616 research outputs found
Experimental and ab-initio calculated vcd spectra of the first OH-stretching overtone of (1R)-(-) and (1S)-(+)-endo-borneol
The near infrared (NIR) absorption and NIR-vibrational circular dichroism (NIR-VCD) spectra
of dilute solutions of the two enantiomers of endo-borneol have been measured in the first
OH-stretching overtone region (1600–1300 nm). By density functional theory (DFT) we calculate
mechanical parameters, i.e. the harmonic mechanical frequency and the anharmonicity constant
for the OH stretching, and anharmonic electrical parameters; i.e. the dependence on OH-bond
length of atomic polar tensors and atomic axial tensors. We evaluate transition integrals for the
calculations of rotational and dipole strengths by Morse anharmonic wavefunctions depending on
mechanical harmonic frequencies and mechanical anharmonicity parameters that are calculated
ab initio. Experimental and calculated spectra compare quite well and this fact allows us to
associate differently signed NIR-VCD features with different conformational states of the
OH-bond. Absorption features for the fundamental and for the second overtone of the OH
stretching are also compared with experiment
NIR-VCD, vibrational circular dichroism in the near-infrared: Experiments, theory and calculations
The first well documented experiments of Near Infrared Vibrational Circular
Dichroism (NIR-VCD) were performed around 1975. We review the thirty year history
of NIR-VCD, encompassing both instrumental development and theoretical/computational
methods that allow interpretation of experimental spectra, harvesting useful structural
information therefrom. We hope to stimulate interest in this still scarcely explored
spectroscopy of chiral molecule
Harmonic and Anharmonic Features of IR and NIR Absorption and VCD Spectra of Chiral 4-X-[2.2]Paracyclophanes
The vibrational absorption spectra and vibrational circular dichroism (VCD) spectra of both enantiomers of
4-X-[2.2]paracyclophanes (X ) COOCD3, Cl, I) have been recorded for a few regions in the range of 900-
12000 cm-1. The analysis of the VCD spectra for the two IR regions, 900-1600 cm-1 and 2800-3200 cm-1,
is conducted by comparing with DFT calculations of the corresponding spectra; the latter region reveals
common motifs of vibrational modes for the three molecules for aliphatic CH stretching fundamentals, whereas
in the mid-IR region, one is able to identify specific signatures arising from the substituent groups X. In the
CH stretching region between 2900 and 2800 cm-1, we identify and interpret a group of three IR VCD bands
due to HCH bending overtone transitions in Fermi resonance with CH stretching fundamental transitions.
The analysis of the NIR region between 8000 and 9000 cm-1 for X ) COOCD3 reveals important features
of the aromatic CH stretching overtones that are of value since the aromatic CH stretching fundamentals are
almost silent. The intensifying of such overtones is attributed to electrical anharmonicity terms, which are
evaluated here by ab initio methods and compared with literature data
Dipole and rotational strengths for overtone transitions of a C2-symmetry HCCH molecular fragment using Van Vleck perturbation theory
Contact transformation theory up to second order is employed to treat CH-stretching overtone
transitions and to calculate dipole and rotational strengths. A general Hamiltonian describing two
interacting CH-stretching oscillators is considered, and the Darling–Dennison resonance is
appropriately taken into account. The two CH bonds are supposed to be dissymmetrically disposed,
so as to represent a chiral HCCH fragment, endowed with C2 symmetry. Analytical expressions of
transition moments and dipole and rotational strengths are given in the hypothesis of general electric
and magnetic dipole moments with quadratic dependence on coordinates and momenta. Dipole and
rotational strengths are then calculated together with frequencies for the fundamental and first three
overtone regions in the simplifying hypothesis of the valence optical approach on the
coupled-oscillator framework. Simplified analytical expressions thereof in the relevant parameters
are presented
Finding Person Relations in Image Data of the Internet Archive
The multimedia content in the World Wide Web is rapidly growing and contains
valuable information for many applications in different domains. For this
reason, the Internet Archive initiative has been gathering billions of
time-versioned web pages since the mid-nineties. However, the huge amount of
data is rarely labeled with appropriate metadata and automatic approaches are
required to enable semantic search. Normally, the textual content of the
Internet Archive is used to extract entities and their possible relations
across domains such as politics and entertainment, whereas image and video
content is usually neglected. In this paper, we introduce a system for person
recognition in image content of web news stored in the Internet Archive. Thus,
the system complements entity recognition in text and allows researchers and
analysts to track media coverage and relations of persons more precisely. Based
on a deep learning face recognition approach, we suggest a system that
automatically detects persons of interest and gathers sample material, which is
subsequently used to identify them in the image data of the Internet Archive.
We evaluate the performance of the face recognition system on an appropriate
standard benchmark dataset and demonstrate the feasibility of the approach with
two use cases
Basic Human Values and Moral Foundations Theory in ValueNet Ontology
Values, as intended in ethics, determine the shape and validity of moral and social norms, grounding our everyday individual and community behavior on commonsense knowledge. The attempt to untangle human moral and social value-oriented structure of relations requires investigating both the dimension of subjective human perception of the world, and socio-cultural dynamics and multi-agent social interactions. Formalising latent moral content in human interaction is an appealing perspective that would enable a deeper understanding of both social dynamics and individual cognitive and behavioral dimension. To formalize this broad knowledge area, in the context of ValueNet, a modular ontology representing and operationalising moral and social values, we present two modules aiming at representing two main informal theories in literature: (i) the Basic Human Values theory by Shalom Schwartz and (ii) the Moral Foundations Theory by Graham and Haidt. ValueNet is based on reusable Ontology Design Patterns, is aligned to the DOLCE foundational ontology, and is a component of the Framester factual-linguistic knowledge graph
Absorption flattening as one cause of distortion of circular dichroism spectra of Delta-RuPhen(3) . H(2)TPPS complex
To extend the model that explains why and how much absorption flattening
(AF) influences circular dichroism (CD) signals, we have investigated the interesting
case of exciton CD in the Soret region of a noncovalent complex formed by (DRuPhen3)
21 and the tetraanionic porphyrin H2TPPS. Different concentrations have been
studied by using an AF emulator and spectra simulation. The CD spectra of this compound
occasionally show distortions in the solution sampling mode with the increase of
concentration; the inhomogeneous distribution in the cell volume is due to aggregation
and is the source of the AF effect. On the basis of these results, we conclude that AF is
an important cause of distortions in CD spectra for D-RuPhen3 H2TPPS complexes and
might affect the CD bands of other aggregated systems as wel
Vibrational Excitons in CH-Stretching Fundamental and Overtone Vibrational Circular Dichroism Spectra
A set of vibrational circular dichroism (VCD) spectra in the CH-stretching fundamental
region for about twenty compounds belonging to the class of essential oils was empirically analyzed by
the use of a sort of vibrational exciton mechanism, involving three centers. Through a general formula
applicable to many coupled dipole oscillators, the rotational strengths of the previously identified
vibrational excitons are evaluated. The results are then critically reviewed by the use of recent ab
initio methodology, as applied to selected molecules of the original set. Further insight is gained by
model calculations adding up the contribution of the coupling between electric dipole moments associated
with normal mode behavior and that of the polarizability from polarizable groups. The former
part is responsible for the excitonic behavior of the VCD spectra. For the same selected molecules we
have also investigated whether some excitonic behavior is taking place in the second overtone region,
and have concluded that this is not the case
Reification and Truthmaking Patterns
Reification is a standard technique in conceptual modeling, which consists of including in the domain of discourse entities that may otherwise be hidden or implicit. However, deciding what should be rei- fied is not always easy. Recent work on formal ontology offers us a simple answer: put in the domain of discourse those entities that are responsible for the (alleged) truth of our propositions. These are called truthmakers. Re-visiting previous work, we propose in this paper a systematic analysis of truthmaking patterns for properties and relations based on the ontolog- ical nature of their truthmakers. Truthmaking patterns will be presented as generalization of reification patterns, accounting for the fact that, in some cases, we do not reify a property or a relationship directly, but we rather reify its truthmakers
Glycosylated copper(II) ionophores as prodrugs for â-glucosidase activation in targeted cancer therapy.
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