Low Molecular Mass Compounds Research Articles

A stable prostacyclin-like substance produced by the medicinal leech Hirudo medicinalis

The medicinal leech Hirudo medicinalis produces a low-molecular mass compound with properties similar to those of prostacyclin. It extracted with organic solvent, had affinity to 6-keto-PGF 1α antibodies, inhibited human platelet aggregation induced in vitro by thrombin (by 50% at 4 pg/ml), and caused hypotension and secretion of plasminogen (t-PA) into the blood stream of rats. A main distinction from prostacyclin is stability of the substance due to covalent binding with the polypeptide chain of destabilase. Because of the high aggregability of destabilase, the molecules of the protein-lipid complex are organized into micelles that can change their spatial orientation depending on the nature of the solvent. Incorporation of hirudin and blood plasma kallikrein inhibitor into the micelle structure causes the formation of liposomes (with a molecular mass of the structural monomer 25 kDa). This complex with polypeptides provides not only stability but also rapid transmembrane penetration. The pure prostacyclin-like substance has a molecular mass of 391 Da and can be produced on destruction of the destabilase polypeptide chain.

PYOVERDINE PRODUCTION BYPSEUDOMONAS AERUGINOSAEXPOSED TO METALS OR AN OXIDATIVE STRESS AGENT

Siderophores are low molecular mass compounds used by many microor- ganisms to scavenge dissolved iron, which is typically rare in environments. Pseudomonas aeruginosa (PAO1) was exposed to metals and methyl viologen in low-iron medium in order to monitor the abundance of a specific siderophore (pyoverdine) and monitor growth over time. In this study it was discovered that cadmium can stimulate pyoverdine abundance. Cadmium may interact with and sequester the Fur regulatory protein, which represses siderophore synthesis under conditions of iron sufficiency. Mercury did not stimulate pyov- erdine production at concentrations that strongly inhibited bacterial growth, suggesting that pyoverdine production is not governed as part of a general stress response. Methyl viologen is an oxygen radical generator, and it was discovered that exposure to it decreased pyov- erdine production. Decreased pyoverdine production may be a mechanism for reducing the iron potentiation of oxygen toxicity. It is hypothesized that factors stimulating production of siderophores may increase the susceptibility of microorganisms to oxidative damage. In general, our research suggests new opportunities for predicting ecotoxicological outcomes based on understanding of molecular mechanisms and the effect of xenobiotics or stress factors on fundamentally important microbial processes.

99/01003 Transformation of carbon black sludge to stable combustible emulsion : Coroiu, C. et al. Rom. RO 106,577 (Cl. C10L1/32), 31 May 1993, Appl. 144,455, 15 Mar 1990, 4 pp. (In Romanian)

A series of semi-cokes, containing from virtually 0 to 100% mesophase, were produced from the THF-soluble fraction of a soft coal tar pitch. The mesophase contents were estimated by high temperature in situ 1H NMR and optical microscopy with extremely close agreement being obtained between the two techniques. Quantitative solid state 13C NMR measurements using the single pulse excitation technique indicated that the extent of anisotropy in the pitch is a function of the condensation of the aromatic structure, where isotropic pitches contain 5–6 rings on average, assuming pericondensation, which increases to 9–10 rings for the fully converted mesophase pitches. Characterisation of the pyridine-solubles (PS) and insolubles (PI) from the pitches confirmed that development of mesophase in the coal tar pitch is limited by the loss of low molecular mass compounds, in that the PS contain 5–6 rings throughout the series while the PI, even in largely the initial isotropic state, are as condensed as in the anisotropic pitches.

99/00997 Studies on preparation of hot-formed coke by lean coal : Cao, Q. et al. Meitan Zhuanhua, 1997, 20, (4), 86–89. (In Chinese)

A series of semi-cokes, containing from virtually 0 to 100% mesophase, were produced from the THF-soluble fraction of a soft coal tar pitch. The mesophase contents were estimated by high temperature in situ 1H NMR and optical microscopy with extremely close agreement being obtained between the two techniques. Quantitative solid state 13C NMR measurements using the single pulse excitation technique indicated that the extent of anisotropy in the pitch is a function of the condensation of the aromatic structure, where isotropic pitches contain 5–6 rings on average, assuming pericondensation, which increases to 9–10 rings for the fully converted mesophase pitches. Characterisation of the pyridine-solubles (PS) and insolubles (PI) from the pitches confirmed that development of mesophase in the coal tar pitch is limited by the loss of low molecular mass compounds, in that the PS contain 5–6 rings throughout the series while the PI, even in largely the initial isotropic state, are as condensed as in the anisotropic pitches.

Structure-based Discovery of a Pore-binding Ligand: Towards Assembly Inhibitors for Cholera and Related AB 5Toxins

Cholera toxin (CT) and Escherichia coli heat-labile enterotoxin (LT) are two closely related multi-subunit AB 5proteins responsible for significant morbidity and mortality worldwide. An attractive strategy to prevent disease by these organisms is to interfere with the assembly process of these toxins, since prevention of toxin formation is better than preventing the effects of a toxin which is already formed. The B subunits form a ring with a central pore which surrounds the C-terminal residues of the A subunit. Low molecular mass compounds which would bind in the pore are likely to inhibit proper assembly of the AB 5toxins. In a pharmacophore search based on two side-chains of the A subunit, 3-methylthio-1,4-diphenyl-1H-1,3,4-triazolium (MDT) was identified as a candidate ligand which might “plug” the pore. A 2.0 Å co-crystal structure revealed that a triplet of MDTs indeed bound to the targeted region in two independent LT B pentamers in a remarkably similar manner. Clearly, MDT is a lead for developing assembly antagonists of CT and LT.

Bioactive agents from natural sources: trends in discovery and application.

About 30% of the worldwide sales of drugs are based on natural products. Though recombinant proteins and peptides account for increasing sales rates, the superiority of low-molecular mass compounds in human diseases therapy remains undisputed mainly due to more favorable compliance and bioavailability properties. In the past, new therapeutic approaches often derived from natural products. Numerous examples from medicine impressively demonstrate the innovative potential of natural compounds and their impact on progress in drug discovery and development. However, natural products are currently undergoing a phase of reduced attention in drug discovery because of the enormous effort which is necessary to isolate the active principles and to elucidate their structures. To meet the demand of several hundred thousands of test samples that have to be submitted to high-throughput screening (HTS) new strategies in natural product chemistry are necessary in order to compete successfully with combinatorial chemistry. Today, pharmaceutical companies have to spend approximately US $350 million to develop a new drug. Currently, approaches to improve and accelerate the joint drug discovery and development process are expected to arise mainly from innovation in drug target elucidation and lead finding. Breakthroughs in molecular biology, cell biology, and genetic engineering in the 1980 s gave access to understanding diseases on the molecular or on the gene level. Subsequently, constructing novel target directed screening assay systems of promising therapeutic significance, automation, and miniaturization resulted in HTS approaches changing the industrial drug discovery process drastically. Furthermore, elucidation of the human genome will provide access to a dramatically increased number of new potential drug targets that have to be evaluated for drug discovery. HTS enables the testing of an increasing number of samples. Therefore, new concepts to generate large compound collections with improved structural diversity are desirable.

Asymmetric Triaryldiamines as Thermally Stable Hole Transporting Layers for Organic Light-Emitting Devices

The synthesis of a series of asymmetric triaryldiamines has provided a number of materials with a wide range of thermal, electrochemical, and spectroscopic properties. The asymmetric materials described herein have two different diarylamine groups bound to a 1,4-phenylene or 4,4‘-biphenylene core, i.e., Ar1Ar2N−C6H4−NAr1‘Ar3 or Ar1Ar2N-biphenyl-NAr1‘Ar3, respectively. The diarylamines studied include diphenylamine, phenyl-m-tolylamine, naphthylphenylamine, iminostilbene, iminodibenzyl, and carbazole. These materials were prepared by copper- and palladium-catalyzed coupling of aryl halides and diarylamines. The asymmetry inherent in these compounds prevents these low molecular mass compounds from crystallizing, thus yielding higher thermal stability over that of the symmetric derivatives. In all cases, the asymmetric diamines form stable glasses, with glass transition temperatures up to 125 °C. HOMO levels for these materials, estimated by cyclic voltammetry, show a broad range of values, with oxidation potentials both lower and higher than those of common hole transport materials used in organic light emitting devices.

Structural Aspects of Modification of Polymers with Low-Molecular-Mass Substances

Specific features of polymer modification based on complexation between low-molecular-mass modifying agents and polymers were discussed in terms of structural inhomogeneity of amorphous glassy polymers. Complexation between low-molecular-mass compounds (LMs) and polymer macrochains in structural regions with different packing densities was shown to be responsible for the distribution of LMs between two forms, which are characterized by different energetics of interaction with polymer matrix. The occurrence of such distribution was controlled by chemical structure of LM molecules and local packing of polymer macrochains. This distribution was responsible for a complicated character of molecular dynamics in the polymer/LM systems and mechanical behavior of such materials in whole. The cases, when macroscopic mechanical behavior of as-modified polymers was primarily controlled by the form, in which the modifying agent existed in polymer matrix, were considered. The future development of this direction of polymer modification was discussed and possibilities of its practical application for controlled improvement in mechanical response of polymer materials were outlined.

Rapid methods for screening low molecular mass compounds non-covalently bound to proteins using size exclusion and mass spectrometry applied to inhibitors of human cytomegalovirus protease.

General and rapid methods were developed for determining the extent of non-covalent binding between small molecules and proteins, using the model system of human cytomegalovirus protease and several drug candidates which inhibit the protease by non-covalently binding to it. The assay was performed by off-line coupling of size-exclusion methods with mass spectrometry in the following manner. The protease and inhibitor were incubated together under native conditions and then subjected to separation based on size, by use of a spin column (gel permeation chromatography) and/or a microconcentrator (ultrafiltration). The spin column selectively passed the high molecular mass (M(r)) protease and trapped low M(r) molecules. Alternatively, the microconcentrator passed low M(r) molecules and retained the protease. If the inhibitor bound non-covalently to the protease, both the inhibitor and protease passed through the spin column (or were retained by the microconcentrator). Electrospray ionization mass spectrometry was used to assay the spin column eluate (or the microconcentrator retentate) and to characterize the amounts of protease and inhibitor based on known standards. An advantage of these techniques is that a mixture containing inhibitors can be analyzed in the presence of the protease, and inhibitors with the greatest binding affinity can be identified. Non-covalent binding specificity was demonstrated using spin columns by comparing the binding affinity of inhibitors using several mutants of cytomegalovirus protease. The techniques described are applicable to the rapid screening of compound libraries for selecting substances which bind non-covalently to a known protein.

An improved approximate solution of the Lamm equation for the simultaneous estimation of sedimentation and diffusion coefficients from sedimentation velocity experiments

Sedimentation and diffusion coefficients are important parameters to describe size and shape of macromolecules in solution. The data can be obtained from sedimentation velocity experiments by a nonlinear fitting procedure using approximate solutions for the Lamm equation. Here, we present a modification of such a model function that was originally proposed by Fujita [H. Fujita, Mathematical Theory of Sedimentation Analysis, Wiley, New York, 1962]. The extended model function is well suitable to study low molecular mass compounds. The improvement of this solution given here is based on using an adjustable value for the explicit integration variable, z, the reduced radius. This modification leads to more accurate sedimentation and diffusion coefficients compared to using a constant value of 0.5 as used by Fujita. The advantage of our modification was demonstrated by the analysis of noise-free curves calculated using the finite element method, as well as experimental curves obtained for the peptides angiotensin I and II. The relatively low sedimentation and diffusion coefficients found for both substances indicate that the peptides exist as extended chains of about 3.65 nm (angiotensin I) or 3.04 nm length (angiotensin II) in solution. The lack of higher-order structure of the peptides that was derived also from CD spectra might facilitate receptor binding, and could be one reason for the fast proteolytic digestion of the free peptides.

Solid state 13C NMR and high temperature 1H NMR determination of bulk structural properties for mesophase-containing semi-cokes prepared from coal tar pitch

A series of semi-cokes, containing from virtually 0 to 100% mesophase, were produced from the THF-soluble fraction of a soft coal tar pitch. The mesophase contents were estimated by high temperature in situ 1H NMR and optical microscopy with extremely close agreement being obtained between the two techniques. Quantitative solid state 13C NMR measurements using the single pulse excitation technique indicated that the extent of anisotropy in the pitch is a function of the condensation of the aromatic structure, where isotropic pitches contain 5–6 rings on average, assuming pericondensation, which increases to 9–10 rings for the fully converted mesophase pitches. Characterisation of the pyridine-solubles (PS) and insolubles (PI) from the pitches confirmed that development of mesophase in the coal tar pitch is limited by the loss of low molecular mass compounds, in that the PS contain 5–6 rings throughout the series while the PI, even in largely the initial isotropic state, are as condensed as in the anisotropic pitches.

Transformations of low rank coal by Phanerochaete chrysosporium and other wood-rot fungi

There is a substantial body of evidence that the organic fraction of low rank coal (LRC) is chemically transformed by wood-rot fungi. These fungi and the oxidases they secrete have variously been shown to solubilise, polymerise, depolymerise and decolourise macromolecules derived from LRC. The white-rot fungus, Phanerochaete chrysosporium, is able to depolymerise and decolourise alkali-soluble acid-precipitable LRC macromolecules (AS-coal), converting them to a form not recoverable by alkali washing. Transformation of AS-coal is enhanced in N-limiting media under hyperbaric oxygen and is believed to be due, at least in part, to oxidation by manganese peroxidase (MnP) and lignin peroxidase (LiP). The precise role these enzymes play is not yet clear but enzyme and mutant studies show AS-coal can be both polymerised and depolymerised by MnP and its mimetic Mn(III), without change to its absorbance at 400 nm. LiP decolourises AS-coal without apparently altering its molecular mass. Culture filtrates containing MnP and LiP acting on methylated AS-coal yield an array of low molecular mass moieties. Coal-derived monomers have not been recovered from cultures of P. chrysosporium, consistent with them being taken-up by the fungal cells. This suggests that cellular transformations may permit the diverse catabolic products derived from LRC to be converted to specific low molecular mass compounds in usable yield.

Antiferroelectric and ferrielectric liquid crystalline low molar mass materials and polymers

Novel liquid crystalline Low Molecular Mass (LMM) materials bearing two chiral lactate groups, as well as compounds of like structure to MHPOBC have been synthesized. All the LMM compounds exhibit the SmC*A (antiferroelectric) and/or SmC*gamma (ferrielectric) phases. The mesogens have been incorporated as pendant groups on polymer backbones of three different natures to prepare side chain liquid crystalline copolysiloxanes, homopolysiloxanes and homopolyacrylates. The investigation of the polymers by means of miscibility studies showed that the antiferro- and ferri-electric phases are strongly destabilized in the coposiloxanes and homopolysiloxanes, while in the homopolyacrylates a large temperature range mesophase is found to be miscible with the SmC*A phase. The physical properties of the mesophases and their stability, both for the LMM materials and the polymers, are presented and discussed.

Mass Spectrometry of Low Molecular Mass Solids by Matrix-assisted Laser Desorption/Ionization

Matrix-assisted laser desorption/ionization combined with time-of-flight mass spectrometry (MALDI/TOF-MS) was used for the analysis of low molecular mass compounds. Three classes of molecules were studied: organic acids, salts of oxyanions and amine-based chelating compounds. Mass spectra from samples of citric, propionic, butyric, oxalic and stearic acid; ethylenediaminetetraacetic acid (EDTA), N-(2-hydroxyethyl) ethylenediaminetriacetic acid (HEDTA), ethylenediamine N,N′-diacetic acid (EDDA) and nitrilotriacetic acid (NTA); and sulfate, nitrate, nitrite and phosphate salts were obtained. These species were analyzed alone and as mixtures in both the positive and negative ion modes. The organic acids and oxyanion salts displayed much stronger signals in the negative ion detection mode whereas chelating compounds, which contain basic amine functional groups, yielded stronger signals in the positive ion mode. This implies that detection sensitivity is often better for a particular ion mode in the analysis of small molecules containing limited classes of functional groups. In all analyses, the presence of high concentrations of sodium was found to quench the MALDI signals. To increase the detection sensitivity, some samples were processed through an ion-exchange column to remove sodium ions. This step was found to enhance the signal by two orders of magnitude over untreated samples. © 1997 by John Wiley & Sons, Ltd.

Mass Spectrometric Study of a Specific Derivatization Reaction BetweenN,N-Dimethylformamide Dimethylacetal and the Ethanolamine Moiety of β-Agonistic Drugs

In a study designed to examine the nature of a specific reaction which was shown to occur between the ethanolamine moiety of β-agonists and N,N-dimethylformamide dimethylacetal (DMF-DMA), several mass spectrometric techniques were used to identify the main reaction intermediates and/or products. In particular, the use of fast atom bombardment (FAB) ionization made the study of polar and thermosensitive low molecular mass compounds possible. High-resolution (R≊10000) and linked-scan experiments performed on reverse-geometry double-focusing mass spectrometers were helpful to confirm structural hypotheses. From this study, it appeared that the secondary amine of the ethanolamine group of β-agonists can react with DMF-DMA (DMA being the active part of the reagent) to give mainly an ethanolamide intermediate. Apart from this ethanolamide intermediate, three reaction products which are partly due to a dehydration step of the ethanolamide that occurs at high temperatures were identified. Two of them are the results of a cleavage of the side-chain which gives a styrene and an isocyanate derivative; the third one corresponds to an azetidine derivative stemming from a side-chain cyclization. These unexpected findings may be of great help for the survey of β-agonist residues. Actually, the above-mentioned reaction products could be easily detected and identified in biological samples by means of gas chromatography (Ross injector, 280°C) coupled to mass spectrometry (GC/MS); the side-chain cleavage observed during the formation of the styrene and isocyanate derivatives was useful to broaden the range of detection and to facilitate the identification of new analogues. On the other hand, the analysis of ethanolamide intermediates via liquid or thin-layer chromatography coupled to FABMS would also appear to offer valuable analytical solutions. © John Wiley & Sons, Ltd.

Potential of lactic acid bacteria and novel antimicrobials against Gram-negative bacteria

Lactic acid bacteria (LAB) produce a variety of low molecular mass compounds including acids, alcohols, carbon dioxide, diacetyl, hydrogen peroxide and other metabolites. Many of these metabolites have a broad activity spectrum against other species, and their production is largely affected by the food matrix itself. Bacteriocins inhibit only closely related species or other Gram-positive microorganisms. Several recent reports have described the synergistic effects between various antimicrobials, thus widening their application potential. New insights with respect to the effective control of Gram-negative bacteria using potential antibacterial agents should be realized by investigating possible mechanisms that either disrupt or bypass the permeability barrier function of the outer membrane.

Molecular mass determination by sedimentation velocity experiments and direct fitting of the concentration profiles

A new method for the direct molecular mass determination from sedimentation velocity experiments is presented. It is based on a nonlinear least squares fitting procedure of the concentration profiles and simultaneous estimation of the sedimentation and diffusion coefficients using approximate solutions of the Lamm equation. A computer program, LAMM, was written by using five different model functions derived by Fujita (1962, 1975) to describe the sedimentation of macromolecules during centrifugation. To compare the usefulness of these equations for the analysis of hydrodynamic results, the approach was tested on data sets of Claverie simulations as well as experimental curves of some proteins. A modification for one of the model functions is suggested, leading to more reliable sedimentation and diffusion coefficients estimated by the fitting procedure. The method seems useful for the rapid molecular mass determination of proteins larger than 10 kDa. One of the equations of the Archibald type is also suitable for compounds of low molecular mass, probably less than 10 kDa, because this model function requires neither the plateau region nor a meniscus free of solute.

Analysis of glycosaminoglycans and their oligosaccharide fragments by capillary electrophoresis.

Glycosaminoglycans are high molecular mass polymers found in living tissues. They are degraded by site specific enzymes to oligosaccharide fragments. Polymers and oligomers all carry negative charge and are found as salts soluble in water. Consequently, capillary electrophoresis has come to the fore as an analytical technique in this field. This review discusses application of the technique to the chondroitin-dermatan, heparin and hyaluronan groups of polymer and the derived oligosaccharides. Direct and indirect UV detection are discussed as well as detection methods involving precolumn derivatization. Capillary electrophoresis has found use in the characterisation of heparin and in following the changes in chondroitin and hyaluronan during the onset of arthritic disease in humans. Some glycosaminoglycans have been used as asymmetric anions in the separation of enantiomers of low molecular mass compounds by capillary electrophoresis.

The 25 degrees-36 degrees region of the Bacillus subtilis chromosome: determination of the sequence of a 146 kb segment and identification of 113 genes.

We determined a 146 kb contiguous sequence at the 25 degrees-36 degrees region of the Bacillus subtilis chromosome containing the amyE-srfA segment. Among the 113 ORFs identified, 33 are already known. functions were assigned to 38 ORFs by a search of non-redundant protein sequence data banks and those of 16 ORFs were suggested through significant similarity with reported sequences. The amino acid sequences of 13 of the ORfs were similar to proteins of unknown function of Escherichia coli, Haemophilus influenzae and other species. We did not find similarities for 29 ORFs to any known proteins. The 146 kb region is rich in enzymes (35 ORFs) related to the metabolism of low molecular mass compounds and five genes for surfactin production occupy about 26 kb of the region.

Removal of Hazardous Substances from Water Using Ultrafiltration in Conjunction with Soluble Polymers

The applications of separation techniques using ultrafiltration in connection with functional soluble polymers for the removal of environmentally relevant and toxic substances from waters are reviewed. The types of interactions of the soluble polymers with low molecular mass compounds, the criteria for selecting the appropriate polymeric agents, and the binding conditions are discussed. Several factors influencing the separation of the target substances such as membrane type, solution composition, synergism, polymer adsorption, deformation of macromolecules, and hydrodynamics are evaluated and highlighted. Chemical, electrochemical, and thermal regeneration aspects are also covered. Finally, an overview on varius preparative and analytical application examples is presented.