Search Results (9)

A visible-light-active photocatalyst, SnP/AA@TiO₂, was fabricated by utilizing the coordination chemistry between the axial hydroxo-ligand in the (trans-dihydroxo)(5,10,15,20-tetraphenylporphyrinato)Sn(IV) complex (SnP) and adipic acid (AA) on the surface of TiO₂ nanoparticles. The SnP center was strongly bonded to the surface of the TiO₂ nanoparticles via the adipic acid linkage in SnP/AA@TiO₂, as confirmed by various instrumental techniques. SnP/AA@TiO₂ exhibited remarkably enhanced photocatalytic activity toward the degradation of rhodamine B dye (RhB) in aqueous solution under visible-light irradiation. The RhB degradation efficiency of SnP/AA@TiO₂ was 95% within 80 min, with a rate constant of 0.0366 min⁻¹. The high degradation efficiency, low catalyst loading and high reusability make SnP-anchored photocatalysts more efficient than other photocatalysts, such as TiO₂ and SnP@TiO₂. Full article

To develop the structural and functional modeling chemistry of [NiFe]-H₂ases, we have carried out a study regarding the synthesis, structural characterization and reactivity of a new series of [NiFe]-H₂ase model complexes. Thus, treatment of diphosphine dppb-chelated Ni complex (dppb)NiCl₂ (dppb = 1,2-(Ph₂P)₂C₆H₄) with (dppv)Fe(CO)₂(pdt) (dppv = 1,2-(Ph₂P)₂C₂H₂, pdt = 1,3-propanedithiolate) and NaBF₄ gave dicarbonyl complex [(dppb)Ni(pdt)Fe(CO)₂(dppv)](BF₄)₂ ([A](BF₄)₂). Further treatment of [A](BF₄)₂ with Me₃NO and Bu₄NCN or KSCN afforded t-cyanido and t-isothiocyanato complexes [(dppb)Ni(pdt)Fe(CO)(t-R)(dppv)]BF₄ ([1]BF₄, R = CN; [2]BF₄, R = NCS), respectively. While azadiphosphine MeN(CH₂PPh₂)₂-chelated t-hydride complex [MeN(CH₂PPh₂)₂Ni(pdt)Fe(CO)(t-H)(dppv)]BF₄ ([3]BF₄) was prepared by treatment of dicarbonyl complex [MeN(CH₂PPh₂)₂Ni(pdt)Fe(CO)₂(dppv)](BF₄)₂ ([B](BF₄)₂) with Me₃NO and 1.5 MPa of H₂, treatment of dicarbonyl complex [B](BF₄)₂ with Me₃NO (without H₂) in pyridine resulted in formation of a novel monocarbonyl complex [MeN(CH₂PPh₂)₂Ni(SCHCH₂CH₂S)Fe(CO)(dppv)]BF₄ ([4]BF₄) via the unexpected sp³ C-H bond activation reaction. Furthermore, azadiphosphine PhN(CH₂PPh₂)₂-chelated µ-mercapto complex [PhN(CH₂PPh₂)₂Ni(pdt)Fe(CO)(µ-SH)(dppv)]BF₄ ([5]BF₄) was prepared by treatment of dicarbonyl complex [PhN(CH₂PPh₂)₂Ni(pdt)Fe(CO)₂(dppv)](BF₄)₂ ([C](BF₄)₂) with Me₃NO and H₂S gas, whereas treatment of azadiphosphine Ph₂CHN(CH₂PPh₂)₂-chelated dicarbonyl complex [Ph₂CHN(CH₂PPh₂)₂Ni(pdt)Fe(CO)₂(dppe)](BF₄)₂ ([D](BF₄)₂, dppe = 1,2-(Ph₂P)₂C₂H₄) with Me₃NO⋅2H₂O gave rise to µ-hydroxo complex [Ph₂CHN(CH₂PPh₂)₂Ni(pdt)Fe(CO)(µ-OH)(dppe)]BF₄ ([6]BF₄). All the possible pathways for formation of the new model complexes are briefly discussed, and their structures were fully characterized by various spectroscopic techniques and for six of them by X-ray crystallography. Full article

Adenyl cobamide (commonly known as pseudovitamin B₁₂) is synthesized by intestinal bacteria or ingested from edible cyanobacteria. The effect of pseudovitamin B₁₂ on the activities of cobalamin-dependent enzymes in mammalian cells has not been studied well. This study was conducted to investigate the effects of pseudovitamin B₁₂ on the activities of the mammalian vitamin B₁₂-dependent enzymes methionine synthase and methylmalonyl-CoA mutase in cultured mammalian COS-7 cells to determine whether pseudovitamin B₁₂ functions as an inhibitor or a cofactor of these enzymes. Although the hydoroxo form of pseudovitamin B₁₂ functions as a coenzyme for methionine synthase in cultured cells, pseudovitamin B₁₂ does not activate the translation of methionine synthase, unlike the hydroxo form of vitamin B₁₂ does. In the second enzymatic reaction, the adenosyl form of pseudovitamin B₁₂ did not function as a coenzyme or an inhibitor of methylmalonyl-CoA mutase. Experiments on the cellular uptake were conducted with human transcobalamin II and suggested that treatment with a substantial amount of pseudovitamin B₁₂ might inhibit transcobalamin II-mediated absorption of a physiological trace concentration of vitamin B₁₂ present in the medium. Full article

Lactovegetarians (n = 35) with low vitamin B12 (B12) status were intervened for eight weeks capsules containing cyano-B12 (CN-B12), (2 × 2.8 µg/day), or equivalent doses of endogenous B12 (mainly hydroxo-B12 (HO-B12)) in whey powder. Blood samples were examined at baseline, every second week during the intervention, and two weeks post-intervention. The groups did not differ at baseline in [global median (min/max)] plasma B12 [112(61/185)] pmol/L, holotranscobalamin [20(4/99)] pmol/L, folate [13(11/16)], the metabolites total homocysteine [18(9/52)] µmol/L and methylmalonic acid [0.90(0.28/2.5)] µmol/L, and the combined indicator of B12 status (4cB12) [−1.7(−3.0/−0.33)]. Both supplements caused significant effects, though none of the biomarkers returned to normal values. Total plasma B12 showed a higher increase in the capsule group compared to the whey powder group (p = 0.02). However, the increase of plasma holotranscobalamin (p = 0.06) and the lowering of the metabolites (p > 0.07) were alike in both groups. Thereby, the high total plasma B12 in the capsule group was not mirrored in enhanced B12 metabolism, possibly because the B12 surplus was mainly accumulated on an “inert” carrier haptocorrin, considered to be of marginal importance for tissue delivery of B12. In conclusion, we demonstrate that administration of whey powder (HO-B12) or capsules (CN-B12) equivalent to 5.6 µg of B12 daily for eight weeks similarly improves B12 status but does not normalize it. We document that the results for plasma B12 should be interpreted with caution following administration of CN-B12, since the change is disproportionately high compared to the responses of complementary biomarkers. Full article

We assessed improvements in the vitamin B12 status of Indian lactovegetarians receiving four weeks supplementation with natural B12 in milk versus cyano-B12 in capsules. Three groups (n = 22, 23, 22) received daily oral doses of cyano-B12 (2 × 0.76 µg) or milk (2 × 200 mL) from a cow or buffalo (amounting to B12 ≈ 2 × 0.76 µg). Their blood was examined at baseline and each following week. The baselines (median (min/max)) indicated a low B12 status: plasma B12 (116(51/314)) pmol/L, holotranscobalamin (holoTC) (30(7/119)) pmol/L, total homocysteine (Hcy) (24(10/118)) µmol/L, methylmalonic acid (MMA) (0.58(0.15/2.2)) µmol/L and combined B12 index (cB12) (−1.32 − (−3.12/+0.29)). Shifts from the baselines (B12, holoTC, cB12) and ratios to the baselines (Hcy, MMA) were analyzed over time. The cyano-B12 treatment gave more total B12 in plasma at week one (+29 pmol/L, p = 0.004) but showed no further increase. Other biomarkers changed more comparably between the three groups (p ≥ 0.05): holoTC showed a transient spike that leveled off, Hcy finally decreased to 0.8 × baseline, while MMA showed marginal changes. The combined indexes improved comparably (p = 0.6) in all groups (+0.2(−0.3/+0.9), p ≤ 0.002). In conclusion, the tested formulations similarly improved B12 status, but did not normalize it. Full article

The crystal structure of a novel natural uranyl sulfate, Ca(UO₂)₆(SO₄)₂O₂(OH)₆·12H₂O (CaUS), has been determined using data collected under ambient conditions at the Swiss–Norwegian beamline BM01 of the European Synchrotron Research Facility (ESRF). The compound is monoclinic, P2₁/c, a = 11.931(2), b = 14.246(6), c = 20.873(4) Å, β = 102.768(15), V = 3460.1(18) ų, and R₁ = 0.172 for 3805 unique observed reflections. The crystal structure contains six symmetrically independent U⁶⁺ atoms forming (UO₇) pentagonal bipyramids that share O^…O edges to form hexamers oriented parallel to the (010) plane and extended along [1–20]. The hexamers are linked via (SO₄) groups to form [(UO₂)₆(SO₄)₂O₂(OH)₆(H₂O)₄]²⁻ chains running along the c-axis. The adjacent chains are arranged into sheets parallel to (010). The Ca²⁺ ions are coordinated by seven O atoms, and are located in between the sheets, providing their linkage into a three-dimensional structure. The crystal structure of CaUS is closely related to that of uranopilite, (UO₂)₆(SO₄)O₂(OH)₆·14H₂O, which is also based upon uranyl sulfate chains consisting of hexameric units formed by the polymerization of six (UO₇) pentagonal bipyramids. However, in uranopilite, each (SO₄) tetrahedron shares its four O atoms with (UO₇) bipyramids, whereas in CaUS, each sulfate group is linked to three uranyl ions only, and has one O atom (O16) linked to the Ca²⁺ cation. The chains are also different in the U:S ratio, which is equal to 6:1 for uranopilite and 3:1 for CaUS. The information-based structural complexity parameters for CaUS were calculated taking into account H atoms show that the crystal structure of this phase should be described as very complex, possessing 6.304 bits/atom and 1991.995 bits/cell. The high structural complexity of CaUS can be explained by the high topological complexity of the uranyl sulfate chain based upon uranyl hydroxo/oxo hexamers and the high hydration character of the phase. Full article

Vitamin B12 deficiency during pregnancy has been associated with poor fetal outcome. Here we investigate the influence of a one-carbon (1C) imbalanced diet (low B12, high folate, high methionine) on maternal B12 status, fetal outcome, B12 distribution, and on the 24-h distribution of synthetic cyano-B12 (CN-B12) and natural hydroxo-B12 (HO-B12). Female Wistar rats were mated while on a 1C balanced (n = 12) or imbalanced diet starting two weeks (n = 10) or four weeks (n = 9) prior to pregnancy and continuing throughout pregnancy. At gestation day 18 (out of 21), all rats received an oral dose of labeled CN-B12 or HO-B12. After 24 h, the rats were sacrificed. Fetuses were inspected, and maternal tissues and fetuses were measured for endogenous and labeled B12. Pregnancy caused a redistribution of B12 from the kidneys to the liver and fetal compartment (uterus, placenta, fetuses). The 1C imbalanced diet reduced maternal kidney B12 and gave rise to lower-weight fetuses with visual malformations. In contrast, fetal B12 did not reflect fetal outcome. This suggests that maternal B12 is more important for fetal outcome than fetal B12. The 24-h distribution of labeled B12 in the rats on the 1C imbalanced diet showed a higher fetal accumulation of CN-B12 than HO-B12, while the opposite was seen in the maternal tissues. Full article

Foods contain natural vitamin B12 forms, such as hydroxo–B12 (HO–B12), whereas vitamin pills contain the synthetic cyano–B12 (CN–B12). Recent studies in rats showed different tissue distributions of CN–B12 and HO–B12 24 h after oral administration. Here, we investigate whether these differences are sustained or leveled out with time in both B12-deplete and -replete rats, thereby assessing if the two forms are equally good at maintaining a normal B12 status. Male Wistar rats were fed diets with low (n = 16) or high (n = 12) B12 content for 17 days. At day 10, the rats received a single oral dose of [⁵⁷Co]-labeled CN–B12 or HO–B12 (n = 6 and n = 8, respectively, in each diet group). The rats were sacrificed on day 17 and endogenous B12 and [⁵⁷Co]–B12 were measured in liver, kidney, and plasma. We found that the low-B12 diet introduced a B12-deplete state as judged from medians of endogenous B12 compared to rats on a (high-B12 diet): Plasma (565 (1410) pmol/L), liver (28.2 (33.2) pmol/g), and kidneys (123 (1300) pmol/g). One week after oral administration, the labeled B12 was distributed as follows: HO–B12 > CN–B12 (liver) and CN–B12 > HO–B12 (kidneys, plasma). The tissue/plasma ratios showed different equilibriums for labeled CN–B12 and HO–B12 in the B12-deplete and -replete groups. The equilibrium of endogenous B12 resembled [⁵⁷Co]CN–B12 in replete rats but differed from both [⁵⁷Co]CN–B12 and [⁵⁷Co]HO–B12 in deplete rats. The data suggest long-term differences in tissue utilization of the two B12 forms and warrant further studies concerning the possible benefits of consuming HO–B12 instead of CN–B12 in oral B12 replacement. Full article

Vitamin B12 (B12) is present in foods of animal origin, and vegans are encouraged to take supplements with synthetic B12 in order to ensure a sufficient uptake. Recent rat studies suggest that natural (hydroxo-B12, HO-B12) and synthetic (cyano-B12, CN-B12) B12 behave differently in the body. Here, we test if a daily vitamin pill matches dietary B12 in ability to restore a low B12 status in rats. B12-depleted male Wistar rats (n = 60) were divided into five groups (n = 12 in each) and subjected to two weeks intervention with various schemes of B12 supplementation. Two “dietary” groups received a low-B12 chow that was fortified with either HO-B12 or CN-B12 providing a continuous supply. Two “pill” groups received a single daily dose of CN-B12, where the vitamin content either matched or exceeded by factor four the provisions for the “dietary” groups. A control group received the low-B12 chow without B12 fortification. B12 was measured in plasma and tissues. Dietary B12 provides 35% more B12 to the tissues than an equivalent single daily dose (p < 0.0001). Natural B12 delivers 25% more B12 to the liver than synthetic B12 (p = 0.0007). A fourfold increase in B12, supplemented as a single daily dose, does not provide any extra B12 to the tissues (p = 0.45). We conclude that dietary B12 is better at rescuing a low B12 status than a daily vitamin pill. Full article