Topological Rotational Strengths as Chirality Descriptors for Fullerenes

2003 ◽  
Vol 9 (3) ◽  
pp. 644-651 ◽  
Author(s):  
André Rassat ◽  
Istvàn Làszló ◽  
Patrick W. Fowler
Keyword(s):  
Rotational Strengths

scholarly journals Conventional versus helical blade screw insertion following the removal of the femoral head screw: a biomechanical evaluation using trochanteric gamma 3 locking nail versus PFN antirotation

2021 ◽  
Vol 22 (1) ◽  
Author(s):  
Hong Man Cho ◽  
Kwang Min Park ◽  
Tae Gon Jung ◽  
Ji Yeon Park ◽  
Young Lee
Keyword(s):  
Experimental Models ◽  
Biomechanical Study ◽  
Original Model ◽  
Screw Insertion ◽  
Rotational Strength ◽  
Helical Blade ◽  
Locking Nail ◽  
Biomechanical Evaluation ◽  
Hip Screw ◽  
Rotational Strengths

Abstract Objective When a hip screw needs to be changed, choosing between the conventional (C-type) and helical blade (H-type) types is difficult. In this biomechanical study, we compared these two screw types relative to the type of the initial screw used. Methods C- or H-type screws were inserted (leading screw) in three types of polyurethane bone models (Sawbone, Pacific Research Laboratories, Inc., Washington, USA: 130 × 180 × 40 mm) of different bone mineral densities (pounds per cubic feet [PCF] 5, 80 kg/m3; PCF 10, 160 kg/m3; and PCF 15, 240 kg/m3), and then successively or alternately inserted (following screw) after the leading screw removal. An original model (original C and H) of a leading screw without removal was created as a control. The strengths of resistance to pullout (PO) and rotational stress were measured. For each experimental condition, there were 30 experimental models. Results The original C screw was superior in PO strength, and the original H-type screw was superior in rotational strength. When the C- or H-type screw was the leading screw, using the C-type screw again as the following screw (C1-C2, H1-C2) showed the greatest resistance to PO, and using the H-type screw as the following screw (C1-H2, H1-H2) showed superior resistance to rotational strength. However, the rotational strength of the C2 screw decreased by more than 50% compared with that of the original C screw. Moreover, the PO and rotational strengths of the H2 screw decreased to less than 30% overall compared with those of the original H screw. Conclusion The H-type screw should be used for second-time screw insertion procedures in cases where it is difficult to choose between PO and rotational strengths.

Electronic and Vibrational Circular Dichroism of Model β-Lactams: 3-Methyl- and 4-Methylazetidin-2-one

1996 ◽  
Vol 50 (5) ◽  
pp. 630-641 ◽  
Author(s):  
Jennifer McCann ◽  
Arvi Rauk ◽  
Gennadii V. Shustov ◽  
Hal Wieser ◽  
Danya Yang
Keyword(s):  
Circular Dichroism ◽  
Ab Initio ◽  
Electronic Transition ◽  
Vibrational Circular Dichroism ◽  
Protic Solvent ◽  
Free Energies ◽  
Chiroptical Properties ◽  
Circular Dichroïsm ◽  
Rotational Strengths ◽  
Simple Modeling

The chiroptical properties of the simplest chiral β-lactams, 3- and 4-methylazetidin-2-one, 1 and 2, respectively, were investigated. The experimental vibrational circular dichroism (VCD) and electronic circular dichroism (ECD) spectra were measured and compared with ab initio predictions. Both compounds were found to form dimers with calculated binding enthalpies and free energies of about −51 kJ/mol and −6 to −8 kJ/mol, respectively. The experimentally measured IR and VCD spectra were measured in concentrated nonpolar (CCl4) solution and are in agreement with the predicted IR and VCD spectra of the dimeric forms, 12 and 22, but not the monomers. The most intense dimer VCD bands originate from in-plane N-H wags, which perturb the H-bonded cyclic array. At the more dilute concentrations employed for the ECD spectra, the experimental ECD spectra in heptane were interpreted satisfactorily as arising from a mixture consisting predominantly of monomers. In protic solvent (H2O, MeOH), the ECD spectra are consistent with H-bonded monomers. Simple modeling suggests that the rotational strengths of the first electronic transition gain most of their intensity from the nonplanarity of the amide chromophore, the contributions of which follow a spiral rule previously enunciated.

Optical Activity of Symmetric Compounds in Chiral Media. I. Induced Circular Dichroism of Unbound Substrates

1971 ◽  
Vol 49 (4) ◽  
pp. 624-631 ◽  
Author(s):  
L. D. Hayward ◽  
R. N. Totty
Keyword(s):  
Circular Dichroism ◽  
Carbonyl Compounds ◽  
Optical Rotation ◽  
Optically Active ◽  
Asymmetric Induction ◽  
Azo Compounds ◽  
Induced Circular Dichroism ◽  
Chiral Media ◽  
Circular Dichroïsm ◽  
Rotational Strengths

In the presence of chiral environment compounds, C, optical rotation is induced in symmetric substrates, S, and may be detected as circular dichroism in the electronic spectra of the solutions. Thus the n − π* transitions of symmetric and racemic carbonyl compounds, and of symmetric nitro and azo compounds, become optically active when these S are dissolved in chiral hydrocarbons, ketones, or carbinols, or in solutions of these C in achiral solvents. The rotational strengths of the induced circular dichroism bands of S are solvent, temperature, and concentration dependent. Only limited correlation of the sign and magnitude of the induced bands with the stereochemistry of C and S is evident on the data so far accumulated. Halogenated achiral solvents enhance the intensity, and, in some cases reverse the sign of the induced bands.A new mechanism of asymmetric induction is proposed in which specific bonding of C with S is not prerequisite.

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