Thermochemical Research on Furfurylamine and 5-Methylfurfurylamine: Experimental and Computational Insights.

The need to transition from fossil fuels to renewables arises from factors such as depletion, price fluctuations, and environmental considerations. Lignocellulosic biomass, being abundant, and quickly renewable, and not interfering with food supplies, offers a standout alternative for chemical production. This paper explores the energetic characteristics of two derivatives of furfural-a versatile chemical obtained from biomass with great potential for commercial sustainable chemical and fuel production. The standard (p° = 0.1 MPa) molar enthalpies of formation of the liquids furfurylamine and 5-methylfurfurylamine were derived from the standard molar energies of combustion, determined in oxygen and at T = 298.15 K, by static bomb combustion calorimetry. Their standard molar enthalpies of vaporization were also determined at the same temperature using high-temperature Calvet microcalorimetry. By combining these data, the gas-phase enthalpies of formation at T = 298.15 K were calculated as -(43.5 ± 1.4) kJ·mol-1 for furfurylamine, and -(81.2 ± 1.7) kJ·mol-1 for 5-methylfurfurylamine. Furthermore, a theoretical analysis using G3 level calculations was performed, comparing the calculated enthalpies of formation with the experimental values to validate both results. This method has been successfully applied to similar molecules. The discussion looks into substituent effects in terms of stability and compares them with similar compounds.

Anchorless Onlay Dynamic Anterior Stabilization of the Shoulder Using a Guided Posterior Double Endobutton Fixation.

The treatment of shoulder instability in the presence of a subcritical glenoid defect poses challenges, as simple Bankart seems insufficient, and the Latarjet procedure may be excessive. Recently, a dynamic anterior stabilization technique involving anterior transposition of the long head of the biceps (LHB) through a subscapularis split was described for that purpose. Previously published results demonstrated good short-term results, but several technical pitfalls have also been mentioned. We describe an onlay, anchorless, and intra-articular knotless method of fixing the LHB into the anterior glenoid that provides the important stabilizing "sling effect" of the dynamic anterior stabilization while avoiding some of the pitfalls described by other techniques.

Arthroscopic Anatomical Acromioclavicular Joint Reconstruction using a Button Device and a Semitendinosus Graft.

OBJECTIVE: To report a new technique for anatomical acromioclavicular (AC) joint reconstruction. METHODS: In order to minimize such complications, the authors describe a new anatomical and biological AC joint repair. This technique aims to provide greater stability by using two anatomically placed clavicular tunnels and a combined construct with a double endobutton cortical fixation for primary stabilization, and to be biologically advantageous by using an autologous semitendinosus (ST) tendon graft. Additionally, the coracoclavicular ligament reconstruction is complemented with an AC joint cerclage and capsular reinforcement, which will protect the biological construction in its initial stage of healing. RESULTS: This technique provides adequate primary and secondary biomechanical stability by passing both a semitendinosus autogenous graft and a double endobutton device, through anatomically placed and small diameter clavicle holes, without the need for coracoid drilling. Our technique showed encouraging results regarding pain resolution, range of motion, and function. At final follow-up we experienced excellent results with average pain score of 1.6, and average ROM of 159° of forward flexion, 160° of abduction, 68° of external rotation, and internal rotation level at T11. Postoperative function also showed great improvements with average ASES of 85 points, an average Constant Score of 87 and a Subjective Shoulder Value of 89 points. This technique also achieved perfectly acceptable radiographic results, with an average coracoclavicular distance increase of 0.8 mm. Regarding complications, our sample showed one case of AC join subluxation, two cases of internal saphenous nerve injury, and two partial graft tears at the suture-button interface, with none of these requiring surgical revision. CONCLUSION: This technique is advantageous in treatment of acromioclavicular joint dislocation and can be performed in both the subacute and chronic setting.

Distal Biceps Reconstruction With an Alternative Technique for Tendon Tensioning and Fixation: A Case Report.

CASE: A 41-year-old right-handed male patient presented to our institution with a chronic distal biceps rupture after failed primary surgery 6 months previously. We performed a reconstruction with semitendinosus autograft fixed proximally with a Pulvertaft weave and distally with a cortical button plus interference screw. The patient showed complete pain resolution and excellent functional results. CONCLUSION: This is the first case described with the use of a cortical button plus interference screw distally for distal biceps reconstruction after chronic distal biceps rupture. The option of doing the Pulvertaft proximally first also allowed us to fine-tune the final graft tension.

Cost effectiveness of outpatient lumbar discectomy.

BACKGROUND: Microdiscectomy is the most commonly performed spine surgery and the first transitioning for outpatient settings. However, this transition was never studied, in what comes to cost-utility assessment. Accordingly, this economic study aims to access the cost-effectiveness of outpatient lumbar microdiscectomy when compared with the inpatient procedure. METHODS: This is a cost utility study, adopting the hospital perspective. Direct medical costs were retrieved from the assessment of 20 patients undergoing outpatient lumbar microdiscectomy and 20 undergoing inpatient lumbar microdiscectomy Quality-adjusted life-years were calculated from Oswestry Disability Index values (ODI). ODI was prospectively assessed in outpatients in pre and 3- and 6-month post-operative evaluations. Inpatient ODI data were estimated from a meta-analysis. A probabilistic sensitivity analysis was performed and incremental cost-effectiveness ratio (ICER) calculated. RESULTS: Outpatient procedure was cost-saving in all models tested. At 3-month assessment ICER ranged from €135,753 to €345,755/QALY, higher than the predefined threshold of €60,000/QALY gained. At 6-month costs were lower and utilities were higher in outpatient, overpowering the inpatient procedure. Probabilistic sensitivity analysis showed that in 65% to 73% of simulations outpatient was the better option. The savings with outpatient were about 55% of inpatient values, with similar utility scores. No 30-day readmissions were recorded in either group. CONCLUSION: This is the first economic study on cost-effectiveness of outpatient lumbar microdiscectomy, showing a significant reduction in costs, with a similar clinical outcome, proving it cost-effective.

Orthosis in Thoracolumbar Fractures: A Systematic Review and Meta-analysis of Randomized Controlled Trials.

STUDY DESIGN: Systematic review and meta-analysis of randomized controlled trial (RCT). OBJECTIVE: The aim of this study was to evaluate radiological and clinical outcomes of acute traumatic thoracolumbar fractures in skeletally mature patients treated with orthosis, versus no immobilization. SUMMARY OF BACKGROUND DATA: Orthosis is traditionally used in conservative treatment of thoracolumbar fractures. However, recent studies suggest no benefit, and a possible negative impact in recovery. METHODS: Databases were searched from inception to June 2019. Studies were selected in two phases by two blinded reviewers; disagreements were solved by consensus. Inclusion criteria were: RCT; only patients with acute traumatic thoracolumbar fractures; primary conservative treatment; comparison between orthosis and no orthosis. Exclusion criteria were inclusion of nonacute fractures, patients with other significant known diseases and comparison of groups different than use of an orthosis. Two independent reviewers performed data extraction and quality assessment. Fixed-effects models were used upon no heterogeneity, and random-effects model in the remaining cases. A previous plan for extraction of radiological (kyphosis progression; loss of anterior height) and clinical (pain; disability; length of stay) outcomes was applied. PRISMA guidelines were followed. RESULTS: Eight articles/five studies were included (267 participants). None reported significant differences in pain, kyphosis progression, and loss of anterior height. One reported a better ODI with orthosis at 12 but not at 24 weeks. No other study reported differences in disability. All authors concluded an equivalence between treatments.Meta-analysis showed a significant increase of 3.47days (95% confidence interval 1.35-5.60) in mean admission time in orthosis group. No differences were found in kyphosis at 6 and 12 months; kyphosis progression between 0 to 6 and 0 to 12 months; loss of anterior height 0 to 6 months; VAS for pain at 6 months; VAS change 0 to 6 months. CONCLUSION: Orthosis seems to add no benefit in conservative treatment of acute thoracolumbar fractures. This should be considered in guidelines and reviews of health care policies. LEVEL OF EVIDENCE: 3.

Minimum of 10-year follow-up of V-rod technique in lumbar spondylolysis.

PURPOSE: To describe and analyze the use of the V-rod technique described by Gillet to repair spondylolysis in both early and late postoperative periods. METHODS: Patients submitted to surgical correction of lumbar spondylolysis with a V-rod system were selected upon exclusion of adjacent disk degenerative changes and high-grade spondylolisthesis. A preoperative clinical (ODI and VAS) and radiological evaluation was performed, along with assessments on the early (clinical evaluation-up to 1 year) and late (clinical and radiological-at least 10 years) postoperative periods. RESULTS: Twenty-two patients were included, 21 with L5 spondylolysis. Fifty percent had grade I spondylolisthesis. A significant decrease in ODI and VAS was observed from pre- to early and late post-op evaluation (all p < 0.05) but not during post-op evaluations. Changes from pre- to postoperative of both ODI and VAS were significantly higher than the minimal clinically important difference. Preoperative ODI and VAS were significantly higher in overweight/obese but similar postoperatively. No additional instability was found in late postoperative X-rays. Three patients needed revision surgery, with a survival rate of 81.8% for Gillet instrumentation at a mean follow-up of 687.7 ± 60.0 weeks. CONCLUSIONS: Surgical treatment with V-rod system is associated with a significant improvement in ODI and VAS and radiologic stability, with an equal benefit in obese/overweight patients. This study reports for the first time an improvement that is maintained even 10 years after the initial intervention, associated with a low rate of failure. These slides can be retrieved under Electronic Supplementary Material.

Ozone therapy for low back pain. A systematic review.

BACKGROUND: Low back pain associated with lumbar disc herniation is common in the general population, with evident repercussion in quality of life and a significant economic burden. Patients refractory to conservative treatment seek additional treatment and minimally invasive interventions were proposed as valid options. Ozone therapy has been suggested as an alternative due to its potential analgesic and anti-inflammatory effect. OBJECTIVE: This systematic review aims to investigate the effectiveness and safety of ozone therapy for low back pain in patients with lumbar disc herniation. MATERIAL AND METHODS: A systematic search was performed in Pubmed and Scopus, followed by a three-step selection process. Data was processed by 2 independent reviewers and information was gathered based in pre-defined variables. Only articles performed in humans; original and English written; on treatment with ozone; comparing the result of ozone therapy (experimental group) with another non-ozone intervention (control group); and on patients with lumbar pain and disc hernia, were included. RESULTS: From 439 references retrieved after duplicates removal, inclusion and exclusion criteria were applied, and 7 studies were included in the final revision. One article compared treatment with ozone versus placebo, one ozone and global postural re-education versus global postural re-education alone, two the combination of ozone with steroid versus steroid alone, two ozone versus steroid and one ozone versus micro-discectomy. All but the study comparing ozone application with micro-discectomy, showed similar or better results in the experimental group. Only three studies evaluated the presence of side effects. In two papers no complication was reported, and in the other, a low percentage of adverse effects was observed, not significantly different between the two study groups. CONCLUSIONS: Only a small number of poor quality studies on ozone effect in low back pain and disc herniation were available for inclusion in our review. Nevertheless, these reported an improvement in pain and functional scores with its application. Complications, mostly minor, but potentially serious are underreported. Additional studies with adequate and consistent methodologies are needed before the role of ozone can be established in the management of low back pain.

Long Biceps Subpectoral Tenodesis With Suspensory Button and Bicortical Fixation.

Tenodesis of the long head of the biceps (LHB) tendon has long been recognized as a valid alternative to address pathologic conditions of this tendon. However, the location and type of fixation is still a matter of discussion, because common complications associated with this procedure include failure of the repair, persistent pain, reaction to the fixation device, cosmetic deformity, and fracture. The authors describe a method of subpectoral LHB tenodesis that aims to preserve bone stock and allows a strong, easy, and reproducible type of fixation with a minimal approach. LHB tenotomy is performed arthroscopically in a standard fashion, and the tenodesis is completed with bicortical fixation in the humerus using a knotless suspensory button with an appropriate pusher originally developed for another purpose. Magnetic resonance imaging showed a safe distance between the implant and important vasculonervous structures. In the cases where subpectoral fixation is chosen, this method seems to offer additional safety as a result of the minimal amount of bone removed and the very small size of the implant.

[Analysis of the Cochrane Review: Pedicle Screw Fixation for Traumatic Fractures of the Thoracic and Lumbar Spine. Cochrane Database Syst Rev. 2013;05:CD009073]. / Análise da Revisão Cochrane: Fixação com Parafusos Pediculares de Fraturas Traumáticas da Coluna Vertebral Torácica e Lombar. Cochrane Database Syst Rev. 2013;05:CD009073.

Traumatic fractures of the thoracic and lumbar spine are common causes of spine surgery. Pedicle screw fixation is usually chosen, using monosegmentar, short or long segment instrumentations, with or without bone graft. This review aims to evaluate the effect of transpedicular fixation in traumatic fractures of the thoracic and lumbar spine. A systematic search on controlled, randomized or quasi-randomized trials comparing different methods of surgical treatment of this fractures was performed, followed by a process of article selection, data extraction and bias assessment by 3 independent authors. Eight articles were included in a total of 5 comparisons, between different transpedicular fixation techniques. No significant differences on function or quality of life, neurologic status or limitation of motion were found. Only instrumentation with fracture level screw incorporation showed significant decrease of pain when compared with instrumentation alone. Several techniques resulted in significant improvements of different radiological parameters. Significantly, surgeries with smaller duration were associated with lesser blood loss. Bone graft use caused a significant raise in post-operative complications, namely donor site pain. So, this paper showed that significative improvements in radiological parameters do not associate with correspondent clinical benefits, and only instrumentation with level screw incorporation is associated with a clear benefit on pain. Moreover, the need for bone graft is questioned, since it leads to no clinic-radiological improvement with a raise of complications. However, a small number of controlled studies is available on this topic.

As fraturas da coluna vertebral torácica e lombar são causa comum de cirurgia da coluna vertebral. A fixação com parafusos pediculares é geralmente escolhida para a sua estabilização, com recurso a instrumentações curtas, longas ou monosegmentares com ou sem enxerto ósseo. O objetivo desta revisão é avaliar o efeito da fixação transpedicular nas fraturas vertebrais torácicas e lombares traumáticas. Foi realizada uma pesquisa sistemática de estudos controlados aleatorizados ou quasi-aleatorizados que comparassem diferentes técnicas de tratamento cirúrgico destas fraturas, seguida de um processo de seleção, extração de dados e avaliação de viéses por três autores independentes. Oito estudos foram incluídos, num total de cinco comparações entre diferentes fixações com parafusos pediculares. Não se encontraram diferenças significativas quanto à melhoria da função e qualidade de vida, dos défices neurológicos ou da mobilidade. Apenas a instrumentação com parafusos pediculares no nível da fratura mostrou melhoria significativa da dor quando comparada com instrumentação posterior sem parafuso no nível. Várias técnicas resultaram em melhoria significativa dos parâmetros imagiológicos, sem melhoria clínica correspondente. De modo significativo tempos cirúrgicos mais curtos associaram-se a menores perdas sanguíneas. O uso de enxerto ósseo causou um aumento significativo das complicações pós-operatórias, nomeadamente dor no local dador. Assim, os resultados mostram que melhorias imagiológicas significativas não se associam a impactos clínicos correspondentes, e que apenas o uso de fixação transpedicular no nível da fratura se associa a melhoria clínica evidente da dor. Adicionalmente, a necessidade de enxerto ósseo é posta em causa, pela ausência de melhoria clínico-imagiológica, com aumento das complicações. Contudo, o número de estudos controlados disponíveis acerca deste tópico é reduzido.

Immune response and innervation signatures in aseptic hip implant loosening.

BACKGROUND: Aseptic loosening (AL) of hip prosthesis presents inflammation and pain as sign and symptom similarly to arthritis pathologies. Still, the immune and innervation profiles in hip AL remain unclear and their interplay is poorly explored. Herein, local tissue inflammatory response, sensory and sympathetic innervation as well as associated local mediators were assessed in hip joint microenvironment underlying AL and compared to osteoarthritis (OA). METHODS: Histopathological analysis, immune cells (macrophages, T, B cells and PMNs) as well as sensory and sympathetic nerve fibers (SP(+), CGRP(+), TH(+)) distribution and profiles were analyzed on tissues retrieved from patients with failed hip prostheses due to AL (n = 20) and hip OA (n = 15) by immunohistochemistry. Additionally, transcriptional levels of pro-inflammatory cytokines (TNF-α, IL-1ß, IL-6, IL-12a, iNOS), anti-inflammatory cytokine (IL-10), osteoclastic factor (RANKL) and bone remodeling factor (TGF-ß1) were locally evaluated by qRT-PCR. Serum TGF-ß1 levels were assessed preoperatively by ELISA. RESULTS: Histopathological analysis revealed that tissues, aseptic interface membranes of AL patients had distinct tissue architecture and immune cells profile when compared to OA synovial tissues. Macrophages, T cells and B cells showed significant differences in tissue distribution. In OA, inflammation is mostly confined to the vicinity of synovial membrane while in AL macrophages infiltrated throughout the tissue. This differential immune profile is also accompanied with a distinct pattern of sensory and sympathetic innervation. Importantly, in AL patients, a lack of sympathetic innervation aseptic interface membranes without compensation mechanisms at cellular levels was observed with simultaneous reorganization of sensorial innervation. Despite the different histopathological portrait, AL and OA patients exhibited similar transcriptional levels of genes encoding key proteins in local immune response. Nevertheless, in both pathologies, TGF-ß1 expression was prominent in sites where the inflammation is occurring. However, at systemic level no differences were found. CONCLUSION: These findings indicate that AL patients exhibit different local inflammatory response and innervation signatures from OA patients in hip joint. These insights shed the light on neuro-immune interplay in AL and highlight the need to better understand this crosstalk to unravel potential mechanisms for targeted-therapies to improve hip joint lifetime and treatment.

Paediatric cervical spine injures. Nineteen years experience of a single centre.

PURPOSE: This observational study aims to describe pediatric C-spine injuries from a level 1 trauma centre through a period of 19 years. METHODS: Clinical records of pediatric trauma patients admitted to a level 1 trauma centre between 1991 and 2009 were analyzed. Patients were stratified by age into groups A (8 or less) and B (9 to 16), and in lower (C0-C2) and upper (C3-C7) spine injuries. Several variables were studied. RESULTS: Seventy-five cases of C-spine injuries (nine SCIWORA) were identified. Group A included 23 patients and group B 52. In group A, skeletal injuries at the upper C-spine were more common than injuries at the lower C-spine, whereas in group B, injuries of the lower C-spine were more frequent (p = 0.035). Motor vehicle accidents were the main cause of injury (44 %); 25.3 % of patients were surgically treated. Thirty-nine patients presented neurologic deficits, 16 of which improved. The overall mortality rate was 18.7 % and significantly higher in patients with neurological damages (p < 0.001) CONCLUSIONS: This study revealed a low incidence of cervical spine injuries in the paediatric population. As in previous reports younger children mainly sustained injuries at the upper C-spine, higher incidence of spinal injuries, and higher risk of death than older children.

Thermodynamic and conformational study of proline stereoisomers.

Amino acids play fundamental roles both as building blocks of proteins and as intermediates in metabolism. Proline, one of the 20 natural amino acids, has a primordial function in enzymes, peptide hormones, and proteins. The energetic characterization of these molecules provides information concerning stability and reactivity and has great importance in understanding the activity and behavior of larger molecules containing these structures as fragments. In the present work, parallel experimental and computational studies have been performed. The experimental studies have been based on calorimetric and effusion techniques, from which the enthalpy of formation in the crystalline phase and the enthalpy of sublimation of the sterioisomers L-, D-, and the DL-mixture of proline have been derived. Additionally, vapor pressure measurements have also enabled the determination of the entropies and Gibbs energies of sublimation, at T = 298.15 K. From the former results, the experimental standard (p(o) = 0.1 MPa) molar enthalpies of formation, in the gaseous phase, at T = 298.15 K, of L-proline, D-proline, and DL-proline have been calculated as -388.6 ± 2.3, -391.9 ± 2.0, and -391.5 ± 2.4 kJ·mol(-1), respectively. A computational study at the G3 and G4 levels has been carried out. Conformational analysis has been done and the enthalpy of formation of proline as well as other intrinsic properties such as acidity, basicity, adiabatic ionization enthalpy, electron and proton affinities, and bond dissociation enthalpies have been calculated. There is a very good agreement between calculated and experimental values, when they are available.

From 2,4-dimethoxypyrimidine to 1,3-dimethyluracil: isomerization and hydrogenation enthalpies and noncovalent interactions.

An enthalpic value for the N-methyllactam/O-methyllactim isomerization, in the gaseous phase, is reported in this work for the conversion between 2,4-dimethoxypyrimidine and 1,3-dimethyluracil. For this purpose, the enthalpy of formation of 2,4-dimethoxypyrimidine, in the gaseous phase, was obtained experimentally combining results from combustion calorimetry and Calvet microcalorimetry, and the enthalpy of formation of 1,3-dimethyluracil, in the gaseous phase, reported previously in the literature, is also discussed. The enthalpy of hydrogenation of 1,3-dimethyluracil is compared with the enthalpy of hydrogenation of uracil and interpreted in terms of aromaticity, considering the influence of the hyperconjugation and the hindrance of the solvation of the ring by the methyl groups. The enthalpy of sublimation of 2,4-dimethoxypyrimidine was obtained combining Calvet microcalorimetry and differential scanning calorimetry results. This enthalpy is compared with the enthalpy of sublimation of 1,3-dimethyluracil previously reported in the literature and analyzed herein. From the interplay between the experimental results and the theoretical simulation of dimers of these molecules, the influence of stereochemical hindrance on the in-plane intermolecular contacts and aromaticity on the π···π interactions is analyzed.

Energetic study of 4(3H)-pyrimidinone: aromaticity of reactions, hydrogen bond rules, and support for an anomeric effect.

4(3H)-Pyrimidinone is observed in nature in equilibrium with other tautomeric forms, mimicking the tautomeric equilibrium in pyrimidine nucleobases. In this work, the enthalpy of formation in the gaseous phase of 4(3H)-pyrimidinone was derived from the combination of the enthalpy of formation in the crystalline phase, obtained by static bomb combustion calorimetry, and the enthalpy of sublimation, obtained by Knudsen effusion. The gaseous phase enthalpy of formation of 4(3H)-pyrimidinone was interpreted in terms of isodesmic reactions that consider the enthalpic effects of hydroxypyridines and pyrimidine. After comparison of the experimental and computational results, the same type of isodesmic reactions was used to study the substituent effects of the hydroxyl functional group of 2-, 4-, and 5-hydroxypyrimidines. The influence of aromaticity on the energetics of hydroxypyrimidines was evaluated using the variation of nucleus-independent chemical shifts for several reactions. The influence of intramolecular hydrogen bonds was investigated using the quantum theory of atoms in molecules and the geometric rule of Baker and Hubbard to identify hydrogen bonds. The energetic results obtained were also interpreted in terms of an in plane anomeric effect in the pyrimidine ring.

Thermodynamic study of chlorobenzonitrile isomers: a survey on the polymorphism, pseudosymmetry, and the chloro···cyano interaction.

The relationships among structural and thermodynamic properties of 2-, 3-, and 4-chlorobenzonitrile were investigated, in the present work, using several experimental techniques (Knudsen effusion, differential scanning calorimetry, and combustion calorimetry) and computational studies. The CN···Cl intermolecular interactions are weaker in 2-chlorobenzonitrile, reflecting a lower enthalpy of sublimation. The two polymorphic forms of 4-chlorobenzonitrile were observed by differential scanning calorimetry and interpreted in terms of the strength of CN···Cl intermolecular interactions. The entropic differentiation due to the pseudosymmetry observed in the crystalline packing of 2-chlorobenzonitrile was evaluated. Using adequate working reactions and the respective standard molar enthalpies of formation, in the gaseous phase, the halogen-cyano intramolecular interaction was also evaluated. The theoretically estimated gas-phase enthalpies of formation were calculated using high-level ab initio molecular orbital calculations at the G3MP2B3 and MP2/cc-pVTZ levels of theory. The computed values support very well the experimental results obtained in this work.

From 2-hydroxypyridine to 4(3H)-pyrimidinone: computational study on the control of the tautomeric equilibrium.

In this work is investigated why the entrance of a nitrogen atom in the ring of cis-2-hydroxypyridine and 2-pyridinone, resulting in cis-4-hydroxypyrimidine and 4(3H)-pyrimidinone, respectively, shifts the tautomeric equilibrium from the hydroxyl form, in the pyridine derivative, to the ketonic form, in the pyrimidine derivative. The conclusions obtained for these model systems allow us to understand how to control the gaseous-phase keto-enol tautomeric equilibrium in nitrogen heterocyclic rings and justify the tautomeric preference in pyrimidine nucleobases. The experimental and computational energetics of tautomeric equilibrium were interpreted in terms of the aromaticity, intramolecular hydrogen bonds, and electronic delocalization, evaluated using nucleus independent chemical shifts, quantum theory of atoms in molecules, natural bond orbital analysis, and the thermodynamic changes of appropriate reactions.

Molecular energetics of alkyl pyrrolecarboxylates: calorimetric and computational study.

The pyrrole subunit plays an important role in material science as the building block of polypyrroles, an important representative class of conducting polymers, which found widely applications in the area of new materials due to their chemical, thermal, and electrical properties associated with their easiness and low cost of production, making them especially promising for commercial applications. The energetic characterization of this kind of molecules provides information concerning stability, reactivity, and biodegrability of chemical compounds in environment being, for example, helpful in choosing the most adequate method for their elimination by converting the waste into harmless compounds or even decreasing the production of toxic substances in industrial processes. This work reports a combination of calorimetric and computational determinations of several alkyl pyrrolecarboxylates (alkyl = methyl or ethyl) whose main purpose is the calculation of their standard (p° = 0.1 MPa) molar enthalpies of formation, in the gaseous phase, at T = 298.15 K. Experimentally, for methyl 1-pyrrolecarboxylate (M1PC), methyl 2-pyrrolecarboxylate (M2PC), and ethyl 2-pyrrolecarboxylate (E2PC), these values were derived from the standard (p° = 0.1 MPa) molar enthalpies of formation, in the condensed phase, ΔfHm° (cr,l), at T = 298.15 K, obtained by static bomb combustion calorimetry, and from the standard molar enthalpies of phase transition, Δcr,l(g)Hm°, at T = 298.15 K, determined by high-temperature Calvet microcalorimetry. Standard ab initio molecular calculations, at the G3(MP2)//B3LYP level, were performed, and the standard enthalpies of formation of these three compounds were estimated. A very good agreement between the calculated and the experimental data was obtained. Thereby, we have extended these calculations to other alkyl pyrrolecarboxylates, namely, ethyl 1-pyrrolecarboxylate (E1PC), methyl 3-pyrrolecarboxylate (M3PC), and ethyl 3-pyrrolecarboxylate (E3PC), whose study was not performed experimentally. The computational analysis, at the B3LYP/6-31G(d) level of theory, of the six molecules allowed a detailed inspection and a better knowledge about their molecular structure and geometrical parameters.

Energetic study applied to the knowledge of the structural and electronic properties of monofluorobenzonitriles.

The present work reports an energetic and structural study of 2-fluoro-, 3-fluoro-, and 4-fluorobenzonitrile. The standard molar enthalpies of formation, in the condensed phase, of the three isomers were derived from the standard molar energies of combustion, in oxygen, at T = 298.15 K. The standard molar enthalpies of vaporization or sublimation (for 4-fluorobenzonitrile), at T = 298.15 K, were measured using high-temperature Calvet microcalorimetry. The combination of these two parameters yields the standard molar enthalpies of formation in the gaseous phase. The vapor-pressure study of the referred compounds was performed by a static method, and the enthalpies of phase transition derived from the application of the Clarke and Glew equation. Theoretically estimated gas-phase enthalpies of formation, basicities, proton and electron affinities, and adiabatic ionization enthalpies were calculated from the G3MP2B3 level of theory. In order to evaluate the electronic properties, the geometries were reoptimized at MP2/cc-pVTZ level, and the QTAIM and NICS were computed. On the basis of the donor-acceptor system, another approach for evaluating the electronic effect for these compounds, using the NBO is suggested. The UV-vis spectroscopy study for the three isomers was performed. The intensities and the band positions were correlated with the thermodynamic properties calculated computationally.

Diaminobenzenes: an experimental and computational study.

In the present work, the values of the standard (p(o) = 0.1 MPa) molar enthalpies of formation, in the gaseous phase, at T = 298.15 K, of 1,2-diaminobenzene, 1,3-diaminobenzene, and 1,4-diaminobenzene are reported as 86.6 ± 1.6, 89.6 ± 1.6, and 99.7 ± 1.7 kJ·mol⁻¹, respectively. These values were derived from experimental thermodynamic parameters, namely the standard (p(o) = 0.1 MPa) molar enthalpies of formation, in the crystalline phase, Δf H(m)(o)(cr), at T = 298.15 K, obtained from the standard molar enthalpies of combustion, Δ(c) H(m)(o), measured by static bomb combustion calorimetry, and the standard molar enthalpies of sublimation, at T = 298.15 K, derived from the temperature-vapor pressure dependence, determined by the Knudsen mass loss effusion method. The results were compared with estimates obtained by standard ab initio molecular calculations at the G3(MP2)//B3LYP level. Experimental and calculated data are in very good agreement and show that the 1,2-diaminobenzene is, thermodynamically, the most stable isomer. Finally, proton and electron affinities, basicities and adiabatic ionization enthalpies were also computed at the same level.