Formation Of Self-associates Research Articles

H-bonded acid-base type associates of sulfoheteryl substituted porphyrins and their influence on chromophoric properties

Directed synthesis of novel water-soluble asymmetric porphyrins containing in a molecule three sulfo-phenyl fragments and residues of small heterocyclic molecules (benzothiazole (S-spor), benzoxazole (O-spor) and benzo-N-methylimidazole (N-spor)) was performed using metal-complex catalysis method. The state of the synthesised porphyrins in water media was examined by spectrophotometric and potentiometric titration. It was shown that in the case of porphyrins with benzothiazole and benzoxazole residues two interconnected processes - protonation of the reaction centre and formation of self-associates from protonated O-spor and S-spor forms - occur in water. For the porphyrin with benzo-N-methylimidazole residual, the protonation processes dominate and revealed association was less evident compared to O-spor and S-spor. It was proved that formation of associates from protonated forms of anionic porphyrins does not result from π-π-interaction; the porphyrins under study form the H-bonded acid-base type associates’ stabilisation of which is due to specific bindings through direct participation of sulfo groups as well as monoheteryl substitutes in the case of O-spor and S-spor. Potentiometric and spectrophotopotentiometric titrations were conducted, the pKa values which reflect the protonation process of the porphyrin reaction centre were determined. Acid strength increased in the order O-spor < N-spor < S-spor and correlated with electronegativity of heteroatom in the peripheral porphyrin’s substitute.

Bulk and surface properties of liquid Ga–Tl and Zn–Cd alloys

Abstract A simple thermodynamic model, based on the formation of self-associates, has been used to correlate the bulk and surface properties of mixing of liquid Ga–Tl and Zn–Cd alloys at temperatures of 973 K and 900 K, respectively. The model enables us to explain the positive deviation of the properties of mixing of the two liquid alloys from the ideal solution behavior. Our calculations indicate that the degree of phase separation in Zn–Cd, as measured using the Warren –Cowley short-range order parameter, is less than that in Ga–Tl.With regards to the surface, we show that the surface decomposition in Zn–Cd liquid alloys is greater than in Ga–Tl. We explain the contrast in the bulk and surface properties in terms of the possible roles of the entropic and enthalpic effects on the properties of mixing.

Speciation of Substituted Benzoic Acids in Solution: Evaluation of Spectroscopic and Computational Methods for the Identification of Associates and Their Role in Crystallization

Self-association of four benzoic acid derivatives 2-chloro-4-nitrobenzoic acid, 2-methyl-4-nitrobenzoic acid, 3-hydroxybenzoic acid, and 2,6-dimethoxybenzoic acid in solution was investigated using spectroscopic measurements (Fourier transform infrared and 1H and 13C NMR spectroscopy) and molecular simulation methods. Based on the formation of hydrogen bonds, solvents can be divided into two groups: apolar solvents or solvents with a low hydrogen bond acceptor propensity, in which the benzoic acid derivatives form hydrogen-bonded dimers, and solvents with hydrogen bond acceptor propensity β > 0.3, interacting with the carboxylic group of benzoic acid, thus screening its interaction in the formation of self-associates. The formation propensity and structure of self-associates stabilized by weak interactions, such as π···π stacking and CH3···π interactions, however, are determined by the substituents in the benzene ring. Despite all the studied compounds being polymorphic, in none of the cases, an unequivocal structural link between self-associates present in the solution and the crystal form was observed.

Master regulators in the foam cell formation; the role of phagocytosis

Abstract Background Foam cell formation caused by modified LDL is the earliest and most noticeable manifestation of atherosclerosis. The mechanisms of foam cell formation are not fully understood and can involve altered lipid uptake, impaired lipid metabolism, or both. 10 inflammation-related master regulators, which were involved in the cholesterol accumulation in cultured macrophages induced by the incubation with modified LDL, have been identified. Objective We hypothesised that the primary event occurring upon the interaction of modified LDL and macrophages is the stimulation of phagocytosis, which subsequently triggers the pro-inflammatory immune response. Methods Cholesterol accumulation was evaluated in primary macrophages with master regulator genes knock-downed by siRNA for either IL15, EIF2AK3, F2RL1, TSPYL2, or ANXA1. Analysis of enriched transcription factor binding sites in promoters of differentially expressed genes and identification of master regulators in the signal transduction network were performed with TRANSFAC and TRANSPATH databases. Results Genes which were up- or downregulated following the exposure of cultured cells to modified LDL or latex beads were determined. Most of the identified master regulators were involved in the innate immune response, and some of them were encoding major pro-inflammatory proteins. Comparative analysis of master regulators revealed similarities in the genetic regulation of the interaction of macrophages with naturally occurring LDL and desialylated LDL. Oxidized and desialylated LDL affected a different spectrum of genes than naturally occurring LDL. These observations suggest that desialylation is the most important modification of LDL occurring in vivo. Thus, modified LDL caused the gene regulation characteristic of the stimulation of phagocytosis. The knock-down of the EIF2AK3 and IL15 genes completely prevented cholesterol accumulation in cultured macrophages, whereas atherogenic naturally occurring LDL caused significant cholesterol accumulation in the control cells. The ANXA1 gene knock-down caused a further decrease in cholesterol content in cultured macrophages. At the same time, knock-down of F2RL1 and TSPYL2 did not cause an effect. Conclusions The results, showing that inflammatory response and the cholesterol accumulation are related, may confirm our hypothesis of atherogenesis development based on the following viewpoints: LDL particles undergo atherogenic modifications that, in turn, accompanied by the formation of self-associates; large LDL associates stimulate phagocytosis; as a result of phagocytosis stimulation, pro-inflammatory molecules are secreted; these molecules cause or at least contribute to the accumulation of intracellular cholesterol. Therefore, it became obvious that the primary event in this sequence is not the accumulation of cholesterol but an inflammatory response. Funding Acknowledgement Type of funding source: Foundation. Main funding source(s): The Russian Science Foundation

Signaling Pathways Potentially Responsible for Foam Cell Formation: Cholesterol Accumulation or Inflammatory Response-What is First?

Accumulation of lipid-laden (foam) cells in the arterial wall is known to be the earliest step in the pathogenesis of atherosclerosis. There is almost no doubt that atherogenic modified low-density lipoproteins (LDL) are the main sources of accumulating lipids in foam cells. Atherogenic modified LDL are taken up by arterial cells, such as macrophages, pericytes, and smooth muscle cells in an unregulated manner bypassing the LDL receptor. The present study was conducted to reveal possible common mechanisms in the interaction of macrophages with associates of modified LDL and non-lipid latex particles of a similar size. To determine regulatory pathways that are potentially responsible for cholesterol accumulation in human macrophages after the exposure to naturally occurring atherogenic or artificially modified LDL, we used transcriptome analysis. Previous studies of our group demonstrated that any type of LDL modification facilitates the self-association of lipoprotein particles. The size of such self-associates hinders their interaction with a specific LDL receptor. As a result, self-associates are taken up by nonspecific phagocytosis bypassing the LDL receptor. That is why we used latex beads as a stimulator of macrophage phagocytotic activity. We revealed at least 12 signaling pathways that were regulated by the interaction of macrophages with the multiple-modified atherogenic naturally occurring LDL and with latex beads in a similar manner. Therefore, modified LDL was shown to stimulate phagocytosis through the upregulation of certain genes. We have identified at least three genes (F2RL1, EIF2AK3, and IL15) encoding inflammatory molecules and associated with signaling pathways that were upregulated in response to the interaction of modified LDL with macrophages. Knockdown of two of these genes, EIF2AK3 and IL15, completely suppressed cholesterol accumulation in macrophages. Correspondingly, the upregulation of EIF2AK3 and IL15 promoted cholesterol accumulation. These data confirmed our hypothesis of the following chain of events in atherosclerosis: LDL particles undergo atherogenic modification; this is accompanied by the formation of self-associates; large LDL associates stimulate phagocytosis; as a result of phagocytosis stimulation, pro-inflammatory molecules are secreted; these molecules cause or at least contribute to the accumulation of intracellular cholesterol. This chain of events may explain the relationship between cholesterol accumulation and inflammation. The primary sequence of events in this chain is related to inflammatory response rather than cholesterol accumulation.

Role of Phagocytosis in the Pro-Inflammatory Response in LDL-Induced Foam Cell Formation; a Transcriptome Analysis.

Excessive accumulation of lipid inclusions in the arterial wall cells (foam cell formation) caused by modified low-density lipoprotein (LDL) is the earliest and most noticeable manifestation of atherosclerosis. The mechanisms of foam cell formation are not fully understood and can involve altered lipid uptake, impaired lipid metabolism, or both. Recently, we have identified the top 10 master regulators that were involved in the accumulation of cholesterol in cultured macrophages induced by the incubation with modified LDL. It was found that most of the identified master regulators were related to the regulation of the inflammatory immune response, but not to lipid metabolism. A possible explanation for this unexpected result is a stimulation of the phagocytic activity of macrophages by modified LDL particle associates that have a relatively large size. In the current study, we investigated gene regulation in macrophages using transcriptome analysis to test the hypothesis that the primary event occurring upon the interaction of modified LDL and macrophages is the stimulation of phagocytosis, which subsequently triggers the pro-inflammatory immune response. We identified genes that were up- or downregulated following the exposure of cultured cells to modified LDL or latex beads (inert phagocytosis stimulators). Most of the identified master regulators were involved in the innate immune response, and some of them were encoding major pro-inflammatory proteins. The obtained results indicated that pro-inflammatory response to phagocytosis stimulation precedes the accumulation of intracellular lipids and possibly contributes to the formation of foam cells. In this way, the currently recognized hypothesis that the accumulation of lipids triggers the pro-inflammatory response was not confirmed. Comparative analysis of master regulators revealed similarities in the genetic regulation of the interaction of macrophages with naturally occurring LDL and desialylated LDL. Oxidized and desialylated LDL affected a different spectrum of genes than naturally occurring LDL. These observations suggest that desialylation is the most important modification of LDL occurring in vivo. Thus, modified LDL caused the gene regulation characteristic of the stimulation of phagocytosis. Additionally, the knock-down effect of five master regulators, such as IL15, EIF2AK3, F2RL1, TSPYL2, and ANXA1, on intracellular lipid accumulation was tested. We knocked down these genes in primary macrophages derived from human monocytes. The addition of atherogenic naturally occurring LDL caused a significant accumulation of cholesterol in the control cells. The knock-down of the EIF2AK3 and IL15 genes completely prevented cholesterol accumulation in cultured macrophages. The knock-down of the ANXA1 gene caused a further decrease in cholesterol content in cultured macrophages. At the same time, knock-down of F2RL1 and TSPYL2 did not cause an effect. The results obtained allowed us to explain in which way the inflammatory response and the accumulation of cholesterol are related confirming our hypothesis of atherogenesis development based on the following viewpoints: LDL particles undergo atherogenic modifications that, in turn, accompanied by the formation of self-associates; large LDL associates stimulate phagocytosis; as a result of phagocytosis stimulation, pro-inflammatory molecules are secreted; these molecules cause or at least contribute to the accumulation of intracellular cholesterol. Therefore, it became obvious that the primary event in this sequence is not the accumulation of cholesterol but an inflammatory response.

Study of Simvastatin Self-Association Using Electrospray-Ionization Mass Spectrometry

Self-association of simvastatin, which is widely used to treat coronary heart disease, was investigated using electrospray-ionization mass spectrometry. Formation of simvastatin self-associates in various solvents was demonstrated using mass spectrometry. Solvation effects were shown to play a special role in the formation of the self-associates. Self-associates containing from two to fi ve simvastatin molecules were detected in mass spectra of an aqueous MeOH (20%) solution of simvastatin. The formation of simvastatin self-associates could compete with the complexation of supramolecular structures during the synthesis of new generation drugs.

Circular dichroism study of the interaction between mutagens and bilirubin bound to different binding sites of serum albumins

Although recent investigations have shown that bilirubin not only has a negative role in the organism but also exhibits significant antimutagenic properties, the mechanisms of interactions between bilirubin and mutagens are not clear. In this study, interaction between bilirubin bound to different binding sites of mammalian serum albumins with structural analogues of the mutagens 2-aminofluorene, 2,7-diaminofluorene and mutagen 2,4,7-trinitrofluorenone were investigated by circular dichroism and absorption spectroscopy. Homological human and bovine serum albumins were used as chiral matrices, which preferentially bind different conformers of bilirubin in the primary binding sites and make it observable by circular dichroism. These molecular systems approximated a real system for the study of mutagens in blood serum. Differences between the interaction of bilirubin bound to primary and to secondary binding sites of serum albumins with mutagens were shown. For bilirubin bound to secondary binding sites with low affinity, partial displacement and the formation of self-associates were observed in all studied mutagens. The associates of bilirubin bound to primary binding sites of serum albumins are formed with 2-aminofluorene and 2,4,7-trinitrofluorenone. It was proposed that 2,7-diaminofluorene does not interact with bilirubin bound to primary sites of human and bovine serum albumins due to the spatial hindrance of the albumins binding domains. The spatial arrangement of the bilirubin bound to serum albumin along with the studied mutagens was modelled using ligand docking, which revealed a possibility of an arrangement of the both bilirubin and 2-aminofluorene and 2,4,7-trinitrofluorenone in the primary binding site of human serum albumin.

Structure of associates of vinyl molecules and maleic anhydride in CCl4 solution

The self-association of styrene, acrylonitrile, methylmethacrylate, N-vinylpyrrolidone, and maleic anhydride molecules is considered in dependence on the nature of the monomer, i.e., on the conjugation between functional groups. The AM1, Hartree-Fock (RHF), and density functional theory (DFT) methods of calculation are used in our investigations. Charge distributions on the atoms of interacting groups and contributions from overlapping molecular orbitals to the energy of formation of self-associates are found. The calculated parameters are compared with experimental data on absorption band shifts in IR spectra and on chemical shifts ΔH and ΔC for the hydrogen and carbon atoms of =CH, =CH2, C=O groups of bound molecules in 1H and 13C NMR spectra. The formation of π-H, CH…O, and CH…N bonds is proved. Analysis of CCl4/monomer dependences shows that dimers are present in dilute solutions, while the presence of trimers in concentrated solutions cannot be excluded. Self-association constants are determined along with the degree of self-association, which lies within the range of 40–60% for 50 mol% of a monomer in solution.

Isomers of some vinyl and allyl compounds

The structures of two rotational isomers of styrene, methyl methacrylate, N-vinylpyrrolidone, and allyl benzoate found by AM1 calculations are discussed. Their formation is indicated by the presence of two minima on the curves of the rotation barriers around the C1-C2, C2-N3 and C(=O)-O, O-C(H2) bonds. The structures of the isomers of allyl compounds were detected capable of providing the cyclization reaction and hydrogen atom elimination. It was found that both double bonds were of similar reactivity. The suggested structures of the isomers can participate in intermolecular interactions with the formation of self-associates and heteroassociates (molecular complexes) due to the presence of C=C and C=O groups with different degree of conjugation.

Bulk and surface properties of liquid Ga–Tl and Zn–Cd alloys

Abstract A simple thermodynamic model, based on the formation of self-associates, has been used to correlate the bulk and surface properties of mixing of liquid Ga–Tl and Zn–Cd alloys at temperatures of 973K and 900K, respectively. The model enables us to explain the positive deviation of the properties of mixing of the two liquid alloys from the ideal solution behavior. Our calculations indicate that the degree of phase separation in Zn–Cd, as measured using the Warren–Cowley short-range order parameter, is less than that in Ga–Tl. With regards to the surface, we show that the surface decomposition in Zn–Cd liquid alloys is greater than in Ga–Tl. We explain the contrast in the bulk and surface properties in terms of the possible roles of the entropic and enthalpic effects on the properties of mixing.

Osmotic and activity coefficients of some pyridine complexes with halogenoacetic acids in benzene at 25°C

Abstract Osmotic coefficients measured by vapour pressure osmometry are reported for benzene solutions of complexes of pyridine with trifluoroacetic, dichloroacetic and chloroacetic acids at 25°C. Solute activities decrease with increasing concentration due to formation of self-associates. It is suggested that dipole-dipole interactions contribute substantially to the stability of the associates.