Mechanism of product release in NO detoxification from Mycobacterium tuberculosis truncated hemoglobin N

The capability of Mycobacterium tuberculosis to rest in latency in the infected organism appears to be related to the disposal of detoxification mechanisms, which converts the nitric oxide (NO) produced by macrophages during the initial growth infection stage into a nitrate anion. Such a reaction appears to be associated with the truncated hemoglobin N (trHbN). Even though previous experimental and theoretical studies have examined the pathways used by NO and O2 to access the heme cavity, the eggression pathway of the nitrate anion is still a challenging question. In this work we present results obtained by means of classical and quantum chemistry simulations that show that trHbN is able to release rapidly the nitrate anion using an eggression pathway other than those used for the entry of both O2 and NO and that its release is promoted by hydration of the heme cavity. These results provide a detailed understanding of the molecular basis of the NO detoxification mechanism used by trHbN to guarantee an efficient NO detoxification and thus warrant survival of the microorganism under stress conditions.     

Cyclocondensation of 3,3-diamino-1-phenylpropenone with pyridine and quinoline N-oxides containing an electrophilic group in position 3

The cyclocondensation of the N-oxide of the methyl ester of nicotinic acid with 3,3-diamino-1-phenylpropenone and the ethyl ester of 3,3-diaminoacrylic acid in the presence of benzenesulfonyl chloride gives the corresponding 2,7-naphthyridines. The cyclocondensation of 3,3-diamino-1-phenylpropene with the N-oxides of dimethyl 3,5-pyridinedicarboxylate and quinolines containing an electrophilic group at in position 3 yields products of the nucleophilic attack of the carbon nucleophilic site of the enediamine at the 2-pyridine ring position, while the amine group binds to the exocyclic electrophilic group. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 578–584, April, 2008.     

Pressurized liquid extraction and microwave-assisted extraction in the determination of organochlorine pesticides in fish muscle samples

This paper describes a comparative study of 2 extraction methods, pressurized liquid extraction (PLE) and microwave-assisted extraction (MAE), for the determination of organochlorine pesticides (OCPs) in fish muscle samples. In both cases, samples were extracted with hexane-acetone (50 + 50), and the extracts were purified by solid-phase extraction using a carbon cartridge as the adsorbent. Pesticides were eluted with hexane-ethyl acetate (80 + 20) and determined by gas chromatography with electron-capture detection. Both methods demonstrated good linearity over the range studied (0.005-0.100 microg/mL). Detection limits ranged from 0.029 to 0.295 mg/kg for PLE and from 0.003 to 0.054 mg/kg for MAE. For most of the pesticides, analytical recoveries with both methods were between 80 and 120%, and the relative standard deviations were < 10%. The proposed methods were shown to be powerful techniques for the extraction of OCPs from fish muscle samples. Although good recovery rates were obtained with both extraction methods, MAE provided advantages with regard to sample handling, cost, analysis time, and solvent consumption. Acceptable validation parameters were obtained although MAE was shown to be more sensitive than PLE.     

Chemoselective cyclocondensation of α-acylacetamidines with 2-methylsulfanyl-4,6-dichloropyrimidine-5-carbaldehyde

Cyclocondensation of α-acylacetamidine with 2-methylsulfanyl-4,6-dichloropyrimidine-5-carbaldehyde proceeds chemo- and regioselectively involving replacement by the α-carbon of the amidine of the chlorine in the aromatic ring and a reaction of the amino group with the formyl group.     

The effect of different interfaces and confinement on the structure of the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide entrapped in cationic and anionic reverse micelles

The behavior of the ionic liquid (IL) 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][Tf(2)N]) entrapped in two reverse micelles (RMs) formed in an aromatic solvent as dispersant pseudophase: [bmim][Tf(2)N]/benzyl-n-hexadecyldimethylammonium chloride (BHDC)/chlorobenzene and [bmim][Tf(2)N]/sodium 1,4-bis-2-ethylhexylsulfosuccinate (AOT)/chlorobenzene, was investigated using dynamic light scattering (DLS), FT-IR and (1)H NMR spectroscopies. DLS results reveal the formation of RMs containing [bmim][Tf(2)N] as a polar component since the droplet size values increase as the W(s) (W(s) = [[bmim][Tf(2)N]]/[surfactant]) increases. Furthermore, it shows that the RMs consist of discrete spherical and non-interacting droplets of [bmim][Tf(2)N] stabilized by the surfactants. Important differences in the structure of [bmim][Tf(2)N] entrapped inside BHDC RMs, in comparison with the neat IL, are observed from the FT-IR and (1)H NMR measurements. The electrostatic interactions between anions and cations from [bmim][Tf(2)N] and BHDC determine the solvent structure encapsulated inside the nano-droplets. It seems that the IL structure is disrupted due to the electrostatic interaction between the [Tf(2)N](-) and the cationic BHDC polar head (BHD(+)) giving a high ion pair degree between BHD(+) and [Tf(2)N](-) at a low IL content. On the other hand, for the AOT RMs there is no evidence of strong IL-surfactant interaction. The electrostatic interaction between the SO(3)(-) group and the Na(+) counterion in AOT seems to be stronger than the possible [bmim](+)-SO(3)(-) interaction at the interface. Thus, the structure of [bmim][Tf(2)N] encapsulated is not particularly disrupted by the anionic surfactant at all W(s) studied, in contrast to the BHDC RM results. Nevertheless, there is evidence of confinement in the AOT RMs because the [bmim](+)-[Tf(2)N](-) interaction is stronger than in bulk solution. Thus, the IL is more associated upon confinement. Our results reveal that the [bmim][Tf(2)N] structure can be modified in a different manner inside RMs by varying the kind of surfactant used to create the RMs and the IL content (W(s)). These facts can be very important if these media are used as nanoreactors because unique microenvironments can be easily created by simply changing the RM components and W(s).     

Effects of anionic and cationic micelles on the oxidation of d-dextrose by diperiodatoargentate(III)

The oxidative behavior of d-dextrose toward diperiodatoargentate(III) (DPA) has been studied in the absence and presence of anionic and cationic micelles of sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB), respectively. The kinetics is based on the reduction of silver(III) to silver(I) by d-dextrose under pseudo-first-order conditions. The monoperiodatoargentate(III) ions act as active oxidants in comparison to that of DPA. The reactions are first- and fractional-order dependence with respect to [DPA] and [d-dextrose], respectively. The reaction rates decrease with [H⁺] and [periodate]. The premicellar environment of SDS and CTAB strongly inhibits the reaction rate. Inhibition is due to favorable thermodynamic/electrostatic binding between the Ag(III) complex and CTAB monomer aggregates. A suitable mechanism involving a one-electron transfer (rate-determining step) from d-dextrose to the silver(III) species has been proposed. Activation parameters have been evaluated and discussed.     

Heme protein oxygen affinity regulation exerted by proximal effects

Heme proteins are found in all living organisms and are capable of performing a wide variety of tasks, requiring in many cases the binding of diatomic ligands, namely, O(2), CO, and/or NO. Therefore, subtle regulation of these diatomic ligands' affinity is one of the key issues for determining a heme protein's function. This regulation is achieved through direct H-bond interactions between the bound ligand and the protein, and by subtle tuning of the intrinsic heme group reactivity. In this work, we present an investigation of the proximal regulation of oxygen affinity in Fe(II) histidine coordinated heme proteins by means of computer simulation. Density functional theory calculations on heme model systems are used to analyze three proximal effects: charge donation, rotational position, and distance to the heme porphyrin plane of the proximal histidine. In addition, hybrid quantum-classical (QM-MM) calculations were performed in two representative proteins: myoglobin and leghemoglobin. Our results show that all three effects are capable of tuning the Fe-O(2) bond strength in a cooperative way, consistently with the experimental data on oxygen affinity. The proximal effects described herein could operate in a large variety of O(2)-binding heme proteins-in combination with distal effects-and are essential to understand the factors determining a heme protein's O(2) affinity.     

Dependence of chymosin and pepsin partition coefficient with phase volume and polymer pausidispersity in polyethyleneglycol-phosphate aqueous two-phase system

The influence of the phase volume ratio and polymer pausidispersity on chymosin and pepsin partition in polyethylenglycol-phosphate aqueous two-phase systems was studied. Both proteins showed a high affinity for the polyethylenglycol rich phase with a partition coefficient from 20 to 100 for chymosin and from 20 to 180 for pepsin, when the polyethyleneglycol molecular mass in the system varied between 1450 and 8000. The partition coefficient of chymosin was not affected by the volume phase ratio, while the pepsin coefficient showed a significant decrease in its partition coefficient with the increase in the top/bottom phase volume ratio.     

The underaddressed optical multiple-input, multiple-output channel: capacity and outage

We study an optical space-division multiplexed system where the number of modes that are addressed by the transmitter and receiver is allowed to be smaller than the total number of optical modes supported by the fiber. This situation will be of relevance if, for instance, fibers supporting more modes than can be processed with current multiple-input, multiple-output technology are deployed with the purpose of future-proof installation. We calculate the ergodic capacity and the outage probability of the link and study their dependence on the number of addressed modes at the transmitter and receiver.