Ultraviolet absorption spectra ot derivatives of symmetric triazine—II

Hirt, R. C.; Schmitt, R. G.

doi:10.1016/0371-1951(58)80025-9

Cited by 86 publications

(40 citation statements)

References 10 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Mukherjee and Ren studied the thermochemical properties of melamine using mass spectrometry measurements in parallel with computational studies using DFT. The p K a 1 values of melamine and its hydrolysis products ammeline and ammelide have been experimentally estimated to be 5.0–5.1, 4.4–4.5, and 1.8, respectively . These can be compared to p K a 1 values of 4.9, 4.4, and 1.3, respectively, obtained using DFT .…”

Section: Introductionmentioning

confidence: 88%

See 1 more Smart Citation

A computational mechanistic study of the deamination reaction of melamine

Almatarneh

Abu‐Saleh

Uddin

et al. 2016

Int. J. Quantum Chem.

View full text Add to dashboard Cite

A detailed computational study of the deamination reaction of melamine by OH–, nH2O/OH–, nH2O (where n = 1, 2, 3), and protonated melamine with H2O, has been carried out using density functional theory and ab initio calculations. All structures were optimized at M06/6‐31G(d) level of theory, as well as with the B3LYP functional with each of the basis sets: 6‐31G(d), 6‐31 + G(d), 6‐31G(2df,p), and 6‐311++G(3df,3pd). B3LYP, M06, and ωB97XD calculations with 6‐31 + G(d,p) have also been performed. All structures were optimized at B3LYP/6‐31 + G(d,p) level of theory for deamination simulations in an aqueous medium, using both the polarizable continuum solvation model and the solvation model based on solute electron density. Composite method calculations have been conducted at G4MP2 and CBS‐QB3. Fifteen different mechanistic pathways were explored. Most pathways consisted of two key steps: formation of a tetrahedral intermediate and in the final step, an intermediate that dissociates to products via a 1,3‐proton shift. The lowest overall activation energy, 111 kJ mol−1 at G4MP2, was obtained for the deamination of melamine with 3H2O/OH−.

show abstract

Section: Introductionmentioning

confidence: 88%

“…estimated to be 5.0-5.1, 4.4-4.5, and 1.8, respectively. [24][25][26][27] These can be compared to pKa 1 values of 4.9, 4.4, and 1.3, respectively, obtained using DFT. [28] The spectral characteristics (NMR, IR, and Raman) of the melamine molecule were studied experimentally, [17,23,[29][30][31][32][33] and theoretically using ab initio and DFT calculations.…”

mentioning

confidence: 99%

A computational mechanistic study of the deamination reaction of melamine

Almatarneh

Abu‐Saleh

Uddin

et al. 2016

Int. J. Quantum Chem.

View full text Add to dashboard Cite

show abstract

“…R 2 m ≥300 mM −1 ·s −1 Fe at 7 T and R 1 m ~20–30 mM −1 ·s −1 Fe at 0.5 T) and excellent aqueous stabilities—allowing the sensitivity of their MR responses to the local chemical environment and the effects of dendron-generation number to be investigated in detail. R 2 m and R 2 m * values at 7 T were found to exhibit great sensitivity to pH at physiologically-relevant ionic strengths, with sharp inflections observed at pH values near the p K a of the melamine monomer (~5.0 43 ). Opposing behavior in the R 2 m and R 2 m * trends may be exploited to provide a ratiometric MR response to solution pH—potentially allowing such SPIONs to act as concentration-independent pH-sensors for generating MRI contrast.…”

Section: Introductionmentioning

confidence: 99%

pH-Sensitive MR Responses Induced by Dendron-Functionalized SPIONs

et al. 2013

View full text Add to dashboard Cite

We report a series of investigations of the pH-sensitive magnetic resonance (MR) responses of various surface-functionalized SPIONs (superparamagnetic iron oxide nanoparticles). First, functionalization of ~12 nm highly monocrystalline SPION cores with three different generations of melamine-dendrons was optimized to give agents with high molar relaxivities (e.g. R2m~300 mM−1·s−1 at 7 T and R1m~20–30 mM−1·s−1 at 0.5 T) and excellent aqueous stabilities. Molar relaxivities were found to exhibit great sensitivity to pH at physiologically-relevant ionic strengths, with sharp inflections observed at pH values near the pKa of the melamine monomer. The strength of the effect was observed to grow with increasing dendron generation (with concomitant shift in the position of the main pH inflection). Opposing behavior in R2m and R2m* trends may be exploited to provide a ratiometric MR response to pH. Combined with TEM and corresponding MR measurements from solutions of varying ionic strengths, these results are consistent with the pH-sensitive behavior originating from transient, reversible SPION clustering modulated by an interplay between SPION surface charge density and solution ionic strength. Studies of SPION cellular uptake and MR response in HeLa cell cultures are also presented. Finally, comparisons with the MR responses of SPIONs with alternative functionalities—derivatives of nitrilotriacetic acid or poly(1-vinylimidazole)—indicate that these types of pH-sensitive MR responses can be highly dependent upon the chemical composition of the surface species (and thus amenable to modulation through rational design).

show abstract

“…The NH 2 groups are approximately coplanar with the least-squares plane through the melaminium ring, the angle of the least-squares plane through the amino group and the melaminium ring being 0.9(2), 3.8(2) and 0.8(1)8 for N (6), N(7), and N(11), respectively.…”

mentioning

confidence: 99%

“…Melamine can be protonated either at the endocyclic N-atoms in the triazene ring or the exocyclic NH 2 groups. Based on UV-absorption experiments, Hirt and Schmitt [6] predicted that the endocyclic N-atoms are more basic than the NH 2 groups. Preferred ring protonation was also suggested by molecular-orbital (MO) calculations.…”

mentioning

confidence: 99%

Crystal Structure of Melaminium Orthophosphate from High‐Resolution Synchrotron Powder‐Diffraction Data

Ridder

Brodski

Peschar

et al. 2004

Helvetica Chimica Acta

View full text Add to dashboard Cite

The crystal structure of melaminium orthophosphate (MP) has been determined from high-resolution synchrotron powder-diffraction data. The crystal packing consists of melaminium layers and pairs of orthophosphate chains connected by H-bonds almost perpendicular to the layers. The distance between melaminium layers is 3.62 ä. Neighboring melaminium molecules do not lie in the same plane, but in two parallel planes at close distance (0.79 ä), and are shifted with respect to each other. The orthophosphate chains are connected by both intra-chain and inter-chain H-bonds. The melamine is singly protonated at an endocyclic N-atom. The powder-diffraction data were corroborated by solid-state NMR experiments.

show abstract

Ultraviolet absorption spectra ot derivatives of symmetric triazine—II

Cited by 86 publications

References 10 publications

A computational mechanistic study of the deamination reaction of melamine

A computational mechanistic study of the deamination reaction of melamine

pH-Sensitive MR Responses Induced by Dendron-Functionalized SPIONs

Crystal Structure of Melaminium Orthophosphate from High‐Resolution Synchrotron Powder‐Diffraction Data

Contact Info

Product

Resources

About