Treatment of Hip Displacement in Children With Cerebral Palsy: A 5-year Comparison of Proximal Femoral Osteotomy and Combined Femoral-Pelvic Osteotomy in 163 Children.

BACKGROUND: This study compared the 5-year outcomes of isolated proximal femoral varus osteotomy (FO) and combined proximal femoral varus and pelvic osteotomy (FPO) for the treatment of hip displacement in children with cerebral palsy (CP) in Sweden, focusing on the number of reoperations and residual hip displacement. METHODS: The study included 163 children with a 5-year follow-up after FO or FPO in the national Swedish CP surveillance program, CPUP. Descriptive statistics and univariate and multivariate Cox regression analyses were used to identify whether the age at surgery, sex, Gross Motor Function Classification System level, CP dominant symptom, hip migration percentage (MP), type of surgery (unilateral/bilateral), and history of soft tissue hip surgery were related to the 5-year outcomes after surgery. Failure after hip surgery was defined as a skeletal reoperation involving the hip and/or MP >50%. RESULTS: During the period 2001 to 2017, 163 children (65 girls) underwent 246 femoral and/or pelvic osteotomies (154 FO, 47 bilaterally; 92 FPO, 16 bilaterally) and had a 5-year follow-up; 95 and 74 children had ≥1 FO or FPO as the primary skeletal surgery, respectively. The mean preoperative MP (51%±18% for FO and 59%±17% for FPO, P=0.001) and age at surgery (6.2±2.5 years for FO and 7.3±2.8 years for FPO, P=0.014) differed between procedures. At the 5-year follow-up, 5 hips (5%) had reoperations and 5 hips (5%) had radiological failure among the 92 FPOs, and 33 (21%) had reoperations and 14 (9%) radiological failure among the 154 FOs. The difference in outcome failure rate was significant (P<0.001). Multivariate Cox regression analysis showed a lower risk for failure with FPO [hazard ratio (HR)=0.32, 95% CI: 0.15-0.68] compared with FO. A higher preoperative MP increased the risk for outcome failure (HR=1.21, 95% CI: 1.15-1.36 for each 5% increment). CONCLUSIONS: FPO had a higher mean preoperative MP but a lower 5-year outcome failure rate compared with FO. A higher preoperative MP was associated with an increased risk of failure. LEVEL OF EVIDENCE: Level II-prospective comparative study.

[Significant medical improvements with CPUP - a combined follow-up program and national quality registry for cerebral palsy]. / CPUP ­ från reaktiv till preventiv behandling av cerebral pares.

CPUP is a combined follow-up program and national quality registry for cerebral palsy (CP). Since its inception in southern Sweden in 1994, CPUP has expanded geographically to cover all of Sweden, and similar programs are used in several northern European countries. Over 95% of all children with CP in Sweden, and a growing proportion of adults, are followed according to CPUP. The content of CPUP has been developed to involve most professions working with CP. CPUP has led to significant medical improvements. As an example, the percentage of individuals developing hip dislocation has decreased from 10% to 0.5%. The program's strengths include its interdisciplinary collaboration, user involvement, and the ability to inform and improve the quality of care systematically. Nevertheless, challenges include the need for ongoing funding and support. CPUP's success exemplifies how national quality registers can integrate into healthcare, enabling a shift from reactive to proactive care.

First Sampled High-Sensitive Cardiac Troponin T is Associated With One-Year Mortality in Sepsis Patients and 30- to 365-Day Mortality in Sepsis Survivors.

BACKGROUND: Previous studies using cardiac troponin levels to investigate the relationship between myocardial injury and mortality in sepsis patients have been conflicting. Our aim was to investigate the relationship between plasma high-sensitive cardiac troponin T (hs-cTnT) level and 30-day and 1-year mortality in sepsis patients and 30- to 365-day mortality in sepsis survivors. METHODS: Sepsis patients requiring vasopressor support and admitted to our institution between 2012 and 2021 (n = 586) were included in this retrospective cohort study. Elevated hs-cTnT values (≥15 ng/L) were divided into quartiles (Q): Q1 15-35 ng/L; Q2 36-61 ng/L; Q3 62-125 ng/L; Q4 126-8630 ng/L. Stratified Kaplan-Meier curves and multivariable Cox regression were used for survival analyses. RESULTS: First sampled hs-cTnT was elevated in 529 (90%) patients. One-year mortality was 45% (n = 264). Increasing level of hs-cTnT was independently associated with higher adjusted hazard ratios (HR) for 1-year mortality compared with normal levels: Q1 HR 2.9 (95% confidence interval [CI], 1.03-8.1); Q2 HR 3.5 (95% CI, 1.2-9.8); Q3 HR 4.8 (95% CI, 1.7-13.4); Q4 HR 5.7 (95% CI, 2.1-16). In acute phase survivors, first sampled hs-cTnT was an independent predictor of 30- to 365-day mortality (HR 1.3; 95% CI, 1.1-1.6 per loge hs-cTnT). CONCLUSIONS: First sampled plasma hs-cTnT in critically ill sepsis patients was independently associated with 30-day and 1-year mortality. Importantly, first sampled hs-cTnT was associated with mortality during the convalescence phase (30- to 365-day) and could be a feasible marker to identify acute phase survivors at high risk of death.

Orthopedic surgical procedures in 3,305 children and young adults with cerebral palsy: a register-based cohort study.

BACKGROUND AND PURPOSE: Few reports have described the panorama of orthopedic surgeries that children with cerebral palsy (CP) undergo. We analyzed the risk of a first surgery, and describe the frequency of orthopedic surgeries in terms of age, sex, anatomical location, and Gross Motor Function Classification System (GMFCS) level in children and young adults with CP. PATIENTS AND METHODS: This was a register-based cohort study of 3,305 individuals followed until 2-25 years of age. We used data from 2 national Swedish registers: the CPUP CP surveillance program and the Swedish National Patient Register. Kaplan-Meier survival curves were calculated to describe the risk of undergoing a first orthopedic surgery, related to age. RESULTS: We included data for 3,311 orthopedic operations in 1,717 surgical sessions. The percentage of children operated on before age 15 years increased from 22% (95% CI 19-26) for GMFCS level I to 70% (CI 64-75) for level V. Ankle and foot surgery was predominant as first surgery for GMFCS I-II, and hip and femur surgery for GMFCS IV-V. Spinal surgery occurred almost exclusively for GMFCS IV-V. Descriptive data showed repeated surgical sessions to be frequent for higher GMFCS levels. INTERPRETATION: The risk of having a first orthopedic surgical treatment increased with increasing GMFCS level and was initiated at younger age in children with higher GMFCS level.

Risk factors for death in adult COVID-19 patients: Frailty predicts fatal outcome in older patients.

OBJECTIVES: This study investigated demographics, comorbidities, and death rate in hospitalized patients with confirmed COVID-19. In addition, we hypothesized that functional status, according to the Clinical Frailty Scale (CFS), in patients aged 65 years or older is a better predictor of poor outcome than age and comorbidities. METHODS: A total of 255 randomly selected COVID-19 patients admitted to a university hospital were included and followed up for 60 days. Patient data were extracted manually from the electronic health records with use of a standardized protocol. RESULTS: The age of the study population ranged between 20 and 103 years (mean age 66 years ± 17 years). Hypertension, diabetes mellitus, and obesity were the three most prevalent comorbidities. At the 60-day follow-up, 70 patients (27%) had died. In multivariate analyses, age, chronic kidney disease, and previous stroke were associated with death. Most fatal cases (90%) occurred in patients aged 65 years or older. Among such patients, CFS level was the only predictor of death in multivariate analyses. CONCLUSIONS: This study shows that increasing age, chronic kidney disease, and previous stroke significantly contribute to a fatal outcome in hospitalized patients with COVID-19. In patients aged 65 years or older, CFS level was the strongest prognostic factor for death.

Primary surgery to prevent hip dislocation in children with cerebral palsy in Sweden: a minimum 5-year follow-up by the national surveillance program (CPUP).

Background and purpose - Children with cerebral palsy (CP) have an increased risk of hip dislocation. Outcome studies after surgery to prevent hip dislocation in children with CP are usually retrospective series from single tertiary referral centers. According to the national CP surveillance program in Sweden (CPUP), hip surgery should preferably be performed at an early age to prevent hip dislocation. Preventive operations are performed in 12 different Swedish hospitals. We compared the outcomes between soft tissue release and femoral osteotomy in children with CP treated in these hospitals. Patients and methods - 186 children with CP underwent either adductor-iliopsoas tenotomy (APT) or femoral osteotomy (FO) as the primary, preventive surgery because of hip displacement. They were followed for a minimum of 5 years (mean 8 years) regarding revision surgery and hip migration. A good outcome was defined as the absence of revision surgery and a migration percentage (MP) < 50% at the latest follow-up. Logistic and Cox regression analysis were used to investigate the influence of age, sex, preoperative MP, Gross Motor Function Classification System (GMFCS) level, and CP subtype. Results - APT was performed in 129 (69%) children. After 5 years, the reoperation rate was 43%, and 2 children (2%) had an MP > 50%. For the 57 children who underwent FO, the corresponding figures were 39% and 9%. Of the potential risk factors studied, the outcome was statistically significantly associated with preoperative MP only in children who underwent APT, but not in those who underwent FO. None of the other factors were significantly associated with the outcome in the 2 procedure groups. Interpretation - Reoperation rates after preventive surgery are high and indicate the importance of continued postoperative follow-up. Age, sex, GMFCS level, and CP subtype did not influence the outcome significantly.

Self-rated walking disability and dynamic ankle joint stiffness in children and adolescents with Juvenile Idiopathic Arthritis receiving intraarticular corticosteroid joint injections of the foot.

BACKGROUND: Children and adolescents with Juvenile Idiopathic Arthritis (JIA) exhibit deviations in ankle dynamic joint stiffness (DJS, or moment-angle relationship) compared to healthy peers, but the relationship between ankle DJS and self-reported walking impairments has not been studied. This secondary analysis aimed to investigate the relationship between ankle DJS and self-reported walking disability in juveniles with JIA, and to determine whether intraarticular corticosteroid foot injections (IACI) were associated with long term changes in ankle DJS. RESEARCH QUESTIONS: Is ankle DJS altered in children with JIA reporting walking difficulties compared to children with JIA reporting no walking difficulties? Are IACIs associated with persistent alterations in ankle DJS? METHODS: Gait dynamics (DJS), foot pain, and foot-related disability were assessed in 33 children with JIA before intraarticular corticoid foot injection (IACI), and three months after IACI. Using self-reported walking capacity scores, children were classified as either having no walking difficulties (ND) or having walking difficulties (WD). Inferential statistics were used to compare demographics, pain, impairment scores, and ankle DJS between the groups. RESULTS: Before treatment, in the WD group, ankle DJS was significantly decreased both in the early rising phase (ERP = 0.03+0.02 vs. 0.05+0.02 Nm(kg*deg)- 1) and late rising phase (LRP = 0.11+0.06 vs. 0.24+0.22 Nm(kg*deg)-1) compared to the ND group. At three months, the ERP was still significantly decreased in the WD group (ERP = 0.03+0.01 vs. 0.05+0.03 Nm(kg*deg)-1). SIGNIFICANCE: Among children and adolescents with JIA who reported walking difficulties prior to IACIs, alterations in DJS in early stance phase (decreased ERP) remained three months after IACI suggesting persistent gait adaptations, possibly related to pain. Pre-treatment gait analysis may aid in identifying children who will not have long term benefit from IACIs in terms of improved gait, and therefore, may be informed and have the choice to be spared the risk of side effects associated with this treatment.

Geometrical flexibility of platinum nanoclusters: impacts on catalytic decomposition of ethylene glycol.

Catalytic decomposition of ethylene glycol on the Pt13 cluster was studied as a model system for hydrogen production from a lignocellulosic material. Ethylene glycol was chosen as a starting material because of two reasons, it is the smallest oxygenate with a 1 : 1 carbon to oxygen ratio and it contains the C-H, O-H, C-C, and C-O bonds also present in biomass. Density functional theory calculations were employed for predictions of reaction pathways for C-H, O-H, C-C and C-O cleavages, and Brønsted-Evans-Polanyi relationships were established between the final state and the transition state for all mechanisms. The results show that Pt13 catalyzes the cleavage reactions of ethylene glycol more favourably than a Pt surface. The flexibility of Pt13 clusters during the reactions is the key factor in reducing the activation barrier. Overall, the results demonstrate that ethylene glycol and thus biomass can be efficiently converted into hydrogen using platinum nanoclusters as catalysts.

Septic shock and the use of norepinephrine in an intermediate care unit: Mortality and adverse events.

BACKGROUND: Septic shock is associated with high mortality. Aged and multimorbid patients are not always eligible for intensive care units. Norepinephrine is an accepted treatment for hypotension in septic shock. It is unknown whether norepinephrine has a place in treatment outside an intensive care unit and when given peripherally. OBJECTIVES: To describe mortality, Acute Physiology And Chronic Health Evaluation (APACHE-II), time to mean arterial pressure >65 mmHg, and adverse events in patients with septic shock receiving norepinephrine peripherally in an intermediate care unit. METHODS: From a retrospective chart review of 91 patients with septic shock treated with norepinephrine for hypotension, ward mortality, 30-, 60- and 90-day mortality, standardized mortality ratio (SMR) and adverse events (necrosis and arrhythmia) were analysed. Administration route via peripheral venous catheter or central venous catheter was registered. RESULTS: Median age was 81 (43-96) years and median APACHE-II score was 26 (12-42). Observed ward mortality was 27.5% (SMR 0.443, 95% CI: 0.287-0.654), and 30-day and 90-day mortality were 47.2% and 58.2%, respectively. CONCLUSIONS: Elderly patients with septic shock treated with norepinephrine displayed a better survival in the ward and at 30 days than expected. Our retrospective study did not indicate frequent complications when administering norepinephrine via a peripheral venous catheter.

Solvent Effects on Optical Rotation: On the Balance between Hydrogen Bonding and Shifts in Dihedral Angles.

Optical rotations of several conformers of four fluorinated molecules containing the 1-naphthalene or 4-(benzyloxy)phenyl group at the stereocenter have been calculated both in the gas phase and in an aqueous environment. For the compounds containing the 4-(benzyloxy)phenyl group, solvent effects on the optical rotations have also been investigated in chloroform as solvent. Optical rotations have been obtained by time-dependent density functional theory (TDDFT) with the CAM-B3LYP functional and the aug-cc-pVDZ basis set at λ = 589 nm. Implicit and explicit solvent effects were investigated through the polarizable continuum model (PCM) and a microsolvation approach in conjunction with PCM, respectively. In the latter model, solvent molecules are considered as an explicit solvent and their positions are obtained by geometry optimizations for different conformers of the chiral molecule. For molecules containing the 1-naphthalene group, this model gives the same optical rotation signs for all conformers as compared to both gas phase and PCM results and reduces absolute deviations between calculations and experiment. Also, the microsolvation model reproduces the sign of the experimental optical rotations for the molecules containing the 4-(benzyloxy)phenyl group using both water and chloroform as solvent. In a microsolvation model, however, the water and chloroform solvent molecules have similar hydrogen bonds but different effects on the conformation and thereby on the optical rotation since one dihedral angle, having a large effect on the optical rotation, is strongly sensitive to hydrogen bonding to water but not to chloroform. Our investigations demonstrate that a microsolvation approach in conjunction with PCM predicts optical rotations in reasonable agreements with experiments for both sign and magnitude.

Optical Rotation Calculations for Fluorinated Alcohols, Amines, Amides, and Esters.

We have calculated the optical rotation at λ = 589 nm for 45 fluorinated alcohols, amines, amides, and esters using both time-dependent density functional theory (TDDFT) with the CAM-B3LYP functional and the second-order approximate coupled-cluster singles and doubles (CC2) method, where the aug-cc-pVDZ basis set was adopted in both methods. Comparison of CAM-B3LYP and CC2 results to experiments illustrates that both methods are able to reproduce the experimental optical rotation results for both sign and magnitude. Several conformers for molecules containing the benzyloxy and naphthalene groups needed to be considered to obtain consistent signs with experiments, and these conformers are discussed in detail. We have also used a two-point inverse power extrapolation of the basis set to investigate the optical rotation in the basis set limit at the CC2 level, however, we only found small differences compared to the aug-cc-pVTZ results. Our results demonstrate that the least computationally expensive method investigated here, the CAM-B3LYP functional with the aug-cc-pVDZ basis set, is a reliable method to predict the optical rotation for large molecules and thereby the absolute configuration of chiral molecules.

The role of visual stimuli on standing posture in children with bilateral cerebral palsy.

BACKGROUND: In children with bilateral cerebral palsy (CP) maintaining a standing position can be difficult. The fundamental motor task of standing independently is achieved by an interaction between the visual, somatosensory, and vestibular systems. In CP, the motor disorders are commonly accompanied by sensory and perceptual disturbances. Our aims were to examine the influence of visual stimuli on standing posture in relation to standing ability. METHODS: Three dimensional motion analysis with surface electromyography was recorded to describe body position, body movement, and muscle activity during three standing tasks: in a self-selected position, while blindfolded, and during an attention-demanding task. Participants were twenty-seven typically-developing (TD) children and 36 children with bilateral CP, of which 17 required support for standing (CP-SwS) and 19 stood without support (CP-SwoS). RESULTS: All children with CP stood with a more flexed body position than the TD children, even more pronounced in the children in CP-SwS. While blindfolded, the CP-SwS group further flexed their hips and knees, and increased muscle activity in knee extensors. In contrast, the children in CP-SwoS maintained the same body position but increased calf muscle activity. During the attention-demanding task, the children in CP-SwoS stood with more still head and knee positions and with less muscle activity. CONCLUSIONS: Visual input was important for children with CP to maintain a standing position. Without visual input the children who required support dropped into a further crouched position. The somatosensory and vestibular systems alone could not provide enough information about the body position in space without visual cues as a reference frame. In the children who stood without support, an intensified visual stimulus enhanced the ability to maintain a quiet standing position. It may be that impairments in the sensory systems are major contributors to the difficulties to stand erect in children with CP.

Optical Rotation Calculations for a Set of Pyrrole Compounds.

Optical rotation of 14 molecules containing the pyrrole group is calculated by employing both time-dependent density functional theory (TDDFT) with the CAM-B3LYP functional and the second-order approximate coupled-cluster singles and doubles (CC2) method. All optical rotations have been provided using the aug-cc-pVDZ basis set at λ = 589 nm. The two methods predict similar results for both sign and magnitude for the optical rotation of all molecules. The obtained signs are consistent with experiments as well, although several conformers for four molecules needed to be studied to reproduce the experimental sign. We have also calculated excitation energies and rotatory strengths for the six lowest lying electronic transitions for several conformers of the two smallest molecules and found that each rotatory strength has various contributions for each conformer which can cause different optical rotations for different conformers of a molecule. Our results illustrate that both methods are able to reproduce the experimental optical rotations, and that the CAM-B3LYP functional, the least computationally expensive method used here, is an applicable and reliable method to predict the optical rotation for these molecules in line with previous studies.

Optical Rotation from Coupled Cluster and Density Functional Theory: The Role of Basis Set Convergence.

We have calculated the electronic optical rotation of seven molecules using coupled cluster singles-doubles (CCSD) and the second-order approximation (CC2) employing the aug-cc-pVXZ (X = D, T, or Q) basis sets. We have also compared to time-dependent density functional theory (TDDFT) by utilizing two functionals B3LYP and CAM-B3LYP and the same basis sets. Using relative and absolute error schemes, our calculations demonstrate that the CAM-B3LYP functional predicts optical rotation with the minimum deviations compared to CCSD at λ = 355 and 589.3 nm. Furthermore, our results illustrate that the aug-cc-pVDZ basis set provides the optical rotation in good agreement with the larger basis sets for molecules not possessing small-angle optical rotation at λ = 589.3 nm. We have also performed several two-point inverse power extrapolations for the basis set convergence, i.e., OR(∞) + AX(-n), using the CC2 model at λ = 355 and 589.3 nm. Our results reveal that a two-point inverse power extrapolation with the aug-cc-pVTZ and aug-cc-pVQZ basis sets at n = 5 provides optical rotation deviations similar to those of aug-cc-pV5Z with respect to the basis limit.

A test on reactive force fields for the study of silica dimerization reactions.

We studied silica dimerization reactions in the gas and aqueous phase by density functional theory (DFT) and reactive force fields based on two parameterizations of ReaxFF. For each method (both ReaxFF force fields and DFT), we performed constrained geometry optimizations, which were subsequently evaluated in single point energy calculations using the other two methods. Standard fitting procedures typically compare the force field energies and geometries with those from quantum mechanical data after a geometry optimization. The initial configurations for the force field optimization are usually the minimum energy structures of the ab initio database. Hence, the ab initio method dictates which structures are being examined and force field parameters are being adjusted in order to minimize the differences with the ab initio data. As a result, this approach will not exclude the possibility that the force field predicts stable geometries or low transition states which are realistically very high in energy and, therefore, never considered by the ab initio method. Our analysis reveals the existence of such unphysical geometries even at unreactive conditions where the distance between the reactants is large. To test the effect of these discrepancies, we launched molecular dynamics simulations using DFT and ReaxFF and observed spurious reactions for both ReaxFF force fields. Our results suggest that the standard procedures for parameter fitting need to be improved by a mutual comparative method.

Density Functional Theory Study on the Interactions of Metal Ions with Long Chain Deprotonated Carboxylic Acids.

In this work, interactions between carboxylate ions and calcium or sodium ions are investigated via density functional theory (DFT). Despite the ubiquitous presence of these interactions in natural and industrial chemical processes, few DFT studies on these systems exist in the literature. Special focus has been placed on determining the influence of the multibody interactions (with up to 4 carboxylates and one metal ion) on an effective pair-interaction potential, such as those used in molecular mechanics (MM). Specifically, DFT calculations are employed to quantify an effective pair-potential that implicitly includes multibody interactions to construct potential energy curves for carboxylate-metal ion pairs. The DFT calculated potential curves are compared to a widely used molecular mechanics force field (OPLS-AA). The calculations indicate that multibody effects do influence the energetic behavior of these ionic pairs and the extent of this influence is determined by a balance between (a) charge transfer from the carboxylate to the metal ions which stabilizes the complex and (b) repulsion between carboxylates, which destabilizes the complex. Additionally, the potential curves of the complexes with 1 and 2 carboxylates and one counterion have been examined to higher separation distance (20 Å) by the use of relaxed scan optimization and constrained density functional theory (CDFT). The results from the relaxed scan optimization indicate that near the equilibrium distance, the charge transfer between the metal ion and the deprotonated carboxylic acid group is significant and leads to non-negligible differences between the DFT and MM potential curves, especially for calcium. However, at longer separation distances the MM calculated interaction potential functions converge to those calculated with CDFT, effectively indicating the approximate domain of the separation distance coordinate where charge transfer between the ions is occurring.

Local Field Factors and Dielectric Properties of Liquid Benzene.

Local electric field factors are calculated for liquid benzene by combining molecular dynamic simulations with a subsequent force-field model based on a combined charge-transfer and point-dipole interaction model for the local field factor. The local field factor is obtained as a linear response of the local field to an external electric field, and the response is calculated at frequencies through the first absorption maximum. It is found that the largest static local field factor is around 2.4, while it is around 6.4 at the absorption frequency. The linear susceptibility, the dielectric constant, and the first absorption maximum of liquid benzene are also studied. The electronic contribution to the dielectric constant is around 2.3 at zero frequency, in good agreement with the experimental value around 2.2, while it increases to 6.3 at the absorption frequency. The π → π* excitation energy is around 6.0 eV, as compared to the gas-phase value of around 6.3 eV, while the experimental values are 6.5 and 6.9 eV for the liquid and gas phase, respectively, demonstrating that the gas-to-liquid shift is well-described.

Lithium ion-water clusters in strong electric fields: a quantum chemical study.

We use density functional theory to investigate the impact that strong electric fields have on the structure and energetics of small lithium ion-water clusters, Li(+)·nH2O, with n = 4 or 6. We find that electric field strengths of ∼0.5 V/Å are sufficient to break the symmetry of the n = 4 tetrahedral energy minimum structure, which undergoes a transformation to an asymmetric cluster consisting of three water molecules bound to lithium and one additional molecule in the second solvation shell. Interestingly, this cluster remains the global minimum configuration at field strengths ≳0.15 V/Å. The 6-coordinated cluster, Li(+)·6H2O, features a similar transition to 5- and 4-coordinated clusters at field strengths of ∼0.2 and ∼0.3 V/Å, respectively, with the tetra-coordinated structure being the global minimum even in the absence of the field. Our findings are relevant to understanding the behavior of the Li(+) ion in aqueous environments under strong electric fields and in interfacial regions where field gradients are significant.

Complex frequency-dependent polarizability through the π → π* excitation energy of azobenzene molecules by a combined charge-transfer and point-dipole interaction model.

The complex frequency-dependent polarizability and π → π* excitation energy of azobenzene compounds are investigated by a combined charge-transfer and point-dipole interaction (CT/PDI) model. To parametrize the model, we adopted time-dependent density functional theory (TDDFT) calculations of the frequency-dependent polarizability extended with excited-state lifetimes to include also its imaginary part. The results of the CT/PDI model are compared with the TDDFT calculations and experimental data demonstrating that the CT/PDI model is fully capable to reproduce the static polarizability as well as the π → π* excitation energy for these compounds. In particular, azobenzene molecules with different functional groups in the para-position have been included serving as a severe test of the model. The π → π* excitation is to a large extent localized to the azo bond, and substituting with electron-donating or electron-attracting groups on the phenyl rings results in charge-transfer effects and a shift in the excitation energy giving rise to azobenzene compounds with a range of different colors. In the CT/PDI model, the π → π* excitation in azobenzenes is manifested as drastically increasing atomic induced dipole moments in the azo group as well as in the adjacent carbon atoms, whereas the shifts in the excitation energies are due to charge-transfer effects.

Thermo-molecular orientation effects in fluids of dipolar dumbbells.

We use molecular dynamics simulations in applied thermal gradients to study thermomolecular orientation (TMO) of size-asymmetric dipolar dumbbells with different molecular dipole moments. We find that the direction of the TMO is the same as in apolar dumbbells of the same size, i.e. the smaller atom in the dumbbell tends to orient towards the colder temperature. The ratio of the electrical polarization to the magnitude of the thermal gradient does not vary much with the magnitude of the molecular dipole moment. We also investigate a novel second order TMO that persists even in size-symmetric dipolar dumbbells where molecules have a slight tendency to orient perpendicular to the gradient except very close to the hot region, where (anti-)parallel orientations are preferred. Finally, we investigate rotational correlation functions and characteristic rotational times in these systems in an attempt to model possible spectroscopic signatures of TMO in experiments. Although we cannot detect any difference in integrated rotational times between equilibrium simulations and simulations in a thermal gradient, more careful modelling of the anisotropic rotational dynamics in the thermal gradient may be more successful.