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At least 19 recordsLinked to original sources
PubMed1978

Hydrogen-deuterium substitution and solvent effects on the nitrogen-15 nuclear magnetic resonance of gramicidin S: evaluation of secondary structure.

Complete assignments of nitrogen-15 resonances of gramicidin S have been made in dimethyl sulfoxide, trifluoroethanol, and in a solvent mixture of dimethyl sulfoxide (50%) and methanol (50%). The assignments are achieved by utilizing the secondary structure of gramicidin S, by comparing the nitrogen-15 spectrum of gramicidin S with that of di-N-methylphenylalanine-gramicidin S and by taking into account the distinguishable value of nitrogen-15 chemical shift for valine in model compounds. Deuterium substitution for labile peptide protons was performed to delineate solvent shielded and deshielded peptide nitrogens and to substantiate further the signal assignments. The solvent titration on going from dimethyl sulfoxide to trifluoroethanol was also performed and shown to have a large deshielding effect on the peptide nitrogen whose corresponding peptide carbonyl, within the peptide moiety, was accessible to the trifluroethanol solvent.

Deuterium↗
PubMed2026

Evaluating Substitution of Hazardous Solvents in USP Monograph HPLC Methods.

BACKGROUND: Hazardous solvents, such as dichloromethane (DCM), n-hexane, and acetonitrile (ACN), are widely used in HPLC methods, posing significant health and environmental risks. OBJECTIVE: To evaluate the feasibility and impact of substituting hazardous solvents with greener alternatives in USP monograph methods. METHODS: Six high-impact solvents were identified from USP-NF monographs. Two representative monographs per solvent were selected. Substitution strategies were assessed, and performance was compared using system suitability and sample acceptance criteria. Greenness improvement was evaluated using the Analytical GREEnness (AGREE) metric. RESULTS: Performance remained equivalent across all twelve substitution cases. In almost every instance, only the mobile phase required modification, either by direct substitution or by adjusting the solvent-to-buffer ratio, except for one case that required a minor adjustment in column temperature. The AGREE Greenness metric increased by 18-65% in ten out of twelve cases; for n-hexane, improvements were modest at just 6% when replaced with n-heptane but exceeded 40% when substituted with supercritical CO₂. CONCLUSIONS: Greener solvents are highly likely to replace hazardous solvents used in compendial chromatography methods without loss of performance. HIGHLIGHTS: Demonstrated performance equivalency for greener solvent substitutions; Quantified greenness improvements using AGREE; Discussed strategies to implement greener solvents in USP monograph methods.

HPLC↗
PubMed2026

Evaluation of the effects of domestic tomato processing on biopesticide residue using natural deep eutectic solvents (NADES) extractions.

The present study evaluated the fate of fourteen botanical biopesticides in processed tomato samples. Various processing methods were employed, including washing, dehydration, and the preparation of juice and sauce. The extraction was performed using more sustainable techniques, aimed at minimizing the environmental impact of conventional organic solvents by substituting them with natural deep eutectic solvents (NADES). Solid-liquid extraction (SLE) and dispersive liquid-liquid microextraction with solidification of floating organic drop (DLLME-SFOD) were utilized for solid and liquid tomato samples, respectively. The NADES used was choline chloride:2,3-butanediol (ChClBt) at a 1:4 molar ratio for both techniques, resulting in recovery values ranging from 69.2 to 106.2% for SLE, and extraction efficiencies reaching up to 46.2% for DLLME-SFOD. The impact of these processes was evaluated employing the processing factor (PF), yielding PF values of less than 1 in all cases. Compounds as pyrethrins, azadirachtin, and rotenone persisted after processing, posing a potential consumer risk.

Solanum lycopersicum↗
PubMed1977

Cytochemical and ultrastructural studies on the synaptonemal complex of rat spermatocytes.

The effects of several dehydration treatments on the synaptonemal complex (SC), histone solubility in 2.0 M NaCl, and histone-DNA interaction in unfixed rat spermatocytes were evaluated. Freeze substitution with ethanol or dehydration with polyethylene glygol resulted in loss of the SC, preservation of histone solubility and DNA-histone salt linkages. Dehydration with ethylene gylcol or hexylene glycol resulted in preservation of SC with a clear delineation of attachment of the chromatin fibrils to the lateral elements, but a loss of histone solubility and histone-DNA linkages. Dehydration to a fifty percent concentration with glycerol with completion of dehydration with ethylene glycol had the same effect but also resulted in an even distribution of chromatin fibrils. Dehydration with glycerol alone resulted in clumping of chromatin and loss of SC structure, histone solubility and histone-DNA linkages. Partial dehydration to a fifty percent concentration with these three solvents followed by freeze substitution with ethanol resulted in the loss of SC structure and histone solubility but the preservation of histone-DNA linkages. It is likely that these nonaqueous solvents affected the histone hydrophobic groups and thereby altered histone conformation and interactions. These alterations, depending on the treatment used, resulted in the loss or preservation of SC, histone solubility and histone-DNA interactions thereby indicating that the hydrophobic interactions of the histones are crucial for the preservation of these feature of meiotic chromosomes. These results also demonstrate that neither does the preservation of the histone-DNA salt linkages suffice for the preservation of the SC nor does their disruption necessarily result in its loss. The lysine-rich histones, particularly that one unique to meiotic cells, may through their interactions play a crucial role in SC structure.

Animals↗
PubMed1977

Solvent denaturation of globular proteins: unfolding by the monoalkyl- and dialkyl-substituted formamides and ureas.

The effects of the monoalkyl and dialkyl-substituted formamide series of denaturants on the native conformation of sperm whale myoglobin, horse heart cytochrome c, and Glycera dibranciata (single chain) hemoglobin have been investigated by spectral measurements in the Soret region (409 and 422 nm) and optical rotation measurements (265nm). The effectiveness of these two classes of protein denaturants is similar to the other straight-chain compounds of the urea, amide, and alcohol classes, examined in previous investigations from our laboratory. Their denaturing effectiveness is found to increase with increasing chain length or hydrocarbon content of the substituent alkyl groups. Application of the Peller and Flory equation to the denaturation data of the formamides shows that both the polar and the nonpolar group contributions to the protein-denaturant interactions have to be taken into account in order to correctly predict the observed denaturation midpoints. Additivity of the hydrophobic, KHø, and the polar, Kp, group contributions to the binding constants, KB = nKHø + Kp, with n = 1 or 2 for the mono- of the di-alkyl substituted denaturants gave best account of the experimental data. The KHø values used were based on free energy transfer data of various alkyl groups or the Scheraga-Nemethy theory of hydrophobic bonding. The assumption of group contributions of the denaturant to KB were also applied to the denaturation data of the unsubstituted amides and some examples of the monoalkyl and symmetrically substituted dialkyl ureas, taken from the literature.

Cytochrome c Group↗
PubMed1975

On the interaction of 3,4,5,6-tetrahydrouridine with human liver cytidine deaminase.

In contrast to the rapid inhibition of bacterial cytidine deaminase by 3,4,5,6-tetrahydrouridine, the onset of inhibition of the enzyme from human liver was found to be relatively slow. Inhibition was found to be reversible, and the corrected rate constants for binding (kon = 2.4 x 10(4) M-1 sec-1) and release (koff = 5.6 x 10(-4) sec-1) were in reasonable agreement with a Ki value (2.9 x 10(-8) M) measured separately under steady-state conditions, which was several orders of magnitude lower than estimates previously reported in the literature. Rates of binding and release of this potential transition state analogue were not appreciably affected by the substitution of deuterium oxide for solvent water. The slow onset of inhibition, which was also observed for cytidine deaminase from HeLa cells, suggests that structural reorganization precedes the formation of a stable enzyme-inhibitor complex. 6-Azacytidine, which favors a "high-anti" configuration at the glycosidic bond, was found to be active as a substrate for cytidine deaminase, with a turnover number exceeding that of cytidine. 2,2'-Anhydro-1-beta-D-arabinofuranosylcytosine, which is restricted to the "syn" configuration, was found to be without activity as a substrate or an inhibitor.

Azacitidine↗
PubMed1976

Structural studies of insulin and insulin derivatives using various immunologic indicators and antibody populations.

These studies suggest that the immunologic indicator in the radioimmune assay, 125I-iodoinsulin, selects antibody populations from within the antiserum that interact with determinants distant from the solvent surface on the insulin molecule to which iodine is substituted. Evidence is presented that the connecting peptide of proinsulin is in close proximity to regions on the solvent surface of the A-chain of insulin that include the tyrosyl residues at A-14 and A-19. A marked immunologic cross-reaction between derivatives of insulin with perturbations in the regions of tyrosyl A-14 and A-19 was noted in the radioimmune assay employing desalanine-(B-30)-desasparagine-(A-21)-insulin antiserum. This observation is consistent with the presence of a restricted population of antibodies in such antisera that is directed toward immunologic determinants in or near the insulin dimer site. The apparent immunologic activity of insulin derivatives depends on which antibody populations from the antiserum pool can react with the immunologic indicatory employed on the one hand and on the composition of antibodies in that antiserum on the other. These studies indicate that the specificity of antibody populations in a given antiserum can be identified and their levels quantitated with several assay systems, each employing one of a variety of indicators.

Amino Acid Sequence↗
PubMed1976

Synthetic flavinyl peptides related to the active site of mitochondrial monoamine oxidase II. Fluorescence properties.

The fluorescence properties of various 8alpha-sulfur-linked flavinyl peptides and related flavin analogues were investigated as the pH solvent, temperature, and flavin concentration were varied. Substitution in the 8alpha position by a thioether-linked peptide brings about a marked quenching of fluorescence (up to 98% in water), a slight bathochromic shift and broadening of the fluorescence emission spectra, and a slight decrease in the fluorescence lifetimes. Oxidation of the thioether function to a sulfone partially releases this fluorescence quenching without further changes in the fluorescence emission spectra. The primary effect on the fluorescence intensity is due to an interaction between the nonbonding electrons of the thioether, the hydrogen-bonding, polar solvent, and the isoalloxazine ring. Dissolving these flavinyl peptides in nonaqueous solvents increases the fluorescence intensity as much as 20-fold. A secondary effect on flavinyl fluorescence can be attributed to a collisional quenching by the vicinal tyrosyl residue within tyrosine-containing flavinyl peptides. The fluorescence properties provide further confirmation of the identity of the synthetic and naturally obtained flavinyl peptides and of the interaction between the free-hydroxyl functions of the ribityl side chain and the thioether.

Binding Sites↗
PubMed1977

Procedure for the embedment and ultrastructural visualization of cells cultured on plastic microtest plates.

The polystyrene Microtest plate has served as an excellent means of quantitation in the interaction of immunological, chemotherapeutic and radiobiological treatments with cultured cells. In order to assess the accompanying ultrastructural changes it was necessary to develop a technique which allowed cells grown in the wells of the plates to be embedded for electron microscopy. Conventional epoxy resin embedding techniques require the use of propylene oxide as a clearing agent. Unfortunately propylene oxide is a solvent of the polystyrene plates. By the substitution of absolute ethanol for propylene oxide, toluidine blue staining during the procedure and other preparative techniques it was feasible to prepare reacted cells grown in Microtest plates for electron microscopy.

Cells, Cultured↗
PubMed1979

Taste responses to deuterium oxide.

Substitution of deuterium oxide (D2O) as the solvent in taste stimuli elicits neural responses which differ from ordinary water (H2O). Previous reports have shown that D2O is toxic to many animals and rats avoid drinking it when offered H2O simultaneously. In the current study, summated responses were recorded from the chorda tympani nerves of rats after NaCl, KCl, sucrose and quinine were applied to the tongue in solutions of either D2O or H2O. Both solvents were used as the adapting or rinse solution in separate series. On tongues adapted to H2O, D2O elicited mean responses which were equivalent to 29% of the response to 0.1 M NaCl. The threshold concentration of D2O in H2O was between 25% and 50%. Solutes in D2O yielded responses which were greater than corresponding solutions of H2O when adapting rinse was H2O. Adaptation to D2O diminished the responses to D2O solutions of NaCl, KCl and sucrose but not quinine. This observation suggests that some portion of the augmented response to stimuli in D2O is due to the solvent itself. The taste of water has been examined by both electrophysiological methods and by behavior, but none of the mechanisms espoused for its effect seem adequate to explain the response to D2O. Water structure at the interface between molecular components of the cell membrane and the bulk phase of the surrounding medium is considered as a locus for disparity in the taste responses to D2O and H2O in the rat.

Animals↗
PubMed1975

[127-I]- or carrier-free [125-I]monoiodoinsulin.

Insulin was enzymatically moniodinated with 127-I or 125-I, and an improved method of purification by anion exchange chromatography was employed. (127-I)Monoiodoinsulin was identified by spectrophotometric analysis and its molar extinction coefficient determined to be 6.31 times 10-3 M-1 cm minus 1. The observed specific activity of carrier-free (125-I)monoidoinsulin was close to the theoretical value (378mCi/mg). The monoiodotyrosyl residue of monoidoinsulin was shown to be solvent-exposed. The ionic properties of the substituted hormone were altered at pH values close to the pK of monoiodotyrosine (8.85), but the pI was unchanged (5.65). (127-I)Monoiodoinsulin formed rhombohedral crystals and co-crystallized with native insulin. Monoidoinsulin was indistinguishable from insulin with respect to binding to two out of three guinea pig anti-insulin sera, to binding to IM9 cultured human lymphocytes, and to binding to isolated rat hepatocyte plasma membranes. The potency of monoidoinsulin was not statistically different from that of insulin in the rat fat cell bioassay and in the mouse convulsion assay. An insulin-degrading enzyme extracted from rat liver degraded monoiodoinsulin less readily than native insulin; monoiodoinsulin was a competitive inhibitor of insulin degradation, and the Km values were 30 nM AND 78 NM for monoidoinsulin and native insulin, respectively. It is concluded that monoidination does not markedly alter the three-dimensional structure of the molecule and that only a few sensitive biological systems are able to distinguish the monoidinated from the native hormone.

Adipose Tissue↗
PubMed1979

An in vitro model for assessing drug availability from lipophilic vehicles.

An apparatus for studying the rate of release of a solute from a water-immiscible solvent into an acidic, aqueous liquid, followed by permeation through a simulated lipid membrane, is described. The object was to imitate the absorption of a drug after oral administration in a soft gelatin capsule. Rate constants of transfer were determined for a series of substituted benzoic acids, using octanol and isopropyl myristate as solvents. The quantity of solute in the acidic phase did not correlate with the solvent-water distribution coefficient, but was linearly related to the rate constant for transfer from solvent to water. A dynamic system was therefore postulated, rather than one in which the two phases are in equilibrium. In vivo studies on two of the solutes confirmed the in vitro observations. No simple relationship could be derived between blood concentrations and any in vitro parameter, but the rank order of magnitude of the blood concentrations fitted the postulated dynamic mechanism.

Benzoates↗
PubMed1975

Interpretation of the doublet at 850 and 830 cm-1 in the Raman spectra of tyrosyl residues in proteins and certain model compounds.

The doublet at 850 and 830 cm-1 in the Raman spectra of proteins containing tyrosyl residues has been examined as to its origin and the relation of its components to the environment of the phenyl ring, the state of the phenolic hydroxyl group, and the conformation of the amino acid backbone. Raman spectral studies on numerous model molecules related to tyrosine, including certain deuterium derivatives, show that the doublet is due to Fermi resonance between the ring-breathing vibration and the overtone of an out-of-plane ring-bending vibration of the para-substituted benzenes. Further examination of the effects of pH and solvents on the Fermi doublet and of the crystallographic data demonstrates that the intensity ratio of the two components depends on changes in the relative frequencies of the two vibrations. These in turn are found to be sensitive to the nature of the hydrogen bonding of the phenolic hydroxyl group of its ionization, but much less so to the environment of the phenyl ring and the conformation of the amino acid backbone. By use of the relative intensities of the doublet in model systems where the phenolic hydroxyl group is strongly hydrogen-bonded, weakly hydrogen-bonded, free or ionized, the reported Raman intensities of the doublets observed in the Raman spectra of several proteins have been interpreted. The results are compared with those obtained by other techniques.

Hydrogen Bonding↗
PubMed1976

Biotransformation of drugs: quantitative structure-activity relationships for barbiturates, tertiary amines, and substituted imidazoles.

When using free energy-related physicochemical parameters, stimulation of NADPH oxidation by barbiturates and the N-oxidation of tertiary amines was found to be primarily dependent upon the lipophilic character of the substrates as measured by log P, where P is the partition coefficient from either 1-octanol-water or corn oil-water solvent systems. In contrast, the inhibition of epoxidation of aldrin by a series of substituted imidazoles appears to be much more dependent on electronic (sigma) and steric (Es) effects of the inhibitors.

Aldrin↗
PubMed1975

Formaldehyde as a probe of DNA structure. I. Reaction with exocyclic amino groups of DNA bases.

A comprehensive description is given of both the equilibrium and the kinetic aspects of the reaction of formaldehyde with the exocyclic amino groups of derivatives of adenine, cytosine, and guanine; the results extend previous data in the literature to the point where formaldehyde can now be used as a quantitative probe of DNA structure and dynamic behavior. The main results are: (i) the reaction product is proven (by isolation followed by nuclear magnetic resonance (NMR) spectroscopy) to be a hydroxymethyl group; (ii) a dihydroxymethyl adduct is shown to exist at high formaldehyde concentrations; (iii) equilibrium constants at 25 degrees for forming the monoadduct with adenine and cytosine compounds are about 12 (M-1), while those for forming the dihydroxymethyl adduct are about 0.4 (M-1); (iv) the standard enthalpies for forming the monoadducts with adenine and cytosine compounds are about minus 4 to minus 6 kcal/mol; (v) indirect evidence is presented suggesting that a monohydroxymethyl group on adenine or cytosine derivatives exists preferentially as that rotational isomer which blocks Watson-Crick hydrogen bonding; (vi) in derivatives of guanine, it is shown that the N-1 endocyclic imino group can react with formaldehyde, as well as the amino group, the overall equilibrium constant being about 6 (M-1); (vii) all rate constants are reported, as well as their response to temperature, pH, and various solvent additives known to perturb DNA structure; (viii) using a series of substituted anilines, a linear free energy relation is obtained between the logarithm of both the forward and the reverse rate constant for the formaldehyde reaction and the amine pK, over a range of 10-8 change in amie basicity; (ix) using this relation, the pK's for protonating the nucleoside amino groups are estimated to lie in the range of minus 2 to minus 4; (x) a reaction mechanism is proposed; and (xi) some implications of these results forpolynucleotide studies are discussed.

Adenine↗
PubMed1979

1,N6-Etheno-2-aza-adenosine 3', 5'-cyclic phosphate: human erythrocyte membrane binding and activation of membrane protein kinase.

The relative efficiency of 1,N6-etheno-2aza-adenosine 3', 5'-monophosphate (cyclic 2-aza-epsilon AMP), 1,N6-etenoadenosine 3', 5'-monophosphate (cyclic epsilon AMP) and cyclic AMP in activation of membrane protein kinase and binding to membrane was examined using isolated membranes from human erythrocytes. Cyclic 2-aza-epsilon AMP was 81% as active as cyclic AMP in erythrocyte membrane binding and activation of membrane protein kinase. On the other hand, cyclic epsilon AMP was 37% as active toward membrane protein kinase and 29% toward membrane cyclic AMP binding. Since we have previously shown that the fluorescence of cyclic 2-aza-epsilon AMP is highly sensitive to the polarity of solvents, the high efficiency of cyclic 2-aza-epsilon AMP to substitute for cyclic amp suggests that it may be a suitable microenvironmental fluorescent probe for cyclic AMP binding sites.

Aza Compounds↗
PubMedDate not supplied

Influence of ions and chelating agents on the haemolymphacetylcholinesterase of Mytilus edulis.

By use of different inhibitors as well as atomic absorption spectrophotometry it has been shown that the haemolymph-acetylcholinesterase (E. c. 3.1.1.7) of the sea mussel Mytilus edulis is a metalloprotein containing 2,95 Fe2+-ions per subunit. All inhibitors used (1,10-phenanthroline, salicylic aldehyde, 2,2'-dipyridyl, 8-hydroxyquinoline) showed a non-competitive inhibition, which was not pH-dependent. Some divalent cations caused a marked increase of the enzyme activity, some heavy metals inhibited the enzyme almost completely; monovalent inorganic cations did not influence the enzyme at all. Besides NaF and Na2SiF6, which showed a non-competitive inhibition comparable to the inhibition observed with the chelating agents, and NaN3, whose mode of action was not identifiable, no inhibition by different mono- and divalent inorganic anions was to be observed. Ammonium ions caused no enzyme inhibition, but length the inhibition power of substituted ammonium ions increased with an increasing C-chain. The influence of some organic solvents on the enzyme activity is demonstrated.

Acetylcholinesterase↗
PubMedDate not supplied

Tautomerism of isoguanosine and solvent-induced keto-enol equilibrium.

Ultraviolet and infrared absorption spectroscopy, in aqueous and non-aqueous media, have been employed to study the tautomerism of 9-substituted isoguanines, including the nucleoside isoguanosine. With the aid of a series of model compounds, it was shown that 9-substituted isoguanines, and isoguanosine, in aqueous medium are predominantly in the form N (1) H, 2-keto-6-amino. In dioxane solution the tautomeric equilibrium is shifted in the direction of the enol form. The shift towards this form is accentuated for those analogues in which the exocyclic amino group is methylated. With the aid of N6,N6, 9-trimethylisoguanine, and 9-octyl analogue, the tautomeric constant was studied as a function of concentration, temperature, and solvent polarity, and the results applied to evaluate the tautomeric equilibria of 9-methylisoguanine and isoguanosine as a function of these variables. In general the enol form is favoured by a decrease in solvent polarity, by a decrease in concentration in dioxane, or an increase in temperature in chloroform solution. Syntheses are described for several N6 amino and methylamino derivatives of 2-methoxy-9-methylpurine, and 3-methyl-5-oxo-7,8-dihydroimidazo (2,1-i) purine, which served as an analogue of the unavailable 1,9-dimethylisoguanine.

Chemical Phenomena↗