Modulating the structure and properties of cell membranes: the molecular mechanism of action of dimethyl sulfoxide

Dimethyl sulfoxide (DMSO) is a small amphiphilic molecule which is widely employed in cell biology as an effective penetration enhancer, cell fusogen, and cryoprotectant. Despite the vast number of experimental studies, the molecular basis of its action on lipid membranes is still obscure. A recent simulation study employing coarse-grained models has suggested that DMSO induces pores in the membrane (Notman, R.; Noro, M.; O'Malley, B.; Anwar, J. J. Am. Chem. Soc. 2006, 128, 13982-13983). We report here the molecular mechanism for DMSO's interaction with phospholipid membranes ascertained from atomic-scale molecular dynamics simulations. DMSO is observed to exhibit three distinct modes of action, each over a different concentration range. At low concentrations, DMSO induces membrane thinning and increases fluidity of the membrane's hydrophobic core. At higher concentrations, DMSO induces transient water pores into the membrane. At still higher concentrations, individual lipid molecules are desorbed from the membrane followed by disintegration of the bilayer structure. The study provides further evidence that a key aspect of DMSO's mechanism of action is pore formation, which explains the significant enhancement in permeability of membranes to hydrophilic molecules by DMSO as well as DMSO's cryoprotectant activity. The reduction in the rigidity and the general disruption of the membrane induced by DMSO are considered to be prerequisites for membrane fusion processes. The findings also indicate that the choice of DMSO concentration for a given application is critical, as the concentration defines the specific mode of the solvent's action. Knowledge of the distinct modes of action of DMSO and associated concentration dependency should enable optimization of current application protocols on a rational basis and also promote new applications for DMSO.     

Impact of foods nutritionally enhanced through biotechnology in alleviating malnutrition in developing countries

According to United Nations (UN) projections, the world's population will grow from 6.1 billion in 2000 to 8 billion in 2025 and 9.4 billion in 2050. Most (93%) of the increase will take place in developing countries. The rapid population growth in developing countries creates major challenges for governments regarding food and nutrition security. According to current World Health Organization estimates, more than 3 billion people worldwide, especially in developing countries, are malnourished in essential nutrients. Malnutrition imposes severe costs on a country's population due to impaired physical and cognitive abilities and reduced ability to work. Little progress has been made in improving malnutrition over the past few decades. The Food and Agriculture Organization of the UN would like to see more nutrient-rich foods introduced into these countries, because supplements are expensive and difficult to distribute widely. Biofortification of staple crops through modern biotechnology can potentially help in alleviating malnutrition in developing countries. Several genetically modified crops, including rice, potatoes, oilseeds, and cassava, with elevated levels of essential nutrients (such as vitamin A, iron, zinc, protein and essential amino acids, and essential fatty acids); reduced levels of antinutritional factors (such as cyanogens, phytates, and glycoalkaloid); and increased levels of factors that influence bioavailability and utilization of essential nutrients (such as cysteine residues) are advancing through field trial stage and regulatory processes towards commercialization. The ready availability and consumption of the biofortified crops would have a significant impact in reducing malnutrition and the risk of chronic disease in developing countries.     

Determination of Hansen Parameters of Nanoparticles: A Comparison of Two Methods Using Titania,Carbon Black,and Silicon/Carbon Composite Materials

Hansen solubility parameters (HSPs), for particles understood as Hansen similarity parameters, can provide valuable information about the surface behavior of nanoparticles. In the past years, several methodologies are developed for scoring and ranking of probe liquids for HSP determination. Two methods available to carry out this determination in a structured way are based on integral extinctions (IE) by Süß et al. and particle size determinations by Anwar et al., respectively. In this study, these two methods of HSP determination are applied on titania, carbon black, and silicon/carbon composites. The differences in scoring and subsequent ranking of a probe liquid list are compared between both methods. Comparable HSPs from both methods are reported as a best-practice example and additional considerations that need to be considered to properly derive HSPs from the IE-based method are emphasized.     

Extended Hückel tight-binding approach to electronic excitations

In this work, we propose the application of a self-consistent extended Huckel tight-binding (EHTB) method in the computation of the absorption optical spectrum of molecules within the linear response time dependent density functional formalism. The EHTB approach is presented as an approximation to the Kohn-Sham energy functional. The method is applied to the computation of excitation energies and oscillator strengths of benzene, pyridine, naphthalene, diazines, and the fullerenes: C(60)(I(h)), C(70)(D(5h)), and C(80)(D(2)). The very good agreement with experimental data is very encouraging and suggests the possibility of using the EHTB as a computational efficient and reliable tool to study optical properties of a wide variety of molecular systems.     

Preparation,characterization and biodistribution of the <Superscript>99m</Superscript>Tc-salicylidenediamine-N-dione complex

A tetradentate set of N₂O₂ salicylaldehyde-amine-N-dione Schiff base was prepared by condensation with salicylaldehyde, ethylenediamine, 2,4-dione and reduction with NaBH₄. The ligand system was characterized by ¹H-NMR and FT-IR spectroscopy and HPLC. Radiolabeling studies of the ^99mTc-complex were performed using stannous ions as the reducing agent. The purity of the complex was determined by ascending solvent system on paper chromatography and instant thin-layer chromatography (ITLC). The yield of the complex was >90%. Biodistribution of the ^99mTc-complex of the precursor was studied in rabbits. A significant uptake and retention of injected activity was observed in the liver and cleared through the bladder. A faint activity was also observed in kidneys. These results indicate that the proposed system may be suitable for development of a liver/spleen imaging agent for future clinical applications.     

Temperature-Dependence of the Rates of Reaction of Trifluoroacetic Acid with Criegee Intermediates

The rate coefficients for gas-phase reaction of trifluoroacetic acid (TFA) with two Criegee intermediates, formaldehyde oxide and acetone oxide, decrease with increasing temperature in the range 240–340 K. The rate coefficients k(CH₂OO + CF₃COOH)=(3.4±0.3)×10⁻¹⁰ cm³ s⁻¹ and k((CH₃)₂COO + CF₃COOH)=(6.1±0.2)×10⁻¹⁰ cm³ s⁻¹ at 294 K exceed estimates for collision-limited values, suggesting rate enhancement by capture mechanisms because of the large permanent dipole moments of the two reactants. The observed temperature dependence is attributed to competitive stabilization of a pre-reactive complex. Fits to a model incorporating this complex formation give k [cm³ s⁻¹]=(3.8±2.6)×10⁻¹⁸ T² exp((1620±180)/T) + 2.5×10⁻¹⁰ and k [cm³ s⁻¹]=(4.9±4.1)×10⁻¹⁸ T² exp((1620±230)/T) + 5.2×10⁻¹⁰ for the CH₂OO + CF₃COOH and (CH₃)₂COO + CF₃COOH reactions, respectively. The consequences are explored for removal of TFA from the atmosphere by reaction with biogenic Criegee intermediates.     

Synthetic strategies toward the synthesis of enoxacin-, levofloxacin-, and gatifloxacin-based compounds: A review

Enoxacin, levofloxacin, and gatifloxacin represent one of the most important prerogative scaffolds in drug development. They possess broad spectrum antimicrobial and anti-inflammatory activities. They inhibit bacterial growth by blocking their topoisomerase enzyme which is necessary for the proper functioning of bacterial DNA. In this article, we have reviewed the synthetic approaches involved in the synthesis of derivatives of enoxacin, levofloxacin, and gatifloxacin.     

A regioselective and convenient one-pot multicomponent synthesis of 9-amino-3,5-diaryl-4,9-dihydro-5H-[1,2,4]triazolo[5,1-c][1,2,4]triazepine-8-thiol

An efficient and environment-friendly procedure for the synthesis of a new series of nitrogen bridge-head [1,2,4]triazolo[5,1-c][1,2,4]triazepine derivatives through one-pot three-component reaction of polyfunctional triazole with aromatic aldehydes and acetophenone derivatives using alcoholic sodium hydroxide solution. The same new products were prepared in classical route through reaction of triazole with the corresponding chalcones under the same conditions.     

The 143 and 300 K polymorphs of hexa­methyl­enetetraminium 2,4-di­nitro­phenolate monohydrate

The title compound, 3,5,7-tri­aza-1-azoniatri­cyclo­[3.3.1.1^3,7]­decane 2,4-di­nitro­phenolate monohydrate, C₆H₁₃N₄⁺·C₆H₃N₂O₅⁻·H₂O, the 1:1 hydrate adduct of hexa­methyl­enetetr­amine (HMT) and 2,4-di­nitro­phenol, undergoes a temperature phase transition. In the room-temperature phase, the adduct crystallizes in the monoclinic P2₁/m space group, whereas in the low-temperature phase, the adduct crystallizes in the triclinic P space group. This phase transition is reversible, with the transition temperature at 273 K, and the phase transition is governed by hydrogen bonds and weak interactions. In both these temperature-dependent polymorphs, the crystal structure is alternately layered with sheets of hexa­methyl­enetetr­amine and sheets of di­nitro­phenol stacked along the c axis. The hexa­methyl­enetetr­amine and di­nitro­phenol moieties are linked by intermolecular hydrogen bonds. The water mol­ecule in the adduct plays an important role, forming O—H⋯O hydrogen bonds which, together with C—H⋯O hydrogen bonds, bridge the adducts into molecular ribbons. Extra hydrogen bonds and weak interactions exist for the low-temperature polymorph and these interconnect the molecular ribbons into a three-dimensional packing structure. Also in these two temperature-dependent polymorphs, di­nitro­phenol acts as a hydrogen-bond acceptor and HMT acts as a hydrogen-bond donor.     

Physical characteristics of X-ray scattering in fat and blood

A Monte Carlo simulation program is constructed in order to trace the histories of photon interactions inside fat and blood under tissue-characterization conditions (energies from 7 to 60 keV and samples from 0.5 to 20 cm). The effect of incident photon energy on the number of coherent and incoherent interactions up to the 3rd order scattering is studied for three different sample sizes. The ratio of scattering to total interactions (including photoelectric absorption) is also studied for fat and blood under the same scattering conditions. Results show considerable differences in the scattering properties of fat and blood over a wide range of energies. This may explain the experimental differences reported by Evans et al. and Kosanetzky et al. The percentage of photons making three incoherent interactions recorded a maximum of 10% which implies the need to correct for multiple scattering in incoherent scattering measurements intended for tissue characterization.