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1.
Vasc Endovascular Surg ; : 1538574420941298, 2020 Jul 28.
Artigo em Inglês | MEDLINE | ID: mdl-32721190

RESUMO

PURPOSE: Vascular closure device (VCD) use following antegrade femoral access may present unique challenges relative to retrograde access. We retrospectively compared safety and efficacy of these devices between antegrade and retrograde patient cohorts undergoing percutaneous intervention. MATERIALS AND METHODS: Over a 5-year period, a consecutive series of 107 limbs in 84 patients underwent VCD arteriotomy closure following percutaneous revascularization using an antegrade approach (VCD-A). Device deployment success rates, time to ambulation, and complication rates were compared to a contemporaneous control group of 401 limbs in 305 patients who underwent closure following retrograde access (VCD-R) during revascularization or embolization procedures. RESULTS: Closure was attempted in VCD-A using 53 StarClose, 35 Perclose, and 19 Angio-Seal devices. Hemostasis (without supplemental manual compression) was achieved in 86/107 (80.4%) limbs. Closure was attempted in VCD-R using 215 StarClose, 119 Perclose, and 67 Angio-Seal devices with hemostasis in 357/401 (89.0%) limbs. Device deployment failure occurred in 7/107 (6.5%) of VCD-A and 20/401 (5.0%) of VCD-R (P = .52), independent of specific device type. Femoral pseudoaneurysm developed in 1/107 and 1/401 of VCD-A and VCD-R (P = .31), and minor hematoma developed in 3/107 and 8/401 of the VCD-A and VCD-R (P = .61). Mean time to ambulation was 204.1 minutes in VCD-A and 204.8 minutes in VCD-R (P = .97). CONCLUSION: Antegrade femoral closure was associated with high rates of technical success and low complications, similar to retrograde closure. Time to ambulation was the same in both groups despite higher heparin doses in the antegrade patients.

2.
Proc Natl Acad Sci U S A ; 117(27): 15414-15422, 2020 Jul 07.
Artigo em Inglês | MEDLINE | ID: mdl-32571939

RESUMO

We report on a combined activation mechanism for a class B G-protein-coupled receptor (GPCR), the glucagon receptor. By computing the conformational free-energy landscape associated with the activation of the receptor-agonist complex and comparing it with that obtained with the ternary complex (receptor-agonist-G protein) we show that the agonist stabilizes the receptor in a preactivated complex, which is then fully activated upon binding of the G protein. The proposed mechanism contrasts with the generally assumed GPCR activation mechanism, which proceeds through an opening of the intracellular region allosterically elicited by the binding of the agonist. The mechanism found here is consistent with electron cryo-microscopy structural data and might be general for class B GPCRs. It also helps us to understand the mode of action of the numerous allosteric antagonists of this important drug target.

3.
J Phys Chem A ; 2020 Jul 07.
Artigo em Inglês | MEDLINE | ID: mdl-32567862

RESUMO

Triplet-excited-state energies of perylene-monoimides (PMIs) lie in the range 1.12 eV ± 2 meV when compared to singlet-excited-state energies of about 2.39 eV ± 2 meV; therefore, the corresponding naphthalene-linked PMI-Dimer was investigated as a novel singlet-fission (SF) material. Ultrafast transient absorption measurements demonstrated the (S1S0)-to-1(T1T1) transformation and the involvement of a mediating step in the overall 1(T1T1) formation. The intermediate is a charge-transfer state that links the initial (S1S0) with the final 1(T1T1), and imposes charge-transfer character on both, which are thus denoted (S1S0)CT and 1(T1T1)CT. At room temperature, the decorrelation and stability of 1(T1T1)CT is affected by the geminate triplet-triplet recombination (G-TTR) of the two triplets. Independent confirmation for G-TTR to afford up-converted (S1S0)UC in fsTA and nsTA measurements with PMI-Dimer, came from probing PMI-Monomer (T1)s in triplet-triplet annihilation up-conversion (TTA-UC). The G-TTR channel, active in the PMI-Dimer at room temperature, is suppressed by working at either low temperatures (∼140 K) or in polar solvents (benzonitrile): Both scenarios assist in stabilizing (T1T1)CT. As a consequence, the triplet quantum yields are 4.2% and 14.9% at room temperature and 140 K, respectively, in 2-methyltetrahydrofuran.

4.
Artigo em Inglês | MEDLINE | ID: mdl-32492240

RESUMO

Red-emissive π-expanded diketopyrrolopyrroles (DPPs) with fluorescence reaching λ=750 nm can be easily synthesized by a three-step strategy involving the preparation of diketopyrrolopyrrole followed by N-arylation and subsequent intramolecular palladium-catalyzed direct arylation. Comprehensive spectroscopic assays combined with first-principles calculations corroborated that both N-arylated and fused DPPs reach a locally excited (S1 ) state after excitation, followed by internal conversion to states with solvent and structural relaxation, before eventually undergoing intersystem crossing. Only the structurally relaxed state is fluorescent, with lifetimes in the range of several nanoseconds and tens of picoseconds in nonpolar and polar solvents, respectively. The lifetimes correlate with the fluorescence quantum yields, which range from 6 % to 88 % in nonpolar solvents and from 0.4 % and 3.2 % in polar solvents. A very inefficient (T1 ) population is responsible for fluorescence quantum yields as high as 88 % for the fully fused DPP in polar solvents.

5.
J Am Chem Soc ; 142(28): 11988-11992, 2020 Jul 15.
Artigo em Inglês | MEDLINE | ID: mdl-32594742

RESUMO

Phosphonate-directed ortho C-H borylation of aromatic phosphonates is reported. Using simple starting materials and commercially accessible catalysts, this method provides steady access to o-phosphonate arylboronic esters bearing pendant functionality and flexible substitution patterns. These products serve as flexible precursors for a variety of highly substituted phosphoarenes, and in situ downstream functionalization of the products is described.

6.
J Vasc Interv Radiol ; 31(7): 1148-1155, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-32534972

RESUMO

PURPOSE: To compare clinical performance of 2 widely used symmetric-tip hemodialysis catheters. MATERIALS AND METHODS: Patients with end-stage renal disease initiating or resuming hemodialysis were randomized to receive an Arrow-Clark VectorFlow (n = 50) or Palindrome catheter (n = 50). Primary outcome was 90-d primary unassisted catheter patency. Secondary outcomes were Kt/V ([dialyzer urea clearance × total treatment time]/total volume of urea distribution), urea reduction ratio (URR), and effective blood flow (QB). RESULTS: Primary unassisted patency rates with the VectorFlow catheter at 30, 60, and 90 d were 95.5% ± 3.3, 87.2% ± 7.3, and 80.6% ± 9.8, respectively, compared with 89.1% ± 6.2, 79.4% ± 10.0, and 71.5% ± 12.6 with the Palindrome catheter (P = .20). Patients with VectorFlow catheters had a mean Kt/V of 1.5 at 30-, 60-, and 90-day time points, significantly higher than the mean Kt/V of 1.3 among those with Palindrome catheters (P = .0003). URRs were not significantly different between catheters. Catheter QB rates exceeded National Kidney Foundation-recommended thresholds of 300 mL/min at all time points for both catheters and were similar for both catheters (median, 373 mL/min). Catheter failure, ie, poor flow rate requiring guide-wire exchange or removal, within the 90-day primary outcome occurred in 3 VectorFlow subjects and 5 Palindrome subjects (P = .72). Infection rates were similar, with 0.98 infections per 1,000 catheter days for VectorFlow catheters compared with 2.62 per 1,000 catheter days for Palindrome catheters (P = .44). CONCLUSIONS: The 90-day primary patency rates of Palindrome and VectorFlow catheters were not significantly different, and both achieved sustained high QB through 90 day follow-up. However, dialysis adequacy based on Kt/V was consistently better with the VectorFlow catheter versus the Palindrome.

7.
J Vasc Interv Radiol ; 31(6): 993-999.e1, 2020 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-32376177

RESUMO

PURPOSE: To compare outcomes of transradial access for endovascular treatment of nonmaturing hemodialysis fistulae compared to brachial arteriography followed by unidirectional or bidirectional fistula access for intervention. MATERIALS AND METHODS: In this institutional review board-approved, retrospective, case-control study, 56 consecutive patients with nonmaturing arteriovenous fistulae underwent percutaneous intervention between 2015 and 2018. The transradial group (n = 28) underwent radial artery access for diagnostic fistulography and intervention. The control group (n = 28) underwent retrograde brachial artery access for fistulography followed by unidirectional/bidirectional fistula access for intervention. Both groups had similar demographics, fistula characteristics, and stenosis locations. RESULTS: Fewer punctures were required in the transradial group compared to controls (1.2 vs 2.4, P < .0001), and procedure time was shorter (64.9 vs 91.3 minutes, P = .0016). Anatomic, technical, and clinical success rates trended higher in the transradial group compared to controls (93% vs 86%, 96% vs 89%, and 82% vs 64%, respectively). Nonmaturation resulting in fistula abandonment was lower in the transradial group (3.7% vs 25%, P = .025). Primary unassisted patency at 3, 6, and 12 months was 77.1% ± 8.2%, 73.1% ± 8.7%, and 53.3% ± 10.6% in the transradial group, respectively, and 63.0% ± 9.3%, 55.6% ± 9.6%, and 48.1% ± 9.6% in the control group, respectively (P = .76). Primary assisted patency at 12 months was 92.3% ± 5.3% in the transradial group compared to 61.8% ± 9.6% at 12 months in the control group (P = .021). No major complications occurred. Minor complications were lower in the transradial group than in the control group (14% vs 39%, P = .068). CONCLUSIONS: Treatment of nonmaturing fistulae via a transradial approach was safe, improved midterm patency, and was associated with lower rates of fistula abandonment.

8.
Abdom Radiol (NY) ; 2020 May 11.
Artigo em Inglês | MEDLINE | ID: mdl-32394042

RESUMO

PURPOSE: The objectives of this study were to determine the effects of expanded polytetrafluoroethylene (PTFE)-covered stent location and TIPS extension on primary patency. METHODS: This retrospective cohort study examined patients with PTFE-covered TIPS creation between 07/2002 and 06/2016. Clinical information and patency outcomes at 24 months were extracted. At TIPS creation, extension was performed at the discretion of the operator. Kaplan-Meier curves of primary patency were generated with conditional variables of HVO-HCJ distance, extension status, and covered versus uncovered extensions. Additional logistic regression analyses of distances were performed. RESULTS: Of 393 patients, 115 patients (29%) underwent stent extension, 79 (20% of total cohort) of which were at the HVO end alone. Primary patency for all TIPS was 75%, 68%, and 54% at 3, 6, and 12 months. The data endpoint were transplant or death in 92 (23%) and 116 (30%). Kaplan-Meier curves showed no statistically significant difference between the variables and primary patency at 12 and 24 months: distance up to versus greater than 10 mm (p = 0.32, 0.81); extension versus no extension (p = 0.83, 0.85); uncovered versus covered extensions (p = 0.58, 0.70). Logistic regression analyses showed a trend toward statistical significance. CONCLUSION: In the setting of PTFE-covered TIPS creation, extended TIPSs and unextended well-positioned TIPSs have no difference in primary patency rates. Stent position and extension length may have an effect on primary patency, but were likely obscured by "user recognition" effects.

9.
J Fish Biol ; 97(1): 4-15, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-32243570

RESUMO

Blood sampling through the caudal vasculature is a widely used technique in fish biology for investigating organismal health and physiology. In live fishes, it can provide a quick, easy and relatively non-invasive method for obtaining a blood sample (cf. cannulation and cardiac puncture). Here, a general set of recommendations are provided for optimizing the blood sampling protocol that reflects best practices in animal welfare and sample integrity. This includes selecting appropriate use of anaesthetics for blood sampling as well as restraint techniques for situations where sedation is not used. In addition, ideal sampling environments where the fish can freely ventilate and strategies for minimizing handling time are discussed. This study summarizes the techniques used for extracting blood from the caudal vasculature in live fishes, highlighting the phlebotomy itself, the timing of sampling events and acceptable blood sample volumes. This study further discuss considerations for selecting appropriate physiological metrics when sampling in the caudal region and the potential benefits that this technique provides with respect to long-term biological assessments. Although general guidelines for blood sampling are provided here, it should be recognized that contextual considerations (e.g., taxonomic diversity, legal matters, environmental constraints) may influence the approach to blood sampling. Overall, it can be concluded that when done properly, blood sampling live fishes through the caudal vasculature is quick, efficient and minimally invasive, thus promoting conditions where live release of focal animals is possible.

10.
J Invasive Cardiol ; 32(5): 169-174, 2020 May.
Artigo em Inglês | MEDLINE | ID: mdl-32330117

RESUMO

BACKGROUND: Radial artery hemostasis devices differ in compression mechanisms, which may influence time to hemostasis and hand perfusion. METHODS: Subjects (n = 52) undergoing transradial diagnostic coronary catheterization or percutaneous coronary intervention (PCI) were randomized 1:1 to either focused compression (VasoStat; Forge Medical) or balloon compression device (TR Band; Terumo Medical) for radial artery hemostasis. Time to complete hemostasis enabling device removal was measured in each subject. Hand perfusion was quantitated using the perfusion index (PI) with oximetry (1) before; (2) during device use; (3) during device use with ulnar artery compression; and (4) following device removal. RESULTS: Focused compression resulted in a significantly shorter time to complete hemostasis vs balloon compression (208 min [IQR, 115-320 min] vs 242 min [IQR, 120-439 min], respectively; P=.04). This difference was greatest among the subset undergoing PCI, where the VasoStat resulted in a 43-minute reduction until complete hemostasis (P=.04). Baseline PI was similar between the focused and balloon compression groups (4.9 vs 3.9, respectively; P=.09). Focused compression resulted in a similar reduction in median PI from baseline to during device use compared with balloon compression (-27% vs -18%, respectively; P=.26). Both devices decreased PI over 50% from baseline during simultaneous ulnar artery compression (P<.01), and increased PI over 50% from baseline following device removal (P=.02). No radial artery occlusion occurred, and rates of device manipulation and access-site bleeds were low in both groups. CONCLUSION: Complete hemostasis was achieved earlier with the VasoStat focused compression device compared with the TR Band balloon compression device. Both devices transiently reduced hand perfusion, particularly during ulnar compression, which increased from baseline following device removal. Larger trials comparing these radial hemostasis devices and outcomes are warranted.

11.
J Chem Theory Comput ; 16(4): 2766-2777, 2020 Apr 14.
Artigo em Inglês | MEDLINE | ID: mdl-32125859

RESUMO

Evolution has yielded biopolymers that are constructed from exactly four building blocks and are able to support Darwinian evolution. Synthetic biology aims to extend this alphabet, and we recently showed that 8-letter (hachimoji) DNA can support rule-based information encoding. One source of replicative error in non-natural DNA-like systems, however, is the occurrence of alternative tautomeric forms, which pair differently. Unfortunately, little is known about how structural modifications impact free-energy differences between tautomers of the non-natural nucleobases used in the hachimoji expanded genetic alphabet. Determining experimental tautomer ratios is technically difficult, and so, strategies for improving hachimoji DNA replication efficiency will benefit from accurate computational predictions of equilibrium tautomeric ratios. We now report that high-level quantum-chemical calculations in aqueous solution by the embedded cluster reference interaction site model, benchmarked against free-energy molecular simulations for solvation thermodynamics, provide useful quantitative information on the tautomer ratios of both Watson-Crick and hachimoji nucleobases. In agreement with previous computational studies, all four Watson-Crick nucleobases adopt essentially only one tautomer in water. This is not the case, however, for non-natural nucleobases and their analogues. For example, although the enols of isoguanine and a series of related purines are not populated in water, these heterocycles possess N1-H and N3-H keto tautomers that are similar in energy, thereby adversely impacting accurate nucleobase pairing. These robust computational strategies offer a firm basis for improving experimental measurements of tautomeric ratios, which are currently limited to studying molecules that exist only as two tautomers in solution.

12.
J Am Chem Soc ; 142(17): 7898-7911, 2020 Apr 29.
Artigo em Inglês | MEDLINE | ID: mdl-32172566

RESUMO

We probed a series of multicomponent electron donor2-donor1-acceptor1 conjugates both experimentally and computationally. The conjugates are based on the light harvester and primary electron-donor zinc-porphyrin (ZnP, donor1) to whose ß positions a secondary electron-donor ferrocene (Fc, donor2) and the primary electron-acceptor C60-fullerene (C60, acceptor1) are attached. Linking all of them via p-phenylene-acetylene/acetylene bridges of different lengths to gain full control over shuttling electrons and holes between C60, ZnP, and Fc is novel. Different charge-separation, charge-transfer, and charge-recombination routes have been demonstrated, both by transient absorption spectroscopy measurements on the femto, pico-, nano-, and microsecond time scales and by multiwavelength and target analyses. The molecular wire-like nature of the p-phenylene-acetylene bridges as a function of C60-ZnP and ZnP-Fc distances is decisive in the context of generating distant and long-lived C60•--ZnP-Fc•+ charge-separated states. For the first time, we confirm the presence of two adjacent charge-transfer states, a C60-ZnP•--Fc•+ intermediate in addition to C60•--ZnP•+-Fc, en route to the distant C60•--ZnP-Fc•+ charge-separated state. Our studies demonstrate how the interplay of changes in the reorganization energy and the damping factor of the molecular bridges, in addition to variation in the solvent polarity, affect the outcome of the charge-transfer and corresponding rate constants. The different regions of the Marcus parabola are highly relevant in this matter: The charge recombination of, for example, the adjacent C60•--ZnP•+-Fc charge-separated state is located in the inverted region, while that of the distant C60•--ZnP-Fc•+ charge-separated state lies in the normal region. Here, the larger reorganization energy of Fc relative to ZnP makes the difference.

13.
Cardiovasc Intervent Radiol ; 43(5): 714-720, 2020 May.
Artigo em Inglês | MEDLINE | ID: mdl-32043200

RESUMO

PURPOSE: Upper extremity and tibiopedal arterial access are increasingly used during endovascular therapies. Balloon compression hemostasis devices in these anatomic locations have been described, but most utilize a compression surface extending well beyond the puncture site. We report single-center experience with an arterial puncture-focused compression device following upper extremity and tibiopedal access. PATIENTS AND METHODS: A series of 249 focused compression hemostasis devices (VasoStat, Forge Medical, Bethlehem, Pennsylvania, USA) were used in 209 patients following lower extremity (n = 63) and upper extremity (n = 186; radial: 90%) arterial access procedures using 4-7 French sheaths. Demographic, operative, and follow-up data were collected. Logistic regression was used to evaluate potential association between patient/operative variables and time to hemostasis. RESULTS: Primary hemostasis was achieved in 97.2% (242/249) following sheath removal; in 7 cases (2.8%) puncture site oozing occurred after initial device removal and required reapplication. Secondary hemostasis was 100% (249/249). Seven complications (2.8%) were recorded: 5 minor hematomas (2%) and 2 transient access artery occlusions (0.8%). Mean time to hemostasis enabling device removal was 55 ± 28 min. Elevated body mass index (BMI) was not associated with increased time to hemostasis (p = 0.31). Accessed artery, sheath size, and heparin dose were also not associated with time to hemostasis (p = 0.64; p = 0.74; p = 0.75, respectively). CONCLUSIONS: The focused compression hemostasis device enabled rapid hemostasis with a low complication rate. Time to hemostasis was independent of BMI, access site, sheath size, or heparin dose.

14.
Ann Vasc Surg ; 66: 370-377, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-32027985

RESUMO

BACKGROUND: The use of stents for treating central venous occlusion is well described. Limited evidence exists related to Palmaz balloon-expandable stent use in inferior vena cava (IVC) reconstruction. We analyzed patency and complication rates after IVC reconstruction using Palmaz stents. METHODS: From 2002 to 2019, 37 patients (mean age: 51 year) underwent IVC reconstruction with 68 Palmaz stents. Indications were symptomatic chronic venous obstruction in the infrarenal (n = 25) and intrahepatic (n = 12) IVC. Demographic, operative, and imaging data were evaluated. Clinical data, abdominal CT, and/or duplex ultrasound were used to determine patency at follow-up. RESULTS: Restoration of caval patency was achieved in all patients, with complications in 2/37 (5.4%) patients (thrombus formation within the stent; stent embolization eight days after placement). Follow-up data were available for 27 patients. Primary patency was maintained through last follow-up in 19/27 (70%) patients (mean: 1.1 year), with successful stent redilation performed in 6 patients. Mean duration of primary-assisted patency (n = 5) was 1.2 year. Late lumen loss was (n = 13) was 40% during a mean time to follow-up of 2.0 years. Primary patency in patients with occlusion secondary to malignancy was 109 day (range: 1 day-1.0 year), whereas primary patency in patients with occlusion from other etiologies was 1.1 year (range: 2 day-5.9 year). The Kaplan-Meier analysis demonstrated primary and primary-assisted patency of 66% and 84%, respectively, at 24 and 48 months. CONCLUSIONS: Palmaz balloon-expandable stents for IVC reconstruction is feasible and effective for symptomatic IVC occlusion. Risk of stent migration was low.

15.
J Mol Model ; 26(3): 43, 2020 Feb 03.
Artigo em Inglês | MEDLINE | ID: mdl-32009184

RESUMO

Direct NDDO-based Born-Oppenheimer molecular dynamics (MD) have been implemented in the semiempirical molecular orbital program EMPIRE. Fully quantum mechanical MD simulations on unprecedented time and length scales are possible, since the calculation of self-consistent wavefunctions and gradients is performed in a massively parallel manner. MD simulations can be performed in the NVE and NVT ensembles, using either deterministic (Berendsen) or stochastic (Langevin) thermostats. Furthermore, dynamics for condensed-phase systems can be performed under periodic boundary conditions. We show three exemplary applications: the dynamics of molecular reorganization upon ionization, long timescale dynamics of an endohedral fullerene, and calculation of the vibrational spectrum of a nanoparticle consisting of more than eight hundred atoms. Graphical AbstractA snapshot from an MNDO-H simulation of NH4+@C60 at 4000 K shortly before a proton crosses the fullerene wall to give NH3@C60H+.

16.
Nature ; 577(7790): 370-375, 2020 01.
Artigo em Inglês | MEDLINE | ID: mdl-31915382

RESUMO

The partial pressure of CO2 in the oceans has increased rapidly over the past century, driving ocean acidification and raising concern for the stability of marine ecosystems1-3. Coral reef fishes are predicted to be especially susceptible to end-of-century ocean acidification on the basis of several high-profile papers4,5 that have reported profound behavioural and sensory impairments-for example, complete attraction to the chemical cues of predators under conditions of ocean acidification. Here, we comprehensively and transparently show that-in contrast to previous studies-end-of-century ocean acidification levels have negligible effects on important behaviours of coral reef fishes, such as the avoidance of chemical cues from predators, fish activity levels and behavioural lateralization (left-right turning preference). Using data simulations, we additionally show that the large effect sizes and small within-group variances that have been reported in several previous studies are highly improbable. Together, our findings indicate that the reported effects of ocean acidification on the behaviour of coral reef fishes are not reproducible, suggesting that behavioural perturbations will not be a major consequence for coral reef fishes in high CO2 oceans.


Assuntos
Recifes de Corais , Peixes/fisiologia , Animais , Comportamento Animal , Dióxido de Carbono/análise , Concentração de Íons de Hidrogênio , Oceanos e Mares
17.
Angew Chem Int Ed Engl ; 59(3): 1113-1117, 2020 Jan 13.
Artigo em Inglês | MEDLINE | ID: mdl-31647593

RESUMO

Singlet fission has emerged as a promising strategy to avoid the loss of extra energy through thermalization in solar cells. A family of dimers consisting of nitrogen-doped pyrene-fused acenes that undergo singlet fission with triplet quantum yields as high as 125 % are presented. They provide new perspectives for nitrogenated polycyclic aromatic hydrocarbons and for the design of new materials for singlet fission.

18.
Conserv Physiol ; 7(1): coz088, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31798884

RESUMO

Hypoxia in aquatic ecosystems is becoming increasingly prevalent, potentially reducing fish performance and survival by limiting the oxygen available for aerobic activities. Hypoxia is a challenge for conserving and managing fish populations and demands a better understanding of the short- and long-term impacts of hypoxic environments on fish performance. Fish acclimate to hypoxia via a variety of short- and long-term physiological modifications in an attempt to maintain aerobic performance. In particular, hypoxia exposure during early development may result in enduring cardio-respiratory modifications that affect future hypoxia acclimation capacity, yet this possibility remains poorly investigated. We incubated Atlantic salmon (Salmo salar) in normoxia (~100% dissolved oxygen [DO, as percent air saturation]), moderate hypoxia (~63% DO) or cyclical hypoxia (100-25% DO daily) from fertilization until 113 days post-fertilization prior to rearing all groups in normoxia for a further 8 months. At ~11 months of age, subsets of each group were acclimated to hypoxia (50% DO) for up to 44 days prior to haematology, aerobic metabolic rate and hypoxia tolerance measurements. Hypoxia exposure during incubation (fertilization to 113 days post-fertilization) did not affect the haematology, aerobic performance or hypoxia tolerance of juvenile salmon in later life. Juveniles acclimated to hypoxia increased maximum aerobic metabolic rate and aerobic scope by ~23 and ~52%, respectively, when measured at 50% DO but not at 100% DO. Hypoxia-incubated juveniles also increased haematocrit and haemoglobin concentration but did not affect acute hypoxia tolerance (critical oxygen level and DO at LOE). Thus, while Atlantic salmon possess a considerable capacity to physiologically acclimate to hypoxia by improving aerobic performance in low oxygen conditions, we found no evidence that this capacity is influenced by early-life hypoxia exposure.

19.
J Chem Inf Model ; 59(12): 5057-5064, 2019 12 23.
Artigo em Inglês | MEDLINE | ID: mdl-31722177

RESUMO

Charge transport in two zinc metal-organic frameworks (MOFs) has been investigated using periodic semiempirical molecular orbital calculations with the AM1* Hamiltonian. Restricted Hartree-Fock calculations underestimate the band gap using Koopmans theorem (ca. 2 eV compared to the experimental value of 2.8 eV). However, it almost doubles when the constraint on the wave function to remain spin-restricted is removed and the energies of the UHF Natural Orbitals are used. Charge-transport simulations using propagation of the electron- or hole-density in imaginary time allow charge-transport paths and mechanisms to be determined. The calculated relative mobilities in the directions of the three crystal axes agree with experimental expectations, but the absolute values are not reliable using the current technique. Hole-mobility along the crystal c-axis (along the metal stacks) is found to be 13 times higher in the zinc MOF with anthracene linker (Zn-ANMOF-74) than in the other directions, whereas the factor is far smaller (1.7) for electron mobility. Directional preferences are far less distinct in the equivalent structure with phenyl linkers (Zn-MOF-74). The imaginary-time simulation technique does not give quantitative mobilities. The simulations reveal a change in mechanism between the different directions: Coherent polaron migration is observed along the stacks but tunneling hops between them.

20.
J Phys Chem A ; 123(43): 9403-9412, 2019 Oct 31.
Artigo em Inglês | MEDLINE | ID: mdl-31600441

RESUMO

We present atomic scale models of differently sized eumelanin nanoaggregates from molecular dynamics simulations combined with a simulated annealing procedure. The analysis reveals the formation of secondary structures due to π-stacking on one hand, but on the other hand a broad distribution of stack geometries in terms of stack size, horizontal displacement angles, and relative torsion angles. The displacement angle distribution, which is a measure of the occurrence of zigzag and linear stacking motives, respectively, strongly depends on the aggregate size-and is hence controlled by the interplay of surface and bulk energy terms. Semiempirical spectra calculations of small stacks (up to five protomolecules) reveal a strong dependence on the precise stack structure and allow for a direct structure-property correlation. The observed spectral shifts result in an overall spectral broadening and, hence, further support the geometric disorder model, which complements the chemical disorder model in the interpretation of eumelanin's monotonically increasing broad-band absorption.

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