Publications by authors named "Martin Dahlberg"

18 Publications

  • Page 1 of 1

Perirenal Fat Surface Area and Oncologic Outcome in Elective Colon Cancer Surgery.

Dis Colon Rectum 2021 02;64(2):171-180

Department of Surgery, Södersjukhuset, Karolinska Institutet, Stockholm, Sweden.

Background: Central obesity is associated with surgical difficulties, but few studies explore the relationship with long-term results after colon cancer surgery.

Objective: The purpose of this study was to investigate the association between perirenal fat surface area, a proxy for total visceral fat, and oncologic outcome after intestinal resection for colon cancer.

Design: We investigated the association between perirenal fat surface area (exposure) on recurrence and death (outcome) in patients undergoing surgery with curative intent for colon cancer.

Settings: The study was conducted at Stockholm South General Hospital, serving a population of 600,000.

Patients: Patients (N = 733) without metastases at diagnosis who had a preoperative CT and had undergone elective colon resection between 2006 and 2016 were included.

Main Outcome Measures: We compared overall survival, recurrence-free survival, and cause-specific survival by perirenal fat surface area.

Results: Patients with high perirenal fat surface area (fourth quartile) had more often left-sided tumors (45% vs 32% in the first quartile) and experienced more postoperative complications (29% vs 13%), but there were no differences in pathologic T and N stage, radicality of surgery, or adjuvant chemotherapy treatment. Overall survival decreased by increasing cancer stage but was not different between perirenal fat surface area categories. The HR for recurrence-free survival per centimeter squared increase in perirenal fat surface area was 1.00 (95% CI, 0.99-1.01) adjusted for age, sex, ASA category, tumor location, and postoperative complication Clavien-Dindo ≥2. The cumulative incidence of recurrence with death as a competing risk was not statistically different between perirenal fat surface area categories (p = 0.06). Subgroup analyses showed a nonsignificant tendency for men with low perirenal fat surface area to have a lower risk of recurrence and women a higher risk.

Limitations: In all register-based studies there can be randomly distributed errors. The results can only be generalized to colon resections. Our cohort ranged over a large year span.

Conclusions: We found no association between perirenal fat surface area and overall survival, recurrence-free survival, or cause-specific cumulative incidence of recurrence in patients undergoing colon resection for cancer. See Video Abstract at http://links.lww.com/DCR/B326.

La Superficie De Grasa Perirrenal Y El Resultado Oncolgico En Ciruga Electiva De Cncer De Colon: ANTECEDENTES:La obesidad central está asociada con dificultades quirúrgicas, pero pocos estudios exploran la relación de los resultados a largo plazo después de cirugía de cáncer de colon.OBJETIVO:Investigar la asociación entre la superficie de la grasa perirrenal, como un indicador de la grasa visceral total y el resultado oncológico después de una resección intestinal por cáncer de colon.DISEÑO:Se estudió la asociación entre el área de la superficie de la grasa perirrenal (expuesta) con la recurrencia y la muerte (resultado) de pacientes sometidos a cirugía con intención curativa por cáncer de colon.AJUSTES:Atención brindada por el Hospital General del Sur de Estocolmo a una población de 600,000 habitantes.PACIENTES:Aquellos pacientes sin metástasis (n = 733) en el momento del diagnóstico que tuvieron una tomografía computada preoperatoria y que se sometieron a una resección electiva de colon entre 2006-2016.PRINCIPALES MEDIDAS DE RESULTADO:Comparamos la sobrevida general, la sobrevida libre de recurrencia y la sobrevida específica de la causa, por área de superficie de grasa perirrenal.RESULTADOS:Los pacientes con una mayor área de superficie de grasa perirrenal (cuarto cuartil) tuvieron más frecuentemente tumores del lado izquierdo (45% frente a 32% en el primer cuartil) y sufrieron más complicaciones postoperatorias (29% frente a 13%), pero no hubieron diferencias en el Estadío patológico T y N, ni en lo radical de la cirugía o del tratamiento de quimioterapia adyuvante. La supervivencia general disminuyó al aumentar el estadio del cáncer, pero no fue diferente entre las categorías de área de superficie grasa perirrenal. La razón de riesgo para la sobrevida libre de recurrencia por aumento de cm2 en el área de la superficie grasa perirrenal fue de 1.00 (intervalo de confianza del 95%: 0.99-1.01) ajustada por edad, sexo, categoría de la Sociedad Americana de Anestesiólogos, ubicación del tumor y complicación postoperatoria según Clavien-Dindo ≥ 2) La incidencia acumulada de recurrencia con muerte como un riesgo competitivo no fue estadísticamente diferente entre las categorías de área de superficie grasa perirrenal (p = 0.06). Los análisis de subgrupos mostraron una tendencia no significativa para que los hombres con un área de superficie menor en grasa perirrenal tengan un menor riesgo de recurrencia y las mujeres un mayor riesgo.LIMITACIONES:En todos los estudios basados en registros puede haber errores distribuidos aleatoriamente. Los resultados solo pueden generalizarse a resecciones de colon. Nuestra cohorte osciló durante un gran lapso de años.CONCLUSIONES:No se encontró asociación entre el área de superficie de la grasa perirrenal y la sobrevida general, ni con la sobrevida libre de recurrencia o la incidencia acumulada de recurrencia específica de la causa en pacientes sometidos a resección de colon por cáncer. Consulte Video Resumen en http://links.lww.com/DCR/B326. (Traducción-Dr Xavier Delgadillo).
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1097/DCR.0000000000001746DOI Listing
February 2021

Dosing of thromboprophylaxis and mortality in critically ill COVID-19 patients.

Crit Care 2020 11 23;24(1):653. Epub 2020 Nov 23.

Department of Clinical Science and Education, Södersjukhuset, Karolinska Institutet, Stockholm, Sweden.

Background: A substantial proportion of critically ill COVID-19 patients develop thromboembolic complications, but it is unclear whether higher doses of thromboprophylaxis are associated with lower mortality rates. The purpose of the study was to evaluate the association between initial dosing strategy of thromboprophylaxis in critically ill COVID-19 patients and the risk of death, thromboembolism, and bleeding.

Method: In this retrospective study, all critically ill COVID-19 patients admitted to two intensive care units in March and April 2020 were eligible. Patients were categorized into three groups according to initial daily dose of thromboprophylaxis: low (2500-4500 IU tinzaparin or 2500-5000 IU dalteparin), medium (> 4500 IU but < 175 IU/kilogram, kg, of body weight tinzaparin or > 5000 IU but < 200 IU/kg of body weight dalteparin), and high dose (≥ 175 IU/kg of body weight tinzaparin or ≥ 200 IU/kg of body weight dalteparin). Thromboprophylaxis dosage was based on local standardized recommendations, not on degree of critical illness or risk of thrombosis. Cox proportional hazards regression was used to estimate hazard ratios with corresponding 95% confidence intervals of death within 28 days from ICU admission. Multivariable models were adjusted for sex, age, body mass index, Simplified Acute Physiology Score III, invasive respiratory support, and initial dosing strategy of thromboprophylaxis.

Results: A total of 152 patients were included: 67 received low-, 48 medium-, and 37 high-dose thromboprophylaxis. Baseline characteristics did not differ between groups. For patients who received high-dose prophylaxis, mortality was lower (13.5%) compared to those who received medium dose (25.0%) or low dose (38.8%), p = 0.02. The hazard ratio of death was 0.33 (95% confidence intervals 0.13-0.87) among those who received high dose, and 0.88 (95% confidence intervals 0.43-1.83) among those who received medium dose, as compared to those who received low-dose thromboprophylaxis. There were fewer thromboembolic events in the high (2.7%) vs medium (18.8%) and low-dose thromboprophylaxis (17.9%) groups, p = 0.04.

Conclusions: Among critically ill COVID-19 patients with respiratory failure, high-dose thromboprophylaxis was associated with a lower risk of death and a lower cumulative incidence of thromboembolic events compared with lower doses.

Trial Registration: Clinicaltrials.gov NCT04412304 June 2, 2020, retrospectively registered.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1186/s13054-020-03375-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7680989PMC
November 2020

Prone positioning in mechanically ventilated patients with severe acute respiratory distress syndrome and coronavirus disease 2019.

Acta Anaesthesiol Scand 2021 03 22;65(3):360-363. Epub 2020 Nov 22.

Department of Clinical Science and Education Södersjukhuset, Section for Anesthesiology and Intensive Care, Karolinska Institutet, Stockholm, Sweden.

Background: The management of COVID-19 ARDS is debated. Although current evidence does not suggest an atypical acute respiratory distress syndrome (ARDS), the physiological response to prone positioning is not fully understood and it is unclear which patients benefit. We aimed to determine whether proning increases oxygenation and to evaluate responders.

Methods: This case series from a single, tertiary university hospital includes all mechanically ventilated patients with COVID-19 and proning between 17 March 2020 and 19 May 2020. The primary measure was change in PaO :FiO .

Results: Forty-four patients, 32 males/12 females, were treated with proning for a total of 138 sessions, with median (range) two (1-8) sessions. Median (IQR) time for the five sessions was 14 (12-17) hours. In the first session, median (IQR) PaO :FiO increased from 104 (86-122) to 161 (127-207) mm Hg (P < .001). 36/44 patients (82%) improved in PaO :FiO , with a significant increase in PaO :FiO in the first three sessions. Median (IQR) FiO decreased from 0.7 (0.6-0.8) to 0.5 (0.35-0.6) (<0.001). A significant decrease occurred in the first three sessions. PaO , tidal volumes, PEEP, mean arterial pressure (MAP), and norepinephrine infusion did not differ. Primarily, patients with PaO :FiO approximately < 120 mm Hg before treatment responded to proning. Age, sex, BMI, or SAPS 3 did not predict success in increasing PaO :FiO .

Conclusion: Proning increased PaO :FiO , primarily in patients with PaO :FiO approximately < 120 mm Hg, with a consistency over three sessions. No characteristic was associated with non-responding, why proning may be considered in most patients. Further study is required to evaluate mortality.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/aas.13741DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7894343PMC
March 2021

Re: Entrapment is an essential feature of sigmoid volvulus.

ANZ J Surg 2020 09;90(9):1823-1824

Department of Clinical Science and Education Södersjukhuset (KI SÖS) , Karolinska Institutet, Stockholm, Sweden.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/ans.16053DOI Listing
September 2020

Plasma Sodium and Age Are Important Markers of Risk of Perforation in Acute Appendicitis.

J Gastrointest Surg 2021 01 31;25(1):287-289. Epub 2020 Aug 31.

Department of Surgery, Södersjukhuset, Karolinska Institute, Sjukhusbacken 10, 118 83, Stockholm, Sweden.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1007/s11605-020-04753-wDOI Listing
January 2021

Long-Term Results after Anastomotic Leakage following Rectal Cancer Surgery: A Comparison of Treatment with Endo-Sponge and Transanal Irrigation.

Dig Surg 2020 23;37(6):456-462. Epub 2020 Aug 23.

Department of Clinical Science and Education, Södersjukhuset, Karolinska Institutet, Stockholm, Sweden,

Objective: We aimed to evaluate long-term results in patients from regular health care treated with endoscopic transanal closure system, that is, endoscopic vacuum-assisted closure system (EVAC) compared to transanal irrigation.

Methods: In this retrospective, medical chart-based, observational study, we included patients with anastomotic leakage after low anterior resection for rectal cancer from 3 Stockholm hospitals 2006-2016 and compared time to first stoma closure in a Kaplan-Meier model and the proportion of patients who were stoma-free at end of follow-up.

Results: Anastomotic leakage was found in 81 patients who were followed up in median 5.9 years (min-max: 0.53-13). EVAC was used on 14 (17%) patients and transanal irrigation on 34 (42%) patients. The remaining 33 (41%) patients either got a permanent colostomy or were treated only with antibiotics and percutaneous drainage. Treatment with EVAC or transanal irrigation led to similar rates of stoma closure, both when comparing all patients, and when comparing patients with similar defects. At the end of follow-up, 43% of patients treated with EVAC and 50% of patients treated with repeated irrigation were stoma-free (p = 0.75).

Conclusions: We found no evidence of better outcomes in patients treated with EVAC. The study was, however, limited by small sample size.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1159/000508935DOI Listing
September 2021

Decompressing Stoma vs Stent in Left-Sided Obstructive Colon Cancer.

JAMA Surg 2020 08;155(8):788

Department of Clinical Science and Education Södersjukhuset, Karolinska Institutet, Stockholm, Sweden.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1001/jamasurg.2020.1662DOI Listing
August 2020

Entrapment is an essential feature of sigmoid volvulus.

ANZ J Surg 2020 09 3;90(9):1540-1541. Epub 2020 Apr 3.

Department of Clinical Science and Education Södersjukhuset (KI SÖS), Karolinska Institutet, Stockholm, Sweden.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/ans.15758DOI Listing
September 2020

Intraoperative cultures during appendectomy in children are poor predictors of pathogens and resistance patterns in cultures from postoperative abscesses.

Pediatr Surg Int 2019 Mar 8;35(3):341-346. Epub 2019 Jan 8.

Department of Pediatric Surgery, Astrid Lindgren Children's Hospital, Karolinska University Hospital, Stockholm, Sweden.

Background: Intraoperative cultures are commonly sent in complicated appendicitis. Culture-guided antibiotics used to prevent postoperative infectious complications are debated. In this study, we describe the microbial overlap between intraoperative and abscess cultures, and antibiotic resistance patterns.

Method: A local register of a children's hospital treating children 0-15 years old with appendicitis between 2006 and 2013 was used to find cases with intraoperative cultures, and cultures from drained or aspirated postoperative intraabdominal abscesses. Culture results, administered antibiotics, their nominal coverage of the identified microorganisms, and rationales given for changes in antibiotic regimens were collected from electronic medical records.

Results: In 25 of 35 patients who met inclusion criteria, there was no overlap between the intraoperative and abscess cultures. In 33 of 35 patients, all identified intraoperative organisms were covered with postoperative antibiotics. In 14 patients, organisms in the abscess culture were not covered by administered antibiotics. Enterococci not found in the intraoperative culture were found in 12 of 35 abscesses. We found no difference in the antibiotic coverage between rationales given for antibiotic changes.

Conclusion: The overlap between intraoperative cultures and cultures from subsequent abscesses was small. Lack of antibiotic coverage of intraoperative cultures was not an important factor in abscess formation.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1007/s00383-018-04428-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6394779PMC
March 2019

Risk of Appendicitis in IgE-Mediated Allergy.

JAMA Pediatr 2019 03;173(3):290-291

Department of Clinical Science and Education, Stockholm South General Hospital, Södersjukhuset, Karolinska Institutet, Stockholm, Sweden.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1001/jamapediatrics.2018.4850DOI Listing
March 2019

Retained sex toys: an increasing and possibly preventable medical condition.

Int J Colorectal Dis 2019 Jan 20;34(1):181-183. Epub 2018 Jul 20.

Department of Clinical Science and Education and Department of Surgery, Södersjukhuset, Karolinska Institutet, Stockholm South General Hospital (Södersjukhuset), Sjukhusbacken 10, 118 83, Stockholm, Sweden.

Purpose: Retained foreign rectal objects may require surgical removal. To estimate the magnitude of this problem, we report the incidence and treatment of retained rectal objects at a large emergency hospital, and calculate incidence rates at the national level in Sweden.

Methods: All local patient records during 2009-2017 with the diagnosis foreign body in anus and rectum (ICD-10 T185) were accessed and analyzed retrospectively. All Swedish in- and outpatient visits during 2005-2016 with the code T185 were accessed from the National Patient Register.

Results: We show an increasing incidence in rectal foreign bodies in Swedish national data. The increase was most noticeable in men, and in our local register there was an overrepresentation of sex toys leading to laparotomy and stoma.

Conclusions: To mitigate surgical cost and comorbidity, policies to decrease the risk of retained sex toys could be considered.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1007/s00384-018-3125-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6318238PMC
January 2019

Trends in the Management of Acute Appendicitis in a Single-Center Quality Register Cohort of 5,614 Patients.

Dig Surg 2018 24;35(2):144-154. Epub 2017 Jun 24.

Department of Surgery, Clinical Science and Education, Stockholm South General Hospital (Södersjukhuset), Karolinska Institute, Stockholm, Sweden.

Acute appendicitis is one of the most common reasons for emergency surgery. At Stockholm South General Hospital, information on all patients - 15 years or older - undergoing surgery for acute appendicitis is included in a quality register. Data on surgical method, preoperative imaging, hospital stay, intraoperative findings, and 30-day complications were recorded for each patient. From January 2004 to December 2014, 5,614 consecutive patients were registered. The percentage of patients examined with preoperative imaging increased from 30% in 2004 to 93% in 2014. The use of laparoscopic appendectomy increased from 6 to 79%. Negative appendectomies decreased from 7.5-10 to 1.7%. The mean perforation rate was 28.6%. Some form of postoperative complication occurred in 6.6% of those on whom laparoscopy was performed and 10.5% of those who underwent an open surgery, with a significant difference (p < 0.001) in the rate of surgical site infections (surgical site infections, higher in open cases) but with no difference in the number of deep postoperative abscesses. The overall hospital stay decreased from 2004 to 2014 for perforated and non-perforated appendicitis. The overall 30-day mortality rate was 0.12%. Changes in preoperative imaging and treatment strategy for appendicitis during this period resulted in a lower rate of negative appendectomies with acceptable complication rates and shortened hospital stay.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1159/000477269DOI Listing
September 2018

Molecular dynamics simulations of membranes composed of glycolipids and phospholipids.

J Phys Chem B 2012 Jan 16;116(1):244-52. Epub 2011 Dec 16.

Department of Materials and Environmental Chemistry, Division of Physical Chemistry, Arrhenius Laboratory, Stockholm University, Stockholm, Sweden.

Lipid membranes composed of 1,2-di-(9Z,12Z,15Z)-octadecatrienoyl-3-O-β-D-galactosyl-sn-glycerol or monogalactosyldiacylglycerol (MGDG) and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) were studied by means of molecular dynamics (MD) computer simulations. Three lipid compositions were considered: 0%, 20%, and 45% MGDG (by mole) denoted as MG-0, MG-20, and MG-45, respectively. The article is focused on the calculation of NMR dipolar interactions, which were confronted with previously reported experimental couplings. Dynamical processes and orientational distributions relevant for the averaging of dipolar interactions were evaluated. Furthermore, several parameters important for characterization of the bilayer structure, molecular organization, and dynamics were investigated. In general, only a minor change in DMPC properties was observed upon the increased MGDG/DMPC ratio, whereas properties related to MGDG undergo a more pronounced change. This effect was ascribed to the fact that DMPC is a bilayer (L(α)) forming lipid, whereas MGDG prefers a reverse hexagonal (H(II)) arrangement.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/jp209268pDOI Listing
January 2012

Mechanical Properties of Coarse-Grained Bilayers Formed by Cardiolipin and Zwitterionic Lipids.

J Chem Theory Comput 2010 May;6(5):1638-49

Division of Physical Chemistry, Arrhenius Laboratory, Stockholm University, S-106 91 Stockholm, Sweden.

Lipid shape and charge are connected with the physical properties and the biological function of membranes. Cardiolipin, a double phospholipid with four chains and the potential of changing its charge with pH, is crucially connected with mitochondrial inner membrane shape, and recent experiments suggest that local pH changes allow highly curved local geometries. Here, we use a coarse-grained molecular dynamics model to investigate the mechanical properties of cardiolipin bilayers, systematically varying the headgroup charge and the composition in mixtures with zwitterionic 1,2-dioleoyl-glycero-3-phosphatidylcholine (DOPC) or 1,2-dioleoyl-glycero-3-phosphatidylethanolamine (DOPE). Low cardiolipin charge, corresponding to low pH, was found to induce bending moduli on the order of kBT and curved microdomains. On the length scale investigated, in contrast to continuum theoretical models, we found the area modulus and bending modulus to be inversely correlated for mixtures of cardiolipin and DOPC/DOPE, explainable by changes in the effective headgroup volume.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/ct900654eDOI Listing
May 2010

Quantum chemical modeling of the cardiolipin headgroup.

J Phys Chem A 2010 Apr;114(12):4375-87

Division of Physical Chemistry, Arrhenius Laboratory, Stockholm University, S-106 91 Stockholm, Sweden.

Cardiolipin is a key lipid component in many biological membranes. Proton conduction and proton-lipid interactions on the membrane surface are thought to be central to mitochondrial energy production. However, details on the cardiolipin headgroup structure are lacking and the protonation state of this lipid at physiological pH is not fully established. Here we present ab initio DFT calculations of the cardiolipin (CL) headgroup and its 2'-deoxy derivative (dCL), with the aim of establishing a connection between structure and acid-base equilibrium in CL. Furthermore, we investigate the effects of solvation on the molecular conformations. In our model, both CL and dCL showed a significant gap between the two pK(a) values, with pK(a2) above the physiological range, and intramolecular hydrogen bonds were found to play a central role in the conformations of both molecules. This behavior was also observed experimentally in CL. Structures derived from the DFT calculations were compared with those obtained experimentally, collected for CL in the Protein Data Bank, and conformations from previous as well as new molecular dynamics simulations of cardiolipin bilayers. Transition states for proton transfer in CL were investigated, and we estimate that protons can exchange between phosphate groups with an approximate 4-5 kcal/mol barrier. Computed NMR and IR spectral properties were found to be in reasonable agreement with experimental results available in the literature.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/jp9110019DOI Listing
April 2010

Molecular dynamics simulations of cardiolipin bilayers.

J Phys Chem B 2008 Sep 20;112(37):11655-63. Epub 2008 Aug 20.

Division of Physical Chemistry, Arrhenius Laboratory, Stockholm University, Stockholm, Sweden.

Cardiolipin is a key lipid component in the inner mitochondrial membrane, where the lipid is involved in energy production, cristae structure, and mechanisms in the apoptotic pathway. In this article we used molecular dynamics computer simulations to investigate cardiolipin and its effect on the structure of lipid bilayers. Three cardiolipin/POPC bilayers with different lipid compositions were simulated: 100, 9.2, and 0% cardiolipin. We found strong association of sodium counterions to the carbonyl groups of both lipid types, leaving in the case of 9.2% cardiolipin virtually no ions in the aqueous compartment. Although binding occurred primarily at the carbonyl position, there was a preference to bind to the carbonyl groups of cardiolipin. Ion binding and the small headgroup of cardiolipin gave a strong ordering of the hydrocarbon chains. We found significant effects in the water dipole orientation and water dipole potential which can compensate for the electrostatic repulsion that otherwise should force charged lipids apart. Several parameters relevant for the molecular structure of cardiolipin were calculated and compared with results from analyses of coarse-grained simulations and available X-ray structural data.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/jp803414gDOI Listing
September 2008

Polymorphic phase behavior of cardiolipin derivatives studied by coarse-grained molecular dynamics.

Authors:
Martin Dahlberg

J Phys Chem B 2007 Jun 2;111(25):7194-200. Epub 2007 Jun 2.

Division of Physical Chemistry, Arrhenius Laboratory, Stockholm University, Stockholm, Sweden.

Cardiolipin (CL) is a negatively charged four acyl chain lipid, associated with energy production in bacterial and mitochondrial membranes. Due to the shape of CL, negative curvatures of aggregates are favorable if the charges in the head group can be reduced. The phase polymorphism of CL, and of associated derivatives with 2, 3, 4, or 5 chains, has been determined previously and offers a model system in which micellar, lamellar, and inverse hexagonal phases can be observed. We present an extension to a previously established coarse-grained molecular dynamics model with the aim of reproducing the different CL phases with two adjustable parameters: the number of acyl chains and the effective head group charge. With molecular dynamics simulations of large lipid systems, we observed transitions between different phases on the nanosecond to microsecond time scale. Charge screening by high salt or low pH was successfully modeled by a reduction of phosphate charge, which led to the adoption of aggregates with more negative curvature. Although specific ion binding at the interface and other atomistic details are sacrificed in the coarse-grained model, we found that it captures general phase features over a large range of aggregate geometries.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/jp071954fDOI Listing
June 2007

Preferential solvation of phenol in binary solvent mixtures. A molecular dynamics study.

J Phys Chem A 2006 Feb;110(6):2253-8

Division of Physical Chemistry, Arrhenius Laboratory, Stockholm University, SE-106 91, Stockholm, Sweden.

Molecular dynamics computer simulations were carried out to study the preferential solvation of phenol in equimolar acetonitrile-water and ethanol-water binary mixtures. Two water models were used to investigate the model dependence of preferential solvation. The results are compared to recent intermolecular 1H NOESY experiments reported on the same systems. In the case of acetonitrile-water the local mole fraction obtained from simulations agrees quite well with experiments. In the case of ethanol-water there was a qualitative difference, which was observed for both water models. However, when comparing the degree of preferential solvation of the two cosolvents ethanol and acetonitrile with each of the two water models, the trend obtained from the simulations agrees with experimental data.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/jp056463eDOI Listing
February 2006
-->