Chemical structure and physico-chemical properties of agar

Advances in the chemistry and physico-chemical properties of agar since the review of Araki at the Fifth International Seaweed Symposium in 1965 are discussed. These advances are essentially the result of better separation techniques of the heterogeneous family of polysaccharides known as agar, the use of nuclear magnetic resonance spectroscopy, the use of agarases and, particularly, the use of combinations of the three approaches. Although physico-chemical methods have evolved, particularly molecular-weight determinations, X-ray diffraction data and molecular modelling of agar, correlations between chemical and functional properties of agar and agarose and their gelation mechanisms remain to be studied.     

Biological properties of poly-L-lysine-DNA complexes generated by cooperative binding of the polycation.

We have evaluated the effect of NaCl concentration on the mode of binding of poly-L-lysine to DNA and the resulting structural and functional features of the condensed DNA particles using DNA precipitation, DNase I resistance, electron microscopy, and receptor-mediated gene transfer assays. At a high concentration of NaCl and in the presence of excess DNA, poly-L-lysine interacted with DNA cooperatively, fully condensing some of the DNA and leaving the rest of the DNA unbound. At low NaCl concentrations, poly-L-lysine molecules interacted with DNA in a noncooperative fashion, i.e. they bind randomly to the whole population of DNA molecules. Cooperative binding of poly-L-lysine to DNA occurred over a narrow range of NaCl concentrations, and the specific salt concentration depended on the length of the poly-L-lysine. The ability of condensed DNA to withstand digestion by DNase I was correlated with the structural features of the condensed DNA as determined by electron microscopy. Using our condensation procedure, cooperative binding of poly-L-lysine to DNA is a necessary prerequisite for the preparation of condensed DNA having a spherical shape and a diameter of 15-30 nm. Condensed DNA, containing galactosylated poly-L-lysine, was evaluated further for the extent and specificity of receptor-mediated gene transfer into HuH-7 human hepatoma cells via the asialoglycoprotein receptor. Efficient receptor-mediated transfection occurred only when condensed DNA complexes had a spherical shape with a diameter of 15-30 nm; asialofetuin, a natural ligand for the asialoglycoprotein receptor, inhibited this process by up to 90%. Our results support the importance of appropriate DNA condensation for the uptake and ultimate expression of DNA in hepatic cells.     

Effect of gamma-irradiation on some biological and physico-chemical properties of polyene antibiotics]

Deep effect of gamma-rays on polyenic antibiotics was studied. It was shown that gamma-radiation induced radiation-chemical oxidation of the substances. The chromatographic analysis showed that the levorin degradation products were identical to the polyenic products of the antibiotic oxidative destruction. As for mycoheptin and amphotericin B, destruction of their molecules to non-polyenic products was observed. It was found that toxicity of the levorin aromatic heptaen did not practically change after gamma-irradiation in high doses. The toxicity of mycoheptin and amphotericin B, non-aromatic heptaens increased after exposure to high doses of gamma-rays.     

Effect of albumin and polyanion on the structure of DNA complexes with polycation containing hydrophilic nonionic block.

Self-assembling systems based on ionic complexes of DNA with block copolymer of N-(2-hydroxypropyl)methacrylamide with 2-(trimethylammonio)ethyl methacrylate were studied as systems suitable for gene delivery. In this study, the influence of albumin and polyanion on parameters of the DNA polyelectrolyte complexes in aqueous solutions was investigated. Static and dynamic light-scattering methods were used as a main tool for characterizing these interactions. It was found that albumin is not able to release free DNA, but it can rather bind to the complexes forming ternary DNA-polycation-albumin complexes with increased hydrodynamic radii of about 10 nm. Polyanion tested, sodium poly(styrenesulfonate), was able to release free DNA in the presence of a low-molecular-weight electrolyte. In the absence of a low-molecular-weight electrolyte, only formation of ternary complexes and no DNA release was observed. The in vivo biodistribution analysis of DNA complexes showed no effect of the presence of hydrophilic nonionic poly(HPMA) on the circulatory time or organ distribution. The interaction of DNA complexes with albumin and other plasma proteins was suggested to be a major reason for the short circulatory times.     

Effect of physico-chemical factors and species specificity on the structure of dinitrosyl iron complexes

Formation in mouse, rat and man's blood of iron nitrosyl complexes with pair thiol groups of proteins (complexes 2.03) was shown by ESR method. This formation was initiated by the introduction in blood in vitro or in vivo of low molecular dinitrosyl complexes of iron with phosphate, thiosulphate, cysteine or reduced gluthatione. Three forms of these complexes were found. They were characterized by ESR signals with rhombic or axial symmetry of g-factor tensor. These forms pass into one another under the effect of a number of thiol-containing compounds or at blood freezing. The life time of the complexes 2.03 in the blood in vivo is several hours.     

Extrinsic cotton effect and helix-coil transition in a DNA-polycation complex

A strong, positive, extrinsic CD band ([θ]_242.5 = ～2 × 10^?3 deg cm²/dmole) has been observed for a α-bromo-poly[methylene-1,4-phenylenecarbonyloxyethylene(dimethylamino) bromide] (I). The extrinsic Cotton effect is attributed to the ordered arrangement of the aromatic chromophores along the DNA helix. The extrinsic band had a linear dependence on the amount of polycation I added from r ≤ 0.3 to r = ～0.5, but decreased thereafter. Addition of the polycation decreased the positive CD band of DNA at 275 nm. The transformation of B → C form in the presence of salts or other polycations caused similar changes. The decrease in [θ]₂₇₅ was reversed at higher concentrations of the polycation (r > 0.4). Thermal denaturation studies indicated both stabilization of the helix conformation (Δt_m = 21°C) and a high degree of cooperativity in the melting of DNA-polycation complex as compared to native calf thymus DNA. Using the linear relationship between r (polycation residue/DNA phosphate) and F (fraction of bound base pairs), a value of 0.6 was derived for β (number of monomer residues of polycation/nucleotide). Both electrostatic and hydrophobic effects probably influence the stability of the DNA-polycation complex, since the strength of the 242.5 nm CD band is a function of both salt and urea concentrations.     

Chemical and biological properties of pentaammineruthenium-bleomycin complexes

The reaction of [(H2O)(NH3)5RuII]2+ with bleomycin forms at least two stable products following oxidation to the Ru(III) analog. Spectroscopic and electrochemical measurements indicate monodentate binding of [(NH3)5RuIII] to the imidazole and pyrimidine moieties, with coordination to the latter involving the exocyclic amine nitrogen. DNA cleavage studies show the complexes to be ineffective in DNA strand scission. In vitro biological studies reveal these adducts to be cytotoxic.     

Synthesis, structural, physico-chemical and biological properties of new palladium(II) complexes with 2,6-dimethyl-4-nitropyridine

This paper describes the synthesis and properties of two new palladium(II) complexes with 2,6-dimethyl-4-nitro-pyridine (dmnp): mononuclear [Pd(dmnp)2Cl2] and dinuclear [Pd2(dmnp)2Cl4]. Complexes were characterized on the basis of chemical and chromatographic analyses, MS and conductometric measurements, as well as by IR and NMR (1H and 13C) spectral studies. The crystal structures of ligand and mononuclear complex, trans-dichlorobis(2,6-dimethyl-4-nitro-pyridine)palladium(II), were determined by three-dimensional X-ray methods. The crystals of both compounds are monoclinic, space groups P21/c with a=19.075(4), b=5.419(1), c=15.045(3) A and beta=108.15(3)degrees for (dmnp), and a=7.544(2), b=14.509(3), c=8.032(2) A and beta=90.32(3)degrees for [Pd(dmnp)2Cl2]. In the (dmnp) there are two crystallographically independent molecules in the unit cell. The nitro groups and methyl C atoms are coplanar with the ring plane. The hydrogen bond of the type C-H...O links the molecules into pairs around center of symmetry. These dimers are held together by contacts of the van der Waals type. In the crystal structure of [Pd(dmnp)2Cl2] the Pd atom lies on an inversion center and is four-coordinated by two pyridine N atoms and by two Cl atoms in trans positions. The coordination geometry is square-planar, with Pd-N and Pd-Cl distances of 2.033(2) and 2.311(1) A, respectively. The two pyridine rings are mutually parallel, but they are twisted from the PdN2Cl2 coordination plane by about 88.5degrees. The preliminary assessments of anti-tumor properties of both complexes and ligand were evaluated as in vitro anti-proliferative activity in four human cancer cell lines: SW707 (adenocarcinoma of the rectum), T47D (breast cancer), HCV (bladder cancer) and A549 (non-small cell lung carcinoma). The [Pd(dmnp)2Cl2] exhibits strong cytotoxic activity against all cell lines whereas the free ligand and dinuclear [Pd2(dmnp)2Cl4] are only moderate active.     

Synthesis and structure of cycloruthenated carbonyl complexes and their emission, redox and biological properties

An interesting series of mononuclear organoruthenium complexes of formulation [Ru(CO)(PPh3)2(ap-R)] (where ap-R = -H, -Cl, -Me, -OMe, -OEt) have been synthesized from the reaction of five 2-(arylazo)phenol ligands with ruthenium(II) precursor [RuH(Cl)(CO)(PPh3)3] in benzene under reflux. The 2-(arylazo)phenolate ligands behave as dianionic tridentate ligand and are coordinated to ruthenium through C, N and O by dissociation of the phenolic and phenyl proton at the ortho position of the phenyl ring forming two five-membered chelate rings. These complexes have been characterized by elemental analysis, FT-IR, 1H NMR and UV-visible spectroscopy. In dichloromethane solution all the metal complexes exhibit characteristic metal-to-ligand charge transfer (MLCT) absorption and emission bands in the visible region. The structures of [Ru(CO)(PPh3)2(ap-H)] and [Ru(CO)(PPh3)2(ap-Cl)] have been determined by X-ray crystallography. Cyclic voltammetric data of all the complexes show a Ru(III)/Ru(II) oxidation and reduction Ru(II)/Ru(I) within the range 0.74-0.84 V and -0.38 to -0.50 V vs saturated calomel electrode (SCE) respectively. The potentials are observed with respect to the electronic nature of substituents (R) in the 2-(arylazo)phenolate ligands. Further, the free ligands and their ruthenium complexes have also been screened for their antibacterial and antifungal activities, which have shown great promise in inhibiting the growth of both gram +ve and gram -ve bacteria Staphylococcus aureus and Escherichia coli and fungus Candida albicans and Aspergillus niger. These results made it desirable to delineate a comparison between free ligands and their complexes.     

Copper(II) complexes of the beta-blocker pindolol: properties, structure, biological activity

The complex formation between copper(II) and the antihypertensive drug pindolol (HPin) was studied both in aqueous and methanolic media. Two complexes are formed at different metal-to-ligand molar ratios. The mononuclear complex Cu(Pin)₂(HPin)₂ contains two ligands in an anionic bidentate form and two - in a neutral form bound monodentately. The second complex Cu₂Pin₂Cl₂ is dinuclear and its structure was determined by X-ray diffraction. The compound crystallizes in the monoclinic group C2/c with cell components a = 14.4998(13)Å, b = 18.511(2)Å, c = 14.2982(13)Å, =90 °, =109.556(2)°, =90 ° and Z = 12 at 293K. A pharmacological study on the influence of pindolol and its mononuclear complex on the heart rate of rats was performed. The complex is more active and has a longer effect in comparison with the pure non-coordinated pindolol in equitoxic doses.     

Effect of microwave radiation on physico-chemical properties and structure of potato and tapioca starches

The time-temperature profiles of selected starch-water systems subjected to microwave processing were established and the effect of microwave radiation on the physico-chemical properties and structure of potato and tapioca starches was studied. The experimental starch samples were examined by the Brabender rheological method, light microscopy, scanning electron microscopy and X-ray diffractometry. Microwave radiation was evidenced to affect the temperature and moisture contents of the experimental starches, with a strong correlation between the moisture content and the rate of temperature rise. An isothermal transformation was revealed with the samples of moisture contents over 20%, causing a rise in the gelatinisation temperature of the starch and a drop in its solubility in water. The most pronounced change was observed in the case of potato starch: its crystal structure changed from type B to type A. The tapioca starch underwent similar but less marked changes.     

Study of the physico-chemical properties of prostaglandin F2 alpha and its complexes

To study the intracellular action mechanisms of prostaglandin F2 alpha its interaction with lipid components of biological membranes was investigated. It has been found that prostaglandin forms a complex with phosphatidylcholine and cholesterol. Immobilization ability of phospholipids is changed in the course of complex formation. Ability of prostaglandin F2 alpha for complex formation with insulin was also observed. Combination of monolayer technique and electron microscopy made possible to discover molecular reconstructions when prostaglandin is incorporated into monolayer of biologically active compounds.     

Nucleoprotein complexes of yeast and their biological effect on T-lymphocytes

Complexes of nucleic acids and acid nuclear proteins that are active toward human T-lymphocytes were isolated from cells of bakers' yeast Saccharomyces cerevisiae. The conditions of isolation of nucleoprotein complexes by acid extraction followed by microfiltration for concentration of macromolecular components were optimized. Gel filtration and electrophoresis were used to study the composition and molecular weights of components of the preparations obtained. It was shown that nucleoprotein complex had a molecular weight of 1430 kDa. However, only one zone was determined by electrophoresis of the protein component with a molecular weight of 30 kDa.     

Gene carriers based on hexanediol diacrylate linked oligoethylenimine: effect of chemical structure of polymer on biological properties

Two biodegradable polycations based on hexanediol diacrylate linked oligoethylenimine (OEI) were synthesized by applying different reaction temperatures, 20 degrees C (LT-OEI-HD) and 60 degrees C (HT-OEI-HD). Their structural properties were analyzed by NMR, FTIR, and SEC/MALLS (size exclusion chromatography coupled with multiangle laser light scattering detection). Reaction temperature strongly influenced molecular weight and ester/amide ratio and thus resulted in polycations with different biological activities and degradation profiles. LT-OEI-HD was an ester-based polycation of 8.7 kDa which degraded rapidly at pH 7 and pH 9 respectively. HT-OEI-HD had a molecular weight of 26.6 kDa, was mainly based on amides, and degraded more slowly than LT-OEI-HD. Both polymers mediated gene transfer as efficiently as linear polyethylenimine of 22 kDa in two cell lines while being less toxic at their optimal conjugate/plasmid (C/P) ratios. LT-OEI-HD needed higher C/P ratios for gene delivery; however, it was significantly less toxic than HT-OEI-HD.     

Effect of modification on physico-chemical and biological properties of haptoglobin. Acetylation, iodination and nitration.

Human haptoglobin (Hp) type 2-1 was modified with N-acetylimidazole, iodine or tetranitromethane (TNM), and the ability of the obtained derivatives to form with haemoglobin (Hb) complexes with peroxidase activity, was estimated. At low reagent to protein molar ratios, 11 tyrosine residues were nitrated, 12 acetylated and 13 iodinated. The biological activity of NO2-Hp and I-Hp amounted to 40% of the activity of native Hp whereas the activity of Ac-Hp only to 16%. The derivatives modified at high ratios of N-acetylimidazole or iodine lost the ability to bind with Hb. Deacylation. of tyrosines and partial liberation of acetylated xi-amino groups resulted in partial recovery of the activity. As demonstrated by polyacrylamide-gel electrophoresis, the modification of Hp with high excess of TNM or iodine induced polymer formation