Nuclear Quadrupole Resonance (<scp>NQR</scp>) Spectroscopy

Wulfsberg, Gary

doi:10.1002/0470862106.ia320

Cited by 9 publications

(15 citation statements)

References 58 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The electronegativity ( x p ) of the metal element also needs to be considered due to its effect on the hydrolysis reactions. Table 1 shows the estimated p K a values of the metal ions investigated in this study, as originally described by G. Wulfsberg according to eqs 1 ( x p < 1.5) and 2 ( x p > 1.5) from ref ( 43 ) : The acidity of the PNF solutions was tested before and after the 24 h incubation to ensure the equilibrium of reaction in Figure 3 b was reached, since more hydrolysis and formation of hydroxides and oxides should show as hydronium ions in the solutions (pH). Table 1 shows that the pH values of the solutions were in the range from 0.7 to 2.9 depending on the size and radius of the metal ions (in agreement with the estimated p K a values of the metal ions, eqs 1 and 2 ), confirming that the smallest and most charged ions could be associated with the lowest pH values.…”

Section: Resultsmentioning

confidence: 99%

“… a Note: The values for the radius and electronegativity were taken from refs ( 43 − 45 ). Storage moduli of the PNF solution/hydrogel (in the liquid state) 46 were extracted at 1.0 Hz from the results of the frequency sweep.…”

Section: Resultsmentioning

confidence: 99%

“…The coordination and organization of water molecules in the vicinity of the differently sized metal cations were previously described by Baes, Messmer and Wulfsberg et al . 43 , 44 Omta et al ., 47 Soper et al ., 48 Bylaska et al ., 49 Marcus, 50 and Mähler et al . 51 suggested that a first hydration shell exist around most ions, even large monovalent ones ( e.g ., Na + ), whereas well-defined second hydration shells are common around more highly charged ions, for example, Al 3+ ( Figure 3 a).…”

Section: Resultsmentioning

confidence: 99%

See 2 more Smart Citations

Protein Nanofibrils and Their Hydrogel Formation with Metal Ions

Capezza

Xiao

et al. 2021

ACS Nano

View full text Add to dashboard Cite

Protein nanofibrils (PNFs) have been prepared by whey protein fibrillation at low pH and in the presence of different metal ions. The effect of the metal ions was systematically studied both in terms of PNF suspension gelation behavior and fibrillation kinetics. A high valence state and a small ionic radius ( e.g ., Sn 4+ ) of the metal ion resulted in the formation of hydrogels already at a metal ion concentration of 30 mM, whereas an intermediate valence state and larger ionic radius (Co 2+ , Ni 2+ , Al 3+ ) resulted in the hydrogel formation occurring at 60 mM. A concentration of 120 mM of Na + was needed to form a PNF hydrogel, while lower concentrations showed liquid behaviors similar to the reference PNF solution where no metal ions had been introduced. The hydrogel mechanics were investigated at steady-state conditions after 24 h of incubation/gelation, revealing that more acidic (smaller and more charged) metal ions induced ca . 2 orders of magnitude higher storage modulus as compared to the less acidic metal ions (with smaller charge and larger radius) for the same concentration of metal ions. The viscoelastic nature of the hydrogels was attributed to the ability of the metal ions to coordinate water molecules in the vicinity of the PNFs. The presence of metal ions in the solutions during the growth of the PNFs typically resulted in curved fibrils, whereas an upper limit of the concentration existed when oxides/hydroxides were formed, and the hydrogels lost their gel properties due to phase separation. Thioflavin T (ThT) fluorescence was used to determine the rate of the fibrillation to form 50% of the total PNFs ( t 1/2 ), which decreased from 2.3 to ca . 0.5 h depending on the specific metal ions added.

show abstract

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Protein Nanofibrils and Their Hydrogel Formation with Metal Ions

Capezza

Xiao

et al. 2021

ACS Nano

View full text Add to dashboard Cite

show abstract

“…The effectiveness of metal oxide NPs as PVC stabilizers could be due to their basicity thus acting as HCl scavengers. The strength of metal acidity is highly dependent on the ratio of charge to size, electronegativity, and hardness [ 54 ]. However, the basicity of metal oxides is not the only factor that contributes to their ability to act as PVC stabilizers.…”

Section: Resultsmentioning

confidence: 99%

Metal Oxide Nanoparticles Containing Clotrimazole to Suppress Photodegradation of Poly(Vinyl Chloride) Thin Films

et al. 2023

View full text Add to dashboard Cite

Pol(vinyl chloride) or PVC has functional properties that enable its use in many industrial applications. It suffers from aging, however, in harsh conditions (e.g., elevated temperature or high humidity levels) if oxygen is present. One way to enhance the photostability of PVC is to blend it with additives. Thus, thin films were made by mixing PVC with clotrimazole, and five metal oxide (titanium, copper, cobalt, chromium, and nickel oxides) additives. The metal oxides and clotrimazole were added at concentrations of 0.1 and 0.5% by weight, respectively. The effect of the metal oxide nanoparticles accompanied by clotrimazole on the photodegradation of PVC was then assessed. The results indicated that the additives have a stabilizing effect and protect PVC against photodegradation significantly. The formation of polymeric fragments of small molecular weight containing carbon-carbon double bonds and carbonyl groups was lower in the blends containing metal oxide nanoparticles and clotrimazole than in unblended PVC. Similarly, the decrease in weight was much less for the films blended with additives. Additionally, surface analysis of the irradiated polymeric films showed significantly lower damage in the materials containing additives. The most effective additive in the stabilization of PVC was nickel oxide nanoparticles. The metal oxides are highly alkaline and act as scavengers for the hydrogen chloride produced during the photodegradation of PVC. They additionally act as peroxide decomposers. In contrast, clotrimazole can absorb harmful radiation and act as an ultraviolet absorber due to its heteroatom and aromatic content. Thus, the use of a combination of metal oxide nanoparticles and clotrimazole led to significant improvement in the resistance of PVC toward photodegradation.

show abstract

“…It is noteworthy that whereas both the nickel and the cadmium metal ions are considered weakly acidic metal ions in aqueous solutions, the nickel ions are slightly more prone to forming hydroxides at pH 3–4 than the cadmium ions, possibly affecting its interactions towards the CNF and the electrode. 24,52,53…”

Section: Resultsmentioning

confidence: 99%