arXiv subjects

Cherif F. Matta

Publications and source records attributed to Cherif F. Matta.

14 recordsLinked to original sources

arXiv2026

Concerns regarding recurrent fluorescence's impact on smaller diffuse ISM aromatics

Recent research implied that recurrent fluorescence (RF) could bolster smaller aromatics against fragmentation in the diffuse ISM, yet that hypothesis is contested by timescales for unrelenting dissociative recombination (electrons), and unceasing dissociating photons. Specifically, neutral cyanonaphthalene can sustain $13.6$ eV photoionization, and the ensuing cation's excess energy is channeled through intramolecular vibrational redistribution (IVR), with RF providing the radiative stabilization pathway ($\simeq7$ eV negligible survival limit). However, that cation endures dissociative recombination every $τ\approx0.5^{+5.6}_{-0.4}$ years, which deposits $\simeq 8.6$ eV and exceeds the limit. Moreover, that is paired with $7-13.6$ eV photodestruction each $τ\approx16^{+223}_{-14}$ years (total visual dust extinction $A_V=0-1$, and $τ\approx4^{+7}_{-2}$ years for $A_V\approx0$). Recent laboratory characterizations of RF were seminal, but the mechanism may not overturn models indicating a gap in smaller $N_C\approx7-11$ diffuse ISM aromatics, nor support those molecules as viable diffuse interstellar band carriers.

astro-ph.GA↗

arXiv2026

Decoding the Hot-Mitochondrion Paradox

In a 2018 paper and a subsequent article published in 2023, researchers reported that mitochondria maintain temperatures 10oC-15oC higher than the surrounding cytoplasm-a finding that deviates by five to six orders of magnitude from theoretical predictions based on Fourier's law of heat conduction. In 2022, we proposed a solution to this apparent paradox. In the present perspective, we build upon that framework and introduce new ideas to further unravel how a biological membrane-whether of an organelle or a whole cell-can become significantly warmer than its environment. We propose that ion-translocating proteins embedded in the inner mitochondrial membrane (IMM) can be modeled as ratchet engines, introducing a novel, previously overlooked mode of heat transfer. This mechanism, coupled with localized heat release during the cyclical dehydration-translocation-hydration of ions through membrane proteins, may generate transient but substantial temperature spikes. The cumulative thermal occupancy of these microscopic events across the three-dimensional surface of the IMM can account for the elevated temperatures detected by molecular probes.

q-bio.SC↗

arXiv2026

Benchmarking Astrochemistry Paradigms: Relative Absence of C6H5CN+ in the Diffuse ISM

The detectability of C6H5CN+ (benzonitrile cation) in the diffuse ISM is re-evaluated. A holistic evidentiary framework suggests C6H5CN+ is relatively absent in the diffuse ISM owing to the following concurrently: a marginal intramolecular vibrational energy redistribution (IVR) favoring fragmentation, recurrent fluorescence being an improbable mechanism in this case to prevent dissociation, unceasing photon strikes, mismatches between observed DIBs and experimental results, and the hitherto absence of DIBs matching any similarly sized cations. The putative gap in bottom-up synthesis is reaffirmed (diffuse ISM), and although DIB sources are largely unknown, within a broader approach the lines can help benchmark astrochemistry paradigms. The results relied on new advantageous Daly et al. experimental spectra, an expanded observational DIB analysis (APO catalog), and complementary $ω$B97X-D/cc-pVTZ computations.

astro-ph.GA↗

arXiv2026

On the Anticipation of Lunar Travel in the Early 20th Century: A Pedagogical Exercise

This article examines, from historical and pedagogical perspectives, Alphonse Berget's anticipation of Earth-Moon travel in Le Ciel (Larousse, 1923), decades before the beginning of the space age. The discussion is triggered by Le Ciel, a richly illustrated French popular science work, which has a devoted chapter examining lunar and interplanetary travel within a Newtonian framework. Although Berget's treatment was not developed in isolation and reflects a broader early 20th century context that included pioneers such as French aero-engineer Robert Esnault-Pelterie, the book provides a striking pedagogical synthesis of elementary celestial mechanics and scientific popularization. Unlike earlier fictional treatments such as Jules Verne's De la Terre a la Lune, Berget approached space travel using physical reasoning grounded in Newtonian gravitation. Using qualitative and semi-quantitative arguments based on the inverse-square law, he identified the principal phases of an Earth-Moon trajectory: escape from Earth, inertial translunar motion, transition through competing Earth-Moon gravitational fields, and final lunar capture and deceleration. His estimated Earth-Moon travel time of approximately 49 hours is of the same order of magnitude as Apollo mission transit times (approx. 72 h). We compare these early ideas with modern elementary concepts of astrodynamics, including restricted three-body trajectories, Lagrange-point dynamics, and distant retrograde orbits associated with the Artemis program. We also examine Berget's discussion of interplanetary travel, lunar landscapes, and human factors associated with prolonged voyages, including confinement, food supply, and travel duration. The analysis highlights the pedagogical value of historically grounded scientific reasoning underpinning spaceflight mechanics.

physics.hist-ph↗

arXiv2026

The Great Chicken-and-Egg of Chemistry: Bonding vs. Stability Revisited

The chemical bond is a central organizing concept in chemistry, yet it is absent from the molecular Hamiltonian and no "bond operator" exists. Bonding is therefore not a primitive physical entity but a derived descriptor emerging from the quantum state. The logical consequences of this observation are revisited. Statements such as "bonding stabilizes structure" when taken literally risk circular reasoning (petitio principii), whereby bonding is inferred from a stationary structure and then invoked as its cause. The same caution applies to concepts such as steric repulsion, which is also a derived descriptor. Bonding accompanies stable or metastable states and correlates with their properties without constituting their cause. Illustrative examples are drawn from QTAIM, non-covalent interaction (NCI) approach, protein structure, and hydrogen-hydrogen bonding. Causation, language, and the autonomy of chemistry are also briefly discussed. The aim is not at all to diminish the role of bonding, but to place it at the correct logical level, that is, as a powerful, state-dependent descriptor that organizes, classifies, and predicts chemical behavior without serving as its fundamental cause.

physics.chem-ph↗

arXiv2025

The Critical 9365 Å Diffuse Interstellar Band and C$_{60}^{+}$ Association

The detection of interstellar C$_{60}^{+}$ has been debated for 30 years. The contested attribution of a weaker DIB at 9365 Å was re-evaluated here on the basis of a Pearson correlation relative to 9577 Å, which was previously tied to C$_{60}^{+}$ by diverse collaborations. An assessment of 11 sightlines revealed a high correlation amongst 9365$-$9577 Å equivalent widths ($r=0.93 \pm 0.05$), after contamination from an adjacent line was mitigated using both numerical integration and Gaussian fits. In tandem with a recent separate study's high-$r$ evaluation linking 9577$-$9632 Å across a sizable baseline: three interrelated DIBs matching C$_{60}^{+}$ laboratory findings were independently reaffirmed (9365, 9577, 9632 Å). Yet further investigations are required to strengthen the case via two other weak DIBs disputedly linked to C$_{60}^{+}$, particularly owing to potential overlapping lines arising from an expansive chemical space (PAHs).

astro-ph.GA↗

arXiv2025

Rotational Dynamics of ATP Synthase: Mechanical Constraints and Energy Dissipative Channels

The proton motive force (PMF) across the inner mitochondrial membrane delivers approximately 0.2 eV of energy per proton, powering the FoF1-ATP synthase molecular motor. Here, we provide a detailed accounting of how this energy is utilized: Approximately 75-83% is transduced into the chemical free energy of ATP synthesis, while the remaining 17-25% is dissipated through internal friction, viscous drag, proton leakage, electroviscous effects, elastic deformations, and information-theoretic costs. Each dissipation channel is quantitatively evaluated, revealing that internal friction in the F1 motor is the dominant loss mechanism. In this work, we did not account for the energy supplied/injected due to the intrinsic electrostatic potential of the enzyme itself. In addition to this energy bookkeeping, we also examine the quantum mechanical constraints on the Fo unit's rotation. We find that, as can be expected, the energy spacing between quantized rotational states is several orders of magnitude smaller than thermal energies at physiological temperature, and that the tunneling probability through rotational barriers practically totally non-existent. Furthermore, the biological rotation speed (100-650 revolutions per second (rps)) is between one and three orders of magnitude below the quantum limit implied by quantization of angular momentum of the c-ring (which would have been ca. 13,000 to 62,000 rps (depending on the size of the c-ring (17 to 8 subunits, respectively)) in the first rotational energy level of the c-ring). Nevertheless, experimental estimates of the rotation rates in isolated c-ring suggest rates in the vicinity of 43,000 rps, right within our theoretical quantum estimates. However, ATP synthase as a whole operates firmly within the classical regime, despite its nanoscale dimensions, and highlight its evolutionary optimization for robust and efficient energy conversion....

q-bio.BM↗

arXiv2024

A Travelling Salesman Paths within nxn (n = 3, 4, 5) Magic Squares

Intriguing symmetries are uncovered regarding all magic squares of orders 3, 4, and 5, with 1, 880, and 275,305,224 distinct configurations, respectively. In analogy with the travelling salesman problem, the distributions of the total topological distances of the paths travelled by passing through all the vertices (matrix elements) only once and spanning all elements of the matrix are analyzed. Symmetries are found to characterise the distributions of the total topological distances in these instances. These results raise open questions about the symmetries found in higher-order magic squares and the formulation of their minimum and maximum total path lengths.

math.GM↗

arXiv2022

ATP Synthase: A Moonlighting Enzyme with Unprecedented Functions

ATP synthase's intrinsic molecular electrostatic potential (MESP) adds constructively to, and hence reinforces, the chemiosmotic voltage. This ATP synthase voltage represents a new free energy term that appears to have been overlooked. This term is at least roughly equal in order of magnitude and opposite in sign to the energy needed to be dissipated as a Maxwell's demon (Landauer principle).

physics.bio-ph↗

arXiv2021

The Hot Mitochondrion Paradox: Reconciling Theory and Experiment

Experiments by Chretien and co-workers suggest that mitochondria are 10oC hotter than their surroundings. Steady-state theoretical estimates place this difference at a maximum of 10^-5 oC. This million-fold disagreement may be called the hot mitochondrion paradox. It is suggested that every proton translocated via ATP synthase sparks a picosecond temperature-difference spike of the order of magnitude measured by Chretien et al. Time-averaging of these spikes recovers the theoretical value. Further, a temporal and spatial superposition of the fluorescence intensity of a very large number of molecular thermometer molecules in the sample can give the appearance of a steady signal. The inner mitochondrial membrane appears to be flanked by temperature differences fluctuating in time and along the membrane s surface, with hot and cold spots as ultrashort temperature spikes.

physics.bio-ph↗

arXiv2021

Quantum Crystallography N-Representability

Linus Pauling contributions span structural biology, chemistry in its broadest definition, quantum mechanical theory, valence bond theory, and even nuclear physics. A principal tool developed and used by Pauling is Xray, and electron, diffraction. One possible extension of the Pauling oeuvre could be the marriage of crystallography and quantum mechanics. Such an effort dates back to the sixties and has now flourished into an entire subfield termed quantum crystallography. Quantum crystallography could be achieved through the application of Clinton equations to yield N-representable density matrices consistent with experimental data. The implementation of the Clinton equations is qualitatively different for small and for large systems. For a small system, quantum mechanics is extracted from Xray data while for a large system, the quantum mechanics is injected into the system. In both cases, Nrepresentability is imposed by the use of the Clinton equations.

quant-ph↗

arXiv2021

Quantum Crystallography: Projectors and kernel subspaces preserving N-representability

Consider a projector matrix P, representing the first order reduced density matrix in a basis of orthonormal atom-centric basis functions. A mathematical question arises, and that is, how to break P into its natural component kernel projector matrices, while preserving N-representability of P. The answer relies upon 2- projector triple products, P'jPP'j. The triple product solutions, applicable within the quantum crystallography of large molecules, are determined by a new form of the Clinton equations, which - in their original form - have long been used to ensure N-representability of density matrices consistent with X-ray diffraction scattering factors.

quant-ph↗

arXiv2020

Manipulation of Diatomic Molecules with 'Oriented External Electric Fields': Linear Correlations in Atomic Properties Lead to Non-Linear Molecular Responses

'Oriented external electric fields (OEEFs)' have been shown to have great potential in being able to provide unprecedented control of chemical reactions, catalysis and selectivity with applications ranging from H2 storage to molecular machines. We report a theoretical study of the atomic origins of molecular changes due to OEEFs; understanding the characteristics of OEEF-induced couplings between atomic and molecular properties is an important step toward comprehensive understanding of the effects of strong external fields on molecular structure, stability, and reactivity. We focus on the atomic and molecular (bond) properties of a set of homo- (H2, N2, O2, F2, and Cl2) and hetero-diatomic (HF, HCl, CO, and NO) molecules under intense external electric fields in the context of quantum theory of atoms in molecules (QTAIM). It is shown that atomic properties (atomic charges and energies, and localization index) correlate linearly with the field strengths, but molecular properties (bond length, electron density at bond critical point, bond length, and electron delocalization index) exhibit non-linear responses to the imposed fields. In particular, the changes in the electron density distribution alter the shapes and locations of the zero-flux surfaces, atomic volumes, atomic electron population, and localization/delocalization indices. At the molecular level, the topography and topology of the molecular electrostatic potential undergo dramatic changes. The external fields also perturb the covalent-polar-ionic characteristic of the studied chemical bonds, hallmarking the impact of electric fields on the stability and reactivity of chemical compounds. The findings are well-rationalized within the framework of the quantum theory of atoms in molecules and form a coherent conceptual understanding of these effects in prototypical molecules such as diatomics.

physics.chem-ph↗

arXiv2019

Anionic hydrogen clusters as a source of diffuse interstellar bands (DIBs)

The sources behind numerous key diffuse interstellar bands (DIBs) remain elusive, and thus evidence is presented here that a family of seven anionic hydrogen atomic clusters (H(-)2n+1, n = 1 to 7) are pertinent contributors. Configuration interaction calculations show hat these charge-induced dipole clusters are stable at temperatures characteristic of the interstellar medium, and emerge from the most abundant element in the Universe. The clusters' spectra yield 25 absorption optical lines that align with observed DIBs to within the computational uncertainties. The absorption bands are due to excitations from the ground states of the clusters to metastable states.

astro-ph.GA↗