Molecular Radius Research Articles

195Pt and 15N NMR Data in Square Planar Platinum(II) Complexes of the Type [Pt(NH3)aXb]n (Xb = Combination of Halides): “NMR Effective Molecular Radius” of Coordinated Ammonia

By studying a model set of square‐planar [Pt(NH3)aXb]n (a + b = 4; Xb = combination of b halido ligands; n = 2 – b) complexes, we found that their δ(195Pt) NMR chemical shift decreases proportionally to the platinum bonded halido ligands' ionic radii overall sum. This confirms also for these systems, the already observed NMR shielding attributed to pseudo ring currents, circulating around the M–X bond axis. Moreover, the present data show that also the NH3 ligands are characterized by a constant NMR shielding ability toward the central metal. This could be rationalized in term of a “NMR effective molecular radius” of the NH3 ligand, affecting the observed δ(195Pt) as previously found for halido ligands. Interestingly, a δ(15N) decrease is observed in Pt bonded NH3 ligands if the ionic radius of a cis halido ligand is increased. The opposite occurs if the ionic radius of a trans halido ligand is increased. The two contrasting effects stem from both shielding electric ring currents affecting the cis ligands and prevailing trans‐influence due to coordinated halido ligands.

Adaptability of Polymer Molecular Coil Dimension in the Pore Structure of the Reservoir

A series of experiments was carried out to study the matching relationship between the pore structure in the reservoir and the molecular radius of gyration. The hydrodynamic radius Dh (molecular coil dimension) was tested by dynamic light scattering and was be used to characterize the crimping degree of polymer chains and molecular coil dimension. The storage modulus and loss modulus were studied through creep recovery. CT scan was used to measure the parameters of pore throat structure in the reservoir. Finally, a polymer injection experiment has been carried out to evaluate the adaptability of polymer molecular coil dimension in the pore structure of the reservoir. Comparing pore radius with the molecular radius of gyration, it was shown that the storage modulus ratio is the key critical factor of oil displacement efficiency and its value is in the range of 10-20. It was also shown that the optimal stable pressure gradient is in the range of 0.05-0.3 MPa/s; a medium stable pressure gradient of 0.3-0.6 MPa/s is acceptable; and a stable pressure gradient above 0.6 MPa/s or no stable pressure gradient is poor. Greater molecular weight and higher concentration of polymer in the core with low permeability do not provide stable pressure.

Estimation of thermodynamic properties of ionic liquids

In the present study experimental data of density, ultrasonic velocity and viscosity of four ionic liquids: 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]), 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim][PF6]), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Bmim][NTf2]) and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide([Emim][NTf2]) have been employed to deduce a number of important and useful thermodynamic properties on the basis of theoretical models available. Theoretically, computed properties include adiabatic compressibility, isothermal compressibility, thermal expansion coefficient, acoustic impedance, heat capacities ratio, heat capacity at constant volume, pseudo Grüneisen parameter, internal pressure, energy of vaporization, heat of vaporization, cohesive energy density, solubility parameter, molar sound velocity, molar compressibility, Debye temperature, molecular radius, intermolecular free length and non-linearity parameter for above mentioned pure ionic liquids.

Questions on the role of biofilms for the adaptation of microorganisms to unfavorable environmental factors by the example of P. aeruginosa

Pseudomonas aeruginosa is a widely represented species of bacteria possessing of a pathogenic potential. This infectious agent is causing wound infections, fibrotic cystitis, fibrosing pneumonia, bacterial sepsis, etc. The microorganism is highly resistant to antiseptics, disinfectants, immune system responses of the body. The responses of a quorum sense of this kind of bacteria ensure the inclusion of many pathogenicity factors. The analysis of the scientific literature made it possible to formulate four questions concerning the role of biofilms for the adaptation of P. aeruginosa to adverse environmental factors: Is another person appears to be predominantly of a source an etiological agent or the source of P. aeruginosa infection in the environment? Does the formation of biofilms influence on the antibiotic resistance? How the antagonistic activity of microorganisms is realized in biofilm form? What is the main function of biofilms in the functioning of bacteria? A hypothesis has been put forward the effect of biofilms on the increase of antibiotic resistance of bacteria and, in particular, P. aeruginosa to be secondary in charcter. It is more likely a biofilmboth to fulfill the function of storing nutrients and provide topical competition in the face of food scarcity. In connection with the incompatibility of the molecular radii of most antibiotics and pores in biofilm, biofilm is doubtful to be capable of performing a barrier function for protecting against antibiotics. However, with respect to antibodies and immunocompetent cells, the barrier function is beyond doubt. The biofilm is more likely to fulfill the function of storing nutrients and providing topical competition in conditions of scarcity of food resources.

Catabolism of Saccharina japonica polysaccharides and oligosaccharides by human fecal microbiota

Saccharina japonica polysaccharides (SJPs) and S. japonica oligosaccharides (SJOs) produced by mild acid hydrolysis, were used for in vitro fecal fermentation to evaluate their potential nutritional benefits. Changes in fecal microbiota and functional metabolites (short-chain fatty acids, SCFAs) were determined during the fermentation. The fermentation behavior of SJPs and SJOs were characterized using high-performance size-exclusion chromatography coupled with multi-angle laser light scattering, viscometry, and refractive index detector and fluorophore-assisted carbohydrate gel electrophoresis (FACE). The main monosaccharides of SJPs consist of mannose, glucuronic acid, galactose, and fucose. The total SCFAs levels increased significantly, with the relative substrate fermentability of samples at 24 h in the order: SJOs > fructo-oligosaccharides > SJPs > blank control. Moreover, SJPs and SJOs could modulate gut microbiota composition by increasing the relative abundances of phylum Bacteroidetes, while decreasing that of Proteobacteria. The molecular weight, intrinsic viscosity, and radius of gyration of SJPs were all decreased during the fermentation, while the FACE results showed that SJOs were degraded. Overall, S. japonica derived polysaccharides and oligosaccharides have great potential use as prebiotics and functional food products.

Hydrogen Bonding in a l-Glutamine-Based Polyamidoamino Acid and its pH-Dependent Self-Ordered Coil Conformation.

This paper reports on synthesis, acid–base properties, and self-structuring in water of a chiral polyamidoamino acid, M-l-Gln, obtained from the polyaddition of N,N′-methylenebisacrylamide with l-glutamine, with the potential of establishing hydrogen bonds through its prim-amide pendants. The M-l-Gln showed pH-responsive circular dichroism spectra, revealing ordered conformations. Structuring was nearly insensitive to ionic strength but sensitive to denaturing agents. The NMR diffusion studies were consistent with a population of unimolecular nanoparticles thus excluding aggregation. The M-l-Gln had the highest molecular weight and hydrodynamic radius among all polyamidoamino acids described. Possibly, transient hydrogen bonds between l-glutamine molecules and M-l-Gln growing chains facilitated the polyaddition reaction. Theoretical modeling showed that M-l-Gln assumed pH-dependent self-ordered coil conformations with main chain transoid arrangements reminiscent of the protein hairpin motif owing to intramolecular dipole moments and hydrogen bonds. The latter were most numerous at the isoelectric point (pH 4.5), where they mainly involved even topologically distant main chain amide N–H and side chain amide C=O brought to proximity by structuring. Hydrogen bonds at pH 4.5 were also suggested by variable temperature NMR. The 2D NOESY experiments at pH 4.5 confirmed the formation of compact structures through the analysis of the main chain/side chain hydrogen contacts, in line with MD simulations.

Ultrasonic-Assisted Extraction, Structural Characterization, Chain Conformation, and Biological Activities of a Pectic-Polysaccharide from Okra (Abelmoschus esculentus).

The purpose of this study was to better understand the chemical characteristics and chain conformation of okra polysaccharides extracted by ultrasonic-assisted extraction. A pectic-polysaccharide, named OPP-D, was obtained, which was mainly composed of rhamnose, galacturonic acid, and galactose with a molar ratio of 1.01:1.00:2.31. Combined with NMR analysis, -4)-α-d-GalAp-(1,2,4)-α-l-Rhap-(1- were identified as the backbone with galactan side chains substituted partly at O-4 of Rhap. Molecular weight and radius of gyration of OPP-D were determined as 2.19 × 105 Da and 27.0 nm, respectively. OPP-D was determined as an air-core sphere with branching chains in 0.9% NaCl solution by high-performance size-exclusion chromatography coupled with multi-angle laser light scattering and dynamic light scattering for the first time. Moreover, OPP-D exhibited typical shear-thinning behavior. In addition, OPP-D exhibited remarkable in vitro antioxidant activities and prebiotic activities, while the relatively high molecular weight, high degree of esterification, high content of uronic acids, and highly branched globular conformation of OPP-D might contribute to its in vitro anti-diabetic activities and binding capacities. Results can contribute to a better understanding of the structure–bioactivity relationship of OPPs, and OPP-D has great potential applications in the functional food and pharmaceutical industries.

Anisotropic Diffusivity Tensor in Articular Cartilage: Effective Medium Approach.

Due to the avascular nature of articular cartilage, molecular transport occurs via interstitial fluid flow as well as via diffusion. Diffusion in cartilage has been studied experimentally, but no mathematical models have been developed to interpret the experimental results and the observed isotropy or anisotropy in the different cartilage zones. Here, we propose a model for the determination of the diffusivity tensor of uncharged macromolecules in articular cartilage, accounting for the inhomogeneity and anisotropy arising from fiber arrangement, volumetric fraction, and radius. We study a representative element of volume (REV) comprising a fiber surrounded by fluid-saturated proteoglycan matrix. The REV permeability tensor is evaluated using a previously developed model, while the REV diffusivity tensor is obtained by incorporating the hydrodynamic effect and the steric effect of the fiber-reinforced matrix. Both effects are represented by anisotropic second-order tensors. The overall diffusivity tensor is obtained as the averaging integral of the REV diffusivity, weighted by the probability distribution of fiber orientation. The model's predictions of the trend of the magnitude of the diffusivity of spheroidal macromolecules as a function of molecular radius agree with published experimental results. For large linear macromolecules, the model underestimates the diffusivity magnitude (i.e., the equivalent isotropic diffusivity). The model correctly predicts the anisotropic behavior for linear macromolecules, although it underestimates the numerical value of the diffusivity anisotropy ratio of large linear macromolecules in the superficial zone, and overestimates it in the deep zone. In summary, this model constitutes a first step toward understanding the relation between diffusivity and permeability in articular cartilage.

Molecular and physical characterization of octenyl succinic anhydride-modified starches with potential applications in pharmaceutics.

Five commercially available starches modified with octenyl succinic anhydride (OSA) are characterized at a molecular, physicochemical and bulk level providing useful data for designing pharmaceutical products. The degree of substitution (DS) of the starches range from 0.017 to 0.032 and their molecular weights (Mw) and radius of gyration (Rz) are lower than those of native starch, suggesting additional modification processes besides the chemical treatment with OSA. The ability of the starches to reduce the water surface tension keeps a direct relationship with the DS and an inverse association with the Mw. Thermal properties, crystallinity assays and morphology evidence that most modified starches characterize by amorphous aggregated structures, possibly generated by gelatinization processes, which favor the flow properties of the powders. Water sorption and surface energy behaviors seem to be related to the number of octenyl succinate (OS) moieties. After dispersion in water, shear-thinning and Newtonian behaviors also depend on the type of OS-starch.

Effect of multielectron polarization in the strong-field ionization of the oriented CO molecule

We discuss the mechanism by which the inclusion of multielectron polarization improves the solution of the time-dependent Schr\"{o}dinger equation (TDSE) for the oriented CO molecule in a strong external laser pulse within the single-active-electron (SAE) approximation. A challenging problem of using the SAE approximation is that the active electron, instead of undergoing ionization, may be driven by the external field to lower-lying orbitals. For the oriented CO molecule, dipole coupling to the lower-lying bound states of the potential depends on the orientation angle, thereby affecting the orientation-dependent ionization dynamics. By including multielectron polarization, the external field is turned off within the molecular radius, thereby minimizing dipole coupling of the highest occupied molecular orbital to the lower-lying states of the potential. We discuss how turning off the external field within an appropriate molecular radius without accounting for the induced dipole term in the effective potential beyond this radial cut-off distance, constitutes an effective and accurate approach to describe strong-field ionization of CO and to minimize dipole coupling to lower-lying bound states.

Structure, properties and potential applications of phytoglycogen and waxy starch subjected to carboxymethylation

The structure and properties of phytoglycogen (PG) and waxy starch (WS) from different mutants subjected to carboxymethylation (CM) were investigated. FT-IR analysis confirmed the carboxymethylation of PG and WS. The degree of substitution (DS) increased with increasing of the ratio of monochloroacetic acid to anhydroglucose unit, while DS of CM-PG was higher than that of CM-WS using equivalent modification conditions. The weight-average molecular weight (Mw) and radius of gyration (Rz) of CM-WS increased with the DS, whereas the Mw increased and Rz was nearly constant for CM-PG. The zeta-potential of CM-WS reduced and the viscosity increased significantly as DS increased, while the viscosity of CM-PG was remarkably lower than that of CM-WS with equivalent of DS. The increase of DS in CM-starches resulted in a substantial reduction of RDS accompanied by the increase of SDS and RS. The results revealed the promising application of CM-PG as a potential carrier system for bioactive ingredients.

Self-Assembly of Exendin-4-Derived Dual Peptide Agonists is Mediated by Acylation and Correlated to the Length of Conjugated Fatty Acyl Chains

Dual glucagon-like peptide-1/glucagon receptor agonists have emerged as promising candidates for the treatment of diabetes and obesity. Issues of degradation sensitivity and rapid renal clearance are addressed, for example, by the conjugation of peptides to fatty acid chains, promoting reversible albumin binding. We use combined dynamic and static light scattering to directly measure the self-assembly of a set of dual peptide agonists based on the exendin-4 structure with varying fatty acid chain lengths in terms of apparent molecular mass and hydrodynamic radius (RS). We use NMR spectroscopy to gain an insight into the molecular architecture of the assembly. We investigate conformational changes of the monomeric subunits resulting from peptide self-assembly and assembly stability as a function of the fatty acid chain length using circular dichroism and fluorescence spectroscopy. Our results demonstrate that self-assembly of the exendin-4-derived dual agonist peptides is essentially driven by hydrophobic interactions involving the conjugated acyl chains. The fatty acid chain length affects assembly equilibria and the assembly stability, although the peptide subunits in the assembly retain a dynamic secondary structure. The assembly architecture is characterized by juxtaposition of the fatty acyl side chains and a hydrophobic cluster of the peptide moiety. This cluster experiences local conformational changes in the assembly compared to the monomeric unit leading to a reduction in solvent exposure. The N-terminal half of the peptide and a C-terminal loop are not in contact with neighboring peptide subunits in the assemblies. Altogether, our study contributes to a thorough understanding of the association characteristics and the tendency toward self-assembly in response to lipidation. This is important not only to achieve the desired bioavailability but also with respect to the physical stability of peptide solutions.

Fabrication of hexagonal boron nitride based 2D nanopore sensor for the assessment of electro-chemical responsiveness of human serum transferrin protein.

In this work, we present a step-by-step workflow for the fabrication of 2D hexagonal boron nitride (h-BN) nanopores which are then used to sense holo-human serum transferrin (hSTf) protein at pH ∼8 under applied voltages ranging from +100mV to +800mV. 2D nanopores are often used for DNA, however, there is a great void in the literature for single-molecule protein sensing and this, to the best of our knowledge, is the first time where h-BN-a material with large band-gap, low dielectric constant, reduced parasitic capacitance and minimal charge transfer induced noise-is used for protein profiling. The corresponding ΔG (change in pore conductance due to analyte translocation) profiles showed a bimodal Gaussian distribution where the lower and higher ΔG distributions were attributed to (pseudo-) folded and unfolded conformations respectively. With increasing voltage, the voltage induced unfolding increased (evident by decrease in ΔG) and plateaued after ∼400mV of applied voltage. From the ΔG versus voltage profile corresponding to the pseudo-folded state, we calculated the molecular radius of hSTf, and was found to be ∼3.1nm which is in close concordance with the literature reported value of ∼3.25nm.

Reservoir applicability and flooding effect of amphoteric ion crosslinked polymer solution

Instrumental detection and physical simulation methods were used to study the viscosity, molecular aggregate dimension (Dh), micro-morphology, seepage characteristics, permeability limit, matching relationship between molecular dimension and radius of pore throat of rocks, and flooding effects of the amphoteric ion polymer solution (AIPS) and the amphoteric ion crosslinked polymer solution (AICPS) according to the actual needs of oilfields and in order to enhance oil recovery. It was found the crosslinking reaction of AICPS took place on a large scale in a ground flask, resulting in a great increase of viscosity. Both AIPS and AICPS had net structures. Among them, AIPS had physically crosslinked net structure, and AICPS had both chemically and physically crosslinked net structures, which were more compact. At the initial stage of solution preparation, the AIPS and AICPS had similar permeability limit. At the polymer concentration between 0 and 4000 mg/L, the AIPS and AICPS (CC = 0.2 wt%, CA = 0.02 wt%) had the minimum matching coefficient of 8.781–13.586 during injection and migration in reservoirs. AICPS showed the optimal profile control and flooding effect only within a certain range of average permeability and permeability variation coefficient of reservoirs. When three layers of heterogeneous cores had the permeability variation coefficient of 0.25, 0.59 and 0.72, respectively, the AICPS (CP = 2500 mg/L, CC = 0.2 wt%, CA = 0.02 wt%) had the average permeability of 2100 × 10−3, 3300 × 10−3 and 4100 × 10−3 µm2 at maximum enhanced oil recovery after profile control and flooding, respectively.

Emulsion stability of sugar beet pectin increased by genipin crosslinking

This work aimed to enhance the emulsifying properties of sugar beet pectin (SBP) by adopting a crosslinking strategy that covalently bridged the amino groups (–NH2) of lysine residues of the proteinaceous moiety using genipin (GP) as the crosslinker. Compared to control-SBP (C-SBP), GP crosslinked SBP (G-SBP) was larger in molecular weight (from 3.04 × 105 g/mol to 1.31 × 106 g/mol) and mean radius of gyration (from 34.8 nm to 39.2 nm), and showed a more compact conformation, as supported by analysis of high-performance size exclusion chromatography coupled with multiple angle light scattering (SEC-MALLS) and atomic force microscopy (AFM). G-SBP was featured by a new absorbance peak at ~595 nm, resulting in a distinct blue color of the aqueous solution. G-SBP suffered a slight decrease in interfacial properties and emulsifying activities in comparison to C-SBP, leading to a lower specific surface area and a larger volume-weighted mean diameter (d4,3) for the fresh emulsion. Nevertheless, the G-SBP stabilized emulsion was more stable than the C-SBP stabilized emulsion during storage for 21 d with d4,3 increasing from 0.541 μm and 0.425 μm to 0.625 μm and 1.66 μm for G-SBP and C-SBP, respectively. The improved emulsifying stability of G-SBP can be ascribed to the combination of the following two aspects: 1) G-SBP exerted a lager viscosity-enhancing effect to slow down droplet collision and flocculation; 2) the carbohydrate moiety of G-SBP formed a dense and compact hydrated layer providing strong steric stabilization for the oil droplets to resist flocculation and coalescence. Altogether, this work demonstrates that GP is a favorable agent to crosslink the side chains of SBP and modify its emulsification performance.

Characterization of Flagellar Filaments and Flagellin through Optical Microscopy and Label-Free Nanopore Responsiveness.

In this study, we investigated the translocation characteristics of flagellar filaments (Salmonella typhimurium) and flagellin subunits through silicon nitride nanopores in tandem with optical microscopy analysis. Even though untagged flagella are dark to the optical method, the label-free nature of the nanopore sensor allows it to characterize both tagged (Cy3) and pristine forms of flagella (including real-time developments). Flagella were depolymerized to flagellin subunits at ∼65 °C (most commonly reported temperature), ∼70 °C, ∼75 °C, and ∼80 °C to investigate the effect of temperature (Tdepol)on depolymerization. The change in conductance (ΔG) profiles corresponding to Tdepol ∼65 °C and ∼70 °C were bracketed within the flagellin monomer profile whereas those of ∼75 °C and ∼80 °C extended beyond this profile, suggesting a change to the native protein state. The molecular radius calculated from the excluded electrolyte volume of flagellin through nanopore-based ΔG characteristics for each Tdepol of ∼65 °C, ∼70 °C, ∼75 °C, and ∼80 °C yielded ∼4.2 ± 0.2 nm, ∼4.3 ± 0.3 nm, ∼4.1 ± 0.2 nm, and ∼4.7 ± 0.5 nm, respectively. This, along with ΔG (plateaued values) and translocation time profiles, points to the possibility offlagellin misfolding at ∼80 °C.

Phenomenological Changes in Lignin Following Polymerization and Its Effects on Flocculating Clay Particles.

Cationic kraft lignin (CKL) macromolecules were produced via polymerizing kraft lignin (KL) with [2-(acryloyloxy)ethyl]trimethylammonium chloride (ATAC) or [2-(methacryloyloxy)ethyl]trimethylammonium methyl sulfate (METAM). Despite slightly different charge densities (2.3-2.5 mmol/g) of CKL, lignin-METAM (KL-METAM) had a significantly larger molecular weight and radius of gyration. A correlation was observed between the structure of CKLs and their impacts on the surface hydrophilicity of kaolin particles. In interacting with kaolin particles, KL-METAM generated larger and stronger flocs with looser structures than did KL-ATAC. Compared to ATAC, METAM had one additional methyl substituent on its structure, which provided fundamental evidence on how a small group (i.e., a methyl group) on the structure of a cationic monomer can have a substantial influence on its polymerization with lignin and subsequently on the efficiency of the induced macromolecule as a flocculant in a kaolin suspension system.

Influence of wax inhibitor molecular weight: Fractionation and effect on crystallization of polydisperse waxes

The influence of wax inhibitor molecular weight on wax crystallization was investigated in three steps: (1) Wax inhibitor fractionation via stepwise precipitation or ultrasonic disintegration, (2) characterization of inhibitor and sub-fractions in terms of molecular weight distribution, hydrodynamic radius, and precipitation from pure solvent, and (3) inhibitor effect on wax appearance temperature (WAT), waxy gelling, and wax crystal morphology. Stepwise precipitation yielded narrower molecular weight distributions, whereas ultrasonic disintegration reduced the average molecular weight and increase the polydispersity index. Changes in inhibitor molecular weight could improve as well as diminish WAT depression. Waxy gelation temperature showed similar trends, but overall effects were more pronounced. It was concluded the wax inhibitor molecular weight is a parameter that can be used to fine-tune additives to a particular waxy oil, but only after an effective PPD type has been identified.

Calculation of the Viscosity of a Disperse System of Silver Nanoparticles with Adsorption Polymeric Layer of Copolymer of Ethylene and Maleic Acid in Aqueous Medium

A model of stabilization of spherical silver nanoparticles by amphiphilic macromolecules of a copolymer of ethylene and maleic acid in an aqueous medium based on experimental data previously obtained by transmission electron microscopy and dynamic light scattering is presented. The applicability of various viscometric equations for describing the behavior of a polydisperse system in the course of electrostatic stabilization of nanoparticles is considered. An expression for the relative viscosity of dispersions of spherical silver nanoparticles with an adsorption layer of a copolymer of ethylene and maleic acid in an aqueous medium is obtained. This equation relates the relative viscosity to the chemical structure of the polymer and the molecular weight, concentration, and radius of nanoparticles taking into account the presence of an adsorption polymer layer.

Calculation of the Effective Macromolecular Radii of Human Serum Albumin from the Shear Viscosity Data for Its Aqueous Solutions

The Malomuzh–Orlov theory is used to analyze the experimental shear viscosity data obtained for aqueous solutions of human serum albumin (HSA) at pH = 7.0 in wide temperature and concentration intervals, which allowed the effective radii of HSA macromolecules to be calculated. It is shown that three intervals of the effective molecular radius of HSA with different behaviors can be distinguished in a temperature interval of 278–318 K: 1) below the crossover concentration, the effective molecular radius of HSA remains constant; 2) in the interval from the crossover concentration to about 10 wt%, the effective molecular radius of HSA in the aqueous solution nonlinearly decreases; and 3) at concentrations of 10.2–23.8 wt%, the effective radius of HSA macromolecules linearly decreases, as the concentration grows. The assumption is made that the properties of water molecules in the solution bulk play a crucial role in the dynamics of HSA macromolecules at the vital concentrations of HSA in the solutions. The role of water near the surface of HSA macromolecules and the corresponding changes of its physical properties have been discussed.