scholarly journals The Impact of Halogen Substituents on the Synthesis and Structure of Co-Crystals of Pyridine Amides

Molecules ◽  
2021 ◽  
Vol 26 (4) ◽  
pp. 1147
Author(s):  
Amila M. Abeysekera ◽  
Abhijeet S. Sinha ◽  
Christer B. Aakeroy
Keyword(s):  
Hydrogen Bond ◽  
Halogen Bond ◽  
A Priori ◽  
Dicarboxylic Acids ◽  
Halogen Bonds ◽  
Target Molecules ◽  
Crystal Synthesis ◽  
Py Motif ◽  
The Impact ◽  
Structural Influence

Strategies for co-crystal synthesis tend to employ either hydrogen- or halogen-bonds between different molecules. However, when both interactions are present, the structural influence that they may exert on the resulting assembly is difficult to predict a priori. To shed some light on this supramolecular challenge, we attempted to co-crystallize ten aliphatic dicarboxylic acids (co-formers) with three groups of target molecules; N-(pyridin-2-yl)picolinamides (2Pyr-X), N-(pyridin-2-yl)nicotinamides (3Pyr-X), N-(pyridin-2-yl)isonicotinamides (4Pyr-X); X=Cl/ Br/ I. The structural outcomes were compared with co-crystals prepared from the non-halogenated targets. As expected, none of the reactions with 2Pyr-X produced co-crystals due to the presence of a very stable intramolecular N-H···N hydrogen bond. In the 3Pyr series, all six structures obtained showed the same synthons, –COOH···N(py) and –COOH···N(py)-NH, that were found in the non-halogenated parent 3Pyr and were additionally accompanied by structure directing X···O(OH) interactions (X=Br/I). The co-crystals of the unhalogenated parent 4Pyr co-crystals assembled via intermolecular –COOH···N(py) and –COOH···N(py)-NH synthons. Three of the analogues 4Pyr-X co-crystals displayed only COOH···N(py) and –COOH···N(py)-NH interactions. The three co-crystals of 4Pyr-X with fumaric acid (for which no analogues structures with 4Pyr are known) formed –COOH···N(py)-NH and –NH···O=C hydrogen bonds and showed no structure-directing halogen bonds. In three co-crystals of 4Pyr-I in which –COOH···N(py)-NH hydrogen bond was present, a halogen-bond based –I···N(py) synthon replaced the –COOH···N(py) motif observed in the parent structures. The structural influence of the halogen atoms increased in the order of Cl < Br < I, as the size of σ-holes increased. Finally, it is noteworthy that isostructurality among structures of the homomeric targets was not translated to structural similarities between their respective co-crystals.

Competition and selectivity in supramolecular synthesis: structural landscape around 1-(pyridylmethyl)-2,2′-biimidazoles

2017 ◽  
Vol 203 ◽  
pp. 371-388 ◽  
Author(s):  
C. A. Gunawardana ◽  
J. Desper ◽  
A. S. Sinha ◽  
M. Ðaković ◽  
C. B. Aakeröy
Keyword(s):  
Hydrogen Bond ◽  
Solid State ◽  
Proton Transfer ◽  
Halogen Bond ◽  
Crystal Formation ◽  
Halogen Bonds ◽  
Supramolecular Architectures ◽  
Hydrogen Bond Interactions ◽  
Structure Extension ◽  
The Impact

Three isomeric forms of 1-(pyridylmethyl)-2,2′-biimidazole, A1–A3, have been synthesized and subjected to systematic co-crystallizations with selected hydrogen- and halogen-bond donors in order to explore the impact of electrostatics and geometry on the resulting supramolecular architectures. The solid-state supramolecular behavior of A1–A3 is largely consistent in halogen-bonded co-crystals. Only two types of primary interactions, the N–H⋯N/N⋯H–N homomeric hydrogen-bond interactions responsible for the pairing of biimidazole moieties and the I⋯N(pyridine) halogen bonds responsible for the co-crystal formation and structure extension, are present in these systems. The co-crystallizations with hydrogen-bond donors (carboxylic acids), however, lead to multiple possible structural outcomes because of the presence of the biimidazole–acid N–H⋯OC/N⋯H–O heterosynthon that can compete with biimidazole–biimidazole N–H⋯N/N⋯H–N homosynthon. In addition, the somewhat unpredictable nature of proton transfer makes the hydrogen-bonded co-crystals structurally less consistent than their halogen-bonded counterparts.

The15N NMR chemical shift in the characterization of weak halogen bonding in solution

2017 ◽  
Vol 203 ◽  
pp. 333-346 ◽  
Author(s):  
Sebastiaan B. Hakkert ◽  
Jürgen Gräfenstein ◽  
Mate Erdelyi
Keyword(s):  
Hydrogen Bond ◽  
Chemical Shift ◽  
Halogen Bond ◽  
Molar Fraction ◽  
Halogen Bonding ◽  
Relative Strength ◽  
Lewis Base ◽  
Halogen Bonds ◽  
Bonded Complexes

We have studied the applicability of15N NMR spectroscopy in the characterization of the very weak halogen bonds of nonfluorinated halogen bond donors with a nitrogenous Lewis base in solution. The ability of the technique to detect the relative strength of iodine-, bromine- and chlorine-centered halogen bonds, as well as solvent and substituent effects was evaluated. Whereas computations on the DFT level indicate that15N NMR chemical shifts reflect the diamagnetic deshielding associated with the formation of a weak halogen bond, the experimentally observed chemical shift differences were on the edge of detectability due to the low molar fraction of halogen-bonded complexes in solution. The formation of the analogous yet stronger hydrogen bond of phenols have induced approximately ten times larger chemical shift changes, and could be detected and correlated to the electronic properties of substituents of the hydrogen bond donors. Overall,15N NMR is shown to be a suitable tool for the characterization of comparably strong secondary interactions in solution, but not sufficiently accurate for the detection of the formation of thermodynamically labile, weak halogen bonded complexes.

Halogenide anions as halogen and hydrogen bond acceptors in iodopyridinium halogenides

CrystEngComm ◽  
2020 ◽  
Vol 22 (23) ◽  
pp. 4039-4046 ◽  
Author(s):  
Luka Fotović ◽  
Vladimir Stilinović
Keyword(s):  
Hydrogen Bond ◽  
Halogen Bond ◽  
Halogen Bonds

Structures of iodopyridinium halogenides have demonstrated why iodide, the weakest halogen bond acceptor among the halogenides, preferentially forms halogen bonds.

scholarly journals The Amine Group as Halogen Bond Acceptor in Cocrystals of Aromatic Diamines and Perfluorinated Iodobenzenes

Crystals ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 529
Author(s):  
Erik Uran ◽  
Luka Fotović ◽  
Nikola Bedeković ◽  
Vladimir Stilinović ◽  
Dominik Cinčić
Keyword(s):  
Hydrogen Bond ◽  
Primary Amine ◽  
Halogen Bond ◽  
Halogen Bonds ◽  
Hydrogen Atoms ◽  
Amine Nitrogen Atom ◽  
Aromatic Diamines ◽  
Amine Nitrogen ◽  
Amine Hydrogen ◽  
Amine Groups

In order to study the proclivity of primary amine groups to act as halogen bond acceptors, three aromatic diamines (p-phenylenediamine (pphda), benzidine (bnzd) and o-tolidine (otol)) were cocrystallised with three perfluorinated iodobenzenes (1,4-tetrafluorodiiodobenzene (14tfib), 1,3-tetrafluorodiiodobenzene (13tfib) and 1,3,5-trifluorotriiodobenzene (135tfib)) as halogen bond donors. Five cocrystals were obtained: (pphda)(14tfib), (bnzd)(13tfib)2, (bnzd)(135tfib)4, (otol)(14tfib) and (otol)(135tfib)2. In spite of the variability of both stoichiometries and structures of the cocrystals, in all the prepared cocrystals the amine groups form exclusively I···N halogen bonds, while the amine hydrogen atoms participate mostly in N–H⋯F contacts. The preference of the amine nitrogen atom toward the halogen bond, as opposed to the hydrogen bond (with amine as a donor), is rationalised by means of computed hydrogen and halogen bond energies, indicating that the halogen bond energy between a simple primary amine (methylamine) and a perfluorinated iodobenzene (pentafluoroiodobenze ne) is ca. 15 kJ mol−1 higher than the energy of the (H)NH∙∙∙NH2 hydrogen bond between two amine molecules.

Competition between hydrogen bonds and halogen bonds: a structural study

2018 ◽  
Vol 42 (13) ◽  
pp. 10539-10547 ◽  
Author(s):  
Janaka C. Gamekkanda ◽  
Abhijeet S. Sinha ◽  
John Desper ◽  
Marijana Đaković ◽  
Christer B. Aakeröy
Keyword(s):  
Hydrogen Bond ◽  
Solid State ◽  
Hydrogen Bonds ◽  
Structural Study ◽  
Halogen Bond ◽  
Halogen Bonds ◽  
Hydrogen Bond Donors

O–H hydrogen-bond donors and R–CC–I halogen-bond donors are close competitors for suitable acceptor sites in solid-state assembly.

scholarly journals Nature of the Hydrogen Bond Enhanced Halogen Bond

Molecules ◽  
2021 ◽  
Vol 26 (7) ◽  
pp. 1885
Author(s):  
Susana Portela ◽  
Israel Fernández
Keyword(s):  
Hydrogen Bond ◽  
Bond Strength ◽  
State Of The Art ◽  
Halogen Bond ◽  
Significant Degree ◽  
Halogen Bonds ◽  
Hydrogen Atoms ◽  
Aryl Group ◽  
Hydrogen Bond Acceptor ◽  
Orbital Interactions

The factors responsible for the enhancement of the halogen bond by an adjacent hydrogen bond have been quantitatively explored by means of state-of-the-art computational methods. It is found that the strength of a halogen bond is enhanced by ca. 3 kcal/mol when the halogen donor simultaneously operates as a halogen bond donor and a hydrogen bond acceptor. This enhancement is the result of both stronger electrostatic and orbital interactions between the XB donor and the XB acceptor, which indicates a significant degree of covalency in these halogen bonds. In addition, the halogen bond strength can be easily tuned by modifying the electron density of the aryl group of the XB donor as well as the acidity of the hydrogen atoms responsible for the hydrogen bond.

Structural effects of halogen bonding in iodochalcones

2021 ◽  
Vol 77 (3) ◽  
Author(s):  
Victoria Hamilton ◽  
Connah Harris ◽  
Charlie L. Hall ◽  
Jason Potticary ◽  
Matthew E. Cremeens ◽  
...  
Keyword(s):  
Nitro Group ◽  
Crystal Engineering ◽  
Halogen Bond ◽  
Halogen Bonding ◽  
Structural Motif ◽  
Halogen Bonds ◽  
Linear Motif ◽  
Hole Making ◽  
Donor Acceptor ◽  
The Impact

The structures of three iodochalcones, functionalized with fluorine or a nitro group, have been investigated to explore the impact of different molecular electrostatic distributions on the halogen bonding within each crystal structure. The strongly withdrawing nitro group presented a switch of the halogen bond from a lateral to a linear motif. Surprisingly, this appears to be influenced by a net positive shift in charge distribution around the lateral edges of the σ-hole, making the lateral I...I bonding motif less preferable. A channel of amphoteric I...I type II halogen bonds is observed for a chalcone molecule, which was not previously reported in chalcones, alongside an example of the common synthon involving extended linear chains of I...O2N donor–acceptor halogen bonds. This work shows that halogenated chalcones may be an interesting target for developing halogen bonding as a significant tool within crystal engineering, a thus far underexplored area for this common structural motif.

The Impact of Competitive Quasi-Market on Service Delivery in Benue State University, Makurdi Nigeria

GIS Business ◽  
2019 ◽  
Vol 14 (4) ◽  
pp. 85-98
Author(s):  
Idoko Peter
Keyword(s):  
Service Delivery ◽  
A Priori ◽  
Least Square ◽  
Secondary Source ◽  
State University ◽  
Ordinary Least Square ◽  
Negative Effect ◽  
The Impact ◽  
The Relationship

This research the impact of competitive quasi market on service delivery in Benue State University, Makurdi Nigeria. Both primary and secondary source of data and information were used for the study and questionnaire was used to extract information from the purposively selected respondents. The population for this study is one hundred and seventy three (173) administrative staff of Benue State University selected at random. The statistical tools employed was the classical ordinary least square (OLS) and the probability value of the estimates was used to tests hypotheses of the study. The result of the study indicates that a positive relationship exist between Competitive quasi marketing in Benue State University, Makurdi Nigeria (CQM) and Transparency in the service delivery (TRSP) and the relationship is statistically significant (p<0.05). Competitive quasi marketing (CQM) has a negative effect on Observe Competence in Benue State University, Makurdi Nigeria (OBCP) and the relationship is not statistically significant (p>0.05). Competitive quasi marketing (CQM) has a positive effect on Innovation in Benue State University, Makurdi Nigeria (INVO) and the relationship is statistically significant (p<0.05) and in line with a priori expectation. This means that a unit increases in Competitive quasi marketing (CQM) will result to a corresponding increase in innovation in Benue State University, Makurdi Nigeria (INVO) by a margin of 22.5%. It was concluded that government monopoly in the provision of certain types of services has greatly affected the quality of service experience in the institution. It was recommended among others that the stakeholders in the market has to be transparent so that the system will be productive to serve the society effectively

scholarly journals Frame me if you must: PrEP framing and the impact on adherence to HIV Pre-exposure Prophylaxis

2017 ◽  
Vol 4 (suppl_1) ◽  
pp. S439-S439
Author(s):  
Eric Ellorin ◽  
Jill Blumenthal ◽  
Sonia Jain ◽  
Xiaoying Sun ◽  
Katya Corado ◽  
...  
Keyword(s):  
A Priori ◽  
Social Groups ◽  
Continuous Measure ◽  
Gay Community ◽  
Randomized Controlled ◽  
Exposure Prophylaxis ◽  
The Impact ◽  
Actual Prevalence ◽  
Tenofovir Diphosphate

Abstract Background “PrEP whore” has been used both as a pejorative by PrEP opponents in the gay community and, reactively, by PrEP advocates as a method to reclaim the label from stigmatization and “slut-shaming.” The actual prevalence and impact of such PrEP-directed stigma on adherence have been insufficiently studied. Methods CCTG 595 was a randomized controlled PrEP demonstration project in 398 HIV-uninfected MSM and transwomen. Intracellular tenofovir-diphosphate (TFV-DP) levels at weeks 12 and 48 were used as a continuous measure of adherence. At study visits, participants were asked to describe how they perceived others’ reactions to them being on PrEP. These perceptions were categorized a priori as either “positively framed,” “negatively framed,” or both. We used Wilcoxon rank-sum to determine the association between positive and negative framing and TFV-DP levels at weeks 12 and 48. Results By week 4, 29% of participants reported perceiving positive reactions from members of their social groups, 5% negative, and 6% both. Reporting decreased over 48 weeks, but positive reactions were consistently reported more than negative. At week 12, no differences in mean TFV-DP levels were observed in participants with positively-framed reactions compared with those reporting no outcome or only negatively-framed (1338 [IQR, 1036-1609] vs. 1281 [946-1489] fmol/punch, P = 0.17). Additionally, no differences were observed in those with negative reactions vs. those without (1209 [977–1427] vs. 1303 [964–1545], P = 0.58). At week 48, mean TFV-DP levels trended toward being higher among those that report any reaction, regardless if positive (1335 [909–1665] vs. 1179 [841–1455], P = 0.09) or negative (1377 [1054–1603] vs. 1192 [838–1486], P = 0.10) than those reporting no reaction. At week 48, 46% of participants reported experiencing some form of PrEP-directed judgment, 23% reported being called “PrEP whore,” and 21% avoiding disclosing PrEP use. Conclusion Over 48 weeks, nearly half of participants reported some form of judgment or stigmatization as a consequence of PrEP use. However, individuals more frequently perceived positively framed reactions to being on PrEP than negative. Importantly, long-term PrEP adherence does not appear to suffer as a result of negative PrEP framing. Disclosures All authors: No reported disclosures.

scholarly journals Using Unstated Cases to Correct for COVID-19 Pandemic Outbreak and Its Impact on Easing the Intervention for Qatar

Biology ◽  
2021 ◽  
Vol 10 (6) ◽  
pp. 463
Author(s):  
Narjiss Sallahi ◽  
Heesoo Park ◽  
Fedwa El Mellouhi ◽  
Mustapha Rachdi ◽  
Idir Ouassou ◽  
...  
Keyword(s):  
Public Health ◽  
A Priori ◽  
Epidemiological Models ◽  
Sir Epidemic Model ◽  
Gulf Region ◽  
Epidemiological Modeling ◽  
Public Health Policies ◽  
Sir Epidemic ◽  
The Impact ◽  
Case Data

Epidemiological Modeling supports the evaluation of various disease management activities. The value of epidemiological models lies in their ability to study various scenarios and to provide governments with a priori knowledge of the consequence of disease incursions and the impact of preventive strategies. A prevalent method of modeling the spread of pandemics is to categorize individuals in the population as belonging to one of several distinct compartments, which represents their health status with regard to the pandemic. In this work, a modified SIR epidemic model is proposed and analyzed with respect to the identification of its parameters and initial values based on stated or recorded case data from public health sources to estimate the unreported cases and the effectiveness of public health policies such as social distancing in slowing the spread of the epidemic. The analysis aims to highlight the importance of unreported cases for correcting the underestimated basic reproduction number. In many epidemic outbreaks, the number of reported infections is likely much lower than the actual number of infections which can be calculated from the model’s parameters derived from reported case data. The analysis is applied to the COVID-19 pandemic for several countries in the Gulf region and Europe.

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