The effect of sequence on the conformational stability of a model heteropolymer in explicit water

We investigate the properties of a two-dimensional lattice heteropolymer model for a protein in which water is explicitly represented. The model protein distinguishes between hydrophobic and polar monomers through the effect of the hydrophobic monomers on the entropy and enthalpy of the hydrogen bonding of solvation shell water molecules. As experimentally observed, model heteropolymer sequences fold into stable native states characterized by a hydrophobic core to avoid unfavorable interactions with the solvent. These native states undergo cold, pressure, and thermal denaturation into distinct configurations for each type of unfolding transition. However, the heteropolymer sequence is an important element, since not all sequences will fold into stable native states at positive pressures. Simulation of a large collection of sequences indicates that these fall into two general groups, those exhibiting highly stable native structures and those that do not. Statistical analysis of important patterns in sequences shows a strong tendency for observing long blocks of hydrophobic or polar monomers in the most stable sequences. Statistical analysis also shows that alternation of hydrophobic and polar monomers appears infrequently among the most stable sequences. These observations are not absolute design rules and, in practice, these are not sufficient to rationally design very stable heteropolymers. We also study the effect of mutations on improving the stability of the model proteins, and demonstrate that it is possible to obtain a very stable heteropolymer from directed evolution of an initially unstable heteropolymer.     

HPTLC determination of rabeprazole and domperidone in capsules and its validation

This paper describes a validated high-performance thin-layer chromatography (HPTLC) method for simultaneous estimation of rabeprazole (RA) and domperidone (DO) in pure powder and in capsule formulations. An HPTLC method separation is achieved on an aluminum sheet of silica gel 60F(254) using ethyl acetate-methanol-benzene-acetonitrile (30:20:30:20 v/v) as mobile phase. Quantitation is achieved with UV detection at 287 nm over a concentration range of 400-1200 ng/spot and 600-1800 ng/spot with mean recovery of 99.82 +/- 0.74 and 99.43 +/- 0.68 for RA and DO, respectively, in the HPTLC method. This method is simple, precise, and sensitive, and it is applicable for the simultaneous determination of RA and DO in pure powder and in capsule formulation.     

Studies in synthesis of furoflavones possessing anti‐cancer activity

Several new furoflavanones (3a‐3I) have been synthesized from the in‐situ generated chalcones by the reaction of ortho‐hydroxy acetyl benzofuran and aryl aldehyde in presence of piperidine. Ethanolic sodium hydroxide (1%) gave chalcones (2a‐2I) as the exclusive product. Flavindogenides (3‐arylidene flavanones) (5a‐5d) have been isolated as the co‐product along with chalcones and flavanones in cases where excess of aryl aldehyde was used. The stereochemistry of 3‐arylidene flavanones has been established by the preparation of both Z (6) and E (5a‐5d) diastereomers. Single crystal X‐ray diffraction data shows the flavanone ring to exist in quasi chair conformation with phenyl ring equatorial. Furoflavanones were finally dehydrogenated to furoflavones (4a‐4I) using DDQ (2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone). The compounds have been screened for in‐vitro cytotoxicity against human cancer cell lines.     

Multifunctional particles: Magnetic nanocrystals and gold nanorods coated with fluorescent dye-doped silica shells

Multifunctional colloidal core-shell nanoparticles of magnetic nanocrystals (of iron oxide or FePt) or gold nanorods encapsulated in silica shells doped with the fluorescent dye, Tris(2,2′-bipyridyl)dichlororuthenium(II) hexahydrate (Rubpy) were synthesized. The as-prepared magnetic nanocrystals are initially hydrophobic and were coated with silica using a microemulsion approach, while the as-prepared gold nanorods are hydrophilic and were coated with silica using a Stöber type of process. Each approach yielded monodisperse nanoparticles with uniform fluorescent dye-doped silica shells. These colloidal heterostructures have the potential to be used as dual-purpose tags—exhibiting a fluorescent signal that could be combined with either dark-field optical contrast (in the case of the gold nanorods), or enhanced contrast in magnetic resonance images (in the case of magnetic nanocrystal cores). The optical and magnetic properties of the fluorescent silica-coated gold nanorods and magnetic nanocrystals are reported.     

Temperature triggered self-assembly of polypeptides into multivalent spherical micelles

We report herein thermally responsive elastin-like polypeptides (ELPs) in a linear AB diblock architecture with an N-terminal peptide ligand that self-assemble into spherical micelles when heated slightly above body temperature. A series of 10 ELP block copolymers (ELP(BC)'s ) with different molecular weights and hydrophilic-to-hydrophobic block ratios were genetically synthesized by recursive directional ligation. The self-assembly of these polymers from unimers into micelles was investigated by light scattering, fluorescence spectroscopy, and cryo-TEM. These ELP(BC)'s undergo two phase transitions as a function of solution temperature: a unimer-to-spherical micelle transition at an intermediate temperature and a micelle-to-bulk aggregate transition at a higher temperature when the hydrophilic-to-hydrophobic block ratio is between 1:2 and 2:1. The critical micelle temperature is controlled by the length of the hydrophobic block, and the size of the micelle is controlled by both the total ELP(BC) length and hydrophilic-to-hydrophobic block ratio. These polypeptide micelles display a critical micelle concentration in the range 4-8 microM demonstrating the high stability of these structures. These studies have also identified a subset of ELP(BC)'s bearing terminal peptide ligands that are capable of forming multivalent spherical micelles that present multiple copies of the ligand on their corona in the clinically relevant temperature range 37-42 degrees C and target cancer cells. These ELP(BC)'s may be useful for drug targeting by thermally triggered multivalency. More broadly, the design rules uncovered by this study should be applicable to the design of other thermally reversible nanoparticles for diverse applications in medicine and biology.     

Continuous amperometric detection of co-released serotonin and melatonin from the mucosa in the ileum

Serotonin (5-HT) and melatonin (MEL) are well known neurotransmitters and paracrine signalling molecules. Both compounds are present in enterochromaffin (EC) cells in the mucosa of the gastrointestinal tract and are thought to play a role in controlling gut motility. To date there are no real-time analytical methods for the detection of these two molecules and it is not clear if MEL is actually released from the EC cells. In this paper, I used boron-doped diamond (BDD) microelectrodes to record 5-HT and MEL overflow from EC cells in the mucosa of rabbit ileum. The BDD microelectrode was extremely stable and sensitive for measurements of both compounds when assessed using differential pulse voltammetry (DPV) and flow injection analysis (FIA) using amperometric detection. MEL release was detected in the mucosa, where it is most likely from the EC cells. Mechanical stimulation of individual villi increased 5-HT but not MEL overflow. Application of the serotonin transporter (SERT) inhibitor, fluoxetine, elevated the 5-HT but not the MEL signal. Differences in the amounts of the two gastrointestinal compounds released and the mechanism of which they are released will provide insights to the physiology of the EC cell and disease states.     

Estimation of L-dopa from Mucuna pruriens LINN and formulations containing M. pruriens by HPTLC method

A selective, precise, and accurate high-performance thin-layer chromatographic (HPTLC) method has been developed for the analysis of L-dopa in Mucuna pruriens seed extract and its formulations. The method involves densitometric evaluation of L-dopa after resolving it by HPTLC on silica gel plates with n-butanol-acetic acid-water (4.0+1.0+1.0, v/v) as the mobile phase. Densitometric analysis of L-dopa was carried out in the absorbance mode at 280 nm. The relationship between the concentration of L-dopa and corresponding peak areas was found to be linear in the range of 100 to 1200 ng/spot. The method was validated for precision (inter and intraday), repeatability, and accuracy. Mean recovery was 100.30%. The relative standard deviation (RSD) values of the precision were found to be in the range 0.64-1.52%. In conclusion, the proposed TLC method was found to be precise, specific and accurate and can be used for identification and quantitative determination of L-dopa in herbal extract and its formulations.     

Stability-Indicating HPTLC Method for Analysis of Moclobemide, and Use of the Method to Study Degradation Kinetics

A sensitive, selective, precise, and stability-indicating HPTLC method for analysis of moclobemide in the bulk drug and in formulations has been established and validated. Aluminium TLC plates precoated with silica gel 60 F₂₅₄ were used with benzene–methanol–40% ammonia 7:3:0.1 (v/v) as mobile phase. Densitometric analysis was performed in absorbance mode at 238 nm. Compact bands were obtained for moclobemide (R _F 0.67 ± 0.02; n = 6). The drug was subjected to acidic and alkaline hydrolysis, oxidation, dry heat treatment, and photodegradation. The drug undergoes degradation under acidic, basic, and oxidising conditions. The degradation products were well resolved from the pure drug with significantly different R _F values, so the method can be regarded as stability-indicating. Response to moclobemide was a linear function of amount in the range 50–600 ng per band, with a correlation coefficient, r ², of 0.9967 ± 0.51. LOD and LOQ, determined experimentally, were 10 and 30 ng per band, respectively. Statistical analysis proves the method is repeatable and specific for analysis of moclobemide. The method was used to investigate the kinetics of alkaline degradation. The Arrhenius plot was constructed and the activation energy calculated.     

Development and validation of a visible absorption densitometry method for quantitation of conessine in Holarrhena antidysenterica (Kurchi)

A selective, precise, and accurate high-performance thin-layer chromatographic (HPTLC) method has been proposed for the analysis of conessine in Holarrhena antidysenterica. The method involves visible densitometric evaluation of conessine resolving it by HPTLC on aluminium-based silica gel plates. For visible densitometric evaluation, peak areas were recorded at 520 nm after the resolved bands were derivatized with Dragendorff's reagent and then sprayed with a 10% solution of aqueous sodium nitrite which resulted in reddish brown color. The correlation between the concentration and area was found to be linear within the range of 10 to 60 ng/spot. The method was validated for precision (interday and intraday), repeatability, and accuracy. Mean recovery for conessine was 98.34-100.25%. The method was applied for the quantitation of conessine in Kurchi. The proposed HPTLC method was found to be precise, specific, sensitive, and accurate and can be used for routine analysis of Kurchi.     

Simultaneous estimation of acetylsalicylic acid and clopidogrel bisulfate in pure powder and tablet formulations by high-performance column liquid chromatography and high-performance thin-layer chromatography

This paper describes validated high-performance column liquid chromatographic (HPLC) and high-performance thin-layer chromatographic (HPTLC) methods for simultaneous estimation of acetylsalicylic acid (ASA) and clopidogrel bisulfate (CLP) in pure powder and formulations. The HPLC separation was achieved on a Nucleosil C8 column (150 mm length x 4.6 mm id, 5 microm particle size) using acetonitrile-phosphate buffer, pH 3.0 (55 + 45, v/v) mobile phase at a flow rate of 1.0 mL/min at ambient temperature. The HPTLC separation was achieved on an aluminum-backed layer of silica gel 60F254 using ethyl acetate-methanol-toluene-glacial acetic acid (5.0 + 1.0 + 4.0 + 0.1, v/v/v/v) mobile phase. Quantitation was achieved with UV detection at 235 nm over the concentration range 4-24 microg/mL for both drugs, with mean recoveries of 99.98 +/- 0.28 and 100.16 +/- 0.66% for ASA and CLP, respectively, using the HPLC method. Quantitation was achieved with UV detection at 235 nm over the concentration range of 400-1400 ng/spot for both drugs, with mean recoveries of 99.93 +/- 0.55 and 100.21 +/- 0.83% for ASA and CLP, respectively, using the HPTLC method. These methods are simple, precise, and sensitive, and they are applicable for the simultaneous determination of ASA and CLP in pure powder and formulations.