Chlorine Atoms Research Articles

Structural investigation of interactions between halogenated flavonoids and the lipid membrane along with their role as cytotoxic agents

This study focuses on understanding the structural and molecular changes in lipid membranes under the influence of six halogenated flavonoid derivatives differing in the number and position of substitution of chlorine and bromine atoms (D1–D6). Utilizing various analytical techniques, including fluorometric methods, dynamic light scattering (DLS), attenuated Fourier transform infrared spectroscopy (ATR- FTIR), and FT-Raman spectroscopy, the research aims to elucidate the mechanisms underlying the interaction of flavonoids with cell membranes. Additionally, the study includes in silico analyses to explore the physicochemical properties of these compounds and their potential pharmaceutical applications, along with toxicity studies to assess their effects on cancer, normal, and red blood cells. Our study showed the ability of halogenated derivatives to interact mostly with the outer part of the membrane, especially in the lipid heads region however, some of them were able to penetrate deeper into the membrane and affect the fluidity of hydrocarbon chains. The potential to reduce cancer cell viability, the lack of toxicity towards erythrocytes, and the favourable physicochemical and pharmacokinetic properties suggest these halogenated flavonoids potential candidates for exploring their potential for medical use.

Exploring the structure and dynamics of a fluorescent schiff base (1E,1′E)-1,1′-(1,4-phenylene) bis(N-(4-chlorophenyl) methamine: Synthesis, spectroscopic analysis, thermal, electronic and crystallographic study with biological applications

Schiff bases have emerged as attractive biological agents with a wide range of uses due to the extraordinary physical, chemical, and pharmacological characteristics that they possess. This study focuses on the effective synthesis of a Schiff base that is produced from 4-chloroaniline and terephthaldehyde. The success of this synthesis is supported by a variety of spectroscopic methods and Single crystal XRD analysis. The chemical that was synthesised had significant fluorescence qualities, with measured values at 457.13, 481.49, and 524.15 nm, highlighting the fact that it has the potential to be utilised in a variety of applications within the field. Using thermogravimetric analysis, the thermal stability of the compound was studied, which revealed an excellent stability at 399 °C. Thermal stability is an essential component of compound usefulness. Molecular insights were obtained by the utilisation of Density Functional Theory, which revealed an energy gap of 1.70 electron volts (eV) and electrophilic behaviour in certain atoms. The distribution of charges was brought to light through the use of Mulliken charges and molecular electrostatic potential analysis, which brought attention to the distinctive qualities of the subject molecule. An examination of the electron localization function revealed that the electron density inside carbon, nitrogen, and chlorine atoms had been delocalized. Additionally, the localised orbital locator wave function and reduced density gradient maps offered vital insights into the non-covalent interactions that were taking place within the system under investigation. In the course of the evaluation of antimicrobial efficacy, it was discovered that the chemical exhibited more powerful antibacterial activity against gram-positive B. subtilis than the conventional antibiotic amoxicillin. The antibacterial findings were further supported by molecular docking tests, which involved using particular proteins from the target species. These investigations showed that B. subtilis had a higher affinity for binding. These findings were further validated by molecular dynamic simulations. The synthesised chemical was subjected to in silico toxicity assessment using seven models, which demonstrated its non-irritating properties on the skin and eyes. The extensive analysis that is given here lays the groundwork for more targeted research on novel antibacterial drugs, with a particular focus on the safety, molecular interactions, and effectiveness of these compounds. As a result of the compound's potential applicability in biocompatible antimicrobial formulations, it is a viable candidate for improving the development of antibacterial medicines that are both effective and safe.

Synthesis, structural characterization of phenoxo-bridged zinc(II) complexes and their binding interaction with the spike protein of SARS-CoV-2

The research article reports the synthesis and structural study of the optimized geometry of selenium (Se) bearing 24- and 28- membered macrocyclic Schiff bases, LaH2 , LbH2 and their reactions with zinc metal ion. The reactions of the macrocyclic Schiff bases with ZnCl2 in 1:2 molar ratios result in the formation of bimetallic Zn(II) complexes having molecular composition [Se{(CH2)2N = CPh(4-CH3-C6H2O) PhC = O}2 · Zn2Cl2], (1) and [Se{(CH2)3N = CPh(4-CH3-C6H2O)PhC = O}2 · Zn2Cl2], (2). Moreover, as confirmed by various physico-chemical techniques such as elemental analysis, UV–Vis, FTIR,1H NMR, and mass spectrometry, the proligands underwent partial hydrolytic cleavage at one of the C = N positions and behave like hexadentate (N2O4) ligands binding to two Zn(II) ions via bridging through the Ophenolic atoms, which results in a square pyramidal geometry around Zn(II) with the chlorine atom occupying axial positions. Further, following density functional study, the stable optimized configuration of the Schiff bases LaH2 and LbH2 is found to adopt bowl shape geometry. Conversely, in molecular docking studies, the synthesized complex 1 exhibits a significantly stronger binding affinity (−8.7 kcal/mol) to the spike protein of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) as compared to the common coronavirus disease 2019 (COVID-19) treatment drugs such as chloroquine, hydroxychloroquine, and remdesivir with activity percentage showing more than 20% overall effectiveness than remdesivir and thus indicating its potential for COVID-19 therapeutics.

Phase Transition and Luminescent Property Change Induced by Different Organic Cations in One-Dimensional Double Perovskites.

Double perovskites (DPs) have attracted attention in the field of luminescence due to their inherent broadband emission of self-trapping excitons. In this work, we choose [(CH3)3NCH2CHCH2]+ and [CH3CHOHCH2NH2]+ as organic cations to synthesize two new organic-inorganic hybrid DPs, [(CH3)3NCH2CHCH2]2KInCl6 (1) and [CH3CHOHCH2NH2]2KInCl6 (2). The [KCl6]3- and [InCl6]3- octahedra are interchangeably connected by sharing two opposite faces, forming a one-dimensional coordination chain. Each K atom coordinates with six chlorine atoms in 1, while it coordinates with two oxygen atoms in addition to the six chlorine atoms in 2. The coordination between ions K and O in compound 2 may have significantly reduced its luminescence. As a result, compound 1 shows bright-yellow light with a quantum yield of more than 90%, while 2 shows weak blue light with a quantum yield of only 0.98%. In addition, different from no phase transition found in 2, 1 undergoes a reversible phase transition at 324/307 K in the heating-cooling cycle. Through structural and spectral analysis and density functional theory calculation, we conclude that the larger degree of [InCl6]3- octahedral distortion and the larger anion distance (In···In) also cause the PLQY of compound 1 to be higher than that of compound 2.

تحضير ، تشخيص دراسة التحلل الحراري فعالية مضادات الاكسدة لمعقدات العناصر الانتقالية مع ليكاند صبغة الازو

تم إجراء تفاعل ديازوتيزيشن بين 1- (6,4,2-ثلاثي هيدروكسي-فينيل) -إيثانون وأملاح ديازونيوم مما أدى إلى تكوين ليكاند 4- (3-أسيتيل -2،4،6-ثلاثي هيدروكسي-فينيل ازو) -N- (5-ميثيل-إيزوكسازول-3-يل) -بنزين سلفوناميد ، وهذا بدوره يتفاعل مع أيونات المعادن التالية (+V4، +Cr3، +Mn2 و +Cu2) مكونة معقدات مستقرة ثمانية السطوح لكل من الكروم والمنغنيز والنحاس و هرمي مربع القاعدة لـلفناديوم الرباعي .تم اكتشاف إنشاء مثل هذه المعقدات من خلال استخدام الوسائل الطيفية التي تنطوي على الأشعة فوق البنفسجية التي أثبتت الأشكال الهندسية التي تم الحصول عليها ، وأثبت IR تكوين مجموعة الآزو والتنسيق مع أيون المعدن من خلالها. أثبتت دراسات الانحلال الحراري (TGA & DSC) تنسيق بقايا الماء مع أيونات المعادن داخل مجال التناسق وكذلك ذرات الكلور. علاوة على ذلك ، التحليل الجزئي للعنصر و AAS الذي أعطى النتيجة المقابلة مع نتيجة العد النظري. (H &13C-NMR1) والكميات المغناطيسية يمكن أن تشير أيضًا إلى تكوين ليكاند H3L وحدوث التنسيق. تم حساب الثوابت الديناميكية الحرارية (H∆, S∆, G∆). سيتم استخدام طريقة الكسح الجذري DPPH لتقييم الأنشطة المضادة للأكسدة للمركبات التي أظهرت قدرتها المضادة للأكسدة على اخماد الجذور الحرة.

Modeling of experimental excess molar enthalpy with Wilson, UNIQUAC, and NRTL for mixtures of acetophenone with chloro derivatives of ethane and ethene at T = 298.15 K

The excess molar enthalpy HmE, was determined for systems consisting of acetophenone with chloro alkanes and alkenes derivatives. These derivatives include 1,2-dichloroethane, 1,1,1-trichloroethane, 1,1,2,2-tetrachloroethane, trichloroethene and tetrachloroethene at a temperature of T = 298.15 K. The Redlich-Kister relation fitting was used to analyze the HmE values obtained from this experimental data. Additionally, the excess partial molar enthalpy HiE was derived from the experimental HmE values. The intermolecular interaction function such as ∂HiE∂xi and ∂HjE∂xjwere also calculated. For the system consisting of acetophenone + 1,1,1-trichloroethane or + tetrachloroethene, the HmE values were found to be positive. Conversely, the HmE values for acetophenone + 1,2-dichloroethane or + 1,1,2,2- tetrachloroethane or + trichloroethene were observed to be negative. The magnitude of the HmE values increased in chloroethanes as the number of chlorine atoms increased, and became more negative in chloroethenes. Based on the local composition theory, the Wilson model, the universal quasichemical (UNIQUAC) model, and the non-random two-liquid (NRTL) model were used to correlate these thermodynamic data. The results showed good agreement with the experimental enthalpy data.

Chlorination Design for Highly Stable Electrolyte toward High Mass Loading and Long Cycle Life Sodium-Based Dual-Ion Battery.

Sodium-based dual ion batteries (SDIBs) have garnered significant attention as novel energy storage devices offering the advantages of high-voltage and low-cost. Nonetheless, conventional electrolytes exhibit low resistance to oxidation and poor compatibility with electrode materials, resulting in rapid battery failure. In this study, for the first time, a chlorination design of electrolytes for SDIB, is proposed. Using ethyl methyl carbonate (EMC) as a representative, chlorine (Cl)-substituted EMC not only demonstrates increased oxidative stability ascribed to the electron-withdrawing characteristics of chlorine atom, electrolyte compatibility with both the cathode and anode is also greatly improved by forming Cl-containing interface layers. Consequently, a discharge capacity of 104.6 mAh g-1 within a voltage range of 3.0-5.0V is achieved for Na||graphite SDIB that employs a high graphite cathode mass loading of 5.0mg cm-2, along with almost no capacity decay after 900 cycles. Notably, the Na||graphite SDIB can be revived for an additional 900 cycles through the replacement of a fresh Na anode. As the mass loading of graphite cathode increased to 10mg cm-2, Na||graphite SDIB is still capable of sustaining over 700 times with ≈100% capacity retention. These results mark the best outcome among reported SDIBs. This study corroborates the effectiveness of chlorination design in developing high-voltage electrolytes and attaining enduring cycle stability of Na-based energy storage devices.

Ethylene homo and co‐polymerization catalyzed by extensively bulky nickel catalysts with shielding wings of chlorine atoms

AbstractDesigning the catalysts to get high molecular weight polyethylene is an art. The catalysts bearing imine functionality derived from 8‐arylnaphthyl amines are more impressive and attractive in this regard. In this work, we synthesize 2,4‐dibenzhydryl‐8‐(3,5‐dichlorophenyl)naphthalen‐1‐amine to condense with picolinaldehyde, pyridine‐N‐oxide‐2‐carbaldehyde and 3,4‐dibutanone and then subsequently the treatment of resulting ligands with nickel precursors to get the corresponding catalysts. It was hypothesized that 3,5‐dichlorophenyl having extended wings of chlorine atoms along with bulky dibenzhydryl groups can provide good shielding on both apical positions of metal in response to slow down the chain transfer. More interestingly, the polymerization was done in industrially claimed n‐heptane solvent. All the catalysts showed activity in an order of 106, whereas a value of 1.04 × 107 g mol−1 h−1 has been recorded from keto‐imine based Ni‐3 catalyst. All catalysts generates polymer with high molecular weight with maximum value was recorded by Ni‐2 up to 37.4 × 104 g mol−1. Ni‐3 can also incorporate methyl 10‐undecenoate up to 2.6% in polyethylene backbone.

Method for the production of a compact source of atomic line spectra in the vacuum ultraviolet

Atomic emission spectra provide a means to identify and to gain insight into the electronic structure of emitting or absorbing matter. Detailed procedures are provided for the construction of low-pressure electrodeless discharge lamps that yield targeted emission in the vacuum ultraviolet for the spectroscopic study of water vapor and halogen species aboard an array of airborne observation platforms in the upper atmosphere, as well as in laboratory environments. While specific to the production of Lyman-alpha, atomic chlorine, and atomic bromine emissions in this study, the configuration of the lamps and their interchangeability with respect to operation lend these procedures to constructing sources engaging a wide selection of atomic and molecular spectra with straightforward modifications. The features and limitations of each type of lamp are discussed, as well as methods to improve spectral purity and factors affecting operational lifetime.

Facile construction of a stable core-shell spherically magnetic polyimide covalent organic framework for efficient extraction of phenylurea herbicides

Efficient enrichment is crucial for the highly sensitive monitoring of phenylurea herbicides (PUHs) in various environmental waters. In this work, a stable core-shell spherically magnetic polyimide covalent organic framework (COF) was synthesized via a simple template-mediated precipitation polymerization method under mild conditions using tri(4-aminophenyl)amine (TAPA) and 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) as the building units (denoted as Fe3O4@TAPA-BPDA). The Fe3O4@TAPA-BPDA exhibits remarkable adsorption performance for PUHs with an optimized adsorption time of only 10 min. The adsorption of PUHs by Fe3O4@TAPA-BPDA followed the pseudo-second-order kinetic model and the Langmuir model. Furthermore, hydrogen bonding, halogen bonding, hydrophobic interaction, electro donor-acceptor interaction and π-π interactions are identified as the dominant mechanisms contributing to excellent adsorption performance. It was demonstrated that halogen bonds play an important role in the adsorption of substances containing chlorine atoms. The Fe3O4@TAPA-BPDA is easy to operate and highly regenerable. A simple magnetic solid-phase extraction (MSPE) method based on the Fe3O4@TAPA-BPDA was then developed for the rapid extraction of five PUHs in real samples, coupled with high-performance liquid chromatography (HPLC) determination. The analytical method developed has a linear range of 0.5–50 ng/mL, and the limit of detection (LOD) ranges from 0.06 to 0.10 ng/mL. The method exhibits good accuracy with recoveries ranged from 74.5 % to 111.4 %. The analytical method was successfully applied to the highly sensitive detection of PUHs in environmental water samples, which highlighting the potential application of the Fe3O4@TAPA-BPDA in the sample pretreatment.

Supramolecular architecture of Mn(II) complex with 5,5´-dimethyl-2,2´-bipyridine and 4-hydroxybenzoic acid: Synthesis, crystal structure, Hirshfeld surface analyses, catalytic and antimicrobial activities

A novel complex [Mn(5,5´-dmbipy)2Cl2](4-hba)2 (1) (5,5´-dmbipy=5,5´-dimethyl-2,2´-bipyridine and 4-hba=4-hydroxybenzoic acid) was successfully synthesized using methanol by steam reflux. The complex is characterized using SC-XRD, IR, UV and thermogravimetric analysis. Single crystal X-ray analysis of 1 indicates a distorted octahedral coordinated Mn2+ centre with two molecules of 5,5´-dmbipy and two chlorine ions and the presence of two uncoordinated 4-hba in the complex. The two chlorine atoms (Cl1 and Cl2) form intermolecular H-bonding with 4-hba. The complex crystallizes in monoclinic space group P21/c forming a helical like 1D polymeric supramolecular architech through H- bonding. Presence of halogen-hydrogen bond C(sp2)-OH—Cl-M between uncoordinated -OH and Cl ion in 1 significantly provides a path of extending supramolecular network forming a unique architect of the complex. Interestingly, presence of pyridine-benzene system forming π-π stacking is confirmed from SC-XRD. Hirshfeld surface analysis is carried out to explore the noncovalent interactions in the crystal. Mn3O4 nanoparticles synthesized from complex 1 are characterized using PXRD and HRTEM, and successfully employed as catalyst for the degradation of dyes. Both complex 1 and Mn3O4 nanoparticles show appreciable biological activities.

Effect of substitution on thermal decomposition of formaldehyde: A theoretical study

Unimolecular decomposition of organic compounds is strongly influenced by substituted functional group. The present work focusses to explore the energetics and kinetics of unimolecular decomposition of formaldehyde and chloro- substituted formaldehydes. Dissociation of molecular systems are observed to compete between molecular elimination reaction and bond dissociation reaction. It is observed that degradation of formaldehyde and formyl chloride ruled by 3-centered concerted mechanism produced H2 and HCl fragments respectively. On the other hand, Cl2 elimination reaction is generated via formation of isohalon structure. Despite of presence of isohalon intermediate, molecular elimination in phosgene required higher energy as compared to formyl chloride. Ease of molecular elimination in case of formyl chloride is attributed to favourable electrostatic interaction between hydrogen and chlorine atom, which assist in lower activation barrier. Further, the kinetic analysis suggested the applied temperature and pressure play a key role in formation of dominant elimination channel during decomposition reaction.

Artemyriantholides A–K, guaiane-type sesquiterpenoid dimers from Artemisia myriantha var. pleiocephala and their antihepatoma activity

Artemyriantholides A−K (1−11) as well as 14 known compounds (12−25) were isolated from Artemisia myriantha var. pleiocephala (Asteraceae). The structures and absolute configuration of compounds 2 and 8−9 were confirmed by the single crystal X-ray diffraction analyses, and the others were elucidated by MS, NMR spectral data and electronic circular dichroism calculations. All compounds were chemically characterized as guaiane-type sesquiterpenoid dimers (GSDs). Compound 1 was the first example of the GSD fused via C-3/C-11′ and C-5/C-13′ linkages, and compounds 2 and 5 were rare GSDs containing chlorine atoms. Eleven compounds showed obvious inhibitory activity in HepG2, Huh7 and SK-Hep-1 cell lines by antihepatoma assay to provide the IC50 values ranging from 7.9 to 67.1 μM. Importantly, compounds 5 and 8 exhibited the best inhibitory activity with IC50 values of 14.2 and 18.8 (HepG2), 9.0 and 11.5 (Huh7), and 8.8 and 11.3 μM (SK-Hep-1), respectively. The target of compound 5 was predicted to be MAP2K2 by a computational prediction model. The interaction between compound 5 and MAP2K2 was conducted to give docking score of −9.0 kcal/mol by molecular docking and provide KD value of 43.7 μM by Surface Plasmon Resonance assay.

On the Dependence of the Rate of Deactivation of Triplet Excitations of a Number of Molecules on Their Ionization Potential and the Charge of the Nucleus of Heavy Atoms of the Solvent

Purpose. Establish the nature and reasons for the dependence of the change in the radiative rate constant of deactivation of triplet excitations of a number of molecules, caused by the effect of an external heavy atom, on their ionization potential from the ground state and the energy of the first excited singlet state.Methods. Kinetic methods were used to determine the rate constant for the deactivation of triplet excitations of organic molecules in solid solutions at 77 K. The solvents were n-heptane (neutral), carbon tetrachloride and benzene bromide (containing heavy chlorine and bromine atoms). The molecules studied were coronene, triphenylene, phenanthrene, naphthalene and biphenyl.Results. A linear relationship has been established between an increase in the ionization potential, the energy value of the first excited singlet state, and an increase in the change in the rate of radiative deactivation of triplet excitations of the studied molecules in carbon tetrachloride. It is shown that the increase in the change in the radiative deactivation rate of these molecules with an increase in their ionization potential is due to a decrease in the difference between the ionization energies and the first excited singlet state.Conclusion. The results of the study showed that there is a linear relationship between the increase in the radiative deactivation rate of triplet excitations of the studied molecules and their ionization potential. A linear relationship is also observed between the increase in the rate of radiative deactivation of triplet excitations of these molecules and the first excited singlet state. As the ionization potentials of the molecules under study increase, the difference between the ionization energy and the energy of the first excited singlet state decreases. This is the reason for the increase in the rate of deactivation of triplet excitations of molecules with an increase in their ionization potential.

Interaction of 6-Bromo- and 6-Chloro-Ubiquinone derivatives with mitochondrial electron transfer system

To understand the reaction mechanism of quinone-mediated electron transfer, a series of ubiquinone (Q)-derivatives with a bromine or chlorine atom at the 6-position and a different alkyl side chains at the 5-position of the benzoquinone ring were synthesized and characterized. The chemical properties and electron transfer activities were compared with the native ubiquinone, Q0C10. The redox midpoint potential of 6-Bromo- and 6-chloro-Q derivatives is 142 mV and 148 mV, respectively. These 6-halo-Q derivatives are reducible by ascorbate alone or by succinate in the presence of succinate-ubiquinone reductase. The reduced 6-halo-Q (6-halo-QH2) can be oxidized by cytochrome c alone or via ubiquinol-cytochrome c reductase. In the presence of cytochrome c oxidase and cytochrome c, 6-halo-QH2 is oxidizable by oxygen. 6-Halo-Q derivatives are reducible by succinate via succinate-ubiquinone reductase. They function as an electron-mediator connecting succinate-Q reductase and cytochrome c oxidase and bypass ubiquinol-cytochrome c reductase in the mitochondrial electron-transfer chain. This bypassing results in a decrease in energy coupling efficiency and a lower P/O ratio. These compounds might have therapeutic value in treating diseases that are caused by the oversupply of energy.

The quantum spin Hall insulator with large bandgap in functionalized AlBi monolayer

The quantum spin Hall (QSH) insulator exhibits various interesting physical properties. Therefore, researchers have been seeking QSH insulators with large bandgaps suitable for room temperature applications. Here, based on first-principles calculations, we predict that the chlorine atom functionalized AlBi monolayer forms a topological insulator with a large bandgap (Eg = 0.215 eV). Chlorination and SOC effect induce AlBi(Cl)2 band inversion, and phonon spectra calculations demonstrate excellent dynamic stability for AlBi(Cl)2. The Z2 topological invariants, as well as the topological nontrivial edge states further confirm these findings. In addition, we applied the biaxial strains ranging from −5% to 5% to the monolayer, revealing a topological phase transition at −3%, resulting in the emergence of a normal insulator. These interesting features suggest that chlorinated AlBi is a promising material for room temperature spintronic devices.

Investigation into the Reaction of Hydrogen Iodide with a Chlorine Atom in the Atmosphere above the Sea

Investigation into the Reaction of Hydrogen Iodide with a Chlorine Atom in the Atmosphere above the Sea

The study of the interaction of 1,2- and 1,4-naphthoquinones with aminophosphonic esters

A number of new biologically active phosphorus-containing quinones were prepared by the reaction of 2,3-dichloro-1,4-naphthoquinone and sodium 1,2-naphthoquinone-4-sulfonate with phosphonate nucleophilic reagents, aminophosphonic acid esters. The structures of the synthesized compoumds were confirmed by ESI-MS, 1H NMR, IR-spectroscopies and elemental analysis. It was shown that aminophosphonic esters form products of nucleophilic substitution of a chlorine atom of 1,4-naphthoquinone or a sulfonyl group of 1,2-naphthoquinone on an aminophosphonic fragment. The products of the interaction of sodium 1,2-naphthoquinone-4-sulfonate with primary aminophosphonates existed in solution in 1,2-quinoid or 2-hydroxy-1,4-quinonimine tautomeric form depending on pH. The antimicrobial activity of the prepared compounds was investigated against Escherichia coli В-906, Staphylococcus aureus 209-Р, Mycobacterium luteum В-917, Candida tenuis VKM Y-70 and Aspergillus niger VKM F-1119 strains by the method of diffusion in agar of their 0.1% and 0.5% solutions. 1,2-Naphthoquinone derivatives showed good activity against S. aureus at a concentration of 0.1%, in its turn 1,4-napthoquinone derivatives showed activity against M. luteum at a concentration of 0.5%.

The OH stretching region in infrared spectra of the apatite OH-Cl binary system

Abstract Polarized Fourier Transform Infrared (FTIR) microspectroscopy of the OH stretching region of hydroxylapatite-chlorapatite solid solutions presents novel problems for the assignment of peaks to specific OH-Cl pairs. Crystal structure refinements of Hughes et al. (2016) identified new positions for column anions in synthetic mixed Cl-OH apatites, with three different column anion arrangements depending on composition. These structural refinements, combined with bond valence calculations, allow for interpretation of the OH stretching region. A peak at 3574 cm-1 is identified as that from end member hydroxylapatite. A second major peak at 3548 cm-1 is only found in mixed chlorapatite-hydroxylapatite solid solutions, as is a third peak at 3592 cm-1. Both represent perturbations of the OH stretching vibration as compared to hydroxylapatite, to lower and higher frequency, respectively. Both of the new peaks are the result of a Clb-OH sequence, with adjacent anions in crystallographically similar positions, both above or both below adjacent mirror planes. One configuration has the hydrogen atom pointed towards the chlorine atom. The second has the hydrogen of the OH group pointed away from the chlorine atom. Both configurations present novel problems. The shift to lower wavenumber at 3548 cm-1 is characteristic of hydrogen bonding in fluorapatite-hydroxylapatite mixtures, yet the distance between O(H) and Clb is too great to allow it. The shift of OH stretching vibrations to lower wavenumber is produced through changes in polarization of intervening Cl-Ca2’ (or Ca2) and Ca2(’)-O3 bonds, which are affected by the presence of the large chlorine atom. Lowering the OH stretching vibration mimics the expected effect of a chlorine on a neighboring OH group in the apatite c-axis column, though without hydrogen bonding. The shift to higher wavenumbers, i.e. higher frequency at 3592 cm-1, is the opposite of that expected for hydrogen bonding between column anions in the apatite mineral group. It is ascribed to interaction between an adjacent Clb and the oxygen end of an adjacent OH dipole. This pairing places an oxygen and a chlorine atom in close proximity. Possible means of accommodation are discussed. A ubiquitous peak at 3498 cm-1 represents hydrogen bonding between an OH and the OHa site, with an interoxygen distance of about 2.9 Å. Published modeling supports the hypothesis that the OHa site is occupied by an O rather than an OH. However, no clear counterpart to this pairing is observed in crystal structure refinements for specimens lacking OHa, although the infrared absorbance is present. The existence of oxyapatite is inferred from studies of plasma-sprayed biomaterials, but the crystallographic details of the substitution have remained elusive. A minor shoulder at 3517 cm-1 does not have a clear counterpart in the structural refinements. Sequences of three columnar anions (e.g. OH-Cl-OH or Cl-OH-OH) can be ruled out, but unequivocal assignment awaits further research.

Redox-Neutral Multicatalytic Cerium Photoredox-Enabled Cleavage of O-H Bearing Substrates.

The need for synthetic methodologies capable of rapidly altering molecular structure are in high demand. Most existing methods to modify scaffolds rely on net exothermicity to drive the desired transformation. We sought to develop a general strategy for the cleavage of C-C bonds β to hydroxyl groups independent of inherent substrate strain. To this end we have applied a multicatalytic cerium photoredox-based system capable of activating O-H bonds in lactols to deliver formate esters. The same system is also capable of effecting hydrodecarboxylation and hydrodecarbonylation reactions. Initial mechanistic probes demonstrate atomic chlorine (Cl⋅) is generated under the reaction conditions, but substrate activation through cerium-alkoxides or -carboxylates cannot be ruled out.