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Dileep Kumar - One of the best experts on this subject based on the ideXlab platform.
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Kinetic study of the metal-dipeptide complex with ninhydrin facilitated by gemini (m-s-m) surfactant micelles
Scientific Reports, 2020Co-Authors: Naved Azum, Dileep KumarAbstract:The three Gemini (m-s-m; m (head group) = 16 and s (spacer) = 4, 5, 6) surfactants have been synthesized and their impact on reaction of zinc(II)-Glycylleucine complex ([Zn(II)-Gly-Leu]^+) and ninhydrin were studied at temperature (343 K) and pH (5.0) using spectroscopic method. Influence of several factors, viz., [Zn(II)-Gly-Leu]^+, [ninhydrin], temperature and pH were also carried out on title reaction in geminis. Rates of reaction are the first-order path in concentration of [Zn(II)-Gly-Leu]^+ complex and fractional order path in concentration of ninhydrin. The catalysis of gemini 16-s-16 surfactant micelles was investigated below and above their critical micelle concentration (cmc) value and detailed elaboration were provided in the text. In the present case, rate constants, k_ψ, increased on increasing geminis ([gemini] are below their cmc, region I) and stayed nearly constant (region II). The shape of (region I and II) surfactants ([gemini] = 0 to 400 × 10^−5 mol dm^−3) are similar to a cetyltrimethylammonium bromide, CTAB (single hydrophilic head group and hydrophobic part). Later, a sharp increment in rate was observed with higher [gemini] (region III, (Fig. 5). The study was catalyzed and accelerated quite enough by geminis (at concentrations below their cmc) compared to aqueous. An appropriate mechanism has been proposed for accounting for the distribution of reactants between aqueous and micellar pseudo phases. Resulting kinetic data were used to determine the binding constants of micelle-substrate (K_B) and micelle-ninhydrin (K_Nin).
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Influence of dimeric gemini surfactant micelles on the study of nickel-Glycylleucine dipeptide and ninhydrin
Journal of Dispersion Science and Technology, 2019Co-Authors: Dileep Kumar, Malik Abdul RubAbstract:Influence of dimeric gemini surfactant micelles on the study of nickel-Glycylleucine dipeptide ([Ni(II)-Gly-Leu]+) and ninhydrin was carried out in the temperature ranging from 333 K to 353 K. An U...
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Role of cetyltrimethylammonium bromide (CTAB) surfactant micelles on kinetics of [Zn(II)-Gly-Leu]+ and ninhydrin
Journal of Molecular Liquids, 2019Co-Authors: Dileep Kumar, Malik Abdul RubAbstract:Abstract At present work, role of cetyltrimethylammonium bromide (CTAB) surfactant micelles on kinetics of zinc-Glycylleucine [Zn(II)-Gly-Leu]+ and ninhydrin has been studied. The effect of different variables, viz., ninhydrin, [Zn(II)-Gly-Leu]+ complex, temperature and pH was also undertaken on the title reaction. Role of CTAB on kinetics of complex and ninhydrin has been carried out using spectrophotometric technique. CTAB was observed more efficient for the [Zn(II)-Gly-Leu]+ and ninhydrin reaction than aqueous. The rate constant kψ-values enhanced with increase in [CTAB] from 0 to 50 mol dm−3 and further increase has a slow decrease in rate. Conductometric technique was used to evaluate critical micelle concentration (cmc) of surfactant. The relationship of rate constant (kψ) with CTAB concentration was discussed and described in sufficient details. Analysis of kinetic data was rationalized in terms of model of surfactant micelles (pseudo-phase). Various parameters have also been evaluated including thermodynamic and binding constant.
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Studies of interaction between ninhydrin and Gly-Leu dipeptide: Influence of cationic surfactants (m-s-m type Gemini)
Journal of Molecular Liquids, 2018Co-Authors: Dileep Kumar, Malik Abdul RubAbstract:Abstract Herein, we have reported the studies of interaction between ninhydrin and Glycylleucine (Gly-Leu) dipeptide in cationic Gemini surfactants (m-s-m; m = 16; s = 4, 5, 6) by using spectrophotometric technique. The rate constant values, kψ, were determined at different temperatures and pH. The effect of concentration of reactants and surfactants was also carried out on the title reaction. It was also observed that the reaction was accelerated and catalyzed by 16-s-16 Gemini surfactants even at low critical micelle concentration (cmc) value of surfactants. The variation of Gemini surfactants on the reaction of ninhydrin with Glycylleucine has been analyzed with the help pseudo-phase model of surfactants proposed by Menger and Portnoy and developed by Bunton. The binding constants for reactants (ninhydrin and Gly-Leu) have been computed using a computer based program.
Malik Abdul Rub - One of the best experts on this subject based on the ideXlab platform.
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Influence of dimeric gemini surfactant micelles on the study of nickel-Glycylleucine dipeptide and ninhydrin
Journal of Dispersion Science and Technology, 2019Co-Authors: Dileep Kumar, Malik Abdul RubAbstract:Influence of dimeric gemini surfactant micelles on the study of nickel-Glycylleucine dipeptide ([Ni(II)-Gly-Leu]+) and ninhydrin was carried out in the temperature ranging from 333 K to 353 K. An U...
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Role of cetyltrimethylammonium bromide (CTAB) surfactant micelles on kinetics of [Zn(II)-Gly-Leu]+ and ninhydrin
Journal of Molecular Liquids, 2019Co-Authors: Dileep Kumar, Malik Abdul RubAbstract:Abstract At present work, role of cetyltrimethylammonium bromide (CTAB) surfactant micelles on kinetics of zinc-Glycylleucine [Zn(II)-Gly-Leu]+ and ninhydrin has been studied. The effect of different variables, viz., ninhydrin, [Zn(II)-Gly-Leu]+ complex, temperature and pH was also undertaken on the title reaction. Role of CTAB on kinetics of complex and ninhydrin has been carried out using spectrophotometric technique. CTAB was observed more efficient for the [Zn(II)-Gly-Leu]+ and ninhydrin reaction than aqueous. The rate constant kψ-values enhanced with increase in [CTAB] from 0 to 50 mol dm−3 and further increase has a slow decrease in rate. Conductometric technique was used to evaluate critical micelle concentration (cmc) of surfactant. The relationship of rate constant (kψ) with CTAB concentration was discussed and described in sufficient details. Analysis of kinetic data was rationalized in terms of model of surfactant micelles (pseudo-phase). Various parameters have also been evaluated including thermodynamic and binding constant.
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Studies of interaction between ninhydrin and Gly-Leu dipeptide: Influence of cationic surfactants (m-s-m type Gemini)
Journal of Molecular Liquids, 2018Co-Authors: Dileep Kumar, Malik Abdul RubAbstract:Abstract Herein, we have reported the studies of interaction between ninhydrin and Glycylleucine (Gly-Leu) dipeptide in cationic Gemini surfactants (m-s-m; m = 16; s = 4, 5, 6) by using spectrophotometric technique. The rate constant values, kψ, were determined at different temperatures and pH. The effect of concentration of reactants and surfactants was also carried out on the title reaction. It was also observed that the reaction was accelerated and catalyzed by 16-s-16 Gemini surfactants even at low critical micelle concentration (cmc) value of surfactants. The variation of Gemini surfactants on the reaction of ninhydrin with Glycylleucine has been analyzed with the help pseudo-phase model of surfactants proposed by Menger and Portnoy and developed by Bunton. The binding constants for reactants (ninhydrin and Gly-Leu) have been computed using a computer based program.
K. Schümann - One of the best experts on this subject based on the ideXlab platform.
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Longitudinal Pattern of Enzymatic and Absorptive Functions in the Small Intestine of Rats After Short-Term Exposure to Dietary Cadmium Chloride
Archives of Environmental Contamination and Toxicology, 1999Co-Authors: B. Elsenhans, G. Hunder, G. Strugala, K. SchümannAbstract:In vitro and in situ findings suggest an impairment of digestive and absorptive functions in the small intestine by enteral cadmium salts. In the rat, diets with up to 1 mmol Cd/kg are well tolerated, however, so that the impairment might not be this drastic or compensated by adaptive changes. To elucidate whether small intestinal functions are altered, we studied the effect of dietary cadmium on the longitudinal pattern of mucosal enzymes and the in vitro uptake of methyl α-D-glucoside in the small intestine of female rats. Three groups of rats were employed, a control group and two groups receiving dietary CdCl_2 either at 0.3 or 1.0 mmol Cd/kg of diet. Rats were killed after 1 week of feeding. The entire small intestine was removed, rinsed with ice-cold saline and divided into 12 segments of equal length. Mucosal scrapings from each segment were used to measure mucosal cadmium levels, sucrase, lactase, alkaline phosphatase, Glycylleucine-hydrolase, and diamine oxidase activities. Sugar uptake was determined in vitro in all segments using everted rings tissue accumulation method. Although cadmium levels in the mucosa were high (>100 ng Cd/mg protein or >100 μmol Cd/kg WW) most enzyme activities were only slightly changed. When significant decreases in activity were detected, they were only observed in the proximal small intestine. Sugar uptake was also impaired only in proximal segments, the maximal transport capacity was reduced by approximately 20%. These findings suggest that cadmium even at dietary levels of 1 mmol/kg do not lead to a drastic impairment of digestive and absorptive functions in the small intestine and that in the rat presently observed, mostly proximal impairments are easily compensated by unaltered distal functions. Certainly, absorption of micronutrients, for which an impaired proximal function cannot be compensated, e.g. iron, might be critical in this respect.
Karl Lohner - One of the best experts on this subject based on the ideXlab platform.
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Membrane Thinning Is Not A Unique Signal Of Pore Formation By Antimicrobial Peptides
Biophysical Journal, 2009Co-Authors: Georg Pabst, Sabine Danner-pongratz, Karl Lohner, Stephan L. Grage, Weiguo Jing, Anne S. Ulrich, Anthony Watts, Andrea HickelAbstract:We have observed a hydrocarbon chain length dependent perturbation of saturated acyl chain phosphatidylglycerol bilayers by the antimicrobial peptide peptidyl-Glycylleucine-carboxyamide (PGLa) using X-ray diffraction, solid-state 2H-NMR, differential scanning calorimetry and dilatometry. In the gel phase, PGLa assumes a surface alignment and induces a quasi-interdigitated phase, previously reported also for other peptides. This effect is most pronounced for C18 phosphatidylglycerol. Above the lipid chain melting transition, in the fluid phase, the PGLa helix inserts into the membrane above a certain threshold concentration. In this case we found an increase of the membrane thickness and NMR order parameter for C14 and C16 phosphatidylglycerol bilayers, though not for C18. The data is best understood in terms of a close hydrophobic match between the C18 bilayer core and the peptide length when PGLa is inserted with its helical axis normal to the bilayer surface. The C16 acyl chains appear to stretch in order to accommodate PGLa, whereas tilting within the bilayer seems to be energetically favorable for the peptide when inserted into bilayers of C14 phosphatidylglycerol. In contrast to the commonly accepted membrane thinning effect of antimicrobial peptides, the data demonstrate that pore formation does not necessarily relate to changes in the overall bilayer structure.
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Membrane Thickening by the Antimicrobial Peptide PGLa
Biophysical Journal, 2008Co-Authors: Georg Pabst, Sabine Danner-pongratz, Karl Lohner, Stephan L. Grage, Weiguo Jing, Anne S. Ulrich, Anthony Watts, Andrea HickelAbstract:Using x-ray diffraction, solid-state 2 H-NMR, differential scanning calorimetry, and dilatometry, we have observed a perturbation of saturated acyl chain phosphatidylglycerol bilayers by the antimicrobial peptide peptidyl-Glycylleucine- carboxyamide (PGLa) that is dependent on the length of the hydrocarbon chain. In the gel phase, PGLa induces a quasi- interdigitated phase, previously reported also for other peptides, which is most pronounced for C18 phosphatidylglycerol. In the fluid phase, we found an increase of the membrane thickness and NMR order parameter for C14 and C16 phosphatidylglycerol bilayers, though not for C18. The data is best understood in terms of a close hydrophobic match between the C18 bilayer core and the peptide length when PGLa is inserted with its helical axis normal to the bilayer surface. The C16 acyl chains appear to stretch to accommodate PGLa, whereas tilting within the bilayer seems to be energetically favorable for the peptide when inserted into bilayers of C14 phosphatidylglycerol. In contrast to the commonly accepted membrane thinning effect of antimicrobial peptides, the data demonstrate that pore formation does not necessarily relate to changes in the overall bilayer structure.
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Influence of antimicrobial peptides on the formation of nonlamellar lipid mesophases.
Biochimica et Biophysica Acta, 2008Co-Authors: Andrea Hickel, Sabine Danner-pongratz, Heinz Amenitsch, Gabor Degovics, Michael Rappolt, Karl Lohner, Georg PabstAbstract:article i nfo Lipid/peptide interaction Pore formation Membrane electrostatics Phase transition X-ray diffraction Differential scanning calorimetry We have studied the influence of four antimicrobial peptides of different secondary and ternary structure - melittin (Mel), protegrin-1 (PG-1), peptidyl-Glycylleucine-carboxyamide (PGLa), and gramicidin S (GS) - on the lamellar-to-nonlamellar transition of palmitoyloleoyl phosphatidylethanolamine (POPE) applying differential scanning calorimetry and small-angle X-ray diffraction. None of the peptides studied led to the formation of an inverted hexagonal phase observed for pure POPE at high temperatures. Instead either cubic or lamellar phases were stabilized to different degrees. GS was most effective in inducing a cubic phase, whereas Mel fully stabilized the lamellar phase. The behavior of POPE in the presence of PG-1 and PGLa was intermediate to GS and Mel. In addition to the known role of membrane elasticity we propose two mechanisms, which cause stabilization of the lamellar phase: electrostatic repulsion and lipid/peptide pore formation. Both mechanisms prevent transmembrane contact required to form either an inverted hexagonal phase or fusion pores, as precursors of the cubic phase.
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Structural aspects of the interaction of peptidyl-Glycylleucine-carboxyamide, a highly potent antimicrobial peptide from frog skin, with lipids.
FEBS Journal, 1997Co-Authors: Angelika Latal, Gabor Degovics, Raquel F. Epand, Karl LohnerAbstract:The interaction of PGLa (peptidyl-Glycylleucine-carboxyamide), a 21-amino-acid residue cationic peptide, isolated from the skin of the South African clawed frog, Xenopus laevis, with model membrane systems was investigated. Our studies focussed on the importance of the difference in the phospholipid composition of bacterial and erythrocyte membranes. This is of particular interest to gain information on the specificity of membranolysis exhibited by this peptide against bacteria but not against erythrocytes. In phosphate buffer at physiological pH, as well as in the presence of the zwitterionic phosphatidylcholine and sphingomyelin. the peptide had a random structure but it adopted an alpha-helical conformation in the presence of negatively charged lipids. Furthermore, calorimetric experiments showed that PGLa had no effects on the thermotropic phase behavior of liposomes composed of the choline phosphatides, while separation of a distinct peptide-rich domain was observed for phosphatidylglycerol liposomes. In addition to the main transition of pure 1,2-dipalmitoylglycerophosphoglycerol at 40 degrees C a second transition owing to the peptide-perturbed lipid domains was found at 41 degrees C. This conclusion is supported by X-ray diffraction experiments which indicated that PGLa penetrates into the hydrophobic core of the bilayer inducing an untilting of the hydrocarbon chains as observed in the gel phase of the pure lipid. These results demonstrate that this antibacterial peptide specifically interacts with negatively charged lipid membranes, which are characteristic of bacterial membranes. This can be explained based on the structural features of PGLa.
Anne S. Ulrich - One of the best experts on this subject based on the ideXlab platform.
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damage of the bacterial cell envelope by antimicrobial peptides gramicidin s and pgla as revealed by transmission and scanning electron microscopy
Antimicrobial Agents and Chemotherapy, 2010Co-Authors: Mareike Hartmann, Marina Berditsch, Jacques Hawecker, Mohammad Fotouhi Ardakani, D Gerthsen, Anne S. UlrichAbstract:Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to examine the ultrastructural changes in bacteria induced by antimicrobial peptides (AMPs). Both the β-stranded gramicidin S and the α-helical peptidyl-Glycylleucine-carboxyamide (PGLa) are cationic amphiphilic AMPs known to interact with bacterial membranes. One representative Gram-negative strain, Escherichia coli ATCC 25922, and one representative Gram-positive strain, Staphylococcus aureus ATCC 25923, were exposed to the AMPs at sub-MICs and supra-MICs in salt-free medium. SEM revealed a shortening and swelling of the E. coli cells, and multiple blisters and bubbles formed on their surface. The S. aureus cells seemed to burst upon AMP exposure, showing open holes and deep craters in their envelope. TEM revealed the formation of intracellular membranous structures in both strains, which is attributed to a lateral expansion of the lipid membrane upon peptide insertion. Also, some morphological alterations in the DNA region were detected for S. aureus. After E. coli was incubated with AMPs in medium with low ionic strength, the cells appeared highly turgid compared to untreated controls. This observation suggests that the AMPs enhance osmosis through the inner membrane, before they eventually cause excessive leakage of the cellular contents. The adverse effect on the osmoregulatory capacity of the bacteria is attributed to the membrane-permeabilizing action of the amphiphilic peptides, even at low (sub-MIC) AMP concentrations. Altogether, the results demonstrate that both TEM and SEM, as well as appropriate sample preparation protocols, are needed to obtain detailed mechanistic insights into peptide function.
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Membrane Thinning Is Not A Unique Signal Of Pore Formation By Antimicrobial Peptides
Biophysical Journal, 2009Co-Authors: Georg Pabst, Sabine Danner-pongratz, Karl Lohner, Stephan L. Grage, Weiguo Jing, Anne S. Ulrich, Anthony Watts, Andrea HickelAbstract:We have observed a hydrocarbon chain length dependent perturbation of saturated acyl chain phosphatidylglycerol bilayers by the antimicrobial peptide peptidyl-Glycylleucine-carboxyamide (PGLa) using X-ray diffraction, solid-state 2H-NMR, differential scanning calorimetry and dilatometry. In the gel phase, PGLa assumes a surface alignment and induces a quasi-interdigitated phase, previously reported also for other peptides. This effect is most pronounced for C18 phosphatidylglycerol. Above the lipid chain melting transition, in the fluid phase, the PGLa helix inserts into the membrane above a certain threshold concentration. In this case we found an increase of the membrane thickness and NMR order parameter for C14 and C16 phosphatidylglycerol bilayers, though not for C18. The data is best understood in terms of a close hydrophobic match between the C18 bilayer core and the peptide length when PGLa is inserted with its helical axis normal to the bilayer surface. The C16 acyl chains appear to stretch in order to accommodate PGLa, whereas tilting within the bilayer seems to be energetically favorable for the peptide when inserted into bilayers of C14 phosphatidylglycerol. In contrast to the commonly accepted membrane thinning effect of antimicrobial peptides, the data demonstrate that pore formation does not necessarily relate to changes in the overall bilayer structure.
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Membrane Thickening by the Antimicrobial Peptide PGLa
Biophysical Journal, 2008Co-Authors: Georg Pabst, Sabine Danner-pongratz, Karl Lohner, Stephan L. Grage, Weiguo Jing, Anne S. Ulrich, Anthony Watts, Andrea HickelAbstract:Using x-ray diffraction, solid-state 2 H-NMR, differential scanning calorimetry, and dilatometry, we have observed a perturbation of saturated acyl chain phosphatidylglycerol bilayers by the antimicrobial peptide peptidyl-Glycylleucine- carboxyamide (PGLa) that is dependent on the length of the hydrocarbon chain. In the gel phase, PGLa induces a quasi- interdigitated phase, previously reported also for other peptides, which is most pronounced for C18 phosphatidylglycerol. In the fluid phase, we found an increase of the membrane thickness and NMR order parameter for C14 and C16 phosphatidylglycerol bilayers, though not for C18. The data is best understood in terms of a close hydrophobic match between the C18 bilayer core and the peptide length when PGLa is inserted with its helical axis normal to the bilayer surface. The C16 acyl chains appear to stretch to accommodate PGLa, whereas tilting within the bilayer seems to be energetically favorable for the peptide when inserted into bilayers of C14 phosphatidylglycerol. In contrast to the commonly accepted membrane thinning effect of antimicrobial peptides, the data demonstrate that pore formation does not necessarily relate to changes in the overall bilayer structure.