3D printed microchannels for sub-nL NMR spectroscopy

Nuclear magnetic resonance (NMR) experiments on subnanoliter (sub-nL) volumes are hindered by the limited sensitivity of the detector and the difficulties in positioning and holding such small samples in proximity of the detector. In this work, we report on NMR experiments on liquid and biological entities immersed in liquids having volumes down to 100 pL. These measurements are enabled by the fabrication of high spatial resolution 3D printed microfluidic structures, specifically conceived to guide and confine sub-nL samples in the sub-nL most sensitive volume of a single-chip integrated NMR probe. The microfluidic structures are fabricated using a two-photon polymerization 3D printing technique having a resolution better than 1 \u3bcm3. The high spatial resolution 3D printing approach adopted here allows to rapidly fabricate complex microfluidic structures tailored to position, hold, and feed biological samples, with a design that maximizes the NMR signals amplitude and minimizes the static magnetic field inhomogeneities. The layer separating the sample from the microcoil, crucial to exploit the volume of maximum sensitivity of the detector, has a thickness of 10 \u3bcm. To demonstrate the potential of this approach, we report NMR experiments on sub-nL intact biological entities in liquid media, specifically ova of the tardigrade Richtersius coronifer and sections of Caenorhabditis elegans nematodes. We show a sensitivity of 2.5x1013spins/ Hz1/2on1H nuclei at 7 T, sufficient to detect 6 pmol of1H nuclei of endogenous compounds in active volumes down to 100 pL and in a measurement time of 3 hours. Spectral resolutions of 0.01 ppm in liquid samples and of 0.1 ppm in the investigated biological entities are also demonstrated. The obtained results may indicate a route for NMR studies at the single unit level of important biological entities having sub-nL volumes, such as living microscopic organisms and eggs of several mammalians, humans included

Non-monogenity of multiquadratic number fields

AbstractLet m, n be distinct square-free rational integers and let K=Q(√m, √n). Combining Baker-type inequalities with a suitable version of the Baker-Davenport reduction method we give a computational algorithm for determining all elements with minimal index in such number fields

Equilibrium studies on copper(II)- and iron(III)-monohydroxamates

Chelating properties exhibited by a series of monohydroxamic acids toward copper(II) and iron(III) ions were studied by pH-metric, spectrophotometric and EPR methods. The ligands can be divided into three groups: (i) ligands with alkyl substituents either on the hydroxamate carbon atom (acetohydroxamic acid, Aha; propanohydroxamic acid, Pha; and hexanohydroxamic acid, Hha) or on both the carbon and nitrogen atoms (N-methyl-acetohydroxamic acid, MAha; N-isopropyl-acetohydroxamic acid, iPAha) (ii) ligands with aryl substituents (benzohydroxamic acid, Bha; N-phenyl-acetohydroxamic acid, PhAha; and N-phenyl-benzohydroxamic acid, PhBha); (iii) cyclic derivatives (the natural 2,4-dihydroxy-2H-1,4-benzoxazin-3-(4H)-on-glucoside, DIBOA-gl; and 2-hydroxypyridine-N-oxide,PYRha).In addition to the complexes with the well-known hydroxamate type chelate(s), 1:2 species containing one or both of the coordinated ligands in hydroximato (RC-CONO2-) form, have been found in the copper(II)-Aha and copper(II)-Bha systems. Complex formation with iron(III) starts at a very acidic pH and in the most systems, if the ligand excess is high enough, the 1:3 species solely exists in the pH range ca. 4-8. Hydroxo complexes are generally formed above pH 8-8.5. However, in the cases of iron(III)-iPAha or -Hha, where the ligands have quite large bulky groups, the hydrolysis starts at somewhat lower pH if the metal to ligand ratios are below 1:5 and precipitation starts to form in iron(III)-DIBOA-gl system at ca. pH 5-5.5. In all systems, the stability constants were determined only for the complexes formed below hydrolytic regions. Evaluation of calculated stability constants show that they are determined by a combination of different substituent effects (electronic, resonance and steric effects). The most significant effects are due to substituents on the nitrogen atom in the hydroxamate moieties. The phenyl ring on carbon atom results in somewhat higher stabilities of the complexes

Kaolinite mobilisation in unconsolidated porous media: Effect of brine salinity and salt type Na- and Ca salts

SPE-191922-MS. Day 2 - Session 4: ePoster Session 4.Existence of clay particles in reservoir rock plays a major role in both oil recovery and formation damage. Clay mobilisation and consecutive formation damage have been observed during injection of low-salinity water in oil fields and laboratory coreflood experiments. Hence, this research aimed at understanding and quantifying the effect of clay type, clay content and composition of injected brine on clay mobilisation. In order to study the effect of clay content, several unconsolidated cores using kaolinite and sand are prepared. The clay content of each sample is controlled by mixing an accurately measured mass of kaolinite with sand. A new procedure is developed to assure: a uniform distribution of kaolinite along the core length, reproducible preparation of sand-clay mixture, identical compaction of the mixture in all experiments using axial and overburden stresses, and reproducible permeability data. Each core is initially saturated with high salinity brine (equivalent to sea water salinity) by creating a constant flow rate of 0.6 M solution through the core. The experiments continue with stepwise reduction of salinity of the injected solution (6 steps down to DI water). Around 150 PV of solutions is injected at each step until permeability stabilization. This indicates that no more kaolinite particles are mobilised. Differential pressure across the core is measured continuously and particle concentration and the conductivity of the effluent samples are also measured The kaolinite concentration, solution salinity and valency of ionic species (salt type) are found to be the controlling factors for clay mobilisation. The following correlations are established: relationships between initial kaolinite concentration and initial core permeability, initial kaolinite concentration and degree of permeability damage, and salt type and permeability damage due to salinity reduction. Experimental data show that a core with lower kaolinite content has higher undamaged/initial permeability. It is also observed that the lower is kaolinite content the higher is permeability damage during injection of low salinity water. Significant permeability decline during low-salinity corefloods is due to mobilization of the kaolinite particles and their capture in pore throats. The results also show that injection of solution containing divalent ions (Ca) stabilises the kaolinite particles and prevents their migration during low salinity brine injection.This study is novel in several aspects including: developing a new methodology for unconsolidated core preparation with desired clay content, studying the effect of clay content on initial permeability and severity of formation damage and studying the effect of divalent ions on clay behaviour during low salinity brine injection. The results of this study could be used to engineer the composition of injected water to minimise formation damage based on rock clay content.Thomas Russell, Duy Pham, Genna Petho, Mahdi Tavvakoli Neishaboor, Alexander Badalyan, Aron Behr, Luis Genolet, Patrick Kowollik, Abbas Zeinijahromi and Pavel Bedrikovetsk