Matrix-assisted laser desorption/ionization-mass spectrometry of cuticular lipid profiles can differentiate sex, age, and mating status of Anopheles gambiae mosquitoes

Malaria is a devastating mosquito-borne disease, which affects hundreds of millions of people each year. It is transmitted predominantly by Anopheles gambiae, whose females must be >10 days old to become infective. In this study, cuticular lipids from a laboratory strain of this mosquito species were analyzed using a mass spectrometry method to evaluate their utility for age, sex and mating status differentiation. Matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS), in conjunction with an acenaphthene/silver nitrate matrix preparation, was shown to be 100% effective in classifying A. gambiae females into 1, 7–10, and 14 days of age. MALDI-MS analysis, supported by multivariate statistical methods, was also effective in detecting cuticular lipid differences between the sexes and between virgin and mated females. The technique requires further testing, but the obtained results suggest that MALDI-MS cuticular lipid spectra could be used for age grading of A. gambiae females with precision greater than with other available methods.     

Preferential formation of the different hydrogen bonds and their effects in tetrahydrofuran and tetrahydropyran microhydrated complexes

The role of cycloether-water (c-w) and water-water (w-w) hydrogen bonds (H-bonds) on the stability of the tetrahydrofuran THF/(H(2)O)(n) and the tetrahydropyran THP/(H(2)O)(n) complexes with n = 1-4 was investigated herein using the density functional and ab initio methods and the atoms in molecules theory. Geometry optimizations for these complexes were carried out with various possible initial guess structures. It was revealed that the major contributions of the mono and dihydrated complexes came from c-w H-bonds. A competition between c-w and w-w H-bonds contribution was observed for trihydrated complexes. For most of tetrahydrated complexes, the inter-water H-bonds provided the greatest contribution, whereas the c-w contributions were small but not negligible. It was confirmed that to produce a hydrophobic hydration of cycloethers, the C-H···O(w) H-bond should be associated with a network of H-bonds that connects both portions of the solute, through the formation of a bifunctional H-bond. A linear correlation is obtained for the sum of electron density at the bond critical points (ρ(b)) with the interaction energy (ΔE) and with the solute-solvent interaction energy (ΔE(s-w)) of the microhydrated complexes. In addition, a new way to estimate the energetic contribution as well as the preferential formation of the different H-bonds based completely on ρ(b) was found. Even more, it allows to differentiate the contribution from c-w interactions in both hydrophilic and hydrophobic contributions, it is therefore a useful tool for studying the hydration of large biomolecules. The analysis of the modifications in the atomic and group properties brought about by successive addition of H(2)O molecules allowed to pinpoint the atoms or molecular groups that undergo the greatest changes in electron population and energetic stabilization. It was identified that the remarkable stabilization of the water oxygen atoms is crucial for the stabilization of the complexes.     

Thermodynamics of alpha-Cyclodextrin-p-Nitrophenyl Glycoside Complexes. A Simple System To Understand the Energetics of Carbohydrate Interactions in Water

Thermodynamic studies of the binding of a series of p-nitrophenyl glycosides (PNPGly) of varying stereochemistry to alpha-cyclodextrin (alpha-CD) were performed at three different temperatures (25, 35, and 42 degrees C) using a microcalorimetric technique. The system p-nitrophenol (PNP) at pH = 3 and alpha-CD was also studied for the sake of comparison. All these complexes were found to be enthalpy driven with a favorable enthalpic term clearly dominant over an unfavorable entropic term. A clear enthalpy-entropy compensation effect was observed at all the temperatures, with a slope close to unity (alpha = 1.02) and an intercept TDeltaS degrees (o) = 2.91 kcal mol(-)(1). This thermodynamic pattern is in agreement with those usually found for lectin-carbohydrate associations and for the binding processes of several host-guest systems. This pattern is explained in terms of the contribution of primarily two driving forces: the van der Waals interactions between the host and the guest, and the solvation/desolvation processes which accompany the association reaction. The presence of the carbohydrate molecule in the PNP ring causes a slight destabilization of the complex at 25 degrees C with respect to the alpha-CD-PNP (pH = 3) complex, although a different behavior has been observed depending on the axial/equatorial configuration of the glycoside and the temperature. This behavior is modulated by the stereochemistry of the glycoside. Differences were observed between the deoxy-derivatives (LAra and LFuc) and those derivatives with a hydroxymethyl group (Glc, Gal, Man). DeltaC(p) degrees values were obtained from the dependency of DeltaH degrees on temperature (=( partial differentialDeltaH degrees / partial differentialT)(p)). These values are small and negative except for alphaMan complex. For the latter complex, discrepancy between the calorimetric and the calculated van't Hoff enthalpies was observed. Parallels are drawn between the thermodynamics of our model and those proposed for carbohydrate-protein associations.     

Matrices with Heterogeneous Distribution of the Binding Sites for Immobilization of Biomacromolecules

The coupling of photosensitive reagents has been carried out with the goal of obtaining the predetermined distribution of binding sites either for “surface” or “spacial” immobilization of biomacromolecules. The correlation holds between light intensity and the number of readant groups emerged in a matrix.     

A Facile Route to Substituted Dimethoxy Phosphonothionates Using Dimethyl Thiophosphite

Dimethyl thiophosphite reacts with aliphatic aldehydes and ketones, Michael acceptors, and N-benzyl imines to afford excellent yields of f -hydroxy phosphonothionates, g -substituted phosphonothionates and f -amino phosphonothionates, respectively. Dealkylation of f -amino phosphonothionates affords N-benzyl f -amino phosphonothioic acids. Dimethyl thiophosphite reacts with electrophiles at a significantly greater rate than dimethyl phosphite.     

Concise synthesis of orthogonally diprotected l-glyceraldehyde

Orthogonally diprotected l-glyceraldehyde was efficiently prepared from readily available starting materials, allowing to obtain a highly stable and synthetically versatile chiral building block compared to known symmetrically protected derivatives.     

Reactivity Studies of Iridium Pyridylidenes [TpMe2Ir(C6H5)2(C(CH)3C(R)NH] (R=H,Me, Ph)

The reactivity of a series of iridium? pyridylidene complexes with the formula [Tp^Me2Ir(C₆H₅)₂(C(CH)₃C(R)N H] ( 1 a – 1 c ) towards a variety of substrates, from small molecules, such as H₂, O₂, carbon oxides, and formaldehyde, to alkenes and alkynes, is described. Most of the observed reactivity is best explained by invoking 16 e^? unsaturated [Tp^Me2Ir(phenyl)(pyridyl)] intermediates, which behave as internal frustrated Lewis pairs (FLPs). H₂ is heterolytically split to give hydride? pyridylidene complexes, whilst CO, CO₂, and H₂C?O provide carbonyl, carbonate, and alkoxide species, respectively. Ethylene and propene form five‐membered metallacycles with an IrCH₂CH(R)N (R=H, Me) motif, whereas, in contrast, acetylene affords four‐membered iridacycles with the IrC(?CH₂)N moiety. C₆H₅(C?O)H and C₆H₅C?CH react with formation of Ir? C₆H₅ and Ir? C?CPh bonds and the concomitant elimination of a molecule of pyridine and benzene, respectively. Finally the reactivity of compounds 1 a – 1 c against O₂ is described. Density functional theory calculations that provide theoretical support for these experimental observations are also reported.     

A prototype calix[4]arene-based receptor for carbohydrate recognition containing peptide and phosphate binding groups

A novel class of macrobicyclic receptors for carbohydrate recognition based on upper rim, peptide-bridged calix[4]arenes has been designed and synthesized. Receptor 12, in which a charged phosphate group cooperates with peptide hydrogen-bonding donor and acceptor groups in the binding process, is the most efficient and selective in the complexation of simple carbohydrate derivatives. The selectivity observed is toward beta-glucoside 13a, which is better bound (DeltaG degrees = 19.6 kJ mol(-)(1)) compared to the corresponding alpha anomer 13b (DeltaG degrees = 17.0 kJ mol(-)(1)) and to the beta-galactoside 13c (DeltaG degrees = 17.7 kJ mol(-)(1)) in CDCl(3). A substantial drop in the stability constant is observed by esterification of the phosphate group in the host 12 or by alkylation of the OH groups in the 2 and 3 positions in the beta-glucoside and beta-galactoside derivatives. On the basis of a careful analysis of the (1)H NMR data available, a binding mode of the beta-octylglucoside 13a to receptor 12 is proposed.     

Do solid surface potential barriers retard convoy peak electrons?

Using a coaxial cylindric electron spectrometer and an electrostatic ion energy analyzer in tandem, a direct measurement of the difference of the energy of convoy peak electron and the electron equivalent ion energy of protons emerging from the downstream surface of C, Au and Al foils is performed in the proton energy range from 60 to 250 keV. This measurement is made possible using the accepted evidence that for a gas target these energies are equal. It is found that also for the beam foil convoy peak electrons, within an experimental average uncertainty of about ±0.1 eV, there is no difference between these energies. If one accepts that the origin of convoy electrons is from inside the solid, the conclusion is that no retardation by the solid surface potential barrier, which is of the order of a few eV, is observed. This is attributed to the strong electron-ion Coulomb interaction which almost completely overshadows the force exerted on the electron by the field of the surface barrier.