Rate Of Hydrolysis Research Articles

MgH2@Mg(BH4)2 Core-Shell-like Nanostructures: Synthesis, Hydrolysis Performance, and Promotion Mechanism.

The hydrolysis of hydrides, represented by MgH2, delivers substantial capacity and presents an appealing prospect for an on-site hydrogen supply. However, the sluggish hydrolysis kinetics and low hydrogen yield of MgH2 caused by the formation of a passivation Mg(OH)2 layer hinder its practical application. Herein, we present a dual strategy encompassing microstructural design and compounding, leading to the successful synthesis of a core-shell-like nanostructured MgH2@Mg(BH4)2 composite, which demonstrates excellent hydrolysis performance. Specifically, the optimal composite with a low Ea of 9.05 kJ mol-1 releases 2027.7 mL g-1 H2 in 60 min, and its hydrolysis rate escalates to 1356.7 mL g-1 min-1 H2 during the first minute at room temperature. The nanocoating Mg(BH4)2 plays a key role in enhancing the hydrolysis kinetics through the release of heat and the formation of local concentration of Mg2+ field after its hydrolysis. This work offers an innovative concept for the design of hydrolysis materials.

A supramolecular assembly of sulfobutyl ether-β-cyclodextrin and viologen calix[4]resorcinol as the master key to sustainable and eco-friendly catalyst for paraoxon hydrolysis

The search for effective ways of paraoxon (POX) degradation becomes an extremely urgent problem, which can be solved by creating effective bioscavengers in the form of three-dimensional macrocycles. In this work, supramolecular interactions in an aqueous medium were studied between (4-sulfobutyl)-β-cyclodextrin, the hydrophobic cavity of which is capable of binding POX, and viologen calix[4]resorcinol, the cationic groups of which are able to facilitate the nucleophilic attack on the phosphorus atom of the pesticide. A complex of physicochemical methods revealed the nature of the interactions between these cyclodextrin and calix[4]resorcinol, as a result of which the spontaneous formation of nanoparticles occurs. The kinetics of POX hydrolysis reaction using these nanoparticles was studied at room temperature in aqueous Tris-buffer medium by spectrophotometric method. Pure cyclodextrin does not exhibit catalytic activity in the POX hydrolysis, but its presence in a mixture with calix[4]resorcinol leads to a fivefold increase in the hydrolysis rate constant compared to pure calix[4]resorcinol.

Organochlorine Insecticide-Dicofol Resilience in Soil Ecosystems: Sorption, Persistence, and Fate Investigations

ABSTRACT Understanding of dicofol’s behavior in soil is crucial for more precise pest control and minimal environmental effect. Therefore, the goal of this study was to assess how the physicochemical characteristics of 10 selected soils effects the sorption and degradation of dicofol behavior. The behavior of dicofol, including its adsorption and desorption properties as well as its rates of hydrolysis and photolysis degradation, was thoroughly examined via definitive studies. Standard batch equilibration mode for sorption revealed that it was dependent on the physical and chemical properties of the soil. Exothermic and spontaneous adsorption processes, which were characterized by a negative Gibbs free energy value, were convincingly proven by thermodynamic study. The current investigation’s ΔG estimations varied from −18.6 kjmol−1 for soil-6 to −24.25 kjmol−1 for soil-9. The soil-7 with a notable organic matter content (1.81%) showed the maximum adsorption, and subsequently producing a C-type isotherm that was analyzed using a linear and Freundlich model. An analytical process using UV-VIS spectrophotometry to determine the fate of dicofol in soil matrices. Hydrolysis and photolysis studies yielded minimum half-lives of 13.4 and 1.32 days, respectively. It has been demonstrated that dicofol molecules interact strongly with soils, principally via physio-sorption mechanisms. In contrast to its strong soil affinity and permanence, dicofol exhibits a counterintuitive behavior that makes it vulnerable to sunlight-induced deterioration. Future studies will concentrate on enhancing these pathways to assist sustainable pesticide management strategies and creative pollution mitigation techniques.

Insight into sulfapyridine degradation mechanism and antibacterial activity change using enhanced hydrolysis

AbstractAntibiotics in wastewater may inhibit the operation of biological treatment systems. Sulfapyridine (SPY) not only has antibacterial activity, but also chelates with other substances, and its antibacterial activity becomes stronger. An enhanced hydrolysis was applied to remove antibiotics as a promising pretreatment. An increase of 10°C accelerated the SPY hydrolysis rate by 1.98–2.40 fold, and the hydrolysis half‐life of SPY was shortened by 2.92 fold when pH was increased from 3 to 11 at 85°C. Herein, the contribution of hydrolysis to the SPY degradation increased as temperature, and the cleavage of bond is mainly way of SPY hydrolysis. The trend in the TP1 concentration indicate that NC cleavage may occur at the beginning of the reaction. According to result, the contribution of SPY to antibacterial activity decreased as the reaction progressed. The hydrolysis half‐life of SPY was shortened by condition optimization under normal pressure. The optimal conditions are pH = 10.8 and 60°C through response surface methodology (RSM) and EEO value with SPY concentration, antibacterial activity removal efficiency and low energy consumption as targets. Enhanced hydrolysis broken chemical bonds through hydrolysis and oxidation, shortening the hydrolysis half‐life of SPY at high temperature and alkaline. The energy consumption of SPY hydrolysis was calculated for the first time. Under the conditions of pH = 11 and 65°C, the energy consumption of per unit concentration SPY degradation was minimal. The results of this study demonstrated that enhanced hydrolysis is effective and energy conservation as a pretreatment technology for antibiotic.

Low-cost and efficient strategy for brown algal hydrolysis: Combination of alginate lyase and cellulase

Brown algae are rich in biostimulants that not only stimulate the overall development and growth of plants but also have great beneficial effects on the whole soil–plant system. However, alginate, the major component of brown algae, is comparatively difficult to degrade. The cost of preparing alginate oligosaccharides (AOSs) is still too high to produce seaweed fertilizer. In this work, the marine bacterium Vibrio sp. B1Z05 is found to be capable of efficient alginate depolymerization and harbors an extended pathway for alginate metabolism. The B1Z05 extracellular cell-free supernatant exhibited great potential for AOS production at low cost, which, together with cellulase, can efficiently hydrolyze seaweed. The brown algal hydrolysis rates were significantly greater than those of the commercial alginate lyase product CE201, and the obtained seaweed extracts were rich in phytohormones. This work provides a low-cost but efficient strategy for the sustainable production of desirable AOSs and seaweed fertilizer.

Sulfobetaine-Siloxanes: A Class of Self-Destructive Surfactants.

The hydrolytic susceptibility of sulfobetaine-siloxane surfactants is investigated by comparison of a homologous series in this subclass of surfactants (R-(CH2)3N+(Me)2(CH2)3SO3-; R = (Me3SiO)3Si-, (Me3SiO)2Si(Me)-, (Me2SiO)3-Si(Me)-) with an analogue series of oxyethylene-siloxane surfactants (R-(CH2)3(OCH2CH2)10.2OH; R = (Me3SiO)3Si-, (Me3SiO)2Si(Me)-, (Me2SiO)3-Si(Me)-). Nuclear magnetic resonance (NMR) monitoring of these surfactants in an aqueous solution shows that the presence of the sulfobetaine head structure greatly enhances the hydrolysis rate of the siloxane tail as compared with oxyethylene-siloxane analogue control experiments. This sulfobetaine effect is confirmed by adding a model compound, (Me)3N+(CH2)3SO3-, to the oxyethylene-siloxane surfactants and observing the large hydrolysis enhancement. Measurements of pH indicate the sulfobetaine presence greatly enhances acidity, but rigorous analysis could discover no source of acid other than the presence of the sulfobetaine structure. Titration measurements confirmed the presence of a tightly bound hydration layer of 4-7 water molecules per sulfobetaine group. It is speculated that the source of acidity may originate from an aqueous exclusion zone nucleated by the hydrated sulfobetaine at the interface of a sulfobetaine-siloxane surfactant bilayer aggregate. Hydrolysis prevention is investigated by addition of a pH 7 phosphate buffer, of an alkyl polyglycoside cosurfactant, and of a combination of both, with a finding of very significant but not complete suppression of the hydrolysis.

Adding gamma-aminobutyric acid to modulate the in vitro digestive characteristics of tapioca pearls

The effects of gamma-aminobutyric acid (GABA) on gelatinization, pasting and rheological properties of the blend of hydroxypropyl distarch phosphate and tapioca starch were studied to examine the in vitro digestive characteristics of tapioca pearls. The addition of higher GABA contents resulted in lower starch hydrolysis rates and release rates of GABA during the digestion process, which indicated that GABA could modulate the digestive properties of tapioca pearls. RVA and DSC results showed that GABA inhibited the gelatinization of mixed starch and hindered the recrystallization of starch, leading to enhanced thermal stability and reduced viscosity. Also, the addition of GABA limited the water absorption and expansion of starch to some extent, resulting in decreased elastic and viscous moduli. XRD results showed that GABA changed the crystal structure of original mixed starch with reduced crystallinity. Moreover, the addition of GABA resulted in a reduction of RDS content and a significant increase in RS, which would provide potential applications for GABA in starchy health food.

Catalytic hydrolysis of monochlorodifluoromethane over ZnO/ZrO2 catalysts at low temperatures.

Monochlorodifluoromethane (HCFC-22) has been identified as a significant contributor to the depletion of the Earth's ozone layer, garnering considerable attention within the scientific community. Consequently, the investigation of Freon degradation has become a central focus of current research efforts. In this study, we opted to employ catalytic hydrolysis as it offers numerous advantages for the degradation of HCFC-22. Specifically, we prepared ZnO/ZrO2 catalysts with hexahedral rod-like structures through citric acid complexation. We examined the impact of various preparation conditions (such as the molar ratio of ZnO to ZrO2, calcination temperature, and calcination time) as well as catalytic hydrolysis conditions (including the amount of catalyst, total flow rate, and catalytic hydrolysis temperature) on the hydrolysis rate of HCFC-22. Characterization of the catalysts was performed using techniques such as XRD, SEM, EDS, TG-DTG, FTIR, N2 adsorption-desorption, CO2-TPD, and NH3-TPD. Our experimental findings revealed the optimal preparation conditions: a catalytic hydrolysis temperature of 100°C, a molar ratio of ZnO to ZrO2 of 0.7, a water bath temperature of 90°C, a roasting temperature of 400°C, and a roasting time of 4h. At a catalytic hydrolysis temperature of 100°C, the hydrolysis rate of HCFC-22 reached 99.81%, with the main hydrolyzed products being HCl, HF, and CO2.

β-galactosidase orodispersible dosage forms for the treatment of lactose intolerance

Lactose intolerance is associated with the insurgence of mild to severe gastrointestinal symptoms. The administration of β-galactosidase (β-gal) tablets or capsules, which are unsuitable for the dysphagic population, is the main symptomatic treatment. This work aimed to demonstrate the feasibility of β-gal orodispersible films (ODF) prepared by solvent casting technique. Since the preparation involves thermal and mechanical stresses, which can compromise the enzyme stability, in vitro performances of ODF were compared to those of oral lyophilizates (OL).ODF were made of maltodextrin DE6, glycerol and Capryol®90. OL made of different grades of maltodextrins, and sorbitol or trehalose were prepared in aluminium blisters. ODF and OL were assayed for disintegration time and β-gal activity. The hydrolysis rate of lactose was determined using: a) a placebo capsule (500 mg lactose) disintegrated in a glass of water; b) 150 mL milk in biorelevant media. ODF (6 cm2) and OL (made of maltodextrin DE19 and trehalose). ODF and OL loaded with about 4000 UI of β-gal were stable over 3 months of storage at 25 °C/60% RH. Both of them allowed the hydrolysis of lactose in water within 15 min. The complex composition of milk affected the hydrolysis rate (K) of lactose: the reaction was faster in fasted-state media (K ≈ −0.07 min−1) than in those simulating the fed state of subjects with physiologically appreciable residual gastric fluid in the stomach (grade 1 antrum: 20 mL, K ≈ −0.005 min−1; grade 2 antrum: 180 mL, K ≈ −0.01 min−1). No significant differences were noticed between ODF and OL. Overall, ODF can be proposed to hydrolyse lactose contained in immediate release dosage forms, improving the patient's adherence to therapy. Moreover, the dependence of the lactose degradation kinetic not only on the fed or fasted conditions, but also on the antrum phenotype may allow the development of ODF in a more patient-centric perspective.

Unraveling the Significance of Mg2+ Dependency and Nucleotide Binding Specificity of H-RAS.

RAS is a small GTPase and acts as a binary molecular switch; the transition from its active to inactive state plays a crucial role in various cell signaling processes. Molecular dynamics simulations at the atomistic level suggest that the absence of cofactor Mg2+ ion generally leads to pronounced structural changes in the Switch-I than Switch-II regions and assists GTP binding. The presence of the Mg2+ ion also restricts the rotation of ϒ phosphate and enhances the hydrolysis rate of GTP. Further, the simulations reveal that the stability of the protein is almost uncompromised when Mg2+ is replaced with Zn2+ and not the Ca2+ ion. The specificity of H-RAS to GTP was evaluated by substituting with ATP and CTP, which indicates that the binding pocket tolerates purine bases over pyrimidine bases. However, the D119 residue specifically interacts with the guanine base and serves as one of the primary interactions that leads to the selectivity of GTP over ATP. The ring displacement of 32Y serves as gate dynamics in H-RAS which are important for its interaction with GAP for the nucleotide exchange and is restricted in the presence of ATP. Finally, the point mutations 61, 16, and 32 influence the structural changes, specifically in the Switch-II region, which are expected to impact the GTP hydrolysis and thus are termed oncogenic mutations.

Electrochemical Acetylcholinesterase Sensors for Anti-Alzheimer's Disease Drug Determination.

Neurodegenerative diseases and Alzheimer's disease (AD), as one of the most common causes of dementia, result in progressive losses of cholinergic neurons and a reduction in the presynaptic markers of the cholinergic system. These consequences can be compensated by the inhibition of acetylcholinesterase (AChE) followed by a decrease in the rate of acetylcholine hydrolysis. For this reason, anticholinesterase drugs with reversible inhibition effects are applied for the administration of neurodegenerative diseases. Their overdosage, variation in efficiency and recommendation of an individual daily dose require simple and reliable measurement devices capable of the assessment of the drug concentration in biological fluids and medications. In this review, the performance of electrochemical biosensors utilizing immobilized cholinesterases is considered to show their advantages and drawbacks in the determination of anticholinesterase drugs. In addition, common drugs applied in treating neurodegenerative diseases are briefly characterized. The immobilization of enzymes, nature of the signal recorded and its dependence on the transducer modification are considered and the analytical characteristics of appropriate biosensors are summarized for donepezil, huperzine A, rivastigmine, eserine and galantamine as common anti-dementia drugs. Finally, the prospects for the application of AChE-based biosensors in clinical practice are discussed.

Synthesis and Characterization of Organic Peroxides from Monoterpene-Derived Criegee Intermediates in Secondary Organic Aerosol.

Ozonolysis of alkenes is known to produce reactive intermediates─stabilized Criegee intermediates (SCIs), and their subsequent bimolecular reactions with various carboxylic acids can form α-acyloxyalkyl hydroperoxides (AAHPs), which is considered a major class of organic peroxides in secondary organic aerosol (SOA). Despite their atmospheric and health importance, the molecular-level identification of organic peroxides in atmospheric aerosols is highly challenging, preventing further assessment of their environmental fate. Here, we synthesize 20 atmospherically relevant AAHPs through liquid-phase ozonolysis, in which two types of monoterpene-derived SCIs from either α-pinene or 3-carene are scavenged by 10 different carboxylic acids to form AAHPs with diverse structures. These AAHPs are identified individually by liquid chromatography coupled with high-resolution mass spectrometry. AAHPs were previously thought to decompose quickly in an aqueous environment such as cloud droplets, but we demonstrate here that AAHPs hydrolysis rates are highly compound-dependent with rate constants differing by 2 orders of magnitude. In contrast, the aqueous-phase formation rate constants between SCI and various carboxylic acids vary only within a factor of 2-3. Finally, we identified two of the 20 synthesized AAHPs in α-pinene SOA and two in 3-carene SOA, contributing ∼0.3% to the total SOA mass. Our results improve the current molecular-level understanding of organic peroxides and are useful for a more accurate assessment of their environmental fate and health impact.

A missense mutation in the Hspa8 gene encoding heat shock cognate protein 70 causes neuroaxonal dystrophy in rats.

Neuroaxonal dystrophy (NAD) is a neurodegenerative disease characterized by spheroid (swollen axon) formation in the nervous system. In the present study, we focused on a newly established autosomal recessive mutant strain of F344-kk/kk rats with hind limb gait abnormalities and ataxia from a young age. Histopathologically, a number of axonal spheroids were observed throughout the central nervous system, including the spinal cord (mainly in the dorsal cord), brain stem, and cerebellum in F344-kk/kk rats. Transmission electron microscopic observation of the spinal cord revealed accumulation of electron-dense bodies, degenerated abnormal mitochondria, as well as membranous or tubular structures in the axonal spheroids. Based on these neuropathological findings, F344-kk/kk rats were diagnosed with NAD. By a positional cloning approach, we identified a missense mutation (V95E) in the Hspa8 (heat shock protein family A (Hsp70) member 8) gene located on chromosome 8 of the F344-kk/kk rat genome. Furthermore, we developed the Hspa8 knock-in (KI) rats with the V95E mutation using the CRISPR-Cas system. Homozygous Hspa8-KI rats exhibited ataxia and axonal spheroids similar to those of F344-kk/kk rats. The V95E mutant HSC70 protein exhibited the significant but modest decrease in the maximum hydrolysis rate of ATPase when stimulated by co-chaperons DnaJB4 and BAG1 in vitro, which suggests the functional deficit in the V95E HSC70. Together, our findings provide the first evidence that the genetic alteration of the Hspa8 gene caused NAD in mammals.

Phosphate Triester Hydrolysis by Mononuclear Iron(III) Complexes: The Role of Benzimidazole in the Second Coordination Sphere

AbstractOver the years, phosphate ester hydrolysis catalyzed by coordination compounds has attracted extensive research on developing new bioinspired compounds. However, the literature lacks sufficient examples displaying activity toward phosphate triesters specifically, limiting the understanding of efficient strategies for the hydrolysis of this compound hydrolysis. Herein, we report preparing and characterizing three mononuclear iron(III) complexes (1, 2, and 3) and their hydrolase‐like activity. Complexes 2 and 3 have benzimidazole (BIMZ) moieties and were strategically designed to separate the BIMZ moiety from the first coordination sphere, and complex 1 (without BIMZ) was used as a reference. Several techniques provided structural information, including spectrophotometry, spectrometry, electrochemistry, elemental analysis, and 57Fe Mossbauer. Density functional theory (DFT) revealed distorted octahedral geometries due to the presence of the BIMZ groups. These groups also directly affected the protonation equilibria and catalytic activity. The phosphate triester diethyl‐2,4‐dinitrophenylphosphate (DEDNPP) hydrolysis was enhanced at least 27 times compared to the uncatalyzed reaction, with complexes 2 and 3, thus showing higher catalytic rates (kcat). Moreover, a longer carbon chain led to a higher hydrolysis rate but less interaction with substrate. These findings provide background for further investigations and the development of efficient catalysts for agrochemical degradation.

Improving BioWin Modeling of Phosphorus Solubilization in Acid-Phase Digesters

BioWin 6.0 does not accurately predict phosphorus (P) speciation in acidogenic anaerobic digesters under default kinetics characterization and parameterization. The accurate modeling of acid-phase digestion is needed to predict the performance of novel nutrient recovery technologies that act on these digester effluents. The main thrust of this work was to identify and correct the causes of inaccurate P partitioning and precipitation within BioWin models of acid-phase digestion reactors. A BioWin configuration including an organic acid digester was parameterized and recalibrated based on the known traits of acid-phase digestion and then validated against a full-scale digester in a municipal wastewater treatment plant. This digester, with pH 5.14 and 61–74% solubilized P, was predicted by BioWin default parameters to have only 27% soluble P and a net formation of P precipitates. Corrections to the polyphosphate-accumulating organism decay, endogenous product decay, hydrolysis rate, and brushite behavior resulted in 67% solubilization with no precipitate formation. Cabinet configurations showed similar behavior when modified to include an acid-phase digester under default parameters, but predictions were similarly amended by our parameter changes. This improved modeling technique should allow operators to effectively characterize acid digesters for their own treatment trains and allow engineers to predict the performance of novel nutrient recovery technologies acting on acidogenic digest.

Development of a non-radioactive based assay to measure GTP and ATP hydrolysis rates

Development of a non-radioactive based assay to measure GTP and ATP hydrolysis rates

The Dynamic Chemistry of Orthoesters and Trialkoxysilanes: Making Supramolecular Hosts Adaptive, Fluxional, and Degradable.

ConspectusThe encapsulation of ions into macro(bi)cyclic hosts lies at the core of supramolecular chemistry. While chemically inert hosts such as crown ethers (synthesis) and cyclodextrins (Febreze) have enabled real-world applications, there is a wider and accelerating trend toward functional molecules and materials that are stimuli-responsive, degradable, or recyclable. To endow supramolecular hosts with these properties, a deviation from ether C-O bonds is required, and functional groups that engage in equilibrium reactions under relatively mild conditions are needed.In this Account, we describe our group's work on supramolecular hosts that comprise orthoester and trialkoxysilane bridgeheads. In their simplest structural realization, these compounds resemble both Cram's crown ethers (macrocycles with oxygen donor atoms) and Lehn's cryptands (macrobicycles with 3-fold symmetry). It is therefore not surprising that these new hosts were found to have a natural propensity to bind cations relatively strongly. In recent work, we were also able to create anion-binding hosts by placing disubstituted urea motifs at the center of the tripodal architecture. Structural modifications of either the terminal substituents (e.g., H vs CH3 on the bridgehead), the diol (e.g., chiral), or the bridgehead atom itself (Si vs C) were found to have profound implications on the guest-binding properties.What makes orthoester/trialkoxysilane hosts truly unique is their dynamic covalent chemistry. The ability to conduct exchange reactions with alcohols at the bridgehead carbon or silicon atom is first and foremost an opportunity to develop highly efficient syntheses. Indeed, all hosts presented in this Account were prepared via templated self-assembly in yields of up to 90%. This efficiency is remarkable because the macrobicyclic architecture is established in one single step from at least five components. A second opportunity presented by dynamic bridgeheads is that suitable mixtures of orthoester hosts or their subcomponents can be adaptive, i.e. they respond to the presence of guests such that the addition of a certain guest can dictate the formation of a preferred host. In an extreme example of dynamic adaptivity, we found that ammonium ions can fulfill the dual role of catalyst for orthoester exchange and cationic template for efficient host formation, representing an unprecedented example of a fluxional supramolecular complex. The third implication of dynamic bridgeheads is due to the reaction of orthoesters and trialkoxysilanes with water instead of alcohols. We describe in detail how the hydrolysis rate differs strongly between O,O,O-orthoesters, S,S,S-trithioorthoesters, and trialkoxysilanes and how it is tunable by the choice of substituents and pH.We expect that the fundamental insights into exchange and degradation kinetics described in this Account will be useful far beyond supramolecular chemistry.

Rice husk-based biogenic silica-anchored Sn-Co bimetallic catalysts for cellulose hydrogenolysis: Structural regulation and mechanism study

The production of high value-added chemicals and materials from renewable biomass is significant for the sustainable development of chemical industry. Herein, rice husk-based biogenic silica-anchored Sn-Co catalysts with adjustable activity are successfully prepared for biomass valorization. By regulating the pretreatment method and carbothermal reduction temperature of catalysts, the interaction between Co, Sn and biogenic silica can be regulated, thereby regulating the catalytic activity of the catalyst for cellulose hydrogenolysis. 50.7 % yield of acetol and 63.4 % yield of C3 products can be obtained. A series of characterizations show that the hydrothermal pretreatment in CoCl2 solution promotes the combination of Co2+ and biogenic silica, which inhibits the excessive doping of Sn4+ and promotes the formation of Co3Sn2 alloy. The Sn-O-Si and Co3Sn2 species in 3Sn-5Co@RHC are the key active sites catalyzing glucose isomerization and fructose retro-aldol condensation. The intermediates experiments show that controlling the hydrolysis rate of cellulose to avoid excessive concentration of monosaccharide intermediates in the reaction system is crucial for inhibiting side reactions and improving the yield of acetol. The use of agroforestry waste-based catalytic materials for biomass conversion in this work can provide inspiration for exploiting the intrinsic characteristics of biomass to develop high value-added materials and chemicals.

Pulsed inputs of high molecular weight organic matter shift the mechanisms of substrate utilisation in marine bacterial communities.

Heterotrophic bacteria hydrolyze high molecular weight (HMW) organic matter extracellularly prior to uptake, resulting in diffusive loss of hydrolysis products. An alternative 'selfish' uptake mechanism that minimises this loss has recently been found to be common in the ocean. We investigated how HMW organic matter addition affects these two processing mechanisms in surface and bottom waters at three stations in the North Atlantic Ocean. A pulse of HMW organic matter increased cell numbers, as well as the rate and spectrum of extracellular enzymatic activities at both depths. The effects on selfish uptake were more differentiated: in Gulf Stream surface waters and productive surface waters south of Newfoundland, selfish uptake of structurally simple polysaccharides increased upon HMW organic matter addition. The number of selfish bacteria taking up structurally complex polysaccharides, however, was largely unchanged. In contrast, in the oligotrophic North Atlantic gyre, despite high external hydrolysis rates, the number of selfish bacteria was unchanged, irrespective of polysaccharide structure. In deep bottom waters (> 4000 m), structurally complex substrates were processed only by selfish bacteria. Mechanisms of substrate processing-and the extent to which hydrolysis products are released to the external environment-depend on substrate structural complexity and the resident bacterial community.

Hydrolysis and Transport Characteristics of Phospholipid Complex of Alkyl Gallates: Potential Sustained Release of Alkyl Gallate and Gallic Acid.

Phospholipid complexes of alkyl gallates (A-GAs) including ethyl gallate (EG), propyl gallate (PG), and butyl gallate (BG) were successfully prepared by the thin film dispersion method. HPLC-UV analysis in an everted rat gut sac model indicated that A-GAs can be liberated from phospholipid complexes, which were further hydrolyzed by intestinal lipase to generate free gallic acid (GA). Both A-GAs and GA are able to cross the membrane, and the hydrolysis rate of A-GAs and the transport rate of GA are positively correlated with the alkyl chain length. Especially, compared with the corresponding physical mixtures, the phospholipid complexes exhibit slower sustained-release of A-GAs and GA. Therefore, the formation of phospholipid complexes is an effective approach to prolong the residence time in vivo and additionally enhance the bioactivities of A-GAs and GA. More importantly, through regulating the carbon skeleton lengths, controlled-release of alkyl gallates and gallic acid from phospholipid complexes will be achieved.