[5-Leucin]enkephalin-Related Glycoconjugates: Structurally Novel Agents Effective against HIV-1

A series of [Leu⁵]enkephalin-related glycoconjugates with an ester-, ether-, or amide-type linkage were synthesized and evaluated for antiviral activity against HIV-1 in a cell-culture system using peripheral blood lymphocytes. All tested glycoconjugates exhibited a certain antiviral activity which was significantly higher than the activity of the parent peptide compound itself. These results indicate that synthetic glycoconjugates of opioid peptides are good candidates for the development of anti-HIV agents.     

Tracing glycoprotein structures: electrospray ionization tandem mass spectrometric analysis of sugar-peptide adducts

Owing to the diversity of carbohydrate structures and their significance for the function of many biopolymers, structural analysis of various carbohydrate-related compounds is of great importance. Electrospray ionization tandem mass spectrometry (ESI-MS/MS) was used to establish the fragmentation behaviour of a range of sugar-peptide adducts as model compounds of widespread glycoprotein structures. The compounds used in this study were chosen to provide correlation of distinct fragment ions with specific structural differences, namely position and type of carbohydrate-peptide bond and structure of the sugar moiety. All compounds show N- and C-terminal sequence ions along with losses of up to three water molecules. Fructose-related Amadori compounds exhibit M + 78 modified N-terminal peptide fragment ions. Fragmentation of glucose-peptide esters is characterized by the sugar ring fragmentation. Additionally, under the ESI-MS conditions applied, the esters studied undergo intramolecular reaction giving cyclic sugar-peptide structures that can be traced by the presence of N-terminal peptide M + 42 adducts. Detailed analysis of cyclic fructose-related compound comprising structural features of both studied groups revealed a rich fragmentation pattern derived from amino acid residues and water molecules losses from [M - 2H(2)O + H](+) ion. Also, some interesting differences were found with respect to the nature of carbohydrate moieties.     

Determination of pKa values of active pharmaceutical ingredients

The acid dissociation constant is an important physicochemical parameter of a substance, and knowledge of it is of fundamental importance in a wide range of applications and research areas. We present a critical review of published methods and approaches for the determination of acid dissociation constants, with a special emphasis on the pK_a values of active pharmaceutical ingredients.     

Thermal degradation of epoxy-silica organic-inorganic hybrid materials

Degradation kinetics of organic-inorganic hybrid materials based on epoxy resin were investigated by thermogravimetric analysis (TGA). The hybrid materials were prepared from diglycidyl ether of bisphenol A (DGEBA) and 3-glycidyloxypropyltrimethoxysilane (GLYMO) polymerised simultaneously by poly(oxypropylene)diamine (Jeffamine D230). Nanometric level of homogeneity in the hybrids was verified by electron microscopy. Energy of activation of degradation for the hybrids with varying inorganic content, as well as for the unmodified epoxy-amine system, was determined by the isoconversional Kissinger-Akahira-Sunose method, and was found to be significantly higher for the hybrid materials than for the unmodified epoxy-amine system. The degradation process was described by empirical kinetic models. The results indicated that presence of the inorganic network influences the mechanism of degradation of organic phase. Greater thermal stability of hybrid materials was confirmed by other parameters obtained from TGA curves.     

One-step Bioluminescence ATPase Assay for the Evaluation of Neurotoxic Effects of Metal Ions

Summary. Membrane-bound ATPases, such as Na,K-ATPase and nucleotide triphospho-diphosphohydrolase (NTPDase), being one of the first targets of a toxic action are generally considered as good markers for estimating toxicity. A bioluminescence assay was applied for fast and sensitive evaluation of heavy metals effect on the rat brain synaptosomal membrane ATPase activity. The assay consists of ATP-consuming reaction catalyzed by synaptic plasma membrane ATPases coupled to the luminescent firefly luciferase reaction, which consumes residual ATP after the course of ATPase reaction. The bioluminescence ATPase assay was applied to study the effect of heavy and transitional metals (Cu²⁺, Pb²⁺, Cd²⁺, Hg²⁺) on rat brain ATPase activity after assay optimization. All metals applied inhibited synaptic membrane ATPase activity in a concentration dependent manner. The IC ₅₀ values (Hg²⁺ < Cu²⁺ < Cd²⁺ < Pb²⁺) obtained with the bioluminescence assay were highly correlated with those obtained by the spectrophotometric method. The fast bioluminescence ATPase assay with small sample and substrate requirements could be adjusted for high-throughput environmental and pharmacological screening.     

Apparent Molar Volume and Apparent Molar Expansibility of Rubidium, Cesium, and Ammonium Cyclohexylsulfamate in Aqueous Solution

The apparent molar volume of rubidium, caesium, and ammonium cyclohexylsulfamate was determined from the density data of their aqueous solutions at 293.15, 298.15, 303.15, 313.15, 323.15, and 333.15 K. From the apparent molar volume, determined at various temperatures, the apparent molar expansibility was calculated. The limiting apparent molar volume and apparent molar expansibility were evaluated and apportioned into their ionic components. The limiting partial molar ionic volumes and expansibilities are discussed in terms of the various effects of the ion in solution on the structure of water. It was shown that the limiting partial molar ionic expansibilities of the alkali-metal cations increase with their ionic radii. The coefficients of thermal expansion of the investigated solutions at 298.15 K were calculated and are presented graphically together with some alkali-metal cyclohexylsulfamates and tetramethylammonium cyclohexylsulfamate. The densities of the investigated solutions can be adequately represented by an equation derived by Redlich.     

Viscosity of Aqueous Solutions of Lithium,Sodium, Potassium,Rubidium and Caesium Cyclohexylsulfamates from 293.15 to 323.15 K

The viscosities of aqueous solutions of lithium, sodium, potassium, rubidium and caesium cyclohexylsulfamates were measured at 293.15, 298.15, 303.15, 313.15 and 323.15 K. The relative viscosity data were analyzed and interpreted in terms of the Kaminsky equation, η _r=1+Ac ^1/2+Bc+Dc ². The viscosity A-coefficient was calculated from the Falkenhagen-Dole theory. The viscosity B-coefficients are positive and relatively large. Their temperature coefficient ∂ B/∂ T is negative or near zero for lithium and sodium salts whereas for potassium, rubidium and caesium salts it is positive. The viscosity D-coefficient is positive. This was explained by the size of the ions, structural solute–solute interactions, hydrodynamic effect, and by higher terms of the long-range Debye-Hückel type of forces. From the viscosity B-coefficients the thermodynamic functions of activation of viscous flow were calculated. The limiting partial molar Gibbs energy of activation of viscous flow of the solute was divided into contributions due to solvent molecules and the solute in the transition state. The activation energy of the solvent molecules was calculated using the limiting Gibbs energy of activation for the conductance of the solute ions. The activation energy of the solvent molecules was then discussed in terms of the nature of the alkali-metal ions and their influence on the structure of water. The limiting activation entropy and enthalpy of the solute for activation of viscous flow were interpreted by ion-solvent bond formation or breaking in the transition state of the solvent. The hydration numbers of the investigated electrolytes were calculated from the specific viscosity of the solutions.     

Sample Preparation for TLC — Genetic Algorithm-Based Optimization of Microwave-Assisted Extraction

JPC – Journal of Planar Chromatography – Modern TLC - Optimization of microwave-assisted extraction (MAE) as a method of sample preparation in thin-layer chromatographic (TLC) analysis...     

Determination of arsenic in ambient water at sub-part-per-trillion levels by hydride generation Pd coated platform collection and GFAAS detection

A method for trace determination of total arsenic in ambient waters is described. Arsenic is separated on-line from a large volume water sample by hydride generation and purging, pre-collected on a Pd coated pyrolytic platform cuvette using a simple and inexpensive system, and finally detected by GFAAS. Instrument parameters, hydride generation, transportation, and collection were optimized. The analytical behavior for major species including As(3+), As(5+), monomethyl As (MMA), and dimethyl As (DMA) were investigated individually. Problems arising from use of the system were discussed and eliminated. The necessity of sample digestion and an efficient digestion method were studied. Sample digestion for water with low organic content such as tap water and clean ground water and some clean surface water can be omitted. The method detection limit (MDL) is 0.3 ng l(-1) for a 25 ml water sample. Recoveries close to 100% with R.S.D.<5% can be easily achieved. Typical aqueous samples including tap, ground, lake, river, rain, sewage effluent, and saline water from different origins in the US, China, and Canada were collected and analyzed using ultra clean sampling and analysis techniques. The background levels of As in most water analyzed were established for the first time, and found to be far above the EPA's health effect criteria, 18 ng l(-1).