Structures ofN-acetyl-DL-isoleucine,N-acetyl-DL-alloisoleucine and their ammonium salts; role of ammonium ions in crystal structure formation

2016 ◽  
Vol 72 (4) ◽  
pp. 650-657
Author(s):  
Tatsuo Yajima ◽  
Makiko Kimura ◽  
Yoshihiro Hori ◽  
Tadashi Shiraiwa
Keyword(s):  
Hydrogen Bond ◽  
Room Temperature ◽  
Optically Active ◽  
Ammonium Salts ◽  
Ammonium Ion ◽  
Amino Group ◽  
Ammonium Ions ◽  
Screw Axis ◽  
Crystal Structure Formation

The crystal structures ofN-acetyl-DL-isoleucine,N-acetyl-DL-alloisoleucine and their ammonium salts show that these four compounds exist as racemic compounds around room temperature. The two ammonium salts are arranged around a 21screw axis, forming a helical column which consists of ammonium ions and single enantiomeric anions similar to the crystals of the ammonium salts of optically activeN-acetyl-L-isoleucine andN-acetyl-D-alloisoleucine. The ammonium ion and the carboxylate ion in the helix are connected by three hydrogen bonds, the fourth hydrogen bond being formed between the ammonium ion and an external acetyl amino group of the neighboring helical column. The fourth hydrogen bond is formed between the ammonium ion and an external acetyl amino group of the neighboring 21column. AmmoniumN-acetyl-DL-alloisoleucinate was revealed to exist as an unstable racemic compound due to conformational similarity between the racemic and optically active compounds in the solid state and was optically resolved by fractional crystallization at 293 K.

Infrared spectra of the ammonium ion in crystals. Part XII. Low-temperature transitions in ammonium dichromate, (NH4)2Cr2O7

1982 ◽  
Vol 60 (15) ◽  
pp. 1972-1977
Author(s):  
Gábor Keresztury ◽  
Osvald Knop ◽  
Michael Falk
Keyword(s):  
Hydrogen Bonding ◽  
Infrared Spectra ◽  
Room Temperature ◽  
Abundance Ratio ◽  
Ammonium Ion ◽  
Ammonium Ions ◽  
Hydrogen Bonding Interactions ◽  
Wide Range ◽  
Ammonium Dichromate ◽  
The Difference

Examination of the infrared spectra of the probe ions NH3D+ and NHD3+ in ammonium dichromate confirms the existence of the lowest (Ttr ~ 125 K) of the three transitions that are known, from nonspectroscopic evidence, to occur in this crystal below room temperature. Below Ttr the ammonium ions are of two types, in an abundance ratio of 1:1 and both of symmetry C1. Above Ttr the probe ion spectra are difficult to interpret in detail. The strength of the hydrogen-bonding interactions covers a wide range, as indicated by the difference between the highest and the lowest values of the isotopically isolated ND stretching frequencies at 10 K, 2392 and 2234 cm−1.

Metal-free redox active deep eutectic solvents

2017 ◽  
Vol 53 (72) ◽  
pp. 9983-9985 ◽  
Author(s):  
J. C. Goeltz ◽  
L. N. Matsushima
Keyword(s):  
Hydrogen Bond ◽  
Room Temperature ◽  
Deep Eutectic Solvents ◽  
Ammonium Salts ◽  
Metal Free ◽  
Freezing Points ◽  
Redox Active ◽  
Hydrogen Bond Donors

Metal-free deep eutectic solvents composed of hydrogen bond donors and viologen-based ammonium salts exhibit reversible electrochemistry with viologen concentrations of 4.2 M and freezing points near room temperature.

Infrared spectra of the ammonium ion in crystals. Part IX. Ammonium tetraphenylborate, NH4B(C6H5)4: crystal structure at room temperature and at 120 K, and evidence of hydrogen bonding

1980 ◽  
Vol 58 (13) ◽  
pp. 1355-1364 ◽  
Author(s):  
Wolfgang J. Westerhaus ◽  
Osvald Knop ◽  
Michael Falk
Keyword(s):  
Crystal Structure ◽  
Infrared Spectra ◽  
Room Temperature ◽  
Ammonium Ion ◽  
Ammonium Ions ◽  
Coulombic Interaction ◽  
Phenyl Rings ◽  
Librational Motion ◽  
A Site

A determination of the crystal structure of ammonium tetraphenylborate (ATPB) at 120 K shows that the ammonium ion in this crystal, at a site of symmetry D2d, is oriented in a way consistent with the expectation from a simple model based on Coulombic interaction. Infrared spectra of the isotopic ammonium ions obtained between 10 K and room temperature indicate that the effect of the tetraphenylborate anion on the strength of the N—H bond (as measured by the stretching frequency) is small and independent of temperature, and that the distortion of the ammonium ion from Td symmetry is slight. From the combined evidence it is concluded that the ammonium ion in ATPB must be regarded as hydrogen-bonded, but the potential field due to the four phenyl rings surrounding the ammonium ion offers little resistance to the bending (and probably also to the librational) motion of the ion.

Infrared Spectra of the Ammonium Ion in Crystals. II. The Ammonium Ion in Trigonal Environments, with a Consideration of Hydrogen Bonding

1975 ◽  
Vol 53 (22) ◽  
pp. 3394-3400 ◽  
Author(s):  
Ian A. Oxton ◽  
Osvald Knop ◽  
Michael Falk
Keyword(s):  
Hydrogen Bond ◽  
Hydrogen Bonding ◽  
Infrared Spectra ◽  
Isotopic Dilution ◽  
Ammonium Ion ◽  
Ammonium Ions ◽  
Dilution Technique ◽  
Intensity Ratios ◽  
Normal Hydrogen ◽  
Trifurcated Hydrogen Bond

Infrared spectra of polycrystalline (NH4)2GeF6, β-(NH4)2SiF6, and (NH4)2Pb(SO4)2 have been recorded at room and liquid-nitrogen temperatures. The N—D stretching and bending fundamentals of the isotopically dilute NH3D+ ion in these compounds have been studied with particular attention. The occurrence of N—D stretching doublets and bending triplets, of approximate intensity ratios 1:3 and 2:3:3 respectively, confirms the C3v symmetry of the ammonium ion and suggests that the isotopic dilution technique will prove useful as a diagnostic tool for ascertaining site symmetries of the ammonium ion. The spectra are consistent with non-rotating ammonium ions. The frequencies of dilute NH3D+ ions suggest that for the ammonium ion in (NH4)2Pb(SO4)2 a trifurcated hydrogen bond is stronger than a normal hydrogen bond.

Optical analysis of ink and other contaminants in process waters

TAPPI Journal ◽  
2012 ◽  
Vol 11 (8) ◽  
pp. 51-58
Author(s):  
ANTTI HAAPALA ◽  
MIKA KÖRKKÖ ◽  
ELISA KOIVURANTA ◽  
JOUKO NIINIMÄKI
Keyword(s):  
Optically Active ◽  
Process Water ◽  
Paper Machine ◽  
Optical Analysis ◽  
Direct Process ◽  
Active Components ◽  
Water Contaminants ◽  
Dependent Measurement ◽  
Measurement Methodology

Analysis methods developed specifically to determine the presence of ink and other optically active components in paper machine white waters or other process effluents are not available. It is generally more interest¬ing to quantify the effect of circulation water contaminants on end products. This study compares optical techniques to quantify the dirt in process water by two methods for test media preparation and measurement: direct process water filtration on a membrane foil and low-grammage sheet formation. The results show that ink content values obtained from various analyses cannot be directly compared because of fundamental issues involving test media preparation and the varied methodologies used to formulate the results, which may be based on different sets of assumptions. The use of brightness, luminosity, and reflectance and the role of scattering measurements as a part of ink content analysis are discussed, along with fine materials retention and measurement media selection. The study concludes with practical tips for case-dependent measurement methodology selection.

Clustering-Triggered Efficient Room Temperature Phosphorescence from Nonconventional Luminophores

2019 ◽  
Author(s):  
Shuyuan Zheng ◽  
Taiping Hu ◽  
Xin Bin ◽  
Yunzhong Wang ◽  
Yuanping Yi ◽  
...  
Keyword(s):  
Room Temperature ◽  
High Efficiency ◽  
Spin Orbit Coupling ◽  
Design Rationale ◽  
Emission Mechanism ◽  
Room Temperature Phosphorescence ◽  
Electronic Interactions ◽  
Energy Gaps ◽  
Theoretical Results

Pure organic room temperature phosphorescence (RTP) and luminescence from nonconventional luminophores have gained increasing attention. However, it remains challenging to achieve efficient RTP from unorthodox luminophores, on account of the unsophisticated understanding of the emission mechanism. Here we propose a strategy to realize efficient RTP in nonconventional luminophores through incorporation of lone pairs together with clustering and effective electronic interactions. The former promotes spin-orbit coupling and boost the consequent intersystem crossing, whereas the latter narrows energy gaps and stabilizes the triplets, thus synergistically affording remarkable RTP. Experimental and theoretical results of urea and its derivatives verify the design rationale. Remarkably, RTP from thiourea solids with unprecedentedly high efficiency of up to 24.5% is obtained. Further control experiments testify the crucial role of through-space delocalization on the emission. These results would spur the future fabrication of nonconventional phosphors, and moreover should advance understanding of the underlying emission mechanism.<br>

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