Ab initio calculations on large molecules using molecular fragments. Initial studies on open shell systems

An ab initio procedure, designed for investigation of large molecules and based upon studies of molecular fragments, is extended to open shell systems using the unrestricted Hartree-Fock method. Investigated initially are the ethyl and vinyl radicals, and the ethylene triplet state.     

Bonded granulates

A Material consisting of polyhedral grains separated by thin layers with characteristics different from those of the grains is envisaged. For the case of elastic or viscoelastic components, relations between overall stresses and strains are established on the basis of simple kinematical assumptions.     

Evidence for simultaneous sound production in the bowhead whale (Balaena mysticetus)

Simultaneous production of two harmonically independent sounds, the two-voice phenomenon, is a well-known feature in bird song. Some toothed whales can click and whistle simultaneously, and a few studies have also reported simultaneous sound production by baleen whales. The mechanism for sound production in toothed whales has been largely uncovered within the last three decades, whereas mechanism for sound production in baleen whales remains poorly understood. This study provides three lines of evidence from recordings made in 2008 and 2009 in Disko Bay, Western Greenland, strongly indicating that bowhead whales are capable of simultaneous dual frequency sound production. This capability may function to enable more complex singing in an acoustically mediated reproductive advertisement display, as has been suggested for songbirds, and/or have significance in individual recognition.     

Prolonged bone marrow T1-relaxation in acute leukaemia. In vivo tissue characterization by magnetic resonance imaging

In vivo tissue characterization by measurement of T1- and T2-relaxation processes is one of the greatest potentials of magnetic resonance imaging (MRI). This may be especially useful in the evaluation of bone marrow disorders as the MRI-signal from bone marrow is not influenced by the overlying osseous tissue. Nine patients with acute leukaemia, one patient with myelodysplastic syndrome, and ten normal volunteers were included in the study. The T1- and T2-relaxation processes were measured in the lumbar spine bone marrow using a wholebody superconductive MR-scanner operating at 1.5 Tesla. In the patients MRI was done at the time of diagnosis and during follow-up of chemotherapy and related to bone marrow biopsies taken within three days of the MRI. At the time of diagnosis T1-relaxation time was increased two to three times in the patients (range 0.7-3.0 sec.) compared to the controls (range 0.38-0.60 sec.). No significant difference was seen in the T2-relaxation process. In relation to chemotherapy T1 decreased towards the normal range in the patients who obtained complete remission, whereas T1 remained prolonged in the patients who did not respond successfully to the treatment. The results indicate that MRI may be a non-invasive clinically useful tool in the evaluation of acute leukaemia especially as a follow-up control of chemotherapy.     

Ab initio calculations on large molecules using molecular fragments. Preliminary investigation of ethyl chlorophyllide a and related molecules

Ab initio SCF calculations using the molecular fragment method are reported for four molecules related to chlorophyll a, i.e., free-base porphine, magnesium porphine, magnesium chlorin, and ethyl chlorophyllide a. Molecular orbital structure, the “four-orbital model”, reactivity sites, and Mg···N interactions are discussed.     

Explicitly correlated configuration interaction studies using spherical Gaussians. II. Exploratory studies on LiH

Ab initio self-consistent-field and configuration interaction studies have been carried out on the ground state of the LiH molecule at its equilibrium distance. Floating spherical Gaussian basis orbitals (FSGO ) were employed, along with spherical Gaussian correlation factors, using the procedure described in the preceding paper. A near-Hartree–Fock function was found using only 13 FSGO . Exploratory configuration interaction studies recovered approximately 73% of the inner shell correlation energy and approximately 56% of the total correlation energy with five configurations plus the Hartree–Fock configuration. These studies indicate that, by using spherical Gaussian correlation factors, direct introduction of interelectronic coordinates into trial wave functions can be accomplished for molecular systems. It was also shown that correlating configurations need not utilize the full Hartree–Fock basis, but may use substantially smaller bases and still recover correlation energy effectively. Finally, the results indicate that, in spite of their improper cusp behavior, FSGOS and spherical Gaussian correlation factors can be used for construction of high accuracy wave functions.     

STEREOELECTRONIC PROPERTIES OF PHOTOSYNTHETIC AND RELATED SYSTEMS—VII. AB INITIO QUANTUM MECHANICAL CHARACTERIZATION OF THE ELECTRONIC STRUCTURE AND SPECTRA OF CHLOROPHYLLIDE a AND BACTERIOCHLOROPHYLLIDE a CATION RADICALS

Abstract— Ab initio configuration interaction wavefunctions and energies are reported for 29 doublet states and three quartet states of the cation radicals of ethyl chlorophyllide a (Et-Chl a⁺) and ethyl bacteriochlorophyllide a (Et-BChl a⁺). In Et-Chl a.⁺ I the lowest excited doublet state D₁ is estimated to lie 5220 cm^-1 above the ground state D₀, with a negligibly small D₁← D₀ transition probability. The lowest quartet state, Q₁, is estimated to lie 7980 cm^-1 above D₁. The absorption spectrum up to 20,000cm^-1 is shown to consist primarily of numerous low-intensity ‘background’ transitions, with transitions to D₅ and D₁₁ accounting for the observed peaks at 12,200cm^-1 and 17,500cm^-1, respectively. The large intense band at 25,000cm^-1 is due primarily to transitions to D₂₂ and D₂₃, with numerous lower-intensity transitions to neighboring states. In Et-BChl a.⁺ D₁ is estimated to lie 7112 cm-¹ above D₀, and Q, is approximately 5725 cm^-1 above D. A pair of states, D₃ and D₅, account for the absorption at 11,000 cm^-1, while another pair of states, D₁₃ and D₁₄, are associated with the broad, weak absorption near 20,000 cm^-1. The two prominent intense peaks at 23,700 cm^-1 and 27,700 cm^-1 are assigned to D₂₃ and D₂₈, respectively, while the shoulder located at 25,500cm^-1 is attributed to transitions to D₂₄ and D₂₆. As in Et-Chl at, numerous background transitions are found throughout the spectrum. The π spin density distribution in D₀ of both molecules is similar, with spin density found predominantly on the α-carbon atoms. In both systems, approximately 65% of the π spin density in D₁ is found on the methine carbon atoms, with the remainder found largely on the nitrogen atoms.     

STEREOELECTRONIC PROPERTIES OF PHOTOSYNTHETIC AND RELATED SYSTEMS—VI. AB INITIO CONFIGURATION INTERACTION CALCULATIONS ON THE GROUND AND LOWER EXCITED SINGLET AND TRIPLET STATES OF ETHYL BACTERIOCHLOROPHYLLIDE-a AND ETHYL BACTERIOPHEOPHORBIDE-a‡

Abstract— Ab initio quantum mechanical calculations on ethyl bacteriochlorophyllide-a (Et-BChl-a) and ethyl bacteriopheophorbide-a (Et-BPheo-a) are presented, including self-consistent-field (SCF) molecular orbital studies on the ground states using the molecular fragment procedure, and configuration interaction (CI) calculations on the low-lying singlet and triplet states and absorption spectra. A characterization and comparison of many of the higher-lying molecular orbitals obtained from the SCF studies is presented. The estimated first ionization potentials are 5.66 and 5.97 eV for Et-BChl-a and Et-BPheo-a, respectively. Excited state calculations show that the visible spectrum of both molecules consists of an intense, y-polarized S₁← S₀ transition and a weakly-allowed, x-polarized S₂← S₀ transition. Both S₁ and S₂ states are ¹(π, π*) in character, and are described by a four-orbital model. Transitions to the remaining calculated states, S₃-S₁₂, appear in the Soret region of the spectrum of both molecules. However, only transitions to S₉(‘x’), S₁₀(‘x’) and S₁₁(‘y’) of Et-BChl-a, and S₇(‘x’) and S₁₀(‘y’) of Et-BPheo-a are of high intensity. The composition of the high intensity Soret states is ¹(π, π*) and strongly “four-orbital” in nature. The lowest triplet state, T₁, is predicted to lie 9752 cm^-1 and 7880 cm^-1 above S₀ for Et-BPheo-a and Et-BChl-a, respectively. In each molecule T₂ and S₁ are nearly degenerate, suggesting a favorable pathway for intersystem crossing. Calculated T_n← T₁ transitions indicate that the y-polarized T₁₂← T₁ transition in Et-BChl-a corresponds to the observed intense 24,400 cm^-1 absorption in the triplet-triplet spectrum of BChl-a. A similar type spectrum is also predicted for BPheo-a.     

Epilogue to the Gerald Maggiora Festschrift: a tribute to an exemplary mentor,colleague, collaborator,and innovator

Journal of Computer-Aided Molecular Design - In May 2022, JCAMD published a Special Issue in honor of Gerald (Gerry) Maggiora, whose scientific leadership over many decades advanced the fields of...