl, nonyl and decyl derivatives form only the lamellar phases and the micellar solution on contact with water at room temperature.

The structures of 1-deoxy-(N-methyloctanamido)-D-glucitol (MEGA-8) and 1-deoxy-(N-methylundecanamido)-D-glucitol (MEGA-11).

1-Deoxy-(N-methyloctanamido)-D-glucitol, C15H31NO6 (MEGA-8), crystallizes in space group P2(1)2(1)2(1), Mr = 321.4, a = 4.865 (1), b = 9.186 (3), c = 39.097 (9) A, V = 1747.24 A3, Z = 4, Dx = 1.22 Mg m-3, lambda (Cu K alpha) = 1.5418 A, mu = 0.78 mm-1, F(000) = 704, R = 0.035 for 1318 reflections. 1-Deoxy-(N-methylundecanamido)-D-glucitol, C18H37-NO6 (MEGA-11), crystallizes in space group P1, Mr = 363.5, a = 4.950 (1), b = 5.6027 (8), c = 19.162 (4) A, alpha = 83.19 (2), beta = 89.76 (2), gamma = 76.28 (2) degrees, V = 512.64 A3, Z = 1, Dx = 1.18 Mg m-3, lambda (Mo K alpha) = 0.7107 A, mu = 0.093 mm-1, F(000) = 200, R = 0.061 for 1898 reflections. The glucitol C-atom-chain conformation is different in the two structures. In MEGA-8 it is fully extended, whereas in MEGA-11 it is bent. The alkyl C-atom chains are fully extended in both structures. The molecular packing is different. In MEGA-8 it is head-to-head bilayer with intercalating alkyl chains, whereas in MEGA-11 it is monolayer head-to-tail with non-intercalating alkyl chains. The hydrogen bonding in MEGA-8 is a finite chain; in MEGA-11 it includes a homodromic four-bond cycle.