Molecular mechanics studies (MM4) of sulfides and mercaptans

Allinger, Norman L.; Fan, Yi

doi:10.1002/(sici)1096-987x(19971130)18:15<1827::aid-jcc1>3.0.co;2-q

Cited by 34 publications

(10 citation statements)

References 58 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Such changes generally occur in CXCC systems, where X is an atom carrying a lone pair of electrons. They are again due to hyperconjugation and were previously discussed 7…”

Section: Parametersmentioning

confidence: 69%

Molecular mechanics calculations on carbonyl compounds. II. Open‐chain ketones

2001

Self Cite

View full text Add to dashboard Cite

ABSTRACT:Open-chain aliphatic ketones were studied with the molecular mechanics (MM4) force field. A total of seven compounds were examined. Structures were well fit, including moments of inertia. Rotational barriers, vibrational spectra, and dipole moments were also well fit. The overall root mean square errors for MM3 and MM4 were 0.27 and 0.18%, respectively, for the six moments of inertia (known experimentally for two compounds) and 31 and 20 cm −1 , respectively, for the vibrational frequencies (over 99 weighted modes).

show abstract

“…Such changes generally occur in CXCC systems, where X is an atom carrying a lone pair of electrons. They are again due to hyperconjugation and were previously discussed 7…”

Section: Parametersmentioning

confidence: 69%

Molecular mechanics calculations on carbonyl compounds. II. Open‐chain ketones

2001

Self Cite

View full text Add to dashboard Cite

show abstract

“…Similarly, the calculated and observed shifts of the NH stretching mode are in good agreement with one another; however, calculated frequencies for the three modeled anhydrate forms reveal a 27 cm –1 shift between the double and single helices, which can directly be attributed to hydrogen bonding between secondary amines, and an additional 61 cm –1 difference between the single helix and linear anhydrate forms that is therefore due to differences in conformation/structure between the two forms of LPEI. These conformation-dependent, or more specifically C–N torsion-angle-dependent, frequency shifts in the C–H and N–H stretching region are known as the Bohlmann effect. − …”

Section: Resultsmentioning

confidence: 99%

Effects of Relative Humidity on the Surface and Bulk Structures of Linear Polyethylenimine Thin Films

Lott¹,

King²,

Hill³

et al. 2014

J. Phys. Chem. C

View full text Add to dashboard Cite

Polyethylenimine (PEI) polymers have become increasingly utilized for a myriad of applications including self-decontaminating materials and nonviral gene transfection. While the bulk properties of PEIs have been studied in detail, their surfacespecific structure/behavior remain unexplored. Here, we report the effects of relative humidity on the surface structure of linear polyethylenimine (LPEI), as investigated by vibrational sum frequency generation (VSFG) spectroscopy. Results show that the surface structure of (as prepared) anhydrate LPEI is highly dependent on relative humidity. As the relative humidity is varied from 0% to 75%, surface spectra of LPEI in the C−H and N−H stretching regions reveal multiple crystalline and amorphous states, including the gel-phase amorphous state that has previously only been observed in appreciable quantities above LPEI's upper critical solution temperature (64°C). Utilizing DFT calculations, we have assigned large characteristic frequency shifts (∼50 cm −1 ) of LPEI anhydrate crystalline methylene modes to the Bohlmann effect, which is the delocalization of the nitrogen lone electron pair causing a weakening of the C−H bonds of methylene moieties adjacent to the amine functionality. Similar frequency shifts (∼20 cm −1 ) observed in the hydrated crystalline forms are likely due to intermolecular interactions mediated by hydrogen bonding within the LPEI/water matrix. ■ INTRODUCTIONPolyethylenimines (PEIs) have found widespread utility in numerous fields including chemical and biological sensing, 1 carbon dioxide capture, 2 and electrical energy storage. 3 Recently, some of the more interesting and impactful applications are based around PEI's biocompatibility, where it is being investigated for its use as a nonviral vector for gene transfection, 4−8 enzyme or protein stabilization, 9,10 and cell culture. 11 Additionally, due to the generally high concentration of reactive amine moieties present in PEI materials, they are also of interest for reactive/self-decontaminating technologies for protection against nerve-type chemical warfare agents (CWAs), wherein amine groups hydrolyze CWAs to produce less lethal or nonlethal byproducts. Although surface reorganization of various polymeric materials due to environmental adsorbates (water and organics) has been established, 12−16 the characterization of self-decontaminating materials' environmentally mediated surface reorganization and its effects on surface functionality and reactivity is largely absent. To these ends, developing a surface-specific, molecular level understanding of the behavior of polyethylenimine films in varied environmental conditions will provide valuable insights into the molecular-level details that mediate the functionality of these materials for numerous applications.In the present study, we employ linear polyethylenimine (LPEI) as a model system for understanding the effects of relative humidity, and therefore hydrogen bonding (amine− amine, water−amine, and water−water hydrogen bonding), on the surface stru...

show abstract

“…However, additional crossterms have been added in MM4, which have been formulated to more accurately model the physical properties of molecules, including vibrational spectra. MM4 work has already been completed for saturated hydrocarbons,2 alkenes,3 conjugated hydrocarbons,4 and sulfides 5. Descriptions of both the MM36–8 and MM42–5 force fields have been published in earlier articles.…”

Section: Introductionmentioning

confidence: 99%

Molecular mechanics (MM4) calculations on carbonyl compounds part I: aldehydes

2001

Self Cite

View full text Add to dashboard Cite

Aliphatic aldehydes have been studied with the aid of the MM4 force field. The structures, moments of inertia, vibrational spectra, conformational energies, barriers to internal rotation, and dipole moments have been examined for six compounds (nine conformations). MM4 parameters have been developed to fit the indicated quantities to the wide variety of experimental data. Ab initio (MP2) and density functional theory (B3LYP) calculations have been used to augment and/or replace experimental data, as appropriate. Because more, and to some extent, better, data have become available since MM3 was developed, it was anticipated that the overall accuracy of the information calculated with MM4 would be better than with MM3. The best single measure of the overall accuracy of a force field is the accuracy to which the moments of inertia of a set of compounds (from microwave spectroscopy) can be reproduced. For all of the 20 moments (seven conformations) experimentally known for the aldehyde compounds, the MM4 rms error is 0.30%, while with MM3, the most accurate force field presently available, the rms error over the same set is 1.01%. The calculation of the vibrational spectra was also improved overall. For the four aldehydes that were fully analyzed (over a total of 78 frequencies), the rms errors with MM4 and MM3 are 18 and 38 cm −1 , respectively. These improvements came from several sources, but the major ones were separate parameters involving the carbonyl carbon for formaldehyde, the alkyl aldehydes and the ketones, and new crossterms featured in the MM4 force field that are not present in the MM3 version.

show abstract

Molecular mechanics studies (MM4) of sulfides and mercaptans

Cited by 34 publications

References 58 publications

Molecular mechanics calculations on carbonyl compounds. II. Open‐chain ketones

Molecular mechanics calculations on carbonyl compounds. II. Open‐chain ketones

Effects of Relative Humidity on the Surface and Bulk Structures of Linear Polyethylenimine Thin Films

Molecular mechanics (MM4) calculations on carbonyl compounds part I: aldehydes

Contact Info

Product

Resources

About