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This paper applies iterative learning control to point-to-point tracking problems with a general networked structure. The data is quantised and transmitted through restricted communication channels from the controller to the actuator. Combining a logarithmic quantizer with an encoding and decoding mechanism to quantise the input signals reduces the influence of the quantisation error. New design algorithms are developed with conditions for convergence of the tracking error and an extension to fault-tolerant performance under actuator failures. A numerical-based case study demonstrates the application of the new designs, which includes a comparison with another ILC law and the relative merits of the encoding and decoding schemes. [ABSTRACT FROM AUTHOR]

This study presents a straightforward solution to the challenge of elucidating the structures of nitrogen containing compounds undergoing isomerization. When spectral line broadening occurs related to isomerization, be it prototropic tautomerism or bond rotations, this poses a significant obstacle to structural elucidation. By adding acids, we demonstrate a simple approach to overcome this issue and effectively sharpen NMR signals for acid stable prototropic tautomers as well as the conformational isomers containing a morpholine or piperazine ring. [ABSTRACT FROM AUTHOR]

The population of twist or boat conformers is absent in the 5-alkyl-substituted 1,3,2-dioxaphosphorinane rings that are diequatorially linked to the five-coordinated phosphorus. The absence of the nonchair conformation is due to the repulsive P-O4 bond interactions with the pseudo-axial bowsprit C5 hydrogen. The chair-chair equilibrium of phosphoranes having the 1,3,2-dioxaphosphorinane rings is disturbed by the methyl substitution at C5. The conformational energies are calculated.

A study of a series of 1,3,2-oxazaphosphorinanes having 3-coordinate phosphorus using 1H, 31P and 13C nuclear magnetic spectroscopy shows that substitution of the phosphorus at N(3) with a smaller methyl substituent alters chair-chair and chair-twist confirmational equilibria from having Me2N on phosphorus axial to having it on phosphorus equatorial. This is caused by a decrease in unstable, repulsive interactions between the equatorial Me2N and the subsituent at N(3).

A study was done on the chair conformation of six-membered rings attached diequatorially to five-coordinate phosphorus. Results have shown that for all phophoranes a chair-form ring, rather than a boat or twist conformation is also populated in solution. These results suggest that it is unlikely for a thymidine-based phosphorane to populate in solution measurable amounts of a permutational isomer with its ring attached to phosphorus in diequatorial fashion.

Purpose: To investigate the influence of the pH of the dissolution medium on immediate release 850 mg metformin hydrochloride tablets. Methods: A traditional wet granulation method was used to manufacture metformin hydrochloride tablets with or without a disintegrant. Tablet dissolution was conducted using the USP apparatus I at 100 rpm. Results: In spite of its pH-independent high solubility, metformin hydrochloride tablets dissolved significantly slower in 0.1 N HCl (pH 1.2) and 50 mM pH 4.5 acetate buffer compared with 50 mM pH 6.8 phosphate buffer, the dissolution medium in the USP. Metformin hydrochloride API compressed into a round 1200 mg disk showed a similar trend. When basket rotation speed was increased from 100 to 250 rpm, the dissolution of metformin hydrochloride tablets was similar in all three media. Incorporation of 2% w/w crospovidone in the tablet formulation improved the dissolution although the pH-dependent trend was still evident, but incorporation of 2% w/w croscarmellose sodium resulted in rapid pH-independent tablet dissolution. Conclusion: In absence of a disintegrant in the tablet formulation, the dissolution was governed by the erosion-diffusion process. Even for a highly soluble drug, a super-disintegrant was needed in the formulation to overcome the diffusion layer limitation and change the dissolution mechanism from erosion-diffusion to disintegration. [ABSTRACT FROM AUTHOR]

Highlights: [•] An external standard–internal reference approach for improving quantitative NMR. [•] Roles of internal reference are limited to chemical and spectral compatibilities. [•] Exact purity and accurate weighing of internal reference substance are not required. [•] Another external standard may be used for method accuracy check. [ABSTRACT FROM AUTHOR]

Investigates the conformations of the six-membered rings of a series of oxazaphosphorinanes. Preparation; Single-crystal x-ray structures; Nuclear magnetic resonance (NMR) parameters and conformations; Chair-chair equilibrium constants; Chair-twist equilibria for cis- and trans-isomers; Chemical shifts.