Increasing Ring Size Research Articles

Theoretical Insight into Complexation Between Cyclocarbons and C60 Fullerene.

This work conducts a comprehensive theoretical study on the non-covalent complexation between cyclocarbons and C60 fullerene for the first time. The binding energy between cyclocarbons and C60 fullerene is significantly stronger than that between two C18 or two C60 fullerenes, indicating a particularly strong affinity. The cyclocarbons and C60 fullerene can spontaneously assemble into complexes in the gas phase at room temperature, and the hydrophobic effect caused by the solvent environment can promote this binding. The binding strength with C60 fullerene increases almost linearly with the increase of cyclocarbon size, and the C34@C60 dimer exhibits a perfect nano-Saturn structure. As the ring size increases, the angle between the two cyclocarbons of the 2 : 1 trimers formed by cyclocarbons and C60 fullerene gradually decreases. In C60@2 C34 trimer, the fullerene is symmetrically surrounded by two cyclocarbons. The results on the trimers formed by cyclocarbon and C60 fullerenes in a 1 : 2 ratio showed when the cyclocarbon sandwiched between two fullerenes is not quite large, the trimers exhibit an ideal dumbbell-like structure, and the presence of the first fullerene has a significant synergistic effect on the binding of the second one. The cyclocarbon greatly promotes the dimerization of fullerenes, which acted as a "molecular glue".

Insight into evolution characteristics of pyrolysis products of HLH and HL coal with Py-VUVPI-MS and DFT

To achieve a comprehensive understanding of the influence of chemical structure on the evolution characteristics of coal pyrolysis products, pyrolysis reaction of two kinds of low rank coal (Huolinhe and Huangling coal) were investigated with pyrolysis-vacuum ultraviolet photoionization mass spectrometry (Py-VUVPI-MS). The soft ionized mass spectral detection can provide evolved information of original pyrolysis product. The chemical structure of coal samples was characterized by solid-state 13C-NMR, indicating HLH coal with more branched chain and longer aliphatic chain structure. The bond dissociation enthalpies (BDE) of β-Cal-Cal and β-Cal-O within model compounds were obtained with density functional theory. The difference of peak temperature with maximum evolution was collected to investigate the effect of the chemical environment on evolution behavior of pyrolysis products. The results reveal that branched and long aliphatic side-chains can reduces BDE of β-Cal-Cal and β-Cal-O, resulting in the lower peak temperature of pyrolysis products derived from HLH coal. Substituent groups (such as alkyl and hydroxyl groups) attached on the aromatic rings can reduce peak temperatures. Moreover, the effects of the different substituted position on the aromatic ring of the methyl group presented on differences of the BDE. An increase in aromatic ring size correlates with a certain degree of reduction in BDE for β-Cal-Cal; consequently, peak temperature of pyrolysis products with larger aromatic rings is lower. The pyrolysis behavior of coal were discussed based on the experimental observations and theoretical calculation, which are beneficial to understand the reaction route and mechanism of coal pyrolysis.

Conformation and Photodissociation Process of Benzo-15-Crown-5 and Benzo-18-Crown-6 Complexes with Ammonium Ions Investigated by Cold UV and IR Spectroscopy in the Gas Phase.

We examined the conformation of benzo-15-crown-5 (B15C5) and benzo-18-crown-6 (B18C6) complexes with ammonium ions, NH4+, CH3NH3+ (MeNH3+), CH3CH2NH3+ (EtNH3+), and CH3CH2CH2NH3+ (PrNH3+), using cold UV and IR spectroscopy in the gas phase. We measured the UV photodissociation (UVPD) spectra of the ammonium complexes and compared them with those of the K+(B15C5) and K+(B18C6) complexes in order to identify the conformation on the basis of the band position. The number of possible conformations for the ammonium complexes of B15C5 is limited compared with alkali metal ions with similar ionic radii. The NH4+(B15C5), MeNH3+(B15C5), and EtNH3+(B15C5) complexes show two conformers, whereas the K+(B15C5) complex has three stable conformers. In the case of the PrNH3+(B15C5) complex, one conformer was found predominantly in the UVPD spectrum. The ammonium complexes of B15C5 prefer to adopt crown conformations with large dihedral angles on the C-O-C-C atoms around the benzene moiety. In the case of the ammonium complexes of B18C6, two or three conformers were found in the UVPD spectra. One conformation of the B18C6 complexes is similar to that of the K+(B18C6) complex, which has a planar form on the C-O-C-C atoms around the benzene moiety. The other but dominant conformations of the ammonium complexes could be attributed to those with large C-O-C-C dihedral angles. These conformational findings for the ammonium complexes suggest that the benzo-crown ethers tend to adopt nonplanar conformations around the benzene moiety to encapsulate the ammonium ions. The IR-UV double-resonance (DR) spectra of the B15C5 and B18C6 complexes were compared to those of benzo-12-crown-4 (B12C4) and dibenzo-18-crown-6 (DB18C6) complexes. The N-H···O hydrogen bond (H-bond) is weaker with increasing ring size from B12C4 to B18C6, although the calculated binding energy is smaller for B12C4 than for B18C6. This result indicates that cooperative H-bonds with three N-H groups can strengthen the intermolecular bond between the ammonium ions and B18C6. The difference in the conformational preference between the ammonium and K+ complexes is attributed to directed N-H···O H-bonds in the ammonium complexes. Proton transfer and dissociation of the crown ring were also observed for the photoexcitation of the NH4+(B15C5) and NH4+(B18C6) complexes.

Impact of ring size on the C[sbnd]H activation reactivity of iron(IV)–oxo complexes: A computational study with TMC macrocycles

Here, a DFT investigation has been presented to demonstrate the relevance of the macrocyclic ligand ring size of the high-valent Fe(IV)O complex-catalyzed CH activation process. A nonheme iron-oxo compound bound with extensively studied macrocycle tetramethylcyclam (TMC) with varying ring size measures in terms of n = 12, 13, 14, 15, and 16 in [Fe(IV)O(n-TMC)(CH3CN)]2+ has been considered as the oxidant and dihydroanthracene as the general substrate. Counterions, as always, have been considered to avoid the self-interaction error in these DFT calculations. Computations were carried out to determine the effect of the axial ligand, acetonitrile, on the CH activation reactivity. It has been discovered that the complexes without axial ligands turned out to be more reactive compared to their axially coordinated counterparts. The most intriguing finding, however, has been that reactivity increased steadily with ring size increments, giving us the trend 12 < 13 < 14 < 15 < 16. Behind this typical pattern of reactivity, several factors played a role, including the energy of the electron acceptor orbital, which sequentially decreases, and the distortion energy to achieve the transition state, which also decreases as we move on from n = 12 to 16. The triplet-quintet energy difference of the oxidants also has a part to play, as it decreases with increased ring size, with the quintet becoming more and more dominant. The current studies have also been able to corroborate the experimental data that was published regarding Fe(IV)O(13-TMC) (without axial syn form) having a higher CH activation reactivity than Fe(IV)O(14-TMC) (with axial anti form). On the whole, this computational exploration gives us a reactivity pattern based on the ring size commutes and can lead to successful experimental results if pursued based on this reaction.

Investigation of the thermal conductivity of SiO2 glass using molecular dynamics simulations

AbstractA recent study showed that generating local crystalline paths within a glassy matrix provides only a moderate increase in thermal conductivity until the path fills most of the total volume. It was indicated that percolation theory governs the thermal conductivity in such crystalline‐implanted glass composites. In this study, we use computer simulations to investigate the effect of partial vitrification by breaking structural order of silica crystals by local vitrification. Such locally vitrified crystal structures are made by the bond‐transposition method, where the extent of vitrification can be tuned. Also, we test melt‐quenching of three SiO2 crystalline structures (α‐quartz, coesite, and stishovite) to make silica glasses with different densities. The cooling rates and pressures were varied during the melting process in order to obtain glass structures with varied degrees of order. Our results show that the thermal conductivity of silica glasses calculated using Green–Kubo relation decreases rapidly as soon as the crystallinity is disturbed by bond transition or generated local glassy phase. This implies the phonon mean free path rapidly shrinks with even a small number of scatterers, regardless of the original polymorph. Through the investigation of the pressure effect, a strong proportional relation between the thermal conductivity and the density is found among all silica samples. Such correlation can be accounted by assuming a constant integral term in the Green–Kubo relation without the volume scaling, which is reasonable based on a weak dependence of κV on the density of silica glass except with a slight increase at low quench pressures. We hypothesize that when the quench pressure increases moderately, an increase of characteristic ring size tends to generate a more flexible SiO2 structure which results more phonon scattering. Green–Kubo modal analysis further shows that the contribution from modes at low frequencies is suppressed when SiO2 is melt‐quenched at higher pressure and vice versa.

Effect of Guanine Adduct Size, Shape, and Linker Type on the Conformation of Adducted DNA: A DFT and Molecular Dynamics Study.

DNA is damaged through various exogenous sources (e.g., automobile exhaust, tobacco smoke, and processed foods), which can yield diverse C8-dG bulky aryl adducts. Adducts are known to induce structural changes to DNA that can lead to various biological outcomes, ranging from cell death to diseases such as cancer. Unfortunately, the relationship between the chemical composition of the damaged product, the adducted DNA structure, and the biological consequences is not well understood, which limits the development of disease detection and prevention strategies. The present study uses density functional theory (DFT) calculations and quintuplicate 1 μs molecular dynamics (MD) simulations to characterize the structure of DNA containing 21 model C8-dG adducts that systematically differ in size (phenyl to pyrenyl), shape (α (2,3), β (3,4) fusion, or ring substitution), and nucleobase-aryl group linkage (N, O, and C-linked). DFT calculations reveal that the inherent structural features of the G nucleobase adducts are impacted by linker type and bulky moiety shape, but not size, with the conformational flexibility reducing with α-ring fusion and linker composition as N > O > C. These structural properties are maintained in nucleoside models, which also reveal an increased propensity for anti-to-syn rotation about the glycosidic bond with N < O < C linker type. Although these diverse chemical features do not influence the global structure of adducted DNA, the adducts differentially impact the conformation local to the adducted site, including the relative populations of structures with the bulky moiety in the major groove (B conformer) and intercalated (stacked) into the helix (S conformer). Specifically, while the smallest phenyl adducts favor the B conformation and the largest pyrenyl-derived adducts stabilize the S conformation, the B/S ratio decreases with an increase in ring size and N > O > C linker composition. The shape and size (length) of the adduct can further finetune the B/S ratio, with β-fused naphthyl or α-fused phenanthryl N-linked adducts and O or C-linked adducts containing ring substitution increasing the prevalence of the S adducted DNA conformation. Overall, this work uncovers the significant effect of bulky moiety size and linker type, as well as the lesser impact of aryl group shape, on adducted DNA structure, which suggests differential replication and repair outcomes, and thereby represents an important step toward rationalizing connections between the structure and biological consequences of diverse DNA adducts.

FRI452 A Rare Case of Klinefelter Syndrome, 48XXYY

Abstract Disclosure: P. Kachhadia: None. S. Khan: None. S. Aldasouqi: None. A. Abu Limon: None. Introduction: Klinefelter Syndrome (KS), 47XXY, is the most commonly seen chromosomal abnormality causing infertility, or primary hypogonadism. Other chromosomal variants are rare. We present a very rare case of nondisjunction of the sex chromosome resulting in a 48XXYY KS variant. Case Presentation: The patient is a 45-year-old male was referred to our clinic for evaluation of early onset osteoporosis. The patient was accompanied by his sister, given his cognitive delay. On initial physical exam, there was a concern about acromegaly with signs of frontal bossing, increased hand size, increased ring size and increased shoe size. More recent pictures of the patient showed significant changes in his facial appearance from few years prior. Other symptoms included night sweats. Physical exam revealed decreased testicular volume (less than 3mL bilaterally). Pituitary labs showed elevated prolactin, elevated LH, FSH and low free and total testosterone. GH, IGF-1 levels were within normal range. Chromosomal analysis showed an unexpected pattern of 48XXYY. In addition, MRI of the pituitary was done which showed increased infundibular stalk and increase in size of the pituitary gland which was thought to be secondary to pituitary microadenoma. DEXA scan confirmed osteoporosis. Patient was treated with testosterone injections and alendronate. The rationale for alendronate therapy was considered as a bridge to prevent fractures while the bone density would expectedly improve with androgen therapy, over time. Discussion: Although KS is commonly seen at a frequency of 1:500-1:1000 males, less common and variable phenotypical presentations can occur and can lead to a delayed diagnosis. The reason for the delay of diagnosis in these rare KS variants is the cognitive impairment which leads to delayed evaluation of fertility or hypogonadism, as contrasted to patients with the common variant, KS 47XXY. Additionally, unlike the classic KS variant, these rare variants are often associated with learning disabilities and gross bony features. Conclusion: Clinicians should be familiar with different clinical presentations of the less common KS genetic variants, in contrast to classical KS variants. Patients with classical KS typically present early in view of recognizable complaints of infertility, while patients with the less common KS variants may not present early on due to cognitive delay. Thus, familiarity with the additional manifestations of the less common KS variants (e.g., gross bony features) can help clinicians to suspect the possibility of these variants, prompting chromosomal analysis for further evaluation in such patients. Presentation Date: Friday, June 16, 2023

FRI206 A Rare Case Of Coexisting Acromegaly And Adrenal Cushing’s Syndrome

Abstract Disclosure: T. Chamakkala: None. T. Gallagher: None. Introduction: Acromegaly has been associated with higher risk of cancer morbidity and mortality. Acromegaly coexisting with adrenal Cushing’s disease has been rarely described in literature. We present a patient who was found to have acromegaly during evaluation for Cushing’s syndrome. Clinical Case: A 50-year-old woman presented to the office for endocrinology evaluation at the referral of PCP for elevated 24h urine cortisol level 176ug/24h. She had noticed facial plethora over several years, fatigue, and easy bruising. She had recently been diagnosed with hypertension, poorly controlled on two medications at the time of evaluation. Repeat 24h urine cortisol and midnight salivary cortisol levels were elevated; dexamethasone suppression test was positive. ACTH was &amp;lt;1.5pg/mL, consistent with ACTH independent hypercortisolemia. Adrenal CT showed 2.6x3cm left adrenal adenoma. She underwent left adrenalectomy and pathology showed adrenal cortical adenoma. During evaluation for Cushing’s disease and new onset hypertension, IGF1 was evaluated and found to be elevated at 354ng/mL. She additionally endorsed symptoms of worsening carpal tunnel syndrome and increasing ring size. After adrenalectomy, IGF1 was repeated and remained elevated at 429ng/mL. Growth hormone suppression test showed nadir of 0.56ng/mL which is higher than &amp;lt;0.3ng/mL expected of high sensitivity GH assays. Pituitary MRI showed three suspected pituitary microadenomas, 4mm and 5mm in left gland, 7mm in right gland. Given difficulty with surgical approach and higher risk of hypopituitarism, she was started on lanreotide for treatment without surgery. She underwent genetic counseling and was offered genetic testing. Conclusion: This case highlights the rare coexistence of acromegaly and adrenal Cushing’s disease in a 50 year old woman. Though the relationship between acromegaly and cancer has been historically controversial, more recent studies have shown an increased risk of both benign and malignant tumors with acromegaly. Untreated Cushing’s Disease has been associated with mildly elevated IGF1 which then decreases after remission; it is unclear if the same pathological process is involved in other etiologies of hypercortisolemia like adrenal Cushing’s syndrome, but re-evaluation of IGF1 after treatment of Cushing’s should be considered. As Cushing’s and acromegaly share similar consequences such as worsening HTN, changing facial appearance, and worsening diabetes, it is prudent to consider each as differential diagnoses when signs do not remit after treatment. Acromegaly has additionally been associated with other endocrinopathies in syndromes including MEN1 syndrome, McCune Albright Syndrome, and Carney Complex. Evaluation for these syndromes and consideration for genetic testing should be considered in the evaluation of a patient with acromegaly and additional associated endocrinopathies. Presentation: Friday, June 16, 2023

THU022 A Case Of Delayed Diagnosis Of Acromegaly

Abstract Disclosure: K. Blanchard: None. C. Musurakis: None. A. Havrylyan: None. A 57-year-old hispanic female with hypertension, prediabetes, hyperlipidemia, and uterine leiomyomata with hysterectomy one year ago presented to our emergency department with sensations of numbness, tingling, and pressure on the top of her head for 12 days’ duration and left eye blurred vision with photosensitivity for 3 days’ duration. Physical exam was significant for evident enlarged facial features including macroglossia, macrognathia, separation of teeth, enlarged lips, enlarged ears and increased size of hands and feet with thickening of the skin on the fingers and toes. Many skin tags were noted on the neck and chest. She reported noticing these changes gradually over the past five years, as well as noticing an increase in shoe size and ring size. Admission labs were significant for IGF-1 965 ng/mL (47-236), Glucagon 172 ng/mL (0.05-8.00), AM cortisol 24 ug/dL (6.7-22.6), ACTH 29.6 pg/mL (7.2-63.3), FSH 13.22 mIU/mL (16.74-113.59), LH 3.79 mIU/mL (10.87-58.64), and Prolactin 24.3 ng/mL (2.74-19.64). Hemoglobin A1c was 5.8% (&amp;lt;5.7) and lipid profile was significant for triglycerides of 202 mg/dL (&amp;lt;150). TSH was within normal limits. A chest x-ray showed no cardiomegaly. An echocardiogram showed no cardiomyopathy. A CT scan of the brain showed a hyperdense sellar/suprasellar mass measuring 2.1 x 0.7 x 2.4 cm with mass effect on the optic chiasm and intracranial optic nerve not excluded. An MRI brain confirmed a large pituitary macroadenoma measuring 2.7 x 2.5 x 2.2 cm with mass effect on the optic chiasm and pituitary stalk. In addition to the above workup, we recommended Neurosurgery evaluation for symptomatic macroadenoma with optic chiasm mass effect, Ophthalmology evaluation for visual fields testing, and referral to a tertiary care center for evaluation and treatment of acromegaly. The patient was discharged with Neurosurgery and Endocrinology outpatient follow-up, but unfortunately did not attend her appointments. Acromegaly is a rare condition with a prevalence of 60 cases per million. While the mean age of occurrence is 32 years, the mean age of diagnosis is 40 to 45 years, highlighting a persisting delay in the diagnosis. The changes associated with acromegaly occur slowly and therefore can be overlooked by the patient, their family members, and even physicians. Left untreated, continued exposure to increased levels of growth hormone and IGF-1 leads to development of comorbidities including Cushing’s disease, cardiovascular disease, diabetes, arthralgias, decreased bone mineral density, sleep apnea, and uterine leiomyomata, as well as increased mortality and decreased quality of life. This case highlights the importance of physicians in all specialties being familiarized with the symptoms and physical features of acromegaly to aid in timely diagnosis. Presentation: Thursday, June 15, 2023

The effect of the CPP size on the nonlinear optical properties of the new necklace-type molecules formed by carborane and [n]Cycloparaphenylenes(n = 8–11)

The new necklace-type molecules were formed by [8–13]CPP and carborane, which further manipulated the size of the macroring, revealing the effect of size on its luminescence behavior. In this work, the effects of ring size on the absorption spectrum, electron excitation and nonlinear optical properties of the compounds were investigated in detail, aiming to reveal an effective way to improve the optical properties of these necklace-type compounds. The absorption spectra of the compounds showed that the size of the CPP ring had little effect on the spectral shape and position, but the electron transition information showed that there were the significant charge transfer within the CPP ring and a gradual enhancement of interfragment charge transfer from the CPP ring to carborane. The increasing order of polarizability, first and second hyperpolarizability values of these compounds with the increase of CPP size indicated that increasing the size of the CPP ring was an effective way to increase the nonlinear optical properties of necklace-type molecules. Among the frequency dependent hyperpolarizability values, the γ(-ω;ω,0,0) value increased by a factor of 4 from complex 1 to 6 with the increase of CPP ring size, which indicated that increasing the size of the CPP ring was an effective way to increase the optical Kerr effect of necklace-type molecules. Therefore, these the new necklace-type nolecules formed by carborane and [n]Cycloparaphenylenes would be excellent nonlinear optical materials in the field of the all-optical switch.

PAH laser diagnostics and soot particle dynamics in gasoline co-flow flames doped with n-butanol

As a carbon-neutral fuel, bio-butanol mixed with gasoline has become a potential decarbonization method in transportation field. In this work, the effects of n-butanol addition to gasoline on PAH and soot formation were investigated experimentally and numerically. As n-butanol ratio increases, flame lift-off height, flame height and OH/CH chemiluminescence intensity decrease gradually. The n-butanol addition has inhibitory effect on PAH with different sizes, and the inhibitory effect increases with the increasing aromatic-ring size. As ring size increases, the high concentration region gradually evolves from the center of upper flame to the two wings of downstream flame. The primary particle size and number density show a monotonically decreasing trend with n-butanol ratio, attributing to the significant decrease of nucleation and surface growth rate. For particle surface growth, the decreasing trend of PAH condensation is higher than that of HACA with the n-butanol ratio. The contribution of HACA to particle growth increases with n-butanol ratio, and replaces PAH condensation as the main mechanism when n-butanol ratio exceeds 60%. For particle oxidation, n-butanol addition leads to a slight increase in OH oxidation rate and a significant decrease in O2 oxidation rate, while O2 oxidation is always the dominant mechanism for particle oxidation.

Effect of the Temperature on the Process of Preferential Solvation of 1,4-Dioxane, 12-Crown-4, 15-Crown-5 and 18-Crown-6 Ethers in the Mixture of N-Methylformamide with Water: Composition of the Solvation Shell of the Cyclic Ethers.

The aim of the work was to analyze the preferential solvation process, and determine the composition of the solvation shell of cyclic ethers using the calorimetric method. The heat of solution of 1,4-dioxane, 12-crown-4, 15-crown-5 and 18-crown-6 ethers in the mixture of N-methylformamide with water was measured at four temperatures, 293.15 K, 298.15 K, 303.15 K, and 308.15 K, and the standard partial molar heat capacity of cyclic ethers has been discussed. 18-crown-6 (18C6) molecules can form complexes with NMF molecules through the hydrogen bonds between -CH3 group of NMF and the oxygen atoms of 18C6. Using the model of preferential solvation, the cyclic ethers were observed to be preferentially solvated by NMF molecules. It has been proved that the molar fraction of NMF in the solvation shell of cyclic ethers is higher than that in the mixed solvent. The exothermic, enthalpic effect of preferential solvation of cyclic ethers increases with increasing ring size and temperature. The increase in the negative effect of the structural properties of the mixed solvent with increase in the ring size in the process of preferential solvation of the cyclic ethers indicates an increasing disturbance of the mixed solvent structure, which is reflected in the influence of the energetic properties of the mixed solvent.

Crystal structures of three homologues with increasing ring size: 2-meth-oxy-4-(thio-phen-2-yl)-5,6,7,8-tetra-hydro-quinoline-3-carbo-nitrile, 2-meth-oxy-4-(thio-phen-2-yl)-6,7,8,9-tetra-hydro-5H-cyclo-hepta-[b]pyridine-3-carbo-nitrile and 2-meth-oxy-4-(thio-phen-2-yl)-5,6,7,8,9,10-hexa-hydrocyclo-octa[b]pyridine-3-carbo-nitrile.

The title compounds, C15H14N2OS (1a), C16H16N2OS (1b), and C17H18N2OS (1c), form a homologous series in which the size of the saturated ring increases from six- to eight-membered (with four, five and six methyl-ene groups respectively). For 1b and 1c, the central (CH2) n moieties are all displaced to the same side of their ring, and the CH2-CH2-CH2 angles are much wider than the standard sp 3 value; a database search indicates that these are general features of such ring systems. For 1a, the thio-phene ring lies with the sulfur atom on the opposite side of the Cthio-phene-Cpyridine bond to the cyano group, in contrast to 1b and 1c. For each compound, the packing may be described in terms of two 'weak' C-H⋯N hydrogen bonds, which link the mol-ecules to form one-dimensional (1a, 1c) or three-dimensional (1b) assemblies.

Why Cyclohexatriene (C&lt;SUB&gt;6&lt;/SUB&gt;H&lt;SUB&gt;6&lt;/SUB&gt;, p&lt;i&gt;K&lt;/i&gt;&lt;SUB&gt;a&lt;/SUB&gt; = 43) is Less Acidic than Cyclopentadiene (C&lt;SUB&gt;5&lt;/SUB&gt;H&lt;SUB&gt;6&lt;/SUB&gt;, p&lt;i&gt;K&lt;/i&gt;&lt;SUB&gt;a&lt;/SUB&gt; = 15) and Cycloheptatriene (C&lt;SUB&gt;7&lt;/SUB&gt;H&lt;SUB&gt;8&lt;/SUB&gt;, p&lt;i&gt;K&lt;/i&gt;&lt;SUB&gt;a&lt;/SUB&gt; = 36): A Freshmen Chemical Education Undergraduate Exercise

The pKa of Cyclohexatriene (Benzene) is 43. And that of Cyclopentadiene and Cycloheptatriene are 15 and 36 respectively. In the ascending order of number of carbon atoms of the three cyclic hydrocarbons, Cyclohexatriene lies between Cyclopentadiene and Cycloheptatriene. It is a tempting belief of undergraduate chemists who begin to pursue their undergraduate course that the pKas will be in the same increasing order with increase in ring size. But surprisingly pKa of Cyclohexatriene is more than that of either Cyclopentadiene and or Cycloheptatriene. Suitable explanations are given.

Understanding electrostatics and covalency effects in highly anisotropic organometallic sandwich dysprosium complexes [Dy(CmRm)2] (where R = H, SiH3, CH3 and m = 4 to 9): a computational perspective.

In this article, we have thoroughly studied the electronic structure and 4f-ligand covalency of six mononuclear dysprosium organometallic sandwich complexes [Dy(CmRm)2]n+/- (where R = H, SiH3, CH3; m = 4 to 9; n = 1, 3) using both the scalar relativistic density functional and complete active space self-consistent field (CASSCF) and N-electron valence perturbation theory (NEVPT2) method to shed light on the ligand field effects in fine-tuning the magnetic anisotropy of these complexes. Energy decomposition analysis (EDA) and ab initio-based ligand field theory AILFT calculations predict the sizable 4f-ligand covalency in all these complexes. The analysis of CASSCF/NEVPT2 computed spin-Hamiltonian (SH) parameters indicates the stabilization of mJ |±15/2〉 for [Dy(C4(SiH3)4)2]- (1), [Dy(C5(CH3)5)2]+ (2) and [Dy(C6H6)2]3+ (3) complexes with the Ucal value of 1867.5, 1621.5 and 1070.8 cm-1, respectively. On the other hand, we observed mJ |±9/2〉 as the ground state for [Dy(C7H7)2]3- (4) and [Dy(C8H8)2]- (5) complexes with significantly smaller Ucal values of 237.1 and 38.6 cm-1 respectively. For the nine-membered ring [Dy(C9H9)2]+ (6) complex, we observed the stabilization of the mJ |±1/2〉 ground state, with the first excited state being located ∼29 cm-1 higher in energy. AILFT-NEVPT2 ligand field splitting analysis indicates that the presence of π-type 4f-ligand interactions in complexes 1-3 help generate the axial-ligand field, while the δ-type interactions in complexes 4-5 generate the equatorial ligand field despite the ligands approaching from the axial direction. As the ring size increases, φ-type interactions dominate, generating a pure equatorial ligand field stabilising mJ |±1/2〉 as the ground state for 6. Calculations suggest that the nature of the ligand field mainly governs the Ucal values in the following order: 4f-Lσ > 4f-Lπ > 4f-Lδ > 4f-Lφ. Calculations were performed by replacing ligands with CHELPG charges to access the crystal field (CF) effects which suggests the stabilization of pure mJ |±15/2〉 in all the charge-embedded models (1Q-6Q). Our findings point out that the crystal field and ligand field effects complement each other and generate a giant barrier for magnetic relaxation in the small ring complexes 1-3, while a relatively weak crystal field and adverse 4f-Lδ/4f-Lφ interactions diminish the SMM behaviour in the large ring complexes 4-6.

Size selectivity of the scallop fishery in the southern Gulf of St. Lawrence: Effects of ring size and washer type

In the southern Gulf of St. Lawrence (sGSL), there is a mostly supplementary fishery for sea scallops (Placopecten magellanicus) concentrated on three primary scallop beds in the Northumberland Strait. The fishery is not subject to an enforced minimum size limit and small scallops (<90 mm shell height) are often removed from this population before they have had time to adequately contribute to population recruitment, resulting in sub-optimal fishery yields and a partially size-suppressed population. This study aimed to provide stakeholders with information related to gear configuration changes that could potentially reduce catches of small scallops in the sGSL fishery by quantifying size-selectivity of different ring sizes (82.6 mm and 88.9 mm) and washer types (rubber and steel). We also compared the catches of small, fecund scallops (45–90 mm) across the different gear configurations. The gears with 82.6 mm rings had high retention of small scallops, with lengths of 50 % retention estimated to be 72.8 and 76.0 mm with rubber and steel washers, respectively. This increased to 87.9 mm and 95.5 mm, respectively, in the gears with 88.9 mm rings. It was estimated that with rubber washers, increasing ring size from 82.6 mm to 88.9 mm will reduce catch of small fecund scallops by 51 %, while reducing catch of large scallops by 27 %. Increasing ring size was more effective than changing washer type at increasing size selectivity of the gear. Previous research on scallop life history suggests that this reduction of large scallops will be temporary because the larger gear will ultimately shift the population size distribution towards larger scallops resulting in higher yield-per-recruit. These results will be useful to resource managers and stakeholders for stock assessments, and for future gear type decisions.

Pd-catalyzed methylene γ-C(sp3)—H alkenylation of N-picolinoylcycloalkylamines with alkenyl iodides promoted by 2-tert-butyl-1,4-benzoquinone

A palladium(II) acetate-catalyzed alkenylation of the methylene sp3 γ-carbon-hydrogen bonds of N-picolinoylcycloalkylamines with alkenyl iodides in the presence of silver carbonate was promoted by 2-tert-butyl-1,4-benzoquinone (TBBQ). This functionalization of N-picolinoylcyclohexylamine with alkenyl iodides exclusively provided a range of cis-3-(1-alkenyl)-N-picolinoylcyclohexylamines in up to 82% yield. In contrast, the TBBQ-promoted alkenylation of a macrocyclic substrate, N-picolinoylcyclododecylamine, gave only trans-3-(1-alkenyl)-N-picolinoylcyclododecylamine as a monoalkenylation-product in up to 52% yield. Interestingly, the stereoselectivity of the product was reversed due to the increased ring size of the substrate. This is the first example of trans-γ-CH alkenylation.

Intramolecular relaxation of ring polymers in dilute solutions

The intramolecular relaxation dynamics of unconcatenated ring polymers in dilute solutions is theoretically investigated within the framework of the Rouse–Zimm theory. The excluded volume interactions (EVIs) between the nonbonded monomers are modeled by a harmonic potential, where the interaction parameter is evaluated from Flory’s mean-field approach. The hydrodynamic interactions (HIs) between the pairs of monomers are approximated by a preaveraged Oseen tensor. The mechanical moduli are dominated by the smaller relaxation rates corresponding to the collective relaxation modes in the low frequency regime, while they are governed by the higher relaxation rates corresponding to the local relaxation modes in the high frequency regime. EVI decreases the relaxation rates of the normal modes where the decrease for the collective modes is larger than that for the local modes, which consequently expands the width of the relaxation spectrum. The characteristic overall relaxation time is evaluated from the inverse of the crossover frequency, which is the same for rings of various sizes with HI and with both HI and EVI, while it shifts to lower frequencies with increasing ring size for the Rouse rings.

Pyridyldiimine macrocyclic ligands: Influences of template ion, linker length and imine substitution on ligand synthesis, structure and redox properties

A series of 2,6-diiminopyridine-derived macrocyclic ligands have been synthesized via [2 + 2] condensation around alkaline earth metal triflate salts. The inclusion of a tert-butyl group at the 4-position of the pyridine ring of the macrocyclic synthons results in macrocyclic complexes that are soluble in common organic solvents, thereby enabling a systematic comparison of the physical properties of the complexes by NMR spectroscopy, mass spectrometry, solution-phase UV–Vis spectroscopy, cyclic voltammetry and single-crystal X-ray crystallography. Solid-state structures determined crystallographically demonstrate increased twisting in the ligand, concurrent with either a decrease in ion size or an increase in macrocycle ring size (18, 20, or 22 membered rings). The degree of folding and twisting within the macrocycle can be quantified using parameters derived from the Npyr-M-Npyr bond angle and the relative orientation of the pyridinediimine (PDI) and pyridinedialdimine (PDAI) fragments to each other within the solid state structures. Cyclic voltammetry and UV–Vis spectroscopy were used to compare the relative energies of the imine π* orbital of the redox active PDI and PDAI components in the macrocycle when coordinated to redox inactive metals. Both methods indicate the change from a methyl to hydrogen substitution on the imine carbon lowers the energy of the ligand π* system.

On development of a ring type mechanical force transducer: Shape optimization, modification and characterization with different optimization codes

This research paper focuses on the design and optimization of a ring type mechanical force transducer known as a proving ring. Three different optimization codes were used and compared to develop a universal ring design with optimum stress and enhanced ring sensitivity. In the optimization section, minimum ring thickness was found between 45 and 60° with maximum thickness at point of load application across all three optimization codes. Generalized reduced gradient code (GRG) yielded the largest decrease in maximum stress at 98% with a ring sensitivity increased by 19.5%. Bidirectional evolutionary structural optimization code (BESO) sees a slight reduction of stress at horizontal location at 8.3% but sensitivity was increased by 8%. ABAQUS shape optimization codes saw significant decrease in stress at horizontal location with reduction of 66.5% with ring sensitivity having the largest increase by 48.7%. From the optimization results, a simple geometric modification of the circular ring was made. Using finite element analysis, the modified ring design showed increased sensitivity as well as better stress levels compared to the conventional circular and octagonal ring shapes. With respect to the stress and deflection characteristics of the modified ring, the design can be said to be universal due to no minimal change in those factors when ring size increases. A last design modification was made to the modified ring by implementing a double ring design with two curved sections. It was found that the double ring design had lower stress levels compared to the modified ring with a slight increase in ring sensitivity.