Synthesis, structure and photocatalytic activity of a remarkably bent, cofacial ethene-linked diiron (III) μ-oxobisporphyrin

Synthesis and characterization of cis and trans 1,2-bis[Chloroiron(III) 5-(2,3,7,8,12,13,17,18-octaethylporphyrinyl)]ethenes are described. Upon treatment with 5% NaOH, cis form of the molecule immediately converts to remarkably bent diiron (III)-μ-oxo bisporphyrin which transforms to cis bisChloroFe(III)porphyrin again by the addition of 5% HCl. This facile transformation is reversible with sharp change in color in which the bisporphyrin platform ‘open’ and ‘close’ its binding pockets with very high vertical flexibility in a single molecular framework. Single crystal X-ray structural characterization reveals cis diiron(III)-μ-oxo bisporphyrin in which Fe-O-Fe unit is remarkable bent with 150.9(2)° angle. Two porphyrin rings in the molecule are not slipped but face-to-face in a fully eclipsed geometry and are placed so close that some of the carbon atoms from each of the macrocycles are driven to be essentially less than the van der Waals contacts (<3.4 Å). Two rings in the oxo-bridged dimer also make the interplanar angle of 27.7° instead of expected angle of 60° due to the bridging alkenic bond. EPR, ¹H NMR and Mössbauer spectral data are indicative of strong anti-ferromagnetic coupling between two high-spin iron(III) centers via bridging oxo group. The complex catalyzes the rapid photoinduced oxygenation of phosphites under mild condition using aerial O₂. Electrochemical data reveals that the diiron(III)-μ-oxo bisporphyrin in dichloromethane undergoes four reversible/quasi-reversible one electron oxidation and one electron reductions. The presence of two porphyrin macrocycles within a short distance in the μ-oxo species makes the porphyrin core highly nonplanar and more electron rich that might responsible for easier oxidations compared to [Fe(OEP)]₂O.     

Association of homocysteine and methylene tetrahydrofolate reductase (MTHFR C677T) gene polymorphism with coronary artery disease (CAD) in the population of North India

The implications of the methylene tetrahydrofolate reductase (MTHFR) gene and the level of homocysteine in the pathogenesis of coronary artery disease (CAD) have been extensively studied in various ethnic groups. Our aim was to discover the association of MTHFR (C677T) polymorphism and homocysteine level with CAD in north Indian subjects. The study group consisted of 329 angiographically proven CAD patients, and 331 age and sex matched healthy individuals as controls. MTHFR (C677T) gene polymorphism was detected based on the polymerase chain reaction and restriction digestion with HinfI. Total homocysteine plasma concentration was measured using immunoassay. T allele frequency was found to be significantly higher in patients than in the control group. We found significantly elevated levels of mean homocysteine in the patient group when compared to the control group (p = 0.00). Traditional risk factors such as diabetes, hypertension, smoking habits, a positive family history and lipid profiles (triglyceride, total cholesterol, HDL-cholesterol, LDL-cholesterol, VLDL-cholesterol), were found significantly associated through univariate analysis. Furthermore, multivariable logistics regression analysis revealed that CAD is significantly and variably associated with diabetes, hypertension, smoking, triglycerides and HDL-cholesterol. Our findings showed that MTHFR C677T polymorphism and homocysteine levels were associated with coronary artery disease in the selected population.     

Bioavailability and metabolism of fucoxanthin in rats: structural characterization of metabolites by LC-MS (APCI)

This study reports bioavailability and metabolism of fucoxanthin (FUCO) from brown algae Padina tetrastromatica in rats. Rats were divided into two groups (n = 25/group). Group one was fed basal diet (control) while the group two received retinol deficient diet (RD group) for 8 weeks. After confirmed RD in blood (0.53 μmol/l), rats were further sub-grouped (n = 5/sub group), intubated a dose of FUCO (0.83 μmol) and killed after 0, 2, 4, 6 and 8 h. The plasma levels (area under curve/8 h) of FUCO (fucoxanthinol (FUOH) + amarouciaxanthin (AAx)) was 2.93 (RD group) and 2.74 pmol/dl (control), respectively. No newly formed retinol was detected in RD rats intubated with FUCO. Besides FUOH (m/z 617 (M+H)⁺) and AAx (m/z 617 (M+H^?)⁺), other deacetylated, hydrolyzed and demethylated metabolites of bearing molecular mass at m/z 600.6 (FUOH–H₂O), m/z 597 (AAx–H₂O), m/z 579 (AAx–2H₂O+1), m/z 551 (AAx–2H₂O–2CH₃+2) and m/z 523 (AAx–2H₂O–4CH₃+4) were also detected in plasma and liver by LC-MS (APCI). Although biological functions of FUCO metabolites need thorough investigation, this is the first detailed report on FUCO metabolites in rats.     

Probing the role of metal ions in the catalysis of Helicobacter pylori 3-deoxy-D-manno-octulosonate-8-phosphate synthase using a transient kinetic analysis

3-Deoxy-d-manno-2-octulosonate-8-phosphate (KDO8P) synthase catalyzes the net condensation of phosphoenolpyruvate and d-arabinose 5-phosphate to form KDO8P and inorganic phosphate (Pi). Two classes of KDO8P synthases have been identified. The Class I KDO8P synthases (e.g. Escherchia coli KDO8P synthase) catalyze the condensation reaction in a metal-independent fashion, whereas the Class II enzymes (e.g. Aquifex aeolicus) require metal ions for catalysis. Helicobacter pylori (H. pylori) KDO8P synthase, a Zn2+-dependent metalloenzyme, has recently been found to be a Class II enzyme and has a high degree of clinical significance since it is an attractive molecular target for the design of novel antibiotic therapy. Although the presence of a divalent metal ion in Class II KDO8P synthases is essential for catalysis, there is a paucity of mechanistic information on the role of the metal ions and functional differences as compared with Class I enzymes. Using H. pylori KDO8P synthase as a prototypical Class II enzyme, a steady-state and transient kinetic approach was undertaken to understand the role of the metal ion in catalysis and define the kinetic reaction pathway. Metal reconstitution experiments examining the reaction kinetics using Zn2+, Cd2+, Cu2+, Co2+, Mn2+, and Ni2+ yielded surprising results in that the Cd2+ enzyme has the greatest activity. Unlike Class-I KDO8P synthases, the Class II metallo-KDO8P synthases containing Zn2+, Cd2+, Cu2+, and Co2+ show cooperativity. This study presents the first detailed kinetic characterization of a metal-dependent Class II KDO8P synthase and offers mechanistic insight for how the divalent metal ions modulate catalysis through effects on chemistry as well as quaternary protein structure.     

Purification and characterization of an extracellular polysaccharide from haloalkalophilic Bacillus sp. I-450

During the course of investigation of haloalkalophilic bacteria, we screened some heavily polluted soil samples from the mudflats surrounding the city of Inchon, Korea, for their bioflocculant producing ability. Based on the screening, one isolate no. 450 tentatively identified as Bacillus sp. produced an extracellular polysaccharide having flocculation activity. The isolate produced the polysaccharide during the late logarithmic growth phase. The polymer could be recovered from the supernatant of the fermented medium by cold ethanol precipitation and purified by treating with cetylpyridinium chloride (CPC). The polymer was identified as an acidic polysaccharide containing neutral sugars, namely, galactose, fructose, glucose and raffinose, and uronic acids as major and minor components, respectively. The amount of neutral sugars, uronic acid and amino sugars were 52.4, 17.2 and 2.4%, respectively. The molecular weight of the polysaccharide was found to be 2.2×10⁶ Da. The Fourier transform infrared spectrophotometer (FT-IR) revealed typical characteristics of polysaccharides. ¹H NMR spectrum showed that the polymer is a heteroglycan. Thermogravimetric (TGA) analysis indicated the degradation temperature (T_d) at 290 °C. The rheological analysis of the polymer 450 revealed the pseudoplastic property with shear-thinning effect, while the compression test indicated that the polymer had high gel strength, and the S.E.M. studies showed that the polymer has a porous structure with small pore-size distribution indicating the compactness of the polymer.     

An antisense RNA regulates the bidirectional silencing property of the Kcnq1 imprinting control region

The Kcnq1 imprinting control region (ICR) located in intron 10 of the Kcnq1 gene is unmethylated on the paternal chromosome and methylated on the maternal chromosome and has been implicated in the manifestation of parent-of-origin-specific expression of six neighboring genes. The unmethylated Kcnq1 ICR harbors bidirectional silencer activity and drives expression of an antisense RNA, Kcnq1ot1, which overlaps the Kcnq1 coding region. To elucidate whether the Kcnq1ot1 RNA plays a role in the bidirectional silencing activity of the Kcnq1 ICR, we have characterized factor binding sites by genomic footprinting and tested the functional consequence of various deletions of these binding sites in an episome-based system. Deletion of the elements necessary for Kcnq1ot1 promoter function resulted in the loss of silencing activity. Furthermore, interruption of Kcnq1ot1 RNA production by the insertion of a polyadenylation sequence downstream of the promoter also caused a loss of both silencing activity and methylation spreading. Thus, the antisense RNA plays a key role in the silencing function of the ICR. Double-stranded RNA (dsRNA)-mediated RNA interference is unlikely to be involved, as the ICR is active irrespective of the simultaneous production of dsRNA from the genes it silences.     

Hydrogen peroxide commences copper induced DNA damage isolated from human blood: in vitro study

The present study revealed the damaging effects of copper and hydrogen peroxide on DNA isolated from human blood in in vitro. Ultra violet spectral studies showed that copper and H2O2 alone (at 20 mM) caused destabilization of DNA structure. Notwithstanding, the effect was more prominent in combination of copper and H2O2. Further, agarose gel electrophoretic studies revealed that neither copper nor H2O2 alone had DNA fragmentation (up to 40 mM concentration), while copper and H2O2 together caused massive DNA fragmentation even at lower concentrations (4 mM copper + 4 mM H2O2). Therefore, it was concluded from the present study that the observed destabilization of DNA associated with alterations in configuration and subsequently massive DNA fragmentation was in response to copper and H2O2. Further, fluorescence spectroscopy and TUNNEL assay will address destabilization and fragmentation of naked DNA more precisely.