Rapid Release Of CO Research Articles

Multifunctional BODIPY embedded non-woven fabric for CO release and singlet oxygen generation.

Materials that can simultaneously release CO and generate singlet oxygen upon visible light irradiation under ambient conditions are highly desirable for therapeutic applications. Furthermore, materials that can sequester the undesirable side products into the matrix without affecting the release of CO and singlet oxygen generation would allow them to be used for practical applications. Focussing on these aspects, we prepared two dipicolylamine appended BODIPY‑manganese(I) tricarbonyl complexes wherein the metal core was systematically tethered at 5- and 8- positions of the BODIPY core. The complexes were embedded into a polymer matrix via electrospinning and the resulting non-woven fabrics showed CO release as well as singlet oxygen generation upon irradiation. While the hybrid materials were non-toxic in dark, they were strongly photocytotoxic to c6 cancer cells when exposed to light. Rapid CO release alongside significant singlet oxygen generation, indefinite dark stability, good biocompatibility and negligible dark toxicity makes these fabrics a potent candidate for phototherapeutic applications.

Photoinduced in Vivo Magnetic Resonance Imaging (MRI) with Rapid CO Release from an MnCO-Protein Needle Composite.

Construction of an artificial protein needle (PN), which includes the membrane puncturing needle domain of bacteriophage T4 conjugated to Mn carbonyl (MnCO) complexes, is reported. The responsiveness to visible light of the MnCO complex makes it useful as a photoinduced in vivo magnetic resonance imaging contrast reagent (MRI CR), because the PN carrier has the potential to deliver the MnCO complex into mouse tumors with retention of coordination structure within the in vivo environment. Moreover, the composite has higher relaxivity and longer circulation as an MRI CR than the corresponding MnCO complex. These results demonstrate construction of a responsive in vivo MRI CR by using an artificial metalloprotein.

Rapid green and blue light‐induced CO release from bromazepam Mn(I) and Ru(II) carbonyls: synthesis, density functional theory and biological activity evaluation

Two new photoactivatable carbon monoxide‐releasing molecules (CORMs), fac‐[Mn(CO)3(BZM)Br] (1) and [RuCl2(BZM)(CO)2] (2), derived from the anti‐anxiety drug bromazepam (BZM) and capable of rapid release of CO upon the illumination with light‐emitting diode (LED) source light (470–525 nm) have been synthesized and characterized. The photo‐delivery of CO to myoglobin solution could be achieved via the illumination of 1 at 525 nm for 10 min or at 470 nm for 1 min. The addition of water to a dimethylsulfoxide (DMSO) solution of 1 increases its stability, but it decreases the rate of the CO‐releasing process. CORM 2 behaves as a good visible photoCORM, whereby its two CO molecules are released within 10 min upon exposure to LED light source at 470 nm in DMSO. The illumination profile of 2 was also examined using solution infrared spectroscopy. The cis/trans stereochemistry around the Ru(II) ion was determined using quantum chemical calculations. The formation of photoCORMs leads to an improvement in the toxicity of BZM against tested microbes.

Exceptionally rapid CO release from a manganese(i) tricarbonyl complex derived from bis(4-chloro-phenylimino)acenaphthene upon exposure to visible light

Two manganese(i) carbonyl complexes derived from α,α'-diimine ligands with extended conjugated framework namely [MnBr(CO)3(BIAN)] () and [MnBr(CO)3(MIAN)] (), have been synthesized and structurally characterized. Unlike the previously reported photoactive CO-releasing molecules (photoCORMs), these two complexes exhibit unusually high sensitivity toward low power (0.3-10 mW) visible light (λ ≥ 520 nm) even in the solid state and rapidly release carbon monoxide (CO) upon illumination. The role of the ligand frames in such activity has been examined with the help of theoretical calculations. Application of these photoCORMs in delivering high fluxes of CO to biological targets is anticipated.

Potential Vulnerability of Deep Carbon Deposits of Forested Swamps to Drought

Climate warming is resulting in increases in the frequency and intensity of summer droughts in the Great Lakes–St. Lawrence forest region (Ontario, Canada), raising concerns for the fate of C stores. We hypothesized that deeper peat historically existing beneath the water table would produce significant CO 2 efflux during summer droughts. To test this hypothesis, we collected saturated peat cores, partitioned them into depth intervals, incubated the peat under conditions that resulted in peat drying, and monitored daily CO 2 production together with potential drivers of CO 2 production, including peat quality, microbial biomass, and microbial extracellular enzyme activity. Peat CO 2 production (μ mol CO 2 min −1 g −1 dry soil) was highest in the top 30 cm of the peat profile, with the highest production at intermediate volumetric water content (VWC). Peat substrates fuelling CO 2 production had quotients of C to N of <20 and were characterized by more labile forms of C. Microbial biomass C (mg C g −1 dry soil) and most microbial extracellular enzymes (nmol g −1 h −1 ) were also highest in the top 30 cm of the peat profile. Activities of microbial extracellular enzymes shifted in their contribution to CO 2 production as the peat dried, with hydrolases positively related to CO 2 under dry conditions (5–35%) and negatively under wet conditions (65 and 85%), with phenol oxidase showing the opposite pattern. Currently, the relatively poor quality (i.e., high C/N) of peat in catotelm limits rapid release of CO 2 with water table declines. However, this substantial C store may be vulnerable to decomposition if constraints on quality are alleviated. Abbreviations: FTIR, Fourier transform infrared; TLW, Turkey Lakes Watershed; VWC, volumetric water content.

Thermal and Photochemical Reactivity of Manganese Tricarbonyl and Tetracarbonyl Complexes with a Bulky Diazabutadiene Ligand

The manganese tricarbonyl complex fac-Mn(Br)(CO)3((i)Pr2Ph-DAB) (1) [(i)Pr2Ph-DAB = (N,N'-bis(2,6-di-isopropylphenyl)-1,4-diaza-1,3-butadiene)] was synthesized from the reaction of Mn(CO)5Br with the sterically encumbered DAB ligand. Compound 1 exhibits rapid CO release under low power visible light irradiation (560 nm) suggesting its possible use as a photoCORM. The reaction of compound 1 with TlPF6 in the dark afforded the manganese(I) tetracarbonyl complex, [Mn(CO)4((i)Pr2Ph-DAB)][PF6] (2). While 2 is comparatively more stable than 1 in light, it demonstrates high thermal reactivity such that dissolution in CH3CN or THF at room temperature results in rapid CO loss and formation of the respective solvate complexes. This unusual reactivity is due to the large steric profile of the DAB ligand which results in a weak Mn-CO binding interaction.

Elucidation of the Selectivity of Proton-Dependent Electrocatalytic CO2 Reduction by fac-Re(bpy)(CO)3Cl

A complete mechanism for the proton-dependent electrocatalytic reduction of CO2 to CO by fac-Re(bpy)(CO)3Cl that is consistent with experimental observations has been developed using first principles quantum chemistry. Calculated one-electron reduction potentials, nonaqueous pKa's, reaction free energies, and reaction barrier heights provide deep insight into the complex mechanism for CO2 reduction as well as the origin of selectivity for this catalyst. Protonation and then reduction of a metastable Re-CO2 intermediate anion precedes Brønsted-acid-catalyzed C-O cleavage and then rapid release of CO at negative applied potentials. Conceptually understanding the mechanism of this rapid catalytic process provides a useful blueprint for future work in artificial photosynthesis.

Rapid CO release from a Mn(i) carbonyl complex derived from azopyridine upon exposure to visible light and its phototoxicity toward malignant cells

Two Mn(I) carbonyl complexes namely [MnBr(azpy)(CO)3] and [Mn(azpy)(CO)3(PPh3)](ClO4) (azpy = 2-phenylazopyridine) have been synthesized and characterized. Both complexes exhibit rapid CO release upon exposure to low power visible light. [MnBr(azpy)(CO)3] shows significant phototoxicity toward two malignant cell lines HeLa and MDA-MB-231.

Transfusion of hemoglobin-based oxygen carriers in the carboxy state is beneficial during transient focal cerebral ischemia

Exchange transfusion of large volumes of hemoglobin (Hb)-based oxygen carriers can protect the brain from middle cerebral artery occlusion (MCAO). Hb in the carboxy state (COHb) may provide protection at relatively low volumes by enhancing vasodilation. We determined whether transfusion of rats with 10 ml/kg PEGylated COHb [polyethylene glycol (PEG)-COHb] at 20 min of 2-h MCAO was more effective in reducing infarct volume compared with non-carbon monoxide (CO) PEG-Hb. After PEG-COHb transfusion, whole blood and plasma COHb was <3%, indicating rapid release of CO. PEG-COHb transfusion significantly reduced infarct volume (15 ± 5% of hemisphere; mean ± SE) compared with that in the control group (35 ± 6%), but non-CO PEG-Hb did not (24 ± 5%). Chemically dissimilar COHb polymers were also effective. Induction of MCAO initially produced 34 ± 2% dilation of pial arterioles in the border region that subsided to 10 ± 1% at 2 h. Transfusion of PEG-COHb at 20 min of MCAO maintained pial arterioles in a dilated state (40 ± 5%) at 2 h, whereas transfusion of non-CO PEG-Hb had an intermediate effect (22 ± 3%). When transfusion of PEG-COHb was delayed by 90 min, laser-Doppler flow in the border region increased from 57 ± 9 to 82 ± 13% of preischemic baseline. These data demonstrate that PEG-COHb is more effective than non-CO PEG-Hb at reducing infarct volume, sustaining cerebral vasodilation, and improving collateral perfusion in a model of transient focal cerebral ischemia when given at a relatively low dose (plasma Hb concentration < 1 g/dl). Use of acellular Hb as a CO donor that is rapidly converted to an oxygen carrier in vivo may permit potent protection at low transfusion volumes.

Improved intraischemic perfusion and pial arteriolar dilation by transfusion of pegylated hemoglobin in the carbon monoxide state

Transfusion of chemically‐modifed, cell‐free hemoglobin (Hb) during middle cerebral artery occlusion (MCAO) can reduce infarct volume, but large amounts are typically required. We tested the concept that transfusion of Hb in the CO state would promote vasodilation during MCAO without requiring large amounts of Hb to be transfused. Transfusion of 10 ml/kg of a 4% solution of pegylated COHb (PEG‐COHb) in anesthetized rats resulted in rapid release of CO and equilibration of CO with red cell‐based Hb (2–3% COHb in whole blood and plasma). Plasma [Hb] was ~0.5 g/dL. Induction of MCAO initially produced 37±8% (±SD) dilation of pial arterioles in the MCA border region that gradually subsided to 7±7% at 2 h in controls. Transfusion of PEG‐COHb at 20 min of MCAO maintained pial arterioles in a dilated state (40±13%) at 2 h, whereas transfusion of albumin (25±13%) or PEG‐Hb without CO (22±8%) had intermediate effects. When transfusion of PEG‐COHb was delayed by 90 min, penumbral laser‐Doppler flow increased from 58% to 80% of pre‐ischemic baseline, whereas transfusion of albumin or PEG‐Hb produced no significant change. We conclude that PEG‐COHb can serve as a CO donor that effectively prevents time‐dependent loss of pial arteriolar dilation during MCAO and improves blood flow in the penumbral region to levels above the threshold typically associated with eventual infarction. (Supported by NIH NS38684).

Evidence for the occurrence of photorespiration in synurophyte algae

The fluxes of CO(2) and oxygen during photosynthesis by cell suspensions of Tessellaria volvocina and Mallomonas papillosa were monitored mass spectrometrically. There was no rapid uptake of CO(2,) only a slow drawdown to compensation concentrations of 26 μM for T. volvocina and 18 μM for M. papillosa, when O(2) evolution ceased, indicating a lack of active bicarbonate uptake by the cells. Darkening of the cells after a period of photosynthesis did not cause rapid release of CO(2), indicating the absence of an intracellular inorganic carbon pool. However, upon darkening a brief burst of CO(2) was observed similar to the post-illumination burst characteristic of C(3) higher plants. Treatment of the cells of both species with the membrane-permeable carbonic anhydrase inhibitor ethoxyzolamide had no adverse effect on photosynthetic rate, but stimulated the dark CO(2) burst indicating the dark oxidation of a compound formed in the light. In the absence of any active accumulation of inorganic carbon photosynthesis in these species should be inhibited by O(2). This was investigated in four synurophyte species T. volvocina, M. papillosa, Synura petersenii, and Synura uvella: photosynthetic O(2) evolution rates in all four algae, measured by O(2) electrode, were significantly higher (40-50%) in media at low O(2) (4%) than in air-equilibrated (21% O(2)) media, indicating an O(2) inhibition of photosynthesis (Warburg effect) and thus the occurrence of photorespiration in these species.

Development of a Polymeric Patch Impregnated with Naproxen as a Model of Transdermal Sustained Release System

This paper describes the preparation and characterization of transdermal patches impregnated with naproxen. A mixture of ethylene vinyl acetate and Eudragit E100 (80:20, w/w) is used as a polymeric matrix to obtain a thin membrane to be impregnated. Drug impregnation is carried out under pressurized CO(2) as a processing medium according to a two-step procedure. The patch is first soaked at 1000 psi and 22 °C for 2 h, and then foamed as a result of the rapid release of CO(2) pressure in order to increase the porosity of the surface. Subsequently, the naproxen solution is placed in contact with the membrane and then soaked in CO(2) at 450 psi and 37 °C for 2.5 h to enhance the mass transfer of drug into the polymer matrix. The characterization of the resulting samples by liquid chromatography, microscopy, and calorimetry provides information on naproxen content and distribution. Patches synthesized in this way are loaded with about 1% naproxen. The drug release and diffusion process through a membrane have been studied chromatographically using a Franz diffusion cell. Results have shown that a sustained delivery for more than 24 h is obtained.

Group 6 Carbon Monoxide-Releasing Metal Complexes with Biologically-Compatible Leaving Groups

A series of carbon monoxide-releasing molecules (CO-RMs) based on the M(CO)(5) framework (M = Cr, Mo, W) is reported. The metal carbonyl anions [MCl(CO)(5)](-) are shown to be highly versatile precursors to Group 6 pentacarbonyl complexes containing amino-ester groups, namely, [M(CO)(5)(NH(2)CH{R}CO(2)R')]. The structures of five of the complexes, including an enantiomeric pair based on (R) and (S)-alanine, were determined by single crystal X-ray diffraction. These species exhibit rapid CO-release, as shown by a myoglobin-based assay. The rate of release is affected by the nature of both the metal and the amino-ester employed. A mechanistic study shows that a common intermediate is formed corresponding to loss of the amino-ester from the metal. In addition, a further series of potential CO-RMs have been prepared based on Fischer-type carbenes complexes, which contain either amino esters or amino acids. The amino esters and amino acids are introduced into the coordination sphere of the metal by a nucleophilic substitution reaction at the carbene carbon atom. The Michael addition of NH(2)CH(2)CO(2)Et across the triple bond in [Cr(CO)(5)(═C{OMe}-C≡CPh)] affords crystallographically characterized [Cr(CO)(5)(═C{OMe}-(Z)-CH═C{Ph}NHCH(2)CO(2)Et)]. The rate of CO-release from the carbene complexes depends primarily on the specific heteroatom connected to the carbene center. Rapid CO-release is observed in the case of sulfur- and methoxy-stabilized carbenes whereas in the case of amino-substituted carbenes, release is far more sluggish. This may be correlated with the electrophilic character at the carbene carbon atom.

CARBON CYCLE FOR RAPESEED OIL BIODIESEL FUELS

The greenhouse effect, thought to be responsible for global warming, is caused by gases accumulating in the earth's atmosphere. Carbon dioxide, which makes up half of the gas accumulation problem, is produced during respiration and combustion processes. This paper provides an outline of the carbon cycle for rapeseed oil-derived fuels. Plant processes, fuel chemistry and combustion are examined with respect to carbon. A diagram is presented to interpret the information presented graphically. A comparison of carbon dioxide emissions from the combustion of rapeseed oil biodiesel and petroleum diesel is made. Complete combustion converts hydrocarbon fuels to carbon dioxide and water. The carbon cycle consists of the fixation of carbon and the release of oxygen by plants through the process of photosynthesis, then the recombining of oxygen and carbon to form CO 2 through the processes of combustion and respiration. The carbon dioxide released by petroleum diesel was fixed from the atmosphere during the formative years of the earth. Carbon dioxide released by biodiesel is fixed by the plant in a recent year and is recycled. Many scientists believe that global warming is occurring because of the rapid release of CO 2 in processes such as the combustion of petroleum diesel. Using biodiesel could reduce the accumulation of CO 2 in the atmosphere.

The adaptation of the dichromate digestion method for total mercury determination by cold-vapor atomic absorption spectrometry to the analysis of soils, sediments and sludges

Previous research demonstrated the overall validity of a two-component wet digestion procedure based on the action of K 2Cr 2O 7 + H 2SO 4 (50%, v/v) at boiling temperature (180°C) with vapors refluxing in an air condenser in the treatment of biological samples to be analyzed for total mercury by cold-vapor atomic absorption spectrometry (CVAAS). This study explored the ability of this procedure to cope with soils, sediments and sewage sludges. After demonstrating that cinnabar (HgS) is completely dissolved under the experimental conditions employed, a set of nine standard reference materials having a mercury content ranging from 0.0568 to 9.49 μg g −1 was analyzed. One difficulty was posed by chloride containing samples and was due to the formation of chlorine, a strong inhibitor of the spectrometric signal. Evidence is given that this effect is ascribable to the re-oxidation of elemental mercury by the chlorine present inside the reduction-aeration system. The elimination of chlorine by simply running the digestion without a condenser proved effective in some cases. However, when the samples had a high content of organic matter or carbonates the absence of the condenser caused mercury losses. A study employing mercuric nitrate and methylmercury chloride showed that the escape of mercury from the digestion tube not surmounted by the condenser is related to the rapid release of CO 2 when organic matter and carbonates react with the digestion mixture at its boiling point; high temperature alone is not sufficient for mercury to be lost. Therefore, the digestion procedure was duly reconsidered and split in two parts: (a) an initial 60 min period with the condenser in place during which the destruction of all organic matter and carbonates takes place followed by (b) a 30 min span without condenser to allow chlorine and other potential interfering vapors and gases to leave the digest. The modified procedure was applied to the same reference materials as above and additionally to a biological standard of mussel tissue. The analytical results showed that total mercury could be determined in all samples with consistently good precision and accuracy (R.S.D.% range = 1.2–4.5; error %range = −3.8 to + 8.7).

The degradation of 14C-labelled phosphatidyl choline in soil

When phosphatidyl [ N-methyl- 14CO]choline or phosphatidyl choline di[l- 14C]palmitoyl were incubated in a low phosphorus status soil there was an early and rapid release of CO 2 and a concurrent increase in NaHCO 3-extractable inorganic phosphorus, indicating mineralization of the added organic phosphorus. Mineraiization slowed dramatically and by 20 days only 50% of the carbon from the molecule was accounted for as microbial biomass or respiration. The rates of release of 14CO 2 from the two labelled substrates indicated that 14CO 2 measured as respiration initially arose more swiftly from the carbon portion of the molecules with easiest access to enzymic degradation.