Defining the Macromolecules of Tomorrow through Synergistic Sustainable Polymer Research.

Transforming how plastics are made, unmade, and remade through innovative research and diverse partnerships that together foster environmental stewardship is critically important to a sustainable future. Designing, preparing, and implementing polymers derived from renewable resources for a wide range of advanced applications that promote future economic development, energy efficiency, and environmental sustainability are all central to these efforts. In this Chemical Reviews contribution, we take a comprehensive, integrated approach to summarize important and impactful contributions to this broad research arena. The Review highlights signature accomplishments across a broad research portfolio and is organized into four wide-ranging research themes that address the topic in a comprehensive manner: Feedstocks, Polymerization Processes and Techniques, Intended Use, and End of Use. We emphasize those successes that benefitted from collaborative engagements across disciplinary lines.

Structural Characterization of the [CuOR]2+ Core.

Formal Cu(III) complexes bearing an oxygen-based auxiliary ligand ([CuOR]2+, R = H or CH2CF3) were stabilized by modulating the donor character of supporting ligand LY (LY = 4-Y, N,N'-bis(2,6-diisopropylphenyl)-2,6-pyridinedicarboxamide, Y = H or OMe) and/or the basicity of the auxiliary ligand, enabling the first characterization of these typically highly reactive cores by NMR spectroscopy and X-ray crystallography. Enhanced lifetimes in solution and slowed rates of PCET with a phenol substrate were observed. NMR spectra corroborate the S = 0 ground states of the complexes, and X-ray structures reveal shortened Cu-ligand bond distances that match well with theory.

Sulfur-Containing Analogues of the Reactive [CuOH]2+ Core.

With the aim of drawing comparisons to the highly reactive complex LCuOH (L = bis(2,6-diisopropylphenylcarboxamido)pyridine), the complexes [Bu4N][LCuSR] (R = H or Ph) were prepared, characterized by spectroscopy and X-ray crystallography, and oxidized at low temperature to generate the species assigned as LCuSR on the basis of spectroscopy and theory. Consistent with the smaller electronegativity of S versus O, redox potentials for the LCuSR-/0 couples were ∼50 mV lower than for LCuOH-/0, and the rates of the proton-coupled electron transfer reactions of LCuSR with anhydrous 1-hydroxy-2,2,6,6-tetramethyl-piperidine at -80 °C were significantly slower (by more than 100 times) than the same reaction of LCuOH. Density functional theory (DFT) and time-dependent DFT calculations on LCuZ (Z = OH, SH, SPh) revealed subtle differences in structural and UV-visible parameters. Further comparison to complexes with Z = F, Cl, and Br using complete active space (CAS) self-consistent field and localized orbital CAS configuration interaction calculations along with a valence-bond-like interpretation of the wave functions showed differences with previously reported results ( J. Am. Chem. Soc. 2020, 142, 8514), and argue for a consistent electronic structure across the entire series of complexes, rather than a change in the nature of the ligand field arrangement for Z = F.

Effect of Ancillary Ligands (A) on Oxidative Addition of CH4 to Rhenium(III) Complexes: A = B, Al, CH, SiH, N, and P Using MP2, CCSD(T), and MCSCF Methods.

A computational study of oxidative addition (OA) of methane to Re(OC2H4)3A (A = ancillary ligand, which thus may interact with the metal) was carried out. The choice of ancillary ligands has been made based on their electronic properties: A = B or Al (Lewis acid), CH or SiH (electron precise), N (σ-donor), and P (σ-donor/π-acid). The main objective of this study was to understand how variation in A affects the structural and electronic properties of the reactant d4-Re(III) complex, which can ultimately tune the kinetics and thermodynamics of OA. Results obtained from MP2 calculations revealed that, for OA of CH4 to Re(OC2H4)3A, the order of ΔG‡ for a choice of ancillary ligand is B > Al > SiH > CH > N > P. Single point calculations for ΔG‡ obtained with CCSD(T) showed excellent agreement with those computed with MP2 methods. MCSCF calculations indicated that oxidative addition transition states are well described by a single electronic configuration, giving further confidence in the MP2 approach used for geometry optimization and ΔG‡ determination, and that the transition states are more electronically similar to the d4-Re(III) reactant than the d2-Re(V) product.

A family of structural and functional models for the active site of a unique dioxygenase: Acireductone dioxygenase (ARD).

We report the synthesis and biomimetic activity of a family of model complexes with relevance to acireductone dioxygenase (ARD), an enzyme that displays dual function based on metal identity found in the methionine salvage pathway (MSP). Three complexes with related structural motifs were synthesized and characterized derived from phenolate, and pyridine N4O Schiff-base ligands. They display pseudo-octahedral Ni(II)-N4O ligand coordination with water at the sixth site, in close alignment to the structure in the resting state of ARD. The three featured complexes exhibit carbon­carbon bond cleavage activation of lithium acetylacetonate, which was used as a model enzyme substrate. Computationally derived mechanistic routes for the observed reactivity consistent with experimental conditions are herein proposed. The mechanism suggests the possibility of Ni(II)-substrate interactions, followed by oxygen insertion. These results constitute only the third functional model system of ARD, in an attempt to further advance biomimetic contributions to the ongoing debate of ARD's unique metal mediated, regioselective oxidative cleavage.

Modifying the luminescent properties of a Cu(i) diphosphine complex using ligand-centered reactions in single crystals.

Here we report how reactions at a chemically reactive diphosphine shift the long-lived luminescent colour of a crystalline three-coordinate Cu(i) complex from green to blue. The results demonstrate how vapochromism and single-crystal-to-single-crystal transformations can be achieved using ligand-centered reactions.

Carcinoembryonic antigen (CEA) levels in hookah smokers, cigarette smokers and non-smokers.

OBJECTIVE: To find CEA levels in smokers of different categories (hookah smokers, cigarette smokers smoking different brands of cigarettes and different number of cigarettes per day) and to correlate CEA levels with type and rate of smoking. METHODS: A total of 122 cigarette smokers (115 men and 7 women) and 14 hookah smokers (all men) with age ranging from 16-80 years were studied. CEA levels were also measured in 36 non-smokers who served as controls. Enhanced chemilumiscent immunometeric technique was applied to measure CEA levels in our subjects. RESULTS: The mean CEA levels of cigarette smokers were compared with the mean CEA levels observed in hookah smokers (7.16 +/- 10.4 ng/ml) and non-smokers (2.15 +/- 0.68 ng/ml). The mean value of CEA level observed in cigarette smokers, 9.19 +/- 14.9 ng/ml (n=122) was significantly higher than the levels in non-smokers and hookah smokers (p < 0.0067). It was also observed that CEA levels increased with the number of cigarettes smoked per day. The highest levels were observed in smokers who smoke more than 31 cigarettes per day. The smokers that use relatively cheaper brands of cigarettes had higher levels of CEA compared to those who use high quality brands. CONCLUSION: It was concluded that the brands of cigarettes (which were ranked on the basis of price) and the rate of smoking both play an important role in raising the CEA levels. Further the common belief that hookah also called narghile or shisha is a relatively safe mode of smoking is not completely correct; a significant proportion of hookah smokers have high levels of CEA although mean levels of hookah smokers were low compared to cigarette smokers.

Thyroid function in pulmonary tuberculosis.

OBJECTIVE: To evaluate the thyroid hormone economy in pulmonary tuberculosis (PTB). DESIGN: Cohort comparative study. PLACE AND DURATION OF STUDY: Multan Institute of Radiotherapy and Nuclear Medicine (MINAR) from January 2003 to June 2005. PATIENTS AND METHODS: The study included 266 confirmed cases of pulmonary tuberculosis (PTB), aged between 11 and 65 years, who had completed short course of chemotherapy. Two samples were collected from each patient, first after final diagnosis and second after completion of the treatment. Initial analysis of samples showed that 31 samples had both T3 (triiodothyronine) and T4 (thyroxine) in lower than normal range. One more sample in the middle of treatment was collected for these patients. Radioimmunoassays and immunoradiometeric assays were applied to estimate mean TT3, TT4 and TSH (thyroid stimulating hormone) levels. Students t-test was used to compare patient and normal values derived from 713 volunteers. RESULTS: The age had no effect on levels of T3, T4 and TSH in normal persons. Mean T3 and T4 values (0.74 nmol/l and 91.9 nmol/l) in PTB patients were significantly decreased (p < 0.001) with 50% and 11.6 % cases in lower than normal range respectively. Follow-up data on subgroup of 31 patients showed that both T3 and T4 levels improved after chemotherapy. TSH levels remained unaffected throughout. CONCLUSION: Both T3 and T4 levels were decreased in PTB but T4 levels were less affected. TSH was found unaffected by the disease. This confirms that PTB produces euthyroid sick syndrome (SES) i.e., decreased T3 and T4, and no change affected by 5'deiodinase (an enzyme that causes deiodination of T4). The levels improved after chemotherapy.

Correlations of skin fold thickness and validation of prediction equations using DEXA as the gold standard for estimation of body fat composition in Pakistani children.

OBJECTIVE: To determine the correlation between dual energy X-ray absorptiometry (DEXA) and skin fold thickness (SKF) equations for estimation of body fat (BF) composition in secondary school children and validation of prediction equations by Slaughter, Goran and Dezenberg. DESIGN: Cross sectional analytical study. SETTING: Joint Commission for International Accredited (JCIA) tertiary care hospital of Karachi, Pakistan from January 2010 to May 2010. PARTICIPANTS: The study was approved by the Hospital's ethical review committee. Written and verbal consents were obtained from principals of two schools and parents of 99 children (mean age of 14±1.89 years; min-max 9-19 years; 54 men and 45 women) accrued in study. DEXA scan was acquired and SKF was measured at angle of the scapula, iliac crest and mid-arm for bicep and tricep skin folds using Holtain Callipers. Correlations were established between estimated fat mass (FM) and per cent BF (%BF) calculated by DEXA and those predicted by prediction equations. On obtaining significant correlation of >0.5, overall accuracy, precision and bias was calculated. RESULTS: There was an overall increased adiposity in females with FM of 3.57 kg and %BF 6.2% higher than male counterparts (p<0.05). Slaughter equation predicted %BF accurately with overall high accuracy, minimal bias and with good precision with DEXA. Dezenberg and Goran equations had significant bias in prediction of FM which was statistically significant with low level of accuracy of the Goran equation. CONCLUSIONS: We conclude that Slaughter equation for estimating %BF showed reasonable validation with DEXA. Nevertheless further studies with consideration for maturity and ethnicity are warranted for better results. However, for estimation of FM, previously formulated equations by Goran and Dezenberg showed significant difference in our population. We do recommend further studies for developing and validation of skin fold equations specific to Pakistani paediatric population.